Santander Uk 6-K 13 Aug 20 2020 Q2 Current report (foreign) Financial data

Cover Page

Cover Page	6 Months Ended
	Jun. 30, 2020
Document And Entity Information [Line Items]
Document Type	6-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Registrant Name	SANTANDER UK GROUP HOLDINGS PLC
Entity Central Index Key	0001649373
Current Fiscal Year End Date	--12-31

Condensed Consolidated Income S

Condensed Consolidated Income Statement - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Profit (loss) [abstract]
Interest and similar income	£ 2,650	£ 2,997
Interest expense and similar charges	(1,108)	(1,326)
Net interest income	1,542	1,671
Fee and commission income	408	540
Fee and commission expense	(187)	(205)
Net fee and commission income	221	335
Net trading and other income	85	111
Total operating income	1,848	2,117
Operating expenses before credit impairment losses, provisions and charges	(1,257)	(1,267)
Credit impairment losses	(376)	(69)
Provisions for other liabilities and charges	(68)	(206)
Total operating credit impairment losses, provisions and charges	(444)	(275)
Profit before tax	147	575
Tax on profit	(35)	(164)
Profit after tax	112	411
Attributable to:
Equity holders of the parent	84	385
Non-controlling interests	28	26
Profit after tax	£ 112	£ 411

Condensed Consolidated Statemen

Condensed Consolidated Statement of Comprehensive Income - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Statement of comprehensive income [abstract]
Profit after tax	£ 112	£ 411
Movement in fair value reserve (debt instruments):
- Change in fair value	146	167
- Income statement transfers	(166)	(152)
- Taxation	5	(4)
Other comprehensive income fair value reserve (debt instruments)	(15)	11
Cash flow hedges:
- Effective portion of changes in fair value	2,603	362
- Income statement transfers	(2,039)	(41)
- Taxation	(160)	(81)
Other comprehensive income cash flow hedges, total	404	240
Currency translation on foreign operations	(2)	0
Net other comprehensive income/(expense) that may be reclassified to profit or loss subsequently	387	251
Pension remeasurement:
- Change in fair value	(376)	(280)
- Taxation	97	70
Pension remeasurement, total	(279)	(210)
Own credit adjustment:
- Change in fair value	19	(58)
- Taxation	(5)	15
Own credit adjustment, total	14	(43)
Net other comprehensive (expense)/income that will not be reclassified to profit or loss subsequently	(265)	(253)
Total other comprehensive (expense)/income net of tax	122	(2)
Total comprehensive income	234	409
Attributable to:
Equity holders of the parent	207	383
Non-controlling interests	27	26
Total comprehensive income	£ 234	£ 409

Condensed Consolidated Balance

Condensed Consolidated Balance Sheet - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets
Cash and balances at central banks	£ 35,887	£ 26,395
Financial assets at fair value through profit or loss:
- Derivative financial instruments	5,291	3,363
- Other financial assets at fair value through profit or loss	866	973
Financial assets at amortised cost
Loans and advances to customers	211,156	207,498
- Loans and advances to banks	2,637	2,583
- Reverse repurchase agreements - non trading	23,901	23,636
- Other financial assets at amortised cost	4,879	7,056
Financial assets at fair value through other comprehensive income	10,338	9,747
Interests in other entities	127	117
Intangible assets	1,725	1,776
Property, plant and equipment	1,822	1,971
Current tax assets	246	186
Retirement benefit assets	522	670
Other assets	3,422	2,517
Total assets	302,819	288,488
Financial liabilities at fair value through profit or loss:
- Derivative financial instruments	1,747	1,709
- Other financial liabilities at fair value through profit or loss	1,620	1,713
Financial liabilities at amortised cost:
- Deposits by customers	186,797	179,006
- Deposits by banks	17,995	14,359
- Repurchase agreements - non trading	20,786	18,286
- Debt securities in issue	50,252	50,171
- Subordinated liabilities	3,257	3,528
Other liabilities	2,798	2,373
Provisions	485	577
Deferred tax liabilities	196	145
Retirement benefit obligations	402	280
Total liabilities	286,335	272,147
Equity
Share capital	7,060	7,060
Other equity instruments	2,241	2,241
Retained earnings	5,997	6,251
Other reserves	781	394
Total shareholders' equity	16,079	15,946
Non-controlling interests	405	395
Total equity	16,484	16,341
Total liabilities and equity	£ 302,819	£ 288,488

Condensed Consolidated Cash Flo

Condensed Consolidated Cash Flow Statement - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Profit after tax	£ 112	£ 411
Adjustments for:
Non-cash items included in profit	793	61
Change in operating assets	(4,032)	728
Change in operating liabilities	9,700	1,032
Corporation taxes paid	(110)	(169)
Effects of exchange rate differences	1,555	(314)
Net cash flows from operating activities	8,018	1,749
Cash flows from investing activities
Purchase of property, plant and equipment and intangible assets	(152)	(67)
Proceeds from sale of property, plant and equipment and intangible assets	92	32
Purchase of financial assets at amortised cost and financial assets at fair value through other comprehensive income	(2,626)	(4,141)
Proceeds from sale and redemption of financial assets at amortised cost and financial assets at fair value through other comprehensive income	2,581	4,259
Net cash flows from investing activities	(105)	83
Cash flows from financing activities
Issue of debt securities and subordinated notes	4,742	2,770
Issuance costs of debt securities and subordinated notes	(10)	(9)
Repayment of debt securities	(6,133)	(4,693)
Repurchase of non-controlling interests and other equity instruments	0	(14)
Dividends paid on ordinary shares	0	(138)
Dividends paid on other equity instruments	(74)	(73)
Dividends paid on non-controlling interests	(17)	(18)
Net cash flows from financing activities	(1,492)	(2,175)
Change in cash and cash equivalents	6,421	(343)
Cash and cash equivalents at beginning of the year	33,234	30,969
Effects of exchange rate changes on cash and cash equivalents	94	3
Cash and cash equivalents at the end of the year	39,749	30,629
Cash and cash equivalents consist of:
Cash and balances at central banks			£ 35,887	£ 25,967
Less: regulatory minimum cash balances			(788)	(678)
Cash and bank balances at central banks less regulatory minimum cash balances			35,099	25,289
Net trading other cash equivalents			0	0
Net non-trading other cash equivalents			4,650	5,340
Cash and cash equivalents at the end of the period	£ 39,749	£ 30,629	£ 39,749	£ 30,629

Condensed Consolidated Statem_2

Condensed Consolidated Statement of Changes in Equity - GBP (£) £ in Millions	Total	Share Capital	Other Equity Instruments	Retained Earnings	Other Reserves Fair Value Reserves	Other Reserves Cash Flow Hedging	Other Reserves Currency Translation	Total	Non-Controlling Interests
Beginning balance at Dec. 31, 2018	£ 16,220	£ 7,060	£ 2,041	£ 6,439	£ 24	£ 251	£ 5	£ 15,820	£ 400
- Profit after tax	411			385				385	26
Other comprehensive income, net of tax:
- Fair value reserve (debt instruments)	11				11			11
- Cash flow hedges	240					240		240
- Pension remeasurement	(210)			(210)				(210)
- Own credit adjustment	(43)			(43)				(43)
Total comprehensive income	409			132	11	240		383	26
Repurchase of non-controlling interests and other equity instruments	(14)								(14)
Dividends on ordinary shares	(138)			(138)				(138)
Dividends on other equity instruments	(73)			(73)				(73)
Dividends on non-controlling interests	(18)								(18)
Ending balance at Jun. 30, 2019	16,386	7,060	2,041	6,360	35	491	5	15,992	394
Beginning balance at Dec. 31, 2019	16,341	7,060	2,241	6,251	24	368	2	15,946	395
- Profit after tax	112			84				84	28
Other comprehensive income, net of tax:
- Fair value reserve (debt instruments)	(15)				(15)			(15)
- Cash flow hedges	404					404		404
- Pension remeasurement	(279)			(278)				(278)	(1)
- Own credit adjustment	14			14				14
- Currency translation on foreign operations	(2)						(2)	(2)
Total comprehensive income	234			(180)	(15)	404	(2)	207	27
Dividends on other equity instruments	(74)			(74)				(74)
Dividends on non-controlling interests	(17)								(17)
Ending balance at Jun. 30, 2020	£ 16,484	£ 7,060	£ 2,241	£ 5,997	£ 9	£ 772	£ 0	£ 16,079	£ 405

Accounting Policies

Accounting Policies	6 Months Ended
	Jun. 30, 2020
Statement [Line Items]
Accounting Policies	1. ACCOUNTING POLICIES The Condensed Consolidated Interim Financial Statements reflect all adjustments that, in the opinion of management, are necessary for a fair statement of the results of operations for the interim period. All such adjustments to the financial information are of a normal, recurring nature. Because the results from common banking activities are so closely related and responsive to changes in market conditions, the results for any interim period are not necessarily indicative of the results that can be expected for the year. 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 sourcebook 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 Santander UK Group Holdings plc (the Santander UK group) for the year ended 31 December 2019 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 International Financial Reporting Standards as adopted by the European Union as there are no applicable differences between the two frameworks for the periods presented. 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 2019 Annual Report. At 30 June 2020, for the Santander UK group, there were no significant new or revised standards and interpretations, and amendments thereto, which have been issued but which are not yet effective or which have otherwise not been early adopted where permitted. Going concern In light of the current economic uncertainty, the Directors updated their going concern assessment in preparing these Condensed Consolidated Interim Financial Statements. After making enquiries, the Directors have a reasonable expectation that Santander UK has adequate resources to continue in operational existence for at least twelve months from the date of this report and, therefore, having reassessed the principal risks and uncertainties, the Directors consider it appropriate for the Condensed Consolidated Interim Financial Statements to be prepared on a going concern basis. In making their going concern assessment in connection with preparing the Condensed Consolidated Interim Financial Statements, the Directors considered a wide range of information that included Santander UK’s long-term business and strategic plans, forecasts and projections, estimated capital, funding and liquidity requirements, contingent liabilities and the reasonably possible changes in trading performance arising from potential economic, market and product developments. The Directors' assessment specifically considered the impacts of Covid-19, including for the following areas: – Economic scenarios : These underpin our IFRS 9 ECL impairment allowances and are discussed in detail in the Credit risk section of the Risk review. The Directors reviewed the economic scenarios, revised as a result of Covid-19, to ensure that they captured the wide range of potential outcomes for the UK economy. These include a re-emergence of the virus and further lockdown measures being imposed, a slower recovery that is more akin to the ‘U’ shape of past recessions, and hysteresis effects caused by higher and longer unemployment rates. – Liquidity: Although the key aim of the UK Government financial support measures introduced in H120 was to limit damage to the wider economy from Covid-19, they had the side-effect of reducing any potential liquidity risks arising due to Covid-19. Although Covid-19 did not trigger a liquidity stress, its immediate negative impacts on liquidity, such as the drawing of committed credit and liquidity facilities, were largely offset by deposits from those same drawings as corporates reduced their spending. Similarly, the impact of the initial effective shutdown of the mortgage market and the payment holidays granted to customers was offset by better than expected retail deposit balances as customers reduced their spending. – Capital: Santander UK remains strongly capitalised and Covid-19 did not trigger a capital stress. As part of the Bank of England Interim Financial Stability Report (May 2020), the PRA developed a desktop stress scenario, which had less of an impact over the first two years of the scenario on the core banking system than their 2019 Stress Test, where our CET1 drawdown was the lowest across UK banks and we exceeded CET1 capital ratio and Tier 1 Leverage ratio hurdle rates across the projection horizon. In line with other UK banks, we also announced that we will not pay quarterly or interim dividends, or make share buybacks on ordinary shares until the end of 2020. – Customers: Santander UK has supported many thousands of individuals and businesses affected by Covid-19 with a range of measures, including payment holidays on mortgages, personal loans and credit cards as well as taking an active part in UK Government loan schemes to help businesses. We are working with those customers who took a payment holiday to understand their individual situations and help them resume payments. – Operations: All our operations continue to operate effectively with a significant majority of staff working from home and the majority of branches remaining open and returning to more normal hours. The current operating model could be sustained indefinitely with additional resilience being continuously implemented and is not affecting our ability to operate all our services, or raising concerns about our Business Continuity Planning, and – Key suppliers: Suppliers are being closely monitored in line with our Third Party Risk Management Framework. No significant service issues have been reported across our cohort of critical suppliers, and no material issues have been reported across our broader (non-critical) supply chain. Isolated supplier impacts have been seen, but these are being managed. CRITICAL JUDGEMENTS AND ACCOUNTING ESTIMATES The preparation of the Condensed Consolidated Interim Financial Statements requires management to make judgements and accounting estimates 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 judgements and accounting estimates, which are based on historical experience and on various other factors that are believed to be reasonable under the circumstances, on an ongoing basis. Actual results may differ from these accounting estimates under different assumptions or conditions. In the course of preparing the Condensed Consolidated Interim Financial Statements, no significant judgements have been made in the process of applying the accounting policies, other than those involving estimations about credit impairment losses, provisions, contingent liabilities and pensions. a) Credit impairment allowance The application of the ECL impairment methodology for calculating credit impairment allowances is highly susceptible to change from period to period. The methodology requires management to make a number of judgmental assumptions in determining 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. The impact of Covid-19 has increased the uncertainty around ECL impairment calculations, and has required management to make additional judgements and accounting estimates that affect the reported amount of assets and liabilities at the reporting date and the reported amount of income and expenses during the reporting period. The key additional judgements arising from the impact of Covid-19 mainly reflect the increased uncertainty around forward-looking economic information and the need for additional post model adjustments. Key areas of judgement in accounting estimates The key judgements made by management in applying the ECL impairment methodology are set out below. – Definition of default – Forward-looking information – Probability weights – SICR – Post model adjustments. For more on each of these key judgements, including the impact of Covid-19 on them, see the ‘Credit risk – Santander UK group level – credit risk management’ section of the Risk review. Sensitivity of ECL allowance For detailed disclosures, see the ‘Credit risk – Santander UK group level – credit risk management’ section of the Risk review. b) Pensions The Santander UK group operates a number of defined benefit pension schemes as described in Note 28 of the Consolidated Financial Statements in the 2019 Annual Report. Key areas of judgement in accounting estimates In H120 management amended the general price inflation assumptions to reflect the expectation that the Retail Price Index would be brought in line with the Consumer Price Index from 2030. For more see the ‘Actuarial assumptions’ section in Note 24. Sensitivity of defined benefit pension scheme estimates Detailed disclosures on the actuarial assumption sensitivities of the schemes can be found in the ‘Actuarial assumption sensitivities’ section of Note 24.

Segments

Segments	6 Months Ended
	Jun. 30, 2020
Disclosure of operating segments [abstract]
Segments	2. SEGMENTS Santander UK’s principal activity is financial services, mainly in the UK. The business is managed and reported on the basis of four segments, which are strategic business units that offer different products and services, have different customers and require different technology and marketing strategies. Results by segment Half year to Retail Banking Corporate & Commercial Banking Corporate & Investment Banking Corporate Centre Total 30 June 2020 £m £m £m £m £m Net interest income/(expense) 1,393 150 26 (27) 1,542 Non-interest income 235 40 28 3 306 Total operating income/(expense) 1,628 190 54 (24) 1,848 Operating expenses before credit impairment losses, provisions and charges (1,010) (134) (62) (51) (1,257) Credit impairment losses (247) (106) (12) (11) (376) Provisions for other liabilities and (charges)/release (56) 3 (4) (11) (68) Total operating credit impairment losses, provisions and charges (303) (103) (16) (22) (444) Profit/(loss) before tax 315 (47) (24) (97) 147 Revenue from external customers 2,004 237 55 (448) 1,848 Inter-segment revenue (376) (47) (1) 424 — Total operating income/(expense) 1,628 190 54 (24) 1,848 Revenue from external customers includes the following fee and commission income disaggregated by income type: (1) – Current account and debit card fees 253 13 5 — 271 – Insurance, protection and investments 31 — — — 31 – Credit cards 33 — — — 33 – Non-banking and other fees (2) 26 22 23 2 73 Total fee and commission income 343 35 28 2 408 Fee and commission expense (169) (9) (4) (5) (187) Net fee and commission income/(expense) 174 26 24 (3) 221 30 June 2020 Customer loans 184,862 16,604 4,040 4,030 209,536 Total assets (3) 193,692 16,604 4,949 87,574 302,819 Customer deposits 151,091 19,538 6,784 8,302 185,715 Total liabilities 152,171 19,563 7,230 107,371 286,335 1. The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. 2. Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance. 3. Includes customer loans, net of credit impairment loss allowances. Half year to Retail Banking Corporate & Commercial Banking Corporate & Investment Banking Corporate Centre Total 30 June 2019 £m £m £m £m £m Net interest income/(expense) 1,465 189 32 (15) 1,671 Non-interest income 353 38 47 8 446 Total operating income/(expense) 1,818 227 79 (7) 2,117 Operating expenses before credit impairment losses, provisions and charges (1,011) (138) (83) (35) (1,267) Credit impairment (losses)/releases (63) (9) 4 (1) (69) Provisions for other liabilities and charges (95) (1) (11) (99) (206) Total operating credit impairment losses, provisions and charges (158) (10) (7) (100) (275) Profit/(loss) before tax 649 79 (11) (142) 575 Revenue from external customers 2,166 281 85 (415) 2,117 Inter-segment revenue (348) (54) (6) 408 — Total operating income/(expense) 1,818 227 79 (7) 2,117 Revenue from external customers includes the following fee and commission income disaggregated by income type: (1) – Current account and debit card fees 345 15 14 — 374 – Insurance, protection and investments 37 — — — 37 – Credit cards 42 — — — 42 – Non-banking and other fees (2) 36 26 24 1 87 Total fee and commission income 460 41 38 1 540 Fee and commission expense (184) (12) (7) (2) (205) Net fee and commission income/(expense) 276 29 31 (1) 335 31 December 2019 Customer loans 180,398 16,297 4,114 4,489 205,298 Total assets (3) 187,556 16,297 4,727 79,908 288,488 Customer deposits 145,050 18,234 6,101 8,437 177,822 Total liabilities 145,917 18,260 6,500 101,470 272,147 1. The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. 2. Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance. 3. Includes customer loans, net of credit impairment loss allowances.

