Santander UK (SANS+) 6-K 16 Aug 19 2019 Q2 Current report (foreign) Financial data

Document and Entity Information

Document and Entity Information	6 Months Ended
	Jun. 30, 2019
Document and entity information [abstract]
Document Type	6-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Registrant Name	Santander UK plc
Entity Central Index Key	0001087711
Current Fiscal Year End Date	--12-31

Consolidated Income Statement

Consolidated Income Statement - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Profit (loss) [abstract]
Interest and similar income	£ 2,970	£ 3,001
Interest expense and similar charges	(1,302)	(1,190)
Net interest income	1,668	1,811
Fee and commission income	539	584
Fee and commission expense	(204)	(204)
Net fee and commission income	335	380
Net trading and other income	118	121
Total operating income	2,121	2,312
Operating expenses before credit impairment losses, provisions and charges	(1,257)	(1,283)
Credit impairment losses	(69)	(91)
Provisions for other liabilities and charges	(206)	(33)
Total operating credit impairment losses, provisions and charges	(275)	(124)
Profit before tax	589	905
Tax on profit	(170)	(233)
Profit after tax for the period	419	672
Attributable to:
Equity holders of the parent	410	660
Non-controlling interests	9	12
Profit after tax for the period	£ 419	£ 672

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement of comprehensive income [abstract]
Profit after tax for the period	£ 419	£ 672
Movement in fair value reserve (debt instruments)
- Change in fair value	167	(94)
- Income statement transfers	(152)	67
- Taxation	(4)	6
Other comprehensive income fair value reserve (debt instruments)	11	(21)
Cash flow hedges:
- Effective portion of changes in fair value	360	84
- Income statement transfers	(42)	(190)
- Taxation	(82)	21
Other comprehensive income cash flow hedges, total	236	(85)
Net other comprehensive income that may be reclassified to profit or loss subsequently	247	(106)
Pension remeasurement:
- Change in fair value	(280)	529
- Taxation	70	(132)
Pension remeasurement, total	(210)	397
Own credit adjustment:
- Change in fair value	(58)	(31)
- Taxation	15	8
Own credit adjustment, total	(43)	(23)
Net other comprehensive income that will not be reclassified to profit or loss subsequently	(253)	374
Total other comprehensive income for the period net of tax	(6)	268
Total comprehensive income	413	940
Attributable to:
Equity holders of the parent	405	927
Non-controlling interests	8	13
Total comprehensive income	£ 413	£ 940

Consolidated Balance Sheet

Consolidated Balance Sheet - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Assets
Cash and balances at central banks	£ 21,936	£ 19,747
Financial assets at fair value through profit or loss:
- Derivative financial instruments	5,445	5,259
- Other financial assets at fair value through profit or loss	745	5,617
Financial assets at amortised cost:
- Loans and advances to customers	202,516	201,289
- Loans and advances to banks	2,065	2,799
- Reverse repurchase agreements - non trading	22,409	21,127
- Other financial assets at amortised cost	7,137	7,229
Financial assets at fair value through other comprehensive income	13,438	13,302
Interests in other entities	96	88
Intangible assets	1,793	1,808
Property, plant and equipment	2,069	1,832
Current tax assets	180	153
Retirement benefit assets	779	842
Other assets	3,919	2,280
Total assets	284,527	283,372
Financial liabilities at fair value through profit or loss:
- Derivative financial instruments	1,775	1,369
- Other financial liabilities at fair value through profit or loss	1,633	6,286
Financial liabilities at amortised cost:
- Deposits by customers	180,617	178,090
- Deposits by banks	16,489	17,221
- Repurchase agreements - non trading	14,771	10,910
- Debt securities in issue	44,574	46,692
- Subordinated liabilities	3,645	3,601
Other liabilities	3,904	2,448
Provisions	547	509
Deferred tax liabilities	256	223
Retirement benefit obligations	252	114
Total liabilities	268,463	267,463
Equity
Share capital	3,105	3,119
Share premium	5,620	5,620
Other equity instruments	1,991	1,991
Retained earnings	4,658	4,744
Other reserves	531	284
Total shareholders' equity	15,905	15,758
Non-controlling interests	159	151
Total equity	16,064	15,909
Total liabilities and equity	£ 284,527	£ 283,372

Consolidated Cash Flow Statemen

Consolidated Cash Flow Statement - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Profit after tax for the period	£ 419	£ 672
Adjustments for:
Non-cash items included in profit	86	187
Change in operating assets	1,135	(2,644)
Change in operating liabilities	1,328	(1,176)
Corporation taxes paid	(166)	(236)
Effects of exchange rate differences	(334)	583
Net cash flows from operating activities	2,468	(2,614)
Cash flows from investing activities
Investments in other entities		(66)
Purchase of property, plant and equipment and intangible assets	(66)	(350)
Proceeds from sale of property, plant and equipment and intangible assets	32	13
Purchase of financial assets at amortised cost and financial assets at fair value through other comprehensive income	(4,141)	(5,047)
Proceeds from sale and redemption of financial assets at amortised cost and financial assets at fair value through other comprehensive income	4,259	1,301
Net cash flows from investing activities	84	(4,149)
Cash flows from financing activities
Issue of debt securities and subordinated notes	2,770	6,452
Issuance costs of debt securities and subordinated notes	(9)	(13)
Repayment of debt securities and subordinated notes	(4,693)	(4,601)
Repurchase of preference shares and other equity instruments	(14)
Dividends paid on ordinary shares	(164)	(250)
Dividends paid on preference shares and other equity instruments	(80)	(90)
Dividends paid on non-controlling interests	0	0
Net cash flows from financing activities	(2,190)	1,498
Change in cash and cash equivalents	362	(5,265)
Cash and cash equivalents at beginning of the period	26,029	42,226
Effects of exchange rate changes on cash and cash equivalents	3	206
Cash and cash equivalents at the end of the period	26,394	37,167
Cash and cash equivalents consist of:
Cash and balances at central banks	21,936	21,342
Less: regulatory minimum cash balances	(670)	(631)
Cash and bank balances at central banks less regulatory minimum cash balances	21,266	20,711
Net trading other cash equivalents		2,591
Net non-trading other cash equivalents	5,128	13,865
Cash and cash equivalents at the end of the period	£ 26,394	£ 37,167

Consolidated Statement of Chang

Consolidated Statement of Changes in Equity - GBP (£) £ in Millions	Total	Share Capital [member]	Share Premium [member]	Other Equity Instruments [member]	Other Reserves Available-For-Sale [member]	Reserve of gains and losses on financial assets measured at fair value through other comprehensive income [member]	Other Reserves Cash Flow Hedging [member]	Other Reserves Currency Translation [member]	Retained Earnings [member]	Total [member]	Non-Controlling Interests [member]
Beginning balance (Previously Stated [member]) at Dec. 31, 2017	£ 16,205	£ 3,119	£ 5,620	£ 2,281	£ 68		£ 228	£ 5	£ 4,732	£ 16,053	£ 152
Beginning balance (Adjustment for Adoption of IFRS 9 [member]) at Dec. 31, 2017	(192)				£ (68)	£ 63			(187)	(192)
Beginning balance at Dec. 31, 2017	16,013	3,119	5,620	2,281		63	228	5	4,545	15,861	152
Statement [LineItems]
Profit after tax	672								660	660	12
Other comprehensive income, net of tax:
- Fair value reserve (debt instrument)	(21)					(21)				(21)
- Cash flow hedges	(85)						(85)			(85)
- Pension remeasurement	397								396	396	1
- Own credit adjustment	(23)								(23)	(23)
Total comprehensive income	940					(21)	(85)		1,033	927	13
Other	(45)								(45)	(45)
Dividends on ordinary shares	(250)								(250)	(250)
Dividends on preference shares and other equity instruments	(90)								(90)	(90)
Ending balance at Jun. 30, 2018	16,568	3,119	5,620	2,281		42	143	5	5,193	16,403	165
Beginning balance at Dec. 31, 2018	15,909	3,119	5,620	1,991		23	256	5	4,744	15,758	151
Statement [LineItems]
Profit after tax	419								410	410	9
Other comprehensive income, net of tax:
- Fair value reserve (debt instrument)	11					11				11
- Cash flow hedges	236						236			236
- Pension remeasurement	(210)								(209)	(209)	(1)
- Own credit adjustment	(43)								(43)	(43)
Total comprehensive income	413					11	236		158	405	8
Repurchase of preference shares and other equity instruments	(14)	(14)								(14)
Dividends on ordinary shares	(164)								(164)	(164)
Dividends on preference shares and other equity instruments	(80)								(80)	(80)
Ending balance at Jun. 30, 2019	£ 16,064	£ 3,105	£ 5,620	£ 1,991		£ 34	£ 492	£ 5	£ 4,658	£ 15,905	£ 159

Accounting Policies

Accounting Policies	6 Months Ended
	Jun. 30, 2019
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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 plc (the Santander UK group) for the year ended 31 December 2018 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. Except as noted below, the same accounting policies, presentation and methods of computation are followed in these Condensed Consolidated Interim Financial Statements as were applied in the presentation of the Santander UK group’s 2018 Annual Report. Recent accounting developments IFRS 16 On 1 January 2019 the Santander UK group adopted IFRS 16 ‘Leases’ (IFRS 16) and the revised accounting policies as lessee which have been applied from 1 January 2019 are set out below. Comparatives have not been restated. The impact of applying IFRS 16 is disclosed in section (ii). i) Accounting policy change The Santander UK group as lessee The Santander UK group assesses whether a contract is or contains a lease at the inception of the contract and recognises a right-of-use The lease liability, which is included within Other liabilities on the balance sheet, is initially measured at the present value of the lease payments that are not paid at the commencement date, discounted using the incremental borrowing rate appropriate to the lease term. The lease liability is subsequently measured at amortised cost using the effective interest rate method. Remeasurement of the lease liability occurs if there is a change in the lease payments (when a corresponding adjustment is made to the ROU asset), the lease term or in the assessment of an option to purchase the underlying asset. At inception, the ROU asset, which is included within Property, plant and equipment on the balance sheet, comprises the lease liability, initial direct costs and the obligations to restore the asset, less any incentives granted by the lessor. The ROU asset is depreciated over the shorter of the lease term or the useful life of the underlying asset and is reviewed for indications of impairment as for owned assets. The obligation to restore the asset is included within Provisions on the balance sheet. ii) Impact of adoption IFRS 16 became effective for periods beginning on or after 1 January 2019. The standard sets out the principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. For lessee accounting, IFRS 16 introduces a single lessee accounting model which requires the recognition of a ROU asset representing the lessee’s right to use the underlying leased asset and a lease liability representing its obligation to make lease payments. For lessor accounting, IFRS 16 substantially carries forward the requirements from the previous leasing standard (IAS 17) and a lessor continues to classify its leases as operating leases or finance leases and to account for those two types of leases differently. The Santander UK group elected to apply the modified retrospective approach whereby the ROU asset at the date of initial application was measured at an amount equal to the lease liability. The ROU asset was adjusted for any prepaid lease payments and incentives relating to the relevant leases that were recognised on the balance sheet at 31 December 2018 and included an estimate of the costs of restoring the underlying assets to the condition required by the terms of the lease. The application of IFRS 16 at 1 January 2019 increased property, plant and equipment by £211m (being the net increase in ROU assets referred to above), reduced other assets by £12m, increased other liabilities by £182m from recognising lease liabilities, and increased provisions by £17m (see Note 21). There was no impact on shareholders’ equity. The amount of the lease liabilities above differed from the amount of operating lease commitments disclosed in Note 32 to the Consolidated Financial Statements in the 2018 Annual Report due to the effects of discounting the lease liabilities and excluding short-term leases that are outside the scope of IFRS 16. In addition to the choice of transition approach, the determination of the discount rate is the most significant area of judgement. The Santander UK group applies an incremental borrowing rate (based on 3-month IAS 12 The Santander UK group has also applied the amendment to IAS 12 ‘Income Taxes’ (part of ‘Annual Improvements to IFRS Standards 2015-2017 Cycle’) in these Condensed Consolidated Interim Financial Statements. The amendment clarifies that the income tax consequences of dividends on financial instruments classified as equity should be recognised according to where the past transactions or events that generated distributable profits were recognised. This means that, to the extent that profits from which dividends on equity instruments were recognised in the income statement, the income tax consequences would be similarly recognised in the same statement. The amendment, which has been applied retrospectively, reduces the effective tax rate where the tax relief on dividends in respect of other equity instruments is recognised in the income statement rather than in equity. There was no impact on shareholders’ equity from applying the amendment to IAS 12 at 1 January 2019. The impact of the amendment to IAS 12 on the income statement for H119 was to reduce tax on profit by £21m (H118: £23m), increasing profit after tax by the same amount. Going Concern 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 that the balance sheet is signed. Having reassessed the principal risks and uncertainties, the Directors consider it appropriate to adopt the ‘going concern’ basis of accounting in preparing the Condensed Consolidated Interim Financial Statements. CRITICAL 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, conduct remediation and pensions. There have been no significant changes in the basis upon which judgements and accounting estimates have been determined compared to that applied in the 2018 Annual Report. a) Credit impairment allowance Sensitivity of ECL allowance At 30 June 2019, the probability-weighted ECL allowance totalled £817m (2018: £807m), of which £801m (2018: £789m) related to exposures in Retail Banking, Corporate & Commercial Banking and Corporate Centre, and £16m (2018: £18m) related to exposures in Corporate & Investment Banking. Probability weights The amounts shown in the tables below illustrate the ECL allowances that would have arisen had management applied a 100% weighting to each economic scenario, and were calculated using the same methodology described in Note 1 to the Consolidated Financial Statements, and the Credit risk section of the Risk review, within the 2018 Annual Report. ECL for Retail Banking, Corporate & Commercial Banking and Corporate Centre Upside 2 Upside 1 Base case Downside 1 Downside 2 30 June 2019 601 629 667 861 1,726 31 December 2018 554 596 648 843 1,930 ECL for Corporate & Investment Banking (1) Upside Base case Downside 30 June 2019 7 14 23 31 December 2018 8 17 27 (1) As described in more detail in the ‘Santander UK Group Level – Credit Risk Management’ section in the 2018 Annual Report, our Corporate & Investment Banking segment uses three forward-looking economic scenarios, whereas our other segments use five scenarios. The results of the 100% weighting ECL for the Corporate & Investment Banking segment are therefore presented separately. b) Provisions Sensitivity of PPI conduct remediation provision At 30 June 2019, the remaining provision for redress and related costs was £248m (2018: £246m). We made an additional provision of £70m in Q219 reflecting an increase in PPI claims volumes, additional industry activities and having considered guidance provided by the FCA, in advance of the PPI claims deadline on 29 August 2019. Had management used different assumptions around future expected claims, a larger or smaller provision charge would have resulted that could have had a material impact on the Santander UK group’s reported profit before tax. For more on the provision for PPI conduct remediation, including details on the future expected claims assumption, and the associated sensitivity, see Note 21.

