National Grid (NGG) 20-F 25 Jun 20 2020 FY Annual report (foreign) Financial data

Document And Entity Information

Document And Entity Information	12 Months Ended
	Mar. 31, 2020shares
Document And Entity Information [Abstract]
Document Annual Report	true
Document Transition Report	false
Document Shell Company Report	false
Entity Registrant Name	NATIONAL GRID PLC
Entity Central Index Key	0001004315
Current Fiscal Year End Date	--03-31
Document Type	20-F
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes
Entity Common Stock, Shares Outstanding	3,780,237,016
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Accounting Standard	IFRS
Amendment Flag	false
Entity Shell Company	false

Consolidated income statement

Consolidated income statement - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Profit or loss [abstract]
Revenue	£ 14,540	£ 14,933	£ 15,250
Provision for bad and doubtful debts	(234)	(181)	(36)
Other operating costs	(11,526)	(11,882)	(11,721)
Operating profit/(loss)	2,780	2,870	3,493
Finance income	54	88	127
Finance costs	(1,167)	(1,157)	(1,009)
Share of post-tax results of joint ventures and associates	87	40	49
Profit/(loss) before tax	1,754	1,841	2,660
Tax	(480)	(339)	889
Profit/(loss) after tax from continuing operations	1,274	1,502	3,549
Profit/(loss) after tax from discontinued operations	(9)	12	2
Total profit/(loss) for the year	1,265	1,514	3,551
Attributable to:
Equity shareholders of the parent	1,264	1,511	3,550
Non-controlling interests from continuing operations	£ 1	£ 3	£ 1
Earnings per share (pence)
Basic earnings per share (continuing) (in GBP per share)	£ 0.368	£ 0.443	£ 1.025
Diluted earnings per share (continuing) (in GBP per share)	0.366	0.441	1.021
Basic earnings per share (continuing and discontinued) (in GBP per share)	0.365	0.446	1.026
Diluted earnings per share (continuing and discontinued) (in GBP per share)	£ 0.363	£ 0.444	£ 1.021

Consolidated statement of compr

Consolidated statement of comprehensive income - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of analysis of other comprehensive income by item [line items]
Profit after tax from continuing operations		£ 1,274	£ 1,502	£ 3,549
Items from continuing operations that will never be reclassified to profit or loss:
Remeasurement (losses)/gains on pension assets and post-retirement benefit obligations		(724)	68	1,313
Net losses on equity instruments designated at fair value through other comprehensive income		(9)
Net (losses)/gains on financial liability designated at fair value through profit and loss attributable to changes in own credit risk		(3)	7	0
Net losses in respect of cash flow hedging of capital expenditure		(17)	(13)	0
Tax on items that will never be reclassified to profit or loss		212	(15)	(530)
Total items from continuing operations that will never be reclassified to profit or loss		(541)	47	783
Items from continuing operations that may be reclassified subsequently to profit or loss:
Exchange adjustments		551	347	(505)
Net (losses)/gains in respect of cash flow hedges		(128)	(40)	16
Net losses in respect of cost of hedging		(78)	(66)	0
Net losses on available-for-sale investments				(30)
Transferred to profit or loss on sale of available-for-sale investments				(73)
Net (losses)/gains on investment in debt instruments measured at fair value through other comprehensive income		(15)	2	0
Share of other comprehensive (losses)/income of associates, net of tax		(5)	1	0
Tax on items that may be reclassified subsequently to profit or loss		35	12	33
Total items that may be reclassified subsequently to profit or loss		360	256	(559)
Other comprehensive income for the year, net of tax from continuing operations		(181)	303	224
Other comprehensive income for the year, net of tax from discontinued operations	[1]	6	36	147
Other comprehensive income for the year, net of tax		(175)	339	371
Total comprehensive income for the year from continuing operations		1,093	1,805	3,773
Total comprehensive income for the year from discontinued operations		(3)	48	149
Total comprehensive income for the year		1,090	1,853	3,922
Attributable to:
Comprehensive income, attributable to equity shareholders of the parent		1,088	1,849	3,922
Continuing operations
Attributable to:
Comprehensive income, attributable to equity shareholders of the parent		1,091	1,801	3,773
Comprehensive income, attributable to non-controlling interests		2	4	0
Discontinued operations
Items from continuing operations that will never be reclassified to profit or loss:
Total items from continuing operations that will never be reclassified to profit or loss		0	36	142
Items from continuing operations that may be reclassified subsequently to profit or loss:
Share of other comprehensive (losses)/income of associates, net of tax		0	0	5
Total items that may be reclassified subsequently to profit or loss		6	0	5
Other comprehensive income for the year, net of tax		6	36	147
Total comprehensive income for the year		(3)	48	149
Attributable to:
Comprehensive income, attributable to equity shareholders of the parent		£ (3)	£ 48	£ 149
[1]	The other comprehensive income from discontinued operations relates to the items of other comprehensive income of Cadent (investment through Quadgas HoldCo Limited). Refer to note 10 for details.

Consolidated statement of chang

Consolidated statement of changes in equity - GBP (£) £ in Millions		Total	Total shareholders’ equity	Share capital	Share premium account	Retained earnings	Other equity reserves	[1]	Non-controlling interests
Equity, beginning balance at Mar. 31, 2017		£ 20,384	£ 20,368	£ 449	£ 1,324	£ 22,582	£ (3,987)		£ 16
Profit for the year		3,551	3,550			3,550	0		1
Other comprehensive (loss)/income for the year		371	372			925	(553)		(1)
Total comprehensive income for the year		3,922	3,922			4,475	(553)		0
Equity dividends		(4,487)	(4,487)			(4,487)
Scrip dividend-related share issue	[2]	0	0	3	(3)
Purchase of treasury shares		(1,017)	(1,017)			(1,017)
Issue of treasury shares		33	33			33
Purchase of own shares		(5)	(5)			(5)
Share-based payments		16	16			16
Tax on share-based payments		2	2			2
Equity, ending balance at Mar. 31, 2018		18,848	18,832	452	1,321	21,599	(4,540)		16
Profit for the year		1,514	1,511			1,511	0		3
Other comprehensive (loss)/income for the year		339	338			89	249		1
Total comprehensive income for the year		1,853	1,849			1,600	249		4
Equity dividends		(1,160)	(1,160)			(1,160)
Scrip dividend-related share issue	[2]	(1)	(1)	6	(7)
Issue of treasury shares		18	18			18
Purchase of own shares		(2)	(2)			(2)
Share-based payments		27	27			27
Cash flow hedges transferred to the statement of financial position, net of tax		(18)	(18)				(18)
Equity, ending balance at Mar. 31, 2019		19,369	19,349	458	1,314	21,814	(4,237)		20
Profit for the year		1,265	1,264			1,264	0		1
Other comprehensive (loss)/income for the year		(175)	(176)			(509)	333		1
Total comprehensive income for the year		1,090	1,088			755	333		2
Equity dividends		(892)	(892)			(892)
Scrip dividend-related share issue	[2]	(1)	(1)	12	(13)
Issue of treasury shares		17	17			17
Purchase of own shares		(6)	(6)			(6)
Share-based payments		19	19			19
Tax on share-based payments		3	3			3
Cash flow hedges transferred to the statement of financial position, net of tax		(15)	(15)				(15)
Equity, ending balance at Mar. 31, 2020		£ 19,584	£ 19,562	£ 470	£ 1,301	£ 21,710	£ (3,919)		£ 22
[1]	For further details of other equity reserves, see note 28.
[2]	Included within the share premium account are costs associated with scrip dividends.

Consolidated statement of finan

Consolidated statement of financial position - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Non-current assets
Goodwill	£ 6,233	£ 5,869
Other intangible assets	1,295	1,084
Property, plant and equipment	48,770	43,913
Other non-current assets	354	264
Pension assets	1,849	1,567
Financial and other investments	543	667
Investments in joint ventures and associates	995	608
Derivative financial assets	1,249	1,045
Total non-current assets	61,288	55,017
Current assets
Inventories and current intangible assets	549	370
Trade and other receivables	2,986	3,153
Current tax assets	102	126
Financial and other investments	1,998	1,981
Derivative financial assets	93	108
Cash and cash equivalents	73	252
Assets held for sale	0	1,956
Total current assets	5,801	7,946
Total assets	67,089	62,963
Current liabilities
Borrowings	(4,072)	(4,472)
Derivative financial liabilities	(380)	(350)
Trade and other payables	(3,602)	(3,769)
Contract liabilities	(76)	(61)
Current tax liabilities	(86)	(161)
Provisions	(348)	(316)
Total current liabilities	(8,564)	(9,129)
Non-current liabilities
Borrowings	(26,722)	(24,258)
Derivative financial liabilities	(954)	(833)
Other non-current liabilities	(891)	(808)
Contract liabilities	(1,082)	(933)
Deferred tax liabilities	(4,184)	(3,965)
Pensions and other post-retirement benefit obligations	(2,802)	(1,785)
Provisions	(2,306)	(1,883)
Total non-current liabilities	(38,941)	(34,465)
Total liabilities	(47,505)	(43,594)
Net assets (liabilities)	19,584	19,369
Equity
Share capital	470	458
Share premium account	1,301	1,314
Retained earnings	21,710	21,814
Other equity reserves	(3,919)	(4,237)
Total shareholders’ equity	19,562	19,349
Non-controlling interests	22	20
Total equity	£ 19,584	£ 19,369

Consolidated cash flow statemen

Consolidated cash flow statement - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Total operating profit from continuing operations		£ 2,780	£ 2,870	£ 3,493
Adjustments for:
Depreciation, amortisation and impairment		1,640	1,725	1,530
Share-based payments		19	27	16
Changes in working capital	[1]	394	(36)	108
Changes in provisions	[1]	198	18	(206)
Changes in pensions and other post-retirement benefit obligations		(117)	(140)	(239)
Cash generated from operations – continuing operations		4,914	4,464	4,702
Tax (paid)/recovered		(199)	(75)	8
Net cash inflow from operating activities – continuing operations		4,715	4,389	4,710
Net cash used in operating activities – discontinued operations		(97)	(71)	(207)
Cash flows from investing activities
Acquisition of financial investments		(108)	(89)	(2)
Acquisition of Geronimo and Emerald		(139)	0	0
Investments in joint ventures and associates		(82)	(143)	(129)
Loans to joint ventures and associates		0	(31)	(68)
Disposal of financial investments		63	18	134
Disposal of 61% interest in UK Gas Distribution		0	0	(20)
Disposal of interests in Quadgas HoldCo Limited		1,965	0	0
Purchases of intangible assets		(317)	(306)	(173)
Purchases of property, plant and equipment		(4,583)	(3,635)	(3,738)
Disposals of property, plant and equipment		68	38	10
Dividends received from joint ventures and associates		75	68	69
Interest received		73	68	30
Net movements in short-term financial investments		7	822	5,953
Net movements in derivatives	[2]	(223)	(412)	330
Net cash flow (used in)/from investing activities – continuing operations		(3,201)	(3,602)	2,396
Net cash flow used in investing activities – discontinued operations		6	156	171
Cash flows from financing activities
Purchase of treasury shares		0	0	(1,017)
Proceeds from issue of treasury shares		16	17	33
Purchase of own shares		(6)	(2)	(5)
Proceeds received from loans		4,218	2,932	1,941
Repayment of loans		(3,253)	(1,969)	(2,156)
Payments of lease liabilities		(121)	(70)	(71)
Net movements in short-term borrowings		(424)	179	(764)
Net movements in derivatives¹	[2]	(187)	35	(267)
Interest paid		(957)	(914)	(853)
Dividends paid to shareholders		(892)	(1,160)	(4,487)
Net cash flow used in financing activities – continuing operations		(1,606)	(952)	(7,646)
Net cash flow (used in)/from financing activities – discontinued operations		0	0	(231)
Net decrease in cash and cash equivalents		(183)	(80)	(807)
Exchange movements		4	3	(3)
Cash and cash equivalents, beginning balance		252	329	1,139
Cash and cash equivalents, ending balance		£ 73	£ 252	£ 329
[1]	For 2020, we have ceased to present exceptional items and remeasurements separately on the face of the consolidated income statement. For the purposes of presenting the consolidated cash flow statement, we accordingly no longer present either a non-cash adjustment to add back exceptional items and remeasurements, or cash flows relating to operating exceptional items as a separate line item. For the purposes of re-presenting comparative cash flow financial information on a comparable basis, we have accordingly reclassified amounts previously disclosed within these categories as follows: 2019: Net impact of cash flows relating to exceptional items of £172 million: comprising a £137 million increase in depreciation, amortisation and impairment, a £76 million decrease to changes in working capital, a £128 million increase in changes in provisions and a £17 million decrease in pensions and other post-retirement obligations. 2018: Net impact of cash flows relating to exceptional items of £10 million: reflected as a £10 million decrease to changes in working capital.
[2]	Certain derivative balances have been represented for all periods presented to reflect a reclassification from financing activities to investing activities to reflect a change in accounting policy (see note 1 for details).

Consolidated cash flow statem_2

Consolidated cash flow statement (Parenthetical) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Disclosure of reclassifications or changes in presentation [line items]
Impact on depreciation, amortisation and impairment		£ 1,725	£ 1,530
Impact on changes in working capital	[1]	36	(108)
Impact on changes in provisions	[1]	18	(206)
Impact on changes in pensions and other post-retirement benefit obligations		(140)	(239)
Reclassification of exceptional items and remeasurements within the statement of cash flows [member]
Disclosure of reclassifications or changes in presentation [line items]
Net impact of cash flows relating to exceptional items		172	(10)
Impact on depreciation, amortisation and impairment		137
Impact on changes in working capital		76	£ 10
Impact on changes in provisions		128
Impact on changes in pensions and other post-retirement benefit obligations		£ (17)
[1]	For 2020, we have ceased to present exceptional items and remeasurements separately on the face of the consolidated income statement. For the purposes of presenting the consolidated cash flow statement, we accordingly no longer present either a non-cash adjustment to add back exceptional items and remeasurements, or cash flows relating to operating exceptional items as a separate line item. For the purposes of re-presenting comparative cash flow financial information on a comparable basis, we have accordingly reclassified amounts previously disclosed within these categories as follows: 2019: Net impact of cash flows relating to exceptional items of £172 million: comprising a £137 million increase in depreciation, amortisation and impairment, a £76 million decrease to changes in working capital, a £128 million increase in changes in provisions and a £17 million decrease in pensions and other post-retirement obligations. 2018: Net impact of cash flows relating to exceptional items of £10 million: reflected as a £10 million decrease to changes in working capital.

Basis of preparation and recent

Basis of preparation and recent accounting developments	12 Months Ended
	Mar. 31, 2020
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
Basis of preparation and recent accounting pronouncements	Basis of preparation and recent accounting developments Accounting policies describe our approach to recognising and measuring transactions and balances in the year. The accounting policies applicable across the financial statements are shown below, whereas accounting policies that are specific to a component of the financial statements have been incorporated into the relevant note. This section also shows areas of judgement and key sources of estimation uncertainty in these financial statements. In addition, we have summarised new International Accounting Standards Board (IASB) accounting standards, amendments and interpretations and whether these are effective for this year end or in later years, explaining how significant changes are expected to affect our reported results. National Grid’s principal activities involve the transmission and distribution of electricity and gas in Great Britain and northeastern US. The Company is a public limited liability company incorporated and domiciled in England and Wales, with its registered office at 1–3 Strand, London WC2N 5EH. The Company, National Grid plc, which is the ultimate parent of the Group, has its primary listing on the London Stock Exchange and is also quoted on the New York Stock Exchange. These consolidated financial statements were approved for issue by the Board on 17 June 2020 . These consolidated financial statements have been prepared in accordance with International Accounting Standards (IAS) and International Financial Reporting Standards (IFRS) and related interpretations as issued by the IASB and IFRS as adopted by the EU. They are prepared on the basis of all IFRS accounting standards and interpretations that are mandatory for periods ended 31 March 2020 and in accordance with the Companies Act 2006 applicable to companies reporting under IFRS and Article 4 of the EU IAS Regulation. The comparative financial information has also been prepared on this basis. The consolidated financial statements have been prepared on a historical cost basis, except for the recording of pension assets and liabilities, the revaluation of derivative financial instruments and certain commodity contracts and certain financial assets and liabilities measured at fair value. These consolidated financial statements are presented in pounds sterling, which is also the functional currency of the Company. The notes to the financial statements have been prepared on a continuing basis unless otherwise stated. A. Going concern As at the date of approving these financial statements, the impact of COVID-19 on the Group’s operations is continually being assessed and subject to rapid change. The Directors have assessed the principal risks, including by modelling both a base case and a reasonable worst case scenario. The reasonable worst-case scenario covers the cash flow impact associated with an extended lockdown for a period of 12 months across both the UK and US. The main cash flow impacts identified in the reasonable worst-case scenario are: • a significant reduction in cash collections over an extended 12 -month period driven by lower customer demand and increased bad debt in our US businesses; • additional working capital required to fund payment term extensions and charge deferrals in the UK electricity market, intended to help customers and end-user consumers; • one-off increases in other costs such as cleaning, safety equipment and IT; offset by ◦ a reduction in non-essential capital expenditure across the Group driven by increased absenteeism, supply chain issues and difficulty in accessing sites; and ◦ a reduction in discretionary spend across all areas (e.g. recruitment, travel and consultancy spend) . As part of their analysis, the Board also considered the following potential levers at their discretion to improve the position identified by the reasonable worst-case scenario in the event that the debt capital markets are not accessible: • further significant changes in the phasing of the Group’s capital programme with elements of non-essential works and programmes delayed beyond June 2021; • a number of further reductions in operating expenditure across the Group primarily related to workforce cost reductions in both the UK and the US; and • the payment of dividends to shareholders. Having considered the reasonable worst-scenario and further levers at the Board’s discretion, the Group continues to have headroom against the Group’s committed facilities identified in note 33 to the financial statements. In addition to the above, the ability to raise new financing was separately included in the analysis and the Directors noted the £0.9 billion debt issuances completed in April 2020 (disclosed in note 21 to the financial statements) as evidence of the Group’s ability to continue to have access to the debt capital markets if needed. Other factors considered by the Board as part of their Going Concern assessment included the potential impact of Brexit trade talks, the Group’s various ongoing rate case determinations in the UK and US alongside inherent uncertainties in cash flow forecasts (such as the impact of storms in our US business). Based on the above, the Directors have concluded the Group is well placed to manage its financing and other business risks satisfactorily, and have a reasonable expectation that the Group will have adequate resources to continue in operation for at least 12 months from the signing date of these consolidated financial statements. They therefore consider it appropriate to adopt the going concern basis of accounting in preparing the financial statements. 1. Basis of preparation and recent accounting developments continued B. Basis of consolidation The consolidated financial statements incorporate the results, assets and liabilities of the Company and its subsidiaries, together with a share of the results, assets and liabilities of joint operations. A subsidiary is defined as an entity controlled by the Group. Control is achieved where the Group is exposed to, or has the rights to, variable returns from its involvement with the entity and has the power to affect those returns through its power over the entity. The Group accounts for joint ventures and associates using the equity method of accounting, where the investment is carried at cost plus post-acquisition changes in the share of net assets of the joint venture or associate, less any provision for impairment. Losses in excess of the consolidated interest in joint ventures and associates are not recognised, except where the Company or its subsidiaries have made a commitment to make good those losses. Where necessary, adjustments are made to bring the accounting policies used in the individual financial statements of the Company, subsidiaries, joint operations, joint ventures and associates into line with those used by the Group in its consolidated financial statements under IFRS. Intercompany transactions are eliminated. The results of subsidiaries, joint operations, joint ventures and associates acquired or disposed of during the year are included in the consolidated income statement from the effective date of acquisition or up to the effective date of disposal, as appropriate. Acquisitions are accounted for using the acquisition method, where the purchase price is allocated to the identifiable assets acquired and liabilities assumed on a fair value basis and the remainder recognised as goodwill. C. Treatment of interests in Quadgas HoldCo Limited (Quadgas) – discontinued operations and held for sale At the end of June 2019, we completed the disposal of our retained 39% interest in the UK Gas Distribution business (held through Quadgas) that was classified as held for sale. We have treated the results and cash flows of Quadgas as a discontinued operation in the consolidated income statement and consolidated cash flow statement. Refer to note 10 for further details. D. Foreign currencies Transactions in currencies other than the functional currency of the Company or subsidiary concerned are recorded at the rates of exchange prevailing on the dates of the transactions. At each reporting date, monetary assets and liabilities that are denominated in foreign currencies are retranslated at closing exchange rates. Non-monetary assets are not retranslated unless they are carried at fair value. Gains and losses arising on the retranslation of monetary assets and liabilities are included in the income statement, except where the application of hedge accounting requires inclusion in other comprehensive income (see note 32(e)). On consolidation, the assets and liabilities of operations that have a functional currency different from the Company’s functional currency of pounds sterling, principally our US operations that have a functional currency of US dollars, are translated at exchange rates prevailing at the reporting date. Income and expense items are translated at the average exchange rates for the period where these do not differ materially from rates at the date of the transaction. Exchange differences arising are recognised in other comprehensive income and transferred to the consolidated translation reserve within other equity reserves (see note 28). E. Areas of judgement and key sources of estimation uncertainty The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities, and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from these estimates. Information about such judgements and estimations is in the notes to the financial statements, and the key areas are summarised below. Areas of judgement that have the most significant effect on the amounts recognised in the financial statements are as follows: • the judgement that notwithstanding legislation enacted and targets established during the year ended 31 March 2020 committing the UK, New York State and Massachusetts to achieving net zero greenhouse gas emissions by 2050, these do not trigger a reassessment of the remaining useful economic lives of our gas network assets (see estimate below and note 13 ); and • following the legal separation of the Electricity System Operator on 1 April 2019, we concluded that the Electricity System Operator acts as an agent in respect of certain Transmission Network Use of Service revenues, principally those collected on behalf of the Scottish and Offshore transmission operators , as detailed in note 3 . Key sources of estimation uncertainty that have a significant risk of causing a material adjustment to the carrying amounts of assets and liabilities within the next financial year are as follows: • the valuation of liabilities for pensions and other post-retirement benefits (see note 25 ); and • the cash flows applied in determining the environmental provisions, in particular relating to three US Superfund sites (see note 26 ). In light of the current ongoing impact of the COVID-19 pandemic, valuations of certain assets and liabilities are necessarily more subjective. In particular, two further areas of estimation uncertainty impacting the Group's position as at 31 March 2020 have been identified: • the valuation of certain pension assets, in particular unquoted equities, properties and diversified alternatives, in light of the volatile economic markets (see note 25) ; and • the recoverability of customer receivables, particularly in relation to US retail customers, in light of the suspension of debt collection activities and customer termination activities (see note 19 ). In addition, we also highlight the estimates made regarding the useful economic lives of our gas network assets due to the length over which they are being depreciated, the potential for new and evolving technologies over that period, and the range of potential pathways for meeting net zero targets (see note 13 for details and sensitivity analysis ). In order to illustrate the impact that changes in assumptions for the valuation of pension assets and liabilities and cash flows for environmental provisions could have on our results and financial position, we have included sensitivity analyses in note 35. Information on what we believe a reasonably possible range of outcomes to be on recoverability of customer receivables are included in note 19. 1. Basis of preparation and recent accounting developments continued F. Accounting policy choices IFRS provides certain options available within accounting standards. Choices we have made, and continue to make, include the following: • Presentational formats: we use the nature of expense method for our income statement and aggregate our statement of financial position to net assets and total equity. • Financial instruments: we normally opt to apply hedge accounting in most circumstances where this is permitted (see note 32(e)). • Cash flow statement: Following a review in the year, we have changed our accounting policy in relation to the presentation of derivatives in the cash flow statement, which has resulted in £412 million of cash outflows for 2019 and £330 million of cash inflows from 2018 to be presented as investing activities rather than financing activities. The reclassified cash flows are in relation to derivatives associated with our net investment hedges, and given they are designated in a hedge relationship, the Group has decided to present them together with the underlying hedged item rather than as part of our overall financing activities. G. New IFRS accounting standards and interpretations effective for the year ended 31 March 2020 The Group adopted IFRS 16 ‘Leases’ with effect from 1 April 2019. We have applied the modified retrospective approach permitted in the standard whereby prior year comparatives have not been restated on adoption. Instead, any cumulative transition adjustments are reflected through reserves. Refer to note 37 for full details of the impact and transition adjustments arising on adoption. The UK’s Financial Conduct Authority announced that LIBOR will cease to exist by the end of 2021, and will be replaced by alternative reference rates. In September 2019, the IASB amended IFRS 9 and IFRS 7 by issuing Interest Rate Benchmark Reform, which provides exceptions to specific hedge accounting requirements to ensure that hedging relationships are not considered to be modified as a result of the change in the reference rate. The amendments were endorsed in January 2020 for adoption in the EU. The Group early-adopted these changes to IFRS 9 and IFRS 7 with effect from 1 April 2019. There were no transition adjustments on adoption. Refer to note 32(e) for further details of the impact in the current period. The Group has also adopted the following amendments to standards, which have had no material impact on the Group’s results or financial statement disclosure: • IFRIC 23 ‘Uncertainty over Income Tax Treatments’; • Amendments to IAS 28 ‘Investments in Associates – Long-term Interests in Associates and Joint Ventures’; • Annual Improvements to IFRS Standards 2015–2017 Cycle; and • Amendments to IAS 19 ‘Employee Benefits’. H. New IFRS accounting standards and interpretations not yet adopted The following new accounting standards and amendments to existing standards have been issued but are not yet effective: • IFRS 17 ‘Insurance Contracts’; • Amendments to IFRS 3 ‘Business Combinations’; • Amendments to the References to the Conceptual Framework; • Amendments to IAS 1 and IAS 8: Definition of material; and • Amendments to IAS 1 'Presentation of Financial Statements'. The Group is currently assessing the impact of the above standards, but they are not expected to have a material impact. The Group has not adopted any other standard, amendment or interpretation that has been issued but is not yet effective.

Segmental analysis

Segmental analysis	12 Months Ended
	Mar. 31, 2020
Operating Segments [Abstract]
Segmental analysis	Segmental analysis This note sets out the financial performance for the year split into the different parts of the business (operating segments). The performance of these operating segments is monitored and managed on a day-to-day basis. Revenue and the results of the business are analysed by operating segment, based on the information the Board of Directors uses internally for the purposes of evaluating the performance of each operating segment and determining resource allocation between them. The Board is National Grid’s chief operating decision maker (as defined by IFRS 8 ‘Operating Segments’) and assesses the profitability of operations principally on the basis of operating profit before exceptional items and remeasurements (see note 5). As a matter of course, the Board also considers profitability by segment, excluding the effect of timing. However, the measure of profit disclosed in this note is operating profit before exceptional items and remeasurements as this is the measure that is most consistent with the IFRS results reported within these financial statements. The results of our three principal businesses are reported to the Board of Directors and are treated as reportable operating segments. The following table describes the main activities for each reportable operating segment: UK Electricity Transmission The high-voltage electricity transmission networks in England and Wales and independent Great Britain system operator. UK Gas Transmission The high-pressure gas transmission networks in Great Britain and system operator in Great Britain. US Regulated Gas distribution networks, electricity distribution networks and high-voltage electricity transmission networks in New York and New England and electricity generation facilities in New York. The UK Electricity Transmission segment also includes the independent Electricity System Operator (ESO). Although there is a separate governance structure (including a separate Executive Committee), the Board receives financial information on an aggregated UK Electricity Transmission basis, which includes the results of the ESO, and accordingly the ESO is included within the reportable segment. National Grid Ventures (NGV) is our only other operating segment. It does not currently meet the thresholds set out in IFRS 8 to be identified as a separate reportable segment and therefore its results are not required to be separately presented. Instead, NGV’s results are reported alongside the results of all other operating businesses on an aggregated basis as “NGV and Other”, with certain additional disclosure included in footnotes. NGV represents our key strategic growth area outside our regulated core business in competitive markets across the US and the UK. The business comprises all commercial operations in metering, LNG at the Isle of Grain in the UK, electricity interconnectors and our new investments in Geronimo Energy LLC (Geronimo) and Emerald Energy Venture LLC (Emerald). Geronimo is a developer of wind and solar generation based in Minneapolis in the US. The acquisition is National Grid’s first ownership stake in wind generation and an expansion of our activities in solar generation. Other activities that do not form part of any of the segments in the above table or NGV primarily relate to our UK property business together with insurance and corporate activities in the UK and US and the Group’s investments in technology and innovation companies through National Grid Partners. The segmental information is presented in relation to continuing operations only and therefore does not include the profits and losses relating to our interest in Quadgas for any period presented (see note 10 ). (a) Revenue Revenue primarily represents the sales value derived from the generation, transmission and distribution of energy, together with the sales value derived from the provision of other services to customers. Refer to note 3 for further details. Sales between operating segments are priced considering the regulatory and legal requirements to which the businesses are subject. The analysis of revenue by geographical area is on the basis of destination. There are no material sales between the UK and US geographical areas. 2020 2019 2018 Total £m Sales between segments £m Sales to third parties £m Total Sales Sales Total Sales Sales Operating segments – continuing operations: UK Electricity Transmission 3,702 (8 ) 3,694 3,351 (20 ) 3,331 4,154 (28 ) 4,126 UK Gas Transmission 927 (16 ) 911 896 (12 ) 884 1,091 (9 ) 1,082 US Regulated 9,205 — 9,205 9,846 — 9,846 9,272 — 9,272 NGV and Other¹ 736 (6 ) 730 876 (4 ) 872 776 (6 ) 770 Total revenue from continuing operations 14,570 (30 ) 14,540 14,969 (36 ) 14,933 15,293 (43 ) 15,250 Split by geographical areas – continuing operations: UK 5,282 5,045 5,938 US 9,258 9,888 9,312 14,540 14,933 15,250 1. Included within NGV and Other is £608 million ( 2019 : £597 million ; 2018 : £593 million ) of revenue relating to NGV. 2. Segmental analysis continued (b) Operating profit A reconciliation of the operating segments’ measure of profit to profit before tax from continuing operations is provided below. Further details of the exceptional items and remeasurements are provided in note 5 . Before exceptional items After exceptional items 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m Operating segments – continuing operations: UK Electricity Transmission 1,320 1,015 1,041 1,316 778 1,041 UK Gas Transmission 348 303 487 347 267 487 US Regulated 1,397 1,724 1,698 880 1,425 1,734 NGV and Other 1,2 242 400 231 237 400 231 Total operating profit from continuing operations 3,307 3,442 3,457 2,780 2,870 3,493 Split by geographical area – continuing operations: UK 1,925 1,695 1,840 1,915 1,422 1,840 US 1,382 1,747 1,617 865 1,448 1,653 3,307 3,442 3,457 2,780 2,870 3,493 Below we reconcile total operating profit from continuing operations to profit before tax from continuing operations. Total operating exceptional items and remeasurements of £527 million charge ( 2019 : £572 million charge ; 2018: £36 million gain ) are detailed in note 5 . This is comprised of a £4 million charge ( 2019 : £237 million charge ; 2018 : £nil ) attributable to UK Electricity Transmission; £1 million charge ( 2019 : £36 million charge ; 2018 : £nil ) to UK Gas Transmission; £517 million charge ( 2019 : £299 million charge ; 2018 : £36 million gain ) to US Regulated; and £5 million charge ( 2019 : £nil ; 2018 : £nil ) to NGV and Other. Reconciliation to profit before tax: Operating profit from continuing operations 3,307 3,442 3,457 2,780 2,870 3,493 Finance income 70 73 127 54 88 127 Finance costs (1,119 ) (1,066 ) (1,128 ) (1,167 ) (1,157 ) (1,009 ) Share of post-tax results of joint ventures and associates 88 40 44 87 40 49 Profit before tax from continuing operations 2,346 2,489 2,500 1,754 1,841 2,660 1. Included within NGV and Other is £269 million ( 2019 : £263 million ; 2018 : £234 million ) of operating profit before exceptional items and remeasurements and £268 million of operating profit after exceptional items and remeasurements ( 2019 : £263 million ; 2018 : £234 million ), relating to NGV. 2. In 2019 , NGV and Other included gains of £95 million in relation to cash received in respect of two legal settlements. (c) Capital expenditure Capital expenditure represents additions to property, plant and equipment and non-current intangibles but excludes additional investments in and loans to joint ventures and associates. In 2020, we transferred certain software assets and properties which are held outside the US rate base and operate for the benefit of our US Regulated businesses, that were previously included within the NGV and Other segment, to the US Regulated segment. See footnote 2. Net book value of property, plant and Capital expenditure Depreciation, amortisation and impairment 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Operating segments: UK Electricity Transmission 13,788 13,288 13,028 1,043 925 999 (469 ) (628 ) (475 ) UK Gas Transmission 4,513 4,412 4,280 249 308 310 (171 ) (181 ) (194 ) US Regulated² 29,623 24,542 20,953 3,228 2,650 2,424 (855 ) (700 ) (635 ) NGV and Other 1,2 2,141 2,755 2,491 559 438 341 (145 ) (226 ) (226 ) Total from continuing operations 50,065 44,997 40,752 5,079 4,321 4,074 (1,640 ) (1,735 ) (1,530 ) Split by geographical area – continuing operations: UK 20,427 19,343 18,772 1,847 1,584 1,527 (784 ) (931 ) (804 ) US 29,638 25,654 21,980 3,232 2,737 2,547 (856 ) (804 ) (726 ) 50,065 44,997 40,752 5,079 4,321 4,074 (1,640 ) (1,735 ) (1,530 ) Asset type: Property, plant and equipment 48,770 43,913 39,853 4,727 4,015 3,901 (1,464 ) (1,560 ) (1,392 ) Non-current intangible assets 1,295 1,084 899 352 306 173 (176 ) (175 ) (138 ) Total from continuing operations 50,065 44,997 40,752 5,079 4,321 4,074 (1,640 ) (1,735 ) (1,530 ) 1. Included within NGV and Other are assets with a net book value of £2,080 million ( 2019 : £1,635 million ; 2018 : £1,454 million ), capital expenditure of £550 million ( 2019 : £317 million ; 2018 : £186 million ) and depreciation, amortisation and impairment of £124 million ( 2019 : £114 million ; 2018 : £143 million ) relating to NGV. 2. In 2020, US Regulated includes certain software assets and properties in the US which are outside the US rate base and operate for the benefit of our US regulated businesses. These assets were included within NGV and Other in 2019 and 2018. The assets had a net book value of £1,062 million in 2019 and £998 million in 2018, capital expenditure of £87 million in 2019 and £161 million in 2018 and depreciation, amortisation and impairment of £102 million in 2019 and £80 million in 2018. Total non-current assets other than financial instruments and pension assets located in the UK and US were £31,780 million and £25,867 million respectively as at 31 March 2020 ( 31 March 2019 : UK £30,072 million , US £21,787 million ; 31 March 2018 : UK £20,816 million , US £27,663 million ).

Revenue

Revenue	12 Months Ended
	Mar. 31, 2020
Disclosure of revenue from contracts with customers [Abstract]
Revenue	Revenue Revenue arises in the course of ordinary activities and principally comprises: • transmission services; • distribution services; and • generation services. Transmission services, distribution services and certain other services (excluding rental income but including metering) fall within the scope of IFRS 15 ‘Revenue from Contracts with Customers’, whereas generation services (which solely relate to the contract with the Long Island Power Authority (LIPA) in the US) are accounted for under the leasing standard as rental income, also presented within revenue. Revenue is measured based on the consideration specified in a contract with a customer and excludes amounts collected on behalf of third parties and value added tax. The Group recognises revenue when it transfers control over a product or service to a customer. IFRS 15 was adopted in the prior year and applied prospectively from 1 April 2018. Therefore, the analysis below is only provided for the current period and the immediate comparative period. Below, we include a description of principal activities, by reportable segment, from which the Group generates its revenue. For more detailed information about our segments, see note 2. (a) UK Electricity Transmission The UK Electricity Transmission segment principally generates revenue by providing electricity transmission services (both as transmission owner in England and Wales and system operator in Great Britain). Our business operates as a monopoly regulated by Ofgem, which has established price control mechanisms that set the amount of annual allowed returns our business can earn (along with the Scottish and Offshore transmission operators amongst others). The IFRS revenues we record are principally a function of volumes and price. Price is determined prior to our financial year-end with reference to the regulated allowed returns and estimated annual volumes. Where revenue received or receivable exceeds the maximum amount permitted by regulatory agreement, adjustments will be made to future prices to reflect this over-recovery. No liability is recognised, as such an adjustment to future prices relates to the provision of future services. Similarly, no asset is recognised where a regulatory agreement permits adjustments to be made to future prices in respect of an under-recovery. As part of our regulatory agreements we are entitled to recover certain costs directly from customers (pass-through costs). These amounts are included in the overall calculation of allowed revenue as stipulated by regulatory agreements. The System Operator earns revenue for balancing supply and demand of electricity on the transmission system, where it acts as principal. Revenue is recognised as the service is provided. The System Operator also collects revenues on behalf of transmission operators, principally NGET and the Scottish and Offshore transmission operators, from users who connect to or use the transmission system. However, these amounts are paid to the transmission operators before the System Operator has collected payment from the users (electricity suppliers) and therefore the System Operator does hold some exposure to credit losses with electricity suppliers. The System Operator must set the charges paid by electricity suppliers by reference to the price control mechanism described above. That mechanism does not grant the System Operator with discretion to deviate from that mechanism. The transmission operators own and maintain the electricity network and receive direct feedback from electricity suppliers on the quality of the network they provide. There is a judgement about whether the System Operator acts as a principal or agent in respect of the transmission network revenues collected on behalf of the Scottish and Offshore transmission operators (as set out in note 1). We have concluded that it acts as an agent in respect of these transmission revenues and therefore records the attributable revenue net of operating costs. The transmission of high-voltage electricity encompasses the following principal services: • the supply of high-voltage electricity (including both transmission and system operator charges); and • construction work (principally for connections). For the supply of high-voltage electricity, revenue is recognised based on capacity and volumes. Our performance obligation is satisfied over time as our customers make use of our network. We bill monthly in arrears and our payment terms are up to 60 days. For construction work relating to connections, customers can either pay over the useful life of the connection or upfront. Revenue is recognised over time, as we provide access to our network, and where the customer pays upfront, revenues are deferred and released over the life of the connection. For other construction where there is no consideration for any future services, for example diversions (being the re-routing of network assets at our customers’ request), revenues are recognised as the construction work is completed. (b) UK Gas Transmission The UK Gas Transmission segment of the Group principally generates revenue by providing gas transmission services to our customers (both as transmission owner and as system operator) in Great Britain. Similar to our UK Electricity Transmission business, our business operates as a monopoly regulated by Ofgem. The price control mechanism in place that determines our annual allowances is also similar, as is the way in which revenue is recorded. The transmission of gas encompasses the following principal services: • the supply of high-pressure gas (including both transmission and system operator charges); and • construction work (principally for connections). For the supply of high-pressure gas, revenue is recognised based on capacity and volumes. Our performance obligation is satisfied over time as our customers make use of our network, and we bill monthly in arrears with payment terms of up to 45 days. For construction work relating to connections, customers pay for the connection upfront. Revenue is recognised over time, as we provide access to our network. Where revenues are received upfront, they are deferred and released over the life of the connection. For other construction where there is no consideration for any future services (such as diversions), revenues are recognised when the construction work is completed. 3. Revenue continued (c) US Regulated The US Regulated segment of the Group principally generates revenue by providing gas and electricity distribution services in New York and New England, high voltage electricity transmission services in New York and New England, and electricity generation in New York. Distribution services Provision of gas and electricity distribution services in New York and New England. This comprises the following principal services: • Gas and electricity distribution: revenue is recognised based on usage by customers (over time) and billed monthly. Payment terms are 30 days; and • Connections: revenue is recognised over time, as we provide access to our network. Where payments are made upfront, they are deferred over the life of the asset. Transmission services Provision of electricity transmission services to customers and operation of electricity transmission facilities. Our principal services are: • Electricity transmission: revenue is recognised based on usage by customers (over time) and billed monthly. Payment terms are 30 days; and • Connections: revenue is recognised over time, as we provide access to our network. Where payments are made upfront, they are deferred over the life of the asset. Electricity generation Provision of energy services and supply capacity to produce energy for the use of customers of the Long Island Power Authority (LIPA) through a power supply agreement. This falls within the scope of the leasing standard, where we act as lessor with rental income being recorded as other income, which forms part of total revenue. (d) NGV and Other NGV and Other includes electricity interconnectors, LNG at the Isle of Grain, Geronimo, metering, sales from our UK property business, rental income and insurance. The Group recognises revenue from transmission services through interconnectors and LNG at the Isle of Grain by means of customers’ use of capacity and volumes. Revenue is recognised over time and is billed monthly. Payment terms are up to 30 days. Other revenue in the scope of IFRS 15 principally includes revenues from our UK metering business and sales of renewables projects from Geronimo to Emerald (see note 38 ). Revenue is recognised as it is earned. In the case of the UK metering business, revenue is billed monthly and payment terms are up to 30 days. Other revenue, recognised in accordance with standards other than IFRS 15, includes property sales by our UK commercial property business (including sales to our St William joint venture) and rental income. Property sales are recorded at a point in time (when the sale is legally completed) and rental income is recorded over time. (e) Disaggregation of revenue In the following tables, revenue is disaggregated by primary geographical market and major service lines. The table reconciles disaggregated revenue with the Group’s reportable segments (see note 2 ). Revenue for the year ended 31 March 2020 UK Electricity Transmission UK Gas Transmission US Regulated NGV and Other Total Revenue under IFRS 15 Transmission 1,992 649 425 309 3,375 Distribution — — 8,319 — 8,319 System Operator 1,610 214 — — 1,824 Other 69 15 12 296 392 Total IFRS 15 revenue 3,671 878 8,756 605 13,910 Other revenue Generation — — 369 — 369 Other 23 33 80 125 261 Total other revenue 23 33 449 125 630 Total revenue from continuing operations 3,694 911 9,205 730 14,540 Geographical split for the year ended 31 March 2020 UK Electricity Transmission £m UK Gas Transmission £m US Regulated £m NGV and Other £m Total £m Revenue under IFRS 15 UK 3,671 878 — 567 5,116 US — — 8,756 38 8,794 Total IFRS 15 revenue 3,671 878 8,756 605 13,910 Other revenue UK 23 33 — 110 166 US — — 449 15 464 Total other revenue 23 33 449 125 630 Total revenue from continuing operations 3,694 911 9,205 730 14,540 3. Revenue continued (e) Disaggregation of revenue continued Revenue for the year ended 31 March 2019 UK Electricity Transmission UK Gas Transmission US Regulated NGV and Other Total Revenue under IFRS 15 Transmission 1,909 661 370 313 3,253 Distribution — — 8,941 — 8,941 System Operator 1,416 172 — — 1,588 Other — — — 284 284 Total IFRS 15 revenue 3,325 833 9,311 597 14,066 Other revenue Generation — — 367 — 367 Other 6 51 168 275 500 Total other revenue 6 51 535 275 867 Total revenue from continuing operations 3,331 884 9,846 872 14,933 Geographical split for the year ended 31 March 2019 UK Electricity Transmission £m UK Gas Transmission £m US Regulated £m NGV and Other £m Total £m Revenue under IFRS 15 UK 3,325 833 — 585 4,743 US — — 9,311 12 9,323 Total IFRS 15 revenue 3,325 833 9,311 597 14,066 Other revenue UK 6 51 — 245 302 US — — 535 30 565 Total other revenue 6 51 535 275 867 Total revenue from continuing operations 3,331 884 9,846 872 14,933 Revenue to be recognised in future periods, presented as contract liabilities of £1,158 million ( 2019 : £994 million ) (see note 23 ), relates to contributions in aid of construction. Revenue is recognised over the life of the asset. The asset lives for connections in UK Electricity Transmission, UK Gas Transmission, NGV and US Regulated are 40 years, 36 years (to 2055), 15 years and up to 51 years respectively. The weighted average amortisation period is 18 years. Future revenues in relation to unfulfilled performance obligations not yet received in cash amount to £3.1 billion ( 2019 : £3.5 billion ). £1.5 billion ( 2019 : £1.6 billion ) relates to connection contracts in UK Electricity Transmission which will be recognised as revenue over 29 years and £1.5 billion ( 2019 : £1.8 billion ) relates to revenues to be earned under Grain LNG contracts until 2029 . The remaining amount will be recognised as revenue over 5 years. The amount of revenue recognised for the year ended 31 March 2020 from performance obligations satisfied (or partially satisfied) in previous periods, mainly due to the changes in the estimate of the stage of completion, is £nil ( 2019 : £nil ).

Operating costs

Operating costs	12 Months Ended
	Mar. 31, 2020
Analysis of income and expense [abstract]
Operating costs	Operating costs Below we have presented separately certain items included in our operating costs from continuing operations. These include a breakdown of payroll costs (including disclosure of amounts paid to key management personnel) and fees paid to our auditors. 2020 2019 2018 £m £m £m Depreciation, amortisation and impairment 1,640 1,735 1,530 Payroll costs 1,684 1,852 1,648 Provision for bad and doubtful debts 234 181 36 Purchases of electricity 1,403 1,454 1,285 Purchases of gas 1,316 1,642 1,543 Property and other taxes 1,191 1,108 1,057 Balancing Services Incentive Scheme 1,317 1,196 1,012 Payments to other UK network owners¹ — — 1,043 Other 2,975 2,895 2,603 11,760 12,063 11,757 Operating costs include: Inventory consumed 328 415 367 Research and development expenditure 14 19 13 1. Under IFRS 15, with effect from 1 April 2018, revenue and associated payments to other UK network owners are presented on a net basis. (a) Payroll costs 2020 2019 2018 £m £m £m Wages and salaries¹ 2,188 2,084 1,998 Social security costs 168 156 157 Defined contribution scheme costs 75 72 65 Defined benefit pension costs 135 232 156 Share-based payments 19 27 16 Severance costs (excluding pension costs) 1 76 7 2,586 2,647 2,399 Less: payroll costs capitalised (902 ) (795 ) (751 ) Total payroll costs 1,684 1,852 1,648 1. Included within wages and salaries are US other post-retirement benefit costs of £45 million ( 2019 : £48 million ; 2018 : £46 million ). For further information refer to note 25. (b) Number of employees 31 March Monthly 31 March Monthly 31 March Monthly UK 6,321 6,151 5,962 6,227 6,517 6,431 US 16,748 16,679 16,614 16,669 16,506 16,274 Total number of employees 23,069 22,830 22,576 22,896 23,023 22,705 4. Operating costs continued (c) Key management compensation 2020 2019 2018 £m £m £m Short-term employee benefits 7 7 8 Compensation for loss of office 1 — — Post-employment benefits 1 1 1 Share-based payments 3 3 3 Total key management compensation 12 11 12 Key management compensation relates to the Board, including the Executive Directors and Non-executive Directors for the years presented. (d) Auditors’ remuneration Auditors’ remuneration is presented below in accordance with the requirements of the Companies Act 2006 and the principal accountant fees and services disclosure requirements of Item 16C of Form 20-F: 2020 2019 2018 £m £m £m Audit fees payable to the parent Company’s auditors and their associates in respect of: Audit of the parent Company’s individual and consolidated financial statements¹ 1.9 1.6 2.7 The auditing of accounts of any associate of the Company² 8.7 8.5 9.3 Other services supplied³ 6.3 5.2 3.9 16.9 15.3 15.9 Total other services 4 Tax fees: Tax compliance services — — 0.3 Tax advisory services — — — All other fees: Other assurance services 5 0.6 1.1 0.7 Services relating to corporate finance transactions not covered above — — — Other non-audit services not covered above 6 0.5 2.2 0.9 1.1 3.3 1.9 Total auditors’ remuneration 18.0 18.6 17.8 1. Audit fees in each year represent fees for the audit of the Company’s financial statements and regulatory reporting for the years ended 31 March 2020 , 2019 and 2018 . 2. The 2019 comparative has been updated following finalisation of the 2019 audit fee with the Audit Committee. 3. Other services supplied represent fees payable for services in relation to other statutory filings or engagements that are required to be carried out by the auditors. In particular, this includes fees for reports under section 404 of the US Public Company Accounting Reform and Investor Protection Act of 2002 (Sarbanes-Oxley), audit reports on regulatory returns and the review of interim financial statements for the six-month periods ended 30 September 2019 , 2018 and 2017 respectively. 4. There were no audit related fees as described in Item 16C(b) of Form 20-F. 5. Principally amounts relating to assurance services provided in relation to comfort letters for debt issuances. 6. In 2020 , non-audit services include auction monitor work on Contracts for Difference, IT project assurance and a review of controls over our data on New York customers. In 2019 and 2018 , non-audit services primarily related to the UK Property business in respect of the evaluation of possible options for the use of property assets. The Audit Committee considers and makes recommendations to the Board, to be put to shareholders for approval at each AGM, in relation to the appointment, re-appointment, removal and oversight of the Company’s independent auditors. The Committee also considers and approves the audit fees on behalf of the Board in accordance with the Competition and Market Authority Audit Order 2014. The auditors’ remuneration is then put to shareholders at each AGM. Certain services are prohibited from being performed by the external auditors under the Sarbanes-Oxley Act. Of the above services, none were prohibited.

Exceptional items and remeasure

Exceptional items and remeasurements	12 Months Ended
	Mar. 31, 2020
Exceptional Items And Remeasurements [Abstract]
Exceptional items and remeasurements	Exceptional items and remeasurements To monitor our segmental financial performance, we use a profit measure that excludes certain income and expenses. We call that measure ‘business performance’ or ‘adjusted profit’. Business performance (which excludes exceptional items and remeasurements as defined below) is used by management to monitor financial performance as it is considered that it aids the comparability of our reported financial performance from year to year. We exclude items from business performance because, if included, these items could distort understanding of our performance for the year and the comparability between periods. This note analyses these items, which are included in our results for the year but are excluded from business performance. Exceptional items and remeasurements from continuing operations 2020 2019 2018 £m £m £m Included within operating profit Exceptional items: Environmental charges (402 ) — — Cost efficiency and restructuring programmes — (204 ) — Massachusetts Gas labour dispute — (283 ) — Impairment of nuclear connection development costs — (137 ) — Final settlement of LIPA MSA Transition — — 26 (402 ) (624 ) 26 Remeasurements – commodity contract derivatives (125 ) 52 10 (527 ) (572 ) 36 As disclosed in note 8, the Group also presents an adjusted earnings per share measure that is calculated before exceptional items and remeasurements. This measure is presented after tax and therefore details of tax exceptional items and the tax effect of exceptional items and remeasurements are also provided in this note. 2020 2019 2018 £m £m £m Included within finance income and costs Remeasurements: Net gains/(losses) on financing derivatives 1 (40 ) 119 Net (losses)/gains on financial assets at fair value through profit and loss (16 ) 15 — Net losses on financial liabilities at fair value through profit and loss (49 ) (51 ) — (64 ) (76 ) 119 Included within share of post-tax results of joint ventures and associates Exceptional items: Deferred tax arising on the reduction in US corporation tax rate — — 5 Remeasurements: Net losses on financial instruments (1 ) — — Total included within profit before tax (592 ) (648 ) 160 Included within tax Exceptional items – credits/(debits) arising on items not included in profit before tax: Deferred tax arising on the reduction in the US corporation tax rate — — 1,510 Deferred tax arising on the reversal of the reduction in UK corporation tax rate (192 ) — — Tax on exceptional items 103 144 (9 ) Tax on remeasurements 42 5 (28 ) (47 ) 149 1,473 Total exceptional items and remeasurements after tax (639 ) (499 ) 1,633 Analysis of total exceptional items and remeasurements after tax Exceptional items after tax (491 ) (480 ) 1,532 Remeasurements after tax (148 ) (19 ) 101 Total exceptional items and remeasurements after tax (639 ) (499 ) 1,633 5. Exceptional items and remeasurements continued Exceptional items Management uses an exceptional items framework that has been discussed and approved by the Audit Committee. This follows a three-step process which considers the nature of the event, the financial materiality involved and any particular facts and circumstances. In considering the nature of the event, management focuses on whether the event is within the Group’s control and how frequently such an event typically occurs. In determining the facts and circumstances, management considers factors such as ensuring consistent treatment between favourable and unfavourable transactions, the precedent for similar items, the number of periods over which costs will be spread or gains earned, and the commercial context for the particular transaction. Items of income or expense that are considered by management for designation as exceptional items include significant restructurings, write-downs or impairments of non-current assets, significant changes in environmental or decommissioning provisions, integration of acquired businesses, gains or losses on disposals of businesses or investments and significant debt redemption costs as a consequence of transactions such as significant disposals or issues of equity, and the related tax, as well as deferred tax arising on changes to corporation tax rates. Costs arising from restructuring programmes include redundancy costs. Redundancy costs are charged to the consolidated income statement in the year in which a commitment is made to incur the costs and the main features of the restructuring plan have been announced to affected employees. Set out below are details of the transactions against which we have considered the application of our exceptional items framework in each of the years for which results are presented. 2020 We concluded that the increase in costs associated with the changes in our environmental provisions ( £402 million ) and the additional deferred tax charge reflecting the impact of the remeasurement of the Group’s deferred tax liabilities as a result of a change in the substantively enacted UK corporation tax rate ( £192 million ) meet the criteria to be classified as exceptional. A further £10 million of COVID-19 related costs incurred in the year have similarly not been classified as exceptional in view of the quantum involved and all costs associated with the settlement reached with the State of New York in respect of the Downstate New York Gas Moratorium have also been treated as part of adjusted profit. Environmental charges: In the US, the most significant component of our £1.9 billion environmental provision relates to several Superfund sites, and arose from former manufacturing gas plant facilities, formerly owned or operated by the Group or its predecessor companies. The sites are subject to both State and Federal law in the US. Under Federal and State Superfund laws, potential liability for the historical contamination may be imposed on responsible parties jointly and severally, without regard to fault, even if the activities were lawful when they occurred. The provisions and the Group's share of estimated costs are re-evaluated at each reporting period. As a result of notices issued by governmental authorities and newly developed cost estimates prepared by third-party engineers, we have re-evaluated our estimates of total costs and cost sharing allocations borne by the Company, and accordingly have increased our provision by £326 million . Under the terms of our rate plans, we are entitled to recovery of environmental clean-up costs from rate payers, but under IFRS no asset can be recognised for this recovery. Also included in the total environmental charge is the £76 million impact of the change in the real discount rate applied to the environmental provisions across the Group, of which £66 million relates to the US and £10 million to the UK. Given the substantial and sustained change in gilts and corporate bond yields, we concluded it was appropriate to reduce the real discount rate from 1% to 0.5% . The weighted average remaining duration of our cash flows is now around 10 years . 2019 In assessing certain items of income and expenditure against our exceptional items framework, we concluded that the costs associated with the Massachusetts Gas labour dispute ( £283 million ), our cost efficiency and restructuring programme ( £204 million ) and impairments relating to two nuclear connection cancellations ( £137 million ) should be treated as exceptional (as described further below). We also considered whether the £95 million income from two legal settlements received in the period should be classified as exceptional. However, we concluded it was appropriate to recognise the income in earnings before exceptional items (within NGV and Other), in line with the treatment of the original costs. Cost efficiency and restructuring programmes: Our UK and US businesses incurred restructuring charges as we reviewed organisational structures, operational activities and relevant roles and responsibilities to ensure we are able to operate more efficiently and to continue to drive outperformance for customers and shareholders. The cash outflow for the year was £93 million . Massachusetts Gas labour dispute: Between June 2018 and January 2019, National Grid implemented a workforce contingency plan across its Massachusetts Gas business following the expiration of contracts for the 1,250 members of the existing workforce. The net incremental cost of the experienced contractors working alongside supervisors and workers from other areas of the business was £283 million , reflecting the financial performance of the US regulated business had the workforce contingency plan not been implemented. The total cash outflow related to the labour dispute was £320 million for the year. Impairment of nuclear connection development costs: In 2018, Toshiba announced the cancellation of its NuGen project to build a new nuclear power station at Moorside in Cumbria, and NuGen terminated its connection agreement with UK Electricity Transmission. In February 2019, Hitachi terminated its connection agreements in respect of its Horizon projects at Wylfa and Oldbury. As there was no realistic prospect of these schemes continuing in their present form, we concluded that it was appropriate to impair the assets we had been developing for over 10 years. After deducting cash inflows relating to termination fees received of £13 million , the net impairment charge was £137 million . 2018 Final settlement of LIPA MSA transition: During the year, the Group reached an agreement with LIPA on an amount in final settlement of receivables and payables that arose following the cessation of the Management Services Agreement with LIPA in December 2013. The settlement resulted in a gain of £26 million , which was recorded as exceptional, consistent with the treatment of gains and losses on the original transaction. 5. Exceptional items and remeasurements continued Remeasurements Remeasurements comprise unrealised gains or losses recorded in the consolidated income statement arising from changes in the fair value of certain of our financial assets and liabilities accounted for at fair value through profit and loss (FVTPL). These assets and liabilities include commodity contract derivatives and financing derivatives to the extent that hedge accounting is not achieved or is not effective. The unrealised gains or losses reported in profit and loss on certain additional assets and liabilities now treated at FVTPL are also classified within remeasurements. These relate to financial assets (which fail the 'solely payments of principal and interest test' under IFRS 9), the money market fund investments used by Group Treasury for cash management purposes and certain financial liabilities which we elected to designate at FVTPL. In all cases, these fair values increase or decrease because of changes in foreign exchange, commodity or other financial indices over which we have no control. We report unrealised gains or losses relating to certain discrete classes of financial assets accounted for at FVTPL within business performance. These comprise our portfolio of investments made by National Grid Partners, our investment in Sunrun Neptune 2016 LLC and the contingent consideration arising on the acquisition of Geronimo (all within NGV and Other). The performance of these assets (including changes in fair value) are included in our assessment of business performance for the relevant business units. Remeasurements excluded from business performance are made up of the following categories: i. Net gains/(losses) on commodity contract derivatives represent mark-to-market movements on certain physical and financial commodity contract obligations in the US. These contracts primarily relate to the forward purchase of energy for supply to customers, or to the economic hedging thereof, that are required to be measured at fair value and that do not qualify for hedge accounting. Under the existing rate plans in the US, commodity costs are recoverable from customers although the timing of recovery may differ from the pattern of costs incurred; ii. Net gains/(losses) on financing derivative financial instruments comprise gains and losses arising on derivative financial instruments reported in the consolidated income statement in relation to risk management of interest rate and foreign exchange exposures. These exclude gains and losses for which hedge accounting has been effective, and have been recognised directly in the consolidated statement of other comprehensive income or are offset by adjustments to the carrying value of debt (see notes 17 and 32) ; iii. Net gains/(losses) on financial assets measured at FVTPL comprise gains and losses on the investment funds held by our insurance captives which are categorised as FVTPL (see note 15) ; iv. Net gains/(losses) on financial liabilities measured at FVTPL comprises the change in the fair value (excluding changes due to own credit risk) of a financial liability that was designated at FVTPL on transition to IFRS 9 to reduce a measurement mismatch (see note 21) ; and v. Unrealised net gains/(losses) on derivatives and other financial instruments within our joint ventures and associates. Items included within tax 2020 The Finance Act 2016, which was enacted on 15 September 2016, reduced the main UK corporation tax rate to 17% with effect from 1 April 2020. Deferred tax balances were calculated at this rate for the years ended 31 March 2017 to 2019. On 17 March 2020, the UK Government utilised the Provisional Collection of Taxes Act 1968 to substantively enact a reversal of the reduction in the main UK corporation tax rate to 17% with effect from 1 April 2020, resulting in the rate remaining at 19%. Deferred taxes at the reporting date have been measured using enacted tax rates and reflected in these financial statements, resulting in a £192 million deferred tax charge, principally due to the remeasurement of deferred tax liabilities. The treatment of this charge as exceptional is consistent with the treatment for the year ended 31 March 2017 when the original reduction in the tax rate was substantively enacted, resulting in the recognition of an exceptional tax credit of £94 million . 2018 The Tax Cuts and Jobs Act (Tax Reform), which was enacted on 22 December 2017, reduced the US corporate tax rate from 35% to 21% with effect from 1 January 2018. Deferred taxes at the reporting date have been measured using these enacted tax rates. This resulted in a one-off deferred tax credit in the year ended 31 March 2018. However, as described in note 11, we expect the overall impact of Tax Reform to be economically neutral for the Group.