Net Trading and Other Income

Net Trading and Other Income	6 Months Ended
	Jun. 30, 2020
Net Trading And Other Income [abstract]
Net Trading and Other Income	3. NET TRADING AND OTHER INCOME In H120, the Santander UK group repurchased certain debt securities and subordinated liabilities as part of ongoing liability management exercises, resulting in a loss of £17m. In H119, the Santander UK group did not repurchase any of its debt securities or subordinated liabilities. Included in net trading and other income in H119 is additional consideration of £15m in connection with the 2017 Vocalink Holdings Limited shareholding sale.

Operating Expenses Before Credi

Operating Expenses Before Credit Impairment Losses, Provisions and Charges	6 Months Ended
	Jun. 30, 2020
Expenses by nature [abstract]
Operating Expenses Before Credit Impairment Losses, Provisions and Charges	4. OPERATING EXPENSES BEFORE CREDIT IMPAIRMENT LOSSES, PROVISIONS AND CHARGES Half year to Half year to 30 June 2020 30 June 2019 £m £m Staff costs 608 653 Other administration expenses 377 354 Depreciation, amortisation and impairment 272 260 1,257 1,267

Credit Impairment Losses and Pr

Credit Impairment Losses and Provisions	6 Months Ended
	Jun. 30, 2020
Disclosure of credit impairment loss and provisions [Abstract]
Credit Impairment Losses and Provisions	5. CREDIT IMPAIRMENT LOSSES AND PROVISIONS Half year to Half year to 30 June 2020 30 June 2019 £m £m Credit impairment losses: Loans and advances to customers 396 108 Recoveries of loans and advances, net of collection costs (15) (38) Off-balance sheet exposures (See Note 23) (5) (1) 376 69 Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 23) 68 205 Provisions for residual value and voluntary termination — 1 68 206 444 275 In H120 and H119 there were no material credit impairment losses on loans and advances to banks, non-trading reverse repurchase agreements, other financial assets at amortised cost and financial assets at fair value through other comprehensive income.

Taxation

Taxation	6 Months Ended
	Jun. 30, 2020
Major components of tax expense (income) [abstract]
Taxation	6. TAXATION The Santander UK group’s estimated effective tax rate for H120 based on forecast profit before tax was 23.8% (H119: 28.5%). The tax on profit before tax differs from the theoretical amount that would arise using the basic corporation tax rate of the Company as follows: Half year to Half year to 30 June 2020 30 June 2019 £m £m Profit before tax 147 575 Tax calculated at a tax rate of 19% (H119: 19%) 28 109 Bank surcharge on profits 7 38 Non-deductible preference dividends paid 3 5 Non-deductible UK Bank Levy 6 13 Non-deductible conduct remediation, fines and penalties — 11 Other non-deductible costs and non-taxable income 2 9 Effect of change in tax rate on deferred tax provision 6 — Tax relief on dividends in respect of other equity instruments (13) (21) Adjustment to prior year provisions (4) — Tax charge 35 164

Dividends on Ordinary Shares

Dividends on Ordinary Shares	6 Months Ended
	Jun. 30, 2020
Statement [Line Items]
Dividends on Ordinary Shares	7. DIVIDENDS ON ORDINARY SHARES No interim dividend was declared on the Company’s ordinary shares in issue (H119: £138m).

Derivative Financial Instrument

Derivative Financial Instruments	6 Months Ended
	Jun. 30, 2020
Disclosure of nature and extent of risks arising from financial instruments [abstract]
Derivative Financial Instruments	8. DERIVATIVE FINANCIAL INSTRUMENTS 30 June 2020 31 December 2019 Fair value Fair value Notional amount Assets Liabilities Notional amount Assets Liabilities £m £m £m £m £m £m Derivatives held for trading: Exchange rate contracts 21,304 628 378 14,249 136 199 Interest rate contracts 47,591 864 530 47,045 754 566 Equity and credit contracts 2,344 162 113 2,583 292 167 Total derivatives held for trading 71,239 1,654 1,021 63,877 1,182 932 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 1,758 148 11 1,482 166 2 Interest rate contracts 99,899 1,218 2,235 94,550 1,022 1,488 101,657 1,366 2,246 96,032 1,188 1,490 Designated as cash flow hedges: Exchange rate contracts 32,145 3,370 121 28,502 2,023 462 Interest rate contracts 21,500 567 25 17,451 184 35 Equity derivative contracts — — — 49 — 4 53,645 3,937 146 46,002 2,207 501 Total derivatives held for hedging 155,302 5,303 2,392 142,034 3,395 1,991 Derivative netting (1) (1,666) (1,666) (1,214) (1,214) Total derivatives 226,541 5,291 1,747 205,911 3,363 1,709 (1) Derivative netting excludes the effect of cash collateral, which is offset against the gross derivative position. The amount of cash collateral received that had been offset against the gross derivative assets was £465m (2019: £222m) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was £1,047m (2019: £629m). LIBOR Reform The table below shows the notional value of hedging instruments by benchmark interest rate impacted by LIBOR reform. 30 June 2020 31 December 2019 GBP USD Other Total GBP USD Other Total £m £m £m £m £m £m £m £m Total notional value of hedging instruments: – Cash flow hedges 19,948 5,836 — 25,784 23,396 8,001 — 31,397 – Fair value hedges 42,473 4,533 789 47,795 53,244 5,070 1,187 59,501 62,421 10,369 789 73,579 76,640 13,071 1,187 90,898 Maturing after 31 December 2021: – Cash flow hedges 11,007 2,828 — 13,835 11,773 2,644 — 14,417 – Fair value hedges 12,991 413 722 14,126 16,455 1,897 740 19,092 23,998 3,241 722 27,961 28,228 4,541 740 33,509

Other Financial Assets At Fair

Other Financial Assets At Fair Value Through Profit Or Loss	6 Months Ended
	Jun. 30, 2020
Financial assets at fair value through profit or loss [abstract]
Other Financial Assets At Fair Value Through Profit Or Loss	9. OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS 30 June 2020 31 December 2019 £m £m Loans and advances to customers: Loans to housing associations 13 12 Other loans 594 528 607 540 Debt securities 125 298 Equity securities 134 135 866 973

Loans and Advances to Customers

Loans and Advances to Customers	6 Months Ended
	Jun. 30, 2020
Net Loans and Advances to Customers [Abstract]
Loans and Advances to Customers	10. LOANS AND ADVANCES TO CUSTOMERS 30 June 2020 31 December 2019 £m £m Loans and advances to customers 212,318 208,344 Credit impairment loss allowances on loans and advances to customers (1,106) (785) RV and voluntary termination provisions on finance leases (56) (61) Net loans and advances to customers 211,156 207,498 For movements in expected credit losses, see the Credit risk section of the Risk review.

Securitisations and Covered Bon

Securitisations and Covered Bonds	6 Months Ended
	Jun. 30, 2020
Disclosure of securitisations and covered bonds [Abstract]
Securitisations and Covered Bonds	11. SECURITISATIONS AND COVERED BONDS The information in this Note relates to securitisations and covered bonds for consolidated structured entities, used to obtain funding or collateral. It excludes structured entities relating to credit protection vehicles. 30 June 2020 31 December 2019 £m £m Mortgage-backed master trust structures: – Holmes 3,603 4,262 – Fosse 3,000 3,708 – Langton 3,142 3,076 9,745 11,046 Other asset-backed securitisation structures: – Motor 321 490 – Auto ABS UK Loans 1,490 1,532 1,811 2,022 Total securitisation programmes 11,556 13,068 Covered bond programmes – Euro 35bn Global Covered Bond Programme 26,709 23,323 Total securitisation and covered bond programmes 38,265 36,391 The following table sets out the internal and external issuances and redemptions in H120 and H119 for each securitisation and covered bond programme. Internal issuances External issuances Internal redemptions External redemptions H120 H119 H120 H119 H120 H119 H120 H119 £bn £bn £bn £bn £bn £bn £bn £bn Mortgage-backed master trust structures: – Holmes — — — — 0.1 — 0.5 0.8 Other asset-backed securitisation structures: – Motor — — — — 0.1 0.1 0.1 0.2 – Auto ABS UK Loans — — — — — — 0.1 0.1 Covered bond programme — — 3.0 1.9 — — 1.8 — — — 3.0 1.9 0.2 0.1 2.5 1.1

Reverse Repurchase Agreements -

Reverse Repurchase Agreements - Non Trading	6 Months Ended
	Jun. 30, 2020
Disclosure of reserve repurchase agreements non-trading [Abstract]
Reverse Repurchase Agreements - Non Trading	12. REVERSE REPURCHASE AGREEMENTS – NON TRADING 30 June 2020 31 December 2019 £m £m Agreements with banks 2,238 2,161 Agreements with customers 21,663 21,475 23,901 23,636

Other Financial Assets At Amort

Other Financial Assets At Amortised Cost	6 Months Ended
	Jun. 30, 2020
Financial assets at fair value through profit or loss [abstract]
Other Financial Assets At Amortised Cost	13. OTHER FINANCIAL ASSETS AT AMORTISED COST 30 June 2020 31 December 2019 £m £m Asset backed securities 507 532 Debt securities 4,372 6,524 4,879 7,056

Financial Assets At Fair Value

Financial Assets At Fair Value Through Other Comprehensive Income	6 Months Ended
	Jun. 30, 2020
Financial assets at fair value through other comprehensive income [abstract]
Financial Assets At Fair Value Through Other Comprehensive Income	14. FINANCIAL ASSETS AT FAIR VALUE THROUGH OTHER COMPREHENSIVE INCOME 30 June 2020 31 December 2019 £m £m Debt securities 10,308 9,691 Loans and advances to customers 30 56 10,338 9,747

Interests in Other Entities

Interests in Other Entities	6 Months Ended
	Jun. 30, 2020
Investments accounted for using equity method [abstract]
Interests in Other Entities	15. INTERESTS IN OTHER ENTITIES There have been no changes to the Santander UK group's interests in subsidiaries, associates, joint ventures and unconsolidated structured entities, as set out in Note 19 to the Consolidated Financial Statements in the 2019 Annual Report.

Intangible Assets

Intangible Assets	6 Months Ended
	Jun. 30, 2020
Disclosure of detailed information about intangible assets [abstract]
Intangible Assets	16. INTANGIBLE ASSETS Goodwill Cost Accumulated impairment Net book value £m £m £m At 31 December 2019, 1 January 2020 and 30 June 2020 1,285 (82) 1,203 Impairment of goodwill In H120 and H119, no impairment of goodwill was recognised. Goodwill is tested for impairment annually, or more frequently when events or changes in circumstances dictate. Having considered the unprecedented uncertainty created by Covid-19 and its potential impact on the carrying value of goodwill, management performed an interim impairment test at 30 June 2020 for all cash-generating units (CGUs). The assumptions included in the expected future cash flows for each CGU have been updated to take into consideration the impact of Covid-19 on the UK economic environment and financial outlook within which the CGU operates. The base case economic scenario used to support the cash flow projections includes key assumptions such as projected house price and GDP growth rates, the level and change in unemployment rates in the UK and the forecast Bank of England base rates. For more on Santander UK’s base case economic scenario, including information on our forecasting approach and the assumptions in place at 30 June 2020 see the Credit risk – Santander UK group level section of the Risk review. The rate used to discount the cash flows is based on a pre-tax rate that reflects the weighted average cost of capital allocated by Santander UK to investments in the business division in which the CGU operates. The growth rate used reflects management’s five-year forecasts, with a terminal growth rate for each year applied thereafter, in line with the estimated long-term average UK GDP growth rate. In H120, the discount rate increased by 2.1 percentage points to 11.9% (2019: 9.8%), reflecting the impact of Covid-19 on the weighted average cost of capital. The discounted future cashflows for each CGU remain higher than the carrying value of the goodwill, and management determined that a reasonably possible change in any of the key assumptions described above would not cause an impairment of goodwill to be recognised.

Other Financial Liabilities at

Other Financial Liabilities at Fair Value Through Profit or Loss	6 Months Ended
	Jun. 30, 2020
Disclosure of financial liabilities [abstract]
Other Financial Liabilities at Fair Value Through Profit or Loss	17. OTHER FINANCIAL LIABILITIES AT FAIR VALUE THROUGH PROFIT OR LOSS 30 June 2020 31 December 2019 £m £m US$30bn Euro Medium Term Note Programme 172 159 Structured Notes Programmes 881 809 Eurobonds 142 137 Structured deposits 415 435 Collateral and associated financial guarantees 10 173 1,620 1,713

Deposits by Customers

Deposits by Customers	6 Months Ended
	Jun. 30, 2020
Deposits from customers [abstract]
Deposits by Customers	18. DEPOSITS BY CUSTOMERS 30 June 2020 31 December 2019 £m £m Demand and time deposits (1) 185,570 177,772 Amounts due to fellow Banco Santander subsidiaries and joint ventures 1,227 1,234 186,797 179,006 (1) Includes equity index-linked deposits of £1,127m (2019: £1,139m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,127m and £16m (2019: £1,139m and £18m) respectively.

Deposits by Banks

Deposits by Banks	6 Months Ended
	Jun. 30, 2020
Disclosure of deposits from banks [Abstract]
Deposits by Banks	19. DEPOSITS BY BANKS 30 June 2020 31 December 2019 £m £m Items in the course of transmission 255 337 Deposits held as collateral 3,853 2,175 Other deposits (1) 13,887 11,847 17,995 14,359 (1) Includes drawdown from the TFS of £10.8bn (2019: £10.8bn) and drawdown from the TFSME of £2.2bn (2019:£nil).

Repurchase Agreements - Non Tra

Repurchase Agreements - Non Trading	6 Months Ended
	Jun. 30, 2020
Disclosure Of Repurchase Agreements [Abstract]
Repurchase Agreements - Non Trading	20. REPURCHASE AGREEMENTS – NON TRADING 30 June 2020 31 December 2019 £m £m Agreements with banks 13,296 10,227 Agreements with customers 7,490 8,059 20,786 18,286

Debt Securities in Issue

Debt Securities in Issue	6 Months Ended
	Jun. 30, 2020
Debt Securities In Issue [Abstract]
Debt Securities in Issue	21. DEBT SECURITIES IN ISSUE 30 June 2020 31 December 2019 £m £m Medium-term notes 24,800 24,522 Euro 35bn Global Covered Bond Programme 20,631 19,004 Certificates of deposit 1,795 2,806 Credit linked notes 55 60 Securitisation programmes 2,971 3,779 50,252 50,171

Subordinated Liabilities

Subordinated Liabilities	6 Months Ended
	Jun. 30, 2020
Disclosure of Subordinated Liabilities [Abstract]
Subordinated Liabilities	22. SUBORDINATED LIABILITIES 30 June 2020 31 December 2019 £m £m 3,257 3,528 In H120, the Santander UK group repurchased certain debt securities and subordinated liabilities as part of ongoing liability management exercises, resulting in a loss of £17m. In H119, the Santander UK group did not repurchase any of its debt securities or subordinated liabilities.

