Santander UK (SANS+) 20-F 5 Mar 24 2023 FY Annual report (foreign) Financial data

Cover Page

Cover Page	12 Months Ended
	Dec. 31, 2023 shares
Document And Entity Information [Line Items]
Document Type	20-F
Document Registration Statement	false
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Document Shell Company Report	false
Entity File Number	001-14928
Entity Registrant Name	Santander UK plc
Entity Incorporation, State or Country Code	X0
Entity Address, Address Line One	2 Triton Square
Entity Address, Address Line Two	Regent’s Place
Entity Address, City or Town	London
Entity Address, Postal Zip Code	NW1 3AN
Entity Address, Country	GB
Title of 15(d) Security	7.95% Term Subordinated Securities due October 26, 2029
Entity Common Stock, Shares Outstanding	31,051,768,866
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Document Accounting Standard	International Financial Reporting Standards
Entity Shell Company	false
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Central Index Key	0001087711
Business Contact
Document And Entity Information [Line Items]
Entity Address, Address Line One	2 Triton Square
Entity Address, Address Line Two	Regent’s Place
Entity Address, City or Town	London
Entity Address, Postal Zip Code	NW1 3AN
Entity Address, Country	GB
Contact Personnel Name	Lee Grant
City Area Code	+44
Local Phone Number	800 085 1491
Contact Personnel Email Address	lee.grant@santander.co.uk
4.000% Notes due 2024, issued by Abbey National Treasury Services plc *
Document And Entity Information [Line Items]
Title of 12(b) Security	4.000% Notes due 2024, issued by Abbey National Treasury Services plc *
Trading Symbol	SAN/24
Security Exchange Name	NYSE
2.875% Notes due 2024, issued by Santander UK plc
Document And Entity Information [Line Items]
Title of 12(b) Security	2.875% Notes due 2024, issued by Santander UK plc
Trading Symbol	SAN/24D
Security Exchange Name	NYSE
10 3/8% Non-cumulative Preference Shares of nominal value of £1 each
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding	200,000,000
8 5/8% Non-cumulative Preference Shares of nominal value of £1 each
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding	125,000,000

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2023
Audit Information [Abstract]
Auditor Firm ID	876
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	London, United Kingdom

Consolidated Income Statement

Consolidated Income Statement - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Profit (loss) [abstract]
Interest and similar income	£ 11,617	£ 6,708	£ 4,762
Interest expense and similar charges	(6,959)	(2,283)	(813)
Net interest income	4,658	4,425	3,949
Fee and commission income	804	839	697
Fee and commission expense	(501)	(509)	(411)
Net fee and commission income	303	330	286
Other operating income	135	201	264
Total operating income	5,096	4,956	4,499
Operating expenses before credit impairment charges, provisions and charges	(2,456)	(2,343)	(2,510)
Credit impairment (charges)/write-backs	205
Credit impairment (charges)/write-backs		(320)	233
Provisions for other liabilities and charges	(335)	(419)	(377)
Total operating credit impairment charges, provisions and charges	(540)	(739)	(144)
Profit (Loss) From Continuing Operations, Before Tax	2,100	1,874	1,845
Tax on profit from continuing operations	(559)	(480)	(492)
Profit from continuing operations after tax	1,541	1,394	1,353
Profit from discontinued operations after tax	0	0	31
Profit after tax	1,541	1,394	1,384
Attributable to:
Equity holders of the parent	1,541	1,394	1,365
Profit (loss), attributable to non-controlling interests	0	0	19
Profit after tax	£ 1,541	£ 1,394	£ 1,384

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of comprehensive income [abstract]
Profit after tax	£ 1,541	£ 1,394	£ 1,384
Movement in fair value reserve (debt instruments):
- Change in fair value	89	(278)	(111)
- Income statement transfers	(105)	247	110
- Taxation	5	11	(2)
Other comprehensive income, fair value reserve (debt instruments)	(11)	(20)	(3)
Cash flow hedges:
- Effective portion of changes in fair value	(169)	425	(873)
- Income statement transfers	1,248	(2,129)	358
- Taxation	(299)	469	141
Other comprehensive income, cash flow hedges, total	780	(1,235)	(374)
Net other comprehensive income/(expense) that may be reclassified to profit or loss subsequently	769	(1,255)	(377)
Pension remeasurement:
- Change in fair value	(598)	(722)	1,264
- Taxation	167	267	(419)
Pension remeasurement, total	(431)	(455)	845
Own credit adjustment:
- Change in fair value	(15)	29	0
- Taxation	4	(9)	0
Own credit adjustment, total	(11)	20	0
Net other comprehensive (expense)/income that will not be reclassified to profit or loss subsequently	(442)	(435)	845
Total other comprehensive income/(expense) net of tax	327	(1,690)	468
Total comprehensive income/(expense)	1,868	(296)	1,852
Attributable to:
Equity holders of the parent	1,868	(296)	1,833
Non-controlling interests	0	0	19
Total comprehensive income/(expense)	£ 1,868	£ (296)	£ 1,852

Consolidated Balance Sheet

Consolidated Balance Sheet - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets
Cash and balances at central banks	£ 38,214	£ 44,190
Derivative financial instruments	1,432	2,407
Other financial assets at fair value through profit or loss	262	129
Loans and advances to customers	207,435	219,716
Loans and advances to banks	1,080	992
Reverse Repurchase agreements - non-trading	12,468	7,348
Other financial assets at amortised cost	152	156
Macro hedge of interest rate risk	(632)	(2,657)
Financial assets at fair value through other comprehensive income	8,481	6,024
Interests in other entities	245	252
Intangible assets	1,548	1,550
Property, plant and equipment	1,494	1,513
Current tax assets	490	478
Retirement benefit assets	723	1,050
Other assets	2,043	2,016
Assets held for sale	13	49
Total assets	275,448	285,213
Liabilities
Derivative financial instruments	818	951
Other financial liabilities at fair value through profit or loss	899	803
Deposits by customers	190,850	195,568
Deposits by banks	20,332	28,525
Repurchase agreements - non-trading	8,411	7,982
Debt securities in issue	33,910	31,531
Subordinated liabilities	2,386	2,332
Macro hedge of interest rate risk	86	95
Other liabilities	2,479	2,581
Provisions	402	378
Deferred tax liabilities	186	35
Retirement benefit obligations	66	25
Total liabilities	260,825	270,806
Equity
Share capital	3,105	3,105
Share premium	5,620	5,620
Other equity instruments	1,956	1,956
Retained earnings	4,295	4,848
Other reserves	(353)	(1,122)
Total equity	14,623	14,407
Total liabilities and equity	£ 275,448	£ 285,213

Consolidated Cash Flow Statemen

Consolidated Cash Flow Statement - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Profit before tax	£ 2,100	£ 1,874	£ 1,888
Non-cash items included in profit
– Depreciation and amortisation	290	296	501
– Provisions for other liabilities and charges	335	419	381
– Impairment losses	195	284	(228)
– Other non-cash items	(749)	1,497	(147)
– Pension charge for defined benefit pension schemes	13	28	38
Total adjustments to reconcile profit (loss)	84	2,524	545
Net change in operating assets and liabilities:
– Cash and balances at central banks	(88)	275	(659)
– Derivative assets	975	(726)	1,725
– Other financial assets at fair value through profit or loss	40	877	1,007
– Loans and advances to banks and customers	12,112	(9,966)	(971)
– Reverse repurchase agreements - non-trading	(3,224)	6,818	7,024
– Other assets	(141)	(574)	324
– Deposits by banks and customers	(13,504)	(3,128)	10,735
– Repurchase agreements - non-trading	704	(4,145)	(7,550)
– Derivative liabilities	(133)	174	(807)
– Other financial liabilities at fair value through profit or loss	102	(973)	(1,109)
– Debt securities in issue	962	3,120	(329)
– Other liabilities	(67)	(98)	(603)
Net change in operating assets and liabilities	(2,262)	(8,346)	8,787
Corporation taxes paid	(537)	(405)	(427)
Effects of exchange rate differences	(518)	1,383	(542)
Net cash flows from operating activities	(1,133)	(2,970)	10,251
Cash flows from investing activities
Purchase of property, plant and equipment and intangible assets	(385)	(496)	(613)
Proceeds from sale of property, plant and equipment and intangible assets	175	159	437
Purchase of financial assets at amortised cost and financial assets at FVOCI	(10,899)	(2,884)	(1,256)
Proceeds from sale and redemption of financial assets at amortised cost and financial assets at FVOCI	8,362	3,023	4,509
Net cash flows from investing activities	(2,747)	(198)	3,077
Cash flows from financing activities
Issue of other equity instruments	0	750	210
Issue of debt securities and subordinated notes	5,276	4,794	2,878
Issuance costs of debt securities and subordinated notes	(18)	(16)	(6)
Repayment of debt securities and subordinated notes	(3,539)	(3,076)	(11,914)
Disposal of non-controlling interests	0	0	(181)
Repurchase of other equity instruments	0	(985)	(210)
Dividends paid on ordinary shares	(1,530)	(1,014)	(1,358)
Dividends paid on preference shares and other equity instruments	(123)	(150)	(147)
Principal elements of lease payments	(47)	(26)	(25)
Net cash flows from financing activities	19	277	(10,753)
Change in cash and cash equivalents	(3,861)	(2,891)	2,575
Cash and cash equivalents at beginning of the year	46,484	49,254	46,697
Effects of exchange rate changes on cash and cash equivalents	(121)	121	(18)
Cash and cash equivalents at the end of the year	42,502	46,484	49,254
Cash and cash equivalents consist of:
Cash and balances at central banks	38,214	44,190	48,139
Less: restricted balances	(2,311)	(2,223)	(2,498)
Cash and bank balances at central banks less regulatory minimum cash balances	35,903	41,967	45,641
Other cash equivalents: Loans and advances to banks - Non-trading	878	904	1,074
Other cash equivalents: Reverse repurchase agreements	5,721	3,613	2,539
Cash and cash equivalents at the end of the year	£ 42,502	£ 46,484	£ 49,254

Consolidated Statement of Chang

Consolidated Statement of Changes in Equity - GBP (£) £ in Millions	Total	Total	Share capital	Share premium	Other equity instruments	Fair value	Cash flow hedging	Currency translation	Retained earnings	Non-controlling interests
Beginning balance at Dec. 31, 2020	£ 15,936	£ 15,774	£ 3,105	£ 5,620	£ 2,191	£ 28	£ 481	£ 1	£ 4,348	£ 162
Profit after tax	1,384	1,365							1,365	19
Other comprehensive (expense)/income, net of tax:
- Fair value reserve (debt instruments)	(3)	(3)				(3)
- Cash flow hedges	(374)	(374)					(374)
- Pension remeasurement	845	845							845	0
- Own credit adjustment	0
Total other comprehensive income/(expense) net of tax	468	468				(3)	(374)		845
Total comprehensive income/(expense)	1,852	1,833				(3)	(374)		2,210	19
Issue of other equity instruments	210	210			210
Repurchase of other equity instruments	(210)	(210)			(210)
Disposal of non-controlling interests	(181)									(181)
Dividends on ordinary shares	(1,358)	(1,358)							(1,358)
Dividends on preference shares and other equity instruments	(147)	(147)							(147)
Ending balance at Dec. 31, 2021	16,102	16,102	3,105	5,620	2,191	25	107	1	5,053	0
Profit after tax	1,394	1,394							1,394
Other comprehensive (expense)/income, net of tax:
- Fair value reserve (debt instruments)	(20)	(20)				(20)
- Cash flow hedges	(1,235)	(1,235)					(1,235)
- Pension remeasurement	(455)	(455)							(455)
- Own credit adjustment	20	20							20
Total other comprehensive income/(expense) net of tax	(1,690)	(1,690)				(20)	(1,235)		(435)
Total comprehensive income/(expense)	(296)	(296)				(20)	(1,235)		959	0
Issue of other equity instruments	750	750			750
Repurchase of other equity instruments	(985)	(985)			(985)
Dividends on ordinary shares	(1,014)	(1,014)							(1,014)
Dividends on preference shares and other equity instruments	(150)	(150)							(150)
Ending balance at Dec. 31, 2022	14,407	14,407	3,105	5,620	1,956	5	(1,128)	1	4,848	0
Profit after tax	1,541	1,541							1,541
Other comprehensive (expense)/income, net of tax:
- Fair value reserve (debt instruments)	(11)	(11)				(11)
- Cash flow hedges	780	780					780
- Pension remeasurement	(431)	(431)							(431)
- Own credit adjustment	(11)	(11)							(11)
Total other comprehensive income/(expense) net of tax	327	327				(11)	780		(442)
Total comprehensive income/(expense)	1,868	1,868				(11)	780		1,099	0
Other	1	1							1
Dividends on ordinary shares	(1,530)	(1,530)							(1,530)
Dividends on preference shares and other equity instruments	(123)	(123)							(123)
Ending balance at Dec. 31, 2023	£ 14,623	£ 14,623	£ 3,105	£ 5,620	£ 1,956	£ (6)	£ (348)	£ 1	£ 4,295	£ 0

Risk Framework

Risk Framework	12 Months Ended
	Dec. 31, 2023
Risk Framework [Abstract]
Risk Framework	Our risk governance structure We are committed to the highest standards of corporate governance in every part of our business, including risk management. For details of our governance, including the Board and its Committees, see the ‘Governance’ section of this Annual Report. The Board delegates certain responsibilities to Board Level Committees as needed and where appropriate. Our risk governance structure strengthens our ability to identify, assess, manage and report risks, as follows: – Committees: A number of Board and Executive committees are responsible for specific parts of our Risk Framework – Key senior management roles: A number of senior roles have specific responsibilities for risk management – Risk organisational structure: We have the ‘three lines of defence’ model built into the way we run our business. Committees The Board and Board Level Committee responsibilities for risk are: Board Level Committee Main risk responsibilities The Board – Has overall responsibility for business execution and for managing risk – Reviews and approves the Risk Framework and Risk Appetite Board Risk Committee (BRC) – Assesses the Risk Framework and recommends it to the Board for approval – Advises the Board on our overall Risk Appetite, tolerance and strategy – Oversees our exposure to risk and our strategy and advises the Board on both – Reviews the effectiveness of our risk management systems and internal controls – Reviews reports from the Chief Compliance Officer (CCO) on the adequacy and effectiveness of the compliance function – Responsible for oversight of cybersecurity risks and receives regular updates on cybersecurity risk position including cybersecurity incidents – Receives regular updates on financial crime compliance and risks including money laundering, bribery and corruption and sanctions compliance and monitors KPIs in line with approved Board risk appetite Board Responsible Banking Committee – Responsible for culture and operational risk from conduct, compliance, competition & legal matters – Ensures that adequate and effective control processes are in place to identify and manage reputational risks – Oversees our Sustainability and Responsible Banking programme and how it impacts on employees, communities, the environment including sustainability and climate change, reputation, brand and market positioning – Reviews updates on key risk issues, customer, reputational and conduct matters Board Audit Committee – Monitors and reviews the financial statements integrity, and any formal announcements on financial performance – Reviews the adequacy and effectiveness of the internal financial controls and whistleblowing arrangements – Monitors and reviews the effectiveness of the internal audit function – Receives regular updates from the internal audit function which performs reviews of cybersecurity risk and controls – Oversees the independence and performance of the external auditors Board Remuneration Committee – Oversees implementation of remuneration policies, ensuring they promote sound and effective risk management The Executive Level Committee responsibilities for risk are: Executive Level Committee Main risk responsibilities Executive Committee (ExCo) – Reviews business plans in line with our Risk Framework and Risk Appetite before they are sent to the Board to approve – Receives updates on key risk issues managed by CEO-level committees and monitors the actions taken Senior Management Committee – Focuses on the responsibilities of the Executive Committee Senior Management Function holders and how they are discharged – Reviews updates on key risk issues, customer, reputational and conduct matters Executive Risk Control Committee (ERCC) – Reviews Risk Appetite proposals before they are sent to the BRC and the Board to approve – Ensures that we comply with our Risk Framework, Risk Appetite and risk policies – Reviews and monitors our risk exposures and approves any corrective steps we need to take Asset and Liability Committee (ALCO) – Reviews liquidity risk appetite (LRA) proposals – Ensures we measure and control structural balance sheet risks, including capital, funding and liquidity, in line with the policies, strategies and plans set by the Board – Reviews and monitors key asset and liability management activities to ensure we keep our exposures within our Risk Appetite Pensions Committee – Reviews pension risk appetite proposals – Approves actuarial valuations and reviews the impact they may have on our contributions, capital and funding – Consults with the pension scheme trustees on the scheme’s investment strategy Capital Committee – Puts in place reporting systems and risk control processes to make sure capital risks are managed within our Risk Framework – Reviews capital adequacy and capital plans, including the ICAAP, before they are sent to the Board to approve Incident Accountability Committee – Considers, calibrates, challenges and agrees any appropriate individual remuneration adjustments – Presents recommendations to the Board Remuneration Committee Credit Approval Committee – Approves corporate and wholesale credit transactions which exceed levels delegated to lower level forums or individuals Economic Crime Committee – Ensures due reporting, consideration, oversight and informed decision making regarding compliance with financial crime laws and regulations, fraud, and best industry practice aligned to our Risk Appetite Key senior management roles Senior roles with specific responsibilities for risk management are: Role Main risk responsibilities Chief Executive Officer (CEO) The Board delegates responsibility for our business activities and managing risk on a day-to-day basis to the CEO. The CEO proposes our strategy and business plan, puts them into practice and manages the risks involved. The CEO must also ensure we have a suitable system of controls to manage risks and report to the Board on them. Chief Risk Officer (CRO) Oversees and challenges risk activities, and ensures that the business activity is conducted within our risk appetite. Responsible for control and oversight of all risk types with regulatory responsibility to report on these risk types to Executive and Board Committees. Chief Financial Officer (CFO) Responsible for developing strategy, leadership and management of the CFO Division. The CFO is responsible for managing interest rate, liquidity, pension and capital risks. The CFO also aims to maximise the return on Regulatory and Economic Capital. Chief Internal Auditor (CIA) Designs and uses an audit system that identifies key risks and evaluates controls. The CIA also develops an audit plan to assess existing risks that involve producing audit, assurance and monitoring reports. Chief Compliance Officer (CCO) Responsible to the CRO for control and oversight of conduct & regulatory, reputational and economic crime risk, but has direct responsibility to report on conduct & regulatory and reputational risk to Executive and Board Committees and the regulator. Money Laundering Reporting Officer (MLRO) Responsible to the CCO for control and oversight of economic crime risk but has regulatory responsibility to report on this risk type to Executive and Board Committees and the regulator.

Credit Risk

Credit Risk	12 Months Ended
	Dec. 31, 2023
Disclosure of credit risk exposure [abstract]
Credit Risk	Credit risk Overview Credit risk is the risk of financial loss due to the default or credit quality deterioration of a customer or counterparty to which we provided credit, or for whom we have assumed a financial obligation. We set out how our exposures arise and our approach to credit risk across the credit risk lifecycle. We discuss our ECL approach and the key inputs to our ECL model. We then analyse our key metrics, credit performance and forbearance. Key metrics Stage 3 ratio of 1.51% ( 2022 : 1.26% ). Loss allowances of £992m ( 2022 : £1,005m ). Balance weighted average LTV of 66% ( 2022 : 69% ) on new mortgage lending. CREDIT RISK MANAGEMENT Exposures (audited) Exposures to credit risk arise in our business segments from: Retail and Business Banking Consumer Finance Corporate & Commercial Banking Corporate Centre In Mortgages: – Residential mortgages for customers with good credit quality (prime lending). – We provide these mostly for owner- occupiers, with buy-to-let mortgages for non-professional landlords. In Everyday Banking: – Unsecured lending to individuals, such as loans, credit cards and overdrafts. – Banking services to businesses with turnover up to £ 6.5 m per annum and simpler borrowing needs. We offer loans, credit cards and overdrafts. – Financing for cars, vans, motorbikes and leisure vehicles through Santander Consumer (UK) plc (SCUK). – Through our joint ventures, Hyundai Capital UK Ltd and Volvo Car Financial Services UK Limited, we provide retail point of sale customer finance and wholesale finance facilities (stock finance). – Loans, bank accounts, treasury services, invoice discounting, cash transmission, trade finance and asset finance. – We provide these to SMEs and mid- sized corporates with turnover up to £ 500 m per annum, Commercial Real Estate and Social Housing associations. – Asset and liability management of our balance sheet. – Exposures include financial institutions (derivatives and other treasury products), structured products, and sovereign and supranational assets chosen for diversification and liquidity. Our approach to credit risk We manage our portfolios across the credit risk lifecycle, from drawing up our risk strategy and planning, through assessment and origination, monitoring, arrears management and debt recovery. We make sure the actual risk profile of our exposures stays in line with our business plans and within our Risk Appetite. We tailor the way we manage risk to the type of product and regularly review our approach and refine it when we need to. 1. Risk strategy and planning ( audited) All relevant areas of the business work together to create our business plans. We aim to balance our strategy, goals, and financial and technical resources with our Risk Appetite. To do this, we focus on economic and market conditions and forecasts, regulations, conduct matters, profitability, returns and market share. 2. Assessment and origination (audited) Managing credit risk begins with lending responsibly. That means only lending to customers who are committed to paying us back and can afford to, even if their circumstances change. We perform a thorough risk assessment to make sure a customer can meet their obligations before we approve a loan. We take proportionate steps to assess whether a customer will be able to repay the money borrowed. We do this by a series of initial affordability and credit risk assessments. We access each customer’s credit profile and signs of how reliable they are at repaying credit. When a customer applies, we assess the data they provide, plus data from credit reference agencies (for Retail and Business Banking and Consumer Finance) and performance on their other Santander UK accounts (if they have any) against our Credit Policy. Retail and Business Banking In Mortgages, for secured loans, we assess affordability by reviewing the customer’s income and spending, their other credit commitments, and what would happen if interest rates went up. Many of our decisions are automated as we use data available to us. We tailor our process and application assessment based on the product. More complex transactions often need greater manual assessment using our credit underwriters’ skill and experience. In Everyday Banking and Business Banking, many of our decisions are automated. We assess affordability by reviewing the customer’s income and spending, including other credit commitments and adjusting for future inflation and expected interest rates. Credit risk mitigation The types of credit risk mitigation, including collateral, across each of our portfolios are: Portfolio Description Residential mortgages Collateral is in the form of a first legal charge over the property. Before we grant a mortgage, the property is valued either by a surveyor or using automated valuation methodologies where our confidence in the accuracy of this method is high. Unsecured lending There is no collateral or security tied to the loan that can be used to mitigate any potential loss if the customer does not pay us back. Business banking services Business banking lending is unsecured. When lending to incorporated businesses, we typically obtain personal guarantees from each director, but we do not treat these as collateral. We consider the UK Government guarantee supporting losses on amounts lent under its Coronavirus Loan Schemes as collateral with 100% for Bounce Back Loan Scheme (BBLS) and 80% for Coronavirus Business Interruption Loan Scheme (CBILS). Consumer Finance In Consumer Finance, similar to Retail and Business Banking, many decisions are automated and we tailor the process to the product. Residual value risk is one of our top risks. Credit risk mitigation The type of credit risk mitigation, including collateral, is: Portfolio Description Consumer (auto) finance Collateral is in the form of legal ownership of the vehicle for most loans, with the customer being the registered keeper. Only a very small proportion of business is underwritten as a personal loan. In these cases, there is no collateral or security tied to the loan. We use a leading vehicle valuation company to assess the LTV at the proposal stage to ensure the value of the vehicle is appropriate. Corporate & Commercial Banking We assign each customer a credit rating according to the internal rating threshold, using our internal rating scale (see ‘Credit quality’ in ‘Santander UK group level – credit risk review’ section). To do this, we look at the customer’s financial history and trends in the economy, backed up by the expert judgement of a risk analyst. We review our internal ratings on a dynamic basis and at least once a year for those clients that are rated. We also assess the underlying risk of the transaction, taking account of any mitigating factors (see the tables below) and how it fits with our risk policies, limits and Risk Appetite. Responsible lending, including climate change and the transition to a low carbon economy As part of the Banco Santander group, we comply with the Equator Principles to factor social, ethical and environmental impacts into our risk analysis and decision making for qualifying financial transactions. We are committed to supporting clients and economies in their transition to a low carbon economy, providing financial products and/or services to business activities that are environmentally and socially responsible. Our Environmental, Social and Climate Change (ESCC) policy sets out how we identify, assess, monitor and manage environmental and social risks and other climate change related activities in the Oil and Gas, Power Generation and Mining and Metals sectors and those arising from businesses engaged in soft commodities. Our ESCC policy prohibits project-related financing for new coal-fired power plants (CFPP) worldwide and we will only work with new clients with CFPPs to provide specific financing for renewable energy projects. In line with Banco Santander's commitment, by 2030 we will eliminate all exposure to thermal coal mining and stop providing financial services to power generation clients with more than 10% of revenue from thermal coal. Credit risk mitigation The types of credit risk mitigation, including collateral, across each of our portfolios are as follows. In addition, from time to time, at a portfolio level we execute significant risk transfer transactions, which typically reduce RWAs. Portfolio Description SME and mid corporate Includes secured and unsecured lending. We can take mortgage debentures or a first charge on commercial property as collateral. Before agreeing the loan, we get an independent professional valuation of the property. Loan agreements typically allow us to obtain revaluations during the term of the loan. We can also take guarantees, but we do not treat them as collateral unless they are supported by a tangible asset charged to us. We also lend against assets (like vehicles and equipment) and invoices for some customers. We value assets before we lend. For invoices, we review the customers' ledgers regularly and lend against debtors who meet agreed criteria. Commercial Real Estate We take a first charge on commercial property as collateral. The loan is subject to criteria such as the property condition, age and location, tenant quality, lease terms and length, and the sponsor’s experience and creditworthiness. Before advancing the loan and where appropriate, a bank representative visits the property. We also get an independent professional valuation which typically includes a site visit. Loan agreements typically allow us to obtain revaluations during the term of the loan. Social Housing We take a first charge on portfolios of residential real estate owned and let by UK Housing Associations as collateral, in most cases. We revalue this every three to five years (in line with industry practice), using the standard methods for property used for Social Housing. Corporate Centre Credit risk mitigation The types of credit risk mitigation, including collateral, across each of our portfolios are as follows. In addition, from time to time, at a portfolio level we execute significant risk transfer transactions, which typically reduce RWAs. Portfolio Description Sovereign and Supranational In line with market practice, there is no collateral against these assets. Structured Products These are our High Quality Liquid Assets (HQLA) in our Eligible Liquidity Pool. They are mainly Asset Backed Securities (ABS) and covered bonds, which hold senior positions in the creditor hierarchy. Their credit rating reflects over-collateralisation in the structure and the assets that underpin their cash flows. Financial Institutions We use standard legal agreements to reduce credit risk via netting and collateralisation on derivatives, repos and reverse repos, and stock borrowing/lending. We also reduce risk by clearing trades through central counterparties (CCPs) where possible. 3. Monitoring (audited) We measure and monitor changes in our credit risk profile on a regular and systematic basis against our budgets, limits and benchmarks. Credit concentrations A core part of our monitoring and management is a focus on credit concentrations, such as the proportion of our lending that goes to specific borrowers, groups or industries. We set and monitor concentration limits in line with our Risk Appetite and review them on a regular basis. – Geographical concentrations: We set exposure limits to countries and geographies, with reference to the country limits set by Banco Santander and our own Risk Appetite. For more geographical information, see ‘Country risk exposures’. – Industry concentrations: We also set exposure limits by industry sector. We set these limits based on the industry outlook, our strategic aims and desired level of concentration, and relevant limits set by Banco Santander. We analyse committed exposures in the ‘Credit risk review’ section that follows. Retail and Business Banking We use IT systems and data available to us to monitor accounts. The main parts are: – Behavioural scoring: we use statistical models that help predict whether a customer will have problems repaying, based on how they use their accounts – Credit reference agencies: we often use data from agencies on how the borrower is handling credit from other lenders in our behaviour scoring models – Other Santander UK accounts: each month, we also look at how the customer uses their other accounts with us, so we can identify problems early. Our day-to-day retail credit risk monitoring relies on a mix of product, customer and portfolio performance measures as described above. However, changes in the wider UK economy also impact our Mortgages and Everyday Banking portfolios. As part of our day-to-day risk monitoring, we use a Retail Risk Playbook tolerance framework that sets out the most relevant macroeconomic variables to retail portfolio performance. We monitor these variables against our forecasts. If the economy deviates materially from our forecasts, such as due to the effects of the cost of living crisis or high inflation, we formally review our retail risk management policy and strategy. We also use the Retail Risk Playbook tolerance framework and management judgements to ensure that portfolio quality remains within our Risk Appetite by measuring against trigger values for key risk profile and performance metrics. For secured lending, our monitoring also takes account of changes in property prices. We estimate the property’s value every three months. In most cases, we use statistical models based on recent sales prices and valuations in that local area. Use of this model is subject to Model Risk Governance. Where a lack of data means the model’s valuation is not available, we use the original surveyor valuation with a House Price Index (HPI) adjustment as needed. For unsecured personal lending like credit cards and overdrafts, monitoring might lead us to raise or lower credit limits. For business banking services, we review revolving credit facilities each year to ensure the facilities remain appropriate for the customer's financial circumstances. Consumer Finance In Consumer Finance, similar to Retail and Business Banking, we use IT systems and data available to us to monitor accounts, and we use the Retail Risk Playbook tolerance framework and management judgements to ensure that portfolio quality remains within Risk Appetite. We also check the Residual Value of our portfolio each month, using triggers set to identify any material change in trends. Corporate & Commercial Banking and Corporate Centr e We regularly monitor and report our credit risk by portfolio, segment, industry, location and customer. We monitor detailed analyses of our credit exposures and risk trends each month. We also report our larger exposures and risks to the BRC each month. Our Watchlist We also use a Watchlist for exposures subject to annual reviews to help identify potential problem debt early. Just because a customer is on our Watchlist does not mean they have defaulted. It just means that their probability of default has increased, such as they have breached a covenant or lost a major contract. We classify Watchlist cases as: – Enhanced monitoring: for less urgent cases. We monitor these cases more often and where appropriate may consider more collateral. – Pr oactive management: for more urgent or serious cases. We may take steps to restructure debt including extending the term, taking more collateral, agreeing a lower credit limit, or seeking repayment of the loan through refinancing or other means. We assess Watchlist cases for impairment as set out in the ‘Significant Increase in Credit Risk (SICR)’ section. When a customer is in enhanced monitoring, we do not consider it has suffered a SICR for ECL purposes, so it remains in Stage 1 for our loss allowance calculations. When a customer is in proactive management, we consider it has suffered a SICR, so we transfer it to Stage 2 and apply a lifetime ECL for our loss allowance calculations. We take into account any forbearance we offer. This includes any extra security, guarantees or equity available and the potential to enhance value by asset management. In Corporate & Commercial Banking, as part of our annual reviews, for loans nearing maturity, we look at the prospect of refinancing the loan on current market terms and applicable credit policy. If this is unlikely, we put the case on our Watchlist. We manage exposures not subject to annual reviews, mainly high volume and low value cases, using early warning indicators including credit reference agency data, supported by teams of expert analysts. In Corporate Centre, we typically monitor the credit quality of our exposures daily. We use internal and third-party data to detect any potential credit deterioration. 4. Arrears management ( audited) Retail and Business Banking and Consumer Finance We have several strategies to manage arrears that we can use as early as the day after a missed payment. We also reach out to up-to-date customers who may be at risk of going into arrears for support purposes. We assess the financial difficulties a customer is having, so we can offer them the right support to manage their agreement whilst in arrears. The strategy we use depends on the risk and the customer’s circumstances. Corporate & Commercial Banking and Corporate Centre We identify problem debt by close monitoring, supported by our Watchlist process for exposures subject to annual review. We aim to identify warning signs early by monitoring customers’ financial and trading data, checking to see they do not breach covenants, and having regular dialogue with them. We tailor our strategy to the type of customer, their circumstances and the level of risk. We try to help our customers find their own way out of financial difficulty and agree on a plan that works for both of us. We engage our Restructuring & Recoveries team as needed on Watchlist cases and we may hand over more serious cases to them. For exposures not subject to annual review, we have strategies to manage arrears that we can use as early as the day of the missed payment. If a case becomes more urgent or needs specialist attention, and if it transfers to Stage 3, we transfer it to our Restructuring & Recoveries team. For more, see the Forbearance section. 5. Debt recovery (audited) Sometimes, even when we have taken all reasonable and responsible steps to manage arrears in our Financial Support area, they are not effective. If this happens, we may choose to end our agreement with the customer and try to recover the outstanding balance (with recourse to any associated collateral), or as much of it as we can. Retail and Business Banking In Mortgages and Everyday Banking, we may use a debt collection agency, sell the debt, or take the customer to court. For retail mortgages, we may repossess the property as a last resort or to protect it from damage or third-party claims. We make sure our estimated losses from repossessed properties are realistic by getting two independent valuations and the estimated selling costs, and using them in our loss allowances calculations. Where we repossess a property, we do not take ownership. We use agents to realise the value and settle the debt. Any surplus funds are returned to the borrower or dealt with in line with insolvency rules. Consumer Finance In Consumer Finance, similar to Retail and Business Banking, we may use a debt collection agency or a specialist law firm to recover the balance outstanding. We may also consider the sale of debt where all avenues have been explored. Corporate & Commercial Banking and Corporate Centre Where we look for an exit, we aim to do this, if we can, by agreeing with the borrower that they will sell some or all their assets on a voluntary basis or agreeing to give them time to refinance their debt with another lender. Where we cannot reach an agreement, we consider recovery options. This can be through an insolvency proceeding, enforcing over any collateral or selling debt on the secondary market. We may also consider other legal action to recover what we are owed. If there is a shortfall, we write it off against our loss allowances. In very rare cases, we may act as mortgagee in possession of assets held as collateral against non-performing commercial lending. In such cases, we carry the assets on our balance sheet and classify them in line with our accounting policies. Loan modifications (audited) We sometimes change the terms of a loan when a customer gets into financial difficulty (this is known as forbearance), or for other commercial reasons. Forbearance (audited) We can change the terms of a customer's loan, temporarily or permanently, to help them through temporary periods of difficulty so they can get back on to sustainable terms. We assess what we offer to make sure the customer can afford it. Forbearance improves our customer relationships and we review our approach regularly to make sure it is still effective. We try to offer forbearance before a customer defaults and we only foreclose or repossess as a last resort. The main types of forbearance we offer are: Action Description Term extension We can extend the loan term, making each monthly payment smaller. We may offer this if the customer is up to date with payments but shows signs of financial difficulties. We may also offer this if the loan is about to mature and refinancing is not possible on market terms. Interest-only Historical interest-only payments due to financial difficulties are classed as forborne. For corporate customers, interest-only concessions are considered on a case by case basis. Concessions are only granted if the nature of the financial difficulties is assessed to be temporary. Counterparties are expected to recover in full and resume making full capital and interest payments once they are in a stronger financial position. Other payment rescheduling, including capitalisation For retail customers, we may add the arrears to the mortgage balance (this is known as capitalisation) if they cannot afford to increase their monthly payment to pay off their arrears in a reasonable time but have been making their monthly payments, usually for at least six months. We can also capitalise property charges due to a landlord. We pay them for the customer to avoid the lease being forfeited. We may combine this help with term extensions and, in the past, interest-only concessions. In certain cases, we may offer interest rate concessions. For corporate customers, we may lower or stop their payments until they have time to recover. We may reschedule payments to better match the customer’s cash flow – for example if the business is seasonal - or provide a temporary increase in facilities to cover peak demand ahead of their trading improving. We might do this by arrears capitalisation or drawing from an overdraft. We may also offer to provide new facilities, interest rate concessions and interest roll-up. In rare cases, we agree to forgive or reduce part of the debt. When we agree forbearance, we consider the account has suffered a significant increase in credit risk (SICR), as we explain later on, and we classify it as Stage 2 or 3. A non-performing forborne account is one that has forbearance carried out in Stage 3, and a performing forborne account is one that has forbearance carried out in Stage 2. If an account is already in Stage 2, we keep it in Stage 2 unless the account is deemed unlikely to pay, involves forgiving fees and interest or debt, or is being granted multiple forbearances. In these cases, we move it into Stage 3. If an account is already in Stage 3, we keep it in Stage 3. A loan moves out of forbearance once the exit criteria below are met. We monitor the performance of all forborne loans. We signed up to the HM Treasury Mortgage Charter published in June 2023, that aims to provide more support for customers who may be struggling to maintain their mortgage repayments. We made more customer support solutions available from July 2023, allowing customers who are up-to-date with their payments to make interest-only payments for six months or extend their mortgage term to reduce their monthly payments. Volumes of accounts seeking more support were less than 1% of active mortgage account stock. Mortgage Charter support solutions are not automatically classed as forbearance, unless other forbearance criteria are met. Exit from forbearance criteria Exit from Conditions to be met Cure Stage 3 to Stage 2 For an account in Stage 3 to exit non-performing forbearance, all the following conditions must be met: If the account was classed as Stage 3 due to being more than 90 days past due, then the account should be 90 days or less past due The customer has no other material default debt with us more than 90 days past due If the account was classed as Stage 3 due to being unlikely to pay, then the account should no longer be deemed unlikely to pay Account has exited its forbearance trigger for 12 consecutive months If all the conditions are met, the account is re-classed as Stage 2 forbearance until the Stage 2 forbearance exit conditions set out below are also met Stage 2 to Stage 1 For an account in Stage 2 to exit forbearance, all the following conditions must be met: The account is no longer in arrears, and the customer has no other material debts with us which are more than 30 days in arrears The account no longer triggers SICR The account has been classed as Stage 2 for at least two years since the end of the latest forbearance strategy If an account fails whilst in probation to cure, i.e. in the 12 months backstop in Stage 3 or the two years in Stage 2, the probation period is reset and the account is moved back to Stage 3. Other forms of debt management and modifications Retail and Business Banking In Mortgages, apart from forbearance, we have sometimes changed the contract terms to keep a good relationship with a customer. In Mortgages and Everyday Banking, we do not classify insolvency solutions for any unsecured retail customers as forbearance. This is in line with industry guidelines. Consumer Finance We do not classify insolvency solutions for any unsecured retail customers as forbearance. This is in line with industry guidelines. Corporate & Commercial Banking and Corporate Centre When customers are in financial difficulty, we can also manage debt in other ways, depending on the facts of the specific case: Action Description Waiving or changing covenants If a borrower breaks a covenant, we can either waive it or change it, taking their latest and future financial position into account. We may also add a condition on the use of any surplus cash (after operating costs) to pay down their debt to us. Asking for more collateral or guarantees If a borrower has unencumbered assets, we may accept more collateral in return for revised financing terms. We may also take a guarantee from companies in the same group and/or major shareholders. We only do this where we believe the guarantor can meet their commitment. Asking for more equity Where a borrower can no longer pay the interest on their debt, we may accept fresh equity capital from new or existing investors to change the capital structure in return for better terms on the existing debt. Risk measurement and control We measure and control credit risk at all stages across the credit risk lifecycle. We have a range of tools, processes and approaches. Retail and Business Banking and Consumer Finance These businesses involve managing large numbers of accounts, so they produce a huge amount of data. This allows us to take a more analytical and data intense approach to measuring risk. This is reflected in the wide range of statistical models we use across the credit risk lifecycle. We use: – Risk strategy and planning: econometric models – Assessment and origination: application scorecards, and attrition, pricing, loss allowance and capital models – Monitoring: behavioural scorecards and profitability models – Arrears management: models to estimate the proportion of cases that will result in possession (known as roll rates) – Debt recovery: recovery models. We assess and review our loss allowances regularly and have them independently reviewed. We look at factors such as the cash flow available to service debt. We also use an agency to value any collateral – mainly mortgages. Corporate & Commercial Banking and Corporate Centre We measure the credit risk on treasury products by adding their potential future exposure to market movements over their lives to their fair value. Then we add it to any other exposure and measure the total against our credit limits for each client. We assess our loss allowances regularly by looking at factors such as the cash flow available to service debt and the value of collateral based on third-party professiona l valuations. Key metrics (audited) We use a number of key metrics to measure and control credit risk, as follows: Metric Description Expected Credit Loss (ECL) ECL tells us what credit risk is expected to cost us either over the next 12 months or over the lifetime of the exposure where there is evidence of a SICR since origination. We explain how we calculate ECL below. Stages 1, 2 and 3 We assess each facility’s credit risk profile to determine which stage to allocate them to, and we monitor where there is a SICR and transfers between the Stages including monitoring of coverage ratios for each stage. Stage 3 ratio The Stage 3 ratio is the sum of Stage 3 drawn and Stage 3 undrawn assets divided by the sum of total drawn assets and Stage 3 undrawn assets. The Stage 3 ratio is a key indicator used to monitor underlying asset performance. Expected Loss (EL) EL is based on the CRD IV regulatory capital rules and gives us another view of credit risk. It is the product of the probability of default, exposure at default and loss given default, and we include direct and indirect costs. We base it on our risk models and our assessment of each customer’s credit quality. The rest of our Risk review, impairments, losses and loss allowances refer to calculations in accordance with IFRS, unless we specifically say they relate to CRD IV. For our IFRS impairment accounting policy, see Note 1 to the Consolidated Financial Statements. We also assess risks from other perspectives, such as geography, business area, product and process to identify areas to focus on. We also use stress testing to establish vulnerabilities to economic deterioration. Our business segments tailor their approach to credit risk to their customers, as we explain later on. Recognising ECL (audited) The ECL approach estimates the credit losses arising from defaults in the next 12 months on qualifying exposures, or defaults over the lifetime of the exposure where there is evidence of a Significant Increase in Credit Risk (SICR) since the origination date. The ECL approach considers forward-looking data, including a range of possible outcomes, which should be unbiased and probability-weighted to reflect the risk of a loss being incurred even when it is unlikely. Critical judgements and accounting estimates applied in calculating ECL (audited) The application of the ECL impairment methodology for calculating credit impairment allowances is susceptible to change from period to period. The methodology requires management to make judgmental assumptions in determining the estimates. For more on our approach to making critical judgements and accounting estimates applied in calculating ECL see 'Critical judgements and accounting estimates' Note 1 to the Consolidated Financial Statements. Multiple economic scenarios and probability weights (audited) For all our portfolios, we use five forward-looking economic scenarios. For 2023 , they consisted of a central base case, one upside scenario and three downside scenarios. We use five scenarios to reflect a wide range of possible outcomes for the UK economy. Our forecasting approach We derive our scenarios in part by using a set of parameters in GDP fan charts published by the Office for Budget Responsibility (OBR). These fan charts reflect the probability distribution of a deviation from the OBR’s central forecast to show the uncertainty about the outcome of a variable, in this case GDP. Once we have established the GDP paths for each scenario, we run them through the Oxford Global Economic Model (OGEM) to derive the other macroeconomic variables, such as unemployment and house prices. These variables are the product of the GDP growth paths we have forecast and the output of the OGEM for these growth paths. We then review them to ensure cons

Liquidity Risk

Liquidity Risk	12 Months Ended
	Dec. 31, 2023
Disclosure Of Liquidity Risk Exposure [Abstract]
Liquidity Risk	Liquidity risk Overview Liquidity risk is the risk that we do not have sufficient liquid financial resources available to meet our obligations when they fall due, or we can only secure such resources at excessive cost. In this section, we describe our sources and uses of liquidity and how we manage liquidity risk. We also analyse our key liquidity metrics, including our LCRs and our eligible liquidity pools. We then explain our funding strategy and structure and we analyse our wholesale funding. Finally, we analyse how we have encumbered some of our assets to support our funding activities. Key metrics LCR of 159% ( 2022 : 157% ) RFB DoLSub NSFR of 136% ( 2022 : 135% ) RFB DoLSub LCR of 157% ( 2022 : 152% ) Wholesale funding with maturity <1 year £ 11.9 bn ( 2022 : £ 11.0 bn) RFB DoLSub LCR eligible liquidity pool of £ 48.3 bn ( 2022 : £ 46.3 bn) OUR KEY LIQUIDITY RISKS (audited) Through our Liquidity Risk Appetite (LRA) framework, we manage our funding or structural contingent and market liquidity risks wherever they arise. This can be in retail and corporate deposit outflows, wholesale secured and unsecured liquidity outflows and off-balance sheet activities. Other risks our framework covers include funding concentrations, intra-day cash flows, intra-group commitments and support, franchise retention and cross currency risk. Our main sources of liquidity Customer deposits finance most of our customer lending. Although these funds are mostly callable, in practice they give us a stable and predictable core of funding. This is due to the nature of retail accounts and the breadth of our retail customer relationships. We have a strong wholesale funding investor base, diversified across product types and geographies. Through the wholesale markets, we have active relationships in many sectors including banks, other financial institutions, corporates, pensions and investment funds. We access the wholesale funding markets through the issuance of capital, senior unsecured debt, covered bonds, structured notes and short-term funding. We also access these markets through securitisations of certain assets of Santander UK plc and our operating subsidiaries. For more on our programmes, see Notes 14 , 26 and 27 in the Consolidated Financial Statements. We generate funding on the strength of our own balance sheet, our own profitability and our own network of investors. In addition, we have access to UK Government funding schemes. We comply with rules set by the PRA, other regulators, and Banco Santander standards. While we manage, consolidate and monitor liquidity risk centrally, we also manage and monitor it in the business area it comes from. Our main uses of liquidity Our main uses of liquidity are to fund our lending in Retail and Business Banking, Consumer Finance and Corporate & Commercial Banking, to pay interest and dividends, and to repay debt. Our ability to pay dividends depends on various factors. These include our regulatory capital needs, the level of our distributable reserves, and our financial performance. We also use liquidity to pay for business combinations. LIQUIDITY RISK MANAGEMENT Introduction We manage liquidity risk on a consolidated basis in our CFO division, which is our centralised function for managing funding, liquidity and capital. We created our governance, oversight and control frameworks, and our LRA, on the same consolidated basis. Under the PRA’s liquidity rules, Santander UK plc and its subsidiary Cater Allen Limited form the RFB Domestic Liquidity Sub-group (the RFB DoLSub), which allows them to collectively meet regulatory requirements to manage liquidity risk. Each member of the RFB DoLSub will support the other by transferring surplus liquidity in times of stress. Risk appetite Our LRA is based on the principles of liquidity management we use to manage our balance sheet. It also supports our need to meet or exceed regulatory rules. In line with our liquidity management principles, we avoid an over-reliance on funding from a single product, customer or counterparty. We also maintain enough unencumbered customer assets to support current and future funding and collateral requirements and maintain enough capacity to monetise liquid assets and other counterbalancing capacity on a timely basis. Our LRA is proposed to the Risk division and the Board, which is then approved under advice from the Board Risk Committee. Our LRA, in the context of our overall Risk Appetite, is reviewed and approved by the Board each year, or more often if needed. Risk measurement We use a number of metrics to manage liquidity risk. These include metrics that show the difference between cash and collateral inflows and outflows in different periods. They also include structural metrics, such as our level of encumbered assets. Ongoing business management Within our framework of prudent funding and liquidity management, we manage our activities to our liquidity risk appetite. We have clear responsibilities for short- term funding, medium-term funding, encumbrance, collateral and liquid asset management. This ensures we manage liquidity risks as part of our daily operations, strategy and planning. Our liquidity management framework is split between short-term and strategic activities. Our short-term activities focus on intra-day collateral management and maintaining liquid assets to cover unexpected demands on cash in a stress, such as large and unexpected deposit withdrawals by customers and loss of wholesale funding. Our strategic activities focus on ensuring we are not over reliant on any one source for funding and that we avoid excessive concentrations in the maturity of our funding. We regularly test the liquidity of our eligible liquidity pool, in line with PRA rules and Basel guidelines. We do this by realising some of the assets by repurchase or outright sale to the market. We make sure that over any 12-month period we realise a significant part of our eligible liquidity pool. As well as our eligible liquidity pool, we always hold a portfolio of unencumbered liquid assets. Our LRA and PRA requirements determine the size and composition of this portfolio. These assets give us a source of contingent liquidity, as we can realise some of them in a stress to create liquidity by repurchase or outright sale to the market. Stress testing Our liquidity stress testing framework is central to our LRA measurement and monitoring. To fit with our Risk Appetite, the liquidity outflows that come from these stress tests must be fully covered with high-quality liquid assets, other liquid assets and appropriate management actions. Our Risk division runs a range of stress tests. Our LRA stress test consists of three tests that cover idiosyncratic, market-wide and combined scenarios. Our other tests consider scenarios such as a global economic slowdown that results in reduced confidence in banks, a slowdown in a major economy or a decline in access to liquidity. These are considered on both an acute and protracted basis. We also run severe combined stress tests which look at both a deep and prolonged UK recession that results in a reduction in wholesale funding availability and an idiosyncratic shock that would lead to retail and commercial outflows. We run climate change stresses, these include severe physical risks which result in a reduction in retail deposits, increased use of corporate lending facilities and an increase in mortgage defaults and a scenario where there is disorderly transition to net zero, resulting in supply shocks and data transparency concerns. We also conduct sensitivity analysis and reverse stress testing for instant liquidity shocks by each key liquidity risk. We do this to understand the impacts they would have on our LRA and our regulatory liquidity metrics. We monitor our LCR and our Net Stable Funding Ratio (NSFR) to ensure we continue to meet the requirements. Risk mitigation (audited) The Board aims to make our balance sheet resilient at all times and for it to be perceived as such by stakeholders. This preserves our short and long-term viability. The Board recognises that as we are involved in maturity transformation, we cannot hold enough liquidity to cover all possible stress scenarios. The Board requires us to hold enough liquidity to make sure we will survive three plausible but severe stress scenarios (our LRA stress test, described above). We do this by maintaining a prudent balance sheet structure and approved liquid resources. Recovery and Resolution framework The CFO is the accountable SMF for recovery and resolution and the related work is managed by the CFO division. They are overseen by the Board Audit Committee and the Board. We review and refresh our recovery plan each year. It sets out the risks, the indicators we use to monitor those risks, and the actions that are available to mitigate capital, liquidity or combined stress event. We are confident that we have sufficient credible and executable options to respond to a wide range of stresses, be they market-wide or idiosyncratic, in a timely and effective manner. Recovery indicators are both qualitative and quantitative and we have embedded them into our risk frameworks. We monitor recovery capacity, headroom to recovery triggers and recovery indicators regularly. If needed, we would invoke recovery early to mitigate the effects of a stress and restore our financial position and balance sheet strength. Our resolution capabilities are underpinned by comprehensive governance, testing and assurance arrangements, which seek to ensure that our resolution readiness is maintained and enhanced on an ongoing basis. In October 2023, we submitted our second resolvability self-assessment report to the PRA. This builds on the first self-assessment report submitted in October 2021, as summarised in our June 2022 resolvability public disclosure. The next resolvability public disclosures by the Bank of England and Santander UK are due in June 2024. Risk monitoring and reporting (audited) We monitor liquidity risk daily, weekly and monthly. We do this through different committees and levels of management, including ALCO and the BRC. LIQUIDITY RISK REVIEW Liquidity Coverage Ratio This table shows our LCR at 31 December 2023 and 31 December 2022 . 2023 2022 RFB DoLSub LCR (2) £bn £bn Eligible liquidity pool (liquidity value) (1) 47.8 46.2 Net stress outflows (30.4) (30.4) Surplus 17.4 15.8 Eligible liquidity pool as a percentage of anticipated net cash flows 157 % 152 % (1) The liquidity value is calculated as applying an applicable haircut to the carrying value. (2) The RFB LCR was 159% ( 2022 : 157% ). LCR eligible liquidity pool This table shows the carrying value of our eligible liquidity pool assets at 31 December 2023 and 31 December 2022 . It also shows the weighted average carrying value in the year. RFB DoLSub Carrying value Weighted average carrying value in the year 2023 2022 2023 2022 Level 1 Level 2 Total Level 1 Level 2 Total Total Total £bn £bn £bn £bn £bn £bn £bn £bn Cash and balances at central banks 36.1 — 36.1 42.1 — 42.1 38.6 43.5 Government bonds 8.7 0.3 9.0 2.9 — 2.9 6.8 3.8 Supranational bonds and multilateral development banks 0.3 — 0.3 0.3 — 0.3 0.1 0.1 Covered bonds 1.2 1.0 2.2 0.1 0.9 1.0 1.7 0.9 Asset-backed securities — 0.7 0.7 — — — 0.4 0.1 46.3 2.0 48.3 45.4 0.9 46.3 47.6 48.4 Term duration in the LCR eligible liquidity pool is hedged with swaps to offset mark to market movements from interest rate changes. Currency analysis This table shows the carrying value of our eligible liquidity pool by major currencies at 31 December 2023 and 31 December 2022 . The composition of the pool is consistent with the currency profile of our net liquidity outflows. RFB DoLSub US Dollar Euro Sterling Other Total £bn £bn £bn £bn £bn 2023 2.4 1.1 44.0 0.8 48.3 2022 0.8 1.3 44.2 — 46.3 RFB DoLSub Net Stable Funding Ratio (NSFR) 2023 2022 % % RFB DoLSub NSFR 136 135 2023 compared to 2022 We remain in a strong liquidity position. We hold sufficient liquid resources and have adequate governance and controls in place to manage the liquidity risks arising from our business and strategy. At 31 December 2023 and 31 December 2022 , the LCR and NSFR significantly exceeded regulatory requirements. FUNDING RISK MANAGEMENT Funding strategy Our funding strategy continues to be based on maintaining a conservatively structured balance sheet and diverse sources of funding to meet the needs of our business strategy and plans. The CFO Division maintains a funding plan that complies with the LRA and regulatory liquidity and capital requirements. Most of our funding comes from customer deposits. We source the rest from a mix of secured and unsecured funding in the wholesale markets. Overall, this means that we do not rely too heavily on wholesale funds. We manage funding requirements by targeting a specific Liquidity Coverage Ratio, we ensure maturities are prefunded and capital/Minimum Requirements for Eligible Liabilities (MREL) requirements are prioritised. We also have checks and controls to limit our asset encumbrance from our secured funding operations. As part of maintaining a diverse funding base, we raise funding in a number of currencies, including EUR and USD, and convert it into sterling through currency swaps to fund our commercial assets which are largely sterling denominated. Our base of stable retail and corporate deposits is a key funding source for us. We leverage our large and diverse customer base to offer products that give us a long-term sustainable source of funding. We do this by focusing on building long-term relationships. At 31 December 2023, 86% of our total core retail customer liabilities were covered by the Financial Services Compensation Scheme (the FSCS). Behavioural maturities The contractual maturity of our balance sheet assets and liabilities highlights the maturity transformation that underpins the role of banks to lend long term, but to fund themselves mainly with shorter-term liabilities, like customer deposits. We do this by diversifying our funding operations across a wide customer base, both in numbers and by type of depositor. In practice, the behavioural profiles of many liabilities show more stability and longer maturity than their contractual maturity. This is especially true of many retail and corporate deposits that, while they may be repayable on demand or at short notice, have shown good stability even in times of stress. We model behaviour profiles using our experience of customer behaviour. We use this data to determine the funds transfer pricing rates at which we reward and charge our business units for sources and uses of funds. We apply this rate until a customer changes to a different product or service offered by us or by one of our competitors. We continue to maintain the quality of our retail, commercial and wholesale deposits. We aim to deepen our customer relationships across all customer segments. We do this to lengthen the contractual and behavioural profile of our liability base. FUNDING RISK REVIEW Our funding strategy continues to be based on maintaining a conservatively structured balance sheet and diverse sources of funding to meet the needs of our business strategy and plans. The CFO Division maintains a funding plan that complies with our LRA and regulatory liquidity and capital requirements. Reconciliation of wholesale funding to the balance sheet (audited) This table reconciles our wholesale funding to our balance sheet at 31 December 2023 and 31 December 2022 . Balance sheet line item Funding analysis Deposits by banks (1) Deposits by customers (2) Repurchase agreements - non trading Financial liabilities designated at fair value Debt securities in issue Subordinated liabilities Other equity instruments (3) 2023 £bn £bn £bn £bn £bn £bn £bn £bn Deposits by banks 1.1 1.1 — — — — — — Certificates of deposit and commercial paper 4.3 — — — — 4.3 — — Senior unsecured – public benchmark 12.7 — 1.6 — — 11.1 — — – privately placed 0.8 — 0.1 — 0.6 0.1 — — Covered bonds 14.8 — — — — 14.8 — — Securitisation and structured issuance 2.7 — — — — 2.7 — — TFSME 17.0 17.0 — — — — — — Subordinated liabilities and equity 4.2 — — — — — 2.2 2.0 Total wholesale funding 57.6 18.1 1.7 — 0.6 33.0 2.2 2.0 Repos 8.4 — — 8.4 — — — — Foreign exchange and hedge accounting 1.1 — — — — 0.9 0.2 — Other 2.5 2.2 — — 0.3 — — — Balance sheet total 69.6 20.3 1.7 8.4 0.9 33.9 2.4 2.0 2022 Deposits by banks 0.5 0.5 — — — — — — Certificates of deposit and commercial paper 4.7 — — — — 4.7 — — Senior unsecured – public benchmark 14.3 — 4.6 — — 9.7 — – privately placed 0.6 — 0.1 — 0.4 0.1 — — Covered bonds 14.9 — — — — 14.9 — — Securitisation and structured issuance 1.0 — — — — 1.0 — — TFSME 25.0 25.0 — — — — — — Subordinated liabilities and equity 3.9 — — — — — 1.9 2.0 Total wholesale funding 64.9 25.5 4.7 — 0.4 30.4 1.9 2.0 Repos 8.0 — — 8.0 — — — — Foreign exchange and hedge accounting 1.6 — 0.1 — — 1.1 0.4 — Other 3.4 3.0 — — 0.4 — — — Balance sheet total 77.9 28.5 4.8 8.0 0.8 31.5 2.3 2.0 (1) Consists of Perpetual Capital Securities . See Note 33 to the Consolidated Financial Statements. (2) This is included in our balance sheet total of 190,850 m( 2022 : £ 195,568 m ). (3) Other consists of items in the course of transmission and other deposits. See Note 24 to the Consolidated Financial Statements. Maturity profile of wholesale funding (audited) This table shows our main sources of wholesale funding. It does not include securities finance agreements. The table is based on exchange rates at issue and scheduled repayments and call dates. It does not reflect the final contractual maturity of the funding. For details of the maturities of financial liabilities and off-balance sheet commitments, see Note 39 to the Consolidated Financial Statements . ≤ 1 month >1 and ≤ 3 months >3 and ≤ 6 months >6 and ≤ 9 months >9 and ≤ 12 months Sub-total ≤ 1 year >1 and ≤ 2 years >2 and ≤ 5 years >5 years Total 2023 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Downstreamed from Santander UK Group Holdings plc to Santander UK plc (1) Senior unsecured – public benchmark — 1.6 — — — 1.6 2.4 6.8 0.4 11.2 – privately placed — — — — — — — 0.1 — 0.1 Subordinated liabilities and equity (incl. AT1) — — 0.5 — — 0.5 0.8 1.3 0.9 3.5 — 1.6 0.5 — — 2.1 3.2 8.2 1.3 14.8 Other Santander UK plc Deposits by banks 0.3 0.8 — — — 1.1 — — — 1.1 Certificates of deposit and commercial paper 1.0 3.3 — — — 4.3 — — — 4.3 Senior unsecured – public benchmark — 0.6 0.2 — — 0.8 0.4 — 0.3 1.5 – privately placed — — — 0.1 — 0.1 0.1 0.2 0.3 0.7 Covered bonds 0.1 1.0 0.9 0.4 1.0 3.4 1.1 9.2 1.1 14.8 Securitisation & structured issuance (2) — — — — 0.1 0.1 — 2.1 — 2.2 TFSME — — — — — — 17.0 — — 17.0 Subordinated liabilities — — — — — — — — 0.7 0.7 1.4 5.7 1.1 0.5 1.1 9.8 18.6 11.5 2.4 42.3 Other group entities Securitisation & structured issuance (3) — — — — — — 0.5 — — 0.5 31 December 2023 1.4 7.3 1.6 0.5 1.1 11.9 22.3 19.7 3.7 57.6 Of which: – Secured 0.1 1.0 0.9 0.4 1.1 3.5 18.6 11.3 1.1 34.5 – Unsecured 1.3 6.3 0.7 0.1 — 8.4 3.7 8.4 2.6 23.1 2022 Total at 31 December 2022 2.6 5.2 0.5 1.5 1.2 11.0 6.6 42.2 5.1 64.9 Of which: – Secured 0.1 1.0 0.2 0.9 — 2.2 3.5 34.0 1.2 40.9 – Unsecured 2.5 4.2 0.3 0.6 1.2 8.8 3.1 8.2 3.9 24.0 (1) 96% of senior unsecured debt issued from Santander UK Group Holdings plc has been downstreamed to Santander UK plc as ‘secondary non-preferential debt’ in line with the guidelines from the Bank of England for Internal MREL. (2) Includes funding from mortgage-backed securitisation vehicles where Santander UK plc is the asset originator. (3) Includes funding from asset-backed securitisation vehicles where entities other than Santander UK plc are the asset originator. 2023 compared to 2022 Together with our immediate parent, Santander UK Group Holdings plc, o ur overall funding strategy remains to develop and sustain a diversified funding base. We also need to fulfil regulatory requirements as well as support our credit ratings. We have stable and diversified wholesale funding programmes. We repaid £8.0bn of TFSME in 2023 as planned, with £17.0bn outstanding. At 31 December 2023 , 79% (2022: 83% ) of wholesale funding had a maturity of greater than one year, with an overall residual duration of 35 months (2022: 37 months). Currency composition of wholesale funds (audited) This table shows our wholesale funding by major currency at 31 December 2023 and 31 December 2022 . 2023 2022 Sterling US Dollar Euro Other Sterling US Dollar Euro Other % % % % % % % % Downstreamed from Santander UK Group Holdings plc to Santander UK plc Senior unsecured – public benchmark 23 60 17 — 18 58 24 — – privately placed — — — 100 — — — 100 Subordinated liabilities and equity (incl. AT1) 87 13 — — 75 25 — — 38 48 13 1 27 52 20 1 Other Santander UK plc Deposits by banks 1 97 2 — 29 71 — — Certificates of deposit and commercial paper 29 70 — 1 56 42 2 — Senior unsecured – public benchmark 21 56 23 — 18 62 20 — – privately placed 98 — 2 — 95 — 5 — Covered bonds 54 5 39 2 43 12 45 — Securitisation & structured issuance 100 — — — 100 — — — TFSME 100 — — — 100 — — — Subordinated liabilities 76 24 — — 48 52 — — 71 14 15 — 74 12 14 — Other group entities Securitisation & structured issuance 100 — — — — — — — Total 63 23 14 — 63 21 16 — Term issuance (audited) In 2023 , our external term issuance (sterling equivalent) was: Sterling US Dollar Euro Other 2023 2022 £bn £bn £bn £bn £bn £bn Downstreamed from Santander UK Group Holdings plc to Santander UK plc Senior unsecured – public benchmark 0.4 1.1 — — 1.5 3.9 Subordinated debt and equity (inc. AT1) 1.1 1.1 0.8 1.5 1.1 — — 2.6 4.7 Other Santander UK plc Securitisations and other secured funding 1.5 — — — 1.5 0.6 Covered bonds 1.5 — — 0.3 1.8 4.0 Senior unsecured – public benchmark — — — — — — Senior unsecured – privately placed 0.3 — — — 0.3 0.1 3.3 — — 0.3 3.6 4.7 Other group entities Securitisations 0.5 — — — 0.5 — Total gross issuances 5.3 1.1 — 0.3 6.7 9.4 In 2023 we issued c£5.6bn medium-term funding across a range of currencies, including c£1.5bn of issuance to Santander UK Group Holdings plc and c£4.1bn of other secured issuance . We also issued £1.1bn of Tier 2 securities which were bought by Santander UK Group Holdings plc . Encumbrance We encumber an asset if we pledge or transfer it as collateral against a liability. This means it is no longer available to secure funding, meet our collateral needs or be sold to reduce funding needs. Being able to pledge or transfer assets as collateral is a key part of a bank’s operations. The main ways we encumber assets are that we: enter into securitisation, covered bonds, and repurchase agreements to access medium and long-term funding; enter into short-term funding transactions (including repurchase agreements and stock borrowing) as part of our liquidity management; pledge collateral as part of participating in payment and settlement systems; and post collateral as part of derivatives activity. We control levels of encumbrance by setting a minimum level of unencumbered assets after we factor in our funding plans, whether we can use our assets for our future collateral needs, the impact of a stress and our current encumbrance level. Assets classified as readily available for encumbrance include cash and securities in our eligible liquidity pool. They also include other unencumbered assets that give us a source of contingent liquidity. We do not rely on these extra unencumbered assets in our LRA, but we might use them in a stress. We can create liquidity by using them as collateral for secured funding or through outright sale. This includes excess collateral already in a secured funding structure and collateral pre- positioned at central banks that is available for use in secured funding. All other loans and advances are classified as not readily available for encumbrance, however, they may still be suitable for use in secured funding structures. Encumbrance of customer loans and advances We issued securitised products to a diverse investor base through our prime mortgage-backed and other asset-backed funding programmes. We raised funding with mortgage-backed notes, both issued to third parties and retained – the latter being central bank eligible collateral for funding purposes in other Bank of England facilities. We also have a covered bond programme, under which we issue securities to investors secured by a pool of residential mortgages. For more on these programmes, see Notes 14 and 26 to the Consolidated Financial Statements . On-balance sheet encumbered and unencumbered assets (audited) Encumbered with counterparties other than central banks Assets positioned at central banks (3) Covered bonds Securitis- ations Other Total 2023 £m £m £m £m £m Cash and balances at central banks (1)(2) — — 1,480 1,480 831 Financial assets at FVTPL: – Derivative financial instruments — — — — — – Other financial assets at FVTPL — — — — — Financial assets at amortised cost: – Loans and advances to customers 21,880 5,208 59 27,147 58,489 – Loans and advances to banks — — 254 254 — – Repurchase agreements – non trading — — — — — – Other financial assets at amortised cost — — 14 14 — Financial assets at FVOCI — — 5,183 5,183 — Interests in other entities — — — — — Intangible assets — — — — — Property, plant and equipment — — — — — Current tax assets — — — — — Retirement benefit assets — — — — — Other assets — — — — — Total assets 21,880 5,208 6,990 34,078 59,320 2022 Cash and balances at central banks (1)(2) — — 1,330 1,330 893 Financial assets at FVTPL: – Derivative financial instruments — — — — — – Other financial assets at FVTPL — — — — — Financial assets at amortised cost: – Loans and advances to customers 21,304 2,851 56 24,211 68,535 – Loans and advances to banks — — 163 163 — – Repurchase agreements – non trading — — — — — – Other financial assets at amortised cost — — 48 48 — Financial assets at FVOCI — — 4,365 4,365 — Interests in other entities — — — — — Intangible assets — — — — — Property, plant and equipment — — — — — Current tax assets — — — — — Retirement benefit assets — — — — — Other assets — — — — — Total assets 21,304 2,851 5,962 30,117 69,428 (1) Encumbered cash and balances at central banks include minimum cash balances we have to hold at central banks for regulatory purposes. (2) Readily realisable cash and balances at central banks are amounts held at central banks as part of our liquidity management activities. (3) Comprises pre-positioned assets and encumbered assets.

Capital Risk

Capital Risk	12 Months Ended
	Dec. 31, 2023
Disclosure Of Capital Risk Exposure [Abstract]
Capital Risk	Capital risk Overview Capital risk is the risk that we do not have an adequate amount or quality of capital to meet our business objectives, regulatory requirements and market expectations. In this section, we set out how we are regulated. We explain how we manage capital on a standalone basis as a subsidiary in the Banco Santander group. We then analyse our capital resources and key capital ratios including our RWAs. Key metrics CET1 capital ratio of 15.4% ( 2022 : 15.4% ) Total qualifying regulatory capital of £ 14.6 bn ( 2022 : £ 14.3 bn) THE SCOPE OF OUR CAPITAL ADEQUACY Regulatory supervision For capital purposes, we are subject to prudential supervision by the PRA, as a UK banking group, and by the European Central Bank (ECB) as part of the Banco Santander group. The ECB supervises Banco Santander as part of the Single Supervisory Mechanism (SSM). Although we are part of the Banco Santander group, we do not have a guarantee from Banco Santander SA and we operate as a standalone subsidiary. As we are part of the UK sub-group regulated by the PRA, we have to meet the PRA capital requirements on a standalone basis. We also have to show the PRA that we can withstand capital stress tests without the support of our parent. Reinforcing our corporate governance framework, the PRA exercises oversight through its rules and regulations on the Board and senior management appointments. Santander UK Group Holdings plc is the holding company of Santander UK plc and is the head of the Santander UK group for regulatory capital and leverage purposes. Santander UK plc is the head of the ring-fenced bank sub-group and is subject to regulatory capital and leverage rules in relation to that sub-group. Our basis of consolidation for our capital disclosures is substantially the same as for our Consolidated Financial Statements. CAPITAL RISK MANAGEMENT The Board is responsible for capital management strategy and policy and ensuring that we monitor and control our capital within regulatory and internal limits. We manage our funding and maintain capital adequacy on a standalone basis. We operate within the capital risk framework and appetite approved by our Board. This reflects the environment we operate in, our strategy for each material risk and the potential impact of adverse scenarios or stresses on our capital. Management of capital requirements (audited) Our capital risk appetite aims to maintain capital levels appropriate to the level of stress applied, and the expected regulatory response. In: – An adverse economic stress, which we expect once in 20 years, the firm should remain profitable and exceed all regulatory capital minimums at all times. – A very severe economic stress, which we expect once in 100 years, and which has been designed to test any specific weaknesses of a firm’s business model, the firm should meet all regulatory capital minimums at all times. This is subject to using regulatory buffers designed to absorb losses in such a stress. Management of capital resources (audited) We use a mix of regulatory and EC ratios and limits, internal buffers and restrictions to manage our capital resources. We also take account of the costs of differing capital instruments and capital management techniques. We also use these to shape the best structure for our capital needs. We decide how to allocate our capital resources as part of our strategic planning process. We base this in part on the relative returns on capital using both EC and regulatory capital measures. We plan for severe stresses and we set out what action we would take if an extremely severe stress threatened our viability and solvency. This could include not paying dividends, selling assets, reducing our business and issuing more capital. Risk measurement We apply Banco Santander’s approach to capital measurement and risk management for CRD IV. Santander UK plc is classified as a significant subsidiary of Banco Santander SA. For more on the CRD IV risk measurement of our exposures, see Banco Santander’s Pillar 3 report. Key metrics The main metrics we use to measure capital risk are CET1 capital ratio and total capital ratio . We continue to be in excess of overall capital requirements, minimum leverage requirements and minimum requirements for own funds and eligible liabilities (MREL). Stress testing Each year we create a capital plan, as part of our ICAAP. We share our ICAAP with the PRA. The PRA then tells us how much capital (Pillar 2A), and of what quality, it thinks we should hold on top of our Pillar 1 requirements and buffer levels. We also develop a series of economic scenarios to stress test our capital needs and confirm that we have enough regulatory capital to meet our projected and stressed capital needs and to meet our obligations as they fall due. In 2022, we developed a Climate Internal Scenario Analysis (CISA) to help understand better the potential impact of climate change on our business portfolios and balance sheet. Since then, we have invested in a strategic solution to deliver capability to run long-term horizon multi-scenario assessments which will inform future strategic decisions and enhance risk management capabilities (CISA Development). The model capability will support in exploring scenarios which would reflect a range of climate outcomes, covering shorter and longer-term (30-year) horizons and reflect physical and transition risks. The CISA outputs will form the basis of our future ICAAP exercises for climate risk and will help us prioritise our actions for the next five years. We augment our regulatory minimum capital with internal buffers. We hold buffers to ensure we have enough time to take action against unexpected changes. Risk mitigation We designed our capital risk framework, policies and procedures to ensure that we operate within our Risk Appetite. We manage capital transferability between our subsidiaries in line with our business strategy, our risk and capital management policies, UK laws and regulations. There are no legal restrictions on us moving capital resources promptly, or repaying liabilities, between the Company and its subsidiaries except for distributions between Santander UK entities in the ring- fenced bank sub-group and Santander UK entities that are not members of the ring-fenced bank sub-group, where the PRA is required to assess the impact of proposed distribution prior to payment. For details on our Recovery framework in the event of a capital stress, see 'risk mitigation' in the ‘Liquidity risk’ section. At 31 December 2023 , Santander UK plc, Cater Allen Limited, Santander ISA Managers Limited and certain other non-regulated subsidiaries of Santander UK plc were party to a capital support deed entered into on 17 December 2021 and effective from 1 January 2022 (the RFB Sub-Group Capital Support Deed). These parties were permitted by the PRA to form a core UK group as defined in the PRA Rulebook, a permission which expires on 31 December 2024. Exposures of each of the regulated entities to other members of the core UK group are exempt from large exposure limits that would otherwise apply and these exposures are risk-weighted at 0% . Where applicable this permission also provides for intra-group exposures to be excluded from the leverage exposure measure. The purpose of the RFB Sub-Group Capital Support Deed is to facilitate the prompt transfer of available capital resources from, or repayment of liabilities by, the non-regulated parties to any of the regulated parties in the event that one of the regulated parties breached or was at risk of breaching its capital resources or risk concentrations requirements. Risk monitoring and reporting We monitor and report regularly against our capital plan. We do this to identify any change in our business performance that might affect our capital. Each month, we also review the economic assumptions we use to create and stress test our capital plan. We do this to identify any potential reduction in our capital. CAPITAL RISK REVIEW Meeting evolving capital requirements We target a CET1 management buffer of sufficient size to absorb volatility in CET1 deductions, capital supply and capital demand whilst remaining above the current and expected future regulatory CET1 requirement. Distribution restrictions would be expected to be applied if we were unable to meet both our minimum requirement, which consists of the Pillar 1 minimum plus Pillar 2A, the CRD IV buffers consisting of the Capital Conservation Buffer (CCB), the Countercyclical Capital Buffer (CCyB), and the Other Systemically Important Institutions Buffer (O-SII) . Impact of IFRS 9 on regulatory capital Our ECL methodology takes account of forward-looking data and covers a range of possible economic outcomes, and so provision movements may result in increased pro-cyclicality of risk-based capital and leverage ratios. However, the impact is currently mitigated by our surplus of IRB model regulatory expected losses over provisions for exposures using the IRB approach. For such exposures (which include residential mortgages) the adverse impact on CET1 capital of provision increases from reserve movements is offset by the related reduction of the negative CET1 capital adjustment for regulatory expected loss amounts. Also, the UK CRR transitional rules for the capital impact of IFRS 9 mean that adverse CET1 effects from increases in ECL-based provisions from the level of such provisions at 1 January 2018 are partly reduced until the end of 2024. We reflect projections of ECL provisions in our capital position forecasting under base case and stress scenarios for ICAAP and capital management purposes. We also consider the dynamics of ECL in how we assess and manage capital risk. A period of economic instability, such as that seen in early 2020 due to the impacts of the Covid-19 pandemic, could significantly impact our results and our financial assets. It could also impact the amount of capital we have to hold. We take into account the volatility of ECL in our capital planning strategy. Key capital ratios 2023 2022 % % CET1 capital ratio 15.4 15.4 AT1 2.9 2.8 Tier 2 3.2 2.2 Total capital ratio 21.5 20.4 The total subordination available to Santander UK plc senior unsecured bondholders was 21.5% ( 2022 : 20.4% ) of RWAs. Return on assets - profit after tax divided by average total assets was 0.55 % ( 2022 : 0.49 %). 2023 compared to 2022 The CET1 capital ratio remained stable at 15.4% . Higher profit and a reduction in RWA exposure was partially offset by the dividends paid in 2023. Regulatory capital resources (audited) This table shows our qualifying regulatory capital: 2023 2022 £m £m CET1 capital 10,443 10,799 AT1 capital 1,956 1,956 Tier 1 capital 12,399 12,755 Tier 2 capital 2,172 1,548 Total regulatory capital (1) 14,571 14,303 (1) Capital resources include a transitional IFRS 9 benefit at 31 December 2023 of £43m ( 2022 : £19m ). Risk-weighted assets Total RWAs at 31 December 2023 were £67.8bn ( 2022 : £70.1bn ) which are consistent with our regulatory filings. RWAs decreased with lower mortgage lending and active balance sheet management.

Market Risk

Market Risk	12 Months Ended
	Dec. 31, 2023
Disclosure Of Market Risk Exposure [Abstract]
Market Risk	BALANCE SHEET ALLOCATION BY MARKET RISK CLASSIFICATION (AUDITED) We classify all our assets and liabilities exposed to market risk as non-traded market risk, except for certain portfolios that we must classify as trading books for regulatory purposes (such as selling derivatives or derivative-based products to clients), of which we must fair value for accounting reasons (such as assets in the eligible liquidity pool). For accounting purposes, we classify all derivatives as held for trading unless they are designated as being in a hedging relationship. For more, see Note 11 to the Consolidated Financial Statements. NON-TRADED MARKET RISK OUR KEY NON-TRADED MARKET RISKS (audited) Non-traded market risk mainly comes from providing banking products and services to our customers, as well as our structural balance sheet exposures. It arises in all our business segments. In Retail and Business Banking, Consumer Finance and Corporate & Commercial Banking, it is a by-product of us writing customer business and we transfer most of these risks to Corporate Centre to manage. The only types of non-traded market risk that we keep in Retail and Business Banking, Consumer Finance and Corporate & Commercial Banking are short-term mismatches due to forecasting variances in prepayment and launch risk. This is where customers repay their loans earlier than their expected maturity date or do not take the expected volume of new products. Corporate Centre also manages our structural balance sheet exposures, such as foreign exchange and Income Statement volatility risk. Our key non-traded market risks are: Key risks Description Interest rate risk Yield curve risk: comes from timing mismatches in repricing fixed and variable rate assets, liabilities and off-balance sheet instruments. It also comes from investing non-rate sensitive liabilities in interest-earning assets. Basis risk: comes from pricing assets using a different rate index to the liabilities that fund them. We are exposed to basis risks associated with Bank of England bank rate, reserve rate linked assets we deposit with central banks, and the Sterling Overnight Index Average (SONIA) rate. Since the cessation of LIBOR at the end of 2021, basis risk exposure has been immaterial. Spread risk Spread risk arises when the value of assets or liabilities which are accounted for at fair value (either through Other Comprehensive Income or through Profit and Loss) are affected by changes in the credit spread. We measure these spreads as the difference between the discount rate we use to value the asset or liability, and an underlying interest rate curve. Foreign exchange risk Our banking businesses operate mainly in sterling markets, so we do not create significant foreign exchange exposures. The only exception to this is money we raise in foreign currencies. For more on this, see ‘Wholesale funding’ in the ‘Liquidity risk’ section. Income statement volatility risk We measure most of the assets and liabilities in our banking book balance sheet at amortised cost. We sometimes manage their risk profile by using derivatives. As all derivatives are accounted for at fair value, the mismatch in their accounting treatment can lead to volatility in our Income Statement. This happens even if the derivative is an economic hedge of the asset or liability. NII and EVE sensitivities (audited) The calculations for NII and EVE sensitivities to interest rate moves involve many assumptions, including expected customer behaviour (such as early repayment of loans) and the projected evolution and repricing of our balance sheet. These assumptions are a key part of our overall control framework, so we update and review them regularly. Our NII and EVE sensitivities include the interest rate risk from all our banking book positions. Our banking book positions generate almost all our reported net interest income. Net Interest Income (NII) sensitivity – NII sensitivity is an income-based measure we use to forecast the changes to interest income and interest expense in different scenarios. It gives us a combined impact on net interest income over a given period – usually 12 or 36 months. – We calculate NII sensitivity as the change in NII for a defined set of instantaneous parallel and non-parallel shifts in the yield curve. EVE sensitivity – We calculate EVE sensitivity as the change in the net present value of all the interest rate sensitive items in the banking book balance sheet for a defined set of instantaneous parallel and non-parallel shifts in the yield curve. The limitations of sensitivities We use sensitivities to measure the impact of standard, instantaneous, parallel shifts in relevant yield curves. The advantage of using standard parallel shifts is they generally give us a constant measure of the size of our market risk exposure, with a simple and consistent stress. We also run non-parallel stress tests, to calculate the impact of some plausible non-parallel scenarios, and over various time periods for income stresses, usually one or three years. Value at Risk (VaR) (audited) VaR – VaR indicates the losses that we might suffer because of unfavourable changes in the markets under normal (non-stressed) market conditions. – We run a historical simulation using historical daily price moves to find how much we might lose, normally at a 99% confidence level. The limitations of VaR VaR is a useful and important market standard measure of risk, but it does have some limitations. These include: – VaR assumes what happened in the past is a reliable way to predict what will happen in the future. This may not always be the case – VaR is based on positions at the end of the business day so it doesn’t include intra-day positions – VaR does not predict how big the loss could be on the 1 % of trading days that it is greater than the VaR – Using a time horizon of one day means VaR does not tell us everything about exposures that we cannot liquidate or hedge within a day, or products with infrequent pricing. Back-testing – comparing VaR estimates with reality To check that the way we estimate VaR is reasonable, we back-test our VaR by comparing it against both actual and hypothetical profits and losses, using a one- day time horizon. Back-testing allows us to identify exceptions – times when the predictions were out of line with what happened. We can then look for trends in these exceptions, which can help us decide whether we need to recalibrate our VaR model. Risk mitigation (audited) We typically hedge the interest rate risk of the securities we hold for liquidity and investment purposes with interest rate swaps. We retain spread exposures, and these are the key drivers of the VaR and stress tests we use to assess the risk of the portfolio. We mitigate Income Statement volatility mainly through hedge accounting. We monitor any hedge accounting ineffectiveness that might lead to Income Statement volatility with a VaR measure and trigger, reported monthly. For our accounting policies for derivatives and hedge accounting, see Note 1 to the Consolidated Financial Statements. We hedge our foreign currency funding positions back to sterling, so our foreign exchange positions tend to be residual exposures that remain after hedging. These exposures could be, for example, to ‘spot’ foreign exchange rates or to cross currency basis. We monitor foreign exchange risk against absolute net exposures and VaR-based limits and triggers. For more on this, see ‘Funding strategy‘ and ‘Term issuance’ in the ‘Liquidity risk’ section. Risk monitoring and reporting (audited) We monitor our non-traded market risks using NII and EVE sensitivities, VaR and stress tests. We report them against limits and triggers to senior management daily and to ALCO and ERCC each month. The VaR we report captures all key sources of volatility (including interest rate and spread risks) to fully reflect potential volatility.

Accounting Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2023
Corporate information and statement of IFRS compliance [abstract]
Accounting Policies	1. ACCOUNTING POLICIES These financial statements are prepared for Santander UK plc (the Company) and the Santander UK plc group (the Santander UK group) under the UK Companies Act 2006. The principal activity of the Santander UK group is the provision of a wide range of banking and financial services to personal, business and corporate customers. Santander UK plc is a public company, limited by shares and incorporated in England and Wales having a registered office at 2 Triton Square, Regent’s Place, London, NW1 3AN . It is an operating company undertaking banking and financial services transactions. Basis of preparation These financial statements incorporate the financial statements of the Company and entities it controls (its subsidiaries) made up to 31 December each year. The consolidated financial statements have been prepared on the going concern basis using the historical cost convention, except for financial assets and liabilities that have been measured at fair value. An assessment of the appropriateness of the adoption of the going concern basis of accounting is disclosed in the statement of going concern in the Directors’ report. Compliance with International Financial Reporting Standards (IFRS) The consolidated financial statements of the Santander UK group and the separate financial statements of the Company comply with UK-adopted International Accounting Standards (IAS). The financial statements are also prepared in accordance with IFRS as issued by the International Accounting Standards Board (IASB), including interpretations issued by the IFRS Interpretations Committee, as there are no applicable differences from IFRS as issued by the IASB for the periods presented. Disclosures required by IFRS 7 ‘Financial Instruments: Disclosure’ relating to the nature and extent of risks arising from financial instruments, and IAS 1 ‘Presentation of Financial Statements’ relating to objectives, policies and processes for managing capital, have been included in the Risk review section of this Annual Report. This information forms an integral part of these financial statements by this cross reference, is marked as audited, and is covered by the Independent auditors' report. Climate change Santander UK continues to develop its assessment of the potential impacts that climate change and the transition to a low carbon economy may have on the assets and liabilities recognised and presented in its financial statements. Santander UK is mindful of its responsibilities as a responsible lender and is focused on ways to meet the objectives of the Paris Agreement on climate change and to support the UK’s transition to a climate-resilient, net zero economy. Santander UK's current climate change strategy focuses on three main areas to achieve Banco Santander's ambition to reach net zero emissions by 2050: 1. Managing climate risks by integrating climate considerations into risk management frameworks, screening and stress testing our portfolio for climate related financial risks, and setting risk appetites to help steer our portfolio in line with the Paris Agreement, 2. Supporting our customers’ transition by developing products and services that promote a reduction in CO 2 emissions, and 3. Reducing emissions in our operations and supply chain by focusing on continuous improvement in our operations, and environmental and energy management systems in accordance with ISO14001 and 15001, promoting responsible procurement practices and employee engagement. Santander UK's current climate change strategy and its view of the risks associated with climate change and the transition to a low carbon economy are reflected in its critical judgements and accounting estimates, although climate change risk did not have a material impact at 31 December 2023 and 2022, consistent with management's assessment that climate change and the transition to a low carbon economy are not currently expected to have a meaningful impact on the viability of the Santander UK group in the medium term. At 31 December 2023 and 2022, management specifically considered the potential impact of climate change and the transition to a low carbon economy on: – Loans and advances to customers ( see Note 13 and the credit risk section of the Risk review). Some climate change risks arise due to the requirements of IFRS 9 and others relate to specific portfolios and sectors: – ECL calculations are based on multiple forward-looking economic scenarios developed by management covering a period of 5 years , during which timeframe climate change risks may crystallise; – For mortgages in Retail & Business Banking and commercial real estate lending in Corporate & Commercial Banking, the value of property collateral might be affected by physical impacts related to the frequency and scale of extreme weather events, such as flood and subsidence risk, or changing environmental performance standards for property. – For automotive loans in Consumer Finance, the residual value of automotive vehicles might be impacted by diesel obsolescence and the transition to electric vehicles. – For corporate lending in Corporate & Commercial Banking, certain sectors give rise to fossil fuel exposures, such as Oil & Gas, Mining & Extraction and Power Generation. – Goodwill impairment assessment (see Note 20). Estimates underpinning the determination of whether or not goodwill balances are impaired are partly based on forecast business performance beyond the time horizon for management's detailed plans. Future changes to Santander UK's climate change strategy may impact Santander UK's critical judgements and accounting estimates and result in material changes to financial results and the carrying values of certain assets and liabilities in future reporting periods. Future accounting developments At 31 December 2023 , for the Santander UK group, there were no significant new or revised standards and interpretations, and amendments thereto, which have been issued but which are not yet effective, or which have otherwise not been early adopted where permitted. Comparative information As required by US public company reporting requirements, these financial statements include two years of comparative information for the consolidated income statement, consolidated statement of comprehensive income, consolidated statement of changes in equity, consolidated statement of cash flows and related notes. Material accounting policy information The following material accounting policies have been applied in preparing these financial statements. For material accounting policies which involve the application of judgements or accounting estimates that are determined to be critical to the preparation of these financial statements see 'Critical judgements and accounting estimates'. Consolidation The consolidated financial statements incorporate the financial statements of the Company and entities (including structured entities) controlled by it and its subsidiaries. The acquisition method of accounting is used to account for the acquisition of subsidiaries which meet the definition of a business. Business combinations between entities under common control (i.e. fellow subsidiaries of Banco Santander SA, the ultimate parent) are outside the scope of IFRS 3 – ‘Business Combinations’, and there is no other guidance for such transactions under IFRS. The Santander UK group elects to account for business combinations between entities under common control at their book values in the acquired entity by including the acquired entity’s results from the date of the business combination and not restating comparatives. Reorganisations of entities within the Santander UK group are also accounted for at their book values. Credit protection entities established as part of significant risk transfer (SRT) transactions are not consolidated by the Santander UK group in cases where third party investors have the exposure, or rights, to all of the variability of returns from the performance of the entities. Revenue recognition a) Interest income and expense Interest and similar income and expense are recognised in the income statement using the effective interest rate method for: all financial instruments measured at amortised cost; debt instruments measured at FVOCI; and the effective part of any related accounting hedging instruments. Interest income is calculated by applying the effective interest rate to the gross carrying amount of financial assets, except for financial assets that have subsequently become credit-impaired (i.e. Stage 3), for which interest revenue is calculated by applying the effective interest rate to their amortised cost (i.e. net of the ECL provision). For more information on stage allocations of credit risk exposures, see ‘Significant increase in credit risk’ in the ‘Santander UK group level – credit risk management’ section of the Risk review. b) Fee and commission income and expense Fees and commissions that are not an integral part of the effective interest rate are recognised when the service is performed. Most fee and commission income is recognised at a point in time. Certain commitment, upfront and management fees are recognised over time but are not material. For retail and corporate products, fee and commission income consists principally of collection services fees, commission on foreign currencies, commission and other fees received from retailers for processing credit card transactions, fees received from other credit card issuers for providing cash advances for their customers through the Santander UK group’s branch and ATM networks, annual fees payable by credit card holders and fees for non-banking financial products. For insurance products, fee and commission income consists principally of commissions and profit share arising from the sale of building and contents insurance and life protection insurance. Commissions arising from the sale of buildings and contents insurance are recognised over the period of insurance cover, adjusted to take account of cancelled policies. Profit share income from the sale of buildings and contents insurance which is not subject to any adjustment is recognised when the profit share income is earned. Commissions and profit share arising from the sale of life protection insurance is subject to adjustment for cancellations of policies within 3 years from inception. Fee and commission income which forms an integral part of the effective interest rate of a financial instrument (for example certain loan commitment fees) is recognised as an adjustment to the effective interest rate and recorded in ‘Interest income’. c) Other operating income Other operating income includes all gains and losses from changes in the fair value of financial assets and liabilities held at fair value through profit or loss (comprising financial assets and liabilities held for trading, trading derivatives and other financial assets and liabilities at fair value through profit or loss), together with related interest income, expense, dividends, and changes in fair value of any derivatives managed in conjunction with these assets and liabilities. Other operating income also includes hedge ineffectiveness arising from fair value and cash flow hedging, income from operating lease assets, and profits and losses arising on the sales of property, plant and equipment and subsidiary undertakings. Defined benefit pension schemes (see 'Critical judgements and accounting estimates') A defined benefit scheme is a pension scheme that guarantees an amount of pension benefit to be provided, usually as a function of one or more factors such as age, years of service or compensation. Pension costs are charged to ‘Administration expenses’, within the line item ‘Operating expenses before impairment losses, provisions and charges’ with the net interest on the defined benefit asset or liability included within ‘Net interest income’ in the income statement. The asset or liability recognised in respect of defined benefit pension schemes is the present value of the defined benefit obligation at the balance sheet date, less the fair value of scheme assets. The defined benefit obligation is calculated annually by independent actuaries using the projected unit credit method. The assets of the schemes are measured at their fair values at the balance sheet date. The present value of the defined benefit obligation is estimated by projecting forward the growth in current accrued pension benefits to reflect inflation and salary growth to the date of pension payment, then discounted to present value using the yield applicable to high-quality AA rated corporate bonds of the same currency and which have terms to maturity closest to the terms of the scheme liabilities, adjusted where necessary to match those terms. In determining the value of scheme liabilities, demographic and financial assumptions are made by management about life expectancy, inflation, discount rates, pension increases and earnings growth, based on past experience and future expectations. Financial assumptions are based on market conditions at the balance sheet date and can generally be derived objectively. Demographic assumptions require a greater degree of estimation and judgement to be applied to externally derived data. Any surplus or deficit of scheme assets over liabilities is recognised in the balance sheet as an asset (surplus) or liability (deficit). An asset is only recognised to the extent that the surplus can be recovered through reduced contributions in the future or through refunds from the scheme. Share-based payments The Santander UK group engages in cash-settled and equity-settled share-based payment transactions in respect of services received from certain of its employees. Shares of the Santander UK group’s parent, Banco Santander SA are purchased in the open market by the Santander UK group (for the Employee Sharesave scheme) or are purchased by Banco Santander SA or another Banco Santander subsidiary (including awards granted under the Long-Term Incentive Plan and the Deferred Shares Bonus Plan) to satisfy share options or awards as they vest. Options granted under the Employee Sharesave scheme and awards granted under the Transformation Incentive Plan are accounted for as cash-settled share- based payment transactions. Awards granted under the Long-Term Incentive Plan and Deferred Shares Bonus Plan are accounted for as equity-settled share- based payment transactions. The fair value of the options granted under the Employee Sharesave scheme is determined using an option pricing model, which takes into account the exercise price of the option, the current share price, the risk-free interest rate, the expected volatility of the Banco Santander SA share price over the life of the option and the dividend growth rate. The fair value of the awards granted for the Long-Term Incentive Plan was determined at the grant date using an option pricing model, which takes into account the share price at grant date, the risk-free interest rate, the expected volatility of the Banco Santander SA share price over the life of the award and the dividend growth rate. Goodwill and other intangible assets (for goodwill see 'Critical judgements and accounting estimates') Goodwill represents the excess of the cost of an acquisition, as well as the fair value of any interest previously held, over the fair value of the share of the identifiable net assets of the acquired subsidiary, or business at the date of acquisition. Goodwill on the acquisition of subsidiaries and businesses is included in intangible assets. Goodwill is tested for impairment annually, or more frequently when events or changes in circumstances dictate and carried at cost less accumulated impairment losses. Gains and losses on the disposal of an entity or business include the carrying amount of goodwill relating to the entity or business sold. Other intangible assets are recognised if they arise from contractual or other legal rights or if they are capable of being separated or divided from Santander UK and sold, transferred, licensed, rented or exchanged. The value of such intangible assets, where they are available for use, is amortised on a straight-line basis over their useful economic life of three to seven years and the assets are reviewed annually for impairment indicators and tested for impairment where indicators are present. Other intangible assets that are not yet available for use are tested for impairment annually or more frequently when events or changes in circumstances dictate. Software development costs are capitalised when they are direct costs associated with identifiable and unique software products that are expected to provide future economic benefits and the cost of those products can be measured reliably. These costs include payroll, materials, services and directly attributable overheads. Internally developed software meeting these criteria and externally purchased software are classified in intangible assets on the balance sheet and amortised on a straight-line basis over their useful life of three to seven years, unless the software is an integral part of the related computer hardware, in which case it is treated as property, plant and equipment as described below. Capitalisation of costs ceases when the software is capable of operating as intended. Costs of maintaining software are expensed as incurred. Property, plant and equipment Property, plant and equipment include owner-occupied properties (including leasehold properties), office fixtures and equipment and computer software. Property, plant and equipment also includes operating leases where the Santander UK group is the lessor and right-of-use assets where the Santander UK group is the lessee. Internally developed software meeting the criteria set out in ‘Goodwill and other intangible assets’ above and externally purchased software are classified in property, plant and equipment where the software is an integral part of the related computer hardware (for example, the operating system of a computer). Classes of property, plant and equipment are depreciated on a straight-line basis over their useful life, as follows: Owner-occupied properties Not exceeding 50 years Office fixtures and equipment 3 to 15 years Computer software 3 to 7 years Right-of-use assets Shorter of the lease term or the useful life of the underlying asset Operating lease assets - vehicles 1 to 4 years Depreciation is not charged on freehold land. Depreciation of operating lease assets where the Santander UK group is the lessor is described in 'Leases' below. Financial instruments (for impairment of debt instrument financial assets see 'Critical judgements and accounting estimates: Credit impairment losses') a) Initial recognition and measurement Financial assets and liabilities are initially recognised when the Santander UK group becomes a party to the contractual terms of the instrument. The Santander UK group determines the classification of its financial assets and liabilities at initial recognition and measures a financial asset or financial liability at its fair value plus or minus, in the case of a financial asset or financial liability not at FVTPL, transaction costs that are incremental and directly attributable to the acquisition or issue of the financial asset or financial liability. Transaction costs of financial assets and financial liabilities carried at FVTPL are expensed in profit or loss. Immediately after initial recognition, an expected credit loss (ECL) allowance is recognised for financial assets measured at amortised cost and investments in debt instruments measured at FVOCI. A regular way purchase or sale is a purchase or sale of a financial asset under a contract whose terms require delivery of the asset within the timeframe established generally by regulation or convention in the marketplace concerned. Regular way purchases and sales of financial assets measured at amortised cost are recognised on settlement date; all other regular way purchases and sales of financial assets are recognised on trade date. b) Financial assets and liabilities i) Classification and subsequent measurement The Santander UK group classifies its financial assets in the measurement categories of amortised cost, FVOCI and FVTPL. Financial assets and financial liabilities are classified as FVTPL where there is a requirement to do so or where they are otherwise designated at FVTPL on initial recognition. Financial assets and financial liabilities which are required to be held at FVTPL include: – Financial assets and financial liabilities held for trading. – Debt instruments that do not have solely payments of principal and interest (SPPI) characteristics. Otherwise, such instruments are measured at amortised cost or FVOCI, and – Equity instruments that have not been designated as held at FVOCI. Financial assets and financial liabilities are classified as held for trading if they are derivatives or if they are acquired or incurred principally for the purpose of selling or repurchasing in the near-term, or form part of a portfolio of financial instruments that are managed together and for which there is evidence of short-term profit taking. In certain circumstances, other financial assets and financial liabilities are designated at FVTPL where this results in more relevant information. This may arise because it significantly reduces a measurement inconsistency that would otherwise arise from measuring assets or liabilities or recognising the gains or losses on them on a different basis, where the assets and liabilities are managed and their performance evaluated on a fair value basis or, in the case of financial liabilities, where it contains one or more embedded derivatives which are not closely related to the host contract. The classification and measurement requirements for financial asset debt and equity instruments and financial liabilities are set out below. Financial assets: debt instruments Debt instruments are those instruments that meet the definition of a financial liability from the issuer’s perspective, such as loans and government and corporate bonds. Classification and subsequent measurement of debt instruments depend on the Santander UK group’s business model for managing the asset, and the cash flow characteristics of the asset. Business model The business model reflects how the Santander UK group manages the assets in order to generate cash flows and, specifically, whether the Santander UK group’s objective is solely to collect the contractual cash flows from the assets or is to collect both the contractual cash flows and cash flows arising from the sale of the assets. If neither of these is applicable, such as where the financial assets are held for trading purposes, then the financial assets are classified as part of an ‘other’ business model and measured at FVTPL. Factors considered in determining the business model for a group of assets include past experience on how the cash flows for these assets were collected, how the assets’ performance is evaluated and reported to key management personnel, and how risks are assessed and managed. SPPI Where the business model is to hold assets to collect contractual cash flows or to collect contractual cash flows and sell, the Santander UK group assesses whether the assets’ cash flows represent SPPI. In making this assessment, the Santander UK group considers whether the contractual cash flows are consistent with a basic lending arrangement (i.e. interest includes only consideration for the time value of money, credit risk, other basic lending risks and a profit margin that is consistent with a basic lending arrangement). Where the contractual terms introduce exposure to risk or volatility that is inconsistent with a basic lending arrangement, the related asset is classified and measured at FVTPL. Financial assets with embedded derivatives are considered in their entirety when determining whether their cash flows are SPPI. Based on these factors, the Santander UK group classifies its debt instruments into one of the following measurement categories: – Amortised cost – Financial assets that are held for collection of contractual cash flows where those cash flows represent SPPI, and that are not designated at FVTPL, are measured at amortised cost. The carrying amount of these assets is adjusted by any ECL recognised and measured as presented in Note 13 . Interest income from these financial assets is included in ‘Interest and similar income’ using the effective interest rate method. When estimates of future cash flows are revised, the carrying amount of the respective financial assets is adjusted to reflect the new estimate discounted using the original effective interest rate. Any changes are recognised in the income statement. – FVOCI – Financial assets that are held for collection of contractual cash flows and for selling the assets, where the assets’ cash flows represent SPPI, and that are not designated at FVTPL, are measured at FVOCI. Movements in the carrying amount are recognised in OCI, except for the recognition of impairment gains or losses, interest revenue and foreign exchange gains and losses which are recognised in profit or loss. When the financial asset is derecognised, the cumulative gain or loss previously recognised in OCI is reclassified from equity to profit or loss and recognised in ‘Other operating income’. Interest income from these financial assets is included in ‘Interest and similar income’ using the effective interest rate method. – FVTPL – Financial assets that do not meet the criteria for amortised cost or FVOCI are measured at FVTPL. A gain or loss on a debt instrument that is subsequently measured at FVTPL, including any debt instruments designated at fair value, is recognised in profit or loss and presented in the income statement in ‘Other operating income’ in the period in which it arises. The Santander UK group reclassifies financial assets when and only when its business model for managing those assets changes. The reclassification takes place from the start of the first reporting period following the change. Such changes are expected to be very infrequent. Financial assets: equity instruments Equity instruments are instruments that meet the definition of equity from the issuer’s perspective, being instruments that do not contain a contractual obligation to pay cash and that evidence a residual interest in the issuer’s net assets. All equity investments are subsequently measured at FVTPL; management may elect, at initial recognition, to irrevocably designate an equity investment at FVOCI but has not currently done so. When this election is used, fair value gains and losses are recognised in OCI and are not subsequently reclassified to profit or loss, including on disposal. ECLs (and reversal of ECLs) are not reported separately from other changes in fair value. Dividends, when representing a return on such investments, continue to be recognised in profit or loss as other income when the right to receive payments is established. Gains and losses on equity investments at FVTPL are included in ‘Other operating income’ in the income statement. Financial liabilities Financial liabilities, which include deposits by banks, deposits by customers, debt securities in issue and subordinated liabilities, are classified as subsequently measured at amortised cost, except for: – Financial liabilities at FVTPL (see Note 22 ): this classification is applied to derivatives and other financial liabilities designated as such at initial recognition. Gains or losses on financial liabilities designated at FVTPL are presented partially in other comprehensive income (the amount of change in the fair value of the financial liability that is attributable to changes in the credit risk of that liability) and partially in profit or loss (the remaining amount of change in the fair value of the liability) – Financial liabilities arising from the transfer of financial assets which did not qualify for derecognition, whereby a financial liability is recognised for the consideration received for the transfer. In subsequent periods, the Santander UK group recognises any expense incurred on the financial liability, and – Financial guarantee contracts and loan commitments. Preference shares which carry a contractual obligation to transfer economic benefits are classified as financial liabilities and are presented in subordinated liabilities. The coupon on these preference shares is recognised in the income statement as interest expense on an amortised cost basis using the effective interest method. Contracts involving the receipt of cash on which customers receive an index-linked return are accounted for as equity index-linked deposits. The principal products are Capital Guaranteed/Protected Products which give the customers a limited participation in the upside growth of an equity index. In the event the index falls in price, a cash principal element is guaranteed/protected. The equity index-linked deposits contain embedded derivatives. These embedded derivatives, in combination with the principal cash deposit element, are designed to replicate the investment performance profile tailored to the return agreed in the contracts with customers. The cash principal element is accounted for as deposits by customers at amortised cost. The embedded derivatives are separated from the host instrument and are separately accounted for as derivatives. Sale and repurchase agreements (including stock borrowing and lending) Securities sold subject to a commitment to repurchase them at a predetermined price (repos) under which substantially all the risks and rewards of ownership are retained by the Santander UK group remain on the balance sheet and a liability is recorded in respect of the consideration received. Securities purchased under commitments to resell (reverse repos) are not recognised on the balance sheet and the consideration paid is recorded as an asset. The difference between the sale and repurchase price is treated as trading income in the income statement, except where the repo is not treated as part of the trading book, in which case the difference is recorded in interest income or expense. Securities lending and borrowing transactions are generally secured, with collateral in the form of securities or cash advanced or received. Securities borrowed are not reflected on the balance sheet. Collateral in the form of cash received or advanced is recorded as a deposit or a loan. Collateral in the form of securities is not recognised. Day One profit adjustments The fair value of a financial instrument on initial recognition is generally its transaction price (that is, the fair value of the consideration given or received). However, sometimes the fair value will be based on other observable current market transactions in the same instrument, without modification or repackaging, or on a valuation technique whose variables include only data from observable markets, such as interest rate yield curves, option volatilities and currency rates. When such evidence exists, the Santander UK group recognises a trading gain or loss at inception (Day One gain or loss), being the difference between the transaction price and the fair value. When significant unobservable parameters are used, the entire Day One gain or loss is deferred and is recognised in the income statement over the life of the transaction until the transaction matures, is closed out, the valuation inputs become observable, or an offsetting transaction is entered into. ii) Impairment of debt instrument financial assets The Santander UK group assesses on a forward-looking basis the ECL associated with its debt instrument assets carried at amortised cost and FVOCI and with the exposure arising from financial guarantee contracts and loan commitments. The Santander UK group recognises a loss allowance for such losses at each reporting date. The measurement of ECL reflects: – An unbiased and probability-weighted amount that is determined by evaluating a range of possible outcomes. – The time value of money, and – Reasonable and supportable information that is available without undue cost or effort at the reporting date about past events, current conditions and forecasts of future economic conditions. Grouping of instruments for losses measured on a collective basis We typically group instruments and assess them for impairment collectively where they share risk characteristics (as described in the Credit risk section of the Risk review) using one or more statistical models. Where w