Segments

Segments	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Segments	2. SEGMENTS The Santander UK group’s business is managed and reported on the basis of the following segments: Retail Banking, Corporate & Commercial Banking, Corporate & Investment Banking and Corporate Centre. The segments are strategic business units that offer different products and services. They are managed separately because each business has different customers and requires different technology and marketing strategies. The segmental basis of presentation in these Condensed Consolidated Interim Financial Statements has been changed, and the prior period has been restated, for the following: • To report our short term markets business in Corporate Centre rather than in Corporate & Investment Banking. This reflects the run down or transfer to Banco Santander London Branch of the prohibited part of the business in 2018, as part of the transition to our ring-fenced model, with the remaining permitted business forming part of our liquidity risk management function. • As reflected in the Consolidated Financial Statements in the 2018 Annual Report, to report our Jersey and Isle of Man branches in Corporate Centre rather than in Retail Banking, as a result of their transfer from Santander UK plc to ANTS in December 2018. Results by segment Half year to 30 June 2019 Retail Corporate & Corporate & Corporate Total £m Net interest income/(expense) 1,465 189 32 (18 ) 1,668 Non-interest 353 38 47 15 453 Total operating income/(expense) 1,818 227 79 (3 ) 2,121 Operating expenses before credit impairment losses, provisions and charges (1,011 ) (138 ) (83 ) (25 ) (1,257 ) 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 ) (128 ) 589 Revenue from external customers 2,166 281 85 (411 ) 2,121 Inter-segment revenue (348 ) (54 ) (6 ) 408 — Total operating income/(expense) 1,818 227 79 (3 ) 2,121 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 (2) 36 26 24 — 86 Total fee and commission income 460 41 38 — 539 Fee and commission expense (184 ) (12 ) (7 ) (1 ) (204 ) Net fee and commission income 276 29 31 (1 ) 335 30 June 2019 Customer loans 174,590 17,365 4,060 4,343 200,358 Total assets (3) 182,785 17,365 4,929 79,448 284,527 Customer deposits 142,814 18,021 6,059 2,855 169,749 Total liabilities 143,788 18,045 6,946 99,684 268,463 (1) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (2) Non-banking (3) Includes customer loans, net of credit impairment loss allowances. Half year to 30 June 2018 (1) Retail Corporate & Corporate & Corporate Total Net interest income 1,565 202 33 11 1,811 Non-interest 304 40 115 42 501 Total operating income 1,869 242 148 53 2,312 Operating expenses before credit impairment losses, provisions and charges (957 ) (134 ) (145 ) (47 ) (1,283 ) Credit impairment (losses)/releases (52 ) (22 ) (18 ) 1 (91 ) Provisions for other liabilities and charges (34 ) 8 (2 ) (5 ) (33 ) Total operating credit impairment losses, provisions and (charges)/releases (86 ) (14 ) (20 ) (4 ) (124 ) Profit/(loss) before tax 826 94 (17 ) 2 905 Revenue from external customers 2,183 322 177 (370 ) 2,312 Inter-segment revenue (314 ) (80 ) (29 ) 423 — Total operating income/(expense) 1,869 242 148 53 2,312 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) – Current account and debit card fees 311 13 14 — 338 – Insurance, protection and investments 46 — — — 46 – Credit cards 45 — — — 45 – Non-banking (3) 67 32 50 6 155 Total fee and commission income 469 45 64 6 584 Fee and commission expense (183 ) (13 ) (8 ) — (204 ) Net fee and commission income 286 32 56 6 380 31 December 2018 Customer loans 172,747 17,702 4,613 4,524 199,586 Total assets (4) 179,572 17,702 8,607 77,491 283,372 Customer deposits 142,065 17,606 4,853 2,791 167,315 Total liabilities 142,839 17,634 8,885 98,105 267,463 (1) Restated to reflect the resegmentation of our short term markets business and our Jersey and Isle of Man branches to Corporate Centre. (2) 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. (3) Non-banking (4) Includes customer loans, net of credit impairment loss allowances.

Net Trading and Other Income

Net Trading and Other Income	6 Months Ended
	Jun. 30, 2019
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Net Trading and Other Income	3. NET TRADING AND OTHER INCOME Half year to Half year to Net trading and other income 118 121 Included in net trading and other income in H119 is additional consideration of £15m in connection with the 2017 Vocalink Holdings Limited shareholding sale. In H119 and H118, the Santander UK group did not repurchase any of its debt instruments.

Operating Expenses Before Credi

Operating Expenses Before Credit Impairment Losses, Provisions and Charges	6 Months Ended
	Jun. 30, 2019
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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 Staff costs 641 691 Other administration expenses 356 411 Depreciation, amortisation and impairment 260 181 1,257 1,283

Credit Impairment Losses and Pr

Credit Impairment Losses and Provisions	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Credit Impairment Losses and Provisions	5. CREDIT IMPAIRMENT LOSSES AND PROVISIONS Half year to Half year to Credit impairment losses: Loans and advances to customers (See Note 10) 108 102 Recoveries of loans and advances, net of collection costs (38 ) (21 ) Off-balance (1 ) 10 69 91 Provisions for other liabilities and charges (excluding off-balance 205 33 Provisions for residual value (RV) and voluntary termination (See Note 10) 1 — 206 33 275 124 There were no material credit impairment losses on loans and advances to banks, non-trading

Taxation

Taxation	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Taxation	6. TAXATION Half year to Half year to (1) Profit before tax 589 905 Tax calculated at a tax rate of 19% (H118: 19%) 112 172 Bank surcharge on profits 39 64 Non-deductible 5 5 Non-deductible 13 13 Non-deductible 11 (2 ) Net disallowable items and non-taxable 11 10 Tax relief on dividends in respect of other equity instruments (21 ) (23 ) Adjustment to prior period provisions — (6 ) Tax charge 170 233 (1) Adjusted to reflect the amendment to IAS 12, as described in Note 1. Interim period corporation tax is accrued based on the estimated average annual effective corporation tax for the year of 28.9% (H118: 25.7%). The standard rate of UK corporation tax was 27% for banking entities and 19% for non-banking non-banking

Dividends on Ordinary Shares

Dividends on Ordinary Shares	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Dividends on Ordinary Shares	7. DIVIDENDS ON ORDINARY SHARES An interim dividend of £164m was declared on 18 June 2019 and paid on 27 June 2019 on the Company’s ordinary shares in issue (H118: £250m).

Derivative Financial Instrument

Derivative Financial Instruments	6 Months Ended
	Jun. 30, 2019
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Derivative Financial Instruments	8. DERIVATIVE FINANCIAL INSTRUMENTS 30 June 2019 31 December 2018 Fair value Fair value Notional amount Assets Liabilities Notional amount Assets Liabilities Derivatives held for trading Exchange rate contracts 17,087 861 710 13,830 454 351 Interest rate contracts 50,698 793 284 79,038 1,421 1,105 Equity and credit contracts 2,586 272 150 2,762 251 168 Total derivatives held for trading 70,371 1,926 1,144 95,630 2,126 1,624 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 1,542 229 14 3,010 357 — Interest rate contracts 91,598 1,020 1,636 86,422 1,065 1,315 Equity derivative contracts — — — — — — 93,140 1,249 1,650 89,432 1,422 1,315 Designated as cash flow hedges: Exchange rate contracts 32,870 3,334 203 33,901 3,537 200 Interest rate contracts 19,333 197 39 18,808 46 102 Equity derivative contracts — — — — — — 52,203 3,531 242 52,709 3,583 302 Total derivatives held for hedging 145,343 4,780 1,892 142,141 5,005 1,617 Derivative netting (1) (1,261 ) (1,261 ) (1,872 ) (1,872 ) Total derivatives 215,714 5,445 1,775 237,771 5,259 1,369 (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 £218m (2018: £9m) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was £756m (2018: £354m).

Other Financial Assets At Fair

Other Financial Assets At Fair Value Through Profit Or Loss	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Other Financial Assets At Fair Value Through Profit Or Loss	9. OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS 30 June 2019 31 December 2018 Loans and advances to customers: Loans to housing associations 13 13 Other loans 81 81 94 94 Debt securities 651 3,251 Equity securities — — Reverse repurchase agreements – non trading — 2,272 745 (1) 5,617 (1) (1) Comprised of £13m (2018: £1,095m) of financial assets designated at FVTPL and £732m (2018: £4,522m) of financial assets mandatorily at FVTPL. In H119 £2.1bn of senior tranches of credit linked notes, which were previously classified as debt securities in the table above, were presented on a net basis. This followed a deed of amendment, including a legal right of set-off

Loans and Advances to Customers

Loans and Advances to Customers	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Loans and Advances to Customers	10. LOANS AND ADVANCES TO CUSTOMERS 30 June 2019 31 December 2018 Loans and advances to customers 201,016 200,095 Amounts due from fellow Banco Santander subsidiaries and joint ventures 2,329 2,014 Loans and advances to customers 203,345 202,109 Credit impairment loss allowances on loans and advances to customers (760 ) (751 ) RV and voluntary termination provisions on finance leases (69 ) (69 ) Net loans and advances to customers 202,516 201,289 Movement in credit impairment loss allowances: Loans secured £m Corporate £m Finance Other £m Total At 1 January 2019 234 226 85 206 751 (Release)/charge to the income statement (18 ) 30 18 78 108 Write-offs and other items (6 ) (7 ) (17 ) (69 ) (99 ) At 30 June 2019 210 249 86 215 760 At 31 December 2017 225 490 46 179 940 Adoption of IFRS 9 (1) 47 99 11 54 211 Re-allocation off-balance (1) (3 ) (25 ) — (22 ) (50 ) At 1 January 2018 269 564 57 211 1,101 (Release)/charge to the income statement (13 ) 24 17 74 102 Write-offs and other items (7 ) (318 ) (15 ) (71 ) (411 ) At 30 June 2018 249 270 59 214 792 (1) The adjustment for the adoption of IFRS 9 related to the re-measurement re-allocation off-balance

Securitisations and Covered Bon

Securitisations and Covered Bonds	6 Months Ended
	Jun. 30, 2019
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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 unconsolidated structured entities, including credit protection vehicles that are described in more detail in Note 15. The gross assets securitised, or for the covered bond programme assigned, at 30 June 2019 and 31 December 2018 were: 30 June 2019 31 December Mortgage-backed master trust structures: – Holmes 4,256 4,414 – Fosse 4,200 4,646 – Langton 2,671 3,034 11,127 12,094 Other asset-backed securitisation structures: – Motor 737 1,055 – Auto ABS UK Loans 1,358 1,468 2,095 2,523 Total securitisation programmes 13,222 14,617 Covered bond programme: – Euro 35bn Global Covered Bond Programme 23,157 21,578 Total securitisation and covered bond programmes 36,379 36,195 The following table sets out the internal and external issuances and redemptions for the half year ended 30 June 2019 and the half year ended 30 June 2018 for each securitisation and covered bond programme. Internal issuances External issuances Internal External H119 H118 H119 H118 H119 H118 H119 H118 £bn £bn £bn £bn £bn £bn £bn £bn Mortgage-backed master trust structures: – Holmes — — — 1.0 — — 0.8 — – Fosse — — — — — — — 0.4 Other asset-backed securitisation structures: – Motor — — — — 0.1 0.1 0.2 — – Auto ABS UK Loans — — — — — — 0.1 — Covered bond programme — — 1.9 2.4 — 0.5 — 1.9 — — 1.9 3.4 0.1 0.6 1.1 2.3

Reverse Repurchase Agreements -

Reverse Repurchase Agreements - Non Trading	6 Months Ended
	Jun. 30, 2019
Reverse repurchase agreements - non-trading [member]
Statement [LineItems]
Reverse Repurchase Agreements - Non Trading	12. REVERSE REPURCHASE AGREEMENTS – NON TRADING 30 June 2019 31 December 2018 Agreements with banks’ 4,258 3,254 Agreements with customers 18,151 17,873 22,409 21,127

Other Financial Assets At Amort

Other Financial Assets At Amortised Cost	6 Months Ended
	Jun. 30, 2019
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Other Financial Assets At Amortised Cost	13. OTHER FINANCIAL ASSETS AT AMORTISED COST 30 June 2019 31 December 2018 Asset backed securities 455 720 Debt securities 6,682 6,509 7,137 7,229 A significant portion of the debt securities are held in our eligible liquidity pool and consist mainly of government bonds and covered bonds. Detailed disclosures can be found in the ‘Liquidity risk’ section of the Risk review.

Financial Assets At Fair Value

Financial Assets At Fair Value Through Other Comprehensive Income	6 Months Ended
	Jun. 30, 2019
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Financial Assets At Fair Value Through Other Comprehensive Income	14. FINANCIAL ASSETS AT FAIR VALUE THROUGH OTHER COMPREHENSIVE INCOME 30 June 2019 31 December 2018 Debt securities 13,369 13,229 Loans and advances to customers 69 73 13,438 13,302 A significant portion of the debt securities are held in our eligible liquidity pool and consist mainly of government bonds and covered bonds. Detailed disclosures can be found in the ‘Liquidity risk’ section of the Risk review.