Provisions

Provisions	6 Months Ended
	Jun. 30, 2020
Disclosure of other provisions [abstract]
Provisions	23. PROVISIONS Conduct remediation PPI Other products Bank Levy Property Off balance sheet ECL Regulatory and other Total £m £m £m £m £m £m £m At 1 January 2020 189 25 48 61 78 176 577 Additional provisions — — — 1 — 82 83 Provisions released — (5) — (2) (5) (8) (20) Utilisation (38) — (39) (7) — (71) (155) At 30 June 2020 151 20 9 53 73 179 485 Conduct remediation At 30 June 2020, the remaining provision for Payment Protection Insurance (PPI) redress and related costs was £151m (2019: £189m). There was no additional provision in H120. Cumulative complaints from the inception of the PPI complaints process to 30 June 2020, regardless of the likelihood of Santander UK incurring a liability, were 4.5m. This included c 290,000 that were still being reviewed, which reflected the temporary scaling back of non-critical remediation activity as we focused on supporting our customers through the Covid-19 pandemic. The provision for conduct remediation recognised represents management’s best estimate of Santander UK’s liability in respect of mis-selling of PPI policies. Regulatory and other In H120 there was a charge of £17m relating to breaches of certain requirements to provide SMS warning alerts to customers regarding overdraft charges in our Retail Banking business. It also included a charge for operational risk provisions of £37m, and smaller charges for legal and redundancy provisions.

Retirement Benefit Plans

Retirement Benefit Plans	6 Months Ended
	Jun. 30, 2020
Disclosure of net defined benefit liability (asset) [abstract]
Retirement Benefit Plans	24. RETIREMENT BENEFIT PLANS The amounts recognised in the balance sheet were as follows: 30 June 2020 31 December 2019 £m £m Assets/(liabilities) Funded defined benefit pension scheme - surplus 522 670 Funded defined benefit pension scheme - deficit (358) (239) Unfunded pension and post retirement medical benefits (44) (41) Total net assets 120 390 The amounts recognised in other comprehensive income were as follows: Half year to Half year to 30 June 2020 30 June 2019 £m £m Return on plan assets (excluding amounts included in net interest expense) (1,115) (916) Actuarial losses arising from changes in demographic assumptions 38 — Actuarial gains arising from experience adjustments (10) (5) Actuarial losses arising from changes in financial assumptions 1,463 1,201 Pension remeasurement 376 280 The net assets recognised in the balance sheet were determined as follows: 30 June 2020 31 December 2019 £m £m Present value of defined benefit obligations (13,617) (12,165) Fair value of scheme assets 13,737 12,555 Net defined benefit assets 120 390 Actuarial assumptions The principal actuarial assumptions used for the defined benefit schemes were: 30 June 2020 31 December 2019 % % To determine benefit obligations: – Discount rate for scheme liabilities 1.4 2.1 – General price inflation 2.9 3.0 – General salary increase 1.0 1.0 – Expected rate of pension increase 2.8 2.9 Years Years Longevity at 60 for current pensioners, on the valuation date: – Males 27.3 27.3 – Females 29.8 29.8 Longevity at 60 for future pensioners currently aged 40, on the valuation date: – Males 28.9 28.9 – Females 31.3 31.3 In H120 management amended the general price inflation assumptions to reflect the expectation that the Retail Price Index would be brought in line with the Consumer Price Index from 2030. At 30 June 2020 this change increased the liabilities of the Scheme by £63m. Actuarial assumption sensitivities The sensitivity analyses below have been determined based on reasonably possible changes of the respective assumptions occurring at the end of the reporting period, while holding all other assumptions constant. (Decrease)/increase Change in pension obligation at period end from 30 June 2020 31 December 2019 Assumption £m £m Discount rate 25 bps increase (666) (564) General price inflation 25 bps increase 495 407 Mortality Each additional year of longevity assumed 504 419

Contingent Liabilities and Comm

Contingent Liabilities and Commitments	6 Months Ended
	Jun. 30, 2020
Disclosure of contingent liabilities [abstract]
Contingent Liabilities and Commitments	25. CONTINGENT LIABILITIES AND COMMITMENTS 30 June 2020 31 December 2019 £m £m Guarantees given to third parties 1,026 1,198 Formal standby facilities, credit lines and other commitments with original term to maturity of: – One year or less 16,592 18,256 – Later than one year 21,029 22,154 38,647 41,608 Other legal actions and regulatory matters Santander UK engages in discussion, and co-operates, with the FCA, PRA, CMA and other regulators and government agencies in various jurisdictions in their supervision and review of Santander UK including reviews exercised under statutory powers, regarding its interaction with past and present customers, both as part of general thematic work and in relation to specific products, services and activities. During the ordinary course of business, Santander UK is also subject to complaints and threatened legal proceedings brought by or on behalf of current or former employees, customers, investors or other third parties, in addition to legal and regulatory reviews, challenges and tax or enforcement investigations or proceedings in various jurisdictions. All such matters are assessed periodically to determine the likelihood of Santander UK incurring a liability. In those instances where it is concluded that it is not yet probable that a quantifiable payment will be made, for example because the facts are unclear or further time is required to fully assess the merits of the case or to reasonably quantify the expected payment, no provision is made. In addition, where it is not currently practicable to estimate the possible financial effect of these matters, no provision is made. Payment Protection Insurance In relation to a specific PPI portfolio of complaints, a legal dispute regarding allocation of liability is ongoing and remains in its early stages. The dispute relates to the liability for PPI mis-selling complaints relating to pre-2005 PPI policies underwritten by Financial Insurance Company Ltd (FICL) and Financial Assurance Company Ltd (FACL) and involves two Santander UK plc subsidiaries, Santander Cards UK Limited and Santander Insurance Services Limited (the Santander Entities). During the relevant period, FICL and FACL were owned by Genworth Financial International Holdings, Inc. In July 2015 AXA S.A. (AXA) acquired FICL and FACL from Genworth. In July 2017, Santander UK plc notified AXA that the Santander Entities did not accept liability for losses on PPI policies relating to this period. Santander UK plc entered into a Complaints Handling Agreement (CHA) with FICL and FACL pursuant to which it agreed to handle complaints on their behalf, and FICL and FACL agreed to pay redress assessed to be due to relevant policyholders on a without prejudice basis. A related dispute between AXA and (1) Genworth Financial International Holdings, Inc. and (2) Genworth Financial, Inc. (Genworth) concerning, inter alia, the proper construction of an alleged obligation to make payment on demand of a sum equal to 90% of all applicable PPI mis-selling losses (the Construction Issue) in a sale and purchase agreement dated 17 September 2015 (SPA) was determined by the High Court (Court) in December 2019. The Santander Entities were joined as third parties in connection with an application for declaratory relief by Genworth. This application related to Genworth’s assertion that upon any payment to AXA under the SPA, Genworth would have rights of subrogation against the Santander Entities (the Subrogation Issue). The Court found against Genworth and in favour of AXA on the Construction Issue, and against Genworth and in favour of the Santander Entities in relation to the Subrogation Issue. Genworth subsequently failed in its application for permission on appeal. On 20 July 2020 Genworth issued a press release stating that it had reached a settlement with AXA. Genworth has agreed to pay AXA £624m in aggregate for losses incurred by AXA or its subsidiaries relating to the subject of the dispute. This sum is broken down into: (i) £100m that has already been paid by Genworth as an interim payment; (ii) a £100m payment due to be paid on 23 July 2020; (iii) two payments deferred until 2022, totalling £317m and (iv) an estimated £107m for claimed mis-selling losses that are still being processed. More generally, there are ongoing factual issues to be resolved which may have legal consequences including in relation to liability. These issues create uncertainties which mean that it is not currently practicable to reliably predict the resolution of the matter including timing or the significance of the possible impact. The Regulatory and other provision in Note 23 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 to Santander UK’s interests in connection with the dispute. In addition, and in relation to PPI more generally, there are legal claims being made by Claims Management Companies challenging the FCA’s industry guidance on the treatment of Plevin /recurring non-disclosure assessments. No provision has been made as it is not possible to make a reliable estimate of the possible outflow of economic resource relating to this risk. German dividend tax arbitrage transactions In June 2018 the Cologne Criminal Prosecution Office and the German Federal Tax Office commenced an investigation in relation to the historical involvement of Santander UK plc, Santander Financial Services plc and Cater Allen International Limited (all subsidiaries of Santander UK Group Holdings plc) in German dividend tax arbitrage transactions (known as cum/ex transactions). These transactions allegedly exploited a feature of a specific German settlement mechanism through short-selling and complex derivative structuring which resulted in the German government either refunding withholding tax where such tax had not been paid or refunding it more than once. The German authorities are investigating numerous institutions and individuals in connection with alleged transactions and practices which may be found to be illegal under German law. Since commencement of the investigation we have cooperated with the German authorities and, with the assistance of external experts, to progress an internal investigation into the matters in question. From Santander UK plc’s perspective the investigation is focused principally on the period 2009-2011 and remains on-going. There remain factual issues to be resolved which may have legal consequences including potentially material financial penalties. These issues create uncertainties which mean that it is difficult to predict the resolution of the matter including timing or the significance of the possible impact. Consumer credit The Santander UK group’s unsecured lending and other consumer credit business is governed by consumer credit law and related regulations, including the CCA. Claims brought by customers in relation to these requirements, including potential breaches, could result in costs to the Santander UK group where such potential breaches are not found to be de minimis. The CCA includes very detailed and prescriptive requirements for lenders, including in relation to post contractual information. As described in Note 27 to the 2019 Annual Report, other provisions include an amount of £58m arising from a systems-related historical issue identified by Santander UK, relating to compliance with certain requirements of the CCA. This provision has been based on detailed reviews of relevant systems related to consumer credit business operations, supported by external legal and regulatory advice. Reviews of systems, commercial agreements and the legal and regulatory position are ongoing, such that the potential for additional remedial action is still being determined. The Regulatory and other provision in Note 23 includes our best estimate of Santander UK’s liability for the specific issue. The actual cost of customer compensation could differ from the amount provided. It is not currently practicable to provide an estimate of the risk and amount of any further financial impact. Taxation The Santander UK group engages in discussion, and co-operates, with HM Revenue & Customs (HMRC) in their oversight of the Santander UK group’s tax matters. The Santander UK group adopted the UK’s Code of Practice on Taxation for Banks in 2010. Certain leases in which the Santander UK group is or was the lessor are currently under review by HMRC in connection with claims for tax allowances. Under the terms of the lease agreements, the Santander UK group is fully indemnified in all material respects by the respective lessees for any liability arising from the disallowance of tax allowances plus accrued interest, which could be up to £150m. Whilst legal opinions have been obtained to support the Santander UK group’s position, the matter remains uncertain pending formal resolution with HMRC and any subsequent litigation. In 2020, as required under the terms of the leases these matters have moved to formal litigation and it is currently anticipated that hearings will be held at the First Tier Tax Tribunal in 2021.

Other Equity Instruments

Other Equity Instruments	6 Months Ended
	Jun. 30, 2020
Disclosure of classes of share capital [abstract]
Other Equity Instruments	26. OTHER EQUITY INSTRUMENTS Interest rate 30 June 2020 31 December 2019 % Next call date £m £m AT1 securities: – £500m Fixed Rate Reset Perpetual AT1 Capital Securities 6.75 June 2024 496 496 – £750m Fixed Rate Reset Perpetual AT1 Capital Securities 7.375 June 2022 745 745 – £500m Fixed Rate Reset Perpetual AT1 Capital Securities 5.33 September 2020 500 500 – £500m Fixed Rate Reset Perpetual AT1 Capital Securities 6.30 March 2025 500 500 2,241 2,241

Non-Controlling Interests

Non-Controlling Interests	6 Months Ended
	Jun. 30, 2020
Disclosure Of Non Controlling Interests [Abstract]
Non-Controlling Interests	27. NON-CONTROLLING INTERESTS Initial interest rate 30 June 2020 31 December 2019 % First call date £m £m Santander UK plc issued: – £300m Step-up Callable Perpetual Reserve Capital Instruments 7.037 February 2026 235 235 PSA Finance UK Limited 170 160 405 395

Assets Charged As Security For

Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets	6 Months Ended
	Jun. 30, 2020
Disclosure of assets pledged as security [Abstract]
Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets	28. ASSETS CHARGED AS SECURITY FOR LIABILITIES AND COLLATERAL ACCEPTED AS SECURITY FOR ASSETS Securitisations and covered bonds As described in Note 14 to the Consolidated Financial Statements in the 2019 Annual Report, Santander UK plc and certain of its subsidiaries issue securitisations and covered bonds. At 30 June 2020, there were £38,265m (2019: £36,391m) of gross assets in these secured programmes and £1,200m (2019: £166m) of these related to internally retained issuances that were available for use as collateral for liquidity purposes in the future. At 30 June 2020, a total of £4,796m (2019: £4,728m) of notes issued under securitisation and covered bond programmes had been retained internally, a proportion of which had been used as collateral for raising funds via third party bilateral secured funding transactions, which totalled £1,581m at 30 June 2020 (2019: £1,581m), or for use as collateral for liquidity purposes in the future.

Related Party Disclosures

Related Party Disclosures	6 Months Ended
	Jun. 30, 2020
Disclosure of transactions between related parties [abstract]
Related Party Disclosures	29. RELATED PARTY DISCLOSURES The financial position and performance of the Santander UK group have not been materially affected in H120 by any related party transactions, or changes to related party transactions. These transactions were made in the ordinary course of business, on substantially the same terms as for comparable transactions with third party counterparties, and within limits acceptable to the PRA. Such transactions do not involve more than the normal risk of collectability or present any unfavourable features. In addition, transactions with pension schemes operated by the Santander UK group are described in Note 28 to the Consolidated Financial Statements in the 2019 Annual Report.