Segments

Segments	12 Months Ended
	Dec. 31, 2023
Disclosure of operating segments [abstract]
Segments	2. SEGMENTS Santander UK’s principal activity is financial services, mainly in the UK. The business is managed and reported on the basis of four segments, which are strategic business units that offer different products and services, have different customers and require different technology and marketing strategies. Geographical information is not provided, as substantially all of Santander UK’s activities are in the UK. Retail & Business Banking (formerly Retail Banking) consists of two business units, Mortgages and Everyday Banking. Mortgages provides prime UK mortgage lending to owner occupiers and buy-to-let landlords with small portfolios. Everyday Banking provides banking services and unsecured lending to individuals and small businesses as well alongside wealth management for high-net-worth clients. – Consumer Finance provides prime auto consumer financing for individuals, businesses, and automotive distribution networks. – Corporate & Commercial Banking provides banking products and services to SMEs, mid-sized and larger corporates, typically with annual turnovers of between £2m and £500m as well as to Local Authorities and Housing Associations. – Corporate Centre provides treasury services for asset and liability management of our balance sheet. Retail & Business Banking delivers products through our omni-channel presence comprising branches, ATMs, telephony, digital and intermediary channels. Consumer Finance business is primarily introduced by car dealerships acting as our intermediary along with a small amount of new business introduced via digital channels. Corporate and Commercial Banking expertise is provided by relationship managers, product specialists and through digital and telephony channels, and cover clients' needs both in the UK and overseas. In addition, Corporate and Investment Banking (CIB) provided services to corporate clients with an annual turnover of £500m and above. Santander UK transferred a significant part of the CIB business to the London branch of Banco Santander SA under a part VII banking business transfer scheme which completed on 11 October 2021. The residual parts of the business were wound down or transferred to other segments. The segmental data is prepared on a statutory basis of accounting, in line with the accounting policies set out in Note 1 . Transactions between segments are on normal commercial terms and conditions. Internal charges and internal UK transfer pricing adjustments are reflected in the results of each segment, and eliminate on consolidation. Revenue sharing agreements are used to allocate external customer revenues to a segment on a reasonable basis. Funds are ordinarily reallocated between segments, resulting in funding cost transfers disclosed in operating income. Interest charged for these funds is based on Santander UK’s cost of wholesale funding. Interest income and interest expense have not been reported separately. The majority of segment revenues are interest income in nature and net interest income is relied on primarily to assess segment performance and to make decisions on the allocation of segment resources. Results by segment 3 For the year ended 31 December Retail & Business Banking Consumer Finance Corporate & Commercial Banking Corporate Centre Total 2023 £m £m £m £m £m Net interest income/(expense) 3,716 156 841 (55) 4,658 Non-interest income/(expense) 182 192 135 (71) 438 Total operating income/(expense) 3,898 348 976 (126) 5,096 Operating expenses before credit impairment charges, provisions and charges (1,813) (141) (351) (151) (2,456) Credit impairment charges (149) (15) (40) (1) (205) Provisions for other liabilities and charges (233) (18) (15) (69) (335) Total operating credit impairment charges, provisions and charges (382) (33) (55) (70) (540) Profit/(loss) from continuing operations before tax 1,703 174 570 (347) 2,100 Revenue from external customers 3,597 663 712 124 5,096 Inter-segment revenue/(expense) 301 (315) 264 (250) — Total operating income/(expense) 3,898 348 976 (126) 5,096 Revenue from external customers includes the following fee and commission income: (1) – Current account and debit card fees 493 — 49 — 542 – Insurance, protection and investments 47 — — — 47 – Credit cards 94 — — — 94 – Non-banking and other fees (2) 3 25 79 14 121 Total fee and commission income 637 25 128 14 804 Fee and commission expense (458) (6) (11) (26) (501) Net fee and commission income/(expense) 179 19 117 (12) 303 Customer loans 179,887 5,228 17,939 — 203,054 Customer deposits 158,329 — 24,066 5,050 187,445 Average number of full-time equivalent staff 16,330 816 2,376 24 19,546 (1) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (2) Non-banking and other fees include mortgages (except mortgage account fees), consumer finance, commitment commission, asset finance, invoice finance and trade finance. (3) Total assets and total liabilities are no longer included in reports provided to the chief operating decision maker. Retail & Business Banking Consumer Finance Corporate & Commercial Banking Corporate Centre Total 2022 £m £m £m £m £m Net interest income/(expense) 3,671 180 580 (6) 4,425 Non-interest income/(expense) 209 195 146 (19) 531 Total operating income 3,880 375 726 (25) 4,956 Operating expenses before credit impairment charges, provisions and charges (1,682) (144) (342) (175) (2,343) Credit impairment charges (262) (27) (31) — (320) Provisions for other liabilities and charges (394) (6) (8) (11) (419) Total operating credit impairment charges, provisions and charges (656) (33) (39) (11) (739) Profit/(loss) from continuing operations before tax 1,542 198 345 (211) 1,874 Revenue/(expense) from external customers 4,109 513 732 (398) 4,956 Inter-segment revenue/(expense) (229) (138) (6) 373 — Total operating income/(expense) 3,880 375 726 (25) 4,956 Revenue from external customers includes the following fee and commission income: (1) – Current account and debit card fees 502 — 60 — 562 – Insurance, protection and investments 78 — — — 78 – Credit cards 95 — — — 95 – Non-banking and other fees (2) 2 20 77 5 104 Total fee and commission income 677 20 137 5 839 Fee and commission expense (478) (5) (18) (8) (509) Net fee/(expense) and commission income 199 15 119 (3) 330 31 December 2022 Customer loans 191,836 5,384 18,518 — 215,738 Customer deposits 161,748 — 24,798 3,365 189,911 Average number of full-time equivalent staff 15,212 531 2,336 44 18,123 Retail & Business Banking Consumer Finance Corporate & Commercial Banking Corporate & Investment Banking Corporate Centre Total 2021 £m £m £m £m £m £m Net interest income/(expense) 3,356 233 397 — (37) 3,949 Non-interest income 205 178 112 — 55 550 Total operating income 3,561 411 509 — 18 4,499 Operating expenses before credit impairment (charges)/write-backs, provisions and charges (1,701) (163) (365) — (281) (2,510) Credit impairment (charges)/write-backs 98 33 90 — 12 233 Provisions for other liabilities and charges (185) 4 (34) — (162) (377) Total operating credit impairment (charges)/write-backs, provisions and charges (87) 37 56 — (150) (144) Profit/(loss) from continuing operations before tax 1,773 285 200 — (413) 1,845 Revenue from external customers 4,010 489 619 — (619) 4,499 Inter-segment revenue (449) (78) (110) — 637 — Total operating income 3,561 411 509 — 18 4,499 Revenue from external customers includes the following fee and commission income: (1) – Current account and debit card fees 428 — 50 — — 478 – Insurance, protection and investments 67 — — — — 67 – Credit card fees 73 — — — — 73 – Non-banking and other fees (2) 2 10 62 — 5 79 Total fee and commission income 570 10 112 — 5 697 Fee and commission expense (380) — (22) — (9) (411) Net fee and commission income 190 10 90 — (4) 286 Customer loans 183,023 4,984 19,281 — — 207,288 Customer deposits 156,991 — 26,466 — 2,758 186,215 Average number of full-time equivalent staff 16,149 670 2,281 528 76 19,704 (1) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (2) Non-banking and other fees include mortgages (except mortgage account fees), consumer finance, commitment commission, asset finance, invoice finance and trade finance. (3) Total assets and total liabilities are no longer included in reports provided to the chief operating decision maker. The table below shows the relationships between Customer assets and Loans and advances to customers as presented in the Consolidated Balance Sheet. Customer assets exclude Joint ventures, as they carry low credit risk and therefore have an immaterial ECL, and Other items, mainly accrued interest that we have not yet charged to the customer's account, and cash collateral. It also shows the relationship between customer liabilities (see above) and Deposits by customers as presented in the Consolidated Balance Sheet. Assets Liabilities 2023 2022 2023 2022 £m £m £m £m Customer balances (gross) 203,054 215,738 187,445 189,911 Loan loss allowance (914) (931) — — Customer balances (net) 202,140 214,807 187,445 189,911 Intercompany balances 4,544 4,161 2,825 5,981 Accrued interest 739 649 830 230 Other items 12 99 (250) (554) Loans and advances to customers / Deposits by customers 207,435 219,716 190,850 195,568

Net Interest Income

Net Interest Income	12 Months Ended
	Dec. 31, 2023
Analysis of income and expense [abstract]
Net Interest Income	3. NET INTEREST INCOME Group 2023 2022 2021 £m £m £m Interest and similar income: Loans and advances to customers 8,767 5,774 4,619 Loans and advances to banks 1,751 618 52 Reverse repurchase agreements – non-trading 626 149 35 Other 473 167 56 Total interest and similar income (1) 11,617 6,708 4,762 Interest expense and similar charges: Deposits by customers (3,230) (905) (430) Deposits by banks (1,165) (496) (25) Repurchase agreements – non-trading (538) (120) (3) Debt securities in issue (1,852) (650) (252) Subordinated liabilities (169) (108) (92) Other (5) (4) (11) Total interest expense and similar charges (2) (6,959) (2,283) (813) Net interest income 4,658 4,425 3,949 (1) Includes £230m ( 2022 : £87m , 2021 : £22m ) of interest income on financial assets at FVOCI. (2) Includes £706m ( 2022 : £6m , 2021 : £317m ) of interest expense on the effective part of derivatives hedging debt issuances and £3m ( 2022 : £3m , 2021 : £3m ) of interest expense on lease liabilities.

Net Fee and Commission Income

Net Fee and Commission Income	12 Months Ended
	Dec. 31, 2023
Fee and commission income (expense) [abstract]
Net Fee and Commission Income	4. NET FEE AND COMMISSION INCOME Group 2023 2022 2021 £m £m £m Fee and commission income: Current account and debit card fees 542 562 478 Insurance, protection and investments 47 78 67 Credit cards 94 95 73 Non-banking and other fees (1) 121 104 79 Total fee and commission income 804 839 697 Total fee and commission expense (501) (509) (411) Net fee and commission income 303 330 286 (1) Non-banking and other fees include mortgages (except mortgage account fees), consumer finance, commitment commission, asset finance, invoice finance and trade finance.

Other Operating Income

Other Operating Income	12 Months Ended
	Dec. 31, 2023
Net Trading And Other Income [Abstract]
Other Operating Income	5. OTHER OPERATING INCOME Group 2023 2022 2021 £m £m £m Net (losses)/gains on financial instruments designated at fair value through profit or loss (1) (57) 62 (24) Net (losses) on financial instruments mandatorily at fair value through profit or loss (2) (11) (75) (2) Hedge ineffectiveness 19 29 13 Net profit on sale of financial assets at fair value through other comprehensive income — — 6 Income from operating lease assets 117 129 136 Other 67 56 135 135 201 264 (1) Net gains/ (losses) on financial instruments designated at fair value through profit or loss include losses of £24m on deposits ( 2022 : £35m gains, 2021 £18m losses), losses of £32m on debt securities ( 2022 : £31m gains, 2021 : £nil ). (2) Net gains /(losses) on financial instruments mandatorily at fair value through profit or loss include gains of £5m on debt securities ( 2022 : £13m gains, 2021 : £10m losses). Net gains on financial instruments mandatorily at FVTPL includes fair value losses of £12m ( 2022 : gains of £14m , 2021 : losses of £15m ) on embedded derivatives bifurcated from certain equity index-linked deposits, as described in the derivatives accounting policy in Note 1 . The embedded derivatives are economically hedged, the results of which are also included in this line item and amounted to gains of £12m ( 2022 : losses of £14m , 2021 : gains of £15m ). As a result, the net fair value movements recognised on the equity index-linked deposits and the related economic hedges were net gains of £nil ( 2022 : £nil , 2021 : £nil ). Group 2023 2022 2021 £m £m £m Exchange rate differences in the consolidated income statement on items not at fair value through profit and loss 1,288 (2,163) 242 These are principally offset by related releases from the cash flow hedge reserve (1,248) 2,129 (358) In 2023 , the Santander UK group repurchased certain debt securities and subordinated liabilities as part of ongoing liability management exercises. For more, see Note 27 . In 2022, Other includes £7m of losses on the sale of property under our transformation programme. In 2021, Other includes £73m of property gains from the sale of our London head office and branch properties.

Operating Expenses Before Credi

Operating Expenses Before Credit Impairment Charges, Provisions and Charges	12 Months Ended
	Dec. 31, 2023
Expenses by nature [abstract]
Operating Expenses Before Credit Impairment Charges, Provisions and Charges	6. OPERATING EXPENSES BEFORE CREDIT IMPAIRMENT CHARGES, PROVISIONS AND CHARGES For the year ended 31 December Group 2023 2022 2021 £m £m £m Staff costs: Wages and salaries 839 745 745 Performance-related payments 162 170 183 Social security costs 115 112 112 Pensions costs: – defined contribution plans 71 60 64 – defined benefit plans 13 28 38 Other personnel costs 41 44 41 1,241 1,159 1,183 Other administration expenses 925 888 826 Depreciation, amortisation and impairment 290 296 501 2,456 2,343 2,510 Staff costs Performance-related payments’ include bonuses paid in cash and share awards granted under the arrangements described in Note 36 . Included in this are equity- settled share-based payments, none of which related to option-based schemes. These are disclosed in the table below as ‘Shares awards’. Performance-related payments above include amounts related to deferred performance awards as follows: Costs recognised in 2023 Costs expected to be recognised in 2024 or later Arising from awards in current year Arising from awards in prior year Total Arising from awards in current year Arising from awards in prior year Total £m £m £m £m £m £m Cash 3 4 7 5 7 12 Shares 2 5 7 4 7 11 5 9 14 9 14 23 The following table shows the amount of bonus awarded to employees for the performance year 2023 . In the case of deferred cash and shares awards, the final amount paid to an employee is influenced by forfeiture provisions and any performance conditions to which the awards are subject. The deferred shares award amount is based on the fair value of the awards at the date of grant. Expenses charged in the year Expenses deferred to future periods Total 2023 2022 2023 2022 2023 2022 £m £m £m £m £m £m Cash award – not deferred 140 145 — — 140 145 – deferred 7 8 12 14 19 22 Shares award – not deferred 8 9 — — 8 9 – deferred 7 8 11 14 18 22 Total discretionary bonus 162 170 23 28 185 198 Other share-based payments’ consist of options granted under the Employee Sharesave scheme which comprise the Santander UK group’s cash-settled share- based payments. For more, see Note 36 . The average number of full-time equivalent staff was 19,546 ( 2022 : 18,123 , 2021 : 19,704 ) . Depreciation, amortisation and impairment In 2023 , depreciation, amortisation and impairment included depreciation of £64m ( 2022 : £73m , 2021 : £81m ) on operating lease assets (where the Santander UK group is the lessor) with a carrying amount of £488m at 31 December 2023 ( 2022 : £577m , 2021 : £595m ). It also included depreciation of £30m ( 2022 : £19m , 2021 : £19m ) on right-of-use assets with a carrying amount of £90m at 31 December 2023 ( 2022 : £112m , 2021 : £117m ) . Other administration expenses includes £19m ( 2022 : £21m , 2021 : £23m ) related to short-term leases. In 2023 , depreciation, amortisation and impairment included an impairment charge of £25m ( 2022 : £10m , 2021 : £88m ) associated with branch and head office site closures as part of the transformation programme. For more, see Note 21 .

Audit and Other Services

Audit and Other Services	12 Months Ended
	Dec. 31, 2023
Audit And Other Services [Abstract]
Audit and Other Services	7. AUDIT AND OTHER SERVICES Group 2023 2022 2021 £m £m £m Audit fees: Fees payable to the Company’s auditor and its associates for the audit of the Santander UK group’s annual accounts 13.9 11.8 11.2 Fees payable to the Company’s auditor and its associates for other services to the Santander UK group: – Audit of the Santander UK group's subsidiaries 0.6 0.7 0.9 Total audit fees (1) 14.5 12.5 12.1 Non-audit fees: Audit-related assurance services 0.7 0.6 0.8 Other assurance services 0.5 0.3 0.1 Other non-audit services 0.1 — 0.2 Total non-audit fees 1.3 0.9 1.1 (1) 2023 audit fees included £0.7m ( 2022 : £0.6m , 2021 : £1.2m ) which related to the prior year. Audit-related assurance services mainly comprised services performed in connection with review of the financial information of the Company and reporting to the Company's UK regulators. Other assurance services mainly comprised services performed in support of various debt issuance programmes. Of the total non-audit fees, £0.3m ( 2022 : £0.2m , 2021 : £0.4m ) accords with the definition of 'Audit Fees' per US Securities and Exchange Commission (SEC) guidance, £1.0m ( 2022 : £0.7m , 2021 : £0.7m ) accords with the definition of 'Audit related fees' per that guidance and £12,550 ( 2022 : £nil , 2021 : £nil ) accords with the definition of 'All other fees' per that guidance. In 2023 , the Company’s auditors earned no fees ( 2022 : £nil , 2021 : £27,000 fees) payable by entities outside the Santander UK group for the review of the financial position of corporate and other borrowers. In 2023 , the Company's auditors earned £1.6m ( 2022 : £1.6m , 2021 : £1.4m ), in relation to incremental work undertaken in support of the audit of Banco Santander SA.

Credit Impairment Charges and P

Credit Impairment Charges and Provisions	12 Months Ended
	Dec. 31, 2023
Disclosure Of Credit Impairment Loss And Provisions [Abstract]
Credit Impairment Charges and Provisions	8. CREDIT IMPAIRMENT CHARGES AND PROVISIONS For the year ended 31 December Group 2023 2022 2021 £m £m £m Credit impairment charges/(write-backs): Loans and advances to customers 191 248 (186) Recoveries of loans and advances, net of collection costs 10 36 (17) Off-balance sheet credit exposures (See Note 29) 4 36 (30) 205 320 (233) Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 29) 334 422 386 Releases for residual value and voluntary termination 1 (3) (9) 335 419 377 540 739 144 In 2023 , 2022 and 2021 there were no material credit impairment charges on loans and advances to banks, non-trading reverse repurchase agreements, other financial assets at amortised cost and financial assets at FVOCI.

Taxation

Taxation	12 Months Ended
	Dec. 31, 2023
Major components of tax expense (income) [abstract]
Taxation	9. TAXATION Group 2023 2022 2021 £m £m £m Current tax: UK corporation tax on profit for the year 475 526 401 Adjustments in respect of prior years (15) (81) (24) Total current tax 460 445 377 Deferred tax: Charge/(credit) for the year 106 (29) 100 Adjustments in respect of prior years (7) 64 15 Total deferred tax 99 35 115 Tax on profit from continuing operations 559 480 492 The standard rate of UK corporation tax was 28% for banking entities and 24% for non-banking entities ( 2022 : 27% for banking entities and 19% for non-banking entities; 2021 : 27% for banking entities and 19% for non-banking entities) following the introduction of a surcharge on banking companies in 2016. Taxation for other jurisdictions is calculated at the rates prevailing in the relevant jurisdictions. The Santander UK group’s effective tax rate for 2023 was 26.6% ( 2022 : 25.6% , 2021 : 26.7% ). The tax on profit from continuing operations before tax differs from the theoretical amount that would arise using the basic corporation tax rate as follows: For the year ended 31 December Group 2023 2022 2021 £m £m £m Profit from continuing operations before tax 2,100 1,874 1,845 Tax calculated at a tax rate of 23.5% (2022:19%, 2021: 19%) 494 356 351 Bank surcharge on profits 85 121 104 Non-deductible preference dividends paid 9 9 9 Non-deductible UK Bank Levy 10 13 14 Non-deductible conduct remediation, fines and penalties 13 48 6 Other non-deductible costs and non-taxable income 2 29 37 Effect of change in tax rate on deferred tax provision 2 (29) 9 Tax relief on dividends in respect of other equity instruments (34) (40) (40) Adjustment to prior year provisions (22) (27) 2 Tax on profit from continuing operations 559 480 492 On 20 June 2023, Finance (No.2) Act 2023 was substantively enacted in the UK to implement the OECD Pillar Two model rules and which introduces a global minimum effective tax rate of 15% with effect from 1 January 2024. Santander UK will therefore fall within the scope of these rules from 2024. It is not anticipated that the rules will impact Santander UK but the position will be kept under review. Current tax assets and liabilities Movements in current tax assets and liabilities during the year were as follows: Group 2023 2022 £m £m Assets 478 347 At 1 January 478 347 Income statement charge (including discontinued operations) (460) (445) Other comprehensive income (charge)/credit (70) 159 Corporate income tax received 537 405 Other movements 5 12 490 478 Assets 490 478 At 31 December 490 478 The amount of corporation income tax paid differs from the tax charge for the period as a result of the timing of payments due to the tax authorities, the effects of movements in deferred tax, adjustments to prior period current tax provisions and current tax recognised directly in other comprehensive income. Santander UK proactively engages and cooperates with relevant tax authorities in their oversight of the company's tax matters. The accounting policy for recognising provisions for any tax risks identified is described in Note 1 . It is not expected that there will be any material movement in such provisions within the next 12 months. The Santander UK group has applied the UK’s Code of Practice on Taxation for Banks following its adoption in 2010. For more information, see our Taxation Strategy on our website aboutsantander.co.uk. Deferred tax The table below shows the deferred tax balances including the movement in the deferred tax account during the year. Deferred tax balances are presented in the balance sheet after offsetting assets and liabilities where the Santander UK group has the legal right to offset and intends to settle on a net basis. Group Fair value of financial instruments Pension remeasurement Cash flow hedges Fair value reserve Tax losses carried forward Accelerated tax depreciation Other temporary differences Total £m £m £m £m £m £m £m £m At 1 January 2023 27 (290) 305 (1) — 35 (111) (35) Income statement (charge)/credit (35) (63) — — — (18) 17 (99) Transfers/reclassifications — — (3) (1) — 1 4 1 Credited/(charged) to other comprehensive income — 167 (229) 5 — — 4 (53) At 31 December 2023 (8) (186) 73 3 — 18 (86) (186) At 1 January 2022 (123) (508) (7) (12) 8 68 (5) (579) Income statement credit/(charge) 150 (49) — — (7) (33) (96) (35) Transfers/reclassifications — — 2 — (1) — (1) — Credited/(charged) to other comprehensive income — 267 310 11 — — (9) 579 At 31 December 2022 27 (290) 305 (1) — 35 (111) (35) The deferred tax assets and liabilities above have been recognised in the Santander UK group on the basis that sufficient future taxable profits are forecast within the foreseeable future, in excess of the profits arising from the reversal of existing taxable temporary differences, to allow for the utilisation of the assets as they reverse. Based on the conditions at the balance sheet date, management determined that a reasonably possible change in any of the key assumptions underlying the estimated future taxable profits in the Santander UK group’s three-year plan (described in Note 20 ) would not cause a reduction in the deferred tax assets recognised. There are £nil unrecognised deferred tax assets on capital losses carried forward ( 2022 : £ nil ).

Dividends on Ordinary Shares

Dividends on Ordinary Shares	12 Months Ended
	Dec. 31, 2023
Dividends On Ordinary Shares [Abstract]
Dividends on Ordinary Shares	10. DIVIDENDS ON ORDINARY SHARES Dividends on ordinary shares declared and paid in the year were as follows: Group Group 2023 2022 2021 2023 2022 2021 Pence per share Pence per share Pence per share £m £m £m In respect of current year – first interim 1.32 1.25 0.90 410 389 281 – second interim 3.61 2.01 3.47 1,120 625 1,077 4.93 3.26 4.37 1,530 1,014 1,358 In 2023 an interim dividend of £1,530m ( 2022 : £1,014m , 2021 : £1,358m ) was paid on the Company's ordinary shares in issue. In 2023, £750m ( 2022 : £300m ) of the dividend was a special dividend. These were paid following review and approval by the Board in line with our dividend policy.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2023
Disclosure of nature and extent of risks arising from financial instruments [abstract]
Derivative Financial Instruments	11. DERIVATIVE FINANCIAL INSTRUMENTS a) Use of derivatives Santander UK undertakes derivative activities primarily to provide customers with risk management solutions and to manage and hedge its own risks. These derivative activities do not give rise to significant open positions in portfolios of derivatives. Any residual position is managed to ensure that it remains within acceptable risk levels, with matching transactions used to achieve this where necessary. When entering into derivatives, Santander UK employs the same credit risk management procedures to assess and approve potential credit exposures that are used for traditional lending. b) Analysis of derivatives The table below includes the notional amounts of transactions outstanding at the balance sheet date; they do not represent actual exposures. Group 2023 2022 Fair value Fair value Notional amount Assets Liabilities Notional amount Assets Liabilities £m £m £m £m £m £m Derivatives held for trading: Exchange rate contracts 12,927 92 217 14,006 315 281 Interest rate contracts 28,351 389 583 31,135 465 754 Equity and credit contracts 765 133 20 902 130 25 Total derivatives held for trading 42,043 614 820 46,043 910 1,060 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 1,145 29 2 538 12 4 Interest rate contracts 107,540 1,275 839 77,748 1,777 403 108,685 1,304 841 78,286 1,789 407 Designated as cash flow hedges: Exchange rate contracts 21,618 1,008 289 26,035 1,717 186 Interest rate contracts 50,896 553 915 26,108 164 1,471 72,514 1,561 1,204 52,143 1,881 1,657 Total derivatives held for hedging 181,199 2,865 2,045 130,429 3,670 2,064 Derivative netting (1) — (2,047) (2,047) — (2,173) (2,173) Total derivatives 223,242 1,432 818 176,472 2,407 951 (1) Derivative netting excludes the effect of cash collateral, which is offset against the gross derivative position. The amount of cash collateral received that had been offset against the gross derivative assets was 472m ( 2022 : 1,368m ) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was 12m ( 2022 : 70m ). At 31 December 2023 , the fair value of derivative assets included amounts due from Banco Santander group entities of £762m ( 2022 : £1,319m ) and the fair value of derivative liabilities included amounts due to Banco Santander group entities of £230m ( 2022 : £207m ). For information about the impact of netting arrangements on derivative assets and liabilities in the table above, see Note 40 . The table below analyses the notional and fair values of derivatives by trading and settlement method. Notional Traded over the counter Asset Liability Settled by central counterparties Not settled by central counterparties Total Traded over the counter Traded over the counter 2023 £m £m £m £m £m Exchange rate contracts — 35,690 35,690 1,129 508 Interest rate contracts 174,460 12,327 186,787 170 290 Equity and credit contracts — 765 765 133 20 174,460 48,782 223,242 1,432 818 2022 Exchange rate contracts — 40,579 40,579 2,044 471 Interest rate contracts 124,638 10,353 134,991 233 455 Equity and credit contracts — 902 902 130 25 124,638 51,834 176,472 2,407 951 c) Analysis of derivatives designated as hedges Santander UK applies hedge accounting on both a fair value and cash flow basis depending on the nature of the underlying exposure. We establish the hedge ratio by matching the notional of the derivative with the underlying position being hedged. Only the designated risk is hedged and therefore other risks, such as credit risk are managed but not hedged. For interest rate hedges, the designated hedged risk is determined with reference to the underlying benchmark rate. Fair value hedges Portfolio hedges of interest rate risk Santander UK holds portfolios of fixed rate assets and liabilities which expose it to changes in fair value due to movements in market interest rates. We manage these exposures by entering into interest rate swaps. Each portfolio contains assets or liabilities that are similar in nature and share the risk exposure that is designated as being hedged. The interest rate risk component is the change in fair value of fixed rate instruments for changes in the designated benchmark rate. Such changes are usually the largest component of the overall change in fair value. Separate hedges are maintained for each underlying currency. Effectiveness is assessed by comparing changes in the fair value of the hedged item attributable to changes in the designated benchmark interest rate, with changes in the fair value of the interest rate swaps. Micro hedges of interest rate risk and foreign currency risk Santander UK accesses international markets to obtain funding, to issue fixed rate debt or to invest in fixed rate debt of other issuers as part of maintaining a portfolio of HQLA (High Quality Liquid Assets) in its functional currency and other currencies. We are therefore exposed to changes in fair value due to changes in market interest rates and/or foreign exchange rates, principally in USD and EUR, which we mitigate through the use of receive fixed/pay floating rate interest rate swaps and/or receive fixed/pay floating rate cross currency swaps. The interest rate risk component is the change in fair value of the fixed rate debt due to changes in the benchmark rate. The foreign exchange component is the change in the fair value of the fixed rate debt issuance due to changes in foreign exchange rates prevailing from the time of execution. Effectiveness is assessed by using linear regression techniques to compare changes in the fair value of the debt caused by changes in the benchmark interest rate and foreign exchange rates, with changes in the fair value of the interest rate swaps and/or cross currency swaps. Cash flow hedges Hedges of interest rate risk Santander UK manages its exposure to the variability in cash flows of floating rate assets and liabilities attributable to movements in market interest rates by entering into interest rate swaps. The interest rate risk component is determined with reference to the underlying benchmark rate attributable to the floating rates asset or liability. Designated benchmark rates referenced are currently SONIA or BoE base rate. Effectiveness is assessed by comparing changes in the fair value of the interest rate swap with changes in the fair value of the hedged item attributable to the hedged risk, applying a hypothetical derivative method using linear regression techniques. Hedges of foreign currency risk As Santander UK obtains funding in international markets, we assume significant foreign currency risk exposure, mainly in USD and EUR. In addition, Santander UK also holds debt securities for liquidity purposes which assumes foreign currency exposure, principally in JPY and CHF. Santander UK manages the exposures to the variability in cash flows of foreign currency denominated assets and liabilities to movements in foreign exchange rates by entering into either foreign exchange contracts (spot, forward and swaps) or cross currency swaps. These instruments are entered into to match the cash flow profile and maturity of the estimated interest and principal repayments of the hedged item. The foreign currency risk component is the change in cash flows of the foreign currency debt arising from changes in the relevant foreign currency forward exchange rate. Such changes constitute a significant component of the overall changes in cash flows of the instrument. Effectiveness is assessed by comparing changes in the fair value of the foreign exchange contracts (spot, forward and swaps) or cross currency swaps with changes in the fair value of the hedged debt attributable to the hedged risk applying a hypothetical derivative method using linear regression techniques. Possible sources of hedge ineffectiveness For both fair value and cash flow hedges, hedge ineffectiveness can arise from hedging derivatives with a non-zero fair value at the date of initial designation. In addition, for: Fair value hedges Hedge ineffectiveness can also arise due to differences in discounting between the hedged item and the hedging instrument as cash collateralised swaps discount using Overnight Indexed Swaps discount curves not applied to the hedged item; and where counterparty credit risk impacts the fair value of the derivative but not the hedged item. For portfolio hedges of interest rate risk, it can also arise due to differences in the expected and actual volume of prepayments. Cash flow hedges Hedge ineffectiveness can also arise due to differences in the timing of cash flows between the hedged item and the hedging instrument. For micro hedges of interest rate risk, it can also arise due to differences in the basis of cash flows between the hedged item and the hedging instrument. Maturity profile and average price/rate of hedging instruments The following table sets out the maturity profile and average price/rate of the hedging instruments used in the Santander UK group’s hedging strategies: Group 2023 Hedging Instruments ≤1 month >1 and ≤3 months >3 and ≤12 months >1 and ≤5 years >5 years Total Fair value hedges: Interest rate risk Interest rate contracts - Nominal amount (£m) 3,612 7,141 32,241 60,590 3,008 106,592 Average fixed interest rate - GBP 2.38 % 3.19 % 3.42 % 3.90 % 3.99 % Average fixed interest rate - EUR 1.14 % 0.18 % 0.45 % 0.21 % 3.92 % Average fixed interest rate - USD 2.60 % 2.46 % 4.23 % 1.36 % 4.91 % Interest rate/FX risk Exchange rate contracts - Nominal amount (£m) — 18 — 1,041 86 1,145 Interest rate contracts - Nominal amount (£m) — 18 — 844 86 948 Average GBP - EUR exchange rate — 1.11 — 1.16 1.15 Average GBP - USD exchange rate — — — 1.32 — Average fixed interest rate - EUR — — — 2.77 % 3.48 % Average fixed interest rate - USD — — — 4.83 % — Cash flow hedges: Interest rate risk Interest rate contracts – Nominal amount (£m) 911 2,993 12,770 27,721 1,219 45,614 Average fixed interest rate - GBP 5.06 % 2.98 % 5.39 % 3.83 % 3.45 % FX risk Exchange rate contracts - Nominal amount (£m) 927 3,238 2,692 9,447 588 16,892 Interest rate contracts - Nominal amount (£m) — 2,199 — — 942 3,141 Average GBP - JPY exchange rate 154.14 153.95 167.85 — — Average GBP - CHF exchange rate 1.09 1.09 1.09 1.12 1.12 Average GBP - EUR exchange rate — 1.20 1.17 1.18 — Average GBP - USD exchange rate — 1.39 — 1.28 1.39 Interest rate/FX risk Exchange rate contracts - Nominal amount (£m) 87 785 500 2,896 458 4,726 Interest rate contracts - Nominal amount (£m) — — — 1,975 166 2,141 Average GBP - EUR exchange rate 1.18 — 1.25 1.20 1.19 Average GBP - USD exchange rate — 1.66 — 1.38 1.54 Average fixed interest rate - GBP 2.57 % 2.54 % 2.96 % 2.31 % 4.74 % 2022 Fair value hedges: Interest rate risk Interest rate contracts- Nominal amount (£m) 2,210 4,468 21,678 45,314 3,808 77,478 Average fixed interest rate - GBP 2.58 % 0.88 % 0.56 % 2.07 % 3.78 % Average fixed interest rate - EUR 1.77 % 1.60 % 0.77 % 0.28 % 3.09 % Average fixed interest rate - USD 1.35 % 3.47 % 3.51 % 2.00 % 4.92 % Interest rate/FX risk Exchange rate contracts - Nominal amount (£m) — — 66 465 7 538 Interest rate contracts - Nominal amount (£m) — — — 263 7 270 Average GBP - EUR exchange rate — — 1.20 1.16 1.10 Average GBP - USD exchange rate — — — 1.19 — Average fixed interest rate - EUR — — 3.42 % 2.06 % — Average fixed interest rate - USD — — — 4.63 % — Cash flow hedges: Interest rate risk Interest rate contracts - Nominal amount (£m) 1,042 2,191 1,940 13,197 1,076 19,446 Average fixed interest rate - GBP 1.77 % 2.29 % 1.98 % 2.35 % 1.84 % FX risk Exchange rate contracts - Nominal amount (£m) 2,301 3,135 2,381 10,606 1,163 19,586 Interest rate contracts - Nominal amount (£m) 415 — — 2,325 997 3,737 Average GBP - JPY exchange rate — 157.45 160.04 — — Average GBP - CHF exchange rate — 1.13 — — — Average GBP - EUR exchange rate — — 1.12 1.18 1.17 Average GBP - USD exchange rate 1.22 1.25 1.17 1.31 1.39 Interest rate/FX risk Exchange rate contracts - Nominal amount (£m) — — 1,173 4,626 650 6,449 Interest rate contracts - Nominal amount (£m) — — 585 2,132 208 2,925 Average GBP - EUR exchange rate — — 1.19 1.21 1.20 Average GBP - USD exchange rate — — 1.60 1.50 1.54 Average fixed interest rate - GBP — — 3.27 % 2.58 % 4.59 % Net gains or losses arising from fair value and cash flow hedges included in other operating income Group 2023 2022 2021 £m £m £m Fair value hedging: (Losses)/gains on hedging instruments (1,879) 2,381 852 Gains/(losses) on hedged items attributable to hedged risks 1,896 (2,316) (800) Fair value hedging ineffectiveness 17 65 52 Cash flow hedging ineffectiveness 2 (36) (39) 19 29 13 Hedge ineffectiveness can be analysed by risk category as follows: Group 2023 2022 2021 Change in FV of hedging instruments Change in FV of hedged items Recognised in income statement Change in FV of hedging instruments Change in FV of hedged items Recognised in income statement Change in FV of hedging instruments Change in FV of hedged items Recognised in income statement Fair value hedges: £m £m £m £m £m £m £m £m £m Interest rate risk (1,865) 1,877 12 2,392 (2,333) 59 874 (834) 40 Interest rate/FX risk (14) 19 5 (11) 17 6 (22) 34 12 (1,879) 1,896 17 2,381 (2,316) 65 852 (800) 52 Group Hedging Instruments Recognised in Income Statement Reclassified from reserves to income Income statement line item affected by reclassification Change in FV Recognised in OCI Cash flow hedges: £m £m £m £m 2023 Interest rate risk Net interest income 466 (445) 21 (469) FX risk Net interest income/other operating income (396) 377 (19) (392) Interest rate/FX risk Net interest income/other operating income (237) 237 — (387) (167) 169 2 (1,248) 2022 Interest rate risk Net interest income (1,161) 1,160 (1) (96) FX risk Net interest income/other operating income 1,604 (1,604) — 1,692 Interest rate/FX risk Net interest income/other operating income (54) 19 (35) 533 389 (425) (36) 2,129 2021 Interest rate risk Net interest income (317) 305 (12) 73 FX risk Net interest income/other operating income (54) 54 — (158) Interest rate/FX risk Net interest income/other operating income (541) 514 (27) (273) (912) 873 (39) (358) In 2023 , cash flow hedge accounting of £nil ( 2022 : £ nil ) had to cease due to the hedged cash flows no longer being expected to occur. The following table provides a reconciliation by risk category of components of equity and analysis of OCI items (before tax) resulting from hedge accounting. Group 2023 2022 £m £m Balance at 1 January (1,575) 129 Effective portion of changes in fair value: – Interest rate risk 445 (1,160) – Foreign currency risk (377) 1,604 – Interest rate/foreign currency risk (237) (19) (169) 425 Income statement transfers: – Interest rate risk 469 96 – Foreign currency risk 392 (1,692) – Interest rate/foreign currency risk 387 (533) 1,248 (2,129) Balance at 31 December (496) (1,575) Hedged exposures Santander UK hedges its exposures to various risks, including interest rate risk and foreign currency risk, as set out in the following table. Group 2023 2022 Accumulated amount of FV hedge adjustments Change in value to calculate hedge ineffective ness Accumulated amount of FV hedge adjustments Change in value to calculate hedge ineffectiven ess Carrying value Hedged item Portfolio hedge of interest rate risks Of which Discontinued hedges Carrying value Hedged item Portfolio hedge of interest rate risks Of which Discontinued hedges £m £m £m £m £m £m £m £m £m £m Fair value hedges Interest rate risk: Loans and advances to customers 73,194 — (625) (435) 1,968 60,783 — (2,640) (653) (2,707) Other financial assets at amortised cost 152 1 (8) (8) 5 156 — (12) 2 (14) Reverse repurchase agreements – non trading 6,186 — — — 4 4,045 — (5) (1) — Other financial assets at FVOCI 2,013 (113) — (131) 82 2,325 (200) — 35 (227) Deposits by customers (15,892) 38 (10) — (53) (1,739) 24 5 — 33 Deposits by banks — — — — — — — — — — Debt securities in issue (4,091) 118 (75) (114) (128) (4,735) 321 (94) (172) 528 Subordinated liabilities (522) (27) (1) (42) (1) (250) (27) (6) (63) 54 Interest rate/FX risk: Other financial assets at FVOCI 989 4 — — 12 237 (21) — 1 (9) Debt securities in issue (214) (14) — (24) 8 (290) (18) — (37) 27 Subordinated liabilities — — — — (1) 1 1 — 1 (1) 61,815 7 (719) (754) 1,896 60,533 80 (2,752) (887) (2,316) Group 2023 2022 Change in value to calculate hedge ineffectiveness Cash flow hedge reserve Balances on cash flow hedge reserve for discontinued hedges Change in value to calculate hedge ineffectiveness Cash flow hedge reserve Balances on cash flow hedge reserve for discontinued hedges Hedged item balance sheet line item £m £m £m £m £m £m Cash flow hedges: Interest rate risk: Loans and advances to customers (163) (462) 1 935 (1,010) (1) Cash and balances at central banks (281) 99 (76) 233 (274) (106) Deposits by banks (1) (1) — (8) 7 — FX risk: Other financial assets at FVOCI (253) 1 — — (6) — Not applicable – highly probable forecast transactions 88 1 — (349) 2 — Deposits by customers (33) — — (167) (2) — Debt securities in issue 617 (9) — (1,051) (17) (2) Repurchase agreements - non trading (42) — — (37) — — Interest rate/FX risk: Debt securities in issue/loans and advances to customers 99 (75) — 56 (170) (3) Deposits by customers 94 (39) — — (74) — Subordinated liabilities/loans and advances to customers 44 (11) 52 (37) (31) 77 169 (496) (23) (425) (1,575) (35)

Other Financial Assets at Fair

Other Financial Assets at Fair Value Through Profit or Loss	12 Months Ended
	Dec. 31, 2023
Financial assets at fair value through profit or loss [abstract]
Other Financial Assets at Fair Value Through Profit or Loss	12. OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS Group 2023 2022 £m £m Loans and advances to customers: Loans to housing associations 8 4 Other loans 38 41 46 45 Debt securities 167 15 Other debt instruments 49 69 262 129 For the Santander UK group, other financial assets at FVTPL comprised £8m ( 2022 : £16m ) of financial assets designated at FVTPL and £254m ( 2022 : £113m ) of financial assets mandatorily held at FVTPL. Loans and advances to customers principally represent other loans, being a portfolio of roll-up mortgages . These are managed, and have their performance evaluated, on a fair value basis in accordance with a documented investment strategy, and information about them is provided on that basis to management. Since 2009, the Santander UK group’s policy has been not to designate similar new loans at FVTPL. The net loss in the year attributable to changes in credit risk for loans and advances at FVTPL was £nil ( 2022 : £1m , 2021 : £nil ). The cumulative net loss attributable to changes in credit risk for loans and advances at FVTPL at 31 December 2023 was £3m ( 2022 : £3m , 2021 : £2m ).

Loans and Advances to Customers

Loans and Advances to Customers	12 Months Ended
	Dec. 31, 2023
Net Loans And Advances To Customers [Abstract]
Loans and Advances to Customers	13. LOANS AND ADVANCES TO CUSTOMERS Group 2023 2022 £m £m Loans secured on residential properties 172,854 184,317 Corporate loans 18,267 19,057 Finance leases 4,530 4,645 Other unsecured loans 7,232 7,742 Accrued interest and other adjustments 943 688 Amounts due from fellow Banco Santander subsidiaries and joint ventures 4,489 4,220 Amounts due from Santander UK Group Holdings plc 55 — Amounts due from subsidiaries — — Loans and advances to customers 208,370 220,669 Credit impairment loss allowances on loans and advances to customers (914) (931) Residual value and voluntary termination provisions on finance leases (21) (22) Net loans and advances to customers 207,435 219,716 For movements in expected credit losses, see the 'Movement in total exposures and the corresponding ECL' table in the Santander UK group level - Credit risk review section of the Risk review. Finance lease and hire purchase contract receivables may be analysed as follows: Group 2023 2022 Gross investment Unearned finance income Net investment Gross investment Unearned finance income Net investment £m £m £m £m £m £m No later than one year 1,502 (216) 1,286 1,493 (182) 1,311 Later than one year and not later than two years 1,426 (208) 1,218 1,367 (168) 1,199 Later than two years and not later than three years 1,331 (194) 1,137 1,190 (147) 1,043 Later than three years and not later than four years 882 (129) 753 1,044 (129) 915 Later than four years and not later than five years 99 (14) 85 143 (18) 125 Later than five years 60 (9) 51 59 (7) 52 5,300 (770) 4,530 5,296 (651) 4,645 The Santander UK group enters into finance leasing arrangements primarily for the financing of motor vehicles and a range of assets for its corporate customers. Included in the carrying value of net investment in finance leases and hire purchase contracts is £1,830m ( 2022 : £1,761m ) of unguaranteed RV at the end of the current lease terms, which is expected to be recovered through re-payment, re-financing or sale. Contingent rent income of nil ( 2022 : £ nil , 2021 : £nil ) was earned in the year, which was classified in ‘Interest and similar income’. Finance income on the net investment in finance leases was £266m ( 2022 : £230m , 2021 : £243m ). Finance lease receivable balances are secured over the asset leased. The Santander UK group is not permitted to sell or repledge the asset in the absence of default by the lessee. The Directors consider that the carrying amount of the finance lease receivables approximates to their fair value. Included within loans and advances to customers are advances assigned to bankruptcy remote structured entities and Abbey Covered Bonds LLP. These loans provide security to issues of covered bonds and mortgage-backed or other asset-backed securities issued by the Santander UK group. For more, see Note 14 .

Securitisations and Covered Bon

Securitisations and Covered Bonds	12 Months Ended
	Dec. 31, 2023
Disclosure Of Securitisations And Covered Bonds [Abstract]
Securitisations and covered bonds	14. SECURITISATIONS AND COVERED BONDS The information in this Note relates to securitisations and covered bonds for consolidated structured entities, used to obtain funding or collateral. It excludes structured entities relating to credit protection transactions. The Santander UK group uses structured entities to securitise some of the mortgage and other loans to customers that it originates. The Santander UK group also issues covered bonds, which are guaranteed by, and secured against, a pool of the Santander UK group’s mortgage loans transferred to Abbey Covered Bonds LLP. The Santander UK group issues mortgage-backed securities, other asset-backed securities and covered bonds mainly in order to obtain diverse, low-cost funding, but also to use as collateral for raising funds via third party bilateral secured funding transactions or for liquidity purposes in the future. The Santander UK group has successfully used bilateral secured transactions as an additional form of medium-term funding; this has allowed the Santander UK group to further diversify its medium-term funding investor base. Loans and advances to customers include portfolios of residential mortgage loans, and receivables derived from credit agreements with retail customers for the purchases of financed vehicles, which are subject to non-recourse finance arrangements. These loans and receivables have been purchased by, or assigned to, structured entities or Abbey Covered Bonds LLP, and have been funded primarily through the issue of mortgage-backed securities, other asset-backed securities or covered bonds. No gain or loss has been recognised as a result of these sales. The structured entities and Abbey Covered Bonds LLP are consolidated as subsidiary undertakings. The Company and its subsidiaries do not own directly, or indirectly, any of the share capital of any of the structured entities. a) Securitisations i) Master trust structures The Santander UK group makes use of master trust structures, whereby a pool of residential mortgage loans is assigned to a trust company by the asset originator. A funding entity acquires a beneficial interest in the pool of assets held by the trust company with funds borrowed from qualifying structured entities, which at the same time issue asset-backed securities to third-party investors or the Santander UK group. Santander UK plc and its subsidiaries receive payments from the securitisation companies in respect of fees for administering the loans, and payment of deferred consideration for the sale of the loans. Santander UK plc and its subsidiaries have no right or obligation to repurchase any securitised loan, except if certain representations and warranties given by Santander UK plc or its subsidiaries at the time of transfer are breached and, in certain cases, if there is a product switch or further advance, if a securitised loan is in arrears for over two months or if a securitised loan does not comply with regulatory requirements. ii) Other securitisation structures The Santander UK group also makes use of auto loan securitisations, whereby a pool of auto loans originated by a member of the Santander UK group is sold to a special purpose vehicle by the asset originator. The special purpose vehicle funds the purchase of the auto loans by issuing asset-backed securities to third- party investors. A proportion of the securities are also retained by members of the Santander UK group. Members of the Santander UK group also receive payments from the special purpose vehicle in respect of fees for administering the auto loans, and payment of deferred consideration for the sale of the auto loans. The seller has no right or obligation to repurchase any securitised loan, except if certain representations and warranties given by the seller at the time of transfer are breached and, in certain cases, if there has been a subsequent variation in the terms of the underlying auto loan not permitted under the sale agreement. b) Covered bonds Santander UK plc also issues covered bonds, which are its direct, unsecured and unconditional obligation. The covered bonds benefit from a guarantee from Abbey Covered Bonds LLP. Santander UK plc makes a term advance to Abbey Covered Bonds LLP equal to the sterling proceeds of each issue of covered bonds. Abbey Covered Bonds LLP uses the proceeds of the term advance to purchase portfolios of residential mortgage loans and their security from Santander UK plc. Under the terms of the guarantee, Abbey Covered Bonds LLP has agreed to pay an amount equal to the guaranteed amounts when the same shall become due for payment, but which would otherwise be unpaid by Santander UK plc. c) Analysis of securitisations and covered bonds The Santander UK group’s principal securitisation programmes and covered bond programme, together with the balances of the advances subject to securitisation (or for the covered bond programme assigned) and the carrying value of the notes in issue at 31 December 2023 and 2022 are listed below. Group Gross assets External notes in issue Notes issued to Santander UK plc/subsidiaries as collateral 2023 2022 2023 2022 2023 2022 £m £m £m £m £m £m Mortgage-backed master trust structures: – Holmes 3,242 1,646 2,119 790 300 176 – Fosse 2,048 2,028 100 100 1,382 1,365 5,290 3,674 2,219 890 1,682 1,541 Other asset-backed securitisation structures: – Motor — 6 — 7 — — – Repton 757 — 550 — — — 757 6 550 7 — — Total securitisation programmes 6,047 3,680 2,769 897 1,682 1,541 Covered bond programme: – Euro 35bn Global Covered Bond Programme 21,880 21,304 15,000 15,205 — — Total securitisation and covered bond programmes 27,927 24,984 17,769 16,102 1,682 1,541 The following table sets out the internal and external issuances and redemptions in 2023 and 2022 for each securitisation and covered bond programme. Group Internal issuances External issuances Internal redemptions External redemptions 2023 2022 2023 2022 2023 2022 2023 2022 £m £m £m £m £m £m £m £m Mortgage-backed master trust structures: – Holmes 241 — 1,500 600 121 100 186 200 – Fosse — — — — — — — 200 Other asset-backed securitisation structures: – Motor — — — — — — 7 33 – Repton — — 550 — — — — — Covered bond programme: – Euro 35bn Global Covered Bond Programme — — — 4,200 — 100 — 1,700 241 — 2,050 4,800 121 200 193 2,133 , the remaining asset-backed notes from the Motor securitisation structure were redeemed. In 2023 Repton 2023-1 Limited borrowed £550m through an asset-backed variable funding note facility. Repayment of this will begin in 2025 . Holmes Funding Ltd has a beneficial interest of £2,396m ( 2022 : £796m ) in the residential mortgage loans held by Holmes Trustees Ltd. The remaining share of the beneficial interest in residential mortgage loans held by Holmes Trustees Ltd belongs to Santander UK plc. Fosse Funding (No.1) Ltd has a beneficial interest of £1,393m ( 2022 : £1,465m ) in the residential mortgage loans held by Fosse Trustee (UK) Ltd. The remaining share of the beneficial interest in residential mortgage loans held by Fosse Trustee (UK) Ltd belongs to Santander UK plc. The Holmes securitisation companies have cash deposits of £80m ( 2022 : £112m ), which have been accumulated to finance the redemption of a number of securities issued by the Holmes securitisation companies. The share of Holmes Funding Ltd in the trust assets is therefore reduced by this amount. The Fosse securitisation companies have cash deposits of £108m ( 2022 : £108m ), which have been accumulated to finance the redemption of a number of securities issued by Fosse securitisation companies. The share of Fosse Funding (No.1) Ltd’s beneficial interest in the assets held by Fosse Trustee (UK) Ltd is therefore reduced by this amount.

Transfers of Financial Assets N

Transfers of Financial Assets Not Qualifying for Derecognition	12 Months Ended
	Dec. 31, 2023
Disclosure of transferred financial assets that are not derecognised in their entirety [abstract]
Transfers of Financial Assets Not Qualifying for Derecognition	15. TRANSFERS OF FINANCIAL ASSETS NOT QUALIFYING FOR DERECOGNITION The Santander UK group enters into transactions in the normal course of business by which it transfers recognised financial assets directly to third parties or to structured entities. These transfers may give rise to the full or partial derecognition of those financial assets. Transferred financial assets that do not qualify for derecognition consist of (i) securities held by counterparties as collateral under repurchase agreements, (ii) securities lent under securities lending agreements, and (iii) loans that have been securitised under arrangements by which the Santander UK group retains a continuing involvement in such transferred assets. As a result of these sale and repurchase and securities lending transactions, the Santander UK group is unable to use, sell or pledge the transferred assets for the duration of the transaction. The Santander UK group remains exposed to interest rate risk and credit risk on these pledged instruments. The counterparty’s recourse is not limited to the transferred assets. The Santander UK group securitisation transfers do not qualify for derecognition. The Santander UK group remains exposed to credit risks arising from the mortgage loans or credit agreements and has retained control of the transferred assets. Circumstances in which the Santander UK group has continuing involvement in the transferred assets may include retention of servicing rights over the transferred assets (the servicing fee in respect of which is dependent on the amount or timing of the cash flows collected from, or the non-performance of, the transferred assets), entering into a derivative transaction with the securitisation vehicle, retaining an interest in the securitisation vehicle or providing a cash reserve fund. Where the Santander UK group has continuing involvement, it continues to recognise the transferred assets to the extent of its continuing involvement and recognises an associated liability. The net carrying amount of the transferred assets and associated liabilities reflects the rights and obligations that the Santander UK group has retained. The following table analyses the carrying amount of financial assets that did not qualify for derecognition and their associated financial liabilities: Group 2023 2022 Assets Liabilities Assets Liabilities Nature of transaction £m £m £m £m Sale and repurchase agreements 14 (15) 120 (128) Securities lending agreements 3,136 (2,735) 2,871 (2,509) Securitisations (See Notes 14 and 26) 6,047 (2,769) 3,680 (897) 9,197 (5,519) 6,671 (3,534)

Reverse Repurchase Agreements -

Reverse Repurchase Agreements - Non Trading	12 Months Ended
	Dec. 31, 2023
Disclosure Of Reserve Repurchase Agreements Non-Trading [Abstract]
Reverse Repurchase Agreements - Non Trading	16. REVERSE REPURCHASE AGREEMENTS – NON-TRADING Group 2023 2022 £m £m Agreements with banks 2,397 885 Agreements with customers 10,071 6,463 12,468 7,348

Other Financial Assets at Amort

Other Financial Assets at Amortised Cost	12 Months Ended
	Dec. 31, 2023
Financial assets at fair value through profit or loss [abstract]
Other Financial Assets at Amortised Cost	17. OTHER FINANCIAL ASSETS AT AMORTISED COST Group 2023 2022 £m £m Asset backed securities — — Debt securities 152 156 0 152 156 A significant portion of the debt securities are held in our eligible liquidity pool and consist mainly of government bonds and covered bonds. Detailed disclosures can be found in the 'Liquidity risk' section of the Risk review.

Financial Assets at Fair Value

Financial Assets at Fair Value Through Other Comprehensive Income	12 Months Ended
	Dec. 31, 2023
Financial assets at fair value through other comprehensive income [abstract]
Financial Assets at Fair Value Through Other Comprehensive Income	18. FINANCIAL ASSETS AT FAIR VALUE THROUGH OTHER COMPREHENSIVE INCOME Group 2023 2022 £m £m Debt securities 8,481 6,024 8,481 6,024 A significant portion of the debt securities are held in our eligible liquidity pool and consist mainly of government bonds and covered bonds. Detailed disclosures can be found in the 'Liquidity risk' section of the Risk review.

Interests in Other Entities

Interests in Other Entities	12 Months Ended
	Dec. 31, 2023
Investments accounted for using equity method [abstract]
Interests in Other Entities	19. INTERESTS IN OTHER ENTITIES Group 2023 2022 £m £m Subsidiaries — — Joint Ventures 245 252 0 245 252 The Santander UK group consists of a parent company, Santander UK plc, incorporated and domiciled in the UK and a number of subsidiaries and joint ventures held directly and indirectly by it. a) Interests in subsidiaries The Company holds directly or indirectly 100% of the issued ordinary share capital of its principal subsidiaries. All companies operate principally in their country of incorporation or registration. Interests in consolidated structured entities Structured entities are formed by Santander UK to accomplish specific and well-defined objectives. Santander UK consolidated these structured entities when the substance of the relationship indicates control, as described in Note 1 . In addition to the structured entities disclosed in Note 14 which are used for securitisation and covered bond programmes, the only other structured entities consolidated by Santander UK are described below. All the external assets and liabilities in these entities are included in the financial statements and in relevant Notes. Other than as set out below, no significant judgements were required with respect to control or significant influence. Motor Securities 2018-1 Designated Activity Company (Motor 2018) Motor 2018 is a credit protection entity, and a Designated Activity Company limited by shares, incorporated in Ireland. It issued a series of credit linked notes varying in seniority which referenced a portfolio of Santander UK group auto loans. Concurrently, this entity sold credit protection to SCUK in respect of the referenced loans and, in return for a fee, was liable to make protection payments to SCUK upon the occurrence of a credit event in relation to any of the referenced loans. Motor 2018 is consolidated as Santander UK held a variable interest by retaining the junior tranche of notes issued by the entity. The outstanding notes were redeemed and the transaction terminated in 2023 . b) Interests in joint ventures Santander UK does not have any individually material interests in joint ventures. In 2023 , Santander UK’s share in the profit after tax of its joint ventures was £43m ( 2022 : £36m ) before elimination of transactions between Santander UK and the joint ventures. At 31 December 2023 , the carrying amount of Santander UK’s interest was £245m ( 2022 : £252m ). At 31 December 2023 and 2022 , the joint ventures had no commitments and contingent liabilities. c) Interests in unconsolidated structured entities Structured entities sponsored by the Santander UK group Santander UK has interests in structured entities which it sponsors but does not control. Santander UK considers itself a sponsor of a structured entity when it facilitates the establishment of the structured entity. Other than as set out below, no significant judgements were required with respect to control or significant influence. The structured entities sponsored but not consolidated by Santander UK are as follows: i) Santander (UK) Common Investment Fund (the Fund) The Fund is a common investment fund that was established to hold the assets of the Santander (UK) Group Pension Scheme. The Fund is not consolidated by Santander UK, but its assets of £8,551m ( 2022 : £8,646m ) are accounted for as part of the defined benefit assets and obligations recognised on Santander UK’s balance sheet. For more on the Fund, see Note 30 . As the Fund holds the assets of the pension scheme, it is outside the scope of IFRS 10. Santander UK’s maximum exposure to loss is the carrying amount of the assets held. ii) Credit protection entities Santander UK has established four ( 2022 : four ) unconsolidated credit protection entities, which are Designated Activity Companies limited by shares, incorporated in Ireland. Each entity has issued a series of credit linked notes varying in seniority which reference portfolios of Santander UK group loans. Concurrently, these entities sell credit protection to Santander UK in respect of the referenced loans and, in return for a fee, are liable to make protection payments to Santander UK upon the occurrence of a credit event in relation to any of the referenced loans. Santander UK has no holdings in senior credit linked notes ( 2022 : £180m ). Junior credit linked notes, which amounted to £185m ( 2022 : £465m ), are all held by third party investors and suffer the first losses incurred in the referenced portfolios. Funds raised by the sale of the credit linked notes are deposited with Santander UK as collateral for the credit protection. The senior credit linked notes, along with the deposits and associated guarantees, are presented on a net basis, to reflect a legal right of set-off between the principal amounts of senior notes and the cash deposits. Deposits and associated guarantees in respect of the junior credit linked notes are included in ‘Deposits by customers’ (see Note 23 ). The entities are not consolidated by Santander UK because the third-party investors have the exposure, or rights, to all of the variability of returns from the performance of the entities. No assets are transferred to, or income received from, these entities. Since the credit linked notes (including those held by Santander UK) are fully cash collateralised, Santander UK’s maximum exposure to loss is equal to any unamortised fees paid to the entities in connection with the credit protection outlined above. Structured entities not sponsored by the Santander UK group Santander UK also has interests in structured entities which it does not sponsor or control. These consist of holdings of mortgage and other asset backed securities issued by entities that were established and/or sponsored by other unrelated financial institutions. These securities comprise the asset backed securities included in Note 17 . Management has concluded that the Santander UK group has no control or significant influence over these entities and that the carrying value of the interests held in these entities represents the maximum exposure to loss.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2023
Disclosure of detailed information about intangible assets [abstract]
Intangible Assets	20. INTANGIBLE ASSETS a) Goodwill Group Cost Accumulated impairment Carrying amount £m £m £m At 31 December 2022 and 1 January 2023 and 31 December 2023 1,269 (70) 1,199 Impairment of goodwill In 2023 and 2022 , no impairment of goodwill was recognised. Goodwill is tested for impairment annually, or more frequently, if reviews identify an impairment indicator or when events or changes in circumstances dictate. Goodwill is tested for impairment annually at 31 December, with a review for impairment indicators at 30 June. The annual review identified that the risks of ongoing global conflicts, places increasing uncertainty on the UK economic trajectory, and its potential impact on the carrying value of goodwill as impairment indicators for all cash-generating units (CGUs). As a result, management updated the impairment test at 31 December 2023 for all CGUs. Basis of the recoverable amount The recoverable amount of all CGUs was determined based on its value in use (VIU) methodology at each testing date. For each CGU, the VIU is calculated by discounting management’s cash flow projections for the CGU. The cash flow projections also take account of increased internal capital allocations needed to achieve internal and regulatory capital targets including the leverage ratio. The key assumptions used in the VIU calculation for each CGU are set out below. The Retail & Business Banking segment consists of the Private Banking CGU and the rest of Retail & Business Banking, known as the Personal Financial Services CGU. Carrying amount of Goodwill by CGU and key assumptions in the VIU calculation Goodwill Discount rate Growth rate beyond initial cash flow projections 2023 2022 2023 2022 2023 2022 CGU £m £m % % % % Personal Financial Services 1,169 1,169 16.7 16.6 1.6 1.6 Private Banking 30 30 14.6 15.3 1.6 1.6 1,199 1,199 The CGUs do not carry on their balance sheets any other intangible assets with indefinite useful lives. Management’s judgement in estimating the cash flows of a CGU The cash flow projections for the purpose of impairment testing for each CGU are derived from the latest 3-year plan presented to the Board. The Board challenges and endorses management’s planning assumptions in light of internal capital allocations needed to support Santander UK’s strategy, current market conditions and the macroeconomic outlook. For the goodwill impairment tests conducted at 31 December 2023 , the determination of the carrying amount of the Personal Financial Services CGU was based on an allocation of regulatory capital and management’s cash flow projections until the end of 2026. The assumptions included in the cash flow projections reflect an allocation to the cost of capital to support future growth, as well as the expected impact of recent events in the UK economic environment on the financial outlook within which the CGUs operate. The cash flow projections are supported by Santander UK’s base case economic scenario. For more on the base case economic scenario, including our forecasting approach and the assumptions in place at 31 December 2023 , see the Credit risk – Santander UK group level section of the Risk review. The cash flow projections take into account the likely impact of recent changes to the BoE Bank Rate, inflation and also consider the impact of future climate change. Cash flow projections for the purpose of impairment testing do not take account of any adverse outcomes arising from contingent liabilities (see Note 31 ), whose existence will be confirmed by uncertain future events or where any obligation is not probable or otherwise cannot be measured reliably, nor do they take account of the benefits arising from Santander UK’s transformation plans that had not yet been implemented or committed at 31 December 2023 . Discount rate The rate used to discount the cash flows is based on the cost of equity assigned to each CGU, which is derived using a capital asset pricing model (CAPM) and calculated on a post-tax basis. The CAPM depends on a number of inputs reflecting financial and economic variables, including the risk-free rate and a premium to reflect the inherent risk of the business being evaluated. These variables are based on the market’s assessment of the economic variables and management’s judgement. The inputs to the CAPM are observable on a post-tax basis. In determining the discount rate, management has identified the cost of equity associated with market participants that closely resemble our CGUs and adjusted them for tax to arrive at the pre-tax equivalent rate. The Private Banking CGU has a different discount rate compared to the Personal Financial Services CGU because different market participants closely resemble each CGU. Growth rate beyond initial cash flow projections The growth rate for periods beyond the initial cash flow projections is used to extrapolate the cash flows in perpetuity because of the long-term perspective of CGUs. In line with the accounting requirements, management uses the UK Government’s official estimate of UK long-term average GDP growth rate, as this is lower than management's estimate of the long-term average growth rate of the business. The estimated UK long-term average GDP growth rate has regard to the long-term impact of inherent uncertainties, such as Brexit, climate change and higher living costs, driven by high inflation and rising interest rates. Goodwill arising on the acquisition of Personal Financial Services and Private Banking The VIU of each CGU remains higher than the carrying value of the related goodwill. The VIU review at 31 December 2023 did not indicate the need for an impairment in the Company’s goodwill balances. Management considered the level of headroom and the uncertainty relating to the respective estimates of the VIU for those CGUs but determined that there was a sufficient basis to conclude that no impairment was required. Sensitivities of key assumptions in calculating the value in use At 31 December 2023 and 31 December 2022 , the VIU of the Personal Financial Services CGU was sensitive to reasonably possible changes in the key assumptions supporting the recoverable amount. The table below presents a summary of the key assumptions underlying the most sensitive inputs to the model for the Personal Financial Services CGU, the key risks associated with each and details of a reasonably possible change in assumptions, such as a decrease in mortgage new business. The sensitivity analysis presented below has been prepared on the basis that a change in each key assumption would not have a consequential impact on other assumptions used in the impairment review. However, due to the interrelationships between some of the assumptions, a change in one of the assumptions might impact one or more of the other assumptions and could result in a larger or smaller overall impact. Reasonably possible changes in key assumptions CGU Input Key assumptions Associated risks Reasonably possible change Personal Financial Services Cash flow projections – BoE Bank Rate – UK house price growth – UK mortgage loan market growth – UK unemployment rate – Position in the market – Regulatory capital levels. – Uncertain market outlook – Higher interest rate environment impact on customer affordability – Customer remediation and regulatory action outcomes – Uncertain regulatory capital requirements. – Cash flow projections decrease by 10% ( 2022 : 5% ) . Discount rate – Discount rate used is a reasonable estimate of a suitable market rate for the profile of the business. – Market rates of interest rise. – Discount rate increases by 100 basis points ( 2022 : 100 basis points ) . GDP growth rate – High oil / gas prices – Elevated wage growth – Weak productivity – Large government debt burden – Fragile business and consumer confidence – Inflation and interest rates stay higher for longer, hitting the disposable income of our customers – Affects the profitability of our customers – Limits the scope for tax cuts, hitting the disposable income of our customers – Affects business and consumer spending decisions of our customers – GDP Growth rate decreases by 10% ( 2022 : 10% ) At 31 December 2023 and 31 December 2022 , a reasonably possible change in the key assumptions in relation to the VIU calculation for the goodwill balance in the Personal Financial Services CGU would have resulted in a reduction in headroom as follows. Reduction in headroom 2023 2022 CGU Reasonably possible change £m £m Personal Financial Services Cash flow projections decrease by 10% ( 2022 : 5% ) (818) (538) Discount rate increases by 100 basis points ( 2022 : 100 basis points ) (663) (887) GDP Growth rate decreases by 10% ( 2022 : 10% ) (19) (31) Sensitivity of Value in use changes to current assumptions to achieve nil headroom Although there was no impairment of goodwill relating to the Personal Financial Services CGU or the Private Banking CGU at 31 December 2023 , the test for the Personal Financial Services CGU remains sensitive to some of the assumptions used, as described above. In addition, the changes in assumptions detailed below for the discount rate and cash flow projections would eliminate the current headroom. As a result, there is a risk of impairment in the future should business performance or economic factors diverge from forecasts. In 2023 , there was a decrease in headroom arising from a decline in cash flow forecasts, this is partially offset by a decrease to RWAs which has led to a reduction in the required CET1 capital requirement. The sensitivity analysis presented below has been prepared on the basis that a change in each key assumption would not have a consequential impact on other assumptions used in the impairment review. However, due to the interrelationships between some of the assumptions, a change in one of the assumptions might impact one or more of the other assumptions and could result in a larger or smaller overall impact. 2023 Carrying value Value in use Headroom Increase in discount rate Decrease in GDP growth rate Decrease in cash flows CGU £m £m £m bps % % Personal Financial Services 7,513 8,178 665 101 4 8 2022 Personal Financial Services 8,860 10,752 1,892 239 13 18 b) Other intangibles Group Cost Accumulated amortisation/ impairment Carrying amount £m £m £m At 1 January 2023 1,261 (910) 351 Additions 114 — 114 Disposals (36) 36 — Charge — (116) (116) At 31 December 2023 1,339 (990) 349 At 1 January 2022 1,334 (992) 342 Additions 112 — 112 Disposals (185) 185 — Charge — (100) (100) Impairment — (3) (3) At 31 December 2022 1,261 (910) 351 Other intangibles which consist of computer software, include computer software under development of £157m ( 2022 : £149m ), of which £35m is internally generated ( 2022 : £33m ). The impairment charge of £nil ( 2022 : £3m ) relates to computer software no longer expected to yield future economic benefits as it has become obsolete.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2023
Property, plant and equipment [abstract]
Property, Plant and Equipment	21. PROPERTY, PLANT AND EQUIPMENT Group Property Office fixtures and equipment Computer software Operating lease assets Right-of-use assets Total (1) £m £m £m £m £m £m Cost: At 1 January 2023 889 823 72 722 267 2,773 Additions 87 83 — 85 31 286 Reclassification (to)/from assets held for sale 8 — — — — 8 Disposals (66) (29) (5) (172) (35) (307) At 31 December 2023 918 877 67 635 263 2,760 Accumulated depreciation: At 1 January 2023 270 618 72 145 155 1,260 Charge for the period 17 62 — 64 30 173 Impairment during the period — — — — (11) (11) Disposals (61) (27) (5) (62) (1) (156) At 31 December 2023 226 653 67 147 173 1,266 Carrying amount 692 224 — 488 90 1,494 Group Property Office fixtures and equipment Computer software Operating lease assets Right-of-use assets Total (1) £m £m £m £m £m £m Cost: At 1 January 2022 978 1,049 434 755 254 3,470 Additions 61 86 — 185 38 370 Reclassification to assets held for sale (98) (13) — — — (111) Disposals (52) (299) (362) (218) (25) (956) At 31 December 2022 889 823 72 722 267 2,773 Accumulated depreciation: At 1 January 2022 334 857 434 160 137 1,922 Charge for the year 18 68 1 73 19 179 Impairment during the year 8 2 — — — 10 Reclassification to assets held for sale (49) (13) — — — (62) Disposals (41) (296) (363) (88) (1) (789) At 31 December 2022 270 618 72 145 155 1,260 Carrying amount 619 205 — 577 112 1,513 (1) Property includes investment properties of £17m ( 2022 : £17m ) and assets under construction of £nil ( 2022 : £204m ). In September 2023, we completed the construction of a new head office in Milton Keynes. In 2023 , right-of-use assets were impaired as a result of our multi-year transformation project. The impairment relates to leasehold properties within the scope of our branch network restructuring programme and head office sites which are either closing or consolidating.

Other Financial Liabilities at

Other Financial Liabilities at Fair Value Through Profit or Loss	12 Months Ended
	Dec. 31, 2023
Disclosure of financial liabilities [abstract]
Other Financial Liabilities at Fair Value Through Profit or Loss	22. OTHER FINANCIAL LIABILITIES AT FAIR VALUE THROUGH PROFIT OR LOSS Group 2023 2022 £m £m Structured Notes Programmes 369 375 Structured deposits 426 321 Zero Amortising Guaranteed Notes 104 107 899 803 For the Santander UK group all ( 2022 : all) of the other financial liabilities at FVTPL were designated as such. Gains and losses arising from changes in the credit spread of securities issued by the Santander UK group reverse over the contractual life of the debt, provided that the debt is not repaid at a premium or a discount. The net loss during the year attributable to changes in the Santander UK group’s own credit risk on the above securities was £21m ( 2022 : £25m gain, 2021 : £12m loss). The cumulative net loss attributable to changes in the Santander UK group’s own credit risk on the above securities at 31 December 2023 was £6m ( 2022 : £15m gain, 2021 : £10m loss). At 31 December 2023 , the amount that would be required to be contractually paid at maturity of the securities above was £97m ( 2022 : £138m ) higher than the carrying value.

Deposits by Customers

Deposits by Customers	12 Months Ended
	Dec. 31, 2023
Deposits from customers [abstract]
Deposits by Customers	23. DEPOSITS BY CUSTOMERS Group 2023 2022 £m £m Demand and time deposits (1) 188,004 189,587 Amounts due to other Santander UK Group Holdings plc subsidiaries 114 67 Amounts due to Santander UK Group Holdings plc (2) 1,772 4,759 Amounts due to fellow Banco Santander subsidiaries and joint ventures 960 1,155 190,850 195,568 (1) Includes capital amount guaranteed / protected equity index-linked deposits of £304m ( 2022 : £408m ). (2) Includes downstreamed funding from our immediate parent company Santander UK Group Holdings plc.

Deposits by Banks

Deposits by Banks	12 Months Ended
	Dec. 31, 2023
Disclosure Of Deposits From Banks [Abstract]
Deposits by Banks	24. DEPOSITS BY BANKS Group 2023 2022 £m £m Items in the course of transmission 732 701 Deposits held as collateral 860 1,741 Other deposits (1) 18,737 26,082 Amounts due to Santander UK subsidiaries 3 1 20,332 28,525 (1) Includes drawdown from the TFSME of £17.0bn ( 2022 : £25.0bn ).

Repurchase Agreements - Non Tra

Repurchase Agreements - Non Trading	12 Months Ended
	Dec. 31, 2023
Disclosure Of Repurchase Agreements 1 [Abstract]
Repurchase Agreements - Non Trading	25. REPURCHASE AGREEMENTS – NON TRADING Group 2023 2022 £m £m Agreements with banks 551 50 Agreements with customers 7,860 7,932 8,411 7,982

Debt Securities in Issue

Debt Securities in Issue	12 Months Ended
	Dec. 31, 2023
Debt Securities In Issue [Abstract]
Debt Securities in Issue	26. DEBT SECURITIES IN ISSUE Group 2023 2022 £m £m Medium-term notes: – US $30bn Euro Medium Term Note Programme 744 739 – Euro 30bn Euro Medium Term Note Programme 3,784 3,211 - US SEC-registered Debt Programme - Santander UK plc 7,128 6,694 Medium-term notes 11,656 10,644 Euro 35bn Global Covered Bond Programme 15,000 15,205 US $20bn Commercial Paper Programmes 2,761 1,851 Certificates of deposit 1,530 2,874 Credit linked notes 194 60 Securitisation programmes 2,769 897 33,910 31,531

Subordinated Liabilities

Subordinated Liabilities	12 Months Ended
	Dec. 31, 2023
Disclosure Of Subordinated Liabilities [Abstract]
Subordinated Liabilities	27. SUBORDINATED LIABILITIES Group 2023 2022 £m £m £325m Sterling preference shares 343 344 Undated subordinated liabilities 205 219 Dated subordinated liabilities 1,838 1,769 2,386 2,332 In 2023 , certain subordinated liabilities were repurchased as part of ongoing liability management exercises, resulting in a profit of £4m ( 2022 : a loss of £5m ). The above securities will, in the event of the winding up of the issuer, be subordinated to the claims of depositors and all other creditors of the issuer, other than creditors whose claims rank equally with, or are junior to, the claims of the holders of the subordinated liabilities. The subordination amongst each of the subordinated liabilities upon a winding up of the issuer is specified in their respective terms and conditions. In 2023 and 2022 , the Santander UK group had no defaults of principal, interest or other breaches with respect to its subordinated liabilities. No repayment or purchase by the issuer of the subordinated liabilities may be made prior to their stated maturity without the consent of the PRA. Undated subordinated liabilities Group 2023 2022 First call date £m £m 10.0625% Exchangeable capital securities n/a 205 205 7.125% 30 Year Step-up perpetual callable subordinated notes 2030 — 14 205 219 In common with other debt securities issued by Santander UK group companies and notwithstanding the issuer’s first call dates in the table above, in the event of certain tax changes affecting the treatment of payments of interest on subordinated liabilities in the UK, the 7.125% 30 Year Step-up perpetual callable subordinated notes are redeemable at any time, and the 10.0625% Exchangeable capital securities are redeemable on any interest payment date – each in whole at the option of Santander UK, at their principal amount together with any accrued interest. The 10.0625% Exchangeable capital securities are exchangeable into fully paid 10.375% non-cumulative non-redeemable sterling preference shares of £1 each, at the option of Santander UK, on the business day immediately following any interest payment date. Dated subordinated liabilities Group 2023 2022 Maturity £m £m 5% Subordinated notes 2023 — 591 4.75% Subordinated notes 2025 326 608 7.95% Subordinated notes 2029 193 207 6.50% Subordinated notes 2030 1 22 5.875% Subordinated notes 2031 7 7 5.625% Subordinated notes 2045 222 334 7.869% Subordinated notes 2033 321 — 8.296% Subordinated notes 2033 768 — 1,838 1,769 The dated subordinated liabilities are redeemable in whole at the option of Santander UK in the event of certain tax changes affecting the treatment of payments of interest on the subordinated liabilities in the UK, at their principal amount together with any accrued interest.

Other Liabilities

Other Liabilities	12 Months Ended
	Dec. 31, 2023
Subclassifications of assets, liabilities and equities [abstract]
Other Liabilities	28. OTHER LIABILITIES Group 2023 2022 £m £m Lease liabilities 111 125 Other 2,368 2,456 2,479 2,581

Provisions

Provisions	12 Months Ended
	Dec. 31, 2023
Disclosure of other provisions [abstract]
Provisions	29. PROVISIONS Group Customer remediation Litigation and other regulatory Bank Levy Property ECL on undrawn facilities and guarantees Restructuring Other Total £m £m £m £m £m £m £m £m At 1 January 2023 90 136 3 47 74 21 7 378 Additional provisions (See Note 8) 45 28 44 16 4 56 168 361 Provisions released (See Note 8) (8) — (8) (6) — — — (22) Utilisation and other (21) (32) (95) (10) — (45) (168) (371) Recharge (1) — — 20 — — — — 20 Reclassification from provisions to other assets — — 36 — — — — 36 At 31 December 2023 106 132 — 47 78 32 7 402 Recharge in respect of the UK Bank Levy paid on behalf of other UK entities in the Banco Santander group Provisions expected to be settled within no more than 12 months after 31 December 2023 were £217m ( 2022 : £130m ). a) Customer remediation Net provisions of £37m were recognised in 2023 for customer remediations. An additional provision of £45m was recognised in 2023 for customer remediation exercises relating to our mortgage book. £30m of this relates to the proposed refund of interest inconsistently charged on mortgage products for customers in Financial Support, and £10m relates to the proposed refund of early repayment charges paid by a specific group of customers who historically switched mortgage products. The provisions remain subject to change as additional data becomes available and remediation boundaries are finalised. b) Litigation and other regulatory Litigation and other regulatory provisions principally comprised amounts in respect of litigation and other regulatory charges, operational loss and operational risk provisions, and related expenses. A number of uncertainties exist with respect to these provisions given the uncertainties inherent in litigation and other regulatory matters, that affect the amount and timing of any potential outflows with respect to which provisions have been established. These provisions are reviewed at least quarterly. In 2023 there were charges of £12m for legal provisions and £16m for regulatory fees and other issues. The balance also included an amount in respect of our best estimate of liability relating to a legal dispute regarding allocation of responsibility for a specific PPI portfolio of complaints, further described in Note 31 . No further information on the best estimate is provided on the basis that it would be seriously prejudicial. c) Bank Levy In 2023 , a rate of 0.05% ( 2022 : 0.05% ) was charged on long term chargeable equity and liabilities and 0.10% on short-term chargeable liabilities ( 2022 : 0.10% ). d) Property Property provisions include leasehold vacant property provisions, dilapidation provisions for leased properties within the scope of IFRS 16 and decommissioning and disposal costs relating to vacant freehold properties. Leasehold vacant property provisions are made by reference to an estimate of any expected sub-let income, compared to the head rent, and the possibility of disposing of Santander UK’s interest in the lease, taking into account conditions in the property market. Property provisions included £4m of transformation charges in 2023. These charges consist of costs relating to leasehold head office closures, along with decommissioning costs relating to freehold head office sites which are either closing or consolidating. e) ECL on undrawn facilities and guarantees Provisions include expected credit losses relating to guarantees given to third parties and undrawn loan commitments. f) Restructuring Restructuring provisions relate to severance costs associated with transformation and organisational changes. The provision includes a charge of £51m as part of our multi-year transformation programme to improve future returns, focused on simplifying, digitising and automating the bank. g) Other Other provisions include provisions that do not fit into any of the other categories, such as fraud losses and some categories of operational losses. In 2023 , other provisions included charges for operational risk provisions of £163m , including fraud losses of £136m .

Retirement Benefit Plans

Retirement Benefit Plans	12 Months Ended
	Dec. 31, 2023
Disclosure of net defined benefit liability (asset) [abstract]
Retirement Benefit Plans	30. RETIREMENT BENEFIT PLANS The amounts recognised in the balance sheet were as follows: Group 2023 2022 £m £m Assets/(liabilities) Funded defined benefit pension scheme - surplus 723 1,050 Funded defined benefit pension scheme - deficit (41) — Unfunded pension and post-retirement medical benefits (25) (25) Total net assets 657 1,025 a) Defined contribution pension plans The majority of employees are members of a defined contribution Master Trust, LifeSight. This is the plan into which eligible employees are enrolled automatically. The assets of LifeSight are held in separate trustee-administered funds. Funds arising from Additional Voluntary Contributions (AVCs) are largely held within the main defined benefit scheme operated by the Santander UK group. An expense of £71m ( 2022 : £60m ) was recognised for defined contribution plans in the period and is included in staff costs within operating expenses (see Note 6 ). b) Defined benefit pension schemes The Santander UK group operates a number of defined benefit pension schemes. The main scheme is the Santander (UK) Group Pension Scheme (the Scheme). It comprises seven legally segregated sections. The Scheme covers 7% ( 2022 : 10% ) of the Santander UK group’s current employees and is a funded defined benefit scheme which is closed to new members. Members accrue final salary benefits for each year of service in the Scheme, according to a salary definition which varies across the sections. The corporate trustee of the Scheme is Santander (UK) Group Pension Scheme Trustees Limited (the Trustee), a private limited company incorporated in 1996 and a wholly owned subsidiary of Santander UK Group Holdings plc. The principal duty of the Trustee is to act in the best interests of the members of the Scheme. The Trustee board comprises six ( 2022 : six ) Directors selected by Santander UK Group Holdings plc, plus four ( 2022 : four ) member-nominated Directors selected from eligible members who apply for the role. The assets of the funded schemes including the Scheme are held independently of the Santander UK group’s assets in separate trustee administered funds. Investment strategy across the sections of the Scheme remains under regular review. Responsibility for investment decisions, policy and strategy rests with the Trustee of the Scheme who is required under the Pensions Act 2004 to prepare a statement of investment principles. The defined benefit pension schemes expose the Santander UK group to risks such as investment risk, interest rate risk, longevity risk and inflation risk. The Santander UK group does not hold any insurance policies over the defined benefit pension schemes and has not entered into any significant transactions with them. For IAS 19, an accounting valuation of the assets and liabilities of the defined benefits schemes is prepared at each balance sheet date. For funding purposes, formal actuarial valuations are carried out on at least a triennial basis. Both valuations are carried out by independent professionally qualified actuaries. The Scheme Trustee is responsible for the funding actuarial valuations and in doing so considers, or relies in part on, a report of a third-party expert. The latest triennial funding valuation for the Scheme at 31 March 2022 was finalised in November 2022, with an overall scheme deficit of £183m . The next scheduled triennial funding valuation will be at 31 March 2025. Any funding surpluses can be recovered by Santander UK plc from the Scheme through refunds as the Scheme is run off over time or could be used to pay for the cost of benefits which are accruing. The main differences between the assumptions used for assessing the defined benefit liabilities for the funding valuation and those used for IAS 19 are that the financial and demographic assumptions used for the funding valuation are generally more prudent than those used for the IAS 19 valuation. The total amount charged to the income statement was as follows: Group 2023 2022 2021 £m £m £m Net interest income (54) (30) (5) Current service cost 13 30 38 Past service and GMP costs 1 — — Past service curtailment costs — — 5 Administration costs 7 9 8 (33) 9 46 The amounts recognised in other comprehensive income were as follows: Group 2023 2022 2021 £m £m £m Return on plan assets (excluding amounts included in net interest expense) 352 5,527 (454) Actuarial (gains) arising from changes in demographic assumptions (51) (122) (17) Actuarial losses/(gains) arising from experience adjustments 91 481 (19) Actuarial losses/(gains) arising from changes in financial assumptions 206 (5,164) (774) Pension remeasurement 598 722 (1,264) Movements in the present value of defined benefit scheme obligations were as follows: Group 2023 2022 £m £m At 1 January (7,933) (12,878) Current service cost paid by Santander UK plc (13) (29) Current service cost paid by subsidiaries — (1) Interest cost (379) (241) Employer salary sacrifice contributions (1) (2) Past service cost (1) — Remeasurement due to actuarial movements arising from: – Changes in demographic assumptions 51 122 – Experience adjustments (91) (481) – Changes in financial assumptions (206) 5,164 Benefits paid 372 413 At 31 December (8,201) (7,933) Movements in the fair value of the schemes’ assets were as follows: Group 2023 2022 £m £m At 1 January 8,958 14,413 Interest income 433 271 Contributions paid by employer and scheme members 198 223 Administration costs paid (7) (9) Return on plan assets (excluding amounts included in net interest expense) (352) (5,527) Benefits paid (372) (413) At 31 December 8,858 8,958 The composition and fair value of the schemes’ assets by category was: Group Quoted prices in active markets Prices not quoted in active markets Total Valuation 2023 £m % £m % £m % technique Overseas equities — — 980 11 980 11 A,C Corporate bonds 2,284 26 242 3 2,526 29 A,C Government fixed interest bonds 1,618 18 — — 1,618 18 A Government index-linked bonds 4,422 50 — — 4,422 50 A Property — — 1,080 12 1,080 12 B Derivatives — — (2) — (2) — A Cash — — 586 7 586 7 A Repurchase agreements (1) — — (3,062) (35) (3,062) (35) A Infrastructure — — 408 5 408 5 B,C Annuities — — 293 3 293 3 D Longevity swap — — (16) — (16) — D Other — — 25 — 25 — C 8,324 94 534 6 8,858 100 2022 Overseas equities — — 1,172 13 1,172 13 A,C Corporate bonds 1,991 22 244 3 2,235 25 A,C Government fixed interest bonds 1,138 13 — — 1,138 13 A Government index-linked bonds 5,525 62 — — 5,525 62 A Property — — 1,202 13 1,202 13 B Derivatives — — (78) (1) (78) (1) A Cash — — 1,340 15 1,340 15 A Repurchase agreements (1) — — (4,312) (48) (4,312) (48) A Infrastructure — — 426 5 426 5 B,C Annuities — — 293 3 293 3 D Longevity swap — — (12) — (12) — D Other — — 29 — 29 — C 8,654 97 304 3 8,958 100 (1) Sale and repurchase agreements net of purchase and resale agreements. Valuation techniques The main methods for measuring the fair value of the Scheme’s assets at 31 December 2023 and 2022 are set out below. A. The asset valuation is provided by the asset manager. The valuation is based on observable market data, and where relevant is typically based on bid price values, or the single price if only one price is available. B. The underlying asset valuations are prepared by an independent expert, adjusted for any cash movements where necessary since the latest valuation. C. Assets are valued by reference to the latest manager statements provided by the managers, adjusted for any cash movements since the latest valuation. D. Assets relating to insured liabilities are valued by the actuaries based on our year-end accounting assumptions. The ‘Other’ category includes hedge fund investments. A number of insurance transactions have been entered into that have been included in the asset valuation under annuities and Longevity swap. The transactions were as follows: In May 2020 a pensioner buy-in was entered into by the Trustee. This transaction insured 100% of the SMA section pensioner liabilities and 50% of the SPI section pensioner liabilities based on membership in the Scheme at 31 December 2018. – In March 2021, the Trustee entered into a longevity swap. Approximately 85% of pensioner liabilities were covered by the longevity swap at inception, excluding pensioners in the SMA and SPI sections. – In 2022, a pensioner buy-in was entered into by the Trustee covering pensioners in the SMA and SPI sections who were uninsured at 30 June 2021. – In July 2022, the Trustee entered into a second longevity swap, extending the insurance over uninsured pensioners in the same membership groups covered by the first swap transacted in March 2021, based on membership in the Scheme at 31 December 2021. At 31 December 2023, as highlighted above, the Scheme was invested in certain assets whose values are not based on market observable data, such as the investments in unquoted equities and bonds, as well as property, infrastructure and hedge funds. The valuation of these assets relies on unobservable data as these assets do not have a readily available quoted price in an active market. A large proportion of the property is directly held and valued using a bespoke valuation method taking both the nature of the properties and the tenancy schedules as inputs to derive the fair value. Where there is a time lag between the net asset value and the balance sheet date, management adjusts the value of the assets for any cash movements. Due diligence has been conducted to ensure the values obtained in respect of these assets are appropriate and represent fair value. Given the nature of these investments, we are unable to prepare sensitivities on how their values could vary as market conditions or other variables change. A strategy is in place to manage interest rate and inflation risk relating to the liabilities. The Scheme also hedges a proportion of its foreign exchange exposure to manage currency risk. At 31 December 2023 the currency forwards had a notional value of £859m ( 2022 : £985m ). There have been no significant changes to the asset allocation over 2023 . The Santander UK group’s pension schemes did not directly hold any equity securities of the Company or any of its related parties at 31 December 2023 and 2022 . The Santander UK group’s pension scheme assets do not include any property or other assets that are occupied or used by the Santander UK group. Funding In November 2022, in compliance with the Pensions Act 2004, the Trustee and the Santander UK group agreed to a new recovery plan in respect of the Scheme and a schedule of contributions following the finalisation of the 31 March 2022 actuarial valuation. The funding target for this actuarial valuation is for the Scheme to have sufficient assets to make payments to members in respect of the accrued benefits as and when they fall due. In accordance with the terms of the Trustee agreement in place at the time, the Santander UK group contributed £195m in 2023 ( 2022 : £218m ) to the Scheme, of which £164m ( 2022 : £178m ) was in respect of agreed deficit repair contributions. The agreed schedule of the Santander UK group’s contributions to the Scheme covers the period up to 31 March 2026 , and comprises contingent contributions which become due if the funding position of any section falls behind the agreed plan . The Santander UK group also meets Scheme administration expenses. The funding valuation is used to judge the amount of cash contributions the Santander UK group needs to put into the pension scheme. It will always be different to the IAS 19 accounting position, which is an accounting rule concerning employee benefits and shown on the balance sheet of our financial statements. Actuarial assumptions The principal actuarial assumptions used for the Scheme were: Group 2023 2022 2021 % % % To determine benefit obligations (1) : – Discount rate for scheme liabilities 4.6 % 4.9 1.9 – General price inflation 3.0 % 3.1 3.4 – General salary increase 1.0 % 1.0 1.0 – Expected rate of pension increase 3.0 % 3.0 3.2 Years Years Years Longevity at 60 for current pensioners, on the valuation date: – Males 27.0 27.4 27.5 – Females 29.8 30.1 30.1 Longevity at 60 for future pensioners currently aged 40, on the valuation date: – Males 28.6 28.9 29.0 – Females 31.3 31.6 31.6 (1) The discount rate and inflation related assumptions set out in the table above reflect the assumptions calculated based on the Scheme’s duration and cash flow profile as a whole. The actual assumptions used were determined for each section independently based on each section’s duration and cash flow profile. The majority of the liability movement in 2023 was due to the reduction in credit spreads over the year. Discount rate for scheme liabilities The rate used to discount the retirement benefit obligation for accounting purposes is based on the annual yield at the balance sheet date of high-quality corporate bonds on that date. There are only a limited number of higher quality Sterling-denominated corporate bonds, particularly those that are longer-dated. Therefore, in order to set a suitable discount rate, we need to construct a corporate bond yield curve. The model which we use to construct the curve uses corporate bond data but excludes convertible bonds, asset-backed bonds and government related bonds. The curve is then constructed from this data by extrapolating the spot rates from 30 years to 50 years by holding the spread above nominal gilt spot rates constant. From 50 years onwards, it is assumed that spot rates remain constant. When considering an appropriate assumption, we project forward the expected cash flows of each section of the Scheme and adopt a single equivalent cash flow weighted discount rate for each section, subject to management judgement. General price inflation Consistent with our discount rate methodology, we set the inflation assumption using the expected cash flows for each section of the Scheme, fitting them to an inflation curve to give a weighted average inflation assumption. We then deduct an inflation risk premium to reflect the compensation holders of fixed rate instruments expect to receive for taking on the inflation risk. This premium is subject to a cap, to better reflect management’s view of inflation expectations. General salary increase From 1 March 2015, a cap on pensionable pay increases of 1% each year was applied to staff in the Scheme. Expected rate of pension increase The pension increase assumption methodology uses a stochastic model, which is calibrated to consider both the observed historical volatility term structure and derivative pricing. The model allows for the likelihood that high or low inflation in one year, feeds into inflation remaining high or low in the next year. Mortality assumptions The mortality assumptions are based on an independent analysis of the Scheme’s actual mortality experience, carried out as part of the triennial actuarial valuation, together with recent evidence from the Continuous Mortality Investigation. An allowance is then made for expected future improvements to life expectancy based on the Continuous Mortality Investigation Tables. Following this review the S3 Medium all pensioner mortality table was adopted with appropriate adjustments to reflect the actual mortality experience. At 31 December 2023 the assumption for future improvements was updated and the CMI 2022 projection model was adopted, with model parameters selected having had regard to the Scheme’s membership profile with an initial addition to improvements of 0.25% per annum, together with a long-term rate of future improvements to life expectancy of 1.25% for male and female members. In 2022, the methodology for setting the demographic assumptions was changed to better represent current expectations, following a review carried out by the Trustee as part of the 2022 triennial valuation. These reviews resulted in changes in the assumptions for family statistics, early retirement and the withdrawal assumption, which were retained at 31 December 2023. Actuarial assumption sensitivities The sensitivity analyses below have been determined based on reasonably possible changes of the respective assumptions occurring at the end of the reporting period, while holding all other assumptions constant. Group (Decrease)/increase 2023 2022 Assumption Change in pension obligation at period end from £m £m Discount rate 50 bps increase (507) (501) General price inflation 50 bps increase 385 374 Mortality Each additional year of longevity assumed 223 203 The 50 bps sensitivity to the inflation assumption includes the corresponding impact of changes in future pension increase assumptions before and after retirement. The sensitivity analysis presented above may not be representative of the actual change in the defined benefit obligation as it is unlikely that the changes in assumptions would occur in isolation of one another as some of the assumptions may be correlated. Furthermore, in presenting the sensitivity analysis, the present value of the defined benefit obligation has been calculated using the projected unit credit method at the end of the reporting period, which is the same method used to calculate the defined benefit obligation recognised in the balance sheet. There were no changes in the methods and assumptions used in preparing the sensitivity analyses from prior years. The benefits expected to be paid in each of the next five years, and in the aggregate for the five years thereafter are: Year ending 31 December £m 2024 455 2025 389 2026 404 2027 428 2028 444 Five years ending 2033 2,398 The average duration of the defined benefit obligation at 31 December 2023 was 13.8 years ( 2022 : 14.2 years ). Emerging risks The focus in 2023 shifted to the risks arising from the Scheme’s private market assets, rising interest rates and cybersecurity risk. The Santander UK group collaborated with the Trustee to identify and monitor such risks to ensure they are adequately managed. The Trustee has engaged an independent cybersecurity advisor to review the cybersecurity arrangements of its most critical suppliers and provide recommendations on potential improvements. The Trustee has established the Sustainability Committee which is responsible for overseeing the Scheme’s policies, regulatory obligations and priorities in respect of climate change and wider Environmental, Social and Governance (ESG) related matters. This includes the monitoring of climate change related risks and opportunities, scenario analysis and monitoring of investments from an ESG perspective. The Santander UK group's employee pension funds recognise the magnitude of the challenges that climate and energy transition pose to governments, companies and civil society. They are also aware of their impact on the ability to comply with their fiduciary duty providing long-term risk-adjusted returns to their members. They have committed to a target of net zero by 2050, showing their full support for the Santander UK group's vision, commitment to sustainability and climate change.