Interests in Other Entities

Interests in Other Entities	6 Months Ended
	Jun. 30, 2019
Investments accounted for using equity method [abstract]
Interests in Other Entities	15. INTERESTS IN OTHER ENTITIES The Santander UK group has interests in subsidiaries, associates, joint ventures and unconsolidated structured entities, as set out in Note 21 to the Consolidated Financial Statements in the 2018 Annual Report. Interests in subsidiaries As part of ring-fencing implementation, Santander UK Group Holdings plc adopted a wide ring-fenced bank model with most of our operations within Santander UK plc, the ring-fenced bank. ANTS is outside the RFB and also holds wealth management businesses in the Crown Dependencies, which are not permitted within the ring-fence as they are located outside the UK. To optimise the overall funding structure of the bank Santander UK Group Holdings plc is considering the transfer of some RFB assets to ANTS to enable more efficient use of Crown Dependencies deposits. Interests in unconsolidated structured entities Santander UK has established four (2018: three) credit protection entities, which are Designated Activity Companies limited by shares, incorporated in Ireland. Each entity has issued a series of credit linked notes varying in seniority which reference portfolios of Santander UK group loans. Concurrently, these entities sell credit protection to Santander UK in respect of the referenced loans and, in return for a fee, are liable to make protection payments to Santander UK upon the occurrence of a credit event in relation to any of the referenced loans. Senior credit linked notes, which amounted to £4,786m (2018: £3,053m), are issued to, and held by, Santander UK. Junior credit linked notes, which amounted to £766m (2018: £408m), are all held by third party investors and suffer the first losses incurred in the referenced portfolios. Funds raised by the sale of the credit linked notes are deposited with Santander UK as collateral for the credit protection. £194m (2018: £3,053m) of the senior credit linked notes are presented on a gross basis and included within ‘Other financial assets at fair value through profit or loss’ on the balance sheet (see Note 9). Deposits and associated guarantees relating to the senior notes are included within ‘Other financial liabilities at fair value through profit or loss’ (see Note 16). The remainder of the senior credit linked notes, along with the deposits and associated guarantees, are presented on a net basis, to reflect a legal right of set-off The entities are not consolidated by Santander UK because the third party investors have the exposure, or rights, to all of the variability of returns from the performance of the entities. No assets are transferred to, or income received from, these vehicles. Because the credit linked notes (including those held by Santander UK) are fully cash collateralised, Santander UK’s maximum exposure to loss is equal to any unamortised fees paid to the credit protection entities in connection with the credit protection outlined above.

Other Financial Liabilities at

Other Financial Liabilities at Fair Value Through Profit or Loss	6 Months Ended
	Jun. 30, 2019
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Other Financial Liabilities at Fair Value Through Profit or Loss	16. OTHER FINANCIAL LIABILITIES AT FAIR VALUE THROUGH PROFIT OR LOSS 30 June 2019 31 December 2018 £m £m US$30bn Euro Medium Term Note Programme 168 165 Structured Notes Programmes 773 696 Eurobonds 131 129 Structured deposits 133 133 Collateral and associated financial guarantees 428 3,053 Repurchase agreements – non trading — 2,110 1,633 (1) 6,286 (1) (1) At 30 June 2019 and 31 December 2018 all amounts were designated at fair value through profit or loss. In H119 £2.1bn of senior cash deposits, which were previously included within collateral and associated financial guarantees in the table above, were presented on a net basis. This followed a deed of amendment, including a legal right of set-off

Deposits by Customers

Deposits by Customers	6 Months Ended
	Jun. 30, 2019
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Deposits by Customers	17. DEPOSITS BY CUSTOMERS 30 June 2019 31 December 2018 £m £m Current and demand accounts 86,639 86,207 Savings accounts (1) 65,546 66,039 Time deposits 17,849 15,485 Amounts due to other Santander UK Group Holdings plc subsidiaries 56 83 Amounts due to Santander UK Group Holdings plc (2) 9,223 9,206 Amounts due to fellow Banco Santander subsidiaries and joint ventures 1,304 1,070 180,617 178,090 (1) Includes equity index-linked deposits of £1,122m (2018: £1,176m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,122m and £20m (2018: £1,176m and £28m) respectively. (2) Includes downstreamed funding from our immediate parent company Santander UK Group Holdings plc.

Deposits by Banks

Deposits by Banks	6 Months Ended
	Jun. 30, 2019
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Deposits by Banks	18. DEPOSITS BY BANKS 30 June 2019 31 December 2018 £m £m Items in the course of transmission 326 262 Deposits held as collateral 3,571 4,048 Other deposits (1) 12,592 12,891 Amounts due to Santander UK subsidiaries — 20 16,489 17,221 (1) Includes drawdown from the TFS of £10.8bn (2018: £10.8bn).

Repurchase Agreements - Non Tra

Repurchase Agreements - Non Trading	6 Months Ended
	Jun. 30, 2019
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Repurchase Agreements - Non Trading	19. REPURCHASE AGREEMENTS – NON TRADING 30 June 2019 31 December 2018 £m £m Agreements with banks 9,619 5,865 Agreements with customers 5,152 5,045 14,771 10,910

Debt Securities in Issue

Debt Securities in Issue	6 Months Ended
	Jun. 30, 2019
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Debt Securities in Issue	20. DEBT SECURITIES IN ISSUE 30 June 2019 31 December 2018 £m £m Medium-term notes 17,331 19,984 Euro 35bn Global Covered Bond Programme 19,926 18,114 Certificates of deposit 3,226 3,221 Credit linked notes — 42 Securitisation programmes 4,091 5,331 44,574 46,692

Provisions

Provisions	6 Months Ended
	Jun. 30, 2019
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Provisions	21. PROVISIONS Conduct remediation Other FSCS and Off-balance Regulatory PPI products Bank Levy Property sheet ECL and other Total £m £m £m £m £m £m £m At 31 December 2018 246 30 45 37 56 95 509 Adoption of IFRS 16 (see Note 1) — — — 17 — — 17 At 1 January 2019 246 30 45 54 56 95 526 Additional provisions (see Note 5) 70 — — 38 — 114 222 Provisions released (see Note 5) — — (2 ) (8 ) (1 ) (7 ) (18 ) Utilisation (68 ) (1 ) (41 ) (4 ) — (69 ) (183 ) At 30 June 2019 248 29 2 80 55 133 547 At 31 December 2017 356 47 57 39 59 558 Reallocation of ECL on off-balance (1) — — — — 50 — 50 At 1 January 2018 356 47 57 39 50 59 608 Additional provisions (see Note 5) — — — 11 10 54 75 Provisions released (see Note 5) — (14 ) (4 ) — — (14 ) (32 ) Utilisation (55 ) (2 ) (37 ) (7 ) — (46 ) (147 ) At 30 June 2018 301 31 16 43 60 53 504 (1) ECL on off-balance Conduct remediation At 30 June 2019, the remaining provision for Payment Protection Insurance (PPI) redress and related costs was £248m. This includes a provision for PPI redress as well as our best estimate of liability for a specific portfolio which was disclosed in our 2018 Annual Report. For every additional 25,000 inbound PPI complaints above the future expected claims of c.311k from June to the end of the industry deadline, we would expect an additional charge of £6.9m. 30 June 2019 compared to 31 December 2018 We made an additional provision of £70m in Q219 reflecting an increase in PPI claims volumes, additional industry activities and having considered guidance provided by the FCA, in advance of the PPI claims deadline on 29 August 2019. We will continue to monitor our provision levels and take account of the impact of any further change in claims received and FCA guidance. Property Property provisions include vacant property provisions, as described in Note 30 to the Consolidated Financial Statements in the 2018 Annual Report, and property dilapidation provisions within the scope of IFRS 16. Property provisions were impacted by £38m of transformation charges in H119. These relate to a multi-year project to deliver on our strategic priorities and enhance efficiency in order for us to better serve our customers and meet our medium term targets. Q119 charges largely related to restructuring of our branch network associated with the announcement made earlier in the year to reshape our branch network. Regulatory and other Regulatory and other provisions were impacted by £62m of transformation charges in H119, also relating to the multi-year project described above. In addition to the Q119 charges largely related to the restructuring of our branch network, further charges in Q219 were largely associated with the announced plans to reshape our Corporate & Commercial Banking business.

Retirement Benefit Plans

Retirement Benefit Plans	6 Months Ended
	Jun. 30, 2019
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Retirement Benefit Plans	22. RETIREMENT BENEFIT PLANS The amounts recognised in the balance sheet were as follows: 30 June 2019 31 December 2018 £m £m Assets/(liabilities) Funded defined benefit pension scheme – surplus 779 842 Funded defined benefit pension scheme – deficit (213 ) (75 ) Unfunded defined benefit pension scheme (39 ) (39 ) Total net assets 527 728 a) Defined contribution pension plans An expense of £34m (H118: £23m) was recognised for defined contribution plans in the period and is included in staff costs classified within operating expenses (see Note 4). None of this amount was recognised in respect of key management personnel for H119 and H118. b) Defined benefit pension schemes The total amount charged to the income statement was £10m (H118: £22m). Movements in the present value of defined benefit obligations and fair value of scheme assets in H119 and H118 were as follows: Half year to Half year to 30 June 2019 30 June 2018 £m £m Return on plan assets (excluding amounts included in net interest expense) (916 ) 72 Actuarial (gains)/losses arising from experience adjustments (5 ) 39 Actuarial losses/(gains) arising from changes in financial assumptions 1,201 (640 ) Pension remeasurement 280 (529 ) The net assets recognised in the balance sheet were determined as follows: 30 June 2019 31 December 2018 £m £m Present value of defined benefit obligations (11,980 ) (10,804 ) Fair value of scheme assets 12,507 11,532 Net defined benefit assets 527 728 Actuarial assumptions There have been no significant changes to the methods for setting the principal actuarial assumptions used as set out in Note 31 to the Consolidated Financial Statements in the 2018 Annual Report.

Contingent Liabilities And Comm

Contingent Liabilities And Commitments	6 Months Ended
	Jun. 30, 2019
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Contingent Liabilities And Commitments	23. CONTINGENT LIABILITIES AND COMMITMENTS 30 June 2019 31 December 2018 £m £m Guarantees given to third parties 1,055 1,610 Formal standby facilities, credit lines and other commitments 41,851 40,111 42,906 41,721 At 30 June 2019, the Santander UK group had credit impairment loss provisions relating to guarantees given to third parties and undrawn loan commitments. See Note 21 for further details. There have been no significant changes to the contingent liabilities as set out in Note 32 to the Consolidated Financial Statements in the 2018 Annual Report, including in respect of the following: Other legal actions and regulatory matters Santander UK engages in discussion, and co-operates, In those instances where it is concluded that it is not yet probable that a quantifiable payment will be made, for example because the facts are unclear or further time is required to fully assess the merits of the case or to reasonably quantify the expected payment, no provision is made. In addition where it is not currently practicable to estimate the possible financial effect of these matters, no provision is made. Payment Protection Insurance Note 21 details our provisions including those in relation to PPI. In relation to a specific PPI portfolio of complaints, a legal dispute regarding allocation of liability is ongoing. There are factual issues to be resolved which may have legal consequences including in relation to liability. These issues create uncertainties which mean that it is difficult to reliably predict the resolution of the matter including timing or the significance of the possible impact. The PPI provision includes our best estimate of Santander UK’s liability to the specific portfolio. Further information has not been provided on the basis that it would be seriously prejudicial. German dividend tax arbitrage transactions Santander UK plc, ANTS and Cater Allen International Limited (all subsidiaries of Santander UK Group Holdings plc) are currently under investigation by the Cologne Criminal Prosecution Office and the German Federal Tax Office in relation to historical involvement in German dividend tax arbitrage transactions (known as cum/ex transactions). We are cooperating with the German authorities and are conducting our own internal investigation into the matters in question. There are 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 with reasonable certainty 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 potential breaches of these requirements 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 30 to the 2018 Annual Report, other provisions includes 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, but these reviews are not yet complete, such that the approach and timing to any remediation has not yet been finalised. As a result, the actual cost of customer compensation could differ materially from the amount provided, and it is not currently practicable to provide a reliable estimate of the amount or timing of any additional financial effects.

Assets Charged As Security For

Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets	6 Months Ended
	Jun. 30, 2019
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Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets	24. ASSETS CHARGED AS SECURITY FOR LIABILITIES AND COLLATERAL ACCEPTED AS SECURITY FOR ASSETS Securitisations and covered bonds As described in Note 15 to the Consolidated Financial Statements in the 2018 Annual Report, Santander UK plc and certain of its subsidiaries issue securitisations and covered bonds. At 30 June 2019, there were £36,379m (2018: £36,195m) of gross assets in these secured programmes and £439m (2018: £501m) of these related to internally retained issuances and were available for use as collateral for liquidity purposes in the future. At 30 June 2019, a total of £3,939m (2018: £4,039m) 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 £1,834m at 30 June 2019 (2018: £1,834m), or for use as collateral for liquidity purposes in the future.

Other Equity Instruments

Other Equity Instruments	6 Months Ended
	Jun. 30, 2019
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Other Equity Instruments	25. OTHER EQUITY INSTRUMENTS Interest rate Next call date 30 June 2019 31 December 2018 £300m Step-up 7.037 February 2026 235 235 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 750 750 – £300m Fixed Rate Reset Perpetual AT1 Capital Securities 7.60 December 2019 300 300 – £500m Fixed Rate Reset Perpetual AT1 Capital Securities 5.18 September 2019 210 210 1,991 1,991

Non-Controlling Interests

Non-Controlling Interests	6 Months Ended
	Jun. 30, 2019
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Non-Controlling Interests	26. NON-CONTROLLING 30 June 2019 31 December 2018 £m £m PSA Finance UK Limited 159 151 159 151

Related Party Disclosures

Related Party Disclosures	6 Months Ended
	Jun. 30, 2019
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Related Party Disclosures	27. RELATED PARTY DISCLOSURES The financial position and performance of the Santander UK group have not been materially affected in H119 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 31 to the Consolidated Financial Statements in the 2018 Annual Report.