Finance income and costs

Finance income and costs	12 Months Ended
	Mar. 31, 2020
Analysis of income and expense [abstract]
Finance income and costs	Finance income and costs This note details the interest income generated by our financial assets and interest expense incurred on our financial liabilities, primarily our financing portfolio (including our financing derivatives). It also includes the net interest on our pensions and other post-retirement assets. In reporting business performance, we adjust net financing costs to exclude any net gains or losses on financial instruments included in remeasurements (see note 5). In addition, where debt redemptions relate to exceptional transactions they are typically treated as exceptional. The Group adopted IFRS 9 with effect from 1 April 2018. The comparatives for 2018 were not required to be restated and were accounted for in accordance with IAS 39. Following the adoption of IFRS 9, finance income and costs remeasurements include unrealised gains and losses on certain assets and liabilities now treated at FVTPL. The interest income, dividends and interest expense on these items are included in finance income and finance costs before remeasurements, respectively. 2020 2019 2018 Notes £m £m £m Finance income Interest income on financial instruments: Bank deposits and other financial assets 48 54 54 Dividends received on equities held at fair value through other comprehensive income 2 2 — Gains on disposal of available-for-sale investments — — 73 Other income 20 17 — 70 73 127 Finance costs Net interest on pensions and other post-retirement benefit obligations 25 (23 ) (22 ) (65 ) Interest expense on financial liabilities held at amortised cost: Bank loans and overdrafts (73 ) (72 ) (87 ) Other borrowings¹ (997 ) (970 ) (1,030 ) Interest expense on financial liabilities held at fair value through profit and loss (22 ) (20 ) — Derivatives (39 ) (43 ) 12 Unwinding of discount on provisions 26 (77 ) (74 ) (75 ) Other interest (10 ) — (11 ) Less: interest capitalised² 122 135 128 (1,119 ) (1,066 ) (1,128 ) Remeasurements – Finance income Net (losses)/gains on financial assets held at fair value through profit and loss (16 ) 15 — (16 ) 15 — Remeasurements – Finance costs Net losses on financial liabilities held at fair value through profit and loss (49 ) (51 ) — Net (losses)/gains on financing derivatives³: Derivatives designated as hedges for hedge accounting (13 ) (37 ) 49 Derivatives not designated as hedges for hedge accounting 14 (3 ) 70 (48 ) (91 ) 119 Total remeasurements – Finance income and costs (64 ) (76 ) 119 Finance income 54 88 127 Finance costs (1,167 ) (1,157 ) (1,009 ) Net finance costs from continuing operations (1,113 ) (1,069 ) (882 ) 1. Includes interest expense on lease liabilities (see note 13 for details). 2. Interest on funding attributable to assets in the course of construction in the current year was capitalised at a rate of 3.6% ( 2019 : 3.9% ; 2018 : 4.1% ). In the UK, capitalised interest qualifies for a current year tax deduction with tax relief claimed of £15 million ( 2019 : £19 million ; 2018 : £20 million ). In the US, capitalised interest is added to the cost of plant and qualifies for tax depreciation allowances. 3. Includes a net foreign exchange gain on financing activities of £66 million ( 2019 : £264 million gain ; 2018 : £314 million loss ) offset by foreign exchange losses and gains on financing derivatives measured at fair value.

Tax

Tax	12 Months Ended
	Mar. 31, 2020
Income Taxes [Abstract]
Tax	Tax Tax is payable in the territories where we operate, mainly the UK and the US. This note gives further details of the total tax charge and tax liabilities, including current and deferred tax. The current tax charge is the tax payable on this year’s taxable profits. Deferred tax is an accounting adjustment to provide for tax that is expected to arise in the future due to differences in the accounting and tax bases. The tax charge for the period is recognised in the income statement, the statement of comprehensive income or directly in equity, according to the accounting treatment of the related transaction. The tax charge comprises both current and deferred tax. Current tax assets and liabilities are measured at the amounts expected to be recovered from or paid to the tax authorities. The tax rates and tax laws used to compute the amounts are those that have been enacted or substantively enacted by the reporting date. The Group operates internationally in territories with different and complex tax codes. Management exercises judgement in relation to the level of provision required for uncertain tax outcomes. There are a number of tax positions not yet agreed with the tax authorities where different interpretations of legislation could lead to a range of outcomes. Judgements are made for each position having regard to particular circumstances and advice obtained. Deferred tax is provided for using the balance sheet liability method, and is recognised on temporary differences between the carrying amount of assets and liabilities in the financial statements and the corresponding tax bases. Deferred tax liabilities are generally recognised on all taxable temporary differences, and deferred tax assets are recognised to the extent that it is probable that taxable profits will be available against which deductible temporary differences can be utilised. However, deferred tax assets and liabilities are not recognised if the temporary differences arise from the initial recognition of goodwill or from the initial recognition of other assets and liabilities in a transaction (other than a business combination) that affects neither the accounting nor the taxable profit or loss. Deferred tax liabilities are recognised on taxable temporary differences arising on investments in subsidiaries and joint arrangements except where the Company is able to control the reversal of the temporary difference and it is probable that the temporary difference will not reverse in the foreseeable future. Deferred tax is calculated at the tax rates that are expected to apply in the period when the liability is settled or the asset is realised, based on the tax rates and tax laws that have been enacted or substantively enacted by the reporting date. The carrying amount of deferred tax assets is reviewed at each reporting date and reduced to the extent that it is no longer probable that sufficient taxable profits will be available to allow all or part of the deferred tax asset to be recovered. Unrecognised deferred tax assets are reassessed at each reporting date and are recognised to the extent that it has become probable that future taxable profits will allow the deferred tax asset to be recovered. Deferred tax assets and liabilities are offset when there is a legally enforceable right to offset current tax assets against current tax liabilities and when they relate to income taxes levied by the same tax authority and the Company and its subsidiaries intend to settle their current tax assets and liabilities on a net basis. 7. Tax continued The tax charge/(credit) for the year can be analysed as follows: 2020 2019 2018 £m £m £m Current tax: UK corporation tax at 19% (2019: 19%; 2018: 19%) 179 132 200 UK corporation tax adjustment in respect of prior years (4 ) (12 ) (18 ) 175 120 182 Overseas corporation tax (2 ) 8 15 Overseas corporation tax adjustment in respect of prior years (41 ) (40 ) (4 ) (43 ) (32 ) 11 Total current tax from continuing operations 132 88 193 Deferred tax: UK deferred tax 269 27 65 UK deferred tax adjustment in respect of prior years 6 2 (2 ) 275 29 63 Overseas deferred tax 64 208 (1,155 ) Overseas deferred tax adjustment in respect of prior years 9 14 10 73 222 (1,145 ) Total deferred tax from continuing operations 348 251 (1,082 ) Total tax charge/(credit) from continuing operations 480 339 (889 ) Tax charged/(credited) to the consolidated statement of comprehensive income and equity 2020 2019 2018 £m £m £m Current tax: Available-for-sale investments — — (11 ) Cash flow hedges, cost of hedging and own credit reserve — 3 — Share-based payments — — (3 ) Deferred tax: Available-for-sale investments — — (18 ) Investments at fair value through other comprehensive income (1 ) — — Cash flow hedges, cost of hedging and own credit reserve (40 ) (12 ) (4 ) Remeasurements of pension assets and post-retirement benefit obligations¹ (206 ) 12 530 Share-based payments (3 ) — 1 (250 ) 3 495 Total tax recognised in the statements of comprehensive income from continuing operations (247 ) 3 497 Total tax relating to share-based payments recognised directly in equity from continuing operations (3 ) — (2 ) (250 ) 3 495 1. Remeasurements of gains on pension assets and post-retirement benefit obligations for the year ended 31 March 2018 includes a deferred tax charge of £281 million arising on the reduction in the US corporation tax rate. 7. Tax continued The tax charge/(credit) for the year for the continuing business, is higher ( 2019 : lower tax charge; 2018 : lower tax charge) than the standard rate of corporation tax in the UK of 19% ( 2019 : 19% ; 2018 : 19% ): 2020 2019 2018 £m £m £m Profit before tax from continuing operations Before exceptional items and remeasurements 2,346 2,489 2,500 Exceptional items and remeasurements (592 ) (648 ) 160 Profit before tax from continuing operations 1,754 1,841 2,660 Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2019: 19%; 2018: 19%) 334 350 506 Effect of: Adjustments in respect of prior years¹ (30 ) (36 ) (14 ) Expenses not deductible for tax purposes 29 28 21 Non-taxable income² (18 ) (36 ) (26 ) Adjustment in respect of foreign tax rates 18 56 157 Deferred tax impact of change in UK tax rate 192 (3 ) (7 ) Deferred tax impact of change in US tax rate due to Tax Reform — — (1,510 ) Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax (17 ) (8 ) (9 ) Other³ (28 ) (12 ) (7 ) Total tax charge/(credit) from continuing operations 480 339 (889 ) % % % Effective tax rate – continuing operations 27.4 18.4 (33.4 ) 1. Prior year adjustment is primarily due to agreement of prior period tax returns. 2. Includes gains on chargeable disposals which are offset by previously unrecognised capital losses. 3. Other primarily comprises a recognition of deferred tax on previously unrecognised capital losses and claims for land remediation relief. Factors that may affect future tax charges On 17 March 2020, the UK government utilised the Provisional Collection of Taxes Act 1968 to substantively enact a reversal of the reduction in the main UK corporation tax rate to 17% with effect from 1 April 2020. The main UK corporation tax rate therefore remains at 19%. Deferred tax balances have been calculated at this rate. We will continue to monitor the developments driven by Brexit, the OECD’s Base Erosion and Profit Shifting (BEPS) project and European Commission initiatives including fiscal aid investigations. At this time, we do not expect this to have any material impact on our future tax charges. Governments across the world including the UK and the US have introduced various stimulus/reliefs for businesses to cope with the impact of the COVID-19 pandemic. We will monitor as the details become available for any that may materially impact our future tax charges. 7. Tax continued Tax included within the statement of financial position The following are the major deferred tax assets and liabilities recognised, and the movements thereon, during the current and prior reporting periods: Accelerated Share- Pensions Financial Other net differences 1 £m Total Deferred tax liabilities/(assets) At 31 March 2018 (as previously reported) 4,874 (9 ) (203 ) 21 (1,047 ) 3,636 Impact of transition to IFRS 9 and IFRS 15 19 — — (5 ) (93 ) (79 ) At 1 April 2018 (as restated) 4,893 (9 ) (203 ) 16 (1,140 ) 3,557 Exchange adjustments and other² 275 — (31 ) (3 ) (76 ) 165 (Credited)/charged to income statement 309 — 52 6 (124 ) 243 Charged/(credited) to other comprehensive income and equity — — 12 (12 ) — — At 1 April 2019 5,477 (9 ) (170 ) 7 (1,340 ) 3,965 Exchange adjustments and other² 210 (30 ) (28 ) (3 ) (27 ) 122 (Credited)/charged to income statement 613 (7 ) 44 (13 ) (287 ) 350 Charged/(credited) to other comprehensive income and equity — (2 ) (206 ) (46 ) 1 (253 ) At 31 March 2020 6,300 (48 ) (360 ) (55 ) (1,653 ) 4,184 1. The deferred tax asset of £1,653 million as at 31 March 2020 ( 2019 : £1,340 million ) in respect of other net temporary differences primarily relates to net operating losses of £547 million ( 2019 : £423 million ) and US environmental provisions of £529 million ( 2019 : £409 million ). 2. Exchange adjustments and other comprises foreign exchange arising on translation of the US dollar deferred tax balances. It also includes reclassification of £29 million from other temporary differences to share-based payments. Deferred tax assets and liabilities are only offset where there is a legally enforceable right of offset and there is an intention to settle the balances net. The deferred tax balances (after offset) for statement of financial position purposes consist solely of deferred tax liabilities of £4,184 million ( 2019 : £3,965 million ). This balance is after offset of a deferred tax asset of £547 million ( 2019 : £423 million ) which has been recognised in respect of net operating losses ( £535 million ) and capital losses ( £12 million ). Deferred tax assets in respect of some capital losses as well as trading losses and non-trade deficits have not been recognised as their future recovery is uncertain or not currently anticipated. The deferred tax asset not recognised relating to capital losses has increased due to remeasurement of opening deferred tax asset as a result of change in substantively enacted UK corporation tax rate from 17% to 19%. Hence the total deferred tax assets not recognised are as follows: 2020 2019 £m £m Capital losses 1,626 1,470 Non-trade deficits 1 4 Trading losses 6 5 The capital losses arose in the UK on disposal of certain businesses or assets. They are available to carry forward indefinitely but can only be offset against future capital gains. The UK non-trade deficits arose prior to 1 April 2017 and therefore can only be offset against future non-trade profits. At 31 March 2020 and 31 March 2019 , there were no recognised deferred tax liabilities for taxes that would be payable on the unremitted earnings of the Group’s subsidiaries or its associates as there are no significant corporation tax consequences of the Group’s UK, US or overseas subsidiaries or associates paying dividends to their parent companies. There are also no significant income tax consequences for the Group from the payment of dividends by the Group to its shareholders.

Earnings per share (EPS)

Earnings per share (EPS)	12 Months Ended
	Mar. 31, 2020
Earnings per share [abstract]
Earnings per share (EPS)	Earnings per share (EPS) EPS is the amount of post-tax profit attributable to each ordinary share. Basic EPS is calculated on profit for the year attributable to equity shareholders divided by the weighted average number of shares in issue during the year. Diluted EPS shows what the impact would be if all outstanding share options were exercised and treated as ordinary shares at year end. The weighted average number of shares is increased by additional shares issued as scrip dividends and reduced by shares repurchased by the Company during the year. The earnings per share calculations are based on profit after tax attributable to equity shareholders of the Company which excludes non-controlling interests. Adjusted earnings and EPS, which exclude exceptional items and remeasurements, are provided to reflect the business performance sub-totals used by the Company. We have included reconciliations from this additional EPS measure to earnings for both basic and diluted EPS to provide additional detail for these items. For further details of exceptional items and remeasurements, see note 5. Following the sale of the UK Gas Distribution business on 31 March 2017, National Grid plc returned £3,171 million of proceeds to shareholders through a special dividend, paid on 2 June 2017. In order to maintain the comparability of the Company’s share price before and after the special dividend, this was preceded by a share consolidation undertaken on 22 May 2017, replacing every 12 existing ordinary shares with 11 new ordinary shares. The weighted average number of ordinary shares outstanding for the year ended 31 March 2018 includes the effect of both the share consolidation and the special dividend from the date that the special dividend was paid. The associated share buyback programme which began on 2 June 2017 completed in March 2018. Purchased shares are held as treasury shares. (a) Basic EPS Earnings EPS Earnings EPS Earnings EPS 2020 2020 2019 2019 2018 2018 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,912 55.2 1,998 59.0 1,915 55.3 Exceptional items and remeasurements after tax from continuing operations (639 ) (18.4 ) (499 ) (14.7 ) 1,633 47.2 Earnings from continuing operations 1,273 36.8 1,499 44.3 3,548 102.5 Adjusted earnings from discontinued operations 5 0.2 57 1.7 145 4.2 Exceptional items and remeasurements after tax from discontinued operations (14 ) (0.5 ) (45 ) (1.4 ) (143 ) (4.1 ) Earnings from discontinued operations (9 ) (0.3 ) 12 0.3 2 0.1 Total adjusted earnings 1,917 55.4 2,055 60.7 2,060 59.5 Total exceptional items and remeasurements after tax (including discontinued operations) (653 ) (18.9 ) (544 ) (16.1 ) 1,490 43.1 Total earnings 1,264 36.5 1,511 44.6 3,550 102.6 2020 2019 2018 millions millions millions Weighted average number of ordinary shares – basic 3,461 3,386 3,461 (b) Diluted EPS Earnings EPS Earnings EPS Earnings EPS 2020 2020 2019 2019 2018 2018 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,912 55.0 1,998 58.8 1,915 55.1 Exceptional items and remeasurements after tax from continuing operations (639 ) (18.4 ) (499 ) (14.7 ) 1,633 47.0 Earnings from continuing operations 1,273 36.6 1,499 44.1 3,548 102.1 Adjusted earnings from discontinued operations 5 0.1 57 1.7 145 4.2 Exceptional items and remeasurements after tax from discontinued operations (14 ) (0.4 ) (45 ) (1.4 ) (143 ) (4.2 ) Earnings from discontinued operations (9 ) (0.3 ) 12 0.3 2 — Total adjusted earnings 1,917 55.1 2,055 60.5 2,060 59.3 Total exceptional items and remeasurements after tax (including discontinued operations) (653 ) (18.8 ) (544 ) (16.1 ) 1,490 42.8 Total earnings 1,264 36.3 1,511 44.4 3,550 102.1 2020 2019 2018 millions millions millions Weighted average number of ordinary shares – diluted 3,478 3,401 3,476 8. Earnings per share (EPS) continued (c) Reconciliation of basic to diluted average number of shares 2020 2019 2018 millions millions millions Weighted average number of ordinary shares – basic 3,461 3,386 3,461 Effect of dilutive potential ordinary shares – employee share plans 17 15 15 Weighted average number of ordinary shares – diluted 3,478 3,401 3,476

Dividends

Dividends	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Dividends	Dividends Interim dividends are recognised when they become payable to the Company’s shareholders. Final dividends are recognised when they are approved by shareholders. 2020 2019 2018 Pence per share Cash dividend paid £m Scrip dividend £m Pence per share Cash dividend paid £m Scrip dividend £m Pence per share Cash dividend paid £m Scrip dividend £m Interim dividend in respect of the current year 16.57 335 241 16.08 450 94 15.49 346 176 Special dividend — — — — — — 84.375 3,171 — Final dividend in respect of the prior year 31.26 557 517 30.44 710 319 29.10 970 33 47.83 892 758 46.52 1,160 413 128.965 4,487 209 The Directors are proposing a final dividend for the year ended 31 March 2020 of 32.0p per share that will absorb approximately £1,123 million of shareholders’ equity (assuming all amounts are settled in cash). It will be paid on 19 August 2020 to shareholders who are on the register of members at 3 July 2020 (subject to shareholders’ approval at the AGM). A scrip dividend will be offered as an alternative. Following completion of the sale of the majority interest in UK Gas Distribution, the Company paid a special dividend on 2 June 2017 of 84.375 p per existing ordinary share ( $5.4224 per existing American Depositary Share). This returned £3,171 million to shareholders. No scrip dividend was offered as an alternative.

Discontinued operations and ass

Discontinued operations and assets held for sale	12 Months Ended
	Mar. 31, 2020
Non-current Assets Held For Sale And Discontinued Operations [Abstract]
Discontinued operations	Discontinued operations and assets held for sale The results and cash flows of significant assets or businesses sold during the year are shown separately from our continuing operations, and presented within discontinued operations in the income statement and cash flow statement. Assets and businesses are classified as held for sale when their carrying amounts are recovered through sale rather than through continuing use. They only meet the held for sale condition when the assets are ready for immediate sale in their present condition, management is committed to the sale and it is highly probable that the sale will complete within one year. Depreciation ceases on assets and businesses when they are classified as held for sale and the assets and businesses are impaired if the proceeds less sale costs fall short of the carrying value. In June 2019, the Group sold its remaining 39% interest in Cadent (held through its holding in Quadgas HoldCo Limited (Quadgas)). This interest had been classified as held for sale from 30 June 2018 until the date of disposal, as detailed in the Annual Report and Accounts for the year ended 31 March 2019. The aggregate carrying value of our investment in Quadgas at the disposal date was £1,956 million . This was comprised of the carrying value of the Group’s equity interest in Quadgas of £1,494 million , a shareholder loan to Quadgas of £352 million and a derivative financial asset with a fair value of £110 million . The total sales proceeds were £1,965 million . The gain on disposal was £9 million . We considered the disposal of our 39% investment in Quadgas as the final stage of the plan to dispose of our interest in the UK Gas Distribution business first announced in 2015, and accordingly treated the results and cash flows arising from Quadgas as a discontinued operation on the basis that the sale formed the final part of a ‘single coordinated plan’ to dispose of UK Gas Distribution. As a consequence, we have classified the various elements of income, expense and cash flows within discontinued operations as set out below. Once the assets are treated as ‘held for sale’, equity accounting ceases for our investment in our associate. We therefore ceased to record our share of profits from 30 June 2018. The summary income statement for discontinued operations is as follows: 2020 2019 2018 £m £m £m Revenue — — — Operating costs¹ (23 ) (1 ) (41 ) Operating loss (23 ) (1 ) (41 ) Net finance income 6 23 137 Share of post-tax results of joint ventures and associates² — (5 ) (89 ) (Loss)/profit before tax from discontinued operations (17 ) 17 7 Tax from discontinued operations (1 ) (5 ) (5 ) (Loss)/profit after tax from discontinued operations (18 ) 12 2 Gain on disposal 9 — — Total (loss)/profit after tax from discontinued operations³ (9 ) 12 2 1. Operating costs for the year ended 31 March 2020 relate to final transaction costs and other expenses in relation to Quadgas. Operating costs of £41 million for the year ended 31 March 2018 related to amounts in respect of the disposal of the UK Gas Distribution business, primarily relating to the completion accounts settlement in November 2017. 2. For the year ended 31 March 2019, the amount presented is the net of £43 million impairment charge against the investment in Quadgas (see note 16) and £38 million share of Quadgas post-tax profits recognised prior to classification as held for sale. 3. Of the total profit after tax from discontinued operations, the £23 million of operating expenses and the £9 million gain on disposal are treated as exceptional. For the year ended 31 March 2019, the £43 million impairment charge against the investment in Quadgas, net operating costs of £1 million and the tax thereon are classified as exceptional items. The summary statement of comprehensive income for discontinued operations is as follows: 2020 2019 2018 £m £m £m (Loss)/profit after tax from discontinued operations (9 ) 12 2 Other comprehensive income Items that will never be reclassified to profit or loss: Share of other comprehensive income of associate, net of tax — 36 142 Total items from discontinued operations that will never be reclassified to profit or loss — 36 142 Items that may be reclassified subsequently to profit or loss: Net gains in respect of cash flow hedges 6 — — Share of other comprehensive income of associate, net of tax — — 5 Total items from discontinued operations that may be reclassified subsequently to profit or loss 6 — 5 Other comprehensive income for the year, net of tax from discontinued operations 6 36 147 Total comprehensive (loss)/income for the year from discontinued operations (3 ) 48 149 The summary cash flows for discontinued operations are as follows: Cash flows used in operating activities of £97 million ( 2019 : £71 million ; 2018: £207 million ) primarily related to cash outflows in respect of voluntary contributions totalling £66 million paid to the Warm Homes Fund, the utilisation of provisions and the payment of the final transaction fees incurred in the period. T he utilisation of provisions in 2018 mainly related to payments of professional fees in respect of the disposal of the UK Gas Distribution business. Cash inflows from investing activities of £6 million ( 2019 : £156 million ; 2018: £171 million ) were comprised of dividends received and interest received on the shareholder loan. There were no cash flows for financing activities in 2020 or 2019. In 2018, net cash flows used in financing activities were £231 million for the settlement of RPI swaps relating to the final stages of the Group-wide liability management programme executed as part of sale process of the UK Gas Distribution business .

Goodwill

Goodwill	12 Months Ended
	Mar. 31, 2020
Intangible Assets [Abstract]
Goodwill	Goodwill Goodwill represents the excess of what we paid to acquire businesses over the fair value of their net assets at the acquisition date. We assess whether goodwill is recoverable each year by performing an impairment review. Goodwill is recognised as an asset and is not amortised, but is tested for impairment annually or more frequently if events or changes in circumstances indicate a potential impairment. Any impairment is recognised immediately in the income statement and is not subsequently reversed. Goodwill and fair value adjustments arising on the acquisition of a foreign entity are treated as assets and liabilities of the foreign entity and translated at the closing exchange rate. Goodwill is allocated to cash-generating units and this allocation is made to those cash-generating units that are expected to benefit from the business combination in which the goodwill arose. Impairment is recognised where there is a difference between the carrying value of the cash-generating unit and the estimated recoverable amount of the cash‑generating unit to which that goodwill has been allocated. Any impairment loss is first allocated to the carrying value of the goodwill and then to the other assets within the cash-generating unit. Recoverable amount is defined as the higher of fair value less costs to sell and estimated value-in-use at the date the impairment review is undertaken. Value-in-use represents the present value of expected future cash flows, discounted using a pre-tax discount rate that reflects current market assessments of the time value of money and the risks specific to the asset for which the estimates of future cash flows have not been adjusted. Impairments are recognised in the income statement and are disclosed separately. Total £m Net book value at 1 April 2018 5,444 Exchange adjustments 425 Net book value at 31 March 2019 5,869 Additions 81 Exchange adjustments 283 Net book value at 31 March 2020 6,233 Additions in the period relate to the goodwill recognised on the acquisition of Geronimo. Refer to note 38 for details. There is no significant accumulated impairment charge as at 31 March 2020 or 31 March 2019 . The amounts disclosed above as at 31 March 2020 relate to the following cash-generating units: New York £3,544 million ( 2019 : £3,382 million ); Massachusetts £1,325 million ( 2019 : £1,264 million ); Rhode Island £493 million ( 2019 : £470 million ); Federal £790 million ( 2019 : £753 million ); and Geronimo £81 million ( 2019 : £nil ). Goodwill is reviewed annually for impairment and the recoverability of goodwill has been assessed by comparing the carrying amount of our operations described above (our cash-generating units) with the expected recoverable amount on a value-in-use basis. In each assessment, the value-in-use has been calculated based on five-year plan projections that incorporate our best estimates of future cash flows, customer rates, costs (including changes in commodity prices), future prices and growth. Such projections reflect our current regulatory rate plans taking into account regulatory arrangements to allow for future rate plan filings and recovery of investment. Our plans have proved to be reliable guides in the past and the Directors believe the estimates are appropriate. The future economic growth rate used to extrapolate projections beyond five years is 2.1% ( 2019 : 2.2% ). The growth rate has been determined having regard to data on projected growth in US real gross domestic product (GDP). Based on the position of our business in the underlying US economy, it is appropriate for the terminal growth rate to be based upon the overall growth in real GDP and, given the nature of our operations, to extend over a long period of time. Cash flow projections have been discounted to reflect the time value of money, using a post-tax discount rate of 4.5% ( 2019 : 5.3% ). The equivalent pre-tax discount rate is 4.5% ( 2019 : 5.3% ) as tax is assumed to be a pass-through cost to our customers, recoverable under our rate plans. The discount rate represents the estimated weighted average cost of capital of these operations. In reaching this conclusion, the Directors considered the manner in which Tax Reform has impacted the Group and its future cash flows. In our US business, we are subject to federal and state taxes; however, our regulatory arrangements require us to pass this cost back to our customers. The reduction in the corporation tax rate in 2018 from 35% to 21% is being reflected through lower bills to customers, reducing our revenues (and tax costs) in future periods. For the purposes of the goodwill impairment exercise, we have reflected the lower billing levels through lower revenue forecasts as well as lower tax charges. Historically, as a result of tax losses arising from claiming accelerated depreciation allowances, we have not paid substantial amounts of tax in the US. Accordingly, for IFRS purposes, we have recognised significant deferred tax liabilities in respect of these accelerated allowances. In accounting terms, Tax Reform triggered the remeasurement of our deferred tax liabilities from 35% to 21% for the year ended 31 March 2018. However, the impact for our US business is that the amounts we have previously received from customers assuming a 35% federal tax rate instead of a 21% federal tax rate must now be returned to customers over a period of up to 50 years. Offsetting this change is the additional income we earn, since the rate base grows faster. (Our rate base is net of deferred tax liabilities, which, as a result of Tax Reform, is now smaller.) In overall terms, the outcome is economically neutral. In assessing the carrying value of goodwill, we have sensitised our forecasts to factor in a reduction in revenues and lower tax costs into our cash flow forecasts, but we have not reflected the impact of additional rate base growth on future earnings. While it is possible that a key assumption in the calculation could change, the Directors believe that no reasonably foreseeable change would result in an impairment of goodwill, in view of the long-term nature of the key assumptions and the margin by which the estimated value-in-use exceeds the carrying amount. This remains the case even after taking into account the short-term effects of COVID-19, the most significant of which is an increase in bad debt charges in the short-term.

Other intangible assets

Other intangible assets	12 Months Ended
	Mar. 31, 2020
Intangible Assets [Abstract]
Other intangible assets	Other intangible assets Other intangible assets include software which is written down (amortised) over the period we expect to receive a benefit from the asset. Identifiable intangible assets are recorded at cost less accumulated amortisation and any provision for impairment. Other intangible assets are tested for impairment only if there is an indication that the carrying value of the assets may have been impaired. Impairments of assets are calculated as the difference between the carrying value of the asset and the recoverable amount, if lower. Where such an asset does not generate cash flows that are independent from other assets, the recoverable amount of the cash-generating unit to which that asset belongs is estimated. Impairments are recognised in the consolidated income statement and are disclosed separately. Any assets which suffered impairment in a previous period are reviewed for possible reversal of the impairment at each reporting date. Internally generated intangible assets, such as software, are recognised only if: i) an asset is created that can be identified; ii) it is probable that the asset created will generate future economic benefits; and iii) the development cost of the asset can be measured reliably. Where no internally generated intangible asset can be recognised, development expenditure is recorded as an expense in the period in which it is incurred. Other intangible assets are amortised on a straight-line basis over their estimated useful economic lives. Amortisation periods for intangible assets are: Years Software 1 to 10 Software £m Cost at 1 April 2018 1,797 Exchange adjustments 70 Additions 306 Disposals (15 ) Reclassifications¹ 10 Cost at 31 March 2019 2,168 Exchange adjustments 63 Additions 352 Disposals — Reclassifications¹ — Cost at 31 March 2020 2,583 Accumulated amortisation at 1 April 2018 (898 ) Exchange adjustments (26 ) Amortisation charge for the year (175 ) Accumulated amortisation of disposals 15 Accumulated amortisation at 31 March 2019 (1,084 ) Exchange adjustments (28 ) Amortisation charge for the year (176 ) Accumulated amortisation of disposals — Accumulated amortisation at 31 March 2020 (1,288 ) Net book value at 31 March 2020² 1,295 Net book value at 31 March 2019 1,084 1. Reclassifications includes amounts transferred from property, plant and equipment (see note 13). 2. Included in software is £69 million ( 2019 : £116 million ) relating to the US Enterprise Resource Planning system, which still has a remaining amortisation period of three years.

Property, plant and equipment

Property, plant and equipment	12 Months Ended
	Mar. 31, 2020
Property, plant and equipment [abstract]
Property, plant and equipment	Property, plant and equipment The following note shows the physical assets controlled by us. The cost of these assets primarily represents the amount initially paid for them. This includes both their purchase price and the construction and other costs associated with getting them ready for operation. A depreciation expense is charged to the income statement to reflect annual wear and tear and the reduced value of the asset over time. Depreciation is calculated by estimating the number of years we expect the asset to be used (useful economic life or UEL) and charging the cost of the asset to the income statement equally over this period. We operate an energy networks business and therefore have a significant physical asset base. We continue to invest in our networks to maintain reliability, create new customer connections and ensure our networks are flexible and resilient. Our business plan envisages these additional investments will be funded through a mixture of cash generated from operations and the issue of new debt. Property, plant and equipment is recorded at cost, less accumulated depreciation and any impairment losses. Cost includes the purchase price of the asset; any payroll and finance costs incurred which are directly attributable to the construction of property, plant and equipment; and the cost of any associated asset retirement obligations. Property, plant and equipment includes assets in which the Group’s interest comprises legally protected statutory or contractual rights of use. Additions represent the purchase or construction of new assets, including capital expenditure for safety and environmental assets, and extensions to, enhancements to, or replacement of, existing assets. All costs associated with projects or activities which have not been fully commissioned at the period end are classified within assets in the course of construction. No depreciation is provided on freehold land or assets in the course of construction. Other items of property, plant and equipment are depreciated, on a straight-line basis, at rates estimated to write off their book values over their estimated useful economic lives. In assessing estimated useful economic lives, consideration is given to any contractual arrangements and operational requirements relating to particular assets. The assessments of estimated useful economic lives and residual values of assets are performed annually. Unless otherwise determined by operational requirements, the depreciation periods for the principal categories of property, plant and equipment are, in general, as shown in the table below split between the UK and US, along with the weighted average remaining UEL for each class of property, plant and equipment (which is calculated by applying the annual depreciation charge per class of asset by the net book value of that class of asset). Years UK US Weighted average remaining UEL Freehold and leasehold buildings up to 60 up to 100 26 Plant and machinery: Electricity transmission plant and wires 10 to 100 45 to 80 40 Electricity distribution plant n/a 35 to 85 37 Electricity generation plant 15 to 40 20 to 93 21 Interconnector plant and other 5 to 60 8 to 50 23 Gas plant – mains, services and regulating equipment 10 to 65 47 to 95 49 Gas plant – storage 5 to 40 12 to 65 13 Gas plant – meters 7 to 30 14 to 65 18 Motor vehicles and office equipment up to 10 up to 26 5 Gas asset lives The role that gas networks play in the pathway to achieving the greenhouse gas emissions reductions targets set in the jurisdictions in which we operate is currently uncertain. However, we believe the gas assets which we own and operate today will continue to have a crucial role in maintaining security, reliability and affordability of energy beyond 2050, although the scale and purpose for which the networks will be used is dependent on technological developments and policy choices of governments and regulators. • In the UK, the gas mains, services and regulating assets relating to the National Transmission System (NTS) were subject to a detailed review in January 2019. The most material components of these are our pipeline assets, which are due to be fully depreciated by 2070, with other assets being depreciated over various periods between now and then. That review was undertaken prior to the UK enacting legislation committing to net zero by 2050, but considered scenarios which included an extension of the emissions reduction targets (80% emissions reduction target at the time of the report). The review concluded that the most likely outcome was for the NTS network assets to remain in use beyond 2050, including in those scenarios where the greenhouse gas emissions of gas networks were largely eliminated. We do not believe developments since January 2019 would change the conclusions of this review. • With respect to our US gas distribution assets, asset lives are assessed as part of detailed depreciation studies completed as part of each separate rate proceeding. Depreciation studies consider the physical condition of assets and the expected operational life of an asset. We believe these assessments are our best estimate of the UEL of our gas network assets in the US. The weighted average remaining UEL for our US gas distribution fixed asset base is circa 50 years, however a sizeable proportion of our assets are assumed to have UELs which extend beyond 2080. We continue to believe the lives identified by rate proceedings are the best estimate of the assets’ UELs, although we continue to keep this assumption under review as we learn more about possible future pathways towards net zero. Whilst the targets, goals and ambitions have now been formalised in legislation in the states in which we operate, there is widespread recognition that work needs to be done to define the possible future decarbonisation pathways. Asset depreciation lives feed directly into our regulatory recovery mechanisms, such that any shortening of asset recovery periods as agreed with regulators should be recoverable through future rates, subject to agreement, over future periods, as part of wider considerations around ensuring the continuing affordability of gas in our service territories. 13. Property, plant and equipment continued Given the uncertainty described relating to the UELs of our gas assets, below we provide a sensitivity on the depreciation charge for our UK and US regulated segments were a shorter UEL presumed: Increase in depreciation expense UK regulated £m US regulated £m UELs limited to 2050 37 151 UELs limited to 2060 13 66 UELs limited to 2070 — 26 Note that this sensitivity calculation excludes any assumptions regarding residual value for our asset base and the effect shortening asset depreciation lives would expect to have on our regulatory recovery mechanisms. Items within property, plant and equipment are tested for impairment only if there is some indication that the carrying value of the assets may have been impaired. Impairments of assets are calculated as the difference between the carrying value of the asset and the recoverable amount, if lower. Where such an asset does not generate cash flows that are independent from other assets, the recoverable amount of the cash-generating unit to which that asset belongs is estimated. Impairments are recognised in the income statement and if immaterial are included within the depreciation charge for the year. Land and buildings £m Plant and machinery £m Assets in the course of construction 1 £m Motor vehicles and office equipment £m Total £m Cost at 1 April 2018 2,930 49,374 4,273 857 57,434 Exchange adjustments 114 2,001 70 47 2,232 Additions 34 391 3,533 57 4,015 Disposals (35 ) (357 ) (159 ) (44 ) (595 ) Reclassifications² 295 2,974 (3,292 ) 13 (10 ) Cost at 1 April 2019 (as previously reported) 3,338 54,383 4,425 930 63,076 Right-of-use assets recognised on transition to IFRS 16³ 381 67 — 20 468 Cost at 1 April 2019 (as restated) 3,719 54,450 4,425 950 63,544 Exchange adjustments 98 1,511 53 33 1,695 Additions 130 464 4,029 104 4,727 Disposals (79 ) (486 ) (9 ) (65 ) (639 ) Reclassifications 2,4 29 4,303 (4,433 ) 14 (87 ) Cost at 31 March 2020 3,897 60,242 4,065 1,036 69,240 Accumulated depreciation at 1 April 2018 (674 ) (16,398 ) — (509 ) (17,581 ) Exchange adjustments (19 ) (501 ) — (25 ) (545 ) Depreciation charge for the year (93 ) (1,229 ) (150 ) (101 ) (1,573 ) Disposals 7 335 150 44 536 Reclassifications² 1 (1 ) — — — Accumulated depreciation at 1 April 2019 (778 ) (17,794 ) — (591 ) (19,163 ) Exchange adjustments (16 ) (372 ) — (20 ) (408 ) Depreciation charge for the year (92 ) (1,252 ) — (120 ) (1,464 ) Disposals 36 464 — 58 558 Reclassifications² 3 (7 ) — 11 7 Accumulated depreciation at 31 March 2020 (847 ) (18,961 ) — (662 ) (20,470 ) Net book value at 31 March 2020 3,050 41,281 4,065 374 48,770 Net book value at 31 March 2019 2,560 36,589 4,425 339 43,913 1. In 2019, included within disposals are UK nuclear connections development costs of £150 million (before £13 million of termination income) which were written off. See note 5 for further details. 2. Represents amounts transferred between categories, (to)/from other intangible assets (see note 12), reclassifications from inventories and reclassifications between cost and accumulated depreciation. 3. £468 million of additional right-of-use assets were recognised on transition to IFRS 16 on 1 April 2019. See note 37 for details. 4. Comprises an £87 million reduction in gross cost of assets in the course of construction in our UK Electricity Transmission business for costs previously capitalised and accrued as due to a supplier that are no longer payable. 13. Property, plant and equipment continued Right-of-use assets The Group leases various properties, land, equipment and cars. With effect from 1 April 2019 , new lease arrangements entered into are recognised as a right-of-use asset and a corresponding liability at the date at which the leased asset is available for use by the Group (see note 37). The right-of-use asset and associated lease liability arising from a lease are initially measured at the present value of the lease payments expected over the lease term, plus any other costs. The discount rate applied is the rate implicit in the lease or, if that is not available, then the incremental rate of borrowing for a similar term and similar security. The lease term takes account of exercising any extension options that are at our option if we are reasonably certain to exercise the option and any lease termination options unless we are reasonably certain not to exercise the option. Each lease payment is allocated between the liability and finance cost. The finance cost is charged to the income statement over the lease period using the effective interest rate method. The right-of-use asset is depreciated over the shorter of the asset’s useful life and the lease term on a straight-line basis. For short-term leases (lease term of 12 months or less) and leases of low-value assets (such as computers), the Group continues to recognise a lease expense on a straight-line basis. Included within the net book value of property, plant and equipment at 31 March 2020 are right-of-use assets, split as follows: Land and buildings £m Plant and machinery £m Assets in the course of construction £m Motor vehicles and office equipment £m Total Net book value at 31 March 2020 364 95 — 225 684 Additions 10 1 — 73 84 Depreciation charge for the year ended 31 March 2020 (29 ) (16 ) — (72 ) (117 ) The following balances have been included in the income statement for the year ended 31 March 2020 in respect of right-of-use assets: Total Included within net finance income and costs: Interest expense on lease liabilities (26 ) Included within revenue: Lease income 35 Included within operating expenses: Expenses relating to low-value leases (12 ) The associated lease liabilities are disclosed in note 21. The total of future minimum sub lease payments expected to be received under non-cancellable sub leases is £94 million ( 2019 : £86 million ). 2020 2019 £m £m Information in relation to property, plant and equipment Capitalised interest included within cost 2,118 1,995 Contributions to cost of property, plant and equipment included within: Trade and other payables 84 87 Non-current liabilities 428 372 Contract liabilities – current 76 61 Contract liabilities – non-current 1,082 933

Other non-current assets

Other non-current assets	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Other non-current assets	Other non-current assets Other non-current assets include assets that do not fall into any other non-current asset category (such as goodwill or property, plant and equipment) where the benefit to be received from the asset is not due to be received until after 31 March 2021. 2020 2019 £m £m Other receivables 35 28 Non-current tax assets 65 56 Prepayments 19 7 Accrued income¹ 235 173 354 264 1. Includes accrued income in relation to property sales to the St William joint venture.

Financial and other investments

Financial and other investments	12 Months Ended
	Mar. 31, 2020
Disclosure of financial assets [abstract]
Financial and other investments	Financial and other investments The Group holds a range of financial and other investments. These investments include short-term money funds, quoted investments in equities or bonds of other companies, long-term loans to our joint ventures, investments in our venture capital portfolio (National Grid Partners), bank deposits with a maturity of greater than three months, and cash balances that cannot be readily used in operations, principally collateral pledged against derivative holdings. The Group has reported four categories of financial investments, and the classification for each investment is dependent on its contractual cash flows and the business model it is held under and recognised on trade date. Debt instruments that have contractual cash flows that are solely payments of principal and interest, and which are held within a business model whose objective is to collect contractual cash flows, are held at amortised cost. This category includes our long-term loans to joint ventures as well as receivables in relation to deposits and collateral. Debt investments that have contractual cash flows that are solely payments of principal and interest, and which are held within a business model whose objective is both to collect the contractual cash flows and to sell the debt instruments, are measured at fair value through other comprehensive income. On disposal, any realised gains or losses are recycled to the income statement in investment income (see note 6). Other investments include insurance contracts, measured at fair value, and held to back the present value of unfunded obligations in note 25. The Group has elected to measure equity instruments at fair value through other comprehensive income that are shares held as part of a portfolio of financial instruments which back some long-term employee liabilities. They are not held for trading and so recognising gains and losses on these investments in profit and loss would not be representative of performance in the year. On disposal, any realised gains and losses are transferred to retained profits (see note 28). Other financial investments are subsequently measured at fair value through profit and loss. This primarily comprises our money market funds, insurance company fund investments and corporate venture capital investments held by National Grid Partners. Financial and other investments are initially recognised on trade date. Subsequent to initial recognition, the fair values of financial assets that are quoted in active markets are based on bid prices. When independent prices are not available, fair values are determined using valuation techniques used by the relevant markets. The techniques use observable market data to the extent available. 2020 2019 £m £m Non-current Debt and other investments at fair value through other comprehensive income 352 343 Equity investments at fair value through other comprehensive income 83 93 Investments at fair value through profit and loss 108 62 Loans to joint ventures¹ — 169 543 667 Current Investments at fair value through profit and loss 1,278 1,311 Financial assets at amortised cost 720 670 1,998 1,981 2,541 2,648 Financial and other investments include the following: Investments in short-term money funds² 978 969 Insurance company fund investments³ 300 342 Equities 4 83 93 Bonds 4 132 122 Cash surrender value of life insurance policies 4 220 221 Loans to joint ventures — 169 National Grid Partners and other investments 5 108 62 Restricted balances: Collateral 6 685 637 Other 35 33 2,541 2,648 1. As at 31 March 2019 , this related to a loan to a joint venture, which was measured at amortised cost. 2. Includes £1 million ( 2019 : £6 million ) held as insurance company fund investments and £26 million ( 2019 : £22 million ) US non-qualified plan investments, and therefore restricted. 3. Includes restricted amounts of £300 million ( 2019 : £342 million ) held as insurance company fund investments. 4. Includes restricted amounts of £435 million ( 2019 : £436 million ) relating to US non-qualified plan investments. 5. This includes a series of small unquoted equity investments held by National Grid Partners of £97 million ( 2019 : £51 million ). 6. Refers to collateral placed with counterparties with whom we have entered into a credit support annex to the ISDA (International Swaps and Derivatives Association) Master Agreement. 15. Financial and other investments continued Fair value through profit and loss and fair value through other comprehensive income investments are recorded at fair value. The carrying value of current financial assets at amortised cost approximates their fair values, primarily due to short-dated maturities. The carrying value of the non-current loans to joint ventures approximates their fair values as at 31 March 2019 . The exposure to credit risk at the reporting date is the fair value of the financial investments. For further information on our credit risk, refer to note 32(a). For the purposes of impairment assessment, the investments in bonds are considered to be low risk as they are managed with an investment remit to hold investment grade securities; life insurance policies are held with regulated insurance companies; and deposits, collateral receivable and other financial assets at amortised cost are investment grade. All financial assets held at fair value through other comprehensive income or amortised cost are therefore considered to have low credit risk and have a loss allowance equal to 12-month expected credit losses. In determining the expected credit losses for these assets, some or all of the following information has been considered: credit ratings, the financial position of counterparties, the future prospects of the relevant industries and general economic forecasts. No fair value through other comprehensive income or amortised cost financial assets have had modified cash flows during the period. There has been no change in the estimation techniques or significant assumptions made during the year in assessing the loss allowance for these financial assets. There were no significant movements in the gross carrying value of financial assets during the year that contribute to changes in the loss allowance. No collateral is held in respect of any of the financial investments in the above table. No balances are more than 30 days past due, and no balances were written off during the year.

Investments in joint ventures a

Investments in joint ventures and associates	12 Months Ended
	Mar. 31, 2020
Interests In Other Entities [Abstract]
Investments in joint ventures and associates	Investments in joint ventures and associates Investments in joint ventures and associates represent businesses we do not control but over which we exercise joint control or significant influence. They are accounted for using the equity method. A joint venture is an arrangement established to engage in economic activity, which the Group jointly controls with other parties and has rights to the net assets of the arrangement. An associate is an entity which is neither a subsidiary nor a joint venture, but over which the Group has significant influence. 2020 2019 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 291 317 608 1,807 361 2,168 Exchange adjustments 20 12 32 17 (6 ) 11 Additions 16 156 172 58 85 143 Capitalisation of shareholder loan to Nemo Link Limited — 176 176 — — — Impairment charge against investment in Quadgas — — — (43 ) — (43 ) Transfer of interest in Quadgas to assets held for sale — — — (1,625 ) — (1,625 ) Share of post-tax results for the year 40 47 87 67 11 78 Share of other comprehensive income of associates, net of tax 1 — 1 37 — 37 Dividends received (41 ) (34 ) (75 ) (38 ) (30 ) (68 ) Other movements¹ 14 (20 ) (6 ) 11 (104 ) (93 ) Share of net assets at 31 March 341 654 995 291 317 608 1. Other movements on joint ventures relate to reducing the carrying value of the investment in St William Homes LLP to reflect deferred income we expect to recognise over the next 10 years . A list of joint ventures and associates including the name and proportion of ownership is provided in note 34. Transactions with and outstanding balances with joint ventures and associates are shown in note 31. The joint ventures and associates have no significant contingent liabilities to which the Group is exposed, and the Group has no significant contingent liabilities in relation to its interests in the joint ventures and associates. The Group has capital commitments of £240 million ( 2019 : £18 million ) in relation to joint ventures. 16. Investments in joint ventures and associates continued At 31 March 2020 , the Group had three material joint ventures, being its 50% equity stakes in BritNed and Nemo Link Limited (Nemo) and its 51% stake in Emerald Energy Venture LLC (Emerald). The Group has one material associate, being its 26.25% investment in Millennium Pipeline Company LLC. BritNed is a joint venture with the Dutch transmission system operator, TenneT, and operates the subsea electricity link between Great Britain and the Netherlands, commissioned in 2011. Nemo is a joint venture with the Belgian transmission operator, Elia, and is a subsea electricity interconnector between the UK and Belgium, which became operational on 31 January 2019. BritNed and Nemo have reporting periods ending on 31 December with monthly management reporting information provided to National Grid. Emerald is a joint venture with Washington State Investment Board and builds and operates wind and solar assets. Emerald was acquired on 11 July 2019. Millennium Pipeline Company LLC is an associate that owns a natural gas pipeline from southern New York to the Lower Hudson Valley. Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Limited Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy Venture LLC 2020 2019 2020 2019 2020 2019 2020 £m £m £m £m £m £m £m Statement of financial position Non-current assets 399 370 971 937 582 537 435 Cash and cash equivalents 54 59 33 35 26 47 66 All other current assets 4 2 26 22 5 3 6 Non-current liabilities (45 ) (11 ) (315 ) (326 ) (29 ) 2 (232 ) Current liabilities (16 ) (28 ) (43 ) (84 ) (10 ) (375 ) (2 ) Net assets 396 392 672 584 574 214 273 Group’s ownership interest in joint venture/associate 198 196 176 153 287 107 139 Group adjustment: elimination of profits on sales to joint venture — — — — — — (10 ) Carrying amount of the Group’s investment 198 196 176 153 287 107 129 BritNed Development Limited Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy Venture LLC 2020 2019 2020 2019 2020 2019 2020 £m £m £m £m £m £m £m Income statement Revenue 80 87 206 166 45 12 19 Depreciation and amortisation (14 ) (13 ) (46 ) (34 ) (23 ) (4 ) (7 ) Other costs (10 ) (10 ) (20 ) (24 ) (8 ) (4 ) (10 ) Operating profit 56 64 140 108 14 4 2 Net interest expense — — (22 ) (11 ) — — (3 ) Profit before tax 56 64 118 97 14 4 (1 ) Income tax expense (10 ) (10 ) — — (2 ) — — Profit for the year 46 54 118 97 12 4 (1 ) Group’s share of profit/(loss) 23 27 31 25 6 2 (1 ) Group adjustment: Tax charge — — (9 ) — — — — Group’s share of post-tax results for the year 23 27 22 25 6 2 (1 ) Subsidiary undertakings, joint ventures and associates While we present consolidated results in these financial statements as if we were one company, our legal structure is such that there are a number of different operating and holding companies that contribute to the overall result. This structure has evolved through acquisitions as well as regulatory requirements to have certain activities within separate legal entities. Subsidiary undertakings A list of the Group’s subsidiaries as at 31 March 2020 is given below. The entire share capital of subsidiaries is held within the Group except where the Group’s ownership percentages are shown. These percentages give the Group’s ultimate interest and therefore allow for the situation where subsidiaries are owned by partly owned intermediate subsidiaries. Where subsidiaries have different classes of shares, this is largely for historical reasons, and the effective percentage holdings given represent both the Group’s voting rights and equity holding. Shares in National Grid (US) Holdings Limited, National Grid Holdings One plc and NGG Finance plc are held directly by National Grid plc. All other holdings in subsidiaries are owned by other subsidiaries within the Group. All subsidiaries are consolidated in the Group’s financial statements. Principal Group companies are identified in bold . These companies are incorporated and principally operate in the countries under which they are shown. Incorporated in England and Wales Registered office: 1 – 3 Strand, London WC2N 5EH, UK (unless stated otherwise in footnotes). Beegas Nominees Limited Birch Sites Limited Carbon Sentinel Limited Droylsden Metering Services Limited Gridcom Limited Icelink Interconnector Limited Landranch Limited Lattice Group Employee Benefit Trust Limited Lattice Group Limited Lattice Group Trustees Limited Natgrid Limited NatGrid One Limited NatgridTW1 Limited National Grid Belgium Limited 1 * National Grid Blue Power Limited 1 * National Grid Carbon Limited National Grid Commercial Holdings Limited National Grid Distributed Energy Limited National Grid Electricity Group Trustee Limited National Grid Electricity System Operator Limited National Grid Electricity Transmission plc National Grid Energy Metering Limited National Grid Four Limited 1 * National Grid Fourteen Limited 1 * National Grid Gas Holdings Limited National Grid Gas plc National Grid Grain LNG Limited National Grid Holdings Limited National Grid Holdings One plc National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited National Grid Metering Limited National Grid North Sea Link Limited National Grid Offshore Limited (previously NG Shetland Link Limited) National Grid Partners Limited National Grid Plus Limited (previously National Grid Offshore Limited) National Grid Property Holdings Limited National Grid Seventeen Limited 1 * National Grid Smart Limited National Grid Ten National Grid Thirty Five Limited 1 * National Grid Thirty Six Limited National Grid Twelve Limited National Grid Twenty Eight Limited National Grid Twenty-Five Limited 1 * National Grid Twenty Seven Limited National Grid Twenty Three Limited National Grid UK Limited National Grid UK Pension Services Limited National Grid (US) Holdings Limited National Grid (US) Investments 2 Limited National Grid (US) Investments 4 Limited National Grid (US) Partner 1 Limited National Grid Ventures Limited National Grid Viking Link Limited National Grid William Limited NG Nominees Limited NGC Employee Shares Trustee Limited NGG Finance plc Ngrid Intellectual Property Limited NGT Telecom No. 1 Limited 1 * NGT Two Limited Port Greenwich Limited Stargas Nominees Limited Supergrid Electricity Limited Supergrid Energy Transmission Limited Supergrid Limited Thamesport Interchange Limited The National Grid Group Quest Trustee Company Limited The National Grid YouPlan Trustee Limited Transco Limited Warwick Technology Park Management Company (No 2) Limited ( 60.56% ) 2 1. Registered office: c/o KPMG, 15 Canada Square, London E14 5GL, UK 2. Registered office: Shire Hall, PO Box 9, Warwick CV34 4RL, UK * In liquidation. 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Incorporated in the US Registered office: National Registered Agents, Inc., 1209 Orange Street, Wilmington, DE 19801, USA (unless stated otherwise in footnotes). Alden Solar, LLC Altona Solar, LLC Apple River Solar, LLC Apple Solar, LLC Arapahoe Solar, LLC Argenta Solar, LLC Armenia Solar, LLC Artemisia Solar, LLC 1 Ashland Solar, LLC Athens Solar, LLC Audubon Wind Farm, LLC Banner Solar, LLC Bee Hollow Solar, LLC Benevolent Solar, LLC Blaze Solar, LLC Blue Ridge Wind, LLC Blues Solar, LLC Blue Stone Solar Energy, LLC Bluewater Solar, LLC Boone Solar, LLC Boston Gas Company 2 Brewster Solar, LLC Brilliance Solar, LLC British Transco Capital Inc. 3 British Transco Finance, Inc. 3 Brock Solar, LLC Broken Bridge Corp. 4 Brook Trout Solar, LLC Brookside Solar, LLC Burlington Solar, LLC Burr Ridge Wind, LLC Cage Ranch Solar, LLC Cage Ranch Solar II, LLC Cage Ranch Solar III, LLC Caldwell Solar, LLC Caldwell Solar II, LLC Canby Solar, LLC Cattle Ridge Wind Farm 2, LLC Cepheus Community Solar Gardens LLC 1 Claddagh Solar, LLC 1 Clear Creek Solar, LLC Clermont Solar, LLC Clinton County Solar, LLC Commonwealth Solar, LLC Conestoga Wind, LLC Copperhead Solar, LLC Crocker Wind Farm 2, LLC Cygnus Community Solar Garden, LLC 1 Daybreak Solar, LLC Deer Trail Solar, LLC Dekalb Solar, LLC Desoto Solar, LLC Dodson Creek Solar, LLC Dorado Community Solar Gardens, LLC 1 Dorsey Road Solar, LLC East Galesburg Solar, LLC East Macomb Solar, LLC Eastern Hemlock Solar, LLC Elba Solar, LLC Elburn Solar, LLC Eldena Solar, LLC Elk Creek Solar, LLC Elk Creek Solar 2, LLC Empire Solar, LLC EUA Energy Investment Corporation 2 Falls City Solar, LLC Firstview Wind Farm, LLC Franklin Solar, LLC Front Range Wind Farm, LLC Fulton Solar, LLC Galesburg Solar, LLC Genesee Solar Energy, LLC Geronimo Energy LLC Geronimo E Wind LLC 5 Geronimo Solar Energy, LLC 1 Geronimo Stutsman Wind Farm, LLC Geronimo White Pine Solar, LLC Gladiolus Solar, LLC 1 Glenwood Solar, LLC Glen Rock Solar, LLC Golden Solar, LLC Goldendale Solar, LLC Goldfinch Solar, LLC Granite State Power Link LLC 3 Grant Solar, LLC Grant Solar 2, LLC Grayson Solar, LLC Greenbrier Creek Solar, LLC Greentown Solar, LLC Greenwood Solar, LLC Grid NY, LLC 6 Grindstone Wind Farm, LLC 7 Hale Solar, LLC Hampton Solar, LLC Handley Road Solar, LLC Hardeman County Solar, LLC Harmony Solar ND, LLC Harmony Solar ND 2, LLC Harrington Solar, LLC Hartley Solar, LLC Hearth Solar, LLC Henderson Solar, LLC Heyworth Solar, LLC Honeybee Solar, LLC Hoosier Solar, LLC 1 Hyacinth Solar, LLC 1 Illumination Solar, LLC Innovation Solar, LLC Irwin Solar, LLC Itasca Energy Development, LLC 8 Itasca Energy Services, LLC Jack Rabbit Wind, LLC Jackson County Solar, LLC Jantz Solar, LLC Junction Solar, LLC Kankakee Solar, LLC Keslinger Solar, LLC KeySpan CI Midstream Limited 3 KeySpan Energy Corporation 6 KeySpan Energy Services Inc. 3 KeySpan Gas East Corporation 6 KeySpan International Corporation 3 KeySpan MHK, Inc. 3 KeySpan Midstream Inc. 3 KeySpan Plumbing Solutions, Inc. 6 Kindle Solar, LLC KSI Contracting, LLC 3 KSI Electrical, LLC 3 KSI Mechanical, LLC 3 Lake Iris Solar, LLC Lakeside Solar, LLC Lamdin Solar, LLC Lamplight Solar, LLC Land Management & Development, Inc. 6 Landwest, Inc. 6 Lansing Solar, LLC Lawrence Solar, LLC Leola Wind Farm, LLC Lilac Solar, LLC 1 Lindy Solar, LLC Lockport Solar, LLC Lordsburg Solar, LLC Lydia Solar, LLC Madden Creek Solar, LLC Marigold Community Solar Garden, LLC 1 Massachusetts Electric Company 2 Maverick Wind Farm, LLC Mazon Solar, LLC McFadden Solar, LLC Merton Solar, LLC Metro Energy, LLC 6 Metrowest Realty LLC 3 Miller Creek Solar, LLC Morning Glory Solar, LLC 1 Mottville Solar, LLC Mountain Laurel Solar, LLC Mustang Ridge Wind Farm, LLC Mystic Steamship Corporation 3 Nantucket Electric Company 2 National Grid Algonquin LLC 3 National Grid Connect Inc. 3 National Grid Development Holdings Corp. 3 National Grid Electric Services, LLC 6 National Grid Energy Management, LLC 3 National Grid Energy Services LLC 3 National Grid Energy Trading Services LLC 6 National Grid Engineering & Survey Inc. 6 National Grid Generation LLC 6 National Grid Generation Ventures LLC 6 National Grid Glenwood Energy Center, LLC 3 National Grid IGTS Corp. 6 National Grid Insurance USA Ltd 6 National Grid Islander East Pipeline LLC 3 National Grid LNG GP LLC 3 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Incorporated in the US continued National Grid LNG LLC 3 National Grid LNG LP LLC 3 National Grid Millennium LLC 3 National Grid NE Holdings 2 LLC 2 National Grid North America Inc. 3 National Grid North East Ventures Inc. 3 National Grid Partners Inc. 6 National Grid Partners LLC 3 National Grid Port Jefferson Energy Center LLC 3 National Grid Services Inc. 3 National Grid Transmission Services Corporation 2 National Grid US 6 LLC 3 National Grid US LLC 3 National Grid USA 3 National Grid USA Service Company, Inc. 2 Nees Energy, Inc. 2 New Bremen Solar, LLC New England Electric Transmission Corporation 4 New England Energy Incorporated 2 New England Hydro Finance Company, Inc. ( 53.704% ) 2 New England Hydro-Transmission Corporation ( 53.704% ) 4 New England Hydro-Transmission Electric Company Inc. ( 53.704% ) 2 New England Power Company 2 Newport America Corporation 9 NGNE LLC 3 NGV Emerald Acquisition Co. LLC 3 NGV Emerald Energy Venture Holdings LLC 3 NGV Emerald Holdings LLC 3 NGV US Distributed Energy Inc. 3 (previously National Grid Green Homes Inc.) NGV US Transmission Inc. 3 (previously Grid America Holdings Inc.) Niagara Falls Solar, LLC Niagara Mohawk Energy, Inc. 3 Niagara Mohawk Holdings, Inc. 6 Niagara Mohawk Power Corporation 6 Niobrara Wind, LLC NM Properties, Inc. 6 Nordic Vos, LLC North Adair Solar, LLC Northeast Renewable Link LLC 3 North East Transmission Co., Inc. 3 North Fork Wind, LLC North Rock Solar, LLC North Wonder Lake Solar, LLC Onton Solar, LLC Opinac North America, Inc. 3 Oreana Solar, LLC Patriotic Solar, LLC Pennington Solar, LLC Peony Solar, LLC Perseus Community Solar Garden, LLC 1 Philadelphia Coke Co., Inc. 3 Piper Solar, LLC Pipestone Solar, LLC Pleasant Plains Solar, LLC Plum Creek Wind Farm, LLC Plum Creek Wind Farm 2, LLC Polaris Community Solar Garden, LLC 1 Port of the Islands North, LLC 6 Prairie Oasis Solar, LLC Prairie Rose Wind 2, LLC 1 Prairie Wolf Solar, LLC Prosperity Wind Farm, LLC Prosperity Wind Farm 2, LLC Radiance Solar, LLC 1 Red Rock Solar SD, LLC Regal Solar, LLC Regulus Community Solar Gardens, LLC 1 Rising Solar, LLC River North Solar, LLC River Run Solar, LLC Riverside Solar, LLC Rochester Solar, LLC 1 Rock Falls Solar, LLC Rock Ridge Wind Farm, LLC Ross County Solar, LLC Royal Solar, LLC Royal Solar 2, LLC Royerton Solar, LLC Saginaw Bay Solar, LLC Sandstone Creek Solar, LLC Sandstone Creek Solar 2, LLC Sawmill Wind Farm, LLC Silver City Solar, LLC Scorpius Community Solar Garden, LLC 1 Serenity Solar, LLC 1 Sheas Lake Solar, LLC Sherco Solar, LLC 1 Silver Lake Solar, LLC Sirius Community Solar Gardens, LLC 1 Snowdrop Solar, LLC 1 Somerset Solar, LLC South Belleville Solar, LLC South Macomb Solar, LLC Spotlight Solar, LLC Spring Brook Solar, LLC Springfield Solar Farm, LLC Springfield Wind Farm, LLC 1 Springville Solar, LLC St. Thomas Solar, LLC Stockton Solar, LLC Stony Brook Wind, LLC Stove Creek Solar, LLC Sturgis Solar, LLC Sugar Maple Solar, LLC Summit Lake Solar, LLC Sunbeam Solar, LLC Sunray Solar, LLC Sunrise Solar, LLC Sycamore Creek Solar, LLC The Brooklyn Union Gas Company 6 The Narragansett Electric Company 9 Tilton Solar, LLC Torchlight Solar, LLC 1 Transgas, Inc. 2 Uintah Solar, LLC Upper Hudson Development Inc. 6 Valley Appliance and Merchandising Company 9 Vermont Green Line Devco, LLC 3 ( 90% ) Vibrant Solar, LLC Virgo Community Solar Gardens, LLC 1 Virtue Solar, LLC Vivid Solar, LLC Vulpecula Community Solar Garden, LLC 1 Wayfinder Group, Inc. 2 Wheatfield Solar, LLC Wild Springs Solar, LLC 1 Wildcat Ridge Wind Farm, LLC Wilder Junction Wind Farm, LLC Wildhorse Creek Solar, LLC Willard Solar, LLC Wiregrass Solar, LLC Wonder Lake Solar, LLC Woodlands Solar, LLC Yellowbud Solar, LLC 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Incorporated in Australia Registered office: Level 7, 330 Collins Street, Melbourne, VIC 3000, Australia National Grid Australia Pty Limited Incorporated in Canada Registered office: Stewart McKelvey Stirling Scales, c/o Charles Reagh, 1959 Upper Water Street, Suite 900, Halifax Nova Scotia, B3J 2N2, Canada KeySpan Energy Development Co. Incorporated in Hong Kong Registered office: Level 54, Hopewell Centre, 183 Queen's Road East, Hong Kong National Grid Hong Kong Limited (previously HK NewCo 2019 Limited) Incorporated in the Isle of Man Registered office: Third Floor, St George’s Court, Upper Church Street, Douglas, IM1 1EE, Isle of Man, UK National Grid Insurance Company (Isle of Man) Limited NGT Holding Company (Isle of Man) Limited* Incorporated in Jersey Registered office: 44 Esplanade, St Helier, Jersey JE4 9WG, UK National Grid Jersey Investments Limited** NG Jersey Limited** Incorporated in Luxembourg Registered office: 412F, Route d'Esch, L-2086, Luxembourg, Grand Duchy of Luxembourg National Grid Luxembourg Sarl (previously 21 June Sarl) Incorporated in the Netherlands Registered office: Westblaak 89, 3012 KG Rotterdam, PO Box 21153, 3001 AD, Rotterdam, Netherlands British Transco International Finance B.V. Registered office: Prins Bernhardplein 200, 1097 JB, Amsterdam, Netherlands National Grid Holdings B.V.* Incorporated in the Republic of Ireland Registered office: c/o Moore Stephens Nathans, Third Floor, Ulysses House, 23/24 Foley Street, Dublin 1, D01 W2T2, Ireland National Grid Company (Ireland) Designated Activity Company (previously National Grid Insurance Company (Ireland) Designated Activity Company)* 1. Registered office: c/o Geronimo Energy LLC, 8400 Normandale Lake Bvld. Suite 1200, Bloomington, MN 55437, USA. 2. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, USA. 3. Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington DE 19808, USA. 4. Registered office: Lawyers Incorporating Service, 10 Ferry Street, Suite 313, Concord NH 03301, USA. 5. Registered office: National Registered Agents, Inc., 301 S. Bedford St. Suite 1 Madison, WI 53703, USA. 6. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207-2543, USA. 7. Registered office: National Registered Agents, Inc., 30600 Telegraph Road, Suite2345, Bingham Farms, MI 48025-5720, USA. 8. Registered office: 10710 Town Square Drive NE, Suite 201 Minneapolis, MN 55449, USA. 9. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, USA. * In liquidation. ** Entered liquidation 29 April 2020. 34. Subsidiary undertakings, joint ventures and associates continued Joint ventures A list of the Group’s joint ventures as at 31 March 2020 is given below. All joint ventures are included in the Group’s financial statements using the equity method of accounting. Principal joint ventures are identified in bold . Incorporated in England and Wales Registered office: 1–3 Strand, London WC2N 5EH, UK (unless stated otherwise in footnotes). BritNed Development Limited ( 50% )* Joint Radio Company Limited ( 50% ) 1 ** Nemo Link Limited ( 50% ) NGET/SPT Upgrades Limited ( 50% ) † St William Homes LLP ( 50% ) 2 Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Clean Energy Generation, LLC ( 50% ) Emerald Energy Venture LLC ( 51% ) Goldendale Energy Storage LLC ( 50% ) Island Park Energy Center, LLC ( 50% ) Islander East Pipeline Company, LLC ( 50% ) 3 LI Energy Storage System, LLC ( 50% ) LI Solar Generation, LLC ( 50% ) Swan Lake North Holdings LLC ( 50% ) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, Paris La Defense, CEDEX, France IFA2 SAS ( 50% ) Associates A list of the Group’s associates as at 31 March 2020 is given below. Unless otherwise stated, all associates are included in the Group’s financial statements using the equity method of accounting. Principal associates are identified in bold . Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Clean Line Energy Partners LLC ( 32% ) 3 Connecticut Yankee Atomic Power Company ( 19.5% ) 4 Direct Global Power, Inc. ( 26% ) 3 Energy Impact Fund LP ( 9.42% ) 5 Greeneru, Inc. ( 21.6% ) 3 KHB Venture LLC ( 33% ) 6 Maine Yankee Atomic Power Company ( 24% ) 7 Millennium Pipeline Company, LLC ( 26.25% ) 3 New York Transco LLC ( 28.3% ) 8 Nysearch RMLD, LLC ( 22.63% ) Sunrun Neptune Investor 2016 LLC 3 *** Yankee Atomic Electric Company ( 34.5% ) 9 Incorporated in Belgium Registered office: Avenue de Cortenbergh 71, 1000 Brussels, Belgium Coreso SA ( 15.84% ) Other investments A list of the Group’s other investments as at 31 March 2020 is given below. Incorporated in England and Wales Registered office: 1 More London Place, London SE1 2AF, UK Energis plc ( 33.06% ) ‡ 1. Registered office: Friars House, Manor House Drive, Coventry CV1 2TE, UK. 2. Registered office: Berkeley House, 19 Portsmouth Road, Cobham, Surrey KT11 1JG, UK. 3. Registered office: Corporation Trust Company, 1209 Orange, Wilmington DE 19808, New Castle County, USA. 4. Registered office: Carla Pizzella, 362 Injun Hollow Road, East Hampton CT 06424, USA. 5. Registered office: Harvard Business Services, Inc., 16192 Coastal Highway, Lewes DE 19958, Sussex County, USA. 6. Registered office: De Maximus Inc., 135 Beaver Street, 4th Floor, Waltham MA 02452, USA. 7. Registered office: Joseph D Fay, 321 Old Ferry Road, Wiscasset ME 04578, USA. 8. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 9. Registered office: Karen Sucharzewski, 49 Yankee Road, Rowe MA 01367, USA. * National Grid Interconnector Holdings Limited owns 284,500,000 €0.20 C Ordinary shares and one £1.00 Ordinary A share. ** National Grid Gas plc owns all £1.00 A Ordinary shares. *** NGV US Distributed Energy Inc. owns 1,000 Class A Membership Interests. † National Grid Electricity Transmission plc owns 50 £1.00 A Ordinary shares. ‡ In administration. Our interests and activities are held or operated through the subsidiaries, joint arrangements or associates as disclosed above. These interests and activities (and their branches) are established in – and subject to the laws and regulations of – these jurisdictions.