Contingent Liabilities and Comm

Contingent Liabilities and Commitments	12 Months Ended
	Dec. 31, 2023
Disclosure of contingent liabilities [abstract]
Contingent Liabilities and Commitments	31. CONTINGENT LIABILITIES AND COMMITMENTS Group 2023 2022 £m £m Guarantees given to third parties 452 448 Formal standby facilities, credit lines and other commitments 30,976 31,388 31,428 31,836 At 31 December 2023 , the Santander UK group had credit impairment loss provisions relating to guarantees given to third parties and undrawn loan commitments. See Note 29 for more details. Where the items set out below can be reliably estimated, they are disclosed in the table above. Guarantees given to third parties Guarantees given to third parties consist primarily of letters of credit, bonds and guarantees granted as part of normal product facilities which are offered to customers. Formal standby facilities, credit lines and other commitments Standby facilities, credit lines and other commitments are also granted as part of normal product facilities which are offered to customers. Retail facilities comprise undrawn facilities granted on flexible mortgages, bank overdrafts and credit cards. On flexible mortgages, the credit limit is set at the point of granting the loan through property value and affordability assessments. Ongoing assessments are made to ensure that credit limits remain appropriate considering any change in the security value or the customer’s financial circumstances. For unsecured overdraft facilities and credit cards, the facilities are granted based on new business risk assessment and are reviewed more frequently based on internal, as well as external data. Corporate facilities can comprise standby and revolving facilities which are subject to ongoing compliance with covenants and may require the provision of agreed security. FSCS The FSCS is the UK’s independent statutory compensation fund for customers of authorised financial services firms and pays compensation if a firm is unable to pay certain claims against it. The FSCS is funded by levies on the industry and recoveries and borrowings where appropriate. Loan representations and warranties In connection with the securitisations and covered bond transactions described in Note 14 , the Santander UK group entities selling the relevant loans into the applicable securitisation or covered bond portfolios make representations and warranties with respect to such loans, in each case as of the date of the sale of the loans into the applicable portfolio. These representations and warranties cover, among other things, the ownership of the loan by the relevant Santander UK group entity, absence of a material breach or default by the relevant borrower under the loan, the loan’s compliance with applicable laws and absence of material disputes with respect to the relevant borrower, asset and loan. The specific representations and warranties made by Santander UK group companies which act as sellers of loans in these securitisations and covered bond transactions depend in each case on the nature of the transaction and the requirements of the transaction structure. In the event that there is a material breach of the representations and warranties given by Santander UK plc as seller of loans under the residential mortgage- backed securitisations or the covered bond programmes included in Note 14 , or if such representations and warranties prove to be materially untrue at the date when they were given (being the sale date of the relevant mortgage loans), Santander UK plc may be required to repurchase the affected mortgage loans (generally at their outstanding principal balance plus accrued interest). These securitisations and covered bond programmes are collateralised by prime residential mortgage loans. Santander UK plc is principally a retail prime lender and has no appetite or product offering for any type of sub-prime business. Similarly, under the auto loan securitisations in Note 14 , in the event that there is a breach or inaccuracy in respect of a representation or warranty relating to the loans, the relevant Santander UK group entity who sold the auto loans into the securitisation portfolio will be required to repurchase such loans from the structure (also at their outstanding principal balance plus accrued interest). In addition to breaches of representation and warranties, under the auto loan securitisations, the seller may also have a repurchase obligation if certain portfolio limits are breached (which include, amongst other things, limits as to the size of a loan given to an individual customer, LTV ratio, average term to maturity and average seasoning). In the case of a repurchase of a loan from the relevant securitisation or covered bond programmes, the Santander UK group may bear any subsequent credit loss on such loan. The Santander UK group manages and monitors its securitisation and covered bond activities closely to minimise potential claims. Other legal actions and regulatory matters Santander UK engages in discussion, and co-operates, with the FCA, PRA, CMA and other regulators and government agencies in various jurisdictions in their supervision and review of Santander UK including reviews exercised under statutory powers, regarding its interaction with past and present customers, both as part of general thematic work and in relation to specific products, services and activities. During the ordinary course of business, Santander UK is also subject to complaints and threatened legal proceedings brought by or on behalf of current or former employees, customers, investors or other third parties, in addition to legal and regulatory reviews, challenges and tax or enforcement investigations or proceedings by relevant regulators or government agencies in various jurisdictions. All such matters are assessed periodically to determine the likelihood of Santander UK incurring a liability. In those instances where it is concluded that it is not yet probable that a quantifiable payment will be made, for example because the facts are unclear or further time is required to fully assess the merits of the case or to reasonably quantify the expected payment, no provision is made. In addition, where it is not currently practicable to estimate the possible financial effect of these matters, no provision is made. Payment Protection Insurance AXA France IARD and AXA France Vie (former GE Capital Corporation Group entities (GE Capital), known as Financial Insurance Company Ltd (FICL) and Financial Assurance Company Ltd (FACL), acquired by AXA SA in 2015) (together, AXA France) have brought a claim for £552m (plus interest) against (i) Santander Cards UK Limited (former GE Capital entity known as GE Capital Bank Limited (GECB), which was acquired by Banco Santander SA in 2008 and subsequently transferred to Santander UK plc); and (ii) Santander Insurance Services UK Limited (a Banco Santander SA subsidiary) (together the Santander Entities). The claim relates to the allocation of liability for compensation and associated costs in respect of a large number of PPI policies distributed by GECB pre-2005, which were underwritten by FICL and FACL. AXA France reduced their claim from £670m (plus interest) to £552m (plus interest) in their Re-Re- Amended Particulars of Claim dated 29 June 2023. The Santander Entities strongly refute the claim. Trial has been fixed for six weeks, beginning on 3 March 2025. There are ongoing factual issues to be resolved which may have legal consequences including in relation to liability. These issues create uncertainties which mean that it is difficult to reliably predict the outcome or the timing of the resolution of the matter. The litigation and other regulatory provision in Note 29 includes our best estimate of the Santander Entities’ liability to the specific portfolio. Further information has not been provided on the basis that it would be seriously prejudicial to the Santander Entities’ interests in connection with the dispute. In addition, and in relation to PPI more generally, the PPI provision includes an amount relating to legal claims challenging the FCA’s industry guidance on the treatment of Plevin / recurring non-disclosure assessments. This provision is based on current stock levels, future projected claims, and average redress. There remains a risk that volumes received in future may be higher than forecast. The provision in Note 29 includes our best estimate of Santander UK’s liability for the specific issue. The actual cost of customer compensation could differ from the amount provided. It is not currently practicable to provide an estimate of the risk and amount of any further financial impact. German dividend tax arbitrage transactions In June 2018 the Cologne Criminal Prosecution Office and the German Federal Tax Office commenced an investigation in relation to the historical involvement of Santander UK plc, Santander Financial Services plc and Cater Allen International Limited (all subsidiaries of Santander UK Group Holdings plc) in German dividend tax arbitrage transactions (known as cum/ex transactions). These transactions allegedly exploited a loophole of a specific German settlement mechanism through short-selling and complex derivative structuring which resulted in the German government either refunding withholding tax where such tax had not been paid or refunding it more than once. The German authorities are investigating numerous institutions and individuals in connection with alleged transactions and practices which may be found to be illegal under German law. During 2023 we continued to cooperate with the German authorities and, with the assistance of external experts, to progress an internal investigation into the matters in question. From Santander UK plc’s perspective, t he investigation is focused principally on the period 2009-2011 and remains on-going. There remain factual issues to be resolved which may have legal consequences including potentially material financial penalties. These issues create uncertainties which mean that it is difficult to predict the resolution of the matter including timing or the significance of the possible impact. These uncertainties mean it is not currently practicable to make a reliable assessment of the size of any related potential liability. SCUK - Motor Finance Broker Commissions Following the FCA’s Motor Market review in 2019 which resulted in a change in rules in January 2021, Santander Consumer (UK) plc (SCUK) has received a number of county court claims and complaints in respect of its historical use of discretionary commission arrangements (DCAs) prior to the 2021 rule changes. In the context of the complaints made to the Financial Ombudsman Service relating to such commission arrangements, the FCA announced on 11 January 2024 that it intends to use its powers under s166 of the Financial Services and Markets Act 2000 to review the historical use of DCAs between lenders and credit brokers (the “FCA Review”) and whether redress should be payable. In line with the FCA's announcement, we have paused the response to customer complaints until at least 20 November 2024. A claim has been issued against SCUK, Santander UK plc and others in the Competition Appeal Tribunal (CAT), alleging that SCUK’s historical commission arrangements in respect of used car financing operated in breach of the Competition Act 1998. While it is possible that certain charges may be incurred in relation to existing or future county court claims, Financial Ombudsman Service (FOS) complaints and the CAT proceedings, it is not considered that a legal or constructive obligation has been incurred in relation to these matters that would require a provision to be recognised at this stage. The resolution of such matters is not possible to predict with any certainty and there remain significant inherent uncertainties regarding the existence, scope and timing of any possible outflow which make it impracticable to disclose the extent of any potential financial impact. Other On 2 November 2015, Visa Europe Ltd agreed to sell 100% of its share capital to Visa Inc. The deal closed on 21 June 2016. As a member and shareholder of Visa Europe Ltd, Santander UK received upfront consideration made up of cash and convertible preferred stock. Conversion of the preferred stock into Class A Common Stock of Visa Inc. depends on the outcome of litigation against Visa involving UK & Ireland multilateral interchange fees (UK&I MIFs). The convertible preferred stock is now held by Santander Equity Investments Limited (SEIL), outside the ring-fenced bank. In addition, Santander UK plc and certain other UK&I banks have agreed to indemnify Visa Inc. in the event that the preferred stock is insufficient to meet the costs of this litigation. Visa Inc. has recourse to this indemnity once more than €1bn of losses relating to UK&I MIFs have arisen or once the total value of the preferred stock issued to UK&I banks on closing has been reduced to nil . Santander UK plc's liability under this indemnity is capped at €39.85m . At this stage, it is unclear whether the litigation will give rise to more than €1bn of losses relating to UK&I MIFs which means it is not practicable to predict the resolution of the matter including the timing or the significance of the possible impact. As part of the sale of subsidiaries, businesses and other entities, and as is normal in such circumstances, entities within the Santander UK group have given warranties and/or indemnities to the purchasers. Obligations under stock borrowing and lending agreements Obligations under stock borrowing and lending agreements represent contractual commitments to return stock borrowed. These obligations are offset by a contractual right to receive stock under other contractual agreements. See Note 35 . Other off-balance sheet commitments The Santander UK group has commitments to lend at fixed interest rates which expose us to interest rate risk. For more, see the Risk review. Liquidity support arrangements Under the PRA’s liquidity rules, Santander UK plc and its subsidiary Cater Allen Limited form the RFB Domestic Liquidity Sub-group (the RFB DoLSub), which allows the entities to collectively meet regulatory requirements for the purpose of managing liquidity risk. Each member of the RFB DoLSub will support the other by transferring surplus liquidity in times of stress.

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2023
Disclosure of classes of share capital [abstract]
Share Capital	32. SHARE CAPITAL Group Ordinary shares of £0.10 each Total Issued and fully paid share capital No. £m £m At 31 December 2022, 1 January 2023 and 31 December 2023 31,051,768,866 3,105 3,105 Group 2023 2022 Share premium £m £m At 1 January and 31 December 5,620 5,620

Other Equity Instruments

Other Equity Instruments	12 Months Ended
	Dec. 31, 2023
Disclosure of classes of share capital [abstract]
Other Equity Instruments	33. OTHER EQUITY INSTRUMENTS Group Interest rate 2023 2022 % Next call date £m £m AT1 securities: - £500m Perpetual Capital Securities 6.75 June 2024 496 496 - £500m Perpetual Capital Securities 6.30 March 2025 500 500 - £210m Perpetual Capital Securities 4.25 March 2026 210 210 - £750m Perpetual Capital Securities 6.50 June 2027 750 750 1,956 1,956 AT1 securities The AT1 securities issued by the Company were subscribed for by its immediate parent company, Santander UK Group Holdings plc. The AT1 securities are perpetual and pay a quarterly distribution. At each distribution payment date, the Company can decide whether to pay the distribution, which is non-cumulative, in whole or in part. The distribution rate resets every five years . The securities will be automatically written down and the investors will lose their entire investment in the securities should the CET1 capital ratio of the Santander UK prudential consolidation group , or the Company (calculated on a solo basis), fall below 7% . All AT1 securities are redeemable at the option of the Company, and only with the consent of the PRA.

Notes to Cash Flows

Notes to Cash Flows	12 Months Ended
	Dec. 31, 2023
Cash Flows Explanatory Notes [Abstract]
Notes to Cash Flows	34. NOTES TO CASH FLOWS Changes in liabilities arising from financing activities The table below shows the changes in liabilities arising from financing activities. The changes in equity arising from financing activities are set out in the Consolidated Statement of Changes in Equity. Group Balance sheet line item Debt securities in issue Subordinated liabilities Other equity instruments Lease liabilities Dividends paid Total 2023 £m £m £m £m £m £m At 1 January 31,531 2,332 1,956 125 — 35,944 Proceeds from issue of debt securities 4,208 — — — — 4,208 Repayment of debt securities (2,568) — — — — (2,568) Proceeds from issue of subordinated liabilities — 1,050 — — — 1,050 Repayment of subordinated liabilities — (971) — — — (971) Principal elements of lease payments — — — (47) — (47) Dividends paid — — — — (1,653) (1,653) Liability-related other changes 1,004 25 — 33 — 1,062 Non-cash changes: – Unrealised foreign exchange (651) (22) — — — (673) – Other changes 386 (28) — — 1,653 2,011 At 31 December 33,910 2,386 1,956 111 — 38,363 2022 At 1 January 25,520 2,228 2,191 132 — 30,071 Proceeds from issue of debt securities 4,778 — — — — 4,778 Repayment of debt securities (3,036) — — — — (3,036) Repayment of subordinated liabilities — (40) — — — (40) Issue of other equity instruments — — 750 — — 750 Repurchase of other equity instruments — — (985) — — (985) Principal elements of lease payments — — — (26) — (26) Dividends paid — — — — (1,164) (1,164) Liability-related other changes 3,155 2 — 19 — 3,176 Non-cash changes: – Unrealised foreign exchange 1,554 87 — — — 1,641 – Other changes (440) 55 — — 1,164 779 At 31 December 31,531 2,332 1,956 125 — 35,944 2021 At 1 January 35,566 2,556 2,191 97 — 40,410 Proceeds from issue of debt securities 2,872 — — — — 2,872 Repayment of debt securities (11,910) — — — — (11,910) Repayment of subordinated liabilities — (4) — — — (4) Issue of other equity instruments — — 210 — — 210 Repurchase of other equity instruments — — (210) — — (210) Principal elements of lease payments — — — (25) — (25) Dividends paid — — — — (1,505) (1,505) Liability-related other changes (447) (4) — 60 — (391) Non-cash changes: – Unrealised foreign exchange (806) 6 — — — (800) – Other changes 245 (326) — — 1,505 1,424 At 31 December 25,520 2,228 2,191 132 — 30,071 Footnotes to the consolidated cash flow statement Net cash flows from operating activities includes interest received of £11,395m ( 2022 : £6,508m , 2021 : £4,806m ), interest paid of £6,326m ( 2022 : £2,089m , 2021 : £1,064m ) and dividends received of £nil ( 2022 : £nil , 2021 : £nil ). Total cash outflow for leases was £50m ( 2022 : £28m , 2021 : £28m ). Other matters In 2021, there was a disposal of non-controlling interests of £181m .

Assets Charged as Security for

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets	12 Months Ended
	Dec. 31, 2023
Disclosure Of Assets Pledged As Security [Abstract]
Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets	35. ASSETS CHARGED AS SECURITY FOR LIABILITIES AND COLLATERAL ACCEPTED AS SECURITY FOR ASSETS The following transactions are conducted under terms that are usual and customary to collateralised transactions including, where relevant, standard securities lending and repurchase agreements. a) Assets charged as security for liabilities The financial assets below are analysed between those assets accounted for on-balance sheet and off-balance sheet. Group 2023 2022 £m £m On-balance sheet: Cash and balances at central banks 1,480 1,330 Loans and advances to banks 191 130 Loans and advances to customers - securitisations and covered bonds (See Note 14) 27,088 24,155 Loans and advances to customers - other 20,699 32,001 Other financial assets at amortised cost 14 48 Financial assets at fair value through other comprehensive income 5,183 4,365 Total on-balance sheet 54,655 62,029 Total off-balance sheet 10,185 9,146 Santander UK provides assets as collateral in the following areas of the business. Sale and repurchase agreements Santander UK also enters into sale and repurchase agreements and similar transactions of debt securities. Upon entering into such transactions, Santander UK provides collateral in excess of the borrowed amount. The carrying amount of assets that were so provided at 31 December 2023 was £13,291m ( 2022 : £11,553m ), of which £909m ( 2022 : £900m ) was classified in ‘Loans and advances to customers – securitisations and covered bonds’ in the table above. Securitisations and covered bonds As described in Note 14 , Santander UK plc and certain of its subsidiaries issue securitisations and covered bonds. At 31 December 2023 , there were £27,927m ( 2022 : £24,984m ) of gross assets in these secured programmes and £839m ( 2022 : £829m ) of these related to internally retained issuances that were available for use as collateral for liquidity purposes in the future. At 31 December 2023 , £2,928m ( 2022 : £1,725m ) of notes issued under securitisation and covered bond programmes had been retained internally, a proportion of which had been used as collateral via third party bilateral secured funding transactions, which totalled £1,500m at 31 December 2023 ( 2022 : £500m ), or for use as collateral for liquidity purposes in the future. Stock borrowing and lending agreements Asset balances under stock borrowing and lending agreements represent stock lent by Santander UK. These balances amounted to £23,644m at 31 December 2023 ( 2022 : £34,861m ) and are offset by contractual commitments to return stock borrowed or cash received. Derivatives business In addition to the arrangements described above, collateral is also provided in the normal course of derivative business to counterparties. At 31 December 2023 £1,726m ( 2022 : £1,506m ) of such collateral in the form of cash had been provided by Santander UK and is included in the table. b) Collateral accepted as security for assets The collateral held as security for assets, analysed between those liabilities accounted for on balance sheet and off-balance sheet, was: Group 2023 2022 £m £m On-balance sheet: Deposits by banks 860 1,741 Total on-balance sheet 860 1,741 Total off-balance sheet 14,992 10,141 Purchase and resale agreements Santander UK also enters into purchase and resale agreements and similar transactions of debt securities. Upon entering into such transactions, Santander UK receives collateral in excess of the loan amount. The level of collateral held is monitored daily and if required, further calls are made to ensure the market values of collateral remains at least equal to the loan balance. The subsidiaries are permitted to sell or repledge the collateral held in the absence of default. At 31 December 2023 , the fair value of such collateral received was £12,982m ( 2022 : £8,628m ). Of the collateral received, almost all was sold or repledged. The subsidiaries have an obligation to return collateral that they have sold or pledged. Stock borrowing and lending agreements Obligations representing contractual commitments to return stock borrowed by Santander UK amounted to £2,010m at 31 December 2023 ( 2022 : £1,513m ) and are offset by a contractual right to receive stock lent. Derivatives business In addition to the arrangements described, collateral is also received from counterparties in the normal course of derivative business. At 31 December 2023 , £860m ( 2022 : £1,741m ) of such collateral in the form of cash had been received by Santander UK and is included in the table. Lending activities In addition to the collateral held as security for assets, Santander UK may obtain a charge over a customer’s property in connection with its lending activities. Details of these arrangements are set out in the ‘Credit risk’ section of the Risk review.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2023
Disclosure of terms and conditions of share-based payment arrangement [abstract]
Share-Based Compensation	36. SHARE-BASED COMPENSATION The Santander UK group operates share schemes and arrangements for eligible employees. The main current schemes are the Sharesave Schemes, the Deferred Shares Bonus Plan, the Partnership Shares scheme and the Transformation Incentive Plan. All the share options and awards relate to shares in Banco Santander SA. The amount charged to the income statement in respect of share-based payment transactions is set out in Note 6 . At 31 December 2023 , the carrying amount of liabilities arising from share-based payment transactions, excluding any cash element was £14.7m ( 2022 : £6.6m ), of which £1.1m had vested at 31 December 2023 ( 2022 : £0.1m ). a) Sharesave Schemes The Santander UK group launched its sixteenth HM Revenue & Customs approved Sharesave invitation under Banco Santander SA sponsorship in September 2023 . Sharesave invitations have been offered since 2008 under broadly similar terms. Under the Sharesave Scheme’s HMRC-approved savings limits, eligible employees may enter into contracts to save between £5 and £500 per month. For all schemes, at the end of a fixed term of three or five years after the grant date, the employees can use these savings to buy shares in Banco Santander SA at a discount, calculated in accordance with the rules of the scheme. The option price is calculated as the average middle market quoted price of Banco Santander SA shares over the first three dealing days prior to invitation and discounted by up to 20% . This year a 10% discount was applied. The vesting of awards under the scheme depends on continued employment with the Banco Santander group. Participants in the scheme have six months from the date of vesting to exercise the option. The table below summarises movements in the number of options, and changes in weighted average exercise price over the same period. 2023 2022 Number of options Weighted average exercise price Number of options Weighted average exercise price ‘000 £ ‘000 £ Outstanding at 1 January 29,988 2.00 25,993 2.25 Granted 7,175 2.78 13,068 1.89 Exercised (5,980) 1.70 (242) 1.69 Forfeited/expired (4,044) 2.53 (8,831) 2.59 Outstanding at 31 December 27,139 2.19 29,988 2.00 Exercisable at 31 December 868 1.84 3,439 3.22 The weighted average share price at the date the options were exercised was £3.22 ( 2022 : £2.34 ). The following table summarises the range of exercise prices and weighted average remaining contractual life of the options at 31 December 2023 and 2022 . 2023 2022 Range of exercise prices Weighted average remaining contractual life Weighted average exercise price Weighted average remaining contractual life Weighted average exercise price Years £ Years £ £1 to £2 3 1.84 3 1.79 £2 to £3 3 2.65 2 2.56 £3 to £4 0 3.46 1 3.46 £4 to £5 0 — 0 4.02 The fair value of each option at the date of grant is estimated using an analytical model that also reflects the correlation between EUR and GBP. This model uses assumptions on the share price, the EUR/GBP FX rate, the EUR/GBP risk-free interest rate, dividend yields, the expected volatilities of both the underlying shares and EUR/GBP for the expected lives of options granted. The weighted average grant-date fair value of options granted during the year was £0.33 ( 2022 : £0.23 ). b) Deferred shares bonus plan Deferred bonus awards are designed to align employee performance with shareholder value and encourage increased retention of senior employees. Those employees who are designated as Material Risk Takers receive part of their annual bonus as a deferred award comprising 50% in shares and 50% in cash. Either 40% (for any variable pay award of less than £500,000 ) or 60% (for any variable pay award greater than £500,000 ) is deferred over a four -, five - or seven - year period from the anniversary of the initial award. Deferred bonus awards in shares or share options are subject to an additional one -year retention period from the point of delivery. Any deferred awards are dependent on continued employment and subject to Santander UK's discretion, and the vesting of deferred bonus awards is subject to potential performance adjustment. c) Partnership Shares scheme A Partnership Shares scheme is operated for eligible employees under the Share Incentive Plan (SIP) umbrella. Participants can choose to invest up to £1,800 per tax year (or no more than 10% of an employee’s salary for the tax year) from pre-tax salary to buy Banco Santander SA shares. Shares are held in trust for the participants. There are no vesting conditions attached to these shares, and no restrictions as to when the shares can be removed from the trust. However, if a participant chooses to sell the shares before the end of five years , they will be liable for the taxable benefit received when the shares are taken out of the trust. The shares can be released from trust after five years free of income tax and national insurance contributions. 3,937,473 shares were outstanding at 31 December 2023 ( 2022 : 3,974,698 shares). d) Transformation Incentive Plan This one-off long-term incentive plan was designed to recognise the achievement of financial targets and an enhanced customer experience, whilst maintaining appropriate conduct controls and risk management, over the course of our transformation period. Awards under the plan were granted in 2021 , 2022 and 2023 with performance assessed over the period 1 January 2021 to 31 December 2023 . Awards for Material Risk Takers were granted half in cash and half in share based awards (linked to the Banco Santander SA share price), and will vest in accordance with regulatory requirements. The total value of share-based awards granted in 2023 was £1.3m ( 2022 : £1m ) and the liability arising from share-based payment transactions, excluding any cash element was £3.8m ( 2022 : £1.8m ).

Transactions with Directors and

Transactions with Directors and Other Key Management Personnel	12 Months Ended
	Dec. 31, 2023
Disclosure Of Remuneration Of Directors And Other Key Management Personnel [Abstract]
Transactions with Directors and Other Key Management Personnel	37. TRANSACTIONS WITH DIRECTORS AND OTHER KEY MANAGEMENT PERSONNEL a) Remuneration of Directors and Other Key Management Personnel The remuneration of the Directors and Other Key Management Personnel (KMP) of the Santander UK group is set out in aggregate below. 2023 2022 2021 Directors’ remuneration £ £ £ Salaries and fees 4,733,761 4,696,699 5,488,388 Performance-related payments 1,002,607 3,701,569 3,431,294 Other fixed remuneration (pension and other allowances & non-cash benefits) 222,538 906,201 929,935 Expenses — 27,715 17,097 Total remuneration 5,958,906 9,332,184 9,866,714 Compensation for loss of office (1) — 172,856 356,054 2023 2022 2021 Directors' and Other Key Management Personnel compensation £ £ £ Short-term employee benefits 18,449,360 22,627,595 20,553,672 Post-employment benefits 858,437 1,026,848 988,829 Compensation for loss of office (1) — 1,713,256 356,054 Total compensation 19,307,797 25,367,699 21,898,555 (1) Compensation for loss of office was not paid to Directors or KMPs in 2023 ( 2022 : two Directors, £172,856 and three KMPs, £1,540,400 ; 2021 : two Directors, £356,054 ). In 2023 , the remuneration, excluding pension contributions, of the highest paid Director, was £2,640,491 ( 2022 : £3,510,441 , 2021 : £3,740,810 ) of which £1,002,607 ( 2022 : £1,900,506 , 2021 : £1,864,320 ) was performance related. In 2023 , the accrued defined benefit pension relating to the highest paid director was £nil ( 2022 : £nil , 2021 : £22,119 per annum for a different individual). b) Retirement benefits Defined benefit pension schemes are provided to certain employees. See Note 30 for details of the schemes and the related costs and obligations. No director has a deferred pension benefit accruing under a defined benefit scheme. Ex-gratia pensions paid to former Directors of Santander UK plc in 2023 , which have been provided for previously, amounted to £327,462 ( 2022 : £379,945 ; 2021 : £370,668 ). Since the Company became part of the Banco Santander group, the Board has not awarded any new ex-gratia pensions. c) Transactions with Directors, Other Key Management Personnel and each of their connected persons Directors, Other KMP (defined as the Executive Committee of Santander UK plc who served during the year) and their connected persons have undertaken the following transactions with the Santander UK group in the ordinary course of business. 2023 2022 No. £000 No. £000 Secured loans, unsecured loans and overdrafts At 1 January 10 871 6 360 Net movements (2) 204 4 511 At 31 December 8 1,075 10 871 Deposit, bank and instant access accounts and investments At 1 January 23 4,133 21 6,552 Net movements (6) (2,431) 2 (2,419) At 31 December 17 1,702 23 4,133 In 2023 and 2022 , no Director held any interest in the shares of any company in the Santander UK group and no Director exercised or was granted any rights to subscribe for shares in any company in the Santander UK group. In addition, in 2023 and 2022 , no Directors exercised share options over shares in Banco Santander SA, the ultimate parent company of the Company. Secured loans, unsecured loans and overdrafts are made to Directors, Other KMP and their connected persons, in the ordinary course of business, with terms prevailing for comparable transactions and on the same terms and conditions as applicable to other employees in the Santander UK group. Such loans do not involve more than the normal risk of collectability or present any unfavourable features. Amounts deposited by Directors, Other KMP and their connected persons earn interest at the same rates as those offered to the market or on the same terms and conditions applicable to other employees in the Santander UK group. Deposits, bank and instant access accounts and investments are entered into by Directors, Other KMP and their connected persons on normal market terms and conditions, or on the same terms and conditions as applicable to other employees in Santander UK group. In 2023 , loans were made to two Directors ( 2022 : six Directors), with a principal amount of £495,281 outstanding at 31 December 2023 ( 2022 : £540,450 ). In 2023 , loans were made to six Other KMP ( 2022 : four ), with a principal amount of £579,383 outstanding at 31 December 2023 ( 2022 : £330,972 ). In 2023 and 2022 , there were no other transactions, arrangements or agreements with Santander UK in which Directors, Other KMP or their connected persons had a material interest. In addition, in 2023 and 2022 , no Director had a material interest in any contract of significance with Santander UK other than a service contract or appointment letter, as appropriate.

Related Party Disclosures

Related Party Disclosures	12 Months Ended
	Dec. 31, 2023
Disclosure of transactions between related parties [abstract]
Related Party Disclosures	38. RELATED PARTY DISCLOSURES a) Parent undertaking and controlling party The Company’s immediate parent is Santander UK Group Holdings plc , a company incorporated in England and Wales. Its ultimate parent and controlling party is Banco Santander SA , a company incorporated in Spain. The smallest and largest groups into which the Santander UK group’s results are included are the group accounts of Santander UK Group Holdings plc and Banco Santander SA respectively , copies of which may be obtained from Shareholder Relations, 2 Triton Square, Regent’s Place, London NW1 3AN. b) Transactions with related parties Transactions with related parties during the year and balances outstanding at the year-end: Group Interest, fees and other income received Interest, fees and other expenses paid Amounts owed by related parties Amounts owed to related parties 2023 2022 2021 2023 2022 2021 2023 2022 2023 2022 £m £m £m £m £m £m £m £m £m £m Ultimate parent (8) (710) (164) 414 47 33 800 1,363 (1,062) (1,673) Immediate parent (7) (6) (6) 504 308 263 — 1 (13,279) (14,390) Fellow subsidiaries (38) (69) (57) 203 177 163 101 108 (370) (348) Joint ventures (183) (76) (34) 55 17 4 4,486 4,151 (781) (973) (236) (861) (261) 1,176 549 463 5,387 5,623 (15,492) (17,384) For more on this, see ‘Balances with other Banco Santander group members’ in the Risk review, Note 13. Loans and advances to customers, Note 23. Deposits by customers and Note 33. Other Equity Instruments. In addition, transactions with pension schemes operated by the Santander UK group are described in Note 30 . The above transactions were made in the ordinary course of business, on substantially the same terms as for comparable transactions with third party counterparties, and within limits acceptable to the PRA. Such transactions do not involve more than the normal risk of collectability or present any unfavourable features. In 2021, SCUK sold its entire 50% shareholding in PSA Finance UK Limited to PSA Financial Services Spain EFC SA, a joint venture between Santander Consumer Finance SA, a fellow subsidiary of Banco Santander SA, and Banque PSA Finance SA. In 2021 , a significant part of the CIB business of Santander UK was transferred to the London branch of Banco Santander SA by way of a Part VII banking business transfer scheme. For more details, see Note 42 . In 2021, we sold our then head office site in Triton Square, London to Santander UK Investments Ltd, a wholly owned subsidiary of our ultimate parent. Santander UK occupies space within the building and paid fees of £9m ( 2022 : £6m ) under an occupational licence arrangement. In May 2022, Santander UK plc transferred a portfolio of mortgage assets with a carrying amount of £624m to Santander Financial Services plc for a cash consideration of £631m , including a purchase price premium of £7m . In November 2022, Santander (UK) Group Pension Scheme Trustees Limited entered into an unsecured committed liquidity facility with Santander UK plc for £600m with a maturity date of 31 December 2024. This facility provides an alternate source of short-term liquidity for day-to-day operational needs. At the balance sheet date, no drawings had been made from this facility and the entire facility remained undrawn.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2023
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Abstract]
Financial Instruments	39. FINANCIAL INSTRUMENTS a) Fair value measurement and hierarchy (i) Fair value measurement The fair value of financial instruments is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date in the principal, or in its absence, the most advantageous market to which Santander UK has access at that date. The fair value of a liability reflects its non-performance risk. Financial instruments valued using observable market prices If a quoted market price in an active market is available for an instrument, the fair value is calculated as the current bid price multiplied by the number of units of the instrument held. Financial instruments valued using a valuation technique In the absence of a quoted market price in an active market, management uses internal models to make its best estimate of the price that the market would set for that financial instrument. In order to make these estimations, various techniques are employed, including extrapolation from observable market data and observation of similar financial instruments with similar characteristics. Wherever possible, valuation parameters for each product are based on prices directly observable in active markets or that can be derived from directly observable market prices. Chosen valuation techniques incorporate all the factors that market participants would take into account in pricing transactions. Santander UK manages certain groups of financial assets and liabilities on the basis of its net exposure to either market risks or credit risk. As a result, it has elected to use the exception under IFRS 13 which permits the fair value measurement of a group of financial assets and financial liabilities on the basis of the price that would be received to sell a net long position for a particular risk exposure or paid to transfer a net short position for a particular risk exposure in an orderly transaction between market participants at the measurement date under current market conditions. (ii) Fair value hierarchy Santander UK applies the following fair value hierarchy that prioritises the inputs to valuation techniques used in measuring fair value. The hierarchy establishes three categories for valuing financial instruments, giving the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The three categories are: quoted prices in active markets (Level 1), internal models based on observable market data (Level 2) and internal models based on other than observable market data (Level 3). If the inputs used to measure an asset or a liability fall to different levels within the hierarchy, the classification of the entire asset or liability will be based on the lowest level input that is significant to the overall fair value measurement of the asset or liability. Santander UK categorises assets and liabilities measured at fair value within the fair value hierarchy based on the inputs to the valuation techniques as follows: Level 1 Unadjusted quoted prices for identical assets or liabilities in an active market that Santander UK can access at the measurement date. Active markets are assessed by reference to average daily trading volumes in absolute terms and, where applicable, by reference to market capitalisation for the instrument. Level 2 Quoted prices in inactive markets, quoted prices for similar assets or liabilities, recent market transactions, inputs other than quoted market prices for the asset or liability that are observable either directly or indirectly for substantially the full term, and inputs to valuation techniques that are derived principally from or corroborated by observable market data through correlation or other statistical means for substantially the full term of the asset or liability. Level 3 Significant inputs to the pricing or valuation techniques are unobservable. These unobservable inputs reflect the assumptions that market participants would use when pricing assets or liabilities and are considered significant to the overall valuation. Changes in the observability of significant valuation inputs during the reporting period may result in a transfer of assets and liabilities within the fair value hierarchy. The Santander UK group recognises transfers between levels of the fair value hierarchy when there is a significant change in either its principal market or the level of observability of the inputs to the valuation techniques at the end of the reporting period. b) Valuation techniques The main valuation techniques employed in internal models to measure the fair value of the financial instruments at 31 December 2023 and 2022 are set out below. In substantially all cases, the principal inputs into these models are derived from observable market data. Santander UK did not make any material changes to the valuation techniques and internal models it used in 2023 , 2022 and 2021 . A. In the valuation of financial instruments requiring static hedging (for example interest rate, currency derivatives and property derivatives) and in the valuation of loans and advances and deposits, the ‘present value’ method is used. Expected future cash flows are discounted using the interest rate curves of the applicable currencies or forward house price index levels, as well as credit spreads. The interest rate curves are generally observable market data and reference yield curves derived from quoted interest rates in appropriate time bandings, which match the timings of the cash flows and maturities of the instruments. B. In the valuation of equity financial instruments requiring dynamic hedging (principally equity securities, options and other structured instruments), proprietary local volatility and stochastic volatility models are used. These types of models are widely accepted in the financial services industry. Observable market inputs used in these models include the bid-offer spread, foreign currency exchange rates, volatility and correlation between indices. In limited circumstances, other inputs may be used in these models that are based on unobservable market data, such as the Halifax’s UK HPI volatility, HPI forward growth, HPI spot rate, mortality and mean reversion . C. In the valuation of financial instruments exposed to interest rate risk that require either static or dynamic hedging (such as interest rate futures, caps and floors, and options), the present value method (futures), Black’s model (caps/floors) and the Hull/White and Markov functional models (Bermudan options) are used. These types of models are widely accepted in the financial services industry. The significant inputs used in these models are observable market data, including appropriate interest rate curves, volatilities, correlations and exchange rates. In limited circumstances, other inputs may be used in these models that are based on unobservable market data, such as HPI volatility, HPI forward growth, HPI spot rate and mortality. D. In the valuation of linear instruments such as credit risk and fixed-income derivatives, credit risk is measured using dynamic models similar to those used in the measurement of interest rate risk. In the case of non-linear instruments, if the portfolio is exposed to credit risk such as credit derivatives, the probability of default is determined using the credit default spread market. The main inputs used to determine the underlying cost of credit of credit derivatives are quoted credit risk premiums and the correlation between the quoted credit derivatives of various issuers. The fair values of the financial instruments arising from Santander UK’s internal models take into account, among other things, contract terms and observable market data, which include such factors as bid-offer spread, interest rates, credit risk, exchange rates, the quoted market price of equity securities, volatility and prepayments. In all cases, when it is not possible to derive a valuation for a particular feature of an instrument, management uses judgement to determine the fair value of the particular feature. In exercising this judgement, a variety of tools are used including proxy observable data, historical data and extrapolation techniques. Extrapolation techniques take into account behavioural characteristics of equity markets that have been observed over time, and for which there is a strong case to support an expectation of a continuing trend in the future. Estimates are calibrated to observable market prices when they become available. Santander UK believes its valuation methods are appropriate and consistent with other market participants. Nevertheless, the use of different valuation methods or assumptions, including imprecision in estimating unobservable market inputs, to determine the fair value of certain financial instruments could result in different estimates of fair value at the reporting date and the amount of gain or loss recorded for a particular instrument. Most of the valuation models are not significantly subjective, because they can be tested and, if necessary, recalibrated by the internal calculation of and subsequent comparison to market prices of actively traded securities, where available. c) Control framework Fair values are subject to a control framework designed to ensure that they are either determined or validated by a function independent of the risk-taker. To this end, ultimate responsibility for the determination of fair values lies with the Risk Department. For all financial instruments where fair values are determined by reference to externally quoted prices or observable pricing inputs to models, independent price determination or verification is utilised. In inactive markets, direct observation of a traded price may not be possible. In these circumstances, Santander UK will source alternative market information to validate the financial instrument’s fair value, with greater weight given to information that is considered to be more relevant and reliable. The factors that are considered in this regard include: – The extent to which prices may be expected to represent genuine traded or tradeable prices – The degree of similarity between financial instruments – The degree of consistency between different sources – The process followed by the pricing provider to derive the data – The elapsed time between the date to which the market data relates and the balance sheet date – The manner in which the data was sourced. The source of pricing data is considered as part of the process that determines the classification of the level of a financial instrument. Consideration is given to the quality of the information available that provides the current mark-to-model valuation and estimates of how different these valuations could be on an actual trade, taking into consideration how active the market is. For spot assets that cannot be sold due to illiquidity, forward estimates are discounted to estimate a realisable value over time. Adjustments for illiquid positions are regularly reviewed to reflect changing market conditions. For fair values determined using a valuation model, the control framework may include as applicable, independent development and / or validation of: (i) the logic within the models; (ii) the inputs to those models; and (iii) any adjustments required outside the models. Internal valuation models are validated independently within the Risk Department. A validation report is produced for each model-derived valuation that assesses the mathematical assumptions behind the model, the implementation of the model and its integration within the trading system. d) Fair values of financial instruments carried at amortised cost The following tables analyse the fair value of the financial instruments carried at amortised cost at 31 December 2023 and 2022 , including their levels in the fair value hierarchy - Level 1, Level 2 and Level 3. Cash and balances at central banks, which consist of demand deposits with the Bank of England, together with cash in tills and ATMs, have been excluded from the table as the carrying amount is deemed an appropriate approximation of fair value. Group 2023 2022 Fair value Fair Carrying Fair value Fair Carrying Level 1 Level 2 Level 3 value value Level 1 Level 2 Level 3 value value £m £m £m £m £m £m £m £m £m £m Assets Loans and advances to customers — — 205,917 205,917 207,435 — — 212,479 212,479 219,716 Loans and advances to banks — 1,080 — 1,080 1,080 — 992 — 992 992 Reverse repurchase agreements - non trading — 12,470 — 12,470 12,468 — 7,341 — 7,341 7,348 Other financial assets at amortised cost 144 — — 144 152 144 — — 144 156 144 13,550 205,917 219,611 221,135 144 8,333 212,479 220,956 228,212 Liabilities Deposits by customers — 71 190,561 190,632 190,850 — 51 195,483 195,534 195,568 Deposits by banks — 20,342 40 20,382 20,332 — 27,979 55 28,034 28,525 Repurchase agreements - non trading — 8,413 — 8,413 8,411 — 7,982 — 7,982 7,982 Debt securities in issue 1,689 30,743 1,189 33,621 33,910 2,574 26,349 1,582 30,505 31,531 Subordinated liabilities — 2,591 209 2,800 2,386 19 2,358 224 2,601 2,332 1,689 62,160 191,999 255,848 255,889 2,593 64,719 197,344 264,656 265,938 The carrying value above of any financial assets and liabilities that are designated as hedged items in a portfolio (or macro) fair value hedge relationship excludes gains and losses attributable to the hedged risk, as this is included as a separate line item on the balance sheet. Valuation methodology for financial instruments carried at amortised cost The valuation approach to specific categories of financial instruments is described below. Assets: Loans and advances to customers The approach to estimating the fair value of loans and advances to customers has been determined by discounting expected cash flows to reflect either current market rates or credit spreads relevant to the specific industry of the borrower. The determination of their fair values is an area of considerable estimation and uncertainty as there is no observable market and values are significantly affected by customer behaviour. i) Advances secured on residential property The fair value of the mortgage portfolio is calculated by discounting contractual cash flows by different spreads for each LTV Band, after taking account of expected customer prepayment rates. The spread is based on new business interest rates derived from publicly available competitor market information. ii) Corporate loans The determination of the fair values of performing loans is calculated by discounting the contractual cash flows and also deducting other costs relating to expected credit losses, cost of capital, credit risk capital, operational risk capital, cost of funding and operating costs. iii) Other loans These consist of unsecured personal loans, credit cards, overdrafts and consumer (auto) finance. The weighted average lives of these portfolios are typically short and relate to relatively new business. For unsecured personal loans and consumer (auto) finance loans, a small surplus or deficit has been recognised based on the differential between existing portfolio margins and the current contractual interest rates. Loans and advances to banks These comprise secured loans, short-term placements with banks including collateral and unsettled financial transactions. The secured loans have been valued based on a discounted spread for the term of the loans using valuation technique A as described above. The carrying amount of the other items is deemed a reasonable approximation of their fair value, as the transactions are very short-term in duration. Reverse repurchase agreements - non-trading The fair value of the reverse repurchase agreements - non trading has been estimated using valuation technique A as described above, using a spread appropriate to the underlying collateral. Other financial assets at amortised cost These consist of asset backed securities and debt securities. The asset backed securities can be complex products and in some instances are valued with the assistance of an independent, specialist valuation firm. These fair values are determined using industry-standard valuation techniques, including discounted cash flow models. The inputs to these models used in these valuation techniques include quotes from market makers, prices of similar assets, adjustments for differences in credit spreads, and additional quantitative and qualitative research. The debt security investments consist of a portfolio of government debt securities. The fair value of this portfolio has been determined using quoted market prices. Liabilities: Deposits by customers The majority of deposit liabilities are payable on demand and therefore can be deemed short-term in nature with the fair value equal to the carrying value. Certain of the deposit liabilities are at a fixed rate until maturity. The deficit/surplus of fair value over carrying value of these liabilities has been estimated by reference to the market rates available at the balance sheet date for similar deposit liabilities of similar maturities. The fair value of such deposit liabilities has been estimated using valuation technique A as described above. Deposits by banks The fair value of deposits by banks, including repos, has been estimated using valuation technique A as described above, discounted at the appropriate credit spread. Repurchase agreements - non trading The fair value of the repurchase agreements - non trading has been estimated using valuation technique A as described above, discounted at a spread appropriate to the underlying collateral. Debt securities in issue and subordinated liabilities Where reliable prices are available, the fair value of debt securities in issue and subordinated liabilities has been calculated using quoted market prices. Where reliable prices are not available, internal models have been used to determine fair values, which take into account, among other things, contract terms and observable market data, which include such factors as interest rates, credit risk and exchange rates. In all cases, when it is not possible to derive a valuation for a particular feature of an instrument, management uses judgement to determine the fair value of the particular feature. In exercising this judgement, a variety of tools are used including proxy observable data. e) Fair values of financial instruments measured at fair value The following tables summarise the fair values of the financial assets and liabilities accounted for at fair value at 31 December 2023 and 31 December 2022 , analysed by their levels in the fair value hierarchy - Level 1, Level 2 and Level 3. Group 2023 2022 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Valuation £m £m £m £m £m £m £m £m technique Assets Derivative financial instruments Exchange rate contracts — 1,129 — 1,129 — 2,044 — 2,044 A Interest rate contracts — 2,216 1 2,217 — 2,399 7 2,406 A & C Equity and credit contracts — 98 35 133 — 100 30 130 B & D Netting — (2,047) — (2,047) — (2,173) — (2,173) — 1,396 36 1,432 — 2,370 37 2,407 Other financial assets at FVTPL Loans and advances to customers — — 46 46 — — 45 45 A Debt securities — 167 49 216 — 12 72 84 A, B & D — 167 95 262 — 12 117 129 Financial assets at FVOCI Debt securities 8,293 188 — 8,481 5,996 28 — 6,024 D 8,293 188 — 8,481 5,996 28 — 6,024 Total assets at fair value 8,293 1,751 131 10,175 5,996 2,410 154 8,560 Liabilities Derivative financial instruments Exchange rate contracts — 508 — 508 — 471 — 471 A Interest rate contracts — 2,336 1 2,337 — 2,624 4 2,628 A & C Equity and credit contracts — 11 9 20 — 17 8 25 B & D Netting — (2,047) — (2,047) — (2,173) — (2,173) — 808 10 818 — 939 12 951 Other financial liabilities at FVTPL Debt securities in issue — 369 — 369 — 372 3 375 A Structured deposits — 426 — 426 — 321 — 321 A Zero Amortising Guaranteed — 104 — 104 — 107 — 107 D — 899 — 899 — 800 3 803 Total liabilities at fair value — 1,707 10 1,717 — 1,739 15 1,754 Transfers between levels of the fair value hierarchy In 2023 there were £22m ( 2022 : no significant) transfers of financial instruments between levels of the fair value hierarchy. f) Fair value adjustments The internal models incorporate assumptions that Santander UK believes would be made by a market participant to establish fair value. Fair value adjustments are adopted when Santander UK considers that there are additional factors that would be considered by a market participant that are not incorporated in the valuation model. Santander UK classifies fair value adjustments as either ‘risk-related’ or ‘model-related’. The fair value adjustments form part of the portfolio fair value and are included in the balance sheet values of the product types to which they have been applied. The fair value adjustments are set out in the following table: Group 2023 2022 £m £m Risk-related: - Bid-offer and trade specific adjustments (6) (12) - Uncertainty 6 12 - Credit risk adjustment 1 2 - Funding fair value adjustment 1 1 2 3 Day One profit 1 1 3 4 Risk-related adjustments Risk-related adjustments are driven, in part, by the magnitude of Santander UK’s market or credit risk exposure, and by external market factors, such as the size of market spreads. (i) Bid-offer and trade specific adjustments Portfolios are marked at bid or offer, as appropriate. Valuation models will typically generate mid-market values. The bid-offer adjustment reflects the cost that would be incurred if substantially all residual net portfolio market risks were closed using available hedging instruments or by disposing of or unwinding the position. For debt securities, the bid-offer spread is based on a market price at an individual security level. For other products, the major risk types are identified. For each risk type, the net portfolio risks are first classified into buckets, and then a bid-offer spread is applied to each risk bucket based upon the market bid-offer spread for the relevant hedging instrument. (ii) Uncertainty Certain model inputs may be less readily determinable from market data, and/or the choice of model itself may be more subjective. In these circumstances, a range of possible values exists that the financial instrument or market parameter may assume, and an adjustment may be needed to reflect the likelihood that in estimating the fair value of the financial instrument, market participants would adopt more conservative values for uncertain parameters and/or model assumptions than those used in the valuation model. (iii) Credit risk adjustment Credit risk adjustments comprise credit and debit valuation adjustments. The credit valuation adjustment (CVA) is an adjustment to the valuation of OTC derivative contracts to reflect within fair value the possibility that the counterparty may default, and Santander UK may not receive the full market value of the transactions. The debit valuation adjustment (DVA) is an adjustment to the valuation of the OTC derivative contracts to reflect within the fair value the possibility that Santander UK may default, and that Santander UK may not pay full market value of the transactions. Santander UK calculates a separate CVA and DVA for each Santander UK legal entity, and within each entity for each counterparty to which the entity has exposure. Santander UK calculates the CVA by applying the probability of default of the counterparty to the expected positive exposure to the counterparty, and multiplying the result by the loss expected in the event of default i.e. LGD. Conversely, Santander UK calculates the DVA by applying the PD of the Santander UK group, to the expected positive exposure of the counterparty to Santander UK and multiplying the result by the LGD. Both calculations are performed over the life of the potential exposure. For most products Santander UK uses a simulation methodology to calculate the expected positive exposure to a counterparty. This incorporates a range of potential exposures across the portfolio of transactions with the counterparty over the life of the portfolio. The simulation methodology includes credit mitigants such as counterparty netting agreements and collateral agreements with the counterparty. (iv) Funding fair value adjustment (FFVA) The FFVA is an adjustment to the valuation of OTC derivative positions to include the net cost of funding uncollateralised derivative positions. This is calculated by applying a suitable funding cost to the expected future funding exposure of any uncollateralised component of the OTC derivative portfolio. Model-related adjustments Models used for portfolio valuation purposes may be based upon a simplifying set of assumptions that do not capture all material market characteristics. Additionally, markets evolve, and models that were adequate in the past may require development to capture all material market characteristics in current market conditions. In these circumstances, model limitation adjustments are adopted. As model development progresses, model limitations are addressed within the core revaluation models and a model limitation adjustment is no longer needed. Day One profit adjustments Day One profit adjustments are adopted where the fair value estimated by a valuation model is based on one or more significant unobservable inputs. Day One profit adjustments are calculated and reported on a portfolio basis. The timing of recognition of deferred Day One profit and loss is determined individually. It is deferred until either the instrument’s fair value can be determined using market observable inputs or is realised through settlement. The financial instrument is subsequently measured at fair value, adjusted for the deferred Day One profit and loss. Subsequent changes in fair value are recognised immediately in the Income Statement without immediate reversal of deferred Day One profits and losses. g) Internal models based on information other than market data (Level 3) The table below provides an analysis of financial instruments valued using internal models based on information other than market data together with further details on the valuation techniques used for each type of instrument. Each instrument is initially valued at transaction price: Group Balance sheet value Fair value movements recognised in profit/(loss) 2023 2022 2023 2022 2021 Balance sheet line item Category Financial instrument product type £m £m £m £m £m 1. Derivative assets Equity and credit contracts Reversionary property interests 35 30 12 (8) — 2. FVTPL assets Loans and advances to customers Roll-up mortgage portfolio 24 28 (2) (18) (5) 3. FVTPL assets Loans and advances to customers Other loans 22 17 4 (4) (2) 4. FVTPL assets Debt securities Reversionary property securities 49 70 (3) — 5 130 145 11 (30) (2) Other Level 3 assets 1 9 (1) 10 (9) Other Level 3 liabilities (10) (15) (2) 3 7 Total net assets 121 139 Total income/(expense) 8 (17) (4) Valuation techniques (Group) 1. Derivative assets – Equity and credit contracts These are valued using a probability weighted set of HPI forward prices, which are assumed to be a reasonable representation of the increase in value of the Santander UK group’s reversionary interest portfolio underlying the derivatives. The probability used reflects the likelihood of the homeowner vacating the property and is calculated from mortality rates and acceleration rates which are a function of age and gender, obtained from the relevant mortality tables. Indexing is felt to be appropriate due to the size and geographical dispersion of the reversionary interest portfolio. These are determined using HPI Spot Rates adjusted to reflect estimated forward growth. Non-seasonally adjusted (NSA) national and regional HPI are used in the valuation model to avoid any subjective judgement in the adjustment process, which is made by Markit, which publishes the Halifax House Price Index. The inputs used to determine the value of the reversionary property derivatives are HPI spot, HPI forward growth and mortality rates. The principal pricing parameter is HPI forward growth. 2. FVTPL assets – Loans and advances to customers – roll-up mortgage portfolio These represent roll-up mortgages (sometimes referred to as lifetime mortgages), which are an equity release scheme under which a property owner takes out a loan secured against their home. The owner does not have to make any interest payments during their lifetime in which case the fixed interest payments are rolled up into the mortgage. The loan or mortgage (capital and rolled-up interest) is repaid upon the owner’s vacation of the property and the value of the loan is only repaid from the value of the property. This is known as a ‘no negative equity guarantee’. Santander UK suffers a loss if the sale proceeds from the property are insufficient to repay the loan, as it is unable to pursue the homeowner’s estate or beneficiaries for the shortfall. The value of the mortgage ‘rolls up’ or accretes until the owner vacates the property. In order to value the roll-up mortgages, Santander UK uses a probability- weighted set of European option prices (puts) determined using the Black-Scholes model, in which the ‘no negative equity guarantee’ are valued as short put options. The probability weighting applied is calculated from mortality rates and acceleration rates as a function of age and gender, taken from mortality tables. The inputs used to determine the value of these instruments are HPI spot, HPI forward growth, HPI volatility, mortality rates and repayment rates. The principal pricing parameter is HPI forward growth. The HPI forward growth rate used is unobservable and is the same as used in the valuation of Instrument 1 above. The other parameters do not have a significant effect on the value of the instruments. 3. FVTPL assets – Loans and advances to customers – other loans These relate to loans to transport and education companies. The fair value of these loans is estimated using the ‘present value’ model based on a credit curve derived from current market spreads. Loan specific credit data is unobservable, so a proxy population is applied based on industry sector and credit rating. 4. FVTPL assets – Debt securities These consist of reversionary property securities and are an equity release scheme, where the property owner receives an upfront lump sum in return for paying a fixed percentage of the sales proceeds of the property when the owner vacates the property. These reversionary property securities are valued using a probability- weighted set of HPI forward prices which are assumed to be a reasonable representation of the increase in value of Santander UK’s reversionary interest portfolio underlying the derivatives. The probability weighting used reflects the probability of the homeowner vacating the property through death or moving into care and is calculated from mortality rates and acceleration factors which are a function of age and gender, obtained from the relevant mortality table. The inputs used to determine the value of these instruments are HPI spot, HPI forward growth and mortality rates. The principal pricing parameter is HPI forward growth. Discussion of the HPI spot rate, HPI forward growth rate and mortality rates for this financial instrument is the same as Instrument 1 above. An adjustment is also made to reflect the specific property risk. Specific property risk is from the difference between the specific properties in the portfolio, and the average price as expressed in the regionally weighted house price index. Reconciliation of fair value measurement in Level 3 of the fair value hierarchy The following table sets out the movements in Level 3 financial instruments in 2023 : Group Assets Liabilities Derivatives Other financial assets at FVTPL Financial assets at FVOCI Total Derivatives Other financial liabilities at FVTPL Total £m £m £m £m £m £m £m At 1 January 2023 37 117 — 154 (12) (3) (15) Total gains/(losses) recognised: Fair value movements (2) 10 — — 10 (2) — (2) Purchases — 1 — 1 — — — Netting (1) — (3) — (3) — — — Settlements (11) (20) — (31) 4 3 7 At 31 December 2023 36 95 — 131 (10) — (10) Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the year (2) 10 — — 10 (2) — (2) At 1 January 2022 46 185 18 249 (32) (6) (38) Total (losses)/gains recognised: Fair value movements (2) (2) (18) — (20) 2 1 3 Transfers in — — — — (2) — (2) Netting (1) — (8) — (8) — — — Sales — (5) — (5) — — — Settlements (7) (37) (18) (62) 20 2 22 At 31 December 2022 37 117

Offsetting Financial Assets and

Offsetting Financial Assets and Liabilities	12 Months Ended
	Dec. 31, 2023
Disclosure of offsetting of financial liabilities [abstract]
Offsetting Financial Assets and Liabilities	40. OFFSETTING FINANCIAL ASSETS AND LIABILITIES The following table shows the impact of netting arrangements on: – All financial assets and liabilities that are reported net on the balance sheet – All derivative financial instruments and repurchase agreements and other similar secured lending and borrowing agreements that are subject to enforceable master netting arrangements or similar agreements, but do not qualify for balance sheet netting. The table identifies the amounts that have been offset in the balance sheet and also those amounts that are covered by enforceable netting arrangements (offsetting arrangements and financial collateral) but do not qualify for netting under the requirements described above. For derivative contracts, the ‘Financial instruments’ column identifies financial assets and liabilities that are subject to set off under netting agreements, such as the ISDA Master Agreement or derivative exchange or clearing counterparty agreements, whereby all outstanding transactions with the same counterparty can be offset and close-out netting applied across all outstanding transactions covered by the agreements if an event of default or other predetermined events occur. Financial collateral refers to cash and non-cash collateral obtained, typically daily or weekly, to cover the net exposure between counterparties by enabling the collateral to be realised in an event of default or if other predetermined events occur. For repurchase and reverse repurchase agreements and other similar secured lending and borrowing, the ‘Financial instruments’ column identifies financial assets and liabilities that are subject to set off under netting agreements, such as global master repurchase agreements and global master securities lending agreements, whereby all outstanding transactions with the same counterparty can be offset and close-out netting applied across all outstanding transactions covered by the agreements if an event of default or other predetermined events occur. Financial collateral typically comprises highly liquid securities which are legally transferred and can be liquidated if a counterparty defaults. Santander UK engages in a variety of counterparty credit mitigation strategies in addition to netting and collateral arrangements. Therefore, the net amounts presented in the tables below do not purport to represent Santander UK’s actual credit exposure. Group Amounts subject to enforceable netting arrangements Assets not subject to enforceable netting arrangements (2) Effects of offsetting on balance sheet Related amounts not offset Gross amounts Amounts offset Net amounts on balance sheet Financial instruments Financial collateral (1) Net amount Balance sheet total (3) 2023 £m £m £m £m £m £m £m £m Assets Derivative financial assets 3,429 (2,047) 1,382 (471) (823) 88 50 1,432 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 15,625 (3,157) 12,468 (118) (12,350) — — 12,468 Loans and advances to customers and banks⁽⁴⁾ 5,363 (790) 4,573 — — 4,573 203,942 208,515 24,417 (5,994) 18,423 (589) (13,173) 4,661 203,992 222,415 Liabilities Derivative financial liabilities 2,838 (2,047) 791 (471) (161) 159 27 818 Repurchase, securities lending & similar agreements: – Amortised cost 11,568 (3,157) 8,411 (118) (8,293) — — 8,411 Deposits by customers and banks⁽⁴⁾ 4,218 (790) 3,428 — — 3,428 207,754 211,182 18,624 (5,994) 12,630 (589) (8,454) 3,587 207,781 220,411 2022 Assets Derivative financial assets 4,525 (2,173) 2,352 (515) (1,720) 117 55 2,407 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 8,826 (1,478) 7,348 (9) (7,339) — — 7,348 Loans and advances to customers and banks⁽⁴⁾ 5,169 (908) 4,261 — — 4,261 216,447 220,708 18,520 (4,559) 13,961 (524) (9,059) 4,378 216,502 230,463 Liabilities Derivative financial liabilities 3,085 (2,173) 912 (515) (115) 282 39 951 Repurchase, securities lending & similar agreements: – Amortised cost 9,460 (1,478) 7,982 (9) (7,973) — — 7,982 Deposits by customers and banks⁽⁴⁾ 8,077 (908) 7,169 — — 7,169 216,924 224,093 20,622 (4,559) 16,063 (524) (8,088) 7,451 216,963 233,026 (1) Financial collateral is reflected at its fair value but has been limited to the net balance sheet exposure so as not to include any over-collateralisation. (2) This column includes contractual rights of set-off that are subject to uncertainty under the laws of the relevant jurisdiction. (3) The balance sheet total is the sum of ‘Net amounts reported on the balance sheet’ that are subject to enforceable netting arrangements and ‘Amounts not subject to enforceable netting arrangements’. (4) The amounts offset within loans and advances to customers/banks or deposits by customers/banks relate to offset mortgages which are classified as either and that are subject to netting.

Interest Rate Benchmark Reform

Interest Rate Benchmark Reform	12 Months Ended
	Dec. 31, 2023
Interest Rate Benchmark Reform [Abstract]
Interest Rate Benchmark Reform	41. INTEREST RATE BENCHMARK REFORM Santander UK continues to work with customers and counterparties to transition any remaining agreements referencing 3-month synthetic LIBOR before that setting ends on 31 March 2024. A t 31 December 2023 , these represent an insignificant element of Santander UK’s exposures and there are no remaining exposures which reference other LIBOR settings . The following tables show the notional amounts of assets, liabilities and off-balance sheet commitments at 31 December 2023 and 31 December 2022 affected by IBOR reform that have yet to transition to an alternative benchmark interest rate. Group GBP LIBOR USD LIBOR Total 2023 £m £m £m Assets Financial assets at amortised cost 6 — 6 6 — 6 2022 Assets Derivatives — 1,665 1,665 Financial assets at amortised cost 76 57 133 76 1,722 1,798 Liabilities Derivatives 66 1,846 1,912 66 1,846 1,912 Off-balance sheet commitments given 2 — 2

Discontinued Operations and Ass

Discontinued Operations and Assets and Liabilities Held for Sale	12 Months Ended
	Dec. 31, 2023
Discontinued Operations and Assets and Liabilities Held for Sale [Abstract]
Discontinued Operations and Assets Held for Sale	42. DISCONTINUED OPERATIONS AND ASSETS HELD FOR SALE Discontinued operations Transfer of the CIB Business Santander UK plc transferred a significant part of its CIB business to the London branch of Banco Santander SA under a Part VII banking business transfer scheme, which completed on 11 October 2021. The residual parts of the CIB business were wound down or transferred to other segments. For the periods prior to its sale, the CIB business met the requirements for presentation as discontinued operations. The financial performance and cash flow information relating to the discontinued operations were as follows: For the year ended 31 December 2023 2022 2021 £m £m £m Net interest income — — 32 Net fee and commission income — — 35 Other operating income — — 2 Total operating income — — 69 Operating expenses before credit impairment (charges)/write-backs, provisions and charges — — (33) Credit impairment (charges)/write-backs — — 11 Provisions for other liabilities and charges — — (4) Total operating credit impairment (charges)/write-backs, provisions and charges — — 7 Profit from discontinued operations before tax — — 43 Tax on profit from discontinued operations — — (12) Profit from discontinued operations after tax — — 31 There were no gains or losses recognised on the measurement to fair value less costs to sell or on the disposal of the asset groups constituting the discontinued operations. In 2023 , the net cash flows attributable to the operating activities in respect of discontinued operations were £nil outflow ( 2022 : £nil ou tflow, 2021 : £3,612m outflow). There were no investing or financing activities in respect of discontinued operations. Assets held for sale Sale of property Management considered the sale of part of Santander House (Milton Keynes) under a proposed transaction with the developer for the construction of Unity Place and Buckingham House (Bletchley), to be highly probable at the balance sheet date. As such, the Santander UK group classified these properties, which are included in the Corporate Centre segment and carried at their sales prices, as held for sale. The sale is expected to complete in 2024 with no gain or loss. At 31 December 2023 , assets held for sale comprised: 2023 2022 £m £m Assets Property, plant and equipment 13 49 Total assets held for sale 13 49

Events After the Balance Sheet

Events After the Balance Sheet Date	12 Months Ended
	Dec. 31, 2023
Disclosure of non-adjusting events after reporting period [abstract]
Events After the Balance Sheet Date	43. EVENTS AFTER THE BALANCE SHEET DATE There have been no significant events between 31 December 2023 and the date of approval of these financial statements which would require a change to or additional disclosure in the financial statements.

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Notes and other explanatory information [abstract]
Basis of preparation, future accounting developments and material accounting policy information	Basis of preparation These financial statements incorporate the financial statements of the Company and entities it controls (its subsidiaries) made up to 31 December each year. The consolidated financial statements have been prepared on the going concern basis using the historical cost convention, except for financial assets and liabilities that have been measured at fair value. An assessment of the appropriateness of the adoption of the going concern basis of accounting is disclosed in the statement of going concern in the Directors’ report. Compliance with International Financial Reporting Standards (IFRS) The consolidated financial statements of the Santander UK group and the separate financial statements of the Company comply with UK-adopted International Accounting Standards (IAS). The financial statements are also prepared in accordance with IFRS as issued by the International Accounting Standards Board (IASB), including interpretations issued by the IFRS Interpretations Committee, as there are no applicable differences from IFRS as issued by the IASB for the periods presented. Disclosures required by IFRS 7 ‘Financial Instruments: Disclosure’ relating to the nature and extent of risks arising from financial instruments, and IAS 1 ‘Presentation of Financial Statements’ relating to objectives, policies and processes for managing capital, have been included in the Risk review section of this Annual Report. This information forms an integral part of these financial statements by this cross reference, is marked as audited, and is covered by the Independent auditors' report. Climate change Santander UK continues to develop its assessment of the potential impacts that climate change and the transition to a low carbon economy may have on the assets and liabilities recognised and presented in its financial statements. Santander UK is mindful of its responsibilities as a responsible lender and is focused on ways to meet the objectives of the Paris Agreement on climate change and to support the UK’s transition to a climate-resilient, net zero economy. Santander UK's current climate change strategy focuses on three main areas to achieve Banco Santander's ambition to reach net zero emissions by 2050: 1. Managing climate risks by integrating climate considerations into risk management frameworks, screening and stress testing our portfolio for climate related financial risks, and setting risk appetites to help steer our portfolio in line with the Paris Agreement, 2. Supporting our customers’ transition by developing products and services that promote a reduction in CO 2 emissions, and 3. Reducing emissions in our operations and supply chain by focusing on continuous improvement in our operations, and environmental and energy management systems in accordance with ISO14001 and 15001, promoting responsible procurement practices and employee engagement. Santander UK's current climate change strategy and its view of the risks associated with climate change and the transition to a low carbon economy are reflected in its critical judgements and accounting estimates, although climate change risk did not have a material impact at 31 December 2023 and 2022, consistent with management's assessment that climate change and the transition to a low carbon economy are not currently expected to have a meaningful impact on the viability of the Santander UK group in the medium term. At 31 December 2023 and 2022, management specifically considered the potential impact of climate change and the transition to a low carbon economy on: – Loans and advances to customers ( see Note 13 and the credit risk section of the Risk review). Some climate change risks arise due to the requirements of IFRS 9 and others relate to specific portfolios and sectors: – ECL calculations are based on multiple forward-looking economic scenarios developed by management covering a period of 5 years , during which timeframe climate change risks may crystallise; – For mortgages in Retail & Business Banking and commercial real estate lending in Corporate & Commercial Banking, the value of property collateral might be affected by physical impacts related to the frequency and scale of extreme weather events, such as flood and subsidence risk, or changing environmental performance standards for property. – For automotive loans in Consumer Finance, the residual value of automotive vehicles might be impacted by diesel obsolescence and the transition to electric vehicles. – For corporate lending in Corporate & Commercial Banking, certain sectors give rise to fossil fuel exposures, such as Oil & Gas, Mining & Extraction and Power Generation. – Goodwill impairment assessment (see Note 20). Estimates underpinning the determination of whether or not goodwill balances are impaired are partly based on forecast business performance beyond the time horizon for management's detailed plans. Future changes to Santander UK's climate change strategy may impact Santander UK's critical judgements and accounting estimates and result in material changes to financial results and the carrying values of certain assets and liabilities in future reporting periods. Future accounting developments At 31 December 2023 , for the Santander UK group, there were no significant new or revised standards and interpretations, and amendments thereto, which have been issued but which are not yet effective, or which have otherwise not been early adopted where permitted. Comparative information As required by US public company reporting requirements, these financial statements include two years of comparative information for the consolidated income statement, consolidated statement of comprehensive income, consolidated statement of changes in equity, consolidated statement of cash flows and related notes. Material accounting policy information The following material accounting policies have been applied in preparing these financial statements. For material accounting policies which involve the application of judgements or accounting estimates that are determined to be critical to the preparation of these financial statements see 'Critical judgements and accounting estimates'.
Consolidation	Consolidation The consolidated financial statements incorporate the financial statements of the Company and entities (including structured entities) controlled by it and its subsidiaries. The acquisition method of accounting is used to account for the acquisition of subsidiaries which meet the definition of a business. Business combinations between entities under common control (i.e. fellow subsidiaries of Banco Santander SA, the ultimate parent) are outside the scope of IFRS 3 – ‘Business Combinations’, and there is no other guidance for such transactions under IFRS. The Santander UK group elects to account for business combinations between entities under common control at their book values in the acquired entity by including the acquired entity’s results from the date of the business combination and not restating comparatives. Reorganisations of entities within the Santander UK group are also accounted for at their book values. Credit protection entities established as part of significant risk transfer (SRT) transactions are not consolidated by the Santander UK group in cases where third party investors have the exposure, or rights, to all of the variability of returns from the performance of the entities.
Revenue recognition	Revenue recognition a) Interest income and expense Interest and similar income and expense are recognised in the income statement using the effective interest rate method for: all financial instruments measured at amortised cost; debt instruments measured at FVOCI; and the effective part of any related accounting hedging instruments. Interest income is calculated by applying the effective interest rate to the gross carrying amount of financial assets, except for financial assets that have subsequently become credit-impaired (i.e. Stage 3), for which interest revenue is calculated by applying the effective interest rate to their amortised cost (i.e. net of the ECL provision). For more information on stage allocations of credit risk exposures, see ‘Significant increase in credit risk’ in the ‘Santander UK group level – credit risk management’ section of the Risk review. b) Fee and commission income and expense Fees and commissions that are not an integral part of the effective interest rate are recognised when the service is performed. Most fee and commission income is recognised at a point in time. Certain commitment, upfront and management fees are recognised over time but are not material. For retail and corporate products, fee and commission income consists principally of collection services fees, commission on foreign currencies, commission and other fees received from retailers for processing credit card transactions, fees received from other credit card issuers for providing cash advances for their customers through the Santander UK group’s branch and ATM networks, annual fees payable by credit card holders and fees for non-banking financial products. For insurance products, fee and commission income consists principally of commissions and profit share arising from the sale of building and contents insurance and life protection insurance. Commissions arising from the sale of buildings and contents insurance are recognised over the period of insurance cover, adjusted to take account of cancelled policies. Profit share income from the sale of buildings and contents insurance which is not subject to any adjustment is recognised when the profit share income is earned. Commissions and profit share arising from the sale of life protection insurance is subject to adjustment for cancellations of policies within 3 years from inception. Fee and commission income which forms an integral part of the effective interest rate of a financial instrument (for example certain loan commitment fees) is recognised as an adjustment to the effective interest rate and recorded in ‘Interest income’. c) Other operating income Other operating income includes all gains and losses from changes in the fair value of financial assets and liabilities held at fair value through profit or loss (comprising financial assets and liabilities held for trading, trading derivatives and other financial assets and liabilities at fair value through profit or loss), together with related interest income, expense, dividends, and changes in fair value of any derivatives managed in conjunction with these assets and liabilities. Other operating income also includes hedge ineffectiveness arising from fair value and cash flow hedging, income from operating lease assets, and profits and losses arising on the sales of property, plant and equipment and subsidiary undertakings.
Defined benefit pension schemes	Defined benefit pension schemes (see 'Critical judgements and accounting estimates') A defined benefit scheme is a pension scheme that guarantees an amount of pension benefit to be provided, usually as a function of one or more factors such as age, years of service or compensation. Pension costs are charged to ‘Administration expenses’, within the line item ‘Operating expenses before impairment losses, provisions and charges’ with the net interest on the defined benefit asset or liability included within ‘Net interest income’ in the income statement. The asset or liability recognised in respect of defined benefit pension schemes is the present value of the defined benefit obligation at the balance sheet date, less the fair value of scheme assets. The defined benefit obligation is calculated annually by independent actuaries using the projected unit credit method. The assets of the schemes are measured at their fair values at the balance sheet date. The present value of the defined benefit obligation is estimated by projecting forward the growth in current accrued pension benefits to reflect inflation and salary growth to the date of pension payment, then discounted to present value using the yield applicable to high-quality AA rated corporate bonds of the same currency and which have terms to maturity closest to the terms of the scheme liabilities, adjusted where necessary to match those terms. In determining the value of scheme liabilities, demographic and financial assumptions are made by management about life expectancy, inflation, discount rates, pension increases and earnings growth, based on past experience and future expectations. Financial assumptions are based on market conditions at the balance sheet date and can generally be derived objectively. Demographic assumptions require a greater degree of estimation and judgement to be applied to externally derived data. Any surplus or deficit of scheme assets over liabilities is recognised in the balance sheet as an asset (surplus) or liability (deficit). An asset is only recognised to the extent that the surplus can be recovered through reduced contributions in the future or through refunds from the scheme.
Share-based payments	Share-based payments The Santander UK group engages in cash-settled and equity-settled share-based payment transactions in respect of services received from certain of its employees. Shares of the Santander UK group’s parent, Banco Santander SA are purchased in the open market by the Santander UK group (for the Employee Sharesave scheme) or are purchased by Banco Santander SA or another Banco Santander subsidiary (including awards granted under the Long-Term Incentive Plan and the Deferred Shares Bonus Plan) to satisfy share options or awards as they vest. Options granted under the Employee Sharesave scheme and awards granted under the Transformation Incentive Plan are accounted for as cash-settled share- based payment transactions. Awards granted under the Long-Term Incentive Plan and Deferred Shares Bonus Plan are accounted for as equity-settled share- based payment transactions. The fair value of the options granted under the Employee Sharesave scheme is determined using an option pricing model, which takes into account the exercise price of the option, the current share price, the risk-free interest rate, the expected volatility of the Banco Santander SA share price over the life of the option and the dividend growth rate. The fair value of the awards granted for the Long-Term Incentive Plan was determined at the grant date using an option pricing model, which takes into account the share price at grant date, the risk-free interest rate, the expected volatility of the Banco Santander SA share price over the life of the award and the dividend growth rate.
Goodwill and other intangible assets	Goodwill and other intangible assets (for goodwill see 'Critical judgements and accounting estimates') Goodwill represents the excess of the cost of an acquisition, as well as the fair value of any interest previously held, over the fair value of the share of the identifiable net assets of the acquired subsidiary, or business at the date of acquisition. Goodwill on the acquisition of subsidiaries and businesses is included in intangible assets. Goodwill is tested for impairment annually, or more frequently when events or changes in circumstances dictate and carried at cost less accumulated impairment losses. Gains and losses on the disposal of an entity or business include the carrying amount of goodwill relating to the entity or business sold. Other intangible assets are recognised if they arise from contractual or other legal rights or if they are capable of being separated or divided from Santander UK and sold, transferred, licensed, rented or exchanged. The value of such intangible assets, where they are available for use, is amortised on a straight-line basis over their useful economic life of three to seven years and the assets are reviewed annually for impairment indicators and tested for impairment where indicators are present. Other intangible assets that are not yet available for use are tested for impairment annually or more frequently when events or changes in circumstances dictate. Software development costs are capitalised when they are direct costs associated with identifiable and unique software products that are expected to provide future economic benefits and the cost of those products can be measured reliably. These costs include payroll, materials, services and directly attributable overheads. Internally developed software meeting these criteria and externally purchased software are classified in intangible assets on the balance sheet and amortised on a straight-line basis over their useful life of three to seven years, unless the software is an integral part of the related computer hardware, in which case it is treated as property, plant and equipment as described below. Capitalisation of costs ceases when the software is capable of operating as intended. Costs of maintaining software are expensed as incurred.
Property, plant and equipment	Property, plant and equipment Property, plant and equipment include owner-occupied properties (including leasehold properties), office fixtures and equipment and computer software. Property, plant and equipment also includes operating leases where the Santander UK group is the lessor and right-of-use assets where the Santander UK group is the lessee. Internally developed software meeting the criteria set out in ‘Goodwill and other intangible assets’ above and externally purchased software are classified in property, plant and equipment where the software is an integral part of the related computer hardware (for example, the operating system of a computer). Classes of property, plant and equipment are depreciated on a straight-line basis over their useful life, as follows: Owner-occupied properties Not exceeding 50 years Office fixtures and equipment 3 to 15 years Computer software 3 to 7 years Right-of-use assets Shorter of the lease term or the useful life of the underlying asset Operating lease assets - vehicles 1 to 4 years Depreciation is not charged on freehold land. Depreciation of operating lease assets where the Santander UK group is the lessor is described in 'Leases' below.
Financial instruments	Financial instruments (for impairment of debt instrument financial assets see 'Critical judgements and accounting estimates: Credit impairment losses') a) Initial recognition and measurement Financial assets and liabilities are initially recognised when the Santander UK group becomes a party to the contractual terms of the instrument. The Santander UK group determines the classification of its financial assets and liabilities at initial recognition and measures a financial asset or financial liability at its fair value plus or minus, in the case of a financial asset or financial liability not at FVTPL, transaction costs that are incremental and directly attributable to the acquisition or issue of the financial asset or financial liability. Transaction costs of financial assets and financial liabilities carried at FVTPL are expensed in profit or loss. Immediately after initial recognition, an expected credit loss (ECL) allowance is recognised for financial assets measured at amortised cost and investments in debt instruments measured at FVOCI. A regular way purchase or sale is a purchase or sale of a financial asset under a contract whose terms require delivery of the asset within the timeframe established generally by regulation or convention in the marketplace concerned. Regular way purchases and sales of financial assets measured at amortised cost are recognised on settlement date; all other regular way purchases and sales of financial assets are recognised on trade date. b) Financial assets and liabilities i) Classification and subsequent measurement The Santander UK group classifies its financial assets in the measurement categories of amortised cost, FVOCI and FVTPL. Financial assets and financial liabilities are classified as FVTPL where there is a requirement to do so or where they are otherwise designated at FVTPL on initial recognition. Financial assets and financial liabilities which are required to be held at FVTPL include: – Financial assets and financial liabilities held for trading. – Debt instruments that do not have solely payments of principal and interest (SPPI) characteristics. Otherwise, such instruments are measured at amortised cost or FVOCI, and – Equity instruments that have not been designated as held at FVOCI. Financial assets and financial liabilities are classified as held for trading if they are derivatives or if they are acquired or incurred principally for the purpose of selling or repurchasing in the near-term, or form part of a portfolio of financial instruments that are managed together and for which there is evidence of short-term profit taking. In certain circumstances, other financial assets and financial liabilities are designated at FVTPL where this results in more relevant information. This may arise because it significantly reduces a measurement inconsistency that would otherwise arise from measuring assets or liabilities or recognising the gains or losses on them on a different basis, where the assets and liabilities are managed and their performance evaluated on a fair value basis or, in the case of financial liabilities, where it contains one or more embedded derivatives which are not closely related to the host contract. The classification and measurement requirements for financial asset debt and equity instruments and financial liabilities are set out below. Financial assets: debt instruments Debt instruments are those instruments that meet the definition of a financial liability from the issuer’s perspective, such as loans and government and corporate bonds. Classification and subsequent measurement of debt instruments depend on the Santander UK group’s business model for managing the asset, and the cash flow characteristics of the asset. Business model The business model reflects how the Santander UK group manages the assets in order to generate cash flows and, specifically, whether the Santander UK group’s objective is solely to collect the contractual cash flows from the assets or is to collect both the contractual cash flows and cash flows arising from the sale of the assets. If neither of these is applicable, such as where the financial assets are held for trading purposes, then the financial assets are classified as part of an ‘other’ business model and measured at FVTPL. Factors considered in determining the business model for a group of assets include past experience on how the cash flows for these assets were collected, how the assets’ performance is evaluated and reported to key management personnel, and how risks are assessed and managed. SPPI Where the business model is to hold assets to collect contractual cash flows or to collect contractual cash flows and sell, the Santander UK group assesses whether the assets’ cash flows represent SPPI. In making this assessment, the Santander UK group considers whether the contractual cash flows are consistent with a basic lending arrangement (i.e. interest includes only consideration for the time value of money, credit risk, other basic lending risks and a profit margin that is consistent with a basic lending arrangement). Where the contractual terms introduce exposure to risk or volatility that is inconsistent with a basic lending arrangement, the related asset is classified and measured at FVTPL. Financial assets with embedded derivatives are considered in their entirety when determining whether their cash flows are SPPI. Based on these factors, the Santander UK group classifies its debt instruments into one of the following measurement categories: – Amortised cost – Financial assets that are held for collection of contractual cash flows where those cash flows represent SPPI, and that are not designated at FVTPL, are measured at amortised cost. The carrying amount of these assets is adjusted by any ECL recognised and measured as presented in Note 13 . Interest income from these financial assets is included in ‘Interest and similar income’ using the effective interest rate method. When estimates of future cash flows are revised, the carrying amount of the respective financial assets is adjusted to reflect the new estimate discounted using the original effective interest rate. Any changes are recognised in the income statement. – FVOCI – Financial assets that are held for collection of contractual cash flows and for selling the assets, where the assets’ cash flows represent SPPI, and that are not designated at FVTPL, are measured at FVOCI. Movements in the carrying amount are recognised in OCI, except for the recognition of impairment gains or losses, interest revenue and foreign exchange gains and losses which are recognised in profit or loss. When the financial asset is derecognised, the cumulative gain or loss previously recognised in OCI is reclassified from equity to profit or loss and recognised in ‘Other operating income’. Interest income from these financial assets is included in ‘Interest and similar income’ using the effective interest rate method. – FVTPL – Financial assets that do not meet the criteria for amortised cost or FVOCI are measured at FVTPL. A gain or loss on a debt instrument that is subsequently measured at FVTPL, including any debt instruments designated at fair value, is recognised in profit or loss and presented in the income statement in ‘Other operating income’ in the period in which it arises. The Santander UK group reclassifies financial assets when and only when its business model for managing those assets changes. The reclassification takes place from the start of the first reporting period following the change. Such changes are expected to be very infrequent. Financial assets: equity instruments Equity instruments are instruments that meet the definition of equity from the issuer’s perspective, being instruments that do not contain a contractual obligation to pay cash and that evidence a residual interest in the issuer’s net assets. All equity investments are subsequently measured at FVTPL; management may elect, at initial recognition, to irrevocably designate an equity investment at FVOCI but has not currently done so. When this election is used, fair value gains and losses are recognised in OCI and are not subsequently reclassified to profit or loss, including on disposal. ECLs (and reversal of ECLs) are not reported separately from other changes in fair value. Dividends, when representing a return on such investments, continue to be recognised in profit or loss as other income when the right to receive payments is established. Gains and losses on equity investments at FVTPL are included in ‘Other operating income’ in the income statement. Financial liabilities Financial liabilities, which include deposits by banks, deposits by customers, debt securities in issue and subordinated liabilities, are classified as subsequently measured at amortised cost, except for: – Financial liabilities at FVTPL (see Note 22 ): this classification is applied to derivatives and other financial liabilities designated as such at initial recognition. Gains or losses on financial liabilities designated at FVTPL are presented partially in other comprehensive income (the amount of change in the fair value of the financial liability that is attributable to changes in the credit risk of that liability) and partially in profit or loss (the remaining amount of change in the fair value of the liability) – Financial liabilities arising from the transfer of financial assets which did not qualify for derecognition, whereby a financial liability is recognised for the consideration received for the transfer. In subsequent periods, the Santander UK group recognises any expense incurred on the financial liability, and – Financial guarantee contracts and loan commitments. Preference shares which carry a contractual obligation to transfer economic benefits are classified as financial liabilities and are presented in subordinated liabilities. The coupon on these preference shares is recognised in the income statement as interest expense on an amortised cost basis using the effective interest method. Contracts involving the receipt of cash on which customers receive an index-linked return are accounted for as equity index-linked deposits. The principal products are Capital Guaranteed/Protected Products which give the customers a limited participation in the upside growth of an equity index. In the event the index falls in price, a cash principal element is guaranteed/protected. The equity index-linked deposits contain embedded derivatives. These embedded derivatives, in combination with the principal cash deposit element, are designed to replicate the investment performance profile tailored to the return agreed in the contracts with customers. The cash principal element is accounted for as deposits by customers at amortised cost. The embedded derivatives are separated from the host instrument and are separately accounted for as derivatives. Sale and repurchase agreements (including stock borrowing and lending) Securities sold subject to a commitment to repurchase them at a predetermined price (repos) under which substantially all the risks and rewards of ownership are retained by the Santander UK group remain on the balance sheet and a liability is recorded in respect of the consideration received. Securities purchased under commitments to resell (reverse repos) are not recognised on the balance sheet and the consideration paid is recorded as an asset. The difference between the sale and repurchase price is treated as trading income in the income statement, except where the repo is not treated as part of the trading book, in which case the difference is recorded in interest income or expense. Securities lending and borrowing transactions are generally secured, with collateral in the form of securities or cash advanced or received. Securities borrowed are not reflected on the balance sheet. Collateral in the form of cash received or advanced is recorded as a deposit or a loan. Collateral in the form of securities is not recognised. Day One profit adjustments The fair value of a financial instrument on initial recognition is generally its transaction price (that is, the fair value of the consideration given or received). However, sometimes the fair value will be based on other observable current market transactions in the same instrument, without modification or repackaging, or on a valuation technique whose variables include only data from observable markets, such as interest rate yield curves, option volatilities and currency rates. When such evidence exists, the Santander UK group recognises a trading gain or loss at inception (Day One gain or loss), being the difference between the transaction price and the fair value. When significant unobservable parameters are used, the entire Day One gain or loss is deferred and is recognised in the income statement over the life of the transaction until the transaction matures, is closed out, the valuation inputs become observable, or an offsetting transaction is entered into. ii) Impairment of debt instrument financial assets The Santander UK group assesses on a forward-looking basis the ECL associated with its debt instrument assets carried at amortised cost and FVOCI and with the exposure arising from financial guarantee contracts and loan commitments. The Santander UK group recognises a loss allowance for such losses at each reporting date. The measurement of ECL reflects: – An unbiased and probability-weighted amount that is determined by evaluating a range of possible outcomes. – The time value of money, and – Reasonable and supportable information that is available without undue cost or effort at the reporting date about past events, current conditions and forecasts of future economic conditions. Grouping of instruments for losses measured on a collective basis We typically group instruments and assess them for impairment collectively where they share risk characteristics (as described in the Credit risk section of the Risk review) using one or more statistical models. Where we have used internal capital or similar models as the basis for our ECL models, this typically results in a large number of relatively small homogenous groups which are determined by the permutations of the underlying characteristics in the statistical models. We calculate separate collective provisions for instruments in Stages 1, 2 and 3 where the instrument is not individually assessed, as described below. Individually assessed impairments (IAIs) We assess significant Stage 3 cases individually. We do this for Corporate & Commercial Banking cases, but not for Business Banking cases in Retail & Business Banking which we assess collectively. To calculate the estimated loss, we estimate the future cash flows under several scenarios each of which uses case-specific factors and circumstances. We then probability-weight the net present value of the cash flows under each scenario to arrive at a weighted average provision requirement. We update our assessment process every quarter and more frequently if there are changes in circumstances that might affect the scenarios, cash flows or probabilities we apply. For more on how ECL is calculated, see the Credit risk section of the Risk review. – Write-off For secured loans, a write-off is only made when all collection procedures have been exhausted and the security has been sold and/or a claim made on any mortgage indemnity guarantee or other insurance. In the corporate loan portfolio, there may be occasions where a write-off occurs for other reasons, such as following a consensual restructure or refinancing of the debt or where the debt is sold for strategic reasons into the secondary market at a value lower than its face value. There is no threshold based on past due status beyond which all secured loans are written off as there can be significant variations in the time needed to enforce possession and sale of the security, especially due to the different legal frameworks that apply in different regions of the UK. For unsecured loans, a write-off is only made when all internal avenues of collecting the debt have been exhausted. Where appropriate the debt is passed over to external collection agencies. A past due threshold is applied to unsecured debt where accounts that are 180 days past due are written off unless there is a dispute awaiting resolution. Contact is made with customers with the aim to achieve a realistic and sustainable repayment arrangement. Litigation and/or enforcement of security is usually carried out only when the steps described above have been undertaken without success. All write-offs are assessed / made on a case-by-case basis, taking account of the exposure at the date of write-off, after accounting for the value from any collateral or insurance held against the loan. The exception to this is in cases where fraud has occurred, where the exposure is written off once investigations have been completed and the probability of recovery is minimal. The time span between discovery and write-off will be short and may not result in an impairment loss allowance being raised. The write-off policy is regularly reviewed. Write-offs are charged against previously established loss allowances. – Recoveries Recoveries of credit impairment charges are not included in the impairment loss allowance but are taken to income and offset against credit impairment charges. Recoveries of credit impairment charges are classified in the income statement as ‘Credit impairment charges’. iii) Modifications of financial assets The treatment of a renegotiation or modification of the contractual cash flows of a financial asset normally depends upon whether the renegotiation or modification is due to financial difficulties of the borrower or for other commercial reasons. – Contractual modifications due to financial difficulties of the borrower: where the Santander UK group modifies the contractual conditions to enable the borrower to fulfil their payment obligations, the asset is not derecognised. The gross carrying amount of the financial asset is recalculated as the present value of the renegotiated/modified contractual cash flows that are discounted at the financial asset’s original EIR and any gain or loss arising from the modification is recognised in the income statement. – Contractual modifications for other commercial reasons: an assessment is performed to determine whether the terms of the new agreement are substantially different from the terms of the existing agreement, after considering changes in the cash flows arising from the modified terms and the overall instrument risk profile. Where terms are substantially different, such modifications are treated as a new transaction resulting in derecognition of the original financial asset, and the recognition of a ‘new’ financial asset with any difference between the carrying amount of the derecognised asset and the fair value of the new asset is recognised in the income statement as a gain or loss on derecognition. Where terms are not substantially different, the carrying value of the financial asset is adjusted to reflect the present value of modified cash flows discounted at the original EIR with any gain or loss arising from modification recognised immediately in the income statement. Any other contractual modifications, such as where a regulatory authority imposes a change in certain contractual terms or due to legal reasons, are assessed on a case-by-case basis to establish whether or not the financial asset should be derecognised. For IBOR reform see Note 41 . iv) Derecognition other than on a modification Financial assets are derecognised when the rights to receive cash flows have expired or the Santander UK group has transferred its contractual right to receive the cash flows from the assets and either: (1) substantially all the risks and rewards of ownership have been transferred; or (2) the Santander UK group has neither retained nor transferred substantially all of the risks and rewards but has transferred control. Financial liabilities are derecognised when extinguished, cancelled or expired. c) Financial guarantee contracts and loan commitments Financial guarantee contracts are contracts that require the issuer to make specified payments to reimburse the holder for a loss it incurs because a specified debtor fails to make payments when due, in accordance with the terms of a debt instrument. Such financial guarantees are given to banks, financial institutions and others on behalf of customers to secure loans, overdrafts and other banking facilities. Financial guarantee contracts are initially measured at fair value and subsequently measured at the higher of the amount of the loss allowance, and the premium received on initial recognition less income recognised in accordance with the principles of IFRS 15. Loan commitments are measured as the amount of the loss allowance (determined in accordance with IFRS 9 as described in Credit risk section of the Risk review). The Santander UK group has not provided any commitment to provide loans at a below-market interest rate, or that can be settled net in cash or by delivering or issuing another financial instrument. For financial guarantee contracts and loan commitments, the loss allowance is recognised as a provision and charged to credit impairment charges in the income statement. The loss allowance in respect of revolving facilities is classified in loans and advances to customers to the extent of any drawn balances. The loss allowance in respect of undrawn amounts is classified in provisions. When amounts are drawn, any related loss allowance is transferred from provisions to loans and advances to customers.
Derivative financial instruments (derivatives)	Derivative financial instruments (derivatives) Derivatives are contracts or agreements whose value is derived from one or more underlying indices or asset values inherent in the contract or agreement, which require no or little initial net investment and are settled at a future date. Transactions are undertaken in interest rate, cross currency, equity, residential property and other index-related swaps, forwards, caps, floors, swaptions, as well as credit default and total return swaps, equity index contracts and exchange traded interest rate futures, and equity index options. Derivatives are held for risk management purposes. Derivatives are classified as held for trading unless they are designated as being in a hedge accounting relationship. The Santander UK group chooses to designate certain derivatives as in a hedging relationship if they meet specific criteria, as further described in ‘Hedge accounting’ below. Derivatives are recognised initially (on the date on which a derivative contract is entered into), and are subsequently remeasured, at their fair value. Fair values of exchange-traded derivatives are obtained from quoted market prices. Fair values of over-the-counter derivatives are estimated using valuation techniques, including discounted cash flow and option pricing models. Certain derivatives may be embedded in hybrid contracts. If the hybrid contract contains a host that is a financial asset, then the Santander UK group assesses the entire contract as described in the financial asset section above for classification and measurement purposes. Otherwise, embedded derivatives are treated as separate derivatives when their economic characteristics and risks are not closely related to those of the host contract; the terms of the embedded derivative would meet the definition of a stand-alone derivative if they were contained in a separate contract; and the combined contract is not held for trading or designated at fair value. These embedded derivatives are measured at fair value with changes in fair value recognised in the income statement. Contracts containing embedded derivatives are not subsequently reassessed for separation unless either there has been a change in the terms of the contract which significantly modifies the cash flows (in which case the contract is reassessed at the time of modification) or the contract has been reclassified (in which case the contract is reassessed at the time of reclassification). All derivatives are carried as assets when their fair value is positive and as liabilities when their fair value is negative, except where netting is permitted. The method of recognising fair value gains and losses depends on whether derivatives are held for trading or are designated as hedging instruments and, if the latter, the nature of the risks being hedged. Gains and losses from changes in the fair value of derivatives held for trading are recognised in the income statement and included in Other operating income.
Offsetting financial assets and liabilities	Offsetting financial assets and liabilities Financial assets and liabilities including derivatives are offset and the net amount reported in the balance sheet when there is a legally enforceable right to set off the recognised amounts and there is an intention to settle on a net basis or realise the asset and settle the liability simultaneously. The Santander UK group is party to a number of arrangements, including master netting arrangements under industry standard agreements which facilitate netting of transactions in jurisdictions where netting agreements are recognised and have legal force. These netting arrangements do not generally result in an offset of balance sheet assets and liabilities for accounting purposes, as transactions are usually settled on a gross basis.
Hedge accounting	Hedge accounting The Santander UK group applies hedge accounting to represent, to the maximum possible extent permitted under accounting standards, the economic effects of its risk management strategies. Derivatives are used to hedge exposures to interest rates and exchange rates . At the time a financial instrument is designated as a hedge (i.e. at the inception of the hedge), the Santander UK group formally documents the relationship between the hedging instrument(s) and hedged item(s), its risk management objective and strategy for undertaking the hedge. The documentation includes the identification of each hedging instrument and respective hedged item, the nature of the risk being hedged (including the benchmark interest rate being hedged in a hedge of interest rate risk) and how the hedging instrument’s effectiveness in offsetting the exposure to changes in the hedged item’s fair value attributable to the hedged risk is to be assessed. Accordingly, the Santander UK group formally assesses, both at the inception of the hedge and on an ongoing basis, whether the hedging derivatives have been and will be highly effective in offsetting changes in the fair value attributable to the hedged risk during the period that the hedge is designated. A hedge is normally regarded as highly effective if, at inception and throughout its life, the Santander UK group can expect, and actual results indicate, that changes in the fair value or cash flow of the hedged items are effectively offset by changes in the fair value or cash flow of the hedging instrument. If at any point it is concluded that it is no longer highly effective in achieving its documented objective, hedge accounting is discontinued. Where derivatives are held for risk management purposes, and when transactions meet the required criteria for documentation and hedge effectiveness, the derivatives may be designated as either: (i) hedges of the change in fair value of recognised assets or liabilities or firm commitments (fair value hedges); (ii) hedges of the variability in highly probable future cash flows attributable to a recognised asset or liability, or a forecast transaction (cash flow hedges); or (iii) a hedge of a net investment in a foreign operation (net investment hedges). The Santander UK group applies fair value and cash flow hedge accounting, but not hedging of a net investment in a foreign operation. a) Fair value hedge accounting Changes in the fair value of derivatives that are designated and qualify as fair value hedges are recorded in the income statement, together with the changes in the fair value of the hedged asset or liability that are attributable to the hedged risk. Where the hedged item is measured at amortised cost, the fair value changes due to the hedged risk adjust the carrying amount of the hedged asset or liability. Changes in the fair value of portfolio hedged items are presented separately in the consolidated balance sheet in macro hedge of interest rate risk and recognised in the income statement. If the hedge no longer meets the criteria for hedge accounting, changes in the fair value of the hedged item attributable to the hedged risk are no longer recognised in the income statement. For fair value hedges of interest rate risk, the cumulative adjustment that has been made to the carrying amount of the hedged item is amortised to the income statement using the effective interest method over the period to maturity. For portfolio hedged items, the cumulative adjustment is amortised to the income statement using the straight-line method over the period to maturity. b) Cash flow hedge accounting The effective portion of changes in the fair value of qualifying cash flow hedges is recognised in other comprehensive income in the cash flow hedging reserve. The gain or loss relating to the ineffective portion is recognised immediately in the income statement. Amounts accumulated in equity are reclassified to the income statement in the periods in which the hedged item affects profit or loss. When a hedging instrument expires or is sold, or when a hedge no longer meets the criteria for hedge accounting, any cumulative gain or loss existing in equity at that time remains in equity and is recognised in the income statement when the forecast transaction is ultimately recognised in the income statement. When a forecast transaction is no longer expected to occur, the cumulative gain or loss that was reported in equity is immediately transferred to the income statement. The Santander UK group is exposed to cash flow interest rate risk on its floating rate assets, foreign currency risk on its fixed rate debt issuances denominated in foreign currency and equity price risk arises from the Santander UK group operating the Employee Sharesave scheme. Cash flow hedging is used to hedge the variability in cash flows arising from these risks.
Securitisation transactions	Securitisation transactions The Santander UK group has entered into arrangements where undertakings have issued mortgage-backed and other asset-backed securities or have entered into funding arrangements with lenders in order to finance specific loans and advances to customers. The Santander UK group has also entered into synthetic securitisation arrangements, as part of significant risk transfer (SRT) transactions to reduce its risk-weighted assets, where undertakings have issued credit-linked notes, and in some cases deposited the funds raised as collateral, for credit protection in respect of specific loans and advances to customers. As the Santander UK group has retained substantially all the risks and rewards of the underlying assets, such financial instruments continue to be recognised on the balance sheet, and a liability recognised for the proceeds of the funding transaction, or in the case of SRT transactions, collateral deposited.
Impairment of non-financial assets	Impairment of non-financial assets At each balance sheet date, or more frequently when events or changes in circumstances dictate, property plant and equipment (including operating lease assets) and intangible assets (including goodwill) are assessed for indicators of impairment. If indications are present, these assets are subject to an impairment review. The impairment review comprises a comparison of the carrying value of the asset or cash generating unit with its recoverable amount: the higher of the asset’s or cash-generating unit’s fair value less costs to sell and its value in use. The cash-generating unit represents the lowest level at which non-financial assets, including goodwill, are monitored for internal management purposes and is not larger than an operating segment. The fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Value in use is calculated by discounting management’s expected future cash flows obtainable as a result of the asset’s continued use (after making allowance for increases in regulatory capital requirements), including those resulting from its ultimate disposal, at a market-based discount rate on a pre- tax basis. The recoverable amounts of goodwill have been based on value in use calculations. For conducting goodwill impairment reviews, cash generating units are the lowest level at which management monitors the return on investment on assets.
Leases (as lessor)	Leases (as lessor) Operating lease assets are recorded at cost and the difference between cost and residual value (RV) is depreciated over the life of the asset. Operating lease rental income and depreciation is recognised on a straight-line basis over the life of the asset. After initial recognition, residual values are reviewed regularly, and any changes are recognised prospectively through remaining depreciation charges. Amounts due from lessees under finance leases and hire purchase contracts are recorded as receivables at the amount of the Santander UK group’s net investment in the leases. Finance lease income is allocated to accounting periods to reflect a constant periodic rate of return on the Santander UK group’s net investment outstanding in respect of the leases and hire purchase contracts. A provision is recognised to reflect a reduction in any anticipated unguaranteed RV. A provision is also recognised for voluntary termination of the contract by the customer, where appropriate.
Income taxes, including deferred taxes	Income taxes, including deferred taxes The tax expense represents the sum of the income tax currently payable and deferred income tax. A current tax liability for the current or prior period is measured at the amount expected to be paid to the tax authorities. Where the amount of the final tax liability is uncertain or where a position is challenged by a taxation authority, the liability recognised is the most likely outcome. Where a most likely outcome cannot be determined, a weighted average basis is applied. Deferred tax is calculated at the tax rates that are expected to apply in the period when the liability is settled, or the asset is realised based on rates enacted or substantively enacted at the balance sheet date. Deferred tax is charged or credited in the income statement, except when it relates to items recognised in other comprehensive income or directly in equity, in which case the deferred tax is also recognised in other comprehensive income or directly in equity. Deferred and current tax assets and liabilities are only offset when they arise in the same tax reporting group and where there is both the legal right and the intention to settle on a net basis or to realise the asset and settle the liability simultaneously.
Cash and cash equivalents	Cash and cash equivalents For the purposes of the cash flow statement, cash and cash equivalents comprise balances with less than three months maturity from the date of acquisition, including cash and non-restricted balances with central banks, treasury bills and other eligible bills, loans and advances to banks, reverse repurchase agreements and short-term investments in securities. Balances with central banks represent amounts held at the Bank of England as part of the Santander UK group’s liquidity management activities. It includes certain minimum cash ratio deposits held for regulatory purposes and reserves collateralised accounts in respect of Santander UK’s participation in certain payments schemes which are required to be maintained with the Bank of England and are restricted balances.
Provisions and contingent liabilities	Provisions and contingent liabilities (see 'Critical judgements and accounting estimates') Provisions are recognised for present obligations arising as consequences of past events where it is more likely than not that a transfer of economic benefits will be necessary to settle the obligation, and it can be reliably estimated. Customer remediation provisions are made for the estimated cost of making redress payments with respect to the past sales of products, using conclusions such as the number of claims the number of those that will be upheld, the estimated average settlement per case and other related costs. Provision is made for the anticipated cost of restructuring, including redundancy costs, when an obligation exists. An obligation exists when the Santander UK group has a detailed formal plan for restructuring a business, has raised valid expectations in those affected by the restructuring, and has started to implement the plan or announce its main features. When a leasehold property ceases to be used in the business, provision is made where the unavoidable costs of the future obligations relating to the lease are expected to exceed anticipated rental income. The net costs are discounted using market rates of interest to reflect the long-term nature of the cash flows. Loan commitments are measured as the amount of the loss allowance, determined in line with IFRS 9 as set out in the Credit risk section of the Risk review. Contingent liabilities are possible obligations whose existence will be confirmed only by certain future events or present obligations where the transfer of economic benefit is uncertain or cannot be reliably measured. Contingent liabilities are not recognised but are disclosed unless they are remote.
Critical judgements and accounting estimates	Critical judgements and accounting estimates The preparation of Santander UK's consolidated financial statements in accordance with IFRS requires management to make judgements and assumptions in applying the accounting policies that affect the reported amounts of assets, liabilities, income and expenses. Due to the inherent uncertainty in making estimates, actual results reported in future periods may be based on amounts which differ from those estimates. Estimates, judgements and assumptions are continually evaluated and are based on historical experience and other factors, including expectations of future events that are believed to be reasonable under the circumstances. There has been no change in the inherent sensitivity of the areas of judgement in the period. Management have considered the impact of developments in principal risks and uncertainties, as set out in the Risk review, on critical judgements and accounting estimates. The significant judgements, apart from those involving estimation, made by management in applying Santander UK's accounting policies in these financial statements (key judgements) and the key sources of estimation uncertainty that may have a significant risk of causing a material adjustment to the carrying amount of assets and liabilities within the next financial year (key estimates), which together are considered critical to Santander UK's results and financial position, are as follows: a) Credit impairment charges The application of the ECL impairment methodology for calculating credit impairment allowances is highly susceptible to change from period to period. The methodology requires management to make judgmental assumptions in determining the estimates. Any significant difference between the estimated amounts and actual amounts could have a material impact on the future financial results and financial condition. The impact of the cost of living crisis has increased the uncertainty around ECL impairment calculations and has required management to make additional judgements and accounting estimates that affect the amount of assets and liabilities at the reporting date and the amount of income and expenses in the reporting period. The key additional judgements due to the impact of the cost of living crisis mainly reflect the increased uncertainty around forward-looking economic data and the need for additional judgemental adjustments. Key judgements – Determining an appropriate definition of default – Establishing the criteria for a significant increase in credit risk (SICR) and, for corporate borrowers, internal credit risk rating – Determining the need for any judgemental adjustments – Determining the need to assess corporate Stage 3 exposures individually Key estimates – Forward-looking multiple economic scenario assumptions – Probability weights assigned to multiple economic scenarios For more on each of these key judgements and estimates, see 'Critical judgements and accounting estimates applied in calculating ECL' in the ‘Credit risk – credit risk management’ section of the Risk review. Sensitivity of ECL allowance For detailed disclosures, see 'Sensitivity of ECL allowance' in the ‘Credit risk – credit risk management’ section of the Risk review. b) Provisions and contingent liabilities Key judgements – Determining whether a present obligation exists – Determining the likely outcome of future legal decisions Key estimates – Probability, timing, nature and amount of any outflows that may arise from past events Included in Litigation and other regulatory provisions in Note 29 are amounts in respect of management’s best estimates of liability relating to a legal dispute regarding allocation of responsibility for a specific PPI portfolio of complaints. Note 31 provides disclosure relating to ongoing factual issues and reviews that could impact the timing and amount of any outflows. Note 31 includes disclosure relating to an investigation in relation to the historical involvement of Santander UK plc, Santander Financial Services plc and Cater Allen International Limited (all subsidiaries of Santander UK Group Holdings plc) in German dividend tax arbitrage transactions. It also includes disclosure relating to the historical use of discretionary commission arrangements in Santander Consumer (UK) plc. These judgements are based on the specific facts available and often require specialist professional advice. There can be a wide range of possible outcomes and uncertainties, particularly in relation to legal actions, and regulatory and consumer credit matters. As a result, it is often not possible to make reliable estimates of the likelihood and amount of any potential outflows, or to calculate any resulting sensitivities. For more on these key judgements and estimates, see Notes 29 and 31 . c) Pensions The Santander UK group operates a number of defined benefit pension schemes as described in Note 30 and estimates their position as described in the accounting policy ‘Pensions and other post retirement benefits’. Key judgements – Setting the criteria for constructing the corporate bond yield curve used to determine the discount rate – Determining the methodology for setting the inflation assumption Key estimates – Discount rate applied to future cash flows – Rate of price inflation – Expected lifetime of the schemes' members – Valuation of pension fund assets whose values are not based on market observable data For more on each of these key judgements and estimates, see Note 30 . Sensitivity of defined benefit pension scheme estimates For detailed disclosures, see ‘Actuarial assumption sensitivities’ in Note 30 . The Scheme is invested in certain assets whose values are not based on market observable data, such as investments in private equity funds and property. Due diligence has been conducted to support the values obtained in respect of these assets are appropriate and represent fair value. Given the nature of these investments, we are unable to prepare sensitivities on how their values could vary as market conditions or other variables change. d) Goodwill The carrying amount of goodwill is based on the application of judgements including the basis of goodwill impairment calculation assumptions. Santander UK undertakes an annual assessment to evaluate whether the carrying amount of goodwill is impaired, carrying out this assessment more frequently if reviews identify indicators of impairment or when events or changes in circumstances dictate. Key judgements: – Determining the basis of goodwill impairment testing and the methodology for determining the carrying value of CGUs, including the need for planning assumptions and internal capital allocations Key estimates: – Forecast cash flows for cash generating units, including estimated allocations of regulatory capital – Growth rate beyond initial cash flow projections – Discount rates which factor in risk-free rates and applicable risk premiums All of these variables are subject to fluctuations in external market rates and economic conditions beyond management’s control Santander UK Group undertakes an annual assessment to evaluate whether the carrying amount of goodwill is impaired, carrying out this assessment more frequently if reviews identify indicators of impairment or when events or changes in circumstances dictate. The estimation of future cash flows and the level to which they are discounted is inherently uncertain and requires significant judgement and is subject to potential change over time. For more on each of these key judgements and estimates, see Note 20 . Sensitivity of goodwill For detailed disclosures, see ‘Sensitivities of key assumptions in calculating VIU’ in Note 20 .
Segmentation of business	The segmental data is prepared on a statutory basis of accounting, in line with the accounting policies set out in Note 1 . Transactions between segments are on normal commercial terms and conditions. Internal charges and internal UK transfer pricing adjustments are reflected in the results of each segment, and eliminate on consolidation. Revenue sharing agreements are used to allocate external customer revenues to a segment on a reasonable basis. Funds are ordinarily reallocated between segments, resulting in funding cost transfers disclosed in operating income. Interest charged for these funds is based on Santander UK’s cost of wholesale funding. Interest income and interest expense have not been reported separately. The majority of segment revenues are interest income in nature and net interest income is relied on primarily to assess segment performance and to make decisions on the allocation of segment resources.

