Santander UK (SANS+) 6-K 21 Aug 18 2018 H1 Current report (foreign) Financial data

Document and Entity Information

Document and Entity Information	6 Months Ended
	Jun. 30, 2018
Document - Document and Entity Information [Abstract]
Document Type	6-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	H1
Trading Symbol	CK0001087711
Entity Registrant Name	SANTANDER UK PLC
Entity Central Index Key	1,087,711
Current Fiscal Year End Date	--12-31

Consolidated Income Statement

Consolidated Income Statement - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Profit (loss) [abstract]
Interest and similar income	£ 3,001	£ 2,977
Interest expense and similar charges	(1,190)	(1,055)
Net interest income	1,811	1,922
Fee and commission income	584	609
Fee and commission expense	(204)	(200)
Net fee and commission income	380	409
Net trading and other income	121	182
Total operating income	2,312	2,513
Operating expenses before credit impairment losses, provisions and charges	(1,283)	(1,215)
Credit impairment losses	(91)	(48)
Provisions for other liabilities and charges	(33)	(186)
Total credit impairment losses, provisions and charges	(124)	(234)
Profit before tax	905	1,064
Tax on profit	(256)	(323)
Profit after tax for the period	649	741
Attributable to:
Equity holders of the parent	637	730
Non-controlling interests	12	11
Profit after tax for the period	£ 649	£ 741

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Statement of comprehensive income [abstract]
Profit after tax for the period	£ 649	£ 741
Available-for-sale securities:
- Change in fair value		72
- Income statement transfers		(48)
- Taxation		(5)
Other comprehensive income available-for-sale securities, total		19
Movement in fair value reserve (debt instruments):
- Change in fair value	(94)
- Income statement transfers	67
- Taxation	6
Other comprehensive income fair value reserve (debt instruments)	(21)
Cash flow hedges:
- Effective portion of changes in fair value	84	(48)
- Income statement transfers	(190)	(124)
- Taxation	21	48
Other comprehensive income cash flow hedges, total	(85)	(124)
Net other comprehensive income that may be reclassified to profit or loss subsequently	(106)	(105)
Pension remeasurement:
- Change in fair value	529	79
- Taxation	(132)	(20)
Pension remeasurement, total	397	59
Own credit adjustment:
- Change in fair value	(31)	(23)
- Taxation	8	6
Own credit adjustment, total	(23)	(17)
Net other comprehensive income that will not be reclassified to profit or loss subsequently	374	42
Total other comprehensive income for the period net of tax	268	(63)
Total comprehensive income	917	678
Attributable to:
Equity holders of the parent	904	666
Non-controlling interests	13	12
Total comprehensive income	£ 917	£ 678

Consolidated Balance Sheet

Consolidated Balance Sheet - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets
Cash and balances at central banks	£ 21,342	£ 32,771
Trading assets	19,158	30,555
Derivative financial instruments	3,838	19,942
Other financial assets at fair value through profit or loss	2,710	2,096
Loans and advances to banks	2,410	3,463
Loans and advances to customers	200,950	199,340
Reverse repurchase agreements - non trading	13,611	2,614
Financial investments	20,986	17,611
Interests in other entities	80	73
Intangible assets	1,783	1,742
Property, plant and equipment	1,702	1,598
Current tax assets	46	0
Retirement benefit assets	868	449
Other assets	2,907	2,511
Assets held for sale	24,241	0
Total assets	316,632	314,765
Liabilities
Deposits by banks	15,655	12,708
Deposits by customers	175,885	183,146
Repurchase agreements - non trading	17,447	1,578
Trading liabilities	8,375	31,109
Derivative financial instruments	1,466	17,613
Financial liabilities designated at fair value	1,238	2,315
Debt securities in issue	46,004	42,633
Subordinated liabilities	3,758	3,793
Other liabilities	2,847	2,730
Provisions	504	558
Current tax liabilities	0	3
Deferred tax liabilities	160	88
Retirement benefit obligations	108	286
Liabilities held for sale	26,616	0
Total liabilities	300,063	298,560
Equity
Share capital	3,119	3,119
Share premium	5,620	5,620
Other equity instruments	2,281	2,281
Retained earnings	5,194	4,732
Other reserves	190	301
Total shareholders' equity	16,404	16,053
Non-controlling interests	165	152
Total equity	16,569	16,205
Total liabilities and equity	£ 316,632	£ 314,765

Consolidated Cash Flow Statemen

Consolidated Cash Flow Statement - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Profit after tax for the period	£ 649	£ 741
Adjustments for:
Non-cash items included in profit	210	678
Change in operating assets	(2,644)	(1,445)
Change in operating liabilities	(1,176)	5,442
Corporation taxes paid	(236)	(233)
Effects of exchange rate differences	583	(132)
Net cash flows from operating activities	(2,614)	5,051
Cash flows from investing activities
Investments in other entities	(66)
Purchase of property, plant and equipment and intangible assets	(350)	(217)
Proceeds from sale of property, plant and equipment and intangible assets	13	24
Purchase of financial investments	(5,047)	(419)
Proceeds from sale and redemption of financial investments	1,301	1,186
Net cash flows from investing activities	(4,149)	574
Cash flows from financing activities
Issue of AT1 Capital Securities		500
Issuance costs of AT1 Capital Securities		(4)
Issue of debt securities and subordinated notes	6,452	2,237
Issuance costs of debt securities and subordinated notes	(13)	(9)
Repayment of debt securities and subordinated notes	(4,601)	(6,418)
Dividends paid on ordinary shares	(250)	(276)
Dividends paid on preference shares and other equity instruments	(90)	(80)
Dividends paid on non-controlling interests	0	0
Net cash flows from financing activities	1,498	(4,050)
Change in cash and cash equivalents	(5,265)	1,575
Cash and cash equivalents at beginning of the period	42,226	25,705
Effects of exchange rate changes on cash and cash equivalents	206	(254)
Cash and cash equivalents at the end of the period	37,167	27,026
Cash and cash equivalents consist of:
Cash and balances at central banks	21,342	18,255
Less: regulatory minimum cash balances	(631)	(380)
Cash and bank balances at central banks less regulatory minimum cash balances	20,711	17,875
Net trading other cash equivalents	2,591	6,775
Net non-trading other cash equivalents	13,865	2,376
Cash and cash equivalents at the end of the period	£ 37,167	£ 27,026

Consolidated Statement of Chang

Consolidated Statement of Changes in Equity - GBP (£) £ in Millions	Total	Share Capital [member]	Share premium [member]	Other Equity Instruments [member]	Other Reserves Available-For-Sale [member]	Other Reserves Fair Value Reserves [member]	Other Reserves Cash Flow Hedging [member]	Other Reserves Currency Translation [member]	Retained Earnings [member]	[1]	Total [member]	Non-Controlling Interests [member]
Beginning balance at Dec. 31, 2016	£ 15,453	£ 3,119	£ 5,620	£ 1,785	£ 48		£ 471	£ 5	£ 4,255		£ 15,303	£ 150
Profit after tax	741								730		730	11
Other comprehensive income, net of tax:
- Available-for-sale securities	19				19						19
- Cash flow hedges	(124)						(124)				(124)
- Pension remeasurement	59								58		58	1
- Own credit adjustment	(17)								(17)		(17)
Total comprehensive income	678				19		(124)		771		666	12
Issue of AT1 Capital Securities	496			496							496
Dividends on ordinary shares	(323)								(323)		(323)
Dividends on preference shares and other equity instruments	(80)								(80)		(80)
Tax on other equity instruments	26								26		26
Ending balance at Jun. 30, 2017	16,250	3,119	5,620	2,281	67		347	5	4,649		16,088	162
Beginning balance at Dec. 31, 2017	16,205	3,119	5,620	2,281	68		228	5	4,732		16,053	152
Adjustment for the adoption of IFRS 9 (see Note 1)	(192)				(68)	£ 63			(187)		(192)
Ending balance at Jan. 01, 2018	16,013	3,119	5,620	2,281		63	228	5	4,545		15,861	152
Beginning balance at Dec. 31, 2017	16,205	3,119	5,620	2,281	£ 68		228	5	4,732		16,053	152
Profit after tax	649								637		637	12
Other comprehensive income, net of tax:
- Fair value reserve (debt instruments)	(21)					(21)					(21)
- Cash flow hedges	(85)						(85)				(85)
- Pension remeasurement	397								396		396	1
- Own credit adjustment	(23)								(23)		(23)
Total comprehensive income	917					(21)	(85)		1,010		904	13
Other	(45)								(45)		(45)
Dividends on ordinary shares	(250)								(250)		(250)
Dividends on preference shares and other equity instruments	(90)								(90)		(90)
Tax on other equity instruments	24								24		24
Ending balance at Jun. 30, 2018	£ 16,569	£ 3,119	£ 5,620	£ 2,281		£ 42	£ 143	£ 5	£ 5,194		£ 16,404	£ 165
[1]	Restated to reflect the change in accounting policy relating to business combinations between entities under common control, as described in Note 1 to the Consolidated Financial Statements in the 2017 Annual Report.

Accounting Policies

Accounting Policies	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Accounting Policies	1. ACCOUNTING POLICIES The financial information in these Condensed Consolidated Interim Financial Statements does not constitute statutory accounts as defined in section 434 of the UK Companies Act 2006. Statutory accounts for the year ended 31 December 2017 have been delivered to the Registrar of Companies. The auditor’s report on those accounts was unqualified, did not draw attention to any matters by way of emphasis and did not contain a statement under section 498(2) of the UK Companies Act 2006. The Condensed Consolidated Interim Financial Statements have been prepared in accordance with International Accounting Standard (IAS) 34 ‘Interim Financial Reporting’, as issued by the International Accounting Standards Board (IASB) and adopted by the European Union, and the Disclosure Guidance and Transparency Rules of the Financial Conduct Authority (FCA). They do not include all the information and disclosures normally required for full annual financial statements and should be read in conjunction with the Consolidated Financial Statements of the Santander UK group for the year ended 31 December 2017 which were prepared in accordance with International Financial Reporting Standards as adopted by the European Union. Those Consolidated Financial Statements were also prepared in accordance with International Financial Reporting Standards as issued by the IASB including interpretations issued by the IFRS Interpretations Committee (IFRIC) of the IASB (together IFRS). The Santander UK group has also complied with its legal obligation to comply with IFRS as adopted by the European Union as there are no applicable differences between the two frameworks for the periods presented. In preparing the Condensed Consolidated Interim Financial Statements management makes judgements, estimates and assumptions which impact the application of accounting policies and the reported amounts of assets, liabilities, income and expenses. Because of the inherent uncertainty in making estimates, actual results reported in future periods may differ. Management continually evaluates the judgements, estimates and assumptions applied, including expectations of future events that are believed to be reasonable under the circumstances. Except as noted below, the same accounting policies, presentation and methods of computation are followed in these Condensed Consolidated Interim Financial Statements as were applied in the presentation of the Santander UK group’s 2017 Annual Report. IFRS 5 Non-current Non-current Non-current Recent accounting developments On 1 January 2018, the Santander UK group adopted IFRS 9 ‘Financial Instruments’ (IFRS 9) and IFRS 15 ‘Revenue from Contracts with Customers’ (IFRS 15). The new/revised accounting policies are set out below. The Santander UK group has decided to continue adopting IAS 39 hedge accounting and consequently there have been no changes to the hedge accounting policies and practices set out in the 2017 Annual Report following the adoption of IFRS 9. The impact of applying IFRS 9 is disclosed in Note 25(i). The accounting policy changes for IFRS 9, set out in section (i) below, have been applied from 1 January 2018. Comparatives have not been restated. As a result of the change from IAS 39 to IFRS 9, some disclosures presented in respect of certain financial assets are not comparable because their classification may have changed between the two standards. This means that some IFRS 9 disclosures are not directly comparable and some disclosures that relate to information presented on an IAS 39 basis are no longer relevant in the current period. The application of IFRS 15 had no material impact on the Santander UK group as there were no significant changes in the recognition of in scope income. The accounting policy changes for IFRS 15 are set out in section (ii) below. As explained in Note 25(i), the classification and measurement changes to financial assets that arose on adoption of IFRS 9 have been aligned to the presentation in the balance sheet as: – Loans and receivables amounting to £1,071m and available-for-sale – Social housing loans amounting to £977m were reclassified to amortised cost on adoption of IFRS 9 and, consequently, were moved from other financial assets at FVTPL to loans and advances to customers. – £19m and £180m of other loans and receivables held within hold to collect and sell business models were moved from trading assets and loans and advances to customers respectively, to financial investments, due to their reclassification to FVOCI on adoption of IFRS 9. – The balance sheet category for ‘Financial assets designated at fair value’ has been changed to ‘Other financial assets at fair value through profit or loss’. In addition, non-trading non-trading non-trading non-trading re-presented i) IFRS 9 accounting policy changes Interest income and expense Interest income on financial assets that are classified as amortised cost, investments in debt instruments measured at fair value through other comprehensive income (FVOCI) and interest expense on financial liabilities other than those at fair value through profit or loss (FVTPL) is determined using the effective interest rate method. The effective interest rate is the rate that discounts the estimated future cash payments or receipts over the expected life of the instrument or, when appropriate, a shorter period, to the gross carrying amount of the financial asset (i.e. its amortised cost before any impairment allowance) or to the amortised cost of a financial liability. When calculating the effective interest rate, the future cash flows are estimated after considering all the contractual terms of the instrument excluding expected credit losses (ECLs). The calculation includes all amounts paid or received by the Santander UK group that are an integral part of the overall return, direct incremental transaction costs related to the acquisition, issue or disposal of the financial instrument and all other premiums or discounts. 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 (or ‘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). Interest income on assets classified as amortised cost, investments in debt instruments measured at FVOCI, interest expense on liabilities classified at amortised cost, and interest income and expense on hedging derivatives are recognised in ‘Interest and similar income’ and ‘Interest expense and similar charges’ in the income statement, as appropriate. Financial instruments 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 fair value through profit or loss are expensed in profit or loss. Immediately after initial recognition, an ECL allowance is recognised for financial assets measured at amortised cost and investments in debt instruments measured at FVOCI. A regular way purchase is a purchase 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 market place concerned. Regular way purchases of financial assets classified as amortised cost, issues of equity or financial liabilities measured at amortised cost are recognised on settlement date; all other regular way purchases and issues are recognised on trade date. b) Financial assets and liabilities i) Classification and subsequent measurement From 1 January 2018, the Santander UK group has applied IFRS 9 Financial Instruments and classifies its financial assets in the following measurement categories: – Amortised cost; – FVOCI; – FVTPL. Financial assets and financial liabilities are classified as FVTPL where they are mandatorily held at FVTPL or where they are otherwise designated at FVTPL on initial recognition. Financial assets and financial liabilities which are mandatorily held at FVTPL include: – Financial assets and financial liabilities held for trading (see below); – Debt instruments that would otherwise be measured at amortised cost or FVOCI but which do not have solely payments of principal and interest (SPPI) characteristics; 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 financial assets and financial liabilities other than those that are held for trading are designated at FVTPL where this results in more relevant information 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 or 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. a) 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 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 ‘Other’ business model and measured at FVTPL. Factors considered by the Santander UK group 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 are 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 three 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 25. Interest income from these financial assets is included in ‘Interest and similar income’ using the effective interest rate method. When the group revises the estimates of future cash flows, the carrying amount of the respective financial assets or financial liability 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 on the instrument’s amortised cost 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 ‘Net trading and other 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 ‘Net trading and other 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. b) 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. The Santander UK group subsequently measures all equity investments at FVTPL, except where management has elected, at initial recognition, to irrevocably designate an equity investment at FVOCI. 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 Santander UK group’s right to receive payments is established. Gains and losses on equity investments at FVTPL are included in the ‘Net trading and other income’ line in the income statement. c) Financial liabilities Financial liabilities are classified as subsequently measured at amortised cost, except for: – Financial liabilities at fair value through profit or loss: this classification is applied to derivatives, financial liabilities held for trading and other financial liabilities designated as such at initial recognition. Gains or losses on financial liabilities designated at fair value through profit or loss 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. 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. Further details of how ECL is calculated are provided in the Credit Risk section of the Risk review. iii) Modifications of financial assets The treatment of a renegotiation or modification of the contractual cash flows of a financial asset depends upon whether the renegotiation or modification is done for commercial reasons or because of financial difficulties of the borrower. – Contractual modifications for commercial reasons: such modifications are treated as a new transaction resulting in the derecognition of the original financial asset, and the recognition of a “new” financial asset. 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. – Contractual modifications due to financial difficulties of the borrower: where Santander UK 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. Other contractual modifications are assessed on a case-by-case 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. 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 losses in the income statement. The loss allowance in respect of any revolving facilities is shown as part of loans and advances to customers to the extent of any drawn balances with only the excess recognised as a provision. ii) IFRS 15 accounting policy changes Revenue recognition: 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. 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 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 (e.g. certain loan commitment fees) is recognised as an adjustment to the effective interest rate and recorded in ‘Interest income’. Future accounting developments IFRS 16 ‘Leases’ (IFRS 16) – In January 2016, the IASB issued IFRS 16. The standard is effective for annual periods beginning on or after 1 January 2019. Earlier adoption is permitted for entities that apply IFRS 15 at or before the date of initial application of IFRS 16. IFRS 16 sets out the principles for the recognition, measurement, presentation and disclosure for both lessees and lessors. For lessee accounting, IFRS 16 introduces a single lessee accounting model and requires a lessee to recognise a right-of-use Going Concern After making enquiries, the Directors have a reasonable expectation that the Santander UK group has adequate resources to continue in operational existence for at least twelve months from the date that the balance sheet is signed. Having reassessed the principal risks and uncertainties, the Directors consider it appropriate to adopt the ‘going concern’ basis of accounting in preparing the Condensed Consolidated Interim Financial Statements. CRITICAL ACCOUNTING POLICIES AND AREAS OF SIGNIFICANT MANAGEMENT JUDGEMENT The preparation of the Condensed Consolidated Interim Financial Statements requires management to make estimates and judgements that affect the reported amount of assets and liabilities at the date of the Condensed Consolidated Interim Financial Statements and the reported amount of income and expenses during the reporting period. Management evaluates its estimates and judgements on an ongoing basis. Management bases its estimates and judgements on historical experience and on various other factors that are believed to be reasonable under the circumstances. Actual results may differ from these estimates under different assumptions or conditions. The introduction of IFRS 9 has given rise to areas of significant management judgement in respect of the ECL impairment methodology and these are explained further below. There have been no other significant changes in the basis upon which estimates and judgements have been determined compared to that applied in the 2017 Annual Report. Credit impairment losses – ECL impairment methodology The following estimates and judgements in connection with the application of the ECL impairment methodology are highly susceptible to change from period to period as assumptions are made to calculate the estimates. Any significant difference between the estimated amounts and actual amounts could have a material impact on the Santander UK group’s future financial results and financial condition. – Forward-looking multiple economic scenarios: we use five scenarios, consisting of a central base case, two upside scenarios and two downside scenarios except for our CIB portfolio, where we use a central base case and a single upside and downside scenario. For CIB portfolios, we consider these scenarios sufficient to account for any non-linear non-CIB – Probability weights: in determining our initial scenario probability weightings, we award the highest weight to the base case, whilst the extreme scenarios typically attract lower weights than the more moderate ones. In addition, due to the current economic position and policy concerns evidenced by the PRA and Financial Policy Committee (FPC), and due to political concerns we have applied a higher weighting to the downside scenarios. – Significant increase in credit risk: a combination of quantitative (both absolute and relative), qualitative and backstop criteria are employed to determine exposures that are considered significantly credit deteriorated since initial recognition and which are subject to assessment for lifetime ECL measurement. – Post Model Adjustments: these relate to adjustments which we deem necessary because of identified model limitations – most notably those that have arisen due to challenges in obtaining historical data. We expect these to gradually become redundant as we build up sufficient comparative data over future reporting periods.