Financial Instruments

Financial Instruments	6 Months Ended
	Jun. 30, 2019
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Financial Instruments	28. 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 2018 Annual Report describes how the classes of financial instruments are measured, and how income and expenses, including fair value gains and losses, are recognised. At 30 June 2019 and 31 December 2018, the Santander UK group categorised assets and liabilities measured at fair value within the fair value hierarchy based on the fair value measurement and hierarchy, and valuation techniques, described in Note 41(b) and (c) to the Consolidated Financial Statements in the 2018 Annual Report. b) Fair values of financial instruments carried at amortised cost The following table analyses the fair value of the financial instruments carried at amortised cost at 30 June 2019 and 31 December 2018. 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 41(e) to the Consolidated Financial Statements in the 2018 Annual Report. 30 June 2019 31 December 2018 Fair value Carrying value Fair value Carrying value Assets Loans and advances to customers 207,080 202,516 204,061 201,289 Loans and advances to banks 2,065 2,065 2,799 2,799 Reverse repurchase agreements- non trading 22,416 22,409 21,130 21,127 Other financial assets at amortised cost 7,168 7,137 7,111 7,229 238,729 234,127 235,101 232,444 Liabilities Deposits by customers 180,777 180,617 178,181 178,090 Deposits by banks 16,500 16,489 17,232 17,221 Repurchase agreements- non trading 14,779 14,771 10,923 10,910 Debt securities in issue 45,664 44,574 47,787 46,692 Subordinated liabilities 4,235 3,645 3,877 3,601 261,955 260,096 258,000 256,514 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 2019 and 31 December 2018, analysed by their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. 30 June 2019 31 December 2018 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 Derivatives Exchange rate contracts — 4,402 22 4,424 — 4,323 25 4,348 A Interest rate contracts — 2,005 5 2,010 — 2,526 6 2,532 A & C Equity and credit contracts — 210 62 272 — 188 63 251 B & D Netting — (1,261 ) — (1,261 ) — (1,872 ) — (1,872 ) — 5,356 89 5,445 — 5,165 94 5,259 Other financial assets at FVTPL Loans and advances to customers — — 94 94 — 12 82 94 A Debt securities 17 72 562 651 18 2,339 894 3,251 A, B & D Reverse repurchase agreements – non trading — — — — — 2,272 — 2,272 A 17 72 656 745 18 4,623 976 5,617 Financial assets at FVOCI Debt securities 12,781 588 — 13,369 12,487 742 — 13,229 D Loans and advances to customers — — 69 69 — — 73 73 D 12,781 588 69 13,438 12,487 742 73 13,302 Total assets at fair value 12,798 6,016 814 19,628 12,505 10,530 1,143 24,178 Liabilities Derivatives Exchange rate contracts — 926 1 927 — 528 23 551 A Interest rate contracts — 1,951 8 1,959 — 2,515 7 2,522 A & C Equity and credit contracts — 121 29 150 — 132 36 168 B & D Netting — (1,261 ) — (1,261 ) — (1,872 ) — (1,872 ) — 1,737 38 1,775 — 1,303 66 1,369 Other financial liabilities at FVTPL Debt securities in issue — 1,065 7 1,072 — 983 7 990 A Structured deposits — 104 29 133 — 104 29 133 A Repurchase agreements – non trading — — — — — 2,110 — 2,110 A Collateral and associated financial guarantees — 407 21 428 — 3,040 13 3,053 D — 1,576 57 1,633 — 6,237 49 6,286 Total liabilities at fair value — 3,313 95 3,408 — 7,540 115 7,655 Transfers between levels of the fair value hierarchy During H119, there were no significant transfers of financial instruments from Level 1 to Level 2, or from Level 2 to Level 3 (H118: 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 2019 31 December 2018 £m £m Risk-related: – Bid-offer 17 13 – Uncertainty 37 36 – Credit risk adjustment 8 9 – Funding fair value adjustment 5 4 67 62 Model-related 1 5 68 67 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 41(g) to the Consolidated Financial Statements in the 2018 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 41(h) to the Consolidated Financial Statements in the 2018 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 H119 and H118: Assets Liabilities Other Other financial Financial Assets financial Liabilities assets at assets at Financial held liabilities at held Derivatives FVTPL FVOCI investments for sale Total Derivatives FVTPL for sale Total £m £m £m £m £m £m £m £m £m £m At 1 January 2019 94 976 73 — 1,143 (66 ) (49 ) — (115 ) Total gains/(losses) recognised in profit or loss: – Fair value movements 7 1 — — 8 (3 ) (5 ) — (8 ) – Foreign exchange/other movements — 3 — — 3 — (3 ) — (3 ) Transfers in — 11 — — 11 — — — — Additions 3 188 — — 191 — (2 ) — (2 ) Settlements (15 ) (523 ) (4 ) — (542 ) 31 2 — 33 At 30 June 2019 89 656 69 — 814 (38 ) (57 ) — (95 ) Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the period 7 4 — — 11 (3 ) (8 ) — (11 ) At 31 December 2017 64 240 53 — 357 (63 ) (6 ) — (69 ) Adoption of IFRS 9 — 598 199 (53 ) — 744 — — — — At 1 January 2018 64 838 199 — 1,101 (63 ) (6 ) — (69 ) Total gains/(losses) recognised in profit or loss: – Fair value movements 26 (5 ) (4 ) — 17 4 — — 4 – Foreign exchange/other movements (5 ) — — — (5 ) 5 — — 5 Transfers in — 19 — — 19 — — — — Transfer to held for sale (2 ) (146 ) — 148 — 1 — (1 ) — Additions — — 17 — 17 — — — — Sales — (23 ) — — (23 ) — — — — Settlements (21 ) — (37 ) — (58 ) 15 — — 15 At 30 June 2018 62 683 175 148 1,068 (38 ) (6 ) (1 ) (45 ) Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period 21 (5 ) (4 ) 12 9 — — 9 Effect of changes in significant unobservable assumptions to reasonably possible alternatives (Level 3) Other than as described above, there has been no significant change to the unobservable inputs and sensitivities used in Level 3 fair values as set out in Note 41(h) to the Consolidated Financial Statements in the 2018 Annual Report.

Events After the Balance Sheet

Events After the Balance Sheet Date	6 Months Ended
	Jun. 30, 2019
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Events After the Balance Sheet Date	29. EVENTS AFTER THE BALANCE SHEET DATE There have been no significant events between 30 June 2019 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, 2019
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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 plc (the Santander UK group) for the year ended 31 December 2018 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. Except as noted below, the same accounting policies, presentation and methods of computation are followed in these Condensed Consolidated Interim Financial Statements as were applied in the presentation of the Santander UK group’s 2018 Annual Report. Recent accounting developments IFRS 16 On 1 January 2019 the Santander UK group adopted IFRS 16 ‘Leases’ (IFRS 16) and the revised accounting policies as lessee which have been applied from 1 January 2019 are set out below. Comparatives have not been restated. The impact of applying IFRS 16 is disclosed in section (ii). i) Accounting policy change The Santander UK group as lessee The Santander UK group assesses whether a contract is or contains a lease at the inception of the contract and recognises a right-of-use The lease liability, which is included within Other liabilities on the balance sheet, is initially measured at the present value of the lease payments that are not paid at the commencement date, discounted using the incremental borrowing rate appropriate to the lease term. The lease liability is subsequently measured at amortised cost using the effective interest rate method. Remeasurement of the lease liability occurs if there is a change in the lease payments (when a corresponding adjustment is made to the ROU asset), the lease term or in the assessment of an option to purchase the underlying asset. At inception, the ROU asset, which is included within Property, plant and equipment on the balance sheet, comprises the lease liability, initial direct costs and the obligations to restore the asset, less any incentives granted by the lessor. The ROU asset is depreciated over the shorter of the lease term or the useful life of the underlying asset and is reviewed for indications of impairment as for owned assets. The obligation to restore the asset is included within Provisions on the balance sheet. ii) Impact of adoption IFRS 16 became effective for periods beginning on or after 1 January 2019. The standard sets out the principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. For lessee accounting, IFRS 16 introduces a single lessee accounting model which requires the recognition of a ROU asset representing the lessee’s right to use the underlying leased asset and a lease liability representing its obligation to make lease payments. For lessor accounting, IFRS 16 substantially carries forward the requirements from the previous leasing standard (IAS 17) and a lessor continues to classify its leases as operating leases or finance leases and to account for those two types of leases differently. The Santander UK group elected to apply the modified retrospective approach whereby the ROU asset at the date of initial application was measured at an amount equal to the lease liability. The ROU asset was adjusted for any prepaid lease payments and incentives relating to the relevant leases that were recognised on the balance sheet at 31 December 2018 and included an estimate of the costs of restoring the underlying assets to the condition required by the terms of the lease. The application of IFRS 16 at 1 January 2019 increased property, plant and equipment by £211m (being the net increase in ROU assets referred to above), reduced other assets by £12m, increased other liabilities by £182m from recognising lease liabilities, and increased provisions by £17m (see Note 21). There was no impact on shareholders’ equity. The amount of the lease liabilities above differed from the amount of operating lease commitments disclosed in Note 32 to the Consolidated Financial Statements in the 2018 Annual Report due to the effects of discounting the lease liabilities and excluding short-term leases that are outside the scope of IFRS 16. In addition to the choice of transition approach, the determination of the discount rate is the most significant area of judgement. The Santander UK group applies an incremental borrowing rate (based on 3-month IAS 12 The Santander UK group has also applied the amendment to IAS 12 ‘Income Taxes’ (part of ‘Annual Improvements to IFRS Standards 2015-2017 Cycle’) in these Condensed Consolidated Interim Financial Statements. The amendment clarifies that the income tax consequences of dividends on financial instruments classified as equity should be recognised according to where the past transactions or events that generated distributable profits were recognised. This means that, to the extent that profits from which dividends on equity instruments were recognised in the income statement, the income tax consequences would be similarly recognised in the same statement. The amendment, which has been applied retrospectively, reduces the effective tax rate where the tax relief on dividends in respect of other equity instruments is recognised in the income statement rather than in equity. There was no impact on shareholders’ equity from applying the amendment to IAS 12 at 1 January 2019. The impact of the amendment to IAS 12 on the income statement for H119 was to reduce tax on profit by £21m (H118: £23m), increasing profit after tax by the same amount.
Going Concern	Going Concern 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 that the balance sheet is signed. Having reassessed the principal risks and uncertainties, the Directors consider it appropriate to adopt the ‘going concern’ basis of accounting in preparing the Condensed Consolidated Interim Financial Statements.
Critical 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, conduct remediation and pensions. There have been no significant changes in the basis upon which judgements and accounting estimates have been determined compared to that applied in the 2018 Annual Report. a) Credit impairment allowance Sensitivity of ECL allowance At 30 June 2019, the probability-weighted ECL allowance totalled £817m (2018: £807m), of which £801m (2018: £789m) related to exposures in Retail Banking, Corporate & Commercial Banking and Corporate Centre, and £16m (2018: £18m) related to exposures in Corporate & Investment Banking. Probability weights The amounts shown in the tables below illustrate the ECL allowances that would have arisen had management applied a 100% weighting to each economic scenario, and were calculated using the same methodology described in Note 1 to the Consolidated Financial Statements, and the Credit risk section of the Risk review, within the 2018 Annual Report. ECL for Retail Banking, Corporate & Commercial Banking and Corporate Centre Upside 2 Upside 1 Base case Downside 1 Downside 2 30 June 2019 601 629 667 861 1,726 31 December 2018 554 596 648 843 1,930 ECL for Corporate & Investment Banking (1) Upside Base case Downside 30 June 2019 7 14 23 31 December 2018 8 17 27 (1) As described in more detail in the ‘Santander UK Group Level – Credit Risk Management’ section in the 2018 Annual Report, our Corporate & Investment Banking segment uses three forward-looking economic scenarios, whereas our other segments use five scenarios. The results of the 100% weighting ECL for the Corporate & Investment Banking segment are therefore presented separately. b) Provisions Sensitivity of PPI conduct remediation provision At 30 June 2019, the remaining provision for redress and related costs was £248m (2018: £246m). We made an additional provision of £70m in Q219 reflecting an increase in PPI claims volumes, additional industry activities and having considered guidance provided by the FCA, in advance of the PPI claims deadline on 29 August 2019. Had management used different assumptions around future expected claims, a larger or smaller provision charge would have resulted that could have had a material impact on the Santander UK group’s reported profit before tax. For more on the provision for PPI conduct remediation, including details on the future expected claims assumption, and the associated sensitivity, see Note 21.

Accounting Policies (Tables)

Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Probability Weights Applied for Each Scenario of Expected Credit Losses Allowance	ECL for Retail Banking, Corporate & Commercial Banking and Corporate Centre Upside 2 Upside 1 Base case Downside 1 Downside 2 30 June 2019 601 629 667 861 1,726 31 December 2018 554 596 648 843 1,930 ECL for Corporate & Investment Banking (1) Upside Base case Downside 30 June 2019 7 14 23 31 December 2018 8 17 27 (1) As described in more detail in the ‘Santander UK Group Level – Credit Risk Management’ section in the 2018 Annual Report, our Corporate & Investment Banking segment uses three forward-looking economic scenarios, whereas our other segments use five scenarios. The results of the 100% weighting ECL for the Corporate & Investment Banking segment are therefore presented separately.

Segments (Tables)

Segments (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Results by Segment	Results by segment Half year to 30 June 2019 Retail Corporate & Corporate & Corporate Total £m Net interest income/(expense) 1,465 189 32 (18 ) 1,668 Non-interest 353 38 47 15 453 Total operating income/(expense) 1,818 227 79 (3 ) 2,121 Operating expenses before credit impairment losses, provisions and charges (1,011 ) (138 ) (83 ) (25 ) (1,257 ) 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 ) (128 ) 589 Revenue from external customers 2,166 281 85 (411 ) 2,121 Inter-segment revenue (348 ) (54 ) (6 ) 408 — Total operating income/(expense) 1,818 227 79 (3 ) 2,121 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 (2) 36 26 24 — 86 Total fee and commission income 460 41 38 — 539 Fee and commission expense (184 ) (12 ) (7 ) (1 ) (204 ) Net fee and commission income 276 29 31 (1 ) 335 30 June 2019 Customer loans 174,590 17,365 4,060 4,343 200,358 Total assets (3) 182,785 17,365 4,929 79,448 284,527 Customer deposits 142,814 18,021 6,059 2,855 169,749 Total liabilities 143,788 18,045 6,946 99,684 268,463 (1) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (2) Non-banking (3) Includes customer loans, net of credit impairment loss allowances. Half year to 30 June 2018 (1) Retail Corporate & Corporate & Corporate Total Net interest income 1,565 202 33 11 1,811 Non-interest 304 40 115 42 501 Total operating income 1,869 242 148 53 2,312 Operating expenses before credit impairment losses, provisions and charges (957 ) (134 ) (145 ) (47 ) (1,283 ) Credit impairment (losses)/releases (52 ) (22 ) (18 ) 1 (91 ) Provisions for other liabilities and charges (34 ) 8 (2 ) (5 ) (33 ) Total operating credit impairment losses, provisions and (charges)/releases (86 ) (14 ) (20 ) (4 ) (124 ) Profit/(loss) before tax 826 94 (17 ) 2 905 Revenue from external customers 2,183 322 177 (370 ) 2,312 Inter-segment revenue (314 ) (80 ) (29 ) 423 — Total operating income/(expense) 1,869 242 148 53 2,312 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) – Current account and debit card fees 311 13 14 — 338 – Insurance, protection and investments 46 — — — 46 – Credit cards 45 — — — 45 – Non-banking (3) 67 32 50 6 155 Total fee and commission income 469 45 64 6 584 Fee and commission expense (183 ) (13 ) (8 ) — (204 ) Net fee and commission income 286 32 56 6 380 31 December 2018 Customer loans 172,747 17,702 4,613 4,524 199,586 Total assets (4) 179,572 17,702 8,607 77,491 283,372 Customer deposits 142,065 17,606 4,853 2,791 167,315 Total liabilities 142,839 17,634 8,885 98,105 267,463 (1) Restated to reflect the resegmentation of our short term markets business and our Jersey and Isle of Man branches to Corporate Centre. (2) 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. (3) Non-banking (4) Includes customer loans, net of credit impairment loss allowances.