Credit Risk (Tables)

Credit Risk (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of credit risk exposure [abstract]
Disclosure of Exposures to Credit Risk by Segment	Exposures to credit risk arise in our business segments from: Retail and Business Banking Consumer Finance Corporate & Commercial Banking Corporate Centre In Mortgages: – Residential mortgages for customers with good credit quality (prime lending). – We provide these mostly for owner- occupiers, with buy-to-let mortgages for non-professional landlords. In Everyday Banking: – Unsecured lending to individuals, such as loans, credit cards and overdrafts. – Banking services to businesses with turnover up to £ 6.5 m per annum and simpler borrowing needs. We offer loans, credit cards and overdrafts. – Financing for cars, vans, motorbikes and leisure vehicles through Santander Consumer (UK) plc (SCUK). – Through our joint ventures, Hyundai Capital UK Ltd and Volvo Car Financial Services UK Limited, we provide retail point of sale customer finance and wholesale finance facilities (stock finance). – Loans, bank accounts, treasury services, invoice discounting, cash transmission, trade finance and asset finance. – We provide these to SMEs and mid- sized corporates with turnover up to £ 500 m per annum, Commercial Real Estate and Social Housing associations. – Asset and liability management of our balance sheet. – Exposures include financial institutions (derivatives and other treasury products), structured products, and sovereign and supranational assets chosen for diversification and liquidity.
Disclosure of Type of Credit Risk Mitigation by Portfolio	The types of credit risk mitigation, including collateral, across each of our portfolios are: Portfolio Description Residential mortgages Collateral is in the form of a first legal charge over the property. Before we grant a mortgage, the property is valued either by a surveyor or using automated valuation methodologies where our confidence in the accuracy of this method is high. Unsecured lending There is no collateral or security tied to the loan that can be used to mitigate any potential loss if the customer does not pay us back. Business banking services Business banking lending is unsecured. When lending to incorporated businesses, we typically obtain personal guarantees from each director, but we do not treat these as collateral. We consider the UK Government guarantee supporting losses on amounts lent under its Coronavirus Loan Schemes as collateral with 100% for Bounce Back Loan Scheme (BBLS) and 80% for Coronavirus Business Interruption Loan Scheme (CBILS). The type of credit risk mitigation, including collateral, is: Portfolio Description Consumer (auto) finance Collateral is in the form of legal ownership of the vehicle for most loans, with the customer being the registered keeper. Only a very small proportion of business is underwritten as a personal loan. In these cases, there is no collateral or security tied to the loan. We use a leading vehicle valuation company to assess the LTV at the proposal stage to ensure the value of the vehicle is appropriate. The types of credit risk mitigation, including collateral, across each of our portfolios are as follows. In addition, from time to time, at a portfolio level we execute significant risk transfer transactions, which typically reduce RWAs. Portfolio Description SME and mid corporate Includes secured and unsecured lending. We can take mortgage debentures or a first charge on commercial property as collateral. Before agreeing the loan, we get an independent professional valuation of the property. Loan agreements typically allow us to obtain revaluations during the term of the loan. We can also take guarantees, but we do not treat them as collateral unless they are supported by a tangible asset charged to us. We also lend against assets (like vehicles and equipment) and invoices for some customers. We value assets before we lend. For invoices, we review the customers' ledgers regularly and lend against debtors who meet agreed criteria. Commercial Real Estate We take a first charge on commercial property as collateral. The loan is subject to criteria such as the property condition, age and location, tenant quality, lease terms and length, and the sponsor’s experience and creditworthiness. Before advancing the loan and where appropriate, a bank representative visits the property. We also get an independent professional valuation which typically includes a site visit. Loan agreements typically allow us to obtain revaluations during the term of the loan. Social Housing We take a first charge on portfolios of residential real estate owned and let by UK Housing Associations as collateral, in most cases. We revalue this every three to five years (in line with industry practice), using the standard methods for property used for Social Housing. The types of credit risk mitigation, including collateral, across each of our portfolios are as follows. In addition, from time to time, at a portfolio level we execute significant risk transfer transactions, which typically reduce RWAs. Portfolio Description Sovereign and Supranational In line with market practice, there is no collateral against these assets. Structured Products These are our High Quality Liquid Assets (HQLA) in our Eligible Liquidity Pool. They are mainly Asset Backed Securities (ABS) and covered bonds, which hold senior positions in the creditor hierarchy. Their credit rating reflects over-collateralisation in the structure and the assets that underpin their cash flows. Financial Institutions We use standard legal agreements to reduce credit risk via netting and collateralisation on derivatives, repos and reverse repos, and stock borrowing/lending. We also reduce risk by clearing trades through central counterparties (CCPs) where possible.
Disclosure of Types of Forbearance	The main types of forbearance we offer are: Action Description Term extension We can extend the loan term, making each monthly payment smaller. We may offer this if the customer is up to date with payments but shows signs of financial difficulties. We may also offer this if the loan is about to mature and refinancing is not possible on market terms. Interest-only Historical interest-only payments due to financial difficulties are classed as forborne. For corporate customers, interest-only concessions are considered on a case by case basis. Concessions are only granted if the nature of the financial difficulties is assessed to be temporary. Counterparties are expected to recover in full and resume making full capital and interest payments once they are in a stronger financial position. Other payment rescheduling, including capitalisation For retail customers, we may add the arrears to the mortgage balance (this is known as capitalisation) if they cannot afford to increase their monthly payment to pay off their arrears in a reasonable time but have been making their monthly payments, usually for at least six months. We can also capitalise property charges due to a landlord. We pay them for the customer to avoid the lease being forfeited. We may combine this help with term extensions and, in the past, interest-only concessions. In certain cases, we may offer interest rate concessions. For corporate customers, we may lower or stop their payments until they have time to recover. We may reschedule payments to better match the customer’s cash flow – for example if the business is seasonal - or provide a temporary increase in facilities to cover peak demand ahead of their trading improving. We might do this by arrears capitalisation or drawing from an overdraft. We may also offer to provide new facilities, interest rate concessions and interest roll-up. In rare cases, we agree to forgive or reduce part of the debt.
Disclosure of Other Ways to Manage Debt when Cutomer are in Financial Difficulty	When customers are in financial difficulty, we can also manage debt in other ways, depending on the facts of the specific case: Action Description Waiving or changing covenants If a borrower breaks a covenant, we can either waive it or change it, taking their latest and future financial position into account. We may also add a condition on the use of any surplus cash (after operating costs) to pay down their debt to us. Asking for more collateral or guarantees If a borrower has unencumbered assets, we may accept more collateral in return for revised financing terms. We may also take a guarantee from companies in the same group and/or major shareholders. We only do this where we believe the guarantor can meet their commitment. Asking for more equity Where a borrower can no longer pay the interest on their debt, we may accept fresh equity capital from new or existing investors to change the capital structure in return for better terms on the existing debt.
Disclosure of Key Metrics to Measure and Control Credit Risk	We use a number of key metrics to measure and control credit risk, as follows: Metric Description Expected Credit Loss (ECL) ECL tells us what credit risk is expected to cost us either over the next 12 months or over the lifetime of the exposure where there is evidence of a SICR since origination. We explain how we calculate ECL below. Stages 1, 2 and 3 We assess each facility’s credit risk profile to determine which stage to allocate them to, and we monitor where there is a SICR and transfers between the Stages including monitoring of coverage ratios for each stage. Stage 3 ratio The Stage 3 ratio is the sum of Stage 3 drawn and Stage 3 undrawn assets divided by the sum of total drawn assets and Stage 3 undrawn assets. The Stage 3 ratio is a key indicator used to monitor underlying asset performance. Expected Loss (EL) EL is based on the CRD IV regulatory capital rules and gives us another view of credit risk. It is the product of the probability of default, exposure at default and loss given default, and we include direct and indirect costs. We base it on our risk models and our assessment of each customer’s credit quality. The rest of our Risk review, impairments, losses and loss allowances refer to calculations in accordance with IFRS, unless we specifically say they relate to CRD IV. For our IFRS impairment accounting policy, see Note 1 to the Consolidated Financial Statements.
Schedule of Macroeconomic Assumptions for Each Five Scenarios	Upside Base case Downside 1 Stubborn Inflation Downside 2 Weighted (4) % % % % % % GDP (1) 2022 (actual) 4.3 4.3 4.3 4.3 4.3 4.3 2023 0.6 0.5 0.5 0.5 0.3 0.5 2024 1.0 0.4 (0.1) (1.8) (3.3) (0.4) 2025 2.1 1.3 0.2 (0.9) (1.4) 0.6 2026 2.4 1.5 0.5 0.4 0.6 1.1 2027 2.4 1.4 0.3 0.7 2.2 1.4 2028 2.4 1.4 0.3 0.8 2.6 1.4 5-year average increase/decrease 2.1 1.2 0.3 (0.2) 0.1 N/A Peak/(trough) at (2)(3) — — (0.2) (2.8) (5.1) (1.1) Bank Rate (1) 2022 (actual) 3.50 3.50 3.50 3.50 3.50 3.50 2023 5.25 5.25 5.25 5.25 5.25 5.25 2024 4.25 4.50 5.25 6.50 3.75 4.88 2025 3.25 3.50 4.00 5.00 2.00 3.68 2026 2.75 3.25 3.25 3.75 2.00 3.18 2027 2.75 3.00 3.00 3.00 2.50 2.93 2028 2.75 3.00 3.00 3.00 2.50 2.93 5-year end period 2.75 3.00 3.00 3.00 2.50 N/A Peak/(trough) at 5.25 5.25 5.75 6.50 5.25 5.55 HPI (1) 2022 (actual) 5.0 5.0 5.0 5.0 5.0 5.0 2023 (1.7) (2.2) (4.7) (6.3) (7.8) (3.8) 2024 2.0 (1.0) (11.7) (18.8) (25.8) (7.8) 2025 6.5 2.5 3.4 3.6 3.6 3.3 2026 5.1 3.0 2.1 1.6 1.6 2.7 2027 4.0 3.0 3.0 1.6 1.6 2.7 2028 3.6 3.0 3.1 1.8 1.8 2.7 5-year average increase/decrease 4.3 2.0 (0.8) (3.3) (5.4) N/A Peak/(trough) at (2) (3.7) (6.5) (17.5) (25.5) (33.0) (13.8) Unemployment (1) 2022 (actual) 3.7 3.7 3.7 3.7 3.7 3.7 2023 4.3 4.3 4.3 4.3 4.4 4.3 2024 4.3 4.8 4.8 5.6 8.5 5.3 2025 3.7 4.4 4.9 5.9 8.0 5.1 2026 3.4 4.3 5.2 6.2 7.4 5.0 2027 3.0 4.3 5.4 6.1 6.8 4.9 2028 3.0 4.2 5.3 5.8 6.2 4.7 5-year end period 3.0 4.2 5.3 5.8 6.2 N/A Peak/(trough) at 4.5 4.8 5.5 6.2 8.5 5.5 (1) GDP is the calendar year annual growth rate, HPI is Q4 annual growth rate and all other data points are at 31 December in the year indicated. (2) GDP peak taken from GDP level at Q2-23 and HPI peak taken from HPI level at Q3-22. (3) Reported as Peak/(trough) from 2023 to align with other metrics. (4) The weighted peak to trough and 5 year peak calculations are based on the annual profiles shown. The table below sets out our macroeconomic assumptions and their evolution throughout the forecast period for each of the five scenarios at 31 December 2022 : Upside Base case Downside 1 Stubborn Inflation Downside 2 Weighted (5) % % % % % % GDP (1) 2021 (actual) 7.5 7.5 7.5 7.5 7.5 7.5 2022 4.4 4.4 4.3 4.2 3.7 4.3 2023 (1.0) (1.3) (1.9) (2.7) (6.4) (2.2) 2024 0.8 0.5 (0.3) (0.9) (0.7) — 2025 2.0 1.6 0.5 0.2 1.7 1.2 2026 2.0 1.5 0.4 0.6 1.5 1.2 5-year average increase/decrease 1.2 0.8 (0.2) (0.5) (0.6) 0.3 Cumulative growth/(fall) to peak/(trough) (2)(4) 6.0 3.8 (0.8) (2.2) (3.1) 1.3 Bank Rate (1) 2021 (actual) 0.25 0.25 0.25 0.25 0.25 0.25 2022 3.50 3.50 3.50 3.50 3.50 3.50 2023 3.75 4.00 3.50 6.00 3.75 4.29 2024 3.00 3.25 2.75 5.50 3.00 3.59 2025 2.50 2.75 2.50 3.50 2.75 2.85 2026 2.25 2.50 2.25 3.00 2.50 2.55 5-year end period 2.25 2.50 2.25 3.00 2.50 2.55 Peak/(trough) at (3) 3.75 4.00 3.50 6.00 4.00 4.31 HPI (1) 2021 (actual) 8.7 8.7 8.7 8.7 8.7 8.7 2022 7.6 7.0 7.6 7.6 7.6 7.3 2023 (8.8) (10.0) (10.0) (10.9) (15.8) (10.7) 2024 (4.3) — (6.7) (8.8) (14.3) (4.4) 2025 0.6 2.0 (3.1) (4.9) (4.1) (0.8) 2026 4.1 3.0 (0.2) (0.6) 4.7 2.0 5-year average increase/decrease (0.7) (0.6) (3.8) (4.7) (4.8) (2.3) Peak/(trough) at (3) (12.8) (11.2) (19.0) (23.1) (30.7) (16.8) Unemployment (1) 2021 (actual) 4.0 4.0 4.0 4.0 4.0 4.0 2022 3.7 3.8 3.7 3.7 4.4 3.8 2023 4.7 4.7 5.1 5.5 8.5 5.3 2024 4.5 5.1 5.4 5.9 8.0 5.6 2025 4.5 4.5 5.8 6.4 7.4 5.4 2026 4.4 4.3 6.1 6.6 6.8 5.3 5-year end period 4.2 4.3 6.1 6.4 6.2 5.2 Peak/(trough) at (3) 4.7 5.1 6.1 6.6 8.5 5.9 (1) GDP is the calendar year annual growth rate, HPI is Q4 annual growth rate and all other data points are at 31 December in the year indicated. (2) This is the cumulative growth for the 5-year period. (3) For GDP and house price growth it is the peak to trough change within the 5-year period; for the unemployment rate it is the peak; and for Bank Rate it is the peak or trough. (4) If we had calculated GDP on the peak/(trough) basis as adopted for 2023 our upside scenario would have been (1.5%); base case scenario (1.9%); downside 1 (2.7%); stubborn inflation (4.0%); downside 2 (8.8%). (5) The weighted peak to trough and 5-year peak calculations are based on the annual profiles shown.
Disclosure of Scenario Weights Applied To Scenarios	The scenario weights we applied for 2023 and 2022 were: Upside Base case Downside 1 Stubborn Inflation Downside 2 Weighted Scenario weights % % % % % % 2023 10 50 10 20 10 100 2022 5 50 15 20 10 100
Disclosure of Definition of Default by Segment	We define a financial instrument as in default (i.e. credit impaired) for the purpose of calculating ECL if it is more than three months past due, or if we have data that suggests the customer is unlikely to pay. The data we have on customers varies across our business segments. It typically includes where: Retail and Business Banking and Consumer Finance – They have been reported bankrupt or insolvent and are in arrears – Their loan term has ended, but they still owe us money more than three months later – They have had forbearance while in default and have failed to perform under the new arrangement terms, or have had multiple forbearance. Performing forborne accounts while not in default are reported in Stage 2 – We have suspended their fees and interest because they are in financial difficulties – We have repossessed the property. Corporate & Commercial Banking and Corporate Centre – They have had a winding up notice issued, or something happens that is likely to trigger insolvency – such as another lender calls in a loan – Something happens that makes them less likely to be able to pay us – such as they lose an important client or contract – They have regularly missed or delayed payments, even though they have not gone over the three-month limit for default – Their loan is unlikely to be refinanced or repaid in full on maturity – Their loan has an excessive LTV that is unlikely to be resolved, such as by a change in planning policy, pay-downs, or increase in market value – Loans restructured under financial difficulties, classified as forborne transactions, in last 12 months.
Disclosure of Quantitative Criteria to Identify When Exposure Has Increased Credit Risk	The criteria for 2023 and 2022 were: Retail and Business Banking Consumer Finance (2) Corporate & Commercial Banking Corporate Centre Mortgages Everyday Banking (1) Personal loans Credit cards Overdrafts 30 bps 30 bps 340 bps 260 bps 300 bps 30 bps Internal rating method (1) For larger business banking customers, we apply the same criteria that we use for Corporate & Commercial Banking. (2) Consumer Finance use the comparison of lifetime PDs to determine Stage allocation, unlike other products which first turn the lifetime PD into an average yearly PD (annualised) and then do the comparison.
Disclosure of Qualitative Criteria to Identify When Exposure Has Increased Credit Risk	We also use qualitative criteria to identify where an exposure has increased in credit risk, independent of changes in PD. The criteria for 2023 and 2022 were: Retail and Business Banking Consumer Finance Corporate & Commercial Banking Corporate Centre Mortgages Everyday Banking (1) Personal loans Credit cards Overdrafts – In forbearance – Default in last 24m – 30 Days past due (DPD) in last 12m – Bankrupt – £100+ arrears – In Collections – Default in last 12m – £50+ arrears – In forbearance – Default in last 12m – In Collections – £100+ arrears – Behaviour score indicators – Fees suspended – Default in last 12m – Debit dormant >35 days – Any excess in month – In forbearance – Deceased or Insolvent – Court ‘Return of goods’ order or Police watchlist – Agreement terminated – Payment holiday – Cash Collection – In forbearance – Default in last 12m – Watchlist: proactive management – Default at proxy origination – Watchlist: proactive management (1) For larger business banking customers, we apply the same criteria that we use for Corporate & Commercial Banking.
Disclosure of ECL by Segment	Retail and Business Banking Everyday Banking Consumer Finance CCB Corporate Centre Total Mortgages Credit Cards Other 2023 £m £m £m £m £m £m £m Modelled ECL 132 123 123 62 240 — 680 Individually assessed 4 — — — 124 — 128 ECL before JAs 136 123 123 62 364 — 808 JAs (excluding Affordability and Cost of Living JAs) Long-term indeterminate arrears 16 — — — — — 16 12+ months in arrears 14 — — — — — 14 UPL loss floor — — 6 — — — 6 Model underestimation 36 — — — — — 36 Corporate single large exposure — — — — 23 — 23 Other 12 1 3 4 (31) — (11) Total JAs (excluding Affordability and Cost of Living JAs) 78 1 9 4 (8) — 84 Affordability and Cost of Living JAs Corporate lending to segments affected by supply chain pressures — — — — 24 — 24 Secured affordability 9 — — 4 — — 13 Unsecured affordability — 16 22 — — — 38 Mortgage refinancing risk 19 — — — — — 19 SME debt burden — — 6 — — — 6 Total Affordability and Cost of Living JAs 28 16 28 4 24 — 100 Total JAs 106 17 37 8 16 — 184 Total ECL 242 140 160 70 380 — 992 2022 £m £m £m £m £m £m £m Modelled ECL 133 112 93 65 194 — 597 Individually assessed — — — — 112 — 112 ECL before JAs 133 112 93 65 306 — 709 JAs (excluding Affordability and Cost of Living JAs) Long-term indeterminate arrears 13 — — — — — 13 12+ months in arrears 22 — — — — — 22 UPL loss floor — — 15 — — — 15 Model underestimation 36 2 19 — — — 57 Corporate single large exposure — — — — 23 — 23 Other 20 1 10 2 3 — 36 Total JAs (excluding Affordability and Cost of Living JAs) 91 3 44 2 26 — 166 Affordability and Cost of Living JAs Corporate lending to segments affected by supply chain pressures — — — — 61 — 61 Mortgage affordability 27 — — — — — 27 Retail Unsecured Affordability — 15 20 — — — 35 SME debt burden — — 7 — — — 7 Total Affordability and Cost of Living JAs 27 15 27 — 61 — 130 Total JAs 118 18 71 2 87 — 296 Total ECL 251 130 164 67 393 — 1,005
Disclosure of Base Expected Credit Losses to Probability Weighted Estimated Credit Losses	Upside Base case Downside 1 Stubborn Inflation Downside 2 Weighted 2023 £m £m £m £m £m £m Exposure 294,877 294,877 294,877 294,877 294,877 294,877 Retail and Business Banking 201,977 201,977 201,977 201,977 201,977 201,977 Of which: – Mortgages 181,188 181,188 181,188 181,188 181,188 181,188 Consumer Finance 5,228 5,228 5,228 5,228 5,228 5,228 CCB 27,277 27,277 27,277 27,277 27,277 27,277 Corporate Centre 60,395 60,395 60,395 60,395 60,395 60,395 ECL 833 896 991 1,176 1,410 992 Retail and Business Banking 419 465 536 689 889 542 Of which: – Mortgages 141 174 234 363 562 242 Consumer Finance 68 69 70 72 72 70 CCB 346 362 385 415 449 380 Corporate Centre — — — — — — 2022 £m £m £m £m £m £m Exposure 306,284 306,284 306,284 306,284 306,284 306,284 Retail and Business Banking 213,557 213,557 213,557 213,557 213,557 213,557 Of which: – Mortgages 192,346 192,346 192,346 192,346 192,346 192,346 Consumer Finance 5,740 5,740 5,740 5,740 5,740 5,740 CCB 28,277 28,277 28,277 28,277 28,277 28,277 Corporate Centre 58,710 58,710 58,710 58,710 58,710 58,710 ECL 930 932 993 1,149 1,383 1,005 Retail and Business Banking 489 497 529 647 830 544 Of which: – Mortgages 214 218 244 324 501 251 Consumer Finance 65 66 65 68 69 67 CCB 376 369 399 434 484 394 Corporate Centre — — — — — —
Schedule of Impact on Profit Before Tax of Applying an Immediate and Permanent House Price Increase or Decrease to Our Base Case Economic Scenario Explanatory	Increase/decrease in house prices +20% +10% -10% -20% Increase/(decrease) in profit before tax £m £m £m £m 2023 70 38 (54) (155) 2022 48 32 (61) (176)
Disclosure of Factors to Measure ECL	For accounts not in default at the reporting date, we estimate a monthly ECL for each exposure and for each month over the forecast period. The lifetime ECL is the sum of the monthly ECLs over the forecast period, while the 12-month ECL is limited to the first 12 months. We calculate each monthly ECL as the discounted value for the relevant forecast month of the product of the following factors: Factor Description Survival rate (SR) The probability that the exposure has not closed or defaulted since the reporting date. Probability of default (PD) The likelihood of a borrower defaulting in the following month, assuming it has not closed or defaulted since the reporting date. For each month in the forecast period, we estimate the monthly PD from a range of factors. These include the current risk grade for the exposure, which becomes less relevant further into the forecast period, as well as the expected evolution of the account risk with maturity and factors for changing economics. We support this with historical data analysis. Exposure at default (EAD) The amount we expect to be owed if a default event occurs. We determine EAD for each month of the forecast period by the expected payment profile, which varies by product. For amortising products, we base it on the borrower’s contractual repayments over the forecast period. We adjust this for any expected overpayments on Stage 1 accounts that the borrower may make and for any arrears we expect if the account was to default. For revolving products, or amortising products with an off-balance sheet element, we determine EAD using the balance at default and the contractual exposure limit. We vary these assumptions by product and base them on analysis of recent default data. Loss given default (LGD) Our expected loss if a default event were to occur. We express it as a percentage and calculate it based on factors that we have observed to affect the likelihood and/or value of any subsequent write-offs, which vary according to whether the product is secured or unsecured. If the product is secured, we take into account collateral values as well as the historical discounts to market/book values due to forced sales type.
Disclosure of Maximum and Net Exposure to Credit Risk	The tables below show the main differences between our maximum and net exposure to credit risk. They show the effects of collateral, netting, and risk transfer to mitigate our exposure. The tables only show the financial assets that credit risk affects and to which the impairment requirements in IFRS 9 are applied. For balance sheet assets, the maximum exposure to credit risk is the carrying value after impairment loss allowances. Off-balance sheet exposures are mortgage offers, guarantees, formal standby facilities, credit lines and other commitments. For off-balance sheet guarantees, the maximum exposure is the maximum amount that we would have to pay if the guarantees were called on. For formal standby facilities, credit lines and other commitments that are irrevocable over the life of the facility, the maximum exposure is the total amount of the commitment. Maximum exposure Balance sheet asset Off-balance sheet Collateral (1) Gross amounts Loss allowance Net amounts Gross amounts Loss allowance Net amounts Cash Non-cash Netting (2) Net exposure 2023 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Cash and balances at central banks 38.2 — 38.2 — — — — — — 38.2 Financial assets at amortised cost: – Loans and advances to customers: (3) – Retail Mortgages (4) 172.9 (0.2) 172.7 8.3 — 8.3 — (175.4) — 5.6 – Corporate loans 18.3 (0.3) 18.0 8.9 — 8.9 (0.1) (15.3) — 11.5 – Finance leases 4.6 (0.1) 4.5 — — — — (4.5) — — – Accrued interest and other adjustments 0.9 — 0.9 — — — — — — 0.9 – Other unsecured loans 7.1 (0.3) 6.8 13.8 (0.1) 13.7 — — — 20.5 – Amounts due from fellow Banco Santander group subsidiaries and JVs 4.5 — 4.5 — — — — — — 4.5 Total loans and advances to customers 208.3 (0.9) 207.4 31.0 (0.1) 30.9 (0.1) (195.2) — 43.0 – Loans and advances to banks 1.1 — 1.1 0.5 — 0.5 — — — 1.6 – Reverse repurchase agreements – non trading 12.5 — 12.5 — — — — (12.4) (0.1) — – Other financial assets at amortised cost 0.2 — 0.2 — — — — — — 0.2 Total financial assets at amortised cost 222.1 (0.9) 221.2 31.5 (0.1) 31.4 (0.1) (207.6) (0.1) 44.8 Financial assets at fair value at FVOCI: – Debt securities 8.5 — 8.5 — — — — — — 8.5 Total financial assets at FVOCI 8.5 — 8.5 — — — — — — 8.5 Total 268.8 (0.9) 267.9 31.5 (0.1) 31.4 (0.1) (207.6) (0.1) 91.5 2022 Cash and balances at central banks 44.2 — 44.2 — — — — — — 44.2 Financial assets at amortised cost: – Loans and advances to customers: (3) – Retail Mortgages (4) 184.3 (0.2) 184.1 8.0 — 8.0 — (187.4) — 4.7 – Corporate loans 19.1 (0.4) 18.7 9.3 — 9.3 (0.1) (16.5) — 11.4 – Finance leases 4.6 (0.1) 4.5 0.4 — 0.4 — (4.8) — 0.1 – Accrued interest and other adjustments 0.7 — 0.7 — — — — — — 0.7 – Other unsecured loans 7.7 (0.2) 7.5 13.7 (0.1) 13.6 — — — 21.1 – Amounts due from fellow Banco Santander group subsidiaries and JVs 4.2 — 4.2 — — — — — — 4.2 Total loans and advances to customers 220.6 (0.9) 219.7 31.4 (0.1) 31.3 (0.1) (208.7) — 42.2 – Loans and advances to banks 1.0 — 1.0 0.4 — 0.4 — — — 1.4 – Reverse repurchase agreements – non trading 7.3 — 7.3 — — — — (7.3) — — – Other financial assets at amortised cost 0.2 — 0.2 — — — — — — 0.2 Total financial assets at amortised cost 229.1 (0.9) 228.2 31.8 (0.1) 31.7 (0.1) (216.0) — 43.8 Financial assets at FVOCI: – Debt securities 6.0 — 6.0 — — — — — — 6.0 Total financial assets at FVOCI 6.0 — 6.0 — — — — — — 6.0 Total 279.3 (0.9) 278.4 31.8 (0.1) 31.7 (0.1) (216.0) — 94.0 (1) The forms of collateral we take to reduce credit risk include: residential and commercial property; other physical assets, including motor vehicles; liquid securities, including those transferred under reverse repurchase agreements; cash, including cash used as collateral for derivative transactions; and receivables. Charges on residential property are most of the collateral we take. (2) We can reduce credit risk exposures by applying netting. We do this mainly for derivative and repurchase transactions with financial institutions. For derivatives and securities finance transactions, we use standard master netting agreements. For more on this, see ‘Credit risk mitigation’ in the ‘Credit risk - Credit risk management’ section. (3) Balances include interest we have charged to the customer’s account and accrued interest that we have not charged to the account yet. (4) The collateral value shown against advances secured on residential property is limited to the balance of each associated individual loan. It does not include the impact of over–collateralisation (where the collateral has a higher value than the loan balance) and includes collateral we would receive on draw down of certain off–balance sheet commitments.
Disclosure of Difference Between Maximum and Net Exposure to Credit Risk	The tables below show the main differences between our maximum and net exposure to credit risk on the financial assets that credit risk affects and to which the impairment requirements in IFRS 9 are not applied. Balance sheet asset gross amount Collateral (1) Netting (2) Net exposure Cash Non-cash 2023 £bn £bn £bn £bn £bn Financial assets at FVTPL: – Derivative financial instruments 1.4 (0.8) — (0.5) 0.1 – Other financial assets at FVTPL 0.3 — — — 0.3 Total 1.7 (0.8) — (0.5) 0.4 2022 Financial assets at FVTPL: – Derivative financial instruments 2.4 — (1.7) (0.5) 0.2 – Other financial assets at FVTPL 0.1 — — — 0.1 Total 2.5 — (1.7) (0.5) 0.3 (1) The forms of collateral we take to reduce credit risk include: liquid securities, including those transferred under reverse repurchase agreements; cash, including cash used as collateral for derivative transactions; and receivables. (2) We can reduce credit risk exposures by applying netting. We do this mainly for derivative and repurchase transactions with financial institutions. For derivatives and securities finance transactions, we use standard master netting agreements. They allow us to set off our credit risk exposure to a counterparty against our obligations to the counterparty in relation to transactions under the master netting agreement in the event of default. This gives us a lower net credit exposure. They may also reduce settlement exposure. For more on this, see ‘Credit risk mitigation’ in the ‘Credit risk – Credit risk management’ section.
Disclosure of Equivalent Credit Rating Grade used by Standard and Poors Ratings Services	In the final column of the table we show the approximate equivalent credit rating grade used by Standard & Poor’s Ratings Services (S&P). Santander UK risk grade PD range Mid Lower Upper S&P equivalent % % % 9 0.010 0.000 0.021 AAA to AA+ 8 0.032 0.021 0.066 AA to AA- 7 0.100 0.066 0.208 A+ to BBB 6 0.316 0.208 0.658 BBB- to BB 5 1.000 0.658 2.081 BB- 4 3.162 2.081 6.581 B+ to B 3 10.000 6.581 20.811 B- 2 31.623 20.811 99.999 CCC to C 1 (Default) 100.000 100.000 100.000 D
Disclosure of Credit Rating of Financial Assets Subject to Credit Risk	The tables below show the credit rating of our financial assets to which the impairment requirements in IFRS 9 apply. Financial assets with low risk concentrations are not included and are all investment grade. JAs are incorporated in the balances. For more on the credit rating profiles of key portfolios, see the credit risk review section for each business segment. Santander UK risk grade Loss allowance Total 9 8 7 6 5 4 3 to 1 Other (1)(2) 2023 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Exposures - On balance sheet Financial assets at amortised cost: – Loans and advances to customers (2) 5.3 34.2 84.4 48.9 14.6 8.3 5.4 7.2 (0.9) 207.4 – Stage 1 5.3 33.1 80.4 43.6 10.3 2.8 0.3 6.9 (0.1) 182.6 – Stage 2 — 1.1 4.0 5.3 4.3 5.4 2.4 0.1 (0.4) 22.2 – Stage 3 — — — — — 0.1 2.7 0.2 (0.4) 2.6 Of which mortgages: 5.2 32.5 79.9 41.5 6.6 3.7 3.5 — (0.2) 172.7 – Stage 1 5.2 31.4 75.9 36.3 3.6 0.4 0.2 — — 153.0 – Stage 2 — 1.1 4.0 5.2 3.0 3.2 1.4 — (0.1) 17.8 – Stage 3 — — — — — 0.1 1.9 — (0.1) 1.9 Total off–balance sheet — 6.3 7.0 6.8 4.6 1.7 0.4 4.7 (0.1) 31.4 – Stage 1 — 6.3 6.9 6.7 4.4 1.2 0.1 4.7 — 30.3 – Stage 2 — — 0.1 0.1 0.2 0.5 0.2 — (0.1) 1.0 – Stage 3 — — — — — — 0.1 — — 0.1 Santander UK risk grade Total Coverage Ratio 9 8 7 6 5 4 3 to 1 Other (1)(2) 2023 £bn £bn £bn £bn £bn £bn £bn £bn £bn % ECL - On balance sheet Financial assets at amortised cost: – Loans and advances to customers (2) — — — — 0.2 0.2 0.5 — 0.9 0.4 – Stage 1 — — — — 0.1 — — — 0.1 0.1 – Stage 2 — — — — 0.1 0.2 0.1 — 0.4 1.8 – Stage 3 — — — — — — 0.4 — 0.4 13.3 Of which mortgages: — — — — — 0.1 0.1 — 0.2 0.1 – Stage 1 — — — — — — — — — — – Stage 2 — — — — — 0.1 — — 0.1 0.6 – Stage 3 — — — — — — 0.1 — 0.1 5.0 Total off–balance sheet — — — — — 0.1 — — 0.1 0.3 – Stage 1 — — — — — — — — — — – Stage 2 — — — — — 0.1 — — 0.1 9.1 – Stage 3 — — — — — — — — — — Santander UK risk grade Loss allowance 9 8 7 6 5 4 3 to 1 Other (1)(2) Total 2022 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Exposures - On balance sheet Financial assets at amortised cost: – Loans and advances to customers⁽²⁾ 9.5 35.9 85.6 52.1 15.2 9.2 5.4 7.7 (0.9) 219.7 – Stage 1 9.5 35.6 83.9 47.9 11.1 3.9 0.5 7.3 (0.1) 199.6 – Stage 2 — 0.3 1.7 4.2 4.1 5.2 2.6 0.2 (0.5) 17.8 – Stage 3 — — — — — 0.1 2.3 0.2 (0.3) 2.3 Of which mortgages: 9.5 33.4 82.3 45.0 7.2 3.8 3.1 — (0.2) 184.1 – Stage 1 9.5 33.1 80.7 41.1 4.1 0.5 0.1 — — 169.1 – Stage 2 — 0.3 1.6 3.9 3.1 3.2 1.3 — (0.1) 13.3 – Stage 3 — — — — — 0.1 1.7 — (0.1) 1.7 Total off–balance sheet 0.1 7.2 6.9 6.5 4.9 2.1 0.4 3.7 (0.1) 31.7 – Stage 1 0.1 7.2 6.8 6.4 4.7 1.7 0.2 3.7 — 30.8 – Stage 2 — — 0.1 0.1 0.2 0.4 0.1 — (0.1) 0.8 – Stage 3 — — — — — — 0.1 — — 0.1 Santander UK risk grade Coverage Ratio 9 8 7 6 5 4 3 to 1 Other (1)(2) Total 2022 £bn £bn £bn £bn £bn £bn £bn £bn £bn % ECL - On balance sheet Financial assets at amortised cost: – Loans and advances to customers⁽²⁾ — — — — 0.2 0.2 0.5 — 0.9 0.4 – Stage 1 — — — — 0.1 — — — 0.1 0.1 – Stage 2 — — — — 0.1 0.2 0.2 — 0.5 2.8 – Stage 3 — — — — — — 0.3 — 0.3 13.0 Of which mortgages: — — — — 0.1 0.1 — — 0.2 0.1 – Stage 1 — — — — — — — — — — – Stage 2 — — — — 0.1 — — — 0.1 0.8 – Stage 3 — — — — — 0.1 — — 0.1 5.9 Total off–balance sheet — — — — — — 0.1 — 0.1 0.3 – Stage 1 — — — — — — — — — — – Stage 2 — — — — — — 0.1 — 0.1 12.5 – Stage 3 — — — — — — — — — — (1) Includes Joint Ventures and Business Banking (including BBLs balances) . We use scorecards for these items, rather than rating models. Off-balance sheet exposures also include residential mortgage offers in the pipeline. (2) Includes interest we have charged to the customer’s account and accrued interest we have not charged to the account yet.
Disclosure of Credit Performance	31 December 2023 31 December 2022 % % Mortgages 0.80 0.62 Credit Cards 0.51 0.49 UPL 0.73 0.61 Overdrafts 2.43 2.24 Business Banking 4.15 3.47 Consumer Finance 0.43 0.44 2023 2022 £m £m Mortgage loans and advances to customers 172,859 184,317 of which: – Stage 1 152,975 169,066 – Stage 2 17,876 13,424 – Stage 3 2,008 1,827 Loss allowances (1) 242 251 % % Stage 1 ratio (2) 88.50 91.73 Stage 2 ratio (2) 10.34 7.28 Stage 3 ratio 1.17 1.00 (1) The ECL allowance is for both on and off–balance sheet exposures. (2) Stage 1/Stage 2 exposures as a percentage of customer loans. Portfolio of particular interest (1) Total Interest-only Part interest- only, part repayment (2) Flexible LTV >100% Buy-to-let Other portfolio 2023 £m £m £m £m £m £m £m Mortgage portfolio 172,859 38,825 12,584 5,418 445 15,585 118,981 – Stage 1 152,975 32,012 10,896 4,420 276 13,887 107,834 – Stage 2 17,876 5,829 1,449 744 104 1,647 10,402 – Stage 3 2,008 984 239 254 65 51 745 Stage 3 ratio 1.17% 2.55% 1.90% 5.01% 14.57% 0.33% 0.63% Properties in possession 23 12 3 2 5 1 8 Balance weighted LTV (indexed) 51% 48% 51% 37% 116% 60% 53% 2022 Mortgage portfolio 184,317 40,825 13,510 6,765 370 16,799 126,996 – Stage 1 169,066 35,702 12,143 5,713 217 15,884 118,507 – Stage 2 13,424 4,250 1,149 839 101 876 7,791 – Stage 3 1,827 873 218 213 52 39 698 Stage 3 ratio 1.00% 2.16% 1.62% 3.45% 13.94% 0.23% 0.55% Properties in possession 47 18 8 3 7 1 16 Balance weighted LTV (indexed) 50% 47% 49% 36% 117% 58% 52% (1) Where a loan falls into more than one category, we include it in all the categories that apply. As a result, the sum of the mortgages in the segments of particular interest and the other portfolio does not agree to the total mortgage portfolio. (2) Mortgage balance includes both the interest-only part of £9,531m ( 2022 : £10,010m ) and the non-interest-only part of the loan. Business banking Other unsecured Personal loans Credit cards Overdrafts Total other unsecured Total 2023 £m £m £m £m £m £m Loans and advances to customers 1,819 2,064 2,674 471 5,209 7,028 of which: – Stage 1 1,574 1,743 2,283 207 4,233 5,807 – Stage 2 115 294 345 236 875 990 – Stage 3 130 27 46 28 101 231 Loss allowances (1) 16 66 140 78 284 300 Stage 3 undrawn exposures 2 37 39 Stage 3 ratio 7.25 % 2.65 % 3.83 % Gross write-offs (12 months) 11 119 130 2022 Loans and advances to customers 2,519 1,982 2,558 461 5,001 7,520 of which: – Stage 1 2,223 1,730 2,192 155 4,077 6,300 – Stage 2 133 231 329 282 842 975 – Stage 3 163 21 37 24 82 245 Loss allowances (1) 19 62 130 82 274 293 Stage 3 undrawn exposures 3 32 35 Stage 3 ratio 6.58 % 2.27 % 3.71 % Gross write-offs (12 months) 11 99 110 (1) The ECL allowance is for both on and off–balance sheet exposures. 2023 2022 £m £m Loans and advances to customers 5,228 5,384 of which: – Stage 1 4,870 5,005 – Stage 2 330 350 – Stage 3 28 29 Loss allowances (1) 70 67 Stage 3 ratio 0.53 % 0.54 % Gross write-offs 23 19 (1) The ECL allowance is for both on and off–balance sheet exposures. We monitor exposures that show potentially higher risk characteristics using our Watchlist process. The table below shows the exposures we monitor, and those we classify as Stage 3 by portfolio at 31 December 2023 and 31 December 2022 . Committed exposure Watchlist Fully performing Enhanced monitoring Proactive management Stage 3 Total (1) Loss allowances 2023 £m £m £m £m £m £m SME and mid corporate 10,140 462 1,447 627 12,676 341 Commercial Real Estate 4,734 10 496 118 5,358 39 Social Housing 7,752 — 204 — 7,956 — 22,626 472 2,147 745 25,990 380 2022 SME and mid corporate 11,796 431 1,383 513 14,123 355 Commercial Real Estate 4,765 103 480 59 5,407 38 Social Housing 7,978 46 10 — 8,034 1 24,539 580 1,873 572 27,564 394 (1) Includes committed facilities and derivatives.
Disclosure of IFRS 9 Credit Quality	Total on-balance sheet exposures at 31 December 2023 comprised £203.1 bn of customer loans, loans and advances to banks of £1.1 bn, £12.6 bn of sovereign assets measured at amortised cost, £8.5 bn of assets measured at FVOCI, and £38.2 bn of cash and balances at central banks. Stage 1 Stage 2 Stage 3 Total 2023 £m £m £m £m Exposures On-balance sheet Retail and Business Banking 158,782 18,866 2,239 179,887 Consumer Finance 4,870 330 28 5,228 CCB 13,822 3,418 699 17,939 Corporate Centre 60,395 — — 60,395 Total on-balance sheet 237,869 22,614 2,966 263,449 Off-balance sheet Retail and Business Banking (1) 21,597 434 59 22,090 Consumer Finance — — — — CCB 8,745 547 46 9,338 Corporate Centre — — — — Total off-balance sheet (2) 30,342 981 105 31,428 Total exposures 268,211 23,595 3,071 294,877 ECL On-balance sheet Retail and Business Banking 57 273 169 499 Consumer Finance 21 30 19 70 CCB 64 118 163 345 Corporate Centre — — — — Total on-balance sheet 142 421 351 914 Off-balance sheet Retail and Business Banking 16 26 1 43 Consumer Finance — — — — CCB 12 14 9 35 Corporate Centre — — — — Total off-balance sheet 28 40 10 78 Total ECL 170 461 361 992 Coverage ratio (3) % % % % On-balance sheet Retail and Business Banking — 1.4 7.5 0.3 Consumer Finance 0.4 9.0 68.5 1.3 CCB 0.5 3.5 23.4 1.9 Corporate Centre — — — — Total on-balance sheet 0.1 1.9 11.8 0.3 Off-balance sheet Retail and Business Banking 0.1 6.0 2.8 0.2 Consumer Finance — — — — CCB 0.1 2.5 20.2 0.4 Corporate Centre — — — — Total off-balance sheet 0.1 4.1 10.4 0.2 Total coverage 0.1 2.0 11.8 0.3 (1) Off-balance sheet exposures include £3.3 bn of residential mortgage offers in the pipeline. (2) Off-balance sheet amounts consist of contingent liabilities and commitments. For more, see Note 31 . (3) ECL as a percentage of the related exposure. Total on-balance sheet exposures at 31 December 2022 comprised £215.7 bn of customer loans, loans and advances to banks of £1.0 bn, £7.5 bn of sovereign assets measured at amortised cost, £6.0 bn of assets measured at FVOCI, and £44.2 bn of cash and balances at central banks. Gross write-offs Stage 1 Stage 2 Stage 3 Total 2022 £m £m £m £m £m Exposures On-balance sheet Retail and Business Banking 175,365 14,399 2,072 191,836 Consumer Finance 5,005 350 29 5,384 CCB 14,507 3,476 535 18,518 Corporate Centre 58,710 — — 58,710 Total on-balance sheet 253,587 18,225 2,636 274,448 Off-balance sheet Retail and Business Banking (1) 21,175 490 56 21,721 Consumer Finance 356 — — 356 CCB 9,310 412 37 9,759 Corporate Centre — — — — Total off-balance sheet (2) 30,841 902 93 31,836 Total exposures 284,428 19,127 2,729 306,284 ECL and Gross Write-offs On-balance sheet Retail and Business Banking 113 56 295 151 502 Consumer Finance 19 19 27 21 67 CCB 24 69 155 138 362 Corporate Centre — — — — — Total on-balance sheet 156 144 477 310 931 Off-balance sheet Retail and Business Banking — 12 28 2 42 Consumer Finance — — — — — CCB — 14 11 7 32 Total off-balance sheet — 26 39 9 74 Total ECL 156 170 516 319 1,005 Coverage ratio (3) % % % % On-balance sheet Retail and Business Banking — 2.0 7.3 0.3 Consumer Finance 0.4 7.7 72.4 1.2 CCB 0.5 4.5 25.8 2.0 Corporate Centre — — — — Total on-balance sheet 0.1 2.6 11.8 0.3 Off-balance sheet Retail and Business Banking 0.1 5.7 3.6 0.2 Consumer Finance — — — — CCB 0.2 2.7 18.9 0.3 Total off-balance sheet 0.1 4.3 9.7 0.2 Total coverage 0.1 2.7 11.7 0.3 (1) Off-balance sheet exposures include £2.8 bn of residential mortgage offers in the pipeline. (2) Off-balance sheet amounts consist of contingent liabilities and commitments. For more, see Note 31 . (3) ECL as a percentage of the related exposure.
Disclosure of Stage 2 Exposures by Classification	The following table analyses our Stage 2 exposures and ECL by the reason the exposure is classified as Stage 2. 2023 PD deterioration Forbearance Other 30 DPD Secured affordability Unsecured affordability Mortgage Refinancing High risk corporate Total Retail and Business Banking - Mortgages Exposure £m 5,877 516 265 560 2,889 — 7,769 — 17,876 ECL £m 65 2 3 11 9 — 19 — 109 Consumer Finance Exposure £m 115 — 126 25 64 — — — 330 ECL £m 10 — 5 11 4 — — — 30 CCB Exposure £m 1,809 85 533 93 — — — 898 3,418 ECL £m 75 2 17 2 — — — 22 118 Corporate Centre Exposure £m — — — — — — — — — ECL £m — — — — — — — — — Total Drawn Exposure £m 8,345 601 960 856 2,953 232 7,769 898 22,614 ECL £m 249 4 33 46 13 35 19 22 421 Undrawn ECL £m 28 — 4 3 — 3 — 2 40 Total Reported Exposure £m 9,160 601 1,152 893 2,889 233 7,769 898 23,595 ECL £m 277 4 37 49 13 38 19 24 461 2022 Retail and Business Banking - Mortgages Exposure £m 7,310 449 241 463 4,961 — n/a — 13,424 ECL £m 86 2 5 10 27 — n/a — 130 Consumer Finance Exposure £m 159 — 164 27 — — n/a — 350 ECL £m 11 — 6 10 — — n/a — 27 CCB Exposure £m 1,548 64 684 214 — — n/a 966 3,476 ECL £m 81 4 1 10 — — n/a 59 155 Corporate Centre Exposure £m — — — — — — n/a — — ECL £m — — — — — — n/a — — Total Drawn Exposure £m 9,560 513 1,137 890 4,961 198 n/a 966 18,225 ECL £m 284 6 22 48 27 31 n/a 59 477 Undrawn ECL £m 19 — 8 6 — 4 n/a 2 39 Total Reported Exposure £m 10,323 625 1,116 937 4,961 199 n/a 966 19,127 ECL £m 303 6 30 54 27 35 n/a 61 516
Disclosure of ECL Reconciliation	The table below shows the relationships between disclosures in this Credit risk review section which refer to drawn exposures and the associated ECL , and the total assets as presented in the Consolidated Balance Sheet. The Credit risk review disclosures exclude Joint ventures, as they carry low credit risk and therefore have an immaterial ECL, and Other items, mainly accrued interest that we have not yet charged to the customer's account, and cash collateral. On-balance sheet Off-balance sheet Exposures Loss allowance Net carrying amount Exposures Loss allowance 2023 £m £m £m £m £m Retail and Business Banking (1)(2) 179,887 499 179,388 22,090 43 Consumer Finance 5,228 70 5,158 — — Corporate & Commercial Banking 17,939 345 17,594 9,338 35 Corporate Centre 60,395 — 60,395 — — Total exposures presented in Credit Quality tables 263,449 914 262,535 31,428 78 Joint ventures 4,544 Other items 751 Adjusted net carrying amount 267,830 Assets classified at FVTPL 1,694 Non-financial assets (3) 5,924 Total assets per the Consolidated Balance Sheet 275,448 2022 Retail and Business Banking (1)(2) 191,836 502 191,334 21,721 42 Consumer Finance 5,384 67 5,317 356 — Corporate & Commercial Banking 18,518 362 18,156 9,759 32 Corporate Centre 58,710 — 58,710 — — Total exposures presented in Credit Quality tables 274,448 931 273,517 31,836 74 Joint ventures 4,164 Other items 745 Adjusted net carrying amount 278,426 Assets classified at FVTPL 2,536 Non-financial assets (3) 4,251 Total assets per the Consolidated Balance Sheet 285,213 (1) Off-balance sheet exposures include offers in the pipeline and undrawn flexible mortgages products. (2) Off-balance sheet exposures include credit cards. (3) Non-financial assets include £ 632 m (2022: £ 2,657 m ) of Macro hedge of interest rate risk. The following table shows changes in total on and off-balance sheet exposures, subject to ECL assessment, and the corresponding ECL, in the period. The table presents total gross carrying amounts and ECLs at a Santander UK group level. We present segmental views in the sections below. Stage 1 Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL £m £m £m £m £m £m £m £m At 1 January 2023 284,428 170 19,127 516 2,729 319 306,284 1,005 Transfers from Stage 1 to Stage 2 (3) (12,945) (9) 12,945 9 — — — — Transfers from Stage 2 to Stage 1 (3) 5,913 111 (5,913) (111) — — — — Transfers to Stage 3 (3) (598) (6) (920) (38) 1,518 44 — — Transfers from Stage 3 (3) 28 1 304 15 (332) (16) — — Transfers of financial instruments (7,602) 97 6,416 (125) 1,186 28 — — Net ECL remeasurement on stage transfer (4) — (111) — 145 — 130 — 164 Change in economic scenarios (2) — 29 — (33) — 9 — 5 New lending and assets purchased (5) 25,409 28 562 45 59 20 26,030 93 Redemptions, repayments and assets sold (7) (33,805) (35) (3,017) (53) (886) (46) (37,708) (134) Changes in risk parameters and other movements (6) (219) (8) 507 (34) 395 133 683 91 Assets written off (7) — — — — (412) (232) (412) (232) At 31 December 2023 268,211 170 23,595 461 3,071 361 294,877 992 Net movement in the period (16,217) — 4,468 (55) 342 42 (11,407) (13) ECL (release)/charge to the Income Statement — (55) 274 219 Less: Discount unwind — — (21) (21) Less: Recoveries net of collection costs — — 7 7 Total ECL (release)/charge to the Income Statement — (55) 260 205 At 1 January 2022 292,366 132 17,964 330 3,017 403 313,347 865 Transfers from Stage 1 to Stage 2 (3) (9,100) (25) 9,100 25 — — — — Transfers from Stage 2 to Stage 1 (3) 7,207 133 (7,207) (133) — — — — Transfers to Stage 3 (3) (621) (4) (624) (32) 1,245 36 — — Transfers from Stage 3 (3) 10 1 758 150 (768) (151) — — Transfers of financial instruments (2,504) 105 2,027 10 477 (115) — — Net ECL remeasurement on stage transfer (4) — (110) — 98 — 110 — 98 Change in economic scenarios (2) — 37 — 123 — 3 — 163 New lending and assets purchased (5) 48,194 42 1,119 76 64 24 49,377 142 Redemptions, repayments and assets sold (7) (54,546) (35) (2,065) (60) (950) (35) (57,561) (130) Changes in risk parameters and other movements (6) 918 (1) 82 (61) 375 86 1,375 24 Assets written off (7) — — — — (254) (157) (254) (157) At 31 December 2022 284,428 170 19,127 516 2,729 319 306,284 1,005 Net movement in the period (7,938) 38 1,163 186 (288) (84) (7,063) 140 ECL charge/(release) to the Income Statement 38 186 73 297 Less: Discount unwind — — (13) (13) Less: Recoveries net of collection costs — — 36 36 Total ECL charge/(release) to the Income Statement 38 186 96 320 (1) Exposures that have attracted an ECL, and as reported in the Credit Quality table above. (2) Changes to assumptions in the period. Isolates the impact on ECL from changes to the economic variables for each scenario, the scenarios themselves, and the probability weights from all other movements. Also includes the impact of quarterly revaluation of collateral. The impact of changes in economics on exposure Stage allocations are shown in Transfers of financial instruments. (3) Total impact of facilities that moved Stage(s) in the period. This means, for example, that where risk parameter changes (model inputs) or model changes (methodology) result in a facility moving Stage, the full impact is reflected here (rather than in Other). Stage flow analysis only applies to facilities that existed at both the start and end of the period. Transfers between Stages are based on opening balances and ECL at the start of the period. (4) Relates to the revaluation of ECL following the transfer of an exposure from one Stage to another. (5) Exposures and ECL of facilities that did not exist at the start of the period but did at the end. Amounts in Stage 2 and 3 represent assets which deteriorated in the period after origination in Stage 1. (6) Residual movements on existing facilities that did not change Stage in the period, and which were not acquired in the period. Includes the net increase or decrease in the period of the mortgage pipeline, cash at central banks, the impact of changes in risk parameters in the period, unwind of discount rates and increases in ECL requirements of accounts which ultimately were written off in the period. (7) Exposures and ECL for facilities that existed at the start of the period but not at the end. The following tables show changes in total on and off-balance sheet exposures and ECL in the period. The footnotes to the Santander UK group level table on page 67 also apply to these tables. Stage 1 Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL £m £m £m £m £m £m £m £m At 1 January 2023 176,965 25 13,533 131 1,848 95 192,346 251 Transfers from Stage 1 to Stage 2 (3) (10,791) (3) 10,791 3 — — — — Transfers from Stage 2 to Stage 1 (3) 4,778 30 (4,778) (30) — — — — Transfers to Stage 3 (3) (335) (3) (566) (15) 901 18 — — Transfers from Stage 3 (3) 14 — 277 9 (291) (9) — — Transfers of financial instruments (6,334) 24 5,724 (33) 610 9 — — Net ECL remeasurement on stage transfer (4) — (28) — 40 — 22 — 34 Change in economic scenarios (2) — — — (2) — 3 — 1 New lending and assets purchased (5) 12,947 4 154 3 5 1 13,106 8 Redemptions, repayments and assets sold (7) (23,081) (6) (1,752) (12) (417) (14) (25,250) (32) Changes in risk parameters and other movements (6) 666 5 338 (17) 36 3 1,040 (9) Assets written off (7) — — — — (54) (11) (54) (11) At 31 December 2023 161,163 24 17,997 110 2,028 108 181,188 242 Net movement in the period (15,802) (1) 4,464 (21) 180 13 (11,158) (9) ECL (release)/charge to the Income Statement (1) (21) 24 2 Less: Discount unwind — — (3) (3) Less: Recoveries net of collection costs — — 28 28 Total ECL (release)/charge to the Income Statement (1) (21) 49 27 At 1 January 2022 177,696 13 11,152 88 1,815 89 190,663 190 Transfers from Stage 1 to Stage 2 (3) (5,834) (1) 5,834 1 — — — — Transfers from Stage 2 to Stage 1 (3) 2,961 16 (2,961) (16) — — — — Transfers to Stage 3 (3) (278) (2) (448) (11) 726 13 — — Transfers from Stage 3 (3) 4 — 279 9 (283) (9) — — Transfers of financial instruments (3,147) 13 2,704 (17) 443 4 — — Net ECL remeasurement on stage transfer (4) — (15) — 40 — 8 — 33 Change in economic scenarios (2) — 1 — 21 — 2 — 24 New lending and assets purchased (5) 35,028 7 529 11 1 — 35,558 18 Redemptions, repayments and assets sold (7) (32,565) (3) (1,229) (11) (415) (12) (34,209) (26) Changes in risk parameters and other movements (6) (47) 9 377 (1) 14 7 344 15 Assets written off (7) — — — — (10) (3) (10) (3) At 31 December 2022 176,965 25 13,533 131 1,848 95 192,346 251 Net movement in the period (731) 12 2,381 43 33 6 1,683 61 ECL charge/(release) to the Income Statement 12 43 9 64 Less: Discount unwind — — (2) (2) Less: Recoveries net of collection costs — — (1) (1) Total ECL charge/(release) to the Income Statement 12 43 6 61 The following tables show changes in total on and off-balance sheet exposures and ECL in the period. The footnotes to the Santander UK group level table on page 67 also apply to these tables. Stage 1 Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL £m £m £m £m £m £m £m £m At 1 January 2023 23,838 83 3,888 166 572 145 28,298 394 Transfers from Stage 1 to Stage 2 (3) (1,376) (1) 1,376 1 — — — — Transfers from Stage 2 to Stage 1 (3) 512 10 (512) (10) — — — — Transfers to Stage 3 (3) (118) (3) (258) (8) 376 11 — — Transfers from Stage 3 (3) 1 — 9 1 (10) (1) — — Transfers of financial instruments (981) 6 615 (16) 366 10 — — Net ECL remeasurement on stage transfer (4) — (16) — 29 — 64 — 77 Change in economic scenarios (2) — 30 — (30) — 6 — 6 New lending and assets purchased (5) 7,257 5 132 6 38 10 7,427 21 Redemptions, repayments and assets sold (7) (6,713) (13) (869) (10) (193) (23) (7,775) (46) Changes in risk parameters and other movements (6) (834) (19) 199 (13) 137 28 (498) (4) Assets written off (7) — — — — (175) (68) (175) (68) At 31 December 2023 22,567 76 3,965 132 745 172 27,277 380 Net movement in the period (1,271) (7) 77 (34) 173 27 (1,021) (14) ECL (release)/charge to the Income Statement (7) (34) 95 54 Less: Discount unwind — — (9) (9) Less: Recoveries net of collection costs — — (5) (5) Total ECL (release)/charge to the Income Statement (7) (34) 81 40 Stage 1 Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL £m £m £m £m £m £m £m £m At 1 January 2022 20,604 50 5,914 127 827 248 27,345 425 Transfers from Stage 1 to Stage 2 (3) (2,195) (14) 2,195 14 — — — — Transfers from Stage 2 to Stage 1 (3) 4,023 92 (4,023) (92) — — — — Transfers to Stage 3 (3) (172) (1) (111) (13) 283 14 — — Transfers from Stage 3 (3) — — 463 135 (463) (135) — — Transfers of financial instruments 1,656 77 (1,476) 44 (180) (121) — — Net ECL remeasurement on stage transfer (4) — (72) — (41) — 61 — (52) Change in economic scenarios (2) — 38 — 76 — — — 114 New lending and assets purchased (5) 8,629 16 228 19 43 12 8,900 47 Redemptions, repayments and assets sold (7) (9,019) (15) (584) (32) (53) (17) (9,656) (64) Changes in risk parameters and other movements (6) 1,968 (11) (194) (27) 21 (14) 1,795 (52) Assets written off (7) — — — — (86) (24) (86) (24) At 31 December 2022 23,838 83 3,888 166 572 145 28,298 394 Net movement in the period 3,234 33 (2,026) 39 (255) (103) 953 (31) ECL charge/(release) to the Income Statement 33 39 (79) (7) Less: Discount unwind — — (3) (3) Less: Recoveries net of collection costs — — 42 42 Total ECL charge/(release) to the Income Statement 33 39 (40) 32
Disclosure of Country Risk Exposures	The tables below show our total exposures, which are the total of balance sheet and off–balance sheet values. We calculate balance sheet values in line with IFRS (i.e. after netting allowed under IAS 32) except for credit provisions which we add back. Off–balance sheet values are undrawn facilities and letters of credit. We classify location by country of risk – the country where each client has its main business or assets. That is unless there is a full risk transfer guarantee in place. If so, we use the guarantor’s country of domicile. If a client has operations in many countries, we use their country of incorporation. The table below excludes balances with other Banco Santander group members. We show them separately in the section that immediately follows. 2023 2022 Financial institutions Financial institutions Governments Banks (1) Other Retail Corporate Total (2) Governments Banks (1) Other Retail Corporate Total (2) £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Eurozone Ireland — — 3.1 — 0.1 3.2 — — 2.3 — 0.1 2.4 Spain — — — — — — — — — — — — France 0.1 1.7 0.8 — — 2.6 0.1 0.8 0.5 — — 1.4 Germany — 0.2 0.3 — — 0.5 — 0.3 — — 0.1 0.4 Luxembourg — — 0.5 — 0.1 0.6 — — — — — — Other (3) 0.3 0.7 — — — 1.0 0.3 0.5 — — — 0.8 0.4 2.6 4.7 — 0.2 7.9 0.4 1.6 2.8 — 0.2 5.0 Other countries UK 38.5 1.7 6.5 206.0 25.0 277.7 44.1 1.8 5.8 217.3 26.9 295.9 US — 0.7 — — — 0.7 0.1 0.9 0.1 — — 1.1 Japan 2.0 0.9 — — — 2.9 1.1 0.3 — — — 1.4 Switzerland 2.1 — — — — 2.1 1.2 — — — — 1.2 Other 0.1 1.2 0.2 0.1 0.7 2.3 0.1 0.7 0.2 — 0.5 1.5 42.7 4.5 6.7 206.1 25.7 285.7 46.6 3.7 6.1 217.3 27.4 301.1 Total 43.1 7.1 11.4 206.1 25.9 293.6 47.0 5.3 8.9 217.3 27.6 306.1 (1) Excludes balances with central banks. (2) Excludes cash at hand, interests in other entities, intangible assets, property, plant and equipment, tax assets, retirement benefit assets and other assets. (3) Includes The Netherlands £0.3 bn ( 2022 : £0.1 bn), Belgium £0.5 bn ( 2022 : £ 0.6 bn), and Finland £0.1 bn ( 2022 : £0.1 bn ).
Disclosure of Balances with Other Banco Santander Group Companies	At 31 December 2023 and 31 December 2022 , we had gross balances with other Banco Santander group members as follows: 2023 2022 Financial institutions Financial institutions Banks Other Corporate Total Banks Other Corporate Total £bn £bn £bn £bn £bn £bn £bn £bn Assets Spain 0.8 — — 0.8 1.4 — — 1.4 UK — 4.6 — 4.6 — 4.2 — 4.2 0.8 4.6 — 5.4 1.4 4.2 — 5.6 Liabilities Spain 1.1 0.1 — 1.2 1.7 0.1 — 1.8 UK — 14.3 — 14.3 — 15.6 — 15.6 1.1 14.4 — 15.5 1.7 15.7 — 17.4
Disclosure of Borrower Profile	Stock New business 2023 2022 2023 2022 £m % £m % £m % £m % Home movers (1) 71,931 42 76,357 41 5,009 41 12,221 36 Remortgagers (2) 48,475 28 53,190 29 3,901 32 10,644 31 First-time buyers 36,868 21 37,971 21 3,015 25 8,129 24 Buy-to-let 15,585 9 16,799 9 239 2 3,133 9 172,859 100 184,317 100 12,164 100 34,127 100 (1) 'Home movers’ include both existing customers moving house and taking out a new mortgage with us, and customers who switch their mortgage to us when they move house. (2) 'Remortgagers’ are new customers who are taking a new mortgage with us.
Disclosure of Interest Rate Profile of Mortgage Assets Stock	The interest rate profile of our maturing mortgage asset stock was: 2023 2022 £m % £m % Fixed rate 153,207 89 163,622 89 Of which maturing: – < 12 months 37,630 22 38,233 21 – Later than 1 year but no later than 3 years 65,502 38 38,213 21 – Later than 3 years but no later than 4 years 34,725 20 24,310 13 – Later than 4 years but no later than 5 years 10,977 6 24,888 14 – Later than 5 years 4,373 3 37,978 21 Variable rate 13,761 8 12,430 7 Standard Variable Rate (SVR) 3,915 2 5,645 3 Follow on Rate (FoR) 1,976 1 2,620 1 172,859 100 184,317 100
Disclosure of Geographic Distribution of Mortgage Assets Stock	The geographical distribution of our mortgage asset stock and new business was: Stock New business 2023 2022 2023 2022 Region £bn £bn £bn £bn London 44.0 47.0 2.9 8.3 Midlands and East Anglia 24.2 25.6 1.8 5.3 North 22.9 24.4 1.7 4.7 Northern Ireland 2.6 2.9 0.1 0.3 Scotland 6.4 6.8 0.6 1.2 South East excluding London 54.8 58.4 3.8 10.6 South West, Wales and other 18.0 19.2 1.3 3.7 172.9 184.3 12.2 34.1
Disclosure of Mortgage Loan Size	Mortgage loan size 2023 2022 >£1.0m 2 % 2 % £0.5m to £1.0m 10 % 10 % £0.25m to £0.5m 31 % 31 % <£0.25m 57 % 57 % Average loan size (stock) (1) £187k £183k Average loan size (new business) £228k £237k (1) Average initial advance of existing stock.
Disclosure of LTV Distribution of Mortgage Assets Stock	This table shows the LTV distribution for the gross carrying amount and the related ECL of our total mortgage portfolio and Stage 3 mortgages, and new business. We also show the collateral value and average LTV. We use our estimate of the property value at the balance sheet date and include fees that have been added to the loan. For flexible products, we only include the drawn amount, not undrawn limits. 2023 2022 Stock Stage 3 New Stock Stage 3 New Total ECL Total ECL Business Total ECL Total ECL Business LTV £m £m £m £m £m £m £m £m £m £m Up to 50% 78,673 31 1,106 12 2,616 87,379 37 1,111 14 4,890 >50-60% 32,837 24 347 10 1,604 35,664 29 283 11 4,014 >60-70% 30,874 40 246 16 1,977 33,868 50 197 16 6,104 >70-80% 18,721 48 138 19 2,736 17,824 45 110 15 10,094 >80-90% 8,893 35 67 15 2,318 7,339 29 42 9 6,002 >90-100% 2,416 20 39 11 900 1,873 17 32 9 2,999 >100% 445 44 65 25 13 370 45 52 21 24 172,859 242 2,008 108 12,164 184,317 252 1,827 95 34,127 Collateral value (1) 172,803 1,997 12,164 184,269 1,818 34,126 % % % % % % Average LTV - Balance weighted (2) 51 49 66 50 47 69 (1) Collateral value is limited to the balance of each loan and excludes the impact of any over-collateralisation. Includes collateral against loans in negative equity of £389m ( 2022 : £323m ). (2)
Disclosure of Loan Modifications	The following table sets out the financial assets that were forborne while they had a loss allowance measured at lifetime ECL. 2023 2022 £m £m Financial assets modified in the period: – Amortised cost before modification 346 315 – Net modification loss 5 7 Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period 79 91 2023 2022 Term extension Interest-only Term extension Interest-only £m £m £m £m Stage 1 120 1,166 n/a n/a Stage 2 30 500 n/a n/a Stage 3 2 18 n/a n/a 152 1,684 n/a n/a The following table sets out the financial assets that were forborne while they had a loss allowance measured at lifetime ECL. Business banking Credit cards Overdrafts Total 2023 £m £m £m £m Financial assets modified in the period: – Amortised cost before modification — 13 8 21 – Net modification loss — 14 6 20 Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the loss allowance changed to 12m ECL in the period — 2 1 3 2022 Financial assets modified in the period: – Amortised cost before modification — 7 7 14 – Net modification loss — 7 6 13 Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the loss allowance changed to 12m ECL in the period — 3 1 4 The following table sets out the financial assets that were forborne while they had a loss allowance measured at lifetime ECL. 2023 2022 £m £m Financial assets modified in the period: – Amortised cost before modification 189 240 – Net modification loss 10 8 Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the loss allowance changed to 12-month ECL in the period 27 15
Disclosure of Forbearance Balances	The balances at 31 December 2023 and 31 December 2022 , analysed by their staging at the period-end and the forbearance we applied, were: Capitalisation Term extension Interest-only Concessionary interest rate Total Loss allowances 2023 £m £m £m £m £m £m Stage 2 325 386 211 11 933 7 Stage 3 284 150 64 171 669 30 609 536 275 182 1,602 37 Proportion of portfolio 0.3 % 0.3 % 0.2 % 0.1 % 0.9 % 2022 Stage 2 309 319 240 6 874 11 Stage 3 298 140 65 190 693 31 607 459 305 196 1,567 42 Proportion of portfolio 0.3 % 0.3 % 0.2 % 0.1 % 0.9 % (1) We base forbearance type on the first forbearance on the accounts. The balances at 31 December 2023 and 31 December 2022 were: Interest-only (2) Flexible LTV >100% Buy-to-Let 2023 £m £m £m £m Total 365 74 12 23 – Stage 2 216 55 3 16 – Stage 3 149 19 9 7 2022 Total 290 36 9 15 – Stage 2 111 19 — 11 – Stage 3 179 17 9 4 (1) Where a loan falls into more than one category, we have included it in all the categories that apply. (2) Comprises full interest-only loans and part interest-only, part repayment loans. The balances at 31 December 2023 and 31 December 2022 were: Other unsecured Business banking Personal loans Credit cards Overdrafts Total other unsecured Total 2023 £m £m £m £m £m £m Total 3 1 47 19 67 70 – Stage 2 — 1 5 2 8 8 – Stage 3 3 — 42 17 59 62 2022 Total 3 1 34 16 51 54 – Stage 2 — 1 6 2 9 9 – Stage 3 3 — 28 14 42 45 We only make forbearance arrangements for lending to customers. The balances at 31 December 2023 and 31 December 2022 , analysed by their staging at the period–end and the forbearance we applied, were: 2023 2022 £m £m Stock (1) – Term extension 113 98 – Interest-only 215 238 – Other payment rescheduling 264 219 592 555 Of which: – Stage 1 2 17 – Stage 2 159 173 – Stage 3 431 365 592 555 Proportion of portfolio 2.3% 2.0% (1) We base forbearance type on the first forbearance we applied. Tables only show accounts open at the period-end. Amounts are drawn balances and include off balance sheet balances.
Disclosure of Segments Exposure by Credit Rating	These tables show our credit risk exposure according to our internal rating scale (see the ‘Santander UK group level – credit risk review’ section) for each portfolio. On this scale, the higher the rating, the better the quality of the counterparty. Santander UK risk grade 9 8 7 6 5 4 3 to 1 Other (1) Total 2023 £m £m £m £m £m £m £m £m £m SME and mid corporate — 166 911 2,970 3,497 3,575 1,439 118 12,676 Commercial Real Estate — — 360 1,684 2,132 972 209 1 5,358 Social Housing 43 3,032 4,881 — — — — — 7,956 43 3,198 6,152 4,654 5,629 4,547 1,648 119 25,990 Of which: Stage 1 43 3,130 6,152 4,618 4,715 2,363 141 118 21,280 Stage 2 — 68 — 36 914 2,184 762 1 3,965 Stage 3 — — — — — — 745 — 745 2022 SME and mid corporate — 336 923 2,341 3,299 5,327 1,791 106 14,123 Commercial Real Estate — 2 111 2,044 2,128 936 185 1 5,407 Social Housing 44 4,028 3,956 6 — — — — 8,034 44 4,366 4,990 4,391 5,427 6,263 1,976 107 27,564 Of which: Stage 1 39 4,364 4,944 4,202 4,773 4,289 386 107 23,104 Stage 2 5 2 46 189 654 1,974 1,018 — 3,888 Stage 3 — — — — — — 572 — 572 (1) Smaller exposures mainly in the commercial mortgage portfolio. We use scorecards for them, instead of a rating model. These tables show our credit risk exposure according to our internal rating scale (see the ‘Santander UK group level – credit risk review’ section) for each portfolio. On this scale, the higher the rating, the better the quality of the counterparty. Santander UK risk grade 9 8 7 6 5 4 3 to 1 Other (1) Total 2023 £m £m £m £m £m £m £m £m £m Sovereign and Supranational 42,552 1,896 — — — — — — 44,448 Structured Products 170 1,470 787 — — — — — 2,427 Financial Institutions 1,167 665 393 7 — — — — 2,232 43,889 4,031 1,180 7 — — — — 49,107 Of which: Stage 1 43,889 4,031 1,180 7 — — — — 49,107 Stage 2 — — — — — — — — — Stage 3 — — — — — — — — — 2022 Sovereign and Supranational 47,040 1,077 — — — — — — 48,117 Structured Products 136 1,162 875 — — — — — 2,173 Financial Institutions 1,191 672 521 26 — — — — 2,410 48,367 2,911 1,396 26 — — — — 52,700 Of which: Stage 1 48,367 2,911 1,396 26 — — — — 52,700 Stage 2 — — — — — — — — — Stage 3 — — — — — — — — — (1) Smaller exposures mainly in the commercial mortgage portfolio . We use scorecards for them, instead of a rating model.
Disclosure of Segments Exposure by Geographical Distribution	We typically classify geographical location according to the counterparty’s country of domicile unless a full risk transfer guarantee is in place, in which case we use the guarantor’s country of domicile instead. At 31 December 2023 and 31 December 2022 this is mainly focused in the UK. We typically classify geographical location according to the counterparty’s country of domicile unless a full risk transfer guarantee is in place, in which case we use the guarantor’s country of domicile instead. 2023 2022 UK Europe US Rest of World Total UK Europe US Rest of World Total £m £m £m £m £m £m £m £m £m £m Sovereign and Supranational 39,581 2,063 — 2,804 44,448 43,936 1,886 83 2,212 48,117 Structured Products 1,430 243 — 754 2,427 1,379 422 4 368 2,173 Financial Institutions 884 968 186 194 2,232 988 1,005 230 187 2,410 41,895 3,274 186 3,752 49,107 46,303 3,313 317 2,767 52,700
Disclosure of Segments Exposure by Gross and Net Credit Exposure	Gross exposure Collateral Net exposure Stage 3 Stage 3 Stage 3 2023 £m £m £m SME and mid corporate 627 190 437 Commercial Real Estate 118 28 90 745 218 527 2022 SME and mid corporate 513 169 344 Commercial Real Estate 59 30 29 572 199 373

Liquidity Risk (Tables)

Liquidity Risk (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Liquidity Risk Exposure [Abstract]
Summary of Reconciliation of Wholesale Funding to Balance Sheet	This table reconciles our wholesale funding to our balance sheet at 31 December 2023 and 31 December 2022 . Balance sheet line item Funding analysis Deposits by banks (1) Deposits by customers (2) Repurchase agreements - non trading Financial liabilities designated at fair value Debt securities in issue Subordinated liabilities Other equity instruments (3) 2023 £bn £bn £bn £bn £bn £bn £bn £bn Deposits by banks 1.1 1.1 — — — — — — Certificates of deposit and commercial paper 4.3 — — — — 4.3 — — Senior unsecured – public benchmark 12.7 — 1.6 — — 11.1 — — – privately placed 0.8 — 0.1 — 0.6 0.1 — — Covered bonds 14.8 — — — — 14.8 — — Securitisation and structured issuance 2.7 — — — — 2.7 — — TFSME 17.0 17.0 — — — — — — Subordinated liabilities and equity 4.2 — — — — — 2.2 2.0 Total wholesale funding 57.6 18.1 1.7 — 0.6 33.0 2.2 2.0 Repos 8.4 — — 8.4 — — — — Foreign exchange and hedge accounting 1.1 — — — — 0.9 0.2 — Other 2.5 2.2 — — 0.3 — — — Balance sheet total 69.6 20.3 1.7 8.4 0.9 33.9 2.4 2.0 2022 Deposits by banks 0.5 0.5 — — — — — — Certificates of deposit and commercial paper 4.7 — — — — 4.7 — — Senior unsecured – public benchmark 14.3 — 4.6 — — 9.7 — – privately placed 0.6 — 0.1 — 0.4 0.1 — — Covered bonds 14.9 — — — — 14.9 — — Securitisation and structured issuance 1.0 — — — — 1.0 — — TFSME 25.0 25.0 — — — — — — Subordinated liabilities and equity 3.9 — — — — — 1.9 2.0 Total wholesale funding 64.9 25.5 4.7 — 0.4 30.4 1.9 2.0 Repos 8.0 — — 8.0 — — — — Foreign exchange and hedge accounting 1.6 — 0.1 — — 1.1 0.4 — Other 3.4 3.0 — — 0.4 — — — Balance sheet total 77.9 28.5 4.8 8.0 0.8 31.5 2.3 2.0 (1) Consists of Perpetual Capital Securities . See Note 33 to the Consolidated Financial Statements. (2) This is included in our balance sheet total of 190,850 m( 2022 : £ 195,568 m ). (3) Other consists of items in the course of transmission and other deposits. See Note 24 to the Consolidated Financial Statements.
Summary of Sources of Wholesale Funding by Maturity	≤ 1 month >1 and ≤ 3 months >3 and ≤ 6 months >6 and ≤ 9 months >9 and ≤ 12 months Sub-total ≤ 1 year >1 and ≤ 2 years >2 and ≤ 5 years >5 years Total 2023 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Downstreamed from Santander UK Group Holdings plc to Santander UK plc (1) Senior unsecured – public benchmark — 1.6 — — — 1.6 2.4 6.8 0.4 11.2 – privately placed — — — — — — — 0.1 — 0.1 Subordinated liabilities and equity (incl. AT1) — — 0.5 — — 0.5 0.8 1.3 0.9 3.5 — 1.6 0.5 — — 2.1 3.2 8.2 1.3 14.8 Other Santander UK plc Deposits by banks 0.3 0.8 — — — 1.1 — — — 1.1 Certificates of deposit and commercial paper 1.0 3.3 — — — 4.3 — — — 4.3 Senior unsecured – public benchmark — 0.6 0.2 — — 0.8 0.4 — 0.3 1.5 – privately placed — — — 0.1 — 0.1 0.1 0.2 0.3 0.7 Covered bonds 0.1 1.0 0.9 0.4 1.0 3.4 1.1 9.2 1.1 14.8 Securitisation & structured issuance (2) — — — — 0.1 0.1 — 2.1 — 2.2 TFSME — — — — — — 17.0 — — 17.0 Subordinated liabilities — — — — — — — — 0.7 0.7 1.4 5.7 1.1 0.5 1.1 9.8 18.6 11.5 2.4 42.3 Other group entities Securitisation & structured issuance (3) — — — — — — 0.5 — — 0.5 31 December 2023 1.4 7.3 1.6 0.5 1.1 11.9 22.3 19.7 3.7 57.6 Of which: – Secured 0.1 1.0 0.9 0.4 1.1 3.5 18.6 11.3 1.1 34.5 – Unsecured 1.3 6.3 0.7 0.1 — 8.4 3.7 8.4 2.6 23.1 2022 Total at 31 December 2022 2.6 5.2 0.5 1.5 1.2 11.0 6.6 42.2 5.1 64.9 Of which: – Secured 0.1 1.0 0.2 0.9 — 2.2 3.5 34.0 1.2 40.9 – Unsecured 2.5 4.2 0.3 0.6 1.2 8.8 3.1 8.2 3.9 24.0 (1) 96% of senior unsecured debt issued from Santander UK Group Holdings plc has been downstreamed to Santander UK plc as ‘secondary non-preferential debt’ in line with the guidelines from the Bank of England for Internal MREL. (2) Includes funding from mortgage-backed securitisation vehicles where Santander UK plc is the asset originator. (3) Includes funding from asset-backed securitisation vehicles where entities other than Santander UK plc are the asset originator.
Summary of Wholesale Funding by Currency	This table shows our wholesale funding by major currency at 31 December 2023 and 31 December 2022 . 2023 2022 Sterling US Dollar Euro Other Sterling US Dollar Euro Other % % % % % % % % Downstreamed from Santander UK Group Holdings plc to Santander UK plc Senior unsecured – public benchmark 23 60 17 — 18 58 24 — – privately placed — — — 100 — — — 100 Subordinated liabilities and equity (incl. AT1) 87 13 — — 75 25 — — 38 48 13 1 27 52 20 1 Other Santander UK plc Deposits by banks 1 97 2 — 29 71 — — Certificates of deposit and commercial paper 29 70 — 1 56 42 2 — Senior unsecured – public benchmark 21 56 23 — 18 62 20 — – privately placed 98 — 2 — 95 — 5 — Covered bonds 54 5 39 2 43 12 45 — Securitisation & structured issuance 100 — — — 100 — — — TFSME 100 — — — 100 — — — Subordinated liabilities 76 24 — — 48 52 — — 71 14 15 — 74 12 14 — Other group entities Securitisation & structured issuance 100 — — — — — — — Total 63 23 14 — 63 21 16 —
Summary of External Term Issuance, Sterling Equivalent	In 2023 , our external term issuance (sterling equivalent) was: Sterling US Dollar Euro Other 2023 2022 £bn £bn £bn £bn £bn £bn Downstreamed from Santander UK Group Holdings plc to Santander UK plc Senior unsecured – public benchmark 0.4 1.1 — — 1.5 3.9 Subordinated debt and equity (inc. AT1) 1.1 1.1 0.8 1.5 1.1 — — 2.6 4.7 Other Santander UK plc Securitisations and other secured funding 1.5 — — — 1.5 0.6 Covered bonds 1.5 — — 0.3 1.8 4.0 Senior unsecured – public benchmark — — — — — — Senior unsecured – privately placed 0.3 — — — 0.3 0.1 3.3 — — 0.3 3.6 4.7 Other group entities Securitisations 0.5 — — — 0.5 — Total gross issuances 5.3 1.1 — 0.3 6.7 9.4
Summary of Balance Sheet Encumbered and Unencumbered Assets Explanatory	On-balance sheet encumbered and unencumbered assets (audited) Encumbered with counterparties other than central banks Assets positioned at central banks (3) Covered bonds Securitis- ations Other Total 2023 £m £m £m £m £m Cash and balances at central banks (1)(2) — — 1,480 1,480 831 Financial assets at FVTPL: – Derivative financial instruments — — — — — – Other financial assets at FVTPL — — — — — Financial assets at amortised cost: – Loans and advances to customers 21,880 5,208 59 27,147 58,489 – Loans and advances to banks — — 254 254 — – Repurchase agreements – non trading — — — — — – Other financial assets at amortised cost — — 14 14 — Financial assets at FVOCI — — 5,183 5,183 — Interests in other entities — — — — — Intangible assets — — — — — Property, plant and equipment — — — — — Current tax assets — — — — — Retirement benefit assets — — — — — Other assets — — — — — Total assets 21,880 5,208 6,990 34,078 59,320 2022 Cash and balances at central banks (1)(2) — — 1,330 1,330 893 Financial assets at FVTPL: – Derivative financial instruments — — — — — – Other financial assets at FVTPL — — — — — Financial assets at amortised cost: – Loans and advances to customers 21,304 2,851 56 24,211 68,535 – Loans and advances to banks — — 163 163 — – Repurchase agreements – non trading — — — — — – Other financial assets at amortised cost — — 48 48 — Financial assets at FVOCI — — 4,365 4,365 — Interests in other entities — — — — — Intangible assets — — — — — Property, plant and equipment — — — — — Current tax assets — — — — — Retirement benefit assets — — — — — Other assets — — — — — Total assets 21,304 2,851 5,962 30,117 69,428 (1) Encumbered cash and balances at central banks include minimum cash balances we have to hold at central banks for regulatory purposes. (2) Readily realisable cash and balances at central banks are amounts held at central banks as part of our liquidity management activities. (3) Comprises pre-positioned assets and encumbered assets.