Financial Instruments

Financial Instruments	6 Months Ended
	Jun. 30, 2020
Disclosure of fair value measurement of assets and liabilities [Abstract]
Financial Instruments	30. FINANCIAL INSTRUMENTS a) Measurement basis of financial assets and liabilities Financial assets and financial liabilities are measured on an ongoing basis either at fair value or at amortised cost. Note 1 to the Consolidated Financial Statements in the 2019 Annual Report describes how the classes of financial instruments are measured, and how income and expenses, including fair value gains and losses, are recognised. b) Fair values of financial instruments carried at amortised cost The following tables analyse the fair value of the financial instruments carried at amortised cost at 30 June 2020 and 31 December 2019. 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 38(e) to the Consolidated Financial Statements in the 2019 Annual Report. 30 June 2020 31 December 2019 Carrying Carrying Fair Value value Fair Value value £m £m £m £m Assets Loans and advances to customers 215,327 211,156 212,007 207,498 Loans and advances to banks 2,631 2,637 2,578 2,583 Reverse repurchase agreements - non trading 23,921 23,901 23,634 23,636 Other financial assets at amortised cost 5,064 4,879 7,110 7,056 246,943 242,573 245,329 240,773 Liabilities Deposits by customers 186,961 186,797 179,136 179,006 Deposits by banks 18,006 17,995 14,369 14,359 Repurchase agreements - non trading 20,773 20,786 18,292 18,286 Debt securities in issue 51,434 50,252 51,736 50,171 Subordinated liabilities 3,707 3,257 4,220 3,528 280,881 279,087 267,753 265,350 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 2020 and 31 December 2019, analysed by their levels in the fair value hierarchy - Level 1, Level 2 and Level 3. 30 June 2020 31 December 2019 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Valuation £m £m £m £m £m £m £m £m technique Assets Derivative financial instruments Exchange rate contracts — 4,144 2 4,146 — 2,319 6 2,325 A Interest rate contracts — 2,636 13 2,649 — 1,951 9 1,960 A & C Equity and credit contracts — 112 50 162 — 223 69 292 B & D Netting — (1,666) — (1,666) — (1,214) — (1,214) — 5,226 65 5,291 — 3,279 84 3,363 Other financial assets at FVTPL Loans and advances to customers — 504 103 607 — 448 92 540 A Debt securities — 4 121 125 2 2 294 298 A, B & D Equity securities 15 — 119 134 16 — 119 135 B 15 508 343 866 18 450 505 973 Financial assets at FVOCI Debt securities 9,855 453 — 10,308 9,209 482 — 9,691 D Loans and advances to customers — — 30 30 — — 56 56 D 9,855 453 30 10,338 9,209 482 56 9,747 Total assets at fair value 9,870 6,187 438 16,495 9,227 4,211 645 14,083 Liabilities Derivative financial instruments Exchange rate contracts — 510 — 510 — 659 4 663 A Interest rate contracts — 2,788 2 2,790 — 2,087 2 2,089 A & C Equity and credit contracts — 85 28 113 — 142 29 171 B & D Netting — (1,666) — (1,666) — (1,214) — (1,214) — 1,717 30 1,747 — 1,674 35 1,709 Other financial liabilities at FVTPL Debt securities in issue — 1,189 6 1,195 — 1,099 6 1,105 A Structured deposits — 415 — 415 — 406 29 435 A Collateral and associated financial guarantees — — 10 10 — 147 26 173 D — 1,604 16 1,620 — 1,652 61 1,713 Total liabilities at fair value — 3,321 46 3,367 — 3,326 96 3,422 Transfers between levels of the fair value hierarchy In H120 there were no significant transfers of financial instruments between Levels 1 and 2 or between Levels 2 and 3 (H119: none). d) Fair value adjustments The internal models incorporate assumptions that Santander UK believes would be made by a market participant to establish fair value. Fair value adjustments are adopted when Santander UK considers that there are additional factors that would be considered by a market participant that are not incorporated in the valuation model. Santander UK classifies fair value adjustments as either ‘risk-related’ or ‘model-related’. The fair value adjustments form part of the portfolio fair value and are included in the balance sheet values of the product types to which they have been applied. The magnitude and types of fair value adjustment are listed in the following table: 30 June 2020 31 December 2019 £m £m Risk-related: - Bid-offer and trade specific adjustments (17) (12) - Uncertainty 48 37 - Credit risk adjustment 9 6 - Funding fair value adjustment 9 6 49 37 Model-related 1 — Day One profit 1 — 51 37 Risk-related adjustments Risk-related adjustments are driven, in part, by the magnitude of Santander UK’s market or credit risk exposure, and by external market factors, such as the size of market spreads. For further details, see the ‘Risk-related adjustments’ section in Note 38(g) to the Consolidated Financial Statements in the 2019 Annual Report. e) 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 38(h) to the Consolidated Financial Statements in the 2019 Annual Report. Reconciliation of fair value measurement in Level 3 of the fair value hierarchy The following table sets out the movements in Level 3 financial instruments in H120 and H119: Assets Liabilities Derivatives Other financial assets at FVTPL Financial assets at FVOCI Total Derivatives Other financial liabilities at FVTPL Total £m £m £m £m £m £m £m At 1 January 2020 84 505 56 645 (35) (61) (96) Total (losses)/gains recognised in profit or loss: - Fair value movements (2) (10) 1 (11) (1) 15 14 - Foreign exchange and other movements — 6 — 6 — 2 2 Transfers out — — — — — 28 28 Netting (1) — (37) — (37) — — — Additions — — — — — (1) (1) Sales — (11) (19) (30) — — — Settlements (17) (110) (8) (135) 6 1 7 At 30 June 2020 65 343 30 438 (30) (16) (46) (Losses)/gains recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period (2) (4) 1 (5) (1) 17 16 At 1 January 2019 115 1,055 73 1,243 (70) (49) (119) Total gains/(losses) recognised in profit or loss: - Fair value movements 3 32 — 35 (1) (5) (6) - Foreign exchange and other movements — 3 — 3 — (3) (3) Transfers in — 11 — 11 — — — Netting (1) — (254) — (254) — — — Additions 3 188 — 191 — (2) (2) Settlements (15) (269) (4) (288) 31 2 33 At 30 June 2019 106 766 69 941 (40) (57) (97) Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period 3 35 — 38 (1) (8) (9) 1. This relates to the effect of netting on the fair value of the credit linked notes due to a legal right of set-off between the principal amounts of the senior notes and the associated cash deposits. For more, see ‘ii) Credit protection entities’ in Note 19 in the 2019 Annual Report. Effect of changes in significant unobservable assumptions to reasonably possible alternatives (Level 3)

Events After the Balance Sheet

Events After the Balance Sheet Date	6 Months Ended
	Jun. 30, 2020
Disclosure of non-adjusting events after reporting period [abstract]
Events After the Balance Sheet Date	31. EVENTS AFTER THE BALANCE SHEET DATE There have been no significant events between 30 June 2020 and the date of approval of these financial statements which would require a change to or additional disclosure in the financial statements.

Accounting Policies (Policies)

Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
Statement [Line Items]
Basis of preparation	The Condensed Consolidated Interim Financial Statements reflect all adjustments that, in the opinion of management, are necessary for a fair statement of the results of operations for the interim period. All such adjustments to the financial information are of a normal, recurring nature. Because the results from common banking activities are so closely related and responsive to changes in market conditions, the results for any interim period are not necessarily indicative of the results that can be expected for the year. 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 sourcebook 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 Santander UK Group Holdings plc (the Santander UK group) for the year ended 31 December 2019 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 International Financial Reporting Standards as adopted by the European Union as there are no applicable differences between the two frameworks for the periods presented. 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 2019 Annual Report. At 30 June 2020, for the Santander UK group, there were no significant new or revised standards and interpretations, and amendments thereto, which have been issued but which are not yet effective or which have otherwise not been early adopted where permitted.
Going concern	Going concern In light of the current economic uncertainty, the Directors updated their going concern assessment in preparing these Condensed Consolidated Interim Financial Statements. After making enquiries, the Directors have a reasonable expectation that Santander UK has adequate resources to continue in operational existence for at least twelve months from the date of this report and, therefore, having reassessed the principal risks and uncertainties, the Directors consider it appropriate for the Condensed Consolidated Interim Financial Statements to be prepared on a going concern basis. In making their going concern assessment in connection with preparing the Condensed Consolidated Interim Financial Statements, the Directors considered a wide range of information that included Santander UK’s long-term business and strategic plans, forecasts and projections, estimated capital, funding and liquidity requirements, contingent liabilities and the reasonably possible changes in trading performance arising from potential economic, market and product developments. The Directors' assessment specifically considered the impacts of Covid-19, including for the following areas: – Economic scenarios : These underpin our IFRS 9 ECL impairment allowances and are discussed in detail in the Credit risk section of the Risk review. The Directors reviewed the economic scenarios, revised as a result of Covid-19, to ensure that they captured the wide range of potential outcomes for the UK economy. These include a re-emergence of the virus and further lockdown measures being imposed, a slower recovery that is more akin to the ‘U’ shape of past recessions, and hysteresis effects caused by higher and longer unemployment rates. – Liquidity: Although the key aim of the UK Government financial support measures introduced in H120 was to limit damage to the wider economy from Covid-19, they had the side-effect of reducing any potential liquidity risks arising due to Covid-19. Although Covid-19 did not trigger a liquidity stress, its immediate negative impacts on liquidity, such as the drawing of committed credit and liquidity facilities, were largely offset by deposits from those same drawings as corporates reduced their spending. Similarly, the impact of the initial effective shutdown of the mortgage market and the payment holidays granted to customers was offset by better than expected retail deposit balances as customers reduced their spending. – Capital: Santander UK remains strongly capitalised and Covid-19 did not trigger a capital stress. As part of the Bank of England Interim Financial Stability Report (May 2020), the PRA developed a desktop stress scenario, which had less of an impact over the first two years of the scenario on the core banking system than their 2019 Stress Test, where our CET1 drawdown was the lowest across UK banks and we exceeded CET1 capital ratio and Tier 1 Leverage ratio hurdle rates across the projection horizon. In line with other UK banks, we also announced that we will not pay quarterly or interim dividends, or make share buybacks on ordinary shares until the end of 2020. – Customers: Santander UK has supported many thousands of individuals and businesses affected by Covid-19 with a range of measures, including payment holidays on mortgages, personal loans and credit cards as well as taking an active part in UK Government loan schemes to help businesses. We are working with those customers who took a payment holiday to understand their individual situations and help them resume payments. – Operations: All our operations continue to operate effectively with a significant majority of staff working from home and the majority of branches remaining open and returning to more normal hours. The current operating model could be sustained indefinitely with additional resilience being continuously implemented and is not affecting our ability to operate all our services, or raising concerns about our Business Continuity Planning, and – Key suppliers: Suppliers are being closely monitored in line with our Third Party Risk Management Framework. No significant service issues have been reported across our cohort of critical suppliers, and no material issues have been reported across our broader (non-critical) supply chain. Isolated supplier impacts have been seen, but these are being managed.
Critical judgements and accounting estimates	CRITICAL JUDGEMENTS AND ACCOUNTING ESTIMATES The preparation of the Condensed Consolidated Interim Financial Statements requires management to make judgements and accounting estimates 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 judgements and accounting estimates, which are based on historical experience and on various other factors that are believed to be reasonable under the circumstances, on an ongoing basis. Actual results may differ from these accounting estimates under different assumptions or conditions. In the course of preparing the Condensed Consolidated Interim Financial Statements, no significant judgements have been made in the process of applying the accounting policies, other than those involving estimations about credit impairment losses, provisions, contingent liabilities and pensions. a) Credit impairment allowance The application of the ECL impairment methodology for calculating credit impairment allowances is highly susceptible to change from period to period. The methodology requires management to make a number of judgmental assumptions in determining 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. The impact of Covid-19 has increased the uncertainty around ECL impairment calculations, and has required management to make additional judgements and accounting estimates that affect the reported amount of assets and liabilities at the reporting date and the reported amount of income and expenses during the reporting period. The key additional judgements arising from the impact of Covid-19 mainly reflect the increased uncertainty around forward-looking economic information and the need for additional post model adjustments. Key areas of judgement in accounting estimates The key judgements made by management in applying the ECL impairment methodology are set out below. – Definition of default – Forward-looking information – Probability weights – SICR – Post model adjustments. For more on each of these key judgements, including the impact of Covid-19 on them, see the ‘Credit risk – Santander UK group level – credit risk management’ section of the Risk review. Sensitivity of ECL allowance For detailed disclosures, see the ‘Credit risk – Santander UK group level – credit risk management’ section of the Risk review.

Segments (Tables)

Segments (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of operating segments [abstract]
Summary of Results by Segment	Results by segment Half year to Retail Banking Corporate & Commercial Banking Corporate & Investment Banking Corporate Centre Total 30 June 2020 £m £m £m £m £m Net interest income/(expense) 1,393 150 26 (27) 1,542 Non-interest income 235 40 28 3 306 Total operating income/(expense) 1,628 190 54 (24) 1,848 Operating expenses before credit impairment losses, provisions and charges (1,010) (134) (62) (51) (1,257) Credit impairment losses (247) (106) (12) (11) (376) Provisions for other liabilities and (charges)/release (56) 3 (4) (11) (68) Total operating credit impairment losses, provisions and charges (303) (103) (16) (22) (444) Profit/(loss) before tax 315 (47) (24) (97) 147 Revenue from external customers 2,004 237 55 (448) 1,848 Inter-segment revenue (376) (47) (1) 424 — Total operating income/(expense) 1,628 190 54 (24) 1,848 Revenue from external customers includes the following fee and commission income disaggregated by income type: (1) – Current account and debit card fees 253 13 5 — 271 – Insurance, protection and investments 31 — — — 31 – Credit cards 33 — — — 33 – Non-banking and other fees (2) 26 22 23 2 73 Total fee and commission income 343 35 28 2 408 Fee and commission expense (169) (9) (4) (5) (187) Net fee and commission income/(expense) 174 26 24 (3) 221 30 June 2020 Customer loans 184,862 16,604 4,040 4,030 209,536 Total assets (3) 193,692 16,604 4,949 87,574 302,819 Customer deposits 151,091 19,538 6,784 8,302 185,715 Total liabilities 152,171 19,563 7,230 107,371 286,335 1. The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. 2. Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance. 3. Includes customer loans, net of credit impairment loss allowances. Half year to Retail Banking Corporate & Commercial Banking Corporate & Investment Banking Corporate Centre Total 30 June 2019 £m £m £m £m £m Net interest income/(expense) 1,465 189 32 (15) 1,671 Non-interest income 353 38 47 8 446 Total operating income/(expense) 1,818 227 79 (7) 2,117 Operating expenses before credit impairment losses, provisions and charges (1,011) (138) (83) (35) (1,267) Credit impairment (losses)/releases (63) (9) 4 (1) (69) Provisions for other liabilities and charges (95) (1) (11) (99) (206) Total operating credit impairment losses, provisions and charges (158) (10) (7) (100) (275) Profit/(loss) before tax 649 79 (11) (142) 575 Revenue from external customers 2,166 281 85 (415) 2,117 Inter-segment revenue (348) (54) (6) 408 — Total operating income/(expense) 1,818 227 79 (7) 2,117 Revenue from external customers includes the following fee and commission income disaggregated by income type: (1) – Current account and debit card fees 345 15 14 — 374 – Insurance, protection and investments 37 — — — 37 – Credit cards 42 — — — 42 – Non-banking and other fees (2) 36 26 24 1 87 Total fee and commission income 460 41 38 1 540 Fee and commission expense (184) (12) (7) (2) (205) Net fee and commission income/(expense) 276 29 31 (1) 335 31 December 2019 Customer loans 180,398 16,297 4,114 4,489 205,298 Total assets (3) 187,556 16,297 4,727 79,908 288,488 Customer deposits 145,050 18,234 6,101 8,437 177,822 Total liabilities 145,917 18,260 6,500 101,470 272,147 1. The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. 2. Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance. 3. Includes customer loans, net of credit impairment loss allowances.

Operating Expenses Before Cre_2

Operating Expenses Before Credit Impairment Losses, Provisions and Charges (Tables)	6 Months Ended
	Jun. 30, 2020
Expenses by nature [abstract]
Summary of Operating Expenses Before Credit Impairment Losses, Provisions and Charges	Half year to Half year to 30 June 2020 30 June 2019 £m £m Staff costs 608 653 Other administration expenses 377 354 Depreciation, amortisation and impairment 272 260 1,257 1,267

Credit Impairment Losses and _2

Credit Impairment Losses and Provisions (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of credit impairment loss and provisions [Abstract]
Summary of Impairment Losses and Provisions	Half year to Half year to 30 June 2020 30 June 2019 £m £m Credit impairment losses: Loans and advances to customers 396 108 Recoveries of loans and advances, net of collection costs (15) (38) Off-balance sheet exposures (See Note 23) (5) (1) 376 69 Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 23) 68 205 Provisions for residual value and voluntary termination — 1 68 206 444 275

Taxation (Tables)

Taxation (Tables)	6 Months Ended
	Jun. 30, 2020
Major components of tax expense (income) [abstract]
Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate	). The tax on profit before tax differs from the theoretical amount that would arise using the basic corporation tax rate of the Company as follows: Half year to Half year to 30 June 2020 30 June 2019 £m £m Profit before tax 147 575 Tax calculated at a tax rate of 19% (H119: 19%) 28 109 Bank surcharge on profits 7 38 Non-deductible preference dividends paid 3 5 Non-deductible UK Bank Levy 6 13 Non-deductible conduct remediation, fines and penalties — 11 Other non-deductible costs and non-taxable income 2 9 Effect of change in tax rate on deferred tax provision 6 — Tax relief on dividends in respect of other equity instruments (13) (21) Adjustment to prior year provisions (4) — Tax charge 35 164