Derivative financial instrument

Derivative financial instruments	12 Months Ended
	Mar. 31, 2020
Financial Instruments [Abstract]
Derivative financial instruments	Derivative financial instruments Derivatives are financial instruments that derive their value from the price of an underlying item such as interest rates, foreign exchange rates, credit spreads, commodities, equities or other indices. In accordance with policies approved by the Board, derivatives are transacted generally to manage exposures to fluctuations in interest rates, foreign exchange rates and commodity prices. Our derivatives balances comprise two broad categories: • financing derivatives managing our exposure to interest rates and foreign exchange rates. Specifically, we use these derivatives to manage our financing portfolio, holdings in foreign operations and contractual operational cash flows; and • commodity contract derivatives managing our US customers’ exposure to price and supply risks. Some forward contracts for the purchase of commodities meet the definition of derivatives and are included here. We also enter into derivative financial instruments linked to commodity prices, including index futures, options and swaps. These are used to manage market price volatility. Derivatives are initially recognised at fair value and subsequently remeasured to fair value at each reporting date. Changes in fair values are recorded in the period they arise, in either the consolidated income statement or other comprehensive income as required by IFRS 9. Where the gains or losses recorded in the income statement arise from changes in the fair value of derivatives to the extent that hedge accounting is not applied or is not fully effective, these are recorded as remeasurements, detailed in notes 5 and 6. Where the fair value of a derivative is positive it is carried as a derivative asset, and where negative as a derivative liability. We calculate the fair value of derivative financial instruments by taking the present value of future cash flows, primarily incorporating market observable inputs. The various inputs include foreign exchange spot and forward rates, yield curves of the respective currencies, currency basis spreads between the respective currencies, interest rate and inflation curves, the forward rate curves of underlying commodities, and for those positions that are not fully cash collateralised the credit quality of the counterparties. Certain clauses embedded in non-derivative financial instruments or other contracts are presented as derivatives because they impact the risk profile of their host contracts and they are deemed to have risks or rewards not closely related to those host contracts. Further information on how derivatives are valued and used for risk management purposes is presented in note 32. Information on commodity contracts and other commitments not meeting the definition of derivatives is presented in note 30. The fair values of derivatives by category are as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Financing derivatives 1,267 (1,134 ) 133 1,052 (1,084 ) (32 ) Commodity contract derivatives 75 (200 ) (125 ) 101 (99 ) 2 1,342 (1,334 ) 8 1,153 (1,183 ) (30 ) (a) Financing derivatives The fair values of financing derivatives by type are as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Interest rate swaps 556 (337 ) 219 539 (384 ) 155 Cross-currency interest rate swaps 643 (514 ) 129 470 (443 ) 27 Foreign exchange forward contracts¹ 58 (39 ) 19 41 (41 ) — Inflation-linked swaps — (234 ) (234 ) — (214 ) (214 ) Equity options 10 (10 ) — 2 (2 ) — 1,267 (1,134 ) 133 1,052 (1,084 ) (32 ) 1. Included within the foreign exchange forward contracts balance is £(3) million ( 2019 : £32 million ) of derivatives in relation to hedging of capital expenditure. 17. Derivative financial instruments continued (a) Financing derivatives continued The maturity profile of financing derivatives is as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total Current Less than 1 year 62 (254 ) (192 ) 56 (282 ) (226 ) 62 (254 ) (192 ) 56 (282 ) (226 ) Non-current In 1 to 2 years 480 (51 ) 429 19 (193 ) (174 ) In 2 to 3 years 13 (5 ) 8 416 (1 ) 415 In 3 to 4 years 20 (28 ) (8 ) 11 — 11 In 4 to 5 years 31 (109 ) (78 ) 20 (14 ) 6 More than 5 years 661 (687 ) (26 ) 530 (594 ) (64 ) 1,205 (880 ) 325 996 (802 ) 194 1,267 (1,134 ) 133 1,052 (1,084 ) (32 ) The notional contract 1 amounts of financing derivatives by type are as follows: 2020 2019 £m £m Interest rate swaps (3,101 ) (6,299 ) Cross-currency interest rate swaps (8,097 ) (6,700 ) Foreign exchange forward contracts (3,284 ) (2,937 ) Inflation-linked swaps (500 ) (500 ) Equity options (800 ) (800 ) (15,782 ) (17,236 ) 1. The notional contract amounts of derivatives indicate the gross nominal value of transactions outstanding at the reporting date. (b) Commodity contract derivatives The fair values of commodity contract derivatives by type are as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets Liabilities £m Total £m Commodity purchase contracts accounted for as derivative contracts Forward purchases of gas 64 (108 ) (44 ) 66 (78 ) (12 ) Derivative financial instruments linked to commodity prices Electricity swaps 4 (83 ) (79 ) 29 (19 ) 10 Gas swaps 7 (8 ) (1 ) 5 (1 ) 4 Gas options — (1 ) (1 ) 1 (1 ) — 75 (200 ) (125 ) 101 (99 ) 2 17. Derivative financial instruments continued (b) Commodity contract derivatives continued The maturity profile of commodity contract derivatives is as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than one year 31 (126 ) (95 ) 52 (68) (16) 31 (126 ) (95 ) 52 (68) (16) Non-current In 1 to 2 years 8 (35 ) (27 ) 14 (9) 5 In 2 to 3 years 9 (24 ) (15 ) 9 (8) 1 In 3 to 4 years 8 (12 ) (4 ) 6 (4) 2 In 4 to 5 years 7 (1 ) 6 6 (4) 2 More than 5 years 12 (2 ) 10 14 (6) 8 44 (74 ) (30 ) 49 (31) 18 75 (200 ) (125 ) 101 (99) 2 The notional quantities of commodity contract derivatives by type are as follows: 2020 2019 Forward purchases of gas 1 102m Dth 52m Dth Electricity swaps 12,836 GWh 12,848 GWh Electricity options 0 GWh 10,444 GWh Gas swaps 89m Dth 87m Dth Gas options 26m Dth 34m Dth 1. Forward gas purchases have terms up to four years ( 2019 : two years ). The contractual obligations under these contracts are £128 million ( 2019 : £108 million ).

Inventories and other current i

Inventories and other current intangibles	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Inventories and current intangible assets	Inventories and current intangible assets Inventories represent assets that we intend to use in order to generate revenue in the short term, either by selling the asset itself (for example, fuel stocks) or by using it to fulfil a service to a customer or to maintain our network (consumables). Inventories are stated at the lower of weighted average cost and net realisable value. Where applicable, cost comprises direct materials and direct labour costs as well as those overheads that have been incurred in bringing the inventories to their present location and condition. Emission allowances, principally relating to the emissions of carbon dioxide in the UK and sulphur and nitrous oxides in the US, are recorded as intangible assets within current assets, and they are initially recorded at cost and subsequently at the lower of cost and net realisable value. A liability is recorded in respect of the obligation to deliver emission allowances, and emission charges are recognised in the income statement in the period in which emissions are made. 2020 2019 £m £m Fuel stocks 151 99 Raw materials and consumables 265 184 Current intangible assets – emission allowances 133 87 549 370 There is a provision for obsolescence of £21 million against inventories as at 31 March 2020 ( 2019 : £20 million ).

Trade and other receivables

Trade and other receivables	12 Months Ended
	Mar. 31, 2020
Trade and other receivables [abstract]
Trade and other receivables	Trade and other receivables Trade and other receivables are amounts which are due from our customers for services we have provided. Trade and other receivables are initially recognised at fair value and subsequently measured at amortised cost, less any appropriate allowances for estimated irrecoverable amounts. 2020 2019 £m £m Trade receivables 1,551 1,899 Accrued income 869 883 Prepayments 408 237 Other receivables 158 134 2,986 3,153 Trade receivables are non-interest-bearing and generally have a 30 to 90 days term. Due to their short maturities, the fair value of trade and other receivables approximates their carrying value. The maximum exposure of trade receivables to credit risk is the gross carrying amount of £2,063 million ( 2019 : £2,293 million ). Provision for impairment of receivables A provision for credit losses is recognised at an amount equal to the expected credit losses that will arise over the lifetime of the trade receivables and accrued income. 2020 2019 £m £m At 1 April 394 309 Exchange adjustments 20 24 Charge for the year, net of recoveries 234 181 Uncollectible amounts written off (136 ) (120 ) At 31 March 512 394 The trade receivables balance, accrued income balance and provisions balance split by geography is as follows: As at 31 March 2020 As at 31 March 2019 UK US Total UK US Total £m £m £m £m £m £m Trade receivables 227 1,836 2,063 313 1,980 2,293 Accrued income 461 408 869 445 438 883 Provision for impairment of trade receivables (40 ) (472 ) (512 ) (40 ) (354 ) (394 ) There are no retail customers in the UK businesses. A provision matrix is not used in the UK as an assessment of expected losses on individual debtors is performed, and the provision is not material. In the US, £1,806 million ( 2019 : £1,885 million ) of the trade receivables and unbilled revenue balance is attributable to retail customers. For non-retail US customer receivables, a provision matrix is not used and expected losses are determined on individual debtors. The provision for retail customer receivables in the US is calculated based on a series of provision matrices which are prepared by regulated entity and by customer type. The expected loss rates in each provision matrix are based on historical loss rates adjusted for current and forecasted economic conditions at the balance sheet date. The inclusion of forward-looking information in the provision matrix setting process under IFRS 9 resulted in loss rates that reflect expected future economic conditions and the recognition of an expected loss on all debtors even where no loss event has occurred. In March 2020, the Group's US distribution businesses ceased certain customer cash collection activities in response to regulatory instructions and to changes in State, Federal and City level regulations and guidance, and actions to minimise risk to the Group's employees. The Group has also ceased customer termination activities as requested by relevant local authorities. In addition, we have considered the macroeconomic data including unemployment levels and our previous experience regarding debtor recoverability during and in the aftermath of the 2008/09 financial crisis (which impacted all of our service territories) and that following Superstorm Sandy in 2012 which impacted our downstate New York gas business specifically. Based on our review of these factors, we concluded that a reasonable range for the additional provision recognised in light of the cessation of customer terminations and collections following the moratoriums introduced would lie between £81 million and £161 million ( $100 million and $200 million ). We concluded an additional charge of £117 million represented our best estimate based on the information available, primarily as this represented an impact twice as severe as Superstorm Sandy, adjusted to incorporate all service territories impacted. 19. Trade and other receivables continued The average expected loss rates and gross balances for the retail customer receivables in our US operations are set out below: 2020 2020 2019 2019 % £m % £m Unbilled revenue 5 395 — 420 0 – 30 days 5 623 3 736 30 – 60 days 14 184 12 194 60 – 90 days 29 105 20 89 3 – 6 months 47 119 30 109 6 – 12 months 63 104 39 99 Over 12 months 79 276 68 238 1,806 1,885 The year-on-year movements in average expected loss rates are driven primarily as a result of the moratoriums on cash collection and termination activities outlined above. US retail customer receivables are not collateralised. Trade receivables are written off when regulatory requirements are met. Write-off policies vary between jurisdictions as they are aligned with the local regulatory requirements, which differ between regulators. There were no significant amounts written off during the period that were still subject to enforcement action. Our internal definition of default is aligned with that of the individual regulators in each jurisdiction. For further information on our wholesale and retail credit risk, refer to note 32(a).

Cash and cash equivalents

Cash and cash equivalents	12 Months Ended
	Mar. 31, 2020
Cash and cash equivalents [abstract]
Cash and cash equivalents	Cash and cash equivalents Cash and cash equivalents include cash balances, together with short-term investments with an original maturity of less than three months that are readily convertible to cash. Net cash and cash equivalents reflected in the cash flow statement are net of bank overdrafts, which are reported in borrowings. The carrying amounts of cash and cash equivalents and bank overdrafts approximate their fair values. Cash at bank earns interest at floating rates based on daily bank deposit rates. Short-term deposits are made for periods varying between one day and three months, depending on the immediate cash requirements, and earn interest at the respective short-term deposit rates. Net cash and cash equivalents held in currencies other than sterling have been converted into sterling at year-end exchange rates. For further information on currency exposures, refer to note 32(c). 2020 2019 £m £m Cash at bank 73 177 Short-term deposits — 75 Cash and cash equivalents 73 252

Borrowings

Borrowings	12 Months Ended
	Mar. 31, 2020
Disclosure of detailed information about borrowings [abstract]
Borrowings	Borrowings We borrow money primarily in the form of bonds and bank loans. These are for a fixed term and may have fixed or floating interest rates or are linked to RPI. We use derivatives to manage risks associated with interest rates and foreign exchange. Our price controls and rate plans lead us to fund our networks within a certain ratio of debt to equity and, as a result, we have issued a significant amount of debt. As we continue to invest in our networks, the value of debt is expected to increase over time. To maintain a strong balance sheet and to allow us to access capital markets at commercially acceptable interest rates, we balance the amount of debt we issue with the value of our assets, and we take account of certain other metrics used by credit rating agencies. All borrowings are accounted for at amortised cost, with the exception of one liability measured at fair value through profit and loss, in order to eliminate a measurement mismatch. Borrowings, which include interest-bearing, zero-coupon and inflation-linked debt, overdrafts and collateral payable, are initially recorded at fair value. This normally reflects the proceeds received (net of direct issue costs for liabilities measured at amortised cost). Subsequently, borrowings are stated either: i) at amortised cost; or ii) at fair value though profit and loss. Where a borrowing is held at amortised cost, any difference between the proceeds after direct issue costs and the redemption value is recognised over the term of the borrowing in the income statement using the effective interest method. For the liability held at fair value through profit and loss, interest is calculated using the effective interest method. Where a borrowing or liability is held at fair value, changes in the fair value of the borrowing due to changes in the issuer’s credit risk are recorded in the own credit reserve (see note 28). All other changes in the fair value of the liability are recognised in the income statement within remeasurements (see notes 5 and 6). 2020 2019 £m £m Current Bank loans 1,244 641 Bonds 1,446 1,973 Commercial paper 1,269 1,792 Lease liabilities 112 65 Other loans 1 1 4,072 4,472 Non-current Bank loans 2,819 2,599 Bonds¹ 23,094 21,278 Lease liabilities 623 205 Other loans 186 176 26,722 24,258 Total borrowings 30,794 28,730 1. Includes a liability held at fair value through profit and loss of £741 million ( 2019 : £667 million ). 21. Borrowings continued Total borrowings are repayable as follows: 2020 2019 £m £m Less than 1 year 4,072 4,472 In 1 to 2 years 2,212 2,393 In 2 to 3 years 1,664 1,990 In 3 to 4 years 757 1,553 In 4 to 5 years 2,122 714 More than 5 years: By instalments 870 959 Other than by instalments 19,097 16,649 30,794 28,730 The fair value of borrowings at 31 March 2020 was £34,174 million ( 2019 : £32,252 million ). Where market values were available, fair value of borrowings (Level 1) was £14,059 million ( 2019 : £14,356 million ). Where market values were not available, fair value of borrowings (Level 2) was £20,115 million ( 2019 : £17,896 million ), calculated by discounting cash flows at prevailing interest rates. The notional amount outstanding of the debt portfolio at 31 March 2020 was £30,422 million ( 2019 : £28,417 million ). In April 2020, National Grid Electricity Transmission plc issued a £0.4 billion fixed interest rate bond from the NGET EMTN programme with a 20 -year tenor and The Narragansett Electric Company issued a $0.6 billion ( £0.5 billion ) fixed interest rate bond with a 10 -year tenor. Both issuances are part of the continued Group funding arrangements. During the year, the assets of the Colonial Gas Company were merged with the Boston Gas Company, and have been ringfenced post-merger, and certain gas distribution assets of The Narragansett Electric Company are subject to liens and other charges and are provided as collateral over borrowings totalling £84 million at 31 March 2020 ( 2019 : £81 million ). Collateral is placed with or received from any derivative counterparty where we have entered into a credit support annex to the ISDA Master Agreement once the current mark-to-market valuation of the trades between the parties exceeds an agreed threshold. Included in current bank loans is £785 million ( 2019 : £558 million ) in respect of cash received under collateral agreements. For further details of our borrowing facilities, refer to note 33. For further details of our bonds in issue, please refer to the debt investor section of our website. Unless included herein, the information on our website is unaudited. Financial liability at fair value through profit and loss The financial liability designated at fair value through profit and loss is analysed as follows: i) the fair value of the liability was £741 million ( 2019 : £667 million ), which includes cumulative change in fair value attributable to changes in credit risk recognised in other comprehensive income, post tax of £10 million ( 2019 : £13 million ); ii) the amount repayable at maturity in November 2021 is £759 million ( 2019 : £724 million ); and iii) the difference between carrying amount and contractual amount at maturity is £18 million ( 2019 : £57 million ). This liability has been reclassified in order to eliminate a measurement mismatch with derivatives which provide an economic hedge. The associated derivatives are collateralised and do not contain significant exposure to our own credit risk. The presentation of credit risk in other comprehensive income does not, therefore, create or enlarge an accounting mismatch in profit or loss. The change in the fair value attributable to a change in credit risk is calculated as the difference between the total change in the fair value of the liability and the change in the value of the liability due to changes in market risk factors alone. The change in the fair value due to market risk factors was calculated using benchmark yield curves as at the end of the reporting period holding the credit risk margin constant. The fair value of the liability was calculated using observed market prices. 21. Borrowings continued Lease liabilities The Group adopted IFRS 16 on 1 April 2019, which resulted in the recognition of £474 million of additional lease liabilities. As we applied the modified retrospective approach to transition, comparatives were not restated. Refer to note 37 for details. Lease liabilities are initially measured at the present value of the lease payments expected over the lease term. The discount rate applied is the rate implicit in the lease or if that is not available, then the incremental rate of borrowing for a similar term and similar security. The lease term takes account of exercising any extension options that are at our option if we are reasonably certain to exercise the option and any lease termination options unless we are reasonably certain not to exercise the option. Each lease payment is allocated between the liability and finance cost. The finance cost is charged to the income statement over the lease period using the effective interest rate method. 2020 2019 £m £m Gross lease liabilities are repayable as follows: Less than 1 year 132 65 1 to 5 years 361 183 More than 5 years 481 62 974 310 Less: finance charges allocated to future periods (239 ) (40 ) 735 270 The present value of lease liabilities are as follows: Less than 1 year 112 65 1 to 5 years 297 156 More than 5 years 326 49 735 270

Trade and other payables

Trade and other payables	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Trade and other payables	Trade and other payables Trade and other payables include amounts owed to suppliers, tax authorities and other parties which are due to be settled within 12 months. The total also includes deferred amounts, some of which represent monies received from customers but for which we have not yet delivered the associated service. These amounts are recognised as revenue when the service is provided. Trade and other payables are initially recognised at fair value and subsequently measured at amortised cost. Contingent consideration is measured at fair value. 2020 2019 £m £m Trade payables 2,205 2,404 Deferred payables 137 217 Customer contributions¹ 84 87 Social security and other taxes 202 159 Contingent consideration² 30 — Other payables 944 902 3,602 3,769 1. From government-related entities. 2. Contingent consideration relates to the acquisition of Geronimo (see note 38). Due to their short maturities, the fair value of trade payables approximates their carrying value.

Contract liabilities

Contract liabilities	12 Months Ended
	Mar. 31, 2020
Contract liabilities [abstract]
Contract liabilities	Contract liabilities Contract liabilities primarily relate to the advance consideration received from customers for construction contracts, mainly in relation to connections, for which revenue is recognised over the life of the asset. 2020 2019 £m £m Current 76 61 Non-current 1,082 933 1,158 994 Significant changes in the contract liabilities balances during the period are as follows: 2020 2019 £m £m As at 1 April 994 866 Exchange adjustments 39 29 Revenue recognised that was included in the contract liability balance at the beginning of the period (60 ) (51 ) Increases due to cash received, excluding amounts recognised as revenue during the period 185 155 Changes due to amounts recognised as revenue — (5 ) At 31 March 1,158 994

Other non-current liabilities

Other non-current liabilities	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Other non-current liabilities	Other non-current liabilities Other non-current liabilities include deferred income which will not be recognised as income until after 31 March 2021. It also includes payables that are not due until after that date. Contingent consideration is measured at fair value. All other non-current liabilities are initially recognised at fair value and subsequently measured at amortised cost. 2020 2019 £m £m Deferred income¹ 101 96 Customer contributions² 428 372 Contingent consideration³ 44 — Other payables 318 340 891 808 1. Principally the deferral of profits relating to the sale of property, which we expect to recognise in future years. 2. From government-related entities. 3. Contingent consideration relates to the acquisition of Geronimo (see note 38). There is no material difference between the fair value and the carrying value of other payables.

Pensions and other post retirem

Pensions and other post retirement benefits	12 Months Ended
	Mar. 31, 2020
Employee Benefits [Abstract]
Pensions and other post retirement benefits	Pensions and other post-retirement benefits All of our employees are eligible to participate in a pension plan. We have defined benefit (DB) and defined contribution (DC) pension plans in the UK and the US. In the US we also provide healthcare and life insurance benefits to eligible employees, post-retirement. The fair value of associated plan assets and present value of DB obligations are updated annually in accordance with IAS 19 (revised). We separately present our UK and US pension plans to show geographical split. Below we provide a more detailed analysis of the amounts recorded in the primary financial statements and the actuarial assumptions used to value the DB obligations. National Grid’s UK pension arrangements are held in separate Trustee administered funds. The arrangements are managed by Trustee companies with boards consisting of company- and member-appointed directors. In the US, the assets of the plans are held in trusts and administered by the Retirement Plans Committee comprised of appointed employees of the Company. Defined contribution plans These plans are designed to provide members with a pension pot for their retirement. The risks associated with these plans are assumed by the member. Payments to these DC plans are charged as an expense as they fall due. There is no legal or constructive obligation on National Grid to pay additional contributions into a DC plan if the fund has insufficient assets to pay all employees’ benefits relating to employee service in the current and prior periods. The National Grid YouPlan YouPlan is the qualifying UK pension plan that is used for automatic enrolment of new hires. National Grid pays contributions into YouPlan to provide DC benefits on behalf of employees. National Grid provides a double match of member contributions, up to a maximum Company contribution of 12% of salary as well as the cost of administration and insured benefits. Defined benefit plans On retirement, members of DB plans receive benefits whose value is dependent on factors such as salary and length of pensionable service. National Grid’s obligation in respect of DB pension plans is calculated separately for each DB plan by projecting the estimated amount of future benefit payments that employees have earned for their pensionable service in the current and prior periods. These future benefit payments are discounted to determine the present value of the liabilities. Current service cost and any unrecognised past service cost are recognised immediately. The discount rate used is the yield curve at the valuation date on high-quality corporate bonds. Advice is taken from independent actuaries relating to the appropriateness of the key assumptions applied, including life expectancy, expected salary and pension increases, and inflation. Comparatively small changes in the assumptions used may have a significant effect on the amounts recognised in the consolidated income statement, the consolidated statement of other comprehensive income and the net liability recognised in the consolidated statement of financial position. Remeasurements of pension assets and post-retirement benefit obligations are recognised in full in the period in which they occur in the consolidated statement of other comprehensive income. The principal UK DB pensions plans are the National Grid UK Pension Scheme (NGUKPS) and the National Grid Electricity Group of the Electricity Supply Pension Scheme (NGEG of ESPS). In the US, we have four principal plans and various healthcare and life insurance plans. The COVID-19 pandemic The COVID-19 pandemic has had a global impact on economies, equity and bond markets. Market volatility during March has had an impact on the value of assets held by our DB and DC pension plans. Our UK DB plans have low-risk investment strategies with limited exposure to equities and other return seeking assets, whilst the US plans have a greater exposure to these asset classes. UK Pensions plans The arrangements are subject to independent actuarial funding valuations at least every three years, and following consultation and agreement with us, the qualified actuary certifies the employers’ contributions, which, together with the specified contributions payable by the employees and proceeds from the plans’ assets, are expected to be sufficient to fund the benefits payable. The results of the most recent actuarial valuations are shown below. See page 167 for the assumptions used for IAS 19 (revised) purposes. The actuarial valuations for NGUKPS as at 31 March 2019 have recently been completed, while we expect the valuation for NGEG of ESPS to be finalised by 30 June 2020. Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Latest full actuarial valuation 31 March 2019 31 March 2019 31 March 2016 Actuary Willis Towers Watson Willis Towers Watson Aon Hewitt Market value of plan assets at latest valuation £6,551 million £5,765 million £2,553 million Actuarial value of benefits due to members £6,502 million £5,831 million £3,053 million Market value as percentage of benefits 101% 99% 84% Funding surplus/(deficit) £49 million (£66 million) (£500 million) Funding surplus/(deficit) net of tax £41 million (£55 million) (£415 million) 25. Pensions and other post-retirement benefits continued National Grid UK Pension Scheme NGUKPS consists of three sections, each legally and actuarially separate. Sections A and B are supported by companies within the Group, while Section C is supported by Cadent Gas Limited, now an unrelated third party. The plan closed to new hires on 1 April 2002. Section A Following the latest actuarial valuation at 31 March 2019, Section A remains in surplus, and so no deficit funding contributions are required. National Grid and the Trustees have agreed a schedule of contributions whereby the employers will continue to contribute 51.8% of pensionable salary, less member contributions, in respect of future benefit accrual. As part of the sectionalisation of NGUKPS on 1 January 2017, a guarantee of £1 billion has been provided to Section A. This payment is contingent on insolvency or on failure to pay pension obligations to Section A and can be claimed against National Grid plc, National Grid Holdings One plc or Lattice Group Limited (up to £1 billion in total). Section B The latest full actuarial valuation at 31 March 2019 determined that Section B was in deficit. In addition to a £34 million payment already made in September 2019, National Grid and the Trustees agreed that an additional payment of approximately £32 million will be made by September 2020 to eliminate the funding deficit. In addition, the employers contribute 51.4% of pensionable salary, less member contributions, in respect of future benefit accrual. Pensions buy-ins During the year, the Trustees of the NGUKPS entered into two buy-in arrangements in order to manage various risks. The policies provide bulk annuities in respect of some pensioner and dependant members of Sections A and B of NGUKPS and were funded by existing assets. In Section A, £2.8 billion of gilts were exchanged for a buy-in policy with Rothesay Life. In Section B, £1.6 billion of gilts were exchanged for a buy-in policy with Legal & General. Both policies are held by the Trustee. For both transactions, the pricing of the policies was highly competitive; however, under IAS 19 the methodology for calculating the value of the buy-ins (as an asset held by the pension plan) differs from the price paid. This resulted in the recognition of an actuarial loss of £0.7 billion on purchase, recorded within the consolidated statement of other comprehensive income. National Grid Electricity Group of the Electricity Supply Pension Scheme The last full actuarial valuation for the NGEG of the ESPS determined that the plan was in deficit. National Grid and the Trustees agreed on a schedule of contributions, whereby deficit funding of £48 million is payable each year from 2016 to 2027, which should lead to the elimination of the funding shortfall by March 2027. All deficit funding amounts due will be adjusted for changes in the RPI. In addition, National Grid contributes 40.7% of pensionable salary, less member contributions, in respect of the ongoing service cost. The plan closed to new hires from 1 April 2006. The plan holds a longevity insurance contract which covers improvements in longevity, providing long-term protection to the scheme, should some pensioner and dependant members live longer than currently expected. Administration costs Up to 31 March 2020, National Grid was responsible for the costs of plan administration and the Pension Protection Fund (PPF) levies for both Sections A and B of NGUKPS, and NGEG of ESPS. However, from 1 April 2020 onwards this will only apply to Section B of NGUKPS and NGEG of ESPS, whilst Section A of NGUKPS will fund these costs from the Section’s assets. Security arrangements National Grid has also established security arrangements with charges in favour of the Trustees. Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Value of security arrangements at 31 March 2020 1 £315 million £180 million £239 million Principal supporting employers National Grid plc and National Grid UK Limited National Grid Gas plc (NGG) National Grid Electricity Transmission plc (NGET) Additional amounts payable 2 at 31 March 2020 £72 million A maximum of £280 million A maximum of £500 million 1. Following the completion of the March 2019 valuations for Sections A and B of NGUKPS, these amounts have changed to £186 million for Section A and to £ nil for Section B. 2. These amounts are payable if certain trigger events occur which have been individually agreed between the plans and their relevant supporting employers. The majority of the security is provided in the form of surety bonds with the remainder in letters of credit. The assets held in security will be paid to the respective section or plan in the event that the relevant supporting employer is subject to an insolvency event or fails to make the required contributions; and applicable to NGEG of ESPS only, if NGET loses its licence to operate under relevant legislation. Counter indemnities have also been taken out to ensure the obligations will be fulfilled. 25. Pensions and other post-retirement benefits continued US pension plans National Grid has multiple DC pension plans which allow employee as well as Company contributions. Non-union employees hired after 1 January 2011, as well as new hire represented union employees, receive a core contribution into the DC plan, irrespective of the employee’s contribution into the plan. National Grid sponsors four non-contributory qualified DB pension plans, which provide vested union employees, and vested non-union employees hired before 1 January 2011 with retirement benefits within prescribed limits as defined by the US Internal Revenue Service. National Grid also provides non-qualified DB pension arrangements for a section of current and former employees, which are closed to new entrants. Benefits under the DB plans generally reflect age, years of service and compensation and are paid in the form of an annuity or lump sum. An independent actuary performs valuations annually. The Company funds the DB plans by contributing no less than the minimum amount required, but no more than the maximum tax-deductible amount allowed under US Internal Revenue Service regulations. The range of contributions determined under these regulations can vary significantly depending upon the funded status of the plans. At present, there is some flexibility in the amount that is contributed on an annual basis. In general, the Company’s policy for funding the US pension plans is to contribute the amounts collected in rates and capitalised in the rate base during the year, to the extent that the funding is no less than the minimum amount required. For the current financial year, these contributions amounted to approximately £153 million ( 2019 : £231 million ). US retiree healthcare and life insurance plans National Grid provides healthcare and life insurance benefits to eligible employees, post-retirement. Eligibility is based on certain age and length of service requirements, and in most cases, retirees contribute to the cost of their healthcare coverage. In the US, there is no governmental requirement to pre-fund post-retirement healthcare and life insurance plans. However, in general, the Company’s policy for funding the US retiree healthcare and life insurance plans is to contribute amounts collected in rates and capitalised in the rate base during the year. For the current financial year, these contributions amounted to £18 million ( 2019 : £14 million ). For the last few years it has been the Company’s policy to primarily direct contributions to the DB pension plans due to concerns over tax deductible limitations relating to the retiree and healthcare and life insurance plans. Actuarial assumptions The Company has applied the following financial assumptions in assessing DB liabilities: UK pensions 2020 2019 2018 % % % Discount rate – past service 2.35 2.40 2.60 Discount rate – future service 2.35 2.45 2.65 Salary increases 2.90 3.50 3.40 Rate of increase in RPI – past service 2.65 3.25 3.15 Rate of increase in RPI – future service 2.45 3.20 3.10 At 31 March 2020, single equivalent financial assumptions are shown above for presentational purposes, although full yield curves have been used in our calculations. In 2018 and 2019, single equivalent financial assumptions were set which reflected the average duration for the aggregate past and future service obligations. The discount rate is determined by reference to high-quality UK corporate bonds at the reporting date. The rate of increase in salaries has been set using a promotional scale where appropriate. The rates of increases stated are not indicative of historical increases awarded or a guarantee of future increase, but merely an appropriate assumption used in assessing DB liabilities. Retail Price Index (RPI) is the key assumption that determines assumed increases in pensions in payment and deferment in the UK only. US pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 % % % % % % Discount rate 3.30 3.95 4.00 3.30 3.95 4.00 Salary increases 3.50 3.50 3.50 3.50 3.50 3.50 Initial healthcare cost trend rate n/a n/a n/a 7.00 7.25 7.50 Ultimate healthcare cost trend rate n/a n/a n/a 4.50 4.50 4.50 Discount rates for US pension liabilities have been determined by reference to appropriate yields on high-quality US corporate bonds at the reporting date based on the duration of plan liabilities. The healthcare cost trend rate is expected to reach the ultimate trend rate by 2030 ( 2019 : 2028 ). 2020 2019 2018 UK years US years UK years US years UK years US years Assumed life expectations for a retiree age 65 Males 22.1 20.9 22.0 22.1 22.3 22.0 Females 23.8 23.4 23.6 24.2 23.9 24.2 In 20 years: Males 23.3 22.5 23.3 23.7 23.7 23.6 Females 25.3 25.1 25.2 25.9 25.5 25.8 25. Pensions and other post-retirement benefits continued Maturity profile of DB obligations The weighted average duration of the DB obligation for each category of plan is 14 years for UK pension plans; 14 years for US pension plans and 16 years for US other post-retirement benefit plans. As at the reporting date, the present value of the funded obligations split according to member status was approximately: • UK pensions: 8% active members ( 2019 : 10% ; 2018 : 10% ); 14% deferred members ( 2019 : 16% ; 2018 : 18% ); 78% pensioner members ( 2019 : 74% ; 2018 : 72% ); • US pensions: 36% active members ( 2019 : 37% ; 2018 : 38% ); 9% deferred members ( 2019 : 9% ; 2018 : 8% ); 55% pensioner members ( 2019 : 54% ; 2018 : 54% ); and • US other post-retirement benefits: 35% active members ( 2019 : 39% ; 2018 : 38% ); 0% deferred members ( 2019 : 0% ; 2018 : 0% ); 65% pensioner members ( 2019 : 61% ; 2018 : 62% ). For sensitivity analysis see note 35. Amounts recognised in the consolidated statement of financial position 2020 2019 2018 £m £m £m Present value of funded obligations (24,281 ) (24,609 ) (23,747 ) Fair value of plan assets 23,748 24,793 23,858 (533 ) 184 111 Present value of unfunded obligations (345 ) (330 ) (307 ) Other post-employment liabilities (75 ) (72 ) (67 ) Net defined benefit liability (953 ) (218 ) (263 ) Represented by: Liabilities (2,802 ) (1,785 ) (1,672 ) Assets 1,849 1,567 1,409 (953 ) (218 ) (263 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Present value of funded obligations (12,775 ) (14,200 ) (14,152 ) (7,809 ) (6,901 ) (6,349 ) (3,697 ) (3,508 ) (3,246 ) Fair value of plan assets 14,364 15,507 15,330 6,972 6,646 6,030 2,412 2,640 2,498 1,589 1,307 1,178 (837 ) (255 ) (319 ) (1,285 ) (868 ) (748 ) Present value of unfunded obligations (69 ) (76 ) (74 ) (276 ) (254 ) (233 ) — — — Other post-employment liabilities — — — — — — (75 ) (72 ) (67 ) Net defined benefit asset/(liability) 1,520 1,231 1,104 (1,113 ) (509 ) (552 ) (1,360 ) (940 ) (815 ) Represented by: Liabilities (69 ) (76 ) (74 ) (1,373 ) (769 ) (783 ) (1,360 ) (940 ) (815 ) Assets 1,589 1,307 1,178 260 260 231 — — — 1,520 1,231 1,104 (1,113 ) (509 ) (552 ) (1,360 ) (940 ) (815 ) The recognition of the pension assets in both the UK in relation to the NGUKPS, the NGEG of ESPS and the US in relation to Niagara Mohawk Plan reflects legal and actuarial advice that we have taken regarding recognition of surpluses under IFRIC 14. We have concluded that the Group has an unconditional right to a refund from the individual plans, including from each Section of the NGUKPS and the NGEG of ESPS, in the event of a winding up. In the UK, the Trustees must seek the agreement of the Company to any benefit augmentation beyond the provisions set out in the Scheme Rules. In the US, surplus assets may be used to pay benefits under other Plans, thereby allowing the Company to settle other liabilities under other Plans. 25. Pensions and other post-retirement benefits continued Amounts recognised in the income statement and statement of other comprehensive income 2020 2019 2018 £m £m £m Included within operating costs Administration costs 16 14 16 Included within payroll costs Defined benefit plan costs: Current service cost 178 193 193 Past service cost – augmentations — 5 1 Past service credit – redundancies — (7 ) (1 ) Special termination benefit cost – redundancies 2 55 9 Past service cost – plan amendments¹ — 34 — 180 280 202 Included within finance income and costs Net interest cost 23 22 65 Total included in income statement 219 316 283 Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations² (724 ) 68 1,313 Exchange adjustments (97 ) (101 ) 175 Total included in the statement of other comprehensive income (821 ) (33 ) 1,488 1. For the year ended 31 March 2019, the estimated cost of equalising for the impact of GMP under the most cost-effective permissible methodology (Section A of NGUKPS – £17 million ; Section B of NGUKPS – £12 million ; NGEG of ESPS – £5 million ). 2. For the year ended 31 March 2020, this includes an actuarial loss from the purchase of buy-in policies of £0.7 billion . The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Included within operating costs Administration costs 9 6 6 6 7 9 1 1 1 Included within payroll costs Defined benefit plan costs: Current service cost 33 41 49 100 104 98 45 48 46 Past service cost – augmentations — 5 1 — — — — — — Past service credit – redundancies — (7 ) (1 ) — — — — — — Special termination benefit cost – redundancies 2 55 9 — — — — — — Past service cost – plan amendments — 34 — — — — — — — 35 128 58 100 104 98 45 48 46 Included within finance income and costs Net interest (income)/cost (31 ) (31 ) 3 21 21 27 33 32 35 Total included in income statement 13 103 67 127 132 134 79 81 82 Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations¹ 143 57 1,177 (588 ) (14 ) 27 (279 ) 25 109 Exchange adjustments — — — (42 ) (42 ) 75 (55 ) (59 ) 100 Total included in the statement of other comprehensive income 143 57 1,177 (630 ) (56 ) 102 (334 ) (34 ) 209 1. For the year ended 31 March 2020, UK pensions is stated after an actuarial loss from the purchase of buy-in policies of £0.7 billion . 25. Pensions and other post-retirement benefits continued Reconciliation of the net defined benefit liability 2020 2019 2018 £m £m £m Opening net defined benefit liability (218 ) (263 ) (1,933 ) Cost recognised in the income statement (219 ) (316 ) (283 ) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (821 ) (33 ) 1,488 Employer contributions 327 419 475 Other movements (22 ) (25 ) (10 ) Closing net defined benefit liability (953 ) (218 ) (263 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Opening net defined benefit asset/(liability) 1,231 1,104 (156 ) (509 ) (552 ) (728 ) (940 ) (815 ) (1,049 ) Cost recognised in the income statement (13 ) (103 ) (67 ) (127 ) (132 ) (134 ) (79 ) (81 ) (82 ) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income 143 57 1,177 (630 ) (56 ) 102 (334 ) (34 ) 209 Employer contributions 156 174 150 153 231 208 18 14 117 Other movements 3 (1 ) — — — — (25 ) (24 ) (10 ) Closing net defined benefit 1,520 1,231 1,104 (1,113 ) (509 ) (552 ) (1,360 ) (940 ) (815 ) Changes in the present value of defined benefit obligations (including unfunded obligations) 2020 2019 2018 £m £m £m Opening defined benefit obligations (24,939 ) (24,054 ) (26,230 ) Current service cost (178 ) (193 ) (193 ) Interest cost (751 ) (771 ) (775 ) Actuarial gains/(losses) – experience 148 (69 ) (100 ) Actuarial gains – demographic assumptions 452 266 671 Actuarial (losses)/gains – financial assumptions (84 ) (619 ) 174 Past service credit – redundancies — 7 1 Special termination benefit cost – redundancies (2 ) (55 ) (9 ) Past service cost – augmentations — (5 ) (1 ) Past service cost – plan amendments — (34 ) — Medicare subsidy received (22 ) (19 ) (21 ) Employee contributions (1 ) (1 ) (1 ) Benefits paid 1,282 1,376 1,285 Exchange adjustments (531 ) (768 ) 1,145 Closing defined benefit obligations (24,626 ) (24,939 ) (24,054 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Opening defined benefit obligations (14,276 ) (14,226 ) (15,645 ) (7,155 ) (6,582 ) (7,050 ) (3,508 ) (3,246 ) (3,535 ) Current service cost (33 ) (41 ) (49 ) (100 ) (104 ) (98 ) (45 ) (48 ) (46 ) Interest cost (335 ) (358 ) (366 ) (280 ) (277 ) (273 ) (136 ) (136 ) (136 ) Actuarial gains/(losses) – experience 113 (56 ) (95 ) (45 ) (52 ) (38 ) 80 39 33 Actuarial gains – demographic assumptions 140 224 565 78 — 30 234 42 76 Actuarial gains/(losses) – financial assumptions 798 (568 ) 604 (595 ) (24 ) (279 ) (287 ) (27 ) (151 ) Past service credit – redundancies — 7 1 — — — — — — Special termination benefit cost – redundancies (2 ) (55 ) (9 ) — — — — — — Past service cost – augmentations — (5 ) (1 ) — — — — — — Past service cost – plan amendments — (34 ) — — — — — — — Medicare subsidy received — — — — — — (22 ) (19 ) (21 ) Employee contributions (1 ) (1 ) (1 ) — — — — — — Benefits paid 752 837 770 374 398 362 156 141 153 Exchange adjustments — — — (362 ) (514 ) 764 (169 ) (254 ) 381 Closing defined benefit obligations (12,844 ) (14,276 ) (14,226 ) (8,085 ) (7,155 ) (6,582 ) (3,697 ) (3,508 ) (3,246 ) 25. Pensions and other post-retirement benefits continued Changes in the value of plan assets 2020 2019 2018 £m £m £m Opening fair value of plan assets 24,793 23,858 24,375 Interest income 728 749 710 Return on plan assets (less than)/in excess of interest¹ (1,240 ) 490 568 Administration costs (16 ) (14 ) (16 ) Employer contributions 327 419 475 Employee contributions 1 1 1 Benefits paid (1,279 ) (1,377 ) (1,285 ) Exchange adjustments 434 667 (970 ) Closing fair value of plan assets 23,748 24,793 23,858 Actual return on plan assets (512 ) 1,239 1,278 Expected contributions to plans in the following year 269 307 363 1. For the year ended 31 March 2020, this includes an actuarial loss from the purchase of buy-in policies of £0.7 billion . The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Opening fair value of plan assets 15,507 15,330 15,489 6,646 6,030 6,322 2,640 2,498 2,564 Interest income 366 389 363 259 256 246 103 104 101 Return on plan assets (less than)/ (908 ) 457 103 (26 ) 62 314 (306 ) (29 ) 151 Administration costs (9 ) (6 ) (6 ) (6 ) (7 ) (9 ) (1 ) (1 ) (1 ) Employer contributions 156 174 150 153 231 208 18 14 117 Employee contributions 1 1 1 — — — — — — Benefits paid (749 ) (838 ) (770 ) (374 ) (398 ) (362 ) (156 ) (141 ) (153 ) Exchange adjustments — — — 320 472 (689 ) 114 195 (281 ) Closing fair value of plan assets 14,364 15,507 15,330 6,972 6,646 6,030 2,412 2,640 2,498 Actual return on plan assets (542 ) 846 466 233 318 560 (203 ) 75 252 Expected contributions to plans in the following year 137 148 140 125 150 221 7 9 2 1. For the year ended 31 March 2020, UK pensions includes an actuarial loss from the purchase of buy-in policies of £0.7 billion . The markets for unquoted investments are illiquid and the valuations that have been provided by fund managers as at 31 March 2020 may be based on valuation models that have unobservable inputs. Given the current market volatility that has arisen as a result of COVID-19, this means that the prices provided are subject to additional estimation uncertainty. Sensitivity analyses for changes in private equity, property and diversified alternative valuations have been provided in note 35. Asset allocation strategy Each plan’s investment strategy is formulated in order to target specific asset allocations and returns, and to manage risk. The asset allocation of the plans is as follows: 2020 2019 UK pensions US pensions US other post-retirement benefits UK pensions US pensions US other post-retirement benefits % % % % % % Equities 10.2 36.0 57.6 12.7 40.8 60.2 Corporate bonds 26.7 31.0 0.6 23.4 26.4 0.7 Government securities 14.3 18.2 22.9 39.4 16.0 20.6 Property 4.8 4.4 — 5.5 4.7 — Diversified alternatives 6.2 9.0 13.4 5.0 10.1 12.9 Liability matching assets 34.3 — — 11.1 — — Infrastructure — 1.7 — — 1.5 — Cash and cash equivalents 1.8 0.3 — 1.9 0.3 — Other 1.7 (0.6 ) 5.5 1.0 0.2 5.6 100.0 100.0 100.0 100.0 100.0 100.0 25. Pensions and other post-retirement benefits continued Defined benefit investment strategies and risks DB pension plans can pose a significant risk to future cash flows, as National Grid underwrites the financial and demographic risks associated with these plans. Although the governing bodies have sole responsibility for setting investment strategies and managing risks, National Grid closely works with and supports the governing bodies of each plan, to assist them in mitigating the risks associated with their plans and to ensure that the plans are funded to meet their obligations. In the UK, each plan has a Trustee that is the governing body. The Trustees’ responsibilities are set out in the Trust Deed and Rules. In the US, the fiduciary committee for all the retirement plans is the Retirement Plan Committee (RPC). The RPC is structured in accordance with US laws governing retirement plans under the Employee Retirement Income Security Act (ERISA). The Trustees and RPC, after taking advice from professional investment advisors and in consultation with National Grid, set the key principles, including expected returns, risk and liquidity requirements. In setting these they take into account expected contributions, maturity of the pension liabilities, and in the UK, the strength of the covenant. The Trustees and RPC formulate an investment strategy to manage risk through diversification, including the use of liability-matching assets, which move in line with the long-term liabilities of the plan, and return-seeking assets, some of which are designed to mitigate downside risk. Where appropriate, the strategies may include interest rate and inflation hedging instruments, and currency hedging to hedge overseas holdings. Investments are usually grouped into: • Return-seeking assets: equities, property and diversified funds where the objective is to achieve growth within the constraints of the plans’ risk profiles. These assets should produce returns greater than the liability increase, so improving the funding position, and are assessed by reference to benchmarks and performance targets agreed with the investment managers; and • Liability-matching assets: liability-driven investment (LDI) funds, buy-ins, government securities, corporate bonds and swaps, where the objective is to secure fixed or inflation-adjusted cash flows in future. These investments are generally expected to match the change in liability valuation, so protecting the funding position. Bonds and securities are also measured against certain market benchmarks. Investments are predominantly made in assets considered to be of investment grade. Where investments are made in non-investment grade assets, the higher volatility involved is carefully judged and balanced against the expected higher returns. Similarly, investments are made predominantly in regulated markets. Where investments are made either in non-investment grade assets or outside of regulated markets, investment levels are kept to prudent levels and subject to agreed control ranges, to control the risk. Should these investments fall outside the pre-agreed ranges, corrective actions and timescales are agreed with the investment manager to remedy the position. The governing bodies ensure that the performance of investment managers is regularly reviewed against measurable objectives, consistent with each pension plan’s long-term objectives and accepted risk levels. Where required, the portfolios are amended, or investment managers changed. The Trustees and RPC can generally delegate responsibility for the selection of specific bonds, securities and other investments to appointed investment managers. Investment managers are selected based on the required skills, expertise of those markets, process and financial security to manage the investments. The investment managers use their skill and expertise to manage the investments competently. In some cases, they may further delegate this responsibility, through appointing sub-managers. The pension plans hold sufficient cash to meet benefit requirements, with other investments being held in liquid or realisable assets to meet unexpected cash flow requirements. The plans do not borrow money, or act as guarantor, to provide liquidity to other parties (unless it is temporary). In the UK, both NGUKPS and NGEG of ESPS have Responsible Investment (RI) Policies, which take into account Environmental, Social and Governance (ESG) areas. The NGUKPS RI also incorporates the six UN-backed Principles for Responsible Investment (UNPRI). The Trustees believe that ESG factors can be material to financial outcomes and therefore these should and will be considered alongside other factors. The Trustees recognise that their primary responsibility remains a fiduciary one, i.e. their first duty is to ensure the best possible return on investments with the appropriate level of risk. However, the Trustees also recognise the increasing materiality of ESG factors and that they have a fiduciary and regulatory duty to consider RI, including ESG factors and the potential impact on the quality and sustainability of long-term investment returns and therefore on the Trustees’ primary fiduciary duty. Whilst in the US there is no regulatory requirement to have ESG-specific principles embedded in investment policies, investment managers often utilise ESG principles to inform their decision-making process. The most significant risks associated with the DB plans are: • Asset volatility – the plans invest in a varie

Provisions

Provisions	12 Months Ended
	Mar. 31, 2020
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Provisions	Provisions We make provisions when an obligation exists resulting from a past event, and it is probable that cash will be paid to settle it, but the exact amount of cash required can only be estimated. The main estimates relate to environmental remediation and decommissioning costs for various sites we own or have owned and other provisions, including restructuring plans and lease contracts we have entered into that are now loss making. The evaluation of the likelihood of the contingent events has required best judgement by management regarding the probability of exposure to potential loss. Should circumstances change following unforeseeable developments, the likelihood could alter. Provisions are recognised where a legal or constructive obligation exists at the reporting date, as a result of a past event, where the amount of the obligation can be reliably estimated and where the outflow of economic benefit is probable. Provision is made for decommissioning and environmental costs, based on future estimated expenditures, discounted to present values. An initial estimate of decommissioning and environmental costs attributable to property, plant and equipment is recorded as part of the original cost of the related property, plant and equipment. Changes in the provision arising from revised estimates, discount rates or changes in the expected timing of expenditure that relates to property, plant and equipment, are recorded as adjustments to their carrying value and depreciated prospectively over their remaining estimated useful economic lives; otherwise such changes are recognised in the income statement. The unwinding of the discount is included within the income statement within finance costs. Environmental £m Decommissioning £m Restructuring £m Emissions £m Other £m Total provisions £m At 1 April 2018 1,531 194 3 8 316 2,052 Exchange adjustments 103 7 — — 14 124 Additions¹ 32 18 125 16 35 226 Unused amounts reversed (36 ) (10 ) (3 ) (6 ) (10 ) (65 ) Unwinding of discount 62 5 — — 7 74 Utilised² (53 ) (26 ) (42 ) (9 ) (79 ) (209 ) Transfers³ — — — — (3 ) (3 ) At 31 March 2019 1,639 188 83 9 280 2,199 Exchange adjustments 82 5 — 1 9 97 Additions¹ 437 93 7 12 40 589 Unused amounts reversed (29 ) (16 ) (16 ) — (9 ) (70 ) Unwinding of discount 65 5 — — 7 77 Utilised² (123 ) (21 ) (39 ) (5 ) (50 ) (238 ) At 31 March 2020 2,071 254 35 17 277 2,654 2020 2019 £m £m Current 348 316 Non-current 2,306 1,883 2,654 2,199 1. For the year ended 31 March 2020, £402 million (2019: £nil ) of additions relate to exceptional environmental provisions, of which £76 million relates to the impact of the change in the real discount rate from 1% to 0.5% during the year (see note 5 for details). Additions to other provisions include £15 million ( 2019 : £nil ) in relation to discontinued operations. 2. Utilised amounts for other provisions include £8 million ( 2019 : £20 million ) in relation to discontinued operations. 3. Represents net amounts transferred to trade and other payables (see note 22) of £nil ( 2019 : £3 million ). 26. Provisions continued Environmental provisions The environmental provision represents the estimated restoration and remediation costs relating to a number of sites owned and managed by subsidiary undertakings, together with certain US sites that National Grid no longer owns. The environmental provision is as follows: 2020 2019 Discounted £m Undiscounted £m Real discount rate Discounted £m Undiscounted £m Real discount rate UK sites 175 184 0.5 % 189 210 1 % US sites 1,896 1,955 0.5 % 1,450 1,555 1 % 2,071 2,139 1,639 1,765 The remediation expenditure in the UK relates to old gas manufacturing sites and also to electricity transmission sites. Cash flows are expected to be incurred until 2075 although the weighted average duration of the cash flows is 11 years . A number of estimation uncertainties affect the calculation of the provision, including the impact of regulation, the accuracy of site surveys, unexpected contaminants, transportation costs, the impact of alternative technologies and changes in the real discount rate. This provision incorporates our best estimate of the financial effect of these uncertainties, but future changes in any of the assumptions could materially impact the calculation of the provision. The undiscounted amount is the undiscounted best estimate of the liability having regard to these uncertainties. The remediation expenditure in the US is expected to be incurred until 2069 , of which the majority relates to three Superfund sites (being sites where hazardous substances are present as a result of the historic operations of manufactured gas plants in Brooklyn, New York). The weighted average duration of the cash flows is nine years . The uncertainties regarding the calculation of this provision are similar to those considered in respect of UK sites. Under the terms of our rate plans, we are entitled to recovery of environmental clean-up costs from rate payers. Decommissioning provisions The decommissioning provisions represent £174 million ( 2019 : £80 million ) of expenditure relating to asset retirement obligations estimated to be incurred until 2115 , with additional amounts being recognised in the year relating to both interconnectors and other assets commissioned in the year. In addition, £74 million ( 2019 : £90 million ) of expenditure relating to the demolition of gas holders is estimated to be incurred until 2026 . Restructuring provisions In 2019, a cost-efficiency and restructuring programme was undertaken in both our UK and US businesses, as detailed in note 5, which resulted in the recognition of a £125 million charge in that year. £39 million (2019: £42 million ) was utilised during the current year, resulting in a closing provision of £35 million (2019: £83 million ). Other provisions Included within other provisions at 31 March 2020 are the following amounts: • £37 million ( 2019 : £30 million ) in respect of legacy provisions recognised following the sale of UK Gas Distribution; • £31 million ( 2019 : £29 million ) in respect of onerous lease commitments and rates payable on surplus properties with expenditure expected to be incurred until 2039 ; • £164 million ( 2019 : £164 million ) of estimated liabilities in respect of past events insured by insurance subsidiary undertakings, including employer liability claims. In accordance with insurance industry practice, these estimates are based on experience from previous year s, but we currently expect that cash flows will be incurred until 2049 ; and • £nil ( 2019 : £13 million ) in respect of obligations associated with investments in joint ventures and associates.