Segments

Segments	6 Months Ended
	Jun. 30, 2018
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Segments	2. SEGMENTS The Santander UK group’s business is managed and reported on the basis of the following segments: Retail Banking, Commercial Banking, Corporate & Investment Banking (formerly branded as Global Corporate Banking) and Corporate Centre. The segments are strategic business units that offer different products and services. They are managed separately because each business has different customers and requires different technology and marketing strategies. There has been no change to the descriptions of these segments and segmental accounting as set out in Note 2 to the Consolidated Financial Statements in the 2017 Annual Report. Half year to 30 June 2018 Retail Commercial Corporate & Corporate Total Net interest income/(expense) 1,587 204 33 (13 ) 1,811 Non-interest 305 40 171 (15 ) 501 Total operating income/(expense) 1,892 244 204 (28 ) 2,312 Operating expenses before credit impairment losses, provisions and charges (965 ) (135 ) (150 ) (33 ) (1,283 ) Credit impairment (losses)/releases (52 ) (22 ) (18 ) 1 (91 ) Provisions for other liabilities and charges (33 ) 7 (2 ) (5 ) (33 ) Total credit impairment losses, provisions and charges (85 ) (15 ) (20 ) (4 ) (124 ) Profit/(loss) before tax 842 94 34 (65 ) 905 Revenue from external customers 2,170 319 233 (410 ) 2,312 Inter-segment revenue (278 ) (75 ) (29 ) 382 – Total operating income/(expense) 1,892 244 204 (28 ) 2,312 Revenue from external customers includes the following fee and commission income disaggregated by income type: (1) - Current account and debit card fees 311 13 14 – 338 - Insurance, protection and investments 46 – – – 46 - Credit cards 45 – – – 45 - Non-banking (2) 73 28 49 5 155 Total fee and commission income (3) 475 41 63 5 584 Total assets (4) 177,374 19,028 55,482 64,748 316,632 Of which assets held for sale 306 – 23,814 121 24,241 Total liabilities 148,846 17,064 49,884 84,269 300,063 Of which liabilities held for sale 5,735 – 20,867 15 26,617 Half year to 30 June 2017 (5) Retail £ Commercial £ Corporate & £ Corporate £ Total £ Net interest income 1,657 191 33 41 1,922 Non-interest 300 37 201 53 591 Total operating income 1,957 228 234 94 2,513 Operating expenses before credit impairment losses, provisions and charges (919 ) (109 ) (145 ) (42 ) (1,215 ) Credit impairment (losses)/releases (39 ) (3 ) (9 ) 3 (48 ) Provisions for other liabilities and charges (155 ) (29 ) – (2 ) (186 ) Total credit impairment losses, provisions and (charges)/releases (194 ) (32 ) (9 ) 1 (234 ) Profit before tax 844 87 80 53 1,064 Revenue from external customers 2,272 318 279 (356 ) 2,513 Inter-segment revenue (315 ) (90 ) (45 ) 450 – Total operating income 1,957 228 234 94 2,513 Revenue from external customers includes the following fee and commission income disaggregated by income type: (1) - Current account and debit card fees 330 14 13 – 357 - Insurance, protection and investments 48 – – – 48 - Credit cards 44 – – – 44 - Non-banking (2) 65 30 65 – 160 Total fee and commission income (3) 487 44 78 – 609 31 December 2017 Total assets (4) 174,524 19,391 51,078 69,772 314,765 Total liabilities 150,847 18,697 45,603 83,413 298,560 (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 (3) The majority of 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. Insurance commissions and associated income are recognised over time in accordance with the accounting policy described in Note 1 to these Condensed Consolidated Interim Financial Statements. (4) Includes customer loans, net of impairment loss allowances. (5) Restated on the same basis as described in Note 2 to the Consolidated Financial Statements in the 2017 Annual Report.

Net Trading and Other Income

Net Trading and Other Income	6 Months Ended
	Jun. 30, 2018
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Net Trading and Other Income	3. NET TRADING AND OTHER INCOME Half year to Half year to £ Net trading and other income 121 182 In December 2017, Santander UK exercised its option to call the £175m Fixed/Floating Rate Tier One Preferred Income Capital Securities. These were fully redeemed on 9 February 2018. In September 2017, as part of a capital management exercise, we purchased and redeemed 91% of the 7.375% 20 Year Step-up

Operating Expenses Before Impai

Operating Expenses Before Impairment Losses, Provisions and Charges	6 Months Ended
	Jun. 30, 2018
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Operating Expenses Before Impairment Losses, Provisions and Charges	4. OPERATING EXPENSES BEFORE IMPAIRMENT LOSSES, PROVISIONS AND CHARGES Half year to Half year to £ Staff costs 691 566 Other administration expenses 411 493 Depreciation, amortisation and impairment 181 156 1,283 1,215

Credit Impairment Losses and Pr

Credit Impairment Losses and Provisions	6 Months Ended
	Jun. 30, 2018
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Credit Impairment Losses and Provisions	5. CREDIT IMPAIRMENT LOSSES AND PROVISIONS Half year to Half year to £ Credit Impairment losses: Loans and advances to customers (See Note 11) 102 76 Recoveries of loans and advances, net of collection costs (See Note 11) (21 ) (28 ) Off-balance 10 91 48 Provisions for other liabilities and charges (excluding off-balance 33 181 Provisions for residual value and voluntary termination (See Note 11) – 5 33 186 124 234 The new credit impairment loss allowance requirements introduced by IFRS 9 mandated a change from recognising impairment losses on an incurred loss basis (as reflected in H117) to an expected credit loss (ECL) basis (as reflected in H118). For more details on this change in methodology, refer to the IFRS 9 accounting policy changes in Note 1 and the IFRS 9 transition disclosures in Note 25. There were no material credit impairment losses on loans and advances to banks and financial investments.

Taxation

Taxation	6 Months Ended
	Jun. 30, 2018
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Taxation	6. TAXATION Half year to Half year to £ Profit before tax 905 1,064 Tax calculated at a tax rate of 19% (H117: 19.25%) 172 205 Bank surcharge on profits 64 77 Non-deductible 5 5 Non-deductible 13 18 Non-deductible (2 ) 16 Net disallowable items and non-taxable 10 12 Adjustment to prior period provisions (6 ) (10 ) Tax charge 256 323 Interim period corporation tax is accrued based on the estimated average annual effective corporation tax for the year of 28.3% (H117: 30.4%). The standard rate of UK corporation tax was 27% for banking entities and 19% for non-banking non-banking

Dividends on Ordinary Shares

Dividends on Ordinary Shares	6 Months Ended
	Jun. 30, 2018
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Dividends on Ordinary Shares	7. DIVIDENDS ON ORDINARY SHARES An interim dividend of £250m was declared and paid on 29 June 2018 on the Company’s ordinary shares in issue (H117: £323m).

Trading Assets

Trading Assets	6 Months Ended
	Jun. 30, 2018
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Trading Assets	8. TRADING ASSETS 30 June 2018 31 December 2017 £ Securities purchased under resale agreements 3,740 8,870 Debt securities – 5,156 Equity securities 8,264 9,662 Cash collateral associated with trading balances 7,082 6,156 Short-term loans 72 711 19,158 30,555 Balances at 30 June 2018 exclude assets relating to our ring-fencing plans that have either transferred outside the Santander UK group, or whose transfer is considered highly probable at the balance sheet date and have therefore been reclassified as held for sale. For more details see Note 26 and Note 27.

Derivative Financial Instrument

Derivative Financial Instruments	6 Months Ended
	Jun. 30, 2018
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Derivative Financial Instruments	9. DERIVATIVE FINANCIAL INSTRUMENTS 30 June 2018 31 December 2017 Fair value Fair value Notional Assets Liabilities Notional £ Assets £ Liabilities £ Derivatives held for trading: Exchange rate contracts 9,481 406 334 144,160 2,559 4,130 Interest rate contracts 74,493 482 3 863,151 11,612 11,140 Equity and credit contracts 12,776 799 440 19,814 888 693 Total derivatives held for trading 96,750 1,687 777 1,027,125 15,059 15,963 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 3,339 332 – 2,641 312 6 Interest rate contracts 70,066 7 423 59,610 1,272 1,470 Equity derivative contracts – – – 16 – 4 73,405 339 423 62,267 1,584 1,480 Designated as cash flow hedges: Exchange rate contracts 27,603 1,691 87 23,117 3,206 55 Interest rate contracts 23,992 121 177 12,884 84 115 Equity derivative contracts 50 – 2 26 9 – 51,645 1,812 266 36,027 3,299 170 Total derivatives held for hedging 125,050 2,151 689 98,294 4,883 1,650 Total derivative financial instruments 221,800 3,838 1,466 1,125,419 19,942 17,613 Balances at 30 June 2018 exclude assets that have transferred, or will transfer, outside the Santander UK group as part of our ring-fencing plans, including those reclassified as held for sale. For more details see Note 26 and Note 27.

Loans and Advances to Banks

Loans and Advances to Banks	6 Months Ended
	Jun. 30, 2018
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Loans and Advances to Banks	10. LOANS AND ADVANCES TO BANKS 30 June 2018 31 December 2017 £ Loans and advances to banks 2,410 3,463 Balances at 30 June 2018 exclude assets relating to our ring-fencing plans that have either transferred outside the Santander UK group, or whose transfer is considered highly probable at the balance sheet date and have therefore been reclassified as held for sale. For more details see Note 26 and Note 27.

Loans and Advances to Customers

Loans and Advances to Customers	6 Months Ended
	Jun. 30, 2018
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Loans and Advances to Customers	11. LOANS AND ADVANCES TO CUSTOMERS 30 June 2018 31 December 2017 £ Loans and advances to customers 200,471 199,151 Amounts due from fellow Banco Santander subsidiaries and joint ventures 1,344 1,199 Amounts due from Santander UK Group Holdings plc – 8 Loans and advances to customers 201,815 200,358 Credit impairment loss allowances on loans and advances to customers (792 ) (940 ) Residual value and voluntary termination provisions (73 ) (78 ) Net loans and advances to customers 200,950 199,340 Balances at 30 June 2018 exclude assets relating to our ring-fencing plans that have either transferred outside the Santander UK group, or whose transfer is considered highly probable at the balance sheet date and have therefore been reclassified as held for sale. For more details see Note 26 and Note 27. Movement in credit impairment loss allowances on loans and advances: Loans secured Corporate Finance Other Total At 31 December 2017 225 490 46 179 940 Adjustment for the adoption of IFRS 9 (see Note 1) 47 99 11 54 211 Re-allocation (2) (3 ) (25 ) – (22 ) (50 ) At 1 January 2018 269 564 57 211 1,101 (Release)/charge to the income statement (13 ) 24 17 74 102 Write-offs and other items (1) (7 ) (318 ) (15 ) (71 ) (411 ) At 30 June 2018 249 270 59 214 792 Recoveries, net of collection costs 1 1 3 16 21 At 1 January 2017 279 382 45 215 921 (Release)/charge to the income statement (18 ) 12 17 65 76 Write-offs and other items (1) (10 ) (38 ) (16 ) (69 ) (133 ) At 30 June 2017 251 356 46 211 864 Recoveries, net of collection costs 2 1 4 21 28 (1) Mortgage write-offs exclude the effect of the unwind over time of the discounting in estimating losses, as described in the accounting policy ‘Impairment of financial assets’ in Note 1 to the Consolidated Financial Statements in the 2017 Annual Report. Mortgage write-offs including this effect were £8m (H117: £11m). (2) This relates to ECL on undrawn exposures following the adoption of a methodology to enable its separate identification from ECL on drawn exposures.

Securitisations and Covered Bon

Securitisations and Covered Bonds	6 Months Ended
	Jun. 30, 2018
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Securitisations and Covered Bonds	12. SECURITISATIONS AND COVERED BONDS a) Securitisations The gross assets securitised at 30 June 2018 and 31 December 2017 under the structures described below were: Gross assets securitised 30 June 2018 31 December 2017 £ Master trust structures: – Holmes 3,788 4,299 – Fosse 5,167 5,732 – Langton 3,433 3,893 12,388 13,924 Other securitisation structures: – Motor 1,146 1,318 – Auto ABS UK Loans 1,480 1,498 2,626 2,816 Total 15,014 16,740 i) Master trust structures Holmes During the period, there were £1.0bn of external issuances from Holmes Master Issuer plc (H117: £nil) and no external redemptions of mortgage-backed securities (H117: £0.7bn equivalent). Fosse During the period, there were no external issuances from Fosse Master Issuer plc (H117: £nil). External mortgage-backed notes totalling £0.4bn (H117: £0.7bn) equivalent were redeemed during the period. Langton During the period, there were no external issuances from the Langton issuing companies (H117: £nil) and no external redemptions of mortgage-backed notes (H117: £nil). ii) Other securitisation structures Motor During the period, there were no external issuances from the Motor issuing companies (H117: £nil) and no external redemptions of asset-backed notes (H117: £0.2bn equivalent). Auto ABS UK Loans During the period, there were no external issuances from Auto ABS UK Loans (H117: £0.5bn) and no external redemptions of asset-backed notes (H117: £0.7bn). b) Covered bonds During the period, there were £2.4bn of external issuances from the covered bond programme (H117: £1.0bn). External mortgage-backed notes totalling £1.9bn (H117: £1.8bn) equivalent were redeemed during the period.

Financial Investments

Financial Investments	6 Months Ended
	Jun. 30, 2018
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Financial Investments	13. FINANCIAL INVESTMENTS 30 June 2018 31 December 2017 £ Amortised cost: – Asset backed securities 761 2,180 – Debt securities (1) 6,544 6,578 7,305 8,758 FVOCI: – Debt securities 13,506 – Loans and advances to customers (2) 175 13,681 Available-for-sale: – Debt securities 8,772 – Equity securities 81 8,853 20,986 17,611 (1) These securities were previously classified as held-to-maturity (2) These comprise other loans and receivables held within hold to collect and sell business models that were moved from trading assets and loans and advances to customers at amortised cost, to financial investments, due to their reclassification to FVOCI on adoption of IFRS 9. Balances at 30 June 2018 exclude assets relating to our ring-fencing plans that have either transferred outside the Santander UK group, or whose transfer is considered highly probable at the balance sheet date and have therefore been reclassified as held for sale. For more details see Note 26 and Note 27.

Interests in Other Entities

Interests in Other Entities	6 Months Ended
	Jun. 30, 2018
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Interests in Other Entities	14. INTERESTS IN OTHER ENTITIES The Santander UK group has interests in subsidiaries, associates, joint ventures and unconsolidated structured entities, as set out in Note 19 to the Consolidated Financial Statements in the 2017 Annual Report. The unconsolidated structured entities include Abbey National Capital Trust I and Abbey National Capital LP I, which are 100% owned finance subsidiaries (as defined in Regulation S-X Non-cumulative On 1 January 2018, Santander UK plc acquired 100% of the share capital of Santander UK Operations Ltd (formerly Geoban UK Ltd, a subsidiary of Geoban SA) and Santander UK Technology Ltd (formerly Isban UK Ltd, a subsidiary of Ingenieria De Software Bancario SL), for a final cash consideration of £66m. Immediately prior to this, the UK business of Produban Servicios Informaticos Generales SL was acquired by Santander UK Technology Ltd for a final cash consideration of £13m. These acquisitions will enable the Santander UK group to be more customer-centric by having greater business alignment and end-to-end

Deposits by Banks

Deposits by Banks	6 Months Ended
	Jun. 30, 2018
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Deposits by Banks	15. DEPOSITS BY BANKS 30 June 2018 31 December 2017 £ Items in the course of transmission 326 303 Deposits held as collateral 2,408 1,760 Other deposits (1) 12,921 10,645 15,655 12,708 (1) Includes drawdown from the Term Funding Scheme of £10.8bn (2017: £8.5bn).

Deposits by Customers

Deposits by Customers	6 Months Ended
	Jun. 30, 2018
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Deposits by Customers	16. DEPOSITS BY CUSTOMERS 30 June 2018 31 December 2017 £ Current and demand accounts – interest-bearing 84,656 85,749 – non-interest-bearing 2 2 Savings accounts (1) 65,033 70,461 Time deposits 17,358 19,951 Amounts due to Santander UK Group Holdings plc (2) 8,301 6,256 Amounts due to fellow Banco Santander subsidiaries 535 727 175,885 183,146 (1) Includes equity index-linked deposits of £1,232m (2017: £1,301m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,232m and £44m (2017: £1,301m and £67m) respectively. (2) Includes downstreamed funding from our immediate parent company Santander UK Group Holdings plc. Balances at 30 June 2018 exclude liabilities relating to our ring-fencing plans that have either transferred outside the Santander UK group, or whose transfer is considered highly probable at the balance sheet date and have therefore been reclassified as held for sale. For more details see Note 26 and Note 27.

Trading Liabilities

Trading Liabilities	6 Months Ended
	Jun. 30, 2018
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Trading Liabilities	17. TRADING LIABILITIES 30 June 2018 31 December 2017 £ Securities sold under repurchase agreements 5,612 25,504 Short positions in securities and unsettled trades 190 3,694 Cash collateral associated with trading balances 2,573 1,911 8,375 31,109 Balances at 30 June 2018 exclude liabilities relating to our ring-fencing plans that have either transferred outside the Santander UK group, or whose transfer is considered highly probable at the balance sheet date and have therefore been reclassified as held for sale. For more details see Note 26 and Note 27.