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of nature and extent of risks arising from financial instruments [abstract]
Notional Amounts and Fair Values of Derivatives	30 June 2020 31 December 2019 Fair value Fair value Notional amount Assets Liabilities Notional amount Assets Liabilities £m £m £m £m £m £m Derivatives held for trading: Exchange rate contracts 21,304 628 378 14,249 136 199 Interest rate contracts 47,591 864 530 47,045 754 566 Equity and credit contracts 2,344 162 113 2,583 292 167 Total derivatives held for trading 71,239 1,654 1,021 63,877 1,182 932 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 1,758 148 11 1,482 166 2 Interest rate contracts 99,899 1,218 2,235 94,550 1,022 1,488 101,657 1,366 2,246 96,032 1,188 1,490 Designated as cash flow hedges: Exchange rate contracts 32,145 3,370 121 28,502 2,023 462 Interest rate contracts 21,500 567 25 17,451 184 35 Equity derivative contracts — — — 49 — 4 53,645 3,937 146 46,002 2,207 501 Total derivatives held for hedging 155,302 5,303 2,392 142,034 3,395 1,991 Derivative netting (1) (1,666) (1,666) (1,214) (1,214) Total derivatives 226,541 5,291 1,747 205,911 3,363 1,709 LIBOR Reform The table below shows the notional value of hedging instruments by benchmark interest rate impacted by LIBOR reform. 30 June 2020 31 December 2019 GBP USD Other Total GBP USD Other Total £m £m £m £m £m £m £m £m Total notional value of hedging instruments: – Cash flow hedges 19,948 5,836 — 25,784 23,396 8,001 — 31,397 – Fair value hedges 42,473 4,533 789 47,795 53,244 5,070 1,187 59,501 62,421 10,369 789 73,579 76,640 13,071 1,187 90,898 Maturing after 31 December 2021: – Cash flow hedges 11,007 2,828 — 13,835 11,773 2,644 — 14,417 – Fair value hedges 12,991 413 722 14,126 16,455 1,897 740 19,092 23,998 3,241 722 27,961 28,228 4,541 740 33,509

Other Financial Assets At Fai_2

Other Financial Assets At Fair Value Through Profit Or Loss (Tables)	6 Months Ended
	Jun. 30, 2020
Financial assets at fair value through profit or loss [abstract]
Summary of Other Financial Assets at Fair Value Through Profit or Loss	30 June 2020 31 December 2019 £m £m Loans and advances to customers: Loans to housing associations 13 12 Other loans 594 528 607 540 Debt securities 125 298 Equity securities 134 135 866 973

Loans and Advances to Custome_2

Loans and Advances to Customers (Tables)	6 Months Ended
	Jun. 30, 2020
Net Loans and Advances to Customers [Abstract]
Summary of Net Loans and Advances to Customers	30 June 2020 31 December 2019 £m £m Loans and advances to customers 212,318 208,344 Credit impairment loss allowances on loans and advances to customers (1,106) (785) RV and voluntary termination provisions on finance leases (56) (61) Net loans and advances to customers 211,156 207,498

Securitisations and Covered B_2

Securitisations and Covered Bonds (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of securitisations and covered bonds [Abstract]
Analysis of Securitisations and Covered Bonds	30 June 2020 31 December 2019 £m £m Mortgage-backed master trust structures: – Holmes 3,603 4,262 – Fosse 3,000 3,708 – Langton 3,142 3,076 9,745 11,046 Other asset-backed securitisation structures: – Motor 321 490 – Auto ABS UK Loans 1,490 1,532 1,811 2,022 Total securitisation programmes 11,556 13,068 Covered bond programmes – Euro 35bn Global Covered Bond Programme 26,709 23,323 Total securitisation and covered bond programmes 38,265 36,391
Summary of Issuances and Redemptions of Securitisation and Covered Bond Programme	Internal issuances External issuances Internal redemptions External redemptions H120 H119 H120 H119 H120 H119 H120 H119 £bn £bn £bn £bn £bn £bn £bn £bn Mortgage-backed master trust structures: – Holmes — — — — 0.1 — 0.5 0.8 Other asset-backed securitisation structures: – Motor — — — — 0.1 0.1 0.1 0.2 – Auto ABS UK Loans — — — — — — 0.1 0.1 Covered bond programme — — 3.0 1.9 — — 1.8 — — — 3.0 1.9 0.2 0.1 2.5 1.1

Other Financial Assets At Amo_2

Other Financial Assets At Amortised Cost (Tables)	6 Months Ended
	Jun. 30, 2020
Financial assets at fair value through profit or loss [abstract]
Summary of Other Financial Assets at Amortised Cost	30 June 2020 31 December 2019 £m £m Asset backed securities 507 532 Debt securities 4,372 6,524 4,879 7,056

Financial Assets At Fair Valu_2

Financial Assets At Fair Value Through Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2020
Financial assets at fair value through other comprehensive income [abstract]
Summary of Financial Assets at Fair Value Through Other Comprehensive Income	30 June 2020 31 December 2019 £m £m Debt securities 10,308 9,691 Loans and advances to customers 30 56 10,338 9,747

Intangible Assets (Tables)

Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of detailed information about intangible assets [abstract]
Schedule of Goodwill	Cost Accumulated impairment Net book value £m £m £m At 31 December 2019, 1 January 2020 and 30 June 2020 1,285 (82) 1,203

Other Financial Liabilities a_2

Other Financial Liabilities at Fair Value Through Profit or Loss (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of financial liabilities [abstract]
Summary of Other Financial Liabilities at Fair Value Through Profit or Loss	30 June 2020 31 December 2019 £m £m US$30bn Euro Medium Term Note Programme 172 159 Structured Notes Programmes 881 809 Eurobonds 142 137 Structured deposits 415 435 Collateral and associated financial guarantees 10 173 1,620 1,713

Deposits by Customers (Tables)

Deposits by Customers (Tables)	6 Months Ended
	Jun. 30, 2020
Deposits from customers [abstract]
Schedule of Deposits by Customers	30 June 2020 31 December 2019 £m £m Demand and time deposits (1) 185,570 177,772 Amounts due to fellow Banco Santander subsidiaries and joint ventures 1,227 1,234 186,797 179,006 (1) Includes equity index-linked deposits of £1,127m (2019: £1,139m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,127m and £16m (2019: £1,139m and £18m) respectively.

Deposits by Banks (Tables)

Deposits by Banks (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of deposits from banks [Abstract]
Schedule of Deposits by Banks	30 June 2020 31 December 2019 £m £m Items in the course of transmission 255 337 Deposits held as collateral 3,853 2,175 Other deposits (1) 13,887 11,847 17,995 14,359 (1) Includes drawdown from the TFS of £10.8bn (2019: £10.8bn) and drawdown from the TFSME of £2.2bn (2019:£nil).

Repurchase Agreements - Non T_2

Repurchase Agreements - Non Trading (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure Of Repurchase Agreements [Abstract]
Summary of Repurchase Agreements - Non Trading	30 June 2020 31 December 2019 £m £m Agreements with banks 13,296 10,227 Agreements with customers 7,490 8,059 20,786 18,286

Debt Securities in Issue (Table

Debt Securities in Issue (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Securities In Issue [Abstract]
Summary of Debt Securities in Issue	30 June 2020 31 December 2019 £m £m Medium-term notes 24,800 24,522 Euro 35bn Global Covered Bond Programme 20,631 19,004 Certificates of deposit 1,795 2,806 Credit linked notes 55 60 Securitisation programmes 2,971 3,779 50,252 50,171

Subordinated Liabilities (Table

Subordinated Liabilities (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of Subordinated Liabilities [Abstract]
Schedule of Subordinated Liabilities	30 June 2020 31 December 2019 £m £m 3,257 3,528

Provisions (Tables)

Provisions (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of other provisions [abstract]
Summary of Provisions Reconciliation	Conduct remediation PPI Other products Bank Levy Property Off balance sheet ECL Regulatory and other Total £m £m £m £m £m £m £m At 1 January 2020 189 25 48 61 78 176 577 Additional provisions — — — 1 — 82 83 Provisions released — (5) — (2) (5) (8) (20) Utilisation (38) — (39) (7) — (71) (155) At 30 June 2020 151 20 9 53 73 179 485

Retirement Benefit Plans (Table

Retirement Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of net defined benefit liability (asset) [abstract]
Summary of Retirement Benefit Plans	The amounts recognised in the balance sheet were as follows: 30 June 2020 31 December 2019 £m £m Assets/(liabilities) Funded defined benefit pension scheme - surplus 522 670 Funded defined benefit pension scheme - deficit (358) (239) Unfunded pension and post retirement medical benefits (44) (41) Total net assets 120 390
Summary of Amounts Recognised in Other Comprehensive Income	The amounts recognised in other comprehensive income were as follows: Half year to Half year to 30 June 2020 30 June 2019 £m £m Return on plan assets (excluding amounts included in net interest expense) (1,115) (916) Actuarial losses arising from changes in demographic assumptions 38 — Actuarial gains arising from experience adjustments (10) (5) Actuarial losses arising from changes in financial assumptions 1,463 1,201 Pension remeasurement 376 280
Summary of Net Assets Recognised	The net assets recognised in the balance sheet were determined as follows: 30 June 2020 31 December 2019 £m £m Present value of defined benefit obligations (13,617) (12,165) Fair value of scheme assets 13,737 12,555 Net defined benefit assets 120 390
Summary of Principal Actuarial Assumptions Used for Defined Benefit Schemes	The principal actuarial assumptions used for the defined benefit schemes were: 30 June 2020 31 December 2019 % % To determine benefit obligations: – Discount rate for scheme liabilities 1.4 2.1 – General price inflation 2.9 3.0 – General salary increase 1.0 1.0 – Expected rate of pension increase 2.8 2.9 Years Years Longevity at 60 for current pensioners, on the valuation date: – Males 27.3 27.3 – Females 29.8 29.8 Longevity at 60 for future pensioners currently aged 40, on the valuation date: – Males 28.9 28.9 – Females 31.3 31.3
Summary of Actuarial Assumption Sensitivities	The sensitivity analyses below have been determined based on reasonably possible changes of the respective assumptions occurring at the end of the reporting period, while holding all other assumptions constant. (Decrease)/increase Change in pension obligation at period end from 30 June 2020 31 December 2019 Assumption £m £m Discount rate 25 bps increase (666) (564) General price inflation 25 bps increase 495 407 Mortality Each additional year of longevity assumed 504 419

Contingent Liabilities and Co_2

Contingent Liabilities and Commitments (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of contingent liabilities [abstract]
Summary of Contingent Liabilities and Commitments	30 June 2020 31 December 2019 £m £m Guarantees given to third parties 1,026 1,198 Formal standby facilities, credit lines and other commitments with original term to maturity of: – One year or less 16,592 18,256 – Later than one year 21,029 22,154 38,647 41,608

Other Equity Instruments (Table

Other Equity Instruments (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of classes of share capital [abstract]
Summary of other equity instruments	Interest rate 30 June 2020 31 December 2019 % Next call date £m £m AT1 securities: – £500m Fixed Rate Reset Perpetual AT1 Capital Securities 6.75 June 2024 496 496 – £750m Fixed Rate Reset Perpetual AT1 Capital Securities 7.375 June 2022 745 745 – £500m Fixed Rate Reset Perpetual AT1 Capital Securities 5.33 September 2020 500 500 – £500m Fixed Rate Reset Perpetual AT1 Capital Securities 6.30 March 2025 500 500 2,241 2,241

Non-Controlling Interests (Tabl

Non-Controlling Interests (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure Of Non Controlling Interests [Abstract]
Schedule of Amounts Attributable to Non-Controlling Interests	Initial interest rate 30 June 2020 31 December 2019 % First call date £m £m Santander UK plc issued: – £300m Step-up Callable Perpetual Reserve Capital Instruments 7.037 February 2026 235 235 PSA Finance UK Limited 170 160 405 395

Financial Instruments (Tables)

Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2020
Disclosure of fair value measurement of assets and liabilities [Abstract]
Fair Values of Financial Instruments Carried at Amortised Cost	30 June 2020 31 December 2019 Carrying Carrying Fair Value value Fair Value value £m £m £m £m Assets Loans and advances to customers 215,327 211,156 212,007 207,498 Loans and advances to banks 2,631 2,637 2,578 2,583 Reverse repurchase agreements - non trading 23,921 23,901 23,634 23,636 Other financial assets at amortised cost 5,064 4,879 7,110 7,056 246,943 242,573 245,329 240,773 Liabilities Deposits by customers 186,961 186,797 179,136 179,006 Deposits by banks 18,006 17,995 14,369 14,359 Repurchase agreements - non trading 20,773 20,786 18,292 18,286 Debt securities in issue 51,434 50,252 51,736 50,171 Subordinated liabilities 3,707 3,257 4,220 3,528 280,881 279,087 267,753 265,350
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 2020 and 31 December 2019, analysed by their levels in the fair value hierarchy - Level 1, Level 2 and Level 3. 30 June 2020 31 December 2019 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Valuation £m £m £m £m £m £m £m £m technique Assets Derivative financial instruments Exchange rate contracts — 4,144 2 4,146 — 2,319 6 2,325 A Interest rate contracts — 2,636 13 2,649 — 1,951 9 1,960 A & C Equity and credit contracts — 112 50 162 — 223 69 292 B & D Netting — (1,666) — (1,666) — (1,214) — (1,214) — 5,226 65 5,291 — 3,279 84 3,363 Other financial assets at FVTPL Loans and advances to customers — 504 103 607 — 448 92 540 A Debt securities — 4 121 125 2 2 294 298 A, B & D Equity securities 15 — 119 134 16 — 119 135 B 15 508 343 866 18 450 505 973 Financial assets at FVOCI Debt securities 9,855 453 — 10,308 9,209 482 — 9,691 D Loans and advances to customers — — 30 30 — — 56 56 D 9,855 453 30 10,338 9,209 482 56 9,747 Total assets at fair value 9,870 6,187 438 16,495 9,227 4,211 645 14,083 Liabilities Derivative financial instruments Exchange rate contracts — 510 — 510 — 659 4 663 A Interest rate contracts — 2,788 2 2,790 — 2,087 2 2,089 A & C Equity and credit contracts — 85 28 113 — 142 29 171 B & D Netting — (1,666) — (1,666) — (1,214) — (1,214) — 1,717 30 1,747 — 1,674 35 1,709 Other financial liabilities at FVTPL Debt securities in issue — 1,189 6 1,195 — 1,099 6 1,105 A Structured deposits — 415 — 415 — 406 29 435 A Collateral and associated financial guarantees — — 10 10 — 147 26 173 D — 1,604 16 1,620 — 1,652 61 1,713 Total liabilities at fair value — 3,321 46 3,367 — 3,326 96 3,422
Summary of Fair Value Adjustment	Santander UK classifies fair value adjustments as either ‘risk-related’ or ‘model-related’. The fair value adjustments form part of the portfolio fair value and are included in the balance sheet values of the product types to which they have been applied. The magnitude and types of fair value adjustment are listed in the following table: 30 June 2020 31 December 2019 £m £m Risk-related: - Bid-offer and trade specific adjustments (17) (12) - Uncertainty 48 37 - Credit risk adjustment 9 6 - Funding fair value adjustment 9 6 49 37 Model-related 1 — Day One profit 1 — 51 37
Reconciliation of fair value measurement in Level 3 of the fair value hierarchy	The following table sets out the movements in Level 3 financial instruments in H120 and H119: Assets Liabilities Derivatives Other financial assets at FVTPL Financial assets at FVOCI Total Derivatives Other financial liabilities at FVTPL Total £m £m £m £m £m £m £m At 1 January 2020 84 505 56 645 (35) (61) (96) Total (losses)/gains recognised in profit or loss: - Fair value movements (2) (10) 1 (11) (1) 15 14 - Foreign exchange and other movements — 6 — 6 — 2 2 Transfers out — — — — — 28 28 Netting (1) — (37) — (37) — — — Additions — — — — — (1) (1) Sales — (11) (19) (30) — — — Settlements (17) (110) (8) (135) 6 1 7 At 30 June 2020 65 343 30 438 (30) (16) (46) (Losses)/gains recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period (2) (4) 1 (5) (1) 17 16 At 1 January 2019 115 1,055 73 1,243 (70) (49) (119) Total gains/(losses) recognised in profit or loss: - Fair value movements 3 32 — 35 (1) (5) (6) - Foreign exchange and other movements — 3 — 3 — (3) (3) Transfers in — 11 — 11 — — — Netting (1) — (254) — (254) — — — Additions 3 188 — 191 — (2) (2) Settlements (15) (269) (4) (288) 31 2 33 At 30 June 2019 106 766 69 941 (40) (57) (97) Gains/(losses) recognised in profit or loss/other comprehensive income relating to assets and liabilities held at the end of the period 3 35 — 38 (1) (8) (9) 1. This relates to the effect of netting on the fair value of the credit linked notes due to a legal right of set-off between the principal amounts of the senior notes and the associated cash deposits. For more, see ‘ii) Credit protection entities’ in Note 19 in the 2019 Annual Report.