Share capital

Share capital	12 Months Ended
	Mar. 31, 2020
Share Capital, Reserves And Other Equity Interest [Abstract]
Share capital	Share capital Ordinary share capital represents the total number of shares issued which are publicly traded. We also disclose the number of treasury shares the Company holds, which are shares that the Company has bought itself, predominantly to actively manage scrip issuances and settle employee share option and reward plan liabilities. Share capital is accounted for as an equity instrument. An equity instrument is any contract that includes a residual interest in the consolidated assets of the Company after deducting all its liabilities and is recorded at the proceeds received, net of direct issue costs, with an amount equal to the nominal amount of the shares issued included in the share capital account and the balance recorded in the share premium account. Allotted, called-up and fully paid million £m At 1 April 2018 3,638 452 Issued during the year in lieu of dividends¹ 49 6 At 31 March 2019 3,687 458 Issued during the year in lieu of dividends¹ 93 12 At 31 March 2020 3,780 470 1. The issue of shares under the scrip dividend programme is considered to be a bonus issue under the terms of the Companies Act 2006, and the nominal value of the shares is charged to the share premium account. The share capital of the Company consists of ordinary shares of 12 204 ⁄ 473 pence nominal value each including ADSs. The ordinary shares and ADSs allow holders to receive dividends and vote at general meetings of the Company. The Company holds treasury shares but may not exercise any rights over these shares including the entitlement to vote or receive dividends. There are no restrictions on the transfer or sale of ordinary shares. In line with the provisions of the Companies Act 2006, the Company has amended its Articles of Association and ceased to have authorised share capital. Treasury shares At 31 March 2020 , the Company held 272 million ( 2019 : 277 million ) of its own shares. The market value of these shares as at 31 March 2020 was £2,574 million ( 2019 : £2,359 million ). For the benefit of employees and in connection with the operation of the Company’s various share plans, the Company made the following transactions in respect of its own shares during the year ended 31 March 2020 : i) During the year, 3 million ( 2019 : 3 million ) treasury shares were gifted to National Grid Employee Share Trusts and 2 million ( 2019 : 3 million ) treasury shares were re-issued in relation to employee share schemes, in total representing approximately 0.1% ( 2019 : 0.2% ) of the ordinary shares in issue as at 31 March 2020 . The nominal value of these shares was £1 million ( 2019 : £1 million ) and the total proceeds received were £17 million ( 2019 : £18 million ). National Grid settles share awards under its Long Term Incentive Plan and the Save As You Earn scheme, by the transfer of treasury shares to its employee share trusts. ii) During the year, the Company made payments totalling £6 million ( 2019 : £2 million ) to National Grid Employee Share Trusts to enable the trustees to make purchases of National Grid plc shares to settle share awards in relation to all employee share plans and discretionary reward plans. The cost of such purchases is deducted from retained earnings in the period that the transaction occurs. The maximum number of ordinary shares held in treasury during the year was 277 million ( 2019 : 283 million ) representing approximately 7.3% ( 2019 : 7.7% ) of the ordinary shares in issue as at 31 March 2020 and having a nominal value of £34 million ( 2019 : £35 million ).

Other equity reserves

Other equity reserves	12 Months Ended
	Mar. 31, 2020
Disclosure of reserves within equity [abstract]
Other equity reserves	Other equity reserves Other equity reserves are different categories of equity as required by accounting standards and represent the impact of a number of our historical transactions. Other equity reserves comprise the translation reserve (see accounting policy D in note 1), cash flow hedge reserve and the cost of hedging reserve (see note 32), available-for-sale reserve, debt instruments at fair value through other comprehensive income reserve (FVOCI debt) and equity investments at fair value through other comprehensive income reserve (FVOCI equity) (see note 15), the capital redemption reserve and the merger reserve. The merger reserve arose as a result of the application of merger accounting principles under the then prevailing UK GAAP, which under IFRS 1 was retained for mergers that occurred prior to the IFRS transition date. Under merger accounting principles, the difference between the carrying amount of the capital structure of the acquiring vehicle and that of the acquired business was treated as a merger difference and included within reserves. The merger reserve represents the difference between the carrying value of subsidiary undertaking investments and their respective capital structures following the Lattice demerger from BG Group plc and the 1999 Lattice refinancing. The cash flow hedge reserve will amortise as the committed future cash flows from borrowings are paid or capitalised in fixed assets (as described in note 32). Cost of hedging, FVOCI debt, and FVOCI equity reserves arose as a result of the adoption of IFRS 9 on 1 April 2018. See note 15 for further detail on available-for-sale, FVOCI debt and FVOCI equity reserves and note 32 in respect of cost of hedging reserve. As the amounts included in other equity reserves are not attributable to any of the other classes of equity presented, they have been disclosed as a separate classification of equity. Translation £m Cash flow hedge £m Cost of hedging £m Available- for-sale £m FVOCI equity £m FVOCI debt £m Own credit £m Capital redemption £m Merger £m Total £m At 1 April 2017 894 103 — 162 — — — 19 (5,165 ) (3,987 ) Exchange adjustments¹ (504 ) — — — — — — — — (504 ) Net gains/(losses) taken to equity² — 296 — (30 ) — — — — — 266 Share of net gains of associates taken to equity — 5 — — — — — — — 5 Transferred from profit or loss² — (280 ) — (73 ) — — — — — (353 ) Tax — 4 — 29 — — — — — 33 At 31 March 2018 (as previously reported) 390 128 — 88 — — — 19 (5,165 ) (4,540 ) Transfer on transition to IFRS 9 — (3 ) 76 (88 ) 34 46 7 — — 72 At 1 April 2018 (as restated) 390 125 76 — 34 46 7 19 (5,165 ) (4,468 ) Exchange adjustments¹ 346 — — — — — — — — 346 Net (losses)/gains taken to equity² — (206 ) (107 ) — — 2 7 — — (304 ) Share of net gains of associates taken to equity — 1 — — — — — — — 1 Transferred to profit or loss² — 166 41 — — — — — — 207 Net losses in respect of cash flow hedging of capital expenditure — (13 ) — — — — — — — (13 ) Tax — 6 7 — — — (1 ) — — 12 Cash flow hedges transferred to the statement of financial position, net of tax — (18 ) — — — — — — — (18 ) At 1 April 2019 736 61 17 — 34 48 13 19 (5,165 ) (4,237 ) Exchange adjustments¹ 550 — — — — — — — — 550 Net losses taken to equity — (142 ) (33 ) — (13 ) (15 ) (3 ) — — (206 ) Share of net losses of associates taken to equity — (5 ) — — — — — — — (5 ) Transferred to profit or loss — 14 (45 ) — — — — — — (31 ) Net losses in respect of cash flow hedging of capital expenditure — (17 ) — — — — — — — (17 ) Tax — 29 11 — 4 (2 ) — — — 42 Cash flow hedges transferred to the statement of financial position, net of tax — (15 ) — — — — — — — (15 ) At 31 March 2020 1,286 (75 ) (50 ) — 25 31 10 19 (5,165 ) (3,919 ) 1. The exchange adjustments recorded in the translation reserve comprise a gain of £545 million ( 2019 : gain of £896 million ; 2018 : loss of £1,304 million ) relating to the translation of foreign operations offset by a gain of £5 million ( 2019 : loss of £550 million ; 2018 : gain of £800 million ) relating to borrowings, cross-currency swaps and foreign exchange forward contracts used to hedge the net investment in non-sterling denominated subsidiaries. 2. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in cash flow hedges of foreign currency risk and interest rates. This has no net impact on the consolidated statement of comprehensive income. It has resulted in a prior year gross up to £166 million ( 2018 : £277 million ) to ‘Net losses taken to equity’ with an equal and offsetting gross up to ‘Transferred to profit or loss’.

Net debt

Net debt	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Net debt	Net debt Net debt represents the amount of borrowings and overdrafts less cash, current financial investments and related financing derivatives. Funding and liquidity risk management is carried out by the treasury function under policies and guidelines approved by the Finance Committee of the Board. The Finance Committee is responsible for the regular review and monitoring of treasury activity and for the approval of specific transactions, the authority for which fall outside the delegation of authority to management. The primary objective of the treasury function is to manage our funding and liquidity requirements. A further important objective is to manage the associated financial risks, in the form of interest rate risk and foreign exchange risk, to within pre-authorised parameters. Details of the main risks arising from our financing and commodity hedging activities are included in note 32. Investment of surplus funds, usually in short-term fixed deposits or placements with money market funds that invest in highly liquid instruments of high credit quality, is subject to our counterparty risk management policy. (a) Reconciliation of net cash flow to movement in net debt 2020 2019 2018 £m £m £m Decrease in cash and cash equivalents (183 ) (80 ) (807 ) Decrease in financial investments (7 ) (822 ) (5,953 ) Increase/(decrease) in borrowings and related derivatives¹ (23 ) (708 ) 1,209 Net interest paid on the components of net debt² 888 866 808 Change in debt resulting from cash flows 675 (744 ) (4,743 ) Changes in fair value of financial assets and liabilities and exchange movements (1,081 ) (1,648 ) 2,098 Net interest charge on the components of net debt (1,097 ) (1,076 ) (1,017 ) Other non-cash movements (84 ) (27 ) (66 ) Movement in net debt (net of related derivative financial instruments) in the year (1,587 ) (3,495 ) (3,728 ) Net debt (net of related derivative financial instruments) at start of year (26,529 ) (23,002 ) (19,274 ) Impact of transition to IFRS 16 (2019: IFRS 9) (474 ) (32 ) — Net debt (net of related derivative financial instruments) at end of year (28,590 ) (26,529 ) (23,002 ) Composition of net debt Net debt is comprised as follows: 2020 2019 2018 £m £m £m Cash, cash equivalents and financial investments 2,071 2,233 3,023 Borrowings (30,794 ) (28,730 ) (26,625 ) Financing derivatives¹ 133 (32 ) 600 (28,590 ) (26,529 ) (23,002 ) 1. The financing derivatives balance included in net debt excludes the commodity derivatives (see note 17). 2. Excludes £6 million ( 2019 : £23 million ; 2018 : £27 million ) cash interest from the Quadgas shareholder loan included within discontinued operations in the cash flow statement. 29. Net debt continued (b) Analysis of changes in net debt Cash and cash equivalents £m Financial investments £m Borrowings £m Financing derivatives £m Total 1 £m At 1 April 2017 1,139 8,741 (28,638 ) (516 ) (19,274 ) Cash flow (807 ) (5,983 ) 2,108 (61 ) (4,743 ) Fair value gains and losses and exchange movements (3 ) (149 ) 1,088 1,162 2,098 Interest income/(charges) — 85 (1,117 ) 15 (1,017 ) Other non-cash movements — — (66 ) — (66 ) At 31 March 2018 329 2,694 (26,625 ) 600 (23,002 ) Impact of transition to IFRS 9 — — (32 ) — (32 ) At 1 April 2018 (as restated) 329 2,694 (26,657 ) 600 (23,034 ) Cash flow (80 ) (846 ) (240 ) 422 (744 ) Fair value gains and losses and exchange movements 3 93 (733 ) (1,011 ) (1,648 ) Interest income/(charges) — 29 (1,062 ) (43 ) (1,076 ) Other non-cash movements — 11 (38 ) — (27 ) At 1 April 2019 252 1,981 (28,730 ) (32 ) (26,529 ) Impact of transition to IFRS 16 — — (474 ) — (474 ) Cash flow (183 ) (42 ) 450 450 675 Fair value gains and losses and exchange movements 4 25 (864 ) (246 ) (1,081 ) Interest income/(charges) — 34 (1,092 ) (39 ) (1,097 ) Other non-cash movements — — (84 ) — (84 ) At 31 March 2020 73 1,998 (30,794 ) 133 (28,590 ) Balances at 31 March 2020 comprise: Non-current assets — — — 1,205 1,205 Current assets 73 1,998 — 62 2,133 Current liabilities — — (4,072 ) (254 ) (4,326 ) Non-current liabilities — — (26,722 ) (880 ) (27,602 ) 73 1,998 (30,794 ) 133 (28,590 ) 1. Includes accrued interest at 31 March 2020 of £246 million ( 2019 : £223 million ; 2018 : £197 million ). (c) Reconciliation of cash flow from financing liabilities to cash flow statement 2020 2019 2018 £m £m £m Cash flows per financing activities section of cash flow statement: Proceeds received from loans 4,218 2,932 1,941 Repayment of loans (3,253 ) (1,969 ) (2,156 ) Payments of lease liabilities (121 ) (70 ) (71 ) Net movements in short-term borrowings (424 ) 179 (764 ) Net movements in derivatives (187 ) 35 (267 ) Interest paid (957 ) (914 ) (853 ) Cash flows per financing activities section of cash flow statement (724 ) 193 (2,170 ) Adjustments: Non-net debt-related items 34 24 12 Derivative cash inflow in relation to capital expenditure 13 13 12 Derivative cash flows per investing section of cash flow statement (223 ) (412 ) 330 Discontinued operations — — (231 ) Cash flows relating to financing liabilities within net debt (900 ) (182 ) (2,047 ) Analysis of changes in net debt: Borrowings (450 ) 240 (2,108 ) Financing derivatives (450 ) (422 ) 61 Cash flow movements relating to financing liabilities within net debt (900 ) (182 ) (2,047 ) 29. Net debt continued (d) Reconciliation of changes in liabilities arising from financing activities The table below reconciles changes in liabilities arising from financing activities, including both changes arising from cash flows and non-cash changes. Liabilities arising from financing activities are those for which cash flows were, or future cash flows will be, classified in the statement of cash flows within financing activities. Following a review in the year, we have changed our accounting policy in relation to the presentation of certain derivatives in the cash flow statement to be presented as investing activities rather than financing activities (further detail is disclosed in note 1). The reclassified cash flows are in relation to derivatives associated with our net investment hedges, and given they are designated in a hedge relationship, the Group has decided to present them together with the underlying hedged item rather than as part of our overall financing activities. As a result we have separately disclosed the reconciliation below, excluding derivatives associated with our net investment hedges, given that they are classified in the statement of cash flows within investing activities. Borrowings £m Financing derivatives £m Total £m At 1 April 2017 (28,638 ) 16 (28,622 ) Cash flow 2,108 281 2,389 Fair value gains and losses and exchange movements 1,088 222 1,310 Interest income/(charges) (1,117 ) 34 (1,083 ) Other non-cash movements (66 ) — (66 ) At 31 March 2018 (26,625 ) 553 (26,072 ) Impact of transition to IFRS 9 (32 ) — (32 ) At 1 April 2018 (as restated) (26,657 ) 553 (26,104 ) Cash flow (240 ) 23 (217 ) Fair value gains and losses and exchange movements (733 ) (334 ) (1,067 ) Interest charges (1,062 ) (14 ) (1,076 ) Other non-cash movements (38 ) — (38 ) At 1 April 2019 (28,730 ) 228 (28,502 ) Impact of transition to IFRS 16 (474 ) — (474 ) Cash flow 450 240 690 Fair value gains and losses and exchange movements (864 ) (231 ) (1,095 ) Interest charges (1,092 ) (9 ) (1,101 ) Other non-cash movements (84 ) — (84 ) At 31 March 2020 (30,794 ) 228 (30,566 )

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Mar. 31, 2020
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Commitments and contingencies	Commitments and contingencies Commitments are those amounts that we are contractually required to pay in the future as long as the other party meets its obligations. These commitments primarily relate to energy purchase agreements and contracts for the purchase of assets which, in many cases, extend over a long period of time. Commitments previously included operating lease commitments but on transition to IFRS 16, which was effective from 1 April 2019, substantially all lease commitments are included on the balance sheet as right-of-use assets (see note 13) and lease liabilities (see note 21). Therefore, only low-value leases and short-term leases are off-balance sheet commitments, both of which are immaterial. We also disclose any contingencies, which include guarantees that companies have given, where we pledge assets against current obligations that will remain for a specific period. 2020 2019 £m £m Future capital expenditure Contracted for but not provided 2,629 1,973 Energy purchase commitments¹ Less than 1 year 1,365 1,353 In 1 to 2 years 890 779 In 2 to 3 years 973 651 In 3 to 4 years 955 827 In 4 to 5 years 861 862 More than 5 years 11,314 11,237 16,358 15,709 Guarantees² Guarantee of sublease for US property (expires 2040) 173 173 Guarantees of certain obligations of Grain LNG (expire up to 2025) 34 39 Guarantees of certain obligations for construction of HVDC West Coast Link (expected expiry 2020) 92 139 Guarantees of certain obligations of Nemo Link Limited (expired 2019) — 19 Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates)² 683 865 Guarantees of certain obligations of St William Homes LLP (various expiry dates)³ 30 22 Guarantees of certain obligations for construction of IFA 2 (expected expiry 2022)² 564 505 Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024) 1,096 872 Other guarantees and letters of credit (various expiry dates) 150 341 2,822 2,975 2019 £m Operating lease commitments Less than 1 year 43 In 1 to 2 years 39 In 2 to 3 years 34 In 3 to 4 years 35 In 4 to 5 years 27 More than 5 years 123 301 1. Energy purchase commitments relate to contractual commitments to purchase electricity or gas that are used to satisfy physical delivery requirements to our customers or for energy that we use ourselves (i.e. normal purchase, sale or usage) and hence are accounted for as ordinary purchase contracts (see note 32(f)). Details of commodity contract derivatives that do not meet the normal purchase, sale or usage criteria, and hence are accounted for as derivative contracts, are shown in note 17(b). 2. Included within total guarantees are guarantees to both joint ventures and Engineering, Procurement and Construction contractors regarding the construction of interconnectors of £358 million ( 2019 : £470 million ). 3. Includes guarantees to related parties. Through the ordinary course of our operations, we are party to various litigation, claims and investigations. We do not expect the ultimate resolution of any of these proceedings to have a material adverse effect on our results of operations, cash flows or financial position.

Related party transactions

Related party transactions	12 Months Ended
	Mar. 31, 2020
Related party transactions [abstract]
Related party transactions	Related party transactions Related parties include joint ventures, associates, investments and key management personnel. The following significant transactions with related parties were in the normal course of business. Amounts receivable from and payable to related parties are due on normal commercial terms: 2020 2019 2018 £m £m £m Sales: Goods and services supplied to a pension plan 5 5 3 Sales: Goods and services supplied to joint ventures¹ 101 151 14 Sales: Goods and services supplied to associates² 33 192 220 Purchases: Goods and services received from joint ventures³ 61 26 135 Purchases: Goods and services received from associates³ 56 141 160 Receivable from joint ventures 4 255 584 160 Receivable from associates 4 1 368 376 Payable to joint ventures 72 8 — Payable to associates 4 12 17 Interest income from joint ventures 2 5 4 Interest income from associates 8 23 27 Dividends received from joint ventures 5 34 30 43 Dividends received from associates 6 41 171 170 1. During the year, £38 million ( 2019 : £139 million ) of property sites were sold to a joint venture, St William Homes LLP. A further £32 million of sales were made to NGET/SPT Upgrades Limited in 2020. 2. Sales relate to transactions with Quadgas, until the date it ceased to be a related party following the disposal of our 39% stake in June 2019 (see note 10). Included within this is other income of £31 million ( 2019 : £52 million ) relating to a Transitional Service Agreement following the sale of the UK Gas Distribution business to Quadgas. 3. During the year, the Group received goods and services from a number of US associates, both for the transportation of gas and for pipeline services in the US, most notably, £31 million ( 2019 : £30 million ) of purchases from Millennium Pipeline Company LLC. The Group also purchased capitalised assets of £58 million ( 2019 : £26 million ) from NGET/SPT Upgrades Limited (a joint venture). 4. Amounts receivable from associates includes a loan receivable balance of £242 million ( 2019 : £325 million ) in relation to St William Homes LLP (a joint venture). There is no longer a loan receivable from Quadgas ( 2019 : £352 million ) and Nemo Link (a joint venture) ( 2019 : £258 million ). The loan receivable balance from Nemo Link was transferred to equity during 2020 (see note 16 for details). 5. Dividends of £25 million ( 2019 : £30 million ) were received from BritNed Development Limited. 6. Includes £32 million ( 2019 : £24 million ) of dividend income from Millennium Pipeline Company LLC. No dividends were received from Quadgas this year (2019: £133 million ). Details of investments in principal subsidiary undertakings, joint ventures and associates are disclosed in note 34, and information relating to pension fund arrangements is disclosed in note 25. For details of key management remuneration, refer to note 4(c).

Financial risk management

Financial risk management	12 Months Ended
	Mar. 31, 2020
Financial Instruments [Abstract]
Financial risk management	Financial risk management Our activities expose us to a variety of financial risks including credit risk, liquidity risk, capital risk, currency risk, interest rate risk, inflation risk and commodity price risk. Our risk management programme focuses on the unpredictability of financial markets and seeks to minimise potential volatility of financial performance from these risks. We use financial instruments, including derivative financial instruments, to manage these risks. Risk management related to financing activities is carried out by a central treasury department under policies approved by the Finance Committee of the Board. The objective of the treasury department is to manage funding and liquidity requirements, including managing associated financial risks, to within acceptable boundaries. The Finance Committee provides written principles for overall risk management, and written policies covering the following specific areas: foreign exchange risk, interest rate risk, credit risk, liquidity risk, use of derivative financial instruments and non-derivative financial instruments, and investment of excess liquidity. The Finance Committee has delegated authority to administer the commodity price risk policy and credit policy for US-based commodity transactions to the Energy Procurement Risk Management Committee and the National Grid USA Board of Directors. We have exposure to the following risks, which are described in more detail below: • credit risk; • liquidity risk; • currency risk; • interest rate risk; • commodity price risk; and • capital risk. Where appropriate, derivatives and other financial instruments used for hedging currency and interest rate risk exposures are formally designated as fair value, cash flow or net investment hedges as defined in IFRS 9. Hedge accounting allows the timing of the profit or loss impact of qualifying hedging instruments to be recognised in the same reporting period as the corresponding impact of hedged exposures. To qualify for hedge accounting, documentation is prepared specifying the risk management objective and strategy, the component transactions and methodology used for measurement of effectiveness. 32. Financial risk management continued Hedge accounting relationships are designated in line with risk management activities further described below. Categories designated at National Grid are as follows: • currency risk arising from our forecasted foreign currency transactions (capital expenditure or revenues) is designated in cash flow hedges; • currency risk arising from our net investments in foreign operations is designated in net investment hedges; and • currency and interest rate risk arising from borrowings are designated in cash flow or fair value hedges. Critical terms of hedging instruments and hedged items are transacted to match on a 1 :1 ratio by notional values. Hedge ineffectiveness can nonetheless arise from inherent differences between derivatives and non-derivative instruments and other market factors including credit, correlations, supply and demand, and market volatilities. Ineffectiveness is recognised in the remeasurements component of finance income and costs (see note 6). Hedge accounting is discontinued when a hedging relationship no longer qualifies for hedge accounting. Certain hedging instrument components are treated separately as costs of hedging with the gains and losses deferred in a component of other equity reserves and released systematically into profit or loss to correspond with the timing and impact of hedged exposures, or released in full to finance costs upon an early discontinuation of a hedging relationship. Refer to sections (c) currency risk and (d) interest rate risk below for further details about hedge accounting. (a) Credit risk We are exposed to the risk of loss resulting from counterparties’ default on their commitments including failure to pay or make a delivery on a contract. This risk is inherent in our commercial business activities. Exposure arises from derivative financial instruments, deposits with banks and financial institutions, trade receivables and committed transactions with wholesale and retail customers. Treasury credit risk Counterparty risk arises from the investment of surplus funds and from the use of derivative financial instruments. As at 31 March 2020 , the following limits were in place for investments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 2,049 1,024 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,118 559 Double ‘A+’ G7 sovereign entities (AA+) 1,863 931 Double ‘A’ range institutions (AA) 745 to 931 372 to 465 Single ‘A’ range institutions (A) 261 to 373 130 to 186 The maximum limit applies to all transactions, including long-term transactions. The long-term limit applies to transactions which mature in more than 12 months ’ time. As at 31 March 2020 and 2019 , we had a number of exposures to individual counterparties. In accordance with our treasury policies, counterparty credit exposure utilisations are monitored daily against the counterparty credit limits. Counterparty credit ratings and market conditions are reviewed continually with limits being revised and utilisation adjusted, if appropriate. Management does not expect any significant losses from non-performance by these counterparties. Further information on financial investments subject to impairment provisioning is included in note 15. Commodity credit risk The credit policy for US-based commodity transactions is owned by the Finance Committee to the Board, which establishes controls and procedures to determine, monitor and minimise the credit exposure to counterparties. Wholesale and retail credit risk Our principal commercial exposure in the UK is governed by the credit rules within the regulated codes: Uniform Network Code and Connection and Use of System Code. These set out the level of credit relative to the RAV for each credit rating. In the US, we are required to supply electricity and gas under state regulations. Our policies and practices are designed to limit credit exposure by collecting security deposits prior to providing utility services, or after utility service has commenced if certain applicable regulatory requirements are met. Collection activities are managed on a daily basis. Sales to retail customers are usually settled in cash, cheques, electronic bank payments or by using major credit cards. We are committed to measuring, monitoring, minimising and recording counterparty credit risk in our wholesale business. The utilisation of credit limits is regularly monitored, and collateral is collected against these accounts when necessary. In March 2020, the Group’s US distribution business ceased certain cash collection and termination activities in response to regulatory instructions following the COVID-19 pandemic. This has resulted in the recognition of expected credit losses as at 31 March 2020 (see note 19 for further details). 32. Financial risk management continued (a) Credit risk continued Offsetting financial assets and liabilities The following tables set out our financial assets and liabilities which are subject to offset and to enforceable master netting arrangements or similar agreements. The tables show the amounts which are offset and reported net in the statement of financial position. Amounts which cannot be offset under IFRS, but which could be settled net under terms of master netting arrangements if certain conditions arise, and with collateral received or pledged, are shown to present National Grid’s net exposure. Financial assets and liabilities on different transactions are only reported net if the transactions are with the same counterparty, a currently enforceable legal right of offset exists, and the cash flows are intended to be settled on a net basis. Amounts which do not meet the criteria for offsetting on the statement of financial position, but could be settled net in certain circumstances, principally relate to derivative transactions under ISDA agreements, where each party has the option to settle amounts on a net basis in the event of default of the other party. Commodity contract derivatives that have not been offset on the balance sheet may be settled net in certain circumstances under ISDA or North American Energy Standards Board (NAESB) agreements. For bank account balances and bank overdrafts, the ‘Gross amounts offset’ under cash pooling arrangements is £23 million as at 31 March 2020 ( 2019 : £19 million ). Our UK bank accounts for National Grid subsidiaries participate in GBP, EUR and USD Composite Accounting System overdraft facilities subject to offsetting gross and net overdraft limits. In the US, no offsetting arrangements exist, and cash transactions are settled through Service Company bank accounts with subsequent intercompany payables and receivables reported by subsidiaries with the Service Company. The gross amounts offset for trade payables and receivables, which are subject to general terms and conditions, are insignificant. Related amounts At 31 March 2020 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 1,267 — 1,267 (351 ) (694 ) 222 Commodity contract derivatives 75 — 75 (5 ) (3 ) 67 1,342 — 1,342 (356 ) (697 ) 289 Liabilities Financing derivatives (1,134 ) — (1,134 ) 351 646 (137 ) Commodity contract derivatives (200 ) — (200 ) 5 8 (187 ) (1,334 ) — (1,334 ) 356 654 (324 ) 8 — 8 — (43 ) (35 ) Related amounts At 31 March 2019 Gross carrying amounts £m Gross amounts offset £m Net amount presented in statement of financial position £m Financial instruments £m Cash collateral received/ pledged £m Net amount £m Assets Financing derivatives 1,052 — 1,052 (299 ) (551 ) 202 Commodity contract derivatives 101 — 101 29 — 130 1,153 — 1,153 (270 ) (551 ) 332 Liabilities Financing derivatives (1,084 ) — (1,084 ) 299 615 (170 ) Commodity contract derivatives (99 ) — (99 ) (29 ) — (128 ) (1,183 ) — (1,183 ) 270 615 (298 ) (30 ) — (30 ) — 64 34 32. Financial risk management continued (b) Liquidity risk Our policy is to determine our liquidity requirements by the use of both short-term and long-term cash flow forecasts. These forecasts are supplemented by a financial headroom analysis which is used to assess funding requirements for at least a 24-month period and maintain adequate liquidity for a continuous 12 -month period. We believe our contractual obligations, including those shown in commitments and contingencies in note 30, can be met from existing cash and investments, operating cash flows and other financing that we reasonably expect to be able to secure in the future, together with the use of committed facilities if required. Our debt agreements and banking facilities contain covenants, including those relating to the periodic and timely provision of financial information by the issuing entity and financial covenants such as restrictions on the level of subsidiary indebtedness. Failure to comply with these covenants, or to obtain waivers of those requirements, could in some cases trigger a right, at the lender’s discretion, to require repayment of some of our debt and may restrict our ability to draw upon our facilities or access the capital markets. The following is a maturity profile of our financial liabilities and derivatives: At 31 March 2020 Less than £m 1 to 2 £m 2 to 3 £m More than £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (3,672 ) (2,150 ) (1,611 ) (22,214 ) (29,647 ) Interest payments on borrowings¹ (765 ) (750 ) (714 ) (12,002 ) (14,231 ) Lease liabilities (132 ) (114 ) (99 ) (629 ) (974 ) Other non-interest-bearing liabilities (3,149 ) (318 ) — — (3,467 ) Contingent consideration (32 ) (16 ) (32 ) (16 ) (96 ) Derivative financial liabilities Financing derivatives – receipts² 2,249 986 1,208 3,510 7,953 Financing derivatives – payments² (2,582 ) (1,136 ) (1,463 ) (4,067 ) (9,248 ) Commodity contract derivatives – receipts² 4 2 — — 6 Commodity contract derivatives – payments² (116 ) (50 ) (24 ) (12 ) (202 ) Derivative financial assets Financing derivatives – receipts² 2,469 1,063 570 1,775 5,877 Financing derivatives – payments² (2,271 ) (527 ) (375 ) (1,478 ) (4,651 ) Commodity contract derivatives – receipts² 20 1 1 — 22 Commodity contract derivatives – payments² (21 ) — — — (21 ) (7,998 ) (3,009 ) (2,539 ) (35,133 ) (48,679 ) At 31 March 2019 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (4,129 ) (2,348 ) (1,998 ) (19,673 ) (28,148 ) Interest payments on borrowings¹ (800 ) (733 ) (721 ) (13,465 ) (15,719 ) Lease liabilities (72 ) (63 ) (52 ) (123 ) (310 ) Other non-interest-bearing liabilities (3,306 ) (340 ) — — (3,646 ) Derivative financial liabilities Financing derivatives – receipts² 3,045 1,703 163 2,560 7,471 Financing derivatives – payments² (3,421 ) (2,029 ) (223 ) (3,276 ) (8,949 ) Commodity contract derivatives – receipts² 2 3 1 — 6 Commodity contract derivatives – payments² (98 ) (26 ) (4 ) (1 ) (129 ) Derivative financial assets Financing derivatives – receipts² 1,928 561 863 1,112 4,464 Financing derivatives – payments² (1,251 ) (459 ) (783 ) (875 ) (3,368 ) Commodity contract derivatives – receipts² 23 9 2 — 34 Commodity contract derivatives – payments² — (5 ) (1 ) — (6 ) (8,079 ) (3,727 ) (2,753 ) (33,741 ) (48,300 ) 1. The interest on borrowings is calculated based on borrowings held at 31 March without taking account of future issues. Floating rate interest is estimated using a forward interest rate curve as at 31 March. Payments are included on the basis of the earliest date on which the Company can be required to settle. 2. The receipts and payments line items for derivatives comprise gross undiscounted future cash flows, after considering any contractual netting that applies within individual contracts. Where cash receipts and payments within a derivative contract are settled net, and the amount to be received/(paid) exceeds the amount to be paid/(received), the net amount is presented within derivative receipts/(payments). 32. Financial risk management continued (c) Currency risk National Grid operates internationally with mainly the pound sterling as the functional currency for the UK companies and the US dollar for the US businesses. Currency risk arises from three major areas: funding activities, capital investment and related revenues, and holdings in foreign operations. This risk is managed using financial instruments including derivatives as approved by policy, typically cross-currency interest rate swaps, foreign exchange swaps and forwards. Funding activities – our policy is to borrow in the most advantageous market available. Foreign currency funding gives rise to risk of volatility in the amount of functional currency cash to be repaid. This risk is reduced by swapping principal and interest back into the functional currency of the issuer. All foreign currency debt and transactions are hedged except where they provide a natural offset to assets elsewhere in the Group. Capital investment and related revenues – capital projects often incur costs or generate revenues in a foreign currency, most often euro transactions done by the UK business. Our policy for managing foreign exchange transaction risk is to hedge contractually committed foreign currency cash flows over a prescribed minimum size, typically by buying euro forwards to hedge future expenditure, and selling euro forwards to hedge future revenues. For hedges of forecast cash flows our policy is to hedge a proportion of highly probable cash flows. Holdings in foreign operations – we are exposed to fluctuations on the translation into pounds sterling of our foreign operations. The policy for managing this translation risk is to issue foreign currency debt or to replicate foreign debt using derivatives that pay cash flows in the currency of the foreign operation. The primary managed exposure arises from dollar denominated assets and liabilities held by our US operations, with a smaller euro exposure in respect of joint venture investments. Derivative financial instruments were used to manage foreign currency risk as follows: 2020 2019 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 18 — 55 — 73 97 2 153 — 252 Financial investments 813 — 1,185 — 1,998 965 — 1,016 — 1,981 Borrowings (12,407 ) (4,150 ) (13,217 ) (1,020 ) (30,794 ) (10,591 ) (4,787 ) (12,126 ) (1,226 ) (28,730 ) Pre-derivative position (11,576 ) (4,150 ) (11,977 ) (1,020 ) (28,723 ) (9,529 ) (4,785 ) (10,957 ) (1,226 ) (26,497 ) Derivative effect (1,169 ) 4,341 (4,214 ) 1,175 133 (1,055 ) 4,803 (5,245 ) 1,465 (32 ) Net debt position (12,745 ) 191 (16,191 ) 155 (28,590 ) (10,584 ) 18 (16,202 ) 239 (26,529 ) The exposure to dollars largely relates to our net investment hedge activities; exposure to euros largely relates to hedges for our future non-sterling capital expenditure. The currency exposure on other financial instruments is as follows: 2020 2019 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 306 — 1,403 — 1,709 398 — 1,635 — 2,033 Trade and other payables (1,177 ) — (2,002 ) — (3,179 ) (1,221 ) — (2,085 ) — (3,306 ) Other non-current liabilities (85 ) — (277 ) — (362 ) (93 ) — (247 ) — (340 ) The carrying amounts of other financial instruments are denominated in the above currencies, which in most instances are the functional currency of the respective subsidiaries. Our exposure to dollars is due to activities in our US subsidiaries. We do not have any other significant exposure to currency risk on these balances. Hedge accounting for currency risk Where available, derivatives transacted for hedging are designated for hedge accounting. Economic offset is qualitatively determined because the critical terms (currency and volume) of the hedging instrument match the hedged exposure. If a forecast transaction was no longer expected to occur, the cumulative gain or loss previously reported in equity would be transferred to the income statement. This has not occurred in the current or comparative years. Cash flow hedging of currency risk of capital expenditure and revenues is designated as hedging the exposure to movements in the spot translation rates only; the timing of forecasted transactions is not designated as a hedged risk. Gains and losses on hedging instruments arising from forward points and foreign currency basis spreads are excluded from designation and are recognised immediately in profit or loss, along with any hedge ineffectiveness. On recognition of the hedged purchase or sale in the financial statements, the associated hedge gains and losses, deferred in the cash flow hedge reserve in other equity reserves, are transferred out of reserves and included with the recognition of the underlying transaction. Where a non-financial asset or a non-financial liability results from a forecast transaction or firm commitment being hedged, the amounts deferred in reserves are included directly in the initial measurement of that asset or liability. Net investment hedging is also designated as hedging the exposure to movements in spot translation rates only: spot-related gains and losses on hedging instruments are presented in the cumulative translation reserve within other equity reserves to offset gains or losses on translation of the hedged balance sheet exposure. Any ineffectiveness is recognised immediately in the income statement. Gains and losses arising from forward points and foreign currency basis spreads are excluded from designation and are treated as a cost of hedging, deferred initially in other equity reserves and released into profit or loss over the life of the hedging relationship. Amounts deferred in the cumulative translation reserve with respect to net investment hedges are subsequently recognised in the income statement in the event of disposal of the overseas operations concerned. Any remaining amounts deferred in the cost of hedging reserve are also released to the income statement. Hedges of foreign currency funding are designated as cash flow hedges or fair value hedges of forward exchange risk (hedging both currency and interest rate risk together, where applicable). Hedge accounting for funding is described further in the interest rate risk section below. 32. Financial risk management continued (d) Interest rate risk National Grid’s interest rate risk arises from our long-term borrowings. Our interest rate risk management policy is to seek to minimise total financing costs (being interest costs and changes in the market value of debt). Hedging instruments principally consist of interest rate and cross-currency swaps that are used to translate foreign currency debt into functional currency and to adjust the proportion of fixed-rate and floating-rate in the borrowings portfolio to within a range set by the Finance Committee of the Board. The benchmark interest rates hedged are currently based on LIBOR. LIBOR is being replaced as an interest rate benchmark by alternative reference rates in certain currencies including our functional currencies, USD and GBP, and foreign currencies in which we operate. This impacts contracts including financial liabilities that pay LIBOR-based cash flows, and derivatives that receive or pay LIBOR-based cash flows. The change in benchmark also affects discount rates which can impact valuations. We are managing the risk by planning to replace LIBOR cash flows with alternative reference rates on our affected contracts. We also consider inflation risk and hold some inflation-linked borrowings. We believe that these provide a partial economic offset to the inflation risk associated with our UK inflation-linked revenues. The table in note 21 sets out the carrying amount, by contractual maturity, of borrowings that are exposed to interest rate risk before taking into account interest rate swaps. Net debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2020 2019 Fixed rate £m Floating rate £m Inflation linked £m Other 1 £m Total £m Fixed rate £m Floating rate £m Inflation linked £m Other 1 £m Total £m Cash and cash equivalents 71 10 — (8 ) 73 59 104 — 89 252 Financial investments — 1,966 — 32 1,998 6 1,944 — 31 1,981 Borrowings (20,969 ) (3,085 ) (6,740 ) — (30,794 ) (19,043 ) (3,045 ) (6,642 ) — (28,730 ) Pre-derivative position (20,898 ) (1,109 ) (6,740 ) 24 (28,723 ) (18,978 ) (997 ) (6,642 ) 120 (26,497 ) Derivative effect 2,259 (1,892 ) (234 ) — 133 1,740 (1,559 ) (213 ) — (32 ) Net debt position (18,639 ) (3,001 ) (6,974 ) 24 (28,590 ) (17,238 ) (2,556 ) (6,855 ) 120 (26,529 ) 1. Represents financial instruments which are not directly affected by interest rate risk, such as investments in equity or other similar financial instruments. Hedge accounting for interest rate risk Borrowings paying variable or floating-rates expose National Grid to cash flow interest rate risk, partially offset by cash held at variable rates. Where a hedging instrument results in paying a fixed-rate, it is designated as a cash flow hedge because it has reduced the cash flow volatility of the hedged borrowing. Changes in the fair value of the derivative are initially recognised in other comprehensive income as gains or losses in the cash flow hedge reserve, with any ineffective portion recognised immediately in the income statement. Borrowings paying fixed-rates expose National Grid to fair value interest rate risk. Where the hedging instrument pays a floating-rate, it is designated as a fair value hedge because it has reduced the fair value volatility of the borrowing. Changes in the fair value of the derivative and changes in the fair value of the hedged item in relation to the risk being hedged are both adjusted on the balance sheet and offset in the income statement to the extent the fair value hedge is effective, with the residual difference remaining as ineffectiveness. Both types of hedges are designated as hedging the currency and interest rate risk arising from changes in forward points. Amounts accumulated in the cash flow hedge reserve (cash flow hedges only) and the deferred cost of hedging reserve (both cash flow and fair value hedges) are reclassified from reserves to the income statement on a systematic basis as hedged interest expense is recognised. Adjustments made to the carrying value of hedged items in fair value hedges are similarly released to the income statement to match the timing of the hedged interest expense. When hedge accounting is discontinued, any remaining cumulative hedge accounting balances continue to be released to the income statement to match the impact of outstanding hedged items. Any remaining amounts deferred in the cost of hedging reserve are released immediately to the income statement as finance costs. The Group early-adopted IFRS Interest Rate Benchmark Reform amendments related to hedge accounting, with effect from 1 April 2019. The amendments allow existing hedge designations to continue unchanged during the period of uncertainty relating to the timing and method of benchmark migrations. The amendments will be applied until the earlier point in time where affected cash flows are amended, the relationship is formally discontinued, and any cash flow hedge reserve balance has been released, or formal market conventions ending uncertainty are published and widely adopted. If amended cash flows do not cause a hedging relationship to be discontinued, then the amendments will cease to be applied only when that relationship is discontinued under IFRS 9. The IFRS amendments impact fair value and cash flow hedges of interest rate risk and related hedging instruments, and certain net investment hedges that use cross-currency interest rate swaps to pay a foreign currency floating rate and receive a functional currency floating rate. The notional values of hedging instruments, for each type of hedging relationship impacted, are shown in the hedge accounting tables in note 32(e). These amounts also correspond to the exposures designated as hedged. 32. Financial risk management continued (e) Hedge accounting In accordance with the requirements of IFRS 9, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Year ended 31 March 2020 Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges (143 ) (17 ) — Cost of hedging 5 (7 ) — (30 ) Transferred to profit or loss in respect of: Cash flow hedges — 14 — — Cost of hedging 1 (1 ) — (45 ) Consolidated statement of changes in equity Other equity reserves – cost of hedging balances 2 (8 ) — (43 ) Consolidated statement of financial position Derivatives – carrying value of hedging instruments¹ Assets – current 1 — 4 9 Assets – non-current 247 106 8 — Liabilities – current (1 ) (105 ) (8 ) (82 ) Liabilities – non-current (39 ) (264 ) (12 ) (19 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range May 2020 – Feb 2040 Jul 2020 – Dec 2039 Apr 2020 – Dec 2024 Jun 2020 – Sep 2027 Spot foreign exchange range: GBP:USD 1.64 1.30 – 1.66 1.24 – 1.41 1.21 – 1.49 GBP:EUR 1.19 – 1.24 1.10 – 1.24 1.04 – 1.30 1.14 EUR:USD 1.13 – 1.17 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+408bps 1.331% – 5.850% n/a n/a USD LIBOR -44bps/+ 115bps 1.103% – 3.864% n/a n/a 1. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. 32. Financial risk management continued (e) Hedge accounting continued Year ended 31 March 2019 Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges¹ — (206 ) (12 ) — Cost of hedging (6 ) (12 ) — (90 ) Transferred to profit or loss in respect of: Cash flow hedges¹ — 166 — — Cost of hedging 3 — — 39 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (4 ) — — 32 Consolidated statement of financial position Derivatives – carrying value of hedging instruments² Assets – current 17 — 9 — Assets – non-current 168 78 23 — Liabilities – current (9 ) (28 ) (3 ) (43 ) Liabilities – non-current (25 ) (134 ) (4 ) (249 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Nov 2019 – May 2038 Aug 2019 – Feb 2039 Apr 2019 – Dec 2023 Mar 2020 – Jun 2025 Spot foreign exchange range: GBP:USD 1.64 – 1.65 1.52 – 1.66 1.29 – 1.41 1.49 GBP:EUR 1.19 – 1.24 1.14 – 1.24 1.07 – 1.32 1.15 EUR:USD 1.13 – 1.16 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+561bps 1.795% – 5.850% n/a n/a USD LIBOR -44bps/+115bps 1.103% – 3.864% n/a n/a 1. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in cash flow hedges of foreign currency risk and interest rates. This has no net impact on the consolidated statement of comprehensive income. It has resulted in a prior year gross up of £166 million to net losses in respect of cash flow hedges with an equal and offsetting gross up to transferred to profit and loss in respect of cash flow hedges. 2. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. 32. Financial risk management continued (e) Hedge accounting continued The following tables show the effects of hedge accounting on financial position and year-to-date performance for each type of hedge. These tables also present notional values of hedging instruments (and equal hedged exposures) impacted by IFRS 9 Interest Rate Benchmark Reform amendments. (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2020 Balance of fair value hedge adjustments in borrowings Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings 1,2 (1,751 ) (31 ) (95 ) (42 ) 48 6 1. The carrying value of the hedged borrowings is £1,883 million , of which £72 million is current and £1,811 million is non-current. 2. Included within the hedging instrument notional balance is £1,675 million impacted by Interest Rate Benchmark Reform amendments. As at 31 March 2019 Balance of fair value hedge adjustments in borrowings Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (1,707 ) 11 (117 ) 15 (10 ) 5 1. The carrying value of the hedged borrowings was £1,810 million , of which £202 million was current and £1,608 million was non-current. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in fair value hedges of foreign currency risk and interest rates. It has resulted in a prior year equal and offsetting impact of £4 million to the balances used for the ‘Change in value used for calculating ineffectiveness’. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2020 Balance in cash flow hedge reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (4,127 ) (69 ) (22 ) 142 (143

Borrowing facilities

Borrowing facilities	12 Months Ended
	Mar. 31, 2020
Disclosure of detailed information about borrowings [abstract]
Borrowing facilities	Borrowing facilities To support our liquidity requirements and provide backup to commercial paper and other borrowings, we agree loan facilities with financial institutions over and above the value of borrowings that may be required. These committed credit facilities have never been drawn, and our undrawn amounts are listed below. At 31 March 2020 , we had bilateral committed credit facilities of £5,495 million ( 2019 : £5,463 million ). In addition, we had committed credit facilities from syndicates of banks of £277 million at 31 March 2020 ( 2019 : £264 million ). All committed credit facilities were undrawn in 2020 and 2019 . An analysis of the maturity of these undrawn committed facilities is shown below: 2020 2019 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — — In 1 to 2 years 1,940 — In 2 to 3 years 1,668 2,190 In 3 to 4 years 277 1,668 In 4 to 5 years 1,887 1,869 More than 5 years — — 5,772 5,727 Of the unused facilities at 31 March 2020 , £5,495 million ( 2019 : £5,463 million ) is available for liquidity purposes, while £277 million ( 2019 : £264 million ) is available as backup to specific US borrowings. £1,923 million of the undrawn bilateral facilities due to mature in one to two years, were renegotiated between 1 April and 17 June 2020 with new expiry dates to June 2024. Of the £1,887 million of undrawn committed borrowings facilities due to expire within four to five years, £110 million was renegotiated before 31 March 2020 , with the expiry extended by a further year, with effect from 1 June 2020 . For the separately regulated business of National Grid Electricity System Operator Limited, the Group has a facility of £550 million (2019: £550 million ). This facility is not available as Group general liquidity support and is not represented in the table above. In addition to the above, the Group has Export Credit Agreements (ECAs) totalling £901 million ( 2019 : £859 million ), of which £233 million ( 2019 : £510 million ) is undrawn. Subsequent to the year end, two new ECAs totalling £598 million have been made available and have not been drawn.