Debt Securities in Issue

Debt Securities in Issue	6 Months Ended
	Jun. 30, 2018
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Debt Securities in Issue	18. DEBT SECURITIES IN ISSUE 30 June 2018 31 December 2017 £ Medium-term notes 21,950 18,002 Covered bond programme 16,017 15,799 Certificates of deposit 3,304 4,681 Credit Linked Notes 43 43 Securitisation programmes 4,690 4,108 46,004 42,633

Provisions

Provisions	6 Months Ended
	Jun. 30, 2018
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Provisions	19. PROVISIONS Conduct remediation PPI £ Wealth and £ Other £ Regulatory- £ Vacant £ Other (1) £ Total £ At 31 December 2017 356 3 44 57 39 59 558 Re-allocation – – – – – 50 (2) 50 At 1 January 2018 356 3 44 57 39 109 608 Additional provisions – – – – 11 64 75 Provisions released – (3 ) (11 ) (4 ) – (14 ) (32 ) Utilisation (55 ) – (2 ) (37 ) (7 ) (46 ) (147 ) At 30 June 2018 301 – 31 16 43 113 504 At 1 January 2017 457 22 14 96 47 64 700 Additional provisions 69 – 35 2 6 69 181 Utilisation (121 ) (27 ) (2 ) (53 ) (5 ) (87 ) (295 ) Transfers – 9 – – – – 9 At 30 June 2017 405 4 47 45 48 46 595 (1) At 30 June 2018 this included £53m (2017: £59m) in respect of operational loss and operational risk provisions, restructuring charges and litigation and related expenses. It also included £60m in respect of credit impairment losses for off balance sheet exposures relating to guarantees given to third parties and undrawn loan commitments. See Note 5 for details of the income statement charge. (2) This relates to ECL on loan commitments following the adoption of a methodology to enable its separate identification from ECL on drawn exposures. Conduct remediation The table below sets out the key drivers of the provision balance and forecast assumptions used in calculating the PPI provision, as well as the sensitivity of the provision to changes in the assumptions. It reflects a balanced view across all retail products and portfolios and includes redress for Plevin-related claims. Cumulative to Future expected Sensitivity analysis Inbound complaints (1) 1,858 436 25 = £12.3m Outbound contact (‘000) 488 292 25 = £5.4m Response rate to outbound contact 55% 90% 1% = £1.0m Average uphold rate per claim (2) 44% 72% 1% = £2.7m Average redress per claim (3) £1,363 £537 £100 = £50.5m (1) Includes all claims received regardless of whether we expect to make a payment; i.e. regardless of the likelihood of the Santander UK group incurring a liability. Excludes claims where the complainant has not held a PPI policy. (2) Claims include inbound and responses to outbound contact. (3) The future expected average redress per claim is lower than the cumulative average to date due to the inclusion of Plevin cases in the provision, as well as a shift in the complaint mix to a greater proportion of storecards, which typically held lower average balances. 30 June 2018 compared to 31 December 2017 The remaining provision for PPI redress and related costs was £301m (2017: £356m), in line with our assumptions and claims experience. However, we will continue to monitor our provision levels, and take account of the impact of any further change in claims received. The remaining other conduct provision was £31m (2017: £47m), primarily relating to the sale of interest rate derivatives, following an ongoing review regarding regulatory classification of certain customers potentially eligible for redress. Following further analysis of the impacted population, management has assessed the provision requirements resulting in a release of £11m in H118. Other Other provisions increased in H118 due to the inclusion of expected credit losses for off balance sheet exposures relating to guarantees given to third parties and undrawn loan commitments, following the adoption of IFRS 9. In addition there was a charge of £58m principally relating to additional operational risk losses and restructuring charges.

Retirement Benefit Plans

Retirement Benefit Plans	6 Months Ended
	Jun. 30, 2018
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Retirement Benefit Plans	20. RETIREMENT BENEFIT PLANS The amounts recognised in the balance sheet were as follows: 30 June 2018 31 December 2017 £ Assets/(liabilities) Funded defined benefit pension scheme – surplus 868 449 Funded defined benefit pension scheme – deficit (69 ) (245 ) Unfunded defined benefit pension scheme (39 ) (41 ) Total net assets 760 163 a) Defined contribution pension plans An expense of £23m (H117: £27m) was recognised for defined contribution plans in the period and is included in staff costs classified within operating expenses, see Note 4. None of this amount was recognised in respect of key management personnel for H118 and H117. b) Defined benefit pension schemes The total amount charged to the income statement was £22m (H117: £23m). Movements in the present value of defined benefit obligations and fair value of scheme assets were as follows: 30 June 2018 30 June 2017 Present value of Fair value of Present value of £ Fair value of £ At 1 January (11,583 ) 11,746 (11,082 ) 11,218 Income statement (charge) / income (167 ) 145 (182 ) 156 Contributions paid – 90 – 91 Recognised in other comprehensive income: – Return on plan assets (excluding amounts included in net interest expense) – (72 ) – 85 – Actuarial movements arising from experience adjustments (39 ) – 11 – – Actuarial movements arising from changes in financial assumptions 640 – (17 ) – Benefits paid 221 (221 ) 191 (191 ) At 30 June (10,928 ) 11,688 (11,079 ) 11,359 Actuarial assumptions There have been no significant changes to the methods for setting the principal actuarial assumptions used as set out in Note 28 to the Consolidated Financial Statements in the 2017 Annual Report. Actuarial movements arising from changes in financial assumptions of £640m were mainly due to actuarial gains in H118 driven by widening credit spreads on the discount rate used to value scheme liabilities.

Contingent Liabilities and Comm

Contingent Liabilities and Commitments	6 Months Ended
	Jun. 30, 2018
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Contingent Liabilities and Commitments	21. CONTINGENT LIABILITIES AND COMMITMENTS 30 June 2018 31 December 2017 £ Guarantees given to third parties 1,666 1,557 Formal standby facilities, credit lines and other commitments 40,425 41,942 42,091 43,499 At 30 June 2018, the Santander UK group had credit impairment loss provisions relating to guarantees given to third parties and undrawn loan commitments. See Note 19 for further details. Other legal actions and regulatory matters Santander UK engages in discussion, and co-operates, 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. Note 19 details our provisions including those in relation to PPI. In relation to a specific PPI portfolio of complaints, a legal dispute regarding allocation of liability is in its early stages. There are 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 resolution of the matter including timing or the significance of the possible impact. The PPI provision includes our best estimate of Santander UK’s liability to the specific portfolio. Further information has not been provided on the basis that it would be seriously prejudicial.

Assets Charged as Security for

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets	6 Months Ended
	Jun. 30, 2018
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Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets	22. ASSETS CHARGED AS SECURITY FOR LIABILITIES AND COLLATERAL ACCEPTED AS SECURITY FOR ASSETS Securitisations and covered bonds As described in Note 16 to the Consolidated Financial Statements in the 2017 Annual Report, Santander UK plc and certain of its subsidiaries issue securitisations and covered bonds. At 30 June 2018, there were £35,253m (2017: £36,512m) of gross assets in these secured programmes, £502m (2017: £1,091m) of these related to internally retained issuances and were available for creating collateral which could in the future be used for liquidity purposes. At 30 June 2018, total notes issued externally from secured programmes (securitisations and covered bonds) increased to £20,707m (2017: £19,907m), including gross issuance of £3,375m (H117: £1,000m) and redemptions of £2,318m (H117: £3,538m). At 30 June 2018, a total of £4,006m (2017: £4,359m) of notes issued under securitisation and covered bond programmes had also been retained internally, a proportion of which had been used as collateral for raising funds via third party bilateral secured funding transactions, which totalled £1,834m at 30 June 2018 (2017: £1,834m), or for creating collateral which could in the future be used for liquidity purposes.

Financial Instruments

Financial Instruments	6 Months Ended
	Jun. 30, 2018
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Financial Instruments	23. FINANCIAL INSTRUMENTS a) Measurement basis of financial assets and liabilities At 31 December 2017, the Santander UK group categorised assets and liabilities measured at fair value within the fair value hierarchy based on the inputs to the valuation techniques as described in Note 37(a) to the Consolidated Financial Statements in the 2017 Annual Report. With effect from 1 January 2018, the Santander UK group applied the IFRS 9 classification and measurement requirements as described in Notes 1 and 25 to these Condensed Consolidated Interim Financial Statements. b) Fair values of financial instruments carried at amortised cost The following table analyses the fair value of the financial instruments carried at amortised cost at 30 June 2018 and 31 December 2017. It does not include fair value information for financial assets and financial liabilities carried at amortised cost if the carrying amount is a reasonable approximation of fair value. Details of the valuation methodology of the financial assets and financial liabilities carried at amortised cost can be found in Note 37(c) to the Consolidated Financial Statements in the 2017 Annual Report. 30 June2018 31 December 2017 Fair value Carrying Fair value £ Carrying £ Assets Loans and advances to banks 2,409 2,410 3,451 3,463 Loans and advances to customers 203,578 200,950 201,667 199,340 Reverse repurchase agreements- non trading 13,616 13,611 2,612 2,614 Financial investments 7,121 7,305 8,646 8,758 Assets held for sale (1) 1,733 1,752 – – 228,457 226,028 216,376 214,175 Liabilities Deposits by banks 15,667 15,655 12,721 12,708 Deposits by customers 175,990 175,885 183,227 183,146 Repurchase agreements- non trading 17,504 17,447 1,648 1,578 Debt securities in issue 47,252 46,004 44,296 42,633 Subordinated liabilities 4,120 3,758 4,256 3,793 Liabilities held for sale (1) 5,756 5,756 – – 266,289 264,505 246,148 243,858 (1) Assets and liabilities classified as held for sale are measured in accordance with IFRS 9; any assets and liabilities held for sale which are measured at fair value are included in the fair value table in section (c) below. c) 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 30 June 2018 and 31 December 2017, analysed by their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. 30 June 2018 31 December 2017 Level 1 Level 2 Level 3 Total Level 1 £ Level 2 £ Level 3 £ Total £ Valuation Assets Trading assets Securities purchased under resale agreements – 3,740 – 3,740 – 8,870 – 8,870 A Debt securities – – – – 5,156 – – 5,156 – Equity securities 8,264 – – 8,264 9,662 – – 9,662 – Cash collateral – 7,082 – 7,082 – 6,156 – 6,156 A Short-term loans 35 37 – 72 656 55 – 711 A 8,299 10,859 – 19,158 15,474 15,081 – 30,555 Derivative financial instruments Exchange rate contracts – 2,427 2 2,429 – 6,061 16 6,077 A Interest rate contracts – 610 – 610 – 12,956 12 12,968 A & C Equity and credit contracts – 739 60 799 – 861 36 897 B & D – 3,776 62 3,838 – 19,878 64 19,942 Other financial assets at fair value through profit or loss Loans and advances to customers – 1,604 71 1,675 – 1,485 64 1,549 A Debt securities 189 677 153 1,019 184 187 176 547 A & B Equity securities 16 – – 16 B 205 2,281 224 2,710 184 1,672 240 2,096 Financial investments FVOCI – debt securities 12,807 699 – 13,506 D FVOCI – loans and advances to customers – – 175 175 D Available-for-sale 8,770 2 – 8,772 C Available-for-sale 19 9 53 81 B 12,807 699 175 13,681 8,789 11 53 8,853 Assets held for sale (1) 1,966 20,370 148 22,484 – – – – A, B, C & D 1,966 20,370 148 22,484 – – – – Total assets at fair value 23,277 37,985 609 61,871 24,447 36,642 357 61,446 Liabilities Trading liabilities Securities sold repurchase agreements – 5,612 – 5,612 – 25,504 – 25,504 A Short positions in securities and unsettled trades 190 – – 190 3,694 – – 3,694 – Cash collateral – 2,573 – 2,573 – 1,911 – 1,911 A 190 8,185 – 8,375 3,694 27,415 – 31,109 Derivative financial instruments Exchange rate contracts – 421 – 421 – 4,176 15 4,191 A Interest rate contracts – 603 – 603 – 12,720 5 12,725 A & C Equity and credit contracts – 404 38 442 1 653 43 697 B & D – 1,428 38 1,466 1 17,549 63 17,613 Financial liabilities designated at fair value Debt securities in issue – 1,089 6 1,095 – 1,629 6 1,635 A Structured deposits – 143 – 143 – 680 – 680 A – 1,232 6 1,238 – 2,309 6 2,315 Liabilities held for sale (1) 1,842 19,006 1 20,849 – – – – A, B, C & D 1,842 19,006 1 20,849 – – – – Total liabilities at fair value 2,032 29,851 45 31,928 3,695 47,273 69 51,037 (1) Includes assets and liabilities held for sale which are measured at fair value. Transfers between levels of the fair value hierarchy During H118, there were no significant transfers of financial instruments between Levels 1, 2 and 3 in the fair value hierarchy. There were no transfers during 2017 as disclosed in Note 37(d) to the Consolidated Financial Statements in the 2017 Annual Report. d) Valuation techniques The main valuation techniques employed in internal models to measure the fair value of the financial instruments are disclosed in Note 37(e) to the Consolidated Financial Statements in the 2017 Annual Report. The Santander UK group did not make any material changes to the valuation techniques and internal models it used during H118. e) Fair value adjustments The internal models incorporate assumptions that the Santander UK group believes would be made by a market participant to establish fair value. Fair value adjustments are adopted when the Santander UK group considers that there are additional factors that would be considered by a market participant that are not incorporated in the valuation model. The Santander UK group 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 majority of these adjustments relate to Corporate & Investment Banking. The magnitude and types of fair value adjustment adopted by Corporate & Investment Banking are listed in the following table: 30 June 2018 31 December 2017 £ Risk-related: – Bid-offer 27 34 – Uncertainty 37 43 – Credit risk adjustment 19 36 – Funding fair value adjustment 9 6 92 119 Model-related 9 8 Day One profit – 1 101 128 Risk-related adjustments Risk-related adjustments are driven, in part, by the magnitude of the Santander UK group’s market or credit risk exposure, and by external market factors, such as the size of market spreads. For further details, see the ‘Risk-related adjustments’ section in Note 37 (f) to the Consolidated Financial Statements in the 2017 Annual Report. f) Internal models based on information other than market data (Level 3) Valuation techniques There have been no significant changes to the valuation techniques as set out in Note 37(i) to the Consolidated Financial Statements in the 2017 Annual Report, except as follows. The changes to the classification and measurement of financial assets on transition to IFRS 9 as set out in Note 25 resulted in some loans and advances to customers, primarily consisting of utilities and shipping counterparties, being reclassified from amortised cost to FVTPL and/or FVOCI. These included loans classified as Level 3 and with a fair value of £285m at 1 January 2018. 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. The following table shows the movement in the period of Level 3 financial instruments, measured at fair value using a valuation technique with significant unobservable inputs: Assets Liabilities Derivatives £ Other financial value through £ Financial £ Assets £ Total £ Derivatives £ Financial £ Liabilities £ Total £ At 31 December 2017 64 240 53 – 357 (63 ) (6 ) – (69 ) Adjustment for the adoption of IFRS 9 – 139 146 – 285 – – – – At 1 January 2018 64 379 199 – 642 (63 ) (6 ) – (69 ) Total (losses)/gains recognised in profit or loss: – Fair value movements 26 (5 ) (4 ) – 17 4 – – 4 – Foreign exchange and other movements (5 ) – – – (5 ) 5 – – 5 Transfers in – 19 – – 19 – – – – Transfer to held for sale (2 ) (146 ) – 148 – 1 – (1 ) – Additions – – 17 – 17 – – – – Sales – (23 ) – – (23 ) – – – – Settlements (21 ) – (37 ) – (58 ) 15 – – 15 At 30 June 2018 62 224 175 148 609 (38 ) (6 ) (1 ) (45 ) (Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period 21 (5 ) (4 ) – 12 9 – – 9 At 1 January 2017 103 264 32 – 399 (74 ) (6 ) – (80 ) Total (losses)/gains recognised in profit or loss: – Fair value movements 6 (9 ) – – (3 ) (7 ) – – (7 ) – Foreign exchange and other movements (5 ) – – – (5 ) 5 – – 5 Gains recognised in other comprehensive income – – 9 – 9 – – – – Sales – (3 ) – – (3 ) – – – – Settlements (9 ) – – – (9 ) 7 – – 7 At 30 June 2017 95 252 41 – 388 (69 ) (6 ) – (75 ) Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period 1 (9 ) – – (8 ) (2 ) – – (2 ) Effect of changes in significant unobservable assumptions to reasonably possible alternatives (Level 3) Other than as described above, there has been no significant change to the unobservable inputs and sensitivities used in Level 3 fair values as set out in Note 37(i) to the Consolidated Financial Statements in the 2017 Annual Report.

Related Party Disclosures

Related Party Disclosures	6 Months Ended
	Jun. 30, 2018
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Related Party Disclosures	24. RELATED PARTY DISCLOSURES Related party transactions in H118 were made in the ordinary course of business, except those carried out with Banco Santander SA as part of our ring-fencing plans, 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 addition, transactions with pension schemes operated by the Santander UK group are described in Note 28 to the Consolidated Financial Statements in the 2017 Annual Report. At 30 June 2018, amounts owed by related parties increased to £14,509m (2017: £5,683m) and amounts owed to related parties increased to £23,663m (2017: £13,467m) principally due to the transfer of third party derivative balances to Banco Santander SA as part of our ring-fencing plans. In addition, and following Court approval of our Ring-Fence Transfer Scheme on 11 and 12 June 2018, there were further business transfers to the Banco Santander SA group in July 2018. For more on this, see Note 26 and Note 27.