Segments - Summary of Results b

Segments - Summary of Results by Segment (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2020GBP (£)segment	Jun. 30, 2019GBP (£)	Dec. 31, 2019GBP (£)
Disclosure of operating segments [line items]
Net interest income/(expense)	£ 1,542	£ 1,671
Non-interest income/(expense)	306	446
Total operating income/(expense)	1,848	2,117
Operating expenses before credit impairment losses, provisions and charges	(1,257)	(1,267)
Credit impairment (losses)/releases	(376)	(69)
Provisions for other liabilities and charges	(68)	(206)
Total operating credit impairment losses, provisions and (charges)/releases	(444)	(275)
Profit before tax	147	575
Revenue from external customers	1,848	2,117
Inter-segment revenue	1,848	2,117
Total operating income/(expense)	1,848	2,117
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	271	374
Insurance, protection and investments	31	37
Credit cards	33	42
Non-banking and other fees	73	87
Total fee and commission income	408	540
Fee and commission expense	(187)	(205)
Net fee and commission income	221	335
Customer loans	209,536		£ 205,298
Total assets	302,819		288,488
Customer deposits	185,715		177,822
Total liabilities	£ 286,335		272,147
Number of segments | segment	4
Elimination of Intersegment Amounts
Disclosure of operating segments [line items]
Inter-segment revenue	£ 0	0
Retail banking
Disclosure of operating segments [line items]
Net interest income/(expense)	1,393	1,465
Non-interest income/(expense)	235	353
Total operating income/(expense)	1,628	1,818
Operating expenses before credit impairment losses, provisions and charges	(1,010)	(1,011)
Credit impairment (losses)/releases	(247)	(63)
Provisions for other liabilities and charges	(56)	(95)
Total operating credit impairment losses, provisions and (charges)/releases	(303)	(158)
Profit before tax	315	649
Revenue from external customers	2,004	2,166
Total operating income/(expense)	1,628	1,818
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	253	345
Insurance, protection and investments	31	37
Credit cards	33	42
Non-banking and other fees	26	36
Total fee and commission income	343	460
Fee and commission expense	(169)	(184)
Net fee and commission income	174	276
Customer loans	184,862		180,398
Total assets	193,692		187,556
Customer deposits	151,091		145,050
Total liabilities	152,171		145,917
Retail banking | Elimination of Intersegment Amounts
Disclosure of operating segments [line items]
Inter-segment revenue	(376)	(348)
Corporate and commercial banking
Disclosure of operating segments [line items]
Net interest income/(expense)	150	189
Non-interest income/(expense)	40	38
Total operating income/(expense)	190	227
Operating expenses before credit impairment losses, provisions and charges	(134)	(138)
Credit impairment (losses)/releases	(106)	(9)
Provisions for other liabilities and charges	3	(1)
Total operating credit impairment losses, provisions and (charges)/releases	(103)	(10)
Profit before tax	(47)	79
Revenue from external customers	237	281
Total operating income/(expense)	190	227
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	13	15
Insurance, protection and investments	0	0
Credit cards	0	0
Non-banking and other fees	22	26
Total fee and commission income	35	41
Fee and commission expense	(9)	(12)
Net fee and commission income	26	29
Customer loans	16,604		16,297
Total assets	16,604		16,297
Customer deposits	19,538		18,234
Total liabilities	19,563		18,260
Corporate and commercial banking | Elimination of Intersegment Amounts
Disclosure of operating segments [line items]
Inter-segment revenue	(47)	(54)
Corporate and investment banking
Disclosure of operating segments [line items]
Net interest income/(expense)	26	32
Non-interest income/(expense)	28	47
Total operating income/(expense)	54	79
Operating expenses before credit impairment losses, provisions and charges	(62)	(83)
Credit impairment (losses)/releases	(12)	4
Provisions for other liabilities and charges	(4)	(11)
Total operating credit impairment losses, provisions and (charges)/releases	(16)	(7)
Profit before tax	(24)	(11)
Revenue from external customers	55	85
Total operating income/(expense)	54	79
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	5	14
Insurance, protection and investments	0	0
Credit cards	0	0
Non-banking and other fees	23	24
Total fee and commission income	28	38
Fee and commission expense	(4)	(7)
Net fee and commission income	24	31
Customer loans	4,040		4,114
Total assets	4,949		4,727
Customer deposits	6,784		6,101
Total liabilities	7,230		6,500
Corporate and investment banking | Elimination of Intersegment Amounts
Disclosure of operating segments [line items]
Inter-segment revenue	(1)	(6)
Corporate centre
Disclosure of operating segments [line items]
Net interest income/(expense)	(27)	(15)
Non-interest income/(expense)	3	8
Total operating income/(expense)	(24)	(7)
Operating expenses before credit impairment losses, provisions and charges	(51)	(35)
Credit impairment (losses)/releases	(11)	(1)
Provisions for other liabilities and charges	(11)	(99)
Total operating credit impairment losses, provisions and (charges)/releases	(22)	(100)
Profit before tax	(97)	(142)
Revenue from external customers	(448)	(415)
Total operating income/(expense)	(24)	(7)
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	0	0
Insurance, protection and investments	0	0
Credit cards	0	0
Non-banking and other fees	2	1
Total fee and commission income	2	1
Fee and commission expense	(5)	(2)
Net fee and commission income	(3)	(1)
Customer loans	4,030		4,489
Total assets	87,574		79,908
Customer deposits	8,302		8,437
Total liabilities	107,371		£ 101,470
Corporate centre | Elimination of Intersegment Amounts
Disclosure of operating segments [line items]
Inter-segment revenue	£ 424	£ 408

Net Interest Income - Summary o

Net Interest Income - Summary of Net Interest Income (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Interest and similar income:
Total interest and similar income	£ 2,650	£ 2,997
Interest expense and similar charges:
Total interest expense and similar charges	(1,108)	(1,326)
Net interest income	£ 1,542	£ 1,671

Net Fee and Commission Income -

Net Fee and Commission Income - Summary of Net Fee and Commission Income (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Net Fee And Commission Income [Line Items]
Fee and commission income	£ 408	£ 540
Fee and commission expense	(187)	(205)
Net fee and commission income	£ 221	£ 335

Net Trading and Other Income -

Net Trading and Other Income - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of subordinated liabilities [line items]
Loss on repurchase of debt securities and subordinated liabilities	£ 17
Vocalink Holdings Limited
Disclosure of subordinated liabilities [line items]
Gain on sale of shares		£ 15

Operating Expenses Before Cre_3

Operating Expenses Before Credit Impairment Losses, Provisions and Charges - Summary of Operating Expenses Before Credit Impairment Losses, Provisions and Charges (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Staff costs:
Staff costs	£ 608	£ 653
Other administration expenses	377	354
Depreciation, amortisation and impairment	272	260
Total operating expenses before impairment losses, provisions and charges	£ 1,257	£ 1,267

Credit Impairment Losses and _3

Credit Impairment Losses and Provisions - Summary of Impairment Losses and Provisions (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of credit impairment loss and provisions [Abstract]
Loans and advances to customers	£ 396	£ 108
Recoveries of loans and advances, net of collection costs	(15)	(38)
Off-balance sheet exposures (See Note 27)	(5)	(1)
Impairment loss on financial assets	376	69
Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 27)	68	205
Provisions for RV and voluntary termination	0	1
Provisions for other liabilities and charges	68	206
Total operating impairment losses, provisions and charges	£ 444	£ 275

Credit Impairment Losses and _4

Credit Impairment Losses and Provisions - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of credit impairment loss and provisions [Abstract]
Impairment losses on loans and advances to banks	£ 0	£ 0
Impairment losses on Non-trading reverse repurchase agreements	0	0
Impairment losses on other financial assets at amortised cost	0	0
Impairment losses on financial assets at FVOCI	£ 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, 2020	Jun. 30, 2019
Major components of tax expense (income) [abstract]
Effective tax rate (percentage)	23.80%	28.50%
Profit before tax	£ 147	£ 575
Tax calculated at a tax rate of 19% (H119: 19%)	£ 28	£ 109
Applicable tax rate (percentage)	19.00%	19.00%
Bank surcharge on profits	£ 7	£ 38
Non-deductible preference dividends paid	3	5
Non-deductible UK Bank Levy	6	13
Non-deductible conduct remediation, fines and penalties	0	11
Other non-deductible costs and non-taxable income	2	9
Effect of change in tax rate on deferred tax provision	6	0
Tax relief on dividends in respect of other equity instruments	(13)	21
Adjustment to prior year provisions	(4)	0
Tax on profit	£ 35	£ 164

Dividends on Ordinary - Additio

Dividends on Ordinary - Additional Information (Detail) - GBP (£)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividends declared and paid	£ 0	£ 138,000,000

Derivative Financial Instrume_3

Derivative Financial Instruments - Notional Amounts and Fair Values of Derivatives (Detail) £ in Millions, number in Millions	Jun. 30, 2020GBP (£)	Dec. 31, 2019GBP (£)
Disclosure of detailed information about hedges
Derivative notional	£ 226,541	£ 205,911
Fair value assets	5,291	3,363
Fair value liabilities	£ 1,747	£ 1,709
Notional value of hedging instruments	73,579	90,898
Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	27,961	33,509
GBP LIBOR
Disclosure of detailed information about hedges
Notional value of hedging instruments	62,421	76,640
GBP LIBOR | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	23,998	28,228
USD LIBOR
Disclosure of detailed information about hedges
Notional value of hedging instruments	10,369	13,071
USD LIBOR | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	3,241	4,541
Other
Disclosure of detailed information about hedges
Notional value of hedging instruments	789	1,187
Other | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	722	740
Derivatives Held for Trading
Disclosure of detailed information about hedges
Derivative notional	£ 71,239	£ 63,877
Derivatives Held for Hedging
Disclosure of detailed information about hedges
Derivative notional	£ 155,302	£ 142,034
Cash Flow Hedges
Disclosure of detailed information about hedges
Notional value of hedging instruments	25,784	31,397
Cash Flow Hedges | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	13,835	14,417
Cash Flow Hedges | GBP LIBOR
Disclosure of detailed information about hedges
Notional value of hedging instruments	19,948	23,396
Cash Flow Hedges | GBP LIBOR | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	11,007	11,773
Cash Flow Hedges | USD LIBOR
Disclosure of detailed information about hedges
Notional value of hedging instruments	5,836	8,001
Cash Flow Hedges | USD LIBOR | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	2,828	2,644
Cash Flow Hedges | Other
Disclosure of detailed information about hedges
Notional value of hedging instruments	0	0
Cash Flow Hedges | Other | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	0	0
Fair Value Hedges
Disclosure of detailed information about hedges
Notional value of hedging instruments	47,795	59,501
Fair Value Hedges | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	14,126	19,092
Fair Value Hedges | GBP LIBOR
Disclosure of detailed information about hedges
Notional value of hedging instruments	42,473	53,244
Fair Value Hedges | GBP LIBOR | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	12,991	16,455
Fair Value Hedges | USD LIBOR
Disclosure of detailed information about hedges
Notional value of hedging instruments	4,533	5,070
Fair Value Hedges | USD LIBOR | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	413	1,897
Fair Value Hedges | Other
Disclosure of detailed information about hedges
Notional value of hedging instruments	789	1,187
Fair Value Hedges | Other | Maturing after transition date
Disclosure of detailed information about hedges
Notional value of hedging instruments	722	740
Fair Value Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Derivative notional	£ 101,657	£ 96,032
Cash Flow Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Derivative notional	53,645	46,002
Exchange Rate Contracts | Derivatives Held for Trading
Disclosure of detailed information about hedges
Derivative notional	21,304	14,249
Exchange Rate Contracts | Fair Value Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Derivative notional	1,758	1,482
Exchange Rate Contracts | Cash Flow Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Derivative notional	32,145	28,502
Interest Rate Contracts | Derivatives Held for Trading
Disclosure of detailed information about hedges
Derivative notional	47,591	47,045
Interest Rate Contracts | Fair Value Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Derivative notional	99,899	94,550
Interest Rate Contracts | Cash Flow Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Derivative notional	21,500	17,451
Equity and Credit Contracts | Derivatives Held for Trading
Disclosure of detailed information about hedges
Derivative notional	2,344	2,583
Equity Investments | Cash Flow Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Derivative notional	0	49
Derivative Assets
Disclosure of detailed information about hedges
Cash collateral received subject to enforceable master netting arrangement or similar agreement not set off against financial assets	465	222
Derivative Liabilities
Disclosure of detailed information about hedges
Cash collateral pledged subject to enforceable master netting arrangement or similar agreement not set off against financial liabilities	1,047	629
Fair Value
Disclosure of detailed information about hedges
Fair value assets	5,291	3,363
Fair value liabilities	1,747	1,709
Fair Value | Derivatives Held for Trading
Disclosure of detailed information about hedges
Fair value assets	1,654	1,182
Fair value liabilities	1,021	932
Fair Value | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Fair value assets	5,303	3,395
Fair value liabilities	2,392	1,991
Fair Value | Fair Value Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Fair value assets	1,366	1,188
Fair value liabilities	2,246	1,490
Fair Value | Cash Flow Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Fair value assets	3,937	2,207
Fair value liabilities	146	501
Fair Value | Exchange Rate Contracts | Derivatives Held for Trading
Disclosure of detailed information about hedges
Fair value assets	628	136
Fair value liabilities	378	199
Fair Value | Exchange Rate Contracts | Fair Value Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Fair value assets	148	166
Fair value liabilities	11	2
Fair Value | Exchange Rate Contracts | Cash Flow Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Fair value assets	3,370	2,023
Fair value liabilities	121	462
Fair Value | Interest Rate Contracts | Derivatives Held for Trading
Disclosure of detailed information about hedges
Fair value assets	864	754
Fair value liabilities	530	566
Fair Value | Interest Rate Contracts | Fair Value Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Fair value assets	1,218	1,022
Fair value liabilities	2,235	1,488
Fair Value | Interest Rate Contracts | Cash Flow Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Fair value assets	567	184
Fair value liabilities	25	35
Fair Value | Equity and Credit Contracts | Derivatives Held for Trading
Disclosure of detailed information about hedges
Fair value assets	162	292
Fair value liabilities	113	167
Fair Value | Equity Investments | Cash Flow Hedges | Derivatives Held for Hedging
Disclosure of detailed information about hedges
Fair value assets	0	0
Fair value liabilities	0	4
Fair Value | Netting adjustments
Disclosure of detailed information about hedges
Fair value assets	(1,666)	(1,214)
Fair value liabilities	£ (1,666)	£ (1,214)

Other Financial Assets at Fai_3

Other Financial Assets at Fair Value Through Profit or Loss - Summary of Other Financial Assets at Fair Value Through Profit or Loss (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets at fair value through profit or loss	£ 866	£ 973
Loans and Advances to Customers
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets at fair value through profit or loss	607	540
Loans and Advances to Customers | Loans to Housing Associations
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets at fair value through profit or loss	13	12
Loans and Advances to Customers | Other Loans
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets at fair value through profit or loss	594	528
Debt securities
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets at fair value through profit or loss	125	298
Equity Securities
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets at fair value through profit or loss	£ 134	£ 135

Loans and Advances to Custome_3

Loans and Advances to Customers - Summary of Net Loans and Advances to Customers (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Net Loans and Advances to Customers [Abstract]
Loans and advances to customers	£ 212,318	£ 208,344
Credit impairment loss allowances on loans and advances to customers	(1,106)	(785)
RV and voluntary termination provisions on finance leases	(56)	(61)
Loans and advances to customers	£ 211,156	£ 207,498

Securitisations and Covered B_3

Securitisations and Covered Bonds - Analysis of Securitisations and Covered Bonds (Detail) £ in Millions	Jun. 30, 2020EUR (€)	Jun. 30, 2020GBP (£)	Dec. 31, 2019EUR (€)	Dec. 31, 2019GBP (£)
Disclosure of securitisations and covered bonds [line items]
Gross assets		£ 38,265		£ 36,391
Derivative notional		226,541		205,911
Securitisation Programmes
Disclosure of securitisations and covered bonds [line items]
Gross assets		11,556		13,068
Securitisation Programmes | Master Trust Structures
Disclosure of securitisations and covered bonds [line items]
Gross assets		9,745		11,046
Securitisation Programmes | Other Securitisation Structures
Disclosure of securitisations and covered bonds [line items]
Gross assets		1,811		2,022
Holmes | Securitisation Programmes | Master Trust Structures
Disclosure of securitisations and covered bonds [line items]
Gross assets		3,603		4,262
Fosse | Securitisation Programmes | Master Trust Structures
Disclosure of securitisations and covered bonds [line items]
Gross assets		3,000		3,708
Langton | Securitisation Programmes | Master Trust Structures
Disclosure of securitisations and covered bonds [line items]
Gross assets		3,142		3,076
Motor | Securitisation Programmes | Other Securitisation Structures
Disclosure of securitisations and covered bonds [line items]
Gross assets		321		490
Auto ABS UK Loans | Securitisation Programmes | Other Securitisation Structures
Disclosure of securitisations and covered bonds [line items]
Gross assets		1,490		1,532
Euro 35bn Global Covered Bond Programme | Covered Bond Programme
Disclosure of securitisations and covered bonds [line items]
Gross assets		£ 26,709		£ 23,323
Euro 35bn Global Covered Bond Programme
Disclosure of securitisations and covered bonds [line items]
Derivative notional | €	€ 35,000,000,000		€ 35,000,000,000