Subsidiary undertakings, joint

Subsidiary undertakings, joint ventures and associates	12 Months Ended
	Mar. 31, 2020
Interests In Other Entities [Abstract]
Subsidiary undertakings, joint ventures and associates	Investments in joint ventures and associates Investments in joint ventures and associates represent businesses we do not control but over which we exercise joint control or significant influence. They are accounted for using the equity method. A joint venture is an arrangement established to engage in economic activity, which the Group jointly controls with other parties and has rights to the net assets of the arrangement. An associate is an entity which is neither a subsidiary nor a joint venture, but over which the Group has significant influence. 2020 2019 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 291 317 608 1,807 361 2,168 Exchange adjustments 20 12 32 17 (6 ) 11 Additions 16 156 172 58 85 143 Capitalisation of shareholder loan to Nemo Link Limited — 176 176 — — — Impairment charge against investment in Quadgas — — — (43 ) — (43 ) Transfer of interest in Quadgas to assets held for sale — — — (1,625 ) — (1,625 ) Share of post-tax results for the year 40 47 87 67 11 78 Share of other comprehensive income of associates, net of tax 1 — 1 37 — 37 Dividends received (41 ) (34 ) (75 ) (38 ) (30 ) (68 ) Other movements¹ 14 (20 ) (6 ) 11 (104 ) (93 ) Share of net assets at 31 March 341 654 995 291 317 608 1. Other movements on joint ventures relate to reducing the carrying value of the investment in St William Homes LLP to reflect deferred income we expect to recognise over the next 10 years . A list of joint ventures and associates including the name and proportion of ownership is provided in note 34. Transactions with and outstanding balances with joint ventures and associates are shown in note 31. The joint ventures and associates have no significant contingent liabilities to which the Group is exposed, and the Group has no significant contingent liabilities in relation to its interests in the joint ventures and associates. The Group has capital commitments of £240 million ( 2019 : £18 million ) in relation to joint ventures. 16. Investments in joint ventures and associates continued At 31 March 2020 , the Group had three material joint ventures, being its 50% equity stakes in BritNed and Nemo Link Limited (Nemo) and its 51% stake in Emerald Energy Venture LLC (Emerald). The Group has one material associate, being its 26.25% investment in Millennium Pipeline Company LLC. BritNed is a joint venture with the Dutch transmission system operator, TenneT, and operates the subsea electricity link between Great Britain and the Netherlands, commissioned in 2011. Nemo is a joint venture with the Belgian transmission operator, Elia, and is a subsea electricity interconnector between the UK and Belgium, which became operational on 31 January 2019. BritNed and Nemo have reporting periods ending on 31 December with monthly management reporting information provided to National Grid. Emerald is a joint venture with Washington State Investment Board and builds and operates wind and solar assets. Emerald was acquired on 11 July 2019. Millennium Pipeline Company LLC is an associate that owns a natural gas pipeline from southern New York to the Lower Hudson Valley. Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Limited Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy Venture LLC 2020 2019 2020 2019 2020 2019 2020 £m £m £m £m £m £m £m Statement of financial position Non-current assets 399 370 971 937 582 537 435 Cash and cash equivalents 54 59 33 35 26 47 66 All other current assets 4 2 26 22 5 3 6 Non-current liabilities (45 ) (11 ) (315 ) (326 ) (29 ) 2 (232 ) Current liabilities (16 ) (28 ) (43 ) (84 ) (10 ) (375 ) (2 ) Net assets 396 392 672 584 574 214 273 Group’s ownership interest in joint venture/associate 198 196 176 153 287 107 139 Group adjustment: elimination of profits on sales to joint venture — — — — — — (10 ) Carrying amount of the Group’s investment 198 196 176 153 287 107 129 BritNed Development Limited Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy Venture LLC 2020 2019 2020 2019 2020 2019 2020 £m £m £m £m £m £m £m Income statement Revenue 80 87 206 166 45 12 19 Depreciation and amortisation (14 ) (13 ) (46 ) (34 ) (23 ) (4 ) (7 ) Other costs (10 ) (10 ) (20 ) (24 ) (8 ) (4 ) (10 ) Operating profit 56 64 140 108 14 4 2 Net interest expense — — (22 ) (11 ) — — (3 ) Profit before tax 56 64 118 97 14 4 (1 ) Income tax expense (10 ) (10 ) — — (2 ) — — Profit for the year 46 54 118 97 12 4 (1 ) Group’s share of profit/(loss) 23 27 31 25 6 2 (1 ) Group adjustment: Tax charge — — (9 ) — — — — Group’s share of post-tax results for the year 23 27 22 25 6 2 (1 ) Subsidiary undertakings, joint ventures and associates While we present consolidated results in these financial statements as if we were one company, our legal structure is such that there are a number of different operating and holding companies that contribute to the overall result. This structure has evolved through acquisitions as well as regulatory requirements to have certain activities within separate legal entities. Subsidiary undertakings A list of the Group’s subsidiaries as at 31 March 2020 is given below. The entire share capital of subsidiaries is held within the Group except where the Group’s ownership percentages are shown. These percentages give the Group’s ultimate interest and therefore allow for the situation where subsidiaries are owned by partly owned intermediate subsidiaries. Where subsidiaries have different classes of shares, this is largely for historical reasons, and the effective percentage holdings given represent both the Group’s voting rights and equity holding. Shares in National Grid (US) Holdings Limited, National Grid Holdings One plc and NGG Finance plc are held directly by National Grid plc. All other holdings in subsidiaries are owned by other subsidiaries within the Group. All subsidiaries are consolidated in the Group’s financial statements. Principal Group companies are identified in bold . These companies are incorporated and principally operate in the countries under which they are shown. Incorporated in England and Wales Registered office: 1 – 3 Strand, London WC2N 5EH, UK (unless stated otherwise in footnotes). Beegas Nominees Limited Birch Sites Limited Carbon Sentinel Limited Droylsden Metering Services Limited Gridcom Limited Icelink Interconnector Limited Landranch Limited Lattice Group Employee Benefit Trust Limited Lattice Group Limited Lattice Group Trustees Limited Natgrid Limited NatGrid One Limited NatgridTW1 Limited National Grid Belgium Limited 1 * National Grid Blue Power Limited 1 * National Grid Carbon Limited National Grid Commercial Holdings Limited National Grid Distributed Energy Limited National Grid Electricity Group Trustee Limited National Grid Electricity System Operator Limited National Grid Electricity Transmission plc National Grid Energy Metering Limited National Grid Four Limited 1 * National Grid Fourteen Limited 1 * National Grid Gas Holdings Limited National Grid Gas plc National Grid Grain LNG Limited National Grid Holdings Limited National Grid Holdings One plc National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited National Grid Metering Limited National Grid North Sea Link Limited National Grid Offshore Limited (previously NG Shetland Link Limited) National Grid Partners Limited National Grid Plus Limited (previously National Grid Offshore Limited) National Grid Property Holdings Limited National Grid Seventeen Limited 1 * National Grid Smart Limited National Grid Ten National Grid Thirty Five Limited 1 * National Grid Thirty Six Limited National Grid Twelve Limited National Grid Twenty Eight Limited National Grid Twenty-Five Limited 1 * National Grid Twenty Seven Limited National Grid Twenty Three Limited National Grid UK Limited National Grid UK Pension Services Limited National Grid (US) Holdings Limited National Grid (US) Investments 2 Limited National Grid (US) Investments 4 Limited National Grid (US) Partner 1 Limited National Grid Ventures Limited National Grid Viking Link Limited National Grid William Limited NG Nominees Limited NGC Employee Shares Trustee Limited NGG Finance plc Ngrid Intellectual Property Limited NGT Telecom No. 1 Limited 1 * NGT Two Limited Port Greenwich Limited Stargas Nominees Limited Supergrid Electricity Limited Supergrid Energy Transmission Limited Supergrid Limited Thamesport Interchange Limited The National Grid Group Quest Trustee Company Limited The National Grid YouPlan Trustee Limited Transco Limited Warwick Technology Park Management Company (No 2) Limited ( 60.56% ) 2 1. Registered office: c/o KPMG, 15 Canada Square, London E14 5GL, UK 2. Registered office: Shire Hall, PO Box 9, Warwick CV34 4RL, UK * In liquidation. 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Incorporated in the US Registered office: National Registered Agents, Inc., 1209 Orange Street, Wilmington, DE 19801, USA (unless stated otherwise in footnotes). Alden Solar, LLC Altona Solar, LLC Apple River Solar, LLC Apple Solar, LLC Arapahoe Solar, LLC Argenta Solar, LLC Armenia Solar, LLC Artemisia Solar, LLC 1 Ashland Solar, LLC Athens Solar, LLC Audubon Wind Farm, LLC Banner Solar, LLC Bee Hollow Solar, LLC Benevolent Solar, LLC Blaze Solar, LLC Blue Ridge Wind, LLC Blues Solar, LLC Blue Stone Solar Energy, LLC Bluewater Solar, LLC Boone Solar, LLC Boston Gas Company 2 Brewster Solar, LLC Brilliance Solar, LLC British Transco Capital Inc. 3 British Transco Finance, Inc. 3 Brock Solar, LLC Broken Bridge Corp. 4 Brook Trout Solar, LLC Brookside Solar, LLC Burlington Solar, LLC Burr Ridge Wind, LLC Cage Ranch Solar, LLC Cage Ranch Solar II, LLC Cage Ranch Solar III, LLC Caldwell Solar, LLC Caldwell Solar II, LLC Canby Solar, LLC Cattle Ridge Wind Farm 2, LLC Cepheus Community Solar Gardens LLC 1 Claddagh Solar, LLC 1 Clear Creek Solar, LLC Clermont Solar, LLC Clinton County Solar, LLC Commonwealth Solar, LLC Conestoga Wind, LLC Copperhead Solar, LLC Crocker Wind Farm 2, LLC Cygnus Community Solar Garden, LLC 1 Daybreak Solar, LLC Deer Trail Solar, LLC Dekalb Solar, LLC Desoto Solar, LLC Dodson Creek Solar, LLC Dorado Community Solar Gardens, LLC 1 Dorsey Road Solar, LLC East Galesburg Solar, LLC East Macomb Solar, LLC Eastern Hemlock Solar, LLC Elba Solar, LLC Elburn Solar, LLC Eldena Solar, LLC Elk Creek Solar, LLC Elk Creek Solar 2, LLC Empire Solar, LLC EUA Energy Investment Corporation 2 Falls City Solar, LLC Firstview Wind Farm, LLC Franklin Solar, LLC Front Range Wind Farm, LLC Fulton Solar, LLC Galesburg Solar, LLC Genesee Solar Energy, LLC Geronimo Energy LLC Geronimo E Wind LLC 5 Geronimo Solar Energy, LLC 1 Geronimo Stutsman Wind Farm, LLC Geronimo White Pine Solar, LLC Gladiolus Solar, LLC 1 Glenwood Solar, LLC Glen Rock Solar, LLC Golden Solar, LLC Goldendale Solar, LLC Goldfinch Solar, LLC Granite State Power Link LLC 3 Grant Solar, LLC Grant Solar 2, LLC Grayson Solar, LLC Greenbrier Creek Solar, LLC Greentown Solar, LLC Greenwood Solar, LLC Grid NY, LLC 6 Grindstone Wind Farm, LLC 7 Hale Solar, LLC Hampton Solar, LLC Handley Road Solar, LLC Hardeman County Solar, LLC Harmony Solar ND, LLC Harmony Solar ND 2, LLC Harrington Solar, LLC Hartley Solar, LLC Hearth Solar, LLC Henderson Solar, LLC Heyworth Solar, LLC Honeybee Solar, LLC Hoosier Solar, LLC 1 Hyacinth Solar, LLC 1 Illumination Solar, LLC Innovation Solar, LLC Irwin Solar, LLC Itasca Energy Development, LLC 8 Itasca Energy Services, LLC Jack Rabbit Wind, LLC Jackson County Solar, LLC Jantz Solar, LLC Junction Solar, LLC Kankakee Solar, LLC Keslinger Solar, LLC KeySpan CI Midstream Limited 3 KeySpan Energy Corporation 6 KeySpan Energy Services Inc. 3 KeySpan Gas East Corporation 6 KeySpan International Corporation 3 KeySpan MHK, Inc. 3 KeySpan Midstream Inc. 3 KeySpan Plumbing Solutions, Inc. 6 Kindle Solar, LLC KSI Contracting, LLC 3 KSI Electrical, LLC 3 KSI Mechanical, LLC 3 Lake Iris Solar, LLC Lakeside Solar, LLC Lamdin Solar, LLC Lamplight Solar, LLC Land Management & Development, Inc. 6 Landwest, Inc. 6 Lansing Solar, LLC Lawrence Solar, LLC Leola Wind Farm, LLC Lilac Solar, LLC 1 Lindy Solar, LLC Lockport Solar, LLC Lordsburg Solar, LLC Lydia Solar, LLC Madden Creek Solar, LLC Marigold Community Solar Garden, LLC 1 Massachusetts Electric Company 2 Maverick Wind Farm, LLC Mazon Solar, LLC McFadden Solar, LLC Merton Solar, LLC Metro Energy, LLC 6 Metrowest Realty LLC 3 Miller Creek Solar, LLC Morning Glory Solar, LLC 1 Mottville Solar, LLC Mountain Laurel Solar, LLC Mustang Ridge Wind Farm, LLC Mystic Steamship Corporation 3 Nantucket Electric Company 2 National Grid Algonquin LLC 3 National Grid Connect Inc. 3 National Grid Development Holdings Corp. 3 National Grid Electric Services, LLC 6 National Grid Energy Management, LLC 3 National Grid Energy Services LLC 3 National Grid Energy Trading Services LLC 6 National Grid Engineering & Survey Inc. 6 National Grid Generation LLC 6 National Grid Generation Ventures LLC 6 National Grid Glenwood Energy Center, LLC 3 National Grid IGTS Corp. 6 National Grid Insurance USA Ltd 6 National Grid Islander East Pipeline LLC 3 National Grid LNG GP LLC 3 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Incorporated in the US continued National Grid LNG LLC 3 National Grid LNG LP LLC 3 National Grid Millennium LLC 3 National Grid NE Holdings 2 LLC 2 National Grid North America Inc. 3 National Grid North East Ventures Inc. 3 National Grid Partners Inc. 6 National Grid Partners LLC 3 National Grid Port Jefferson Energy Center LLC 3 National Grid Services Inc. 3 National Grid Transmission Services Corporation 2 National Grid US 6 LLC 3 National Grid US LLC 3 National Grid USA 3 National Grid USA Service Company, Inc. 2 Nees Energy, Inc. 2 New Bremen Solar, LLC New England Electric Transmission Corporation 4 New England Energy Incorporated 2 New England Hydro Finance Company, Inc. ( 53.704% ) 2 New England Hydro-Transmission Corporation ( 53.704% ) 4 New England Hydro-Transmission Electric Company Inc. ( 53.704% ) 2 New England Power Company 2 Newport America Corporation 9 NGNE LLC 3 NGV Emerald Acquisition Co. LLC 3 NGV Emerald Energy Venture Holdings LLC 3 NGV Emerald Holdings LLC 3 NGV US Distributed Energy Inc. 3 (previously National Grid Green Homes Inc.) NGV US Transmission Inc. 3 (previously Grid America Holdings Inc.) Niagara Falls Solar, LLC Niagara Mohawk Energy, Inc. 3 Niagara Mohawk Holdings, Inc. 6 Niagara Mohawk Power Corporation 6 Niobrara Wind, LLC NM Properties, Inc. 6 Nordic Vos, LLC North Adair Solar, LLC Northeast Renewable Link LLC 3 North East Transmission Co., Inc. 3 North Fork Wind, LLC North Rock Solar, LLC North Wonder Lake Solar, LLC Onton Solar, LLC Opinac North America, Inc. 3 Oreana Solar, LLC Patriotic Solar, LLC Pennington Solar, LLC Peony Solar, LLC Perseus Community Solar Garden, LLC 1 Philadelphia Coke Co., Inc. 3 Piper Solar, LLC Pipestone Solar, LLC Pleasant Plains Solar, LLC Plum Creek Wind Farm, LLC Plum Creek Wind Farm 2, LLC Polaris Community Solar Garden, LLC 1 Port of the Islands North, LLC 6 Prairie Oasis Solar, LLC Prairie Rose Wind 2, LLC 1 Prairie Wolf Solar, LLC Prosperity Wind Farm, LLC Prosperity Wind Farm 2, LLC Radiance Solar, LLC 1 Red Rock Solar SD, LLC Regal Solar, LLC Regulus Community Solar Gardens, LLC 1 Rising Solar, LLC River North Solar, LLC River Run Solar, LLC Riverside Solar, LLC Rochester Solar, LLC 1 Rock Falls Solar, LLC Rock Ridge Wind Farm, LLC Ross County Solar, LLC Royal Solar, LLC Royal Solar 2, LLC Royerton Solar, LLC Saginaw Bay Solar, LLC Sandstone Creek Solar, LLC Sandstone Creek Solar 2, LLC Sawmill Wind Farm, LLC Silver City Solar, LLC Scorpius Community Solar Garden, LLC 1 Serenity Solar, LLC 1 Sheas Lake Solar, LLC Sherco Solar, LLC 1 Silver Lake Solar, LLC Sirius Community Solar Gardens, LLC 1 Snowdrop Solar, LLC 1 Somerset Solar, LLC South Belleville Solar, LLC South Macomb Solar, LLC Spotlight Solar, LLC Spring Brook Solar, LLC Springfield Solar Farm, LLC Springfield Wind Farm, LLC 1 Springville Solar, LLC St. Thomas Solar, LLC Stockton Solar, LLC Stony Brook Wind, LLC Stove Creek Solar, LLC Sturgis Solar, LLC Sugar Maple Solar, LLC Summit Lake Solar, LLC Sunbeam Solar, LLC Sunray Solar, LLC Sunrise Solar, LLC Sycamore Creek Solar, LLC The Brooklyn Union Gas Company 6 The Narragansett Electric Company 9 Tilton Solar, LLC Torchlight Solar, LLC 1 Transgas, Inc. 2 Uintah Solar, LLC Upper Hudson Development Inc. 6 Valley Appliance and Merchandising Company 9 Vermont Green Line Devco, LLC 3 ( 90% ) Vibrant Solar, LLC Virgo Community Solar Gardens, LLC 1 Virtue Solar, LLC Vivid Solar, LLC Vulpecula Community Solar Garden, LLC 1 Wayfinder Group, Inc. 2 Wheatfield Solar, LLC Wild Springs Solar, LLC 1 Wildcat Ridge Wind Farm, LLC Wilder Junction Wind Farm, LLC Wildhorse Creek Solar, LLC Willard Solar, LLC Wiregrass Solar, LLC Wonder Lake Solar, LLC Woodlands Solar, LLC Yellowbud Solar, LLC 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Incorporated in Australia Registered office: Level 7, 330 Collins Street, Melbourne, VIC 3000, Australia National Grid Australia Pty Limited Incorporated in Canada Registered office: Stewart McKelvey Stirling Scales, c/o Charles Reagh, 1959 Upper Water Street, Suite 900, Halifax Nova Scotia, B3J 2N2, Canada KeySpan Energy Development Co. Incorporated in Hong Kong Registered office: Level 54, Hopewell Centre, 183 Queen's Road East, Hong Kong National Grid Hong Kong Limited (previously HK NewCo 2019 Limited) Incorporated in the Isle of Man Registered office: Third Floor, St George’s Court, Upper Church Street, Douglas, IM1 1EE, Isle of Man, UK National Grid Insurance Company (Isle of Man) Limited NGT Holding Company (Isle of Man) Limited* Incorporated in Jersey Registered office: 44 Esplanade, St Helier, Jersey JE4 9WG, UK National Grid Jersey Investments Limited** NG Jersey Limited** Incorporated in Luxembourg Registered office: 412F, Route d'Esch, L-2086, Luxembourg, Grand Duchy of Luxembourg National Grid Luxembourg Sarl (previously 21 June Sarl) Incorporated in the Netherlands Registered office: Westblaak 89, 3012 KG Rotterdam, PO Box 21153, 3001 AD, Rotterdam, Netherlands British Transco International Finance B.V. Registered office: Prins Bernhardplein 200, 1097 JB, Amsterdam, Netherlands National Grid Holdings B.V.* Incorporated in the Republic of Ireland Registered office: c/o Moore Stephens Nathans, Third Floor, Ulysses House, 23/24 Foley Street, Dublin 1, D01 W2T2, Ireland National Grid Company (Ireland) Designated Activity Company (previously National Grid Insurance Company (Ireland) Designated Activity Company)* 1. Registered office: c/o Geronimo Energy LLC, 8400 Normandale Lake Bvld. Suite 1200, Bloomington, MN 55437, USA. 2. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, USA. 3. Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington DE 19808, USA. 4. Registered office: Lawyers Incorporating Service, 10 Ferry Street, Suite 313, Concord NH 03301, USA. 5. Registered office: National Registered Agents, Inc., 301 S. Bedford St. Suite 1 Madison, WI 53703, USA. 6. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207-2543, USA. 7. Registered office: National Registered Agents, Inc., 30600 Telegraph Road, Suite2345, Bingham Farms, MI 48025-5720, USA. 8. Registered office: 10710 Town Square Drive NE, Suite 201 Minneapolis, MN 55449, USA. 9. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, USA. * In liquidation. ** Entered liquidation 29 April 2020. 34. Subsidiary undertakings, joint ventures and associates continued Joint ventures A list of the Group’s joint ventures as at 31 March 2020 is given below. All joint ventures are included in the Group’s financial statements using the equity method of accounting. Principal joint ventures are identified in bold . Incorporated in England and Wales Registered office: 1–3 Strand, London WC2N 5EH, UK (unless stated otherwise in footnotes). BritNed Development Limited ( 50% )* Joint Radio Company Limited ( 50% ) 1 ** Nemo Link Limited ( 50% ) NGET/SPT Upgrades Limited ( 50% ) † St William Homes LLP ( 50% ) 2 Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Clean Energy Generation, LLC ( 50% ) Emerald Energy Venture LLC ( 51% ) Goldendale Energy Storage LLC ( 50% ) Island Park Energy Center, LLC ( 50% ) Islander East Pipeline Company, LLC ( 50% ) 3 LI Energy Storage System, LLC ( 50% ) LI Solar Generation, LLC ( 50% ) Swan Lake North Holdings LLC ( 50% ) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, Paris La Defense, CEDEX, France IFA2 SAS ( 50% ) Associates A list of the Group’s associates as at 31 March 2020 is given below. Unless otherwise stated, all associates are included in the Group’s financial statements using the equity method of accounting. Principal associates are identified in bold . Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Clean Line Energy Partners LLC ( 32% ) 3 Connecticut Yankee Atomic Power Company ( 19.5% ) 4 Direct Global Power, Inc. ( 26% ) 3 Energy Impact Fund LP ( 9.42% ) 5 Greeneru, Inc. ( 21.6% ) 3 KHB Venture LLC ( 33% ) 6 Maine Yankee Atomic Power Company ( 24% ) 7 Millennium Pipeline Company, LLC ( 26.25% ) 3 New York Transco LLC ( 28.3% ) 8 Nysearch RMLD, LLC ( 22.63% ) Sunrun Neptune Investor 2016 LLC 3 *** Yankee Atomic Electric Company ( 34.5% ) 9 Incorporated in Belgium Registered office: Avenue de Cortenbergh 71, 1000 Brussels, Belgium Coreso SA ( 15.84% ) Other investments A list of the Group’s other investments as at 31 March 2020 is given below. Incorporated in England and Wales Registered office: 1 More London Place, London SE1 2AF, UK Energis plc ( 33.06% ) ‡ 1. Registered office: Friars House, Manor House Drive, Coventry CV1 2TE, UK. 2. Registered office: Berkeley House, 19 Portsmouth Road, Cobham, Surrey KT11 1JG, UK. 3. Registered office: Corporation Trust Company, 1209 Orange, Wilmington DE 19808, New Castle County, USA. 4. Registered office: Carla Pizzella, 362 Injun Hollow Road, East Hampton CT 06424, USA. 5. Registered office: Harvard Business Services, Inc., 16192 Coastal Highway, Lewes DE 19958, Sussex County, USA. 6. Registered office: De Maximus Inc., 135 Beaver Street, 4th Floor, Waltham MA 02452, USA. 7. Registered office: Joseph D Fay, 321 Old Ferry Road, Wiscasset ME 04578, USA. 8. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 9. Registered office: Karen Sucharzewski, 49 Yankee Road, Rowe MA 01367, USA. * National Grid Interconnector Holdings Limited owns 284,500,000 €0.20 C Ordinary shares and one £1.00 Ordinary A share. ** National Grid Gas plc owns all £1.00 A Ordinary shares. *** NGV US Distributed Energy Inc. owns 1,000 Class A Membership Interests. † National Grid Electricity Transmission plc owns 50 £1.00 A Ordinary shares. ‡ In administration. Our interests and activities are held or operated through the subsidiaries, joint arrangements or associates as disclosed above. These interests and activities (and their branches) are established in – and subject to the laws and regulations of – these jurisdictions.

Sensitivities

Sensitivities	12 Months Ended
	Mar. 31, 2020
Disclosure of sensitivity analysis for actuarial assumptions [abstract]
Sensitivities	Financial risk management Our activities expose us to a variety of financial risks including credit risk, liquidity risk, capital risk, currency risk, interest rate risk, inflation risk and commodity price risk. Our risk management programme focuses on the unpredictability of financial markets and seeks to minimise potential volatility of financial performance from these risks. We use financial instruments, including derivative financial instruments, to manage these risks. Risk management related to financing activities is carried out by a central treasury department under policies approved by the Finance Committee of the Board. The objective of the treasury department is to manage funding and liquidity requirements, including managing associated financial risks, to within acceptable boundaries. The Finance Committee provides written principles for overall risk management, and written policies covering the following specific areas: foreign exchange risk, interest rate risk, credit risk, liquidity risk, use of derivative financial instruments and non-derivative financial instruments, and investment of excess liquidity. The Finance Committee has delegated authority to administer the commodity price risk policy and credit policy for US-based commodity transactions to the Energy Procurement Risk Management Committee and the National Grid USA Board of Directors. We have exposure to the following risks, which are described in more detail below: • credit risk; • liquidity risk; • currency risk; • interest rate risk; • commodity price risk; and • capital risk. Where appropriate, derivatives and other financial instruments used for hedging currency and interest rate risk exposures are formally designated as fair value, cash flow or net investment hedges as defined in IFRS 9. Hedge accounting allows the timing of the profit or loss impact of qualifying hedging instruments to be recognised in the same reporting period as the corresponding impact of hedged exposures. To qualify for hedge accounting, documentation is prepared specifying the risk management objective and strategy, the component transactions and methodology used for measurement of effectiveness. 32. Financial risk management continued Hedge accounting relationships are designated in line with risk management activities further described below. Categories designated at National Grid are as follows: • currency risk arising from our forecasted foreign currency transactions (capital expenditure or revenues) is designated in cash flow hedges; • currency risk arising from our net investments in foreign operations is designated in net investment hedges; and • currency and interest rate risk arising from borrowings are designated in cash flow or fair value hedges. Critical terms of hedging instruments and hedged items are transacted to match on a 1 :1 ratio by notional values. Hedge ineffectiveness can nonetheless arise from inherent differences between derivatives and non-derivative instruments and other market factors including credit, correlations, supply and demand, and market volatilities. Ineffectiveness is recognised in the remeasurements component of finance income and costs (see note 6). Hedge accounting is discontinued when a hedging relationship no longer qualifies for hedge accounting. Certain hedging instrument components are treated separately as costs of hedging with the gains and losses deferred in a component of other equity reserves and released systematically into profit or loss to correspond with the timing and impact of hedged exposures, or released in full to finance costs upon an early discontinuation of a hedging relationship. Refer to sections (c) currency risk and (d) interest rate risk below for further details about hedge accounting. (a) Credit risk We are exposed to the risk of loss resulting from counterparties’ default on their commitments including failure to pay or make a delivery on a contract. This risk is inherent in our commercial business activities. Exposure arises from derivative financial instruments, deposits with banks and financial institutions, trade receivables and committed transactions with wholesale and retail customers. Treasury credit risk Counterparty risk arises from the investment of surplus funds and from the use of derivative financial instruments. As at 31 March 2020 , the following limits were in place for investments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 2,049 1,024 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,118 559 Double ‘A+’ G7 sovereign entities (AA+) 1,863 931 Double ‘A’ range institutions (AA) 745 to 931 372 to 465 Single ‘A’ range institutions (A) 261 to 373 130 to 186 The maximum limit applies to all transactions, including long-term transactions. The long-term limit applies to transactions which mature in more than 12 months ’ time. As at 31 March 2020 and 2019 , we had a number of exposures to individual counterparties. In accordance with our treasury policies, counterparty credit exposure utilisations are monitored daily against the counterparty credit limits. Counterparty credit ratings and market conditions are reviewed continually with limits being revised and utilisation adjusted, if appropriate. Management does not expect any significant losses from non-performance by these counterparties. Further information on financial investments subject to impairment provisioning is included in note 15. Commodity credit risk The credit policy for US-based commodity transactions is owned by the Finance Committee to the Board, which establishes controls and procedures to determine, monitor and minimise the credit exposure to counterparties. Wholesale and retail credit risk Our principal commercial exposure in the UK is governed by the credit rules within the regulated codes: Uniform Network Code and Connection and Use of System Code. These set out the level of credit relative to the RAV for each credit rating. In the US, we are required to supply electricity and gas under state regulations. Our policies and practices are designed to limit credit exposure by collecting security deposits prior to providing utility services, or after utility service has commenced if certain applicable regulatory requirements are met. Collection activities are managed on a daily basis. Sales to retail customers are usually settled in cash, cheques, electronic bank payments or by using major credit cards. We are committed to measuring, monitoring, minimising and recording counterparty credit risk in our wholesale business. The utilisation of credit limits is regularly monitored, and collateral is collected against these accounts when necessary. In March 2020, the Group’s US distribution business ceased certain cash collection and termination activities in response to regulatory instructions following the COVID-19 pandemic. This has resulted in the recognition of expected credit losses as at 31 March 2020 (see note 19 for further details). 32. Financial risk management continued (a) Credit risk continued Offsetting financial assets and liabilities The following tables set out our financial assets and liabilities which are subject to offset and to enforceable master netting arrangements or similar agreements. The tables show the amounts which are offset and reported net in the statement of financial position. Amounts which cannot be offset under IFRS, but which could be settled net under terms of master netting arrangements if certain conditions arise, and with collateral received or pledged, are shown to present National Grid’s net exposure. Financial assets and liabilities on different transactions are only reported net if the transactions are with the same counterparty, a currently enforceable legal right of offset exists, and the cash flows are intended to be settled on a net basis. Amounts which do not meet the criteria for offsetting on the statement of financial position, but could be settled net in certain circumstances, principally relate to derivative transactions under ISDA agreements, where each party has the option to settle amounts on a net basis in the event of default of the other party. Commodity contract derivatives that have not been offset on the balance sheet may be settled net in certain circumstances under ISDA or North American Energy Standards Board (NAESB) agreements. For bank account balances and bank overdrafts, the ‘Gross amounts offset’ under cash pooling arrangements is £23 million as at 31 March 2020 ( 2019 : £19 million ). Our UK bank accounts for National Grid subsidiaries participate in GBP, EUR and USD Composite Accounting System overdraft facilities subject to offsetting gross and net overdraft limits. In the US, no offsetting arrangements exist, and cash transactions are settled through Service Company bank accounts with subsequent intercompany payables and receivables reported by subsidiaries with the Service Company. The gross amounts offset for trade payables and receivables, which are subject to general terms and conditions, are insignificant. Related amounts At 31 March 2020 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 1,267 — 1,267 (351 ) (694 ) 222 Commodity contract derivatives 75 — 75 (5 ) (3 ) 67 1,342 — 1,342 (356 ) (697 ) 289 Liabilities Financing derivatives (1,134 ) — (1,134 ) 351 646 (137 ) Commodity contract derivatives (200 ) — (200 ) 5 8 (187 ) (1,334 ) — (1,334 ) 356 654 (324 ) 8 — 8 — (43 ) (35 ) Related amounts At 31 March 2019 Gross carrying amounts £m Gross amounts offset £m Net amount presented in statement of financial position £m Financial instruments £m Cash collateral received/ pledged £m Net amount £m Assets Financing derivatives 1,052 — 1,052 (299 ) (551 ) 202 Commodity contract derivatives 101 — 101 29 — 130 1,153 — 1,153 (270 ) (551 ) 332 Liabilities Financing derivatives (1,084 ) — (1,084 ) 299 615 (170 ) Commodity contract derivatives (99 ) — (99 ) (29 ) — (128 ) (1,183 ) — (1,183 ) 270 615 (298 ) (30 ) — (30 ) — 64 34 32. Financial risk management continued (b) Liquidity risk Our policy is to determine our liquidity requirements by the use of both short-term and long-term cash flow forecasts. These forecasts are supplemented by a financial headroom analysis which is used to assess funding requirements for at least a 24-month period and maintain adequate liquidity for a continuous 12 -month period. We believe our contractual obligations, including those shown in commitments and contingencies in note 30, can be met from existing cash and investments, operating cash flows and other financing that we reasonably expect to be able to secure in the future, together with the use of committed facilities if required. Our debt agreements and banking facilities contain covenants, including those relating to the periodic and timely provision of financial information by the issuing entity and financial covenants such as restrictions on the level of subsidiary indebtedness. Failure to comply with these covenants, or to obtain waivers of those requirements, could in some cases trigger a right, at the lender’s discretion, to require repayment of some of our debt and may restrict our ability to draw upon our facilities or access the capital markets. The following is a maturity profile of our financial liabilities and derivatives: At 31 March 2020 Less than £m 1 to 2 £m 2 to 3 £m More than £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (3,672 ) (2,150 ) (1,611 ) (22,214 ) (29,647 ) Interest payments on borrowings¹ (765 ) (750 ) (714 ) (12,002 ) (14,231 ) Lease liabilities (132 ) (114 ) (99 ) (629 ) (974 ) Other non-interest-bearing liabilities (3,149 ) (318 ) — — (3,467 ) Contingent consideration (32 ) (16 ) (32 ) (16 ) (96 ) Derivative financial liabilities Financing derivatives – receipts² 2,249 986 1,208 3,510 7,953 Financing derivatives – payments² (2,582 ) (1,136 ) (1,463 ) (4,067 ) (9,248 ) Commodity contract derivatives – receipts² 4 2 — — 6 Commodity contract derivatives – payments² (116 ) (50 ) (24 ) (12 ) (202 ) Derivative financial assets Financing derivatives – receipts² 2,469 1,063 570 1,775 5,877 Financing derivatives – payments² (2,271 ) (527 ) (375 ) (1,478 ) (4,651 ) Commodity contract derivatives – receipts² 20 1 1 — 22 Commodity contract derivatives – payments² (21 ) — — — (21 ) (7,998 ) (3,009 ) (2,539 ) (35,133 ) (48,679 ) At 31 March 2019 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (4,129 ) (2,348 ) (1,998 ) (19,673 ) (28,148 ) Interest payments on borrowings¹ (800 ) (733 ) (721 ) (13,465 ) (15,719 ) Lease liabilities (72 ) (63 ) (52 ) (123 ) (310 ) Other non-interest-bearing liabilities (3,306 ) (340 ) — — (3,646 ) Derivative financial liabilities Financing derivatives – receipts² 3,045 1,703 163 2,560 7,471 Financing derivatives – payments² (3,421 ) (2,029 ) (223 ) (3,276 ) (8,949 ) Commodity contract derivatives – receipts² 2 3 1 — 6 Commodity contract derivatives – payments² (98 ) (26 ) (4 ) (1 ) (129 ) Derivative financial assets Financing derivatives – receipts² 1,928 561 863 1,112 4,464 Financing derivatives – payments² (1,251 ) (459 ) (783 ) (875 ) (3,368 ) Commodity contract derivatives – receipts² 23 9 2 — 34 Commodity contract derivatives – payments² — (5 ) (1 ) — (6 ) (8,079 ) (3,727 ) (2,753 ) (33,741 ) (48,300 ) 1. The interest on borrowings is calculated based on borrowings held at 31 March without taking account of future issues. Floating rate interest is estimated using a forward interest rate curve as at 31 March. Payments are included on the basis of the earliest date on which the Company can be required to settle. 2. The receipts and payments line items for derivatives comprise gross undiscounted future cash flows, after considering any contractual netting that applies within individual contracts. Where cash receipts and payments within a derivative contract are settled net, and the amount to be received/(paid) exceeds the amount to be paid/(received), the net amount is presented within derivative receipts/(payments). 32. Financial risk management continued (c) Currency risk National Grid operates internationally with mainly the pound sterling as the functional currency for the UK companies and the US dollar for the US businesses. Currency risk arises from three major areas: funding activities, capital investment and related revenues, and holdings in foreign operations. This risk is managed using financial instruments including derivatives as approved by policy, typically cross-currency interest rate swaps, foreign exchange swaps and forwards. Funding activities – our policy is to borrow in the most advantageous market available. Foreign currency funding gives rise to risk of volatility in the amount of functional currency cash to be repaid. This risk is reduced by swapping principal and interest back into the functional currency of the issuer. All foreign currency debt and transactions are hedged except where they provide a natural offset to assets elsewhere in the Group. Capital investment and related revenues – capital projects often incur costs or generate revenues in a foreign currency, most often euro transactions done by the UK business. Our policy for managing foreign exchange transaction risk is to hedge contractually committed foreign currency cash flows over a prescribed minimum size, typically by buying euro forwards to hedge future expenditure, and selling euro forwards to hedge future revenues. For hedges of forecast cash flows our policy is to hedge a proportion of highly probable cash flows. Holdings in foreign operations – we are exposed to fluctuations on the translation into pounds sterling of our foreign operations. The policy for managing this translation risk is to issue foreign currency debt or to replicate foreign debt using derivatives that pay cash flows in the currency of the foreign operation. The primary managed exposure arises from dollar denominated assets and liabilities held by our US operations, with a smaller euro exposure in respect of joint venture investments. Derivative financial instruments were used to manage foreign currency risk as follows: 2020 2019 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 18 — 55 — 73 97 2 153 — 252 Financial investments 813 — 1,185 — 1,998 965 — 1,016 — 1,981 Borrowings (12,407 ) (4,150 ) (13,217 ) (1,020 ) (30,794 ) (10,591 ) (4,787 ) (12,126 ) (1,226 ) (28,730 ) Pre-derivative position (11,576 ) (4,150 ) (11,977 ) (1,020 ) (28,723 ) (9,529 ) (4,785 ) (10,957 ) (1,226 ) (26,497 ) Derivative effect (1,169 ) 4,341 (4,214 ) 1,175 133 (1,055 ) 4,803 (5,245 ) 1,465 (32 ) Net debt position (12,745 ) 191 (16,191 ) 155 (28,590 ) (10,584 ) 18 (16,202 ) 239 (26,529 ) The exposure to dollars largely relates to our net investment hedge activities; exposure to euros largely relates to hedges for our future non-sterling capital expenditure. The currency exposure on other financial instruments is as follows: 2020 2019 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 306 — 1,403 — 1,709 398 — 1,635 — 2,033 Trade and other payables (1,177 ) — (2,002 ) — (3,179 ) (1,221 ) — (2,085 ) — (3,306 ) Other non-current liabilities (85 ) — (277 ) — (362 ) (93 ) — (247 ) — (340 ) The carrying amounts of other financial instruments are denominated in the above currencies, which in most instances are the functional currency of the respective subsidiaries. Our exposure to dollars is due to activities in our US subsidiaries. We do not have any other significant exposure to currency risk on these balances. Hedge accounting for currency risk Where available, derivatives transacted for hedging are designated for hedge accounting. Economic offset is qualitatively determined because the critical terms (currency and volume) of the hedging instrument match the hedged exposure. If a forecast transaction was no longer expected to occur, the cumulative gain or loss previously reported in equity would be transferred to the income statement. This has not occurred in the current or comparative years. Cash flow hedging of currency risk of capital expenditure and revenues is designated as hedging the exposure to movements in the spot translation rates only; the timing of forecasted transactions is not designated as a hedged risk. Gains and losses on hedging instruments arising from forward points and foreign currency basis spreads are excluded from designation and are recognised immediately in profit or loss, along with any hedge ineffectiveness. On recognition of the hedged purchase or sale in the financial statements, the associated hedge gains and losses, deferred in the cash flow hedge reserve in other equity reserves, are transferred out of reserves and included with the recognition of the underlying transaction. Where a non-financial asset or a non-financial liability results from a forecast transaction or firm commitment being hedged, the amounts deferred in reserves are included directly in the initial measurement of that asset or liability. Net investment hedging is also designated as hedging the exposure to movements in spot translation rates only: spot-related gains and losses on hedging instruments are presented in the cumulative translation reserve within other equity reserves to offset gains or losses on translation of the hedged balance sheet exposure. Any ineffectiveness is recognised immediately in the income statement. Gains and losses arising from forward points and foreign currency basis spreads are excluded from designation and are treated as a cost of hedging, deferred initially in other equity reserves and released into profit or loss over the life of the hedging relationship. Amounts deferred in the cumulative translation reserve with respect to net investment hedges are subsequently recognised in the income statement in the event of disposal of the overseas operations concerned. Any remaining amounts deferred in the cost of hedging reserve are also released to the income statement. Hedges of foreign currency funding are designated as cash flow hedges or fair value hedges of forward exchange risk (hedging both currency and interest rate risk together, where applicable). Hedge accounting for funding is described further in the interest rate risk section below. 32. Financial risk management continued (d) Interest rate risk National Grid’s interest rate risk arises from our long-term borrowings. Our interest rate risk management policy is to seek to minimise total financing costs (being interest costs and changes in the market value of debt). Hedging instruments principally consist of interest rate and cross-currency swaps that are used to translate foreign currency debt into functional currency and to adjust the proportion of fixed-rate and floating-rate in the borrowings portfolio to within a range set by the Finance Committee of the Board. The benchmark interest rates hedged are currently based on LIBOR. LIBOR is being replaced as an interest rate benchmark by alternative reference rates in certain currencies including our functional currencies, USD and GBP, and foreign currencies in which we operate. This impacts contracts including financial liabilities that pay LIBOR-based cash flows, and derivatives that receive or pay LIBOR-based cash flows. The change in benchmark also affects discount rates which can impact valuations. We are managing the risk by planning to replace LIBOR cash flows with alternative reference rates on our affected contracts. We also consider inflation risk and hold some inflation-linked borrowings. We believe that these provide a partial economic offset to the inflation risk associated with our UK inflation-linked revenues. The table in note 21 sets out the carrying amount, by contractual maturity, of borrowings that are exposed to interest rate risk before taking into account interest rate swaps. Net debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2020 2019 Fixed rate £m Floating rate £m Inflation linked £m Other 1 £m Total £m Fixed rate £m Floating rate £m Inflation linked £m Other 1 £m Total £m Cash and cash equivalents 71 10 — (8 ) 73 59 104 — 89 252 Financial investments — 1,966 — 32 1,998 6 1,944 — 31 1,981 Borrowings (20,969 ) (3,085 ) (6,740 ) — (30,794 ) (19,043 ) (3,045 ) (6,642 ) — (28,730 ) Pre-derivative position (20,898 ) (1,109 ) (6,740 ) 24 (28,723 ) (18,978 ) (997 ) (6,642 ) 120 (26,497 ) Derivative effect 2,259 (1,892 ) (234 ) — 133 1,740 (1,559 ) (213 ) — (32 ) Net debt position (18,639 ) (3,001 ) (6,974 ) 24 (28,590 ) (17,238 ) (2,556 ) (6,855 ) 120 (26,529 ) 1. Represents financial instruments which are not directly affected by interest rate risk, such as investments in equity or other similar financial instruments. Hedge accounting for interest rate risk Borrowings paying variable or floating-rates expose National Grid to cash flow interest rate risk, partially offset by cash held at variable rates. Where a hedging instrument results in paying a fixed-rate, it is designated as a cash flow hedge because it has reduced the cash flow volatility of the hedged borrowing. Changes in the fair value of the derivative are initially recognised in other comprehensive income as gains or losses in the cash flow hedge reserve, with any ineffective portion recognised immediately in the income statement. Borrowings paying fixed-rates expose National Grid to fair value interest rate risk. Where the hedging instrument pays a floating-rate, it is designated as a fair value hedge because it has reduced the fair value volatility of the borrowing. Changes in the fair value of the derivative and changes in the fair value of the hedged item in relation to the risk being hedged are both adjusted on the balance sheet and offset in the income statement to the extent the fair value hedge is effective, with the residual difference remaining as ineffectiveness. Both types of hedges are designated as hedging the currency and interest rate risk arising from changes in forward points. Amounts accumulated in the cash flow hedge reserve (cash flow hedges only) and the deferred cost of hedging reserve (both cash flow and fair value hedges) are reclassified from reserves to the income statement on a systematic basis as hedged interest expense is recognised. Adjustments made to the carrying value of hedged items in fair value hedges are similarly released to the income statement to match the timing of the hedged interest expense. When hedge accounting is discontinued, any remaining cumulative hedge accounting balances continue to be released to the income statement to match the impact of outstanding hedged items. Any remaining amounts deferred in the cost of hedging reserve are released immediately to the income statement as finance costs. The Group early-adopted IFRS Interest Rate Benchmark Reform amendments related to hedge accounting, with effect from 1 April 2019. The amendments allow existing hedge designations to continue unchanged during the period of uncertainty relating to the timing and method of benchmark migrations. The amendments will be applied until the earlier point in time where affected cash flows are amended, the relationship is formally discontinued, and any cash flow hedge reserve balance has been released, or formal market conventions ending uncertainty are published and widely adopted. If amended cash flows do not cause a hedging relationship to be discontinued, then the amendments will cease to be applied only when that relationship is discontinued under IFRS 9. The IFRS amendments impact fair value and cash flow hedges of interest rate risk and related hedging instruments, and certain net investment hedges that use cross-currency interest rate swaps to pay a foreign currency floating rate and receive a functional currency floating rate. The notional values of hedging instruments, for each type of hedging relationship impacted, are shown in the hedge accounting tables in note 32(e). These amounts also correspond to the exposures designated as hedged. 32. Financial risk management continued (e) Hedge accounting In accordance with the requirements of IFRS 9, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Year ended 31 March 2020 Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges (143 ) (17 ) — Cost of hedging 5 (7 ) — (30 ) Transferred to profit or loss in respect of: Cash flow hedges — 14 — — Cost of hedging 1 (1 ) — (45 ) Consolidated statement of changes in equity Other equity reserves – cost of hedging balances 2 (8 ) — (43 ) Consolidated statement of financial position Derivatives – carrying value of hedging instruments¹ Assets – current 1 — 4 9 Assets – non-current 247 106 8 — Liabilities – current (1 ) (105 ) (8 ) (82 ) Liabilities – non-current (39 ) (264 ) (12 ) (19 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range May 2020 – Feb 2040 Jul 2020 – Dec 2039 Apr 2020 – Dec 2024 Jun 2020 – Sep 2027 Spot foreign exchange range: GBP:USD 1.64 1.30 – 1.66 1.24 – 1.41 1.21 – 1.49 GBP:EUR 1.19 – 1.24 1.10 – 1.24 1.04 – 1.30 1.14 EUR:USD 1.13 – 1.17 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+408bps 1.331% – 5.850% n/a n/a USD LIBOR -44bps/+ 115bps 1.103% – 3.864% n/a n/a 1. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. 32. Financial risk management continued (e) Hedge accounting continued Year ended 31 March 2019 Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges¹ — (206 ) (12 ) — Cost of hedging (6 ) (12 ) — (90 ) Transferred to profit or loss in respect of: Cash flow hedges¹ — 166 — — Cost of hedging 3 — — 39 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (4 ) — — 32 Consolidated statement of financial position Derivatives – carrying value of hedging instruments² Assets – current 17 — 9 — Assets – non-current 168 78 23 — Liabilities – current (9 ) (28 ) (3 ) (43 ) Liabilities – non-current (25 ) (134 ) (4 ) (249 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Nov 2019 – May 2038 Aug 2019 – Feb 2039 Apr 2019 – Dec 2023 Mar 2020 – Jun 2025 Spot foreign exchange range: GBP:USD 1.64 – 1.65 1.52 – 1.66 1.29 – 1.41 1.49 GBP:EUR 1.19 – 1.24 1.14 – 1.24 1.07 – 1.32 1.15 EUR:USD 1.13 – 1.16 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+561bps 1.795% – 5.850% n/a n/a USD LIBOR -44bps/+115bps 1.103% – 3.864% n/a n/a 1. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in cash flow hedges of foreign currency risk and interest rates. This has no net impact on the consolidated statement of comprehensive income. It has resulted in a prior year gross up of £166 million to net losses in respect of cash flow hedges with an equal and offsetting gross up to transferred to profit and loss in respect of cash flow hedges. 2. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. 32. Financial risk management continued (e) Hedge accounting continued The following tables show the effects of hedge accounting on financial position and year-to-date performance for each type of hedge. These tables also present notional values of hedging instruments (and equal hedged exposures) impacted by IFRS 9 Interest Rate Benchmark Reform amendments. (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2020 Balance of fair value hedge adjustments in borrowings Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings 1,2 (1,751 ) (31 ) (95 ) (42 ) 48 6 1. The carrying value of the hedged borrowings is £1,883 million , of which £72 million is current and £1,811 million is non-current. 2. Included within the hedging instrument notional balance is £1,675 million impacted by Interest Rate Benchmark Reform amendments. As at 31 March 2019 Balance of fair value hedge adjustments in borrowings Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (1,707 ) 11 (117 ) 15 (10 ) 5 1. The carrying value of the hedged borrowings was £1,810 million , of which £202 million was current and £1,608 million was non-current. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in fair value hedges of foreign currency risk and interest rates. It has resulted in a prior year equal and offsetting impact of £4 million to the balances used for the ‘Change in value used for calculating ineffectiveness’. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2020 Balance in cash flow hedge reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (4,127 ) (69 ) (22 ) 142 (143

Additional disclosures in respe

Additional disclosures in respect of guaranteed securities	12 Months Ended
	Mar. 31, 2020
Separate Financial Statements [Abstract]
Additional disclosures in respect of guaranteed securities	Additional disclosures in respect of guaranteed securities We have preferred shares that are listed on a US national securities exchange and are guaranteed by other companies in the Group. These guarantors commit to honour any liabilities should the company issuing the debt have any financial difficulties. In order to provide debt holders with information on the financial stability of the companies providing the guarantees, we are required to disclose individual financial information for these companies. We have chosen to include this information in the Group financial statements rather than submitting separate stand-alone financial statements. Niagara Mohawk Power Corporation, a wholly owned subsidiary of the Group, has issued preferred shares that are listed on a US national securities exchange and are guaranteed by National Grid plc. In order to provide preferred shareholders with information on the financial stability of the company providing the guarantee, we are required to disclose individual financial information for these companies. We have chosen to include this information in the Group financial statements rather than submitting separate stand-alone financial statements. The following summarised financial information is given in respect of Niagara Mohawk Power Corporation as a result of National Grid plc’s guarantee, dated 29 October 2007, of Niagara Mohawk Power Corporation’s 3.6% and 3.9% issued preferred shares, which amount to £29 million . National Grid plc’s guarantee of Niagara Mohawk Power Corporation’s preferred shares is full and unconditional. There are no restrictions on the payment of dividends by Niagara Mohawk Power Corporation or limitations on National Grid plc’s guarantee of the preferred shares, and there are no factors that may affect payments to holders of the guaranteed securities. The following summarised financial information for National Grid plc and Niagara Mohawk Power Corporation is presented on a combined basis and is intended to provide investors with meaningful and comparable financial information, and is provided pursuant to the early adoption of Rule 13-01 of Regulation S-X in lieu of the separate financial statements of Niagara Mohawk Power Corporation. Summarised financial information is presented, on a combined basis, as at 31 March 2020 . The combined amounts are presented under IFRS measurement principles. Inter-company transactions have been eliminated. Investments in other non-issuer and non-guarantor subsidiaries are included at cost, subject to impairment. Summarised financial information for the year ended 31 March 2020 – IFRS National Grid plc and Niagara Mohawk Power Corporation combined £m Combined statement of financial position Non-current loans to other subsidiaries 363 Non-current assets 8,939 Current loans to other subsidiaries 12,435 Current assets 1,378 Current loans from other subsidiaries (16,226 ) Current liabilities (1,648 ) Non-current loans from other subsidiaries (2,105 ) Non-current liabilities (5,460 ) Net liabilities¹ (2,324 ) Equity (2,324 ) Combined income statement – continuing operations Revenue 2,365 Operating costs (2,131 ) Operating profit 234 Other income from other subsidiaries 3,888 Other income and costs, including taxation (428 ) Profit after tax 3,694 1. Excluded from net liabilities above are investments in other consolidated subsidiaries with a carrying value of £14,362 million .

Transition to new accounting st

Transition to new accounting standards	12 Months Ended
	Mar. 31, 2020
Disclosure of initial application of standards or interpretations [abstract]
Transition to new accounting standards	Transition to new accounting standards (a) Transition to IFRS 16 The Group has adopted IFRS 16 ‘Leases’, with effect from 1 April 2019 . IFRS 16 introduces a single lease accounting model for lessees (rather than the current distinction between operating and finance leases). A contract is, or contains, a lease, if it provides the right to control the use of an identified asset for a specific period of time in exchange for consideration. The new standard results in our operating leases being accounted for in the consolidated statement of financial position as ‘right-of-use’ assets with corresponding lease liabilities also recognised. It therefore increases both our assets and liabilities (including net debt). It also changes the timing and presentation in the consolidated income statement as it results in an increase in finance costs and depreciation largely offset by a reduction in the previously straight-line operating costs. Transition options We have applied IFRS 16 using the modified retrospective approach. Comparatives have not been restated on adoption. Instead, on the opening balance sheet date, right-of-use assets (net of accrued rent or rent-free periods, and reported within property, plant and equipment), additional lease liabilities (reported within borrowings) and any associated deferred tax have been recognised, with no cumulative transition adjustment to reflect through retained earnings. For short-term leases (lease term of 12 months or less) and leases of low-value assets (such as computers), the Group continues to recognise a lease expense on a straight-line basis as permitted by IFRS 16. 37. Transition to new accounting standards continued (a) Transition to IFRS 16 continued We elected to apply the practical expedient to grandfather our previous assessments of whether contracts were previously accounted for as a lease, as permitted by the standard, instead of reassessing all significant contracts as at the date of initial application to determine whether they met the IFRS 16 definition of a lease. We have elected to apply the practical expedient on transition, which permits right-of-use assets to be measured at an amount equal to the lease liability on adoption of the standard (adjusted for any prepaid or accrued lease expenses). In addition, we have also elected the option to adjust the carrying amounts of the right-of-use assets as at 1 April 2019 for any onerous lease provisions that had been recognised on the Group consolidated statement of financial position as at 31 March 2019 , rather than performing impairment assessments on transition. Impact of transition At 31 March 2019 , the Group disclosed non-cancellable operating lease commitments of £0.3 billion , of which the majority were in the US. A further £0.4 billion of lease liabilities were recognised due to the requirement in IFRS 16 to recognise lease liabilities for the term that we are reasonably certain to exercise lease extension or lease termination options for, rather than only for the period of the minimum contractual term that was used in determining our lease liability commitments. This was partially offset by the £0.2 billion impact of discounting our lease liabilities at the incremental borrowing rate for each lease. The weighted average discount rate applied to lease liabilities recognised on the transition date was 2.8% .There were some immaterial short-term and low-value leases, which will be recognised on a straight-line basis as an expense in the consolidated income statement over the remaining lease term. As a result, the Group has recognised additional right-of-use assets of £0.5 billion and lease liabilities (which are included within net debt) of £0.5 billion at 1 April 2019 . No additional net deferred tax has arisen. The transition adjustment is in addition to the £270 million of finance leases already recognised on the consolidated statement of financial position under IAS 17. There has been no impact on net assets as shown in the table below, which shows the impacted balances from the Group consolidated statement of financial position. Impact of transition 31 March 2019 IFRS 16 1 April 2019 £m £m £m Property, plant and equipment – Right-of-use assets Land and buildings 2,560 381 2,941 Plant and machinery 36,589 67 36,656 Assets in the course of construction 4,425 — 4,425 Motor vehicles and office equipment 339 20 359 Total property, plant and equipment 43,913 468 44,381 Borrowings – Lease liabilities Current (65 ) (48 ) (113 ) Non-current (205 ) (426 ) (631 ) Total lease liabilities (270 ) (474 ) (744 ) Other liabilities Trade and other payables (3,769 ) 3 (3,766 ) Other non-current liabilities (808 ) 3 (805 ) Net assets 19,369 — 19,369 Equity Total equity 19,369 — 19,369 The impact of IFRS 16 on profit after tax as a result of adopting the new standard is not material. However, it has resulted in an increase in operating profit due to the operating costs now being replaced with depreciation and interest charges. The impact on the cash flow statement has also not been material, although there has been an increase in operating cash flows and decrease in financing cash flows, because repayment of the principal portion of the lease liabilities is now classified as cash flows from financing activities rather than operating cash flows. Ongoing accounting policy With effect from 1 April 2019, new lease arrangements entered into are recognised as a right-of-use asset and a corresponding liability at the date at which the leased asset is available for use by the Group. The right-of-use asset and associated lease liability arising from a lease are initially measured at the present value of the lease payments expected over the lease term, plus any other costs. The discount rate applied is the rate implicit in the lease or if that is not available, then the incremental rate of borrowing for a similar term and similar security. The lease term takes account of exercising any extension options that are at our option if we are reasonably certain to exercise the option and any lease termination options unless we are reasonably certain not to exercise the option. Each lease payment is allocated between the liability and finance cost. The finance cost is charged to the income statement over the lease period using the effective interest rate method. The right-of-use asset is depreciated over the shorter of the asset's useful life and the lease term on a straight-line basis. For short-term leases (lease term of 12 months or less) and leases of low-value assets (such as computers), the Group continues to recognise a lease expense on a straight-line basis. 37. Transition to new accounting standards continued (b) Transition to IFRS 9 and IFRS 15 On 1 April 2018, the Group adopted IFRS 9 and IFRS 15. Both standards were applied using the modified retrospective approach whereby comparative amounts were not restated on transition, but a cumulative adjustment was made to retained earnings in the opening consolidated statement of financial position as at 1 April 2018. The impact of the transition on the opening consolidated statement of financial position is set out in the following table: Impact of transition 31 March 2018 Transition adjustments 1 April 2018 IFRS 9 IFRS 15 £m £m £m £m Non-current assets Goodwill 5,444 — — 5,444 Other intangible assets 899 — — 899 Property, plant and equipment 39,853 — — 39,853 Other non-current assets 115 — — 115 Pension assets 1,409 — — 1,409 Financial and other investments 899 — 1 — 899 Investments in joint ventures and associates 2,168 — — 2,168 Derivative financial assets 1,319 — — 1,319 Total non-current assets 52,106 — — 52,106 Current assets Inventories and current intangible assets 341 — — 341 Trade and other receivables 2,798 — 2 (3 ) 2,795 Current tax assets 114 — — 114 Financial and other investments 2,694 — 1 — 2,694 Derivative financial assets 405 — — 405 Cash and cash equivalents 329 — — 329 Total current assets 6,681 — (3 ) 6,678 Total assets 58,787 — (3 ) 58,784 Current liabilities Borrowings (4,447 ) — — (4,447 ) Derivative financial liabilities (401 ) — — (401 ) Trade and other payables (3,453 ) — 59 7 (3,394 ) Contract liabilities — — (53) 7 (53 ) Current tax liabilities (123 ) — — (123 ) Provisions (273 ) — — (273 ) Total current liabilities (8,697 ) — 6 (8,691 ) Non-current liabilities Borrowings (22,178 ) (32) 3 — (22,210 ) Derivative financial liabilities (660 ) — — (660 ) Other non-current liabilities (1,317 ) — 567 7 (750 ) Contract liabilities — — (813) 7 (813 ) Deferred tax liabilities (3,636 ) 5 4 74 8 (3,557 ) Pensions and other post-retirement benefit obligations (1,672 ) — — (1,672 ) Provisions (1,779 ) — — (1,779 ) Total non-current liabilities (31,242 ) (27 ) (172 ) (31,441 ) Total liabilities (39,939 ) (27 ) (166 ) (40,132 ) Net assets 18,848 (27 ) (169 ) 18,652 Equity Share capital 452 — — 452 Share premium account 1,321 — — 1,321 Retained earnings 21,599 (99) 5 (169) 9 21,331 Other equity reserves (4,540 ) 72 6 — (4,468 ) Total shareholders’ equity 18,832 (27 ) (169 ) 18,636 Non-controlling interests 16 — — 16 Total equity 18,848 (27 ) (169 ) 18,652 37. Transition to new accounting standards continued (b) Transition to IFRS 9 and IFRS 15 continued IFRS 9: Financial Instruments IFRS 9 has changed the rules concerning the classification and measurement of financial instruments, impairment of financial assets, and hedge accounting. Details of the impact of applying IFRS 9 for the year ended 31 March 2019 are set out below. Adjustments arising in the year ended 31 March 2019 as a result of the transition to IFRS 9: 1. The available-for-sale category for financial assets was replaced with investments held at fair value through profit and loss (FVTPL) and investments held at fair value through other comprehensive income (FVOCI). Changes to the classification and measurement of financial assets did not alter the carrying value of any financial assets held by the Group. The net impact to retained earnings of the reclassification on transition was an £8 million gain. As described in note 15, all recognised financial assets that are within the scope of IFRS 9 are initially recorded at fair value and subsequently measured at amortised cost or fair value based on the Group’s business model for managing the financial assets and the contractual cash flow characteristics of the financial assets. Therefore on 1 April 2018, the Group reclassified its investments as follows: • Money market funds and fund investments held by captive insurance companies were classified as financial assets at FVTPL because their contractual cash flows are not solely payments of principal and interest; • Investments in debt securities that have contractual payments that are solely payments of principal and interest, and which are held as part of the liquidity portfolio or to back employee benefit liabilities, were classified as financial assets at FVOCI because they are held in a business model whose objective is to collect the contractual cash flows and to sell the debt instruments; • The Group has elected to hold investments in equity securities, which are held to back employee benefit liabilities, as financial assets at FVOCI as the Group does not believe that changes in their fair value is reflective of the financial performance of the Group; and • Loans to joint ventures and associates, cash at bank, and short-term deposits are classified at amortised cost as they have contractual cash flows which are solely payments of principal and interest and the Group holds them to collect contractual cash flows. Aside from derivative financial instruments, which remain classified as FVTPL, the Group did not previously have any financial assets or liabilities classified at FVTPL. The table below illustrates those financial assets and liabilities that were reclassified at 1 April 2018: Financial asset/liability Note Original measurement category under IAS 39 New measurement category under IFRS 9 Original carrying amount under IAS 39 Change to measurement basis under IFRS 9 New carrying amount under IFRS 9 £m £m £m Money market funds and fund investments in equities and bonds 15 Available-for-sale investments Financial assets at FVTPL 2,294 — 2,294 Cash surrender value of life insurance policies and investments in debt securities 15 Available-for-sale investments Financial assets at FVOCI 343 — 343 Investments in equity securities 15 Available-for-sale investments Financial assets at FVOCI (equity instruments) 84 — 84 Loans to joint ventures and associates and restricted balances 15 Loans and receivables Financial assets at amortised cost 872 — 872 Borrowings 21 Financial liabilities at amortised cost Financial liabilities at fair value through profit and loss (570 ) (32 ) (602 ) Note that the table above does not include derivative assets, derivative liabilities, trade receivables, cash at bank and short-term deposits, borrowings measured at amortised cost or trade payables. This is because neither the classification nor the measurement of these items has changed on transition to IFRS 9. 2. The change from the incurred loss impairment model of IAS 39 to the expected loss model in IFRS 9 did not have a material impact on the Group’s credit loss provision. The Group calculates its impairment provision on trade receivables using a sophisticated provisions matrix. The inclusion of forward-looking information did not have a significant impact on the matrix as the relevant short-term future economic conditions affecting our retail customers in the US are expected to be similar to recent experience. 3. The Group elected to reclassify an existing liability with a carrying value of £570 million from amortised cost to fair value through profit and loss to reduce a measurement mismatch. At transition, the resultant impacts included an increase in the carrying value of the liability of £32 million , a reduction in retained earnings of £40 million and the establishment of an own credit reserve (within other equity reserves) of £7 million . 4. Deferred tax was recognised on the adjustments recorded on the transition to IFRS 9. Reserve impacts are stated net of related deferred tax. 5. Retained earnings included the impact from adjustments 1, 3 and 6. 6. The Group adopted the hedge accounting requirements of IFRS 9, which more closely align with the Group’s risk management policies. On transition, it was concluded that all IAS 39 hedge relationships are qualifying IFRS 9 relationships with the treatment of the cost of hedging being the main change. The effect was a reclassification in reserves of a £67 million gain from retained earnings and a £10 million gain from the cash flow hedge reserve, into a new cost of hedging reserve (within other equity reserves). In this reserve, qualifying unrealised gains and losses excluded from hedging relationships are deferred and released systematically into profit or loss to match the timing of hedged items. 37. Transition to new accounting standards continued (b) Transition to IFRS 9 and IFRS 15 continued IFRS 15: Revenue from Contracts with Customers IFRS 15 has primarily changed the accounting for our connection and diversion revenues in our regulated businesses. No practical expedients on transition were applied. The accounting for revenue under IFRS 15 did not represent a substantive change from the Group’s previous practice under IAS 18 for recognising revenue from sales to customers with the exception of the following items: • Certain pass-through revenues (principally revenues collected on behalf of the Scottish and Offshore transmission operators) were recorded net of operating costs, whereas previously they were recognised gross of operating costs. Had we not adopted IFRS 15, our revenues and operating costs for the year ended 31 March 2019 would have been £1,197 million higher, with no impact to operating profits; • Contributions for capital works relating to connections for our customers were deferred as contract liabilities on our consolidated statement of financial position on transition, and released over the life of the connection assets. This was a change for our US Regulated business and our UK Gas Transmission business, where previously revenues were recorded once the work was completed. Had we not adopted IFRS 15, our revenues and operating profit for the year ended 31 March 2019 would have been £57 million higher; and • In the UK, contributions for capital works relating to diversions were recognised as the works are completed. This was a change for the UK regulated businesses where revenues were previously deferred over the life of the asset. Had we not adopted IFRS 15, our revenues and operating profit for the year ended 31 March 2019 would have been £26 million and £23 million lower, respectively. Adjustments arising in the year ended 31 March 2019 as a result of the transition to IFRS 15: 7. Deferred income from contributions for capital works were reclassified to contract liabilities. In addition, these liabilities for capital works relating to connections have increased as these capital contributions for connections were cumulatively adjusted for on 1 April 2018 and are now deferred and released over the life of the connection assets. This was a change for our US Regulated business and our UK Gas Transmission business where previously revenues were recorded once the work was completed. Partially offsetting the increase in contract liabilities for connections was the change in accounting treatment for contributions relating to diversions in our UK businesses. These contributions are recognised as revenue as the works are completed where previously revenue was recognised over the life of the assets. 8. Deferred tax was recorded on the incremental amounts recorded against capital contributions and contract liabilities on the transition to IFRS 15. Deferred tax balances have been calculated at the rate substantially enacted at the balance sheet date. 9. The transition adjustment reflected the net of adjustments 7 and 8 above.

Acquisition of Geronimo Energy

Acquisition of Geronimo Energy LLC and Emerald Energy Venture LLC (Notes)	12 Months Ended
	Mar. 31, 2020
Business Combinations [Abstract]
Acquisition of Geronimo Energy LLC and Emerald Energy Venture LLC	Acquisition of Geronimo Energy LLC and Emerald Energy Venture LLC On 11 July 2019, National Grid Ventures acquired 100% of the share capital of Geronimo Energy LLC (Geronimo) and 51% of Emerald Energy Venture LLC (Emerald), which is jointly controlled by National Grid and Washington State Investment Board (WSIB). Geronimo is a leading developer of wind and solar generation based in Minneapolis in the US, and the acquisition is a significant step in National Grid’s commitment to the decarbonisation agenda, towards developing and growing a large-scale renewable generation business in the US, and delivering sustainable, reliable and efficient energy. This is National Grid’s first ownership stake in wind generation and an expansion of our activities in solar generation. Whilst Geronimo develops the assets, Emerald has a right of first refusal to buy, build and operate those assets. The total consideration was £209 million , satisfied by a combination of cash and contingent consideration. The contingent consideration has been recorded within trade and other payables for the amount payable within one year, with the remainder recorded within other non-current liabilities. The fair value of contingent consideration recognised is determined as the present value of our best estimate of the value that we will be required to pay, taking into consideration management’s estimates of the volume of successful development activity by Geronimo over the relevant period. The fair values of the assets and liabilities recognised from both the acquisition of the subsidiary, Geronimo, and the joint venture, Emerald, are set out below. £m Intangible assets 5 Property, plant and equipment 1 Investment in joint venture – Emerald 90 Cash 2 Other identifiable assets and liabilities 30 Total identifiable assets 128 Goodwill 81 Total consideration transferred 209 Satisfied by: Contingent consideration – Geronimo 70 Cash consideration – Geronimo 49 Cash consideration – Emerald 90 209 The goodwill arising from the acquisition comprises the value associated with the potential future projects that will be developed by Geronimo as well as the expertise of the management team that have been acquired, neither of which qualify for recognition as tangible or intangible assets. At the acquisition date, there were no material contingent liabilities. Subsequent to the acquisition date, we made an additional capital contribution of £50 million into Emerald. Total acquisition-related costs of £3 million have been recognised within operating costs within the consolidated income statement, of which £1 million was recognised in the year ended 31 March 2020. Geronimo earns revenue from selling its development stage assets to Emerald and other third parties. Emerald generates revenue from the assets it purchases from Geronimo once they are operational and has no other business (see note 16) . Neither entity has generated significant revenues or profits for the period between the acquisition date and the reporting date. Even if the acquisition had completed on 1 April 2019, there would have been no significant revenues or profits.

Post balance sheet events

Post balance sheet events	12 Months Ended
	Mar. 31, 2020
Events After Reporting Period [Abstract]
Post balance sheet events	Post balance sheet events In the period between 31 March 2020 and 17 June 2020, there have continued to be substantial environmental, economic and social changes in both the UK and US. T hese have had, and will continue to have, significant ramifications for the Group. Other than as disclosed in respect of those areas where forward-looking forecasts are relevant (notably goodwill impairment reviews (note 11) , expected credit losses on financial instruments including trade receivables (notes 19 and 32) and the presumption of the going concern basis generally (note 1) ), none of these developments have impacted or caused adjustment to the financial statements.