Net Trading and Other Income (T

Net Trading and Other Income (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Net Trading and Other Income	Half year to Half year to Net trading and other income 118 121

Operating Expenses Before Cre_2

Operating Expenses Before Credit Impairment Losses, Provisions and Charges (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Operating Expenses Before Credit Impairment Losses, Provisions and Charges	Half year to Half year to Staff costs 641 691 Other administration expenses 356 411 Depreciation, amortisation and impairment 260 181 1,257 1,283

Credit Impairment Losses and _2

Credit Impairment Losses and Provisions (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Impairment Losses and Provisions	Half year to Half year to Credit impairment losses: Loans and advances to customers (See Note 10) 108 102 Recoveries of loans and advances, net of collection costs (38 ) (21 ) Off-balance (1 ) 10 69 91 Provisions for other liabilities and charges (excluding off-balance 205 33 Provisions for residual value (RV) and voluntary termination (See Note 10) 1 — 206 33 275 124

Taxation (Tables)

Taxation (Tables)	6 Months Ended
	Jun. 30, 2019
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Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate	Half year to Half year to (1) Profit before tax 589 905 Tax calculated at a tax rate of 19% (H118: 19%) 112 172 Bank surcharge on profits 39 64 Non-deductible 5 5 Non-deductible 13 13 Non-deductible 11 (2 ) Net disallowable items and non-taxable 11 10 Tax relief on dividends in respect of other equity instruments (21 ) (23 ) Adjustment to prior period provisions — (6 ) Tax charge 170 233 (1) Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Notional Amounts and Fair Values of Derivative Financial Instruments	30 June 2019 31 December 2018 Fair value Fair value Notional amount Assets Liabilities Notional amount Assets Liabilities Derivatives held for trading Exchange rate contracts 17,087 861 710 13,830 454 351 Interest rate contracts 50,698 793 284 79,038 1,421 1,105 Equity and credit contracts 2,586 272 150 2,762 251 168 Total derivatives held for trading 70,371 1,926 1,144 95,630 2,126 1,624 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 1,542 229 14 3,010 357 — Interest rate contracts 91,598 1,020 1,636 86,422 1,065 1,315 Equity derivative contracts — — — — — — 93,140 1,249 1,650 89,432 1,422 1,315 Designated as cash flow hedges: Exchange rate contracts 32,870 3,334 203 33,901 3,537 200 Interest rate contracts 19,333 197 39 18,808 46 102 Equity derivative contracts — — — — — — 52,203 3,531 242 52,709 3,583 302 Total derivatives held for hedging 145,343 4,780 1,892 142,141 5,005 1,617 Derivative netting (1) (1,261 ) (1,261 ) (1,872 ) (1,872 ) Total derivatives 215,714 5,445 1,775 237,771 5,259 1,369 (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 £218m (2018: £9m) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was £756m (2018: £354m).

Other Financial Assets At Fai_2

Other Financial Assets At Fair Value Through Profit Or Loss (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Other Financial Assets at Fair Value Through Profit or Loss	30 June 2019 31 December 2018 Loans and advances to customers: Loans to housing associations 13 13 Other loans 81 81 94 94 Debt securities 651 3,251 Equity securities — — Reverse repurchase agreements – non trading — 2,272 745 (1) 5,617 (1) (1) Comprised of £13m (2018: £1,095m) of financial assets designated at FVTPL and £732m (2018: £4,522m) of financial assets mandatorily at FVTPL.

Loans and Advances to Custome_2

Loans and Advances to Customers (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Net Loans and Advances to Customers	30 June 2019 31 December 2018 Loans and advances to customers 201,016 200,095 Amounts due from fellow Banco Santander subsidiaries and joint ventures 2,329 2,014 Loans and advances to customers 203,345 202,109 Credit impairment loss allowances on loans and advances to customers (760 ) (751 ) RV and voluntary termination provisions on finance leases (69 ) (69 ) Net loans and advances to customers 202,516 201,289
Summary of Movement in Impairment Loss Allowances	Movement in credit impairment loss allowances: Loans secured £m Corporate £m Finance Other £m Total At 1 January 2019 234 226 85 206 751 (Release)/charge to the income statement (18 ) 30 18 78 108 Write-offs and other items (6 ) (7 ) (17 ) (69 ) (99 ) At 30 June 2019 210 249 86 215 760 At 31 December 2017 225 490 46 179 940 Adoption of IFRS 9 (1) 47 99 11 54 211 Re-allocation off-balance (1) (3 ) (25 ) — (22 ) (50 ) At 1 January 2018 269 564 57 211 1,101 (Release)/charge to the income statement (13 ) 24 17 74 102 Write-offs and other items (7 ) (318 ) (15 ) (71 ) (411 ) At 30 June 2018 249 270 59 214 792 (1) The adjustment for the adoption of IFRS 9 related to the re-measurement re-allocation off-balance

Securitisations and Covered B_2

Securitisations and Covered Bonds (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Gross Asset Securitised	The gross assets securitised, or for the covered bond programme assigned, at 30 June 2019 and 31 December 2018 were: 30 June 2019 31 December Mortgage-backed master trust structures: – Holmes 4,256 4,414 – Fosse 4,200 4,646 – Langton 2,671 3,034 11,127 12,094 Other asset-backed securitisation structures: – Motor 737 1,055 – Auto ABS UK Loans 1,358 1,468 2,095 2,523 Total securitisation programmes 13,222 14,617 Covered bond programme: – Euro 35bn Global Covered Bond Programme 23,157 21,578 Total securitisation and covered bond programmes 36,379 36,195
Summary of Issuances and Redemptions of Securitisation and Covered Bond Programme	The following table sets out the internal and external issuances and redemptions for the half year ended 30 June 2019 and the half year ended 30 June 2018 for each securitisation and covered bond programme. Internal issuances External issuances Internal External H119 H118 H119 H118 H119 H118 H119 H118 £bn £bn £bn £bn £bn £bn £bn £bn Mortgage-backed master trust structures: – Holmes — — — 1.0 — — 0.8 — – Fosse — — — — — — — 0.4 Other asset-backed securitisation structures: – Motor — — — — 0.1 0.1 0.2 — – Auto ABS UK Loans — — — — — — 0.1 — Covered bond programme — — 1.9 2.4 — 0.5 — 1.9 — — 1.9 3.4 0.1 0.6 1.1 2.3

Reverse Repurchase Agreements_2

Reverse Repurchase Agreements - Non Trading (Tables)	6 Months Ended
	Jun. 30, 2019
Reverse repurchase agreements - non-trading [member]
Statement [LineItems]
Summary of Reverse Repurchase Agreements - Non Trading	30 June 2019 31 December 2018 Agreements with banks’ 4,258 3,254 Agreements with customers 18,151 17,873 22,409 21,127

Other Financial Assets At Amo_2

Other Financial Assets At Amortised Cost (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Other Financial Assets at Amortised Cost	30 June 2019 31 December 2018 Asset backed securities 455 720 Debt securities 6,682 6,509 7,137 7,229

Financial Assets At Fair Valu_2

Financial Assets At Fair Value Through Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Financial Assets at Fair Value Through Other Comprehensive Income	30 June 2019 31 December 2018 Debt securities 13,369 13,229 Loans and advances to customers 69 73 13,438 13,302

Other Financial Liabilities a_2

Other Financial Liabilities at Fair Value Through Profit or Loss (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Other Financial Liabilities at Fair Value Through Profit or Loss	30 June 2019 31 December 2018 £m £m US$30bn Euro Medium Term Note Programme 168 165 Structured Notes Programmes 773 696 Eurobonds 131 129 Structured deposits 133 133 Collateral and associated financial guarantees 428 3,053 Repurchase agreements – non trading — 2,110 1,633 (1) 6,286 (1) (1) At 30 June 2019 and 31 December 2018 all amounts were designated at fair value through profit or loss.

Deposits by Customers (Tables)

Deposits by Customers (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Schedule of Deposits by Customers	30 June 2019 31 December 2018 £m £m Current and demand accounts 86,639 86,207 Savings accounts (1) 65,546 66,039 Time deposits 17,849 15,485 Amounts due to other Santander UK Group Holdings plc subsidiaries 56 83 Amounts due to Santander UK Group Holdings plc (2) 9,223 9,206 Amounts due to fellow Banco Santander subsidiaries and joint ventures 1,304 1,070 180,617 178,090 (1) Includes equity index-linked deposits of £1,122m (2018: £1,176m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,122m and £20m (2018: £1,176m and £28m) respectively. (2) Includes downstreamed funding from our immediate parent company Santander UK Group Holdings plc.

Deposits by Banks (Tables)

Deposits by Banks (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Schedule of Deposits by Banks	30 June 2019 31 December 2018 £m £m Items in the course of transmission 326 262 Deposits held as collateral 3,571 4,048 Other deposits (1) 12,592 12,891 Amounts due to Santander UK subsidiaries — 20 16,489 17,221 (1) Includes drawdown from the TFS of £10.8bn (2018: £10.8bn).

Repurchase Agreements - Non T_2

Repurchase Agreements - Non Trading (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Repurchase Agreements - Non Trading	30 June 2019 31 December 2018 £m £m Agreements with banks 9,619 5,865 Agreements with customers 5,152 5,045 14,771 10,910

Debt Securities in Issue (Table

Debt Securities in Issue (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Debt Securities in Issue	30 June 2019 31 December 2018 £m £m Medium-term notes 17,331 19,984 Euro 35bn Global Covered Bond Programme 19,926 18,114 Certificates of deposit 3,226 3,221 Credit linked notes — 42 Securitisation programmes 4,091 5,331 44,574 46,692

Provisions (Tables)

Provisions (Tables)	6 Months Ended
	Jun. 30, 2019
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Summary of Provisions Reconciliation	Conduct remediation Other FSCS and Off-balance Regulatory PPI products Bank Levy Property sheet ECL and other Total £m £m £m £m £m £m £m At 31 December 2018 246 30 45 37 56 95 509 Adoption of IFRS 16 (see Note 1) — — — 17 — — 17 At 1 January 2019 246 30 45 54 56 95 526 Additional provisions (see Note 5) 70 — — 38 — 114 222 Provisions released (see Note 5) — — (2 ) (8 ) (1 ) (7 ) (18 ) Utilisation (68 ) (1 ) (41 ) (4 ) — (69 ) (183 ) At 30 June 2019 248 29 2 80 55 133 547 At 31 December 2017 356 47 57 39 59 558 Reallocation of ECL on off-balance (1) — — — — 50 — 50 At 1 January 2018 356 47 57 39 50 59 608 Additional provisions (see Note 5) — — — 11 10 54 75 Provisions released (see Note 5) — (14 ) (4 ) — — (14 ) (32 ) Utilisation (55 ) (2 ) (37 ) (7 ) — (46 ) (147 ) At 30 June 2018 301 31 16 43 60 53 504 (1) ECL on off-balance

Retirement Benefit Plans (Table

Retirement Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Retirement Benefit Plans	The amounts recognised in the balance sheet were as follows: 30 June 2019 31 December 2018 £m £m Assets/(liabilities) Funded defined benefit pension scheme – surplus 779 842 Funded defined benefit pension scheme – deficit (213 ) (75 ) Unfunded defined benefit pension scheme (39 ) (39 ) Total net assets 527 728
Summary of Movements in the Present Value of Defined Benefit Obligations and Fair Value of Scheme Assets	Movements in the present value of defined benefit obligations and fair value of scheme assets in H119 and H118 were as follows: Half year to Half year to 30 June 2019 30 June 2018 £m £m Return on plan assets (excluding amounts included in net interest expense) (916 ) 72 Actuarial (gains)/losses arising from experience adjustments (5 ) 39 Actuarial losses/(gains) arising from changes in financial assumptions 1,201 (640 ) Pension remeasurement 280 (529 )
Summary of Net Assets Recognised	The net assets recognised in the balance sheet were determined as follows: 30 June 2019 31 December 2018 £m £m Present value of defined benefit obligations (11,980 ) (10,804 ) Fair value of scheme assets 12,507 11,532 Net defined benefit assets 527 728

Contingent Liabilities And Co_2

Contingent Liabilities And Commitments (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Contingent Liabilities and Commitments	30 June 2019 31 December 2018 £m £m Guarantees given to third parties 1,055 1,610 Formal standby facilities, credit lines and other commitments 41,851 40,111 42,906 41,721

Other Equity Instruments (Table

Other Equity Instruments (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of other equity instruments	Interest rate Next call date 30 June 2019 31 December 2018 £300m Step-up 7.037 February 2026 235 235 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 750 750 – £300m Fixed Rate Reset Perpetual AT1 Capital Securities 7.60 December 2019 300 300 – £500m Fixed Rate Reset Perpetual AT1 Capital Securities 5.18 September 2019 210 210 1,991 1,991

Non-Controlling Interests (Tabl

Non-Controlling Interests (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Schedule of Amounts Attributable to Non-Controlling Interests	30 June 2019 31 December 2018 £m £m PSA Finance UK Limited 159 151 159 151

Financial Instruments (Tables)

Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Fair Values of Financial Instruments Carried at Amortised Cost	30 June 2019 31 December 2018 Fair value Carrying value Fair value Carrying value Assets Loans and advances to customers 207,080 202,516 204,061 201,289 Loans and advances to banks 2,065 2,065 2,799 2,799 Reverse repurchase agreements- non trading 22,416 22,409 21,130 21,127 Other financial assets at amortised cost 7,168 7,137 7,111 7,229 238,729 234,127 235,101 232,444 Liabilities Deposits by customers 180,777 180,617 178,181 178,090 Deposits by banks 16,500 16,489 17,232 17,221 Repurchase agreements- non trading 14,779 14,771 10,923 10,910 Debt securities in issue 45,664 44,574 47,787 46,692 Subordinated liabilities 4,235 3,645 3,877 3,601 261,955 260,096 258,000 256,514
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 2019 and 31 December 2018, analysed by their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. 30 June 2019 31 December 2018 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 Derivatives Exchange rate contracts — 4,402 22 4,424 — 4,323 25 4,348 A Interest rate contracts — 2,005 5 2,010 — 2,526 6 2,532 A & C Equity and credit contracts — 210 62 272 — 188 63 251 B & D Netting — (1,261 ) — (1,261 ) — (1,872 ) — (1,872 ) — 5,356 89 5,445 — 5,165 94 5,259 Other financial assets at FVTPL Loans and advances to customers — — 94 94 — 12 82 94 A Debt securities 17 72 562 651 18 2,339 894 3,251 A, B & D Reverse repurchase agreements – non trading — — — — — 2,272 — 2,272 A 17 72 656 745 18 4,623 976 5,617 Financial assets at FVOCI Debt securities 12,781 588 — 13,369 12,487 742 — 13,229 D Loans and advances to customers — — 69 69 — — 73 73 D 12,781 588 69 13,438 12,487 742 73 13,302 Total assets at fair value 12,798 6,016 814 19,628 12,505 10,530 1,143 24,178 Liabilities Derivatives Exchange rate contracts — 926 1 927 — 528 23 551 A Interest rate contracts — 1,951 8 1,959 — 2,515 7 2,522 A & C Equity and credit contracts — 121 29 150 — 132 36 168 B & D Netting — (1,261 ) — (1,261 ) — (1,872 ) — (1,872 ) — 1,737 38 1,775 — 1,303 66 1,369 Other financial liabilities at FVTPL Debt securities in issue — 1,065 7 1,072 — 983 7 990 A Structured deposits — 104 29 133 — 104 29 133 A Repurchase agreements – non trading — — — — — 2,110 — 2,110 A Collateral and associated financial guarantees — 407 21 428 — 3,040 13 3,053 D — 1,576 57 1,633 — 6,237 49 6,286 Total liabilities at fair value — 3,313 95 3,408 — 7,540 115 7,655
Summary of Fair Value Adjustment	The magnitude and types of fair value adjustment are listed in the following table: 30 June 2019 31 December 2018 £m £m Risk-related: – Bid-offer 17 13 – Uncertainty 37 36 – Credit risk adjustment 8 9 – Funding fair value adjustment 5 4 67 62 Model-related 1 5 68 67
Movement of Assets and Liabilities Measured at Fair Value Using Valuation Technique With Significant Unobservable Inputs (Level 3)	The following table sets out the movements in Level 3 financial instruments in H119 and H118: Assets Liabilities Other Other financial Financial Assets financial Liabilities assets at assets at Financial held liabilities at held Derivatives FVTPL FVOCI investments for sale Total Derivatives FVTPL for sale Total £m £m £m £m £m £m £m £m £m £m At 1 January 2019 94 976 73 — 1,143 (66 ) (49 ) — (115 ) Total gains/(losses) recognised in profit or loss: – Fair value movements 7 1 — — 8 (3 ) (5 ) — (8 ) – Foreign exchange/other movements — 3 — — 3 — (3 ) — (3 ) Transfers in — 11 — — 11 — — — — Additions 3 188 — — 191 — (2 ) — (2 ) Settlements (15 ) (523 ) (4 ) — (542 ) 31 2 — 33 At 30 June 2019 89 656 69 — 814 (38 ) (57 ) — (95 ) Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the period 7 4 — — 11 (3 ) (8 ) — (11 ) At 31 December 2017 64 240 53 — 357 (63 ) (6 ) — (69 ) Adoption of IFRS 9 — 598 199 (53 ) — 744 — — — — At 1 January 2018 64 838 199 — 1,101 (63 ) (6 ) — (69 ) Total gains/(losses) recognised in profit or loss: – Fair value movements 26 (5 ) (4 ) — 17 4 — — 4 – Foreign exchange/other movements (5 ) — — — (5 ) 5 — — 5 Transfers in — 19 — — 19 — — — — Transfer to held for sale (2 ) (146 ) — 148 — 1 — (1 ) — Additions — — 17 — 17 — — — — Sales — (23 ) — — (23 ) — — — — Settlements (21 ) — (37 ) — (58 ) 15 — — 15 At 30 June 2018 62 683 175 148 1,068 (38 ) (6 ) (1 ) (45 ) Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period 21 (5 ) (4 ) 12 9 — — 9

Accounting Policies - Additiona

Accounting Policies - Additional information (Detail) - GBP (£) £ in Millions	Jan. 01, 2019	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Disclosure of changes in accounting estimates [line items]
Other assets		£ 3,919		£ 2,280
Other liabilities		3,904		2,448
Provisions		547	£ 504	509	£ 558
Amendment to IAS 12 impact on income statement		21	23
Expected credit losses allowance		817		807
Additional provisions		222	£ 75
Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of changes in accounting estimates [line items]
Expected credit losses allowance		801		789
Corporate and investment banking [member]
Disclosure of changes in accounting estimates [line items]
Expected credit losses allowance		16		18
Payment protection insurance [member]
Disclosure of changes in accounting estimates [line items]
Provisions		248		£ 246
Additional provisions		£ 70
IFRS 16 [member]
Disclosure of changes in accounting estimates [line items]
Increase Property, plant and equipment	£ 211
Other assets	(12)
Other liabilities	182
Provisions	£ 17

Accounting Policies - Summary o

Accounting Policies - Summary of Probability Weights Applied for Each Scenario of Expected Credit Losses Allowance (Detail) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Disclosure of probability weightings of scenarios [line items]
ECL	£ 817	£ 807
Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	801	789
Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	16	18
Upside Two Scenario [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	601	554
Upside One Scenario [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	629	596
Base case scenario [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	667	648
Downside One Scenario [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	861	843
Downside Two Scenario [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	1,726	1,930
Downside [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	23	27
Upside [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	7	8
Base case [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	£ 14	£ 17

Segments - Summary of Results b

Segments - Summary of Results by Segment (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disclosure of operating segments [line items]
Net interest income/(expense)	£ 1,668	£ 1,811
Non-interest income/(expense)	453	501
Total operating income/(expense)	2,121	2,312
Operating expenses before credit impairment losses, provisions and charges	(1,257)	(1,283)
Credit impairment (losses)/releases	(69)	(91)
Provisions for other liabilities and charges	(206)	(33)
Total operating credit impairment losses, provisions and (charges)/releases	(275)	(124)
Profit before tax	589	905
Revenue from external customers	2,121	2,312
Inter-segment revenue	2,121	2,312
Total operating income/(expense)	2,121	2,312
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Current account and debit card fees	374	338
- Insurance, protection and investments	37	46
- Credit cards	42	45
- Non-banking and other fees	86	155
Total fee and commission income	539	584
Fee and commission expense	(204)	(204)
Net fee and commission income	335	380
Customer loans	200,358		£ 199,586
Total assets	284,527		283,372
Customer deposits	169,749		167,315
Total liabilities	268,463		267,463
Retail banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	1,465	1,565
Non-interest income/(expense)	353	304
Total operating income/(expense)	1,818	1,869
Operating expenses before credit impairment losses, provisions and charges	(1,011)	(957)
Credit impairment (losses)/releases	(63)	(52)
Provisions for other liabilities and charges	(95)	(34)
Total operating credit impairment losses, provisions and (charges)/releases	(158)	(86)
Profit before tax	649	826
Revenue from external customers	2,166	2,183
Total operating income/(expense)	1,818	1,869
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Current account and debit card fees	345	311
- Insurance, protection and investments	37	46
- Credit cards	42	45
- Non-banking and other fees	36	67
Total fee and commission income	460	469
Fee and commission expense	(184)	(183)
Net fee and commission income	276	286
Customer loans	174,590		172,747
Total assets	182,785		179,572
Customer deposits	142,814		142,065
Total liabilities	143,788		142,839
Retail banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	(348)	(314)
Corporate and commercial banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	189	202
Non-interest income/(expense)	38	40
Total operating income/(expense)	227	242
Operating expenses before credit impairment losses, provisions and charges	(138)	(134)
Credit impairment (losses)/releases	(9)	(22)
Provisions for other liabilities and charges	(1)	8
Total operating credit impairment losses, provisions and (charges)/releases	(10)	(14)
Profit before tax	79	94
Revenue from external customers	281	322
Total operating income/(expense)	227	242
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Current account and debit card fees	15	13
- Non-banking and other fees	26	32
Total fee and commission income	41	45
Fee and commission expense	(12)	(13)
Net fee and commission income	29	32
Customer loans	17,365		17,702
Total assets	17,365		17,702
Customer deposits	18,021		17,606
Total liabilities	18,045		17,634
Corporate and commercial banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	(54)	(80)
Corporate and investment banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	32	33
Non-interest income/(expense)	47	115
Total operating income/(expense)	79	148
Operating expenses before credit impairment losses, provisions and charges	(83)	(145)
Credit impairment (losses)/releases	4	(18)
Provisions for other liabilities and charges	(11)	(2)
Total operating credit impairment losses, provisions and (charges)/releases	(7)	(20)
Profit before tax	(11)	(17)
Revenue from external customers	85	177
Total operating income/(expense)	79	148
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Current account and debit card fees	14	14
- Non-banking and other fees	24	50
Total fee and commission income	38	64
Fee and commission expense	(7)	(8)
Net fee and commission income	31	56
Customer loans	4,060		4,613
Total assets	4,929		8,607
Customer deposits	6,059		4,853
Total liabilities	6,946		8,885
Corporate and investment banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	(6)	(29)
Corporate centre [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	(18)	11
Non-interest income/(expense)	15	42
Total operating income/(expense)	(3)	53
Operating expenses before credit impairment losses, provisions and charges	(25)	(47)
Credit impairment (losses)/releases	(1)	1
Provisions for other liabilities and charges	(99)	(5)
Total operating credit impairment losses, provisions and (charges)/releases	(100)	(4)
Profit before tax	(128)	2
Revenue from external customers	(411)	(370)
Total operating income/(expense)	(3)	53
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Non-banking and other fees		6
Total fee and commission income		6
Fee and commission expense	(1)
Net fee and commission income	(1)	6
Customer loans	4,343		4,524
Total assets	79,448		77,491
Customer deposits	2,855		2,791
Total liabilities	99,684		£ 98,105
Corporate centre [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ 408	£ 423

Net Trading and Other Income -

Net Trading and Other Income - Summary of Net Trading and Other Income (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Net Trading And Other Income [abstract]
Net trading and other income	£ 118	£ 121

Net Trading and Other Income _2

Net Trading and Other Income - Additional Information (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2019GBP (£)
Vocalink Holdings Limited [member]
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, 2019	Jun. 30, 2018
Expenses by nature [abstract]
Staff costs	£ 641	£ 691
Other administration expenses	356	411
Depreciation, amortisation and impairment	260	181
Total operating expenses before impairment losses, provisions and charges	£ 1,257	£ 1,283

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, 2019	Jun. 30, 2018
Disclosure of credit impairment loss and provisions [abstract]
Loans and advances to customers (See Note 10)	£ 108	£ 102
Recoveries of loans and advances, net of collection costs	(38)	(21)
Off-balance sheet exposures (See Note 21)	(1)	10
Impairment loss on financial assets	69	91
Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 21)	205	33
Provisions for residual value (RV) and voluntary termination (See Note 10)	1
Provisions for other liabilities and charges	206	33
Total operating impairment losses, provisions and charges	£ 275	£ 124

Credit Impairment Losses and _4

Credit Impairment Losses and Provisions - Additional Information (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2019GBP (£)
Disclosure of credit impairment loss and provisions [abstract]
Impairment losses on loans and advances to banks	£ 0
Impairment losses on Non-trading reverse repurchase agreements	0
Impairment losses on other financial assets at amortised cost	0
Impairment losses on financial assets at FVOCI	£ 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, 2019	Jun. 30, 2018
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]
Profit before tax	£ 589	£ 905
Tax calculated at a tax rate of 19% (H118: 19%)	112	172
Bank surcharge on profits	39	64
Non-deductible preference dividends paid	5	5
Non-deductible UK Bank Levy	13	13
Non-deductible conduct remediation, fines and penalties	11	(2)
Net disallowable items and non-taxable income	11	10
Tax relief on dividends in respect of other equity instruments	(21)	(23)
Adjustment to prior period provisions		(6)
Tax charge	£ 170	£ 233

Taxation - Schedule of Tax on_2

Taxation - Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]
Standard tax rate	19.00%	19.00%

Taxation - Additional Informati

Taxation - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Income Tax Expense Benefits [line items]
Effective tax rate	28.90%	25.70%
Applicable tax rate	19.00%	19.00%
Bank corporation tax surcharge	8.00%	8.00%
Banking Entities [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	27.00%	27.00%
Non-banking Entities [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	19.00%	19.00%
Finance (No.2) Act 2016 [member] | Bottom of Range [member] | Corporation Tax Rate in 2020 [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	17.00%

Dividends on Ordinary Shares -

Dividends on Ordinary Shares - Additional Information (Detail) - GBP (£) £ in Millions	Jun. 27, 2019	Jun. 18, 2019	Jun. 30, 2019	Jun. 30, 2018
Dividends On Ordinary Shares [abstract]
Interim dividends paid	£ 164		£ 164	£ 250
Interim dividends declared		£ 164	£ 164	£ 250

Derivative Financial Instrume_3

Derivative Financial Instruments - Notional Amounts and Fair Values of Derivative Financial Instruments (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of detailed information about hedges [line items]
Notional amount	£ 215,714	£ 237,771
Fair value assets	5,445	5,259
Fair value liabilities	1,775	1,369
Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount	70,371	95,630
Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	145,343	142,141
Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	93,140	89,432
Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	52,203	52,709
Exchange Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount	17,087	13,830
Exchange Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	1,542	3,010
Exchange Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	32,870	33,901
Interest Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount	50,698	79,038
Interest Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	91,598	86,422
Interest Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount	19,333	18,808
Equity and Credit Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount	2,586	2,762
Fair Value [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	5,445	5,259
Fair value liabilities	1,775	1,369
Fair Value [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	1,926	2,126
Fair value liabilities	1,144	1,624
Fair Value [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	4,780	5,005
Fair value liabilities	1,892	1,617
Fair Value [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	1,249	1,422
Fair value liabilities	1,650	1,315
Fair Value [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	3,531	3,583
Fair value liabilities	242	302
Fair Value [member] | Exchange Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	861	454
Fair value liabilities	710	351
Fair Value [member] | Exchange Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	229	357
Fair value liabilities	14
Fair Value [member] | Exchange Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	3,334	3,537
Fair value liabilities	203	200
Fair Value [member] | Interest Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	793	1,421
Fair value liabilities	284	1,105
Fair Value [member] | Interest Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	1,020	1,065
Fair value liabilities	1,636	1,315
Fair Value [member] | Interest Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	197	46
Fair value liabilities	39	102
Fair Value [member] | Equity and Credit Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	272	251
Fair value liabilities	150	168
Fair Value [member] | Netting Adjustments [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	(1,261)	(1,872)
Fair value liabilities	£ (1,261)	£ (1,872)