Transition to IFRS 9

Transition to IFRS 9	6 Months Ended
	Jun. 30, 2018
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Transition to IFRS 9	25. TRANSITION TO IFRS 9 i) IAS 39 to IFRS 9 reconciliations Statutory balance sheet reconciliation under IAS 39 and IFRS 9 The measurement categories and carrying amounts of financial assets determined in accordance with IAS 39 and IFRS 9 are compared below, illustrating a total net assets decrease of £192m as a result of the application of IFRS 9: IAS 39 IFRS 9 Assets Measurement Carrying amount (31 December £m Reclassifications (1) £m Remeasurement (2) £m Measurement Carrying amount (1 January £m Re-presentation (3) £m IFRS 9 Balance (1 January 2018) £m Cash and balances with central banks Loans & receivables 32,771 – – Amortised cost 32,771 – 32,771 Trading assets FVTPL 30,536 – – FVTPL (Mandatory) 30,536 – 30,536 FVTPL 19 – – FVOCI 19 (19 ) – 30,555 – – 30,555 (19 ) 30,536 Derivative financial instruments FVTPL (Trading) 19,942 – – FVTPL (Mandatory) 19,942 – 19,942 Financial assets designated at fair value (4) FVTPL (Designated) 1,022 (45 ) – Amortised cost 977 (977 ) – FVTPL (Designated) 836 – – FVTPL (Designated) 836 – 836 FVTPL (Designated) 238 – – FVTPL (Mandatory) 238 1,181 1,419 2,096 (45 ) – 2,051 204 2,255 Loans and advances to banks Loans & receivables 3,463 – – Amortised cost 3,463 – 3,463 Loans and advances to customers (5) Loans & receivables 199,218 – (211 ) Amortised cost 199,007 977 199,984 Loans & receivables 181 (1 ) – FVOCI 180 (180 ) – Loans & receivables 91 – – FVTPL (Mandatory) 91 (91 ) – 199,490 (1 ) (211 ) 199,278 706 199,984 Reverse repurchase agreements – non-trading Loans & receivables 2,464 – – Amortised cost 2,464 2,464 Financial investments Loans & receivables 1,198 – – Amortised cost 1,198 – 1,198 Loans & receivables 982 (2 ) – FVTPL (Mandatory) 980 (980 ) – Available-for-sale 8,743 – – FVOCI 8,743 199 8,942 Available-for-sale 29 – – FVTPL (Mandatory) 29 (29 ) – Held-to-maturity 6,578 – – Amortised cost 6,578 – 6,578 Available-for-sale 81 – – FVTPL (Mandatory) 81 (81 ) – 17,611 (2 ) – 17,609 (891 ) 16,718 Other assets Other assets 6,373 (1 ) – Other assets 6,372 – 6,372 Total assets (pre-deferred (6) 314,765 (49 ) (211 ) 314,505 – 314,505 (1) This column captures the gross (pre-tax) (2) This column captures the gross (pre-tax) non-amortised held-to-maturity available-for-sale (3) This column captures the balance sheet category re-presentations available-for-sale (4) The balance sheet category for ‘Financial assets designated at fair value’ has been changed to ‘Other financial assets at fair value through profit or loss’ following the adoption of IFRS 9. (5) Of the £211m of increase in loss allowance, £6m relates to ECL on financial guarantee contracts, which for presentation purposes have been aggregated in the assets section. See loss allowance reconciliation table below. (6) The impact of transition to IFRS 9 gives rise to a deferred tax asset of £68m, of which £14m is attributable to Reclassifications, and £54m to Remeasurement. This deferred tax asset will be offset against our deferred tax liabilities. Loss allowance reconciliation (on adoption of IFRS 9) Loss allowance under IAS 39/ provisions under IAS 37 (31 December 2017) £m Reclassifications £m Re-measurement £m Loss allowance (1 January 2018) £m Loans & receivables (IAS 39)/Financial assets at amortised cost (IFRS 9) (1) Loans and advances to customers 940 – 205 1,145 Provisions for off-balance (2) Financial guarantees – – 6 6 Total 940 – 211 1,151 (1) For financial instruments subject to incurred loss assessment under IAS 39, and amortised cost under IFRS 9. There are no loss allowance movements attributable to held-to-maturity available-for-sale (2) The ECL for off-balance Reserves and retained earnings Impact at 1 January 2018 £m Closing retained earnings and reserves under IAS 39 5,033 Other reserves Closing balance under IAS 39 (1) 301 Reclassification of investment securities (debt and equity) from AFS to FVTPL (2) (5 ) Opening balance under IFRS 9 (3) 296 Retained earnings Closing balance under IAS 39 4,732 Reclassification under IFRS 9 (44 ) Recognition of expected credit losses under IFRS 9 (211 ) Deferred tax asset 68 Opening balance under IFRS 9 4,545 Opening retained earnings and reserves under IFRS 9 4,841 (1) Other reserves consists of the following components under IAS 39: £68m of available-for-sale available-for-sale (2) Consists of loans and receivables which have transferred to FVOCI, and equity instruments which have transferred from available-for-sale non-trading (3) Other reserves consists of the following components under IFRS 9: £63m of fair value reserve, £228m of cash flow hedging reserve, and £5m of foreign currency translation reserves. ii) IFRS 9 areas of significant management judgement Classification and measurement IFRS 9 requires that all financial assets are subsequently measured at AC, FVOCI or FVTPL based on the business model for managing the financial assets and their contractual cash flow characteristics. The business model assessment is an area of significant judgement as it depends upon facts and circumstances and the intentions of an entity in relation to particular investments. ECL impairment methodology We have made a number of management judgements around subjective elements and inputs in order to implement ECL capabilities in the organisation. Some of these judgements pertain to decisions made throughout the design and build of ECL methodology, and others to the application of ECL methodology. Whilst only the latter category will be subject to periodic monitoring and review at subsequent reporting intervals, all of these judgements – to varying degrees – give rise to inherent measurement uncertainty in our reportable ECL. The main design and build judgements, subject to ad-hoc - The definition of default: for IFRS 9 purposes, we use the same default criteria as for the regulatory capital models, or a similar definition if not an IRB portfolio; - SICR – PD at origination: where we have experienced limitations on the availability of origination data, we have made certain proxy assumptions. In these cases, we make adjustments to the PD at the proxy origination date to account for the possibility of the PD already being increased since the actual origination. We consider such adjustments immaterial; - Lifetime periods: to mitigate the computational overhead of running all portfolios out to their natural lifetime, we apply restrictions to certain portfolios with a high volume of accounts (e.g. mortgages and overdrafts on bank accounts). The life of each facility type is the point when the monthly increase in ECL becomes zero or de minimis; and - Effective Interest Rate (EIR): for the majority of our portfolios, the income recognition EIRs that are calculated under IAS 39 are used as the discount factor in the IFRS 9 ECL calculations. Retail EIRs are based on behavioural cash flows, whereas corporate EIRs use contractual cash flows with an adjustment factor to take account of prepayments. The main application judgements are included in the ‘Critical accounting policies and areas of significant management judgement’ section, in the ‘Accounting policies’. We will further assess our measurement uncertainty and sensitivity to changes in economic credit conditions throughout the course of 2018, and anticipate providing our expected inherent quantitative impacts of such management judgements in our 2018 Annual Report. The form and content of such disclosure will be guided by the outcomes of the PRA Taskforce on Disclosures about ECL in which we participate.

Ring-Fencing

Ring-Fencing	6 Months Ended
	Jun. 30, 2018
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Ring-Fencing	26. RING-FENCING We have made significant progress in the implementation of our ring-fence structure this year ahead of the 1 January 2019 ring-fencing legislation deadline. Our model ensures minimal customer disruption and maintains longer-term flexibility. The majority of our customer loans and assets as well as customer deposits and liabilities will remain within Santander UK plc, our principal ring-fenced bank. Prohibited businesses which cannot be transacted within the ring-fence include our derivatives business with financial institutions and certain corporates and elements of our short-term markets business, and will be transferred to Banco Santander London Branch or Banco Santander. A small amount of residual activity or businesses which, for legal or operational reasons cannot remain inside the ring-fence and cannot be transferred, will remain in the Santander UK group, outside the ring-fence bank. This includes legacy contracts, the employee Sharesave scheme and offshore deposits. Our transition to a ‘wide’ ring-fence structure to serve our retail, commercial and corporate customers is now approaching completion following the achievement of several major milestones. We received Court approval of our Ring-Fence Transfer Scheme at the Part VII Sanctions Hearing, which took place on 11 and 12 June 2018. In June 2018, we transferred customer loans totalling £0.7bn from CIB to Banco Santander London Branch. The remaining transfers to Banco Santander London Branch or Banco Santander were completed in July 2018. Furthermore, planned novations were finalised before the Part VII migrations, and short-term funding activity has now been transferred to Santander UK plc from Abbey National Treasury Services plc.

Assets and Liabilities Held for

Assets and Liabilities Held for Sale	6 Months Ended
	Jun. 30, 2018
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Assets and Liabilities Held for Sale	27. ASSETS AND LIABILITIES HELD FOR SALE Following Court approval of our Ring-Fence Transfer Scheme on 11 and 12 June 2018, management considered the related business transfers to be highly probable at 30 June 2018. As such, the Santander UK group reclassified the following assets and liabilities as held for sale: – The prohibited business of Abbey National Treasury Services plc, save for a small pool of residual assets, which mainly included our derivatives business with financial institutions, certain corporates and our gilt-edged market making business. These were transferred to the Banco Santander SA group in July 2018. – The business of the Crown Dependency branches (Jersey and Isle of Man) of Santander UK plc. These will be transferred outside the Santander UK plc group pursuant to transfer schemes effected under relevant Jersey and Isle of Man law. – A small pool of residual assets that will remain in Abbey National Treasury Services plc. Santander UK Group Holdings plc will acquire 100% of the ordinary share capital of Abbey National plc from Santander UK plc. – The assets and liabilities of Santander Equity Investments Limited and its subsidiaries. Santander UK Group Holdings plc will acquire the entire share capital of Santander Equity Investments Limited. At 30 June 2018 these assets and liabilities comprised: Net assets Assets Trading assets 1,967 Derivative financial instruments 19,694 Other financial assets at fair value through profit and loss 823 Loans and advances to banks 506 Loans and advances to customers 1,068 Reverse repurchase agreements- non trading 74 Financial investments 104 Other assets 5 Total assets held for sale 24,241 Liabilities Deposits by banks 31 Deposits by customers 5,725 Trading liabilities 1,842 Derivative financial instruments 19,007 Other liabilities 11 Total liabilities held for sale 26,616 Net liabilities held for sale (2,375 ) These business transfers have been, or will be, made for a cash consideration equivalent to the book value of the associated assets and liabilities, which represents a fair value for the Santander UK group. Costs to sell are expected to be immaterial.

Events After the Balance Sheet

Events After the Balance Sheet Date	6 Months Ended
	Jun. 30, 2018
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Events After the Balance Sheet Date	28. EVENTS AFTER THE BALANCE SHEET DATE In July 2018, as part of our ring-fencing plans, the Santander UK group transferred £22.9bn of assets and £20.7bn of liabilities to the Banco Santander group. These comprised the prohibited business of Abbey National Treasury Services plc, save for a small pool of residual assets. For more details, see Note 27.

Accounting Policies (Policies)

Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2018
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Critical Accounting Policies and Areas of Significant Management Judgement	CRITICAL ACCOUNTING POLICIES AND AREAS OF SIGNIFICANT MANAGEMENT JUDGEMENT The preparation of the Condensed Consolidated Interim Financial Statements requires management to make estimates and judgements that affect the reported amount of assets and liabilities at the date of the Condensed Consolidated Interim Financial Statements and the reported amount of income and expenses during the reporting period. Management evaluates its estimates and judgements on an ongoing basis. Management bases its estimates and judgements on historical experience and on various other factors that are believed to be reasonable under the circumstances. Actual results may differ from these estimates under different assumptions or conditions. The introduction of IFRS 9 has given rise to areas of significant management judgement in respect of the ECL impairment methodology and these are explained further below. There have been no other significant changes in the basis upon which estimates and judgements have been determined compared to that applied in the 2017 Annual Report.

Segments (Tables)

Segments (Tables)	6 Months Ended
	Jun. 30, 2018
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Summary of Results by Segment	Half year to 30 June 2018 Retail Commercial Corporate & Corporate Total Net interest income/(expense) 1,587 204 33 (13 ) 1,811 Non-interest 305 40 171 (15 ) 501 Total operating income/(expense) 1,892 244 204 (28 ) 2,312 Operating expenses before credit impairment losses, provisions and charges (965 ) (135 ) (150 ) (33 ) (1,283 ) Credit impairment (losses)/releases (52 ) (22 ) (18 ) 1 (91 ) Provisions for other liabilities and charges (33 ) 7 (2 ) (5 ) (33 ) Total credit impairment losses, provisions and charges (85 ) (15 ) (20 ) (4 ) (124 ) Profit/(loss) before tax 842 94 34 (65 ) 905 Revenue from external customers 2,170 319 233 (410 ) 2,312 Inter-segment revenue (278 ) (75 ) (29 ) 382 – Total operating income/(expense) 1,892 244 204 (28 ) 2,312 Revenue from external customers includes the following fee and commission income disaggregated by income type: (1) - Current account and debit card fees 311 13 14 – 338 - Insurance, protection and investments 46 – – – 46 - Credit cards 45 – – – 45 - Non-banking (2) 73 28 49 5 155 Total fee and commission income (3) 475 41 63 5 584 Total assets (4) 177,374 19,028 55,482 64,748 316,632 Of which assets held for sale 306 – 23,814 121 24,241 Total liabilities 148,846 17,064 49,884 84,269 300,063 Of which liabilities held for sale 5,735 – 20,867 15 26,617 Half year to 30 June 2017 (5) Retail £ Commercial £ Corporate & £ Corporate £ Total £ Net interest income 1,657 191 33 41 1,922 Non-interest 300 37 201 53 591 Total operating income 1,957 228 234 94 2,513 Operating expenses before credit impairment losses, provisions and charges (919 ) (109 ) (145 ) (42 ) (1,215 ) Credit impairment (losses)/releases (39 ) (3 ) (9 ) 3 (48 ) Provisions for other liabilities and charges (155 ) (29 ) – (2 ) (186 ) Total credit impairment losses, provisions and (charges)/releases (194 ) (32 ) (9 ) 1 (234 ) Profit before tax 844 87 80 53 1,064 Revenue from external customers 2,272 318 279 (356 ) 2,513 Inter-segment revenue (315 ) (90 ) (45 ) 450 – Total operating income 1,957 228 234 94 2,513 Revenue from external customers includes the following fee and commission income disaggregated by income type: (1) - Current account and debit card fees 330 14 13 – 357 - Insurance, protection and investments 48 – – – 48 - Credit cards 44 – – – 44 - Non-banking (2) 65 30 65 – 160 Total fee and commission income (3) 487 44 78 – 609 31 December 2017 Total assets (4) 174,524 19,391 51,078 69,772 314,765 Total liabilities 150,847 18,697 45,603 83,413 298,560 (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 (3) The majority of 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. Insurance commissions and associated income are recognised over time in accordance with the accounting policy described in Note 1 to these Condensed Consolidated Interim Financial Statements. (4) Includes customer loans, net of impairment loss allowances. (5) Restated on the same basis as described in Note 2 to the Consolidated Financial Statements in the 2017 Annual Report.

Net Trading and Other Income (T

Net Trading and Other Income (Tables)	6 Months Ended
	Jun. 30, 2018
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Summary of Net Trading and Other Income	Half year to Half year to £ Net trading and other income 121 182

Operating Expenses Before Imp38

Operating Expenses Before Impairment Losses, Provisions and Charges (Tables)	6 Months Ended
	Jun. 30, 2018
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Summary of Operating Expenses Before Impairment Losses, Provisions and Charges	Half year to Half year to £ Staff costs 691 566 Other administration expenses 411 493 Depreciation, amortisation and impairment 181 156 1,283 1,215

Credit Impairment Losses and 39

Credit Impairment Losses and Provisions (Tables)	6 Months Ended
	Jun. 30, 2018
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Summary of Impairment Losses and Provisions	Half year to Half year to £ Credit Impairment losses: Loans and advances to customers (See Note 11) 102 76 Recoveries of loans and advances, net of collection costs (See Note 11) (21 ) (28 ) Off-balance 10 91 48 Provisions for other liabilities and charges (excluding off-balance 33 181 Provisions for residual value and voluntary termination (See Note 11) – 5 33 186 124 234

Taxation (Tables)

Taxation (Tables)	6 Months Ended
	Jun. 30, 2018
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Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate	Half year to Half year to £ Profit before tax 905 1,064 Tax calculated at a tax rate of 19% (H117: 19.25%) 172 205 Bank surcharge on profits 64 77 Non-deductible 5 5 Non-deductible 13 18 Non-deductible (2 ) 16 Net disallowable items and non-taxable 10 12 Adjustment to prior period provisions (6 ) (10 ) Tax charge 256 323

Trading Assets (Tables)

Trading Assets (Tables)	6 Months Ended
	Jun. 30, 2018
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Disclosure of Trading Assets	30 June 2018 31 December 2017 £ Securities purchased under resale agreements 3,740 8,870 Debt securities – 5,156 Equity securities 8,264 9,662 Cash collateral associated with trading balances 7,082 6,156 Short-term loans 72 711 19,158 30,555

Derivative Financial Instrume42

Derivative Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2018
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Notional Amounts and Fair Values of Derivative Financial Instruments	30 June 2018 31 December 2017 Fair value Fair value Notional Assets Liabilities Notional £ Assets £ Liabilities £ Derivatives held for trading: Exchange rate contracts 9,481 406 334 144,160 2,559 4,130 Interest rate contracts 74,493 482 3 863,151 11,612 11,140 Equity and credit contracts 12,776 799 440 19,814 888 693 Total derivatives held for trading 96,750 1,687 777 1,027,125 15,059 15,963 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 3,339 332 – 2,641 312 6 Interest rate contracts 70,066 7 423 59,610 1,272 1,470 Equity derivative contracts – – – 16 – 4 73,405 339 423 62,267 1,584 1,480 Designated as cash flow hedges: Exchange rate contracts 27,603 1,691 87 23,117 3,206 55 Interest rate contracts 23,992 121 177 12,884 84 115 Equity derivative contracts 50 – 2 26 9 – 51,645 1,812 266 36,027 3,299 170 Total derivatives held for hedging 125,050 2,151 689 98,294 4,883 1,650 Total derivative financial instruments 221,800 3,838 1,466 1,125,419 19,942 17,613

Loans and Advances to Banks (Ta

Loans and Advances to Banks (Tables)	6 Months Ended
	Jun. 30, 2018
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Summary of Loans and Advances to Banks	30 June 2018 31 December 2017 £ Loans and advances to banks 2,410 3,463

Loans and Advances to Custome44

Loans and Advances to Customers (Tables)	6 Months Ended
	Jun. 30, 2018
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Summary of Net Loans and Advances to Customers	30 June 2018 31 December 2017 £ Loans and advances to customers 200,471 199,151 Amounts due from fellow Banco Santander subsidiaries and joint ventures 1,344 1,199 Amounts due from Santander UK Group Holdings plc – 8 Loans and advances to customers 201,815 200,358 Credit impairment loss allowances on loans and advances to customers (792 ) (940 ) Residual value and voluntary termination provisions (73 ) (78 ) Net loans and advances to customers 200,950 199,340
Summary of Movement in Impairment Loss Allowances	Movement in credit impairment loss allowances on loans and advances: Loans secured Corporate Finance Other Total At 31 December 2017 225 490 46 179 940 Adjustment for the adoption of IFRS 9 (see Note 1) 47 99 11 54 211 Re-allocation (2) (3 ) (25 ) – (22 ) (50 ) At 1 January 2018 269 564 57 211 1,101 (Release)/charge to the income statement (13 ) 24 17 74 102 Write-offs and other items (1) (7 ) (318 ) (15 ) (71 ) (411 ) At 30 June 2018 249 270 59 214 792 Recoveries, net of collection costs 1 1 3 16 21 At 1 January 2017 279 382 45 215 921 (Release)/charge to the income statement (18 ) 12 17 65 76 Write-offs and other items (1) (10 ) (38 ) (16 ) (69 ) (133 ) At 30 June 2017 251 356 46 211 864 Recoveries, net of collection costs 2 1 4 21 28 (1) Mortgage write-offs exclude the effect of the unwind over time of the discounting in estimating losses, as described in the accounting policy ‘Impairment of financial assets’ in Note 1 to the Consolidated Financial Statements in the 2017 Annual Report. Mortgage write-offs including this effect were £8m (H117: £11m). (2) This relates to ECL on undrawn exposures following the adoption of a methodology to enable its separate identification from ECL on drawn exposures.

Securitisations and Covered B45

Securitisations and Covered Bonds (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Summary of Gross Asset Securitised	The gross assets securitised at 30 June 2018 and 31 December 2017 under the structures described below were: Gross assets securitised 30 June 2018 31 December 2017 £ Master trust structures: – Holmes 3,788 4,299 – Fosse 5,167 5,732 – Langton 3,433 3,893 12,388 13,924 Other securitisation structures: – Motor 1,146 1,318 – Auto ABS UK Loans 1,480 1,498 2,626 2,816 Total 15,014 16,740

Financial Investments (Tables)

Financial Investments (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Summary of Financial Investments	30 June 2018 31 December 2017 £ Amortised cost: – Asset backed securities 761 2,180 – Debt securities (1) 6,544 6,578 7,305 8,758 FVOCI: – Debt securities 13,506 – Loans and advances to customers (2) 175 13,681 Available-for-sale: – Debt securities 8,772 – Equity securities 81 8,853 20,986 17,611 (1) These securities were previously classified as held-to-maturity (2) These comprise other loans and receivables held within hold to collect and sell business models that were moved from trading assets and loans and advances to customers at amortised cost, to financial investments, due to their reclassification to FVOCI on adoption of IFRS 9.