Capital Risk (Tables)

Capital Risk (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Capital Risk Exposure [Abstract]
Summary of Regulatory Capital Resources	This table shows our qualifying regulatory capital: 2023 2022 £m £m CET1 capital 10,443 10,799 AT1 capital 1,956 1,956 Tier 1 capital 12,399 12,755 Tier 2 capital 2,172 1,548 Total regulatory capital (1) 14,571 14,303 (1) Capital resources include a transitional IFRS 9 benefit at 31 December 2023 of £43m ( 2022 : £19m

Market Risk (Tables)

Market Risk (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Market Risk Exposure [Abstract]
Summary of Key Non-Traded Market Risks	Our key non-traded market risks are: Key risks Description Interest rate risk Yield curve risk: comes from timing mismatches in repricing fixed and variable rate assets, liabilities and off-balance sheet instruments. It also comes from investing non-rate sensitive liabilities in interest-earning assets. Basis risk: comes from pricing assets using a different rate index to the liabilities that fund them. We are exposed to basis risks associated with Bank of England bank rate, reserve rate linked assets we deposit with central banks, and the Sterling Overnight Index Average (SONIA) rate. Since the cessation of LIBOR at the end of 2021, basis risk exposure has been immaterial. Spread risk Spread risk arises when the value of assets or liabilities which are accounted for at fair value (either through Other Comprehensive Income or through Profit and Loss) are affected by changes in the credit spread. We measure these spreads as the difference between the discount rate we use to value the asset or liability, and an underlying interest rate curve. Foreign exchange risk Our banking businesses operate mainly in sterling markets, so we do not create significant foreign exchange exposures. The only exception to this is money we raise in foreign currencies. For more on this, see ‘Wholesale funding’ in the ‘Liquidity risk’ section. Income statement volatility risk We measure most of the assets and liabilities in our banking book balance sheet at amortised cost. We sometimes manage their risk profile by using derivatives. As all derivatives are accounted for at fair value, the mismatch in their accounting treatment can lead to volatility in our Income Statement. This happens even if the derivative is an economic hedge of the asset or liability.
Summary of NII and EVE Sensitivities Measurement	Net Interest Income (NII) sensitivity – NII sensitivity is an income-based measure we use to forecast the changes to interest income and interest expense in different scenarios. It gives us a combined impact on net interest income over a given period – usually 12 or 36 months. – We calculate NII sensitivity as the change in NII for a defined set of instantaneous parallel and non-parallel shifts in the yield curve. EVE sensitivity – We calculate EVE sensitivity as the change in the net present value of all the interest rate sensitive items in the banking book balance sheet for a defined set of instantaneous parallel and non-parallel shifts in the yield curve.
Summary of Detailed Information about VaR	Value at Risk (VaR) (audited) VaR – VaR indicates the losses that we might suffer because of unfavourable changes in the markets under normal (non-stressed) market conditions. – We run a historical simulation using historical daily price moves to find how much we might lose, normally at a 99% confidence level. The limitations of VaR VaR is a useful and important market standard measure of risk, but it does have some limitations. These include: – VaR assumes what happened in the past is a reliable way to predict what will happen in the future. This may not always be the case – VaR is based on positions at the end of the business day so it doesn’t include intra-day positions – VaR does not predict how big the loss could be on the 1 % of trading days that it is greater than the VaR – Using a time horizon of one day means VaR does not tell us everything about exposures that we cannot liquidate or hedge within a day, or products with infrequent pricing. Back-testing – comparing VaR estimates with reality To check that the way we estimate VaR is reasonable, we back-test our VaR by comparing it against both actual and hypothetical profits and losses, using a one- day time horizon. Back-testing allows us to identify exceptions – times when the predictions were out of line with what happened. We can then look for trends in these exceptions, which can help us decide whether we need to recalibrate our VaR model.
Summary of NII and EVE Sensitivity of Interest Rate Risk	The table below shows how our net interest income would be affected by a 100bps parallel shift (both up and down) applied instantaneously to the yield curve at 31 December 2023 and 31 December 2022 . Sensitivity to parallel shifts represents the amount of risk in a way that we think is both simple and scalable. 2023 2022 +100bps -100bps +100bps -100bps £m £m £m £m NII sensitivity (audited) (1) 220 (220) 241 (197) EVE sensitivity (299) 265 (487) 635 (1) Based on modelling assumptions of repricing behaviour.

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Significant Accounting Policies [Abstract]
Schedule of Useful Lives or Depreciation Rates Used for Property, Plant and Equipment	Classes of property, plant and equipment are depreciated on a straight-line basis over their useful life, as follows: Owner-occupied properties Not exceeding 50 years Office fixtures and equipment 3 to 15 years Computer software 3 to 7 years Right-of-use assets Shorter of the lease term or the useful life of the underlying asset Operating lease assets - vehicles 1 to 4 years
Disclosure of Information about Key Judgements and Key Estimates	Key judgements – Determining an appropriate definition of default – Establishing the criteria for a significant increase in credit risk (SICR) and, for corporate borrowers, internal credit risk rating – Determining the need for any judgemental adjustments – Determining the need to assess corporate Stage 3 exposures individually Key estimates – Forward-looking multiple economic scenario assumptions – Probability weights assigned to multiple economic scenarios Key judgements – Determining whether a present obligation exists – Determining the likely outcome of future legal decisions Key estimates – Probability, timing, nature and amount of any outflows that may arise from past events Key judgements – Setting the criteria for constructing the corporate bond yield curve used to determine the discount rate – Determining the methodology for setting the inflation assumption Key estimates – Discount rate applied to future cash flows – Rate of price inflation – Expected lifetime of the schemes' members – Valuation of pension fund assets whose values are not based on market observable data Key judgements: – Determining the basis of goodwill impairment testing and the methodology for determining the carrying value of CGUs, including the need for planning assumptions and internal capital allocations Key estimates: – Forecast cash flows for cash generating units, including estimated allocations of regulatory capital – Growth rate beyond initial cash flow projections – Discount rates which factor in risk-free rates and applicable risk premiums All of these variables are subject to fluctuations in external market rates and economic conditions beyond management’s control

Segments (Tables)

Segments (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of operating segments [abstract]
Summary of Results by Segment	Results by segment 3 For the year ended 31 December Retail & Business Banking Consumer Finance Corporate & Commercial Banking Corporate Centre Total 2023 £m £m £m £m £m Net interest income/(expense) 3,716 156 841 (55) 4,658 Non-interest income/(expense) 182 192 135 (71) 438 Total operating income/(expense) 3,898 348 976 (126) 5,096 Operating expenses before credit impairment charges, provisions and charges (1,813) (141) (351) (151) (2,456) Credit impairment charges (149) (15) (40) (1) (205) Provisions for other liabilities and charges (233) (18) (15) (69) (335) Total operating credit impairment charges, provisions and charges (382) (33) (55) (70) (540) Profit/(loss) from continuing operations before tax 1,703 174 570 (347) 2,100 Revenue from external customers 3,597 663 712 124 5,096 Inter-segment revenue/(expense) 301 (315) 264 (250) — Total operating income/(expense) 3,898 348 976 (126) 5,096 Revenue from external customers includes the following fee and commission income: (1) – Current account and debit card fees 493 — 49 — 542 – Insurance, protection and investments 47 — — — 47 – Credit cards 94 — — — 94 – Non-banking and other fees (2) 3 25 79 14 121 Total fee and commission income 637 25 128 14 804 Fee and commission expense (458) (6) (11) (26) (501) Net fee and commission income/(expense) 179 19 117 (12) 303 Customer loans 179,887 5,228 17,939 — 203,054 Customer deposits 158,329 — 24,066 5,050 187,445 Average number of full-time equivalent staff 16,330 816 2,376 24 19,546 (1) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (2) Non-banking and other fees include mortgages (except mortgage account fees), consumer finance, commitment commission, asset finance, invoice finance and trade finance. (3) Total assets and total liabilities are no longer included in reports provided to the chief operating decision maker. Retail & Business Banking Consumer Finance Corporate & Commercial Banking Corporate Centre Total 2022 £m £m £m £m £m Net interest income/(expense) 3,671 180 580 (6) 4,425 Non-interest income/(expense) 209 195 146 (19) 531 Total operating income 3,880 375 726 (25) 4,956 Operating expenses before credit impairment charges, provisions and charges (1,682) (144) (342) (175) (2,343) Credit impairment charges (262) (27) (31) — (320) Provisions for other liabilities and charges (394) (6) (8) (11) (419) Total operating credit impairment charges, provisions and charges (656) (33) (39) (11) (739) Profit/(loss) from continuing operations before tax 1,542 198 345 (211) 1,874 Revenue/(expense) from external customers 4,109 513 732 (398) 4,956 Inter-segment revenue/(expense) (229) (138) (6) 373 — Total operating income/(expense) 3,880 375 726 (25) 4,956 Revenue from external customers includes the following fee and commission income: (1) – Current account and debit card fees 502 — 60 — 562 – Insurance, protection and investments 78 — — — 78 – Credit cards 95 — — — 95 – Non-banking and other fees (2) 2 20 77 5 104 Total fee and commission income 677 20 137 5 839 Fee and commission expense (478) (5) (18) (8) (509) Net fee/(expense) and commission income 199 15 119 (3) 330 31 December 2022 Customer loans 191,836 5,384 18,518 — 215,738 Customer deposits 161,748 — 24,798 3,365 189,911 Average number of full-time equivalent staff 15,212 531 2,336 44 18,123 Retail & Business Banking Consumer Finance Corporate & Commercial Banking Corporate & Investment Banking Corporate Centre Total 2021 £m £m £m £m £m £m Net interest income/(expense) 3,356 233 397 — (37) 3,949 Non-interest income 205 178 112 — 55 550 Total operating income 3,561 411 509 — 18 4,499 Operating expenses before credit impairment (charges)/write-backs, provisions and charges (1,701) (163) (365) — (281) (2,510) Credit impairment (charges)/write-backs 98 33 90 — 12 233 Provisions for other liabilities and charges (185) 4 (34) — (162) (377) Total operating credit impairment (charges)/write-backs, provisions and charges (87) 37 56 — (150) (144) Profit/(loss) from continuing operations before tax 1,773 285 200 — (413) 1,845 Revenue from external customers 4,010 489 619 — (619) 4,499 Inter-segment revenue (449) (78) (110) — 637 — Total operating income 3,561 411 509 — 18 4,499 Revenue from external customers includes the following fee and commission income: (1) – Current account and debit card fees 428 — 50 — — 478 – Insurance, protection and investments 67 — — — — 67 – Credit card fees 73 — — — — 73 – Non-banking and other fees (2) 2 10 62 — 5 79 Total fee and commission income 570 10 112 — 5 697 Fee and commission expense (380) — (22) — (9) (411) Net fee and commission income 190 10 90 — (4) 286 Customer loans 183,023 4,984 19,281 — — 207,288 Customer deposits 156,991 — 26,466 — 2,758 186,215 Average number of full-time equivalent staff 16,149 670 2,281 528 76 19,704 (1) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (2) Non-banking and other fees include mortgages (except mortgage account fees), consumer finance, commitment commission, asset finance, invoice finance and trade finance. (3) Total assets and total liabilities are no longer included in reports provided to the chief operating decision maker. The table below shows the relationships between Customer assets and Loans and advances to customers as presented in the Consolidated Balance Sheet. Customer assets exclude Joint ventures, as they carry low credit risk and therefore have an immaterial ECL, and Other items, mainly accrued interest that we have not yet charged to the customer's account, and cash collateral. It also shows the relationship between customer liabilities (see above) and Deposits by customers as presented in the Consolidated Balance Sheet. Assets Liabilities 2023 2022 2023 2022 £m £m £m £m Customer balances (gross) 203,054 215,738 187,445 189,911 Loan loss allowance (914) (931) — — Customer balances (net) 202,140 214,807 187,445 189,911 Intercompany balances 4,544 4,161 2,825 5,981 Accrued interest 739 649 830 230 Other items 12 99 (250) (554) Loans and advances to customers / Deposits by customers 207,435 219,716 190,850 195,568
Summary Of Relationship Between Customer Liabilities and Deposits	The table below shows the relationships between Customer assets and Loans and advances to customers as presented in the Consolidated Balance Sheet. Customer assets exclude Joint ventures, as they carry low credit risk and therefore have an immaterial ECL, and Other items, mainly accrued interest that we have not yet charged to the customer's account, and cash collateral. It also shows the relationship between customer liabilities (see above) and Deposits by customers as presented in the Consolidated Balance Sheet. Assets Liabilities 2023 2022 2023 2022 £m £m £m £m Customer balances (gross) 203,054 215,738 187,445 189,911 Loan loss allowance (914) (931) — — Customer balances (net) 202,140 214,807 187,445 189,911 Intercompany balances 4,544 4,161 2,825 5,981 Accrued interest 739 649 830 230 Other items 12 99 (250) (554) Loans and advances to customers / Deposits by customers 207,435 219,716 190,850 195,568

Net Interest Income (Tables)

Net Interest Income (Tables)	12 Months Ended
	Dec. 31, 2023
Analysis of income and expense [abstract]
Summary of Net Interest Income	Group 2023 2022 2021 £m £m £m Interest and similar income: Loans and advances to customers 8,767 5,774 4,619 Loans and advances to banks 1,751 618 52 Reverse repurchase agreements – non-trading 626 149 35 Other 473 167 56 Total interest and similar income (1) 11,617 6,708 4,762 Interest expense and similar charges: Deposits by customers (3,230) (905) (430) Deposits by banks (1,165) (496) (25) Repurchase agreements – non-trading (538) (120) (3) Debt securities in issue (1,852) (650) (252) Subordinated liabilities (169) (108) (92) Other (5) (4) (11) Total interest expense and similar charges (2) (6,959) (2,283) (813) Net interest income 4,658 4,425 3,949 (1) Includes £230m ( 2022 : £87m , 2021 : £22m ) of interest income on financial assets at FVOCI. (2) Includes £706m ( 2022 : £6m , 2021 : £317m ) of interest expense on the effective part of derivatives hedging debt issuances and £3m ( 2022 : £3m , 2021 : £3m ) of interest expense on lease liabilities.

Net Fee and Commission Income (

Net Fee and Commission Income (Tables)	12 Months Ended
	Dec. 31, 2023
Fee and commission income (expense) [abstract]
Summary of Net Fee and Commission Income	Group 2023 2022 2021 £m £m £m Fee and commission income: Current account and debit card fees 542 562 478 Insurance, protection and investments 47 78 67 Credit cards 94 95 73 Non-banking and other fees (1) 121 104 79 Total fee and commission income 804 839 697 Total fee and commission expense (501) (509) (411) Net fee and commission income 303 330 286 (1) Non-banking and other fees include mortgages (except mortgage account fees), consumer finance, commitment commission, asset finance, invoice finance and trade finance.

Other Operating Income (Tables)

Other Operating Income (Tables)	12 Months Ended
	Dec. 31, 2023
Net Trading And Other Income [Abstract]
Summary of Net Trading and Other Income	Group 2023 2022 2021 £m £m £m Net (losses)/gains on financial instruments designated at fair value through profit or loss (1) (57) 62 (24) Net (losses) on financial instruments mandatorily at fair value through profit or loss (2) (11) (75) (2) Hedge ineffectiveness 19 29 13 Net profit on sale of financial assets at fair value through other comprehensive income — — 6 Income from operating lease assets 117 129 136 Other 67 56 135 135 201 264 (1) Net gains/ (losses) on financial instruments designated at fair value through profit or loss include losses of £24m on deposits ( 2022 : £35m gains, 2021 £18m losses), losses of £32m on debt securities ( 2022 : £31m gains, 2021 : £nil ). (2) Net gains /(losses) on financial instruments mandatorily at fair value through profit or loss include gains of £5m on debt securities ( 2022 : £13m gains, 2021 : £10m losses). Group 2023 2022 2021 £m £m £m Exchange rate differences in the consolidated income statement on items not at fair value through profit and loss 1,288 (2,163) 242 These are principally offset by related releases from the cash flow hedge reserve (1,248) 2,129 (358)

Operating Expenses Before Cre_2

Operating Expenses Before Credit Impairment Charges, Provisions and Charges (Tables)	12 Months Ended
	Dec. 31, 2023
Expenses by nature [abstract]
Disclosure Of Operating Expenses Before Credit Impairment Charges Provisions And Charges	For the year ended 31 December Group 2023 2022 2021 £m £m £m Staff costs: Wages and salaries 839 745 745 Performance-related payments 162 170 183 Social security costs 115 112 112 Pensions costs: – defined contribution plans 71 60 64 – defined benefit plans 13 28 38 Other personnel costs 41 44 41 1,241 1,159 1,183 Other administration expenses 925 888 826 Depreciation, amortisation and impairment 290 296 501 2,456 2,343 2,510
Summary of Deferred Performance Awards	Costs recognised in 2023 Costs expected to be recognised in 2024 or later Arising from awards in current year Arising from awards in prior year Total Arising from awards in current year Arising from awards in prior year Total £m £m £m £m £m £m Cash 3 4 7 5 7 12 Shares 2 5 7 4 7 11 5 9 14 9 14 23
Disclosure of Amount of Bonus Awarded to Employees	Expenses charged in the year Expenses deferred to future periods Total 2023 2022 2023 2022 2023 2022 £m £m £m £m £m £m Cash award – not deferred 140 145 — — 140 145 – deferred 7 8 12 14 19 22 Shares award – not deferred 8 9 — — 8 9 – deferred 7 8 11 14 18 22 Total discretionary bonus 162 170 23 28 185 198

Audit and Other Services (Table

Audit and Other Services (Tables)	12 Months Ended
	Dec. 31, 2023
Audit And Other Services [Abstract]
Summary of Audit and Other Services	Group 2023 2022 2021 £m £m £m Audit fees: Fees payable to the Company’s auditor and its associates for the audit of the Santander UK group’s annual accounts 13.9 11.8 11.2 Fees payable to the Company’s auditor and its associates for other services to the Santander UK group: – Audit of the Santander UK group's subsidiaries 0.6 0.7 0.9 Total audit fees (1) 14.5 12.5 12.1 Non-audit fees: Audit-related assurance services 0.7 0.6 0.8 Other assurance services 0.5 0.3 0.1 Other non-audit services 0.1 — 0.2 Total non-audit fees 1.3 0.9 1.1 (1) 2023 audit fees included £0.7m ( 2022 : £0.6m , 2021 : £1.2m ) which related to the prior year.

Credit Impairment Charges and_2

Credit Impairment Charges and Provisions (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Credit Impairment Loss And Provisions [Abstract]
Summary of Impairment Charges and Provisions	Group 2023 2022 2021 £m £m £m Credit impairment charges/(write-backs): Loans and advances to customers 191 248 (186) Recoveries of loans and advances, net of collection costs 10 36 (17) Off-balance sheet credit exposures (See Note 29) 4 36 (30) 205 320 (233) Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 29) 334 422 386 Releases for residual value and voluntary termination 1 (3) (9) 335 419 377 540 739 144

Taxation (Tables)

Taxation (Tables)	12 Months Ended
	Dec. 31, 2023
Major components of tax expense (income) [abstract]
Disclosure of Income Tax and Deferred Taxes Explanatory	Group 2023 2022 2021 £m £m £m Current tax: UK corporation tax on profit for the year 475 526 401 Adjustments in respect of prior years (15) (81) (24) Total current tax 460 445 377 Deferred tax: Charge/(credit) for the year 106 (29) 100 Adjustments in respect of prior years (7) 64 15 Total deferred tax 99 35 115 Tax on profit from continuing operations 559 480 492
Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate	The Santander UK group’s effective tax rate for 2023 was 26.6% ( 2022 : 25.6% , 2021 : 26.7% ). The tax on profit from continuing operations before tax differs from the theoretical amount that would arise using the basic corporation tax rate as follows: For the year ended 31 December Group 2023 2022 2021 £m £m £m Profit from continuing operations before tax 2,100 1,874 1,845 Tax calculated at a tax rate of 23.5% (2022:19%, 2021: 19%) 494 356 351 Bank surcharge on profits 85 121 104 Non-deductible preference dividends paid 9 9 9 Non-deductible UK Bank Levy 10 13 14 Non-deductible conduct remediation, fines and penalties 13 48 6 Other non-deductible costs and non-taxable income 2 29 37 Effect of change in tax rate on deferred tax provision 2 (29) 9 Tax relief on dividends in respect of other equity instruments (34) (40) (40) Adjustment to prior year provisions (22) (27) 2 Tax on profit from continuing operations 559 480 492
Disclosure of Movement in Current Tax Assets and Liabilities	Movements in current tax assets and liabilities during the year were as follows: Group 2023 2022 £m £m Assets 478 347 At 1 January 478 347 Income statement charge (including discontinued operations) (460) (445) Other comprehensive income (charge)/credit (70) 159 Corporate income tax received 537 405 Other movements 5 12 490 478 Assets 490 478 At 31 December 490 478
Schedule of Deferred Taxes	The table below shows the deferred tax balances including the movement in the deferred tax account during the year. Deferred tax balances are presented in the balance sheet after offsetting assets and liabilities where the Santander UK group has the legal right to offset and intends to settle on a net basis. Group Fair value of financial instruments Pension remeasurement Cash flow hedges Fair value reserve Tax losses carried forward Accelerated tax depreciation Other temporary differences Total £m £m £m £m £m £m £m £m At 1 January 2023 27 (290) 305 (1) — 35 (111) (35) Income statement (charge)/credit (35) (63) — — — (18) 17 (99) Transfers/reclassifications — — (3) (1) — 1 4 1 Credited/(charged) to other comprehensive income — 167 (229) 5 — — 4 (53) At 31 December 2023 (8) (186) 73 3 — 18 (86) (186) At 1 January 2022 (123) (508) (7) (12) 8 68 (5) (579) Income statement credit/(charge) 150 (49) — — (7) (33) (96) (35) Transfers/reclassifications — — 2 — (1) — (1) — Credited/(charged) to other comprehensive income — 267 310 11 — — (9) 579 At 31 December 2022 27 (290) 305 (1) — 35 (111) (35)

Dividends on Ordinary Shares (T

Dividends on Ordinary Shares (Tables)	12 Months Ended
	Dec. 31, 2023
Dividends On Ordinary Shares [Abstract]
Disclosure of Dividends on Ordinary Shares Declared and Paid	Dividends on ordinary shares declared and paid in the year were as follows: Group Group 2023 2022 2021 2023 2022 2021 Pence per share Pence per share Pence per share £m £m £m In respect of current year – first interim 1.32 1.25 0.90 410 389 281 – second interim 3.61 2.01 3.47 1,120 625 1,077 4.93 3.26 4.37 1,530 1,014 1,358

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of nature and extent of risks arising from financial instruments [abstract]
Disclosure of Notional Amounts and Fair Values of Derivatives	The table below includes the notional amounts of transactions outstanding at the balance sheet date; they do not represent actual exposures. Group 2023 2022 Fair value Fair value Notional amount Assets Liabilities Notional amount Assets Liabilities £m £m £m £m £m £m Derivatives held for trading: Exchange rate contracts 12,927 92 217 14,006 315 281 Interest rate contracts 28,351 389 583 31,135 465 754 Equity and credit contracts 765 133 20 902 130 25 Total derivatives held for trading 42,043 614 820 46,043 910 1,060 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 1,145 29 2 538 12 4 Interest rate contracts 107,540 1,275 839 77,748 1,777 403 108,685 1,304 841 78,286 1,789 407 Designated as cash flow hedges: Exchange rate contracts 21,618 1,008 289 26,035 1,717 186 Interest rate contracts 50,896 553 915 26,108 164 1,471 72,514 1,561 1,204 52,143 1,881 1,657 Total derivatives held for hedging 181,199 2,865 2,045 130,429 3,670 2,064 Derivative netting (1) — (2,047) (2,047) — (2,173) (2,173) Total derivatives 223,242 1,432 818 176,472 2,407 951 (1) Derivative netting excludes the effect of cash collateral, which is offset against the gross derivative position. The amount of cash collateral received that had been offset against the gross derivative assets was 472m ( 2022 : 1,368m ) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was 12m ( 2022 : 70m ).
Disclosure of Analysis of the Notional and Fair Values of Derivatives by Trading and Settlement Method	Notional Traded over the counter Asset Liability Settled by central counterparties Not settled by central counterparties Total Traded over the counter Traded over the counter 2023 £m £m £m £m £m Exchange rate contracts — 35,690 35,690 1,129 508 Interest rate contracts 174,460 12,327 186,787 170 290 Equity and credit contracts — 765 765 133 20 174,460 48,782 223,242 1,432 818 2022 Exchange rate contracts — 40,579 40,579 2,044 471 Interest rate contracts 124,638 10,353 134,991 233 455 Equity and credit contracts — 902 902 130 25 124,638 51,834 176,472 2,407 951
Disclosure of Maturity Profile and Average Price/Rate of Hedging Instruments Used in Hedging Strategies	The following table sets out the maturity profile and average price/rate of the hedging instruments used in the Santander UK group’s hedging strategies: Group 2023 Hedging Instruments ≤1 month >1 and ≤3 months >3 and ≤12 months >1 and ≤5 years >5 years Total Fair value hedges: Interest rate risk Interest rate contracts - Nominal amount (£m) 3,612 7,141 32,241 60,590 3,008 106,592 Average fixed interest rate - GBP 2.38 % 3.19 % 3.42 % 3.90 % 3.99 % Average fixed interest rate - EUR 1.14 % 0.18 % 0.45 % 0.21 % 3.92 % Average fixed interest rate - USD 2.60 % 2.46 % 4.23 % 1.36 % 4.91 % Interest rate/FX risk Exchange rate contracts - Nominal amount (£m) — 18 — 1,041 86 1,145 Interest rate contracts - Nominal amount (£m) — 18 — 844 86 948 Average GBP - EUR exchange rate — 1.11 — 1.16 1.15 Average GBP - USD exchange rate — — — 1.32 — Average fixed interest rate - EUR — — — 2.77 % 3.48 % Average fixed interest rate - USD — — — 4.83 % — Cash flow hedges: Interest rate risk Interest rate contracts – Nominal amount (£m) 911 2,993 12,770 27,721 1,219 45,614 Average fixed interest rate - GBP 5.06 % 2.98 % 5.39 % 3.83 % 3.45 % FX risk Exchange rate contracts - Nominal amount (£m) 927 3,238 2,692 9,447 588 16,892 Interest rate contracts - Nominal amount (£m) — 2,199 — — 942 3,141 Average GBP - JPY exchange rate 154.14 153.95 167.85 — — Average GBP - CHF exchange rate 1.09 1.09 1.09 1.12 1.12 Average GBP - EUR exchange rate — 1.20 1.17 1.18 — Average GBP - USD exchange rate — 1.39 — 1.28 1.39 Interest rate/FX risk Exchange rate contracts - Nominal amount (£m) 87 785 500 2,896 458 4,726 Interest rate contracts - Nominal amount (£m) — — — 1,975 166 2,141 Average GBP - EUR exchange rate 1.18 — 1.25 1.20 1.19 Average GBP - USD exchange rate — 1.66 — 1.38 1.54 Average fixed interest rate - GBP 2.57 % 2.54 % 2.96 % 2.31 % 4.74 % 2022 Fair value hedges: Interest rate risk Interest rate contracts- Nominal amount (£m) 2,210 4,468 21,678 45,314 3,808 77,478 Average fixed interest rate - GBP 2.58 % 0.88 % 0.56 % 2.07 % 3.78 % Average fixed interest rate - EUR 1.77 % 1.60 % 0.77 % 0.28 % 3.09 % Average fixed interest rate - USD 1.35 % 3.47 % 3.51 % 2.00 % 4.92 % Interest rate/FX risk Exchange rate contracts - Nominal amount (£m) — — 66 465 7 538 Interest rate contracts - Nominal amount (£m) — — — 263 7 270 Average GBP - EUR exchange rate — — 1.20 1.16 1.10 Average GBP - USD exchange rate — — — 1.19 — Average fixed interest rate - EUR — — 3.42 % 2.06 % — Average fixed interest rate - USD — — — 4.63 % — Cash flow hedges: Interest rate risk Interest rate contracts - Nominal amount (£m) 1,042 2,191 1,940 13,197 1,076 19,446 Average fixed interest rate - GBP 1.77 % 2.29 % 1.98 % 2.35 % 1.84 % FX risk Exchange rate contracts - Nominal amount (£m) 2,301 3,135 2,381 10,606 1,163 19,586 Interest rate contracts - Nominal amount (£m) 415 — — 2,325 997 3,737 Average GBP - JPY exchange rate — 157.45 160.04 — — Average GBP - CHF exchange rate — 1.13 — — — Average GBP - EUR exchange rate — — 1.12 1.18 1.17 Average GBP - USD exchange rate 1.22 1.25 1.17 1.31 1.39 Interest rate/FX risk Exchange rate contracts - Nominal amount (£m) — — 1,173 4,626 650 6,449 Interest rate contracts - Nominal amount (£m) — — 585 2,132 208 2,925 Average GBP - EUR exchange rate — — 1.19 1.21 1.20 Average GBP - USD exchange rate — — 1.60 1.50 1.54 Average fixed interest rate - GBP — — 3.27 % 2.58 % 4.59 %
Net Gains or Losses Arising From Hedges Included in Operating Income	Net gains or losses arising from fair value and cash flow hedges included in other operating income Group 2023 2022 2021 £m £m £m Fair value hedging: (Losses)/gains on hedging instruments (1,879) 2,381 852 Gains/(losses) on hedged items attributable to hedged risks 1,896 (2,316) (800) Fair value hedging ineffectiveness 17 65 52 Cash flow hedging ineffectiveness 2 (36) (39) 19 29 13
Disclosure of Information about Hedging Ineffectiveness by Risk Category Explanatory	Hedge ineffectiveness can be analysed by risk category as follows: Group 2023 2022 2021 Change in FV of hedging instruments Change in FV of hedged items Recognised in income statement Change in FV of hedging instruments Change in FV of hedged items Recognised in income statement Change in FV of hedging instruments Change in FV of hedged items Recognised in income statement Fair value hedges: £m £m £m £m £m £m £m £m £m Interest rate risk (1,865) 1,877 12 2,392 (2,333) 59 874 (834) 40 Interest rate/FX risk (14) 19 5 (11) 17 6 (22) 34 12 (1,879) 1,896 17 2,381 (2,316) 65 852 (800) 52 Group Hedging Instruments Recognised in Income Statement Reclassified from reserves to income Income statement line item affected by reclassification Change in FV Recognised in OCI Cash flow hedges: £m £m £m £m 2023 Interest rate risk Net interest income 466 (445) 21 (469) FX risk Net interest income/other operating income (396) 377 (19) (392) Interest rate/FX risk Net interest income/other operating income (237) 237 — (387) (167) 169 2 (1,248) 2022 Interest rate risk Net interest income (1,161) 1,160 (1) (96) FX risk Net interest income/other operating income 1,604 (1,604) — 1,692 Interest rate/FX risk Net interest income/other operating income (54) 19 (35) 533 389 (425) (36) 2,129 2021 Interest rate risk Net interest income (317) 305 (12) 73 FX risk Net interest income/other operating income (54) 54 — (158) Interest rate/FX risk Net interest income/other operating income (541) 514 (27) (273) (912) 873 (39) (358)
Disclosure of Reconciliation by Risk Category of Components of Equity and Analysis of Other Comprehensive Income Items Resulting from Hedge Accounting Explanatory	The following table provides a reconciliation by risk category of components of equity and analysis of OCI items (before tax) resulting from hedge accounting. Group 2023 2022 £m £m Balance at 1 January (1,575) 129 Effective portion of changes in fair value: – Interest rate risk 445 (1,160) – Foreign currency risk (377) 1,604 – Interest rate/foreign currency risk (237) (19) (169) 425 Income statement transfers: – Interest rate risk 469 96 – Foreign currency risk 392 (1,692) – Interest rate/foreign currency risk 387 (533) 1,248 (2,129) Balance at 31 December (496) (1,575)
Disclosure of detailed information about hedges	Hedged exposures Santander UK hedges its exposures to various risks, including interest rate risk and foreign currency risk, as set out in the following table. Group 2023 2022 Accumulated amount of FV hedge adjustments Change in value to calculate hedge ineffective ness Accumulated amount of FV hedge adjustments Change in value to calculate hedge ineffectiven ess Carrying value Hedged item Portfolio hedge of interest rate risks Of which Discontinued hedges Carrying value Hedged item Portfolio hedge of interest rate risks Of which Discontinued hedges £m £m £m £m £m £m £m £m £m £m Fair value hedges Interest rate risk: Loans and advances to customers 73,194 — (625) (435) 1,968 60,783 — (2,640) (653) (2,707) Other financial assets at amortised cost 152 1 (8) (8) 5 156 — (12) 2 (14) Reverse repurchase agreements – non trading 6,186 — — — 4 4,045 — (5) (1) — Other financial assets at FVOCI 2,013 (113) — (131) 82 2,325 (200) — 35 (227) Deposits by customers (15,892) 38 (10) — (53) (1,739) 24 5 — 33 Deposits by banks — — — — — — — — — — Debt securities in issue (4,091) 118 (75) (114) (128) (4,735) 321 (94) (172) 528 Subordinated liabilities (522) (27) (1) (42) (1) (250) (27) (6) (63) 54 Interest rate/FX risk: Other financial assets at FVOCI 989 4 — — 12 237 (21) — 1 (9) Debt securities in issue (214) (14) — (24) 8 (290) (18) — (37) 27 Subordinated liabilities — — — — (1) 1 1 — 1 (1) 61,815 7 (719) (754) 1,896 60,533 80 (2,752) (887) (2,316) Group 2023 2022 Change in value to calculate hedge ineffectiveness Cash flow hedge reserve Balances on cash flow hedge reserve for discontinued hedges Change in value to calculate hedge ineffectiveness Cash flow hedge reserve Balances on cash flow hedge reserve for discontinued hedges Hedged item balance sheet line item £m £m £m £m £m £m Cash flow hedges: Interest rate risk: Loans and advances to customers (163) (462) 1 935 (1,010) (1) Cash and balances at central banks (281) 99 (76) 233 (274) (106) Deposits by banks (1) (1) — (8) 7 — FX risk: Other financial assets at FVOCI (253) 1 — — (6) — Not applicable – highly probable forecast transactions 88 1 — (349) 2 — Deposits by customers (33) — — (167) (2) — Debt securities in issue 617 (9) — (1,051) (17) (2) Repurchase agreements - non trading (42) — — (37) — — Interest rate/FX risk: Debt securities in issue/loans and advances to customers 99 (75) — 56 (170) (3) Deposits by customers 94 (39) — — (74) — Subordinated liabilities/loans and advances to customers 44 (11) 52 (37) (31) 77 169 (496) (23) (425) (1,575) (35)

Other Financial Assets at Fai_2

Other Financial Assets at Fair Value Through Profit or Loss (Tables)	12 Months Ended
	Dec. 31, 2023
Financial assets at fair value through profit or loss [abstract]
Summary of Other Financial Assets at Fair Value Through Profit or Loss	Group 2023 2022 £m £m Loans and advances to customers: Loans to housing associations 8 4 Other loans 38 41 46 45 Debt securities 167 15 Other debt instruments 49 69 262 129

Loans and Advances to Custome_2

Loans and Advances to Customers (Tables)	12 Months Ended
	Dec. 31, 2023
Net Loans And Advances To Customers [Abstract]
Summary of Net Loans and Advances to Customers	Group 2023 2022 £m £m Loans secured on residential properties 172,854 184,317 Corporate loans 18,267 19,057 Finance leases 4,530 4,645 Other unsecured loans 7,232 7,742 Accrued interest and other adjustments 943 688 Amounts due from fellow Banco Santander subsidiaries and joint ventures 4,489 4,220 Amounts due from Santander UK Group Holdings plc 55 — Amounts due from subsidiaries — — Loans and advances to customers 208,370 220,669 Credit impairment loss allowances on loans and advances to customers (914) (931) Residual value and voluntary termination provisions on finance leases (21) (22) Net loans and advances to customers 207,435 219,716
Disclosure of Finance Lease and Hire Purchase Contract Receivables	Finance lease and hire purchase contract receivables may be analysed as follows: Group 2023 2022 Gross investment Unearned finance income Net investment Gross investment Unearned finance income Net investment £m £m £m £m £m £m No later than one year 1,502 (216) 1,286 1,493 (182) 1,311 Later than one year and not later than two years 1,426 (208) 1,218 1,367 (168) 1,199 Later than two years and not later than three years 1,331 (194) 1,137 1,190 (147) 1,043 Later than three years and not later than four years 882 (129) 753 1,044 (129) 915 Later than four years and not later than five years 99 (14) 85 143 (18) 125 Later than five years 60 (9) 51 59 (7) 52 5,300 (770) 4,530 5,296 (651) 4,645
Disclosure of Maturity Analysis of Operating Lease Payments	At 31 December 2023 and 2022 , the Santander UK group had contracted with lessees for the following future undiscounted minimum lease payments receivable under operating leases. Group 2023 2022 £m £m No later than one year 28 31 Later than one year and not later than two years 26 27 Later than two years and not later than three years 18 22 Later than three years and not later than four years 14 13 Later than four years and not later than five years 7 11 Later than five years 18 21 111 125

Securitisations and Covered B_2

Securitisations and Covered Bonds (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Securitisations And Covered Bonds [Abstract]
Disclosure of Analysis of Securitisations and Covered Bonds	Group Gross assets External notes in issue Notes issued to Santander UK plc/subsidiaries as collateral 2023 2022 2023 2022 2023 2022 £m £m £m £m £m £m Mortgage-backed master trust structures: – Holmes 3,242 1,646 2,119 790 300 176 – Fosse 2,048 2,028 100 100 1,382 1,365 5,290 3,674 2,219 890 1,682 1,541 Other asset-backed securitisation structures: – Motor — 6 — 7 — — – Repton 757 — 550 — — — 757 6 550 7 — — Total securitisation programmes 6,047 3,680 2,769 897 1,682 1,541 Covered bond programme: – Euro 35bn Global Covered Bond Programme 21,880 21,304 15,000 15,205 — — Total securitisation and covered bond programmes 27,927 24,984 17,769 16,102 1,682 1,541
Summary of Issuances and Redemptions of Securitisation and Covered Bond Programme	The following table sets out the internal and external issuances and redemptions in 2023 and 2022 for each securitisation and covered bond programme. Group Internal issuances External issuances Internal redemptions External redemptions 2023 2022 2023 2022 2023 2022 2023 2022 £m £m £m £m £m £m £m £m Mortgage-backed master trust structures: – Holmes 241 — 1,500 600 121 100 186 200 – Fosse — — — — — — — 200 Other asset-backed securitisation structures: – Motor — — — — — — 7 33 – Repton — — 550 — — — — — Covered bond programme: – Euro 35bn Global Covered Bond Programme — — — 4,200 — 100 — 1,700 241 — 2,050 4,800 121 200 193 2,133

Transfers of Financial Assets_2

Transfers of Financial Assets Not Qualifying for Derecognition (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of transferred financial assets that are not derecognised in their entirety [abstract]
Carrying Amount of Financial Assets that Did Not Qualify for Derecognition and their Associated Financial Liabilities	The following table analyses the carrying amount of financial assets that did not qualify for derecognition and their associated financial liabilities: Group 2023 2022 Assets Liabilities Assets Liabilities Nature of transaction £m £m £m £m Sale and repurchase agreements 14 (15) 120 (128) Securities lending agreements 3,136 (2,735) 2,871 (2,509) Securitisations (See Notes 14 and 26) 6,047 (2,769) 3,680 (897) 9,197 (5,519) 6,671 (3,534)

Reverse Repurchase Agreements_2

Reverse Repurchase Agreements - Non Trading (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Reserve Repurchase Agreements Non-Trading [Abstract]
Summary of Reverse Repurchase Agreements - Non Trading	Group 2023 2022 £m £m Agreements with banks 2,397 885 Agreements with customers 10,071 6,463 12,468 7,348

Other Financial Assets at Amo_2

Other Financial Assets at Amortised Cost (Tables)	12 Months Ended
	Dec. 31, 2023
Financial assets at fair value through profit or loss [abstract]
Summary of Other Financial Assets at Amortised Cost	Group 2023 2022 £m £m Asset backed securities — — Debt securities 152 156 0 152 156

Financial Assets at Fair Valu_2

Financial Assets at Fair Value Through Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2023
Financial assets at fair value through other comprehensive income [abstract]
Summary of Financial Assets at Fair Value Through Other Comprehensive Income	Group 2023 2022 £m £m Debt securities 8,481 6,024 8,481 6,024

Interests in Other Entities (Ta

Interests in Other Entities (Tables)	12 Months Ended
	Dec. 31, 2023
Investments accounted for using equity method [abstract]
Schedule of Interests in Other Entities	Group 2023 2022 £m £m Subsidiaries — — Joint Ventures 245 252 0 245 252

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of detailed information about intangible assets [abstract]
Schedule of Goodwill	a) Goodwill Group Cost Accumulated impairment Carrying amount £m £m £m At 31 December 2022 and 1 January 2023 and 31 December 2023 1,269 (70) 1,199
Schedule of Goodwill for Cash Generating Units	Basis of the recoverable amount The recoverable amount of all CGUs was determined based on its value in use (VIU) methodology at each testing date. For each CGU, the VIU is calculated by discounting management’s cash flow projections for the CGU. The cash flow projections also take account of increased internal capital allocations needed to achieve internal and regulatory capital targets including the leverage ratio. The key assumptions used in the VIU calculation for each CGU are set out below. The Retail & Business Banking segment consists of the Private Banking CGU and the rest of Retail & Business Banking, known as the Personal Financial Services CGU. Carrying amount of Goodwill by CGU and key assumptions in the VIU calculation Goodwill Discount rate Growth rate beyond initial cash flow projections 2023 2022 2023 2022 2023 2022 CGU £m £m % % % % Personal Financial Services 1,169 1,169 16.7 16.6 1.6 1.6 Private Banking 30 30 14.6 15.3 1.6 1.6 1,199 1,199
Disclosure of Reasonably Possible Changes in Key Assumptions	Reasonably possible changes in key assumptions CGU Input Key assumptions Associated risks Reasonably possible change Personal Financial Services Cash flow projections – BoE Bank Rate – UK house price growth – UK mortgage loan market growth – UK unemployment rate – Position in the market – Regulatory capital levels. – Uncertain market outlook – Higher interest rate environment impact on customer affordability – Customer remediation and regulatory action outcomes – Uncertain regulatory capital requirements. – Cash flow projections decrease by 10% ( 2022 : 5% ) . Discount rate – Discount rate used is a reasonable estimate of a suitable market rate for the profile of the business. – Market rates of interest rise. – Discount rate increases by 100 basis points ( 2022 : 100 basis points ) . GDP growth rate – High oil / gas prices – Elevated wage growth – Weak productivity – Large government debt burden – Fragile business and consumer confidence – Inflation and interest rates stay higher for longer, hitting the disposable income of our customers – Affects the profitability of our customers – Limits the scope for tax cuts, hitting the disposable income of our customers – Affects business and consumer spending decisions of our customers – GDP Growth rate decreases by 10% ( 2022 : 10% ) At 31 December 2023 and 31 December 2022 , a reasonably possible change in the key assumptions in relation to the VIU calculation for the goodwill balance in the Personal Financial Services CGU would have resulted in a reduction in headroom as follows. Reduction in headroom 2023 2022 CGU Reasonably possible change £m £m Personal Financial Services Cash flow projections decrease by 10% ( 2022 : 5% ) (818) (538) Discount rate increases by 100 basis points ( 2022 : 100 basis points ) (663) (887) GDP Growth rate decreases by 10% ( 2022 : 10% ) (19) (31) The sensitivity analysis presented below has been prepared on the basis that a change in each key assumption would not have a consequential impact on other assumptions used in the impairment review. However, due to the interrelationships between some of the assumptions, a change in one of the assumptions might impact one or more of the other assumptions and could result in a larger or smaller overall impact. 2023 Carrying value Value in use Headroom Increase in discount rate Decrease in GDP growth rate Decrease in cash flows CGU £m £m £m bps % % Personal Financial Services 7,513 8,178 665 101 4 8 2022 Personal Financial Services 8,860 10,752 1,892 239 13 18
Disclosure of Intangible Assets	b) Other intangibles Group Cost Accumulated amortisation/ impairment Carrying amount £m £m £m At 1 January 2023 1,261 (910) 351 Additions 114 — 114 Disposals (36) 36 — Charge — (116) (116) At 31 December 2023 1,339 (990) 349 At 1 January 2022 1,334 (992) 342 Additions 112 — 112 Disposals (185) 185 — Charge — (100) (100) Impairment — (3) (3) At 31 December 2022 1,261 (910) 351

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2023
Property, plant and equipment [abstract]
Disclosure of Detailed Information about Property, Plant and Equipment	Group Property Office fixtures and equipment Computer software Operating lease assets Right-of-use assets Total (1) £m £m £m £m £m £m Cost: At 1 January 2023 889 823 72 722 267 2,773 Additions 87 83 — 85 31 286 Reclassification (to)/from assets held for sale 8 — — — — 8 Disposals (66) (29) (5) (172) (35) (307) At 31 December 2023 918 877 67 635 263 2,760 Accumulated depreciation: At 1 January 2023 270 618 72 145 155 1,260 Charge for the period 17 62 — 64 30 173 Impairment during the period — — — — (11) (11) Disposals (61) (27) (5) (62) (1) (156) At 31 December 2023 226 653 67 147 173 1,266 Carrying amount 692 224 — 488 90 1,494 Group Property Office fixtures and equipment Computer software Operating lease assets Right-of-use assets Total (1) £m £m £m £m £m £m Cost: At 1 January 2022 978 1,049 434 755 254 3,470 Additions 61 86 — 185 38 370 Reclassification to assets held for sale (98) (13) — — — (111) Disposals (52) (299) (362) (218) (25) (956) At 31 December 2022 889 823 72 722 267 2,773 Accumulated depreciation: At 1 January 2022 334 857 434 160 137 1,922 Charge for the year 18 68 1 73 19 179 Impairment during the year 8 2 — — — 10 Reclassification to assets held for sale (49) (13) — — — (62) Disposals (41) (296) (363) (88) (1) (789) At 31 December 2022 270 618 72 145 155 1,260 Carrying amount 619 205 — 577 112 1,513 (1) Property includes investment properties of £17m ( 2022 : £17m ) and assets under construction of £nil ( 2022 : £204m ). In September 2023, we completed the construction of a new head office in Milton Keynes.

Other Financial Liabilities a_2

Other Financial Liabilities at Fair Value Through Profit or Loss (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of financial liabilities [abstract]
Summary of Other Financial Liabilities at Fair Value Through Profit or Loss	Group 2023 2022 £m £m Structured Notes Programmes 369 375 Structured deposits 426 321 Zero Amortising Guaranteed Notes 104 107 899 803

Deposits by Customers (Tables)

Deposits by Customers (Tables)	12 Months Ended
	Dec. 31, 2023
Deposits from customers [abstract]
Schedule of Deposits by Customers	Group 2023 2022 £m £m Demand and time deposits (1) 188,004 189,587 Amounts due to other Santander UK Group Holdings plc subsidiaries 114 67 Amounts due to Santander UK Group Holdings plc (2) 1,772 4,759 Amounts due to fellow Banco Santander subsidiaries and joint ventures 960 1,155 190,850 195,568 (1) Includes capital amount guaranteed / protected equity index-linked deposits of £304m ( 2022 : £408m ). (2) Includes downstreamed funding from our immediate parent company Santander UK Group Holdings plc.

Deposits by Banks (Tables)

Deposits by Banks (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Deposits From Banks [Abstract]
Schedule of Deposits by Banks	Group 2023 2022 £m £m Items in the course of transmission 732 701 Deposits held as collateral 860 1,741 Other deposits (1) 18,737 26,082 Amounts due to Santander UK subsidiaries 3 1 20,332 28,525 (1) Includes drawdown from the TFSME of £17.0bn ( 2022 : £25.0bn

Repurchase Agreements - Non T_2

Repurchase Agreements - Non Trading (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Repurchase Agreements 1 [Abstract]
Summary of Repurchase Agreements - Non Trading	Group 2023 2022 £m £m Agreements with banks 551 50 Agreements with customers 7,860 7,932 8,411 7,982

Debt Securities in Issue (Table

Debt Securities in Issue (Tables)	12 Months Ended
	Dec. 31, 2023
Debt Securities In Issue [Abstract]
Summary of Debt Securities in Issue	Group 2023 2022 £m £m Medium-term notes: – US $30bn Euro Medium Term Note Programme 744 739 – Euro 30bn Euro Medium Term Note Programme 3,784 3,211 - US SEC-registered Debt Programme - Santander UK plc 7,128 6,694 Medium-term notes 11,656 10,644 Euro 35bn Global Covered Bond Programme 15,000 15,205 US $20bn Commercial Paper Programmes 2,761 1,851 Certificates of deposit 1,530 2,874 Credit linked notes 194 60 Securitisation programmes 2,769 897 33,910 31,531

Subordinated Liabilities (Table

Subordinated Liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Subordinated Liabilities [Abstract]
Schedule of Subordinated Liabilities	Group 2023 2022 £m £m £325m Sterling preference shares 343 344 Undated subordinated liabilities 205 219 Dated subordinated liabilities 1,838 1,769 2,386 2,332
Disclosure of Undated Subordinated Liabilities Explanatory	Undated subordinated liabilities Group 2023 2022 First call date £m £m 10.0625% Exchangeable capital securities n/a 205 205 7.125% 30 Year Step-up perpetual callable subordinated notes 2030 — 14 205 219
Disclosure of Dated Subordinated Liabilities Explanatory	Dated subordinated liabilities Group 2023 2022 Maturity £m £m 5% Subordinated notes 2023 — 591 4.75% Subordinated notes 2025 326 608 7.95% Subordinated notes 2029 193 207 6.50% Subordinated notes 2030 1 22 5.875% Subordinated notes 2031 7 7 5.625% Subordinated notes 2045 222 334 7.869% Subordinated notes 2033 321 — 8.296% Subordinated notes 2033 768 — 1,838 1,769

Other Liabilities (Tables)

Other Liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Subclassifications of assets, liabilities and equities [abstract]
Disclosure Of Other Liabilities Explanatory	Group 2023 2022 £m £m Lease liabilities 111 125 Other 2,368 2,456 2,479 2,581

Provisions (Tables)

Provisions (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of other provisions [abstract]
Summary of Provisions Reconciliation	Group Customer remediation Litigation and other regulatory Bank Levy Property ECL on undrawn facilities and guarantees Restructuring Other Total £m £m £m £m £m £m £m £m At 1 January 2023 90 136 3 47 74 21 7 378 Additional provisions (See Note 8) 45 28 44 16 4 56 168 361 Provisions released (See Note 8) (8) — (8) (6) — — — (22) Utilisation and other (21) (32) (95) (10) — (45) (168) (371) Recharge (1) — — 20 — — — — 20 Reclassification from provisions to other assets — — 36 — — — — 36 At 31 December 2023 106 132 — 47 78 32 7 402 Recharge in respect of the UK Bank Levy paid on behalf of other UK entities in the Banco Santander group

Retirement Benefit Plans (Table

Retirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of net defined benefit liability (asset) [abstract]
Summary of Retirement Benefit Plans	The amounts recognised in the balance sheet were as follows: Group 2023 2022 £m £m Assets/(liabilities) Funded defined benefit pension scheme - surplus 723 1,050 Funded defined benefit pension scheme - deficit (41) — Unfunded pension and post-retirement medical benefits (25) (25) Total net assets 657 1,025
Disclosure of Total Defined Benefit Plan Amount Charged to the Income Statement	The total amount charged to the income statement was as follows: Group 2023 2022 2021 £m £m £m Net interest income (54) (30) (5) Current service cost 13 30 38 Past service and GMP costs 1 — — Past service curtailment costs — — 5 Administration costs 7 9 8 (33) 9 46
Summary of Amounts Recognised in Other Comprehensive Income	The amounts recognised in other comprehensive income were as follows: Group 2023 2022 2021 £m £m £m Return on plan assets (excluding amounts included in net interest expense) 352 5,527 (454) Actuarial (gains) arising from changes in demographic assumptions (51) (122) (17) Actuarial losses/(gains) arising from experience adjustments 91 481 (19) Actuarial losses/(gains) arising from changes in financial assumptions 206 (5,164) (774) Pension remeasurement 598 722 (1,264)
Disclosure of Movements in Fair Value of Schemes' Assets	Movements in the present value of defined benefit scheme obligations were as follows: Group 2023 2022 £m £m At 1 January (7,933) (12,878) Current service cost paid by Santander UK plc (13) (29) Current service cost paid by subsidiaries — (1) Interest cost (379) (241) Employer salary sacrifice contributions (1) (2) Past service cost (1) — Remeasurement due to actuarial movements arising from: – Changes in demographic assumptions 51 122 – Experience adjustments (91) (481) – Changes in financial assumptions (206) 5,164 Benefits paid 372 413 At 31 December (8,201) (7,933) Movements in the fair value of the schemes’ assets were as follows: Group 2023 2022 £m £m At 1 January 8,958 14,413 Interest income 433 271 Contributions paid by employer and scheme members 198 223 Administration costs paid (7) (9) Return on plan assets (excluding amounts included in net interest expense) (352) (5,527) Benefits paid (372) (413) At 31 December 8,858 8,958
Disclosure of Fair Value of Plan Assets	The composition and fair value of the schemes’ assets by category was: Group Quoted prices in active markets Prices not quoted in active markets Total Valuation 2023 £m % £m % £m % technique Overseas equities — — 980 11 980 11 A,C Corporate bonds 2,284 26 242 3 2,526 29 A,C Government fixed interest bonds 1,618 18 — — 1,618 18 A Government index-linked bonds 4,422 50 — — 4,422 50 A Property — — 1,080 12 1,080 12 B Derivatives — — (2) — (2) — A Cash — — 586 7 586 7 A Repurchase agreements (1) — — (3,062) (35) (3,062) (35) A Infrastructure — — 408 5 408 5 B,C Annuities — — 293 3 293 3 D Longevity swap — — (16) — (16) — D Other — — 25 — 25 — C 8,324 94 534 6 8,858 100 2022 Overseas equities — — 1,172 13 1,172 13 A,C Corporate bonds 1,991 22 244 3 2,235 25 A,C Government fixed interest bonds 1,138 13 — — 1,138 13 A Government index-linked bonds 5,525 62 — — 5,525 62 A Property — — 1,202 13 1,202 13 B Derivatives — — (78) (1) (78) (1) A Cash — — 1,340 15 1,340 15 A Repurchase agreements (1) — — (4,312) (48) (4,312) (48) A Infrastructure — — 426 5 426 5 B,C Annuities — — 293 3 293 3 D Longevity swap — — (12) — (12) — D Other — — 29 — 29 — C 8,654 97 304 3 8,958 100 (1) Sale and repurchase agreements net of purchase and resale agreements.
Summary of Principal Actuarial Assumptions Used for Defined Benefit Schemes	The principal actuarial assumptions used for the Scheme were: Group 2023 2022 2021 % % % To determine benefit obligations (1) : – Discount rate for scheme liabilities 4.6 % 4.9 1.9 – General price inflation 3.0 % 3.1 3.4 – General salary increase 1.0 % 1.0 1.0 – Expected rate of pension increase 3.0 % 3.0 3.2 Years Years Years Longevity at 60 for current pensioners, on the valuation date: – Males 27.0 27.4 27.5 – Females 29.8 30.1 30.1 Longevity at 60 for future pensioners currently aged 40, on the valuation date: – Males 28.6 28.9 29.0 – Females 31.3 31.6 31.6 (1) The discount rate and inflation related assumptions set out in the table above reflect the assumptions calculated based on the Scheme’s duration and cash flow profile as a whole. The actual assumptions used were determined for each section independently based on each section’s duration and cash flow profile.
Summary of Actuarial Assumption Sensitivities	The sensitivity analyses below have been determined based on reasonably possible changes of the respective assumptions occurring at the end of the reporting period, while holding all other assumptions constant. Group (Decrease)/increase 2023 2022 Assumption Change in pension obligation at period end from £m £m Discount rate 50 bps increase (507) (501) General price inflation 50 bps increase 385 374 Mortality Each additional year of longevity assumed 223 203
Disclosure of Defined Benefit Plan Expected Future Benefit Payments	The benefits expected to be paid in each of the next five years, and in the aggregate for the five years thereafter are: Year ending 31 December £m 2024 455 2025 389 2026 404 2027 428 2028 444 Five years ending 2033 2,398

Contingent Liabilities and Co_2

Contingent Liabilities and Commitments (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of contingent liabilities [abstract]
Summary of Contingent Liabilities and Commitments	Group 2023 2022 £m £m Guarantees given to third parties 452 448 Formal standby facilities, credit lines and other commitments 30,976 31,388 31,428 31,836

Share Capital (Tables)

Share Capital (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of classes of share capital [abstract]
Schedule of Share Capital Issued and Fully Paid	Group Ordinary shares of £0.10 each Total Issued and fully paid share capital No. £m £m At 31 December 2022, 1 January 2023 and 31 December 2023 31,051,768,866 3,105 3,105
Summary of Share Premium	Group 2023 2022 Share premium £m £m At 1 January and 31 December 5,620 5,620

Other Equity Instruments (Table

Other Equity Instruments (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of classes of share capital [abstract]
Summary of Other Equity Instruments	Group Interest rate 2023 2022 % Next call date £m £m AT1 securities: - £500m Perpetual Capital Securities 6.75 June 2024 496 496 - £500m Perpetual Capital Securities 6.30 March 2025 500 500 - £210m Perpetual Capital Securities 4.25 March 2026 210 210 - £750m Perpetual Capital Securities 6.50 June 2027 750 750 1,956 1,956

Notes to Cash Flows (Tables)

Notes to Cash Flows (Tables)	12 Months Ended
	Dec. 31, 2023
Cash Flows Explanatory Notes [Abstract]
Summary of Changes in Liabilities Arising from Financing Activities	The table below shows the changes in liabilities arising from financing activities. The changes in equity arising from financing activities are set out in the Consolidated Statement of Changes in Equity. Group Balance sheet line item Debt securities in issue Subordinated liabilities Other equity instruments Lease liabilities Dividends paid Total 2023 £m £m £m £m £m £m At 1 January 31,531 2,332 1,956 125 — 35,944 Proceeds from issue of debt securities 4,208 — — — — 4,208 Repayment of debt securities (2,568) — — — — (2,568) Proceeds from issue of subordinated liabilities — 1,050 — — — 1,050 Repayment of subordinated liabilities — (971) — — — (971) Principal elements of lease payments — — — (47) — (47) Dividends paid — — — — (1,653) (1,653) Liability-related other changes 1,004 25 — 33 — 1,062 Non-cash changes: – Unrealised foreign exchange (651) (22) — — — (673) – Other changes 386 (28) — — 1,653 2,011 At 31 December 33,910 2,386 1,956 111 — 38,363 2022 At 1 January 25,520 2,228 2,191 132 — 30,071 Proceeds from issue of debt securities 4,778 — — — — 4,778 Repayment of debt securities (3,036) — — — — (3,036) Repayment of subordinated liabilities — (40) — — — (40) Issue of other equity instruments — — 750 — — 750 Repurchase of other equity instruments — — (985) — — (985) Principal elements of lease payments — — — (26) — (26) Dividends paid — — — — (1,164) (1,164) Liability-related other changes 3,155 2 — 19 — 3,176 Non-cash changes: – Unrealised foreign exchange 1,554 87 — — — 1,641 – Other changes (440) 55 — — 1,164 779 At 31 December 31,531 2,332 1,956 125 — 35,944 2021 At 1 January 35,566 2,556 2,191 97 — 40,410 Proceeds from issue of debt securities 2,872 — — — — 2,872 Repayment of debt securities (11,910) — — — — (11,910) Repayment of subordinated liabilities — (4) — — — (4) Issue of other equity instruments — — 210 — — 210 Repurchase of other equity instruments — — (210) — — (210) Principal elements of lease payments — — — (25) — (25) Dividends paid — — — — (1,505) (1,505) Liability-related other changes (447) (4) — 60 — (391) Non-cash changes: – Unrealised foreign exchange (806) 6 — — — (800) – Other changes 245 (326) — — 1,505 1,424 At 31 December 25,520 2,228 2,191 132 — 30,071

Assets Charged as Security fo_2

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Assets Pledged As Security [Abstract]
Financial Assets Charged as Security Under On-Balance Sheet and Off-Balance	The financial assets below are analysed between those assets accounted for on-balance sheet and off-balance sheet. Group 2023 2022 £m £m On-balance sheet: Cash and balances at central banks 1,480 1,330 Loans and advances to banks 191 130 Loans and advances to customers - securitisations and covered bonds (See Note 14) 27,088 24,155 Loans and advances to customers - other 20,699 32,001 Other financial assets at amortised cost 14 48 Financial assets at fair value through other comprehensive income 5,183 4,365 Total on-balance sheet 54,655 62,029 Total off-balance sheet 10,185 9,146
Schedule of Collateral Held as Security For Assets	The collateral held as security for assets, analysed between those liabilities accounted for on balance sheet and off-balance sheet, was: Group 2023 2022 £m £m On-balance sheet: Deposits by banks 860 1,741 Total on-balance sheet 860 1,741 Total off-balance sheet 14,992 10,141

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of terms and conditions of share-based payment arrangement [abstract]
Summary of Movement in Share Options	The table below summarises movements in the number of options, and changes in weighted average exercise price over the same period. 2023 2022 Number of options Weighted average exercise price Number of options Weighted average exercise price ‘000 £ ‘000 £ Outstanding at 1 January 29,988 2.00 25,993 2.25 Granted 7,175 2.78 13,068 1.89 Exercised (5,980) 1.70 (242) 1.69 Forfeited/expired (4,044) 2.53 (8,831) 2.59 Outstanding at 31 December 27,139 2.19 29,988 2.00 Exercisable at 31 December 868 1.84 3,439 3.22
Summary of Range of Exercise Prices and Weighted Average Remaining Contractual Life of the Options Outstanding	The following table summarises the range of exercise prices and weighted average remaining contractual life of the options at 31 December 2023 and 2022 . 2023 2022 Range of exercise prices Weighted average remaining contractual life Weighted average exercise price Weighted average remaining contractual life Weighted average exercise price Years £ Years £ £1 to £2 3 1.84 3 1.79 £2 to £3 3 2.65 2 2.56 £3 to £4 0 3.46 1 3.46 £4 to £5 0 — 0 4.02

Transactions with Directors a_2

Transactions with Directors and Other Key Management Personnel (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Remuneration Of Directors And Other Key Management Personnel [Abstract]
Summary of Remuneration of the Directors and Other Key Management Personnel	The remuneration of the Directors and Other Key Management Personnel (KMP) of the Santander UK group is set out in aggregate below. 2023 2022 2021 Directors’ remuneration £ £ £ Salaries and fees 4,733,761 4,696,699 5,488,388 Performance-related payments 1,002,607 3,701,569 3,431,294 Other fixed remuneration (pension and other allowances & non-cash benefits) 222,538 906,201 929,935 Expenses — 27,715 17,097 Total remuneration 5,958,906 9,332,184 9,866,714 Compensation for loss of office (1) — 172,856 356,054 2023 2022 2021 Directors' and Other Key Management Personnel compensation £ £ £ Short-term employee benefits 18,449,360 22,627,595 20,553,672 Post-employment benefits 858,437 1,026,848 988,829 Compensation for loss of office (1) — 1,713,256 356,054 Total compensation 19,307,797 25,367,699 21,898,555 (1) Compensation for loss of office was not paid to Directors or KMPs in 2023 ( 2022 : two Directors, £172,856 and three KMPs, £1,540,400 ; 2021 : two Directors, £356,054 ).
Summary of Transactions with Directors, Other Key Management Personnel	Directors, Other KMP (defined as the Executive Committee of Santander UK plc who served during the year) and their connected persons have undertaken the following transactions with the Santander UK group in the ordinary course of business. 2023 2022 No. £000 No. £000 Secured loans, unsecured loans and overdrafts At 1 January 10 871 6 360 Net movements (2) 204 4 511 At 31 December 8 1,075 10 871 Deposit, bank and instant access accounts and investments At 1 January 23 4,133 21 6,552 Net movements (6) (2,431) 2 (2,419) At 31 December 17 1,702 23 4,133

Related Party Disclosures (Tabl

Related Party Disclosures (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of transactions between related parties [abstract]
Summary of Transactions With Related Parties	Transactions with related parties during the year and balances outstanding at the year-end: Group Interest, fees and other income received Interest, fees and other expenses paid Amounts owed by related parties Amounts owed to related parties 2023 2022 2021 2023 2022 2021 2023 2022 2023 2022 £m £m £m £m £m £m £m £m £m £m Ultimate parent (8) (710) (164) 414 47 33 800 1,363 (1,062) (1,673) Immediate parent (7) (6) (6) 504 308 263 — 1 (13,279) (14,390) Fellow subsidiaries (38) (69) (57) 203 177 163 101 108 (370) (348) Joint ventures (183) (76) (34) 55 17 4 4,486 4,151 (781) (973) (236) (861) (261) 1,176 549 463 5,387 5,623 (15,492) (17,384)

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Abstract]
Disclosure of Analysis of Fair Value of Financial Instruments Carried at Amortised Cost	Group 2023 2022 Fair value Fair Carrying Fair value Fair Carrying Level 1 Level 2 Level 3 value value Level 1 Level 2 Level 3 value value £m £m £m £m £m £m £m £m £m £m Assets Loans and advances to customers — — 205,917 205,917 207,435 — — 212,479 212,479 219,716 Loans and advances to banks — 1,080 — 1,080 1,080 — 992 — 992 992 Reverse repurchase agreements - non trading — 12,470 — 12,470 12,468 — 7,341 — 7,341 7,348 Other financial assets at amortised cost 144 — — 144 152 144 — — 144 156 144 13,550 205,917 219,611 221,135 144 8,333 212,479 220,956 228,212 Liabilities Deposits by customers — 71 190,561 190,632 190,850 — 51 195,483 195,534 195,568 Deposits by banks — 20,342 40 20,382 20,332 — 27,979 55 28,034 28,525 Repurchase agreements - non trading — 8,413 — 8,413 8,411 — 7,982 — 7,982 7,982 Debt securities in issue 1,689 30,743 1,189 33,621 33,910 2,574 26,349 1,582 30,505 31,531 Subordinated liabilities — 2,591 209 2,800 2,386 19 2,358 224 2,601 2,332 1,689 62,160 191,999 255,848 255,889 2,593 64,719 197,344 264,656 265,938
Disclosure of Analysis of Fair Value of Financial Instruments Measured at Fair Value on a Recurring Basis	The following tables summarise the fair values of the financial assets and liabilities accounted for at fair value at 31 December 2023 and 31 December 2022 , analysed by their levels in the fair value hierarchy - Level 1, Level 2 and Level 3. Group 2023 2022 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Valuation £m £m £m £m £m £m £m £m technique Assets Derivative financial instruments Exchange rate contracts — 1,129 — 1,129 — 2,044 — 2,044 A Interest rate contracts — 2,216 1 2,217 — 2,399 7 2,406 A & C Equity and credit contracts — 98 35 133 — 100 30 130 B & D Netting — (2,047) — (2,047) — (2,173) — (2,173) — 1,396 36 1,432 — 2,370 37 2,407 Other financial assets at FVTPL Loans and advances to customers — — 46 46 — — 45 45 A Debt securities — 167 49 216 — 12 72 84 A, B & D — 167 95 262 — 12 117 129 Financial assets at FVOCI Debt securities 8,293 188 — 8,481 5,996 28 — 6,024 D 8,293 188 — 8,481 5,996 28 — 6,024 Total assets at fair value 8,293 1,751 131 10,175 5,996 2,410 154 8,560 Liabilities Derivative financial instruments Exchange rate contracts — 508 — 508 — 471 — 471 A Interest rate contracts — 2,336 1 2,337 — 2,624 4 2,628 A & C Equity and credit contracts — 11 9 20 — 17 8 25 B & D Netting — (2,047) — (2,047) — (2,173) — (2,173) — 808 10 818 — 939 12 951 Other financial liabilities at FVTPL Debt securities in issue — 369 — 369 — 372 3 375 A Structured deposits — 426 — 426 — 321 — 321 A Zero Amortising Guaranteed — 104 — 104 — 107 — 107 D — 899 — 899 — 800 3 803 Total liabilities at fair value — 1,707 10 1,717 — 1,739 15 1,754
Summary of Fair Value Adjustment	The fair value adjustments are set out in the following table: Group 2023 2022 £m £m Risk-related: - Bid-offer and trade specific adjustments (6) (12) - Uncertainty 6 12 - Credit risk adjustment 1 2 - Funding fair value adjustment 1 1 2 3 Day One profit 1 1 3 4
Disclosure of Analysis of Financial Instruments Valued Using Internal Models Based on Information Other than Market Data	The table below provides an analysis of financial instruments valued using internal models based on information other than market data together with further details on the valuation techniques used for each type of instrument. Each instrument is initially valued at transaction price: Group Balance sheet value Fair value movements recognised in profit/(loss) 2023 2022 2023 2022 2021 Balance sheet line item Category Financial instrument product type £m £m £m £m £m 1. Derivative assets Equity and credit contracts Reversionary property interests 35 30 12 (8) — 2. FVTPL assets Loans and advances to customers Roll-up mortgage portfolio 24 28 (2) (18) (5) 3. FVTPL assets Loans and advances to customers Other loans 22 17 4 (4) (2) 4. FVTPL assets Debt securities Reversionary property securities 49 70 (3) — 5 130 145 11 (30) (2) Other Level 3 assets 1 9 (1) 10 (9) Other Level 3 liabilities (10) (15) (2) 3 7 Total net assets 121 139 Total income/(expense) 8 (17) (4)
Summary of Reconciliation of Fair Value Measurement in Level 3 of the Fair Value Hierarchy	The following table sets out the movements in Level 3 financial instruments in 2023 : Group Assets Liabilities Derivatives Other financial assets at FVTPL Financial assets at FVOCI Total Derivatives Other financial liabilities at FVTPL Total £m £m £m £m £m £m £m At 1 January 2023 37 117 — 154 (12) (3) (15) Total gains/(losses) recognised: Fair value movements (2) 10 — — 10 (2) — (2) Purchases — 1 — 1 — — — Netting (1) — (3) — (3) — — — Settlements (11) (20) — (31) 4 3 7 At 31 December 2023 36 95 — 131 (10) — (10) Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the year (2) 10 — — 10 (2) — (2) At 1 January 2022 46 185 18 249 (32) (6) (38) Total (losses)/gains recognised: Fair value movements (2) (2) (18) — (20) 2 1 3 Transfers in — — — — (2) — (2) Netting (1) — (8) — (8) — — — Sales — (5) — (5) — — — Settlements (7) (37) (18) (62) 20 2 22 At 31 December 2022 37 117 — 154 (12) (3) (15) (Losses)/gains recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the year (2) (2) (18) — (20) 2 1 3 This relates to the effect of netting on the fair value of the credit linked notes due to a legal right of set-off between the principal amounts of the senior notes and the associated cash deposits. For more, see ‘ii) Credit protection entities’ in Note 19 (2) Fair value movements relating to derivatives and other financial assets at FVTPL are recognised in other operating income in the income statement.
Disclosure of Effects of Changes in Significant Unobservable Assumptions to Reasonably Possible Alternatives Level Three	Group Significant unobservable input Sensitivity Assumption value Favourable changes Unfavourable changes Fair value Range (1) Weighted average Shift 2023 £m Assumption description £m £m 1. Derivative assets – Equity and credit contracts: 35 HPI Forward growth rate -5% to 5% (0.20) % 1.0 % 2 (2) – Reversionary property derivatives HPI Spot rate (2) n/a 513 10.0 % 2 (4) 2. FVTPL – Loans and advances to customers: 24 HPI Forward growth rate -5% to 5% 1.31 % 1.0 % — — – Roll-up mortgage portfolio 3. FVTPL – Loans and advances to customers: 22 Credit spreads 0.13% - 2.54% 0.97 % 20.0 % — — – Other loans 4. FVTPL – Debt securities: 49 HPI Forward growth rate -5% to 5% -0.20 % 1.0 % — — – Reversionary property securities HPI Spot rate (2) n/a 513 10.0 % 2 (2) 2022 1. Derivative assets – Equity and credit contracts: 30 HPI Forward growth rate -5% to 5% 0.53 % 1.0 % 4 (4) – Reversionary property derivatives HPI Spot rate (2) n/a 513 10.0 % 4 (4) 2. FVTPL – Loans and advances to customers: 28 HPI Forward growth rate -5% to 5% 1.39 % 1.0 % 1 (1) – Roll-up mortgage portfolio 3. FVTPL – Loans and advances to customers: 17 Credit spreads 0.19% to 2.04% 0.98 % 20.0 % — — – Other loans 4. FVTPL – Debt securities: 70 HPI Forward growth rate -5% to 5% 0.53 % 1.0 % 1 (1) – Reversionary property securities HPI Spot rate (2) n/a 513 10.0 % 3 (3) 5. Derivative liabilities – Equity contracts: (8) HPI Forward growth rate -5% to 5% (0.92) % 1.0 % 1 (1) – Property-related options and forwards HPI Spot rate (2) n/a 491 10.0 % 2 (3) (1) The range of actual assumption values used to calculate the weighted average disclosure. (2) The HPI spot rate in the weighted average column represents the HPI spot rate index level at 31 December 2023 and 2022
Disclosure of Maturity Analysis of Undiscounted Cash Flows for Financial Liabilities and Off Balance Sheet Commitments	Group On demand Not later than 3 months Later than 3 months and not later than 1 year Later than 1 year and not later than 5 years Later than 5 years Total 2023 £m £m £m £m £m £m Financial liabilities Derivative financial instruments 1 192 52 478 183 906 Other financial liabilities at fair value through profit or loss — 8 7 538 520 1,073 Deposits by customers 179,732 3,217 3,447 4,690 288 191,374 Deposits by banks 1,454 1,749 573 18,084 — 21,860 Repurchase agreements – non trading — 8,418 8 — — 8,426 Debt securities in issue — 6,380 4,908 17,029 12,216 40,533 Subordinated liabilities — 27 83 876 2,470 3,456 Lease liabilities — — 29 70 23 122 Total financial liabilities 181,187 19,991 9,107 41,765 15,700 267,750 Off-balance sheet commitments given 3,795 15,205 1,408 7,399 3,621 31,428 2022 Financial liabilities Derivative financial instruments — 206 120 496 255 1,077 Other financial liabilities at fair value through profit or loss — — 98 443 438 979 Deposits by customers 180,218 3,875 7,077 4,295 335 195,800 Deposits by banks 2,048 1,309 298 26,141 — 29,796 Repurchase agreements – non trading — 7,984 3 — — 7,987 Debt securities in issue — 5,814 1,485 16,672 9,921 33,892 Subordinated liabilities — 35 691 1,149 1,400 3,275 Lease liabilities — — 32 80 26 138 Total financial liabilities 182,266 19,223 9,804 49,276 12,375 272,944 Off-balance sheet commitments given 19,089 787 898 7,508 3,554 31,836

Offsetting Financial Assets a_2

Offsetting Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2023
Disclosure of offsetting of financial liabilities [abstract]
Summary of Information about Impact of Offsetting of Financial Assets and Liabilities	Group Amounts subject to enforceable netting arrangements Assets not subject to enforceable netting arrangements (2) Effects of offsetting on balance sheet Related amounts not offset Gross amounts Amounts offset Net amounts on balance sheet Financial instruments Financial collateral (1) Net amount Balance sheet total (3) 2023 £m £m £m £m £m £m £m £m Assets Derivative financial assets 3,429 (2,047) 1,382 (471) (823) 88 50 1,432 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 15,625 (3,157) 12,468 (118) (12,350) — — 12,468 Loans and advances to customers and banks⁽⁴⁾ 5,363 (790) 4,573 — — 4,573 203,942 208,515 24,417 (5,994) 18,423 (589) (13,173) 4,661 203,992 222,415 Liabilities Derivative financial liabilities 2,838 (2,047) 791 (471) (161) 159 27 818 Repurchase, securities lending & similar agreements: – Amortised cost 11,568 (3,157) 8,411 (118) (8,293) — — 8,411 Deposits by customers and banks⁽⁴⁾ 4,218 (790) 3,428 — — 3,428 207,754 211,182 18,624 (5,994) 12,630 (589) (8,454) 3,587 207,781 220,411 2022 Assets Derivative financial assets 4,525 (2,173) 2,352 (515) (1,720) 117 55 2,407 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 8,826 (1,478) 7,348 (9) (7,339) — — 7,348 Loans and advances to customers and banks⁽⁴⁾ 5,169 (908) 4,261 — — 4,261 216,447 220,708 18,520 (4,559) 13,961 (524) (9,059) 4,378 216,502 230,463 Liabilities Derivative financial liabilities 3,085 (2,173) 912 (515) (115) 282 39 951 Repurchase, securities lending & similar agreements: – Amortised cost 9,460 (1,478) 7,982 (9) (7,973) — — 7,982 Deposits by customers and banks⁽⁴⁾ 8,077 (908) 7,169 — — 7,169 216,924 224,093 20,622 (4,559) 16,063 (524) (8,088) 7,451 216,963 233,026 (1) Financial collateral is reflected at its fair value but has been limited to the net balance sheet exposure so as not to include any over-collateralisation. (2) This column includes contractual rights of set-off that are subject to uncertainty under the laws of the relevant jurisdiction. (3) The balance sheet total is the sum of ‘Net amounts reported on the balance sheet’ that are subject to enforceable netting arrangements and ‘Amounts not subject to enforceable netting arrangements’. (4) The amounts offset within loans and advances to customers/banks or deposits by customers/banks relate to offset mortgages which are classified as either and that are subject to netting.

Interest Rate Benchmark Reform

Interest Rate Benchmark Reform (Tables)	12 Months Ended
	Dec. 31, 2023
Interest Rate Benchmark Reform [Abstract]
Schedule of Amounts Affected by IBOR Reform	Group GBP LIBOR USD LIBOR Total 2023 £m £m £m Assets Financial assets at amortised cost 6 — 6 6 — 6 2022 Assets Derivatives — 1,665 1,665 Financial assets at amortised cost 76 57 133 76 1,722 1,798 Liabilities Derivatives 66 1,846 1,912 66 1,846 1,912 Off-balance sheet commitments given 2 — 2

Discontinued Operations and A_2

Discontinued Operations and Assets and Liabilities Held for Sale (Tables)	12 Months Ended
	Dec. 31, 2023
Discontinued Operations and Assets and Liabilities Held for Sale [Abstract]
Disclosure of Financial Performance Relating to Discontinued Operations	The financial performance and cash flow information relating to the discontinued operations were as follows: For the year ended 31 December 2023 2022 2021 £m £m £m Net interest income — — 32 Net fee and commission income — — 35 Other operating income — — 2 Total operating income — — 69 Operating expenses before credit impairment (charges)/write-backs, provisions and charges — — (33) Credit impairment (charges)/write-backs — — 11 Provisions for other liabilities and charges — — (4) Total operating credit impairment (charges)/write-backs, provisions and charges — — 7 Profit from discontinued operations before tax — — 43 Tax on profit from discontinued operations — — (12) Profit from discontinued operations after tax — — 31
Disclosure of Assets Classified as Held for Sale	At 31 December 2023 , assets held for sale comprised: 2023 2022 £m £m Assets Property, plant and equipment 13 49 Total assets held for sale 13 49

Credit Risk - Disclosure of Exp

Credit Risk - Disclosure of Exposures to Credit Risk by Segment (Details) - Maximum £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£)
Everyday Banking
Disclosure of credit risk exposure [line items]
Customers, annual turnover	£ 6.5
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Customers, annual turnover	£ 500

Credit Risk - Disclosure of Key

Credit Risk - Disclosure of Key Metrics to Measure and Control Credit Risk (Details) - Credit risk	12 Months Ended
	Dec. 31, 2023
Expected Credit Loss (ECL)
Disclosure of credit risk exposure [line items]
Metric	Expected Credit Loss (ECL)
Description	ECL tells us what credit risk is expected to cost us either over the next 12 months or over the lifetime of the exposure where there is evidence of a SICR since origination. We explain how we calculate ECL below.
Stages 1, 2 and 3
Disclosure of credit risk exposure [line items]
Metric	Stages 1, 2 and 3
Description	We assess each facility’s credit risk profile to determine which stage to allocate them to, and we monitor where there is a SICR and transfers between the Stages including monitoring of coverage ratios for each stage.
Stage 3 ratio
Disclosure of credit risk exposure [line items]
Metric	Stage 3 ratio
Description	The Stage 3 ratio is the sum of Stage 3 drawn and Stage 3 undrawn assets divided by the sum of total drawn assets and Stage 3 undrawn assets. The Stage 3 ratio is a key indicator used to monitor underlying asset performance.
Expected Loss (EL)
Disclosure of credit risk exposure [line items]
Metric	Expected Loss (EL)
Description	EL is based on the CRD IV regulatory capital rules and gives us another view of credit risk. It is the product of the probability of default, exposure at default and loss given default, and we include direct and indirect costs. We base it on our risk models and our assessment of each customer’s credit quality. The rest of our Risk review, impairments, losses and loss allowances refer to calculations in accordance with IFRS, unless we specifically say they relate to CRD IV. For our IFRS impairment accounting policy, see Note 1 to the Consolidated Financial Statements.