Derivative Financial Instrume_4

Derivative Financial Instruments - Notional Amounts and Fair Values of Derivative Financial Instruments (Parenthetical) (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivative Assets [Member]
Disclosure of detailed information about hedges [line items]
Cash collateral received that had been offset against the gross derivative assets	£ 218	£ 9
Derivative Liabilities [Member]
Disclosure of detailed information about hedges [line items]
Cash collateral paid that had been offset against the gross derivative liabilities	£ 756	£ 354

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, 2019	Dec. 31, 2018
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	£ 745	£ 5,617
Loans and Advances to Customers [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	94	94
Loans and Advances to Customers [member] | Loans to Housing Associations [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	13	13
Loans and Advances to Customers [member] | Other Loans [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	81	81
Debt Securities [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	£ 651	3,251
Reverse repurchase agreements - non-trading [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans		£ 2,272

Other Financial Assets at Fai_4

Other Financial Assets at Fair Value Through Profit or Loss - Summary of Other Financial Assets at Fair Value Through Profit or Loss (Parenthetical) (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financial assets at fair value through profit or loss [abstract]
Financial assets designated at FVTPL	£ 13	£ 1,095
Financial assets mandatorily at FVTPL	£ 732	£ 4,522

Other Financial Assets at Fai_5

Other Financial Assets at Fair Value Through Profit or Loss - Additional Information (Detail) £ in Billions	6 Months Ended
	Jun. 30, 2019GBP (£)
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Senior tranches of credit linked notes netted against senior cash deposits	£ 1.8
Debt Securities [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Senior credit linked notes presented on a net basis	£ 2.1

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, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Net Loans and Advances to Customers [abstract]
Loans and advances to customers	£ 201,016	£ 200,095
Amounts due from fellow Banco Santander subsidiaries and joint ventures	2,329	2,014
Loans and advances to customers	203,345	202,109
Credit impairment loss allowances on loans and advances to customers	(760)	(751)	£ (792)	£ (940)
RV and voluntary termination provisions on finance leases	(69)	(69)
Net loans and advances to customers	£ 202,516	£ 201,289

Loans and Advances to Custome_4

Loans and Advances to Customers - Summary of Movement in Impairment Loss Allowances (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	£ 751	£ 940
Adoption of IFRS 9		211
Re-allocation of expected credit losses (ECL) on off-balance sheet exposures		(50)
Balance at 1 January 2018		1,101
(Release)/charge to the income statement	108	102
Write-offs and other items	(99)	(411)
Ending Balance	760	792
Advances Secured on Residential Property [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	234	225
Adoption of IFRS 9		47
Re-allocation of expected credit losses (ECL) on off-balance sheet exposures		(3)
Balance at 1 January 2018		269
(Release)/charge to the income statement	(18)	(13)
Write-offs and other items	(6)	(7)
Ending Balance	210	249
Corporate Loans [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	226	490
Adoption of IFRS 9		99
Re-allocation of expected credit losses (ECL) on off-balance sheet exposures		(25)
Balance at 1 January 2018		564
(Release)/charge to the income statement	30	24
Write-offs and other items	(7)	(318)
Ending Balance	249	270
Finance leases [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	85	46
Adoption of IFRS 9		11
Balance at 1 January 2018		57
(Release)/charge to the income statement	18	17
Write-offs and other items	(17)	(15)
Ending Balance	86	59
Other Unsecured Advances [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning Balance	206	179
Adoption of IFRS 9		54
Re-allocation of expected credit losses (ECL) on off-balance sheet exposures		(22)
Balance at 1 January 2018		211
(Release)/charge to the income statement	78	74
Write-offs and other items	(69)	(71)
Ending Balance	£ 215	£ 214

Securitisations and Covered B_3

Securitisations and Covered Bonds - Summary of Gross Asset Securitised (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	£ 36,379	£ 36,195
Securitisation Programmes [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	13,222	14,617
Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	11,127	12,094
Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	2,095	2,523
Holmes [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	4,256	4,414
Fosse [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	4,200	4,646
Langton [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	2,671	3,034
Motor [member] | Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	737	1,055
Auto ABS UK Loans [member] | Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	1,358	1,468
Euro 35bn Global Covered Bond Programme [member] | Covered Bond Programme [member]
Disclosure of securitisations and covered bonds [line items]
Gross asset securitised	£ 23,157	£ 21,578

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, 2019	Jun. 30, 2018
Internal [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions	£ 0.1	£ 0.6
Internal [member] | Other Securitisation Structures [member] | Motor [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions	0.1	0.1
Internal [member] | Covered Bond Programme [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions		0.5
External [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	1.9	3.4
Internal and external redemptions	1.1	2.3
External [member] | Master Trust Structures [member] | Holmes [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances		1
Internal and external redemptions	0.8
External [member] | Master Trust Structures [member] | Fosse [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions		0.4
External [member] | Other Securitisation Structures [member] | Motor [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions	0.2
External [member] | Other Securitisation Structures [member] | Auto ABS UK Loans [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions	0.1
External [member] | Covered Bond Programme [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	£ 1.9	2.4
Internal and external redemptions		£ 1.9

Reverse Repurchase Agreements_3

Reverse Repurchase Agreements - Non Trading - Summary of Reverse Repurchase Agreements - Non Trading (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	£ 22,409	£ 21,127
Agreements with banks [member]
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	4,258	3,254
Agreements with customers [member]
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	£ 18,151	£ 17,873

Other Financial Assets At Amo_3

Other Financial Assets At Amortised Cost - Summary of Other Financial Assets at Amortised Cost (Detail) - Other Financial Assets [member] - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financial assets at amortised cost [line items]
Financial assets at amortised cost	£ 7,137	£ 7,229
Asset backed securities [member]
Financial assets at amortised cost [line items]
Financial assets at amortised cost	455	720
Debt Securities [member]
Financial assets at amortised cost [line items]
Financial assets at amortised cost	£ 6,682	£ 6,509

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, 2019	Dec. 31, 2018
Financial assets at fair value through other comprehensive income [abstract]
Debt securities	£ 13,369	£ 13,229
Loans and advances to customers	69	73
Financial assets at fair value through other comprehensive income	£ 13,438	£ 13,302

Interests In Other Entities - I

Interests In Other Entities - Interests in Unconsolidated Structured Entities - Additional Information (Detail) £ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019GBP (£)	Dec. 31, 2018GBP (£)
Disclosure of information about unconsolidated subsidiaries [line items]
Number of credit protection vehicles	4	3
Senior Credit Linked Notes issued	£ 4,786	£ 3,053
Junior Credit Linked Notes issued	766	408
Other financial assets at fair value through profit loss [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Senior Credit Linked Notes issued	£ 194	£ 3,053

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) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	£ 1,633	£ 6,286
US$30bn Euro Medium Term Note Programme [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	168	165
Structured Notes Programmes [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	773	696
Eurobonds [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	131	129
Structured Deposits [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	133	133
Collateral and associated financial guarantees [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	£ 428	3,053
Repurchase agreements - non trading [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss		£ 2,110

Other Financial Liabilities a_4

Other Financial Liabilities at Fair Value Through Profit or Loss - Additional Information (Detail) £ in Billions	6 Months Ended
	Jun. 30, 2019GBP (£)
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Senior cash deposits netted against senior credit linked notes	£ 1.8
Collateral and associated financial guarantees [Member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Senior cash deposits presented on a net basis	£ 2.1

Deposits by Customers - Schedul

Deposits by Customers - Schedule of Deposits by Customers (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of deposits from customers [line items]
Deposits from customers	£ 180,617	£ 178,090
Current and Demand Accounts [Member]
Disclosure of deposits from customers [line items]
Deposits from customers	86,639	86,207
Savings Accounts [member]
Disclosure of deposits from customers [line items]
Deposits from customers	65,546	66,039
Time Deposits [member]
Disclosure of deposits from customers [line items]
Deposits from customers	17,849	15,485
Amounts due to other Santander UK Group Holdings plc subsidiaries [member]
Disclosure of deposits from customers [line items]
Deposits from customers	56	83
Amounts due to Santander UK Group Holdings plc [member]
Disclosure of deposits from customers [line items]
Deposits from customers	9,223	9,206
Amounts Due to Fellow Banco Santander Subsidiaries and Joint Ventures [member]
Disclosure of deposits from customers [line items]
Deposits from customers	£ 1,304	£ 1,070

Deposits by Customers - Sched_2

Deposits by Customers - Schedule of Deposits by Customers (Parenthetical) (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of deposits from customers [line items]
Deposits from customers	£ 180,617	£ 178,090
Equity Index Linked Deposits [member]
Disclosure of deposits from customers [line items]
Deposits from customers	1,122	1,176
Capital amount guaranteed or protected	1,122	1,176
Capital amount of return guaranteed	£ 20	£ 28

Deposits by Banks - Schedule of

Deposits by Banks - Schedule of Deposits by Banks (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of deposits from banks [line items]
Deposits from banks	£ 16,489	£ 17,221
Items in Course of Transmission [member]
Disclosure of deposits from banks [line items]
Deposits from banks	326	262
Deposits Held as Collateral [member]
Disclosure of deposits from banks [line items]
Deposits from banks	3,571	4,048
Other Deposits [member]
Disclosure of deposits from banks [line items]
Deposits from banks	£ 12,592	12,891
Amounts due to Santander UK subsidiaries [member]
Disclosure of deposits from banks [line items]
Deposits from banks		£ 20

Deposits by Banks - Schedule _2

Deposits by Banks - Schedule of Deposits by Banks (Parenthetical) (Detail) - GBP (£) £ in Billions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of deposits from banks [abstract]
Drawdown from TFS	£ 10.8	£ 10.8

Repurchase Agreements - Non T_3

Repurchase Agreements - Non Trading - Summary of Repurchase Agreements Non Trading (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements - non trading	£ 14,771	£ 10,910
Agreements with banks [member]
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements - non trading	9,619	5,865
Agreements with customers [member]
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements - non trading	£ 5,152	£ 5,045

Debt Securities In Issue - Summ

Debt Securities In Issue - Summary of Debt Securities in Issue (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt securities in issue [line items]
Debt Securities	£ 44,574	£ 46,692
Medium Term Notes [member]
Debt securities in issue [line items]
Debt Securities	17,331	19,984
Euro 35bn Global Covered Bond Programme [member]
Debt securities in issue [line items]
Debt Securities	19,926	18,114
Certificates of Deposit [member]
Debt securities in issue [line items]
Debt Securities	3,226	3,221
Credit Linked Note [member]
Debt securities in issue [line items]
Credit linked notes		42
Securitisation Programmes [member]
Debt securities in issue [line items]
Debt Securities	£ 4,091	£ 5,331

Provisions - Summary of Provisi

Provisions - Summary of Provisions Reconciliation (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Disclosure of other provisions [line items]
Beginning balance	£ 509	£ 558
Adoption of IFRS 16	17
Reallocation of ECL on off-balance sheet exposures		50
Balance on January 1 2018	526	608
Additional provisions	222	75
Provisions released	(18)	(32)
Utilisation	(183)	(147)
Ending balance	547	504
PPI [member]
Disclosure of other provisions [line items]
Beginning balance	246	356
Balance on January 1 2018	246	356
Additional provisions	70
Utilisation	(68)	(55)
Ending balance	248	301
Other products [member]
Disclosure of other provisions [line items]
Beginning balance	30	47
Balance on January 1 2018	30	47
Provisions released		(14)
Utilisation	(1)	(2)
Ending balance	29	31
FSCS and Bank Levy [member]
Disclosure of other provisions [line items]
Beginning balance	45	57
Balance on January 1 2018	45	57
Provisions released	(2)	(4)
Utilisation	(41)	(37)
Ending balance	2	16
Property [Member]
Disclosure of other provisions [line items]
Beginning balance	37	39
Adoption of IFRS 16	17
Balance on January 1 2018	54	39
Additional provisions	38	11
Provisions released	(8)
Utilisation	(4)	(7)
Ending balance	80	43
Off Balance Sheet Expected Credit Losses [member]
Disclosure of other provisions [line items]
Beginning balance	56
Reallocation of ECL on off-balance sheet exposures		50
Balance on January 1 2018	56	50
Additional provisions		10
Provisions released	(1)
Ending balance	55	60
Regulatory other provisions [member]
Disclosure of other provisions [line items]
Beginning balance	95	59
Balance on January 1 2018	95	59
Additional provisions	114	54
Provisions released	(7)	(14)
Utilisation	(69)	(46)
Ending balance	£ 133	£ 53

Provisions - Additional Informa

Provisions - Additional Information (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2019GBP (£)ComplaintsClaims	Jun. 30, 2018GBP (£)	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)
Disclosure of other provisions [line items]
Provisions	£ 547	£ 504	£ 509	£ 558
Additional provision charge	222	75
PPI [member]
Disclosure of other provisions [line items]
Provisions	248	301	246	356
Additional provision charge	£ 70
PPI [member] | Inbound Complaints [member]
Disclosure of other provisions [line items]
Additional inbound PPI complaints | Complaints	25,000
Future expected PPI claims | Claims	311,000
Future expected additional PPI charge	£ 6.9
Regulatory other provisions [member]
Disclosure of other provisions [line items]
Provisions	133	53	95	59
Additional provision charge	114	54
Transformation charge	62
Property [Member]
Disclosure of other provisions [line items]
Provisions	80	43	£ 37	£ 39
Additional provision charge	38	£ 11
Transformation charge	£ 38

Retirement Benefit Plans - Summ

Retirement Benefit Plans - Summary of Retirement Benefit Plans (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Assets/(liabilities)
Total net assets	£ 527	£ 728
Santander UK Group [member]
Assets/(liabilities)
Total net assets	527	728
Santander UK Group [member] | Unfunded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	(39)	(39)
Santander UK Group [member] | Surplus [member] | Funded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	779	842
Santander UK Group [member] | Deficit [member] | Funded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	£ (213)	£ (75)

Retirement Benefit Plans - Addi

Retirement Benefit Plans - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Disclosure of defined benefit plans [abstract]
Defined contribution expense	£ 34	£ 23
Key management personnel expense	None	None
Total amount charged to the income statement	£ 10	£ 22

Retirement Benefit Plans - Su_2

Retirement Benefit Plans - Summary of Composition and Fair Value of Plan Assets (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Disclosure of net defined benefit liability (asset) [abstract]
Return on plan assets (excluding amounts included in net interest expense)	£ (916)	£ 72
Actuarial (gains)/losses arising from experience adjustments	(5)	39
Actuarial losses/(gains) arising from changes in financial assumptions	1,201	(640)
Pension remeasurement	£ 280	£ (529)