Deposits by Banks (Tables)

Deposits by Banks (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Schedule of Deposits by Banks	30 June 2018 31 December 2017 £ Items in the course of transmission 326 303 Deposits held as collateral 2,408 1,760 Other deposits (1) 12,921 10,645 15,655 12,708 (1) Includes drawdown from the Term Funding Scheme of £10.8bn (2017: £8.5bn).

Deposits by Customers (Tables)

Deposits by Customers (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Schedule of Deposits by Customers	30 June 2018 31 December 2017 £ Current and demand accounts – interest-bearing 84,656 85,749 – non-interest-bearing 2 2 Savings accounts (1) 65,033 70,461 Time deposits 17,358 19,951 Amounts due to Santander UK Group Holdings plc (2) 8,301 6,256 Amounts due to fellow Banco Santander subsidiaries 535 727 175,885 183,146 (1) Includes equity index-linked deposits of £1,232m (2017: £1,301m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,232m and £44m (2017: £1,301m and £67m) respectively. (2) Includes downstreamed funding from our immediate parent company Santander UK Group Holdings plc.

Trading Liabilities (Tables)

Trading Liabilities (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Schedule of Trading Liabilities	30 June 2018 31 December 2017 £ Securities sold under repurchase agreements 5,612 25,504 Short positions in securities and unsettled trades 190 3,694 Cash collateral associated with trading balances 2,573 1,911 8,375 31,109

Debt Securities in Issue (Table

Debt Securities in Issue (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Summary of Debt Securities in Issue	30 June 2018 31 December 2017 £ Medium-term notes 21,950 18,002 Covered bond programme 16,017 15,799 Certificates of deposit 3,304 4,681 Credit Linked Notes 43 43 Securitisation programmes 4,690 4,108 46,004 42,633

Provisions (Tables)

Provisions (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Summary of Provisions Reconciliation	Conduct remediation PPI £ Wealth and £ Other £ Regulatory- £ Vacant £ Other (1) £ Total £ At 31 December 2017 356 3 44 57 39 59 558 Re-allocation – – – – – 50 (2) 50 At 1 January 2018 356 3 44 57 39 109 608 Additional provisions – – – – 11 64 75 Provisions released – (3 ) (11 ) (4 ) – (14 ) (32 ) Utilisation (55 ) – (2 ) (37 ) (7 ) (46 ) (147 ) At 30 June 2018 301 – 31 16 43 113 504 At 1 January 2017 457 22 14 96 47 64 700 Additional provisions 69 – 35 2 6 69 181 Utilisation (121 ) (27 ) (2 ) (53 ) (5 ) (87 ) (295 ) Transfers – 9 – – – – 9 At 30 June 2017 405 4 47 45 48 46 595 (1) At 30 June 2018 this included £53m (2017: £59m) in respect of operational loss and operational risk provisions, restructuring charges and litigation and related expenses. It also included £60m in respect of credit impairment losses for off balance sheet exposures relating to guarantees given to third parties and undrawn loan commitments. See Note 5 for details of the income statement charge. (2) This relates to ECL on loan commitments following the adoption of a methodology to enable its separate identification from ECL on drawn exposures.
Summary of Key Drivers of PPI Provision Balance and Forecast Assumptions Used in Calculating Provision	The table below sets out the key drivers of the provision balance and forecast assumptions used in calculating the PPI provision, as well as the sensitivity of the provision to changes in the assumptions. It reflects a balanced view across all retail products and portfolios and includes redress for Plevin-related claims. Cumulative to Future expected Sensitivity analysis Inbound complaints (1) 1,858 436 25 = £12.3m Outbound contact (‘000) 488 292 25 = £5.4m Response rate to outbound contact 55% 90% 1% = £1.0m Average uphold rate per claim (2) 44% 72% 1% = £2.7m Average redress per claim (3) £1,363 £537 £100 = £50.5m (1) Includes all claims received regardless of whether we expect to make a payment; i.e. regardless of the likelihood of the Santander UK group incurring a liability. Excludes claims where the complainant has not held a PPI policy. (2) Claims include inbound and responses to outbound contact. (3) The future expected average redress per claim is lower than the cumulative average to date due to the inclusion of Plevin cases in the provision, as well as a shift in the complaint mix to a greater proportion of storecards, which typically held lower average balances.

Retirement Benefit Plans (Table

Retirement Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Summary of Retirement Benefit Plans	The amounts recognised in the balance sheet were as follows: 30 June 2018 31 December 2017 £ Assets/(liabilities) Funded defined benefit pension scheme – surplus 868 449 Funded defined benefit pension scheme – deficit (69 ) (245 ) Unfunded defined benefit pension scheme (39 ) (41 ) Total net assets 760 163
Summary of Movements in the Present Value of Defined Benefit Obligations and Fair Value of Scheme Assets	Movements in the present value of defined benefit obligations and fair value of scheme assets were as follows: 30 June 2018 30 June 2017 Present value of Fair value of Present value of £ Fair value of £ At 1 January (11,583 ) 11,746 (11,082 ) 11,218 Income statement (charge) / income (167 ) 145 (182 ) 156 Contributions paid – 90 – 91 Recognised in other comprehensive income: – Return on plan assets (excluding amounts included in net interest expense) – (72 ) – 85 – Actuarial movements arising from experience adjustments (39 ) – 11 – – Actuarial movements arising from changes in financial assumptions 640 – (17 ) – Benefits paid 221 (221 ) 191 (191 ) At 30 June (10,928 ) 11,688 (11,079 ) 11,359

Contingent Liabilities and Co53

Contingent Liabilities and Commitments (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Summary of Contingent Liabilities and Commitments	30 June 2018 31 December 2017 £ Guarantees given to third parties 1,666 1,557 Formal standby facilities, credit lines and other commitments 40,425 41,942 42,091 43,499

Financial Instruments (Tables)

Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Fair Values of Financial Instruments Carried at Amortised Cost	30 June2018 31 December 2017 Fair value Carrying Fair value £ Carrying £ Assets Loans and advances to banks 2,409 2,410 3,451 3,463 Loans and advances to customers 203,578 200,950 201,667 199,340 Reverse repurchase agreements- non trading 13,616 13,611 2,612 2,614 Financial investments 7,121 7,305 8,646 8,758 Assets held for sale (1) 1,733 1,752 – – 228,457 226,028 216,376 214,175 Liabilities Deposits by banks 15,667 15,655 12,721 12,708 Deposits by customers 175,990 175,885 183,227 183,146 Repurchase agreements- non trading 17,504 17,447 1,648 1,578 Debt securities in issue 47,252 46,004 44,296 42,633 Subordinated liabilities 4,120 3,758 4,256 3,793 Liabilities held for sale (1) 5,756 5,756 – – 266,289 264,505 246,148 243,858 (1) Assets and liabilities classified as held for sale are measured in accordance with IFRS 9; any assets and liabilities held for sale which are measured at fair value are included in the fair value table in section (c) below.
Fair Values 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 30 June 2018 and 31 December 2017, analysed by their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. 30 June 2018 31 December 2017 Level 1 Level 2 Level 3 Total Level 1 £ Level 2 £ Level 3 £ Total £ Valuation Assets Trading assets Securities purchased under resale agreements – 3,740 – 3,740 – 8,870 – 8,870 A Debt securities – – – – 5,156 – – 5,156 – Equity securities 8,264 – – 8,264 9,662 – – 9,662 – Cash collateral – 7,082 – 7,082 – 6,156 – 6,156 A Short-term loans 35 37 – 72 656 55 – 711 A 8,299 10,859 – 19,158 15,474 15,081 – 30,555 Derivative financial instruments Exchange rate contracts – 2,427 2 2,429 – 6,061 16 6,077 A Interest rate contracts – 610 – 610 – 12,956 12 12,968 A & C Equity and credit contracts – 739 60 799 – 861 36 897 B & D – 3,776 62 3,838 – 19,878 64 19,942 Other financial assets at fair value through profit or loss Loans and advances to customers – 1,604 71 1,675 – 1,485 64 1,549 A Debt securities 189 677 153 1,019 184 187 176 547 A & B Equity securities 16 – – 16 B 205 2,281 224 2,710 184 1,672 240 2,096 Financial investments FVOCI – debt securities 12,807 699 – 13,506 D FVOCI – loans and advances to customers – – 175 175 D Available-for-sale 8,770 2 – 8,772 C Available-for-sale 19 9 53 81 B 12,807 699 175 13,681 8,789 11 53 8,853 Assets held for sale (1) 1,966 20,370 148 22,484 – – – – A, B, C & D 1,966 20,370 148 22,484 – – – – Total assets at fair value 23,277 37,985 609 61,871 24,447 36,642 357 61,446 Liabilities Trading liabilities Securities sold repurchase agreements – 5,612 – 5,612 – 25,504 – 25,504 A Short positions in securities and unsettled trades 190 – – 190 3,694 – – 3,694 – Cash collateral – 2,573 – 2,573 – 1,911 – 1,911 A 190 8,185 – 8,375 3,694 27,415 – 31,109 Derivative financial instruments Exchange rate contracts – 421 – 421 – 4,176 15 4,191 A Interest rate contracts – 603 – 603 – 12,720 5 12,725 A & C Equity and credit contracts – 404 38 442 1 653 43 697 B & D – 1,428 38 1,466 1 17,549 63 17,613 Financial liabilities designated at fair value Debt securities in issue – 1,089 6 1,095 – 1,629 6 1,635 A Structured deposits – 143 – 143 – 680 – 680 A – 1,232 6 1,238 – 2,309 6 2,315 Liabilities held for sale (1) 1,842 19,006 1 20,849 – – – – A, B, C & D 1,842 19,006 1 20,849 – – – – Total liabilities at fair value 2,032 29,851 45 31,928 3,695 47,273 69 51,037 (1) Includes assets and liabilities held for sale which are measured at fair value.
Summary of Fair Value Adjustment	The magnitude and types of fair value adjustment adopted by Corporate & Investment Banking are listed in the following table: 30 June 2018 31 December 2017 £ Risk-related: – Bid-offer 27 34 – Uncertainty 37 43 – Credit risk adjustment 19 36 – Funding fair value adjustment 9 6 92 119 Model-related 9 8 Day One profit – 1 101 128
Movement of Assets and Liabilities Measured at Fair Value Using Valuation Technique With Significant Unobservable Inputs (Level 3)	The following table shows the movement in the period of Level 3 financial instruments, measured at fair value using a valuation technique with significant unobservable inputs: Assets Liabilities Derivatives £ Other financial value through £ Financial £ Assets £ Total £ Derivatives £ Financial £ Liabilities £ Total £ At 31 December 2017 64 240 53 – 357 (63 ) (6 ) – (69 ) Adjustment for the adoption of IFRS 9 – 139 146 – 285 – – – – At 1 January 2018 64 379 199 – 642 (63 ) (6 ) – (69 ) Total (losses)/gains recognised in profit or loss: – Fair value movements 26 (5 ) (4 ) – 17 4 – – 4 – Foreign exchange and other movements (5 ) – – – (5 ) 5 – – 5 Transfers in – 19 – – 19 – – – – Transfer to held for sale (2 ) (146 ) – 148 – 1 – (1 ) – Additions – – 17 – 17 – – – – Sales – (23 ) – – (23 ) – – – – Settlements (21 ) – (37 ) – (58 ) 15 – – 15 At 30 June 2018 62 224 175 148 609 (38 ) (6 ) (1 ) (45 ) (Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period 21 (5 ) (4 ) – 12 9 – – 9 At 1 January 2017 103 264 32 – 399 (74 ) (6 ) – (80 ) Total (losses)/gains recognised in profit or loss: – Fair value movements 6 (9 ) – – (3 ) (7 ) – – (7 ) – Foreign exchange and other movements (5 ) – – – (5 ) 5 – – 5 Gains recognised in other comprehensive income – – 9 – 9 – – – – Sales – (3 ) – – (3 ) – – – – Settlements (9 ) – – – (9 ) 7 – – 7 At 30 June 2017 95 252 41 – 388 (69 ) (6 ) – (75 ) Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period 1 (9 ) – – (8 ) (2 ) – – (2 )

Transition to IFRS 9 (Tables)

Transition to IFRS 9 (Tables) - IFRS 9 [member]	6 Months Ended
	Jun. 30, 2018
Summary of Measurement Categories and Carrying Amounts of Financial Assets Determined in Accordance with IAS 39 and IFRS 9	The measurement categories and carrying amounts of financial assets determined in accordance with IAS 39 and IFRS 9 are compared below, illustrating a total net assets decrease of £192m as a result of the application of IFRS 9: IAS 39 IFRS 9 Assets Measurement Carrying amount (31 December £m Reclassifications (1) £m Remeasurement (2) £m Measurement Carrying amount (1 January £m Re-presentation (3) £m IFRS 9 Balance (1 January 2018) £m Cash and balances with central banks Loans & receivables 32,771 – – Amortised cost 32,771 – 32,771 Trading assets FVTPL 30,536 – – FVTPL (Mandatory) 30,536 – 30,536 FVTPL 19 – – FVOCI 19 (19 ) – 30,555 – – 30,555 (19 ) 30,536 Derivative financial instruments FVTPL (Trading) 19,942 – – FVTPL (Mandatory) 19,942 – 19,942 Financial assets designated at fair value (4) FVTPL (Designated) 1,022 (45 ) – Amortised cost 977 (977 ) – FVTPL (Designated) 836 – – FVTPL (Designated) 836 – 836 FVTPL (Designated) 238 – – FVTPL (Mandatory) 238 1,181 1,419 2,096 (45 ) – 2,051 204 2,255 Loans and advances to banks Loans & receivables 3,463 – – Amortised cost 3,463 – 3,463 Loans and advances to customers (5) Loans & receivables 199,218 – (211 ) Amortised cost 199,007 977 199,984 Loans & receivables 181 (1 ) – FVOCI 180 (180 ) – Loans & receivables 91 – – FVTPL (Mandatory) 91 (91 ) – 199,490 (1 ) (211 ) 199,278 706 199,984 Reverse repurchase agreements – non-trading Loans & receivables 2,464 – – Amortised cost 2,464 2,464 Financial investments Loans & receivables 1,198 – – Amortised cost 1,198 – 1,198 Loans & receivables 982 (2 ) – FVTPL (Mandatory) 980 (980 ) – Available-for-sale 8,743 – – FVOCI 8,743 199 8,942 Available-for-sale 29 – – FVTPL (Mandatory) 29 (29 ) – Held-to-maturity 6,578 – – Amortised cost 6,578 – 6,578 Available-for-sale 81 – – FVTPL (Mandatory) 81 (81 ) – 17,611 (2 ) – 17,609 (891 ) 16,718 Other assets Other assets 6,373 (1 ) – Other assets 6,372 – 6,372 Total assets (pre-deferred (6) 314,765 (49 ) (211 ) 314,505 – 314,505 (1) This column captures the gross (pre-tax) (2) This column captures the gross (pre-tax) non-amortised held-to-maturity available-for-sale (3) This column captures the balance sheet category re-presentations available-for-sale (4) The balance sheet category for ‘Financial assets designated at fair value’ has been changed to ‘Other financial assets at fair value through profit or loss’ following the adoption of IFRS 9. (5) Of the £211m of increase in loss allowance, £6m relates to ECL on financial guarantee contracts, which for presentation purposes have been aggregated in the assets section. See loss allowance reconciliation table below. (6) The impact of transition to IFRS 9 gives rise to a deferred tax asset of £68m, of which £14m is attributable to Reclassifications, and £54m to Remeasurement. This deferred tax asset will be offset against our deferred tax liabilities.
Summary of Reconciliation of Loss Allowance	Loss allowance reconciliation (on adoption of IFRS 9) Loss allowance under IAS 39/ provisions under IAS 37 (31 December 2017) £m Reclassifications £m Re-measurement £m Loss allowance (1 January 2018) £m Loans & receivables (IAS 39)/Financial assets at amortised cost (IFRS 9) (1) Loans and advances to customers 940 – 205 1,145 Provisions for off-balance (2) Financial guarantees – – 6 6 Total 940 – 211 1,151 (1) For financial instruments subject to incurred loss assessment under IAS 39, and amortised cost under IFRS 9. There are no loss allowance movements attributable to held-to-maturity available-for-sale (2) The ECL for off-balance
Summary of Reserves and Retained Earnings	Reserves and retained earnings Impact at 1 January 2018 £m Closing retained earnings and reserves under IAS 39 5,033 Other reserves Closing balance under IAS 39 (1) 301 Reclassification of investment securities (debt and equity) from AFS to FVTPL (2) (5 ) Opening balance under IFRS 9 (3) 296 Retained earnings Closing balance under IAS 39 4,732 Reclassification under IFRS 9 (44 ) Recognition of expected credit losses under IFRS 9 (211 ) Deferred tax asset 68 Opening balance under IFRS 9 4,545 Opening retained earnings and reserves under IFRS 9 4,841 (1) Other reserves consists of the following components under IAS 39: £68m of available-for-sale available-for-sale (2) Consists of loans and receivables which have transferred to FVOCI, and equity instruments which have transferred from available-for-sale non-trading (3) Other reserves consists of the following components under IFRS 9: £63m of fair value reserve, £228m of cash flow hedging reserve, and £5m of foreign currency translation reserves.