Securitisations and Covered B_4

Securitisations and Covered Bonds - Summary of Issuances and Redemptions of Securitisation and Covered Bond Programme (Detail) - GBP (£) £ in Billions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Internal
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	£ 0	£ 0
Internal and external redemptions	0.2	0.1
Internal | Master Trust Structures | Holmes
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0.1	0
Internal | Other Securitisation Structures | Motor
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0.1	0.1
Internal | Other Securitisation Structures | Auto ABS UK Loans
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0	0
Internal | Covered Bond Programme
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0	0
External
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	3	1.9
Internal and external redemptions	2.5	1.1
External | Master Trust Structures | Holmes
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0.5	0.8
External | Other Securitisation Structures | Motor
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0.1	0.2
External | Other Securitisation Structures | Auto ABS UK Loans
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0
Internal and external redemptions	0.1	0.1
External | Covered Bond Programme
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	3	1.9
Internal and external redemptions	£ 1.8	£ 0

Reverse Repurchase Agreements_2

Reverse Repurchase Agreements - Non Trading - Summary of Reverse Repurchase Agreements - Non Trading (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of reserve repurchase agreements non-trading [line items]
- Reverse repurchase agreements - non trading	£ 23,901	£ 23,636
Agreements with banks
Disclosure of reserve repurchase agreements non-trading [line items]
- Reverse repurchase agreements - non trading	2,238	2,161
Agreements with customers
Disclosure of reserve repurchase agreements non-trading [line items]
- Reverse repurchase agreements - non trading	£ 21,663	£ 21,475

Other Financial Assets At Amo_3

Other Financial Assets At Amortised Cost - Summary of Other Financial Assets at Amortised Cost (Detail) - Other Financial Assets - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financial assets at amortised cost [line items]
Financial assets at amortised cost	£ 4,879	£ 7,056
Asset backed securities
Financial assets at amortised cost [line items]
Financial assets at amortised cost	507	532
Debt securities
Financial assets at amortised cost [line items]
Financial assets at amortised cost	£ 4,372	£ 6,524

Financial Assets At Fair Valu_3

Financial Assets At Fair Value Through Other Comprehensive Income - Summary of Financial Assets at Fair Value Through Other Comprehensive Income (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of financial assets at fair value through other comprehensive income [line items]
Financial assets at fair value through other comprehensive income	£ 10,338	£ 9,747
Debt securities
Disclosure of financial assets at fair value through other comprehensive income [line items]
Financial assets at fair value through other comprehensive income	10,308	9,691
Loans and Advances to Customers
Disclosure of financial assets at fair value through other comprehensive income [line items]
Financial assets at fair value through other comprehensive income	£ 30	£ 56

Intangible Assets - Schedule of

Intangible Assets - Schedule of Goodwill (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of goodwill [line items]
Carrying amount	£ 1,203	£ 1,203
Cost
Disclosure of goodwill [line items]
Carrying amount	1,285	1,285
Accumulated Impairment
Disclosure of goodwill [line items]
Carrying amount	£ (82)	£ (82)

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - GBP (£)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Disclosure of detailed information about intangible assets [abstract]
Goodwill impairment recognised	£ 0	£ 0
Increase/(decrease) in discount rate percentage	2.10%
Discount rate percentage	11.90%		9.80%

Intangible Assets - Schedule _2

Intangible Assets - Schedule of Goodwill for Cash Generating Units (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of information for cash-generating units [line items]
Goodwill	£ 1,203	£ 1,203
Discount rate	11.90%	9.80%
Personal financial services
Disclosure of information for cash-generating units [line items]
Goodwill	£ 1,169	£ 1,169
Discount rate	11.90%	9.80%
Growth rate	0.00%	3.40%
Private banking
Disclosure of information for cash-generating units [line items]
Goodwill	£ 30	£ 30
Discount rate	11.90%	9.80%
Growth rate	0.00%	3.60%
Other
Disclosure of information for cash-generating units [line items]
Goodwill	£ 4	£ 4
Discount rate	11.90%	9.80%
Growth rate	0.00%	3.40%

Intangible Assets - Schedule _3

Intangible Assets - Schedule of Goodwill for Cash Generating Units (Parenthetical) (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Disclosure of detailed information about intangible assets [abstract]
Terminal growth rate	1.60%	1.60%

Other Financial Liabilities a_3

Other Financial Liabilities at Fair Value Through Profit or Loss - Summary of Other Financial Liabilities at Fair Value Through Profit or Loss (Detail) £ in Millions	Jun. 30, 2020USD ($)	Jun. 30, 2020GBP (£)	Dec. 31, 2019USD ($)	Dec. 31, 2019GBP (£)
Disclosure of other financial liabilities at fair value through profit or loss
Financial liabilities at fair value		£ 1,620		£ 1,713
Derivative notional		226,541		205,911
US$30bn Euro Medium Term Note Programme
Disclosure of other financial liabilities at fair value through profit or loss
Financial liabilities at fair value		172		159
Structured Notes Programmes
Disclosure of other financial liabilities at fair value through profit or loss
Financial liabilities at fair value		881		809
Eurobonds
Disclosure of other financial liabilities at fair value through profit or loss
Financial liabilities at fair value		142		137
Structured Deposits
Disclosure of other financial liabilities at fair value through profit or loss
Financial liabilities at fair value		415		435
Collateral and associated financial guarantees
Disclosure of other financial liabilities at fair value through profit or loss
Financial liabilities at fair value		£ 10		£ 173
Euro 30bn Euro Medium Term Note Programme | Medium Term Notes
Disclosure of other financial liabilities at fair value through profit or loss
Derivative notional | $	$ 30,000,000,000		$ 30,000,000,000

Deposits by Customers - Schedul

Deposits by Customers - Schedule of Deposits by Customers (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of deposits from customers [line items]
- Deposits by customers	£ 186,797	£ 179,006
Current and Demand Accounts
Disclosure of deposits from customers [line items]
- Deposits by customers	185,570	177,772
Amounts Due to Fellow Banco Santander Subsidiaries and Joint Ventures
Disclosure of deposits from customers [line items]
- Deposits by customers	£ 1,227	£ 1,234

Deposits by Customers - Sched_2

Deposits by Customers - Schedule of Deposits by Customers (Parenthetical) (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of deposits from customers [line items]
- Deposits by customers	£ 186,797	£ 179,006
Equity Index Linked Deposits
Disclosure of deposits from customers [line items]
- Deposits by customers	1,127	1,139
Capital amount guaranteed or protected	1,127	1,139
Capital amount of return guaranteed	£ 16	£ 18

Deposits by Banks - Schedule of

Deposits by Banks - Schedule of Deposits by Banks (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of deposits from banks [line items]
- Deposits by banks	£ 17,995	£ 14,359
Items in the course of transmission
Disclosure of deposits from banks [line items]
- Deposits by banks	255	337
Deposits held as collateral
Disclosure of deposits from banks [line items]
- Deposits by banks	3,853	2,175
Other deposits
Disclosure of deposits from banks [line items]
- Deposits by banks	£ 13,887	£ 11,847

Deposits by Banks - Schedule _2

Deposits by Banks - Schedule of Deposits by Banks (Parenthetical) (Detail) - GBP (£) £ in Billions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of deposits from banks [Abstract]
Drawdown from TFS	£ 10.8	£ 10.8
Drawdown from TFSME	£ 2.2	£ 0

Repurchase Agreements - Non T_3

Repurchase Agreements - Non Trading - Summary of Repurchase Agreements Non Trading (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements–non trading	£ 20,786	£ 18,286
Agreements with banks
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements–non trading	13,296	10,227
Agreements with customers
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements–non trading	£ 7,490	£ 8,059

Debt Securities In Issue - Summ

Debt Securities In Issue - Summary of Debt Securities in Issue (Detail) £ in Millions	Jun. 30, 2020EUR (€)	Jun. 30, 2020GBP (£)	Dec. 31, 2019EUR (€)	Dec. 31, 2019GBP (£)
Debt securities in issue [line items]
Debt securities		£ 50,252		£ 50,171
Derivative notional		226,541		205,911
Medium Term Notes
Debt securities in issue [line items]
Debt securities		24,800		24,522
Euro 35bn Global Covered Bond Programme
Debt securities in issue [line items]
Debt securities		20,631		19,004
Derivative notional | €	€ 35,000,000,000		€ 35,000,000,000
Certificates of Deposit
Debt securities in issue [line items]
Debt securities		1,795		2,806
Credit Linked Note
Debt securities in issue [line items]
Credit linked notes		55		60
Securitisation Programmes
Debt securities in issue [line items]
Debt securities		£ 2,971		£ 3,779

Subordinated Liabilities - Sche

Subordinated Liabilities - Schedule of Subordinated Liabilities (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Disclosure of Subordinated Liabilities [Abstract]
- Subordinated liabilities	£ 3,257	£ 3,528
Loss on repurchase of debt securities and subordinated liabilities	£ 17

Provisions - Summary of Provisi

Provisions - Summary of Provisions Reconciliation (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2020GBP (£)
Provisions [Roll Forward]
Beginning balance	£ 577
Additional provision charge	83
Provisions released	(20)
Utilisation and other	(155)
Ending balance	485
PPI
Provisions [Roll Forward]
Beginning balance	189
Additional provision charge	0
Provisions released	0
Utilisation and other	(38)
Ending balance	151
Other products
Provisions [Roll Forward]
Beginning balance	25
Additional provision charge	0
Provisions released	(5)
Utilisation and other	0
Ending balance	20
FSCS And Bank Levy
Provisions [Roll Forward]
Beginning balance	48
Additional provision charge	0
Provisions released	0
Utilisation and other	(39)
Ending balance	9
Vacant Property
Provisions [Roll Forward]
Beginning balance	61
Additional provision charge	1
Provisions released	(2)
Utilisation and other	(7)
Ending balance	53
Off- balance sheet ECL
Provisions [Roll Forward]
Beginning balance	78
Additional provision charge	0
Provisions released	(5)
Utilisation and other	0
Ending balance	73
Regulatory and other
Provisions [Roll Forward]
Beginning balance	176
Additional provision charge	82
Provisions released	(8)
Utilisation and other	(71)
Ending balance	£ 179

Provisions - Additional Informa

Provisions - Additional Information (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2020GBP (£)Complaints
Future expected provision number
Cumulative complaints | Complaints	4,500,000
Complaints reviewing | Complaints	290,000
Additional provision charge	£ 83
Regulatory And Other, SMS Overdraft Warnings
Future expected provision number
Additional provision charge	17
Operational Risk Provisions
Future expected provision number
Additional provision charge	£ 37

Retirement Benefit Plans - Summ

Retirement Benefit Plans - Summary of Retirement Benefit Plans (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets/(liabilities)
Total net assets	£ 120	£ 390
Santander UK Group
Assets/(liabilities)
Total net assets	120	390
Santander UK Group | Unfunded Pension And Post Retirement Medical Benefits
Assets/(liabilities)
Surplus (deficit) in plan	(44)	(41)
Surplus | Santander UK Group | Funded Defined Benefit Pension Scheme
Assets/(liabilities)
Surplus (deficit) in plan	522	670
Deficit | Santander UK Group | Funded Defined Benefit Pension Scheme
Assets/(liabilities)
Surplus (deficit) in plan	£ (358)	£ (239)

Retirement Benefit Plans - Addi

Retirement Benefit Plans - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of net defined benefit liability (asset) [abstract]
Defined contribution expense	£ 33	£ 34
Post-employment benefit expense, defined benefit plans	17	£ 10
Increase (decrease) in net defined benefit liability (asset)	£ 63

Retirement Benefit Plans - Su_2

Retirement Benefit Plans - Summary of Amounts Recognised in Other Comprehensive Income (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of net defined benefit liability (asset) [abstract]
Return on plan assets (excluding amounts included in net interest expense)	£ (1,115)	£ (916)
Actuarial losses/(gains) arising from changes in demographic assumptions	38	0
Actuarial (gains)/losses arising from experience adjustments	(10)	(5)
Actuarial losses/(gains) arising from changes in financial assumptions	1,463	1,201
Pension remeasurement	£ 376	£ 280

Retirement Benefit Plans - Su_3

Retirement Benefit Plans - Summary of Net Assets Recognised (Details) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of net defined benefit liability (asset) [abstract]
Defined benefit obligation, at present value	£ (13,617)	£ (12,165)
Net defined benefit liability (asset)	13,737	12,555
Total net assets	£ 120	£ 390

Retirement Benefit Plans - Su_4

Retirement Benefit Plans - Summary of Principal Actuarial Assumptions Used for Defined Benefit Schemes (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Disclosure of net defined benefit liability (asset) [abstract]
- Discount rate for scheme liabilities	140.00%	210.00%
- General price inflation	290.00%	300.00%
- General salary increase	100.00%	100.00%
- Expected rate of pension increase	280.00%	290.00%
Longevity at Sixty for Current Pensioners, on Valuation Date [abstract]
- Males	27 years 3 months 18 days	27 years 3 months 18 days
- Females	29 years 9 months 18 days	29 years 9 months 18 days
Longevity at 60 for future pensioners currently aged 40, on the valuation date:
Longevity for future pensioners females one	28 years 10 months 24 days	28 years 10 months 24 days
Longevity for future pensioners males one	31 years 3 months 18 days	31 years 3 months 18 days

Retirement Benefit Plans - Su_5

Retirement Benefit Plans - Summary of Actuarial Assumption Sensitivities (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Actuarial Assumption of Discount Rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Description of changes in methods and assumptions	25 bps increase
Increase decrease in defined benefit obligation	£ (666)	£ (564)
Actuarial Assumption of Expected Rates of Inflation
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Description of changes in methods and assumptions	25 bps increase
Increase decrease in defined benefit obligation	£ 495	407
Actuarial Assumption of Expected Rates of Mortality
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Description of changes in methods and assumptions	Each additional year of longevity assumed
Increase decrease in defined benefit obligation	£ 504	£ 419

Contingent Liabilities and Co_3

Contingent Liabilities and Commitments - Summary of Contingent Liabilities and Commitments (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of contingent liabilities and commitments [line items]
Guarantees and formal standby facilities, credit lines and other commitments	£ 38,647	£ 41,608
Contingent Liability for Guarantees
Disclosure of contingent liabilities and commitments [line items]
Guarantees given to third parties	1,026	1,198
Loan commitments | Not Later Than 1 Year
Disclosure of contingent liabilities and commitments [line items]
Formal standby facilities, credit lines and other commitments	16,592	18,256
Loan commitments | More than One Year
Disclosure of contingent liabilities and commitments [line items]
Formal standby facilities, credit lines and other commitments	£ 21,029	£ 22,154

Contingent Liabilities and Co_4

Contingent Liabilities and Commitments - Additional Information (Detail) £ in Millions	Nov. 02, 2015	Jun. 30, 2020GBP (£)	Jun. 30, 2020EUR (€)	Jul. 20, 2020GBP (£)	Jun. 30, 2020GBP (£)	Dec. 31, 2019GBP (£)
Disclosure of contingent liabilities and commitments [line items]
Decrease in convertible preferred stock fair value		£ 10
Compliance with Consumer Credit Act
Disclosure of contingent liabilities and commitments [line items]
Additional operational risk losses and restructuring provision						£ 58
Genworth Financial International Holdings Inc
Disclosure of contingent liabilities and commitments [line items]
Percentage of litigation on settlement			90.00%		90.00%
Santander UK Group
Disclosure of contingent liabilities and commitments [line items]
Liability arising through disallowance of tax allowance					£ 150
Visa Europe Ltd
Disclosure of contingent liabilities and commitments [line items]
Visa Europe Ltd sale to Visa Inc	100.00%
Entering into significant commitments or contingent liabilities [member] | Genworth Financial International Holdings Inc
Disclosure of contingent liabilities and commitments [line items]
Amount awarded to other party				£ 624
Bottom of Range
Disclosure of contingent liabilities and commitments [line items]
Losses on litigation settlements | €			€ 1,000,000,000
Top of Range
Disclosure of contingent liabilities and commitments [line items]
Santander UK liability under indemnity cap | €			39,850,000
UK&I Banks
Disclosure of contingent liabilities and commitments [line items]
Preferred stock issued, threshold value | €			€ 0
Previously Paid | Entering into significant commitments or contingent liabilities [member] | Genworth Financial International Holdings Inc
Disclosure of contingent liabilities and commitments [line items]
Amount awarded to other party				100
Due 23 July 2020 | Entering into significant commitments or contingent liabilities [member] | Genworth Financial International Holdings Inc
Disclosure of contingent liabilities and commitments [line items]
Amount awarded to other party				100
Due 2022 | Entering into significant commitments or contingent liabilities [member] | Genworth Financial International Holdings Inc
Disclosure of contingent liabilities and commitments [line items]
Amount awarded to other party				317
Claimed Mis-Selling Losses | Entering into significant commitments or contingent liabilities [member] | Genworth Financial International Holdings Inc
Disclosure of contingent liabilities and commitments [line items]
Amount awarded to other party				£ 107