Retirement Benefit Plans - Su_3

Retirement Benefit Plans - Summary of Net Assets Recognised (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of net defined benefit liability (asset) [abstract]
Present value of defined benefit obligations	£ (11,980)	£ (10,804)
Fair value of scheme assets	12,507	11,532
Net defined benefit assets	£ 527	£ 728

Contingent Liabilities and Co_3

Contingent Liabilities and Commitments - Summary of Contingent Liabilities and Commitments (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of contingent liabilities and commitments [line items]
Guarantees and formal standby facilities, credit lines and other commitments	£ 42,906	£ 41,721
Contingent Liability for Guarantees [Member]
Disclosure of contingent liabilities and commitments [line items]
Guarantees given to third parties	1,055	1,610
Loan commitments [member]
Disclosure of contingent liabilities and commitments [line items]
Formal standby facilities, credit lines and other commitments	£ 41,851	£ 40,111

Contingent Liabilities and Co_4

Contingent Liabilities and Commitments - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Compliance with Consumer Credit Act [member]
Disclosure of contingent liabilities and commitments [line items]
Additional operational risk losses and restructuring charges	£ 58

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, 2019	Dec. 31, 2018
Disclosure of assets pledged as security [line items]
Gross assets charged as security for liabilities	£ 36,379	£ 36,195
Internally Retained [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Notes issued under securitisation and covered bond programmes retained internally	3,939	4,039
Third Party Bilateral Secured Funding Transactions [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	1,834	1,834
Santander UK Plc [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Gross assets charged as security for liabilities	36,379	36,195
Santander UK Plc [member] | Internally Retained [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Internally retained securitisation and covered bond issuances available for creating collateral	£ 439	£ 501

Other Equity Instruments - Summ

Other Equity Instruments - Summary of Other Equity Instruments (Detail) - GBP (£) £ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Disclosure of other equity instruments [line items]
Other equity instruments	£ 1,991	£ 1,991
300m Step-up Callable Perpetual Reserve Capital Instruments [member]
Disclosure of other equity instruments [line items]
Interest rate	7.037%
Next call date	2026-02
Other equity instruments	£ 235	235
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Interest rate	6.75%
Next call date	2024-06
Other equity instruments	£ 496	496
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Interest rate	7.375%
Next call date	2022-06
Other equity instruments	£ 750	750
300m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Interest rate	7.60%
Next call date	2019-12
Other equity instruments	£ 300	300
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Interest rate	5.18%
Next call date	2019-09
Other equity instruments	£ 210	£ 210

Other Equity Instruments - Su_2

Other Equity Instruments - Summary of Other Equity Instruments (Parenthetical) (Detail) £ in Millions	6 Months Ended
	Jun. 30, 2019GBP (£)
300m Step-up Callable Perpetual Reserve Capital Instruments [member]
Disclosure of other equity instruments [line items]
Capital securities	£ 300
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	500
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	750
300m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	300
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	£ 500

Non-Controlling Interests - Sch

Non-Controlling Interests - Schedule of Amounts Attributable to Non-Controlling Interests (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure of noncontrolling interests [line items]
Non-controlling interests	£ 159	£ 151
PSA Finance UK Limited [member]
Disclosure of noncontrolling interests [line items]
Non-controlling interests	£ 159	£ 151

Financial Instruments - Analysi

Financial Instruments - Analysis of Fair Value of Financial Instruments Carried at Amortised (Detail) - GBP (£) £ in Millions	Jun. 30, 2019	Dec. 31, 2018
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	£ 202,516	£ 201,289
Loans and advances to banks	2,065	2,799
Reverse repurchase agreements - non trading	22,409	21,127
Deposits by customers	180,617	178,090
Deposits by banks	16,489	17,221
Repurchase agreements - non trading	14,771	10,910
Debt securities in issue	44,574	46,692
Subordinated liabilities	3,645	3,601
Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Carrying value	234,127	232,444
Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Carrying value	260,096	256,514
Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by customers	180,617	178,090
Deposits by Banks [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by banks	16,489	17,221
Repurchase agreements - non trading [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements - non trading	14,771	10,910
Debt Securities [Member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Debt securities in issue	44,574	46,692
Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	3,645	3,601
Loans and Advances to Customers [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	202,516	201,289
Loans and Advances to Banks [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	2,065	2,799
Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	22,409	21,127
Other financial assets at amortised cost [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	7,137	7,229
Fair Value [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Carrying value	238,729	235,101
Fair Value [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Carrying value	261,955	258,000
Fair Value [member] | Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by customers	180,777	178,181
Fair Value [member] | Deposits by Banks [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by banks	16,500	17,232
Fair Value [member] | Repurchase agreements - non trading [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements - non trading	14,779	10,923
Fair Value [member] | Debt Securities [Member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Debt securities in issue	45,664	47,787
Fair Value [member] | Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [Member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	4,235	3,877
Fair Value [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	207,080	204,061
Fair Value [member] | Loans and Advances to Banks [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	2,065	2,799
Fair Value [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	22,416	21,130
Fair Value [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost, class [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	£ 7,168	£ 7,111

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, 2019	Dec. 31, 2018
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 19,628	£ 24,178
Liabilities at fair value	3,408	7,655
Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,775	1,369
Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,633	6,286
Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	5,445	5,259
Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	745	5,617
Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	13,438	13,302
Level 1 [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	12,798	12,505
Level 1 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	17	18
Level 1 [Member] | Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	12,781	12,487
Level 2 [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	6,016	10,530
Liabilities at fair value	3,313	7,540
Level 2 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,737	1,303
Level 2 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,576	6,237
Level 2 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	5,356	5,165
Level 2 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	72	4,623
Level 2 [Member] | Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	588	742
Level 3 [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	814	1,143
Liabilities at fair value	95	115
Level 3 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	38	66
Level 3 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	57	49
Level 3 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	89	94
Level 3 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	656	976
Level 3 [Member] | Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	69	73
Debt Securities [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 651	3,251
Valuation technique	A, B & D
Debt Securities [member] | Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 13,369	13,229
Valuation technique	D
Debt Securities [member] | Level 1 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 17	18
Debt Securities [member] | Level 1 [Member] | Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	12,781	12,487
Debt Securities [member] | Level 2 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	72	2,339
Debt Securities [member] | Level 2 [Member] | Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	588	742
Debt Securities [member] | Level 3 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 562	894
Exchange Rate Contracts [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 927	551
Exchange Rate Contracts [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 4,424	4,348
Valuation technique	A
Exchange Rate Contracts [Member] | Level 2 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 926	528
Exchange Rate Contracts [Member] | Level 2 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	4,402	4,323
Exchange Rate Contracts [Member] | Level 3 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1	23
Exchange Rate Contracts [Member] | Level 3 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 22	25
Interest Rate Contracts [member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A & C
Liabilities at fair value	£ 1,959	2,522
Interest Rate Contracts [member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 2,010	2,532
Valuation technique	A & C
Interest Rate Contracts [member] | Level 2 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 1,951	2,515
Interest Rate Contracts [member] | Level 2 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	2,005	2,526
Interest Rate Contracts [member] | Level 3 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	8	7
Interest Rate Contracts [member] | Level 3 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 5	6
Equity and Credit Contracts [member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	B & D
Liabilities at fair value	£ 150	168
Equity and Credit Contracts [member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 272	251
Valuation technique	B & D
Equity and Credit Contracts [member] | Level 2 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 121	132
Equity and Credit Contracts [member] | Level 2 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	210	188
Equity and Credit Contracts [member] | Level 3 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	29	36
Equity and Credit Contracts [member] | Level 3 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	62	63
Netting [member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	(1,261)	(1,872)
Netting [member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	(1,261)	(1,872)
Netting [member] | Level 2 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	(1,261)	(1,872)
Netting [member] | Level 2 [Member] | Derivative Assets [Member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	(1,261)	(1,872)
Loans and Advances to Customers [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 94	94
Valuation technique	A
Loans and Advances to Customers [member] | Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 69	73
Valuation technique	D
Loans and Advances to Customers [member] | Level 2 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value		12
Loans and Advances to Customers [member] | Level 3 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 94	82
Loans and Advances to Customers [member] | Level 3 [Member] | Financial assets at fair value through other comprehensive income, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 69	73
Reverse repurchase agreements - non-trading [member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value		2,110
Reverse repurchase agreements - non-trading [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value		2,272
Valuation technique	A
Reverse repurchase agreements - non-trading [member] | Level 2 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value		2,110
Reverse repurchase agreements - non-trading [member] | Level 2 [Member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value		2,272
Debt Securities [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 1,072	990
Debt Securities [Member] | Level 2 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,065	983
Debt Securities [Member] | Level 3 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 7	7
Structured Deposits [member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 133	133
Structured Deposits [member] | Level 2 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	104	104
Structured Deposits [member] | Level 3 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 29	29
Collateral and associated financial guarantees [member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	D
Liabilities at fair value	£ 428	3,053
Collateral and associated financial guarantees [member] | Level 2 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	407	3,040
Collateral and associated financial guarantees [member] | Level 3 [Member] | Other financial liabilities at fair value through profit or loss [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 21	£ 13

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Disclosure of financial assets [abstract]
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 3	0	0
Disclosure of financial liabilities [abstract]
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 3	£ 0	£ 0

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value Adjustment (Detail) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Disclosure of financial assets [line items]
Fair value adjustments	£ 68	£ 67
Bid-Offer and Trade Specific Adjustments [Member]
Disclosure of financial assets [line items]
Fair value adjustments	17	13
Uncertainty [Member]
Disclosure of financial assets [line items]
Fair value adjustments	37	36
Credit Risk Adjustment [Member]
Disclosure of financial assets [line items]
Fair value adjustments	8	9
Funding Fair Value Adjustment [Member]
Disclosure of financial assets [line items]
Fair value adjustments	5	4
Risk Related Adjustments [Member]
Disclosure of financial assets [line items]
Fair value adjustments	67	62
Model-Related [Member]
Disclosure of financial assets [line items]
Fair value adjustments	£ 1	£ 5

Financial Instruments - Liabili

Financial Instruments - Liabilities Reconciliation of Fair Value Measurements in Level 3 of the Fair Value Hierarchy (Detail) - GBP (£) £ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	£ (267,463)
Transfers in	0		£ 0
Ending Balance	(268,463)		(267,463)
Level 3 [Member] | Fair Value Through P&L [member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(49)	£ (6)	(6)
Adoption of IFRS 9		0
At 1 January 2018		(6)
Total gains/(losses) recognised in profit/loss, fair value movements	(5)
Total gains/(losses) recognised in profit/loss, foreign exchange and other movements	(3)
Transfers in	0	0
Transfer to held for sale
Additions	(2)
Sales		0
Settlements	2
Ending Balance	(57)	(6)	(49)
Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period	(8)
Level 3 [Member] | Financial Liabilities at Fair Value, Class [member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(115)	(69)	(69)
Adoption of IFRS 9		0
At 1 January 2018		(69)
Total gains/(losses) recognised in profit/loss, fair value movements	(8)	4
Total gains/(losses) recognised in profit/loss, foreign exchange and other movements	(3)	5
Transfers in	0	0
Transfer to held for sale
Additions	(2)
Sales		0
Settlements	33	15
Ending Balance	(95)	(45)	(115)
Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period	(11)	9
Level 3 [Member] | Derivative Liabilities [Member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(66)	(63)	(63)
Adoption of IFRS 9		0
At 1 January 2018		(63)
Total gains/(losses) recognised in profit/loss, fair value movements	(3)	4
Total gains/(losses) recognised in profit/loss, foreign exchange and other movements		5
Transfers in	0	0
Transfer to held for sale		1
Sales		0
Settlements	31	15
Ending Balance	(38)	(38)	£ (66)
Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period	(3)	9
Level 3 [Member] | Liabilities held for sale[member]
Disclosure of fair value measurement of liabilities [line items]
Adoption of IFRS 9		0
Transfers in	£ 0	0
Transfer to held for sale		(1)
Sales		0
Ending Balance		£ (1)

Financial Instruments - Assets

Financial Instruments - Assets Reconciliation of Fair Value Measurements in Level 3 of the Fair Value Hierarchy (Detail) - GBP (£) £ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Disclosure of fair value measurement of assets [line items]
Beginning balance	£ 283,372
Transfers in	0		£ 0
Ending Balance	284,527		283,372
Level 3 [Member]
Disclosure of fair value measurement of assets [line items]
Beginning balance	1,143	£ 357	357
Adoption of IFRS 9		744
At 1 January 2018		1,101
Total gains/(losses) recognised in profit/loss, fair value movements	8	17
Total gains/(losses) recognised in profit/loss, foreign exchange and other movements	3	(5)
Transfers in	11	19
Transfer to held for sale
Additions	191	17
Sales		(23)
Settlements	(542)	(58)
Ending Balance	814	1,068	1,143
Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period	11	12
Level 3 [Member] | Fair Value Through P&L [Member]
Disclosure of fair value measurement of assets [line items]
Beginning balance	976	240	240
Adoption of IFRS 9		598
At 1 January 2018		838
Total gains/(losses) recognised in profit/loss, fair value movements	1	(5)
Total gains/(losses) recognised in profit/loss, foreign exchange and other movements	3
Transfers in	11	19
Transfer to held for sale		(146)
Additions	188
Sales		(23)
Settlements	(523)
Ending Balance	656	683	976
Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period	4	(5)
Level 3 [Member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets [line items]
Beginning balance	73
Adoption of IFRS 9		199
At 1 January 2018		199
Total gains/(losses) recognised in profit/loss, fair value movements		(4)
Transfers in
Transfer to held for sale
Additions		17
Settlements	(4)	(37)
Ending Balance	69	175	73
Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period		(4)
Level 3 [Member] | Asset Held For Sale [member]
Disclosure of fair value measurement of assets [line items]
Transfer to held for sale		148
Ending Balance		148
Level 3 [Member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets [line items]
Beginning balance	94	64	64
At 1 January 2018		64
Total gains/(losses) recognised in profit/loss, fair value movements	7	26
Total gains/(losses) recognised in profit/loss, foreign exchange and other movements		(5)
Transfer to held for sale		(2)
Additions	3
Settlements	(15)	(21)
Ending Balance	89	62	94
Gains/(losses) recognised in profit or loss on assets and liabilities held at the end of the period	£ 7	21
Level 3 [Member] | Financial Investments [member]
Disclosure of fair value measurement of assets [line items]
Beginning balance		53	£ 53
Adoption of IFRS 9		£ (53)