Assets and Liabilities Held f56

Assets and Liabilities Held for Sale (Tables)	6 Months Ended
	Jun. 30, 2018
Text block1 [abstract]
Summary of Assets and Liabilities Held for Sale	At 30 June 2018 these assets and liabilities comprised: Net assets Assets Trading assets 1,967 Derivative financial instruments 19,694 Other financial assets at fair value through profit and loss 823 Loans and advances to banks 506 Loans and advances to customers 1,068 Reverse repurchase agreements- non trading 74 Financial investments 104 Other assets 5 Total assets held for sale 24,241 Liabilities Deposits by banks 31 Deposits by customers 5,725 Trading liabilities 1,842 Derivative financial instruments 19,007 Other liabilities 11 Total liabilities held for sale 26,616 Net liabilities held for sale (2,375 )

Accounting Policies - Additiona

Accounting Policies - Additional Information (Detail) - IFRS 9 [member] £ in Millions	Jan. 01, 2018GBP (£)
Other Financial assets at fair value through profit or loss, category [member] | FVTPL (Mandatory) [member]
Disclosure of voluntary change in accounting policy [line items]
Loans and receivables	£ 1,071
Available-for-sale financial assets	110
Loans and advances to customers [member] | Amortised cost [member]
Disclosure of voluntary change in accounting policy [line items]
Social housing loans	977
Loans and advances to customers [member] | FVOCI [member]
Disclosure of voluntary change in accounting policy [line items]
Other loans and receivables	180
Trading Assets [member] | FVOCI [member]
Disclosure of voluntary change in accounting policy [line items]
Other loans and receivables	£ 19

Segments - Summary of Results b

Segments - Summary of Results by Segment (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Disclosure of operating segments [line items]
Net interest income/(expense)	£ 1,811	£ 1,922
Non-interest income/(expense)	501	591
Total operating income/(expense)	2,312	2,513
Operating expenses before credit impairment losses, provisions and charges	(1,283)	(1,215)
Credit impairment (losses)/releases	(91)	(48)
Provisions for other liabilities and charges	(33)	(186)
Total credit impairment losses, provisions and (charges)/releases	(124)	(234)
Profit before tax	905	1,064
Revenue from external customers	2,312	2,513
Inter-segment revenue	2,312	2,513
Total operating income/(expense)	2,312	2,513
Current account and debit card fees	338	357
Insurance, protection and investments	46	48
Credit cards	45	44
Non-banking and other fees	155	160
Total fee and commission income	584	609
Total assets	316,632		£ 314,505	£ 314,765
Of which assets held for sale	24,241			0
Total liabilities	300,063			298,560
Of which liabilities held for sale	26,616			0
Retail Banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	1,587	1,657
Non-interest income/(expense)	305	300
Total operating income/(expense)	1,892	1,957
Operating expenses before credit impairment losses, provisions and charges	(965)	(919)
Credit impairment (losses)/releases	(52)	(39)
Provisions for other liabilities and charges	(33)	(155)
Total credit impairment losses, provisions and (charges)/releases	(85)	(194)
Profit before tax	842	844
Revenue from external customers	2,170	2,272
Total operating income/(expense)	1,892	1,957
Current account and debit card fees	311	330
Insurance, protection and investments	46	48
Credit cards	45	44
Non-banking and other fees	73	65
Total fee and commission income	475	487
Total assets	177,374			174,524
Of which assets held for sale	306
Total liabilities	148,846			150,847
Of which liabilities held for sale	5,735
Commercial Banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	204	191
Non-interest income/(expense)	40	37
Total operating income/(expense)	244	228
Operating expenses before credit impairment losses, provisions and charges	(135)	(109)
Credit impairment (losses)/releases	(22)	(3)
Provisions for other liabilities and charges	7	(29)
Total credit impairment losses, provisions and (charges)/releases	(15)	(32)
Profit before tax	94	87
Revenue from external customers	319	318
Total operating income/(expense)	244	228
Current account and debit card fees	13	14
Non-banking and other fees	28	30
Total fee and commission income	41	44
Total assets	19,028			19,391
Total liabilities	17,064			18,697
Corporate And Investment Banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	33	33
Non-interest income/(expense)	171	201
Total operating income/(expense)	204	234
Operating expenses before credit impairment losses, provisions and charges	(150)	(145)
Credit impairment (losses)/releases	(18)	(9)
Provisions for other liabilities and charges	(2)
Total credit impairment losses, provisions and (charges)/releases	(20)	(9)
Profit before tax	34	80
Revenue from external customers	233	279
Total operating income/(expense)	204	234
Current account and debit card fees	14	13
Non-banking and other fees	49	65
Total fee and commission income	63	78
Total assets	55,482			51,078
Of which assets held for sale	23,814
Total liabilities	49,884			45,603
Of which liabilities held for sale	20,867
Corporate Centre [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	(13)	41
Non-interest income/(expense)	(15)	53
Total operating income/(expense)	(28)	94
Operating expenses before credit impairment losses, provisions and charges	(33)	(42)
Credit impairment (losses)/releases	1	3
Provisions for other liabilities and charges	(5)	(2)
Total credit impairment losses, provisions and (charges)/releases	(4)	1
Profit before tax	(65)	53
Revenue from external customers	(410)	(356)
Total operating income/(expense)	(28)	94
Non-banking and other fees	5
Total fee and commission income	5
Total assets	64,748			69,772
Of which assets held for sale	121
Total liabilities	84,269			£ 83,413
Of which liabilities held for sale	15
Elimination of Intersegment Amounts [member] | Retail Banking [member]
Disclosure of operating segments [line items]
Inter-segment revenue	(278)	(315)
Elimination of Intersegment Amounts [member] | Commercial Banking [member]
Disclosure of operating segments [line items]
Inter-segment revenue	(75)	(90)
Elimination of Intersegment Amounts [member] | Corporate And Investment Banking [member]
Disclosure of operating segments [line items]
Inter-segment revenue	(29)	(45)
Elimination of Intersegment Amounts [member] | Corporate Centre [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ 382	£ 450

Net Trading and Other Income -

Net Trading and Other Income - Summary of Net Trading and Other Income (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Net Trading And Other Income [Abstract]
Net trading and other income	£ 121	£ 182

Net Trading and Other Income 60

Net Trading and Other Income - Additional Information (Detail) - GBP (£) £ in Millions	1 Months Ended
	Sep. 30, 2017	Feb. 09, 2018
7.375% 20 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Percentage of notes purchased and redeemed	91.00%
Interest rate	7.375%
Maturity year	20 Year
175m Sterling Fixed/Floating Rate Tier One Preferred Income Capital Securities [member]
Disclosure of subordinated liabilities [line items]
Notional amount		£ 175

Operating Expenses Before Imp61

Operating Expenses Before Impairment Losses, Provisions and Charges - Summary of Operating Expenses Before Impairment Losses, Provisions and Charges (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Expenses by nature [abstract]
Staff costs	£ 691	£ 566
Other administration expenses	411	493
Depreciation, amortisation and impairment	181	156
Total operating expenses before impairment losses, provisions and charges	£ 1,283	£ 1,215

Credit Impairment Losses and 62

Credit Impairment Losses and Provisions - Summary of Impairment Losses and Provisions (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of credit impairment loss and provisions [abstract]
Loans and advances to customers (See Note 11)	£ 102	£ 76
Recoveries of loans and advances, net of collection costs (See Note 11)	(21)	(28)
Off-balance sheet credit exposures (See Note 19)	10
Impairment loss on financial assets	91	48
Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 19)	33	181
Provisions for residual value and voluntary termination (See Note 11)	0	5
Provisions for other liabilities and charges	33	186
Total operating impairment losses, provisions and charges	£ 124	£ 234

Credit Impairment Losses and 63

Credit Impairment Losses and Provisions - Additional Information (Detail) - GBP (£)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of credit impairment loss and provisions [abstract]
Impairment losses on loans and advances to banks	£ 0	£ 0
Impairment losses on financial investments	£ 0	£ 0

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 (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]
Profit before tax	£ 905	£ 1,064
Tax calculated at a tax rate of 19% (H117: 19.25%)	172	205
Bank surcharge on profits	64	77
Non-deductible preference dividends paid	5	5
Non-deductible UK Bank Levy	13	18
Non-deductible conduct remediation	(2)	16
Net disallowable items and non-taxable income	10	12
Adjustment to prior period provisions	(6)	(10)
Tax charge	£ 256	£ 323

Taxation - Additional Informati

Taxation - Additional Information (Detail)	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Tax Expense Benefits [line items]
Effective tax rate	28.30%	30.40%
Bank corporation tax surcharge	8.00%		8.00%
Banking Entities [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	27.00%		27.25%
Non-banking Entities [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	19.00%		19.25%
Top of Range [member]
Income Tax Expense Benefits [line items]
Applicable tax rate			20.00%
Bottom of Range [member]
Income Tax Expense Benefits [line items]
Applicable tax rate			19.00%
Finance (No.2) Act 2015 [member] | Top of Range [member] | Corporation Tax Rate in 2020 [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	18.00%
Finance (No.2) Act 2016 [member] | Bottom of Range [member] | Corporation Tax Rate in 2020 [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	17.00%

Dividends on Ordinary Shares -

Dividends on Ordinary Shares - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Dividends On Ordinary Shares [Abstract]
Interim dividends paid	£ 250
Interim dividends declared	£ 250	£ 323

Trading Assets - Disclosure of

Trading Assets - Disclosure of Trading Assets (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of financial assets held for trading [line items]
Total trading assets	£ 19,158	£ 30,555
Securities Purchased Under Resale Agreements [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	3,740	8,870
Debt Securities [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	0	5,156
Equity Securities [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	8,264	9,662
Cash Collateral Associated with Trading Balances [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	7,082	6,156
Short-term Loans [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	£ 72	£ 711

Derivative Financial Instrume68

Derivative Financial Instruments - Notional Amounts and Fair Values of Derivative Financial Instruments (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of detailed information about hedges [line items]
Notional amount	£ 221,800	£ 1,125,419
Fair value assets	3,838	19,942
Fair value liabilities	1,466	17,613
Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount	96,750	1,027,125
Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	125,050	98,294
Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	73,405	62,267
Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	51,645	36,027
Exchange Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount	9,481	144,160
Exchange Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	3,339	2,641
Exchange Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	27,603	23,117
Interest Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount	74,493	863,151
Interest Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	70,066	59,610
Interest Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	23,992	12,884
Equity and Credit Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount	12,776	19,814
Equity Investments [Member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	0	16
Equity Investments [Member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	50	26
Fair Value [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	3,838	19,942
Fair value liabilities	1,466	17,613
Fair Value [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	1,687	15,059
Fair value liabilities	777	15,963
Fair Value [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	2,151	4,883
Fair value liabilities	689	1,650
Fair Value [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	339	1,584
Fair value liabilities	423	1,480
Fair Value [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	1,812	3,299
Fair value liabilities	266	170
Fair Value [member] | Exchange Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	406	2,559
Fair value liabilities	334	4,130
Fair Value [member] | Exchange Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	332	312
Fair value liabilities	0	6
Fair Value [member] | Exchange Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	1,691	3,206
Fair value liabilities	87	55
Fair Value [member] | Interest Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	482	11,612
Fair value liabilities	3	11,140
Fair Value [member] | Interest Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	7	1,272
Fair value liabilities	423	1,470
Fair Value [member] | Interest Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	121	84
Fair value liabilities	177	115
Fair Value [member] | Equity and Credit Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	799	888
Fair value liabilities	440	693
Fair Value [member] | Equity Investments [Member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	0	0
Fair value liabilities	0	4
Fair Value [member] | Equity Investments [Member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	0	9
Fair value liabilities	£ 2	£ 0

Loans and Advances to Banks - S

Loans and Advances to Banks - Summary of Loans and Advances to Banks (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Loans and advances to banks [Abstract]
Loans and advances to banks	£ 2,410	£ 3,463

Loans and Advances to Custome70

Loans and Advances to Customers - Summary of Net Loans and Advances to Customers (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Disclosure of loans and advances to customers [line items]
Loans and advances to customers	£ 200,471	£ 199,151
Loans and advances to customers	201,815	200,358
Credit impairment loss allowances on loans and advances to customers	(792)	(940)	£ (864)	£ (921)
Residual value and voluntary termination provisions	(73)	(78)
Net loans and advances to customers	200,950	199,340
Fellow Banco Santander subsidiaries and joint ventures [member]
Disclosure of loans and advances to customers [line items]
Amounts due from related parties	£ 1,344	1,199
Santander UK Group Holdings plc [member]
Disclosure of loans and advances to customers [line items]
Amounts due from related parties		£ 8

Loans and Advances to Custome71

Loans and Advances to Customers - Summary of Movement in Impairment Loss Allowances (Detail) - GBP (£) £ in Millions	Jan. 01, 2018	Jun. 30, 2018	Jun. 30, 2017
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	£ 940	£ 940	£ 921
(Release)/charge to the income statement		102	76
Adjustment for the adoption of IFRS 9 (see Note 1)	211
Write-offs and other items		(411)	(133)
Re-allocation of ECL on undrawn exposures	(50)
Ending Balance		792	864
Balance on January 1 2018	1,101
Recoveries, net of collection costs		21	28
Advances Secured on Residential Property [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	225	225	279
(Release)/charge to the income statement		(13)	(18)
Adjustment for the adoption of IFRS 9 (see Note 1)	47
Write-offs and other items		(7)	(10)
Re-allocation of ECL on undrawn exposures	(3)
Ending Balance		249	251
Balance on January 1 2018	269
Recoveries, net of collection costs		1	2
Corporate Loans [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	490	490	382
(Release)/charge to the income statement		24	12
Adjustment for the adoption of IFRS 9 (see Note 1)	99
Write-offs and other items		(318)	(38)
Re-allocation of ECL on undrawn exposures	(25)
Ending Balance		270	356
Balance on January 1 2018	564
Recoveries, net of collection costs		1	1
Finance leases [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	46	46	45
(Release)/charge to the income statement		17	17
Adjustment for the adoption of IFRS 9 (see Note 1)	11
Write-offs and other items		(15)	(16)
Re-allocation of ECL on undrawn exposures	0
Ending Balance		59	46
Balance on January 1 2018	57
Recoveries, net of collection costs		3	4
Other Unsecured Advances [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	179	179	215
(Release)/charge to the income statement		74	65
Adjustment for the adoption of IFRS 9 (see Note 1)	54
Write-offs and other items		(71)	(69)
Re-allocation of ECL on undrawn exposures	(22)
Ending Balance		214	211
Balance on January 1 2018	£ 211
Recoveries, net of collection costs		£ 16	£ 21

Loans and Advances to Custome72

Loans and Advances to Customers - Summary of Movement in Impairment Loss Allowances (Parenthetical) (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of impairment loss recognised or reversed [abstract]
Mortgage write-offs of financial assets	£ 8	£ 11

Securitisations and Covered B73

Securitisations and Covered Bonds - Summary of Gross Asset Securitised (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of gross asset securitised [line items]
Gross asset securitised	£ 15,014	£ 16,740
Master Trust Structures [member]
Disclosure of gross asset securitised [line items]
Gross asset securitised	12,388	13,924
Other Securitisation Structures [member]
Disclosure of gross asset securitised [line items]
Gross asset securitised	2,626	2,816
Holmes [member] | Master Trust Structures [member]
Disclosure of gross asset securitised [line items]
Gross asset securitised	3,788	4,299
Fosse [member] | Master Trust Structures [member]
Disclosure of gross asset securitised [line items]
Gross asset securitised	5,167	5,732
Langton [member] | Master Trust Structures [member]
Disclosure of gross asset securitised [line items]
Gross asset securitised	3,433	3,893
Motor [member] | Other Securitisation Structures [member]
Disclosure of gross asset securitised [line items]
Gross asset securitised	1,146	1,318
Auto ABS UK Loans [member] | Other Securitisation Structures [member]
Disclosure of gross asset securitised [line items]
Gross asset securitised	£ 1,480	£ 1,498

Securitisations and Covered B74

Securitisations and Covered Bonds - Additional Information (Detail) - GBP (£) £ in Billions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of gross asset securitised [line items]
Covered bonds issued	£ 2.4	£ 1
Covered bonds redeemed	1.9	1.8
Holmes Master Issuer Plc [member]
Disclosure of gross asset securitised [line items]
Issue of notes, mortgaged-backed	1	0
Redemption of securities, mortgaged-backed	0	0.7
Fosse [member]
Disclosure of gross asset securitised [line items]
Issue of notes, mortgaged-backed	0	0
Redemption of securities, mortgaged-backed	0.4	0.7
Langton [member]
Disclosure of gross asset securitised [line items]
Issue of notes, mortgaged-backed	0	0
Redemption of securities, mortgaged-backed	0	0
Motor [member]
Disclosure of gross asset securitised [line items]
Issue of notes, mortgaged-backed	0	0
Redemption of securities, mortgaged-backed	0	0.2
Auto ABS UK Loans Plc [member]
Disclosure of gross asset securitised [line items]
Issue of notes, mortgaged-backed	0	0.5
Redemption of securities, mortgaged-backed	£ 0	£ 0.7

Financial Investments - Summary

Financial Investments - Summary of Financial Investments (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of financial investments [line items]
Financial investments	£ 20,986	£ 17,611
Amortised Cost [member]
Disclosure of financial investments [line items]
Financial investments	7,305	8,758
Amortised Cost [member] | Asset-backed Securities [member]
Disclosure of financial investments [line items]
Financial investments	761	2,180
Amortised Cost [member] | Debt Securities [member]
Disclosure of financial investments [line items]
Financial investments	6,544	6,578
FVOCI [member]
Disclosure of financial investments [line items]
Financial investments	13,681
FVOCI [member] | Debt Securities [member]
Disclosure of financial investments [line items]
Financial investments	13,506
FVOCI [member] | Loans and advances to customers [member]
Disclosure of financial investments [line items]
Financial investments	£ 175
Available-for-Sale [member]
Disclosure of financial investments [line items]
Financial investments		8,853
Available-for-Sale [member] | Debt Securities [member]
Disclosure of financial investments [line items]
Financial investments		8,772
Available-for-Sale [member] | Equity Securities [member]
Disclosure of financial investments [line items]
Financial investments		£ 81

Interests In Other Entities - A

Interests In Other Entities - Additional Information (Detail) £ in Millions	Jan. 01, 2018GBP (£)Employees	Feb. 07, 2000USD ($)	Jun. 30, 2018
Disclosure of information about unconsolidated subsidiaries [line items]
Non-cumulative trust preferred securities issued | $		$ 1,000,000,000
Non-cumulative trust preferred securities interest rate		8.963%
Santander Uk Operations Ltd And Santander UK Ttechnology Ltd [member] | Events After Reporting Period [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Ownership interest in trust preferred entities by Santander UK plc	100.00%
Cash consideration	£ 66
Produban servicios informaticos generales SI [member] | Events After Reporting Period [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Cash consideration	£ 13
Santander UK Plc [member] | Events After Reporting Period [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Number of employees transferred | Employees	4,900
Abbey National Capital Trust I [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Ownership interest in trust preferred entities by Santander UK plc			100.00%
Name of subsidiary			Abbey National Capital Trust I
Abbey National Capital LP I [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Ownership interest in trust preferred entities by Santander UK plc			100.00%
Name of subsidiary			Abbey National Capital LP I

Deposits by Banks - Schedule of

Deposits by Banks - Schedule of Deposits by Banks (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of deposits from banks [line items]
Deposits from banks	£ 15,655	£ 12,708
Items in Course of Transmission [member]
Disclosure of deposits from banks [line items]
Deposits from banks	326	303
Deposits Held as Collateral [member]
Disclosure of deposits from banks [line items]
Deposits from banks	2,408	1,760
Other Deposits [member]
Disclosure of deposits from banks [line items]
Deposits from banks	£ 12,921	£ 10,645

Deposits by Banks - Schedule 78

Deposits by Banks - Schedule of Deposits by Banks (Parenthetical) (Detail) - GBP (£) £ in Billions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of deposits from banks [abstract]
Drawdown from TFS	£ 10.8	£ 8.5

Deposits by Customers - Schedul

Deposits by Customers - Schedule of Deposits by Customers (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of deposits from customers [line items]
Deposits from customers	£ 175,885	£ 183,146
Santander UK Group Holdings plc [member]
Disclosure of deposits from customers [line items]
Deposits from customers	8,301	6,256
Current and Demand Accounts - Interest Bearing [member]
Disclosure of deposits from customers [line items]
Deposits from customers	84,656	85,749
Current and Demand Accounts - Non-interest Bearing [member]
Disclosure of deposits from customers [line items]
Deposits from customers	2	2
Savings Accounts [member]
Disclosure of deposits from customers [line items]
Deposits from customers	65,033	70,461
Time Deposits [member]
Disclosure of deposits from customers [line items]
Deposits from customers	17,358	19,951
Amounts Due to Fellow Banco Santander Subsidiaries [member]
Disclosure of deposits from customers [line items]
Deposits from customers	£ 535	£ 727