Credit Risk - Schedule of Macro

Credit Risk - Schedule of Macroeconomic Assumptions for Each Five Scenarios (Details)	Dec. 31, 2023	Dec. 31, 2022
Upside One Scenario [member]
Disclosure of credit risk exposure [line items]
GDP growth, year 1	4.30%	7.50%
GDP growth, year 2	0.60%	4.40%
GDP growth, year 3	1%	(1.00%)
GDP growth, year 4	2.10%	0.80%
GDP growth, year 5	2.40%	2%
GDP growth, year 6	2.40%	2%
GDP growth, year 7	2.40%
GDP growth rate, five-year average	2.10%	1.20%
GDP growth rate, peak/(trough)	0%	6%
Bank of England base rate, year 1	3.50%	0.25%
Bank of England base rate, year 2	5.25%	3.50%
Bank of England base rate, year 3	4.25%	3.75%
Bank of England base rate, year 4	3.25%	3%
Bank of England base rate, year 5	2.75%	2.50%
Bank of England base rate, year 6	2.75%	2.25%
Bank of England base rate, year 7	2.75%
Bank of England base rate, five-year end period	2.75%	2.25%
Bank of England base rate, peak/(trough)	5.25%	3.75%
House price growth, year 1	5%	8.70%
House price growth, year 2	(1.70%)	7.60%
House price growth, year 3	2%	(8.80%)
House price growth, year 4	6.50%	(4.30%)
House price growth, year 5	5.10%	0.60%
House price growth, year 6	4%	4.10%
House price growth, year 7	3.60%
House price growth rate, five-year average	4.30%	(0.70%)
House price growth rate, peak/(trough)	(3.70%)	(12.80%)
Unemployment rate, year 1	3.70%	4%
Unemployment rate, year 2	4.30%	3.70%
Unemployment rate, year 3	4.30%	4.70%
Unemployment rate, year 4	3.70%	4.50%
Unemployment rate, year 5	3.40%	4.50%
Unemployment rate, year 6	3%	4.40%
Unemployment rate, year 7	3%
Unemployment rate, five-year end period	3%	4.20%
Unemployment rate, peak/(trough)	4.50%	4.70%
Base Case Scenario [Member]
Disclosure of credit risk exposure [line items]
GDP growth, year 1	4.30%	7.50%
GDP growth, year 2	0.50%	4.40%
GDP growth, year 3	0.40%	(1.30%)
GDP growth, year 4	1.30%	0.50%
GDP growth, year 5	1.50%	1.60%
GDP growth, year 6	1.40%	1.50%
GDP growth, year 7	1.40%
GDP growth rate, five-year average	1.20%	0.80%
GDP growth rate, peak/(trough)	0%	3.80%
Bank of England base rate, year 1	3.50%	0.25%
Bank of England base rate, year 2	5.25%	3.50%
Bank of England base rate, year 3	4.50%	4%
Bank of England base rate, year 4	3.50%	3.25%
Bank of England base rate, year 5	3.25%	2.75%
Bank of England base rate, year 6	3%	2.50%
Bank of England base rate, year 7	3%
Bank of England base rate, five-year end period	3%	2.50%
Bank of England base rate, peak/(trough)	5.25%	4%
House price growth, year 1	5%	8.70%
House price growth, year 2	(2.20%)	7%
House price growth, year 3	(1.00%)	(10.00%)
House price growth, year 4	2.50%	0%
House price growth, year 5	3%	2%
House price growth, year 6	3%	3%
House price growth, year 7	3%
House price growth rate, five-year average	2%	(0.60%)
House price growth rate, peak/(trough)	(6.50%)	(11.20%)
Unemployment rate, year 1	3.70%	4%
Unemployment rate, year 2	4.30%	3.80%
Unemployment rate, year 3	4.80%	4.70%
Unemployment rate, year 4	4.40%	5.10%
Unemployment rate, year 5	4.30%	4.50%
Unemployment rate, year 6	4.30%	4.30%
Unemployment rate, year 7	4.20%
Unemployment rate, five-year end period	4.20%	4.30%
Unemployment rate, peak/(trough)	4.80%	5.10%
Downside One Scenario [member]
Disclosure of credit risk exposure [line items]
GDP growth, year 1	4.30%	7.50%
GDP growth, year 2	0.50%	4.30%
GDP growth, year 3	(0.10%)	(1.90%)
GDP growth, year 4	0.20%	(0.30%)
GDP growth, year 5	0.50%	0.50%
GDP growth, year 6	0.30%	0.40%
GDP growth, year 7	0.30%
GDP growth rate, five-year average	0.30%	(0.20%)
GDP growth rate, peak/(trough)	(0.20%)	(0.80%)
Bank of England base rate, year 1	3.50%	0.25%
Bank of England base rate, year 2	5.25%	3.50%
Bank of England base rate, year 3	5.25%	3.50%
Bank of England base rate, year 4	4%	2.75%
Bank of England base rate, year 5	3.25%	2.50%
Bank of England base rate, year 6	3%	2.25%
Bank of England base rate, year 7	3%
Bank of England base rate, five-year end period	3%	2.25%
Bank of England base rate, peak/(trough)	5.75%	3.50%
House price growth, year 1	5%	8.70%
House price growth, year 2	(4.70%)	7.60%
House price growth, year 3	(11.70%)	(10.00%)
House price growth, year 4	3.40%	(6.70%)
House price growth, year 5	2.10%	(3.10%)
House price growth, year 6	3%	(0.20%)
House price growth, year 7	3.10%
House price growth rate, five-year average	(0.80%)	(3.80%)
House price growth rate, peak/(trough)	(17.50%)	(19.00%)
Unemployment rate, year 1	3.70%	4%
Unemployment rate, year 2	4.30%	3.70%
Unemployment rate, year 3	4.80%	5.10%
Unemployment rate, year 4	4.90%	5.40%
Unemployment rate, year 5	5.20%	5.80%
Unemployment rate, year 6	5.40%	6.10%
Unemployment rate, year 7	5.30%
Unemployment rate, five-year end period	5.30%	6.10%
Unemployment rate, peak/(trough)	5.50%	6.10%
Stubborn Inflation [Member]
Disclosure of credit risk exposure [line items]
GDP growth, year 1	4.30%	7.50%
GDP growth, year 2	0.50%	4.20%
GDP growth, year 3	(1.80%)	(2.70%)
GDP growth, year 4	(0.90%)	(0.90%)
GDP growth, year 5	0.40%	0.20%
GDP growth, year 6	0.70%	0.60%
GDP growth, year 7	0.80%
GDP growth rate, five-year average	(0.20%)	(0.50%)
GDP growth rate, peak/(trough)	(2.80%)	(2.20%)
Bank of England base rate, year 1	3.50%	0.25%
Bank of England base rate, year 2	5.25%	3.50%
Bank of England base rate, year 3	6.50%	6%
Bank of England base rate, year 4	5%	5.50%
Bank of England base rate, year 5	3.75%	3.50%
Bank of England base rate, year 6	3%	3%
Bank of England base rate, year 7	3%
Bank of England base rate, five-year end period	3%	3%
Bank of England base rate, peak/(trough)	6.50%	6%
House price growth, year 1	5%	8.70%
House price growth, year 2	(6.30%)	7.60%
House price growth, year 3	(18.80%)	(10.90%)
House price growth, year 4	3.60%	(8.80%)
House price growth, year 5	1.60%	(4.90%)
House price growth, year 6	1.60%	(0.60%)
House price growth, year 7	1.80%
House price growth rate, five-year average	(3.30%)	(4.70%)
House price growth rate, peak/(trough)	(25.50%)	(23.10%)
Unemployment rate, year 1	3.70%	4%
Unemployment rate, year 2	4.30%	3.70%
Unemployment rate, year 3	5.60%	5.50%
Unemployment rate, year 4	5.90%	5.90%
Unemployment rate, year 5	6.20%	6.40%
Unemployment rate, year 6	6.10%	6.60%
Unemployment rate, year 7	5.80%
Unemployment rate, five-year end period	5.80%	6.40%
Unemployment rate, peak/(trough)	6.20%	6.60%
Downside Two Scenario [Member]
Disclosure of credit risk exposure [line items]
GDP growth, year 1	4.30%	7.50%
GDP growth, year 2	0.30%	3.70%
GDP growth, year 3	(3.30%)	(6.40%)
GDP growth, year 4	(1.40%)	(0.70%)
GDP growth, year 5	0.60%	1.70%
GDP growth, year 6	2.20%	1.50%
GDP growth, year 7	2.60%
GDP growth rate, five-year average	0.10%	(0.60%)
GDP growth rate, peak/(trough)	(5.10%)	(3.10%)
Bank of England base rate, year 1	3.50%	0.25%
Bank of England base rate, year 2	5.25%	3.50%
Bank of England base rate, year 3	3.75%	3.75%
Bank of England base rate, year 4	2%	3%
Bank of England base rate, year 5	2%	2.75%
Bank of England base rate, year 6	2.50%	2.50%
Bank of England base rate, year 7	2.50%
Bank of England base rate, five-year end period	2.50%	2.50%
Bank of England base rate, peak/(trough)	5.25%	4%
House price growth, year 1	5%	8.70%
House price growth, year 2	(7.80%)	7.60%
House price growth, year 3	(25.80%)	(15.80%)
House price growth, year 4	3.60%	(14.30%)
House price growth, year 5	1.60%	(4.10%)
House price growth, year 6	1.60%	4.70%
House price growth, year 7	1.80%
House price growth rate, five-year average	(5.40%)	(4.80%)
House price growth rate, peak/(trough)	(33.00%)	(30.70%)
Unemployment rate, year 1	3.70%	4%
Unemployment rate, year 2	4.40%	4.40%
Unemployment rate, year 3	8.50%	8.50%
Unemployment rate, year 4	8%	8%
Unemployment rate, year 5	7.40%	7.40%
Unemployment rate, year 6	6.80%	6.80%
Unemployment rate, year 7	6.20%
Unemployment rate, five-year end period	6.20%	6.20%
Unemployment rate, peak/(trough)	8.50%	8.50%
Weighted average [member]
Disclosure of credit risk exposure [line items]
GDP growth, year 1	4.30%	7.50%
GDP growth, year 2	0.50%	4.30%
GDP growth, year 3	(0.40%)	(2.20%)
GDP growth, year 4	0.60%	0%
GDP growth, year 5	1.10%	1.20%
GDP growth, year 6	1.40%	1.20%
GDP growth, year 7	1.40%
GDP growth rate, five-year average		0.30%
GDP growth rate, peak/(trough)	(1.10%)	1.30%
Bank of England base rate, year 1	3.50%	0.25%
Bank of England base rate, year 2	5.25%	3.50%
Bank of England base rate, year 3	4.88%	4.29%
Bank of England base rate, year 4	3.68%	3.59%
Bank of England base rate, year 5	3.18%	2.85%
Bank of England base rate, year 6	2.93%	2.55%
Bank of England base rate, year 7	2.93%
Bank of England base rate, five-year end period		2.55%
Bank of England base rate, peak/(trough)	5.55%	4.31%
House price growth, year 1	5%	8.70%
House price growth, year 2	(3.80%)	7.30%
House price growth, year 3	(7.80%)	(10.70%)
House price growth, year 4	3.30%	(4.40%)
House price growth, year 5	2.70%	(0.80%)
House price growth, year 6	2.70%	2%
House price growth, year 7	2.70%
House price growth rate, five-year average		(2.30%)
House price growth rate, peak/(trough)	(13.80%)	(16.80%)
Unemployment rate, year 1	3.70%	4%
Unemployment rate, year 2	4.30%	3.80%
Unemployment rate, year 3	5.30%	5.30%
Unemployment rate, year 4	5.10%	5.60%
Unemployment rate, year 5	5%	5.40%
Unemployment rate, year 6	4.90%	5.30%
Unemployment rate, year 7	4.70%
Unemployment rate, five-year end period		5.20%
Unemployment rate, peak/(trough)	5.50%	5.90%

Credit Risk - Disclosure of Sce

Credit Risk - Disclosure of Scenario Weights Applied To Scenarios (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Upside One Scenario [member]
Disclosure of credit risk exposure [line items]
Probability weightings of scenarios, percentage	10%	5%
Base Case Scenario [Member]
Disclosure of credit risk exposure [line items]
Probability weightings of scenarios, percentage	50%	50%
Downside One Scenario [member]
Disclosure of credit risk exposure [line items]
Probability weightings of scenarios, percentage	10%	15%
Downside Two Scenario [Member]
Disclosure of credit risk exposure [line items]
Probability weightings of scenarios, percentage	10%	10%
Stubborn Inflation [Member]
Disclosure of credit risk exposure [line items]
Probability weightings of scenarios, percentage	20%	20%
Weighted average [member]
Disclosure of credit risk exposure [line items]
Probability weightings of scenarios, percentage	100%	100%

Credit Risk - Disclosure of Qua

Credit Risk - Disclosure of Quantitative Criteria of Credit Risk Exposure (Details) - Probability of default (PD)	12 Months Ended
	Dec. 31, 2023
Mortgages
Disclosure of credit risk exposure [line items]
PD threshold for measuring significant increase in credit risk	0.30%
Consumer Finance
Disclosure of credit risk exposure [line items]
PD threshold for measuring significant increase in credit risk	3%
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
PD threshold for measuring significant increase in credit risk	0.30%
Personal loans | Everyday Banking
Disclosure of credit risk exposure [line items]
PD threshold for measuring significant increase in credit risk	0.30%
Credit Cards | Everyday Banking
Disclosure of credit risk exposure [line items]
PD threshold for measuring significant increase in credit risk	3.40%
Overdrafts | Everyday Banking
Disclosure of credit risk exposure [line items]
PD threshold for measuring significant increase in credit risk	2.60%

Credit Risk - Disclosure of Q_2

Credit Risk - Disclosure of Qualitative Criteria of Credit Risk Exposure (Details)	12 Months Ended
	Dec. 31, 2023
Mortgages
Disclosure of credit risk exposure [line items]
Qualitative criteria for measuring SICR	– In forbearance– Default in last 24m– 30 Days past due (DPD) in last 12m– Bankrupt– £100+ arrears
Consumer Finance
Disclosure of credit risk exposure [line items]
Qualitative criteria for measuring SICR	– In forbearance– Deceased or Insolvent– Court ‘Return of goods’ order or Police watchlist– Agreement terminated– Payment holiday– Cash Collection
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Qualitative criteria for measuring SICR	– In forbearance– Default in last 12m– Watchlist: proactive management– Default at proxy origination
Corporate Centre
Disclosure of credit risk exposure [line items]
Qualitative criteria for measuring SICR	– Watchlist: proactive management
Personal loans | Everyday Banking
Disclosure of credit risk exposure [line items]
Qualitative criteria for measuring SICR	– In Collections– Default in last 12m– £50+ arrears
Credit Cards | Everyday Banking
Disclosure of credit risk exposure [line items]
Qualitative criteria for measuring SICR	– In forbearance– Default in last 12m– In Collections– £100+ arrears– Behaviour score indicators
Overdrafts | Everyday Banking
Disclosure of credit risk exposure [line items]
Qualitative criteria for measuring SICR	– Fees suspended– Default in last 12m– Debit dormant >35 days– Any excess in month

Credit Risk - Group Level Credi

Credit Risk - Group Level Credit Risk Management, Additional Information (Details) £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£) cIIThreshold	Dec. 31, 2022 GBP (£)
Disclosure of credit risk exposure [line items]
Minimum ECL to recognise judgemental adjustments	£ 1
Loan Loss Allowances		£ 1,005
Loss allowance	£ 992
Climate change, period covered for ECL calculations	5 years
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		393
Loss allowance	£ 380
ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		709
Loss allowance	808
ECL before JAs | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		306
Loss allowance	364
ECL before JAs | Individually assessed
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		112
Loss allowance	128
ECL before JAs | Individually assessed | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		112
Loss allowance	124
Minimum | Stage 3
Disclosure of credit risk exposure [line items]
ECL under reasonably possible judgements	42
Maximum | Stage 3
Disclosure of credit risk exposure [line items]
ECL under reasonably possible judgements	209
Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loss allowance	84
Total JAs (excluding Affordability and Cost of Living JAs) | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	(8)
Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loss allowance	16
Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	0
Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loss allowance	14
Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	0
Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loss allowance	6
Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	0
Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		57
Loss allowance	36
Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Loss allowance	0
Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		23
Loss allowance	23
Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		23
Loss allowance	23
Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loss allowance	(11)
Total JAs (excluding Affordability and Cost of Living JAs) | Other | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	(31)
Total Affordability and Cost of Living JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		130
Loss allowance	100
Total Affordability and Cost of Living JAs | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		61
Loss allowance	24
Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		61
Loss allowance	24
Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		61
Loss allowance	24
Total Affordability and Cost of Living JAs | Secured affordability
Disclosure of credit risk exposure [line items]
Mortgages moved from stage 1 to stage 2	2,900
Loan Loss Allowances		27
Loss allowance	13
Total Affordability and Cost of Living JAs | Secured affordability | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Loss allowance	0
Total Affordability and Cost of Living JAs | Secured affordability | Minimum
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	£ 21
CII Threshold | cIIThreshold	30
Total Affordability and Cost of Living JAs | Secured affordability | Maximum
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	£ 8
CII Threshold | cIIThreshold	50
Total Affordability and Cost of Living JAs | Unsecured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		35
Loss allowance	£ 38
Total Affordability and Cost of Living JAs | Unsecured affordability | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Loss allowance	0
Total Affordability and Cost of Living JAs | Mortgage refinancing risk
Disclosure of credit risk exposure [line items]
Mortgages moved from stage 1 to stage 2	6,800
Loss allowance	19
Total Affordability and Cost of Living JAs | Mortgage refinancing risk | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	0
Total Affordability and Cost of Living JAs | Mortgage refinancing risk | Minimum
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	£ 9
Probability weighted interest rate	0.05
Total Affordability and Cost of Living JAs | Mortgage refinancing risk | Maximum
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	£ 22
Probability weighted interest rate	0.06
Total Affordability and Cost of Living JAs | SME debt burden
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		7
Loss allowance	£ 6
Total Affordability and Cost of Living JAs | SME debt burden | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		£ 0
Loss allowance	0
No delay in repossession | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	12
No delay in repossession | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	6
Corrected model underestimation | Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	13
Model uplift estimation | Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	65
One average losses | Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	12
Three average losses | Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	35
Different sensitivities to PD uplifts | Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures | Minimum
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	16
Different sensitivities to PD uplifts | Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures | Maximum
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	58
Different sensitivities to PD uplifts | Total Affordability and Cost of Living JAs | Unsecured affordability | Minimum
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	31
Different sensitivities to PD uplifts | Total Affordability and Cost of Living JAs | Unsecured affordability | Maximum
Disclosure of credit risk exposure [line items]
Judgemental adjustments under reasonably possible judgements	£ 47

Credit Risk - Disclosure of ECL

Credit Risk - Disclosure of ECL by Segment (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	£ 992
Loan Loss Allowances		£ 1,005
ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	808
Loan Loss Allowances		709
Modelled ECL | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	680
Loan Loss Allowances		597
Individually assessed | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	128
Loan Loss Allowances		112
Total JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	184
Loan Loss Allowances		296
Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	84
Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	16
Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	14
Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	6
Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	36
Loan Loss Allowances		57
Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	23
Loan Loss Allowances		23
Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	(11)
Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		166
Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		13
Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		22
Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		15
Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		36
Total Affordability and Cost of Living JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	100
Loan Loss Allowances		130
Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	24
Loan Loss Allowances		61
Total Affordability and Cost of Living JAs | Secured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	13
Loan Loss Allowances		27
Total Affordability and Cost of Living JAs | Unsecured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	38
Loan Loss Allowances		35
Total Affordability and Cost of Living JAs | Mortgage refinancing risk
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	19
Total Affordability and Cost of Living JAs | SME debt burden
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	6
Loan Loss Allowances		7
Mortgages
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	242
Loan Loss Allowances		251
Mortgages | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	136
Loan Loss Allowances		133
Mortgages | Modelled ECL | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	132
Loan Loss Allowances		133
Mortgages | Individually assessed | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	4
Loan Loss Allowances		0
Mortgages | Total JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	106
Loan Loss Allowances		118
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	78
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	16
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	14
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	36
Loan Loss Allowances		36
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	12
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		91
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		13
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		22
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Mortgages | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		20
Mortgages | Total Affordability and Cost of Living JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	28
Loan Loss Allowances		27
Mortgages | Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Mortgages | Total Affordability and Cost of Living JAs | Secured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	9
Loan Loss Allowances		27
Mortgages | Total Affordability and Cost of Living JAs | Unsecured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Mortgages | Total Affordability and Cost of Living JAs | Mortgage refinancing risk
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	19
Mortgages | Total Affordability and Cost of Living JAs | SME debt burden
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Credit Cards
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	140
Loan Loss Allowances		130
Credit Cards | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	123
Loan Loss Allowances		112
Credit Cards | Modelled ECL | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	123
Loan Loss Allowances		112
Credit Cards | Individually assessed | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Credit Cards | Total JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	17
Loan Loss Allowances		18
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	1
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		2
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	1
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		3
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Credit Cards | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		1
Credit Cards | Total Affordability and Cost of Living JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	16
Loan Loss Allowances		15
Credit Cards | Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Credit Cards | Total Affordability and Cost of Living JAs | Secured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Credit Cards | Total Affordability and Cost of Living JAs | Unsecured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	16
Loan Loss Allowances		15
Credit Cards | Total Affordability and Cost of Living JAs | Mortgage refinancing risk
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Credit Cards | Total Affordability and Cost of Living JAs | SME debt burden
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	160
Loan Loss Allowances		164
Other | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	123
Loan Loss Allowances		93
Other | Modelled ECL | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	123
Loan Loss Allowances		93
Other | Individually assessed | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Other | Total JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	37
Loan Loss Allowances		71
Other | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	9
Other | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Other | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Other | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	6
Other | Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		19
Other | Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Other | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	3
Other | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		44
Other | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Other | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Other | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		15
Other | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		10
Other | Total Affordability and Cost of Living JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	28
Loan Loss Allowances		27
Other | Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Other | Total Affordability and Cost of Living JAs | Secured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Other | Total Affordability and Cost of Living JAs | Unsecured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	22
Loan Loss Allowances		20
Other | Total Affordability and Cost of Living JAs | Mortgage refinancing risk
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Other | Total Affordability and Cost of Living JAs | SME debt burden
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	6
Loan Loss Allowances		7
Consumer Finance
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	70
Loan Loss Allowances		67
Consumer Finance | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	62
Loan Loss Allowances		65
Consumer Finance | Modelled ECL | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	62
Loan Loss Allowances		65
Consumer Finance | Individually assessed | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Consumer Finance | Total JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	8
Loan Loss Allowances		2
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	4
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	4
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		2
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Consumer Finance | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		2
Consumer Finance | Total Affordability and Cost of Living JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	4
Loan Loss Allowances		0
Consumer Finance | Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Consumer Finance | Total Affordability and Cost of Living JAs | Secured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	4
Loan Loss Allowances		0
Consumer Finance | Total Affordability and Cost of Living JAs | Unsecured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Consumer Finance | Total Affordability and Cost of Living JAs | Mortgage refinancing risk
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Consumer Finance | Total Affordability and Cost of Living JAs | SME debt burden
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	380
Loan Loss Allowances		393
Corporate & Commercial Banking | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	364
Loan Loss Allowances		306
Corporate & Commercial Banking | Modelled ECL | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	240
Loan Loss Allowances		194
Corporate & Commercial Banking | Individually assessed | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	124
Loan Loss Allowances		112
Corporate & Commercial Banking | Total JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	16
Loan Loss Allowances		87
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	(8)
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	23
Loan Loss Allowances		23
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	(31)
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		26
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Corporate & Commercial Banking | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		3
Corporate & Commercial Banking | Total Affordability and Cost of Living JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	24
Loan Loss Allowances		61
Corporate & Commercial Banking | Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	24
Loan Loss Allowances		61
Corporate & Commercial Banking | Total Affordability and Cost of Living JAs | Secured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate & Commercial Banking | Total Affordability and Cost of Living JAs | Unsecured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate & Commercial Banking | Total Affordability and Cost of Living JAs | Mortgage refinancing risk
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate & Commercial Banking | Total Affordability and Cost of Living JAs | SME debt burden
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Modelled ECL | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Individually assessed | ECL before JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Total JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | Model underestimation
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | Corporate single large exposure
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs)
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | Long-term indeterminate arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | 12+ months in arrears
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | UPL loss floor
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Corporate Centre | Total JAs (excluding Affordability and Cost of Living JAs) | Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances		0
Corporate Centre | Total Affordability and Cost of Living JAs
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Total Affordability and Cost of Living JAs | Corporate lending to segments affected by supply chain pressures
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Total Affordability and Cost of Living JAs | Secured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Total Affordability and Cost of Living JAs | Unsecured affordability
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Corporate Centre | Total Affordability and Cost of Living JAs | Mortgage refinancing risk
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Corporate Centre | Total Affordability and Cost of Living JAs | SME debt burden
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	£ 0
Loan Loss Allowances		£ 0

Credit Risk - Disclosure of Bas

Credit Risk - Disclosure of Base Expected Credit Losses to Probability Weighted Estimated Credit Losses (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Exposure	£ 207,435	£ 219,716
Loan Loss Allowances	992
Loan Loss Allowances		1,005
Mortgages
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	242
Loan Loss Allowances		251
Credit Cards
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	140
Loan Loss Allowances		130
Other
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	160
Loan Loss Allowances		164
Consumer Finance
Disclosure of credit risk exposure [line items]
Exposure	5,228	5,384
Loan Loss Allowances	70
Loan Loss Allowances		67
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	380
Loan Loss Allowances		393
Corporate Centre
Disclosure of credit risk exposure [line items]
Loan Loss Allowances	0
Loan Loss Allowances		0
Upside One Scenario [member]
Disclosure of credit risk exposure [line items]
Exposure	294,877	306,284
Loan Loss Allowances	833
Loan Loss Allowances		930
Upside One Scenario [member] | Retail and Business Banking
Disclosure of credit risk exposure [line items]
Exposure	201,977	213,557
Loan Loss Allowances	419
Loan Loss Allowances		489
Upside One Scenario [member] | Mortgages
Disclosure of credit risk exposure [line items]
Exposure - of which: mortgages	181,188	192,346
ECL - of which: mortgages	141	214
Upside One Scenario [member] | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposure	5,228	5,740
Loan Loss Allowances	68
Loan Loss Allowances		65
Upside One Scenario [member] | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposure	27,277	28,277
Loan Loss Allowances	346
Loan Loss Allowances		376
Upside One Scenario [member] | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposure	60,395	58,710
Loan Loss Allowances	0
Loan Loss Allowances		0
Base Case Scenario [Member]
Disclosure of credit risk exposure [line items]
Exposure	294,877	306,284
Loan Loss Allowances	896
Loan Loss Allowances		932
Base Case Scenario [Member] | Retail and Business Banking
Disclosure of credit risk exposure [line items]
Exposure	201,977	213,557
Loan Loss Allowances	465
Loan Loss Allowances		497
Base Case Scenario [Member] | Mortgages
Disclosure of credit risk exposure [line items]
Exposure - of which: mortgages	181,188	192,346
ECL - of which: mortgages	174	218
Base Case Scenario [Member] | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposure	5,228	5,740
Loan Loss Allowances	69
Loan Loss Allowances		66
Base Case Scenario [Member] | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposure	27,277	28,277
Loan Loss Allowances	362
Loan Loss Allowances		369
Base Case Scenario [Member] | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposure	60,395	58,710
Loan Loss Allowances	0
Loan Loss Allowances		0
Downside One Scenario [member]
Disclosure of credit risk exposure [line items]
Exposure	294,877	306,284
Loan Loss Allowances	991
Loan Loss Allowances		993
Downside One Scenario [member] | Retail and Business Banking
Disclosure of credit risk exposure [line items]
Exposure	201,977	213,557
Loan Loss Allowances	536
Loan Loss Allowances		529
Downside One Scenario [member] | Mortgages
Disclosure of credit risk exposure [line items]
Exposure - of which: mortgages	181,188	192,346
ECL - of which: mortgages	234	244
Downside One Scenario [member] | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposure	5,228	5,740
Loan Loss Allowances	70
Loan Loss Allowances		65
Downside One Scenario [member] | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposure	27,277	28,277
Loan Loss Allowances	385
Loan Loss Allowances		399
Downside One Scenario [member] | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposure	60,395	58,710
Loan Loss Allowances	0
Loan Loss Allowances		0
Stubborn Inflation [Member]
Disclosure of credit risk exposure [line items]
Exposure	294,877	306,284
Loan Loss Allowances	1,176
Loan Loss Allowances		1,149
Stubborn Inflation [Member] | Retail and Business Banking
Disclosure of credit risk exposure [line items]
Exposure	201,977	213,557
Loan Loss Allowances	689
Loan Loss Allowances		647
Stubborn Inflation [Member] | Mortgages
Disclosure of credit risk exposure [line items]
Exposure - of which: mortgages	181,188	192,346
ECL - of which: mortgages	363	324
Stubborn Inflation [Member] | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposure	5,228	5,740
Loan Loss Allowances	72
Loan Loss Allowances		68
Stubborn Inflation [Member] | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposure	27,277	28,277
Loan Loss Allowances	415
Loan Loss Allowances		434
Stubborn Inflation [Member] | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposure	60,395	58,710
Loan Loss Allowances	0
Loan Loss Allowances		0
Downside Two Scenario [Member]
Disclosure of credit risk exposure [line items]
Exposure	294,877	306,284
Loan Loss Allowances	1,410
Loan Loss Allowances		1,383
Downside Two Scenario [Member] | Retail and Business Banking
Disclosure of credit risk exposure [line items]
Exposure	201,977	213,557
Loan Loss Allowances	889
Loan Loss Allowances		830
Downside Two Scenario [Member] | Mortgages
Disclosure of credit risk exposure [line items]
Exposure - of which: mortgages	181,188	192,346
ECL - of which: mortgages	562	501
Downside Two Scenario [Member] | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposure	5,228	5,740
Loan Loss Allowances	72
Loan Loss Allowances		69
Downside Two Scenario [Member] | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposure	27,277	28,277
Loan Loss Allowances	449
Loan Loss Allowances		484
Downside Two Scenario [Member] | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposure	60,395	58,710
Loan Loss Allowances	0
Loan Loss Allowances		0
Weighted
Disclosure of credit risk exposure [line items]
Exposure	294,877	306,284
Loan Loss Allowances	992
Loan Loss Allowances		1,005
Weighted | Retail and Business Banking
Disclosure of credit risk exposure [line items]
Exposure	201,977	213,557
Loan Loss Allowances	542
Loan Loss Allowances		544
Weighted | Mortgages
Disclosure of credit risk exposure [line items]
Exposure - of which: mortgages	181,188	192,346
ECL - of which: mortgages	242	251
Weighted | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposure	5,228	5,740
Loan Loss Allowances	70
Loan Loss Allowances		67
Weighted | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposure	27,277	28,277
Loan Loss Allowances	380
Loan Loss Allowances		394
Weighted | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposure	60,395	58,710
Loan Loss Allowances	£ 0
Loan Loss Allowances		£ 0

Credit Risk - Schedule of Impac

Credit Risk - Schedule of Impact on Profit Before Tax of Applying an Immediate and Permanent House Price Increase or Decrease to Our Base Case Economic Scenario Explanatory (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [abstract]
Increase in profit before tax due to 20 percentage increase in HPI rate	£ 70	£ 48
Increase in profit before tax due to 10 percentage increase in HPI rate	38	32
Decrease in profit before tax due to 10 percentage decrease in HPI rate	(54)	(61)
Decrease in profit before tax due to 20 percentage decrease in HPI rate	£ (155)	£ (176)

Credit Risk - Disclosure of Fac

Credit Risk - Disclosure of Factors to Measure ECL (Details) - Credit risk	12 Months Ended
	Dec. 31, 2023
Survival rate (SR)
Disclosure of credit risk exposure [line items]
Factor	Survival rate (SR)
Description	The probability that the exposure has not closed or defaulted since the reporting date.
Probability of default (PD)
Disclosure of credit risk exposure [line items]
Factor	Probability of default (PD)
Description	The likelihood of a borrower defaulting in the following month, assuming it has not closed or defaulted since the reporting date. For each month in the forecast period, we estimate the monthly PD from a range of factors. These include the current risk grade for the exposure, which becomes less relevant further into the forecast period, as well as the expected evolution of the account risk with maturity and factors for changing economics. We support this with historical data analysis.
Exposure at default (EAD)
Disclosure of credit risk exposure [line items]
Factor	Exposure at default (EAD)
Description	The amount we expect to be owed if a default event occurs. We determine EAD for each month of the forecast period by the expected payment profile, which varies by product. For amortising products, we base it on the borrower’s contractual repayments over the forecast period. We adjust this for any expected overpayments on Stage 1 accounts that the borrower may make and for any arrears we expect if the account was to default. For revolving products, or amortising products with an off-balance sheet element, we determine EAD using the balance at default and the contractual exposure limit. We vary these assumptions by product and base them on analysis of recent default data.
Loss given default (LGD)
Disclosure of credit risk exposure [line items]
Factor	Loss given default (LGD)
Description	Our expected loss if a default event were to occur. We express it as a percentage and calculate it based on factors that we have observed to affect the likelihood and/or value of any subsequent write-offs, which vary according to whether the product is secured or unsecured. If the product is secured, we take into account collateral values as well as the historical discounts to market/book values due to forced sales type.

Credit Risk - Disclosure of Max

Credit Risk - Disclosure of Maximum and Net Exposure to Credit Risk - IFRS 9 (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Collateral cash	£ (8,454)	£ (8,088)
Netting	(589)	(524)
Net exposure	294,877	306,284
Credit risk
Disclosure of credit risk exposure [line items]
Collateral cash	(100)	(100)
Collateral non-cash	(207,600)	(216,000)
Netting	(100)	0
Net exposure	91,500	94,000
Credit risk | Cash and balances at central banks
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Net exposure	38,200	44,200
Credit risk | Financial assets at FVOCI
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Net exposure	8,500	6,000
Balance sheet asset | Credit risk
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	267,900	278,400
Balance sheet asset | Credit risk | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	268,800	279,300
Balance sheet asset | Credit risk | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	900	900
Balance sheet asset | Credit risk | Cash and balances at central banks
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	38,200	44,200
Balance sheet asset | Credit risk | Cash and balances at central banks | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	38,200	44,200
Balance sheet asset | Credit risk | Cash and balances at central banks | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Balance sheet asset | Credit risk | Financial assets at FVOCI
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	8,500	6,000
Balance sheet asset | Credit risk | Financial assets at FVOCI | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	8,500	6,000
Balance sheet asset | Credit risk | Financial assets at FVOCI | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Off-balance sheet | Credit risk
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	31,400	31,700
Off-balance sheet | Credit risk | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	31,500	31,800
Off-balance sheet | Credit risk | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)	(100)
Off-balance sheet | Credit risk | Cash and balances at central banks
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Off-balance sheet | Credit risk | Cash and balances at central banks | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Off-balance sheet | Credit risk | Cash and balances at central banks | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Off-balance sheet | Credit risk | Financial assets at FVOCI
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Off-balance sheet | Credit risk | Financial assets at FVOCI | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Off-balance sheet | Credit risk | Financial assets at FVOCI | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Credit risk
Disclosure of credit risk exposure [line items]
Collateral cash	(100)	(100)
Collateral non-cash	(207,600)	(216,000)
Netting	(100)	0
Net exposure	44,800	43,800
Financial assets at amortised cost | Credit risk | Loans and advances to customers
Disclosure of credit risk exposure [line items]
Collateral cash	(100)	(100)
Collateral non-cash	(195,200)	(208,700)
Netting	0	0
Net exposure	43,000	42,200
Financial assets at amortised cost | Credit risk | Loans and advances to customers | Loans secured on residential properties
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	(175,400)	(187,400)
Netting	0	0
Net exposure	5,600	4,700
Financial assets at amortised cost | Credit risk | Loans and advances to customers | Corporate loans
Disclosure of credit risk exposure [line items]
Collateral cash	(100)	(100)
Collateral non-cash	(15,300)	(16,500)
Netting	0	0
Net exposure	11,500	11,400
Financial assets at amortised cost | Credit risk | Loans and advances to customers | Accrued interest and other adjustments
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Net exposure	900	700
Financial assets at amortised cost | Credit risk | Loans and advances to customers | Other unsecured loans
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Net exposure	20,500	21,100
Financial assets at amortised cost | Credit risk | Loans and advances to customers | Amounts due from fellow Banco Santander group subsidiaries and JVs
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Net exposure	4,500	4,200
Financial assets at amortised cost | Credit risk | Loans and advances to customers | Finance leases
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	(4,500)	(4,800)
Netting	0	0
Net exposure	0	100
Financial assets at amortised cost | Credit risk | Loans and advances to banks
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Net exposure	1,600	1,400
Financial assets at amortised cost | Credit risk | Reverse repurchase agreements – non trading
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	(12,400)	(7,300)
Netting	(100)	0
Net exposure	0	0
Financial assets at amortised cost | Credit risk | Other financial assets at amortised cost
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Net exposure	200	200
Financial assets at amortised cost | Balance sheet asset | Credit risk
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	221,200	228,200
Financial assets at amortised cost | Balance sheet asset | Credit risk | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	222,100	229,100
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	900	900
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	207,400	219,700
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Loans secured on residential properties
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	172,700	184,100
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Corporate loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	18,000	18,700
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Accrued interest and other adjustments
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	900	700
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Other unsecured loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	6,800	7,500
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Amounts due from fellow Banco Santander group subsidiaries and JVs
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	4,500	4,200
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	208,300	220,600
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Gross amounts | Loans secured on residential properties
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	172,900	184,300
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Gross amounts | Corporate loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	18,300	19,100
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Gross amounts | Accrued interest and other adjustments
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	900	700
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Gross amounts | Other unsecured loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	7,100	7,700
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Gross amounts | Amounts due from fellow Banco Santander group subsidiaries and JVs
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	4,500	4,200
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	900	900
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Loss allowance | Loans secured on residential properties
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	200	200
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Loss allowance | Corporate loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	300	400
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Loss allowance | Accrued interest and other adjustments
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Loss allowance | Other unsecured loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	300	200
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Loss allowance | Amounts due from fellow Banco Santander group subsidiaries and JVs
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Finance leases
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	4,500	4,500
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Gross amounts | Finance leases
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	4,600	4,600
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to customers | Loss allowance | Finance leases
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	100	100
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to banks
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	1,100	1,000
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to banks | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	1,100	1,000
Financial assets at amortised cost | Balance sheet asset | Credit risk | Loans and advances to banks | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Balance sheet asset | Credit risk | Reverse repurchase agreements – non trading
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	12,500	7,300
Financial assets at amortised cost | Balance sheet asset | Credit risk | Reverse repurchase agreements – non trading | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	12,500	7,300
Financial assets at amortised cost | Balance sheet asset | Credit risk | Reverse repurchase agreements – non trading | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Balance sheet asset | Credit risk | Other financial assets at amortised cost
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	200	200
Financial assets at amortised cost | Balance sheet asset | Credit risk | Other financial assets at amortised cost | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	200	200
Financial assets at amortised cost | Balance sheet asset | Credit risk | Other financial assets at amortised cost | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	31,400	31,700
Financial assets at amortised cost | Off-balance sheet | Credit risk | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	31,500	31,800
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)	(100)
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	30,900	31,300
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Loans secured on residential properties
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	8,300	8,000
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Corporate loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	8,900	9,300
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Accrued interest and other adjustments
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Other unsecured loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	13,700	13,600
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Amounts due from fellow Banco Santander group subsidiaries and JVs
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	31,000	31,400
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Gross amounts | Loans secured on residential properties
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	8,300	8,000
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Gross amounts | Corporate loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	8,900	9,300
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Gross amounts | Accrued interest and other adjustments
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Gross amounts | Other unsecured loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	13,800	13,700
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Gross amounts | Amounts due from fellow Banco Santander group subsidiaries and JVs
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)	(100)
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Loss allowance | Loans secured on residential properties
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Loss allowance | Corporate loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Loss allowance | Accrued interest and other adjustments
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Loss allowance | Other unsecured loans
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)	(100)
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Loss allowance | Amounts due from fellow Banco Santander group subsidiaries and JVs
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Finance leases
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	400
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Gross amounts | Finance leases
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	400
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to customers | Loss allowance | Finance leases
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to banks
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	500	400
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to banks | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	500	400
Financial assets at amortised cost | Off-balance sheet | Credit risk | Loans and advances to banks | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Reverse repurchase agreements – non trading
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Reverse repurchase agreements – non trading | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Reverse repurchase agreements – non trading | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Other financial assets at amortised cost
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Other financial assets at amortised cost | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Financial assets at amortised cost | Off-balance sheet | Credit risk | Other financial assets at amortised cost | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Debt securities | Credit risk | Financial assets at FVOCI
Disclosure of credit risk exposure [line items]
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Net exposure	8,500	6,000
Debt securities | Balance sheet asset | Credit risk | Financial assets at FVOCI
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	8,500	6,000
Debt securities | Balance sheet asset | Credit risk | Financial assets at FVOCI | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	8,500	6,000
Debt securities | Balance sheet asset | Credit risk | Financial assets at FVOCI | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Debt securities | Off-balance sheet | Credit risk | Financial assets at FVOCI
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Debt securities | Off-balance sheet | Credit risk | Financial assets at FVOCI | Gross amounts
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	0
Debt securities | Off-balance sheet | Credit risk | Financial assets at FVOCI | Loss allowance
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	£ 0	£ 0

Credit Risk - Disclosure of Dif

Credit Risk - Disclosure of Difference Between Maximum and Net Exposure to Credit Risk - IFRS 9 (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Collateral cash	£ (8,454)	£ (8,088)
Netting	(589)	(524)
Exposures	294,877	306,284
Credit risk
Disclosure of credit risk exposure [line items]
Collateral cash	(100)	(100)
Collateral non-cash	(207,600)	(216,000)
Netting	(100)	0
Exposures	91,500	94,000
Financial assets at fair value through profit loss | Credit risk
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	1,700	2,500
Collateral cash	(800)	0
Collateral non-cash	0	(1,700)
Netting	(500)	(500)
Exposures	400	300
Derivative financial instruments | Credit risk
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	1,400	2,400
Collateral cash	(800)	0
Collateral non-cash	0	(1,700)
Netting	(500)	(500)
Exposures	100	200
Other financial assets at FVTPL | Credit risk
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	300	100
Collateral cash	0	0
Collateral non-cash	0	0
Netting	0	0
Exposures	£ 300	£ 100

Credit Risk - Disclosure of Equ

Credit Risk - Disclosure of Equivalent Credit Rating Grade used by Standard and Poors Ratings Services (Details)	12 Months Ended
	Dec. 31, 2023
Mid | Santander UK risk grade 9
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.01%
Mid | Santander UK risk grade 8
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.032%
Mid | Santander UK risk grade 7
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.10%
Mid | Santander UK risk grade 6
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.316%
Mid | Santander UK risk grade 5
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	1%
Mid | Santander UK risk grade 4
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	3.162%
Mid | Santander UK risk grade 3
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	10%
Mid | Santander UK risk grade 2
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	31.623%
Mid | Santander UK risk grade 1
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	100%
Lower | Santander UK risk grade 9
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0%
Lower | Santander UK risk grade 8
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.021%
Lower | Santander UK risk grade 7
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.066%
Lower | Santander UK risk grade 6
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.208%
Lower | Santander UK risk grade 5
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.658%
Lower | Santander UK risk grade 4
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	2.081%
Lower | Santander UK risk grade 3
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	6.581%
Lower | Santander UK risk grade 2
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	20.811%
Lower | Santander UK risk grade 1
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	100%
Upper | Santander UK risk grade 9
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.021%
Upper | Santander UK risk grade 8
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.066%
Upper | Santander UK risk grade 7
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.208%
Upper | Santander UK risk grade 6
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	0.658%
Upper | Santander UK risk grade 5
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	2.081%
Upper | Santander UK risk grade 4
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	6.581%
Upper | Santander UK risk grade 3
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	20.811%
Upper | Santander UK risk grade 2
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	99.999%
Upper | Santander UK risk grade 1
Disclosure of credit risk exposure [line items]
Standard and poors rating probability of default percent	100%

Credit Risk - Disclosure of Cre

Credit Risk - Disclosure of Credit Rating of Financial Assets Subject to Credit Risk (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of internal credit grades [line items]
Credit impairment loss allowances on loans and advances to customers	£ (992)
Credit impairment loss allowances on loans and advances to customers		£ (1,005)
Coverage ratio	0.30%	0.30%
Balance sheet asset | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 172,700	£ 184,100
Credit impairment loss allowances on loans and advances to customers	(200)
Credit impairment loss allowances on loans and advances to customers		(200)
Balance sheet asset | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	207,400	219,700
Credit impairment loss allowances on loans and advances to customers	(900)
Credit impairment loss allowances on loans and advances to customers		(900)
Balance sheet asset | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 200	£ 200
Coverage ratio	0.10%	0.10%
Balance sheet asset | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	£ 900	£ 900
Coverage ratio	0.40%	0.40%
Balance sheet asset | Internal grade 9 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 5,200	£ 9,500
Balance sheet asset | Internal grade 9 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	5,300	9,500
Balance sheet asset | Internal grade 9 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Internal grade 9 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Internal grade 8 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	32,500	33,400
Balance sheet asset | Internal grade 8 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	34,200	35,900
Balance sheet asset | Internal grade 8 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Internal grade 8 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Internal grade 7 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	79,900	82,300
Balance sheet asset | Internal grade 7 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	84,400	85,600
Balance sheet asset | Internal grade 7 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Internal grade 7 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Internal grade 6 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	41,500	45,000
Balance sheet asset | Internal grade 6 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	48,900	52,100
Balance sheet asset | Internal grade 6 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Internal grade 6 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Internal grade 5 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	6,600	7,200
Balance sheet asset | Internal grade 5 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	14,600	15,200
Balance sheet asset | Internal grade 5 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	100
Balance sheet asset | Internal grade 5 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	200	200
Balance sheet asset | Internal grade 4 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	3,700	3,800
Balance sheet asset | Internal grade 4 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	8,300	9,200
Balance sheet asset | Internal grade 4 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	100	100
Balance sheet asset | Internal grade 4 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	200	200
Balance sheet asset | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	3,500	3,100
Balance sheet asset | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	5,400	5,400
Balance sheet asset | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	100	0
Balance sheet asset | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	500	500
Balance sheet asset | Other | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Other | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	7,200	7,700
Balance sheet asset | Other | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Balance sheet asset | Other | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Off-balance sheet | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	31,400	31,700
Credit impairment loss allowances on loans and advances to customers	(100)
Credit impairment loss allowances on loans and advances to customers		(100)
Off-balance sheet | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Coverage ratio	0.30%	0.30%
Off-balance sheet | Internal grade 9 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 100
Off-balance sheet | Internal grade 9 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Off-balance sheet | Internal grade 8 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	6,300	7,200
Off-balance sheet | Internal grade 8 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Off-balance sheet | Internal grade 7 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	7,000	6,900
Off-balance sheet | Internal grade 7 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Off-balance sheet | Internal grade 6 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	6,800	6,500
Off-balance sheet | Internal grade 6 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Off-balance sheet | Internal grade 5 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	4,600	4,900
Off-balance sheet | Internal grade 5 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Off-balance sheet | Internal grade 4 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	1,700	2,100
Off-balance sheet | Internal grade 4 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	100	0
Off-balance sheet | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	400	400
Off-balance sheet | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	100
Off-balance sheet | Other | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	4,700	3,700
Off-balance sheet | Other | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	153,000	169,100
Credit impairment loss allowances on loans and advances to customers	0
Credit impairment loss allowances on loans and advances to customers		0
Stage 1 | Balance sheet asset | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	182,600	199,600
Credit impairment loss allowances on loans and advances to customers	(100)
Credit impairment loss allowances on loans and advances to customers		(100)
Stage 1 | Balance sheet asset | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 0
Coverage ratio	0%	0%
Stage 1 | Balance sheet asset | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Coverage ratio	0.10%	0.10%
Stage 1 | Balance sheet asset | Internal grade 9 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 5,200	£ 9,500
Stage 1 | Balance sheet asset | Internal grade 9 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	5,300	9,500
Stage 1 | Balance sheet asset | Internal grade 9 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 9 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 8 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	31,400	33,100
Stage 1 | Balance sheet asset | Internal grade 8 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	33,100	35,600
Stage 1 | Balance sheet asset | Internal grade 8 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 8 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 7 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	75,900	80,700
Stage 1 | Balance sheet asset | Internal grade 7 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	80,400	83,900
Stage 1 | Balance sheet asset | Internal grade 7 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 7 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 6 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	36,300	41,100
Stage 1 | Balance sheet asset | Internal grade 6 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	43,600	47,900
Stage 1 | Balance sheet asset | Internal grade 6 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 6 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 5 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	3,600	4,100
Stage 1 | Balance sheet asset | Internal grade 5 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	10,300	11,100
Stage 1 | Balance sheet asset | Internal grade 5 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 5 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	100	100
Stage 1 | Balance sheet asset | Internal grade 4 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	400	500
Stage 1 | Balance sheet asset | Internal grade 4 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	2,800	3,900
Stage 1 | Balance sheet asset | Internal grade 4 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 4 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	200	100
Stage 1 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	300	500
Stage 1 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Other | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Other | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	6,900	7,300
Stage 1 | Balance sheet asset | Other | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Balance sheet asset | Other | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Off-balance sheet | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	30,300	30,800
Credit impairment loss allowances on loans and advances to customers	0
Credit impairment loss allowances on loans and advances to customers		0
Stage 1 | Off-balance sheet | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 0
Coverage ratio	0%	0%
Stage 1 | Off-balance sheet | Internal grade 9 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 100
Stage 1 | Off-balance sheet | Internal grade 9 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Off-balance sheet | Internal grade 8 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	6,300	7,200
Stage 1 | Off-balance sheet | Internal grade 8 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Off-balance sheet | Internal grade 7 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	6,900	6,800
Stage 1 | Off-balance sheet | Internal grade 7 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Off-balance sheet | Internal grade 6 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	6,700	6,400
Stage 1 | Off-balance sheet | Internal grade 6 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Off-balance sheet | Internal grade 5 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	4,400	4,700
Stage 1 | Off-balance sheet | Internal grade 5 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Off-balance sheet | Internal grade 4 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	1,200	1,700
Stage 1 | Off-balance sheet | Internal grade 4 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Off-balance sheet | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	100	200
Stage 1 | Off-balance sheet | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 1 | Off-balance sheet | Other | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	4,700	3,700
Stage 1 | Off-balance sheet | Other | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	17,800	13,300
Credit impairment loss allowances on loans and advances to customers	(100)
Credit impairment loss allowances on loans and advances to customers		(100)
Stage 2 | Balance sheet asset | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	22,200	17,800
Credit impairment loss allowances on loans and advances to customers	(400)
Credit impairment loss allowances on loans and advances to customers		(500)
Stage 2 | Balance sheet asset | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Coverage ratio	0.60%	0.80%
Stage 2 | Balance sheet asset | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	£ 400	£ 500
Coverage ratio	1.80%	2.80%
Stage 2 | Balance sheet asset | Internal grade 9 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 0
Stage 2 | Balance sheet asset | Internal grade 9 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 9 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 9 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 8 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	1,100	300
Stage 2 | Balance sheet asset | Internal grade 8 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	1,100	300
Stage 2 | Balance sheet asset | Internal grade 8 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 8 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 7 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	4,000	1,600
Stage 2 | Balance sheet asset | Internal grade 7 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	4,000	1,700
Stage 2 | Balance sheet asset | Internal grade 7 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 7 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 6 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	5,200	3,900
Stage 2 | Balance sheet asset | Internal grade 6 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	5,300	4,200
Stage 2 | Balance sheet asset | Internal grade 6 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 6 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 5 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	3,000	3,100
Stage 2 | Balance sheet asset | Internal grade 5 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	4,300	4,100
Stage 2 | Balance sheet asset | Internal grade 5 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	100
Stage 2 | Balance sheet asset | Internal grade 5 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	100	100
Stage 2 | Balance sheet asset | Internal grade 4 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	3,200	3,200
Stage 2 | Balance sheet asset | Internal grade 4 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	5,400	5,200
Stage 2 | Balance sheet asset | Internal grade 4 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	100	0
Stage 2 | Balance sheet asset | Internal grade 4 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	200	200
Stage 2 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	1,400	1,300
Stage 2 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	2,400	2,600
Stage 2 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	100	200
Stage 2 | Balance sheet asset | Other | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Other | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	100	200
Stage 2 | Balance sheet asset | Other | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Balance sheet asset | Other | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Off-balance sheet | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	1,000	800
Credit impairment loss allowances on loans and advances to customers	(100)
Credit impairment loss allowances on loans and advances to customers		(100)
Stage 2 | Off-balance sheet | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Coverage ratio	9.10%	12.50%
Stage 2 | Off-balance sheet | Internal grade 9 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 0
Stage 2 | Off-balance sheet | Internal grade 9 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Off-balance sheet | Internal grade 8 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Off-balance sheet | Internal grade 8 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Off-balance sheet | Internal grade 7 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	100	100
Stage 2 | Off-balance sheet | Internal grade 7 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Off-balance sheet | Internal grade 6 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	100	100
Stage 2 | Off-balance sheet | Internal grade 6 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Off-balance sheet | Internal grade 5 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	200	200
Stage 2 | Off-balance sheet | Internal grade 5 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Off-balance sheet | Internal grade 4 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	500	400
Stage 2 | Off-balance sheet | Internal grade 4 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	100	0
Stage 2 | Off-balance sheet | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	200	100
Stage 2 | Off-balance sheet | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	100
Stage 2 | Off-balance sheet | Other | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 2 | Off-balance sheet | Other | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	1,900	1,700
Credit impairment loss allowances on loans and advances to customers	(100)
Credit impairment loss allowances on loans and advances to customers		(100)
Stage 3 | Balance sheet asset | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	2,600	2,300
Credit impairment loss allowances on loans and advances to customers	(400)
Credit impairment loss allowances on loans and advances to customers		(300)
Stage 3 | Balance sheet asset | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Coverage ratio	5%	5.90%
Stage 3 | Balance sheet asset | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	£ 400	£ 300
Coverage ratio	13.30%	13%
Stage 3 | Balance sheet asset | Internal grade 9 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 0
Stage 3 | Balance sheet asset | Internal grade 9 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 9 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 9 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 8 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 8 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 8 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 8 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 7 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 7 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 7 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 7 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 6 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 6 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 6 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 6 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 5 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 5 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 5 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 5 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 4 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	100	100
Stage 3 | Balance sheet asset | Internal grade 4 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	100	100
Stage 3 | Balance sheet asset | Internal grade 4 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	100
Stage 3 | Balance sheet asset | Internal grade 4 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	1,900	1,700
Stage 3 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	2,700	2,300
Stage 3 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	100	0
Stage 3 | Balance sheet asset | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	400	300
Stage 3 | Balance sheet asset | Other | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Other | Credit risk | Exposures - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	200	200
Stage 3 | Balance sheet asset | Other | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Mortgages
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Balance sheet asset | Other | Credit risk | ECL - On balance sheet | Financial assets at amortised cost | Loans and advances to customers
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	100	100
Credit impairment loss allowances on loans and advances to customers	0
Credit impairment loss allowances on loans and advances to customers		0
Stage 3 | Off-balance sheet | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 0
Coverage ratio	0%	0%
Stage 3 | Off-balance sheet | Internal grade 9 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 0
Stage 3 | Off-balance sheet | Internal grade 9 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 8 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 8 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 7 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 7 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 6 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 6 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 5 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 5 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 4 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 4 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Internal grade 3 to 1 | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	100	100
Stage 3 | Off-balance sheet | Internal grade 3 to 1 | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Other | Credit risk | Exposures - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	0	0
Stage 3 | Off-balance sheet | Other | Credit risk | ECL - On balance sheet
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 0

Credit Risk - Disclosure of C_2

Credit Risk - Disclosure of Credit Performance (Details)	Dec. 31, 2023	Dec. 31, 2022
Unsecured personal loans
Disclosure of credit risk exposure [line items]
Percentage of arrears over ninety days past due	73%	61%
Overdrafts
Disclosure of credit risk exposure [line items]
Percentage of arrears over ninety days past due	243%	224%
Retail and Business Banking
Disclosure of credit risk exposure [line items]
Percentage of arrears over ninety days past due	415%	347%
Mortgages
Disclosure of credit risk exposure [line items]
Percentage of arrears over ninety days past due	80%	62%
Credit Cards
Disclosure of credit risk exposure [line items]
Percentage of arrears over ninety days past due	51%	49%
Consumer Finance
Disclosure of credit risk exposure [line items]
Percentage of arrears over ninety days past due	43%	44%

Credit Risk - Disclosure of IFR

Credit Risk - Disclosure of IFRS 9 Credit Quality (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Exposures	£ 294,877	£ 306,284
Loss allowance	992
Loss allowance		1,005
Provisions	402	378
Total ECL	£ 992	£ 1,005
Coverage ratio	0.30%	0.30%
Retail mortgage offers in pipeline	£ 3,300	£ 2,800
Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	263,449	274,448
Loss allowance	£ 914
Gross write-offs		156
Loss allowance		£ 931
Coverage ratio	0.30%	0.30%
Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 31,428	£ 31,836
Gross write-offs		156
Provisions	£ 78	£ 74
Coverage ratio	0.20%	0.20%
Customer loans | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 203,100	£ 215,700
Loans and advances to banks | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	1,100	1,000
Sovereign assets measured at amortized cost | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	12,600	7,500
Financial assets measured at fair value through other comprehensive income | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	8,500	6,000
Cash and balances at central banks | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	38,200	44,200
Retail and Business Banking | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	179,887	191,836
Loss allowance	£ 499
Gross write-offs		113
Loss allowance		£ 502
Coverage ratio	0.30%	0.30%
Retail and Business Banking | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 22,090	£ 21,721
Gross write-offs		0
Provisions	£ 43	£ 42
Coverage ratio	0.20%	0.20%
Consumer Finance
Disclosure of credit risk exposure [line items]
Loss allowance	£ 70
Gross write-offs	23	£ 19
Loss allowance		67
Consumer Finance | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	5,228	5,384
Loss allowance	£ 70
Gross write-offs		19
Loss allowance		£ 67
Coverage ratio	1.30%	1.20%
Consumer Finance | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 356
Gross write-offs		0
Provisions	£ 0	£ 0
Coverage ratio	0%	0%
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	£ 380
Loss allowance		£ 393
Corporate & Commercial Banking | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	17,939	18,518
Loss allowance	£ 345
Gross write-offs		24
Loss allowance		£ 362
Coverage ratio	1.90%	2%
Corporate & Commercial Banking | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 9,338	£ 9,759
Gross write-offs		0
Provisions	£ 35	£ 32
Coverage ratio	0.40%	0.30%
Corporate Centre
Disclosure of credit risk exposure [line items]
Loss allowance	£ 0
Loss allowance		£ 0
Corporate Centre | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	60,395	58,710
Loss allowance	£ 0
Gross write-offs		0
Loss allowance		£ 0
Coverage ratio	0%	0%
Corporate Centre | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 0
Gross write-offs		0
Provisions	£ 0
Coverage ratio	0%
Stage 1
Disclosure of credit risk exposure [line items]
Exposures	£ 268,211	284,428
Total ECL	£ 170	£ 170
Coverage ratio	0.10%	0.10%
Stage 1 | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 237,869	£ 253,587
Loss allowance	£ 142
Loss allowance		£ 144
Coverage ratio	0.10%	0.10%
Stage 1 | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 30,342	£ 30,841
Provisions	£ 28	£ 26
Coverage ratio	0.10%	0.10%
Stage 1 | Retail and Business Banking | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 158,782	£ 175,365
Loss allowance	£ 57
Loss allowance		£ 56
Coverage ratio	0%	0%
Stage 1 | Retail and Business Banking | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 21,597	£ 21,175
Provisions	£ 16	£ 12
Coverage ratio	0.10%	0.10%
Stage 1 | Consumer Finance | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 4,870	£ 5,005
Loss allowance	£ 21
Loss allowance		£ 19
Coverage ratio	0.40%	0.40%
Stage 1 | Consumer Finance | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 356
Provisions	£ 0	£ 0
Coverage ratio	0%	0%
Stage 1 | Corporate & Commercial Banking | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 13,822	£ 14,507
Loss allowance	£ 64
Loss allowance		£ 69
Coverage ratio	0.50%	0.50%
Stage 1 | Corporate & Commercial Banking | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 8,745	£ 9,310
Provisions	£ 12	£ 14
Coverage ratio	0.10%	0.20%
Stage 1 | Corporate Centre | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 60,395	£ 58,710
Loss allowance	£ 0
Loss allowance		£ 0
Coverage ratio	0%	0%
Stage 1 | Corporate Centre | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 0
Provisions	£ 0
Coverage ratio	0%
Stage 2
Disclosure of credit risk exposure [line items]
Exposures	£ 23,595	19,127
Loss allowance	461
Loss allowance		516
Total ECL	£ 461	£ 516
Coverage ratio	2%	2.70%
Stage 2 | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 22,614	£ 18,225
Loss allowance	£ 421
Loss allowance		£ 477
Coverage ratio	1.90%	2.60%
Stage 2 | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 981	£ 902
Provisions	£ 40	£ 39
Coverage ratio	4.10%	4.30%
Stage 2 | Retail and Business Banking | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 18,866	£ 14,399
Loss allowance	£ 273
Loss allowance		£ 295
Coverage ratio	1.40%	2%
Stage 2 | Retail and Business Banking | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 434	£ 490
Provisions	£ 26	£ 28
Coverage ratio	6%	5.70%
Stage 2 | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	£ 330	£ 350
Loss allowance	30
Loss allowance		27
Stage 2 | Consumer Finance | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	330	350
Loss allowance	£ 30
Loss allowance		£ 27
Coverage ratio	9%	7.70%
Stage 2 | Consumer Finance | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 0
Provisions	£ 0	£ 0
Coverage ratio	0%	0%
Stage 2 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	£ 3,418	£ 3,476
Loss allowance	118
Loss allowance		155
Stage 2 | Corporate & Commercial Banking | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	3,418	3,476
Loss allowance	£ 118
Loss allowance		£ 155
Coverage ratio	3.50%	4.50%
Stage 2 | Corporate & Commercial Banking | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 547	£ 412
Provisions	£ 14	£ 11
Coverage ratio	2.50%	2.70%
Stage 2 | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 0
Loss allowance	0
Loss allowance		0
Stage 2 | Corporate Centre | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	£ 0
Loss allowance		£ 0
Coverage ratio	0%	0%
Stage 2 | Corporate Centre | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 0
Provisions	£ 0
Coverage ratio	0%
Stage 3
Disclosure of credit risk exposure [line items]
Exposures	£ 3,071	2,729
Total ECL	£ 361	£ 319
Coverage ratio	11.80%	11.70%
Stage 3 | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 2,966	£ 2,636
Loss allowance	£ 351
Loss allowance		£ 310
Coverage ratio	11.80%	11.80%
Stage 3 | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 105	£ 93
Provisions	£ 10	£ 9
Coverage ratio	10.40%	9.70%
Stage 3 | Retail and Business Banking | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 2,239	£ 2,072
Loss allowance	£ 169
Loss allowance		£ 151
Coverage ratio	7.50%	7.30%
Stage 3 | Retail and Business Banking | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 59	£ 56
Provisions	£ 1	£ 2
Coverage ratio	2.80%	3.60%
Stage 3 | Consumer Finance | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 28	£ 29
Loss allowance	£ 19
Loss allowance		£ 21
Coverage ratio	68.50%	72.40%
Stage 3 | Consumer Finance | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 0
Provisions	£ 0	£ 0
Coverage ratio	0%	0%
Stage 3 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	£ 745	£ 572
Stage 3 | Corporate & Commercial Banking | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	699	535
Loss allowance	£ 163
Loss allowance		£ 138
Coverage ratio	23.40%	25.80%
Stage 3 | Corporate & Commercial Banking | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 46	£ 37
Provisions	£ 9	£ 7
Coverage ratio	20.20%	18.90%
Stage 3 | Corporate Centre | Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 0
Loss allowance	£ 0
Loss allowance		£ 0
Coverage ratio	0%	0%
Stage 3 | Corporate Centre | Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	£ 0	£ 0
Provisions	£ 0
Coverage ratio	0%

Credit Risk - Disclosure of Sta

Credit Risk - Disclosure of Stage 2 Exposures by Classification (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Exposures	£ 294,877	£ 306,284
Loss allowance	£ 992
Loss allowance		£ 1,005
Coverage ratio	0.30%	0.30%
Mortgages
Disclosure of credit risk exposure [line items]
Loss allowance	£ 242
Loss allowance		£ 251
Consumer Finance
Disclosure of credit risk exposure [line items]
Loss allowance	70
Loss allowance		67
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	380
Loss allowance		393
Corporate Centre
Disclosure of credit risk exposure [line items]
Loss allowance	0
Loss allowance		0
Stage 2
Disclosure of credit risk exposure [line items]
Exposures	23,595	19,127
Loss allowance	£ 461
Loss allowance		£ 516
Coverage ratio	2%	2.70%
Stage 2 | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	£ 22,614	£ 18,225
Loss allowance	421
Loss allowance		477
Stage 2 | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	40
Loss allowance		39
Stage 2 | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	17,876	13,424
Loss allowance	109
Loss allowance		130
Stage 2 | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	330	350
Loss allowance	30
Loss allowance		27
Stage 2 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	3,418	3,476
Loss allowance	118
Loss allowance		155
Stage 2 | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | PD deterioration
Disclosure of credit risk exposure [line items]
Exposures	9,160	10,323
Loss allowance	277
Loss allowance		303
Stage 2 | PD deterioration | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	8,345	9,560
Loss allowance	249
Loss allowance		284
Stage 2 | PD deterioration | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	28
Loss allowance		19
Stage 2 | PD deterioration | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	5,877	7,310
Loss allowance	65
Loss allowance		86
Stage 2 | PD deterioration | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	115	159
Loss allowance	10
Loss allowance		11
Stage 2 | PD deterioration | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	1,809	1,548
Loss allowance	75
Loss allowance		81
Stage 2 | PD deterioration | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Forbearance
Disclosure of credit risk exposure [line items]
Exposures	601	625
Loss allowance	4
Loss allowance		6
Stage 2 | Forbearance | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	601	513
Loss allowance	4
Loss allowance		6
Stage 2 | Forbearance | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	0
Loss allowance		0
Stage 2 | Forbearance | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	516	449
Loss allowance	2
Loss allowance		2
Stage 2 | Forbearance | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Forbearance | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	85	64
Loss allowance	2
Loss allowance		4
Stage 2 | Forbearance | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Other
Disclosure of credit risk exposure [line items]
Exposures	1,152	1,116
Loss allowance	37
Loss allowance		30
Stage 2 | Other | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	960	1,137
Loss allowance	33
Loss allowance		22
Stage 2 | Other | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	4
Loss allowance		8
Stage 2 | Other | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	265	241
Loss allowance	3
Loss allowance		5
Stage 2 | Other | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	126	164
Loss allowance	5
Loss allowance		6
Stage 2 | Other | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	533	684
Loss allowance	17
Loss allowance		1
Stage 2 | Other | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | 30 DPD
Disclosure of credit risk exposure [line items]
Exposures	893	937
Loss allowance	49
Loss allowance		54
Stage 2 | 30 DPD | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	856	890
Loss allowance	46
Loss allowance		48
Stage 2 | 30 DPD | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	3
Loss allowance		6
Stage 2 | 30 DPD | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	560	463
Loss allowance	11
Loss allowance		10
Stage 2 | 30 DPD | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	25	27
Loss allowance	11
Loss allowance		10
Stage 2 | 30 DPD | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	93	214
Loss allowance	2
Loss allowance		10
Stage 2 | 30 DPD | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Secured affordability
Disclosure of credit risk exposure [line items]
Exposures	2,889	4,961
Loss allowance	13
Loss allowance		27
Stage 2 | Secured affordability | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	2,953	4,961
Loss allowance	13
Loss allowance		27
Stage 2 | Secured affordability | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	0
Loss allowance		0
Stage 2 | Secured affordability | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	2,889	4,961
Loss allowance	9
Loss allowance		27
Stage 2 | Secured affordability | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	64	0
Loss allowance	4
Loss allowance		0
Stage 2 | Secured affordability | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Secured affordability | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Unsecured affordability
Disclosure of credit risk exposure [line items]
Exposures	233	199
Loss allowance	38
Loss allowance		35
Stage 2 | Unsecured affordability | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	232	198
Loss allowance	35
Loss allowance		31
Stage 2 | Unsecured affordability | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	3
Loss allowance		4
Stage 2 | Unsecured affordability | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Unsecured affordability | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Unsecured affordability | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Unsecured affordability | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | Mortgage Refinancing
Disclosure of credit risk exposure [line items]
Exposures	7,769
Loss allowance	19
Stage 2 | Mortgage Refinancing | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	7,769
Loss allowance	19
Stage 2 | Mortgage Refinancing | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	0
Stage 2 | Mortgage Refinancing | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	7,769
Loss allowance	19
Stage 2 | Mortgage Refinancing | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	0
Loss allowance	0
Stage 2 | Mortgage Refinancing | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	0
Loss allowance	0
Stage 2 | Mortgage Refinancing | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0
Loss allowance	0
Stage 2 | High risk corporate
Disclosure of credit risk exposure [line items]
Exposures	898	966
Loss allowance	24
Loss allowance		61
Stage 2 | High risk corporate | Total Drawn
Disclosure of credit risk exposure [line items]
Exposures	898	966
Loss allowance	22
Loss allowance		59
Stage 2 | High risk corporate | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	2
Loss allowance		2
Stage 2 | High risk corporate | Mortgages
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | High risk corporate | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	0
Loss allowance		0
Stage 2 | High risk corporate | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	898	966
Loss allowance	22
Loss allowance		59
Stage 2 | High risk corporate | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	£ 0
Loss allowance		£ 0

Credit Risk - Disclosure of S_2

Credit Risk - Disclosure of Stage 2 Decomposition Cure and Not Cure Explanatory (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Exposures	£ 294,877	£ 306,284
Loss allowance	£ 992
Loss allowance		£ 1,005
Coverage ratio	0.30%	0.30%

Credit Risk - Disclosure of S_3

Credit Risk - Disclosure of Stage 3 Decomposition Cure and Not Cure Explanatory (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Exposures	£ 294,877	£ 306,284
Loss allowance	£ 992
Loss allowance		£ 1,005
Coverage ratio	0.30%	0.30%

Credit Risk - Disclosure of Rec

Credit Risk - Disclosure of Reconciliation of Exposures, ECL and Net Carrying Amounts (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Exposures	£ 294,877	£ 306,284
Loss allowance	992
Loss allowance		1,005
Assets classified at FVTPL	254	113
Total assets	275,448	285,213
Loss allowance	402	378
Macro hedge of interest rate risk	(632)	(2,657)
Mortgages
Disclosure of credit risk exposure [line items]
Loss allowance	242
Loss allowance		251
Credit Cards
Disclosure of credit risk exposure [line items]
Loss allowance	140
Loss allowance		130
Other
Disclosure of credit risk exposure [line items]
Loss allowance	160
Loss allowance		164
Consumer Finance
Disclosure of credit risk exposure [line items]
Loss allowance	70
Loss allowance		67
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	380
Loss allowance		393
Corporate Centre
Disclosure of credit risk exposure [line items]
Loss allowance	0
Loss allowance		0
Balance sheet asset
Disclosure of credit risk exposure [line items]
Exposures	263,449	274,448
Loss allowance	914
Loss allowance		931
Net carrying amount	262,535	273,517
Joint ventures	4,544	4,164
Other items	751	745
Adjusted net carrying amount	267,830	278,426
Assets classified at FVTPL	1,694	2,536
Non-financial assets	5,924	4,251
Total assets	275,448	285,213
Balance sheet asset | Retail and Business Banking
Disclosure of credit risk exposure [line items]
Exposures	179,887	191,836
Loss allowance	499
Loss allowance		502
Net carrying amount	179,388	191,334
Balance sheet asset | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	5,228	5,384
Loss allowance	70
Loss allowance		67
Net carrying amount	5,158	5,317
Balance sheet asset | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	17,939	18,518
Loss allowance	345
Loss allowance		362
Net carrying amount	17,594	18,156
Balance sheet asset | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	60,395	58,710
Loss allowance	0
Loss allowance		0
Net carrying amount	60,395	58,710
Off-balance sheet
Disclosure of credit risk exposure [line items]
Exposures	31,428	31,836
Loss allowance	78	74
Off-balance sheet | Retail and Business Banking
Disclosure of credit risk exposure [line items]
Exposures	22,090	21,721
Loss allowance	43	42
Off-balance sheet | Consumer Finance
Disclosure of credit risk exposure [line items]
Exposures	0	356
Loss allowance	0	0
Off-balance sheet | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	9,338	9,759
Loss allowance	35	32
Off-balance sheet | Corporate Centre
Disclosure of credit risk exposure [line items]
Exposures	0	0
Loss allowance	£ 0	£ 0

Credit Risk - Disclosure of E_2

Credit Risk - Disclosure of ECL Reconciliation (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	£ 1,005
Ending balance	992	£ 1,005
Less: Recoveries net of collection costs	(10)	(36)	£ 17
Credit impairment (charges)/write-backs	205
ECL charge/(release) to the Income Statement from continued operations		320	(233)
Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Credit impairment (charges)/write-backs	40
ECL charge/(release) to the Income Statement from continued operations		31	(90)
Stage 1
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	170
Ending balance	170	170
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	284,428	292,366
Transfers from Stage 1 to Stage 2	(12,945)	(9,100)
Transfers from Stage 2 to Stage 1	5,913	7,207
Transfers to Stage 3	(598)	(621)
Transfers from Stage 3	28	10
Transfers of financial instruments	(7,602)	(2,504)
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	25,409	48,194
Redemptions and repayments	(33,805)	(54,546)
Changes in risk parameters and other movements	(219)	918
Assets written off	0	0
Ending balance	268,211	284,428	292,366
Net movement in the period	(16,217)	(7,938)
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	176,965	177,696
Transfers from Stage 1 to Stage 2	(10,791)	(5,834)
Transfers from Stage 2 to Stage 1	4,778	2,961
Transfers to Stage 3	(335)	(278)
Transfers from Stage 3	14	4
Transfers of financial instruments	(6,334)	(3,147)
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	12,947	35,028
Redemptions and repayments	(23,081)	(32,565)
Changes in risk parameters and other movements	666	(47)
Assets written off	0	0
Ending balance	161,163	176,965	177,696
Net movement in the period	(15,802)	(731)
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	23,838	20,604
Transfers from Stage 1 to Stage 2	(1,376)	(2,195)
Transfers from Stage 2 to Stage 1	512	4,023
Transfers to Stage 3	(118)	(172)
Transfers from Stage 3	1	0
Transfers of financial instruments	(981)	1,656
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	7,257	8,629
Redemptions and repayments	(6,713)	(9,019)
Changes in risk parameters and other movements	(834)	1,968
Assets written off	0	0
Ending balance	22,567	23,838	20,604
Net movement in the period	(1,271)	3,234
Stage 2
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	516
Ending balance	461	516
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	19,127	17,964
Transfers from Stage 1 to Stage 2	12,945	9,100
Transfers from Stage 2 to Stage 1	(5,913)	(7,207)
Transfers to Stage 3	(920)	(624)
Transfers from Stage 3	304	758
Transfers of financial instruments	6,416	2,027
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	562	1,119
Redemptions and repayments	(3,017)	(2,065)
Changes in risk parameters and other movements	507	82
Assets written off	0	0
Ending balance	23,595	19,127	17,964
Net movement in the period	4,468	1,163
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	13,533	11,152
Transfers from Stage 1 to Stage 2	10,791	5,834
Transfers from Stage 2 to Stage 1	(4,778)	(2,961)
Transfers to Stage 3	(566)	(448)
Transfers from Stage 3	277	279
Transfers of financial instruments	5,724	2,704
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	154	529
Redemptions and repayments	(1,752)	(1,229)
Changes in risk parameters and other movements	338	377
Assets written off	0	0
Ending balance	17,997	13,533	11,152
Net movement in the period	4,464	2,381
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	3,888	5,914
Transfers from Stage 1 to Stage 2	1,376	2,195
Transfers from Stage 2 to Stage 1	(512)	(4,023)
Transfers to Stage 3	(258)	(111)
Transfers from Stage 3	9	463
Transfers of financial instruments	615	(1,476)
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	132	228
Redemptions and repayments	(869)	(584)
Changes in risk parameters and other movements	199	(194)
Assets written off	0	0
Ending balance	3,965	3,888	5,914
Net movement in the period	77	(2,026)
Stage 3
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	319
Ending balance	361	319
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	2,729	3,017
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	1,518	1,245
Transfers from Stage 3	(332)	(768)
Transfers of financial instruments	1,186	477
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	59	64
Redemptions and repayments	(886)	(950)
Changes in risk parameters and other movements	395	375
Assets written off	(412)	(254)
Ending balance	3,071	2,729	3,017
Net movement in the period	342	(288)
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	1,848	1,815
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	901	726
Transfers from Stage 3	(291)	(283)
Transfers of financial instruments	610	443
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	5	1
Redemptions and repayments	(417)	(415)
Changes in risk parameters and other movements	36	14
Assets written off	(54)	(10)
Ending balance	2,028	1,848	1,815
Net movement in the period	180	33
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	572	827
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	376	283
Transfers from Stage 3	(10)	(463)
Transfers of financial instruments	366	(180)
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	38	43
Redemptions and repayments	(193)	(53)
Changes in risk parameters and other movements	137	21
Assets written off	(175)	(86)
Ending balance	745	572	827
Net movement in the period	173	(255)
Exposures - On balance sheet
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	306,284	313,347
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	26,030	49,377
Redemptions and repayments	(37,708)	(57,561)
Changes in risk parameters and other movements	683	1,375
Assets written off	(412)	(254)
Ending balance	294,877	306,284	313,347
Net movement in the period	(11,407)	(7,063)
Exposures - On balance sheet | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	192,346	190,663
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	13,106	35,558
Redemptions and repayments	(25,250)	(34,209)
Changes in risk parameters and other movements	1,040	344
Assets written off	(54)	(10)
Ending balance	181,188	192,346	190,663
Net movement in the period	(11,158)	1,683
Exposures - On balance sheet | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	28,298	27,345
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	7,427	8,900
Redemptions and repayments	(7,775)	(9,656)
Changes in risk parameters and other movements	(498)	1,795
Assets written off	(175)	(86)
Ending balance	27,277	28,298	27,345
Net movement in the period	(1,021)	953
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	170	132
Transfers from Stage 1 to Stage 2	(9)	(25)
Transfers from Stage 2 to Stage 1	111	133
Transfers to Stage 3	(6)	(4)
Transfers from Stage 3	1	1
Transfers of financial instruments	97	105
Net ECL remeasurement on stage transfer	(111)	(110)
Change in economic scenarios	29	37
New lending and assets purchased	28	42
Redemptions and repayments	(35)	(35)
Changes in risk parameters and other movements	(8)	(1)
Assets written off	0	0
Ending balance	170	170	132
Increase decrease in total expected credit losses	0	38
Charge/(release) to the Income Statement	0	38
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	25	13
Transfers from Stage 1 to Stage 2	(3)	(1)
Transfers from Stage 2 to Stage 1	30	16
Transfers to Stage 3	(3)	(2)
Transfers from Stage 3	0	0
Transfers of financial instruments	24	13
Net ECL remeasurement on stage transfer	(28)	(15)
Change in economic scenarios	0	1
New lending and assets purchased	4	7
Redemptions and repayments	(6)	(3)
Changes in risk parameters and other movements	5	9
Assets written off	0	0
Ending balance	24	25	13
Increase decrease in total expected credit losses	(1)	12
Charge/(release) to the Income Statement	(1)	12
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Credit impairment (charges)/write-backs	(1)
ECL charge/(release) to the Income Statement from continued operations		12
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	83	50
Transfers from Stage 1 to Stage 2	(1)	(14)
Transfers from Stage 2 to Stage 1	10	92
Transfers to Stage 3	(3)	(1)
Transfers from Stage 3	0	0
Transfers of financial instruments	6	77
Net ECL remeasurement on stage transfer	(16)	(72)
Change in economic scenarios	30	38
New lending and assets purchased	5	16
Redemptions and repayments	(13)	(15)
Changes in risk parameters and other movements	(19)	(11)
Assets written off	0	0
Ending balance	76	83	50
Increase decrease in total expected credit losses	(7)	33
Charge/(release) to the Income Statement	(7)	33
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Credit impairment (charges)/write-backs	(7)
ECL charge/(release) to the Income Statement from continued operations		33
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	516	330
Transfers from Stage 1 to Stage 2	9	25
Transfers from Stage 2 to Stage 1	(111)	(133)
Transfers to Stage 3	(38)	(32)
Transfers from Stage 3	15	150
Transfers of financial instruments	(125)	10
Net ECL remeasurement on stage transfer	145	98
Change in economic scenarios	(33)	123
New lending and assets purchased	45	76
Redemptions and repayments	(53)	(60)
Changes in risk parameters and other movements	(34)	(61)
Assets written off	0	0
Ending balance	461	516	330
Increase decrease in total expected credit losses	(55)	186
Charge/(release) to the Income Statement	(55)	186
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	131	88
Transfers from Stage 1 to Stage 2	3	1
Transfers from Stage 2 to Stage 1	(30)	(16)
Transfers to Stage 3	(15)	(11)
Transfers from Stage 3	9	9
Transfers of financial instruments	(33)	(17)
Net ECL remeasurement on stage transfer	40	40
Change in economic scenarios	(2)	21
New lending and assets purchased	3	11
Redemptions and repayments	(12)	(11)
Changes in risk parameters and other movements	(17)	(1)
Assets written off	0	0
Ending balance	110	131	88
Increase decrease in total expected credit losses	(21)	43
Charge/(release) to the Income Statement	(21)	43
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Credit impairment (charges)/write-backs	(21)
ECL charge/(release) to the Income Statement from continued operations		43
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	166	127
Transfers from Stage 1 to Stage 2	1	14
Transfers from Stage 2 to Stage 1	(10)	(92)
Transfers to Stage 3	(8)	(13)
Transfers from Stage 3	1	135
Transfers of financial instruments	(16)	44
Net ECL remeasurement on stage transfer	29	(41)
Change in economic scenarios	(30)	76
New lending and assets purchased	6	19
Redemptions and repayments	(10)	(32)
Changes in risk parameters and other movements	(13)	(27)
Assets written off	0	0
Ending balance	132	166	127
Increase decrease in total expected credit losses	(34)	39
Charge/(release) to the Income Statement	(34)	39
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Credit impairment (charges)/write-backs	(34)
ECL charge/(release) to the Income Statement from continued operations		39
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	319	403
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	44	36
Transfers from Stage 3	(16)	(151)
Transfers of financial instruments	28	(115)
Net ECL remeasurement on stage transfer	130	110
Change in economic scenarios	9	3
New lending and assets purchased	20	24
Redemptions and repayments	(46)	(35)
Changes in risk parameters and other movements	133	86
Assets written off	(232)	(157)
Ending balance	361	319	403
Increase decrease in total expected credit losses	42	(84)
Charge/(release) to the Income Statement	274	73
Less: Discount unwind	(21)	(13)
Less: Recoveries net of collection costs	7	36
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	95	89
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	18	13
Transfers from Stage 3	(9)	(9)
Transfers of financial instruments	9	4
Net ECL remeasurement on stage transfer	22	8
Change in economic scenarios	3	2
New lending and assets purchased	1	0
Redemptions and repayments	(14)	(12)
Changes in risk parameters and other movements	3	7
Assets written off	(11)	(3)
Ending balance	108	95	89
Increase decrease in total expected credit losses	13	6
Charge/(release) to the Income Statement	24	9
Less: Discount unwind	(3)	(2)
Less: Recoveries net of collection costs	28	(1)
Credit impairment (charges)/write-backs	49
ECL charge/(release) to the Income Statement from continued operations		6
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	145	248
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	11	14
Transfers from Stage 3	(1)	(135)
Transfers of financial instruments	10	(121)
Net ECL remeasurement on stage transfer	64	61
Change in economic scenarios	6	0
New lending and assets purchased	10	12
Redemptions and repayments	(23)	(17)
Changes in risk parameters and other movements	28	(14)
Assets written off	(68)	(24)
Ending balance	172	145	248
Increase decrease in total expected credit losses	27	(103)
Charge/(release) to the Income Statement	95	(79)
Less: Discount unwind	(9)	(3)
Less: Recoveries net of collection costs	(5)	42
Credit impairment (charges)/write-backs	81
ECL charge/(release) to the Income Statement from continued operations		(40)
ECL - On balance sheet
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	1,005	865
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	164	98
Change in economic scenarios	5	163
New lending and assets purchased	93	142
Redemptions and repayments	(134)	(130)
Changes in risk parameters and other movements	91	24
Assets written off	(232)	(157)
Ending balance	992	1,005	865
Increase decrease in total expected credit losses	(13)	140
Charge/(release) to the Income Statement	219	297
Less: Discount unwind	(21)	(13)
Less: Recoveries net of collection costs	7	36
ECL - On balance sheet | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	251	190
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	34	33
Change in economic scenarios	1	24
New lending and assets purchased	8	18
Redemptions and repayments	(32)	(26)
Changes in risk parameters and other movements	(9)	15
Assets written off	(11)	(3)
Ending balance	242	251	190
Increase decrease in total expected credit losses	(9)	61
Charge/(release) to the Income Statement	2	64
Less: Discount unwind	(3)	(2)
Less: Recoveries net of collection costs	28	(1)
Credit impairment (charges)/write-backs	27
ECL charge/(release) to the Income Statement from continued operations		61
ECL - On balance sheet | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	394	425
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	77	(52)
Change in economic scenarios	6	114
New lending and assets purchased	21	47
Redemptions and repayments	(46)	(64)
Changes in risk parameters and other movements	(4)	(52)
Assets written off	(68)	(24)
Ending balance	380	394	£ 425
Increase decrease in total expected credit losses	(14)	(31)
Charge/(release) to the Income Statement	54	(7)
Less: Discount unwind	(9)	(3)
Less: Recoveries net of collection costs	(5)	42
Credit impairment (charges)/write-backs	£ 40
ECL charge/(release) to the Income Statement from continued operations		£ 32

Credit Risk - Disclosure of Cou

Credit Risk - Disclosure of Country Risk Exposure (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Exposures	£ 294,877	£ 306,284
Total
Disclosure of credit risk exposure [line items]
Exposures	293,600	306,100
Governments
Disclosure of credit risk exposure [line items]
Exposures	43,100	47,000
Banks
Disclosure of credit risk exposure [line items]
Exposures	7,100	5,300
Other
Disclosure of credit risk exposure [line items]
Exposures	11,400	8,900
Retail
Disclosure of credit risk exposure [line items]
Exposures	206,100	217,300
Corporate
Disclosure of credit risk exposure [line items]
Exposures	25,900	27,600
Eurozone | Netherlands
Disclosure of credit risk exposure [line items]
Exposures	300	100
Eurozone | Belgium
Disclosure of credit risk exposure [line items]
Exposures	500	600
Eurozone | Finland
Disclosure of credit risk exposure [line items]
Exposures	100	100
Eurozone | Total
Disclosure of credit risk exposure [line items]
Exposures	7,900	5,000
Eurozone | Total | Ireland
Disclosure of credit risk exposure [line items]
Exposures	3,200	2,400
Eurozone | Total | Spain
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Total | France
Disclosure of credit risk exposure [line items]
Exposures	2,600	1,400
Eurozone | Total | Germany
Disclosure of credit risk exposure [line items]
Exposures	500	400
Eurozone | Total | Luxembourg
Disclosure of credit risk exposure [line items]
Exposures	600	0
Eurozone | Total | Other
Disclosure of credit risk exposure [line items]
Exposures	1,000	800
Eurozone | Governments
Disclosure of credit risk exposure [line items]
Exposures	400	400
Eurozone | Governments | Ireland
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Governments | Spain
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Governments | France
Disclosure of credit risk exposure [line items]
Exposures	100	100
Eurozone | Governments | Germany
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Governments | Luxembourg
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Governments | Other
Disclosure of credit risk exposure [line items]
Exposures	300	300
Eurozone | Banks
Disclosure of credit risk exposure [line items]
Exposures	2,600	1,600
Eurozone | Banks | Ireland
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Banks | Spain
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Banks | France
Disclosure of credit risk exposure [line items]
Exposures	1,700	800
Eurozone | Banks | Germany
Disclosure of credit risk exposure [line items]
Exposures	200	300
Eurozone | Banks | Luxembourg
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Banks | Other
Disclosure of credit risk exposure [line items]
Exposures	700	500
Eurozone | Other
Disclosure of credit risk exposure [line items]
Exposures	4,700	2,800
Eurozone | Other | Ireland
Disclosure of credit risk exposure [line items]
Exposures	3,100	2,300
Eurozone | Other | Spain
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Other | France
Disclosure of credit risk exposure [line items]
Exposures	800	500
Eurozone | Other | Germany
Disclosure of credit risk exposure [line items]
Exposures	300	0
Eurozone | Other | Luxembourg
Disclosure of credit risk exposure [line items]
Exposures	500	0
Eurozone | Other | Other
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Retail
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Retail | Ireland
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Retail | Spain
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Retail | France
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Retail | Germany
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Retail | Luxembourg
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Retail | Other
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Corporate
Disclosure of credit risk exposure [line items]
Exposures	200	200
Eurozone | Corporate | Ireland
Disclosure of credit risk exposure [line items]
Exposures	100	100
Eurozone | Corporate | Spain
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Corporate | France
Disclosure of credit risk exposure [line items]
Exposures	0	0
Eurozone | Corporate | Germany
Disclosure of credit risk exposure [line items]
Exposures	0	100
Eurozone | Corporate | Luxembourg
Disclosure of credit risk exposure [line items]
Exposures	100	0
Eurozone | Corporate | Other
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Total | UK
Disclosure of credit risk exposure [line items]
Exposures	277,700	295,900
Other countries | Total | US
Disclosure of credit risk exposure [line items]
Exposures	700	1,100
Other countries | Total | Japan
Disclosure of credit risk exposure [line items]
Exposures	2,900	1,400
Other countries | Total | Switzerland
Disclosure of credit risk exposure [line items]
Exposures	2,100	1,200
Other countries | Total | Other
Disclosure of credit risk exposure [line items]
Exposures	2,300	1,500
Other countries | Governments | UK
Disclosure of credit risk exposure [line items]
Exposures	38,500	44,100
Other countries | Governments | US
Disclosure of credit risk exposure [line items]
Exposures	0	100
Other countries | Governments | Japan
Disclosure of credit risk exposure [line items]
Exposures	2,000	1,100
Other countries | Governments | Switzerland
Disclosure of credit risk exposure [line items]
Exposures	2,100	1,200
Other countries | Governments | Other
Disclosure of credit risk exposure [line items]
Exposures	100	100
Other countries | Banks | UK
Disclosure of credit risk exposure [line items]
Exposures	1,700	1,800
Other countries | Banks | US
Disclosure of credit risk exposure [line items]
Exposures	700	900
Other countries | Banks | Japan
Disclosure of credit risk exposure [line items]
Exposures	900	300
Other countries | Banks | Switzerland
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Banks | Other
Disclosure of credit risk exposure [line items]
Exposures	1,200	700
Other countries | Other | UK
Disclosure of credit risk exposure [line items]
Exposures	6,500	5,800
Other countries | Other | US
Disclosure of credit risk exposure [line items]
Exposures	0	100
Other countries | Other | Japan
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Other | Switzerland
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Other | Other
Disclosure of credit risk exposure [line items]
Exposures	200	200
Other countries | Retail | UK
Disclosure of credit risk exposure [line items]
Exposures	206,000	217,300
Other countries | Retail | US
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Retail | Japan
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Retail | Switzerland
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Retail | Other
Disclosure of credit risk exposure [line items]
Exposures	100	0
Other countries | Corporate | UK
Disclosure of credit risk exposure [line items]
Exposures	25,000	26,900
Other countries | Corporate | US
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Corporate | Japan
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Corporate | Switzerland
Disclosure of credit risk exposure [line items]
Exposures	0	0
Other countries | Corporate | Other
Disclosure of credit risk exposure [line items]
Exposures	700	500
All countries excluding Eurozone countries | Total
Disclosure of credit risk exposure [line items]
Exposures	285,700	301,100
All countries excluding Eurozone countries | Governments
Disclosure of credit risk exposure [line items]
Exposures	42,700	46,600
All countries excluding Eurozone countries | Banks
Disclosure of credit risk exposure [line items]
Exposures	4,500	3,700
All countries excluding Eurozone countries | Other
Disclosure of credit risk exposure [line items]
Exposures	6,700	6,100
All countries excluding Eurozone countries | Retail
Disclosure of credit risk exposure [line items]
Exposures	206,100	217,300
All countries excluding Eurozone countries | Corporate
Disclosure of credit risk exposure [line items]
Exposures	£ 25,700	£ 27,400

Credit Risk - Disclosure of Bal

Credit Risk - Disclosure of Balances with Other Banco Santander Companies (Details) - Santander UK Group Holdings plc - GBP (£) £ in Billions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of detailed information about financial instruments [line items]
Financial assets	£ 5.4	£ 5.6
Financial liabilities	15.5	17.4
Spain
Disclosure of detailed information about financial instruments [line items]
Financial assets	0.8	1.4
Financial liabilities	1.2	1.8
UK
Disclosure of detailed information about financial instruments [line items]
Financial assets	4.6	4.2
Financial liabilities	14.3	15.6
Banks
Disclosure of detailed information about financial instruments [line items]
Financial assets	0.8	1.4
Financial liabilities	1.1	1.7
Banks | Spain
Disclosure of detailed information about financial instruments [line items]
Financial assets	0.8	1.4
Financial liabilities	1.1	1.7
Banks | UK
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
Financial liabilities	0	0
Other
Disclosure of detailed information about financial instruments [line items]
Financial assets	4.6	4.2
Financial liabilities	14.4	15.7
Other | Spain
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
Financial liabilities	0.1	0.1
Other | UK
Disclosure of detailed information about financial instruments [line items]
Financial assets	4.6	4.2
Financial liabilities	14.3	15.6
Corporate
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
Financial liabilities	0	0
Corporate | Spain
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
Financial liabilities	0	0
Corporate | UK
Disclosure of detailed information about financial instruments [line items]
Financial assets	0	0
Financial liabilities	£ 0	£ 0

Credit Risk - Disclosure of Bor

Credit Risk - Disclosure of Borrower Profile (Details) - Credit risk - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 172,859	£ 184,317
Percentage of residential mortgage loans	100%	100%
New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 12,164	£ 34,127
Percentage of residential mortgage loans	100%	100%
Home movers | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 71,931	£ 76,357
Percentage of residential mortgage loans	42%	41%
Home movers | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 5,009	£ 12,221
Percentage of residential mortgage loans	41%	36%
Remortgagers | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 48,475	£ 53,190
Percentage of residential mortgage loans	28%	29%
Remortgagers | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 3,901	£ 10,644
Percentage of residential mortgage loans	32%	31%
First-time buyers | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 36,868	£ 37,971
Percentage of residential mortgage loans	21%	21%
First-time buyers | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 3,015	£ 8,129
Percentage of residential mortgage loans	25%	24%
Buy-to-let | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 15,585	£ 16,799
Percentage of residential mortgage loans	9%	9%
Buy-to-let | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 239	£ 3,133
Percentage of residential mortgage loans	2%	9%

Credit Risk - Homes Credit Risk

Credit Risk - Homes Credit Risk Review, Additional Information (Details) £ in Thousands	12 Months Ended
	Dec. 31, 2023 GBP (£)	Dec. 31, 2022 GBP (£)
Disclosure of credit risk exposure [line items]
Advances and flexible mortgage drawdowns	£ 700,000	£ 1,200,000
Percentage of customers with a maturing mortgage retained	77%	81%
Average LTV of mortgage total new lending, in London	65%	66%
Re-priced new business and internal transfers	£ 45,000,000
New mortgages reaching end of incentive period within a year	£ 39,000,000
Percentage of new business mortgages that are prime UK retail mortgages	0.85
Average new loan size	£ 228	£ 237
Percentage of new business mortgages that are unsecured retail mortgages	0.03
Proportion of mortgage portfolio in forbearance	0.009	0.009
Proportion of accounts in forbearance in excess of six months since last contractual payment	0.81	0.85
Weighted average LTV of accounts in forbearance	0.44	0.43
Weighted average portfolio LTV	0.51	0.50
Carrying value of mortgages classified as multiple forbearance	£ 121,000	£ 152,000
Mortgages modified since January 2008	£ 1,600,000	£ 1,900,000
Average LTV	0.24	0.24
Percentage of customers that made last six months payments	0.93	0.94
Percentage of accounts ninety days or more in arrears	0.0174	0.0153
Maximum
Disclosure of credit risk exposure [line items]
Percentage of internal transfer customers in arrears	0.01
Internal remortgages
Disclosure of credit risk exposure [line items]
Internal remortgages	£ 31,200,000	£ 24,900,000

Credit Risk - Disclosure of Int

Credit Risk - Disclosure of Interest Rate Profile of Mortgage Assets Stock (Details) - Stock - Credit risk - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 172,859	£ 184,317
Percentage of residential mortgage loans	100%	100%
Fixed rate
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 153,207	£ 163,622
Percentage of residential mortgage loans	89%	89%
Fixed rate | No later than one year
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 37,630	£ 38,233
Percentage of residential mortgage loans	22%	21%
Fixed rate | Later than 1 year but no later than 3 years
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 65,502	£ 38,213
Percentage of residential mortgage loans	38%	21%
Fixed rate | Later than 3 years but no later than 4 years
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 34,725	£ 24,310
Percentage of residential mortgage loans	20%	13%
Fixed rate | Later than 4 years but no later than 5 years
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 10,977	£ 24,888
Percentage of residential mortgage loans	6%	14%
Fixed rate | Later than five years
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 4,373	£ 37,978
Percentage of residential mortgage loans	3%	21%
Variable rate
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 13,761	£ 12,430
Percentage of residential mortgage loans	8%	7%
Standard Variable Rate (SVR)
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 3,915	£ 5,645
Percentage of residential mortgage loans	2%	3%
Follow on Rate (FoR)
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 1,976	£ 2,620
Percentage of residential mortgage loans	1%	1%

Credit Risk - Disclosure of Geo

Credit Risk - Disclosure of Geographic Distribution of Mortgage Assets Stock (Details) - Credit risk - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 172,859	£ 184,317
New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	12,164	34,127
London | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	44,000	47,000
London | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	2,900	8,300
Midlands and East Anglia | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	24,200	25,600
Midlands and East Anglia | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	1,800	5,300
North | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	22,900	24,400
North | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	1,700	4,700
Northern Ireland | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	2,600	2,900
Northern Ireland | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	100	300
Scotland | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	6,400	6,800
Scotland | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	600	1,200
South East excluding London | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	54,800	58,400
South East excluding London | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	3,800	10,600
South West, Wales and other | Stock
Disclosure of credit risk exposure [line items]
Residential mortgage loans	18,000	19,200
South West, Wales and other | New business
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 1,300	£ 3,700

Credit Risk - Disclosure of Mor

Credit Risk - Disclosure of Mortgage Loan Size (Details) - Credit risk - GBP (£) £ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Stock
Disclosure of credit risk exposure [line items]
Mortgage loans average size	£ 187	£ 183
New business
Disclosure of credit risk exposure [line items]
Mortgage loans average size	£ 228	£ 237
Over £1.0m
Disclosure of credit risk exposure [line items]
Mortgage loan size, percentage	2%	2%
£0.5m to £1.0m
Disclosure of credit risk exposure [line items]
Mortgage loan size, percentage	10%	10%
£0.25m to £0.5m
Disclosure of credit risk exposure [line items]
Mortgage loan size, percentage	31%	31%
Below £0.25m
Disclosure of credit risk exposure [line items]
Mortgage loan size, percentage	57%	57%

Credit Risk - Disclosure of LTV

Credit Risk - Disclosure of LTV Distribution of Mortgage Assets Stock (Details) - Credit risk - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	£ 172,859	£ 184,317
Collateral value, stock	172,803	184,269
Loan-to-value, stage 3	2,008	1,827
Collateral value, stage 3	1,997	1,818
Loan-to-value, new business	12,164	34,127
Collateral value, new business	12,164	34,126
Collateral against loans in negative equity	389	323
ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	242	252
Loan-to-value, stage 3	108	95
Up to 50%
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	78,673	87,379
Loan-to-value, stage 3	1,106	1,111
Loan-to-value, new business	2,616	4,890
Up to 50% | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	31	37
Loan-to-value, stage 3	12	14
>50-60%
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	32,837	35,664
Loan-to-value, stage 3	347	283
Loan-to-value, new business	1,604	4,014
>50-60% | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	24	29
Loan-to-value, stage 3	10	11
>60-70%
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	30,874	33,868
Loan-to-value, stage 3	246	197
Loan-to-value, new business	1,977	6,104
>60-70% | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	40	50
Loan-to-value, stage 3	16	16
>70-80%
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	18,721	17,824
Loan-to-value, stage 3	138	110
Loan-to-value, new business	2,736	10,094
>70-80% | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	48	45
Loan-to-value, stage 3	19	15
>80-90%
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	8,893	7,339
Loan-to-value, stage 3	67	42
Loan-to-value, new business	2,318	6,002
>80-90% | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	35	29
Loan-to-value, stage 3	15	9
>90-100%
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	2,416	1,873
Loan-to-value, stage 3	39	32
Loan-to-value, new business	900	2,999
>90-100% | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	20	17
Loan-to-value, stage 3	11	9
>100%
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	445	370
Loan-to-value, stage 3	65	52
Loan-to-value, new business	13	24
>100% | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, stock	44	45
Loan-to-value, stage 3	£ 25	£ 21
Average LTV - Balance weighted
Disclosure of credit risk exposure [line items]
Percentage of loan to value, stock	51%	50%
Percentage of loan to value, stage 3	49%	47%
Percentage of loan to value, new business	66%	69%

Credit Risk - Disclosure of C_3

Credit Risk - Disclosure of Credit Performance by Segment (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 207,435	£ 219,716
Loss allowance	992
Loss allowance		1,005
Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	172,859	184,317
Everyday Banking
Disclosure of credit risk exposure [line items]
Loans and advances to customers	7,028	7,520
Loss allowance	£ 300
Loss allowance		£ 293
Stage 3 ratio	3.83%	3.71%
Gross write-offs	£ 130	£ 110
Everyday Banking | Undrawn
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	39
Stage 3 undrawn exposures		35
Everyday Banking | Business banking
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,819	2,519
Loss allowance	£ 16
Loss allowance		£ 19
Stage 3 ratio	7.25%	6.58%
Gross write-offs	£ 11	£ 11
Everyday Banking | Business banking | Undrawn
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	2
Stage 3 undrawn exposures		3
Everyday Banking | Other unsecured loans
Disclosure of credit risk exposure [line items]
Loans and advances to customers	5,209	5,001
Loss allowance	£ 284
Loss allowance		£ 274
Stage 3 ratio	2.65%	2.27%
Gross write-offs	£ 119	£ 99
Everyday Banking | Other unsecured loans | Undrawn
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	37
Stage 3 undrawn exposures		32
Everyday Banking | Personal loans
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,064	1,982
Loss allowance	66
Loss allowance		62
Everyday Banking | Credit Cards
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,674	2,558
Loss allowance	140
Loss allowance		130
Everyday Banking | Overdrafts
Disclosure of credit risk exposure [line items]
Loans and advances to customers	471	461
Loss allowance	78
Loss allowance		82
Consumer Finance
Disclosure of credit risk exposure [line items]
Loans and advances to customers	5,228	5,384
Loss allowance	£ 70
Loss allowance		£ 67
Stage 3 ratio	0.53%	0.54%
Gross write-offs	£ 23	£ 19
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	380
Loss allowance		393
Maximum exposure to credit risk	25,990	27,564
Loss allowances	380	394
Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	12,676	14,123
Loss allowances	341	355
Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,358	5,407
Loss allowances	39	38
Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7,956	8,034
Loss allowances	0	1
Corporate & Commercial Banking | Fully performing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	22,626	24,539
Corporate & Commercial Banking | Fully performing | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	10,140	11,796
Corporate & Commercial Banking | Fully performing | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,734	4,765
Corporate & Commercial Banking | Fully performing | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7,752	7,978
Corporate & Commercial Banking | Enhanced monitoring
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	472	580
Corporate & Commercial Banking | Enhanced monitoring | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	462	431
Corporate & Commercial Banking | Enhanced monitoring | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	10	103
Corporate & Commercial Banking | Enhanced monitoring | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	46
Corporate & Commercial Banking | Proactive management
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,147	1,873
Corporate & Commercial Banking | Proactive management | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,447	1,383
Corporate & Commercial Banking | Proactive management | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	496	480
Corporate & Commercial Banking | Proactive management | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	204	10
Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	745	572
Corporate & Commercial Banking | Stage 3 | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	627	513
Corporate & Commercial Banking | Stage 3 | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	118	59
Corporate & Commercial Banking | Stage 3 | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Stage 1 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	152,975	169,066
Stage 1 | Everyday Banking
Disclosure of credit risk exposure [line items]
Loans and advances to customers	5,807	6,300
Stage 1 | Everyday Banking | Business banking
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,574	2,223
Stage 1 | Everyday Banking | Other unsecured loans
Disclosure of credit risk exposure [line items]
Loans and advances to customers	4,233	4,077
Stage 1 | Everyday Banking | Personal loans
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,743	1,730
Stage 1 | Everyday Banking | Credit Cards
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,283	2,192
Stage 1 | Everyday Banking | Overdrafts
Disclosure of credit risk exposure [line items]
Loans and advances to customers	207	155
Stage 1 | Consumer Finance
Disclosure of credit risk exposure [line items]
Loans and advances to customers	4,870	5,005
Stage 1 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	21,280	23,104
Stage 2
Disclosure of credit risk exposure [line items]
Loss allowance	461
Loss allowance		516
Stage 2 | Undrawn
Disclosure of credit risk exposure [line items]
Loss allowance	40
Loss allowance		39
Stage 2 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	17,876	13,424
Stage 2 | Everyday Banking
Disclosure of credit risk exposure [line items]
Loans and advances to customers	990	975
Stage 2 | Everyday Banking | Business banking
Disclosure of credit risk exposure [line items]
Loans and advances to customers	115	133
Stage 2 | Everyday Banking | Other unsecured loans
Disclosure of credit risk exposure [line items]
Loans and advances to customers	875	842
Stage 2 | Everyday Banking | Personal loans
Disclosure of credit risk exposure [line items]
Loans and advances to customers	294	231
Stage 2 | Everyday Banking | Credit Cards
Disclosure of credit risk exposure [line items]
Loans and advances to customers	345	329
Stage 2 | Everyday Banking | Overdrafts
Disclosure of credit risk exposure [line items]
Loans and advances to customers	236	282
Stage 2 | Consumer Finance
Disclosure of credit risk exposure [line items]
Loans and advances to customers	330	350
Loss allowance	30
Loss allowance		27
Stage 2 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Loss allowance	118
Loss allowance		155
Maximum exposure to credit risk	3,965	3,888
Stage 3 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 2,008	£ 1,827
Stage 3 ratio	1.17%	1%
Stage 3 | Everyday Banking
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 231	£ 245
Stage 3 | Everyday Banking | Business banking
Disclosure of credit risk exposure [line items]
Loans and advances to customers	130	163
Stage 3 | Everyday Banking | Other unsecured loans
Disclosure of credit risk exposure [line items]
Loans and advances to customers	101	82
Stage 3 | Everyday Banking | Personal loans
Disclosure of credit risk exposure [line items]
Loans and advances to customers	27	21
Stage 3 | Everyday Banking | Credit Cards
Disclosure of credit risk exposure [line items]
Loans and advances to customers	46	37
Stage 3 | Everyday Banking | Overdrafts
Disclosure of credit risk exposure [line items]
Loans and advances to customers	28	24
Stage 3 | Consumer Finance
Disclosure of credit risk exposure [line items]
Loans and advances to customers	28	29
Stage 3 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	745	572
Credit risk | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	172,859	184,317
Loss allowance	£ 242
Loss allowance		£ 251
Stage 1 ratio	88.50%	91.73%
Stage 2 ratio	10.34%	7.28%
Stage 3 ratio	1.17%	1%
Credit risk | Stage 1 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 152,975	£ 169,066
Credit risk | Stage 2 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	17,876	13,424
Credit risk | Stage 3 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 2,008	£ 1,827