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Capital Issued and Fully Paid (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of classes of share capital [abstract]
Issued and fully paid share capital	£ 7,060	£ 7,060

Other Equity Instruments - Summ

Other Equity Instruments - Summary of Other Equity Instruments (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2020GBP (£)	Dec. 31, 2019GBP (£)
Disclosure of other equity instruments [line items]
Other equity instruments	£ 2,241	£ 2,241
500m Fixed Rate Reset Perpetual AT1 Capital Securities
Disclosure of other equity instruments [line items]
Interest rate	0.0675
Other equity interest maturity period	2024-06
Other equity instruments	£ 496	496
750m Fixed Rate Reset Perpetual AT1 Capital Securities
Disclosure of other equity instruments [line items]
Interest rate	0.07375
Other equity interest maturity period	2022-06
Other equity instruments	£ 745	745
500m Fixed Rate Reset Perpetual AT1 Capital Securities
Disclosure of other equity instruments [line items]
Interest rate	0.0533
Other equity interest maturity period	2020-09
Other equity instruments	£ 500	500
500m Fixed Rate Reset Perpetual AT1 Capital Securities
Disclosure of other equity instruments [line items]
Interest rate	0.0630
Other equity interest maturity period	2025-03
Other equity instruments	£ 500	£ 500

Other Equity Instruments - Su_2

Other Equity Instruments - Summary of Other Equity Instruments (Parenthetical) (Detail) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
500m Fixed Rate Reset Perpetual AT1 Capital Securities
Disclosure of other equity instruments [line items]
Capital securities	£ 500	£ 500
750m Fixed Rate Reset Perpetual AT1 Capital Securities
Disclosure of other equity instruments [line items]
Capital securities	750	750
500m Fixed Rate Reset Perpetual AT1 Capital Securities
Disclosure of other equity instruments [line items]
Capital securities	500	500
500m Fixed Rate Reset Perpetual AT1 Capital Securities
Disclosure of other equity instruments [line items]
Capital securities	£ 500	£ 500

Non-Controlling Interests - Sch

Non-Controlling Interests - Schedule of Amounts Attributable to Non-Controlling Interests (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2020GBP (£)	Dec. 31, 2019GBP (£)
Disclosure of noncontrolling interests [line items]
Non-controlling interests	£ 405	£ 395
300m Step-up Callable Perpetual Reserve Capital Instruments
Disclosure of noncontrolling interests [line items]
Reserve Capital Instruments annual bear interest rate	0.07037
First call date	2026-02
Non-controlling interests	£ 235	235
Reserve Capital Instruments annual bear interest rate	0.07037
PSA Finance UK Limited
Disclosure of noncontrolling interests [line items]
Non-controlling interests	£ 170	£ 160

Non-Controlling Interests - S_2

Non-Controlling Interests - Schedule of Amounts Attributable to Non-Controlling Interests (Parenthetical) (Detail) - GBP (£)	Jun. 30, 2020	Dec. 31, 2019
Disclosure of noncontrolling interests [line items]
Derivative notional	£ 226,541,000,000	£ 205,911,000,000
300m Step-up Callable Perpetual Reserve Capital Instruments
Disclosure of noncontrolling interests [line items]
Derivative notional	£ 300,000,000	£ 300,000,000

Assets Charged as Security fo_2

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets - Additional Information (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure of assets pledged as security [line items]
Gross assets charged as security for liabilities	£ 38,265	£ 36,391
Internally Retained | Securitisations and Covered Bonds
Disclosure of assets pledged as security [line items]
Notes issued under securitisation and covered bond programmes retained internally	4,796	4,728
Third Party Bilateral Secured Funding Transactions | Securitisations and Covered Bonds
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	1,581	1,581
Santander UK Plc | Internally Retained | Securitisations and Covered Bonds
Disclosure of assets pledged as security [line items]
Internally retained securitisation and covered bond issuances available for creating collateral	£ 1,200	£ 166

Financial Instruments - Analysi

Financial Instruments - Analysis of Fair Value of Financial Instruments Carried at Amortised (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	£ 211,156	£ 207,498
Loans and advances to banks	2,637	2,583
Reverse repurchase agreements - non trading	23,901	23,636
- Deposits by customers	186,797	179,006
- Deposits by banks	17,995	14,359
Repurchase agreements–non trading	20,786	18,286
- Debt securities in issue	50,252	50,171
Subordinated liabilities	3,257	3,528
Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial assets	242,573	240,773
Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial liabilities	279,087	265,350
Deposits by customers | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
- Deposits by customers	186,797	179,006
Deposits by banks | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
- Deposits by banks	17,995	14,359
Repurchase agreements - non trading | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements–non trading	20,786	18,286
Debt Securities | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
- Debt securities in issue	50,252	50,171
Subordinated liabilities | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	3,257	3,528
Loans and Advances to Customers | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	211,156	207,498
Loans and advances to banks | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	2,637	2,583
Reverse repurchase agreements - non-trading | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	23,901	23,636
Other financial assets at amortised cost | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	4,879	7,056
Fair Value | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial assets	246,943	245,329
Fair Value | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial liabilities	280,881	267,753
Fair Value | Deposits by customers | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
- Deposits by customers	186,961	179,136
Fair Value | Deposits by banks | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
- Deposits by banks	18,006	14,369
Fair Value | Repurchase agreements - non trading | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements–non trading	20,773	18,292
Fair Value | Debt Securities | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
- Debt securities in issue	51,434	51,736
Fair Value | Subordinated liabilities | Financial Liabilities at Amortised Cost, Category
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	3,707	4,220
Fair Value | Loans and Advances to Customers | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	215,327	212,007
Fair Value | Loans and advances to banks | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	2,631	2,578
Fair Value | Reverse repurchase agreements - non-trading | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	23,921	23,634
Fair Value | Other financial assets at amortised cost | Financial assets at amortised cost
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	£ 5,064	£ 7,110

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, 2020	Dec. 31, 2019
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 16,495	£ 14,083
Liabilities at fair value	3,367	3,422
Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,620	1,713
Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,747	1,709
Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	5,291	3,363
Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	866	973
Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	10,338	9,747
Level 1
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	9,870	9,227
Liabilities at fair value	0	0
Level 1 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	0
Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	0
Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Level 1 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	15	18
Level 1 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	9,855	9,209
Level 2
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	6,187	4,211
Liabilities at fair value	3,321	3,326
Level 2 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,604	1,652
Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,717	1,674
Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	5,226	3,279
Level 2 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	508	450
Level 2 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	453	482
Level 3
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	438	645
Liabilities at fair value	46	96
Level 3 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	16	61
Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	30	35
Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	65	84
Level 3 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	343	505
Level 3 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 30	56
Exchange Rate Contracts | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 510	663
Exchange Rate Contracts | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 4,146	2,325
Valuation technique	A
Exchange Rate Contracts | Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 0	0
Exchange Rate Contracts | Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Exchange Rate Contracts | Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	510	659
Exchange Rate Contracts | Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	4,144	2,319
Exchange Rate Contracts | Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	4
Exchange Rate Contracts | Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 2	6
Interest Rate Contracts | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A & C
Liabilities at fair value	£ 2,790	2,089
Interest Rate Contracts | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 2,649	1,960
Valuation technique	A & C
Interest Rate Contracts | Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 0	0
Interest Rate Contracts | Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Interest Rate Contracts | Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	2,788	2,087
Interest Rate Contracts | Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	2,636	1,951
Interest Rate Contracts | Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	2	2
Interest Rate Contracts | Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 13	9
Equity and Credit Contracts | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	B & D
Liabilities at fair value	£ 113	171
Equity and Credit Contracts | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 162	292
Valuation technique	B & D
Equity and Credit Contracts | Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 0	0
Equity and Credit Contracts | Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Equity and Credit Contracts | Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	85	142
Equity and Credit Contracts | Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	112	223
Equity and Credit Contracts | Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	28	29
Equity and Credit Contracts | Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	50	69
Netting | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	(1,666)	(1,214)
Netting | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	(1,666)	(1,214)
Netting | Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	0
Netting | Level 1 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Netting | Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	(1,666)	(1,214)
Netting | Level 2 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	(1,666)	(1,214)
Netting | Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	0
Netting | Level 3 | Derivative financial instruments
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Loans and Advances to Customers | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 607	540
Valuation technique	A
Loans and Advances to Customers | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 30	56
Valuation technique	D
Loans and Advances to Customers | Level 1 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 0	0
Loans and Advances to Customers | Level 1 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Loans and Advances to Customers | Level 2 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	504	448
Loans and Advances to Customers | Level 2 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Loans and Advances to Customers | Level 3 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	103	92
Loans and Advances to Customers | Level 3 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	30	56
Debt securities | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 125	298
Valuation technique	A, B & D
Debt securities | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 10,308	9,691
Valuation technique	D
Debt securities | Level 1 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 0	2
Debt securities | Level 1 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	9,855	9,209
Debt securities | Level 2 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	4	2
Debt securities | Level 2 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	453	482
Debt securities | Level 3 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	121	294
Debt securities | Level 3 | Financial assets at fair value through other comprehensive income
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Equity securities | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 134	135
Valuation technique	B
Equity securities | Level 1 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 15	16
Equity securities | Level 2 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	0
Equity securities | Level 3 | Other Financial assets at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 119	119
Debt Securities | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 1,195	1,105
Debt Securities | Level 1 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	0
Debt Securities | Level 2 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,189	1,099
Debt Securities | Level 3 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 6	6
Structured Deposits | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 415	435
Structured Deposits | Level 1 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	0
Structured Deposits | Level 2 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	415	406
Structured Deposits | Level 3 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 0	29
Collateral and associated financial guarantees | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	D
Liabilities at fair value	£ 10	173
Collateral and associated financial guarantees | Level 1 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	0
Collateral and associated financial guarantees | Level 2 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	147
Collateral and associated financial guarantees | Level 3 | Other Financial Liabilities at fair value through profit or loss, category
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 10	£ 26

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Assets
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 2 to Level 3	0	0
Fair value of financial instruments transferred from Level 3 to Level 2	0	0
Liabilities
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 2 to Level 3	0	0
Fair value of financial instruments transferred from Level 3 to Level 2	£ 0	£ 0

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value Adjustment (Detail) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Disclosure of financial assets [line items]
Fair value adjustments	£ 51	£ 37
Bid-Offer and Trade Specific Adjustments
Disclosure of financial assets [line items]
Fair value adjustments	(17)	(12)
Uncertainty
Disclosure of financial assets [line items]
Fair value adjustments	48	37
Credit Risk Adjustment
Disclosure of financial assets [line items]
Fair value adjustments	9	6
Funding Fair Value Adjustment
Disclosure of financial assets [line items]
Fair value adjustments	9	6
Risk Related Adjustments
Disclosure of financial assets [line items]
Fair value adjustments	49	37
Model-Related
Disclosure of financial assets [line items]
Fair value adjustments	1	0
Day One profit
Disclosure of financial assets [line items]
Fair value adjustments	£ 1	£ 0

Financial Instruments - Assets

Financial Instruments - Assets and Liabilities Reconciliation of Fair Value Measurements in Level 3 of the Fair Value Hierarchy (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Disclosure of fair value measurement of assets [line items]
Beginning balance	£ 288,488
Beginning balance	(272,147)
Transfers in	0	£ 0
Transfers in	0	0
Transfers out	0	0
Transfers out	0	0
Ending Balance	302,819
Ending Balance	(286,335)
Level 3 | Fair Value Through P&L
Disclosure of fair value measurement of assets [line items]
Beginning balance	505	1,055
Total gains/(losses) recognised in profit or loss, fair value movements	(10)	32
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements	6	3
Transfers in		11
Transfers out	0
Netting	(37)	(254)
Additions	0	188
Sales	(11)
Settlements	(110)	(269)
Ending Balance	343	766
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year	(4)	35
Level 3 | Financial assets at FVOCI
Disclosure of fair value measurement of assets [line items]
Beginning balance	56	73
Total gains/(losses) recognised in profit or loss, fair value movements	1	0
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements	0	0
Transfers in		0
Transfers out	0
Netting	0	0
Additions	0	0
Sales	(19)
Settlements	(8)	(4)
Ending Balance	30	69
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year	1	0
Level 3 | Financial assets at Fair Value Class
Disclosure of fair value measurement of assets [line items]
Beginning balance	645	1,243
Total gains/(losses) recognised in profit or loss, fair value movements	(11)	35
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements	6	3
Transfers in		11
Transfers out	0
Netting	(37)	(254)
Additions	0	191
Sales	(30)
Settlements	(135)	(288)
Ending Balance	438	941
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year	(5)	38
Level 3 | Derivative Financial Instruments
Disclosure of fair value measurement of assets [line items]
Beginning balance	84	115
Total gains/(losses) recognised in profit or loss, fair value movements	(2)	3
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements	0	0
Transfers in		0
Transfers out	0
Netting	0	0
Additions	0	3
Sales	0
Settlements	(17)	(15)
Ending Balance	65	106
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year	(2)	3
Derivative Liabilities | Level 3
Disclosure of fair value measurement of assets [line items]
Beginning balance	(35)	(70)
Total gains/(losses) recognised in profit or loss, fair value movements	(1)	(1)
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements	0	0
Transfers in		0
Transfers out	0
Netting	0	0
Additions	0	0
Sales	0
Settlements	6	31
Ending Balance	(30)	(40)
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year	(1)
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		(1)
Fair Value Through P&L | Derivative Liabilities | Level 3
Disclosure of fair value measurement of assets [line items]
Beginning balance	(61)	(49)
Total gains/(losses) recognised in profit or loss, fair value movements	15	(5)
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements	2	(3)
Transfers in		0
Transfers out	28
Netting	0	0
Additions	(1)	(2)
Sales	0
Settlements	1	2
Ending Balance	(16)	(57)
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year	17
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		(8)
Financial Liabilities at Fair Value, Class | Derivative Liabilities | Level 3
Disclosure of fair value measurement of assets [line items]
Beginning balance	(96)	(119)
Total gains/(losses) recognised in profit or loss, fair value movements	14	(6)
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements	2	(3)
Transfers in		0
Transfers out	28
Netting	0	0
Additions	(1)	(2)
Sales	0
Settlements	7	33
Ending Balance	(46)	(97)
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year	£ 16
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		£ (9)

Events After the Balance Shee_2

Events After the Balance Sheet Date - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2020
Disclosure of non-adjusting events after reporting period [abstract]
Description of nature of Non adjusting event after reporting period	There have been no significant events between 30 June 2020 and the date of approval of these financial statements which would require a change to or additional disclosure in the financial statements.

Financial Statements - Addition

Financial Statements - Additional Information - Parent (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Condensed Financial Statements, Captions [Line Items]
- Profit after tax	£ 112	£ 411

Subordinated Liabilities - Summ

Subordinated Liabilities - Summary of Subordinated Liabilities - Parent (Detail) - GBP (£) £ in Millions	Jun. 30, 2020	Dec. 31, 2019
Subordinated liabilities [line items]
- Subordinated liabilities	£ 3,257	£ 3,528

Uncategorized Items - san-20200

Label	Element	Value
Reverse repurchase agreements - non-trading [member]
Disclosure of repurchase and reverse repurchase agreements [text block]	ifrs-full_DisclosureOfRepurchaseAndReverseRepurchaseAgreementsExplanatory	30 June 2020 31 December 2019 £m £m Agreements with banks 2,238 2,161 Agreements with customers 21,663 21,475 23,901 23,636