Deposits by Customers - Sched80

Deposits by Customers - Schedule of Deposits by Customers (Parenthetical) (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of deposits from customers [line items]
Deposits from customers	£ 175,885	£ 183,146
Equity Index Linked Deposits [member]
Disclosure of deposits from customers [line items]
Deposits from customers	1,232	1,301
Capital amount guaranteed or protected	1,232	1,301
Capital amount of return guaranteed	£ 44	£ 67

Trading Liabilities - Schedule

Trading Liabilities - Schedule of Trading Liabilities (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of financial liabilities held for trading [line items]
Trading liabilities	£ 8,375	£ 31,109
Securities Sold Under Repurchase Agreements [member]
Disclosure of financial liabilities held for trading [line items]
Trading liabilities	5,612	25,504
Short Positions in Securities and Unsettled Trades [member]
Disclosure of financial liabilities held for trading [line items]
Trading liabilities	190	3,694
Cash Collateral Associated with Trading Balances [member]
Disclosure of financial liabilities held for trading [line items]
Trading liabilities	£ 2,573	£ 1,911

Debt Securities In Issue - Summ

Debt Securities In Issue - Summary of Debt Securities in Issue (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Debt securities in issue [line items]
Debt Securities	£ 46,004	£ 42,633
Medium Term Notes [member]
Debt securities in issue [line items]
Debt Securities	21,950	18,002
Covered Bond Programme [member]
Debt securities in issue [line items]
Debt Securities	16,017	15,799
Certificates of Deposit [member]
Debt securities in issue [line items]
Debt Securities	3,304	4,681
Credit Linked Note [Member]
Debt securities in issue [line items]
Debt Securities	43	43
Securitisation Programmes [member]
Debt securities in issue [line items]
Debt Securities	£ 4,690	£ 4,108

Provisions - Summary of Provisi

Provisions - Summary of Provisions Reconciliation (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of other provisions [line items]
Beginning balance	£ 558	£ 700
Re-allocation of ECL on undrawn exposures	50
Balance on January 1 2018	608
Additional provisions	75	181
Provisions released	(32)
Utilisation	(147)	(295)
Transfers		9
Ending balance	504	595
PPI [member]
Disclosure of other provisions [line items]
Beginning balance	356	457
Balance on January 1 2018	356
Additional provisions		69
Utilisation	(55)	(121)
Ending balance	301	405
Wealth and Investment [member]
Disclosure of other provisions [line items]
Beginning balance	3	22
Balance on January 1 2018	3
Provisions released	(3)
Utilisation		(27)
Transfers		9
Ending balance		4
Other products [member]
Disclosure of other provisions [line items]
Beginning balance	44	14
Balance on January 1 2018	44
Additional provisions		35
Provisions released	(11)
Utilisation	(2)	(2)
Ending balance	31	47
Regulatory-Related [member]
Disclosure of other provisions [line items]
Beginning balance	57	96
Balance on January 1 2018	57
Additional provisions		2
Provisions released	(4)
Utilisation	(37)	(53)
Ending balance	16	45
Vacant Property [member]
Disclosure of other provisions [line items]
Beginning balance	39	47
Balance on January 1 2018	39
Additional provisions	11	6
Utilisation	(7)	(5)
Ending balance	43	48
Miscellaneous other provisions [member]
Disclosure of other provisions [line items]
Beginning balance	59	64
Re-allocation of ECL on undrawn exposures	50
Balance on January 1 2018	109
Additional provisions	64	69
Provisions released	(14)
Utilisation	(46)	(87)
Ending balance	£ 113	£ 46

Provisions - Summary of Provi84

Provisions - Summary of Provisions Reconciliation (Parenthetical) (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of other provisions [abstract]
Provisions in respect of operational loss and operational risk provisions, restructuring charges and litigation and related expenses	£ 53	£ 59
Provisions in respect of credit impairment losses for off balance sheet exposures relating to guarantees given to third parties	£ 60

Provisions - Summary of Key Dri

Provisions - Summary of Key Drivers of PPI Provision Balance and Forecast Assumptions Used in Calculating Provision (Detail) - PPI [member]	6 Months Ended
	Jun. 30, 2018GBP (£)
Inbound Complaints [member]
Disclosure of other provisions [line items]
Cumulative to 30 June 2018	1,858,000
Future expected (unaudited)	436,000
Sensitivity analysis number	25
Sensitivity analysis increase/decrease in provision	£ 12,300,000
Outbound Complaints [member]
Disclosure of other provisions [line items]
Cumulative to 30 June 2018	488,000
Future expected (unaudited)	292,000
Sensitivity analysis number	25
Sensitivity analysis increase/decrease in provision	£ 5,400,000
Response Rate to Outbound Contact [member]
Disclosure of other provisions [line items]
Cumulative to 30 June 2018	55.00%
Future expected (unaudited)	90.00%
Sensitivity analysis rate	1.00%
Sensitivity analysis increase/decrease in provision	£ 1,000,000
Average Uphold Rate Per Claim [member]
Disclosure of other provisions [line items]
Cumulative to 30 June 2018	44.00%
Future expected (unaudited)	72.00%
Sensitivity analysis rate	1.00%
Sensitivity analysis increase/decrease in provision	£ 2,700,000
Average Redress Per Claim [member]
Disclosure of other provisions [line items]
Cumulative to 30 June 2018	1,363
Future expected (unaudited)	537
Sensitivity analysis amount	100
Sensitivity analysis increase/decrease in provision	£ 50,500,000

Provisions - Additional Informa

Provisions - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Disclosure of other provisions [line items]
Provisions	£ 504	£ 558	£ 595	£ 700
Provisions released	(32)
PPI [member]
Disclosure of other provisions [line items]
Provisions	301	356	405	457
Other products [member]
Disclosure of other provisions [line items]
Provisions	31	44	47	14
Provisions released	(11)
Miscellaneous other provisions [member]
Disclosure of other provisions [line items]
Provisions	113	£ 59	£ 46	£ 64
Provisions released	(14)
Additional operational risk losses and restructuring charges	£ 58

Retirement Benefit Plans - Summ

Retirement Benefit Plans - Summary of Retirement Benefit Plans (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets/(liabilities)
Total net assets	£ 760	£ 163
Unfunded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	(39)	(41)
Surplus [member] | Funded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	868	449
Deficit [member] | Funded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	£ (69)	£ (245)

Retirement Benefit Plans - Addi

Retirement Benefit Plans - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of defined benefit plans [abstract]
Defined contribution expense	£ 23	£ 27
Key management personnel expense	None	None
Defined benefit expense	£ 22	£ 23
Actuarial gain on financial assumptions	£ 640

Retirement Benefit Plans - Su89

Retirement Benefit Plans - Summary of Movements in the Present Value of Defined Benefit Obligations and Fair Value of Scheme Assets (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Present value of defined benefit obligations [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	£ (11,583)	£ (11,082)
Income statement (charge) / income	(167)	(182)
Recognised in other comprehensive income:
- Return on plan assets (excluding amounts included in net interest expense)	0
- Actuarial movements arising from experience adjustments	(39)	11
- Actuarial movements arising from changes in financial assumptions	640	(17)
Benefits paid	221	191
Ending balance	(10,928)	(11,079)
Fair value of scheme assets [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	11,746	11,218
Income statement (charge) / income	145	156
Contributions paid	90	91
Recognised in other comprehensive income:
- Return on plan assets (excluding amounts included in net interest expense)	(72)	85
- Actuarial movements arising from experience adjustments	0
- Actuarial movements arising from changes in financial assumptions	0
Benefits paid	(221)	(191)
Ending balance	£ 11,688	£ 11,359

Contingent Liabilities and Co90

Contingent Liabilities and Commitments - Summary of Contingent Liabilities and Commitments (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure of contingent liabilities and commitments [Line Items]
Guarantees and formal standby facilities, credit lines and other commitments	£ 42,091	£ 43,499
Contingent Liability for Guarantees [Member]
Disclosure of contingent liabilities and commitments [Line Items]
Guarantees given to third parties	1,666	1,557
Loan commitments [member]
Disclosure of contingent liabilities and commitments [Line Items]
Formal standby facilities, credit lines and other commitments	£ 40,425	£ 41,942

Assets Charged as Security fo91

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets - Additional Information (Detail) - Securitisations and Covered Bonds [member] - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Mortgage Loans and Other Loans [member]
Disclosure of assets pledged as security [line items]
Total notes issued externally from secured securitisation and covered bond programmes	£ 20,707	£ 19,907
Gross external note issuances from secured programmes	3,375		£ 1,000
Gross external note redemptions from secured programmes	2,318		£ 3,538
Internally Retained [member]
Disclosure of assets pledged as security [line items]
Notes issued under securitisation and covered bond programmes retained internally	4,006	4,359
Third Party Bilateral Secured Funding Transactions [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	1,834	1,834
Santander UK Plc [member]
Disclosure of assets pledged as security [line items]
Gross assets charged as security for liabilities	35,253	36,512
Santander UK Plc [member] | Internally Retained [member]
Disclosure of assets pledged as security [line items]
Internally retained securitisation and covered bond issuances available for creating collateral	£ 502	£ 1,091

Financial Instruments - Analysi

Financial Instruments - Analysis of Fair Value of Financial Instruments Carried at Amortised (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by banks	£ 15,655	£ 12,708
Deposits by customers	175,885	183,146
Repurchase agreements- non trading	17,447	1,578
Debt securities in issue	46,004	42,633
Subordinated liabilities	3,758	3,793
Liabilities held for sale	26,616	0
Loans and advances to banks	2,410	3,463
Loans and advances to customers	200,950	199,340
Reverse repurchase agreements- non trading	13,611	2,614
Financial investments	20,986	17,611
Assets held for sale	24,241	0
Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Carrying value	226,028	214,175
Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Carrying value	264,505	243,858
Deposits by banks [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by banks	15,655	12,708
Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by customers	175,885	183,146
Repurchase agreements - non trading [Member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Repurchase agreements- non trading	17,447	1,578
Debt Securities [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Debt securities in issue	46,004	42,633
Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Subordinated liabilities	3,758	3,793
Liabilities held for sale [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Liabilities held for sale	5,756	0
Loans and advances to banks [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to banks	2,410	3,463
Loans and advances to customers [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to customers	200,950	199,340
Reverse repurchase agreements - non-trading [Member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Reverse repurchase agreements- non trading	13,611	2,614
Financial investments [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial investments	7,305	8,758
Assets Held For Sale [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Assets held for sale	1,752	0
Fair Value [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Carrying value	228,457	216,376
Fair Value [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Carrying value	266,289	246,148
Fair Value [member] | Deposits by banks [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by banks	15,667	12,721
Fair Value [member] | Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Deposits by customers	175,990	183,227
Fair Value [member] | Repurchase agreements - non trading [Member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Repurchase agreements- non trading	17,504	1,648
Fair Value [member] | Debt Securities [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Debt securities in issue	47,252	44,296
Fair Value [member] | Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Subordinated liabilities	4,120	4,256
Fair Value [member] | Liabilities held for sale [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Liabilities held for sale	5,756	0
Fair Value [member] | Loans and advances to banks [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to banks	2,409	3,451
Fair Value [member] | Loans and advances to customers [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Loans and advances to customers	203,578	201,667
Fair Value [member] | Reverse repurchase agreements - non-trading [Member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Reverse repurchase agreements- non trading	13,616	2,612
Fair Value [member] | Financial investments [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Financial investments	7,121	8,646
Fair Value [member] | Assets Held For Sale [member] | Amortised Cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [Line Items]
Assets held for sale	£ 1,733	£ 0

Financial Instruments - Fair Va

Financial Instruments - Fair Values of Financial Instruments Measured at Fair Value on a Recurring Basis (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 61,871	£ 61,446
Liabilities at fair value	31,928	51,037
Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	8,375	31,109
Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	1,466	17,613
Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 1,238	2,315
Liabilities held for sale [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	A, B, C & D
Liabilities at fair value	£ 20,849
Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	19,158	30,555
Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	3,838	19,942
Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	2,710	2,096
Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	13,681	8,853
Assets Held For Sale [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 22,484
Valuation technique	A, B, C & D
Level 1 [Member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 23,277	24,447
Liabilities at fair value	2,032	3,695
Level 1 [Member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	190	3,694
Level 1 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	0	1
Level 1 [Member] | Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	0	0
Level 1 [Member] | Liabilities held for sale [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	1,842
Level 1 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	8,299	15,474
Level 1 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	0	0
Level 1 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	205	184
Level 1 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	12,807	8,789
Level 1 [Member] | Assets Held For Sale [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	1,966
Level 2 [Member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	37,985	36,642
Liabilities at fair value	29,851	47,273
Level 2 [Member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	8,185	27,415
Level 2 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	1,428	17,549
Level 2 [Member] | Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	1,232	2,309
Level 2 [Member] | Liabilities held for sale [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	19,006
Level 2 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	10,859	15,081
Level 2 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	3,776	19,878
Level 2 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	2,281	1,672
Level 2 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	699	11
Level 2 [Member] | Assets Held For Sale [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	20,370
Level 3 [Member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	609	357
Liabilities at fair value	45	69
Level 3 [Member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	0	0
Level 3 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	38	63
Level 3 [Member] | Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	6	6
Level 3 [Member] | Liabilities held for sale [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	1
Level 3 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	0	0
Level 3 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	62	64
Level 3 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	224	240
Level 3 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	175	53
Level 3 [Member] | Assets Held For Sale [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	148
Securities Purchased Under Resale Agreements [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 3,740	8,870
Valuation technique	A
Securities Purchased Under Resale Agreements [member] | Level 2 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 3,740	8,870
Debt Securities [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		5,156
Valuation technique	-
Debt Securities [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 1,019	547
Valuation technique	A & B
Debt Securities [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 13,506
Valuation technique	D
Debt Securities [member] | Level 1 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		5,156
Debt Securities [member] | Level 1 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 189	184
Debt Securities [member] | Level 1 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	12,807
Debt Securities [member] | Level 2 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	677	187
Debt Securities [member] | Level 2 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	699
Debt Securities [member] | Level 3 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	153	176
Equity Securities [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 8,264	9,662
Valuation technique	-
Equity Securities [member] | Level 1 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 8,264	9,662
Cash Collateral [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	A
Liabilities at fair value	£ 2,573	1,911
Cash Collateral [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 7,082	6,156
Valuation technique	A
Cash Collateral [member] | Level 2 [Member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 2,573	1,911
Cash Collateral [member] | Level 2 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	7,082	6,156
Short-term Loans [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 72	711
Valuation technique	A
Short-term Loans [member] | Level 1 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 35	656
Short-term Loans [member] | Level 2 [Member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 37	55
Exchange Rate Contracts [member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	A
Liabilities at fair value	£ 421	4,191
Exchange Rate Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 2,429	6,077
Valuation technique	A
Exchange Rate Contracts [member] | Level 2 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 421	4,176
Exchange Rate Contracts [member] | Level 2 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	2,427	6,061
Exchange Rate Contracts [member] | Level 3 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value		15
Exchange Rate Contracts [member] | Level 3 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 2	16
Interest Rate Contracts [member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	A & C
Liabilities at fair value	£ 603	12,725
Interest Rate Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 610	12,968
Valuation technique	A & C
Interest Rate Contracts [member] | Level 2 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 603	12,720
Interest Rate Contracts [member] | Level 2 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 610	12,956
Interest Rate Contracts [member] | Level 3 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value		5
Interest Rate Contracts [member] | Level 3 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		12
Equity and Credit Contracts [member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	B & D
Liabilities at fair value	£ 442	697
Equity and Credit Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 799	897
Valuation technique	B & D
Equity and Credit Contracts [member] | Level 1 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value		1
Equity and Credit Contracts [member] | Level 2 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 404	653
Equity and Credit Contracts [member] | Level 2 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	739	861
Equity and Credit Contracts [member] | Level 3 [Member] | Derivative Financial Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	38	43
Equity and Credit Contracts [member] | Level 3 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	60	36
Loans and advances to customers [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 1,675	1,549
Valuation technique	A
Loans and advances to customers [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 175
Valuation technique	D
Loans and advances to customers [member] | Level 2 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 1,604	1,485
Loans and advances to customers [member] | Level 3 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	71	64
Loans and advances to customers [member] | Level 3 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	175
Equity Securities [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 16
Valuation technique	B
Equity Securities [member] | Level 1 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value	£ 16
Available for sale debt securities [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		8,772
Valuation technique	C
Available for sale debt securities [member] | Level 1 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		8,770
Available for sale debt securities [member] | Level 2 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		2
Available for sale debt securities [member] | Level 3 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		0
Available for sale equity securities [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		81
Valuation technique	B
Available for sale equity securities [member] | Level 1 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		19
Available for sale equity securities [member] | Level 2 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		9
Available for sale equity securities [member] | Level 3 [Member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Assets at fair value		53
Securities Sold Under Repurchase Agreements [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	A
Liabilities at fair value	£ 5,612	25,504
Securities Sold Under Repurchase Agreements [member] | Level 2 [Member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 5,612	25,504
Short Positions in Securities and Unsettled Trades [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	-
Liabilities at fair value	£ 190	3,694
Short Positions in Securities and Unsettled Trades [member] | Level 1 [Member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 190	3,694
Debt Securities [member] | Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	A
Liabilities at fair value	£ 1,095	1,635
Debt Securities [member] | Level 2 [Member] | Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	1,089	1,629
Debt Securities [member] | Level 3 [Member] | Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 6	6
Structured Deposits [member] | Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Valuation technique	A
Liabilities at fair value	£ 143	680
Structured Deposits [member] | Level 2 [Member] | Financial Liabilities Designated at Fair Value [member]
Disclosure of fair value measurement of assets and liabilities [Line Items]
Liabilities at fair value	£ 143	£ 680

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - GBP (£)	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Disclosure of financial assets [line items]
Fair value of financial instruments transferred from Level 1 to Level 2	£ 0	£ 0
Fair value of financial instruments transferred from Level 2 to Level 1	0	0
Fair value of financial instruments transferred from Level 1 to Level 3	0	0
Fair value of financial instruments transferred from Level 3 to Level 1	0	0
Fair value of financial instruments transferred from Level 2 to Level 3	0	0
Fair value of financial instruments transferred from Level 3 to Level 2	0	0
Loans and advances to customers	200,950,000,000	£ 199,340,000,000
Level 3 [Member]
Disclosure of financial assets [line items]
Loans and advances to customers	£ 285,000,000

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value Adjustment (Detail) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Disclosure of financial assets [line items]
Fair value adjustments	£ 101	£ 128
Bid-Offer and Trade Specific Adjustments [Member]
Disclosure of financial assets [line items]
Fair value adjustments	27	34
Uncertainty [Member]
Disclosure of financial assets [line items]
Fair value adjustments	37	43
Credit Risk Adjustment [Member]
Disclosure of financial assets [line items]
Fair value adjustments	19	36
Funding Fair Value Adjustment [Member]
Disclosure of financial assets [line items]
Fair value adjustments	9	6
Risk Related Adjustments [Member]
Disclosure of financial assets [line items]
Fair value adjustments	92	119
Model-Related [Member]
Disclosure of financial assets [line items]
Fair value adjustments	9	8
Day One Profit [Member]
Disclosure of financial assets [line items]
Fair value adjustments	£ 0	£ 1