Credit Risk - Disclosure of E_3

Credit Risk - Disclosure of ECL Reconciliation by Segment (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	£ 1,005
Ending balance	992	£ 1,005
Less: Recoveries net of collection costs	(10)	(36)	£ 17
Stage 1
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	170
Ending balance	170	170
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	284,428	292,366
Transfers from Stage 1 to Stage 2	(12,945)	(9,100)
Transfers from Stage 2 to Stage 1	5,913	7,207
Transfers to Stage 3	(598)	(621)
Transfers from Stage 3	28	10
Transfers of financial instruments	(7,602)	(2,504)
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	25,409	48,194
Redemptions, repayments and assets sold	(33,805)	(54,546)
Changes in risk parameters and other movements	(219)	918
Assets written off	0	0
Ending balance	268,211	284,428	292,366
Net movement in the period	(16,217)	(7,938)
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	176,965	177,696
Transfers from Stage 1 to Stage 2	(10,791)	(5,834)
Transfers from Stage 2 to Stage 1	4,778	2,961
Transfers to Stage 3	(335)	(278)
Transfers from Stage 3	14	4
Transfers of financial instruments	(6,334)	(3,147)
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	12,947	35,028
Redemptions, repayments and assets sold	(23,081)	(32,565)
Changes in risk parameters and other movements	666	(47)
Assets written off	0	0
Ending balance	161,163	176,965	177,696
Net movement in the period	(15,802)	(731)
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	23,838	20,604
Transfers from Stage 1 to Stage 2	(1,376)	(2,195)
Transfers from Stage 2 to Stage 1	512	4,023
Transfers to Stage 3	(118)	(172)
Transfers from Stage 3	1	0
Transfers of financial instruments	(981)	1,656
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	7,257	8,629
Redemptions, repayments and assets sold	(6,713)	(9,019)
Changes in risk parameters and other movements	(834)	1,968
Assets written off	0	0
Ending balance	22,567	23,838	20,604
Net movement in the period	(1,271)	3,234
Stage 2
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	516
Ending balance	461	516
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	19,127	17,964
Transfers from Stage 1 to Stage 2	12,945	9,100
Transfers from Stage 2 to Stage 1	(5,913)	(7,207)
Transfers to Stage 3	(920)	(624)
Transfers from Stage 3	304	758
Transfers of financial instruments	6,416	2,027
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	562	1,119
Redemptions, repayments and assets sold	(3,017)	(2,065)
Changes in risk parameters and other movements	507	82
Assets written off	0	0
Ending balance	23,595	19,127	17,964
Net movement in the period	4,468	1,163
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	13,533	11,152
Transfers from Stage 1 to Stage 2	10,791	5,834
Transfers from Stage 2 to Stage 1	(4,778)	(2,961)
Transfers to Stage 3	(566)	(448)
Transfers from Stage 3	277	279
Transfers of financial instruments	5,724	2,704
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	154	529
Redemptions, repayments and assets sold	(1,752)	(1,229)
Changes in risk parameters and other movements	338	377
Assets written off	0	0
Ending balance	17,997	13,533	11,152
Net movement in the period	4,464	2,381
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	3,888	5,914
Transfers from Stage 1 to Stage 2	1,376	2,195
Transfers from Stage 2 to Stage 1	(512)	(4,023)
Transfers to Stage 3	(258)	(111)
Transfers from Stage 3	9	463
Transfers of financial instruments	615	(1,476)
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	132	228
Redemptions, repayments and assets sold	(869)	(584)
Changes in risk parameters and other movements	199	(194)
Assets written off	0	0
Ending balance	3,965	3,888	5,914
Net movement in the period	77	(2,026)
Stage 3
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	319
Ending balance	361	319
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	2,729	3,017
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	1,518	1,245
Transfers from Stage 3	(332)	(768)
Transfers of financial instruments	1,186	477
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	59	64
Redemptions, repayments and assets sold	(886)	(950)
Changes in risk parameters and other movements	395	375
Assets written off	(412)	(254)
Ending balance	3,071	2,729	3,017
Net movement in the period	342	(288)
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	1,848	1,815
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	901	726
Transfers from Stage 3	(291)	(283)
Transfers of financial instruments	610	443
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	5	1
Redemptions, repayments and assets sold	(417)	(415)
Changes in risk parameters and other movements	36	14
Assets written off	(54)	(10)
Ending balance	2,028	1,848	1,815
Net movement in the period	180	33
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	572	827
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	376	283
Transfers from Stage 3	(10)	(463)
Transfers of financial instruments	366	(180)
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	38	43
Redemptions, repayments and assets sold	(193)	(53)
Changes in risk parameters and other movements	137	21
Assets written off	(175)	(86)
Ending balance	745	572	827
Net movement in the period	173	(255)
Exposures - On balance sheet
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	306,284	313,347
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	26,030	49,377
Redemptions, repayments and assets sold	(37,708)	(57,561)
Changes in risk parameters and other movements	683	1,375
Assets written off	(412)	(254)
Ending balance	294,877	306,284	313,347
Net movement in the period	(11,407)	(7,063)
Exposures - On balance sheet | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	192,346	190,663
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	13,106	35,558
Redemptions, repayments and assets sold	(25,250)	(34,209)
Changes in risk parameters and other movements	1,040	344
Assets written off	(54)	(10)
Ending balance	181,188	192,346	190,663
Net movement in the period	(11,158)	1,683
Exposures - On balance sheet | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	28,298	27,345
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	0	0
Change in economic scenarios	0	0
New lending and assets purchased	7,427	8,900
Redemptions, repayments and assets sold	(7,775)	(9,656)
Changes in risk parameters and other movements	(498)	1,795
Assets written off	(175)	(86)
Ending balance	27,277	28,298	27,345
Net movement in the period	(1,021)	953
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	170	132
Transfers from Stage 1 to Stage 2	(9)	(25)
Transfers from Stage 2 to Stage 1	111	133
Transfers to Stage 3	(6)	(4)
Transfers from Stage 3	1	1
Transfers of financial instruments	97	105
Net ECL remeasurement on stage transfer	(111)	(110)
Change in economic scenarios	29	37
New lending and assets purchased	28	42
Redemptions, repayments and assets sold	(35)	(35)
Changes in risk parameters and other movements	(8)	(1)
Assets written off	0	0
Ending balance	170	170	132
Net movement in the period	0	38
ECL (release)/charge to the Income Statement	0	38
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Total ECL (release)/charge to the Income Statement	0	38
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	25	13
Transfers from Stage 1 to Stage 2	(3)	(1)
Transfers from Stage 2 to Stage 1	30	16
Transfers to Stage 3	(3)	(2)
Transfers from Stage 3	0	0
Transfers of financial instruments	24	13
Net ECL remeasurement on stage transfer	(28)	(15)
Change in economic scenarios	0	1
New lending and assets purchased	4	7
Redemptions, repayments and assets sold	(6)	(3)
Changes in risk parameters and other movements	5	9
Assets written off	0	0
Ending balance	24	25	13
Net movement in the period	(1)	12
ECL (release)/charge to the Income Statement	(1)	12
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Stage 1 | Subject to 12-month ECL | Financial instruments not credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	83	50
Transfers from Stage 1 to Stage 2	(1)	(14)
Transfers from Stage 2 to Stage 1	10	92
Transfers to Stage 3	(3)	(1)
Transfers from Stage 3	0	0
Transfers of financial instruments	6	77
Net ECL remeasurement on stage transfer	(16)	(72)
Change in economic scenarios	30	38
New lending and assets purchased	5	16
Redemptions, repayments and assets sold	(13)	(15)
Changes in risk parameters and other movements	(19)	(11)
Assets written off	0	0
Ending balance	76	83	50
Net movement in the period	(7)	33
ECL (release)/charge to the Income Statement	(7)	33
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	516	330
Transfers from Stage 1 to Stage 2	9	25
Transfers from Stage 2 to Stage 1	(111)	(133)
Transfers to Stage 3	(38)	(32)
Transfers from Stage 3	15	150
Transfers of financial instruments	(125)	10
Net ECL remeasurement on stage transfer	145	98
Change in economic scenarios	(33)	123
New lending and assets purchased	45	76
Redemptions, repayments and assets sold	(53)	(60)
Changes in risk parameters and other movements	(34)	(61)
Assets written off	0	0
Ending balance	461	516	330
Net movement in the period	(55)	186
ECL (release)/charge to the Income Statement	(55)	186
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Total ECL (release)/charge to the Income Statement	(55)	186
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	131	88
Transfers from Stage 1 to Stage 2	3	1
Transfers from Stage 2 to Stage 1	(30)	(16)
Transfers to Stage 3	(15)	(11)
Transfers from Stage 3	9	9
Transfers of financial instruments	(33)	(17)
Net ECL remeasurement on stage transfer	40	40
Change in economic scenarios	(2)	21
New lending and assets purchased	3	11
Redemptions, repayments and assets sold	(12)	(11)
Changes in risk parameters and other movements	(17)	(1)
Assets written off	0	0
Ending balance	110	131	88
Net movement in the period	(21)	43
ECL (release)/charge to the Income Statement	(21)	43
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Stage 2 | Subject to Lifetime ECL | Financial instruments not credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	166	127
Transfers from Stage 1 to Stage 2	1	14
Transfers from Stage 2 to Stage 1	(10)	(92)
Transfers to Stage 3	(8)	(13)
Transfers from Stage 3	1	135
Transfers of financial instruments	(16)	44
Net ECL remeasurement on stage transfer	29	(41)
Change in economic scenarios	(30)	76
New lending and assets purchased	6	19
Redemptions, repayments and assets sold	(10)	(32)
Changes in risk parameters and other movements	(13)	(27)
Assets written off	0	0
Ending balance	132	166	127
Net movement in the period	(34)	39
ECL (release)/charge to the Income Statement	(34)	39
Less: Discount unwind	0	0
Less: Recoveries net of collection costs	0	0
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	319	403
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	44	36
Transfers from Stage 3	(16)	(151)
Transfers of financial instruments	28	(115)
Net ECL remeasurement on stage transfer	130	110
Change in economic scenarios	9	3
New lending and assets purchased	20	24
Redemptions, repayments and assets sold	(46)	(35)
Changes in risk parameters and other movements	133	86
Assets written off	(232)	(157)
Ending balance	361	319	403
Net movement in the period	42	(84)
ECL (release)/charge to the Income Statement	274	73
Less: Discount unwind	(21)	(13)
Less: Recoveries net of collection costs	7	36
Total ECL (release)/charge to the Income Statement	260	96
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	95	89
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	18	13
Transfers from Stage 3	(9)	(9)
Transfers of financial instruments	9	4
Net ECL remeasurement on stage transfer	22	8
Change in economic scenarios	3	2
New lending and assets purchased	1	0
Redemptions, repayments and assets sold	(14)	(12)
Changes in risk parameters and other movements	3	7
Assets written off	(11)	(3)
Ending balance	108	95	89
Net movement in the period	13	6
ECL (release)/charge to the Income Statement	24	9
Less: Discount unwind	(3)	(2)
Less: Recoveries net of collection costs	28	(1)
Stage 3 | Subject to Lifetime ECL | Financial instruments credit-impaired | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	145	248
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	11	14
Transfers from Stage 3	(1)	(135)
Transfers of financial instruments	10	(121)
Net ECL remeasurement on stage transfer	64	61
Change in economic scenarios	6	0
New lending and assets purchased	10	12
Redemptions, repayments and assets sold	(23)	(17)
Changes in risk parameters and other movements	28	(14)
Assets written off	(68)	(24)
Ending balance	172	145	248
Net movement in the period	27	(103)
ECL (release)/charge to the Income Statement	95	(79)
Less: Discount unwind	(9)	(3)
Less: Recoveries net of collection costs	(5)	42
ECL - On balance sheet
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	1,005	865
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	164	98
Change in economic scenarios	5	163
New lending and assets purchased	93	142
Redemptions, repayments and assets sold	(134)	(130)
Changes in risk parameters and other movements	91	24
Assets written off	(232)	(157)
Ending balance	992	1,005	865
Net movement in the period	(13)	140
ECL (release)/charge to the Income Statement	219	297
Less: Discount unwind	(21)	(13)
Less: Recoveries net of collection costs	7	36
Total ECL (release)/charge to the Income Statement	205	320
ECL - On balance sheet | Mortgages
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	251	190
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	34	33
Change in economic scenarios	1	24
New lending and assets purchased	8	18
Redemptions, repayments and assets sold	(32)	(26)
Changes in risk parameters and other movements	(9)	15
Assets written off	(11)	(3)
Ending balance	242	251	190
Net movement in the period	(9)	61
ECL (release)/charge to the Income Statement	2	64
Less: Discount unwind	(3)	(2)
Less: Recoveries net of collection costs	28	(1)
ECL - On balance sheet | Corporate & Commercial Banking
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	394	425
Transfers from Stage 1 to Stage 2	0	0
Transfers from Stage 2 to Stage 1	0	0
Transfers to Stage 3	0	0
Transfers from Stage 3	0	0
Transfers of financial instruments	0	0
Net ECL remeasurement on stage transfer	77	(52)
Change in economic scenarios	6	114
New lending and assets purchased	21	47
Redemptions, repayments and assets sold	(46)	(64)
Changes in risk parameters and other movements	(4)	(52)
Assets written off	(68)	(24)
Ending balance	380	394	£ 425
Net movement in the period	(14)	(31)
ECL (release)/charge to the Income Statement	54	(7)
Less: Discount unwind	(9)	(3)
Less: Recoveries net of collection costs	£ (5)	£ 42

Credit Risk - Disclosure of Loa

Credit Risk - Disclosure of Loan Modification by Segment (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Mortgages
Disclosure of credit risk exposure [line items]
Amortised cost before modification	£ 346	£ 315
Net modification loss	5	7
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	79	91
Everyday Banking
Disclosure of credit risk exposure [line items]
Amortised cost before modification	21	14
Net modification loss	20	13
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	3	4
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Amortised cost before modification	189	240
Net modification loss	10	8
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	27	15
Business banking | Everyday Banking
Disclosure of credit risk exposure [line items]
Amortised cost before modification	0	0
Net modification loss	0	0
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	0	0
Credit Cards | Everyday Banking
Disclosure of credit risk exposure [line items]
Amortised cost before modification	13	7
Net modification loss	14	7
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	2	3
Overdrafts | Everyday Banking
Disclosure of credit risk exposure [line items]
Amortised cost before modification	8	7
Net modification loss	6	6
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	£ 1	£ 1

Credit Risk - Disclosure of For

Credit Risk - Disclosure of Forbearance Balances by Segment (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Mortgages
Disclosure of credit risk exposure [line items]
Capitalisation	£ 609	£ 607
Term extension	536	459
Interest-only	275	305
Concessionary interest rate	182	196
Forbearance	1,602	1,567
Loss allowances	£ 37	£ 42
Loans capitalisation forbearance percentage	0.30%	0.30%
Loans term extension forbearance percentage	0.30%	0.30%
Loans interest only forbearance percentage	0.20%	0.20%
Loans concessionary interest rate forbearance percentage	0.10%	0.10%
Loans forbearance percentage	0.90%	0.90%
Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	£ 70	£ 54
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Capitalisation	264	219
Term extension	113	98
Interest-only	215	238
Forbearance	£ 592	£ 555
Proportion of portfolio	2.30%	2%
Stage 1 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Forbearance	£ 2	£ 17
Stage 2 | Mortgages
Disclosure of credit risk exposure [line items]
Capitalisation	325	309
Term extension	386	319
Interest-only	211	240
Concessionary interest rate	11	6
Forbearance	933	874
Loss allowances	7	11
Stage 2 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	8	9
Stage 2 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Forbearance	159	173
Stage 3 | Mortgages
Disclosure of credit risk exposure [line items]
Capitalisation	284	298
Term extension	150	140
Interest-only	64	65
Concessionary interest rate	171	190
Forbearance	669	693
Loss allowances	30	31
Stage 3 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	62	45
Stage 3 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Forbearance	431	365
Business banking | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	3	3
Business banking | Stage 2 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	0	0
Business banking | Stage 3 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	3	3
Total other unsecured | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	67	51
Total other unsecured | Stage 2 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	8	9
Total other unsecured | Stage 3 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	59	42
Personal loans | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	1	1
Personal loans | Stage 2 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	1	1
Personal loans | Stage 3 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	0	0
Credit Cards | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	47	34
Credit Cards | Stage 2 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	5	6
Credit Cards | Stage 3 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	42	28
Overdrafts | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	19	16
Overdrafts | Stage 2 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	2	2
Overdrafts | Stage 3 | Everyday Banking
Disclosure of credit risk exposure [line items]
Forbearance	£ 17	£ 14

Credit Risk - Disclosure of Oth

Credit Risk - Disclosure of Other Loan Modification by Segment (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Mortgages
Disclosure of credit risk exposure [line items]
Amortised cost before modification	£ 346	£ 315
Net modification loss	5	7
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	79	91
Everyday Banking
Disclosure of credit risk exposure [line items]
Amortised cost before modification	21	14
Net modification loss	20	13
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	3	4
Other loans | Mortgages | Term Extension
Disclosure of credit risk exposure [line items]
Amortised cost before modification	152
Other loans | Mortgages | Term Extension | Stage 1
Disclosure of credit risk exposure [line items]
Amortised cost before modification	120
Other loans | Mortgages | Term Extension | Stage 2
Disclosure of credit risk exposure [line items]
Amortised cost before modification	30
Other loans | Mortgages | Term Extension | Stage 3
Disclosure of credit risk exposure [line items]
Amortised cost before modification	2
Other loans | Mortgages | Interest Only
Disclosure of credit risk exposure [line items]
Amortised cost before modification	1,684
Other loans | Mortgages | Interest Only | Stage 1
Disclosure of credit risk exposure [line items]
Amortised cost before modification	1,166
Other loans | Mortgages | Interest Only | Stage 2
Disclosure of credit risk exposure [line items]
Amortised cost before modification	500
Other loans | Mortgages | Interest Only | Stage 3
Disclosure of credit risk exposure [line items]
Amortised cost before modification	18
Other loans | Consumer Finance
Disclosure of credit risk exposure [line items]
Gross carrying amount of financial assets for which the loss allowance changed to 12 months ECL in the period	£ 30	£ 95

Credit Risk - Disclosure of Hom

Credit Risk - Disclosure of Homes Portfolios of Particular Interest by Credit Performance (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 207,435	£ 219,716
Properties in possession	£ 23	£ 47
Balance weighted LTV (indexed)	51%	50%
Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 172,859	£ 184,317
Interest-only
Disclosure of credit risk exposure [line items]
Properties in possession	£ 12	£ 18
Balance weighted LTV (indexed)	48%	47%
Interest-only | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 38,825	£ 40,825
Part interest-only, part repayment
Disclosure of credit risk exposure [line items]
Properties in possession	£ 3	£ 8
Balance weighted LTV (indexed)	51%	49%
Mortgage loan including interest-only part	£ 9,531	£ 10,010
Part interest-only, part repayment | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	12,584	13,510
Flexible
Disclosure of credit risk exposure [line items]
Properties in possession	£ 2	£ 3
Balance weighted LTV (indexed)	37%	36%
Flexible | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 5,418	£ 6,765
LTV >100%
Disclosure of credit risk exposure [line items]
Properties in possession	£ 5	£ 7
Balance weighted LTV (indexed)	116%	117%
LTV >100% | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 445	£ 370
Buy-to-Let
Disclosure of credit risk exposure [line items]
Properties in possession	£ 1	£ 1
Balance weighted LTV (indexed)	60%	58%
Buy-to-Let | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 15,585	£ 16,799
Other portfolio
Disclosure of credit risk exposure [line items]
Properties in possession	£ 8	£ 16
Balance weighted LTV (indexed)	53%	52%
Other portfolio | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 118,981	£ 126,996
Stage 1 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	152,975	169,066
Stage 1 | Interest-only | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	32,012	35,702
Stage 1 | Part interest-only, part repayment | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	10,896	12,143
Stage 1 | Flexible | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	4,420	5,713
Stage 1 | LTV >100% | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	276	217
Stage 1 | Buy-to-Let | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	13,887	15,884
Stage 1 | Other portfolio | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	107,834	118,507
Stage 2 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	17,876	13,424
Stage 2 | Interest-only | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	5,829	4,250
Stage 2 | Part interest-only, part repayment | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,449	1,149
Stage 2 | Flexible | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	744	839
Stage 2 | LTV >100% | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	104	101
Stage 2 | Buy-to-Let | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,647	876
Stage 2 | Other portfolio | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	10,402	7,791
Stage 3 | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 2,008	£ 1,827
Stage 3 ratio	1.17%	1%
Stage 3 | Interest-only | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 984	£ 873
Stage 3 ratio	2.55%	2.16%
Stage 3 | Part interest-only, part repayment | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 239	£ 218
Stage 3 ratio	1.90%	1.62%
Stage 3 | Flexible | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 254	£ 213
Stage 3 ratio	5.01%	3.45%
Stage 3 | LTV >100% | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 65	£ 52
Stage 3 ratio	14.57%	13.94%
Stage 3 | Buy-to-Let | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 51	£ 39
Stage 3 ratio	0.33%	0.23%
Stage 3 | Other portfolio | Mortgages
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 745	£ 698
Stage 3 ratio	0.63%	0.55%

Credit Risk - Disclosure of H_2

Credit Risk - Disclosure of Homes Portfolios of Particular Interest by Forbearance Balances (Details) - Mortgages - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Forbearance	£ 1,602	£ 1,567
Stage 2
Disclosure of credit risk exposure [line items]
Forbearance	933	874
Stage 3
Disclosure of credit risk exposure [line items]
Forbearance	669	693
Interest-only
Disclosure of credit risk exposure [line items]
Forbearance	365	290
Interest-only | Stage 2
Disclosure of credit risk exposure [line items]
Forbearance	216	111
Interest-only | Stage 3
Disclosure of credit risk exposure [line items]
Forbearance	149	179
Flexible
Disclosure of credit risk exposure [line items]
Forbearance	74	36
Flexible | Stage 2
Disclosure of credit risk exposure [line items]
Forbearance	55	19
Flexible | Stage 3
Disclosure of credit risk exposure [line items]
Forbearance	19	17
LTV >100%
Disclosure of credit risk exposure [line items]
Forbearance	12	9
LTV >100% | Stage 2
Disclosure of credit risk exposure [line items]
Forbearance	3	0
LTV >100% | Stage 3
Disclosure of credit risk exposure [line items]
Forbearance	9	9
Buy-to-Let
Disclosure of credit risk exposure [line items]
Forbearance	23	15
Buy-to-Let | Stage 2
Disclosure of credit risk exposure [line items]
Forbearance	16	11
Buy-to-Let | Stage 3
Disclosure of credit risk exposure [line items]
Forbearance	£ 7	£ 4

Credit Risk - Disclosure of Seg

Credit Risk - Disclosure of Segments Exposure by Credit Rating (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 25,990	£ 27,564
Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	21,280	23,104
Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,965	3,888
Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	745	572
Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	12,676	14,123
Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,358	5,407
Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7,956	8,034
Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	49,107	52,700
Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	49,107	52,700
Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	44,448	48,117
Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,427	2,173
Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,232	2,410
Internal grade 9 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	43	44
Internal grade 9 | Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	43	39
Internal grade 9 | Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	5
Internal grade 9 | Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 9 | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 9 | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 9 | Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	43	44
Internal grade 9 | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	43,889	48,367
Internal grade 9 | Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	43,889	48,367
Internal grade 9 | Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 9 | Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 9 | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	42,552	47,040
Internal grade 9 | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	170	136
Internal grade 9 | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,167	1,191
Internal grade 8 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,198	4,366
Internal grade 8 | Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,130	4,364
Internal grade 8 | Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	68	2
Internal grade 8 | Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 8 | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	166	336
Internal grade 8 | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	2
Internal grade 8 | Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,032	4,028
Internal grade 8 | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,031	2,911
Internal grade 8 | Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,031	2,911
Internal grade 8 | Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 8 | Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 8 | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,896	1,077
Internal grade 8 | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,470	1,162
Internal grade 8 | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	665	672
Internal grade 7 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,152	4,990
Internal grade 7 | Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,152	4,944
Internal grade 7 | Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	46
Internal grade 7 | Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 7 | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	911	923
Internal grade 7 | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	360	111
Internal grade 7 | Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,881	3,956
Internal grade 7 | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,180	1,396
Internal grade 7 | Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,180	1,396
Internal grade 7 | Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 7 | Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 7 | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 7 | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	787	875
Internal grade 7 | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	393	521
Internal grade 6 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,654	4,391
Internal grade 6 | Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,618	4,202
Internal grade 6 | Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	36	189
Internal grade 6 | Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 6 | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,970	2,341
Internal grade 6 | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,684	2,044
Internal grade 6 | Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	6
Internal grade 6 | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7	26
Internal grade 6 | Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7	26
Internal grade 6 | Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 6 | Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 6 | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 6 | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 6 | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7	26
Internal grade 5 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,629	5,427
Internal grade 5 | Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,715	4,773
Internal grade 5 | Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	914	654
Internal grade 5 | Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 5 | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,497	3,299
Internal grade 5 | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,132	2,128
Internal grade 5 | Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 5 | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 5 | Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 5 | Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 5 | Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 5 | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 5 | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 5 | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,547	6,263
Internal grade 4 | Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,363	4,289
Internal grade 4 | Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,184	1,974
Internal grade 4 | Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,575	5,327
Internal grade 4 | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	972	936
Internal grade 4 | Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 4 | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 3 to 1 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,648	1,976
Internal grade 3 to 1 | Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	141	386
Internal grade 3 to 1 | Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	762	1,018
Internal grade 3 to 1 | Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	745	572
Internal grade 3 to 1 | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,439	1,791
Internal grade 3 to 1 | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	209	185
Internal grade 3 to 1 | Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 3 to 1 | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 3 to 1 | Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 3 to 1 | Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 3 to 1 | Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 3 to 1 | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 3 to 1 | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Internal grade 3 to 1 | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	119	107
Other | Corporate & Commercial Banking | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	118	107
Other | Corporate & Commercial Banking | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1	0
Other | Corporate & Commercial Banking | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	118	106
Other | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1	1
Other | Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate Centre | Stage 1
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate Centre | Stage 2
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate Centre | Stage 3
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	0
Other | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 0	£ 0

Credit Risk - Disclosure of S_4

Credit Risk - Disclosure of Segments Exposure by Geographical Distribution (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 25,990	£ 27,564
Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	12,676	14,123
Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,358	5,407
Corporate & Commercial Banking | Social Housing
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7,956	8,034
Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	49,107	52,700
Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	44,448	48,117
Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,427	2,173
Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,232	2,410
UK | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	41,895	46,303
UK | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	39,581	43,936
UK | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,430	1,379
UK | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	884	988
Europe | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,274	3,313
Europe | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,063	1,886
Europe | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	243	422
Europe | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	968	1,005
US | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	186	317
US | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	83
US | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	4
US | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	186	230
Rest of World | Corporate Centre
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,752	2,767
Rest of World | Corporate Centre | Sovereign and Supranational
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,804	2,212
Rest of World | Corporate Centre | Structured Products
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	754	368
Rest of World | Corporate Centre | Financial Institutions
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 194	£ 187

Credit Risk - Disclosure of S_5

Credit Risk - Disclosure of Segments Exposure by Gross and Net Credit Exposure (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of credit risk exposure [line items]
Exposures	£ 294,877	£ 306,284
Stage 3
Disclosure of credit risk exposure [line items]
Exposures	3,071	2,729
Stage 3 | Corporate & Commercial Banking
Disclosure of credit risk exposure [line items]
Exposures	745	572
Collateral	218	199
Net exposure	527	373
Stage 3 | Corporate & Commercial Banking | SME and mid corporate
Disclosure of credit risk exposure [line items]
Exposures	627	513
Collateral	190	169
Net exposure	437	344
Stage 3 | Corporate & Commercial Banking | Commercial Real Estate
Disclosure of credit risk exposure [line items]
Exposures	118	59
Collateral	28	30
Net exposure	£ 90	£ 29

Liquidity Risk - Summary of Rec

Liquidity Risk - Summary of Reconciliation of Wholesale Funding to Balance Sheet (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Deposits by banks	£ 20,332	£ 28,525
Deposits by customers	190,850	195,568
Repurchase agreements - non trading	8,411	7,982
Debt securities in issue	33,910	31,531
Subordinated liabilities	2,386	2,332
Liquidity risk
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	69,600	77,900
Deposits by banks	20,300	28,500
Deposits by customers	1,700	4,800
Repurchase agreements - non trading	8,400	8,000
Financial liabilities designated at fair value	900	800
Debt securities in issue	33,900	31,500
Subordinated liabilities	2,400	2,300
Other equity instruments	2,000	2,000
Liquidity risk | Repos
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	8,400	8,000
Deposits by banks	0	0
Deposits by customers	0	0
Repurchase agreements - non trading	8,400	8,000
Financial liabilities designated at fair value	0	0
Debt securities in issue	0	0
Subordinated liabilities	0	0
Other equity instruments	0	0
Liquidity risk | Foreign exchange and hedge accounting
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	1,100	1,600
Deposits by banks	0	0
Deposits by customers	0	100
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	0	0
Debt securities in issue	900	1,100
Subordinated liabilities	200	400
Other equity instruments	0	0
Liquidity risk | Other
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	2,500	3,400
Deposits by banks	2,200	3,000
Deposits by customers	0	0
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	300	400
Debt securities in issue	0	0
Subordinated liabilities	0	0
Other equity instruments	0	0
Liquidity risk | Wholesale funding
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	57,600	64,900
Deposits by banks	18,100	25,500
Deposits by customers	1,700	4,700
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	600	400
Debt securities in issue	33,000	30,400
Subordinated liabilities	2,200	1,900
Other equity instruments	2,000	2,000
Liquidity risk | Wholesale funding | Deposits by banks
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	1,100	500
Deposits by banks	1,100	500
Deposits by customers	0	0
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	0	0
Debt securities in issue	0	0
Subordinated liabilities	0	0
Other equity instruments	0	0
Liquidity risk | Wholesale funding | Certificates of deposit and commercial paper
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	4,300	4,700
Deposits by banks	0	0
Deposits by customers	0	0
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	0	0
Debt securities in issue	4,300	4,700
Subordinated liabilities	0	0
Other equity instruments	0	0
Liquidity risk | Wholesale funding | Senior unsecured – public benchmark
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	12,700	14,300
Deposits by banks	0	0
Deposits by customers	1,600	4,600
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	0	0
Debt securities in issue	11,100	9,700
Subordinated liabilities	0
Other equity instruments	0	0
Liquidity risk | Wholesale funding | Senior unsecured – privately placed
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	800	600
Deposits by banks	0	0
Deposits by customers	100	100
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	600	400
Debt securities in issue	100	100
Subordinated liabilities	0	0
Other equity instruments	0	0
Liquidity risk | Wholesale funding | Covered bonds
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	14,800	14,900
Deposits by banks	0	0
Deposits by customers	0	0
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	0	0
Debt securities in issue	14,800	14,900
Subordinated liabilities	0	0
Other equity instruments	0	0
Liquidity risk | Wholesale funding | Securitisation and structured issuance
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	2,700	1,000
Deposits by banks	0	0
Deposits by customers	0	0
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	0	0
Debt securities in issue	2,700	1,000
Subordinated liabilities	0	0
Other equity instruments	0	0
Liquidity risk | Wholesale funding | TFSME
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	17,000	25,000
Deposits by banks	17,000	25,000
Deposits by customers	0	0
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	0	0
Debt securities in issue	0	0
Subordinated liabilities	0	0
Other equity instruments	0	0
Liquidity risk | Wholesale funding | Subordinated liabilities and equity
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	4,200	3,900
Deposits by banks	0	0
Deposits by customers	0	0
Repurchase agreements - non trading	0	0
Financial liabilities designated at fair value	0	0
Debt securities in issue	0	0
Subordinated liabilities	2,200	1,900
Other equity instruments	£ 2,000	£ 2,000

Liquidity Risk - Summary of Sou

Liquidity Risk - Summary of Sources of Wholesale Funding by Maturity (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	£ 57,600	£ 64,900
Deposits by banks	20,332	28,525
Subordinated liabilities	2,386	2,332
Of which secured	34,500	40,900
Of which unsecured	£ 23,100	24,000
Unsecured debt issued	96%
Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	£ 11,200
Senior unsecured – privately placed	100
Subordinated liabilities and equity (incl. AT1)	3,500
Wholesale fund amount	14,800
Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	1,500
Senior unsecured – privately placed	700
Wholesale fund amount	42,300
Deposits by banks	1,100
Certificates of deposit and commercial paper	4,300
Covered bonds	14,800
Securitisation and structured issuance	2,200
TFSME	17,000
Subordinated liabilities	700
Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	500
≤ 1 month
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	1,400	2,600
Of which secured	100	100
Of which unsecured	1,300	2,500
≤ 1 month | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	0
Senior unsecured – privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	0
≤ 1 month | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	0
Senior unsecured – privately placed	0
Wholesale fund amount	1,400
Deposits by banks	300
Certificates of deposit and commercial paper	1,000
Covered bonds	100
Securitisation and structured issuance	0
TFSME	0
Subordinated liabilities	0
≤ 1 month | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
>1 and ≤ 3 months
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	7,300	5,200
Of which secured	1,000	1,000
Of which unsecured	6,300	4,200
>1 and ≤ 3 months | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	1,600
Senior unsecured – privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	1,600
>1 and ≤ 3 months | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	600
Senior unsecured – privately placed	0
Wholesale fund amount	5,700
Deposits by banks	800
Certificates of deposit and commercial paper	3,300
Covered bonds	1,000
Securitisation and structured issuance	0
TFSME	0
Subordinated liabilities	0
>1 and ≤ 3 months | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
>3 and ≤ 6 months
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	1,600	500
Of which secured	900	200
Of which unsecured	700	300
>3 and ≤ 6 months | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	0
Senior unsecured – privately placed	0
Subordinated liabilities and equity (incl. AT1)	500
Wholesale fund amount	500
>3 and ≤ 6 months | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	200
Senior unsecured – privately placed	0
Wholesale fund amount	1,100
Deposits by banks	0
Certificates of deposit and commercial paper	0
Covered bonds	900
Securitisation and structured issuance	0
TFSME	0
Subordinated liabilities	0
>3 and ≤ 6 months | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
>6 and ≤ 9 months
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	500	1,500
Of which secured	400	900
Of which unsecured	100	600
>6 and ≤ 9 months | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	0
Senior unsecured – privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	0
>6 and ≤ 9 months | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	0
Senior unsecured – privately placed	100
Wholesale fund amount	500
Deposits by banks	0
Certificates of deposit and commercial paper	0
Covered bonds	400
Securitisation and structured issuance	0
TFSME	0
Subordinated liabilities	0
>6 and ≤ 9 months | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
>9 and ≤ 12 months
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	1,100	1,200
Of which secured	1,100	0
Of which unsecured	0	1,200
>9 and ≤ 12 months | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	0
Senior unsecured – privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	0
>9 and ≤ 12 months | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	0
Senior unsecured – privately placed	0
Wholesale fund amount	1,100
Deposits by banks	0
Certificates of deposit and commercial paper	0
Covered bonds	1,000
Securitisation and structured issuance	100
TFSME	0
Subordinated liabilities	0
>9 and ≤ 12 months | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
No later than one year
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	11,900	11,000
Of which secured	3,500	2,200
Of which unsecured	8,400	8,800
No later than one year | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	1,600
Senior unsecured – privately placed	0
Subordinated liabilities and equity (incl. AT1)	500
Wholesale fund amount	2,100
No later than one year | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	800
Senior unsecured – privately placed	100
Wholesale fund amount	9,800
Deposits by banks	1,100
Certificates of deposit and commercial paper	4,300
Covered bonds	3,400
Securitisation and structured issuance	100
TFSME	0
Subordinated liabilities	0
No later than one year | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
Later than 1 year but no later than 3 years
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	22,300	6,600
Of which secured	18,600	3,500
Of which unsecured	3,700	3,100
Later than 1 year but no later than 3 years | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	2,400
Senior unsecured – privately placed	0
Subordinated liabilities and equity (incl. AT1)	800
Wholesale fund amount	3,200
Later than 1 year but no later than 3 years | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	400
Senior unsecured – privately placed	100
Wholesale fund amount	18,600
Deposits by banks	0
Certificates of deposit and commercial paper	0
Covered bonds	1,100
Securitisation and structured issuance	0
TFSME	17,000
Subordinated liabilities	0
Later than 1 year but no later than 3 years | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	500
>2 and ≤ 5 years
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	19,700	42,200
Of which secured	11,300	34,000
Of which unsecured	8,400	8,200
>2 and ≤ 5 years | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	6,800
Senior unsecured – privately placed	100
Subordinated liabilities and equity (incl. AT1)	1,300
Wholesale fund amount	8,200
>2 and ≤ 5 years | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	0
Senior unsecured – privately placed	200
Wholesale fund amount	11,500
Deposits by banks	0
Certificates of deposit and commercial paper	0
Covered bonds	9,200
Securitisation and structured issuance	2,100
TFSME	0
Subordinated liabilities	0
>2 and ≤ 5 years | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
>5 years
Disclosure Of Sources Of Wholesale Funding [Line Items]
Wholesale fund amount	3,700	5,100
Of which secured	1,100	1,200
Of which unsecured	2,600	£ 3,900
>5 years | Santander UK Group Holdings plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	400
Senior unsecured – privately placed	0
Subordinated liabilities and equity (incl. AT1)	900
Wholesale fund amount	1,300
>5 years | Other Santander UK plc
Disclosure Of Sources Of Wholesale Funding [Line Items]
Senior unsecured – public benchmark	300
Senior unsecured – privately placed	300
Wholesale fund amount	2,400
Deposits by banks	0
Certificates of deposit and commercial paper	0
Covered bonds	1,100
Securitisation and structured issuance	0
TFSME	0
Subordinated liabilities	700
>5 years | Other group entities
Disclosure Of Sources Of Wholesale Funding [Line Items]
Securitisation and structured issuance	£ 0

Liquidity Risk - Summary of Who

Liquidity Risk - Summary of Wholesale Funding by Currency (Details) - Liquidity risk	Dec. 31, 2023	Dec. 31, 2022
Sterling
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	63%	63%
Sterling | Santander UK Group Holdings plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	38%	27%
Sterling | Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	23%	18%
Sterling | Santander UK Group Holdings plc | Senior unsecured – privately placed
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Sterling | Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	87%	75%
Sterling | Other Santander UK plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	71%	74%
Sterling | Other Santander UK plc | Senior unsecured – public benchmark
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	21%	18%
Sterling | Other Santander UK plc | Senior unsecured – privately placed
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	98%	95%
Sterling | Other Santander UK plc | Deposits by banks
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	1%	29%
Sterling | Other Santander UK plc | Certificates of deposit and commercial paper
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	29%	56%
Sterling | Other Santander UK plc | Covered bonds
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	54%	43%
Sterling | Other Santander UK plc | Securitisation and structured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	100%	100%
Sterling | Other Santander UK plc | TFSME
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	100%	100%
Sterling | Other Santander UK plc | Subordinated liabilities
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	76%	48%
Sterling | Other group entities | Securitisation and structured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	100%	0%
US Dollar
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	23%	21%
US Dollar | Santander UK Group Holdings plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	48%	52%
US Dollar | Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	60%	58%
US Dollar | Santander UK Group Holdings plc | Senior unsecured – privately placed
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
US Dollar | Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	13%	25%
US Dollar | Other Santander UK plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	14%	12%
US Dollar | Other Santander UK plc | Senior unsecured – public benchmark
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	56%	62%
US Dollar | Other Santander UK plc | Senior unsecured – privately placed
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
US Dollar | Other Santander UK plc | Deposits by banks
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	97%	71%
US Dollar | Other Santander UK plc | Certificates of deposit and commercial paper
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	70%	42%
US Dollar | Other Santander UK plc | Covered bonds
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	5%	12%
US Dollar | Other Santander UK plc | Securitisation and structured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
US Dollar | Other Santander UK plc | TFSME
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
US Dollar | Other Santander UK plc | Subordinated liabilities
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	24%	52%
US Dollar | Other group entities | Securitisation and structured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Euro
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	14%	16%
Euro | Santander UK Group Holdings plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	13%	20%
Euro | Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	17%	24%
Euro | Santander UK Group Holdings plc | Senior unsecured – privately placed
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Euro | Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Euro | Other Santander UK plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	15%	14%
Euro | Other Santander UK plc | Senior unsecured – public benchmark
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	23%	20%
Euro | Other Santander UK plc | Senior unsecured – privately placed
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	2%	5%
Euro | Other Santander UK plc | Deposits by banks
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	2%	0%
Euro | Other Santander UK plc | Certificates of deposit and commercial paper
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	2%
Euro | Other Santander UK plc | Covered bonds
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	39%	45%
Euro | Other Santander UK plc | Securitisation and structured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Euro | Other Santander UK plc | TFSME
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Euro | Other Santander UK plc | Subordinated liabilities
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Euro | Other group entities | Securitisation and structured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Santander UK Group Holdings plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	1%	1%
Other | Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Santander UK Group Holdings plc | Senior unsecured – privately placed
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	100%	100%
Other | Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Other Santander UK plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Other Santander UK plc | Senior unsecured – public benchmark
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Other Santander UK plc | Senior unsecured – privately placed
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Other Santander UK plc | Deposits by banks
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Other Santander UK plc | Certificates of deposit and commercial paper
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	1%	0%
Other | Other Santander UK plc | Covered bonds
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	2%	0%
Other | Other Santander UK plc | Securitisation and structured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Other Santander UK plc | TFSME
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Other Santander UK plc | Subordinated liabilities
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%
Other | Other group entities | Securitisation and structured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Percentage of wholesale funding by major currencies	0%	0%

Liquidity Risk - Summary of Ext

Liquidity Risk - Summary of External Term Issuance, Sterling Equivalent (Details) - Liquidity risk - GBP (£) £ in Billions	Dec. 31, 2023	Dec. 31, 2022
Santander UK Group Holdings plc
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 2.6	£ 4.7
Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	1.5	3.9
Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure of detailed information about borrowings [line items]
Borrowings	1.1	0.8
Other Santander UK plc
Disclosure of detailed information about borrowings [line items]
Borrowings	3.6	4.7
Other Santander UK plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	0	0
Other Santander UK plc | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	1.5	0.6
Other Santander UK plc | Covered bonds
Disclosure of detailed information about borrowings [line items]
Borrowings	1.8	4
Other Santander UK plc | Senior unsecured – privately placed
Disclosure of detailed information about borrowings [line items]
Borrowings	0.3	0.1
Other group entities
Disclosure of detailed information about borrowings [line items]
Borrowings	6.7	9.4
Other group entities | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	0.5	£ 0
Sterling | Santander UK Group Holdings plc
Disclosure of detailed information about borrowings [line items]
Borrowings	1.5
Sterling | Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	0.4
Sterling | Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure of detailed information about borrowings [line items]
Borrowings	1.1
Sterling | Other Santander UK plc
Disclosure of detailed information about borrowings [line items]
Borrowings	3.3
Sterling | Other Santander UK plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Sterling | Other Santander UK plc | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	1.5
Sterling | Other Santander UK plc | Covered bonds
Disclosure of detailed information about borrowings [line items]
Borrowings	1.5
Sterling | Other Santander UK plc | Senior unsecured – privately placed
Disclosure of detailed information about borrowings [line items]
Borrowings	0.3
Sterling | Other group entities
Disclosure of detailed information about borrowings [line items]
Borrowings	5.3
Sterling | Other group entities | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	0.5
US Dollar | Santander UK Group Holdings plc
Disclosure of detailed information about borrowings [line items]
Borrowings	1.1
US Dollar | Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	1.1
US Dollar | Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure of detailed information about borrowings [line items]
Borrowings
US Dollar | Other Santander UK plc
Disclosure of detailed information about borrowings [line items]
Borrowings	0
US Dollar | Other Santander UK plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	0
US Dollar | Other Santander UK plc | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	0
US Dollar | Other Santander UK plc | Covered bonds
Disclosure of detailed information about borrowings [line items]
Borrowings	0
US Dollar | Other Santander UK plc | Senior unsecured – privately placed
Disclosure of detailed information about borrowings [line items]
Borrowings	0
US Dollar | Other group entities
Disclosure of detailed information about borrowings [line items]
Borrowings	1.1
US Dollar | Other group entities | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Santander UK Group Holdings plc
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure of detailed information about borrowings [line items]
Borrowings
Euro | Other Santander UK plc
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Other Santander UK plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Other Santander UK plc | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Other Santander UK plc | Covered bonds
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Other Santander UK plc | Senior unsecured – privately placed
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Other group entities
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro | Other group entities | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other | Santander UK Group Holdings plc
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other | Santander UK Group Holdings plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other | Santander UK Group Holdings plc | Subordinated liabilities and equity
Disclosure of detailed information about borrowings [line items]
Borrowings
Other | Other Santander UK plc
Disclosure of detailed information about borrowings [line items]
Borrowings	0.3
Other | Other Santander UK plc | Senior unsecured – public benchmark
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other | Other Santander UK plc | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other | Other Santander UK plc | Covered bonds
Disclosure of detailed information about borrowings [line items]
Borrowings	0.3
Other | Other Santander UK plc | Senior unsecured – privately placed
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other | Other group entities
Disclosure of detailed information about borrowings [line items]
Borrowings	0.3
Other | Other group entities | Securitisations and other secured funding
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 0

Liquidity Risk - Summary of Bal

Liquidity Risk - Summary of Balance Sheet Encumbered and Unencumbered Assets Explanatory (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Encumbered And Unencumbered Assets [Line Items]
Cash and balances at central banks	£ 38,214	£ 44,190	£ 48,139
Financial assets at fair value through profit or loss [abstract]
Derivative financial instruments	1,432	2,407
Other financial assets at FVTPL	262	129
Financial Assets At Amortised Cost [Abstract]
Loans and advances to customers	207,435	219,716
Loans and advances to banks	1,080	992
Reverse Repurchase agreements - non-trading	12,468	7,348
Financial assets at fair value through other comprehensive income	8,481	6,024
Interests in other entities	245	252
Intangible assets	1,548	1,550
Property, plant and equipment	1,494	1,513
Current tax assets	490	478	£ 347
Retirement benefit assets	723	1,050
Other assets	2,043	2,016
Total assets	275,448	285,213
Liquidity risk | Assets positioned at central banks
Disclosure Of Encumbered And Unencumbered Assets [Line Items]
Cash and balances at central banks	831	893
Financial assets at fair value through profit or loss [abstract]
Derivative financial instruments	0	0
Other financial assets at FVTPL	0	0
Financial Assets At Amortised Cost [Abstract]
Loans and advances to customers	58,489	68,535
Loans and advances to banks	0	0
Reverse Repurchase agreements - non-trading	0	0
Other financial assets at amortised cost	0	0
Financial assets at fair value through other comprehensive income	0	0
Interests in other entities	0	0
Intangible assets	0	0
Property, plant and equipment	0	0
Current tax assets	0	0
Retirement benefit assets	0	0
Total assets	59,320	69,428
Liquidity risk | Assets positioned at central banks | Other assets
Financial Assets At Amortised Cost [Abstract]
Other assets	0	0
Total | Liquidity risk
Disclosure Of Encumbered And Unencumbered Assets [Line Items]
Cash and balances at central banks	1,480	1,330
Financial assets at fair value through profit or loss [abstract]
Derivative financial instruments	0	0
Other financial assets at FVTPL	0	0
Financial Assets At Amortised Cost [Abstract]
Loans and advances to customers	27,147	24,211
Loans and advances to banks	254	163
Reverse Repurchase agreements - non-trading	0	0
Other financial assets at amortised cost	14	48
Financial assets at fair value through other comprehensive income	5,183	4,365
Interests in other entities	0	0
Intangible assets	0	0
Property, plant and equipment	0	0
Current tax assets	0	0
Retirement benefit assets	0	0
Total assets	34,078	30,117
Total | Liquidity risk | Other assets
Financial Assets At Amortised Cost [Abstract]
Other assets	0	0
Covered bonds | Liquidity risk
Disclosure Of Encumbered And Unencumbered Assets [Line Items]
Cash and balances at central banks	0	0
Financial assets at fair value through profit or loss [abstract]
Derivative financial instruments	0	0
Other financial assets at FVTPL	0	0
Financial Assets At Amortised Cost [Abstract]
Loans and advances to customers	21,880	21,304
Loans and advances to banks	0	0
Reverse Repurchase agreements - non-trading	0	0
Other financial assets at amortised cost	0	0
Financial assets at fair value through other comprehensive income	0	0
Interests in other entities	0	0
Intangible assets	0	0
Property, plant and equipment	0	0
Current tax assets	0	0
Retirement benefit assets	0	0
Total assets	21,880	21,304
Covered bonds | Liquidity risk | Other assets
Financial Assets At Amortised Cost [Abstract]
Other assets	0	0
Securitis- ations | Liquidity risk
Disclosure Of Encumbered And Unencumbered Assets [Line Items]
Cash and balances at central banks	0	0
Financial assets at fair value through profit or loss [abstract]
Derivative financial instruments	0	0
Other financial assets at FVTPL	0	0
Financial Assets At Amortised Cost [Abstract]
Loans and advances to customers	5,208	2,851
Loans and advances to banks	0	0
Reverse Repurchase agreements - non-trading	0	0
Other financial assets at amortised cost	0	0
Financial assets at fair value through other comprehensive income	0	0
Interests in other entities	0	0
Intangible assets	0	0
Property, plant and equipment	0	0
Current tax assets	0	0
Retirement benefit assets	0	0
Total assets	5,208	2,851
Securitis- ations | Liquidity risk | Other assets
Financial Assets At Amortised Cost [Abstract]
Other assets	0	0
Other | Liquidity risk
Disclosure Of Encumbered And Unencumbered Assets [Line Items]
Cash and balances at central banks	1,480	1,330
Financial assets at fair value through profit or loss [abstract]
Derivative financial instruments	0	0
Other financial assets at FVTPL	0	0
Financial Assets At Amortised Cost [Abstract]
Loans and advances to customers	59	56
Loans and advances to banks	254	163
Reverse Repurchase agreements - non-trading	0	0
Other financial assets at amortised cost	14	48
Financial assets at fair value through other comprehensive income	5,183	4,365
Interests in other entities	0	0
Intangible assets	0	0
Property, plant and equipment	0	0
Current tax assets	0	0
Retirement benefit assets	0	0
Total assets	6,990	5,962
Other | Liquidity risk | Other assets
Financial Assets At Amortised Cost [Abstract]
Other assets	£ 0	£ 0

Liquidity Risk - Additional Inf

Liquidity Risk - Additional Information (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Notional amount	£ 223,242	£ 176,472
Multi-currency medium term funding
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Notional amount	5,600
Multi-currency medium term funding | Santander UK Group Holdings plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Notional amount	1,500
Multi-currency medium term funding, other secured issuance
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Notional amount	4,100
Tier 2 securities | Santander UK Group Holdings plc
Disclosure Of Currency Composition Of Wholesale Funds [Line Items]
Notional amount	£ 1,100

Capital Risk - Additional Infor

Capital Risk - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023
Disclosure Of Capital Risk Exposure [Abstract]
Possible occurence of adverse economic stress	20 years
Possible occurence of very severe economic stress	100 years

Capital Risk - Summary of Regul

Capital Risk - Summary of Regulatory Capital Resources (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Capital Risk Exposure [Abstract]
CET1 capital	£ 10,443	£ 10,799
AT1 capital	1,956	1,956
Tier 1 capital	12,399	12,755
Tier 2 capital	2,172	1,548
Total regulatory capital	14,571	14,303
Transitional IFRS 9 Benefit	£ 43	£ 19

Market Risk - Summary of Detail

Market Risk - Summary of Detailed Information about VaR (Details)	Dec. 31, 2023
Disclosure Of Market Risk Exposure [Abstract]
VaR, confidence level	99%

Market Risk - Additional Inform

Market Risk - Additional Information (Details)	Dec. 31, 2023
Disclosure Of Market Risk Exposure [Abstract]
VaR, losses greater than VaR estimate, percentage of trading days	1%

Accounting Policies - Additiona

Accounting Policies - Additional Information (Details)	12 Months Ended		180 Months Ended
	Dec. 31, 2023 GBP (£) area shares	Dec. 31, 2022 GBP (£) shares	Dec. 31, 2022 GBP (£) invitation
Disclosure of detailed information about financial instruments [line items]
Climate change objective, number of main focus areas | area	3
Climate change, period covered for ECL calculations	5 years
Liabilities arising from share-based payment transactions	£ 14,700,000	£ 6,600,000	£ 6,600,000
Liabilities arising from share-based payment transactions, vested liabilities	1,100,000	100,000	£ 100,000
Number of sharesave schemes launched | invitation			16
Employee saving on share based compensation	£ 500,000
Price determination period for options	3 days
Maximum discount applicable	20%
Actual discount applied	10%
Expiration term of vested options	6 months
Weighted average grant-date fair value (GBP per share)	£ 0.33	£ 0.23	£ 0.23
Number of shares outstanding | shares	3,937,473	3,974,698
Share Incentive Plans
Disclosure of detailed information about financial instruments [line items]
Percentage of maximum salary that can be invested	10%
Material Risk Takers
Disclosure of detailed information about financial instruments [line items]
Additional retention period for deferred bonus awards	1 year
Minimum
Disclosure of detailed information about financial instruments [line items]
Employee saving on share based compensation	£ 5
Terms of options	3 years
Minimum | Share Incentive Plans
Disclosure of detailed information about financial instruments [line items]
Minimum retention period to sell shares free of income tax	5 years
Maximum
Disclosure of detailed information about financial instruments [line items]
Employee saving on share based compensation	£ 500
Terms of options	5 years
Period one | Material Risk Takers
Disclosure of detailed information about financial instruments [line items]
Deferral period from anniversary of initial award	4 years
Period two | Material Risk Takers
Disclosure of detailed information about financial instruments [line items]
Deferral period from anniversary of initial award	5 years
Period three | Material Risk Takers
Disclosure of detailed information about financial instruments [line items]
Deferral period from anniversary of initial award	7 years
Computer software | Minimum
Disclosure of detailed information about financial instruments [line items]
Useful life measured as period of time, intangible assets other than goodwill	3 years
Computer software | Maximum
Disclosure of detailed information about financial instruments [line items]
Useful life measured as period of time, intangible assets other than goodwill	7 years
–Other intangibles | Minimum
Disclosure of detailed information about financial instruments [line items]
Useful life measured as period of time, intangible assets other than goodwill	3 years
–Other intangibles | Maximum
Disclosure of detailed information about financial instruments [line items]
Useful life measured as period of time, intangible assets other than goodwill	7 years
180 Days | Unsecured Debt
Disclosure of detailed information about financial instruments [line items]
Written off period for past due	180 days

Accounting Policies - Summary o

Accounting Policies - Summary of Useful Lives or Depreciation Rates Used for Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2023
Other intangible | Minimum
Disclosure of detailed information about intangible assets [line items]
Useful life measured as period of time, intangible assets other than goodwill	3 years
Other intangible | Maximum
Disclosure of detailed information about intangible assets [line items]
Useful life measured as period of time, intangible assets other than goodwill	7 years
Computer software | Minimum
Disclosure of detailed information about intangible assets [line items]
Useful life measured as period of time, intangible assets other than goodwill	3 years
Computer software | Maximum
Disclosure of detailed information about intangible assets [line items]
Useful life measured as period of time, intangible assets other than goodwill	7 years

Accounting Policies - Summary_2

Accounting Policies - Summary of Useful Lives or Depreciation Rates Used for Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2023
Owner-occupied properties
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	50 years
Minimum | Office fixtures and equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	3 years
Minimum | Computer software
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	3 years
Minimum | Operating lease assets
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	1 year
Maximum | Office fixtures and equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	15 years
Maximum | Computer software
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	7 years
Maximum | Operating lease assets
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	4 years

Segments - Additional Informati

Segments - Additional Information (Details) £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£) segment business_unit	Dec. 31, 2022 GBP (£)	Dec. 31, 2021 GBP (£)
Disclosure of operating segments [line items]
Number of segments | segment	4
Profit from continuing operations before tax	£ 2,100	£ 1,874	£ 1,888
Retail and Business Banking
Disclosure of operating segments [line items]
Number of business units | business_unit	2
Corporate & Commercial Banking | Minimum
Disclosure of operating segments [line items]
Customers, annual turnover	£ 2
Corporate & Commercial Banking | Maximum
Disclosure of operating segments [line items]
Customers, annual turnover	500
Corporate & Investment Banking
Disclosure of operating segments [line items]
Customers, annual turnover	£ 500

Segments - Summary of Results b

Segments - Summary of Results by Segment (Details) £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£) employee	Dec. 31, 2022 GBP (£) employee	Dec. 31, 2021 GBP (£) employee
Disclosure of operating segments [line items]
Net interest income/(expense)	£ 4,658	£ 4,425	£ 3,949
Non-interest income/(expense)	438	531	550
Total operating income/(expense)	5,096	4,956	4,499
Operating expenses before credit impairment charges, provisions and charges	(2,456)	(2,343)	(2,510)
Credit impairment charges	(205)
Credit impairment (charges)/write-backs		(320)	233
Provisions for other liabilities and charges	(335)	(419)	(377)
Total operating credit impairment charges, provisions and charges	(540)	(739)	(144)
Profit from continuing operations before tax	2,100	1,874	1,845
Revenue/(expense) from external customers	5,096	4,956	4,499
Inter-segment revenue/(expense)	5,096	4,956	4,499
Revenue from external customers includes the following fee and commission income
Current account and debit card fees	542	562	478
Insurance, protection and investments	47	78	67
Credit cards	94	95	73
Non-banking and other fees	121	104	79
Total fee and commission income	804	839	697
Fee and commission expense	(501)	(509)	(411)
Net fee and commission income	303	330	286
Customer loans	203,054	215,738	207,288
Customer deposits	£ 187,445	£ 189,911	£ 186,215
Average number of full-time equivalent staff | employee	19,546	18,123	19,704
Inter-segment revenue/(expense)
Disclosure of operating segments [line items]
Inter-segment revenue/(expense)	£ 0	£ 0	£ 0
Retail and Business Banking
Disclosure of operating segments [line items]
Net interest income/(expense)	3,716	3,671	3,356
Non-interest income/(expense)	182	209	205
Total operating income/(expense)	3,898	3,880	3,561
Operating expenses before credit impairment charges, provisions and charges	(1,813)	(1,682)	(1,701)
Credit impairment charges	(149)
Credit impairment (charges)/write-backs		(262)	98
Provisions for other liabilities and charges	(233)	(394)	(185)
Total operating credit impairment charges, provisions and charges	(382)	(656)	(87)
Profit from continuing operations before tax	1,703	1,542	1,773
Revenue/(expense) from external customers	3,597	4,109	4,010
Revenue from external customers includes the following fee and commission income
Current account and debit card fees	493	502	428
Insurance, protection and investments	47	78	67
Credit cards	94	95	73
Non-banking and other fees	3	2	2
Total fee and commission income	637	677	570
Fee and commission expense	(458)	(478)	(380)
Net fee and commission income	179	199	190
Customer loans	179,887	191,836	183,023
Customer deposits	£ 158,329	£ 161,748	£ 156,991
Average number of full-time equivalent staff | employee	16,330	15,212	16,149
Retail and Business Banking | Inter-segment revenue/(expense)
Disclosure of operating segments [line items]
Inter-segment revenue/(expense)	£ 301	£ (229)	£ (449)
Consumer Finance
Disclosure of operating segments [line items]
Net interest income/(expense)	156	180	233
Non-interest income/(expense)	192	195	178
Total operating income/(expense)	348	375	411
Operating expenses before credit impairment charges, provisions and charges	(141)	(144)	(163)
Credit impairment charges	(15)
Credit impairment (charges)/write-backs		(27)	33
Provisions for other liabilities and charges	(18)	(6)	4
Total operating credit impairment charges, provisions and charges	(33)	(33)	37
Profit from continuing operations before tax	174	198	285
Revenue/(expense) from external customers	663	513	489
Revenue from external customers includes the following fee and commission income
Current account and debit card fees	0	0	0
Insurance, protection and investments	0	0	0
Credit cards	0	0	0
Non-banking and other fees	25	20	10
Total fee and commission income	25	20	10
Fee and commission expense	(6)	(5)	0
Net fee and commission income	19	15	10
Customer loans	5,228	5,384	4,984
Customer deposits	£ 0	£ 0	£ 0
Average number of full-time equivalent staff | employee	816	531	670
Consumer Finance | Inter-segment revenue/(expense)
Disclosure of operating segments [line items]
Inter-segment revenue/(expense)	£ (315)	£ (138)	£ (78)
Corporate & Commercial Banking
Disclosure of operating segments [line items]
Net interest income/(expense)	841	580	397
Non-interest income/(expense)	135	146	112
Total operating income/(expense)	976	726	509
Operating expenses before credit impairment charges, provisions and charges	(351)	(342)	(365)
Credit impairment charges	(40)
Credit impairment (charges)/write-backs		(31)	90
Provisions for other liabilities and charges	(15)	(8)	(34)
Total operating credit impairment charges, provisions and charges	(55)	(39)	56
Profit from continuing operations before tax	570	345	200
Revenue/(expense) from external customers	712	732	619
Revenue from external customers includes the following fee and commission income
Current account and debit card fees	49	60	50
Insurance, protection and investments	0	0	0
Credit cards	0	0	0
Non-banking and other fees	79	77	62
Total fee and commission income	128	137	112
Fee and commission expense	(11)	(18)	(22)
Net fee and commission income	117	119	90
Customer loans	17,939	18,518	19,281
Customer deposits	£ 24,066	£ 24,798	£ 26,466
Average number of full-time equivalent staff | employee	2,376	2,336	2,281
Corporate & Commercial Banking | Inter-segment revenue/(expense)
Disclosure of operating segments [line items]
Inter-segment revenue/(expense)	£ 264	£ (6)	£ (110)
Corporate & Investment Banking
Disclosure of operating segments [line items]
Net interest income/(expense)			0
Non-interest income/(expense)			0
Total operating income/(expense)			0
Operating expenses before credit impairment charges, provisions and charges			0
Credit impairment (charges)/write-backs			0
Provisions for other liabilities and charges			0
Total operating credit impairment charges, provisions and charges			0
Profit from continuing operations before tax			0
Revenue/(expense) from external customers			0
Revenue from external customers includes the following fee and commission income
Current account and debit card fees			0
Insurance, protection and investments			0
Credit cards			0
Non-banking and other fees			0
Total fee and commission income			0
Fee and commission expense			0
Net fee and commission income			0
Customer loans			0
Customer deposits			£ 0
Average number of full-time equivalent staff | employee			528
Corporate & Investment Banking | Inter-segment revenue/(expense)
Disclosure of operating segments [line items]
Inter-segment revenue/(expense)			£ 0
Corporate Centre
Disclosure of operating segments [line items]
Net interest income/(expense)	(55)	(6)	(37)
Non-interest income/(expense)	(71)	(19)	55
Total operating income/(expense)	(126)	(25)	18
Operating expenses before credit impairment charges, provisions and charges	(151)	(175)	(281)
Credit impairment charges	(1)
Credit impairment (charges)/write-backs		0	12
Provisions for other liabilities and charges	(69)	(11)	(162)
Total operating credit impairment charges, provisions and charges	(70)	(11)	(150)
Profit from continuing operations before tax	(347)	(211)	(413)
Revenue/(expense) from external customers	124	(398)	(619)
Revenue from external customers includes the following fee and commission income
Current account and debit card fees	0	0	0
Insurance, protection and investments	0	0	0
Credit cards	0	0	0
Non-banking and other fees	14	5	5
Total fee and commission income	14	5	5
Fee and commission expense	(26)	(8)	(9)
Net fee and commission income	(12)	(3)	(4)
Customer loans	0	0	0
Customer deposits	£ 5,050	£ 3,365	£ 2,758
Average number of full-time equivalent staff | employee	24	44	76
Corporate Centre | Inter-segment revenue/(expense)
Disclosure of operating segments [line items]
Inter-segment revenue/(expense)	£ (250)	£ 373	£ 637

Segments - Summary Of Relations

Segments - Summary Of Relationship Between Customer Liabilities and Deposits (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets
Customer balances (gross)	£ 203,054	£ 215,738
Loan loss allowance	(914)	(931)
Customer balances (net)	202,140	214,807
Accrued interest	739	649
Other items	12	99
Net loans and advances to customers	207,435	219,716
Liabilities
Customer balances (gross)	187,445	189,911
Customer balances (net)	187,445	189,911
Accrued interest	830	230
Other items	(250)	(554)
Deposits by customers	190,850	195,568
Intercompany
Assets
Intercompany balances	4,544	4,161
Liabilities
Intercompany balances	£ 2,825	£ 5,981

Net Interest Income (Details)

Net Interest Income (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Interest and similar income:
Loans and advances to customers	£ 8,767	£ 5,774	£ 4,619
Loans and advances to banks	1,751	618	52
Reverse repurchase agreements – non-trading	626	149	35
Other	473	167	56
Interest and similar income	11,617	6,708	4,762
Interest expense and similar charges:
Deposits by customers	(3,230)	(905)	(430)
Deposits by banks	(1,165)	(496)	(25)
Repurchase agreements – non-trading	(538)	(120)	(3)
Debt securities in issue	(1,852)	(650)	(252)
Subordinated liabilities	(169)	(108)	(92)
Other	(5)	(4)	(11)
Total interest expense and similar charges	(6,959)	(2,283)	(813)
Net interest income	4,658	4,425	3,949
Interest revenue for financial assets measured at fair value through other comprehensive income	230	87	22
Interest expense on derivatives hedging debt issuances	706	6	317
Interest expense on lease liabilities	£ 3	£ 3	£ 3

Net Fee and Commission Income_2

Net Fee and Commission Income (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Fee And Commission Income [Line Items]
Total fee and commission income	£ 804	£ 839	£ 697
Total fee and commission expense	(501)	(509)	(411)
Net fee and commission income	303	330	286
Current account and debit card fees
Net Fee And Commission Income [Line Items]
Total fee and commission income	542	562	478
Insurance, protection and investments
Net Fee And Commission Income [Line Items]
Total fee and commission income	47	78	67
Credit Cards
Net Fee And Commission Income [Line Items]
Total fee and commission income	94	95	73
Non-banking and other fees
Net Fee And Commission Income [Line Items]
Total fee and commission income	£ 121	£ 104	£ 79

Other Operating Income - Summar

Other Operating Income - Summary of Net Trading and Other Income (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of detailed information about financial instruments [line items]
Net (losses)/gains on financial instruments designated at fair value through profit or loss	£ (57)	£ 62	£ (24)
Net (losses) on financial instruments mandatorily at fair value through profit or loss	(11)	(75)	(2)
Hedge ineffectiveness	19	29	13
Net profit on sale of financial assets at fair value through other comprehensive income	0	0	6
Income from operating lease assets	117	129	136
Other	67	56	135
Other operating income (expense)	135	201	264
Exchange rate differences in the consolidated income statement on items not at fair value through profit and loss	1,288	(2,163)	242
These are principally offset by related releases from the cash flow hedge reserve	(1,248)	2,129	(358)
Deposits by banks
Disclosure of detailed information about financial instruments [line items]
Net (losses)/gains on financial instruments designated at fair value through profit or loss	(24)	35	(18)
Debt securities
Disclosure of detailed information about financial instruments [line items]
Net (losses)/gains on financial instruments designated at fair value through profit or loss	(32)	31	0
Net (losses) on financial instruments mandatorily at fair value through profit or loss	£ 5	£ 13	£ (10)

Other Operating Income - Additi

Other Operating Income - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Trading And Other Income [Abstract]
Gains (losses) on embedded derivatives bifurcated from certain equity index-linked deposits	£ (12)	£ 14	£ (15)
Gains (losses) on economic hedging of embedded derivatives bifurcated from certain equity index-linked deposits	12	(14)	15
Net gain on equity index-linked deposits and the related economic hedges	£ 0	0	0
Losses on disposals of property, plant and equipment		£ (7)
Gains on disposals of property, plant and equipment			£ 73

Operating Expenses Before Cre_3

Operating Expenses Before Credit Impairment Charges, Provisions and Charges - Summary of Operating Expenses Before Credit Impairment Losses, Provisions and Charges (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Staff costs:
Wages and salaries	£ 839	£ 745	£ 745
Performance-related payments	162	170	183
Social security costs	115	112	112
Pension costs, defined contribution plans	71	60	64
Pension costs, defined benefit plans	13	28	38
Other personnel costs	41	44	41
Staff costs	1,241	1,159	1,183
Other administration expenses	925	888	826
Depreciation, amortisation and impairment	290	296	501
Total operating expenses before impairment losses, provisions and charges	£ 2,456	£ 2,343	£ 2,510

Operating Expenses Before Cre_4

Operating Expenses Before Credit Impairment Charges, Provisions and Charges - Summary of Deferred Performance Awards (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Deferred Performance Awards [Line Items]
Cash	£ 19	£ 22
Shares	18	22
Expenses charged in the year
Disclosure Of Deferred Performance Awards [Line Items]
Cash	7	8
Shares	7	8
Deferred performance awards	14
Expenses charged in the year | Arising from awards in current year
Disclosure Of Deferred Performance Awards [Line Items]
Cash	3
Shares	2
Deferred performance awards	5
Expenses charged in the year | Arising from awards in prior year
Disclosure Of Deferred Performance Awards [Line Items]
Cash	4
Shares	5
Deferred performance awards	9
Expenses deferred to future periods
Disclosure Of Deferred Performance Awards [Line Items]
Cash	12	14
Shares	11	£ 14
Deferred performance awards	23
Expenses deferred to future periods | Arising from awards in current year
Disclosure Of Deferred Performance Awards [Line Items]
Cash	5
Shares	4
Deferred performance awards	9
Expenses deferred to future periods | Arising from awards in prior year
Disclosure Of Deferred Performance Awards [Line Items]
Cash	7
Shares	7
Deferred performance awards	£ 14

Operating Expenses Before Cre_5

Operating Expenses Before Credit Impairment Charges, Provisions and Charges - Summary of Amount of Bonus Awarded to Employees (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Amount Of Bonus Awarded To Employees [Line Items]
Cash award – not deferred	£ 140	£ 145
Cash award – deferred	19	22
Shares award – not deferred	8	9
Shares award – deferred	18	22
Total discretionary bonus	185	198
Expenses charged in the year
Disclosure Of Amount Of Bonus Awarded To Employees [Line Items]
Cash award – not deferred	140	145
Cash award – deferred	7	8
Shares award – not deferred	8	9
Shares award – deferred	7	8
Total discretionary bonus	162	170
Expenses deferred to future periods
Disclosure Of Amount Of Bonus Awarded To Employees [Line Items]
Cash award – not deferred	0	0
Cash award – deferred	12	14
Shares award – not deferred	0	0
Shares award – deferred	11	14
Total discretionary bonus	£ 23	£ 28

Operating Expenses Before Cre_6

Operating Expenses Before Credit Impairment Charges, Provisions and Charges - Additional Information (Details) £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£) employee	Dec. 31, 2022 GBP (£) employee	Dec. 31, 2021 GBP (£) employee
Operating Expenses Before Credit Impairment Losses Provision And Charges [Line Items]
Average number of full-time equivalent staff | employee	19,546	18,123	19,704
Expense relating to short-term leases	£ 19	£ 21	£ 23
Right-of-use assets
Operating Expenses Before Credit Impairment Losses Provision And Charges [Line Items]
Depreciation for lease assets	30	19	19
Operating lease assets	90	112	117
Branch and head office site closures
Operating Expenses Before Credit Impairment Losses Provision And Charges [Line Items]
Impairment during the period	25	10	88
Operating lease assets
Operating Expenses Before Credit Impairment Losses Provision And Charges [Line Items]
Depreciation, property, plant and equipment	64	73	81
Property, plant and equipment	£ 488	£ 577	£ 595

Audit and Other Services - Summ

Audit and Other Services - Summary of Audit and Other Services (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Audit fees:
Fees payable to the Company’s auditor and its associates for the audit of the Santander UK group’s annual accounts	£ 13.9	£ 11.8	£ 11.2
Audit of the Santander UK group's subsidiaries	0.6	0.7	0.9
Total group audit fees	14.5	12.5	12.1
Non-audit fees:
Audit-related assurance services	0.7	0.6	0.8
Other assurance services	0.5	0.3	0.1
Other non-audit services	0.1	0	0.2
Total non-audit fees	1.3	0.9	1.1
Prior year audit services
Non-audit fees:
Auditors fee	£ 0.7	£ 0.6	£ 1.2

Audit and Other Services - Addi

Audit and Other Services - Additional Information (Details) - GBP (£)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Audit Fees And Non Audit Fees [Line Items]
Audit fees payable for statutory audit	£ 14,500,000	£ 12,500,000	£ 12,100,000
Non-audit fees - Audit fees per US Securities and Exchange Commission guidance	300,000	200,000	400,000
Non-audit fees - Audit related fees per US Securities and Exchange Commission guidance	1,000,000	700,000	700,000
Non-audit fees - All other fees per US Securities and Exchange Commission guidance	12,550	0	0
Incremental work, audit of Banco Santander
Disclosure Of Audit Fees And Non Audit Fees [Line Items]
Audit fees payable for statutory audit	1,600,000	1,600,000	1,400,000
Corporate and other borrowers
Disclosure Of Audit Fees And Non Audit Fees [Line Items]
Audit fees payable for statutory audit	£ 0	£ 0	£ 27,000

Credit Impairment Charges and_3

Credit Impairment Charges and Provisions - Summary of Impairment Losses and Provisions (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Credit Impairment Loss And Provisions [Abstract]
Loans and advances to customers	£ 191	£ 248	£ (186)
Recoveries of loans and advances, net of collection costs	10	36	(17)
Off-balance sheet credit exposures (See Note 29)	4	36	(30)
Impairment loss on financial assets	205
Impairment loss on financial assets		320	(233)
Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 29)	334	422	386
Releases for residual value and voluntary termination	1	(3)	(9)
Provisions for other liabilities and charges	335	419	377
Total operating credit impairment (charges)/write-backs, provisions and charges	£ 540	£ 739	£ 144

Credit Impairment Charges and_4

Credit Impairment Charges and Provisions - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Credit Impairment Loss And Provisions [Abstract]
Impairment losses on loans and advances to banks	£ 0	£ 0	£ 0
Impairment losses on non-trading reverse repurchase agreements	0	0	0
Impairment losses on other financial assets at amortised cost	0	0	0
Impairment losses on financial assets at FVOCI	£ 0	£ 0	£ 0

Taxation - Disclosure of Income

Taxation - Disclosure of Income Tax and Deferred Taxes Explanatory (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current tax:
UK corporation tax on profit for the year	£ 475	£ 526	£ 401
Adjustments in respect of prior years	(15)	(81)	(24)
Total current tax	460	445	377
Deferred tax:
Charge/(credit) for the year	106	(29)	100
Adjustments in respect of prior years	(7)	64	15
Total deferred tax	99	35	115
Tax on profit from continuing operations	£ 559	£ 480	£ 492

Taxation - Additional Informati

Taxation - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Expense Benefits [Line Items]
Unrecognised capital losses carried forward	£ 0	£ 0
Banking entities
Income Tax Expense Benefits [Line Items]
Applicable tax rate (percentage)	28%	27%	27%
Non-banking entities
Income Tax Expense Benefits [Line Items]
Applicable tax rate (percentage)	24%	19%	19%

Taxation - Schedule of Tax on P

Taxation - Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Major components of tax expense (income) [abstract]
Effective tax rate (percentage)	26.60%	25.60%	26.70%
Profit from continuing operations before tax	£ 2,100	£ 1,874	£ 1,845
Tax calculated at a tax rate of 23.5% (2022:19%, 2021: 19%)	494	356	351
Bank surcharge on profits	85	121	104
Non-deductible preference dividends paid	9	9	9
Non-deductible UK Bank Levy	10	13	14
Non-deductible conduct remediation, fines and penalties	13	48	6
Other non-deductible costs and non-taxable income	2	29	37
Effect of change in tax rate on deferred tax provision	2	(29)	9
Tax relief on dividends in respect of other equity instruments	(34)	(40)	(40)
Adjustment to prior year provisions	(22)	(27)	2
Tax on profit from continuing operations	£ 559	£ 480	£ 492

Taxation - Disclosure of Moveme

Taxation - Disclosure of Movements in Current Tax Assets and Liabilities (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Major components of tax expense (income) [abstract]
Assets	£ 478	£ 347
Beginning balance	478	347
Income statement charge (including discontinued operations)	(460)	(445)
Other comprehensive income (charge)/credit	(70)	159
Corporate income tax received	537	405
Other movements	5	12
Ending balance	490	478
Assets	£ 490	£ 478

Taxation - Disclosure of Deferr

Taxation - Disclosure of Deferred Tax Assets and Liabilities Including Movement in Deferred Tax Account (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax liability (asset) beginning balance	£ (35)	£ (579)
Income statement (charge)/credit	(99)	(35)
Transfers/reclassifications	1	0
Credited/(charged) to other comprehensive income	(53)	579
Deferred tax liability (asset) ending balance	(186)	(35)
Fair value of financial instruments
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax liability (asset) beginning balance	27	(123)
Income statement (charge)/credit	(35)	150
Transfers/reclassifications	0	0
Credited/(charged) to other comprehensive income	0	0
Deferred tax liability (asset) ending balance	(8)	27
Pension remeasurement
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax liability (asset) beginning balance	(290)	(508)
Income statement (charge)/credit	(63)	(49)
Transfers/reclassifications	0	0
Credited/(charged) to other comprehensive income	167	267
Deferred tax liability (asset) ending balance	(186)	(290)
Cash flow hedges
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax liability (asset) beginning balance	305	(7)
Income statement (charge)/credit	0	0
Transfers/reclassifications	(3)	2
Credited/(charged) to other comprehensive income	(229)	310
Deferred tax liability (asset) ending balance	73	305
Fair value reserve
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax liability (asset) beginning balance	(1)	(12)
Income statement (charge)/credit	0	0
Transfers/reclassifications	(1)	0
Credited/(charged) to other comprehensive income	5	11
Deferred tax liability (asset) ending balance	3	(1)
Tax losses carried forward
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax liability (asset) beginning balance	0	8
Income statement (charge)/credit	0	(7)
Transfers/reclassifications	0	(1)
Credited/(charged) to other comprehensive income	0	0
Deferred tax liability (asset) ending balance	0	0
Accelerated tax depreciation
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax liability (asset) beginning balance	35	68
Income statement (charge)/credit	(18)	(33)
Transfers/reclassifications	1	0
Credited/(charged) to other comprehensive income	0	0
Deferred tax liability (asset) ending balance	18	35
Other temporary differences
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax liability (asset) beginning balance	(111)	(5)
Income statement (charge)/credit	17	(96)
Transfers/reclassifications	4	(1)
Credited/(charged) to other comprehensive income	4	(9)
Deferred tax liability (asset) ending balance	£ (86)	£ (111)

Dividends on Ordinary Shares -

Dividends on Ordinary Shares - Disclosure of Dividends on Ordinary Shares Declared and Paid (Details) - GBP (£) £ / shares in Units, £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Dividends On Ordinary Shares [Line Items]
Dividend per share	£ 4.93	£ 3.26	£ 4.37
Dividends	£ 1,530	£ 1,014	£ 1,358
First interim
Disclosure Of Dividends On Ordinary Shares [Line Items]
Dividend per share	£ 1.32	£ 1.25	£ 0.90
Dividends	£ 410	£ 389	£ 281
Second interim
Disclosure Of Dividends On Ordinary Shares [Line Items]
Dividend per share	£ 3.61	£ 2.01	£ 3.47
Dividends	£ 1,120	£ 625	£ 1,077

Dividends on Ordinary Shares _2

Dividends on Ordinary Shares - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Dividends On Ordinary Shares [Line Items]
Dividends declared and paid	£ 1,530	£ 1,014	£ 1,358

Derivative Financial Instrume_3

Derivative Financial Instruments - Notional Amounts of Transactions Outstanding (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of detailed information about hedges
Notional amount	£ 223,242	£ 176,472
Assets	1,432	2,407
Liabilities	818	951
Cash collateral received subject to enforceable master netting arrangement or similar agreement not set off against financial assets	13,173	9,059
Collateral cash	8,454	8,088
Derivatives held for trading:
Disclosure of detailed information about hedges
Notional amount	42,043	46,043
Derivatives held for hedging
Disclosure of detailed information about hedges
Notional amount	181,199	130,429
Fair value hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Notional amount	108,685	78,286
Cash flow hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Notional amount	72,514	52,143
Exchange rate contracts
Disclosure of detailed information about hedges
Notional amount	35,690	40,579
Exchange rate contracts | Derivatives held for trading:
Disclosure of detailed information about hedges
Notional amount	12,927	14,006
Exchange rate contracts | Fair value hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Notional amount	1,145	538
Exchange rate contracts | Cash flow hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Notional amount	21,618	26,035
Interest rate contracts
Disclosure of detailed information about hedges
Notional amount	186,787	134,991
Interest rate contracts | Derivatives held for trading:
Disclosure of detailed information about hedges
Notional amount	28,351	31,135
Interest rate contracts | Fair value hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Notional amount	107,540	77,748
Interest rate contracts | Cash flow hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Notional amount	50,896	26,108
Equity and credit contracts
Disclosure of detailed information about hedges
Notional amount	765	902
Equity and credit contracts | Derivatives held for trading:
Disclosure of detailed information about hedges
Notional amount	765	902
Derivative assets
Disclosure of detailed information about hedges
Cash collateral received subject to enforceable master netting arrangement or similar agreement not set off against financial assets	472	1,368
Derivative liabilities
Disclosure of detailed information about hedges
Collateral cash	12	70
Fair value
Disclosure of detailed information about hedges
Assets	1,432	2,407
Liabilities	818	951
Fair value | Group Entities
Disclosure of detailed information about hedges
Assets	762	1,319
Liabilities	230	207
Fair value | Derivatives held for trading:
Disclosure of detailed information about hedges
Assets	614	910
Liabilities	820	1,060
Fair value | Derivatives held for hedging
Disclosure of detailed information about hedges
Assets	2,865	3,670
Liabilities	2,045	2,064
Fair value | Fair value hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Assets	1,304	1,789
Liabilities	841	407
Fair value | Cash flow hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Assets	1,561	1,881
Liabilities	1,204	1,657
Fair value | Exchange rate contracts | Derivatives held for trading:
Disclosure of detailed information about hedges
Assets	92	315
Liabilities	217	281
Fair value | Exchange rate contracts | Fair value hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Assets	29	12
Liabilities	2	4
Fair value | Exchange rate contracts | Cash flow hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Assets	1,008	1,717
Liabilities	289	186
Fair value | Interest rate contracts | Derivatives held for trading:
Disclosure of detailed information about hedges
Assets	389	465
Liabilities	583	754
Fair value | Interest rate contracts | Fair value hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Assets	1,275	1,777
Liabilities	839	403
Fair value | Interest rate contracts | Cash flow hedges | Derivatives held for hedging
Disclosure of detailed information about hedges
Assets	553	164
Liabilities	915	1,471
Fair value | Equity and credit contracts | Derivatives held for trading:
Disclosure of detailed information about hedges
Assets	133	130
Liabilities	20	25
Fair value | Derivative netting
Disclosure of detailed information about hedges
Assets	(2,047)	(2,173)
Liabilities	£ (2,047)	£ (2,173)

Derivative Financial Instrume_4

Derivative Financial Instruments - Analysis of the Notional and Fair Values of Derivatives by Trading and Settlement Method (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	£ 223,242	£ 176,472
Exchange rate contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	35,690	40,579
Interest rate contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	186,787	134,991
Equity and credit contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	765	902
Settled by central counterparties
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	174,460	124,638
Settled by central counterparties | Exchange rate contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	0	0
Settled by central counterparties | Interest rate contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	174,460	124,638
Settled by central counterparties | Equity and credit contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	0	0
Not settled by central counterparties
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	48,782	51,834
Not settled by central counterparties | Exchange rate contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	35,690	40,579
Not settled by central counterparties | Interest rate contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	12,327	10,353
Not settled by central counterparties | Equity and credit contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Notional amount	765	902
Traded over the counter
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Asset	1,432	2,407
Liability	818	951
Traded over the counter | Exchange rate contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Asset	1,129	2,044
Liability	508	471
Traded over the counter | Interest rate contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Asset	170	233
Liability	290	455
Traded over the counter | Equity and credit contracts
Disclosure Of Analysis Of Notional And Fair Values Of Derivatives By Trading And Settlement Method [Line Items]
Asset	133	130
Liability	£ 20	£ 25

Derivative Financial Instrume_5

Derivative Financial Instruments - Summary of Maturity Profile and Average Price/Rate of Hedging Instruments Used in Hedging Strategies (Details) £ in Millions	Dec. 31, 2023 GBP (£)	Dec. 31, 2022 GBP (£)
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 223,242	£ 176,472
Interest rate contracts
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	186,787	134,991
Interest rate contracts | Interest rate risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	106,592	77,478
Interest rate contracts | Interest rate risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	45,614	19,446
Interest rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	948	270
Interest rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	2,141	2,925
Interest rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	3,141	3,737
Exchange rate contracts
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	35,690	40,579
Exchange rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	1,145	538
Exchange rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	4,726	6,449
Exchange rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	16,892	19,586
≤1 month | Interest rate contracts | Interest rate risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 3,612	£ 2,210
≤1 month | Interest rate contracts | Interest rate risk | Fair value hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0238	0.0258
≤1 month | Interest rate contracts | Interest rate risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0114	0.0177
≤1 month | Interest rate contracts | Interest rate risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0260	0.0135
≤1 month | Interest rate contracts | Interest rate risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 911	£ 1,042
≤1 month | Interest rate contracts | Interest rate risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0506	0.0177
≤1 month | Interest rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 0
≤1 month | Interest rate contracts | Interest rate/FX risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0	0
≤1 month | Interest rate contracts | Interest rate/FX risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0	0
≤1 month | Interest rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 0
≤1 month | Interest rate contracts | Interest rate/FX risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0257	0
≤1 month | Interest rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 415
≤1 month | Exchange rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 0
Average GBP - EUR exchange rate	0	0
Average GBP - USD exchange rate	0	0
≤1 month | Exchange rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 87	£ 0
Average GBP - EUR exchange rate	1.18	0
Average GBP - USD exchange rate	0	0
≤1 month | Exchange rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 927	£ 2,301
Average GBP - EUR exchange rate	0	0
Average GBP - USD exchange rate	0	1.22
Average GBP - JPY exchange rate	154.14	0
Average GBP - CHF exchange rate	1.09	0
>1 and ≤ 3 months | Interest rate contracts | Interest rate risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 7,141	£ 4,468
>1 and ≤ 3 months | Interest rate contracts | Interest rate risk | Fair value hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0319	0.0088
>1 and ≤ 3 months | Interest rate contracts | Interest rate risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0018	0.0160
>1 and ≤ 3 months | Interest rate contracts | Interest rate risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0246	0.0347
>1 and ≤ 3 months | Interest rate contracts | Interest rate risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 2,993	£ 2,191
>1 and ≤ 3 months | Interest rate contracts | Interest rate risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0298	0.0229
>1 and ≤ 3 months | Interest rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 18	£ 0
>1 and ≤ 3 months | Interest rate contracts | Interest rate/FX risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0	0
>1 and ≤ 3 months | Interest rate contracts | Interest rate/FX risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0	0
>1 and ≤ 3 months | Interest rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 0
>1 and ≤ 3 months | Interest rate contracts | Interest rate/FX risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0254	0
>1 and ≤ 3 months | Interest rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 2,199	£ 0
>1 and ≤ 3 months | Exchange rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 18	£ 0
Average GBP - EUR exchange rate	1.11	0
Average GBP - USD exchange rate	0	0
>1 and ≤ 3 months | Exchange rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 785	£ 0
Average GBP - EUR exchange rate	0	0
Average GBP - USD exchange rate	1.66	0
>1 and ≤ 3 months | Exchange rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 3,238	£ 3,135
Average GBP - EUR exchange rate	1.20	0
Average GBP - USD exchange rate	1.39	1.25
Average GBP - JPY exchange rate	153.95	157.45
Average GBP - CHF exchange rate	1.09	1.13
>3 and ≤12 months | Interest rate contracts | Interest rate risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 32,241	£ 21,678
>3 and ≤12 months | Interest rate contracts | Interest rate risk | Fair value hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0342	0.0056
>3 and ≤12 months | Interest rate contracts | Interest rate risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0045	0.0077
>3 and ≤12 months | Interest rate contracts | Interest rate risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0423	0.0351
>3 and ≤12 months | Interest rate contracts | Interest rate risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 12,770	£ 1,940
>3 and ≤12 months | Interest rate contracts | Interest rate risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0539	0.0198
>3 and ≤12 months | Interest rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 0
>3 and ≤12 months | Interest rate contracts | Interest rate/FX risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0	0.0342
>3 and ≤12 months | Interest rate contracts | Interest rate/FX risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0	0
>3 and ≤12 months | Interest rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 585
>3 and ≤12 months | Interest rate contracts | Interest rate/FX risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0296	0.0327
>3 and ≤12 months | Interest rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 0
>3 and ≤12 months | Exchange rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 66
Average GBP - EUR exchange rate	0	1.20
Average GBP - USD exchange rate	0	0
>3 and ≤12 months | Exchange rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 500	£ 1,173
Average GBP - EUR exchange rate	1.25	1.19
Average GBP - USD exchange rate	0	1.60
>3 and ≤12 months | Exchange rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 2,692	£ 2,381
Average GBP - EUR exchange rate	1.17	1.12
Average GBP - USD exchange rate	0	1.17
Average GBP - JPY exchange rate	167.85	160.04
Average GBP - CHF exchange rate	1.09	0
>1 and ≤5 years | Interest rate contracts | Interest rate risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 60,590	£ 45,314
>1 and ≤5 years | Interest rate contracts | Interest rate risk | Fair value hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0390	0.0207
>1 and ≤5 years | Interest rate contracts | Interest rate risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0021	0.0028
>1 and ≤5 years | Interest rate contracts | Interest rate risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0136	0.0200
>1 and ≤5 years | Interest rate contracts | Interest rate risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 27,721	£ 13,197
>1 and ≤5 years | Interest rate contracts | Interest rate risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0383	0.0235
>1 and ≤5 years | Interest rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 844	£ 263
>1 and ≤5 years | Interest rate contracts | Interest rate/FX risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0277	0.0206
>1 and ≤5 years | Interest rate contracts | Interest rate/FX risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0483	0.0463
>1 and ≤5 years | Interest rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 1,975	£ 2,132
>1 and ≤5 years | Interest rate contracts | Interest rate/FX risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0231	0.0258
>1 and ≤5 years | Interest rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 2,325
>1 and ≤5 years | Exchange rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 1,041	£ 465
Average GBP - EUR exchange rate	1.16	1.16
Average GBP - USD exchange rate	1.32	1.19
>1 and ≤5 years | Exchange rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 2,896	£ 4,626
Average GBP - EUR exchange rate	1.20	1.21
Average GBP - USD exchange rate	1.38	1.50
>1 and ≤5 years | Exchange rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 9,447	£ 10,606
Average GBP - EUR exchange rate	1.18	1.18
Average GBP - USD exchange rate	1.28	1.31
Average GBP - JPY exchange rate	0	0
Average GBP - CHF exchange rate	1.12	0
>5 years | Interest rate contracts | Interest rate risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 3,008	£ 3,808
>5 years | Interest rate contracts | Interest rate risk | Fair value hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0399	0.0378
>5 years | Interest rate contracts | Interest rate risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0392	0.0309
>5 years | Interest rate contracts | Interest rate risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0491	0.0492
>5 years | Interest rate contracts | Interest rate risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 1,219	£ 1,076
>5 years | Interest rate contracts | Interest rate risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0345	0.0184
>5 years | Interest rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 86	£ 7
>5 years | Interest rate contracts | Interest rate/FX risk | Fair value hedges | Euro
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0348	0
>5 years | Interest rate contracts | Interest rate/FX risk | Fair value hedges | US Dollar
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0	0
>5 years | Interest rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 166	£ 208
>5 years | Interest rate contracts | Interest rate/FX risk | Cash flow hedges | Sterling
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0474	0.0459
>5 years | Interest rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 942	£ 997
>5 years | Exchange rate contracts | Interest rate/FX risk | Fair value hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 86	£ 7
Average GBP - EUR exchange rate	1.15	1.10
Average GBP - USD exchange rate	0	0
>5 years | Exchange rate contracts | Interest rate/FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 458	£ 650
Average GBP - EUR exchange rate	1.19	1.20
Average GBP - USD exchange rate	1.54	1.54
>5 years | Exchange rate contracts | FX risk | Cash flow hedges
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 588	£ 1,163
Average GBP - EUR exchange rate	0	1.17
Average GBP - USD exchange rate	1.39	1.39
Average GBP - JPY exchange rate	0	0
Average GBP - CHF exchange rate	1.12	0

Derivative Financial Instrume_6

Derivative Financial Instruments - Summary of Net Gains or Losses Arising from Fair Value and Cash Flow Hedges Included in Net Trading and Other Income (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of detailed information about hedges
Hedge ineffectiveness	£ 19	£ 29	£ 13
Fair value and cash flow hedges
Disclosure of detailed information about hedges
(Losses)/gains on hedging instruments	(1,879)	2,381	852
Gains/(losses) on hedged items attributable to hedged risks	1,896	(2,316)	(800)
Fair value hedging ineffectiveness	17	65	52
Cash flow hedging ineffectiveness	2	(36)	(39)
Hedge ineffectiveness	£ 19	£ 29	£ 13

Derivative Financial Instrume_7

Derivative Financial Instruments - Summary of Information About Hedging Ineffectiveness by Risk Category (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair value hedges
Disclosure of detailed information about hedges
Change in FV of hedging instruments	£ (1,879)	£ 2,381	£ 852
Change in FV of hedged items	1,896	(2,316)	(800)
Recognised in income statement	17	65	52
Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Change in FV of hedging instruments	(1,865)	2,392	874
Change in FV of hedged items	1,877	(2,333)	(834)
Recognised in income statement	12	59	40
Fair value hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Change in FV of hedging instruments	(14)	(11)	(22)
Change in FV of hedged items	19	17	34
Recognised in income statement	5	6	12
Cash flow hedges
Disclosure of detailed information about hedges
Change in FV of hedging instruments	(167)	389	(912)
Change in FV of hedged items	169	(425)
Recognised in OCI	169	(425)	873
Recognised in income statement	2	(36)	(39)
Reclassified from reserves to income	(1,248)	2,129	(358)
Cash flow hedges | Interest rate risk
Disclosure of detailed information about hedges
Change in FV of hedging instruments	466	(1,161)	(317)
Recognised in OCI	(445)	1,160	305
Recognised in income statement	21	(1)	(12)
Reclassified from reserves to income	(469)	(96)	73
Cash flow hedges | FX risk
Disclosure of detailed information about hedges
Change in FV of hedging instruments	(396)	1,604	(54)
Recognised in OCI	377	(1,604)	54
Recognised in income statement	(19)	0	0
Reclassified from reserves to income	(392)	1,692	(158)
Cash flow hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Change in FV of hedging instruments	(237)	(54)	(541)
Recognised in OCI	237	19	514
Recognised in income statement	0	(35)	(27)
Reclassified from reserves to income	£ (387)	£ 533	£ (273)

Derivative Financial Instrume_8

Derivative Financial Instruments - Additional Information (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of nature and extent of risks arising from financial instruments [abstract]
Ceased cash flow hedge accounting	£ 0	£ 0