Basis of preparation and rece_2

Basis of preparation and recent accounting developments (Policies)	12 Months Ended
	Mar. 31, 2020
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
Description of accounting policy for basis of preparation	These consolidated financial statements have been prepared in accordance with International Accounting Standards (IAS) and International Financial Reporting Standards (IFRS) and related interpretations as issued by the IASB and IFRS as adopted by the EU. They are prepared on the basis of all IFRS accounting standards and interpretations that are mandatory for periods ended 31 March 2020 and in accordance with the Companies Act 2006 applicable to companies reporting under IFRS and Article 4 of the EU IAS Regulation. The comparative financial information has also been prepared on this basis. The consolidated financial statements have been prepared on a historical cost basis, except for the recording of pension assets and liabilities, the revaluation of derivative financial instruments and certain commodity contracts and certain financial assets and liabilities measured at fair value. These consolidated financial statements are presented in pounds sterling, which is also the functional currency of the Company. The notes to the financial statements have been prepared on a continuing basis unless otherwise stated.
Going concern	As at the date of approving these financial statements, the impact of COVID-19 on the Group’s operations is continually being assessed and subject to rapid change. The Directors have assessed the principal risks, including by modelling both a base case and a reasonable worst case scenario. The reasonable worst-case scenario covers the cash flow impact associated with an extended lockdown for a period of 12 months across both the UK and US. The main cash flow impacts identified in the reasonable worst-case scenario are: • a significant reduction in cash collections over an extended 12 -month period driven by lower customer demand and increased bad debt in our US businesses; • additional working capital required to fund payment term extensions and charge deferrals in the UK electricity market, intended to help customers and end-user consumers; • one-off increases in other costs such as cleaning, safety equipment and IT; offset by ◦ a reduction in non-essential capital expenditure across the Group driven by increased absenteeism, supply chain issues and difficulty in accessing sites; and ◦ a reduction in discretionary spend across all areas (e.g. recruitment, travel and consultancy spend) . As part of their analysis, the Board also considered the following potential levers at their discretion to improve the position identified by the reasonable worst-case scenario in the event that the debt capital markets are not accessible: • further significant changes in the phasing of the Group’s capital programme with elements of non-essential works and programmes delayed beyond June 2021; • a number of further reductions in operating expenditure across the Group primarily related to workforce cost reductions in both the UK and the US; and • the payment of dividends to shareholders. Having considered the reasonable worst-scenario and further levers at the Board’s discretion, the Group continues to have headroom against the Group’s committed facilities identified in note 33 to the financial statements. In addition to the above, the ability to raise new financing was separately included in the analysis and the Directors noted the £0.9 billion debt issuances completed in April 2020 (disclosed in note 21 to the financial statements) as evidence of the Group’s ability to continue to have access to the debt capital markets if needed. Other factors considered by the Board as part of their Going Concern assessment included the potential impact of Brexit trade talks, the Group’s various ongoing rate case determinations in the UK and US alongside inherent uncertainties in cash flow forecasts (such as the impact of storms in our US business). Based on the above, the Directors have concluded the Group is well placed to manage its financing and other business risks satisfactorily, and have a reasonable expectation that the Group will have adequate resources to continue in operation for at least 12 months from the signing date of these consolidated financial statements. They therefore consider it appropriate to adopt the going concern basis of accounting in preparing the financial statements.
Basis of consolidation	The consolidated financial statements incorporate the results, assets and liabilities of the Company and its subsidiaries, together with a share of the results, assets and liabilities of joint operations. A subsidiary is defined as an entity controlled by the Group. Control is achieved where the Group is exposed to, or has the rights to, variable returns from its involvement with the entity and has the power to affect those returns through its power over the entity. The Group accounts for joint ventures and associates using the equity method of accounting, where the investment is carried at cost plus post-acquisition changes in the share of net assets of the joint venture or associate, less any provision for impairment. Losses in excess of the consolidated interest in joint ventures and associates are not recognised, except where the Company or its subsidiaries have made a commitment to make good those losses. Where necessary, adjustments are made to bring the accounting policies used in the individual financial statements of the Company, subsidiaries, joint operations, joint ventures and associates into line with those used by the Group in its consolidated financial statements under IFRS. Intercompany transactions are eliminated. The results of subsidiaries, joint operations, joint ventures and associates acquired or disposed of during the year are included in the consolidated income statement from the effective date of acquisition or up to the effective date of disposal, as appropriate. Acquisitions are accounted for using the acquisition method, where the purchase price is allocated to the identifiable assets acquired and liabilities assumed on a fair value basis and the remainder recognised as goodwill.
Discontinued operations and held for sale	At the end of June 2019, we completed the disposal of our retained 39% interest in the UK Gas Distribution business (held through Quadgas) that was classified as held for sale. We have treated the results and cash flows of Quadgas as a discontinued operation in the consolidated income statement and consolidated cash flow statement. The results and cash flows of significant assets or businesses sold during the year are shown separately from our continuing operations, and presented within discontinued operations in the income statement and cash flow statement. Assets and businesses are classified as held for sale when their carrying amounts are recovered through sale rather than through continuing use. They only meet the held for sale condition when the assets are ready for immediate sale in their present condition, management is committed to the sale and it is highly probable that the sale will complete within one year. Depreciation ceases on assets and businesses when they are classified as held for sale and the assets and businesses are impaired if the proceeds less sale costs fall short of the carrying value.
Foreign currencies	Transactions in currencies other than the functional currency of the Company or subsidiary concerned are recorded at the rates of exchange prevailing on the dates of the transactions. At each reporting date, monetary assets and liabilities that are denominated in foreign currencies are retranslated at closing exchange rates. Non-monetary assets are not retranslated unless they are carried at fair value. Gains and losses arising on the retranslation of monetary assets and liabilities are included in the income statement, except where the application of hedge accounting requires inclusion in other comprehensive income (see note 32(e)). On consolidation, the assets and liabilities of operations that have a functional currency different from the Company’s functional currency of pounds sterling, principally our US operations that have a functional currency of US dollars, are translated at exchange rates prevailing at the reporting date. Income and expense items are translated at the average exchange rates for the period where these do not differ materially from rates at the date of the transaction. Exchange differences arising are recognised in other comprehensive income and transferred to the consolidated translation reserve within other equity reserves (see note 28).
Areas of judgement and key sources of estimation uncertainty	The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities, and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from these estimates. Information about such judgements and estimations is in the notes to the financial statements, and the key areas are summarised below. Areas of judgement that have the most significant effect on the amounts recognised in the financial statements are as follows: • the judgement that notwithstanding legislation enacted and targets established during the year ended 31 March 2020 committing the UK, New York State and Massachusetts to achieving net zero greenhouse gas emissions by 2050, these do not trigger a reassessment of the remaining useful economic lives of our gas network assets (see estimate below and note 13 ); and • following the legal separation of the Electricity System Operator on 1 April 2019, we concluded that the Electricity System Operator acts as an agent in respect of certain Transmission Network Use of Service revenues, principally those collected on behalf of the Scottish and Offshore transmission operators , as detailed in note 3 . Key sources of estimation uncertainty that have a significant risk of causing a material adjustment to the carrying amounts of assets and liabilities within the next financial year are as follows: • the valuation of liabilities for pensions and other post-retirement benefits (see note 25 ); and • the cash flows applied in determining the environmental provisions, in particular relating to three US Superfund sites (see note 26 ). In light of the current ongoing impact of the COVID-19 pandemic, valuations of certain assets and liabilities are necessarily more subjective. In particular, two further areas of estimation uncertainty impacting the Group's position as at 31 March 2020 have been identified: • the valuation of certain pension assets, in particular unquoted equities, properties and diversified alternatives, in light of the volatile economic markets (see note 25) ; and • the recoverability of customer receivables, particularly in relation to US retail customers, in light of the suspension of debt collection activities and customer termination activities (see note 19 ). In addition, we also highlight the estimates made regarding the useful economic lives of our gas network assets due to the length over which they are being depreciated, the potential for new and evolving technologies over that period, and the range of potential pathways for meeting net zero targets (see note 13 for details and sensitivity analysis ). In order to illustrate the impact that changes in assumptions for the valuation of pension assets and liabilities and cash flows for environmental provisions could have on our results and financial position, we have included sensitivity analyses in note 35.
New IFRS accounting standards effective for the year ended 31 March 2019 and New IFRS accounting standards and interpretations not yet adopted	The following new accounting standards and amendments to existing standards have been issued but are not yet effective: • IFRS 17 ‘Insurance Contracts’; • Amendments to IFRS 3 ‘Business Combinations’; • Amendments to the References to the Conceptual Framework; • Amendments to IAS 1 and IAS 8: Definition of material; and • Amendments to IAS 1 'Presentation of Financial Statements'. The Group is currently assessing the impact of the above standards, but they are not expected to have a material impact. The Group has not adopted any other standard, amendment or interpretation that has been issued but is not yet effective. The Group adopted IFRS 16 ‘Leases’ with effect from 1 April 2019. We have applied the modified retrospective approach permitted in the standard whereby prior year comparatives have not been restated on adoption. Instead, any cumulative transition adjustments are reflected through reserves. Refer to note 37 for full details of the impact and transition adjustments arising on adoption. The UK’s Financial Conduct Authority announced that LIBOR will cease to exist by the end of 2021, and will be replaced by alternative reference rates. In September 2019, the IASB amended IFRS 9 and IFRS 7 by issuing Interest Rate Benchmark Reform, which provides exceptions to specific hedge accounting requirements to ensure that hedging relationships are not considered to be modified as a result of the change in the reference rate. The amendments were endorsed in January 2020 for adoption in the EU. The Group early-adopted these changes to IFRS 9 and IFRS 7 with effect from 1 April 2019. There were no transition adjustments on adoption. Refer to note 32(e) for further details of the impact in the current period. The Group has also adopted the following amendments to standards, which have had no material impact on the Group’s results or financial statement disclosure: • IFRIC 23 ‘Uncertainty over Income Tax Treatments’; • Amendments to IAS 28 ‘Investments in Associates – Long-term Interests in Associates and Joint Ventures’; • Annual Improvements to IFRS Standards 2015–2017 Cycle; and • Amendments to IAS 19 ‘Employee Benefits’.
Segmental analysis	This note sets out the financial performance for the year split into the different parts of the business (operating segments). The performance of these operating segments is monitored and managed on a day-to-day basis. Revenue and the results of the business are analysed by operating segment, based on the information the Board of Directors uses internally for the purposes of evaluating the performance of each operating segment and determining resource allocation between them. The Board is National Grid’s chief operating decision maker (as defined by IFRS 8 ‘Operating Segments’) and assesses the profitability of operations principally on the basis of operating profit before exceptional items and remeasurements (see note 5). As a matter of course, the Board also considers profitability by segment, excluding the effect of timing. However, the measure of profit disclosed in this note is operating profit before exceptional items and remeasurements as this is the measure that is most consistent with the IFRS results reported within these financial statements.
Revenue	Revenue arises in the course of ordinary activities and principally comprises: • transmission services; • distribution services; and • generation services. Transmission services, distribution services and certain other services (excluding rental income but including metering) fall within the scope of IFRS 15 ‘Revenue from Contracts with Customers’, whereas generation services (which solely relate to the contract with the Long Island Power Authority (LIPA) in the US) are accounted for under the leasing standard as rental income, also presented within revenue. Revenue is measured based on the consideration specified in a contract with a customer and excludes amounts collected on behalf of third parties and value added tax. The Group recognises revenue when it transfers control over a product or service to a customer.
Operating costs	Below we have presented separately certain items included in our operating costs from continuing operations. These include a breakdown of payroll costs (including disclosure of amounts paid to key management personnel) and fees paid to our auditors.
Exceptional items and remeasurements	To monitor our segmental financial performance, we use a profit measure that excludes certain income and expenses. We call that measure ‘business performance’ or ‘adjusted profit’. Business performance (which excludes exceptional items and remeasurements as defined below) is used by management to monitor financial performance as it is considered that it aids the comparability of our reported financial performance from year to year. We exclude items from business performance because, if included, these items could distort understanding of our performance for the year and the comparability between periods. This note analyses these items, which are included in our results for the year but are excluded from business performance.
Finance income and costs	This note details the interest income generated by our financial assets and interest expense incurred on our financial liabilities, primarily our financing portfolio (including our financing derivatives). It also includes the net interest on our pensions and other post-retirement assets. In reporting business performance, we adjust net financing costs to exclude any net gains or losses on financial instruments included in remeasurements (see note 5). In addition, where debt redemptions relate to exceptional transactions they are typically treated as exceptional.
Tax	Tax is payable in the territories where we operate, mainly the UK and the US. This note gives further details of the total tax charge and tax liabilities, including current and deferred tax. The current tax charge is the tax payable on this year’s taxable profits. Deferred tax is an accounting adjustment to provide for tax that is expected to arise in the future due to differences in the accounting and tax bases.
Earnings per share (EPS)	EPS is the amount of post-tax profit attributable to each ordinary share. Basic EPS is calculated on profit for the year attributable to equity shareholders divided by the weighted average number of shares in issue during the year. Diluted EPS shows what the impact would be if all outstanding share options were exercised and treated as ordinary shares at year end. The weighted average number of shares is increased by additional shares issued as scrip dividends and reduced by shares repurchased by the Company during the year. The earnings per share calculations are based on profit after tax attributable to equity shareholders of the Company which excludes non-controlling interests.
Goodwill	Goodwill represents the excess of what we paid to acquire businesses over the fair value of their net assets at the acquisition date. We assess whether goodwill is recoverable each year by performing an impairment review.
Other intangible assets	Other intangible assets include software which is written down (amortised) over the period we expect to receive a benefit from the asset.
Property, plant and equipment	The following note shows the physical assets controlled by us. The cost of these assets primarily represents the amount initially paid for them. This includes both their purchase price and the construction and other costs associated with getting them ready for operation. A depreciation expense is charged to the income statement to reflect annual wear and tear and the reduced value of the asset over time. Depreciation is calculated by estimating the number of years we expect the asset to be used (useful economic life or UEL) and charging the cost of the asset to the income statement equally over this period. We operate an energy networks business and therefore have a significant physical asset base. We continue to invest in our networks to maintain reliability, create new customer connections and ensure our networks are flexible and resilient. Our business plan envisages these additional investments will be funded through a mixture of cash generated from operations and the issue of new debt.
Other non-current assets	Other non-current assets include assets that do not fall into any other non-current asset category (such as goodwill or property, plant and equipment) where the benefit to be received from the asset is not due to be received until after 31 March 2021.
Financial and other investments	The Group holds a range of financial and other investments. These investments include short-term money funds, quoted investments in equities or bonds of other companies, long-term loans to our joint ventures, investments in our venture capital portfolio (National Grid Partners), bank deposits with a maturity of greater than three months, and cash balances that cannot be readily used in operations, principally collateral pledged against derivative holdings.
Investments in joint ventures and associates	Investments in joint ventures and associates represent businesses we do not control but over which we exercise joint control or significant influence. They are accounted for using the equity method. A joint venture is an arrangement established to engage in economic activity, which the Group jointly controls with other parties and has rights to the net assets of the arrangement. An associate is an entity which is neither a subsidiary nor a joint venture, but over which the Group has significant influence. While we present consolidated results in these financial statements as if we were one company, our legal structure is such that there are a number of different operating and holding companies that contribute to the overall result. This structure has evolved through acquisitions as well as regulatory requirements to have certain activities within separate legal entities.
Derivative financial instruments	Derivatives are financial instruments that derive their value from the price of an underlying item such as interest rates, foreign exchange rates, credit spreads, commodities, equities or other indices. In accordance with policies approved by the Board, derivatives are transacted generally to manage exposures to fluctuations in interest rates, foreign exchange rates and commodity prices. Our derivatives balances comprise two broad categories: • financing derivatives managing our exposure to interest rates and foreign exchange rates. Specifically, we use these derivatives to manage our financing portfolio, holdings in foreign operations and contractual operational cash flows; and • commodity contract derivatives managing our US customers’ exposure to price and supply risks. Some forward contracts for the purchase of commodities meet the definition of derivatives and are included here. We also enter into derivative financial instruments linked to commodity prices, including index futures, options and swaps. These are used to manage market price volatility.
Inventories and current intangible assets	Inventories represent assets that we intend to use in order to generate revenue in the short term, either by selling the asset itself (for example, fuel stocks) or by using it to fulfil a service to a customer or to maintain our network (consumables).
Trade and other receivables	Trade and other receivables are amounts which are due from our customers for services we have provided.
Cash and cash equivalents	Cash and cash equivalents include cash balances, together with short-term investments with an original maturity of less than three months that are readily convertible to cash.
Borrowings and Borrowing facilities	We borrow money primarily in the form of bonds and bank loans. These are for a fixed term and may have fixed or floating interest rates or are linked to RPI. We use derivatives to manage risks associated with interest rates and foreign exchange. Our price controls and rate plans lead us to fund our networks within a certain ratio of debt to equity and, as a result, we have issued a significant amount of debt. As we continue to invest in our networks, the value of debt is expected to increase over time. To maintain a strong balance sheet and to allow us to access capital markets at commercially acceptable interest rates, we balance the amount of debt we issue with the value of our assets, and we take account of certain other metrics used by credit rating agencies. To support our liquidity requirements and provide backup to commercial paper and other borrowings, we agree loan facilities with financial institutions over and above the value of borrowings that may be required. These committed credit facilities have never been drawn, and our undrawn amounts are listed below.
Trade and other payables	Trade and other payables include amounts owed to suppliers, tax authorities and other parties which are due to be settled within 12 months. The total also includes deferred amounts, some of which represent monies received from customers but for which we have not yet delivered the associated service. These amounts are recognised as revenue when the service is provided.
Contract liabilities	Contract liabilities primarily relate to the advance consideration received from customers for construction contracts, mainly in relation to connections, for which revenue is recognised over the life of the asset.
Other non-current liabilities	Other non-current liabilities include deferred income which will not be recognised as income until after 31 March 2021. It also includes payables that are not due until after that date.
Pensions and other post-retirement benefits	All of our employees are eligible to participate in a pension plan. We have defined benefit (DB) and defined contribution (DC) pension plans in the UK and the US. In the US we also provide healthcare and life insurance benefits to eligible employees, post-retirement. The fair value of associated plan assets and present value of DB obligations are updated annually in accordance with IAS 19 (revised). We separately present our UK and US pension plans to show geographical split. Below we provide a more detailed analysis of the amounts recorded in the primary financial statements and the actuarial assumptions used to value the DB obligations. National Grid’s UK pension arrangements are held in separate Trustee administered funds. The arrangements are managed by Trustee companies with boards consisting of company- and member-appointed directors. In the US, the assets of the plans are held in trusts and administered by the Retirement Plans Committee comprised of appointed employees of the Company.
Provisions	We make provisions when an obligation exists resulting from a past event, and it is probable that cash will be paid to settle it, but the exact amount of cash required can only be estimated. The main estimates relate to environmental remediation and decommissioning costs for various sites we own or have owned and other provisions, including restructuring plans and lease contracts we have entered into that are now loss making. The evaluation of the likelihood of the contingent events has required best judgement by management regarding the probability of exposure to potential loss. Should circumstances change following unforeseeable developments, the likelihood could alter.
Share capital	Ordinary share capital represents the total number of shares issued which are publicly traded. We also disclose the number of treasury shares the Company holds, which are shares that the Company has bought itself, predominantly to actively manage scrip issuances and settle employee share option and reward plan liabilities.
Other equity reserves	Other equity reserves are different categories of equity as required by accounting standards and represent the impact of a number of our historical transactions.
Net debt	Net debt represents the amount of borrowings and overdrafts less cash, current financial investments and related financing derivatives.
Commitments and contingencies	Commitments are those amounts that we are contractually required to pay in the future as long as the other party meets its obligations. These commitments primarily relate to energy purchase agreements and contracts for the purchase of assets which, in many cases, extend over a long period of time. Commitments previously included operating lease commitments but on transition to IFRS 16, which was effective from 1 April 2019, substantially all lease commitments are included on the balance sheet as right-of-use assets (see note 13) and lease liabilities (see note 21). Therefore, only low-value leases and short-term leases are off-balance sheet commitments, both of which are immaterial. We also disclose any contingencies, which include guarantees that companies have given, where we pledge assets against current obligations that will remain for a specific period.
Related party transactions	Related parties include joint ventures, associates, investments and key management personnel.
Financial risk management	Our activities expose us to a variety of financial risks including credit risk, liquidity risk, capital risk, currency risk, interest rate risk, inflation risk and commodity price risk. Our risk management programme focuses on the unpredictability of financial markets and seeks to minimise potential volatility of financial performance from these risks. We use financial instruments, including derivative financial instruments, to manage these risks.
Sensitivities	In order to give a clearer picture of the impact on our results or financial position of potential changes in significant estimates and assumptions, the following sensitivities are presented. These sensitivities are based on assumptions and conditions prevailing at the year-end and should be used with caution. The effects provided are not necessarily indicative of the actual effects that would be experienced because our actual exposures are constantly changing.
Additional disclosures in respect of guaranteed securities	We have preferred shares that are listed on a US national securities exchange and are guaranteed by other companies in the Group. These guarantors commit to honour any liabilities should the company issuing the debt have any financial difficulties. In order to provide debt holders with information on the financial stability of the companies providing the guarantees, we are required to disclose individual financial information for these companies. We have chosen to include this information in the Group financial statements rather than submitting separate stand-alone financial statements.

Segmental analysis (Tables)

Segmental analysis (Tables)	12 Months Ended
	Mar. 31, 2020
Operating Segments [Abstract]
Schedule of operating segments	A reconciliation of the operating segments’ measure of profit to profit before tax from continuing operations is provided below. Further details of the exceptional items and remeasurements are provided in note 5 . Before exceptional items After exceptional items 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m Operating segments – continuing operations: UK Electricity Transmission 1,320 1,015 1,041 1,316 778 1,041 UK Gas Transmission 348 303 487 347 267 487 US Regulated 1,397 1,724 1,698 880 1,425 1,734 NGV and Other 1,2 242 400 231 237 400 231 Total operating profit from continuing operations 3,307 3,442 3,457 2,780 2,870 3,493 Split by geographical area – continuing operations: UK 1,925 1,695 1,840 1,915 1,422 1,840 US 1,382 1,747 1,617 865 1,448 1,653 3,307 3,442 3,457 2,780 2,870 3,493 Below we reconcile total operating profit from continuing operations to profit before tax from continuing operations. Total operating exceptional items and remeasurements of £527 million charge ( 2019 : £572 million charge ; 2018: £36 million gain ) are detailed in note 5 . This is comprised of a £4 million charge ( 2019 : £237 million charge ; 2018 : £nil ) attributable to UK Electricity Transmission; £1 million charge ( 2019 : £36 million charge ; 2018 : £nil ) to UK Gas Transmission; £517 million charge ( 2019 : £299 million charge ; 2018 : £36 million gain ) to US Regulated; and £5 million charge ( 2019 : £nil ; 2018 : £nil ) to NGV and Other. Reconciliation to profit before tax: Operating profit from continuing operations 3,307 3,442 3,457 2,780 2,870 3,493 Finance income 70 73 127 54 88 127 Finance costs (1,119 ) (1,066 ) (1,128 ) (1,167 ) (1,157 ) (1,009 ) Share of post-tax results of joint ventures and associates 88 40 44 87 40 49 Profit before tax from continuing operations 2,346 2,489 2,500 1,754 1,841 2,660 1. Included within NGV and Other is £269 million ( 2019 : £263 million ; 2018 : £234 million ) of operating profit before exceptional items and remeasurements and £268 million of operating profit after exceptional items and remeasurements ( 2019 : £263 million ; 2018 : £234 million ), relating to NGV. 2. In 2019 , NGV and Other included gains of £95 million in relation to cash received in respect of two legal settlements. The following table describes the main activities for each reportable operating segment: UK Electricity Transmission The high-voltage electricity transmission networks in England and Wales and independent Great Britain system operator. UK Gas Transmission The high-pressure gas transmission networks in Great Britain and system operator in Great Britain. US Regulated Gas distribution networks, electricity distribution networks and high-voltage electricity transmission networks in New York and New England and electricity generation facilities in New York. Net book value of property, plant and Capital expenditure Depreciation, amortisation and impairment 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Operating segments: UK Electricity Transmission 13,788 13,288 13,028 1,043 925 999 (469 ) (628 ) (475 ) UK Gas Transmission 4,513 4,412 4,280 249 308 310 (171 ) (181 ) (194 ) US Regulated² 29,623 24,542 20,953 3,228 2,650 2,424 (855 ) (700 ) (635 ) NGV and Other 1,2 2,141 2,755 2,491 559 438 341 (145 ) (226 ) (226 ) Total from continuing operations 50,065 44,997 40,752 5,079 4,321 4,074 (1,640 ) (1,735 ) (1,530 ) Split by geographical area – continuing operations: UK 20,427 19,343 18,772 1,847 1,584 1,527 (784 ) (931 ) (804 ) US 29,638 25,654 21,980 3,232 2,737 2,547 (856 ) (804 ) (726 ) 50,065 44,997 40,752 5,079 4,321 4,074 (1,640 ) (1,735 ) (1,530 ) Asset type: Property, plant and equipment 48,770 43,913 39,853 4,727 4,015 3,901 (1,464 ) (1,560 ) (1,392 ) Non-current intangible assets 1,295 1,084 899 352 306 173 (176 ) (175 ) (138 ) Total from continuing operations 50,065 44,997 40,752 5,079 4,321 4,074 (1,640 ) (1,735 ) (1,530 ) 1. Included within NGV and Other are assets with a net book value of £2,080 million ( 2019 : £1,635 million ; 2018 : £1,454 million ), capital expenditure of £550 million ( 2019 : £317 million ; 2018 : £186 million ) and depreciation, amortisation and impairment of £124 million ( 2019 : £114 million ; 2018 : £143 million ) relating to NGV. 2. In 2020, US Regulated includes certain software assets and properties in the US which are outside the US rate base and operate for the benefit of our US regulated businesses. These assets were included within NGV and Other in 2019 and 2018. The assets had a net book value of £1,062 million in 2019 and £998 million in 2018, capital expenditure of £87 million in 2019 and £161 million in 2018 and depreciation, amortisation and impairment of £102 million in 2019 and £80 million in 2018. 2020 2019 2018 Total £m Sales between segments £m Sales to third parties £m Total Sales Sales Total Sales Sales Operating segments – continuing operations: UK Electricity Transmission 3,702 (8 ) 3,694 3,351 (20 ) 3,331 4,154 (28 ) 4,126 UK Gas Transmission 927 (16 ) 911 896 (12 ) 884 1,091 (9 ) 1,082 US Regulated 9,205 — 9,205 9,846 — 9,846 9,272 — 9,272 NGV and Other¹ 736 (6 ) 730 876 (4 ) 872 776 (6 ) 770 Total revenue from continuing operations 14,570 (30 ) 14,540 14,969 (36 ) 14,933 15,293 (43 ) 15,250 Split by geographical areas – continuing operations: UK 5,282 5,045 5,938 US 9,258 9,888 9,312 14,540 14,933 15,250 1. Included within NGV and Other is £608 million ( 2019 : £597 million ; 2018 : £593 million ) of revenue relating to NGV.

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Mar. 31, 2020
Disclosure of revenue from contracts with customers [Abstract]
Disclosure of disaggregation of revenue from contracts with customers	In the following tables, revenue is disaggregated by primary geographical market and major service lines. The table reconciles disaggregated revenue with the Group’s reportable segments (see note 2 ). Revenue for the year ended 31 March 2020 UK Electricity Transmission UK Gas Transmission US Regulated NGV and Other Total Revenue under IFRS 15 Transmission 1,992 649 425 309 3,375 Distribution — — 8,319 — 8,319 System Operator 1,610 214 — — 1,824 Other 69 15 12 296 392 Total IFRS 15 revenue 3,671 878 8,756 605 13,910 Other revenue Generation — — 369 — 369 Other 23 33 80 125 261 Total other revenue 23 33 449 125 630 Total revenue from continuing operations 3,694 911 9,205 730 14,540 Geographical split for the year ended 31 March 2020 UK Electricity Transmission £m UK Gas Transmission £m US Regulated £m NGV and Other £m Total £m Revenue under IFRS 15 UK 3,671 878 — 567 5,116 US — — 8,756 38 8,794 Total IFRS 15 revenue 3,671 878 8,756 605 13,910 Other revenue UK 23 33 — 110 166 US — — 449 15 464 Total other revenue 23 33 449 125 630 Total revenue from continuing operations 3,694 911 9,205 730 14,540 3. Revenue continued (e) Disaggregation of revenue continued Revenue for the year ended 31 March 2019 UK Electricity Transmission UK Gas Transmission US Regulated NGV and Other Total Revenue under IFRS 15 Transmission 1,909 661 370 313 3,253 Distribution — — 8,941 — 8,941 System Operator 1,416 172 — — 1,588 Other — — — 284 284 Total IFRS 15 revenue 3,325 833 9,311 597 14,066 Other revenue Generation — — 367 — 367 Other 6 51 168 275 500 Total other revenue 6 51 535 275 867 Total revenue from continuing operations 3,331 884 9,846 872 14,933 Geographical split for the year ended 31 March 2019 UK Electricity Transmission £m UK Gas Transmission £m US Regulated £m NGV and Other £m Total £m Revenue under IFRS 15 UK 3,325 833 — 585 4,743 US — — 9,311 12 9,323 Total IFRS 15 revenue 3,325 833 9,311 597 14,066 Other revenue UK 6 51 — 245 302 US — — 535 30 565 Total other revenue 6 51 535 275 867 Total revenue from continuing operations 3,331 884 9,846 872 14,933

Operating costs (Tables)

Operating costs (Tables)	12 Months Ended
	Mar. 31, 2020
Analysis of income and expense [abstract]
Schedule of expenses by nature	2020 2019 2018 £m £m £m Depreciation, amortisation and impairment 1,640 1,735 1,530 Payroll costs 1,684 1,852 1,648 Provision for bad and doubtful debts 234 181 36 Purchases of electricity 1,403 1,454 1,285 Purchases of gas 1,316 1,642 1,543 Property and other taxes 1,191 1,108 1,057 Balancing Services Incentive Scheme 1,317 1,196 1,012 Payments to other UK network owners¹ — — 1,043 Other 2,975 2,895 2,603 11,760 12,063 11,757 Operating costs include: Inventory consumed 328 415 367 Research and development expenditure 14 19 13 1. Under IFRS 15, with effect from 1 April 2018, revenue and associated payments to other UK network owners are presented on a net basis. (a) Payroll costs 2020 2019 2018 £m £m £m Wages and salaries¹ 2,188 2,084 1,998 Social security costs 168 156 157 Defined contribution scheme costs 75 72 65 Defined benefit pension costs 135 232 156 Share-based payments 19 27 16 Severance costs (excluding pension costs) 1 76 7 2,586 2,647 2,399 Less: payroll costs capitalised (902 ) (795 ) (751 ) Total payroll costs 1,684 1,852 1,648 1. Included within wages and salaries are US other post-retirement benefit costs of £45 million ( 2019 : £48 million ; 2018 : £46 million ). For further information refer to note 25.
Schedule of additional information	Auditors’ remuneration is presented below in accordance with the requirements of the Companies Act 2006 and the principal accountant fees and services disclosure requirements of Item 16C of Form 20-F: 2020 2019 2018 £m £m £m Audit fees payable to the parent Company’s auditors and their associates in respect of: Audit of the parent Company’s individual and consolidated financial statements¹ 1.9 1.6 2.7 The auditing of accounts of any associate of the Company² 8.7 8.5 9.3 Other services supplied³ 6.3 5.2 3.9 16.9 15.3 15.9 Total other services 4 Tax fees: Tax compliance services — — 0.3 Tax advisory services — — — All other fees: Other assurance services 5 0.6 1.1 0.7 Services relating to corporate finance transactions not covered above — — — Other non-audit services not covered above 6 0.5 2.2 0.9 1.1 3.3 1.9 Total auditors’ remuneration 18.0 18.6 17.8 1. Audit fees in each year represent fees for the audit of the Company’s financial statements and regulatory reporting for the years ended 31 March 2020 , 2019 and 2018 . 2. The 2019 comparative has been updated following finalisation of the 2019 audit fee with the Audit Committee. 3. Other services supplied represent fees payable for services in relation to other statutory filings or engagements that are required to be carried out by the auditors. In particular, this includes fees for reports under section 404 of the US Public Company Accounting Reform and Investor Protection Act of 2002 (Sarbanes-Oxley), audit reports on regulatory returns and the review of interim financial statements for the six-month periods ended 30 September 2019 , 2018 and 2017 respectively. 4. There were no audit related fees as described in Item 16C(b) of Form 20-F. 5. Principally amounts relating to assurance services provided in relation to comfort letters for debt issuances. 6. In 2020 , non-audit services include auction monitor work on Contracts for Difference, IT project assurance and a review of controls over our data on New York customers. In 2019 and 2018 , non-audit services primarily related to the UK Property business in respect of the evaluation of possible options for the use of property assets. (b) Number of employees 31 March Monthly 31 March Monthly 31 March Monthly UK 6,321 6,151 5,962 6,227 6,517 6,431 US 16,748 16,679 16,614 16,669 16,506 16,274 Total number of employees 23,069 22,830 22,576 22,896 23,023 22,705 4. Operating costs continued (c) Key management compensation 2020 2019 2018 £m £m £m Short-term employee benefits 7 7 8 Compensation for loss of office 1 — — Post-employment benefits 1 1 1 Share-based payments 3 3 3 Total key management compensation 12 11 12

Exceptional items and remeasu_2

Exceptional items and remeasurements (Tables)	12 Months Ended
	Mar. 31, 2020
Exceptional Items And Remeasurements [Abstract]
Schedule of exceptional items and remeasurements from continuing operations	Exceptional items and remeasurements from continuing operations 2020 2019 2018 £m £m £m Included within operating profit Exceptional items: Environmental charges (402 ) — — Cost efficiency and restructuring programmes — (204 ) — Massachusetts Gas labour dispute — (283 ) — Impairment of nuclear connection development costs — (137 ) — Final settlement of LIPA MSA Transition — — 26 (402 ) (624 ) 26 Remeasurements – commodity contract derivatives (125 ) 52 10 (527 ) (572 ) 36 As disclosed in note 8, the Group also presents an adjusted earnings per share measure that is calculated before exceptional items and remeasurements. This measure is presented after tax and therefore details of tax exceptional items and the tax effect of exceptional items and remeasurements are also provided in this note. 2020 2019 2018 £m £m £m Included within finance income and costs Remeasurements: Net gains/(losses) on financing derivatives 1 (40 ) 119 Net (losses)/gains on financial assets at fair value through profit and loss (16 ) 15 — Net losses on financial liabilities at fair value through profit and loss (49 ) (51 ) — (64 ) (76 ) 119 Included within share of post-tax results of joint ventures and associates Exceptional items: Deferred tax arising on the reduction in US corporation tax rate — — 5 Remeasurements: Net losses on financial instruments (1 ) — — Total included within profit before tax (592 ) (648 ) 160 Included within tax Exceptional items – credits/(debits) arising on items not included in profit before tax: Deferred tax arising on the reduction in the US corporation tax rate — — 1,510 Deferred tax arising on the reversal of the reduction in UK corporation tax rate (192 ) — — Tax on exceptional items 103 144 (9 ) Tax on remeasurements 42 5 (28 ) (47 ) 149 1,473 Total exceptional items and remeasurements after tax (639 ) (499 ) 1,633 Analysis of total exceptional items and remeasurements after tax Exceptional items after tax (491 ) (480 ) 1,532 Remeasurements after tax (148 ) (19 ) 101 Total exceptional items and remeasurements after tax (639 ) (499 ) 1,633

Finance income and costs (Table

Finance income and costs (Tables)	12 Months Ended
	Mar. 31, 2020
Analysis of income and expense [abstract]
Schedule of finance income and costs	2020 2019 2018 Notes £m £m £m Finance income Interest income on financial instruments: Bank deposits and other financial assets 48 54 54 Dividends received on equities held at fair value through other comprehensive income 2 2 — Gains on disposal of available-for-sale investments — — 73 Other income 20 17 — 70 73 127 Finance costs Net interest on pensions and other post-retirement benefit obligations 25 (23 ) (22 ) (65 ) Interest expense on financial liabilities held at amortised cost: Bank loans and overdrafts (73 ) (72 ) (87 ) Other borrowings¹ (997 ) (970 ) (1,030 ) Interest expense on financial liabilities held at fair value through profit and loss (22 ) (20 ) — Derivatives (39 ) (43 ) 12 Unwinding of discount on provisions 26 (77 ) (74 ) (75 ) Other interest (10 ) — (11 ) Less: interest capitalised² 122 135 128 (1,119 ) (1,066 ) (1,128 ) Remeasurements – Finance income Net (losses)/gains on financial assets held at fair value through profit and loss (16 ) 15 — (16 ) 15 — Remeasurements – Finance costs Net losses on financial liabilities held at fair value through profit and loss (49 ) (51 ) — Net (losses)/gains on financing derivatives³: Derivatives designated as hedges for hedge accounting (13 ) (37 ) 49 Derivatives not designated as hedges for hedge accounting 14 (3 ) 70 (48 ) (91 ) 119 Total remeasurements – Finance income and costs (64 ) (76 ) 119 Finance income 54 88 127 Finance costs (1,167 ) (1,157 ) (1,009 ) Net finance costs from continuing operations (1,113 ) (1,069 ) (882 ) 1. Includes interest expense on lease liabilities (see note 13 for details). 2. Interest on funding attributable to assets in the course of construction in the current year was capitalised at a rate of 3.6% ( 2019 : 3.9% ; 2018 : 4.1% ). In the UK, capitalised interest qualifies for a current year tax deduction with tax relief claimed of £15 million ( 2019 : £19 million ; 2018 : £20 million ). In the US, capitalised interest is added to the cost of plant and qualifies for tax depreciation allowances. 3. Includes a net foreign exchange gain on financing activities of £66 million ( 2019 : £264 million gain ; 2018 : £314 million loss ) offset by foreign exchange losses and gains on financing derivatives measured at fair value.

Tax (Tables)

Tax (Tables)	12 Months Ended
	Mar. 31, 2020
Income Taxes [Abstract]
Disclosure of major components of tax expense (income)	The tax charge/(credit) for the year can be analysed as follows: 2020 2019 2018 £m £m £m Current tax: UK corporation tax at 19% (2019: 19%; 2018: 19%) 179 132 200 UK corporation tax adjustment in respect of prior years (4 ) (12 ) (18 ) 175 120 182 Overseas corporation tax (2 ) 8 15 Overseas corporation tax adjustment in respect of prior years (41 ) (40 ) (4 ) (43 ) (32 ) 11 Total current tax from continuing operations 132 88 193 Deferred tax: UK deferred tax 269 27 65 UK deferred tax adjustment in respect of prior years 6 2 (2 ) 275 29 63 Overseas deferred tax 64 208 (1,155 ) Overseas deferred tax adjustment in respect of prior years 9 14 10 73 222 (1,145 ) Total deferred tax from continuing operations 348 251 (1,082 ) Total tax charge/(credit) from continuing operations 480 339 (889 )
Disclosure of tax charged/(credited) to the consolidated statement of comprehensive income and equity	Tax charged/(credited) to the consolidated statement of comprehensive income and equity 2020 2019 2018 £m £m £m Current tax: Available-for-sale investments — — (11 ) Cash flow hedges, cost of hedging and own credit reserve — 3 — Share-based payments — — (3 ) Deferred tax: Available-for-sale investments — — (18 ) Investments at fair value through other comprehensive income (1 ) — — Cash flow hedges, cost of hedging and own credit reserve (40 ) (12 ) (4 ) Remeasurements of pension assets and post-retirement benefit obligations¹ (206 ) 12 530 Share-based payments (3 ) — 1 (250 ) 3 495 Total tax recognised in the statements of comprehensive income from continuing operations (247 ) 3 497 Total tax relating to share-based payments recognised directly in equity from continuing operations (3 ) — (2 ) (250 ) 3 495 1. Remeasurements of gains on pension assets and post-retirement benefit obligations for the year ended 31 March 2018 includes a deferred tax charge of £281 million arising on the reduction in the US corporation tax rate.
Disclosure of reconciliation of accounting profit multiplied by applicable tax rates and average effective tax rate	The tax charge/(credit) for the year for the continuing business, is higher ( 2019 : lower tax charge; 2018 : lower tax charge) than the standard rate of corporation tax in the UK of 19% ( 2019 : 19% ; 2018 : 19% ): 2020 2019 2018 £m £m £m Profit before tax from continuing operations Before exceptional items and remeasurements 2,346 2,489 2,500 Exceptional items and remeasurements (592 ) (648 ) 160 Profit before tax from continuing operations 1,754 1,841 2,660 Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2019: 19%; 2018: 19%) 334 350 506 Effect of: Adjustments in respect of prior years¹ (30 ) (36 ) (14 ) Expenses not deductible for tax purposes 29 28 21 Non-taxable income² (18 ) (36 ) (26 ) Adjustment in respect of foreign tax rates 18 56 157 Deferred tax impact of change in UK tax rate 192 (3 ) (7 ) Deferred tax impact of change in US tax rate due to Tax Reform — — (1,510 ) Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax (17 ) (8 ) (9 ) Other³ (28 ) (12 ) (7 ) Total tax charge/(credit) from continuing operations 480 339 (889 ) % % % Effective tax rate – continuing operations 27.4 18.4 (33.4 ) 1. Prior year adjustment is primarily due to agreement of prior period tax returns. 2. Includes gains on chargeable disposals which are offset by previously unrecognised capital losses. 3. Other primarily comprises a recognition of deferred tax on previously unrecognised capital losses and claims for land remediation relief.
Disclosure of temporary difference, unused tax losses and unused tax credits	The following are the major deferred tax assets and liabilities recognised, and the movements thereon, during the current and prior reporting periods: Accelerated Share- Pensions Financial Other net differences 1 £m Total Deferred tax liabilities/(assets) At 31 March 2018 (as previously reported) 4,874 (9 ) (203 ) 21 (1,047 ) 3,636 Impact of transition to IFRS 9 and IFRS 15 19 — — (5 ) (93 ) (79 ) At 1 April 2018 (as restated) 4,893 (9 ) (203 ) 16 (1,140 ) 3,557 Exchange adjustments and other² 275 — (31 ) (3 ) (76 ) 165 (Credited)/charged to income statement 309 — 52 6 (124 ) 243 Charged/(credited) to other comprehensive income and equity — — 12 (12 ) — — At 1 April 2019 5,477 (9 ) (170 ) 7 (1,340 ) 3,965 Exchange adjustments and other² 210 (30 ) (28 ) (3 ) (27 ) 122 (Credited)/charged to income statement 613 (7 ) 44 (13 ) (287 ) 350 Charged/(credited) to other comprehensive income and equity — (2 ) (206 ) (46 ) 1 (253 ) At 31 March 2020 6,300 (48 ) (360 ) (55 ) (1,653 ) 4,184 1. The deferred tax asset of £1,653 million as at 31 March 2020 ( 2019 : £1,340 million ) in respect of other net temporary differences primarily relates to net operating losses of £547 million ( 2019 : £423 million ) and US environmental provisions of £529 million ( 2019 : £409 million ). 2. Exchange adjustments and other comprises foreign exchange arising on translation of the US dollar deferred tax balances. It also includes reclassification of £29 million from other temporary differences to share-based payments. Deferred tax assets in respect of some capital losses as well as trading losses and non-trade deficits have not been recognised as their future recovery is uncertain or not currently anticipated. The deferred tax asset not recognised relating to capital losses has increased due to remeasurement of opening deferred tax asset as a result of change in substantively enacted UK corporation tax rate from 17% to 19%. Hence the total deferred tax assets not recognised are as follows: 2020 2019 £m £m Capital losses 1,626 1,470 Non-trade deficits 1 4 Trading losses 6 5

Earnings per share (EPS) (Table

Earnings per share (EPS) (Tables)	12 Months Ended
	Mar. 31, 2020
Earnings per share [abstract]
Schedule of earnings per share	(a) Basic EPS Earnings EPS Earnings EPS Earnings EPS 2020 2020 2019 2019 2018 2018 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,912 55.2 1,998 59.0 1,915 55.3 Exceptional items and remeasurements after tax from continuing operations (639 ) (18.4 ) (499 ) (14.7 ) 1,633 47.2 Earnings from continuing operations 1,273 36.8 1,499 44.3 3,548 102.5 Adjusted earnings from discontinued operations 5 0.2 57 1.7 145 4.2 Exceptional items and remeasurements after tax from discontinued operations (14 ) (0.5 ) (45 ) (1.4 ) (143 ) (4.1 ) Earnings from discontinued operations (9 ) (0.3 ) 12 0.3 2 0.1 Total adjusted earnings 1,917 55.4 2,055 60.7 2,060 59.5 Total exceptional items and remeasurements after tax (including discontinued operations) (653 ) (18.9 ) (544 ) (16.1 ) 1,490 43.1 Total earnings 1,264 36.5 1,511 44.6 3,550 102.6 2020 2019 2018 millions millions millions Weighted average number of ordinary shares – basic 3,461 3,386 3,461 (b) Diluted EPS Earnings EPS Earnings EPS Earnings EPS 2020 2020 2019 2019 2018 2018 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,912 55.0 1,998 58.8 1,915 55.1 Exceptional items and remeasurements after tax from continuing operations (639 ) (18.4 ) (499 ) (14.7 ) 1,633 47.0 Earnings from continuing operations 1,273 36.6 1,499 44.1 3,548 102.1 Adjusted earnings from discontinued operations 5 0.1 57 1.7 145 4.2 Exceptional items and remeasurements after tax from discontinued operations (14 ) (0.4 ) (45 ) (1.4 ) (143 ) (4.2 ) Earnings from discontinued operations (9 ) (0.3 ) 12 0.3 2 — Total adjusted earnings 1,917 55.1 2,055 60.5 2,060 59.3 Total exceptional items and remeasurements after tax (including discontinued operations) (653 ) (18.8 ) (544 ) (16.1 ) 1,490 42.8 Total earnings 1,264 36.3 1,511 44.4 3,550 102.1 2020 2019 2018 millions millions millions Weighted average number of ordinary shares – diluted 3,478 3,401 3,476 (c) Reconciliation of basic to diluted average number of shares 2020 2019 2018 millions millions millions Weighted average number of ordinary shares – basic 3,461 3,386 3,461 Effect of dilutive potential ordinary shares – employee share plans 17 15 15 Weighted average number of ordinary shares – diluted 3,478 3,401 3,476

Dividends (Tables)

Dividends (Tables)	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Schedule of Dividends to Shareholders	2020 2019 2018 Pence per share Cash dividend paid £m Scrip dividend £m Pence per share Cash dividend paid £m Scrip dividend £m Pence per share Cash dividend paid £m Scrip dividend £m Interim dividend in respect of the current year 16.57 335 241 16.08 450 94 15.49 346 176 Special dividend — — — — — — 84.375 3,171 — Final dividend in respect of the prior year 31.26 557 517 30.44 710 319 29.10 970 33 47.83 892 758 46.52 1,160 413 128.965 4,487 209

Discontinued operations and a_2

Discontinued operations and assets held for sale (Tables)	12 Months Ended
	Mar. 31, 2020
Non-current Assets Held For Sale And Discontinued Operations [Abstract]
Schedule of discontinued operations	The summary income statement for discontinued operations is as follows: 2020 2019 2018 £m £m £m Revenue — — — Operating costs¹ (23 ) (1 ) (41 ) Operating loss (23 ) (1 ) (41 ) Net finance income 6 23 137 Share of post-tax results of joint ventures and associates² — (5 ) (89 ) (Loss)/profit before tax from discontinued operations (17 ) 17 7 Tax from discontinued operations (1 ) (5 ) (5 ) (Loss)/profit after tax from discontinued operations (18 ) 12 2 Gain on disposal 9 — — Total (loss)/profit after tax from discontinued operations³ (9 ) 12 2 1. Operating costs for the year ended 31 March 2020 relate to final transaction costs and other expenses in relation to Quadgas. Operating costs of £41 million for the year ended 31 March 2018 related to amounts in respect of the disposal of the UK Gas Distribution business, primarily relating to the completion accounts settlement in November 2017. 2. For the year ended 31 March 2019, the amount presented is the net of £43 million impairment charge against the investment in Quadgas (see note 16) and £38 million share of Quadgas post-tax profits recognised prior to classification as held for sale. 3. Of the total profit after tax from discontinued operations, the £23 million of operating expenses and the £9 million gain on disposal are treated as exceptional. For the year ended 31 March 2019, the £43 million impairment charge against the investment in Quadgas, net operating costs of £1 million and the tax thereon are classified as exceptional items. The summary statement of comprehensive income for discontinued operations is as follows: 2020 2019 2018 £m £m £m (Loss)/profit after tax from discontinued operations (9 ) 12 2 Other comprehensive income Items that will never be reclassified to profit or loss: Share of other comprehensive income of associate, net of tax — 36 142 Total items from discontinued operations that will never be reclassified to profit or loss — 36 142 Items that may be reclassified subsequently to profit or loss: Net gains in respect of cash flow hedges 6 — — Share of other comprehensive income of associate, net of tax — — 5 Total items from discontinued operations that may be reclassified subsequently to profit or loss 6 — 5 Other comprehensive income for the year, net of tax from discontinued operations 6 36 147 Total comprehensive (loss)/income for the year from discontinued operations (3 ) 48 149

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Mar. 31, 2020
Intangible Assets [Abstract]
Schedule of changes in intangible assets and goodwill	Impairments are recognised in the income statement and are disclosed separately. Total £m Net book value at 1 April 2018 5,444 Exchange adjustments 425 Net book value at 31 March 2019 5,869 Additions 81 Exchange adjustments 283 Net book value at 31 March 2020 6,233

Other intangible assets (Tables

Other intangible assets (Tables)	12 Months Ended
	Mar. 31, 2020
Intangible Assets [Abstract]
Schedule of intangible assets	Other intangible assets are amortised on a straight-line basis over their estimated useful economic lives. Amortisation periods for intangible assets are: Years Software 1 to 10 Software £m Cost at 1 April 2018 1,797 Exchange adjustments 70 Additions 306 Disposals (15 ) Reclassifications¹ 10 Cost at 31 March 2019 2,168 Exchange adjustments 63 Additions 352 Disposals — Reclassifications¹ — Cost at 31 March 2020 2,583 Accumulated amortisation at 1 April 2018 (898 ) Exchange adjustments (26 ) Amortisation charge for the year (175 ) Accumulated amortisation of disposals 15 Accumulated amortisation at 31 March 2019 (1,084 ) Exchange adjustments (28 ) Amortisation charge for the year (176 ) Accumulated amortisation of disposals — Accumulated amortisation at 31 March 2020 (1,288 ) Net book value at 31 March 2020² 1,295 Net book value at 31 March 2019 1,084 1. Reclassifications includes amounts transferred from property, plant and equipment (see note 13). 2. Included in software is £69 million ( 2019 : £116 million ) relating to the US Enterprise Resource Planning system, which still has a remaining amortisation period of three years.

Property, plant and equipment (

Property, plant and equipment (Tables)	12 Months Ended
	Mar. 31, 2020
Property, plant and equipment [abstract]
Schedule of property, plant and equipment	Given the uncertainty described relating to the UELs of our gas assets, below we provide a sensitivity on the depreciation charge for our UK and US regulated segments were a shorter UEL presumed: Increase in depreciation expense UK regulated £m US regulated £m UELs limited to 2050 37 151 UELs limited to 2060 13 66 UELs limited to 2070 — 26 2020 2019 £m £m Information in relation to property, plant and equipment Capitalised interest included within cost 2,118 1,995 Contributions to cost of property, plant and equipment included within: Trade and other payables 84 87 Non-current liabilities 428 372 Contract liabilities – current 76 61 Contract liabilities – non-current 1,082 933 Unless otherwise determined by operational requirements, the depreciation periods for the principal categories of property, plant and equipment are, in general, as shown in the table below split between the UK and US, along with the weighted average remaining UEL for each class of property, plant and equipment (which is calculated by applying the annual depreciation charge per class of asset by the net book value of that class of asset). Years UK US Weighted average remaining UEL Freehold and leasehold buildings up to 60 up to 100 26 Plant and machinery: Electricity transmission plant and wires 10 to 100 45 to 80 40 Electricity distribution plant n/a 35 to 85 37 Electricity generation plant 15 to 40 20 to 93 21 Interconnector plant and other 5 to 60 8 to 50 23 Gas plant – mains, services and regulating equipment 10 to 65 47 to 95 49 Gas plant – storage 5 to 40 12 to 65 13 Gas plant – meters 7 to 30 14 to 65 18 Motor vehicles and office equipment up to 10 up to 26 5 Land and buildings £m Plant and machinery £m Assets in the course of construction 1 £m Motor vehicles and office equipment £m Total £m Cost at 1 April 2018 2,930 49,374 4,273 857 57,434 Exchange adjustments 114 2,001 70 47 2,232 Additions 34 391 3,533 57 4,015 Disposals (35 ) (357 ) (159 ) (44 ) (595 ) Reclassifications² 295 2,974 (3,292 ) 13 (10 ) Cost at 1 April 2019 (as previously reported) 3,338 54,383 4,425 930 63,076 Right-of-use assets recognised on transition to IFRS 16³ 381 67 — 20 468 Cost at 1 April 2019 (as restated) 3,719 54,450 4,425 950 63,544 Exchange adjustments 98 1,511 53 33 1,695 Additions 130 464 4,029 104 4,727 Disposals (79 ) (486 ) (9 ) (65 ) (639 ) Reclassifications 2,4 29 4,303 (4,433 ) 14 (87 ) Cost at 31 March 2020 3,897 60,242 4,065 1,036 69,240 Accumulated depreciation at 1 April 2018 (674 ) (16,398 ) — (509 ) (17,581 ) Exchange adjustments (19 ) (501 ) — (25 ) (545 ) Depreciation charge for the year (93 ) (1,229 ) (150 ) (101 ) (1,573 ) Disposals 7 335 150 44 536 Reclassifications² 1 (1 ) — — — Accumulated depreciation at 1 April 2019 (778 ) (17,794 ) — (591 ) (19,163 ) Exchange adjustments (16 ) (372 ) — (20 ) (408 ) Depreciation charge for the year (92 ) (1,252 ) — (120 ) (1,464 ) Disposals 36 464 — 58 558 Reclassifications² 3 (7 ) — 11 7 Accumulated depreciation at 31 March 2020 (847 ) (18,961 ) — (662 ) (20,470 ) Net book value at 31 March 2020 3,050 41,281 4,065 374 48,770 Net book value at 31 March 2019 2,560 36,589 4,425 339 43,913 1. In 2019, included within disposals are UK nuclear connections development costs of £150 million (before £13 million of termination income) which were written off. See note 5 for further details. 2. Represents amounts transferred between categories, (to)/from other intangible assets (see note 12), reclassifications from inventories and reclassifications between cost and accumulated depreciation. 3. £468 million of additional right-of-use assets were recognised on transition to IFRS 16 on 1 April 2019. See note 37 for details. 4. Comprises an £87 million reduction in gross cost of assets in the course of construction in our UK Electricity Transmission business for costs previously capitalised and accrued as due to a supplier that are no longer payable.
Schedule of information about right-of-use assets	Included within the net book value of property, plant and equipment at 31 March 2020 are right-of-use assets, split as follows: Land and buildings £m Plant and machinery £m Assets in the course of construction £m Motor vehicles and office equipment £m Total Net book value at 31 March 2020 364 95 — 225 684 Additions 10 1 — 73 84 Depreciation charge for the year ended 31 March 2020 (29 ) (16 ) — (72 ) (117 ) The following balances have been included in the income statement for the year ended 31 March 2020 in respect of right-of-use assets: Total Included within net finance income and costs: Interest expense on lease liabilities (26 ) Included within revenue: Lease income 35 Included within operating expenses: Expenses relating to low-value leases (12 )

Other non-current assets (Table

Other non-current assets (Tables)	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Schedule of other non current assets	2020 2019 £m £m Other receivables 35 28 Non-current tax assets 65 56 Prepayments 19 7 Accrued income¹ 235 173 354 264 1. Includes accrued income in relation to property sales to the St William joint venture.

Financial and other investmen_2

Financial and other investments (Tables)	12 Months Ended
	Mar. 31, 2020
Disclosure of financial assets [abstract]
Schedule of financial assets	2020 2019 £m £m Non-current Debt and other investments at fair value through other comprehensive income 352 343 Equity investments at fair value through other comprehensive income 83 93 Investments at fair value through profit and loss 108 62 Loans to joint ventures¹ — 169 543 667 Current Investments at fair value through profit and loss 1,278 1,311 Financial assets at amortised cost 720 670 1,998 1,981 2,541 2,648 Financial and other investments include the following: Investments in short-term money funds² 978 969 Insurance company fund investments³ 300 342 Equities 4 83 93 Bonds 4 132 122 Cash surrender value of life insurance policies 4 220 221 Loans to joint ventures — 169 National Grid Partners and other investments 5 108 62 Restricted balances: Collateral 6 685 637 Other 35 33 2,541 2,648 1. As at 31 March 2019 , this related to a loan to a joint venture, which was measured at amortised cost. 2. Includes £1 million ( 2019 : £6 million ) held as insurance company fund investments and £26 million ( 2019 : £22 million ) US non-qualified plan investments, and therefore restricted. 3. Includes restricted amounts of £300 million ( 2019 : £342 million ) held as insurance company fund investments. 4. Includes restricted amounts of £435 million ( 2019 : £436 million ) relating to US non-qualified plan investments. 5. This includes a series of small unquoted equity investments held by National Grid Partners of £97 million ( 2019 : £51 million ). 6. Refers to collateral placed with counterparties with whom we have entered into a credit support annex to the ISDA (International Swaps and Derivatives Association) Master Agreement.