Financial Instruments - Movemen

Financial Instruments - Movement of Liabilities Measured at Fair Value Using Valuation Technique With Significant Unobservable Inputs (Level 3) (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	£ (298,560)
Ending Balance	(300,063)
Level 3 [Member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(69)	£ (80)
Adjustment for the adoption of IFRS 9	0
At 1 January 2018	(69)
Total (losses)/gains recognised in profit/loss, fair value movements	4	(7)
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	5	5
Transfers in	0
Transfer to held for sale	0
Additions	0
Sales	0
Settlements	15	7
Ending Balance	(45)	(75)
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	9	(2)
Level 3 [Member] | Fair Value Through P&L [member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(6)	(6)
Adjustment for the adoption of IFRS 9	0
At 1 January 2018	(6)
Total (losses)/gains recognised in profit/loss, fair value movements	0	0
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	0	0
Transfers in	0
Transfer to held for sale	0
Additions	0
Sales	0
Settlements	0	0
Ending Balance	(6)	(6)
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	0	0
Level 3 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(63)	(74)
Adjustment for the adoption of IFRS 9	0
At 1 January 2018	(63)
Total (losses)/gains recognised in profit/loss, fair value movements	4	(7)
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	5	5
Transfers in	0
Transfer to held for sale	1
Additions	0
Sales	0
Settlements	15	7
Ending Balance	(38)	(69)
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	9	(2)
Level 3 [Member] | Liabilities held for sale [member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	0	0
Adjustment for the adoption of IFRS 9	0
At 1 January 2018	0
Total (losses)/gains recognised in profit/loss, fair value movements	0	0
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	0	0
Transfers in	0
Transfer to held for sale	(1)
Additions	0
Sales	0
Settlements	0	0
Ending Balance	(1)	0
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	£ 0	£ 0

Financial Instruments - Movem97

Financial Instruments - Movement of Assets Measured at Fair Value Using ValuationTechnique With Significant Unobservable Inputs (Level 3) (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure of financial assets [line items]
Beginning balance	£ 314,765
Ending Balance	316,632
Level 3 [Member]
Disclosure of financial assets [line items]
Beginning balance	357	£ 399
Adjustment for the adoption of IFRS 9	285
At 1 January 2018	642
Total (losses)/gains recognised in profit/loss, fair value movements	17	(3)
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	(5)	(5)
Transfers in	19
Gains recognised in other comprehensive income		9
Transfer to held for sale	0
Additions	17
Sales	(23)	(3)
Settlements	(58)	(9)
Ending Balance	609	388
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	12	(8)
Level 3 [Member] | Fair Value Through P&L [Member]
Disclosure of financial assets [line items]
Beginning balance	240	264
Adjustment for the adoption of IFRS 9	139
At 1 January 2018	379
Total (losses)/gains recognised in profit/loss, fair value movements	(5)	(9)
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	0	0
Transfers in	19
Gains recognised in other comprehensive income		0
Transfer to held for sale	(146)
Additions	0
Sales	(23)	(3)
Settlements	0	0
Ending Balance	224	252
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	(5)	(9)
Level 3 [Member] | Assets Held For Sale [member]
Disclosure of financial assets [line items]
Beginning balance	0	0
Adjustment for the adoption of IFRS 9	0
At 1 January 2018	0
Total (losses)/gains recognised in profit/loss, fair value movements	0	0
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	0	0
Transfers in	0
Gains recognised in other comprehensive income		0
Transfer to held for sale	148
Additions	0
Sales	0	0
Settlements	0	0
Ending Balance	148	0
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	0	0
Level 3 [Member] | Derivative Financial Instruments [member]
Disclosure of financial assets [line items]
Beginning balance	64	103
Adjustment for the adoption of IFRS 9	0
At 1 January 2018	64
Total (losses)/gains recognised in profit/loss, fair value movements	26	6
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	(5)	(5)
Transfers in	0
Gains recognised in other comprehensive income		0
Transfer to held for sale	(2)
Additions	0
Sales	0	0
Settlements	(21)	(9)
Ending Balance	62	95
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	21	1
Level 3 [Member] | Financial investments [member]
Disclosure of financial assets [line items]
Beginning balance	53	32
Adjustment for the adoption of IFRS 9	146
At 1 January 2018	199
Total (losses)/gains recognised in profit/loss, fair value movements	(4)	0
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	0	0
Transfers in	0
Gains recognised in other comprehensive income		9
Transfer to held for sale	0
Additions	17
Sales	0	0
Settlements	(37)	0
Ending Balance	175	41
(Losses)/gains recognised in profit or loss on assets and liabilities held at the end of the period	£ (4)	£ 0

Related Party Disclosures - Add

Related Party Disclosures - Additional Information (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Related party transactions [abstract]
Amounts owed by related parties	£ 14,509	£ 5,683
Amounts owed to related parties	£ 23,663	£ 13,467

Transition to IFRS 9 - Summary

Transition to IFRS 9 - Summary of Measurement Categories and Carrying Amounts of Financial Assets Determined in Accordance with IAS 39 and IFRS 9 (Detail) - GBP (£) £ in Millions	Jan. 01, 2018	Jun. 30, 2018	Dec. 31, 2017
Transition to IFRS 9 [line items]
Re-classifications	£ (49)
Re-measurement	(211)
Ending balance before re-presentation	314,505
Beginning balance	314,505	£ 316,632	£ 314,765
IFRS 9 [member] | Loans and advances to customers [member]
Transition to IFRS 9 [line items]
Re-classifications	(1)
Re-measurement	(211)
Ending balance before re-presentation	199,278
Re-presentation	706
Beginning balance	199,984
IFRS 9 [member] | Loans and advances to customers [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	91
Re-presentation	(91)
IFRS 9 [member] | Loans and advances to customers [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Re-measurement	(211)
Ending balance before re-presentation	199,007
Re-presentation	977
Beginning balance	199,984
IFRS 9 [member] | Loans and advances to customers [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Re-classifications	(1)
Ending balance before re-presentation	180
Re-presentation	(180)
IFRS 9 [member] | Trading Assets [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	30,555
Re-presentation	(19)
Beginning balance	30,536
IFRS 9 [member] | Trading Assets [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	30,536
Re-presentation	0
Beginning balance	30,536
IFRS 9 [member] | Trading Assets [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	19
Re-presentation	(19)
Beginning balance	0
IFRS 9 [member] | Cash and Balances at Central Banks [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	32,771
Re-presentation	0
Beginning balance	32,771
IFRS 9 [member] | Derivative Financial Instruments [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	19,942
Beginning balance	19,942
IFRS 9 [member] | Financial assets designated at fair value [member]
Transition to IFRS 9 [line items]
Re-classifications	(45)
Ending balance before re-presentation	2,051
Re-presentation	204
Beginning balance	2,255
IFRS 9 [member] | Financial assets designated at fair value [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	238
Re-presentation	1,181
Beginning balance	1,419
IFRS 9 [member] | Financial assets designated at fair value [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Re-classifications	(45)
Ending balance before re-presentation	977
Re-presentation	(977)
IFRS 9 [member] | Financial assets designated at fair value [member] | FVTPL (Designated) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	836
Beginning balance	836
IFRS 9 [member] | Loans and advances to banks [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	3,463
Beginning balance	3,463
IFRS 9 [member] | Reverse repurchase agreements - non-trading [Member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	2,464
Beginning balance	2,464
IFRS 9 [member] | Financial investments [member]
Transition to IFRS 9 [line items]
Re-classifications	(2)
Ending balance before re-presentation	17,609
Re-presentation	(891)
Beginning balance	16,718
IFRS 9 [member] | Financial investments [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Re-classifications	(2)
Ending balance before re-presentation	980
Re-presentation	(980)
IFRS 9 [member] | Financial investments [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	1,198
Beginning balance	1,198
IFRS 9 [member] | Financial investments [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	8,743
Re-presentation	199
Beginning balance	8,942
IFRS 9 [member] | Financial investments [member] | FVTPL (Mandatory)1 [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	29
Re-presentation	(29)
IFRS 9 [member] | Financial investments [member] | Amortised cost1 [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	6,578
Beginning balance	6,578
IFRS 9 [member] | Financial investments [member] | FVTPL (Mandatory)2 [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	81
Re-presentation	(81)
IFRS 9 [member] | Other [member]
Transition to IFRS 9 [line items]
Re-classifications	(1)
Ending balance before re-presentation	6,372
Beginning balance	6,372
IAS 39 [member] | Loans and advances to customers [member]
Transition to IFRS 9 [line items]
Beginning balance	199,490
IAS 39 [member] | Loans and advances to customers [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	199,218
IAS 39 [member] | Loans and advances to customers [member] | Loans and receivable securities1 [member]
Transition to IFRS 9 [line items]
Beginning balance	181
IAS 39 [member] | Loans and advances to customers [member] | Loans and receivable securities2 [member]
Transition to IFRS 9 [line items]
Beginning balance	91
IAS 39 [member] | Trading Assets [member]
Transition to IFRS 9 [line items]
Beginning balance	30,555
IAS 39 [member] | Trading Assets [member] | FVTPL [member]
Transition to IFRS 9 [line items]
Beginning balance	30,536
IAS 39 [member] | Trading Assets [member] | FVTPL1 [member]
Transition to IFRS 9 [line items]
Beginning balance	19
IAS 39 [member] | Cash and Balances at Central Banks [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	32,771
IAS 39 [member] | Derivative Financial Instruments [member] | FVTPL (Trading) [member]
Transition to IFRS 9 [line items]
Beginning balance	19,942
IAS 39 [member] | Financial assets designated at fair value [member]
Transition to IFRS 9 [line items]
Beginning balance	2,096
IAS 39 [member] | Financial assets designated at fair value [member] | FVTPL (Designated) [member]
Transition to IFRS 9 [line items]
Beginning balance	1,022
IAS 39 [member] | Financial assets designated at fair value [member] | FVTPL1 (Designated) [member]
Transition to IFRS 9 [line items]
Beginning balance	836
IAS 39 [member] | Financial assets designated at fair value [member] | FVTPL2 (Designated) [member]
Transition to IFRS 9 [line items]
Beginning balance	238
IAS 39 [member] | Loans and advances to banks [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	3,463
IAS 39 [member] | Reverse repurchase agreements - non-trading [Member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	2,464
IAS 39 [member] | Financial investments [member]
Transition to IFRS 9 [line items]
Beginning balance	17,611
IAS 39 [member] | Financial investments [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	1,198
IAS 39 [member] | Financial investments [member] | Loans and receivable securities1 [member]
Transition to IFRS 9 [line items]
Beginning balance	982
IAS 39 [member] | Financial investments [member] | Available for sale financial assets [member]
Transition to IFRS 9 [line items]
Beginning balance	8,743
IAS 39 [member] | Financial investments [member] | Available for sale financial assets1 [member]
Transition to IFRS 9 [line items]
Beginning balance	29
IAS 39 [member] | Financial investments [member] | Held to maturity investments [member]
Transition to IFRS 9 [line items]
Beginning balance	6,578
IAS 39 [member] | Financial investments [member] | Available for sale financial assets2 [member]
Transition to IFRS 9 [line items]
Beginning balance	81
IAS 39 [member] | Other [member]
Transition to IFRS 9 [line items]
Beginning balance	£ 6,373

Transition to IFRS 9 - Summa100

Transition to IFRS 9 - Summary of Measurement Categories and Carrying Amounts of Financial Assets Determined in Accordance with IAS 39 and IFRS 9 (Parenthetical) (Detail) £ in Millions	Jan. 01, 2018GBP (£)
Transition to IFRS 9 [line items]
Re-measurement	£ (211)
Allowance for credit losses [member]
Transition to IFRS 9 [line items]
Re-measurement	211
IFRS 9 [member]
Transition to IFRS 9 [line items]
Increase in deferred tax asset	68
IFRS 9 [member] | Allowance for credit losses [member]
Transition to IFRS 9 [line items]
Re-measurement	211
IFRS 9 [member] | Reclassifications [member]
Transition to IFRS 9 [line items]
Increase in deferred tax asset	14
IFRS 9 [member] | Remeasurements [member]
Transition to IFRS 9 [line items]
Increase in deferred tax asset	54
Financial guarantee contracts [member] | Provisions for off-balance sheet exposures (IAS 37/IFRS 9) [member] | Allowance for credit losses [member]
Transition to IFRS 9 [line items]
Re-measurement	6
Financial guarantee contracts [member] | Provisions for off-balance sheet exposures (IAS 37/IFRS 9) [member] | IFRS 9 [member] | Allowance for credit losses [member]
Transition to IFRS 9 [line items]
Re-measurement	6
Other Financial assets at fair value through profit or loss, category [member] | IFRS 9 [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Loans and receivables	1,071
Available-for-sale financial assets	110
Loans and advances to customers [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Re-measurement	(211)
Loans and advances to customers [member] | IFRS 9 [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Social housing loans	977
Re-measurement	(211)
Loans and advances to customers [member] | IFRS 9 [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Other loans and receivables	180
Trading Assets [member] | IFRS 9 [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Other loans and receivables	£ 19

Transition to IFRS 9 - Summa101

Transition to IFRS 9 - Summary of Reconciliation of Loss Allowance (Detail) £ in Millions	Jan. 01, 2018GBP (£)
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning Balance	£ 940
Re-classifications	(49)
Re-measurement	(211)
Allowance for credit losses [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Re-classifications	0
Re-measurement	211
Loans & receivables (IAS 39)/ financial assets at amortized cost (IFRS 9 ) [member] | Loans and advances to customers [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning Balance	940
Loans & receivables (IAS 39)/ financial assets at amortized cost (IFRS 9 ) [member] | Allowance for credit losses [member] | Loans and advances to customers [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Re-classifications	0
Re-measurement	205
Provisions for off-balance sheet exposures (IAS 37/IFRS 9) [member] | Allowance for credit losses [member] | Financial guarantee contracts [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Re-classifications	0
Re-measurement	6
IFRS 9 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending Balance	1,151
IFRS 9 [member] | Allowance for credit losses [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Re-measurement	211
IFRS 9 [member] | Loans & receivables (IAS 39)/ financial assets at amortized cost (IFRS 9 ) [member] | Loans and advances to customers [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending Balance	1,145
IFRS 9 [member] | Provisions for off-balance sheet exposures (IAS 37/IFRS 9) [member] | Financial guarantee contracts [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending Balance	6
IFRS 9 [member] | Provisions for off-balance sheet exposures (IAS 37/IFRS 9) [member] | Allowance for credit losses [member] | Financial guarantee contracts [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Re-measurement	£ 6

Transition to IFRS 9 - Summa102

Transition to IFRS 9 - Summary of Reserves and Retained Earnings (Detail) - GBP (£) £ in Millions	Jan. 01, 2018	Jun. 30, 2018	Dec. 31, 2017
Disclosure of reserves and retained earnings within equity [line items]
Other reserves		£ 190	£ 301
Retained earnings		£ 5,194	£ 4,732
Other reserves [member]
Disclosure of reserves and retained earnings within equity [line items]
Reclassification of investment securities (debt and equity) from AFS to FVTPL	£ (5)
Retained Earnings [member]
Disclosure of reserves and retained earnings within equity [line items]
Deferred tax asset	68
IAS 39 [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves	301
Retained earnings	4,732
Retained earnings and reserves	5,033
IFRS 9 [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves	296
Deferred tax asset	68
Retained earnings	4,545
Retained earnings and reserves	4,841
IFRS 9 [member] | Retained Earnings [member]
Disclosure of reserves and retained earnings within equity [line items]
Reclassification under IFRS 9	(44)
Recognition of expected credit losses under IFRS 9	£ (211)

Transition to IFRS 9 - Summa103

Transition to IFRS 9 - Summary of Reserves and Retained Earnings (Parenthetical) (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Disclosure of reserves and retained earnings within equity [line items]
Other reserves	£ 16,569	£ 16,013	£ 16,205	£ 16,250	£ 15,453
Other Reserves Available-For-Sale [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves			68	67	48
Other Reserves Available-For-Sale [member] | IAS 39 [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves		68
Other Reserves Cash Flow Hedging [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves	143	228	228	347	471
Other Reserves Cash Flow Hedging [member] | IAS 39 [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves		228
Other Reserves Cash Flow Hedging [member] | IFRS 9 [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves		228
Other Reserves Currency Translation [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves	5	5	£ 5	£ 5	£ 5
Other Reserves Currency Translation [member] | IAS 39 [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves		5
Other Reserves Currency Translation [member] | IFRS 9 [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves		5
Other Reserves Fair Value Reserves [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves	£ 42	63
Other Reserves Fair Value Reserves [member] | IFRS 9 [member]
Disclosure of reserves and retained earnings within equity [line items]
Other reserves		£ 63

Ring Fencing - Additional Infor

Ring Fencing - Additional Information (Detail) £ in Billions	Jun. 30, 2018GBP (£)
Banco Santander London Branch [member]
Disclosure of transfers of financial assets liabilities [line items]
Customer loans	£ 0.7

Assets and Liabilities Held 105

Assets and Liabilities Held for Sale - Additional Information (Detail)	Jun. 30, 2018
Proportion of shares of subsidiary held for sale [abstract]
Percentage of voting equity interests acquired	100.00%

Assets and Liabilities Held 106

Assets and Liabilities Held for Sale - Summary of Assets and Liabilities Expected to be Transferred (Detail) - GBP (£) £ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets
Trading assets	£ 19,158	£ 30,555
Derivative financial instruments	3,838	19,942
Other financial assets at fair value through profit and loss	2,710	2,096
Loans and advances to banks	2,410	3,463
Loans and advances to customers	200,950	199,340
Reverse repurchase agreements- non trading	13,611	2,614
Financial investments	20,986	17,611
Other assets	2,907	2,511
Total assets held for sale	24,241	0
Liabilities
Deposits by banks	15,655	12,708
Deposits by customers	175,885	183,146
Trading liabilities	8,375	31,109
Derivative financial instruments	1,466	17,613
Other liabilities	2,847	2,730
Total liabilities held for sale	26,616	£ 0
Held For Sale [member]
Assets
Trading assets	1,967
Derivative financial instruments	19,694
Other financial assets at fair value through profit and loss	823
Loans and advances to banks	506
Loans and advances to customers	1,068
Reverse repurchase agreements- non trading	74
Financial investments	104
Other assets	5
Liabilities
Deposits by banks	31
Deposits by customers	5,725
Trading liabilities	1,842
Derivative financial instruments	19,007
Other liabilities	11
Net liabilities held for sale	£ (2,375)

Events After the Balance She107

Events After the Balance Sheet Date (Detail) - GBP (£) £ in Millions	Jul. 31, 2018	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Disclosure of non-adjusting events after reporting period [line items]
Assets		£ 316,632	£ 314,505	£ 314,765
Liabilities		£ 300,063		£ 298,560
Ring Fencing Plan [member] | Banco Santander Group [member]
Disclosure of non-adjusting events after reporting period [line items]
Assets	£ 22,900
Liabilities	£ 20,700