Derivative Financial Instrume_9

Derivative Financial Instruments - Summary of Reconciliation by Risk Category of Components of Equity and Analysis of Other Comprehensive Income Items Resulting from Hedge Accounting (Details) - Cash flow hedges - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of detailed information about hedges
Beginning Balance	£ (1,575)	£ 129
Effective portion of changes in fair value:	(169)	425
Income statement transfers:	1,248	(2,129)
Ending Balance	(496)	(1,575)
Interest rate risk
Disclosure of detailed information about hedges
Effective portion of changes in fair value:	445	(1,160)
Income statement transfers:	469	96
Foreign currency risk
Disclosure of detailed information about hedges
Effective portion of changes in fair value:	(377)	1,604
Income statement transfers:	392	(1,692)
Interest rate/FX risk
Disclosure of detailed information about hedges
Effective portion of changes in fair value:	(237)	(19)
Income statement transfers:	£ 387	£ (533)

Derivative Financial Instrum_10

Derivative Financial Instruments - Summary of Details of Hedged Exposures by Hedging Strategies (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair value hedges
Disclosure of detailed information about hedges
Carrying value of assets	£ 61,815	£ 60,533
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	7	80
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	(719)	(2,752)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(754)	(887)
Change in value to calculate hedge ineffectiveness	1,896	(2,316)	£ (800)
Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	1,877	(2,333)	(834)
Fair value hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	19	17	34
Cash flow hedges
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	169	(425)
Cash flow hedge reserve	(496)	(1,575)	£ 129
Balances on cash flow hedge reserve for discontinued hedges	(23)	(35)
Deposits by customers | Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Carrying value of liabilities	(15,892)	(1,739)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	38	24
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	(10)	5
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	0	0
Change in value to calculate hedge ineffectiveness	(53)	33
Deposits by customers | Cash flow hedges | FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	(33)	(167)
Cash flow hedge reserve	0	(2)
Balances on cash flow hedge reserve for discontinued hedges	0	0
Deposits by banks | Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Carrying value of liabilities	0	0
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	0	0
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	0	0
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	0	0
Change in value to calculate hedge ineffectiveness	0	0
Deposits by banks | Cash flow hedges | Interest rate risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	(1)	(8)
Cash flow hedge reserve	(1)	7
Balances on cash flow hedge reserve for discontinued hedges	0	0
Debt securities in issue | Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Carrying value of liabilities	(4,091)	(4,735)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	118	321
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	(75)	(94)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(114)	(172)
Change in value to calculate hedge ineffectiveness	(128)	528
Debt securities in issue | Fair value hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Carrying value of liabilities	(214)	(290)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	(14)	(18)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	0	0
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(24)	(37)
Change in value to calculate hedge ineffectiveness	8	27
Debt securities in issue | Cash flow hedges | FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	617	(1,051)
Cash flow hedge reserve	(9)	(17)
Balances on cash flow hedge reserve for discontinued hedges	0	(2)
Subordinated liabilities | Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Carrying value of liabilities	(522)	(250)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	(27)	(27)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	(1)	(6)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(42)	(63)
Change in value to calculate hedge ineffectiveness	(1)	54
Subordinated liabilities | Fair value hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Carrying value of liabilities	0	(1)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	0	1
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	0	0
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	0	1
Change in value to calculate hedge ineffectiveness	(1)	(1)
Repurchase agreements - non trading | Cash flow hedges | FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	(42)	(37)
Cash flow hedge reserve	0	0
Balances on cash flow hedge reserve for discontinued hedges	0	0
Loans and advances to customers | Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Carrying value of assets	73,194	60,783
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	0	0
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	(625)	(2,640)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(435)	(653)
Change in value to calculate hedge ineffectiveness	1,968	(2,707)
Loans and advances to customers | Cash flow hedges | Interest rate risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	(163)	935
Cash flow hedge reserve	(462)	(1,010)
Balances on cash flow hedge reserve for discontinued hedges	1	(1)
Other financial assets at amortised cost | Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Carrying value of assets	152	156
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	1	0
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	(8)	(12)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(8)	2
Change in value to calculate hedge ineffectiveness	5	(14)
Reverse repurchase agreements – non trading | Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Carrying value of assets	6,186	4,045
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	0	0
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	0	(5)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	0	(1)
Change in value to calculate hedge ineffectiveness	4	0
Other financial assets at FVOCI | Fair value hedges | Interest rate risk
Disclosure of detailed information about hedges
Carrying value of assets	2,013	2,325
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	(113)	(200)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	0	0
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(131)	35
Change in value to calculate hedge ineffectiveness	82	(227)
Other financial assets at FVOCI | Fair value hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Carrying value of assets	989	237
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	4	(21)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	0	0
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	0	1
Change in value to calculate hedge ineffectiveness	12	(9)
Cash and balances at central banks | Cash flow hedges | Interest rate risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	(281)	233
Cash flow hedge reserve	99	(274)
Balances on cash flow hedge reserve for discontinued hedges	(76)	(106)
Other financial assets at FVOCI | Cash flow hedges | FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	(253)	0
Cash flow hedge reserve	1	(6)
Balances on cash flow hedge reserve for discontinued hedges	0	0
Not applicable – highly probable forecast transactions | Cash flow hedges | FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	88	(349)
Cash flow hedge reserve	1	2
Balances on cash flow hedge reserve for discontinued hedges	0	0
Debt securities in issue/loans and advances to customers | Debt securities in issue/loans and advances to customers | Cash flow hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	99	56
Cash flow hedge reserve	(75)	(170)
Balances on cash flow hedge reserve for discontinued hedges	0	(3)
Deposits by customers | Deposits by customers | Cash flow hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	94	0
Cash flow hedge reserve	(39)	(74)
Balances on cash flow hedge reserve for discontinued hedges	0	0
Subordinated liabilities/loans and advances to customers | Subordinated liabilities/loans and advances to customers | Cash flow hedges | Interest rate/FX risk
Disclosure of detailed information about hedges
Change in value to calculate hedge ineffectiveness	44	(37)
Cash flow hedge reserve	(11)	(31)
Balances on cash flow hedge reserve for discontinued hedges	£ 52	£ 77

Other Financial Assets at Fai_3

Other Financial Assets at Fair Value Through Profit or Loss - Summary of Other Financial Assets at Fair Value Through Profit or Loss (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Other Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at fair value through profit or loss	£ 262	£ 129
Loans and advances to customers
Disclosure Of Other Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at fair value through profit or loss	46	45
Loans and advances to customers | Loans to housing associations
Disclosure Of Other Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at fair value through profit or loss	8	4
Loans and advances to customers | Other loans
Disclosure Of Other Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at fair value through profit or loss	38	41
Debt securities
Disclosure Of Other Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at fair value through profit or loss	167	15
Other debt instruments
Disclosure Of Other Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at fair value through profit or loss	£ 49	£ 69

Other Financial Assets at Fai_4

Other Financial Assets at Fair Value Through Profit or Loss - Additional Information (Details) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Financial assets at fair value through profit or loss [abstract]
Financial assets designated at FVTPL	£ 8,000	£ 16,000
Financial assets mandatorily at FVTPL	254,000	113,000
Net (loss)/gain attributable to changes in credit risk for loans and advances at fair value through profit or loss	0
Net (loss)/gain attributable to changes in credit risk for loans and advances at fair value through profit or loss		(1,000)	£ 0
Cumulative net loss attributable to changes in credit risk for loans and advances at fair value through profit or loss	£ (3,000)
Cumulative net loss attributable to changes in credit risk for loans and advances at fair value through profit or loss		£ (3,000)	£ (2,000)

Loans and Advances to Custome_3

Loans and Advances to Customers - Summary of Net Loans and Advances to Customers (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of major customers [line items]
Loans secured on residential properties	£ 172,854	£ 184,317
Corporate loans	18,267	19,057
Finance leases	4,530	4,645
Other unsecured loans	7,232	7,742
Accrued interest and other adjustments	943	688
Loans and advances to customers	208,370	220,669
Credit impairment loss allowances on loans and advances to customers	(914)	(931)
Residual value and voluntary termination provisions on finance leases	(21)	(22)
Net loans and advances to customers	207,435	219,716
Amounts due from fellow Banco Santander subsidiaries and joint ventures
Disclosure of major customers [line items]
Intercompany balances	4,489	4,220
Amounts due from Santander UK Group Holdings plc
Disclosure of major customers [line items]
Intercompany balances	55	0
Amounts due from subsidiaries
Disclosure of major customers [line items]
Intercompany balances	£ 0	£ 0

Loans and Advances to Custome_4

Loans and Advances to Customers - Summary of Finance Lease and Hire Purchase Contract Receivables (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Finance Lease And Hire Purchase Contract Receivables [Line Items]
Gross investment	£ 5,300	£ 5,296
Unearned finance income	(770)	(651)
Net investment	4,530	4,645
No later than one year
Disclosure Of Finance Lease And Hire Purchase Contract Receivables [Line Items]
Gross investment	1,502	1,493
Unearned finance income	(216)	(182)
Net investment	1,286	1,311
Later than one year and not later than two years
Disclosure Of Finance Lease And Hire Purchase Contract Receivables [Line Items]
Gross investment	1,426	1,367
Unearned finance income	(208)	(168)
Net investment	1,218	1,199
Later than two years and not later than three years
Disclosure Of Finance Lease And Hire Purchase Contract Receivables [Line Items]
Gross investment	1,331	1,190
Unearned finance income	(194)	(147)
Net investment	1,137	1,043
Later than three years and not later than four years
Disclosure Of Finance Lease And Hire Purchase Contract Receivables [Line Items]
Gross investment	882	1,044
Unearned finance income	(129)	(129)
Net investment	753	915
Later than four years and not later than five years
Disclosure Of Finance Lease And Hire Purchase Contract Receivables [Line Items]
Gross investment	99	143
Unearned finance income	(14)	(18)
Net investment	85	125
Later than five years
Disclosure Of Finance Lease And Hire Purchase Contract Receivables [Line Items]
Gross investment	60	59
Unearned finance income	(9)	(7)
Net investment	£ 51	£ 52

Loans and Advances to Custome_5

Loans and Advances to Customers - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Loans And Advances To Customers [Abstract]
Unguaranteed residual value of leases	£ 1,830	£ 1,761
Contingent rent income	0	0	£ 0
Finance income on the net investment in finance leases	£ 266	£ 230	£ 243

Loans and Advances to Custome_6

Loans and Advances to Customers - Disclosure of Maturity Analysis of Operating Lease Payments (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of maturity analysis of operating lease payments [line items]
Undiscounted operating lease payments to be received	£ 111	£ 125
No later than one year
Disclosure of maturity analysis of operating lease payments [line items]
Undiscounted operating lease payments to be received	28	31
Later than one year and not later than two years
Disclosure of maturity analysis of operating lease payments [line items]
Undiscounted operating lease payments to be received	26	27
Later than two years and not later than three years
Disclosure of maturity analysis of operating lease payments [line items]
Undiscounted operating lease payments to be received	18	22
Later than three years and not later than four years
Disclosure of maturity analysis of operating lease payments [line items]
Undiscounted operating lease payments to be received	14	13
Later than four years and not later than five years
Disclosure of maturity analysis of operating lease payments [line items]
Undiscounted operating lease payments to be received	7	11
Later than five years
Disclosure of maturity analysis of operating lease payments [line items]
Undiscounted operating lease payments to be received	£ 18	£ 21

Securitisations and Covered B_3

Securitisations and Covered Bonds - Analysis of Securitisations and Covered Bonds (Details) £ in Millions	Dec. 31, 2023 GBP (£)	Dec. 31, 2023 EUR (€)	Dec. 31, 2022 GBP (£)	Dec. 31, 2022 EUR (€)
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	£ 27,927		£ 24,984
External notes in issue	17,769		16,102
Notes issued to Santander UK plc/subsidiaries as collateral	1,682		1,541
Notional amount	223,242		176,472
Euro 35bn Global Covered Bond Programme
Disclosure Of Securitisations And Covered Bonds [Line Items]
Notional amount | €		€ 35,000,000,000		€ 35,000,000,000
Securitisation programmes
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	6,047		3,680
External notes in issue	2,769		897
Notes issued to Santander UK plc/subsidiaries as collateral	1,682		1,541
Securitisation programmes | Mortgage-backed master trust structures
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	5,290		3,674
External notes in issue	2,219		890
Notes issued to Santander UK plc/subsidiaries as collateral	1,682		1,541
Securitisation programmes | Other asset-backed securitisation structure
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	757		6
External notes in issue	550		7
Notes issued to Santander UK plc/subsidiaries as collateral	0		0
Holmes | Securitisation programmes | Mortgage-backed master trust structures
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	3,242		1,646
External notes in issue	2,119		790
Notes issued to Santander UK plc/subsidiaries as collateral	300		176
Fosse | Securitisation programmes | Mortgage-backed master trust structures
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	2,048		2,028
External notes in issue	100		100
Notes issued to Santander UK plc/subsidiaries as collateral	1,382		1,365
Motor | Securitisation programmes | Other asset-backed securitisation structure
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	0		6
External notes in issue	0		7
Notes issued to Santander UK plc/subsidiaries as collateral	0		0
Repton | Securitisation programmes | Other asset-backed securitisation structure
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	757		0
External notes in issue	550		0
Notes issued to Santander UK plc/subsidiaries as collateral	0		0
Euro 35bn Global Covered Bond Programme | Covered bond programme
Disclosure Of Securitisations And Covered Bonds [Line Items]
Gross assets	21,880		21,304
External notes in issue	15,000		15,205
Notes issued to Santander UK plc/subsidiaries as collateral	£ 0		£ 0

Securitisations and Covered B_4

Securitisations and Covered Bonds - Summary of Issuances and Redemptions of Securitisation and Covered Bond Programme (Details) £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£)	Dec. 31, 2022 GBP (£)	Dec. 31, 2023 EUR (€)	Dec. 31, 2022 EUR (€)
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Notional amount	£ 223,242	£ 176,472
Euro 35bn Global Covered Bond Programme
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Notional amount | €			€ 35,000,000,000	€ 35,000,000,000
Internal issuances
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	241	0
Internal and external redemptions	121	200
Internal issuances | Mortgage-backed master trust structures | Holmes
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	241	0
Internal and external redemptions	121	100
Internal issuances | Mortgage-backed master trust structures | Fosse
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0	0
Internal issuances | Other asset-backed securitisation structure | Motor
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0	0
Internal issuances | Other asset-backed securitisation structure | Repton
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0	0
Internal issuances | Covered bond programme | Euro 35bn Global Covered Bond Programme
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0	100
External issuances
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	2,050	4,800
Internal and external redemptions	193	2,133
External issuances | Mortgage-backed master trust structures | Holmes
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	1,500	600
Internal and external redemptions	186	200
External issuances | Mortgage-backed master trust structures | Fosse
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0	200
External issuances | Other asset-backed securitisation structure | Motor
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	7	33
External issuances | Other asset-backed securitisation structure | Repton
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	550	0
Internal and external redemptions	0	0
External issuances | Covered bond programme | Euro 35bn Global Covered Bond Programme
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	4,200
Internal and external redemptions	£ 0	£ 1,700

Securitisations and Covered B_5

Securitisations and Covered Bonds - Additional Information (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Holmes
Disclosure Of Gross Asset Securitised [Line Items]
Beneficial interest in residential mortgage loans	£ 2,396	£ 796
Cash deposits	80	112
Fosse
Disclosure Of Gross Asset Securitised [Line Items]
Beneficial interest in residential mortgage loans	1,393	1,465
Cash deposits	£ 108	£ 108

Transfers of Financial Assets_3

Transfers of Financial Assets Not Qualifying for Derecognition (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	£ 9,197	£ 6,671
Carrying amount of associated financial liabilities	(5,519)	(3,534)
Sale and repurchase agreements
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	14	120
Carrying amount of associated financial liabilities	(15)	(128)
Securities lending agreements
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	3,136	2,871
Carrying amount of associated financial liabilities	(2,735)	(2,509)
Securitisations (See Notes 14 and 26)
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	6,047	3,680
Carrying amount of associated financial liabilities	£ (2,769)	£ (897)

Reverse Repurchase Agreements_3

Reverse Repurchase Agreements - Non Trading (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Reserve Repurchase Agreements Non-Trading [Line Items]
Reverse Repurchase agreements - non-trading	£ 12,468	£ 7,348
Agreements with banks
Disclosure Of Reserve Repurchase Agreements Non-Trading [Line Items]
Reverse Repurchase agreements - non-trading	2,397	885
Agreements with customers
Disclosure Of Reserve Repurchase Agreements Non-Trading [Line Items]
Reverse Repurchase agreements - non-trading	£ 10,071	£ 6,463

Other Financial Assets at Amo_3

Other Financial Assets at Amortised Cost (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at amortised cost	£ 152	£ 156
Other financial assets
Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at amortised cost	152	156
Other financial assets | Asset backed securities
Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at amortised cost	0	0
Other financial assets | Debt securities
Financial Assets At Fair Value Through Profit Or Loss [Line Items]
Financial assets at amortised cost	£ 152	£ 156

Financial Assets at Fair Valu_3

Financial Assets at Fair Value Through Other Comprehensive Income (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Financial Assets At Fair Value Through Other Comprehensive Income [Line Items]
Financial assets at fair value through other comprehensive income	£ 8,481	£ 6,024
Debt securities
Disclosure Of Financial Assets At Fair Value Through Other Comprehensive Income [Line Items]
Financial assets at fair value through other comprehensive income	£ 8,481	£ 6,024

Interests in Other Entities - S

Interests in Other Entities - Schedule of Interests in Other Entities (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Investments accounted for using equity method [abstract]
Subsidiaries	£ 0	£ 0
Joint ventures	£ 245	£ 252

Interests In Other Entities - A

Interests In Other Entities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 GBP (£)	Dec. 31, 2022 GBP (£)
Disclosure of subsidiaries [line items]
Ownership interest in share capital	100%
Joint ventures	£ 245,000,000	£ 252,000,000
Number of credit protection vehicles	4	4
Senior credit linked notes issued	£ 0	£ 180,000,000
Junior credit linked notes issued	185,000,000	465,000,000
Santander (UK) Common Investment Fund
Disclosure of subsidiaries [line items]
Defined benefit assets and obligations	8,551,000,000	8,646,000,000
Joint ventures
Disclosure of subsidiaries [line items]
Profit after tax	43,000,000	36,000,000
Joint ventures	245,000,000	252,000,000
Commitments and contingent liabilities	£ 0	£ 0

Intangible Assets - Schedule of

Intangible Assets - Schedule of Goodwill (Details) £ in Millions	Dec. 31, 2023 GBP (£)
Disclosure Of Goodwill [Line Items]
Goodwill at beginning of period	£ 1,199
Goodwill at end of period	1,199
Cost
Disclosure Of Goodwill [Line Items]
Goodwill at beginning of period	1,269
Goodwill at end of period	1,269
Accumulated impairment
Disclosure Of Goodwill [Line Items]
Goodwill at beginning of period	(70)
Goodwill at end of period	£ (70)

Intangible Assets - Additional

Intangible Assets - Additional Information (Details) - GBP (£)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of detailed information about intangible assets [abstract]
Goodwill impairment recognised	£ 0	£ 0
Computer software	157,000,000	149,000,000
Internally generated computer software	35,000,000	33,000,000
Impairment charge	£ 0	£ 3,000,000

Intangible Assets - Schedule _2

Intangible Assets - Schedule of Goodwill for Cash Generating Units (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of information for cash-generating units [line items]
Goodwill	£ 1,199	£ 1,199
Personal Financial Services
Disclosure of information for cash-generating units [line items]
Goodwill	£ 1,169	£ 1,169
Discount rate	16.70%	16.60%
Growth rate beyond initial cash flow projections	1.60%	1.60%
Private Banking
Disclosure of information for cash-generating units [line items]
Goodwill	£ 30	£ 30
Discount rate	14.60%	15.30%
Growth rate beyond initial cash flow projections	1.60%	1.60%

Intangible Assets - Disclosure

Intangible Assets - Disclosure of Reasonably Possible Changes in Key Assumptions (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Goodwill [Line Items]
Value in use estimate, impairment increase sensitivity for GDP growth rate adjustment	£ (19)	£ (31)
Personal Financial Services
Disclosure Of Goodwill [Line Items]
Value in use estimate, increase (decrease) in cash flows	10%	5%
Increase (decrease) in discount rate applied to cash flow projections	1%	1%
Increase (Decrease) In GDP Growth Rate Applied To Cash Flow Projections	(10.00%)	(10.00%)
Value in use estimate, impairment increase sensitivity for cash flows adjustment	£ (818)	£ (538)
Value in use estimate, impairment increase sensitivity for discount rate adjustment	£ (663)	£ (887)

Intangible Assets - Sensitivity

Intangible Assets - Sensitivity of VIU Changes to Current Assumptions (Details) - Personal Financial Services - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Goodwill [Line Items]
Carrying value	£ 7,513	£ 8,860
Value in use	8,178	10,752
Headroom	£ 665	£ 1,892
Increase in discount rate	101%	239%
Decrease in GDP growth rate	0.04	0.13
Decrease in cash flows	8%	18%

Intangible Assets - Schedule _3

Intangible Assets - Schedule of Other Intangibles (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of detailed information about intangible assets [line items]
Other intangibles at beginning of period	£ 351	£ 342
Additions	114	112
Disposals	0	0
Charge	(116)	(100)
Impairment	0	(3)
Other intangibles at end of period	349	351
Cost
Disclosure of detailed information about intangible assets [line items]
Other intangibles at beginning of period	1,261	1,334
Additions	114	112
Disposals	(36)	(185)
Charge	0	0
Impairment		0
Other intangibles at end of period	1,339	1,261
Accumulated amortisation/ impairment
Disclosure of detailed information about intangible assets [line items]
Other intangibles at beginning of period	(910)	(992)
Additions	0	0
Disposals	36	185
Charge	116	100
Impairment		3
Other intangibles at end of period	£ (990)	£ (910)

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	£ 1,513
Property, plant and equipment including right-of-use assets at the end of the period	1,494	£ 1,513
Property
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	619
Property, plant and equipment including right-of-use assets at the end of the period	692	619
Office fixtures and equipment
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	205
Property, plant and equipment including right-of-use assets at the end of the period	224	205
Computer software
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	0
Property, plant and equipment including right-of-use assets at the end of the period	0	0
Operating lease assets
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	577
Property, plant and equipment including right-of-use assets at the end of the period	488	577
Right-of-use assets
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	112
Property, plant and equipment including right-of-use assets at the end of the period	90	112
Cost
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	2,773	3,470
Additions	286	370
Reclassification (to)/from assets held for sale	8
Reclassification to assets held for sale		(111)
Disposals	(307)	(956)
Property, plant and equipment including right-of-use assets at the end of the period	2,760	2,773
Cost | Property
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	889	978
Additions	87	61
Reclassification (to)/from assets held for sale	8
Reclassification to assets held for sale		(98)
Disposals	(66)	(52)
Property, plant and equipment including right-of-use assets at the end of the period	918	889
Cost | Office fixtures and equipment
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	823	1,049
Additions	83	86
Reclassification (to)/from assets held for sale	0
Reclassification to assets held for sale		(13)
Disposals	(29)	(299)
Property, plant and equipment including right-of-use assets at the end of the period	877	823
Cost | Computer software
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	72	434
Additions	0	0
Reclassification (to)/from assets held for sale	0
Reclassification to assets held for sale		0
Disposals	(5)	(362)
Property, plant and equipment including right-of-use assets at the end of the period	67	72
Cost | Operating lease assets
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	722	755
Additions	85	185
Reclassification (to)/from assets held for sale	0
Reclassification to assets held for sale		0
Disposals	(172)	(218)
Property, plant and equipment including right-of-use assets at the end of the period	635	722
Cost | Right-of-use assets
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	267	254
Additions	31	38
Reclassification (to)/from assets held for sale	0
Reclassification to assets held for sale		0
Disposals	(35)	(25)
Property, plant and equipment including right-of-use assets at the end of the period	263	267
Accumulated depreciation
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	(1,260)	(1,922)
Additions	(173)	(179)
Reclassification to assets held for sale		62
Disposals	156	789
Property, plant and equipment including right-of-use assets at the end of the period	(1,266)	(1,260)
Accumulated depreciation | Property
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	(270)	(334)
Additions	(17)	(18)
Reclassification to assets held for sale		49
Disposals	61	41
Property, plant and equipment including right-of-use assets at the end of the period	(226)	(270)
Accumulated depreciation | Office fixtures and equipment
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	(618)	(857)
Additions	(62)	(68)
Reclassification to assets held for sale		13
Disposals	27	296
Property, plant and equipment including right-of-use assets at the end of the period	(653)	(618)
Accumulated depreciation | Computer software
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	(72)	(434)
Additions	0	(1)
Reclassification to assets held for sale		0
Disposals	5	363
Property, plant and equipment including right-of-use assets at the end of the period	(67)	(72)
Accumulated depreciation | Operating lease assets
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	(145)	(160)
Additions	(64)	(73)
Reclassification to assets held for sale		0
Disposals	62	88
Property, plant and equipment including right-of-use assets at the end of the period	(147)	(145)
Accumulated depreciation | Right-of-use assets
Disclosure of detailed information about property, plant and equipment [line items]
Property, plant and equipment including right-of-use assets at the beginning of the period	(155)	(137)
Additions	(30)	(19)
Reclassification to assets held for sale		0
Disposals	1	1
Property, plant and equipment including right-of-use assets at the end of the period	(173)	(155)
Loss allowance
Disclosure of detailed information about property, plant and equipment [line items]
Impairment during the period	(11)	10
Loss allowance | Property
Disclosure of detailed information about property, plant and equipment [line items]
Impairment during the period	0	8
Loss allowance | Office fixtures and equipment
Disclosure of detailed information about property, plant and equipment [line items]
Impairment during the period	0	2
Loss allowance | Computer software
Disclosure of detailed information about property, plant and equipment [line items]
Impairment during the period	0	0
Loss allowance | Operating lease assets
Disclosure of detailed information about property, plant and equipment [line items]
Impairment during the period	0	0
Loss allowance | Right-of-use assets
Disclosure of detailed information about property, plant and equipment [line items]
Impairment during the period	£ (11)	£ 0

Property, Plant and Equipment -

Property, Plant and Equipment - Additional Information (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of detailed information about property, plant and equipment [line items]
Investment property	£ 17	£ 17
Head Office, Milton Keynes
Disclosure of detailed information about property, plant and equipment [line items]
Expenditures	£ 0	£ 204

Other Financial Liabilities a_3

Other Financial Liabilities at Fair Value Through Profit or Loss - Summary of Other Financial Liabilities at Fair Value Through Profit or Loss (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Other Financial Liabilities At Fair Value Through Profit Or Loss [Line Items]
Other financial liabilities at fair value through profit or loss	£ 899	£ 803
Structured Notes Programmes
Disclosure Of Other Financial Liabilities At Fair Value Through Profit Or Loss [Line Items]
Other financial liabilities at fair value through profit or loss	369	375
Structured deposits
Disclosure Of Other Financial Liabilities At Fair Value Through Profit Or Loss [Line Items]
Other financial liabilities at fair value through profit or loss	426	321
Zero Amortising Guaranteed Notes
Disclosure Of Other Financial Liabilities At Fair Value Through Profit Or Loss [Line Items]
Other financial liabilities at fair value through profit or loss	£ 104	£ 107

Other Financial Liabilities a_4

Other Financial Liabilities at Fair Value Through Profit or Loss - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of financial liabilities [abstract]
Increase (decrease) in fair value of financial liability, attributable to changes in credit risk of liability	£ (21)	£ 25	£ (12)
Accumulated increase (decrease) in fair value of financial liability, attributable to changes in credit risk of liability	(6)	15	£ (10)
Difference between carrying amount of financial liability and amount contractually required to pay at maturity to holder of obligation	£ 97	£ (138)

Deposits by Customers (Details)

Deposits by Customers (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Deposits From Customers [Line Items]
Deposits by customers	£ 190,850	£ 195,568
Demand and time deposits
Disclosure Of Deposits From Customers [Line Items]
Deposits by customers	188,004	189,587
Amounts due to other Santander UK Group Holdings plc subsidiaries
Disclosure Of Deposits From Customers [Line Items]
Deposits by customers	114	67
Amounts due to Santander UK Group Holdings plc
Disclosure Of Deposits From Customers [Line Items]
Deposits by customers	1,772	4,759
Amounts due to fellow Banco Santander subsidiaries and joint ventures
Disclosure Of Deposits From Customers [Line Items]
Deposits by customers	960	1,155
Equity index linked deposits
Disclosure Of Deposits From Customers [Line Items]
Deposits by customers	£ 304	£ 408

Deposits by Banks (Details)

Deposits by Banks (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Deposits From Banks [Line Items]
Deposits by banks	£ 20,332	£ 28,525
Drawdown from TFSME	17,000	25,000
Items in the course of transmission
Disclosure Of Deposits From Banks [Line Items]
Deposits by banks	732	701
Deposits held as collateral
Disclosure Of Deposits From Banks [Line Items]
Deposits by banks	860	1,741
Other deposits
Disclosure Of Deposits From Banks [Line Items]
Deposits by banks	18,737	26,082
Amounts due to Santander UK subsidiaries
Disclosure Of Deposits From Banks [Line Items]
Deposits by banks	£ 3	£ 1

Repurchase Agreements - Non T_3

Repurchase Agreements - Non Trading (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Repurchase Agreements [Line Items]
Repurchase agreements - non trading	£ 8,411	£ 7,982
Agreements with banks
Disclosure Of Repurchase Agreements [Line Items]
Repurchase agreements - non trading	551	50
Agreements with customers
Disclosure Of Repurchase Agreements [Line Items]
Repurchase agreements - non trading	£ 7,860	£ 7,932

Debt Securities In Issue (Detai

Debt Securities In Issue (Details) £ in Millions	Dec. 31, 2023 GBP (£)	Dec. 31, 2023 EUR (€)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 GBP (£)	Dec. 31, 2022 EUR (€)	Dec. 31, 2022 USD ($)
Debt Securities In Issue [Line Items]
Notional amount	£ 223,242			£ 176,472
Debt securities	33,910			31,531
Medium-term notes
Debt Securities In Issue [Line Items]
Debt securities	11,656			10,644
Euro 35bn Global Covered Bond Programme
Debt Securities In Issue [Line Items]
Notional amount | €		€ 35,000,000,000			€ 35,000,000,000
Debt securities	15,000			15,205
US$20bn Commercial Paper Programmes
Debt Securities In Issue [Line Items]
Notional amount | $			$ 20,000,000,000			$ 20,000,000,000
Debt securities	2,761			1,851
Certificates of deposit
Debt Securities In Issue [Line Items]
Debt securities	1,530			2,874
Credit linked notes
Debt Securities In Issue [Line Items]
Credit linked notes	194			60
Securitisation programmes
Debt Securities In Issue [Line Items]
Debt securities	2,769			897
– US$30bn Euro Medium Term Note Programme | Medium-term notes
Debt Securities In Issue [Line Items]
Notional amount | $			$ 30,000,000,000			$ 30,000,000,000
Debt securities	744			739
– Euro 30bn Euro Medium Term Note Programme | Medium-term notes
Debt Securities In Issue [Line Items]
Notional amount | €		€ 30,000,000,000			€ 30,000,000,000
Debt securities	3,784			3,211
- US SEC-registered Debt Programme - Santander UK plc | Medium-term notes
Debt Securities In Issue [Line Items]
Debt securities	£ 7,128			£ 6,694

Subordinated Liabilities - Sche

Subordinated Liabilities - Schedule of Subordinated Liabilities (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Subordinated liabilities [abstract]
£325m Sterling preference shares	£ 343	£ 344
Undated subordinated liabilities	205	219
Dated subordinated liabilities	1,838	1,769
Subordinated liabilities	2,386	2,332
£325m Sterling preference shares, notional amount	£ 325	£ 325

Subordinated Liabilities - Addi

Subordinated Liabilities - Additional Information (Details) - GBP (£)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Subordinated Liabilities [Line Items]
Defaults of principal, interest or other breaches with respect to subordinated liabilities	£ 0	£ 0
Repayment or purchase of subordinated liabilities before stated maturity allowed	£ 0	£ 0
Par value per share (in GBP per share)	£ 0.10	£ 0.10	£ 0.10
Loss on repurchase of subordinated liabilities	£ 4,000,000	£ (5,000,000)
10.375% non-cumulative non-redeemable sterling preference shares
Disclosure Of Subordinated Liabilities [Line Items]
Par value per share (in GBP per share)	£ 1
7.125% 30 Year Step-up perpetual callable subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	7.125%	7.125%
10.0625% Exchangeable capital securities
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	10.0625%	10.0625%
10.375% exchangeable subordinated capital securities
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	10.375%

Subordinated Liabilities - Summ

Subordinated Liabilities - Summary of Undated Subordinated Liabilities (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Subordinated Liabilities [Line Items]
Undated subordinated liabilities	£ 205	£ 219
10.0625% Exchangeable capital securities
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	10.0625%	10.0625%
First call date	n/a	n/a
Undated subordinated liabilities	£ 205	£ 205
7.125% 30 Year Step-up perpetual callable subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	7.125%	7.125%
Notes maturity, year	30 years	30 years
First call date	2030	2030
Undated subordinated liabilities	£ 0	£ 14

Subordinated Liabilities - Su_2

Subordinated Liabilities - Summary of Dated Subordinated Liabilities (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Subordinated Liabilities [Line Items]
Dated subordinated liabilities	£ 1,838	£ 1,769
5% Subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	5%	5%
Maturity	2023	2023
Dated subordinated liabilities	£ 0	£ 591
4.75% Subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	4.75%	4.75%
Maturity	2025	2025
Dated subordinated liabilities	£ 326	£ 608
7.95% Subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	7.95%	7.95%
Maturity	2029	2029
Dated subordinated liabilities	£ 193	£ 207
6.50% Subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	6.50%	6.50%
Maturity	2030	2030
Dated subordinated liabilities	£ 1	£ 22
5.875% Subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	5.875%	5.875%
Maturity	2031	2031
Dated subordinated liabilities	£ 7	£ 7
5.625%Subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	5.625%	5.625%
Maturity	2045	2045
Dated subordinated liabilities	£ 222	£ 334
7.869% Subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	7.869%
Maturity	2033
Dated subordinated liabilities	£ 321	0
8.296% Subordinated notes
Disclosure Of Subordinated Liabilities [Line Items]
Interest rate	8.296%
Maturity	2033
Dated subordinated liabilities	£ 768	£ 0

Other Liabilities (Details)

Other Liabilities (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Subclassifications of assets, liabilities and equities [abstract]
Lease liabilities	£ 111	£ 125
Other	2,368	2,456
Other liabilities	£ 2,479	£ 2,581

Provisions - Summary of Provisi

Provisions - Summary of Provisions Reconciliation (Details) £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£)
Disclosure of other provisions [line items]
Beginning balance	£ 378
Additional provisions (See Note 8)	361
Provisions released (See Note 8)	(22)
Utilisation and other	(371)
Recharge	20
Reclassification from provisions to other assets	36
Ending balance	402
Customer remediation
Disclosure of other provisions [line items]
Beginning balance	90
Additional provisions (See Note 8)	45
Provisions released (See Note 8)	(8)
Utilisation and other	(21)
Recharge	0
Reclassification from provisions to other assets	0
Ending balance	106
Litigation and other regulatory
Disclosure of other provisions [line items]
Beginning balance	136
Additional provisions (See Note 8)	28
Provisions released (See Note 8)	0
Utilisation and other	(32)
Recharge	0
Reclassification from provisions to other assets	0
Ending balance	132
Bank Levy
Disclosure of other provisions [line items]
Beginning balance	3
Additional provisions (See Note 8)	44
Provisions released (See Note 8)	(8)
Utilisation and other	(95)
Recharge	20
Reclassification from provisions to other assets	36
Ending balance	0
Property
Disclosure of other provisions [line items]
Beginning balance	47
Additional provisions (See Note 8)	16
Provisions released (See Note 8)	(6)
Utilisation and other	(10)
Recharge	0
Reclassification from provisions to other assets	0
Ending balance	47
ECL on undrawn facilities and guarantees
Disclosure of other provisions [line items]
Beginning balance	74
Additional provisions (See Note 8)	4
Provisions released (See Note 8)	0
Utilisation and other	0
Recharge	0
Reclassification from provisions to other assets	0
Ending balance	78
Restructuring
Disclosure of other provisions [line items]
Beginning balance	21
Additional provisions (See Note 8)	56
Provisions released (See Note 8)	0
Utilisation and other	(45)
Recharge	0
Reclassification from provisions to other assets	0
Ending balance	32
Other
Disclosure of other provisions [line items]
Beginning balance	7
Additional provisions (See Note 8)	168
Provisions released (See Note 8)	0
Utilisation and other	(168)
Recharge	0
Reclassification from provisions to other assets	0
Ending balance	£ 7

Provisions - Additional Informa

Provisions - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of other provisions [line items]
Loss allowance	£ 402	£ 378
Additional provisions	361
No later than one year
Disclosure of other provisions [line items]
Loss allowance	217	130
Customer remediation
Disclosure of other provisions [line items]
Loss allowance	106	£ 90
Net provision	37
Additional provisions	45
Customer remediation- mortgage book
Disclosure of other provisions [line items]
Additional provisions	45
Customer remediation- interest refund
Disclosure of other provisions [line items]
Additional provisions	30
Customer remediation- early repayment charges
Disclosure of other provisions [line items]
Additional provisions	£ 10
Regulatory related UK Bank Levy
Disclosure of other provisions [line items]
Bank Levy rate	0.10%	0.10%
Regulatory related UK Bank Levy | Later than one year
Disclosure of other provisions [line items]
Bank Levy rate	0.05%	0.05%
Restructuring
Disclosure of other provisions [line items]
Loss allowance	£ 32	£ 21
Additional provisions	56
Provisions for costs related to transformation programs	51
Operational risk provisions
Disclosure of other provisions [line items]
Additional provisions	163
Fraud losses
Disclosure of other provisions [line items]
Additional provisions	136
Legal provision
Disclosure of other provisions [line items]
Additional provisions	12
Regulatory fees
Disclosure of other provisions [line items]
Additional provisions	16
Property transformation charges
Disclosure of other provisions [line items]
Additional provisions	£ 4

Retirement Benefit Plans - Summ

Retirement Benefit Plans - Summary of Retirement Benefit Plans (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets/(liabilities)
Total net assets	£ 657	£ 1,025
Unfunded pension and post-retirement medical benefits
Assets/(liabilities)
Surplus (deficit) in plan	(25)	(25)
Surplus | Funded defined benefit pension scheme
Assets/(liabilities)
Surplus (deficit) in plan	723	1,050
Deficit | Funded defined benefit pension scheme
Assets/(liabilities)
Surplus (deficit) in plan	£ (41)	£ 0

Retirement Benefit Plans - Addi

Retirement Benefit Plans - Additional Information (Details) £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£) director section	Dec. 31, 2022 GBP (£) director	Dec. 31, 2021 GBP (£)	Mar. 31, 2021	May 31, 2020	Aug. 31, 2019 GBP (£)	Mar. 01, 2015
Disclosure of defined benefit plans [line items]
Defined contribution expense	£ 71	£ 60	£ 64
Number of legally segregated sections | section	7
Percentage of employee covered defined benefit pension schemes	7%	10%
Number of directors selected | director	6	6
Number of directors nominated | director	4	4
Actuarial valuation deficit						£ 183
Percentage of the SMA section pensioner liabilities insured					100%
Percentage of the SPI section pensioner liabilities insured					50%
Contribution to scheme based on agreement	£ 195	£ 218
Period over which the spot rate remain constant	50 years
Percentage of pension pay increase	3%	3%	3.20%				1%
Percentage improvements in membership profile retirement benefits plan	0.25%
Improvements to life expectancy of female employees	1.25%
Improvements to life expectancy of male employees	1.25%
Average duration of defined benefit obligation	13.8 years	14.2 years
Minimum
Disclosure of defined benefit plans [line items]
Forward curve term	30 years
Maximum
Disclosure of defined benefit plans [line items]
Forward curve term	50 years
General price inflation
Disclosure of defined benefit plans [line items]
Percentage of reasonably possible increase in actuarial assumption	0.50%
Deficit Repair Contributions
Disclosure of defined benefit plans [line items]
Contribution to scheme based on agreement	£ 164	£ 178
Currency futures
Disclosure of defined benefit plans [line items]
Gross notional value	£ 859	£ 985
Longevity swap
Disclosure of defined benefit plans [line items]
Percentage of pensioner liabilities covered by longevity swap				85%

Retirement Benefit Plans - Tota

Retirement Benefit Plans - Total Defined Benefit Plan Amount Charged to Income Statement (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of net defined benefit liability (asset) [abstract]
Net interest income	£ 54	£ 30	£ 5
Current service cost	13	30	38
Past service and GMP costs	1	0	0
Past service curtailment costs	0	0	5
Administration costs	7	9	8
Total	£ (33)	£ 9	£ 46

Retirement Benefit Plans - Su_2

Retirement Benefit Plans - Summary of Amounts Recognised in Other Comprehensive Income (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of net defined benefit liability (asset) [abstract]
Return on plan assets (excluding amounts included in net interest expense)	£ 352	£ 5,527	£ (454)
Actuarial (gains) arising from changes in demographic assumptions	(51)	(122)	(17)
Actuarial losses/(gains) arising from experience adjustments	91	481	(19)
Actuarial losses/(gains) arising from changes in financial assumptions	206	(5,164)	(774)
Pension remeasurement	£ 598	£ 722	£ (1,264)

Retirement Benefit Plans - Disc

Retirement Benefit Plans - Disclosure of Movements in Present Value of Defined Benefit Obligations (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset) beginning balance	£ 1,025
Current service cost paid by Santander UK plc	13	£ 30	£ 38
Interest cost	54	30	5
Remeasurement due to actuarial movements arising from:
Changes in demographic assumptions	(51)	(122)	(17)
– Experience adjustments	91	481	(19)
Changes in financial assumptions	206	(5,164)	(774)
Net defined benefit liability (asset) ending balance	657	1,025
Present value of defined benefit obligations
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset) beginning balance	(7,933)	(12,878)
Current service cost paid by Santander UK plc	(13)	(29)
Current service cost paid by subsidiaries	0	(1)
Interest cost	(379)	(241)
Employer salary sacrifice contributions	(1)	(2)
Past service cost	(1)	0
Remeasurement due to actuarial movements arising from:
Changes in demographic assumptions	51	122
– Experience adjustments	(91)	(481)
Changes in financial assumptions	(206)	5,164
Benefits paid	372	413
Net defined benefit liability (asset) ending balance	£ (8,201)	£ (7,933)	£ (12,878)

Retirement Benefit Plans - Di_2

Retirement Benefit Plans - Disclosure of Movements in Fair Value of Scheme Assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	£ (1,025)
Interest income	54	£ 30	£ 5
Return on plan assets (excluding amounts included in net interest expense)	352	5,527	(454)
Ending balance	(657)	(1,025)
Fair value of scheme assets
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	(8,958)	(14,413)
Interest income	433	271
Contributions paid by employer and scheme members	198	223
Administration costs paid	(7)	(9)
Return on plan assets (excluding amounts included in net interest expense)	(352)	(5,527)
Benefits paid	(372)	(413)
Ending balance	£ (8,858)	£ (8,958)	£ (14,413)

Retirement Benefit Plans - Su_3

Retirement Benefit Plans - Summary of Composition and Fair Value of Plan Assets (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of net defined benefit liability (asset) [line items]
Overseas equities	£ 980	£ 1,172
Corporate bonds	2,526	2,235
Government fixed interest bonds	1,618	1,138
Government index-linked bonds	4,422	5,525
Property	1,080	1,202
Derivatives	(2)	(78)
Cash	586	1,340
Repurchase agreements	(3,062)	(4,312)
Infrastructure	408	426
Annuities	293	293
Longevity swap	(16)	(12)
Other	25	29
Total	£ 8,858	£ 8,958
Overseas equities, percentage	11%	13%
Corporate bonds, percentage	29%	25%
Government fixed interest bonds, percentage	18%	13%
Government index-linked bonds, percentage	50%	62%
Property, percentage	12%	13%
Derivatives, percentage	0%	(1.00%)
Cash, percentage	7%	15%
Repurchase agreements, percentage	(35.00%)	(48.00%)
Infrastructure, percentage	5%	5%
Annuities, percentage	3%	3%
Longevity swap, percentage	0%	0%
Other, percentage	0%	0%
Total, percentage	100%	100%
Quoted prices in active markets
Disclosure of net defined benefit liability (asset) [line items]
Overseas equities	£ 0	£ 0
Corporate bonds	2,284	1,991
Government fixed interest bonds	1,618	1,138
Government index-linked bonds	4,422	5,525
Property	0	0
Derivatives	0	0
Cash	0	0
Repurchase agreements	0	0
Infrastructure	0	0
Annuities	0	0
Longevity swap	0	0
Other	0	0
Total	£ 8,324	£ 8,654
Overseas equities, percentage	0%	0%
Corporate bonds, percentage	26%	22%
Government fixed interest bonds, percentage	18%	13%
Government index-linked bonds, percentage	50%	62%
Property, percentage	0%	0%
Derivatives, percentage	0%	0%
Cash, percentage	0%	0%
Repurchase agreements, percentage	0%	0%
Infrastructure, percentage	0%	0%
Annuities, percentage	0%	0%
Longevity swap, percentage	0%	0%
Other, percentage	0%	0%
Total, percentage	94%	97%
Prices not quoted in active markets
Disclosure of net defined benefit liability (asset) [line items]
Overseas equities	£ 980	£ 1,172
Corporate bonds	242	244
Government fixed interest bonds	0	0
Government index-linked bonds	0	0
Property	1,080	1,202
Derivatives	(2)	(78)
Cash	586	1,340
Repurchase agreements	(3,062)	(4,312)
Infrastructure	408	426
Annuities	293	293
Longevity swap	(16)	(12)
Other	25	29
Total	£ 534	£ 304
Overseas equities, percentage	11%	13%
Corporate bonds, percentage	3%	3%
Government fixed interest bonds, percentage	0%	0%
Government index-linked bonds, percentage	0%	0%
Property, percentage	12%	13%
Derivatives, percentage	0%	(1.00%)
Cash, percentage	7%	15%
Repurchase agreements, percentage	(35.00%)	(48.00%)
Infrastructure, percentage	5%	5%
Annuities, percentage	3%	3%
Longevity swap, percentage	0%	0%
Other, percentage	0%	0%
Total, percentage	6%	3%

Retirement Benefit Plans - Su_4

Retirement Benefit Plans - Summary of Principal Actuarial Assumptions Used for Defined Benefit Schemes (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Mar. 01, 2015
Disclosure of net defined benefit liability (asset) [abstract]
Discount rate for scheme liabilities	4.60%	4.90%	1.90%
General price inflation	3%	3.10%	3.40%
General salary increase	1%	1%	1%
Expected rate of pension increase	3%	3%	3.20%	1%
Longevity at 60 for current pensioners, on the valuation date:
Males	27 years	27 years 4 months 24 days	27 years 6 months
Females	29 years 9 months 18 days	30 years 1 month 6 days	30 years 1 month 6 days
Longevity at 60 for future pensioners currently aged 40, on the valuation date:
Males	28 years 7 months 6 days	28 years 10 months 24 days	29 years
Females	31 years 3 months 18 days	31 years 7 months 6 days	31 years 7 months 6 days

Retirement Benefit Plans - Su_5

Retirement Benefit Plans - Summary of Actuarial Assumption Sensitivities (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Discount rate
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.50%
Description of changes in methods and assumptions	bps increase
Increase (decrease) in defined benefit obligation	£ (507)	£ (501)
General price inflation
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage of reasonably possible increase in actuarial assumption	0.50%
Description of changes in methods and assumptions	bps increase
Increase (decrease) in defined benefit obligation	£ 385	374
Mortality
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Description of changes in methods and assumptions	Each additional year of longevity assumed
Increase (decrease) in defined benefit obligation	£ 223	£ 203

Retirement Benefit Plans - Di_3

Retirement Benefit Plans - Disclosure of Benefits Expected To Be Paid (Details) £ in Millions	Dec. 31, 2023 GBP (£)
No later than one year
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	£ 455
Later than one year and not later than two years
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	389
Later than two years and not later than three years
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	404
Later than three years and not later than four years
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	428
Later than four years and not later than five years
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	444
Five years ending 2033
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	£ 2,398

Contingent Liabilities and Co_3

Contingent Liabilities and Commitments - Summary of Contingent Liabilities and Commitments (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of contingent liabilities [line items]
Guarantees and formal standby facilities, credit lines and other commitments	£ 31,428	£ 31,836
Contingent liability for guarantees
Disclosure of contingent liabilities [line items]
Guarantees given to third parties	452	448
Loan commitments
Disclosure of contingent liabilities [line items]
Formal standby facilities, credit lines and other commitments	£ 30,976	£ 31,388

Contingent Liabilities and Co_4

Contingent Liabilities and Commitments - Additional Information (Details) £ in Millions		12 Months Ended
	Nov. 02, 2015	Dec. 31, 2023 EUR (€)	Jun. 29, 2023 GBP (£)	Oct. 21, 2022 GBP (£)
Disclosure of contingent liabilities [line items]
Capital support arrangements, risk-weighted exposures of regulated entities		0%
AXA France
Disclosure of contingent liabilities [line items]
Amount claimed by other party | £			£ 552	£ 670
UK&I Banks
Disclosure of contingent liabilities [line items]
Preferred stock issued, threshold value		€ 0
Visa Europe Ltd
Disclosure of contingent liabilities [line items]
Visa Europe Ltd sale to Visa Inc	100%
Minimum
Disclosure of contingent liabilities [line items]
Losses on litigation settlements		1,000,000,000
Maximum
Disclosure of contingent liabilities [line items]
Santander UK liability under indemnity cap		€ 39,850,000

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Capital Issued and Fully Paid (Details) - GBP (£) £ / shares in Units, £ in Millions	Dec. 31, 2023	Jan. 01, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of classes of share capital [line items]
Ordinary shares, price per share (in GBP per share)	£ 0.10		£ 0.10	£ 0.10
Issued capital	£ 3,105	£ 3,105	£ 3,105
Ordinary shares
Disclosure of classes of share capital [line items]
Number of shares issued and fully paid (in shares)	31,051,768,866	31,051,768,866	31,051,768,866
Issued capital	£ 3,105	£ 3,105	£ 3,105

Share Capital - Summary of Shar

Share Capital - Summary of Share Premium (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Jan. 01, 2023	Dec. 31, 2022	Jan. 01, 2022
Disclosure of classes of share capital [abstract]
Share premium	£ 5,620	£ 5,620	£ 5,620	£ 5,620

Share Capital - Additional Info

Share Capital - Additional Information (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure of classes of share capital [abstract]
£325m Sterling preference shares, notional amount	£ 325	£ 325

Other Equity Instruments - Summ

Other Equity Instruments - Summary of Other Equity Instruments (Details)	12 Months Ended
	Dec. 31, 2023 GBP (£)	Dec. 31, 2022 GBP (£)
Disclosure Of Other Equity Instruments [Line Items]
Other equity instruments	£ 1,956,000,000	£ 1,956,000,000
- £500m Perpetual Capital Securities
Disclosure Of Other Equity Instruments [Line Items]
Capital securities	£ 500,000,000	£ 500,000,000
Interest rate	0.0675	0.0675
Other equity interest maturity period	2024-06	2024-06
Other equity instruments	£ 496,000,000	£ 496,000,000
- £500m Perpetual Capital Securities
Disclosure Of Other Equity Instruments [Line Items]
Capital securities	£ 500,000,000	£ 500,000,000
Interest rate	0.0630	0.0630
Other equity interest maturity period	2025-03	2025-03
Other equity instruments	£ 500,000,000	£ 500,000,000
- £210m Perpetual Capital Securities
Disclosure Of Other Equity Instruments [Line Items]
Capital securities	£ 210,000,000	£ 210,000,000
Interest rate	0.0425	0.0425
Other equity interest maturity period	2026-03	2026-03
Other equity instruments	£ 210,000,000	£ 210,000,000
- £750m Perpetual Capital Securities
Disclosure Of Other Equity Instruments [Line Items]
Capital securities	£ 750,000,000	£ 750,000,000
Interest rate	0.0650	0.0650
Other equity interest maturity period	2027-06	2027-06
Other equity instruments	£ 750,000,000	£ 750,000,000

Other Equity Instruments - Addi

Other Equity Instruments - Additional Information (Details) - AT1 Capital Securities	12 Months Ended
	Dec. 31, 2023
Disclosure Of Other Equity Instruments [Line Items]
Distribution rate reset, period	5 years
Common equity tier 1 capital ratio minimum	7%

Notes to Cash Flows - Summary o

Notes to Cash Flows - Summary of Changes in Liabilities Arising from Financing Activities (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	£ 35,944	£ 30,071	£ 40,410
Proceeds from issue of debt securities	4,208	4,778	2,872
Repayment of debt securities	(2,568)	(3,036)	(11,910)
Proceeds from issue of subordinated liabilities	1,050
Repayment of subordinated liabilities	(971)	(40)	(4)
Issue of other equity instruments		750	210
Repurchase of other equity instruments		(985)	(210)
Principal elements of lease payments	(47)	(26)	(25)
Dividends paid	(1,653)	(1,164)	(1,505)
Liability-related other changes	1,062	3,176	(391)
Non-cash changes:
– Unrealised foreign exchange	(673)	1,641	(800)
– Other changes	2,011	779	1,424
Ending balance	38,363	35,944	30,071
Debt securities in issue
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	31,531	25,520	35,566
Proceeds from issue of debt securities	4,208	4,778	2,872
Repayment of debt securities	(2,568)	(3,036)	(11,910)
Liability-related other changes	1,004	3,155	(447)
Non-cash changes:
– Unrealised foreign exchange	(651)	1,554	(806)
– Other changes	386	(440)	245
Ending balance	33,910	31,531	25,520
Subordinated liabilities
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	2,332	2,228	2,556
Proceeds from issue of subordinated liabilities	1,050
Repayment of subordinated liabilities	(971)	(40)	(4)
Liability-related other changes	25	2	(4)
Non-cash changes:
– Unrealised foreign exchange	(22)	87	6
– Other changes	(28)	55	(326)
Ending balance	2,386	2,332	2,228
Other equity instruments
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	1,956	2,191	2,191
Issue of other equity instruments		750	210
Repurchase of other equity instruments		(985)	(210)
Non-cash changes:
Ending balance	1,956	1,956	2,191
Lease liabilities
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	125	132	97
Principal elements of lease payments	(47)	(26)	(25)
Liability-related other changes	33	19	60
Non-cash changes:
Ending balance	111	125	132
Dividends paid
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	0	0	0
Dividends paid	(1,653)	(1,164)	(1,505)
Non-cash changes:
– Other changes	1,653	1,164	1,505
Ending balance	£ 0	£ 0	£ 0

Notes to Cash Flows - Additiona

Notes to Cash Flows - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Cash Flows Explanatory Notes [Line Items]
Interest received	£ 11,395	£ 6,508	£ 4,806
Interest paid	6,326	2,089	1,064
Dividends received	0	0	0
Cash outflow for leases	50	28	28
Disposal of non-controlling interests	£ 0	£ 0	£ 181

Assets Charged as Security fo_3

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets - Financial Assets Charged as Security Under On-Balance Sheet and Off-Balance (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	£ 1,682	£ 1,541
On-balance sheet:
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	54,655	62,029
On-balance sheet: | Cash and balances at central banks
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	1,480	1,330
On-balance sheet: | Loans and advances to banks
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	191	130
On-balance sheet: | Loans and advances to customers | Securitisations and covered bonds
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	27,088	24,155
On-balance sheet: | Loans and advances to customers | Other
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	20,699	32,001
On-balance sheet: | Other financial assets at amortised cost
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	14	48
On-balance sheet: | Financial assets at fair value through other comprehensive income
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	5,183	4,365
Off-balance sheet
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	£ 10,185	£ 9,146

Assets Charged as Security fo_4

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets - Additional Information (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	£ 1,682	£ 1,541
Gross assets charged as security for liabilities	27,927	24,984
Notes issued under securitisation and covered bond programmes retained internally	17,769	16,102
Purchase and resale agreements
Disclosure Of Assets Pledged As Security [Line Items]
Collateral accepted as security for assets	12,982	8,628
Securitisations and covered bonds | Internally retained
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued under securitisation and covered bond programmes retained internally	2,928	1,725
Securitisations and covered bonds | Third party bilateral secured funding transactions
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	1,500	500
Securities lending
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	23,644	34,861
Collateral accepted as security for assets	2,010	1,513
Derivatives | Cash
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	1,726	1,506
Collateral accepted as security for assets	860	1,741
Fellow subsidiaries | Sale and repurchase agreements
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	13,291	11,553
Fellow subsidiaries | Loans and advances to customers securitisations and covered bonds
Disclosure Of Assets Pledged As Security [Line Items]
Notes issued as collateral	909	900
Santander UK Plc | Securitisations and covered bonds | Internally retained
Disclosure Of Assets Pledged As Security [Line Items]
Internally retained securitisation and covered bond issuances available for creating collateral	£ 839	£ 829

Assets Charged as Security fo_5

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets - Schedule of Collateral Held as Security for Assets (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
On-balance sheet:
Disclosure Of Assets Pledged As Security [Line Items]
Total on-balance sheet/ off-balance sheet	£ 860	£ 1,741
On-balance sheet: | Deposits by banks
Disclosure Of Assets Pledged As Security [Line Items]
Total on-balance sheet/ off-balance sheet	860	1,741
Off-balance sheet
Disclosure Of Assets Pledged As Security [Line Items]
Total on-balance sheet/ off-balance sheet	£ 14,992	£ 10,141

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Details)	12 Months Ended		180 Months Ended
	Dec. 31, 2023 GBP (£) £ / shares shares	Dec. 31, 2022 GBP (£) £ / shares shares	Dec. 31, 2022 GBP (£) invitation
Disclosure of terms and conditions of share-based payment arrangement [line items]
Liabilities arising from share-based payment transactions	£ 14,700,000	£ 6,600,000	£ 6,600,000
Liabilities arising from share-based payment transactions, vested liabilities	1,100,000	£ 100,000	£ 100,000
Number of sharesave schemes launched | invitation			16
Employee saving on share based compensation	£ 500,000
Price determination period for options	3 days
Maximum discount applicable	20%
Actual discount applied	10%
Expiration term of vested options	6 months
Weighted average share price (GBP per share) | £ / shares	£ 3.22	£ 2.34
Weighted average grant-date fair value (GBP per share)	£ 0.33	£ 0.23	£ 0.23
Number of shares outstanding | shares	3,937,473	3,974,698
Material Risk Takers
Disclosure of terms and conditions of share-based payment arrangement [line items]
Additional retention period for deferred bonus awards	1 year
Share Incentive Plans
Disclosure of terms and conditions of share-based payment arrangement [line items]
Maximum investment value per tax year	£ 1,800
Percentage of maximum salary that can be invested	10%
Transformation Incentive Plan
Disclosure of terms and conditions of share-based payment arrangement [line items]
Liabilities arising from share-based payment transactions	£ 3,800,000	£ 1,800,000	£ 1,800,000
Value of awards granted	£ 1,300,000	£ 1,000,000
Shares | Material Risk Takers Option 1
Disclosure of terms and conditions of share-based payment arrangement [line items]
Annual bonus percentage	50%
Cash | Material Risk Takers Option 1
Disclosure of terms and conditions of share-based payment arrangement [line items]
Annual bonus percentage	50%
Minimum
Disclosure of terms and conditions of share-based payment arrangement [line items]
Employee saving on share based compensation	£ 5
Terms of options	3 years
Minimum | Share Incentive Plans
Disclosure of terms and conditions of share-based payment arrangement [line items]
Minimum retention period to sell shares free of income tax	5 years
Maximum
Disclosure of terms and conditions of share-based payment arrangement [line items]
Employee saving on share based compensation	£ 500
Terms of options	5 years
Variable pay of less than 500,000 | Material Risk Takers
Disclosure of terms and conditions of share-based payment arrangement [line items]
Percentage of defer annual bonus	40%
Variable pay at or above 500,000 | Material Risk Takers
Disclosure of terms and conditions of share-based payment arrangement [line items]
Percentage of defer annual bonus	60%
Period one | Material Risk Takers
Disclosure of terms and conditions of share-based payment arrangement [line items]
Deferral period from anniversary of initial award	4 years
Period two | Material Risk Takers
Disclosure of terms and conditions of share-based payment arrangement [line items]
Deferral period from anniversary of initial award	5 years
Period three | Material Risk Takers
Disclosure of terms and conditions of share-based payment arrangement [line items]
Deferral period from anniversary of initial award	7 years

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Movement in Share Options (Details) - Sharesave Schemes number in Thousands	12 Months Ended
	Dec. 31, 2023 £ / shares	Dec. 31, 2022 £ / shares
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options outstanding, beginning balance (in shares)	29,988	25,993
Number of options granted (in shares)	7,175	13,068
Number of options exercised (in shares)	(5,980)	(242)
Number of options forfeited/expired (in shares)	(4,044)	(8,831)
Number of options outstanding, ending balance (in shares)	27,139	29,988
Number of options exercisable (in shares)	868	3,439
Weighted average exercise price outstanding, beginning balance	£ 2	£ 2.25
Weighted average exercise price granted	2.78	1.89
Weighted average exercise price exercised	1.70	1.69
Weighted average exercise price forfeited/expired	2.53	2.59
Weighted average exercise price outstanding, ending balance	2.19	2
Weighted average exercise price exercisable	£ 1.84	£ 3.22

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Range of Exercise Prices and Weighted Average Remaining Contractual Life of the Options Outstanding (Details) - Sharesave Schemes - £ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Weighted average exercise price (in GBP per share)	£ 2.19	£ 2	£ 2.25
£1 to £2
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Weighted average remaining contractual life	3 years	3 years
Weighted average exercise price (in GBP per share)	£ 1.84	£ 1.79
£2 to £3
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Weighted average remaining contractual life	3 years	2 years
Weighted average exercise price (in GBP per share)	£ 2.65	£ 2.56
£3 to £4
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Weighted average remaining contractual life	0 years	1 year
Weighted average exercise price (in GBP per share)	£ 3.46	£ 3.46
£4 to £5
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Weighted average remaining contractual life	0 years	0 years
Weighted average exercise price (in GBP per share)	£ 0	£ 4.02
Minimum | £1 to £2
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	1
Minimum | £2 to £3
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	2
Minimum | £3 to £4
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	3
Minimum | £4 to £5
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	4
Maximum | £1 to £2
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	2
Maximum | £2 to £3
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	3
Maximum | £3 to £4
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	4
Maximum | £4 to £5
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	£ 5

Transactions with Directors a_3

Transactions with Directors and Other Key Management Personnel - Summary of Remuneration of the Directors and Other Key Management Personnel (Details)	12 Months Ended
	Dec. 31, 2023 GBP (£)	Dec. 31, 2022 GBP (£) individual	Dec. 31, 2021 GBP (£) individual
Disclosure Of Directors And Key Management Remuneration [Line Items]
Salaries and fees	£ 4,733,761	£ 4,696,699	£ 5,488,388
Performance-related payments	1,002,607	3,701,569	3,431,294
Other fixed remuneration (pension and other allowances & non-cash benefits)	222,538	906,201	929,935
Expenses	0	27,715	17,097
Total remuneration	5,958,906	9,332,184	9,866,714
Compensation for loss of office	0	1,713,256	356,054
Short-term employee benefits	18,449,360	22,627,595	20,553,672
Post-employment benefits	858,437	1,026,848	988,829
Total compensation	19,307,797	£ 25,367,699	£ 21,898,555
Number key management persons who receives termination benefit | individual		3
Number of Directors who received termination payment | individual		2	2
Director
Disclosure Of Directors And Key Management Remuneration [Line Items]
Compensation for loss of office	£ 0	£ 172,856	£ 356,054
Key Management Personnel
Disclosure Of Directors And Key Management Remuneration [Line Items]
Compensation for loss of office		£ 1,540,400

Transactions with Directors a_4

Transactions with Directors and Other Key Management Personnel - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 GBP (£) director transaction	Dec. 31, 2022 GBP (£) director transaction	Dec. 31, 2021 GBP (£)
Disclosure Of Directors And Key Management Remuneration [Line Items]
Remuneration excluding pension contribution | £	£ 2,640,491	£ 3,510,441	£ 3,740,810
Remuneration excluding pension contribution performance related | £	1,002,607	1,900,506	1,864,320
Accrued defined benefit pension related highest paid director | £	£ 0	0	22,119
Directors with a deferred pension benefit accruing under a defined benefit scheme	0
Ex gratia pensions paid to former Directors | £	£ 327,462	£ 379,945	£ 370,668
Directors who held any interest in the shares	0	0
Directors who exercised or were granted any rights to subscribe for shares	0	0
Directors who exercised share options over shares in Banco Santander	0	0
Number of loan made to directors	2	6
Loans made to directors | £	£ 495,281	£ 540,450
Number of other transactions, arrangements or agreements with material interest | transaction	0	0
Number of Directors undertook sharedealing transactions	0	0
Other key management personnel
Disclosure Of Directors And Key Management Remuneration [Line Items]
Number of loan made to key management personnel	6	4
Loans made to key management personnel | £	£ 579,383	£ 330,972

Transactions with Directors a_5

Transactions with Directors and Other Key Management Personnel - Summary of Transactions with Directors, Other Key Management Personnel (Details) - Key Management Personnel £ in Thousands	12 Months Ended
	Dec. 31, 2023 GBP (£) deposits loans	Dec. 31, 2022 GBP (£) loans deposits
Disclosure Of Directors And Key Management Remuneration [Line Items]
Number of secured loans, unsecured loans and overdrafts, beginning balance | loans	10	6
Number of secured loans, unsecured loans and overdrafts, net movements | loans	(2)	4
Number of secured loans, unsecured loans and overdrafts, ending balance | loans	8	10
Beginning balance	£ 871	£ 360
Net movements	204	511
Ending balance	£ 1,075	£ 871
Number of deposit, bank and instant access accounts and investments, beginning balance | deposits	23	21
Number of deposit, bank and instant access accounts and investments, net movements | deposits	(6)	2
Number of deposit, bank and instant access accounts and investments, ending balance | deposits	17	23
Beginning balance	£ 4,133	£ 6,552
Net movements	(2,431)	(2,419)
Ending balance	£ 1,702	£ 4,133

Related Party Disclosures - Sum

Related Party Disclosures - Summary of Transactions With Related Parties (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	£ (236)	£ (861)	£ (261)
Interest, fees and other expenses paid	1,176	549	463
Amounts owed by related parties	5,387	5,623
Amounts owed to related parties	(15,492)	(17,384)
Ultimate parent
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(8)	(710)	(164)
Interest, fees and other expenses paid	414	47	33
Amounts owed by related parties	800	1,363
Amounts owed to related parties	(1,062)	(1,673)
Immediate parent
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(7)	(6)	(6)
Interest, fees and other expenses paid	504	308	263
Amounts owed by related parties	0	1
Amounts owed to related parties	(13,279)	(14,390)
Fellow subsidiaries
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(38)	(69)	(57)
Interest, fees and other expenses paid	203	177	163
Amounts owed by related parties	101	108
Amounts owed to related parties	(370)	(348)
Joint ventures
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(183)	(76)	(34)
Interest, fees and other expenses paid	55	17	£ 4
Amounts owed by related parties	4,486	4,151
Amounts owed to related parties	£ (781)	£ (973)

Related Party Disclosures - Add

Related Party Disclosures - Additional Information (Details) - GBP (£) £ in Millions	1 Months Ended	12 Months Ended
	May 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Nov. 30, 2022	Dec. 31, 2021
Unsecured committed liquidity facility
Disclosure of transactions between related parties [line items]
Borrowings				£ 600
Santander UK Investments
Disclosure of transactions between related parties [line items]
Rental expense		£ 9	£ 6
Santander Financial Services PLC | Mortgages
Disclosure of transactions between related parties [line items]
Book value of financial assets transferred	£ 624
Proceeds from transfer of financial assets	631
Price premium on transfer of financial assets	£ 7
Santander Consumer (UK) | PSA Finance UK Limited
Disclosure of transactions between related parties [line items]
Proportion of ownership interest in subsidiary sold					50%

Financial Instruments - Disclos

Financial Instruments - Disclosure of Analysis of Fair Value of Financial Instruments Carried at Amortised Cost (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to customers	£ 207,435	£ 219,716
Loans and advances to banks	1,080	992
Reverse repurchase agreements - non trading	12,468	7,348
Other financial assets at amortised cost	152	156
Deposits by customers	190,850	195,568
Deposits by banks	20,332	28,525
Repurchase agreements - non trading	8,411	7,982
Debt securities in issue	33,910	31,531
Subordinated liabilities	2,386	2,332
Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial liabilities	255,889	265,938
Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial assets	221,135	228,212
Deposits by customers | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by customers	190,850	195,568
Deposits by banks | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by banks	20,332	28,525
Repurchase agreements - non trading | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Repurchase agreements - non trading	8,411	7,982
Debt securities in issue | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Debt securities in issue	33,910	31,531
Subordinated liabilities | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Subordinated liabilities	2,386	2,332
Loans and advances to customers | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to customers	207,435	219,716
Loans and advances to banks | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to banks	1,080	992
Reverse repurchase agreements – non trading | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Reverse repurchase agreements - non trading	12,468	7,348
Other financial assets at amortised cost | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Other financial assets at amortised cost	152	156
Level 1 | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial liabilities	1,689	2,593
Level 1 | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial assets	144	144
Level 1 | Deposits by customers | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by customers	0	0
Level 1 | Deposits by banks | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by banks	0	0
Level 1 | Repurchase agreements - non trading | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Repurchase agreements - non trading	0	0
Level 1 | Debt securities in issue | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Debt securities in issue	1,689	2,574
Level 1 | Subordinated liabilities | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Subordinated liabilities	0	19
Level 1 | Loans and advances to customers | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to customers	0	0
Level 1 | Loans and advances to banks | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to banks	0	0
Level 1 | Reverse repurchase agreements – non trading | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Reverse repurchase agreements - non trading	0	0
Level 1 | Other financial assets at amortised cost | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Other financial assets at amortised cost	144	144
Level 2 | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial liabilities	62,160	64,719
Level 2 | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial assets	13,550	8,333
Level 2 | Deposits by customers | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by customers	71	51
Level 2 | Deposits by banks | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by banks	20,342	27,979
Level 2 | Repurchase agreements - non trading | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Repurchase agreements - non trading	8,413	7,982
Level 2 | Debt securities in issue | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Debt securities in issue	30,743	26,349
Level 2 | Subordinated liabilities | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Subordinated liabilities	2,591	2,358
Level 2 | Loans and advances to customers | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to customers	0	0
Level 2 | Loans and advances to banks | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to banks	1,080	992
Level 2 | Reverse repurchase agreements – non trading | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Reverse repurchase agreements - non trading	12,470	7,341
Level 2 | Other financial assets at amortised cost | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Other financial assets at amortised cost	0	0
Level 3 | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial liabilities	191,999	197,344
Level 3 | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial assets	205,917	212,479
Level 3 | Deposits by customers | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by customers	190,561	195,483
Level 3 | Deposits by banks | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by banks	40	55
Level 3 | Repurchase agreements - non trading | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Repurchase agreements - non trading	0	0
Level 3 | Debt securities in issue | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Debt securities in issue	1,189	1,582
Level 3 | Subordinated liabilities | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Subordinated liabilities	209	224
Level 3 | Loans and advances to customers | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to customers	205,917	212,479
Level 3 | Loans and advances to banks | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to banks	0	0
Level 3 | Reverse repurchase agreements – non trading | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Reverse repurchase agreements - non trading	0	0
Level 3 | Other financial assets at amortised cost | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Other financial assets at amortised cost	0	0
Fair value | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial liabilities	255,848	264,656
Fair value | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial assets	219,611	220,956
Fair value | Deposits by customers | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by customers	190,632	195,534
Fair value | Deposits by banks | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by banks	20,382	28,034
Fair value | Repurchase agreements - non trading | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Repurchase agreements - non trading	8,413	7,982
Fair value | Debt securities in issue | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Debt securities in issue	33,621	30,505
Fair value | Subordinated liabilities | Financial liabilities at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Subordinated liabilities	2,800	2,601
Fair value | Loans and advances to customers | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to customers	205,917	212,479
Fair value | Loans and advances to banks | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to banks	1,080	992
Fair value | Reverse repurchase agreements – non trading | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Reverse repurchase agreements - non trading	12,470	7,341
Fair value | Other financial assets at amortised cost | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Other financial assets at amortised cost	£ 144	£ 144

Financial Instruments - Discl_2

Financial Instruments - Disclosure of Analysis of Fair Value of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 10,175	£ 8,560
Liabilities at fair value	1,717	1,754
Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	818	951
Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	899	803
Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	1,432	2,407
Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	262	129
Financial assets at FVOCI
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	8,481	6,024
Level 1
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	8,293	5,996
Liabilities at fair value	0	0
Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	0	0
Level 1 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	0	0
Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Level 1 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Level 1 | Financial assets at FVOCI
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	8,293	5,996
Level 2
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	1,751	2,410
Liabilities at fair value	1,707	1,739
Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	808	939
Level 2 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	899	800
Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	1,396	2,370
Level 2 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	167	12
Level 2 | Financial assets at FVOCI
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	188	28
Level 3
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	131	154
Liabilities at fair value	10	15
Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	10	12
Level 3 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	0	3
Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	36	37
Level 3 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	95	117
Level 3 | Financial assets at FVOCI
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Exchange rate contracts | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 508	471
Valuation technique	A
Exchange rate contracts | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 1,129	2,044
Valuation technique	A
Exchange rate contracts | Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 0	0
Exchange rate contracts | Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Exchange rate contracts | Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	508	471
Exchange rate contracts | Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	1,129	2,044
Exchange rate contracts | Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	0	0
Exchange rate contracts | Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Interest rate contracts | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 2,337	2,628
Valuation technique	A & C
Interest rate contracts | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 2,217	2,406
Valuation technique	A & C
Interest rate contracts | Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 0	0
Interest rate contracts | Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Interest rate contracts | Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	2,336	2,624
Interest rate contracts | Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	2,216	2,399
Interest rate contracts | Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	1	4
Interest rate contracts | Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	1	7
Equity and credit contracts
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	35	30
Equity and credit contracts | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 20	25
Valuation technique	B & D
Equity and credit contracts | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 133	130
Valuation technique	B & D
Equity and credit contracts | Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 0	0
Equity and credit contracts | Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Equity and credit contracts | Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	11	17
Equity and credit contracts | Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	98	100
Equity and credit contracts | Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	9	8
Equity and credit contracts | Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	35	30
Netting | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	(2,047)	(2,173)
Netting | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	(2,047)	(2,173)
Netting | Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	0	0
Netting | Level 1 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Netting | Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	(2,047)	(2,173)
Netting | Level 2 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	(2,047)	(2,173)
Netting | Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	0	0
Netting | Level 3 | Derivative financial instruments
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Loans and advances to customers | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 46	45
Valuation technique	A
Loans and advances to customers | Level 1 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 0	0
Loans and advances to customers | Level 2 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Loans and advances to customers | Level 3 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	46	45
Debt securities | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 216	84
Valuation technique	A, B & D
Debt securities | Financial assets at FVOCI
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 8,481	6,024
Valuation technique	D
Debt securities | Level 1 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	£ 0	0
Debt securities | Level 1 | Financial assets at FVOCI
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	8,293	5,996
Debt securities | Level 2 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	167	12
Debt securities | Level 2 | Financial assets at FVOCI
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	188	28
Debt securities | Level 3 | Other financial assets at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	49	72
Debt securities | Level 3 | Financial assets at FVOCI
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Assets at fair value	0	0
Debt securities in issue | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 369	375
Valuation technique	A
Debt securities in issue | Level 1 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 0	0
Debt securities in issue | Level 2 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	369	372
Debt securities in issue | Level 3 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	0	3
Structured deposits | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 426	321
Valuation technique	A
Structured deposits | Level 1 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 0	0
Structured deposits | Level 2 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	426	321
Structured deposits | Level 3 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	0	0
Zero Amortising Guaranteed Notes | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 104	107
Valuation technique	D
Zero Amortising Guaranteed Notes | Level 1 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 0	0
Zero Amortising Guaranteed Notes | Level 2 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	104	107
Zero Amortising Guaranteed Notes | Level 3 | Other financial liabilities at FVTPL
Disclosure Of Fair Value Measurements Of Assets And Liabilities [Line Items]
Liabilities at fair value	£ 0	£ 0

Financial Instruments - Additio

Financial Instruments - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Assets
Transfers out of Level 1 into Level 2 of fair value hierarchy, assets held at end of reporting period	£ 22	£ 0
Transfers out of Level 2 into Level 1 of fair value hierarchy, assets held at end of reporting period	22	0
Transfers in	22	0
Transfers out	(22)	0
Liabilities
Transfers out of Level 1 into Level 2 of fair value hierarchy, liabilities held at end of reporting period	22	0
Transfers out of Level 2 into Level 1 of fair value hierarchy, liabilities held at end of reporting period	22	0
Transfers into Level 3 of fair value hierarchy, liabilities	22	0
Transfers out	£ 22	£ 0

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value Adjustment (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of financial assets [line items]
Fair value adjustments	£ 3	£ 4
Risk-related
Disclosure of financial assets [line items]
Fair value adjustments	2	3
Day One profit
Disclosure of financial assets [line items]
Fair value adjustments	1	1
- Bid-offer and trade specific adjustments | Risk-related
Disclosure of financial assets [line items]
Fair value adjustments	(6)	(12)
- Uncertainty | Risk-related
Disclosure of financial assets [line items]
Fair value adjustments	6	12
- Credit risk adjustment | Risk-related
Disclosure of financial assets [line items]
Fair value adjustments	1	2
- Funding fair value adjustment | Risk-related
Disclosure of financial assets [line items]
Fair value adjustments	£ 1	£ 1

Financial Instruments - Discl_3

Financial Instruments - Disclosure of Analysis of Financial Instruments Valued Using Internal Models Based on Information Other than Market Data (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure Of Financial Assets And Liabilities [Line Items]
Derivative financial instruments	£ 1,432	£ 2,407
FVTPL assets	262	129
Total net assets	121	139
Total income/(expense)	8	(17)	£ (4)
Level 3
Disclosure Of Financial Assets And Liabilities [Line Items]
Financial assets	130	145
Financial asset liabilities	11	(30)	(2)
Other Level 3 | Level 3
Disclosure Of Financial Assets And Liabilities [Line Items]
Other Level 3 assets	1	9
Other Level 3 liabilities	(10)	(15)
Fair value movements	(1)	10	(9)
Fair value movements	(2)	3	7
Reversionary property interests | Equity and credit contracts
Disclosure Of Financial Assets And Liabilities [Line Items]
Derivative financial instruments	35	30
Fair value movements	12	(8)	0
Reversionary property interests | Debt securities
Disclosure Of Financial Assets And Liabilities [Line Items]
FVTPL assets	49	70
Fair value movements	(3)	0	5
Roll-up mortgage portfolio | Loans and advances to customers
Disclosure Of Financial Assets And Liabilities [Line Items]
FVTPL assets	24	28
Fair value movements	(2)	(18)	(5)
Other loans | Loans and advances to customers
Disclosure Of Financial Assets And Liabilities [Line Items]
FVTPL assets	22	17
Fair value movements	£ 4	£ (4)	£ (2)

Financial Instruments - Summa_2

Financial Instruments - Summary of Reconciliation of Fair Value Measurement in Level 3 of the Fair Value Hierarchy (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disclosure of financial assets [line items]
Beginning balance	£ 285,213
Beginning balance	(270,806)
Transfers in	22	£ 0
Transfers in	(22)	0
Ending Balance	275,448	285,213
Ending Balance	(260,825)	(270,806)
Level 3 | Other financial liabilities at FVTPL
Disclosure of financial assets [line items]
Beginning balance	(3)	(6)
Fair value movements	0	1
Transfers in		0
Purchases	0
Netting	0	0
Sales		0
Settlements	3	2
Ending Balance	0	(3)
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period	0	1
Level 3 | Financial liabilities at fair value
Disclosure of financial assets [line items]
Beginning balance	(15)	(38)
Fair value movements	(2)	3
Transfers in		(2)
Purchases	0
Netting	0	0
Sales		0
Settlements	7	22
Ending Balance	(10)	(15)
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period	(2)	3
Level 3 | Derivative liabilities
Disclosure of financial assets [line items]
Beginning balance	(12)	(32)
Fair value movements	(2)	2
Transfers in		(2)
Purchases	0
Netting	0	0
Sales		0
Settlements	4	20
Ending Balance	(10)	(12)
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period	(2)	2
Level 3 | Other financial assets at FVTPL
Disclosure of financial assets [line items]
Beginning balance	117	185
Fair value movements	0	(18)
Transfers in		0
Purchases	1
Netting	(3)	(8)
Sales		(5)
Settlements	(20)	(37)
Ending Balance	95	117
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period	0	(18)
Level 3 | Financial assets at FVOCI
Disclosure of financial assets [line items]
Beginning balance	0	18
Fair value movements	0	0
Transfers in		0
Purchases	0
Netting	0	0
Sales		0
Settlements	0	(18)
Ending Balance	0	0
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period	0	0
Level 3 | Financial assets at fair value
Disclosure of financial assets [line items]
Beginning balance	154	249
Fair value movements	10	(20)
Transfers in		0
Purchases	1
Netting	(3)	(8)
Sales		(5)
Settlements	(31)	(62)
Ending Balance	131	154
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period	10	(20)
Derivatives | Level 3
Disclosure of financial assets [line items]
Beginning balance	37	46
Fair value movements	10	(2)
Transfers in		0
Purchases	0
Netting	0	0
Sales		0
Settlements	(11)	(7)
Ending Balance	36	37
Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period	£ 10	£ (2)

Financial Instruments - Discl_4

Financial Instruments - Disclosure of Effects of Changes in Significant Unobservable Assumptions to Reasonably Possible Alternatives Level Three (Details) £ in Millions	12 Months Ended
	Dec. 31, 2023 GBP (£) index	Dec. 31, 2022 GBP (£) index
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assets at fair value	£ 10,175	£ 8,560
Liabilities at fair value	(1,717)	(1,754)
Equity and credit contracts
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assets at fair value	£ 35	£ 30
Assumption description	HPI Forward growth rate	HPI Forward growth rate
Shift	1%	1%
Favourable changes	£ 2	£ 4
Unfavourable changes	£ (2)	£ (4)
Equity and credit contracts | Reversionary property derivatives
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Shift	10%	10%
Favourable changes	£ 2	£ 4
Unfavourable changes	£ (4)	(4)
Equity securities
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Liabilities at fair value		£ (8)
Assumption description		HPI Forward growth rate
Shift		1%
Favourable changes		£ 1
Unfavourable changes		£ (1)
Equity securities | Property Related Options And Forwards [member]
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Shift		10%
Favourable changes		£ 2
Unfavourable changes		£ (3)
Weighted average | Equity and credit contracts
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	(0.20%)	0.53%
Weighted average | Equity and credit contracts | Reversionary property derivatives
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
HPI spot rate index level | index	513	513
Weighted average | Equity securities
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value		(0.92%)
Weighted average | Equity securities | Property Related Options And Forwards [member]
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
HPI spot rate index level | index		491
Minimum | Equity and credit contracts
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	(5.00%)	(5.00%)
Minimum | Equity securities
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value		(5.00%)
Maximum | Equity and credit contracts
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	5%	5%
Maximum | Equity securities
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value		5%
Other financial assets at FVTPL | Loans and advances to customers | Roll-up mortgage portfolio
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assets at fair value	£ 24	£ 28
Assumption description	HPI Forward growth rate	HPI Forward growth rate
Shift	1%	1%
Favourable changes	£ 0	£ 1
Unfavourable changes	0	(1)
Other financial assets at FVTPL | Loans and advances to customers | Other loans
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assets at fair value	£ 22	£ 17
Assumption description	Credit spreads	Credit spreads
Shift	20%	20%
Favourable changes	£ 0	£ 0
Unfavourable changes	0	0
Other financial assets at FVTPL | Debt securities in issue
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assets at fair value	£ 49	£ 70
Assumption description	HPI Forward growth rate	HPI Forward growth rate
Shift	1%	1%
Favourable changes	£ 0	£ 1
Unfavourable changes	£ 0	£ (1)
Other financial assets at FVTPL | Debt securities in issue | Reversionary property securities
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Shift	10%	10%
Favourable changes	£ 2	£ 3
Unfavourable changes	£ (2)	£ (3)
Other financial assets at FVTPL | Weighted average | Loans and advances to customers | Roll-up mortgage portfolio
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	1.31%	1.39%
Other financial assets at FVTPL | Weighted average | Loans and advances to customers | Other loans
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	0.97%	0.98%
Other financial assets at FVTPL | Weighted average | Debt securities in issue
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	(0.20%)	0.53%
Other financial assets at FVTPL | Weighted average | Debt securities in issue | Reversionary property securities
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
HPI spot rate index level | index	513	513
Other financial assets at FVTPL | Minimum | Loans and advances to customers | Roll-up mortgage portfolio
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	(5.00%)	(5.00%)
Other financial assets at FVTPL | Minimum | Loans and advances to customers | Other loans
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	0.13%	0.19%
Other financial assets at FVTPL | Minimum | Debt securities in issue
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	(5.00%)	(5.00%)
Other financial assets at FVTPL | Maximum | Loans and advances to customers | Roll-up mortgage portfolio
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	5%	5%
Other financial assets at FVTPL | Maximum | Loans and advances to customers | Other loans
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	2.54%	2.04%
Other financial assets at FVTPL | Maximum | Debt securities in issue
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assumption value	5%	5%
Financial assets at FVOCI
Effect Of Changes In Significant Unobservable Assumptions To Reasonably Possible Alternatives - Level 3 [Line Items]
Assets at fair value	£ 8,481	£ 6,024

Financial Instruments - Discl_5

Financial Instruments - Disclosure of Maturity Analysis of Undiscounted Cash Flows for Financial Liabilities and Off Balance Sheet Commitments (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Maturity Analysis For Financial Liabilities [Line Items]
Other financial liabilities at fair value through profit or loss	£ 899	£ 803
Deposits by customers	190,850	195,568
Deposits by banks	20,332	28,525
Repurchase agreements - non trading	8,411	7,982
Debt securities in issue	33,910	31,531
Subordinated liabilities	2,386	2,332
Lease liabilities	111	125
Undiscounted Cash Flow
Disclosure Of Maturity Analysis For Financial Liabilities [Line Items]
Derivative financial instruments	906	1,077
Other financial liabilities at fair value through profit or loss	1,073	979
Deposits by customers	191,374	195,800
Deposits by banks	21,860	29,796
Repurchase agreements - non trading	8,426	7,987
Debt securities in issue	40,533	33,892
Subordinated liabilities	3,456	3,275
Lease liabilities	122	138
Total financial liabilities	267,750	272,944
Off-balance sheet commitments given	31,428	31,836
Undiscounted Cash Flow | On demand
Disclosure Of Maturity Analysis For Financial Liabilities [Line Items]
Derivative financial instruments	1	0
Other financial liabilities at fair value through profit or loss	0	0
Deposits by customers	179,732	180,218
Deposits by banks	1,454	2,048
Repurchase agreements - non trading	0	0
Debt securities in issue	0	0
Subordinated liabilities	0	0
Lease liabilities	0	0
Total financial liabilities	181,187	182,266
Off-balance sheet commitments given	3,795	19,089
Undiscounted Cash Flow | Not later than 3 months
Disclosure Of Maturity Analysis For Financial Liabilities [Line Items]
Derivative financial instruments	192	206
Other financial liabilities at fair value through profit or loss	8	0
Deposits by customers	3,217	3,875
Deposits by banks	1,749	1,309
Repurchase agreements - non trading	8,418	7,984
Debt securities in issue	6,380	5,814
Subordinated liabilities	27	35
Lease liabilities	0	0
Total financial liabilities	19,991	19,223
Off-balance sheet commitments given	15,205	787
Undiscounted Cash Flow | Later than 3 months and not later than 1 year
Disclosure Of Maturity Analysis For Financial Liabilities [Line Items]
Derivative financial instruments	52	120
Other financial liabilities at fair value through profit or loss	7	98
Deposits by customers	3,447	7,077
Deposits by banks	573	298
Repurchase agreements - non trading	8	3
Debt securities in issue	4,908	1,485
Subordinated liabilities	83	691
Lease liabilities	29	32
Total financial liabilities	9,107	9,804
Off-balance sheet commitments given	1,408	898
Undiscounted Cash Flow | Later than 1 year and not later than 5 years
Disclosure Of Maturity Analysis For Financial Liabilities [Line Items]
Derivative financial instruments	478	496
Other financial liabilities at fair value through profit or loss	538	443
Deposits by customers	4,690	4,295
Deposits by banks	18,084	26,141
Repurchase agreements - non trading	0	0
Debt securities in issue	17,029	16,672
Subordinated liabilities	876	1,149
Lease liabilities	70	80
Total financial liabilities	41,765	49,276
Off-balance sheet commitments given	7,399	7,508
Undiscounted Cash Flow | Later than five years
Disclosure Of Maturity Analysis For Financial Liabilities [Line Items]
Derivative financial instruments	183	255
Other financial liabilities at fair value through profit or loss	520	438
Deposits by customers	288	335
Deposits by banks	0	0
Repurchase agreements - non trading	0	0
Debt securities in issue	12,216	9,921
Subordinated liabilities	2,470	1,400
Lease liabilities	23	26
Total financial liabilities	15,700	12,375
Off-balance sheet commitments given	£ 3,621	£ 3,554

Offsetting Financial Assets a_3

Offsetting Financial Assets and Liabilities (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Offsetting Of Financial Assets And Liabilities [Line Items]
Gross amounts, Assets	£ 24,417	£ 18,520
Amounts offset, Assets	(5,994)	(4,559)
Net amounts reported on the balance sheet, Assets	18,423	13,961
Financial instruments, Assets	(589)	(524)
Financial collateral, Assets	(13,173)	(9,059)
Net amount, Assets	4,661	4,378
Assets not subject to enforceable netting arrangements, Assets	203,992	216,502
Balance sheet total, Assets	222,415	230,463
Gross amounts, Liabilities	18,624	20,622
Amounts offset, Liabilities	(5,994)	(4,559)
Net amounts reported on the balance sheet, Liabilities	12,630	16,063
Financial instruments, Liabilities	(589)	(524)
Financial collateral, Liabilities	(8,454)	(8,088)
Net amount, Liabilities	3,587	7,451
Assets not subject to enforceable netting arrangements, Liabilities	207,781	216,963
Balance sheet total, Liabilities	220,411	233,026
Derivative financial instruments
Disclosure Of Offsetting Of Financial Assets And Liabilities [Line Items]
Gross amounts, Assets	3,429	4,525
Amounts offset, Assets	(2,047)	(2,173)
Net amounts reported on the balance sheet, Assets	1,382	2,352
Financial instruments, Assets	(471)	(515)
Financial collateral, Assets	(823)	(1,720)
Net amount, Assets	88	117
Assets not subject to enforceable netting arrangements, Assets	50	55
Balance sheet total, Assets	1,432	2,407
Amortised cost
Disclosure Of Offsetting Of Financial Assets And Liabilities [Line Items]
Gross amounts, Assets	15,625	8,826
Amounts offset, Assets	(3,157)	(1,478)
Net amounts reported on the balance sheet, Assets	12,468	7,348
Financial instruments, Assets	(118)	(9)
Financial collateral, Assets	(12,350)	(7,339)
Net amount, Assets	0	0
Assets not subject to enforceable netting arrangements, Assets	0	0
Balance sheet total, Assets	12,468	7,348
Gross amounts, Liabilities	11,568	9,460
Amounts offset, Liabilities	(3,157)	(1,478)
Net amounts reported on the balance sheet, Liabilities	8,411	7,982
Financial instruments, Liabilities	(118)	(9)
Financial collateral, Liabilities	(8,293)	(7,973)
Net amount, Liabilities	0	0
Assets not subject to enforceable netting arrangements, Liabilities	0	0
Balance sheet total, Liabilities	8,411	7,982
Loans and advances to customers
Disclosure Of Offsetting Of Financial Assets And Liabilities [Line Items]
Gross amounts, Assets	5,363	5,169
Amounts offset, Assets	(790)	(908)
Net amounts reported on the balance sheet, Assets	4,573	4,261
Financial instruments, Assets	0	0
Financial collateral, Assets	0	0
Net amount, Assets	4,573	4,261
Assets not subject to enforceable netting arrangements, Assets	203,942	216,447
Balance sheet total, Assets	208,515	220,708
Derivative financial liabilities
Disclosure Of Offsetting Of Financial Assets And Liabilities [Line Items]
Gross amounts, Liabilities	2,838	3,085
Amounts offset, Liabilities	(2,047)	(2,173)
Net amounts reported on the balance sheet, Liabilities	791	912
Financial instruments, Liabilities	(471)	(515)
Financial collateral, Liabilities	(161)	(115)
Net amount, Liabilities	159	282
Assets not subject to enforceable netting arrangements, Liabilities	27	39
Balance sheet total, Liabilities	818	951
Deposits by customers and banks
Disclosure Of Offsetting Of Financial Assets And Liabilities [Line Items]
Gross amounts, Liabilities	4,218	8,077
Amounts offset, Liabilities	(790)	(908)
Net amounts reported on the balance sheet, Liabilities	3,428	7,169
Financial instruments, Liabilities	0	0
Financial collateral, Liabilities	0	0
Net amount, Liabilities	3,428	7,169
Assets not subject to enforceable netting arrangements, Liabilities	207,754	216,924
Balance sheet total, Liabilities	£ 211,182	£ 224,093

Interest Rate Benchmark Refor_2

Interest Rate Benchmark Reform - Schedule of Amounts Affected by IBOR Reform (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Assets
Derivative financial instruments	£ 1,432	£ 2,407
Total assets	275,448	285,213
Liabilities
Derivative financial instruments	818	951
Total liabilities	260,825	270,806
Total
Assets
Derivative financial instruments		1,665
Financial assets at amortised cost	6	133
Total assets	6	1,798
Liabilities
Derivative financial instruments		1,912
Total liabilities		1,912
Off-balance sheet commitments given		2
GBP LIBOR
Assets
Derivative financial instruments		0
Financial assets at amortised cost	6	76
Total assets	6	76
Liabilities
Derivative financial instruments		66
Total liabilities		66
Off-balance sheet commitments given		2
USD LIBOR
Assets
Derivative financial instruments		1,665
Financial assets at amortised cost	0	57
Total assets	£ 0	1,722
Liabilities
Derivative financial instruments		1,846
Total liabilities		1,846
Off-balance sheet commitments given		£ 0

Discontinued Operations and A_3

Discontinued Operations and Assets and Liabilities Held for Sale - Disclosure of Financial Performance Relating to Discontinued Operations (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of analysis of single amount of discontinued operations [line items]
Net interest income	£ 4,658	£ 4,425	£ 3,949
Net fee and commission income	303	330	286
Other operating income	135	201	264
Total operating income	5,096	4,956	4,499
Operating expenses before credit impairment charges, provisions and charges	(2,456)	(2,343)	(2,510)
Credit impairment (charges)/write-backs	(205)
Credit impairment (charges)/write-backs		(320)	233
Provisions for other liabilities and charges	(335)	(419)	(377)
Total operating credit impairment charges, provisions and charges	(540)	(739)	(144)
Profit from discontinued operations before tax	0	0	43
Tax on profit from discontinued operations	0	0	(12)
Profit from discontinued operations after tax	0	0	31
Discontinued operations
Disclosure of analysis of single amount of discontinued operations [line items]
Net interest income	0	0	32
Net fee and commission income	0	0	35
Other operating income	0	0	2
Total operating income	0	0	69
Operating expenses before credit impairment charges, provisions and charges	0	0	(33)
Credit impairment (charges)/write-backs	0
Credit impairment (charges)/write-backs		0	11
Provisions for other liabilities and charges	0	0	(4)
Total operating credit impairment charges, provisions and charges	£ 0	£ 0	£ 7

Discontinued Operations and A_4

Discontinued Operations and Assets and Liabilities Held for Sale - Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Discontinued Operations and Assets and Liabilities Held for Sale [Abstract]
Gain (loss) recognised on measurement to fair value less costs to sell or on disposal of assets or disposal groups constituting discontinued operation	£ 0	£ 0
Cash flows from (used in) operating activities, discontinued operations	£ 0	£ 0	£ (3,612)

Discontinued Operations and A_5

Discontinued Operations and Assets and Liabilities Held for Sale - Disclosure of Assets and Liabilities Held for Sale (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022
Disclosure Of Assets And Liabilities Classified As Held For Sale [Line Items]
Assets held for sale	£ 13	£ 49
Property, plant and equipment
Disclosure Of Assets And Liabilities Classified As Held For Sale [Line Items]
Assets held for sale	£ 13	£ 49

Events After the Balance Shee_2

Events After the Balance Sheet Date (Details)	12 Months Ended
	Dec. 31, 2023
Disclosure of non-adjusting events after reporting period [abstract]
Description of nature of non-adjusting event after reporting period	There have been no significant events between 31 December 2023 and the date of approval of these financial statements which would require a change to or additional disclosure in the financial statements.