Investments in joint ventures_2

Investments in joint ventures and associates (Tables)	12 Months Ended
	Mar. 31, 2020
Interests In Other Entities [Abstract]
Disclosure of joint ventures	Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Limited Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy Venture LLC 2020 2019 2020 2019 2020 2019 2020 £m £m £m £m £m £m £m Statement of financial position Non-current assets 399 370 971 937 582 537 435 Cash and cash equivalents 54 59 33 35 26 47 66 All other current assets 4 2 26 22 5 3 6 Non-current liabilities (45 ) (11 ) (315 ) (326 ) (29 ) 2 (232 ) Current liabilities (16 ) (28 ) (43 ) (84 ) (10 ) (375 ) (2 ) Net assets 396 392 672 584 574 214 273 Group’s ownership interest in joint venture/associate 198 196 176 153 287 107 139 Group adjustment: elimination of profits on sales to joint venture — — — — — — (10 ) Carrying amount of the Group’s investment 198 196 176 153 287 107 129 BritNed Development Limited Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy Venture LLC 2020 2019 2020 2019 2020 2019 2020 £m £m £m £m £m £m £m Income statement Revenue 80 87 206 166 45 12 19 Depreciation and amortisation (14 ) (13 ) (46 ) (34 ) (23 ) (4 ) (7 ) Other costs (10 ) (10 ) (20 ) (24 ) (8 ) (4 ) (10 ) Operating profit 56 64 140 108 14 4 2 Net interest expense — — (22 ) (11 ) — — (3 ) Profit before tax 56 64 118 97 14 4 (1 ) Income tax expense (10 ) (10 ) — — (2 ) — — Profit for the year 46 54 118 97 12 4 (1 ) Group’s share of profit/(loss) 23 27 31 25 6 2 (1 ) Group adjustment: Tax charge — — (9 ) — — — — Group’s share of post-tax results for the year 23 27 22 25 6 2 (1 ) 2020 2019 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 291 317 608 1,807 361 2,168 Exchange adjustments 20 12 32 17 (6 ) 11 Additions 16 156 172 58 85 143 Capitalisation of shareholder loan to Nemo Link Limited — 176 176 — — — Impairment charge against investment in Quadgas — — — (43 ) — (43 ) Transfer of interest in Quadgas to assets held for sale — — — (1,625 ) — (1,625 ) Share of post-tax results for the year 40 47 87 67 11 78 Share of other comprehensive income of associates, net of tax 1 — 1 37 — 37 Dividends received (41 ) (34 ) (75 ) (38 ) (30 ) (68 ) Other movements¹ 14 (20 ) (6 ) 11 (104 ) (93 ) Share of net assets at 31 March 341 654 995 291 317 608 1. Other movements on joint ventures relate to reducing the carrying value of the investment in St William Homes LLP to reflect deferred income we expect to recognise over the next 10 years .
Disclosure of associates	2020 2019 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 291 317 608 1,807 361 2,168 Exchange adjustments 20 12 32 17 (6 ) 11 Additions 16 156 172 58 85 143 Capitalisation of shareholder loan to Nemo Link Limited — 176 176 — — — Impairment charge against investment in Quadgas — — — (43 ) — (43 ) Transfer of interest in Quadgas to assets held for sale — — — (1,625 ) — (1,625 ) Share of post-tax results for the year 40 47 87 67 11 78 Share of other comprehensive income of associates, net of tax 1 — 1 37 — 37 Dividends received (41 ) (34 ) (75 ) (38 ) (30 ) (68 ) Other movements¹ 14 (20 ) (6 ) 11 (104 ) (93 ) Share of net assets at 31 March 341 654 995 291 317 608 1. Other movements on joint ventures relate to reducing the carrying value of the investment in St William Homes LLP to reflect deferred income we expect to recognise over the next 10 years . Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Limited Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy Venture LLC 2020 2019 2020 2019 2020 2019 2020 £m £m £m £m £m £m £m Statement of financial position Non-current assets 399 370 971 937 582 537 435 Cash and cash equivalents 54 59 33 35 26 47 66 All other current assets 4 2 26 22 5 3 6 Non-current liabilities (45 ) (11 ) (315 ) (326 ) (29 ) 2 (232 ) Current liabilities (16 ) (28 ) (43 ) (84 ) (10 ) (375 ) (2 ) Net assets 396 392 672 584 574 214 273 Group’s ownership interest in joint venture/associate 198 196 176 153 287 107 139 Group adjustment: elimination of profits on sales to joint venture — — — — — — (10 ) Carrying amount of the Group’s investment 198 196 176 153 287 107 129 BritNed Development Limited Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy Venture LLC 2020 2019 2020 2019 2020 2019 2020 £m £m £m £m £m £m £m Income statement Revenue 80 87 206 166 45 12 19 Depreciation and amortisation (14 ) (13 ) (46 ) (34 ) (23 ) (4 ) (7 ) Other costs (10 ) (10 ) (20 ) (24 ) (8 ) (4 ) (10 ) Operating profit 56 64 140 108 14 4 2 Net interest expense — — (22 ) (11 ) — — (3 ) Profit before tax 56 64 118 97 14 4 (1 ) Income tax expense (10 ) (10 ) — — (2 ) — — Profit for the year 46 54 118 97 12 4 (1 ) Group’s share of profit/(loss) 23 27 31 25 6 2 (1 ) Group adjustment: Tax charge — — (9 ) — — — — Group’s share of post-tax results for the year 23 27 22 25 6 2 (1 )

Derivative financial instrume_2

Derivative financial instruments (Tables)	12 Months Ended
	Mar. 31, 2020
Financial Instruments [Abstract]
Disclosure of detailed information about derivative financial instruments	The fair values of derivatives by category are as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Financing derivatives 1,267 (1,134 ) 133 1,052 (1,084 ) (32 ) Commodity contract derivatives 75 (200 ) (125 ) 101 (99 ) 2 1,342 (1,334 ) 8 1,153 (1,183 ) (30 ) The notional contract 1 amounts of financing derivatives by type are as follows: 2020 2019 £m £m Interest rate swaps (3,101 ) (6,299 ) Cross-currency interest rate swaps (8,097 ) (6,700 ) Foreign exchange forward contracts (3,284 ) (2,937 ) Inflation-linked swaps (500 ) (500 ) Equity options (800 ) (800 ) (15,782 ) (17,236 ) 1. The notional contract amounts of derivatives indicate the gross nominal value of transactions outstanding at the reporting date. The fair values of financing derivatives by type are as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Interest rate swaps 556 (337 ) 219 539 (384 ) 155 Cross-currency interest rate swaps 643 (514 ) 129 470 (443 ) 27 Foreign exchange forward contracts¹ 58 (39 ) 19 41 (41 ) — Inflation-linked swaps — (234 ) (234 ) — (214 ) (214 ) Equity options 10 (10 ) — 2 (2 ) — 1,267 (1,134 ) 133 1,052 (1,084 ) (32 ) 1. Included within the foreign exchange forward contracts balance is £(3) million ( 2019 : £32 million ) of derivatives in relation to hedging of capital expenditure. The notional quantities of commodity contract derivatives by type are as follows: 2020 2019 Forward purchases of gas 1 102m Dth 52m Dth Electricity swaps 12,836 GWh 12,848 GWh Electricity options 0 GWh 10,444 GWh Gas swaps 89m Dth 87m Dth Gas options 26m Dth 34m Dth 1. Forward gas purchases have terms up to four years ( 2019 : two years ). The contractual obligations under these contracts are £128 million ( 2019 : £108 million ). The fair values of commodity contract derivatives by type are as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets Liabilities £m Total £m Commodity purchase contracts accounted for as derivative contracts Forward purchases of gas 64 (108 ) (44 ) 66 (78 ) (12 ) Derivative financial instruments linked to commodity prices Electricity swaps 4 (83 ) (79 ) 29 (19 ) 10 Gas swaps 7 (8 ) (1 ) 5 (1 ) 4 Gas options — (1 ) (1 ) 1 (1 ) — 75 (200 ) (125 ) 101 (99 ) 2
Disclosure of maturity analysis for derivative financial liabilities	The maturity profile of financing derivatives is as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total Current Less than 1 year 62 (254 ) (192 ) 56 (282 ) (226 ) 62 (254 ) (192 ) 56 (282 ) (226 ) Non-current In 1 to 2 years 480 (51 ) 429 19 (193 ) (174 ) In 2 to 3 years 13 (5 ) 8 416 (1 ) 415 In 3 to 4 years 20 (28 ) (8 ) 11 — 11 In 4 to 5 years 31 (109 ) (78 ) 20 (14 ) 6 More than 5 years 661 (687 ) (26 ) 530 (594 ) (64 ) 1,205 (880 ) 325 996 (802 ) 194 1,267 (1,134 ) 133 1,052 (1,084 ) (32 ) The maturity profile of commodity contract derivatives is as follows: 2020 2019 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than one year 31 (126 ) (95 ) 52 (68) (16) 31 (126 ) (95 ) 52 (68) (16) Non-current In 1 to 2 years 8 (35 ) (27 ) 14 (9) 5 In 2 to 3 years 9 (24 ) (15 ) 9 (8) 1 In 3 to 4 years 8 (12 ) (4 ) 6 (4) 2 In 4 to 5 years 7 (1 ) 6 6 (4) 2 More than 5 years 12 (2 ) 10 14 (6) 8 44 (74 ) (30 ) 49 (31) 18 75 (200 ) (125 ) 101 (99) 2

Inventories and other current_2

Inventories and other current intangibles (Tables)	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Schedule of inventories	2020 2019 £m £m Fuel stocks 151 99 Raw materials and consumables 265 184 Current intangible assets – emission allowances 133 87 549 370

Trade and other receivables (Ta

Trade and other receivables (Tables)	12 Months Ended
	Mar. 31, 2020
Trade and other receivables [abstract]
Schedule of trade and other receivables	2020 2019 £m £m Trade receivables 1,551 1,899 Accrued income 869 883 Prepayments 408 237 Other receivables 158 134 2,986 3,153
Schedule of reconciliation of changes in allowance account for credit losses	2020 2019 £m £m At 1 April 394 309 Exchange adjustments 20 24 Charge for the year, net of recoveries 234 181 Uncollectible amounts written off (136 ) (120 ) At 31 March 512 394
Schedule of receivables by geographical area	The trade receivables balance, accrued income balance and provisions balance split by geography is as follows: As at 31 March 2020 As at 31 March 2019 UK US Total UK US Total £m £m £m £m £m £m Trade receivables 227 1,836 2,063 313 1,980 2,293 Accrued income 461 408 869 445 438 883 Provision for impairment of trade receivables (40 ) (472 ) (512 ) (40 ) (354 ) (394 )
Schedule of average expected loss rates and balances	The average expected loss rates and gross balances for the retail customer receivables in our US operations are set out below: 2020 2020 2019 2019 % £m % £m Unbilled revenue 5 395 — 420 0 – 30 days 5 623 3 736 30 – 60 days 14 184 12 194 60 – 90 days 29 105 20 89 3 – 6 months 47 119 30 109 6 – 12 months 63 104 39 99 Over 12 months 79 276 68 238 1,806 1,885

Cash and cash equivalents (Tabl

Cash and cash equivalents (Tables)	12 Months Ended
	Mar. 31, 2020
Cash and cash equivalents [abstract]
Schedule of cash and cash equivalents	2020 2019 £m £m Cash at bank 73 177 Short-term deposits — 75 Cash and cash equivalents 73 252

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Mar. 31, 2020
Disclosure of detailed information about borrowings [abstract]
Schedule of borrowings	2020 2019 £m £m Current Bank loans 1,244 641 Bonds 1,446 1,973 Commercial paper 1,269 1,792 Lease liabilities 112 65 Other loans 1 1 4,072 4,472 Non-current Bank loans 2,819 2,599 Bonds¹ 23,094 21,278 Lease liabilities 623 205 Other loans 186 176 26,722 24,258 Total borrowings 30,794 28,730 1. Includes a liability held at fair value through profit and loss of £741 million ( 2019 : £667 million ). Total borrowings are repayable as follows: 2020 2019 £m £m Less than 1 year 4,072 4,472 In 1 to 2 years 2,212 2,393 In 2 to 3 years 1,664 1,990 In 3 to 4 years 757 1,553 In 4 to 5 years 2,122 714 More than 5 years: By instalments 870 959 Other than by instalments 19,097 16,649 30,794 28,730
Schedule of lease obligations	2020 2019 £m £m Gross lease liabilities are repayable as follows: Less than 1 year 132 65 1 to 5 years 361 183 More than 5 years 481 62 974 310 Less: finance charges allocated to future periods (239 ) (40 ) 735 270 The present value of lease liabilities are as follows: Less than 1 year 112 65 1 to 5 years 297 156 More than 5 years 326 49 735 270

Trade and other payables (Table

Trade and other payables (Tables)	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Schedule of trade and other payables	Trade and other payables are initially recognised at fair value and subsequently measured at amortised cost. Contingent consideration is measured at fair value. 2020 2019 £m £m Trade payables 2,205 2,404 Deferred payables 137 217 Customer contributions¹ 84 87 Social security and other taxes 202 159 Contingent consideration² 30 — Other payables 944 902 3,602 3,769 1. From government-related entities. 2. Contingent consideration relates to the acquisition of Geronimo (see note 38).

Contract liabilities (Tables)

Contract liabilities (Tables)	12 Months Ended
	Mar. 31, 2020
Contract liabilities [abstract]
Summary of contract liabilities	2020 2019 £m £m Current 76 61 Non-current 1,082 933 1,158 994
Explanation of significant changes in contract assets and contract liabilities	Significant changes in the contract liabilities balances during the period are as follows: 2020 2019 £m £m As at 1 April 994 866 Exchange adjustments 39 29 Revenue recognised that was included in the contract liability balance at the beginning of the period (60 ) (51 ) Increases due to cash received, excluding amounts recognised as revenue during the period 185 155 Changes due to amounts recognised as revenue — (5 ) At 31 March 1,158 994

Other non-current liabilities (

Other non-current liabilities (Tables)	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Schedule of other non current liabilities	2020 2019 £m £m Deferred income¹ 101 96 Customer contributions² 428 372 Contingent consideration³ 44 — Other payables 318 340 891 808 1. Principally the deferral of profits relating to the sale of property, which we expect to recognise in future years. 2. From government-related entities. 3. Contingent consideration relates to the acquisition of Geronimo (see note 38).

Pensions and other post retir_2

Pensions and other post retirement benefits (Tables)	12 Months Ended
	Mar. 31, 2020
Employee Benefits [Abstract]
Schedule of results of most recent actuarial valuations	The results of the most recent actuarial valuations are shown below. See page 167 for the assumptions used for IAS 19 (revised) purposes. The actuarial valuations for NGUKPS as at 31 March 2019 have recently been completed, while we expect the valuation for NGEG of ESPS to be finalised by 30 June 2020. Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Latest full actuarial valuation 31 March 2019 31 March 2019 31 March 2016 Actuary Willis Towers Watson Willis Towers Watson Aon Hewitt Market value of plan assets at latest valuation £6,551 million £5,765 million £2,553 million Actuarial value of benefits due to members £6,502 million £5,831 million £3,053 million Market value as percentage of benefits 101% 99% 84% Funding surplus/(deficit) £49 million (£66 million) (£500 million) Funding surplus/(deficit) net of tax £41 million (£55 million) (£415 million)
Schedule of security agreements	Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Value of security arrangements at 31 March 2020 1 £315 million £180 million £239 million Principal supporting employers National Grid plc and National Grid UK Limited National Grid Gas plc (NGG) National Grid Electricity Transmission plc (NGET) Additional amounts payable 2 at 31 March 2020 £72 million A maximum of £280 million A maximum of £500 million 1. Following the completion of the March 2019 valuations for Sections A and B of NGUKPS, these amounts have changed to £186 million for Section A and to £ nil for Section B. 2. These amounts are payable if certain trigger events occur which have been individually agreed between the plans and their relevant supporting employers.
Disclosure of actuarial assumptions	The Company has applied the following financial assumptions in assessing DB liabilities: UK pensions 2020 2019 2018 % % % Discount rate – past service 2.35 2.40 2.60 Discount rate – future service 2.35 2.45 2.65 Salary increases 2.90 3.50 3.40 Rate of increase in RPI – past service 2.65 3.25 3.15 Rate of increase in RPI – future service 2.45 3.20 3.10 US pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 % % % % % % Discount rate 3.30 3.95 4.00 3.30 3.95 4.00 Salary increases 3.50 3.50 3.50 3.50 3.50 3.50 Initial healthcare cost trend rate n/a n/a n/a 7.00 7.25 7.50 Ultimate healthcare cost trend rate n/a n/a n/a 4.50 4.50 4.50 2020 2019 2018 UK years US years UK years US years UK years US years Assumed life expectations for a retiree age 65 Males 22.1 20.9 22.0 22.1 22.3 22.0 Females 23.8 23.4 23.6 24.2 23.9 24.2 In 20 years: Males 23.3 22.5 23.3 23.7 23.7 23.6 Females 25.3 25.1 25.2 25.9 25.5 25.8
Amounts recognised in the statement of financial position	Amounts recognised in the consolidated statement of financial position 2020 2019 2018 £m £m £m Present value of funded obligations (24,281 ) (24,609 ) (23,747 ) Fair value of plan assets 23,748 24,793 23,858 (533 ) 184 111 Present value of unfunded obligations (345 ) (330 ) (307 ) Other post-employment liabilities (75 ) (72 ) (67 ) Net defined benefit liability (953 ) (218 ) (263 ) Represented by: Liabilities (2,802 ) (1,785 ) (1,672 ) Assets 1,849 1,567 1,409 (953 ) (218 ) (263 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Present value of funded obligations (12,775 ) (14,200 ) (14,152 ) (7,809 ) (6,901 ) (6,349 ) (3,697 ) (3,508 ) (3,246 ) Fair value of plan assets 14,364 15,507 15,330 6,972 6,646 6,030 2,412 2,640 2,498 1,589 1,307 1,178 (837 ) (255 ) (319 ) (1,285 ) (868 ) (748 ) Present value of unfunded obligations (69 ) (76 ) (74 ) (276 ) (254 ) (233 ) — — — Other post-employment liabilities — — — — — — (75 ) (72 ) (67 ) Net defined benefit asset/(liability) 1,520 1,231 1,104 (1,113 ) (509 ) (552 ) (1,360 ) (940 ) (815 ) Represented by: Liabilities (69 ) (76 ) (74 ) (1,373 ) (769 ) (783 ) (1,360 ) (940 ) (815 ) Assets 1,589 1,307 1,178 260 260 231 — — — 1,520 1,231 1,104 (1,113 ) (509 ) (552 ) (1,360 ) (940 ) (815 )
Amounts recognised in the income statement and statement of other comprehensive income	Amounts recognised in the income statement and statement of other comprehensive income 2020 2019 2018 £m £m £m Included within operating costs Administration costs 16 14 16 Included within payroll costs Defined benefit plan costs: Current service cost 178 193 193 Past service cost – augmentations — 5 1 Past service credit – redundancies — (7 ) (1 ) Special termination benefit cost – redundancies 2 55 9 Past service cost – plan amendments¹ — 34 — 180 280 202 Included within finance income and costs Net interest cost 23 22 65 Total included in income statement 219 316 283 Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations² (724 ) 68 1,313 Exchange adjustments (97 ) (101 ) 175 Total included in the statement of other comprehensive income (821 ) (33 ) 1,488 1. For the year ended 31 March 2019, the estimated cost of equalising for the impact of GMP under the most cost-effective permissible methodology (Section A of NGUKPS – £17 million ; Section B of NGUKPS – £12 million ; NGEG of ESPS – £5 million ). 2. For the year ended 31 March 2020, this includes an actuarial loss from the purchase of buy-in policies of £0.7 billion . The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Included within operating costs Administration costs 9 6 6 6 7 9 1 1 1 Included within payroll costs Defined benefit plan costs: Current service cost 33 41 49 100 104 98 45 48 46 Past service cost – augmentations — 5 1 — — — — — — Past service credit – redundancies — (7 ) (1 ) — — — — — — Special termination benefit cost – redundancies 2 55 9 — — — — — — Past service cost – plan amendments — 34 — — — — — — — 35 128 58 100 104 98 45 48 46 Included within finance income and costs Net interest (income)/cost (31 ) (31 ) 3 21 21 27 33 32 35 Total included in income statement 13 103 67 127 132 134 79 81 82 Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations¹ 143 57 1,177 (588 ) (14 ) 27 (279 ) 25 109 Exchange adjustments — — — (42 ) (42 ) 75 (55 ) (59 ) 100 Total included in the statement of other comprehensive income 143 57 1,177 (630 ) (56 ) 102 (334 ) (34 ) 209 1. For the year ended 31 March 2020, UK pensions is stated after an actuarial loss from the purchase of buy-in policies of £0.7 billion .
Disclosure of reconciliation of the net defined benefit liability	Reconciliation of the net defined benefit liability 2020 2019 2018 £m £m £m Opening net defined benefit liability (218 ) (263 ) (1,933 ) Cost recognised in the income statement (219 ) (316 ) (283 ) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (821 ) (33 ) 1,488 Employer contributions 327 419 475 Other movements (22 ) (25 ) (10 ) Closing net defined benefit liability (953 ) (218 ) (263 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Opening net defined benefit asset/(liability) 1,231 1,104 (156 ) (509 ) (552 ) (728 ) (940 ) (815 ) (1,049 ) Cost recognised in the income statement (13 ) (103 ) (67 ) (127 ) (132 ) (134 ) (79 ) (81 ) (82 ) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income 143 57 1,177 (630 ) (56 ) 102 (334 ) (34 ) 209 Employer contributions 156 174 150 153 231 208 18 14 117 Other movements 3 (1 ) — — — — (25 ) (24 ) (10 ) Closing net defined benefit 1,520 1,231 1,104 (1,113 ) (509 ) (552 ) (1,360 ) (940 ) (815 ) Changes in the present value of defined benefit obligations (including unfunded obligations) 2020 2019 2018 £m £m £m Opening defined benefit obligations (24,939 ) (24,054 ) (26,230 ) Current service cost (178 ) (193 ) (193 ) Interest cost (751 ) (771 ) (775 ) Actuarial gains/(losses) – experience 148 (69 ) (100 ) Actuarial gains – demographic assumptions 452 266 671 Actuarial (losses)/gains – financial assumptions (84 ) (619 ) 174 Past service credit – redundancies — 7 1 Special termination benefit cost – redundancies (2 ) (55 ) (9 ) Past service cost – augmentations — (5 ) (1 ) Past service cost – plan amendments — (34 ) — Medicare subsidy received (22 ) (19 ) (21 ) Employee contributions (1 ) (1 ) (1 ) Benefits paid 1,282 1,376 1,285 Exchange adjustments (531 ) (768 ) 1,145 Closing defined benefit obligations (24,626 ) (24,939 ) (24,054 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Opening defined benefit obligations (14,276 ) (14,226 ) (15,645 ) (7,155 ) (6,582 ) (7,050 ) (3,508 ) (3,246 ) (3,535 ) Current service cost (33 ) (41 ) (49 ) (100 ) (104 ) (98 ) (45 ) (48 ) (46 ) Interest cost (335 ) (358 ) (366 ) (280 ) (277 ) (273 ) (136 ) (136 ) (136 ) Actuarial gains/(losses) – experience 113 (56 ) (95 ) (45 ) (52 ) (38 ) 80 39 33 Actuarial gains – demographic assumptions 140 224 565 78 — 30 234 42 76 Actuarial gains/(losses) – financial assumptions 798 (568 ) 604 (595 ) (24 ) (279 ) (287 ) (27 ) (151 ) Past service credit – redundancies — 7 1 — — — — — — Special termination benefit cost – redundancies (2 ) (55 ) (9 ) — — — — — — Past service cost – augmentations — (5 ) (1 ) — — — — — — Past service cost – plan amendments — (34 ) — — — — — — — Medicare subsidy received — — — — — — (22 ) (19 ) (21 ) Employee contributions (1 ) (1 ) (1 ) — — — — — — Benefits paid 752 837 770 374 398 362 156 141 153 Exchange adjustments — — — (362 ) (514 ) 764 (169 ) (254 ) 381 Closing defined benefit obligations (12,844 ) (14,276 ) (14,226 ) (8,085 ) (7,155 ) (6,582 ) (3,697 ) (3,508 ) (3,246 ) 25. Pensions and other post-retirement benefits continued Changes in the value of plan assets 2020 2019 2018 £m £m £m Opening fair value of plan assets 24,793 23,858 24,375 Interest income 728 749 710 Return on plan assets (less than)/in excess of interest¹ (1,240 ) 490 568 Administration costs (16 ) (14 ) (16 ) Employer contributions 327 419 475 Employee contributions 1 1 1 Benefits paid (1,279 ) (1,377 ) (1,285 ) Exchange adjustments 434 667 (970 ) Closing fair value of plan assets 23,748 24,793 23,858 Actual return on plan assets (512 ) 1,239 1,278 Expected contributions to plans in the following year 269 307 363 1. For the year ended 31 March 2020, this includes an actuarial loss from the purchase of buy-in policies of £0.7 billion . The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2020 2019 2018 2020 2019 2018 2020 2019 2018 £m £m £m £m £m £m £m £m £m Opening fair value of plan assets 15,507 15,330 15,489 6,646 6,030 6,322 2,640 2,498 2,564 Interest income 366 389 363 259 256 246 103 104 101 Return on plan assets (less than)/ (908 ) 457 103 (26 ) 62 314 (306 ) (29 ) 151 Administration costs (9 ) (6 ) (6 ) (6 ) (7 ) (9 ) (1 ) (1 ) (1 ) Employer contributions 156 174 150 153 231 208 18 14 117 Employee contributions 1 1 1 — — — — — — Benefits paid (749 ) (838 ) (770 ) (374 ) (398 ) (362 ) (156 ) (141 ) (153 ) Exchange adjustments — — — 320 472 (689 ) 114 195 (281 ) Closing fair value of plan assets 14,364 15,507 15,330 6,972 6,646 6,030 2,412 2,640 2,498 Actual return on plan assets (542 ) 846 466 233 318 560 (203 ) 75 252 Expected contributions to plans in the following year 137 148 140 125 150 221 7 9 2 1. For the year ended 31 March 2020, UK pensions includes an actuarial loss from the purchase of buy-in policies of £0.7 billion .
Disclosure of asset allocations	Asset allocations Within the asset allocations below, there is significant diversification across regions, asset managers, currencies and bond categories. UK pensions 2020 2019 2018 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 732 732 1,464 1,181 784 1,965 1,420 813 2,233 Corporate bonds 3,837 — 3,837 3,625 — 3,625 3,949 — 3,949 Government securities 2,051 — 2,051 6,114 — 6,114 5,629 — 5,629 Property 103 585 688 108 749 857 129 834 963 Diversified alternatives — 893 893 — 771 771 99 690 789 Liability-matching assets 1,704 ¹ 3,278 ² 4,982 1,751 — 1,751 1,174 — 1,174 Longevity swap — (51 ) (51 ) — (35 ) (35 ) — — — Cash and cash equivalents 29 222 251 40 259 299 211 215 426 Other (including net current assets and liabilities) — 249 249 — 160 160 — 167 167 8,456 5,908 14,364 12,819 2,688 15,507 12,611 2,719 15,330 1. Consists of pooled funds which invests mainly in fixed interest securities. 2. Comprises the buy-in policies held by NGUKPS. US pensions 2020 2019 2018 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 467 2,043 2,510 533 2,178 2,711 577 1,954 2,531 Corporate bonds 1,640 518 2,158 1,329 425 1,754 1,085 413 1,498 Government securities 535 732 1,267 422 640 1,062 414 565 979 Property — 307 307 — 316 316 — 279 279 Diversified alternatives 162 464 626 183 487 670 198 421 619 Infrastructure — 121 121 — 99 99 — 77 77 Cash and cash equivalents 24 — 24 21 — 21 14 — 14 Other (including net current assets and liabilities) (44 ) 3 (41 ) (8 ) 21 13 6 27 33 2,784 4,188 6,972 2,480 4,166 6,646 2,294 3,736 6,030 US other post-retirement benefits 2020 2019 2018 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 353 1,037 1,390 404 1,184 1,588 412 1,110 1,522 Corporate bonds 15 — 15 19 — 19 24 — 24 Government securities 551 1 552 540 3 543 508 2 510 Diversified alternatives 162 161 323 175 166 341 161 144 305 Other¹ — 132 132 — 149 149 — 137 137 1,081 1,331 2,412 1,138 1,502 2,640 1,105 1,393 2,498 1. Other primarily comprises insurance contracts. Asset allocation strategy Each plan’s investment strategy is formulated in order to target specific asset allocations and returns, and to manage risk. The asset allocation of the plans is as follows: 2020 2019 UK pensions US pensions US other post-retirement benefits UK pensions US pensions US other post-retirement benefits % % % % % % Equities 10.2 36.0 57.6 12.7 40.8 60.2 Corporate bonds 26.7 31.0 0.6 23.4 26.4 0.7 Government securities 14.3 18.2 22.9 39.4 16.0 20.6 Property 4.8 4.4 — 5.5 4.7 — Diversified alternatives 6.2 9.0 13.4 5.0 10.1 12.9 Liability matching assets 34.3 — — 11.1 — — Infrastructure — 1.7 — — 1.5 — Cash and cash equivalents 1.8 0.3 — 1.9 0.3 — Other 1.7 (0.6 ) 5.5 1.0 0.2 5.6 100.0 100.0 100.0 100.0 100.0 100.0

Provisions (Tables)

Provisions (Tables)	12 Months Ended
	Mar. 31, 2020
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Schedule of provisions	Environmental £m Decommissioning £m Restructuring £m Emissions £m Other £m Total provisions £m At 1 April 2018 1,531 194 3 8 316 2,052 Exchange adjustments 103 7 — — 14 124 Additions¹ 32 18 125 16 35 226 Unused amounts reversed (36 ) (10 ) (3 ) (6 ) (10 ) (65 ) Unwinding of discount 62 5 — — 7 74 Utilised² (53 ) (26 ) (42 ) (9 ) (79 ) (209 ) Transfers³ — — — — (3 ) (3 ) At 31 March 2019 1,639 188 83 9 280 2,199 Exchange adjustments 82 5 — 1 9 97 Additions¹ 437 93 7 12 40 589 Unused amounts reversed (29 ) (16 ) (16 ) — (9 ) (70 ) Unwinding of discount 65 5 — — 7 77 Utilised² (123 ) (21 ) (39 ) (5 ) (50 ) (238 ) At 31 March 2020 2,071 254 35 17 277 2,654 2020 2019 £m £m Current 348 316 Non-current 2,306 1,883 2,654 2,199 1. For the year ended 31 March 2020, £402 million (2019: £nil ) of additions relate to exceptional environmental provisions, of which £76 million relates to the impact of the change in the real discount rate from 1% to 0.5% during the year (see note 5 for details). Additions to other provisions include £15 million ( 2019 : £nil ) in relation to discontinued operations. 2. Utilised amounts for other provisions include £8 million ( 2019 : £20 million ) in relation to discontinued operations. 3. Represents net amounts transferred to trade and other payables (see note 22) of £nil ( 2019 : £3 million ).
Schedule of environmental provision	The environmental provision is as follows: 2020 2019 Discounted £m Undiscounted £m Real discount rate Discounted £m Undiscounted £m Real discount rate UK sites 175 184 0.5 % 189 210 1 % US sites 1,896 1,955 0.5 % 1,450 1,555 1 % 2,071 2,139 1,639 1,765

Share capital (Tables)

Share capital (Tables)	12 Months Ended
	Mar. 31, 2020
Share Capital, Reserves And Other Equity Interest [Abstract]
Schedule of share capital	Allotted, called-up and fully paid million £m At 1 April 2018 3,638 452 Issued during the year in lieu of dividends¹ 49 6 At 31 March 2019 3,687 458 Issued during the year in lieu of dividends¹ 93 12 At 31 March 2020 3,780 470 1. The issue of shares under the scrip dividend programme is considered to be a bonus issue under the terms of the Companies Act 2006, and the nominal value of the shares is charged to the share premium account.

Other equity reserves (Tables)

Other equity reserves (Tables)	12 Months Ended
	Mar. 31, 2020
Disclosure of reserves within equity [abstract]
Schedule of reserves within equity	Translation £m Cash flow hedge £m Cost of hedging £m Available- for-sale £m FVOCI equity £m FVOCI debt £m Own credit £m Capital redemption £m Merger £m Total £m At 1 April 2017 894 103 — 162 — — — 19 (5,165 ) (3,987 ) Exchange adjustments¹ (504 ) — — — — — — — — (504 ) Net gains/(losses) taken to equity² — 296 — (30 ) — — — — — 266 Share of net gains of associates taken to equity — 5 — — — — — — — 5 Transferred from profit or loss² — (280 ) — (73 ) — — — — — (353 ) Tax — 4 — 29 — — — — — 33 At 31 March 2018 (as previously reported) 390 128 — 88 — — — 19 (5,165 ) (4,540 ) Transfer on transition to IFRS 9 — (3 ) 76 (88 ) 34 46 7 — — 72 At 1 April 2018 (as restated) 390 125 76 — 34 46 7 19 (5,165 ) (4,468 ) Exchange adjustments¹ 346 — — — — — — — — 346 Net (losses)/gains taken to equity² — (206 ) (107 ) — — 2 7 — — (304 ) Share of net gains of associates taken to equity — 1 — — — — — — — 1 Transferred to profit or loss² — 166 41 — — — — — — 207 Net losses in respect of cash flow hedging of capital expenditure — (13 ) — — — — — — — (13 ) Tax — 6 7 — — — (1 ) — — 12 Cash flow hedges transferred to the statement of financial position, net of tax — (18 ) — — — — — — — (18 ) At 1 April 2019 736 61 17 — 34 48 13 19 (5,165 ) (4,237 ) Exchange adjustments¹ 550 — — — — — — — — 550 Net losses taken to equity — (142 ) (33 ) — (13 ) (15 ) (3 ) — — (206 ) Share of net losses of associates taken to equity — (5 ) — — — — — — — (5 ) Transferred to profit or loss — 14 (45 ) — — — — — — (31 ) Net losses in respect of cash flow hedging of capital expenditure — (17 ) — — — — — — — (17 ) Tax — 29 11 — 4 (2 ) — — — 42 Cash flow hedges transferred to the statement of financial position, net of tax — (15 ) — — — — — — — (15 ) At 31 March 2020 1,286 (75 ) (50 ) — 25 31 10 19 (5,165 ) (3,919 ) 1. The exchange adjustments recorded in the translation reserve comprise a gain of £545 million ( 2019 : gain of £896 million ; 2018 : loss of £1,304 million ) relating to the translation of foreign operations offset by a gain of £5 million ( 2019 : loss of £550 million ; 2018 : gain of £800 million ) relating to borrowings, cross-currency swaps and foreign exchange forward contracts used to hedge the net investment in non-sterling denominated subsidiaries. 2. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in cash flow hedges of foreign currency risk and interest rates. This has no net impact on the consolidated statement of comprehensive income. It has resulted in a prior year gross up to £166 million ( 2018 : £277 million ) to ‘Net losses taken to equity’ with an equal and offsetting gross up to ‘Transferred to profit or loss’.

Net debt (Tables)

Net debt (Tables)	12 Months Ended
	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Reconciliation of net cash flow to movement in net debt	Reconciliation of net cash flow to movement in net debt 2020 2019 2018 £m £m £m Decrease in cash and cash equivalents (183 ) (80 ) (807 ) Decrease in financial investments (7 ) (822 ) (5,953 ) Increase/(decrease) in borrowings and related derivatives¹ (23 ) (708 ) 1,209 Net interest paid on the components of net debt² 888 866 808 Change in debt resulting from cash flows 675 (744 ) (4,743 ) Changes in fair value of financial assets and liabilities and exchange movements (1,081 ) (1,648 ) 2,098 Net interest charge on the components of net debt (1,097 ) (1,076 ) (1,017 ) Other non-cash movements (84 ) (27 ) (66 ) Movement in net debt (net of related derivative financial instruments) in the year (1,587 ) (3,495 ) (3,728 ) Net debt (net of related derivative financial instruments) at start of year (26,529 ) (23,002 ) (19,274 ) Impact of transition to IFRS 16 (2019: IFRS 9) (474 ) (32 ) — Net debt (net of related derivative financial instruments) at end of year (28,590 ) (26,529 ) (23,002 )
Schedule of components of net debt	Net debt is comprised as follows: 2020 2019 2018 £m £m £m Cash, cash equivalents and financial investments 2,071 2,233 3,023 Borrowings (30,794 ) (28,730 ) (26,625 ) Financing derivatives¹ 133 (32 ) 600 (28,590 ) (26,529 ) (23,002 ) 1. The financing derivatives balance included in net debt excludes the commodity derivatives (see note 17). 2. Excludes £6 million ( 2019 : £23 million ; 2018 : £27 million ) cash interest from the Quadgas shareholder loan included within discontinued operations in the cash flow statement.
Schedule of changes in net debt	Analysis of changes in net debt Cash and cash equivalents £m Financial investments £m Borrowings £m Financing derivatives £m Total 1 £m At 1 April 2017 1,139 8,741 (28,638 ) (516 ) (19,274 ) Cash flow (807 ) (5,983 ) 2,108 (61 ) (4,743 ) Fair value gains and losses and exchange movements (3 ) (149 ) 1,088 1,162 2,098 Interest income/(charges) — 85 (1,117 ) 15 (1,017 ) Other non-cash movements — — (66 ) — (66 ) At 31 March 2018 329 2,694 (26,625 ) 600 (23,002 ) Impact of transition to IFRS 9 — — (32 ) — (32 ) At 1 April 2018 (as restated) 329 2,694 (26,657 ) 600 (23,034 ) Cash flow (80 ) (846 ) (240 ) 422 (744 ) Fair value gains and losses and exchange movements 3 93 (733 ) (1,011 ) (1,648 ) Interest income/(charges) — 29 (1,062 ) (43 ) (1,076 ) Other non-cash movements — 11 (38 ) — (27 ) At 1 April 2019 252 1,981 (28,730 ) (32 ) (26,529 ) Impact of transition to IFRS 16 — — (474 ) — (474 ) Cash flow (183 ) (42 ) 450 450 675 Fair value gains and losses and exchange movements 4 25 (864 ) (246 ) (1,081 ) Interest income/(charges) — 34 (1,092 ) (39 ) (1,097 ) Other non-cash movements — — (84 ) — (84 ) At 31 March 2020 73 1,998 (30,794 ) 133 (28,590 ) Balances at 31 March 2020 comprise: Non-current assets — — — 1,205 1,205 Current assets 73 1,998 — 62 2,133 Current liabilities — — (4,072 ) (254 ) (4,326 ) Non-current liabilities — — (26,722 ) (880 ) (27,602 ) 73 1,998 (30,794 ) 133 (28,590 ) 1. Includes accrued interest at 31 March 2020 of £246 million ( 2019 : £223 million ; 2018 : £197 million ).
Reconciliation of cash flow from financing liabilities to cash flow statement	Reconciliation of cash flow from financing liabilities to cash flow statement 2020 2019 2018 £m £m £m Cash flows per financing activities section of cash flow statement: Proceeds received from loans 4,218 2,932 1,941 Repayment of loans (3,253 ) (1,969 ) (2,156 ) Payments of lease liabilities (121 ) (70 ) (71 ) Net movements in short-term borrowings (424 ) 179 (764 ) Net movements in derivatives (187 ) 35 (267 ) Interest paid (957 ) (914 ) (853 ) Cash flows per financing activities section of cash flow statement (724 ) 193 (2,170 ) Adjustments: Non-net debt-related items 34 24 12 Derivative cash inflow in relation to capital expenditure 13 13 12 Derivative cash flows per investing section of cash flow statement (223 ) (412 ) 330 Discontinued operations — — (231 ) Cash flows relating to financing liabilities within net debt (900 ) (182 ) (2,047 ) Analysis of changes in net debt: Borrowings (450 ) 240 (2,108 ) Financing derivatives (450 ) (422 ) 61 Cash flow movements relating to financing liabilities within net debt (900 ) (182 ) (2,047 )
Reconciliation of changes in liabilities arising from financing activities	As a result we have separately disclosed the reconciliation below, excluding derivatives associated with our net investment hedges, given that they are classified in the statement of cash flows within investing activities. Borrowings £m Financing derivatives £m Total £m At 1 April 2017 (28,638 ) 16 (28,622 ) Cash flow 2,108 281 2,389 Fair value gains and losses and exchange movements 1,088 222 1,310 Interest income/(charges) (1,117 ) 34 (1,083 ) Other non-cash movements (66 ) — (66 ) At 31 March 2018 (26,625 ) 553 (26,072 ) Impact of transition to IFRS 9 (32 ) — (32 ) At 1 April 2018 (as restated) (26,657 ) 553 (26,104 ) Cash flow (240 ) 23 (217 ) Fair value gains and losses and exchange movements (733 ) (334 ) (1,067 ) Interest charges (1,062 ) (14 ) (1,076 ) Other non-cash movements (38 ) — (38 ) At 1 April 2019 (28,730 ) 228 (28,502 ) Impact of transition to IFRS 16 (474 ) — (474 ) Cash flow 450 240 690 Fair value gains and losses and exchange movements (864 ) (231 ) (1,095 ) Interest charges (1,092 ) (9 ) (1,101 ) Other non-cash movements (84 ) — (84 ) At 31 March 2020 (30,794 ) 228 (30,566 )

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Mar. 31, 2020
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Schedule of capital commitments and contingent liabilities	2020 2019 £m £m Future capital expenditure Contracted for but not provided 2,629 1,973 Energy purchase commitments¹ Less than 1 year 1,365 1,353 In 1 to 2 years 890 779 In 2 to 3 years 973 651 In 3 to 4 years 955 827 In 4 to 5 years 861 862 More than 5 years 11,314 11,237 16,358 15,709 Guarantees² Guarantee of sublease for US property (expires 2040) 173 173 Guarantees of certain obligations of Grain LNG (expire up to 2025) 34 39 Guarantees of certain obligations for construction of HVDC West Coast Link (expected expiry 2020) 92 139 Guarantees of certain obligations of Nemo Link Limited (expired 2019) — 19 Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates)² 683 865 Guarantees of certain obligations of St William Homes LLP (various expiry dates)³ 30 22 Guarantees of certain obligations for construction of IFA 2 (expected expiry 2022)² 564 505 Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024) 1,096 872 Other guarantees and letters of credit (various expiry dates) 150 341 2,822 2,975 2019 £m Operating lease commitments Less than 1 year 43 In 1 to 2 years 39 In 2 to 3 years 34 In 3 to 4 years 35 In 4 to 5 years 27 More than 5 years 123 301 1. Energy purchase commitments relate to contractual commitments to purchase electricity or gas that are used to satisfy physical delivery requirements to our customers or for energy that we use ourselves (i.e. normal purchase, sale or usage) and hence are accounted for as ordinary purchase contracts (see note 32(f)). Details of commodity contract derivatives that do not meet the normal purchase, sale or usage criteria, and hence are accounted for as derivative contracts, are shown in note 17(b). 2. Included within total guarantees are guarantees to both joint ventures and Engineering, Procurement and Construction contractors regarding the construction of interconnectors of £358 million ( 2019 : £470 million ). 3. Includes guarantees to related parties.

Related party transactions (Tab

Related party transactions (Tables)	12 Months Ended
	Mar. 31, 2020
Related party transactions [abstract]
Schedule of transactions between related parties	The following significant transactions with related parties were in the normal course of business. Amounts receivable from and payable to related parties are due on normal commercial terms: 2020 2019 2018 £m £m £m Sales: Goods and services supplied to a pension plan 5 5 3 Sales: Goods and services supplied to joint ventures¹ 101 151 14 Sales: Goods and services supplied to associates² 33 192 220 Purchases: Goods and services received from joint ventures³ 61 26 135 Purchases: Goods and services received from associates³ 56 141 160 Receivable from joint ventures 4 255 584 160 Receivable from associates 4 1 368 376 Payable to joint ventures 72 8 — Payable to associates 4 12 17 Interest income from joint ventures 2 5 4 Interest income from associates 8 23 27 Dividends received from joint ventures 5 34 30 43 Dividends received from associates 6 41 171 170 1. During the year, £38 million ( 2019 : £139 million ) of property sites were sold to a joint venture, St William Homes LLP. A further £32 million of sales were made to NGET/SPT Upgrades Limited in 2020. 2. Sales relate to transactions with Quadgas, until the date it ceased to be a related party following the disposal of our 39% stake in June 2019 (see note 10). Included within this is other income of £31 million ( 2019 : £52 million ) relating to a Transitional Service Agreement following the sale of the UK Gas Distribution business to Quadgas. 3. During the year, the Group received goods and services from a number of US associates, both for the transportation of gas and for pipeline services in the US, most notably, £31 million ( 2019 : £30 million ) of purchases from Millennium Pipeline Company LLC. The Group also purchased capitalised assets of £58 million ( 2019 : £26 million ) from NGET/SPT Upgrades Limited (a joint venture). 4. Amounts receivable from associates includes a loan receivable balance of £242 million ( 2019 : £325 million ) in relation to St William Homes LLP (a joint venture). There is no longer a loan receivable from Quadgas ( 2019 : £352 million ) and Nemo Link (a joint venture) ( 2019 : £258 million ). The loan receivable balance from Nemo Link was transferred to equity during 2020 (see note 16 for details). 5. Dividends of £25 million ( 2019 : £30 million ) were received from BritNed Development Limited. 6. Includes £32 million ( 2019 : £24 million ) of dividend income from Millennium Pipeline Company LLC. No dividends were received from Quadgas this year (2019: £133 million ).

Financial risk management (Tabl

Financial risk management (Tables)	12 Months Ended
	Mar. 31, 2020
Financial Instruments [Abstract]
Disclosure of treasury credit risk	As at 31 March 2020 , the following limits were in place for investments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 2,049 1,024 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,118 559 Double ‘A+’ G7 sovereign entities (AA+) 1,863 931 Double ‘A’ range institutions (AA) 745 to 931 372 to 465 Single ‘A’ range institutions (A) 261 to 373 130 to 186
Disclosure of offsetting of financial assets and financial liabilities	Related amounts At 31 March 2020 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 1,267 — 1,267 (351 ) (694 ) 222 Commodity contract derivatives 75 — 75 (5 ) (3 ) 67 1,342 — 1,342 (356 ) (697 ) 289 Liabilities Financing derivatives (1,134 ) — (1,134 ) 351 646 (137 ) Commodity contract derivatives (200 ) — (200 ) 5 8 (187 ) (1,334 ) — (1,334 ) 356 654 (324 ) 8 — 8 — (43 ) (35 ) Related amounts At 31 March 2019 Gross carrying amounts £m Gross amounts offset £m Net amount presented in statement of financial position £m Financial instruments £m Cash collateral received/ pledged £m Net amount £m Assets Financing derivatives 1,052 — 1,052 (299 ) (551 ) 202 Commodity contract derivatives 101 — 101 29 — 130 1,153 — 1,153 (270 ) (551 ) 332 Liabilities Financing derivatives (1,084 ) — (1,084 ) 299 615 (170 ) Commodity contract derivatives (99 ) — (99 ) (29 ) — (128 ) (1,183 ) — (1,183 ) 270 615 (298 ) (30 ) — (30 ) — 64 34
Disclosure of maturity analysis for financial liabilities and derivatives	The following is a maturity profile of our financial liabilities and derivatives: At 31 March 2020 Less than £m 1 to 2 £m 2 to 3 £m More than £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (3,672 ) (2,150 ) (1,611 ) (22,214 ) (29,647 ) Interest payments on borrowings¹ (765 ) (750 ) (714 ) (12,002 ) (14,231 ) Lease liabilities (132 ) (114 ) (99 ) (629 ) (974 ) Other non-interest-bearing liabilities (3,149 ) (318 ) — — (3,467 ) Contingent consideration (32 ) (16 ) (32 ) (16 ) (96 ) Derivative financial liabilities Financing derivatives – receipts² 2,249 986 1,208 3,510 7,953 Financing derivatives – payments² (2,582 ) (1,136 ) (1,463 ) (4,067 ) (9,248 ) Commodity contract derivatives – receipts² 4 2 — — 6 Commodity contract derivatives – payments² (116 ) (50 ) (24 ) (12 ) (202 ) Derivative financial assets Financing derivatives – receipts² 2,469 1,063 570 1,775 5,877 Financing derivatives – payments² (2,271 ) (527 ) (375 ) (1,478 ) (4,651 ) Commodity contract derivatives – receipts² 20 1 1 — 22 Commodity contract derivatives – payments² (21 ) — — — (21 ) (7,998 ) (3,009 ) (2,539 ) (35,133 ) (48,679 ) At 31 March 2019 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (4,129 ) (2,348 ) (1,998 ) (19,673 ) (28,148 ) Interest payments on borrowings¹ (800 ) (733 ) (721 ) (13,465 ) (15,719 ) Lease liabilities (72 ) (63 ) (52 ) (123 ) (310 ) Other non-interest-bearing liabilities (3,306 ) (340 ) — — (3,646 ) Derivative financial liabilities Financing derivatives – receipts² 3,045 1,703 163 2,560 7,471 Financing derivatives – payments² (3,421 ) (2,029 ) (223 ) (3,276 ) (8,949 ) Commodity contract derivatives – receipts² 2 3 1 — 6 Commodity contract derivatives – payments² (98 ) (26 ) (4 ) (1 ) (129 ) Derivative financial assets Financing derivatives – receipts² 1,928 561 863 1,112 4,464 Financing derivatives – payments² (1,251 ) (459 ) (783 ) (875 ) (3,368 ) Commodity contract derivatives – receipts² 23 9 2 — 34 Commodity contract derivatives – payments² — (5 ) (1 ) — (6 ) (8,079 ) (3,727 ) (2,753 ) (33,741 ) (48,300 ) 1. The interest on borrowings is calculated based on borrowings held at 31 March without taking account of future issues. Floating rate interest is estimated using a forward interest rate curve as at 31 March. Payments are included on the basis of the earliest date on which the Company can be required to settle. 2. The receipts and payments line items for derivatives comprise gross undiscounted future cash flows, after considering any contractual netting that applies within individual contracts. Where cash receipts and payments within a derivative contract are settled net, and the amount to be received/(paid) exceeds the amount to be paid/(received), the net amount is presented within derivative receipts/(payments).
Disclosure of nature and extent of risks arising from financial instruments	Derivative financial instruments were used to manage foreign currency risk as follows: 2020 2019 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 18 — 55 — 73 97 2 153 — 252 Financial investments 813 — 1,185 — 1,998 965 — 1,016 — 1,981 Borrowings (12,407 ) (4,150 ) (13,217 ) (1,020 ) (30,794 ) (10,591 ) (4,787 ) (12,126 ) (1,226 ) (28,730 ) Pre-derivative position (11,576 ) (4,150 ) (11,977 ) (1,020 ) (28,723 ) (9,529 ) (4,785 ) (10,957 ) (1,226 ) (26,497 ) Derivative effect (1,169 ) 4,341 (4,214 ) 1,175 133 (1,055 ) 4,803 (5,245 ) 1,465 (32 ) Net debt position (12,745 ) 191 (16,191 ) 155 (28,590 ) (10,584 ) 18 (16,202 ) 239 (26,529 ) The currency exposure on other financial instruments is as follows: 2020 2019 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 306 — 1,403 — 1,709 398 — 1,635 — 2,033 Trade and other payables (1,177 ) — (2,002 ) — (3,179 ) (1,221 ) — (2,085 ) — (3,306 ) Other non-current liabilities (85 ) — (277 ) — (362 ) (93 ) — (247 ) — (340 ) 2020 2019 Income statement £m Other equity reserves £m Income statement £m Other equity reserves £m Financial risk (post-tax): UK RPI change of 0.5%¹ 27 — 27 — UK interest rates change of 0.5% 14 47 16 13 US interest rates change of 0.5% 5 27 11 44 US dollar exchange rate change of 10%² 49 216 53 246 1. Excludes sensitivities to LPI curve. Further details on sensitivities are provided in note 32(g). 2. The other equity reserves impact does not reflect the exchange translation in our US subsidiaries’ net assets. It is estimated this would change by £1,319 million ( 2019 : £1,119 million ) in the opposite direction if the dollar exchange rate changed by 10% . Our commodity contract derivatives are sensitive to price risk. Additional sensitivities in respect to commodity price risk and to our derivative fair values are as follows: 2020 2019 Income statement £m Net assets £m Income statement £m Net assets £m Commodity price risk (post-tax): 10% increase in commodity prices 26 26 26 26 10% decrease in commodity prices (27 ) (27 ) (27 ) (27 ) Assets and liabilities carried at fair value (post-tax): 10% fair value change in derivative financial instruments¹ 12 12 (3 ) (3 ) 10% fair value change in commodity contract derivative liabilities 9 9 — — 1. The effect of a 10% change in fair value assumes no hedge accounting. The table below sets out the sensitivity analysis for certain areas of estimation uncertainty set out in note 1E. These estimates are those that have a significant risk of resulting in a material adjustment to the carrying values of assets and liabilities in the next year. Note that the sensitivity analysis for the useful economic lives of our gas network assets is included in note 13. 2020 2019 Income statement £m Net assets £m Income statement £m Net assets £m Pensions and other post-retirement benefit liabilities (pre-tax)¹: UK discount rate change of 0.5%² 6 877 6 1,064 US discount rate change of 0.5%² 10 514 16 688 UK RPI rate change of 0.5%³ 4 670 4 908 UK long-term rate of increase in salaries change of 0.5% 1 39 1 56 US long-term rate of increase in salaries change of 0.5% 2 47 2 46 UK change of one year to life expectancy at age 65 4 1 545 1 610 US change of one year to life expectancy at age 65 4 456 4 406 Assumed US healthcare cost trend rates change of 1% 31 507 32 503 Pension assets: Change in value of unquoted equities by 10% — 381 — 415 Change in value of unquoted properties by 10% — 89 — 107 Change in value of unquoted diversified alternatives by 10% — 152 — 142 Environmental provision: 10% change in estimated future cash flows 210 210 165 165 1. The changes shown are a change in the annual pension or other post-retirement benefit service charge and change in the defined benefit obligations. 2. A change in the discount rate is likely to occur as a result of changes in bond yields and as such would be expected to be offset to a significant degree by a change in the value of the bond assets held by the plans. In the UK, there would also be a £205 million net assets offset from the buy-in policies purchased in the year, where the accounting value of the buy-in asset is set equal to the associated liabilities. 3. The projected impact resulting from a change in RPI reflects the underlying effect on pensions in payment, pensions in deferment and resultant increases in salary assumptions. The buy-in policies purchased during the year would have a £152 million net assets offset to the above. 4. In the UK, the buy-in policies purchased during the year, and the longevity swap entered into previously, would have a £223 million net assets offset to the above.
Disclosure of financial instruments by type of interest rate	Net debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2020 2019 Fixed rate £m Floating rate £m Inflation linked £m Other 1 £m Total £m Fixed rate £m Floating rate £m Inflation linked £m Other 1 £m Total £m Cash and cash equivalents 71 10 — (8 ) 73 59 104 — 89 252 Financial investments — 1,966 — 32 1,998 6 1,944 — 31 1,981 Borrowings (20,969 ) (3,085 ) (6,740 ) — (30,794 ) (19,043 ) (3,045 ) (6,642 ) — (28,730 ) Pre-derivative position (20,898 ) (1,109 ) (6,740 ) 24 (28,723 ) (18,978 ) (997 ) (6,642 ) 120 (26,497 ) Derivative effect 2,259 (1,892 ) (234 ) — 133 1,740 (1,559 ) (213 ) — (32 ) Net debt position (18,639 ) (3,001 ) (6,974 ) 24 (28,590 ) (17,238 ) (2,556 ) (6,855 ) 120 (26,529 ) 1. Represents financial instruments which are not directly affected by interest rate risk, such as investments in equity or other similar financial instruments.
Disclosure of detailed information about hedging instruments	(i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2020 Balance of fair value hedge adjustments in borrowings Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings 1,2 (1,751 ) (31 ) (95 ) (42 ) 48 6 1. The carrying value of the hedged borrowings is £1,883 million , of which £72 million is current and £1,811 million is non-current. 2. Included within the hedging instrument notional balance is £1,675 million impacted by Interest Rate Benchmark Reform amendments. As at 31 March 2019 Balance of fair value hedge adjustments in borrowings Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (1,707 ) 11 (117 ) 15 (10 ) 5 1. The carrying value of the hedged borrowings was £1,810 million , of which £202 million was current and £1,608 million was non-current. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in fair value hedges of foreign currency risk and interest rates. It has resulted in a prior year equal and offsetting impact of £4 million to the balances used for the ‘Change in value used for calculating ineffectiveness’. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2020 Balance in cash flow hedge reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (4,127 ) (69 ) (22 ) 142 (143 ) (1 ) Foreign currency risk on forecasted cash flows (794 ) 8 — 17 (17 ) — 1. Included within the hedging instrument notional balance is £176 million impacted by Interest Rate Benchmark Reform amendments. As at 31 March 2019 Balance in cash flow hedge reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (3,804 ) (17 ) 51 206 (206 ) — Foreign currency risk on forecasted cash flows (697 ) 45 — 12 (12 ) — 1. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in cash flow hedges of foreign currency risk and interest rates. This has no net impact on the consolidated statement of comprehensive income. It has resulted in a prior year equal and offsetting impact of £167 million to the balances used for the ‘Change in value used for calculating ineffectiveness’. (iii) Net investment hedges of foreign currency risk: As at 31 March 2020 Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Currency risk on foreign operations¹ (3,064 ) 45 (2,871 ) (6 ) 6 — 1. Included within the hedging instrument notional balance is £nil impacted by Interest Rate Benchmark Reform amendments. As at 31 March 2019 Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Currency risk on foreign operations (2,974 ) (329 ) (2,502 ) 550 (550 ) — Year ended 31 March 2019 Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges¹ — (206 ) (12 ) — Cost of hedging (6 ) (12 ) — (90 ) Transferred to profit or loss in respect of: Cash flow hedges¹ — 166 — — Cost of hedging 3 — — 39 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (4 ) — — 32 Consolidated statement of financial position Derivatives – carrying value of hedging instruments² Assets – current 17 — 9 — Assets – non-current 168 78 23 — Liabilities – current (9 ) (28 ) (3 ) (43 ) Liabilities – non-current (25 ) (134 ) (4 ) (249 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Nov 2019 – May 2038 Aug 2019 – Feb 2039 Apr 2019 – Dec 2023 Mar 2020 – Jun 2025 Spot foreign exchange range: GBP:USD 1.64 – 1.65 1.52 – 1.66 1.29 – 1.41 1.49 GBP:EUR 1.19 – 1.24 1.14 – 1.24 1.07 – 1.32 1.15 EUR:USD 1.13 – 1.16 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+561bps 1.795% – 5.850% n/a n/a USD LIBOR -44bps/+115bps 1.103% – 3.864% n/a n/a 1. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in cash flow hedges of foreign currency risk and interest rates. This has no net impact on the consolidated statement of comprehensive income. It has resulted in a prior year gross up of £166 million to net losses in respect of cash flow hedges with an equal and offsetting gross up to transferred to profit and loss in respect of cash flow hedges. 2. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. In accordance with the requirements of IFRS 9, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Year ended 31 March 2020 Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges (143 ) (17 ) — Cost of hedging 5 (7 ) — (30 ) Transferred to profit or loss in respect of: Cash flow hedges — 14 — — Cost of hedging 1 (1 ) — (45 ) Consolidated statement of changes in equity Other equity reserves – cost of hedging balances 2 (8 ) — (43 ) Consolidated statement of financial position Derivatives – carrying value of hedging instruments¹ Assets – current 1 — 4 9 Assets – non-current 247 106 8 — Liabilities – current (1 ) (105 ) (8 ) (82 ) Liabilities – non-current (39 ) (264 ) (12 ) (19 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range May 2020 – Feb 2040 Jul 2020 – Dec 2039 Apr 2020 – Dec 2024 Jun 2020 – Sep 2027 Spot foreign exchange range: GBP:USD 1.64 1.30 – 1.66 1.24 – 1.41 1.21 – 1.49 GBP:EUR 1.19 – 1.24 1.10 – 1.24 1.04 – 1.30 1.14 EUR:USD 1.13 – 1.17 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+408bps 1.331% – 5.850% n/a n/a USD LIBOR -44bps/+ 115bps 1.103% – 3.864% n/a n/a 1. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position.
Disclosure of detailed information about hedged items	(i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2020 Balance of fair value hedge adjustments in borrowings Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings 1,2 (1,751 ) (31 ) (95 ) (42 ) 48 6 1. The carrying value of the hedged borrowings is £1,883 million , of which £72 million is current and £1,811 million is non-current. 2. Included within the hedging instrument notional balance is £1,675 million impacted by Interest Rate Benchmark Reform amendments. As at 31 March 2019 Balance of fair value hedge adjustments in borrowings Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (1,707 ) 11 (117 ) 15 (10 ) 5 1. The carrying value of the hedged borrowings was £1,810 million , of which £202 million was current and £1,608 million was non-current. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in fair value hedges of foreign currency risk and interest rates. It has resulted in a prior year equal and offsetting impact of £4 million to the balances used for the ‘Change in value used for calculating ineffectiveness’. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2020 Balance in cash flow hedge reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (4,127 ) (69 ) (22 ) 142 (143 ) (1 ) Foreign currency risk on forecasted cash flows (794 ) 8 — 17 (17 ) — 1. Included within the hedging instrument notional balance is £176 million impacted by Interest Rate Benchmark Reform amendments. As at 31 March 2019 Balance in cash flow hedge reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings¹ (3,804 ) (17 ) 51 206 (206 ) — Foreign currency risk on forecasted cash flows (697 ) 45 — 12 (12 ) — 1. Following a review in the year, we have changed our presentation of spot foreign exchange movements on derivatives designated in cash flow hedges of foreign currency risk and interest rates. This has no net impact on the consolidated statement of comprehensive income. It has resulted in a prior year equal and offsetting impact of £167 million to the balances used for the ‘Change in value used for calculating ineffectiveness’. (iii) Net investment hedges of foreign currency risk: As at 31 March 2020 Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Currency risk on foreign operations¹ (3,064 ) 45 (2,871 ) (6 ) 6 — 1. Included within the hedging instrument notional balance is £nil impacted by Interest Rate Benchmark Reform amendments. As at 31 March 2019 Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Currency risk on foreign operations (2,974 ) (329 ) (2,502 ) 550 (550 ) —
Disclosure of fair value measurement of assets	The changes in value of our Level 3 financial instruments are as follows: Financing derivatives Commodity contract derivatives Other 3,4 Total 2020 2019 2020 2019 2020 2019 2020 2019 £m £m £m £m £m £m £m £m At 1 April (214 ) (219 ) 1 (1 ) 152 194 (61 ) (26 ) Net (losses)/gains for the year 1,2 (20 ) 4 6 (16 ) 26 15 12 3 Purchases — — 26 44 51 57 77 101 Acquisition of Geronimo — — — — (74 ) — (74 ) — Settlements (1 ) 1 (31 ) (26 ) (18 ) (4 ) (50 ) (29 ) Reclassification to held for sale³ — — — — — (110 ) — (110 ) At 31 March (235 ) (214 ) 2 1 137 152 (96 ) (61 ) 1. Loss of £20 million ( 2019 : £4 million gain ) is attributable to derivative financial instruments held at the end of the reporting period and has been recognised in finance costs in the income statement. 2. Loss of £17 million ( 2019 : £21 million loss ) is attributable to commodity contract derivative financial instruments held at the end of the reporting period. 3. Relates to our put and call options over our interests in Quadgas, that were classified as held for sale at 31 March 2019. 4. Other comprises our investments in Sunrun Neptune 2016 LLC, Enbala and the investments made by National Grid Partners, which are accounted for at fair value through profit and loss as well as the contingent consideration arising from the acquisition of Geronimo (see note 38). 2020 2019 Level 1 £m Level 2 £m Level 3 £m Total £m Level 1 £m Level 2 £m Level 3 £m Total £m Assets Investments held at FVTPL 1,278 — 108 1,386 1,311 — 62 1,373 Investments held at FVOCI 83 352 — 435 93 343 — 436 Investments in associates¹ — — 103 103 — — 90 90 Financing derivatives — 1,257 10 1,267 — 1,050 2 1,052 Commodity contract derivatives — 9 66 75 — 33 68 101 1,361 1,618 287 3,266 1,404 1,426 222 3,052 Liabilities Financing derivatives — (889 ) (245 ) (1,134 ) — (868 ) (216 ) (1,084 ) Commodity contract derivatives — (136 ) (64 ) (200 ) — (32 ) (67 ) (99 ) Liabilities held at fair value (741 ) — — (741 ) (667 ) — — (667 ) Contingent consideration² — — (74 ) (74 ) — — — — (741 ) (1,025 ) (383 ) (2,149 ) (667 ) (900 ) (283 ) (1,850 ) 620 593 (96 ) 1,117 737 526 (61 ) 1,202 1. Our Level 3 investments include investments relating to Sunrun Neptune 2016 LLC accounted for at FVTPL. 2. Contingent consideration relates to the acquisition of Geronimo (see note 38). Level 1: Financial instruments with quoted prices for identical instruments in active markets. Level 2: Financial instruments with quoted prices for similar instruments in active markets or quoted prices for identical or similar instruments in inactive markets, and financial instruments valued using models where all significant inputs are based directly or indirectly on observable market data. Level 3: Financial instruments valued using valuation techniques where one or more significant inputs are based on unobservable market data.
Disclosure of fair value measurement of liabilities	The changes in value of our Level 3 financial instruments are as follows: Financing derivatives Commodity contract derivatives Other 3,4 Total 2020 2019 2020 2019 2020 2019 2020 2019 £m £m £m £m £m £m £m £m At 1 April (214 ) (219 ) 1 (1 ) 152 194 (61 ) (26 ) Net (losses)/gains for the year 1,2 (20 ) 4 6 (16 ) 26 15 12 3 Purchases — — 26 44 51 57 77 101 Acquisition of Geronimo — — — — (74 ) — (74 ) — Settlements (1 ) 1 (31 ) (26 ) (18 ) (4 ) (50 ) (29 ) Reclassification to held for sale³ — — — — — (110 ) — (110 ) At 31 March (235 ) (214 ) 2 1 137 152 (96 ) (61 ) 1. Loss of £20 million ( 2019 : £4 million gain ) is attributable to derivative financial instruments held at the end of the reporting period and has been recognised in finance costs in the income statement. 2. Loss of £17 million ( 2019 : £21 million loss ) is attributable to commodity contract derivative financial instruments held at the end of the reporting period. 3. Relates to our put and call options over our interests in Quadgas, that were classified as held for sale at 31 March 2019. 4. Other comprises our investments in Sunrun Neptune 2016 LLC, Enbala and the investments made by National Grid Partners, which are accounted for at fair value through profit and loss as well as the contingent consideration arising from the acquisition of Geronimo (see note 38). 2020 2019 Level 1 £m Level 2 £m Level 3 £m Total £m Level 1 £m Level 2 £m Level 3 £m Total £m Assets Investments held at FVTPL 1,278 — 108 1,386 1,311 — 62 1,373 Investments held at FVOCI 83 352 — 435 93 343 — 436 Investments in associates¹ — — 103 103 — — 90 90 Financing derivatives — 1,257 10 1,267 — 1,050 2 1,052 Commodity contract derivatives — 9 66 75 — 33 68 101 1,361 1,618 287 3,266 1,404 1,426 222 3,052 Liabilities Financing derivatives — (889 ) (245 ) (1,134 ) — (868 ) (216 ) (1,084 ) Commodity contract derivatives — (136 ) (64 ) (200 ) — (32 ) (67 ) (99 ) Liabilities held at fair value (741 ) — — (741 ) (667 ) — — (667 ) Contingent consideration² — — (74 ) (74 ) — — — — (741 ) (1,025 ) (383 ) (2,149 ) (667 ) (900 ) (283 ) (1,850 ) 620 593 (96 ) 1,117 737 526 (61 ) 1,202 1. Our Level 3 investments include investments relating to Sunrun Neptune 2016 LLC accounted for at FVTPL. 2. Contingent consideration relates to the acquisition of Geronimo (see note 38). Level 1: Financial instruments with quoted prices for identical instruments in active markets. Level 2: Financial instruments with quoted prices for similar instruments in active markets or quoted prices for identical or similar instruments in inactive markets, and financial instruments valued using models where all significant inputs are based directly or indirectly on observable market data. Level 3: Financial instruments valued using valuation techniques where one or more significant inputs are based on unobservable market data.
Sensitivity analysis for types of market risk	The impacts on a post-tax basis of reasonably possible changes in significant Level 3 assumptions are as follows: Financing derivatives Commodity contract derivatives Other 3 2020 2019 2020 2019 2020 2019 £m £m £m £m £m £m 10% increase in commodity prices¹ — — 2 (1 ) — — 10% decrease in commodity prices¹ — — — 2 — — +10% market area price change — — (4 ) (10 ) — — -10% market area price change — — 4 10 — — +20 basis points change in Limited Price Inflation (LPI) market curve² (95 ) (88 ) — — — — -20 basis points change in LPI market curve² 90 83 — — — — +50 basis points change in discount rate — — — — (3 ) (3 ) -50 basis points change in discount rate — — — — 4 3 1. Level 3 commodity price sensitivity is included within the sensitivity analysis disclosed in note 35. 2. A reasonably possible change in assumption of other Level 3 derivative financial instruments is unlikely to result in a material change in fair values. 3. The investments acquired in the period were on market terms, and sensitivity is considered insignificant at 31 March 2020 .

Borrowing facilities (Tables)

Borrowing facilities (Tables)	12 Months Ended
	Mar. 31, 2020
Disclosure of detailed information about borrowings [abstract]
Schedule of undrawn committed borrowing facilities	An analysis of the maturity of these undrawn committed facilities is shown below: 2020 2019 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — — In 1 to 2 years 1,940 — In 2 to 3 years 1,668 2,190 In 3 to 4 years 277 1,668 In 4 to 5 years 1,887 1,869 More than 5 years — — 5,772 5,727

Sensitivities (Tables)

Sensitivities (Tables)	12 Months Ended
	Mar. 31, 2020
Disclosure of sensitivity analysis for actuarial assumptions [abstract]
Schedule of sensitivity analysis for actuarial assumptions	Derivative financial instruments were used to manage foreign currency risk as follows: 2020 2019 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 18 — 55 — 73 97 2 153 — 252 Financial investments 813 — 1,185 — 1,998 965 — 1,016 — 1,981 Borrowings (12,407 ) (4,150 ) (13,217 ) (1,020 ) (30,794 ) (10,591 ) (4,787 ) (12,126 ) (1,226 ) (28,730 ) Pre-derivative position (11,576 ) (4,150 ) (11,977 ) (1,020 ) (28,723 ) (9,529 ) (4,785 ) (10,957 ) (1,226 ) (26,497 ) Derivative effect (1,169 ) 4,341 (4,214 ) 1,175 133 (1,055 ) 4,803 (5,245 ) 1,465 (32 ) Net debt position (12,745 ) 191 (16,191 ) 155 (28,590 ) (10,584 ) 18 (16,202 ) 239 (26,529 ) The currency exposure on other financial instruments is as follows: 2020 2019 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 306 — 1,403 — 1,709 398 — 1,635 — 2,033 Trade and other payables (1,177 ) — (2,002 ) — (3,179 ) (1,221 ) — (2,085 ) — (3,306 ) Other non-current liabilities (85 ) — (277 ) — (362 ) (93 ) — (247 ) — (340 ) 2020 2019 Income statement £m Other equity reserves £m Income statement £m Other equity reserves £m Financial risk (post-tax): UK RPI change of 0.5%¹ 27 — 27 — UK interest rates change of 0.5% 14 47 16 13 US interest rates change of 0.5% 5 27 11 44 US dollar exchange rate change of 10%² 49 216 53 246 1. Excludes sensitivities to LPI curve. Further details on sensitivities are provided in note 32(g). 2. The other equity reserves impact does not reflect the exchange translation in our US subsidiaries’ net assets. It is estimated this would change by £1,319 million ( 2019 : £1,119 million ) in the opposite direction if the dollar exchange rate changed by 10% . Our commodity contract derivatives are sensitive to price risk. Additional sensitivities in respect to commodity price risk and to our derivative fair values are as follows: 2020 2019 Income statement £m Net assets £m Income statement £m Net assets £m Commodity price risk (post-tax): 10% increase in commodity prices 26 26 26 26 10% decrease in commodity prices (27 ) (27 ) (27 ) (27 ) Assets and liabilities carried at fair value (post-tax): 10% fair value change in derivative financial instruments¹ 12 12 (3 ) (3 ) 10% fair value change in commodity contract derivative liabilities 9 9 — — 1. The effect of a 10% change in fair value assumes no hedge accounting. The table below sets out the sensitivity analysis for certain areas of estimation uncertainty set out in note 1E. These estimates are those that have a significant risk of resulting in a material adjustment to the carrying values of assets and liabilities in the next year. Note that the sensitivity analysis for the useful economic lives of our gas network assets is included in note 13. 2020 2019 Income statement £m Net assets £m Income statement £m Net assets £m Pensions and other post-retirement benefit liabilities (pre-tax)¹: UK discount rate change of 0.5%² 6 877 6 1,064 US discount rate change of 0.5%² 10 514 16 688 UK RPI rate change of 0.5%³ 4 670 4 908 UK long-term rate of increase in salaries change of 0.5% 1 39 1 56 US long-term rate of increase in salaries change of 0.5% 2 47 2 46 UK change of one year to life expectancy at age 65 4 1 545 1 610 US change of one year to life expectancy at age 65 4 456 4 406 Assumed US healthcare cost trend rates change of 1% 31 507 32 503 Pension assets: Change in value of unquoted equities by 10% — 381 — 415 Change in value of unquoted properties by 10% — 89 — 107 Change in value of unquoted diversified alternatives by 10% — 152 — 142 Environmental provision: 10% change in estimated future cash flows 210 210 165 165 1. The changes shown are a change in the annual pension or other post-retirement benefit service charge and change in the defined benefit obligations. 2. A change in the discount rate is likely to occur as a result of changes in bond yields and as such would be expected to be offset to a significant degree by a change in the value of the bond assets held by the plans. In the UK, there would also be a £205 million net assets offset from the buy-in policies purchased in the year, where the accounting value of the buy-in asset is set equal to the associated liabilities. 3. The projected impact resulting from a change in RPI reflects the underlying effect on pensions in payment, pensions in deferment and resultant increases in salary assumptions. The buy-in policies purchased during the year would have a £152 million net assets offset to the above. 4. In the UK, the buy-in policies purchased during the year, and the longevity swap entered into previously, would have a £223 million net assets offset to the above.

Additional disclosures in res_2

Additional disclosures in respect of guaranteed securities (Tables)	12 Months Ended
	Mar. 31, 2020
Separate Financial Statements [Abstract]
Disclosure of Condensed Balance Sheet	Summarised financial information for the year ended 31 March 2020 – IFRS National Grid plc and Niagara Mohawk Power Corporation combined £m Combined statement of financial position Non-current loans to other subsidiaries 363 Non-current assets 8,939 Current loans to other subsidiaries 12,435 Current assets 1,378 Current loans from other subsidiaries (16,226 ) Current liabilities (1,648 ) Non-current loans from other subsidiaries (2,105 ) Non-current liabilities (5,460 ) Net liabilities¹ (2,324 ) Equity (2,324 ) Combined income statement – continuing operations Revenue 2,365 Operating costs (2,131 ) Operating profit 234 Other income from other subsidiaries 3,888 Other income and costs, including taxation (428 ) Profit after tax 3,694 1. Excluded from net liabilities above are investments in other consolidated subsidiaries with a carrying value of £14,362 million .
Disclosure of Condensed Income Statement	Summarised financial information for the year ended 31 March 2020 – IFRS National Grid plc and Niagara Mohawk Power Corporation combined £m Combined statement of financial position Non-current loans to other subsidiaries 363 Non-current assets 8,939 Current loans to other subsidiaries 12,435 Current assets 1,378 Current loans from other subsidiaries (16,226 ) Current liabilities (1,648 ) Non-current loans from other subsidiaries (2,105 ) Non-current liabilities (5,460 ) Net liabilities¹ (2,324 ) Equity (2,324 ) Combined income statement – continuing operations Revenue 2,365 Operating costs (2,131 ) Operating profit 234 Other income from other subsidiaries 3,888 Other income and costs, including taxation (428 ) Profit after tax 3,694 1. Excluded from net liabilities above are investments in other consolidated subsidiaries with a carrying value of £14,362 million .

Transition to new accounting _2

Transition to new accounting standards (Tables)	12 Months Ended
	Mar. 31, 2020
Disclosure of initial application of standards or interpretations [abstract]
Disclosure of impact of transition to new accounting standards	The impact of the transition on the opening consolidated statement of financial position is set out in the following table: Impact of transition 31 March 2018 Transition adjustments 1 April 2018 IFRS 9 IFRS 15 £m £m £m £m Non-current assets Goodwill 5,444 — — 5,444 Other intangible assets 899 — — 899 Property, plant and equipment 39,853 — — 39,853 Other non-current assets 115 — — 115 Pension assets 1,409 — — 1,409 Financial and other investments 899 — 1 — 899 Investments in joint ventures and associates 2,168 — — 2,168 Derivative financial assets 1,319 — — 1,319 Total non-current assets 52,106 — — 52,106 Current assets Inventories and current intangible assets 341 — — 341 Trade and other receivables 2,798 — 2 (3 ) 2,795 Current tax assets 114 — — 114 Financial and other investments 2,694 — 1 — 2,694 Derivative financial assets 405 — — 405 Cash and cash equivalents 329 — — 329 Total current assets 6,681 — (3 ) 6,678 Total assets 58,787 — (3 ) 58,784 Current liabilities Borrowings (4,447 ) — — (4,447 ) Derivative financial liabilities (401 ) — — (401 ) Trade and other payables (3,453 ) — 59 7 (3,394 ) Contract liabilities — — (53) 7 (53 ) Current tax liabilities (123 ) — — (123 ) Provisions (273 ) — — (273 ) Total current liabilities (8,697 ) — 6 (8,691 ) Non-current liabilities Borrowings (22,178 ) (32) 3 — (22,210 ) Derivative financial liabilities (660 ) — — (660 ) Other non-current liabilities (1,317 ) — 567 7 (750 ) Contract liabilities — — (813) 7 (813 ) Deferred tax liabilities (3,636 ) 5 4 74 8 (3,557 ) Pensions and other post-retirement benefit obligations (1,672 ) — — (1,672 ) Provisions (1,779 ) — — (1,779 ) Total non-current liabilities (31,242 ) (27 ) (172 ) (31,441 ) Total liabilities (39,939 ) (27 ) (166 ) (40,132 ) Net assets 18,848 (27 ) (169 ) 18,652 Equity Share capital 452 — — 452 Share premium account 1,321 — — 1,321 Retained earnings 21,599 (99) 5 (169) 9 21,331 Other equity reserves (4,540 ) 72 6 — (4,468 ) Total shareholders’ equity 18,832 (27 ) (169 ) 18,636 Non-controlling interests 16 — — 16 Total equity 18,848 (27 ) (169 ) 18,652 Impact of transition 31 March 2019 IFRS 16 1 April 2019 £m £m £m Property, plant and equipment – Right-of-use assets Land and buildings 2,560 381 2,941 Plant and machinery 36,589 67 36,656 Assets in the course of construction 4,425 — 4,425 Motor vehicles and office equipment 339 20 359 Total property, plant and equipment 43,913 468 44,381 Borrowings – Lease liabilities Current (65 ) (48 ) (113 ) Non-current (205 ) (426 ) (631 ) Total lease liabilities (270 ) (474 ) (744 ) Other liabilities Trade and other payables (3,769 ) 3 (3,766 ) Other non-current liabilities (808 ) 3 (805 ) Net assets 19,369 — 19,369 Equity Total equity 19,369 — 19,369
Disclosure of financial liabilities at date of initial application of IFRS 9	The table below illustrates those financial assets and liabilities that were reclassified at 1 April 2018: Financial asset/liability Note Original measurement category under IAS 39 New measurement category under IFRS 9 Original carrying amount under IAS 39 Change to measurement basis under IFRS 9 New carrying amount under IFRS 9 £m £m £m Money market funds and fund investments in equities and bonds 15 Available-for-sale investments Financial assets at FVTPL 2,294 — 2,294 Cash surrender value of life insurance policies and investments in debt securities 15 Available-for-sale investments Financial assets at FVOCI 343 — 343 Investments in equity securities 15 Available-for-sale investments Financial assets at FVOCI (equity instruments) 84 — 84 Loans to joint ventures and associates and restricted balances 15 Loans and receivables Financial assets at amortised cost 872 — 872 Borrowings 21 Financial liabilities at amortised cost Financial liabilities at fair value through profit and loss (570 ) (32 ) (602 )
Disclosure of financial assets at date of initial application of IFRS 9	The table below illustrates those financial assets and liabilities that were reclassified at 1 April 2018: Financial asset/liability Note Original measurement category under IAS 39 New measurement category under IFRS 9 Original carrying amount under IAS 39 Change to measurement basis under IFRS 9 New carrying amount under IFRS 9 £m £m £m Money market funds and fund investments in equities and bonds 15 Available-for-sale investments Financial assets at FVTPL 2,294 — 2,294 Cash surrender value of life insurance policies and investments in debt securities 15 Available-for-sale investments Financial assets at FVOCI 343 — 343 Investments in equity securities 15 Available-for-sale investments Financial assets at FVOCI (equity instruments) 84 — 84 Loans to joint ventures and associates and restricted balances 15 Loans and receivables Financial assets at amortised cost 872 — 872 Borrowings 21 Financial liabilities at amortised cost Financial liabilities at fair value through profit and loss (570 ) (32 ) (602 )

Acquisition of Geronimo Energ_2

Acquisition of Geronimo Energy LLC and Emerald Energy Venture LLC (Tables)	12 Months Ended
	Mar. 31, 2020
Business Combinations [Abstract]
Schedule of fair values of the assets and liabilities recognised	The fair values of the assets and liabilities recognised from both the acquisition of the subsidiary, Geronimo, and the joint venture, Emerald, are set out below. £m Intangible assets 5 Property, plant and equipment 1 Investment in joint venture – Emerald 90 Cash 2 Other identifiable assets and liabilities 30 Total identifiable assets 128 Goodwill 81 Total consideration transferred 209 Satisfied by: Contingent consideration – Geronimo 70 Cash consideration – Geronimo 49 Cash consideration – Emerald 90 209

Basis of preparation and rece_3

Basis of preparation and recent accounting developments - Going concern (Details) - GBP (£) £ in Billions	12 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
Extended lockdown period, reasonable worst-case scenario for COVID-19	12 months
Reduced cash collection period, reasonable worst-case scenario for COVID-19	12 months
Fixed interest rate bonds | Borrowings transactions
Disclosure of detailed information about borrowings [line items]
Notional amount		£ 0.9

Basis of preparation and rece_4

Basis of preparation and recent accounting developments - Treatment of interests in Quadgas HoldCo Limited (Quadgas) (Details)	1 Months Ended
	Jun. 30, 2019
UK Gas Distribution (Cadent)
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed	39.00%

Basis of preparation and rece_5

Basis of preparation and recent accounting developments - Accounting policy choices (Details) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
Cash inflow (outflow) for derivatives presented as investing activities	[1]	£ (223)	£ (412)	£ 330
[1]	Certain derivative balances have been represented for all periods presented to reflect a reclassification from financing activities to investing activities to reflect a change in accounting policy (see note 1 for details).

Segmental analysis - Narrative

Segmental analysis - Narrative (Details)	12 Months Ended
	Mar. 31, 2020GBP (£)segment	Mar. 31, 2019GBP (£)	Mar. 31, 2018GBP (£)
Disclosure of operating segments [line items]
Number of operating segments | segment	3
Operating profit/(loss) from continuing operations	£ 2,780,000,000	£ 2,870,000,000	£ 3,493,000,000
UK
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	1,915,000,000	1,422,000,000	1,840,000,000
Total non-current assets other than financial instruments and pension assets	31,780,000,000	30,072,000,000	20,816,000,000
US
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	865,000,000	1,448,000,000	1,653,000,000
Total non-current assets other than financial instruments and pension assets	25,867,000,000	21,787,000,000	27,663,000,000
UK Electricity Transmission | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	1,316,000,000	778,000,000	1,041,000,000
UK Gas Transmission | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	347,000,000	267,000,000	487,000,000
US Regulated | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	880,000,000	1,425,000,000	1,734,000,000
NG Ventures and Other | Unallocated amounts
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	237,000,000	400,000,000	231,000,000
Exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	(527,000,000)	(572,000,000)	36,000,000
Exceptional items and remeasurements | UK Electricity Transmission | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	(4,000,000)	(237,000,000)	0
Exceptional items and remeasurements | UK Gas Transmission | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	(1,000,000)	(36,000,000)	0
Exceptional items and remeasurements | US Regulated | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	(517,000,000)	(299,000,000)	36,000,000
Exceptional items and remeasurements | NG Ventures and Other | Unallocated amounts
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	£ (5,000,000)	£ 0	£ 0

Segmental analysis - Revenue (D

Segmental analysis - Revenue (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of operating segments [line items]
Revenue	£ 14,540	£ 14,933	£ 15,250
UK
Disclosure of operating segments [line items]
Revenue	5,282	5,045	5,938
US
Disclosure of operating segments [line items]
Revenue	9,258	9,888	9,312
UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	3,694	3,331	4,126
UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	911	884	1,082
US Regulated
Disclosure of operating segments [line items]
Revenue	9,205	9,846	9,272
NG Ventures and Other
Disclosure of operating segments [line items]
Revenue	730	872	770
Operating Segments And Unallocated Amounts
Disclosure of operating segments [line items]
Revenue	14,570	14,969	15,293
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	3,702	3,351	4,154
Operating segments | UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	927	896	1,091
Operating segments | US Regulated
Disclosure of operating segments [line items]
Revenue	9,205	9,846	9,272
Unallocated amounts | NG Ventures and Other
Disclosure of operating segments [line items]
Revenue	736	876	776
Unallocated amounts | NG Ventures
Disclosure of operating segments [line items]
Revenue	608	597	593
Sales between segments
Disclosure of operating segments [line items]
Revenue	(30)	(36)	(43)
Sales between segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	(8)	(20)	(28)
Sales between segments | UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	(16)	(12)	(9)
Sales between segments | US Regulated
Disclosure of operating segments [line items]
Revenue	0	0	0
Sales between segments | NG Ventures and Other
Disclosure of operating segments [line items]
Revenue	£ (6)	£ (4)	£ (6)

Segmental analysis - Operating

Segmental analysis - Operating profit from continuing operations (Details) £ in Millions	12 Months Ended
	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)settlement	Mar. 31, 2018GBP (£)
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 2,780	£ 2,870	£ 3,493
Cash received from legal settlements		£ 95
Number of legal settlements | settlement		2
Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	3,307	£ 3,442	3,457
UK
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,915	1,422	1,840
UK | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,925	1,695	1,840
US
Disclosure of operating segments [line items]
Operating profit from continuing operations	865	1,448	1,653
US | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,382	1,747	1,617
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,316	778	1,041
Operating segments | UK Electricity Transmission | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,320	1,015	1,041
Operating segments | UK Gas Transmission
Disclosure of operating segments [line items]
Operating profit from continuing operations	347	267	487
Operating segments | UK Gas Transmission | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	348	303	487
Operating segments | US Regulated
Disclosure of operating segments [line items]
Operating profit from continuing operations	880	1,425	1,734
Operating segments | US Regulated | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,397	1,724	1,698
Unallocated amounts | NG Ventures and Other
Disclosure of operating segments [line items]
Operating profit from continuing operations	237	400	231
Cash received from legal settlements		£ 95
Number of legal settlements | settlement		2
Unallocated amounts | NG Ventures and Other | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	242	£ 400	231
Unallocated amounts | NG Ventures
Disclosure of operating segments [line items]
Operating profit from continuing operations	268	263	234
Unallocated amounts | NG Ventures | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 269	£ 263	£ 234

Segmental analysis - Reconcile

Segmental analysis - Reconcile total operating profit to profit before tax from continuing operations (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 2,780	£ 2,870	£ 3,493
Finance income	54	88	127
Finance costs	(1,167)	(1,157)	(1,009)
Share of post-tax results of joint ventures and associates	87	40	49
Profit/(loss) before tax	1,754	1,841	2,660
Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	3,307	3,442	3,457
Finance income	70	73	127
Finance costs	(1,119)	(1,066)	(1,128)
Share of post-tax results of joint ventures and associates	88	40	44
Profit/(loss) before tax	£ 2,346	£ 2,489	£ 2,500

Segmental analysis - Capital ex

Segmental analysis - Capital expenditure (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	£ 50,065	£ 44,997	£ 40,752
Capital expenditure	5,079	4,321	4,074
Depreciation, amortisation and impairment	(1,640)	(1,735)	(1,530)
Property, plant and equipment
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	48,770	43,913	39,853
Capital expenditure	4,727	4,015	3,901
Depreciation, amortisation and impairment	(1,464)	(1,560)	(1,392)
Non-current intangible assets
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	1,295	1,084	899
Capital expenditure	352	306	173
Depreciation, amortisation and impairment	(176)	(175)	(138)
UK
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	20,427	19,343	18,772
Capital expenditure	1,847	1,584	1,527
Depreciation, amortisation and impairment	(784)	(931)	(804)
US
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	29,638	25,654	21,980
Capital expenditure	3,232	2,737	2,547
Depreciation, amortisation and impairment	(856)	(804)	(726)
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	13,788	13,288	13,028
Capital expenditure	1,043	925	999
Depreciation, amortisation and impairment	(469)	(628)	(475)
Operating segments | UK Gas Transmission
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	4,513	4,412	4,280
Capital expenditure	249	308	310
Depreciation, amortisation and impairment	(171)	(181)	(194)
Operating segments | US Regulated
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	29,623	24,542	20,953
Capital expenditure	3,228	2,650	2,424
Depreciation, amortisation and impairment	(855)	(700)	(635)
Unallocated amounts | NG Ventures and Other
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	2,141	2,755	2,491
Capital expenditure	559	438	341
Depreciation, amortisation and impairment	(145)	(226)	(226)
Unallocated amounts | NG Ventures
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	2,080	1,635	1,454
Capital expenditure	550	317	186
Depreciation, amortisation and impairment	£ (124)	(114)	(143)
2020 Software assets and properties transferred from NGV and Other segment to US Regulated segment, remaining in NG Venture and Other | Unallocated amounts | NG Ventures and Other
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets		1,062	998
Capital expenditure		87	161
Depreciation, amortisation and impairment		£ (102)	£ (80)

Revenue - Disaggregation of rev

Revenue - Disaggregation of revenue (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	£ 13,910	£ 14,066
Other revenue	630	867
Revenue	14,540	14,933	£ 15,250
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,671	3,325
Other revenue	23	6
Revenue	3,694	3,331	4,126
UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	878	833
Other revenue	33	51
Revenue	911	884	1,082
US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,756	9,311
Other revenue	449	535
Revenue	9,205	9,846	9,272
NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	605	597
Other revenue	125	275
Revenue	730	872
UK
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	5,116	4,743
Other revenue	166	302
Revenue	5,282	5,045	£ 5,938
UK | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,671	3,325
Other revenue	23	6
UK | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	878	833
Other revenue	33	51
UK | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0
Other revenue	0	0
UK | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	567	585
Other revenue	110	245
US
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,794	9,323
Other revenue	464	565
US | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0
Other revenue	0	0
US | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0
Other revenue	0	0
US | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,756	9,311
Other revenue	449	535
US | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	38	12
Other revenue	15	30
Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,375	3,253
Transmission | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	1,992	1,909
Transmission | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	649	661
Transmission | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	425	370
Transmission | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	309	313
Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,319	8,941
Distribution | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0
Distribution | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0
Distribution | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,319	8,941
Distribution | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0
System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	1,824	1,588
System Operator | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	1,610	1,416
System Operator | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	214	172
System Operator | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0
System Operator | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0
Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	392	284
Other revenue	261	500
Other | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	69	0
Other revenue	23	6
Other | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	15	0
Other revenue	33	51
Other | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	12	0
Other revenue	80	168
Other | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	296	284
Other revenue	125	275
Generation
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	369	367
Generation | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	0	0
Generation | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	0	0
Generation | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	369	367
Generation | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	£ 0	£ 0

Revenue - Narrative (Details)

Revenue - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2019	Apr. 01, 2018
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contract liabilities	£ 1,158	£ 994	£ 994	£ 866
Future revenues in relation to unfulfilled performance obligations	£ 3,100	3,500
Remaining performance obligation, expected timing of satisfaction, period (years)	5 years
Revenue from performance obligations satisfied or partially satisfied in previous periods	£ 0	0
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 1,500	1,600
Remaining performance obligation, expected timing of satisfaction, period (years)	29 years
National Grid Grain LNG Limited
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 1,500	£ 1,800
Connections | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	40 years
Connections | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	36 years
Connections | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	15 years
Connections | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	51 years
Connections | Weighted average
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	18 years

Operating costs - Analysis of e

Operating costs - Analysis of expenses by nature (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Analysis of income and expense [abstract]
Depreciation, amortisation and impairment	£ 1,640	£ 1,735	£ 1,530
Payroll costs	1,684	1,852	1,648
Provision for bad and doubtful debts	234	181	36
Purchases of electricity	1,403	1,454	1,285
Purchases of gas	1,316	1,642	1,543
Property and other taxes	1,191	1,108	1,057
Balancing Services Incentive Scheme	1,317	1,196	1,012
Payments to other UK network owners	0	0	1,043
Other	2,975	2,895	2,603
Operating expense	11,760	12,063	11,757
Inventory consumed	328	415	367
Research and development expenditure	£ 14	£ 19	£ 13

Operating costs - Payroll costs

Operating costs - Payroll costs (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Analysis of income and expense [abstract]
Wages and salaries	£ 2,188	£ 2,084	£ 1,998
Social security costs	168	156	157
Defined contribution scheme costs	75	72	65
Defined benefit pension costs	135	232	156
Share-based payments	19	27	16
Severance costs (excluding pension costs)	1	76	7
Payroll costs including capitalised costs	2,586	2,647	2,399
Less: payroll costs capitalised	(902)	(795)	(751)
Total payroll costs	1,684	1,852	1,648
US other post retirement benefit costs	£ 45	£ 48	£ 46

Operating costs - Number of emp

Operating costs - Number of employees (Details) - employee	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of operating segments [line items]
Number of employees, year end	23,069	22,576	23,023
Average number of employees	22,830	22,896	22,705
UK
Disclosure of operating segments [line items]
Number of employees, year end	6,321	5,962	6,517
Average number of employees	6,151	6,227	6,431
US
Disclosure of operating segments [line items]
Number of employees, year end	16,748	16,614	16,506
Average number of employees	16,679	16,669	16,274

Operating costs - Key managemen

Operating costs - Key management personnel (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Analysis of income and expense [abstract]
Short-term employee benefits	£ 7	£ 7	£ 8
Compensation for loss of office	1	0	0
Post-employment benefits	1	1	1
Share-based payments	3	3	3
Total key management compensation	£ 12	£ 11	£ 12

Operating costs - Auditors remu

Operating costs - Auditors remuneration (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Analysis of income and expense [abstract]
Audit of the Parent Company’s individual and consolidated financial statements	£ 1.9	£ 1.6	£ 2.7
The auditing of accounts of any associate of the Company	8.7	8.5	9.3
Other services supplied	6.3	5.2	3.9
Auditor's remuneration for audit services	16.9	15.3	15.9
Tax compliance services	0	0	0.3
Tax advisory services	0	0	0
Other assurance services	0.6	1.1	0.7
Services relating to corporate finance transactions not covered above	0	0	0
Other non-audit services not covered above	0.5	2.2	0.9
Auditor's remuneration for tax and other services	1.1	3.3	1.9
Total auditors’ remuneration	£ 18	£ 18.6	£ 17.8

Exceptional items and remeasu_3

Exceptional items and remeasurements (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of associates [line items]
Massachusetts Gas labour dispute	£ (1,684)	£ (1,852)	£ (1,648)
Operating profit/(loss)	2,780	2,870	3,493
Finance income and costs	(1,113)	(1,069)	(882)
Profit/(loss) before tax	1,754	1,841	2,660
Tax expense (income) on exceptional items and remeasurements	(480)	(339)	889
Profit/(loss) after tax from continuing operations	1,274	1,502	3,549
Exceptional items and remeasurements
Disclosure of associates [line items]
Operating profit/(loss)	(527)	(572)	36
Profit/(loss) before tax	(592)	(648)	160
Tax expense (income) on exceptional items and remeasurements	(47)	149	1,473
Profit/(loss) after tax from continuing operations	(639)	(499)	1,633
Exceptional items
Disclosure of associates [line items]
Environmental charges	(402)	0	0
Cost efficiency and restructuring programmes	0	(204)	0
Massachusetts Gas labour dispute	0	(283)	0
Impairment of nuclear connection development costs	0	(137)	0
Final settlement of LIPA MSA Transition	0	0	26
Operating profit/(loss)	(402)	(624)	26
Deferred tax arising on the reduction in US corporation tax rate	0	0	5
Tax expense (income) on exceptional items and remeasurements	103	144	(9)
Profit/(loss) after tax from continuing operations	(491)	(480)	1,532
Remeasurements
Disclosure of associates [line items]
Net gains/(losses) on financing derivatives	1	(40)	119
Net (losses)/gains on financial assets at fair value through profit and loss	(16)	15	0
Net losses on financial liabilities at fair value through profit and loss	(49)	(51)	0
Finance income and costs	(64)	(76)	119
Net losses on financial instruments	(1)	0	0
Tax expense (income) on exceptional items and remeasurements	42	5	(28)
Profit/(loss) after tax from continuing operations	(148)	(19)	101
Remeasurements | Commodity contract derivatives
Disclosure of associates [line items]
Operating profit/(loss)	(125)	52	10
US | Exceptional items
Disclosure of associates [line items]
Deferred tax arising on the reversal of the reduction in UK corporation tax rate	0	0	1,510
UK | Exceptional items
Disclosure of associates [line items]
Deferred tax arising on the reversal of the reduction in UK corporation tax rate	£ (192)	£ 0	£ 0

Exceptional items and remeasu_4

Exceptional items and remeasurements - Narrative (Details)	12 Months Ended
	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)settlementcancellation	Mar. 31, 2018GBP (£)	Mar. 31, 2017GBP (£)	May 31, 2018employee
Disclosure of other provisions [line items]
COVID-19 related costs	£ 10,000,000
Other provisions	2,654,000,000	£ 2,199,000,000	£ 2,052,000,000
Additions	589,000,000	226,000,000
Massachusetts Gas work continuation	1,684,000,000	1,852,000,000	1,648,000,000
Cash received from legal settlements		£ 95,000,000
Number of legal settlements | settlement		2
Environmental
Disclosure of other provisions [line items]
Other provisions	2,071,000,000	£ 1,639,000,000	1,531,000,000
Additions	£ 437,000,000	£ 32,000,000
Real discount rate	0.50%	1.00%
Weighted average duration of cash flows	10 years
Exceptional items
Disclosure of other provisions [line items]
Environmental charges	£ 402,000,000	£ 0	0
Massachusetts Gas work continuation	0	283,000,000	0
Cost efficiency and restructuring programmes	0	£ 204,000,000	0
Number of nuclear connection cancellations (cancellation) | cancellation		2
Impairment of nuclear connection development costs	0	£ 137,000,000	0
Cash outflow for cost efficiency and restructuring programmes		93,000,000
Payments related to work continuation		£ 320,000,000
Development period of assets (over) (in years)		10 years
Proceeds from termination fees received		£ 13,000,000
Final settlement of LIPA MSA Transition	0	0	£ 26,000,000
Deferred tax expense arising from reduction in UK tax rate				£ 94,000,000
Exceptional items | Environmental
Disclosure of other provisions [line items]
Additions	402,000,000	0
Exceptional items, change in estimate of total cost and cost sharing | Environmental
Disclosure of other provisions [line items]
Additions	326,000,000
Exceptional items, impact of change in the real discount rate | Environmental
Disclosure of other provisions [line items]
Additions	76,000,000
UK
Disclosure of other provisions [line items]
Deferred tax expense due to change in substantively enacted UK Corporation tax rate	192,000,000
UK | Environmental
Disclosure of other provisions [line items]
Other provisions	175,000,000	£ 189,000,000
Additions	£ 10,000,000
Real discount rate	0.50%	1.00%
Weighted average duration of cash flows	11 years
US | Environmental
Disclosure of other provisions [line items]
Other provisions	£ 1,896,000,000	£ 1,450,000,000
Additions	£ 66,000,000
Real discount rate	0.50%	1.00%
Weighted average duration of cash flows	9 years
US Regulated | Massachusetts
Disclosure of other provisions [line items]
Number of employees (employee) | employee					1,250

Finance income and costs (Detai

Finance income and costs (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Finance Income And Costs [Line Items]
Finance income	£ 54	£ 88	£ 127
Finance costs	(1,167)	(1,157)	(1,009)
Finance income and costs	(1,113)	(1,069)	(882)
Before exceptional items and remeasurements
Finance Income And Costs [Line Items]
Bank deposits and other financial assets	48	54	54
Dividends received on equities held at fair value through other comprehensive income	2	2	0
Gains on disposal of available-for-sale investments	0	0	73
Other income	20	17	0
Finance income	70	73	127
Net interest on pensions and other post-retirement benefit obligations	(23)	(22)	(65)
Bank loans and overdrafts	(73)	(72)	(87)
Other borrowings¹	(997)	(970)	(1,030)
Interest expense on financial liabilities held at fair value through profit and loss	(22)	(20)	0
Derivatives	(39)	(43)	12
Unwinding of discount on provisions	(77)	(74)	(75)
Other interest	(10)	0	(11)
Less: interest capitalised	122	135	128
Finance costs	£ (1,119)	£ (1,066)	£ (1,128)
Capitalisation rate of borrowing costs eligible for capitalisation	3.60%	3.90%	4.10%
Tax relief on capitalised interest	£ 15	£ 19	£ 20
Remeasurements
Finance Income And Costs [Line Items]
Finance income	(16)	15	0
Finance costs	(48)	(91)	119
Net (losses)/gains on financial assets at fair value through profit and loss	(16)	15	0
Net losses on financial liabilities held at fair value through profit and loss	(49)	(51)	0
Derivatives designated as hedges for hedge accounting	(13)	(37)	49
Derivatives not designated as hedges for hedge accounting	14	(3)	70
Finance income and costs	(64)	(76)	119
Net foreign exchange gain (loss) on financing activities	£ 66	£ 264	£ 314

Tax - Tax charges (Details)

Tax - Tax charges (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Current tax:
Total current tax from continuing operations	£ 132	£ 88	£ 193
Deferred tax:
Total deferred tax from continuing operations	348	251	(1,082)
Total tax charge/(credit) from continuing operations	480	339	(889)
UK
Current tax:
Corporation tax	179	132	200
Corporate tax adjustment in respect of prior years	(4)	(12)	(18)
Total current tax from continuing operations	175	120	182
Deferred tax:
Deferred tax	269	27	65
Deferred tax adjustment in respect of prior years	6	2	(2)
Total deferred tax from continuing operations	275	29	63
Overseas
Current tax:
Corporation tax	(2)	8	15
Corporate tax adjustment in respect of prior years	(41)	(40)	(4)
Total current tax from continuing operations	(43)	(32)	11
Deferred tax:
Deferred tax	64	208	(1,155)
Deferred tax adjustment in respect of prior years	9	14	10
Total deferred tax from continuing operations	£ 73	£ 222	£ (1,145)

Tax - Tax charged_(credited) to

Tax - Tax charged/(credited) to the consolidated statement of comprehensive income and equity (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Deferred tax:
Tax charged/(credited) to other comprehensive income and equity	£ (250)	£ 3	£ 495
Continuing operations
Current tax:
Available-for-sale investments	0	0	(11)
Cash flow hedges, cost of hedging and own credit reserve	0	3	0
Share-based payments	0	0	(3)
Deferred tax:
Available-for-sale investments	0	0	(18)
Investments at fair value through other comprehensive income	(1)	0	0
Cash flow hedges, cost of hedging and own credit reserve	(40)	(12)	(4)
Remeasurements of pension assets and post-retirement benefit obligations	(206)	12	530
Share-based payments	(3)	0	1
Tax charged/(credited) to other comprehensive income and equity	(250)	3	495
Total tax recognised in the statements of comprehensive income from continuing operations	(247)	3	497
Total tax relating to share-based payments recognised directly in equity from continuing operations	£ (3)	£ 0	(2)
Internal Revenue Service (IRS)
Deferred tax:
Remeasurements of pension assets and post-retirement benefit obligations			£ 281

Tax - Effective tax rate reconc

Tax - Effective tax rate reconciliation (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Income Taxes [Line Items]
Applicable tax rate	19.00%	19.00%	19.00%
Profit before tax from continuing operations	£ 1,754	£ 1,841	£ 2,660
Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2019: 19%; 2018: 19%)	334	350	506
Effect of:
Adjustments in respect of prior years	(30)	(36)	(14)
Expenses not deductible for tax purposes	29	28	21
Non-taxable income	(18)	(36)	(26)
Adjustment in respect of foreign tax rates	18	56	157
Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax	(17)	(8)	(9)
Other	(28)	(12)	(7)
Total tax charge/(credit) from continuing operations	£ 480	£ 339	£ (889)
Effective tax rate – continuing operations	27.40%	18.40%	(33.40%)
Before exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Profit before tax from continuing operations	£ 2,346	£ 2,489	£ 2,500
Exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Profit before tax from continuing operations	(592)	(648)	160
Effect of:
Total tax charge/(credit) from continuing operations	47	(149)	(1,473)
UK
Effect of:
Deferred tax impact of change in tax rate	192	(3)	(7)
US
Effect of:
Deferred tax impact of change in tax rate	£ 0	£ 0	£ (1,510)

Tax - Tax included within the s

Tax - Tax included within the statement of financial position (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	£ 3,965	£ 3,636
Impact of transition to IFRS 9 and IFRS 15			£ (79)
Deferred tax liability (asset), as restated				£ 3,557
Exchange adjustments and other	122	165
(Credited)/charged to income statement	350	243
Charged/(credited) to other comprehensive income and equity	(253)	0
Deferred tax liability (asset) end of period	4,184	3,965
Accelerated tax depreciation
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	5,477	4,874
Impact of transition to IFRS 9 and IFRS 15			19
Deferred tax liability (asset), as restated				4,893
Exchange adjustments and other	210	275
(Credited)/charged to income statement	613	309
Charged/(credited) to other comprehensive income and equity	0	0
Deferred tax liability (asset) end of period	6,300	5,477
Share- based payments
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(9)	(9)
Impact of transition to IFRS 9 and IFRS 15			0
Deferred tax liability (asset), as restated				(9)
Exchange adjustments and other	(30)	0
(Credited)/charged to income statement	(7)	0
Charged/(credited) to other comprehensive income and equity	(2)	0
Deferred tax liability (asset) end of period	(48)	(9)
Pensions and other post- retirement benefits
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(170)	(203)
Impact of transition to IFRS 9 and IFRS 15			0
Deferred tax liability (asset), as restated				(203)
Exchange adjustments and other	(28)	(31)
(Credited)/charged to income statement	44	52
Charged/(credited) to other comprehensive income and equity	(206)	12
Deferred tax liability (asset) end of period	(360)	(170)
Financial instruments
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	7	21
Impact of transition to IFRS 9 and IFRS 15			(5)
Deferred tax liability (asset), as restated				16
Exchange adjustments and other	(3)	(3)
(Credited)/charged to income statement	(13)	6
Charged/(credited) to other comprehensive income and equity	(46)	(12)
Deferred tax liability (asset) end of period	(55)	7
Other net temporary differences
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(1,340)	(1,047)
Impact of transition to IFRS 9 and IFRS 15			£ (93)
Deferred tax liability (asset), as restated				£ (1,140)
Exchange adjustments and other	(27)	(76)
(Credited)/charged to income statement	(287)	(124)
Charged/(credited) to other comprehensive income and equity	1	0
Deferred tax liability (asset) end of period	(1,653)	(1,340)
Net operating losses
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(423)
Deferred tax liability (asset) end of period	(547)	(423)
Environmental provisions
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(409)
Deferred tax liability (asset) end of period	(529)	£ (409)
Reclassification from other temporary differences to share-based payments | Share- based payments
Reconciliation of changes in deferred tax liability (asset) [abstract]
Exchange adjustments and other	(29)
Reclassification from other temporary differences to share-based payments | Other net temporary differences
Reconciliation of changes in deferred tax liability (asset) [abstract]
Exchange adjustments and other	£ 29

Tax - Narrative (Details)

Tax - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Income Taxes [Line Items]
Deferred tax liability (asset)	£ 4,184	£ 3,965	£ 3,636
Deferred tax assets	547	423
Net operating losses
Disclosure Of Income Taxes [Line Items]
Deferred tax liability (asset)	(547)	£ (423)
Deferred tax assets	535
Capital losses
Disclosure Of Income Taxes [Line Items]
Deferred tax assets	£ 12

Tax - Deferred tax assets not r

Tax - Deferred tax assets not recognised (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Capital losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused tax losses for which no deferred tax asset recognised	£ 1,626	£ 1,470
Non-trade deficits
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused tax losses for which no deferred tax asset recognised	1	4
Trading losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused tax losses for which no deferred tax asset recognised	£ 6	£ 5

Earnings per share (EPS) - Narr

Earnings per share (EPS) - Narrative (Details) £ in Millions	Jun. 02, 2017GBP (£)	May 22, 2017	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)	Mar. 31, 2018GBP (£)
Summary Of Dividends [Line Items]
Dividends paid			£ 892	£ 1,160	£ 4,487
Stock consolidation ratio		0.9167
Special dividend
Summary Of Dividends [Line Items]
Dividends paid	£ 3,171		£ 0	£ 0	£ 3,171

Earnings per share (EPS) - Sche

Earnings per share (EPS) - Schedule of earnings per share (Details) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Basic EPS
Basic earnings from continuing operations	£ 1,273	£ 1,499	£ 3,548
Basic earnings from discontinued operations	(9)	12	2
Basic total earnings	£ 1,264	£ 1,511	£ 3,550
Basic EPS (continuing) (in GBP per share)	£ 0.368	£ 0.443	£ 1.025
Basic EPS (discontinuing) (in GBP per share)	(0.003)	0.003	0.001
Total basic earnings per share (in GBP per share)	£ 0.365	£ 0.446	£ 1.026
Weighted average number of shares – basic (in shares)	3,461	3,386	3,461
Diluted EPS
Diluted earnings from continuing operations	£ 1,273	£ 1,499	£ 3,548
Diluted earnings from discontinued operations	(9)	12	2
Diluted total earnings	£ 1,264	£ 1,511	£ 3,550
Diluted EPS (continuing) (in GBP per share)	£ 0.366	£ 0.441	£ 1.021
Diluted EPS (discontinuing) (in GBP per share)	(0.003)	0.003	0
Diluted EPS (in GBP per share)	£ 0.363	£ 0.444	£ 1.021
Weighted average number of shares – diluted (in shares)	3,478	3,401	3,476
Reconciliation of basic to diluted average number of shares
Weighted average number of shares – basic (in shares)	3,461	3,386	3,461
Effect of dilutive potential ordinary shares – employee share plans (in shares)	17	15	15
Weighted average number of shares – diluted (in shares)	3,478	3,401	3,476
Before exceptional items and remeasurements
Basic EPS
Basic earnings from continuing operations	£ 1,912	£ 1,998	£ 1,915
Basic earnings from discontinued operations	5	57	145
Basic total earnings	£ 1,917	£ 2,055	£ 2,060
Basic EPS (continuing) (in GBP per share)	£ 0.552	£ 0.590	£ 0.553
Basic EPS (discontinuing) (in GBP per share)	0.002	0.017	0.042
Total basic earnings per share (in GBP per share)	£ 0.554	£ 0.607	£ 0.595
Diluted EPS
Diluted earnings from continuing operations	£ 1,912	£ 1,998	£ 1,915
Diluted earnings from discontinued operations	5	57	145
Diluted total earnings	£ 1,917	£ 2,055	£ 2,060
Diluted EPS (continuing) (in GBP per share)	£ 0.550	£ 0.588	£ 0.551
Diluted EPS (discontinuing) (in GBP per share)	0.001	0.017	0.042
Diluted EPS (in GBP per share)	£ 0.551	£ 0.605	£ 0.593
Exceptional items and remeasurements
Basic EPS
Basic earnings from continuing operations	£ (639)	£ (499)	£ 1,633
Basic earnings from discontinued operations	(14)	(45)	(143)
Basic total earnings	£ (653)	£ (544)	£ 1,490
Basic EPS (continuing) (in GBP per share)	£ (0.184)	£ (0.147)	£ 0.472
Basic EPS (discontinuing) (in GBP per share)	(0.005)	(0.014)	(0.041)
Total basic earnings per share (in GBP per share)	£ (0.189)	£ (0.161)	£ 0.431
Diluted EPS
Diluted earnings from continuing operations	£ (639)	£ (499)	£ 1,633
Diluted earnings from discontinued operations	(14)	(45)	(143)
Diluted total earnings	£ (653)	£ (544)	£ 1,490
Diluted EPS (continuing) (in GBP per share)	£ (0.184)	£ (0.147)	£ 0.470
Diluted EPS (discontinuing) (in GBP per share)	(0.004)	(0.014)	(0.042)
Diluted EPS (in GBP per share)	£ (0.188)	£ (0.161)	£ 0.428

Dividends (Details)

Dividends (Details) - GBP (£) £ / shares in Units, £ in Millions	Jun. 02, 2017	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)		£ 0.4783	£ 0.4652	£ 1.28965
Dividends paid		£ 892	£ 1,160	£ 4,487
Scrip dividend		£ 758	£ 413	£ 209
Interim dividend in respect of the current year
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)		£ 0.1657	£ 0.1608	£ 0.1549
Dividends paid		£ 335	£ 450	£ 346
Scrip dividend		£ 241	£ 94	£ 176
Special dividend
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)	£ 0.84375	£ 0	£ 0	£ 0.84375
Dividends paid	£ 3,171	£ 0	£ 0	£ 3,171
Scrip dividend		£ 0	£ 0	£ 0
Final dividend in respect of the prior year
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)		£ 0.3126	£ 0.3044	£ 0.2910
Dividends paid		£ 557	£ 710	£ 970
Scrip dividend		£ 517	£ 319	£ 33

Dividends - Narrative (Details)

Dividends - Narrative (Details) £ / shares in Units, £ in Millions	Jun. 02, 2017GBP (£)£ / shares	Jun. 02, 2017$ / shares	Mar. 31, 2020GBP (£)£ / shares	Mar. 31, 2019GBP (£)£ / shares	Mar. 31, 2018GBP (£)£ / shares
Summary Of Dividends [Line Items]
Dividends declared before financial statements authorised for issue (GBP per share) | £ / shares			£ 0.320
Dividends declared before financial statements authorised for issue | £			£ 1,123
Cash dividends paid (GBP per share) | £ / shares			£ 0.4783	£ 0.4652	£ 1.28965
Cash dividends paid, special dividend | £			£ 892	£ 1,160	£ 4,487
Special dividend
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share) | £ / shares	£ 0.84375		£ 0	£ 0	£ 0.84375
Cash dividends paid, special dividend | £	£ 3,171		£ 0	£ 0	£ 3,171
Special dividend - American Depositary Share
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share) | $ / shares		$ 5.4224

Discontinued operations and a_3

Discontinued operations and assets held for sale - Narrative (Details) - GBP (£)	1 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of subsidiaries [line items]
Purchase of interests in investments accounted for using equity method		£ 82,000,000	£ 143,000,000	£ 129,000,000
Derivative assets		1,342,000,000	1,153,000,000
Net cash outflow from operating activities – discontinued operations		97,000,000	71,000,000	207,000,000
Net cash outflow from operating activities – discontinued operations, paid to the Warm Homes Fund, utilisation of provisions and payment of the final transaction fees incurred		66,000,000
Net cash inflow from investing activities – discontinued operations		6,000,000	156,000,000	171,000,000
Net cash outflow from financing activities – discontinued operations		0	0	231,000,000
UK Gas Distribution (Cadent)
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed	39.00%
Quadgas HoldCo Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed	39.00%
Purchase of interests in investments accounted for using equity method	£ 1,956,000,000
Investments in associates	1,494,000,000
Receivables due from associates	352,000,000
Derivative assets	110,000,000
Discontinued operations
Disclosure of subsidiaries [line items]
Gain on disposal, after tax	9,000,000	9,000,000	0	0
Net cash outflow from financing activities – discontinued operations		£ 0	£ 0	£ 231,000,000
Discontinued operations | Quadgas HoldCo Limited
Disclosure of subsidiaries [line items]
Proceeds from disposal of non-current assets or disposal groups classified as held for sale and discontinued operations	£ 1,965,000,000

Discontinued operations and a_4

Discontinued operations and assets held for sale - Summary income statement and statement of comprehensive income (Details) - GBP (£) £ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Summary income statement and comprehensive income, discontinued operations [line items]
Revenue		£ 14,540	£ 14,933	£ 15,250
Operating costs		(11,760)	(12,063)	(11,757)
Operating profit/(loss)		2,780	2,870	3,493
Net finance income		(1,113)	(1,069)	(882)
Share of post-tax results of joint ventures and associates		87	40	49
Profit/(loss) before tax		1,754	1,841	2,660
Total (loss)/profit after tax from discontinued operations		(9)	12	2
Impairment charge against investment in Quadgas		0	43
Items that will never be reclassified to profit or loss:
Total items from continuing operations that will never be reclassified to profit or loss		(541)	47	783
Items that may be reclassified subsequently to profit or loss:
Share of other comprehensive (losses)/income of associates, net of tax		(5)	1	0
Total items that may be reclassified subsequently to profit or loss		360	256	(559)
Other comprehensive income for the year, net of tax from discontinued operations		(175)	339	371
Total comprehensive (loss)/income for the year from discontinued operations		1,090	1,853	3,922
Discontinued operations
Summary income statement and comprehensive income, discontinued operations [line items]
Revenue		0	0	0
Operating costs		(23)	(1)	(41)
Operating profit/(loss)		(23)	(1)	(41)
Net finance income		6	23	137
Share of post-tax results of joint ventures and associates		0	(5)	(89)
Profit/(loss) before tax		(17)	17	7
Tax from discontinued operations		(1)	(5)	(5)
(Loss)/profit after tax from discontinued operations		(18)	12	2
Gain on disposal, after tax	£ 9	9	0	0
Total (loss)/profit after tax from discontinued operations		(9)	12	2
Items that will never be reclassified to profit or loss:
Share of other comprehensive income of associate, net of tax		0	36	142
Total items from continuing operations that will never be reclassified to profit or loss		0	36	142
Items that may be reclassified subsequently to profit or loss:
Net gains in respect of cash flow hedges		6	0	0
Share of other comprehensive (losses)/income of associates, net of tax		0	0	5
Total items that may be reclassified subsequently to profit or loss		6	0	5
Other comprehensive income for the year, net of tax from discontinued operations		6	36	147
Total comprehensive (loss)/income for the year from discontinued operations		(3)	48	£ 149
UK Gas Distribution | Discontinued operations
Summary income statement and comprehensive income, discontinued operations [line items]
Operating costs			£ (41)
Quadgas HoldCo Limited | Discontinued operations
Summary income statement and comprehensive income, discontinued operations [line items]
Operating costs		(1)
Impairment charge against investment in Quadgas		43
Share of profit (loss) of associates accounted for using equity method		£ 38

Goodwill - Disclosure of goodwi

Goodwill - Disclosure of goodwill (Details) - Goodwill - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill, beginning balance	£ 5,869	£ 5,444
Additions	81
Exchange adjustments	283	425
Goodwill, ending balance	£ 6,233	£ 5,869

Goodwill - Narrative (Details)

Goodwill - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of reconciliation of changes in goodwill [line items]
Growth rate used to extrapolate cash flow projections	2.10%	2.20%
Discount rate applied to cash flow projections	4.50%	5.30%
Goodwill
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	£ 6,233	£ 5,869	£ 5,444
Goodwill | New York | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	3,544	3,382
Goodwill | Massachusetts | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	1,325	1,264
Goodwill | Rhode Island | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	493	470
Goodwill | Federal | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	790	753
Goodwill | Geronimo CGU | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	£ 81	£ 0

Other intangible assets (Detail

Other intangible assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	£ 1,084	£ 899
Intangible assets other than goodwill, ending balance	1,295	1,084
Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	1,084
Intangible assets other than goodwill, ending balance	£ 1,295	1,084
US ERP System
Disclosure of detailed information about intangible assets [line items]
Amortisation periods for intangible assets	3 years
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	£ 116
Intangible assets other than goodwill, ending balance	69	116
Gross carrying amount | Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	2,168	1,797
Exchange adjustments	63	70
Additions	352	306
Disposals	0	(15)
Reclassifications	0	10
Intangible assets other than goodwill, ending balance	2,583	2,168
Accumulated depreciation/amortisation | Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	(1,084)	(898)
Exchange adjustments	(28)	(26)
Disposals	0	15
Amortisation charge for the year	(176)	(175)
Intangible assets other than goodwill, ending balance	£ (1,288)	£ (1,084)
Bottom of range | Software
Disclosure of detailed information about intangible assets [line items]
Amortisation periods for intangible assets	1 year
Top of range | Software
Disclosure of detailed information about intangible assets [line items]
Amortisation periods for intangible assets	10 years

Property, plant and equipment -

Property, plant and equipment - Useful economic lives (Details)	12 Months Ended
	Mar. 31, 2020
Weighted average | Freehold and leasehold buildings
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	26 years
Weighted average | Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	40 years
Weighted average | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	37 years
Weighted average | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	21 years
Weighted average | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	23 years
Weighted average | Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	49 years
Weighted average | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	13 years
Weighted average | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	18 years
Weighted average | Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	5 years
UK | Bottom of range | Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	10 years
UK | Bottom of range | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	15 years
UK | Bottom of range | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	5 years
UK | Bottom of range | Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	10 years
UK | Bottom of range | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	5 years
UK | Bottom of range | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	7 years
UK | Top of range | Freehold and leasehold buildings
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	60 years
UK | Top of range | Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	100 years
UK | Top of range | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	40 years
UK | Top of range | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	60 years
UK | Top of range | Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	65 years
UK | Top of range | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	40 years
UK | Top of range | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	30 years
UK | Top of range | Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	10 years
US | Bottom of range | Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	45 years
US | Bottom of range | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	35 years
US | Bottom of range | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	20 years
US | Bottom of range | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	8 years
US | Bottom of range | Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	47 years
US | Bottom of range | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	12 years
US | Bottom of range | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	14 years
US | Top of range | Freehold and leasehold buildings
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	100 years
US | Top of range | Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	80 years
US | Top of range | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	85 years
US | Top of range | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	93 years
US | Top of range | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	50 years
US | Top of range | Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	95 years
US | Top of range | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	65 years
US | Top of range | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	65 years
US | Top of range | Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	26 years

Property, plant and equipment_2

Property, plant and equipment - Sensitivity of gas assets (Details) £ in Millions	12 Months Ended
	Mar. 31, 2020GBP (£)
UK Regulated
Disclosure of operating segments [line items]
UELs limited to 2050, impact on depreciation expense	£ 37
UELs limited to 2060, impact on depreciation expense	13
UELs limited to 2070, impact on depreciation expense	0
US Regulated
Disclosure of operating segments [line items]
UELs limited to 2050, impact on depreciation expense	151
UELs limited to 2060, impact on depreciation expense	66
UELs limited to 2070, impact on depreciation expense	£ 26

Property, plant and equipment_3

Property, plant and equipment - Disclosure of property plant and equipment (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2019
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	£ 43,913	£ 39,853
Property, plant and equipment, ending balance	48,770	43,913
Right-of-use assets	684
IFRS 16
Changes in property, plant and equipment [abstract]
Right-of-use assets			£ 468
Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	63,076	57,434
Right-of-use assets recognised on transition to IFRS 16			468
Exchange adjustments	1,695	2,232
Additions	4,727	4,015
Disposals	(639)	(595)
Reclassifications	(87)	(10)
Property, plant and equipment, ending balance	69,240	63,076
Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(19,163)	(17,581)
Exchange adjustments	(408)	(545)
Depreciation charge for the year	(1,464)	(1,573)
Disposals	558	536
Reclassifications	7	0
Property, plant and equipment, ending balance	(20,470)	(19,163)
Land and buildings
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	2,560
Property, plant and equipment, ending balance	3,050	2,560
Land and buildings | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	3,338	2,930
Right-of-use assets recognised on transition to IFRS 16			381
Exchange adjustments	98	114
Additions	130	34
Disposals	(79)	(35)
Reclassifications	29	295
Property, plant and equipment, ending balance	3,897	3,338
Land and buildings | Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(778)	(674)
Exchange adjustments	(16)	(19)
Depreciation charge for the year	(92)	(93)
Disposals	36	7
Reclassifications	3	1
Property, plant and equipment, ending balance	(847)	(778)
Plant and machinery
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	36,589
Property, plant and equipment, ending balance	41,281	36,589
Plant and machinery | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	54,383	49,374
Right-of-use assets recognised on transition to IFRS 16			67
Exchange adjustments	1,511	2,001
Additions	464	391
Disposals	(486)	(357)
Reclassifications	4,303	2,974
Property, plant and equipment, ending balance	60,242	54,383
Plant and machinery | Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(17,794)	(16,398)
Exchange adjustments	(372)	(501)
Depreciation charge for the year	(1,252)	(1,229)
Disposals	464	335
Reclassifications	(7)	(1)
Property, plant and equipment, ending balance	(18,961)	(17,794)
Assets in the course of construction
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	4,425
Property, plant and equipment, ending balance	4,065	4,425
Property, plant and equipment, expenditures recognised in course of its construction	150
Proceeds from termination fees received	13
Assets in the course of construction | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	4,425	4,273
Right-of-use assets recognised on transition to IFRS 16			0
Exchange adjustments	53	70
Additions	4,029	3,533
Disposals	(9)	(159)
Reclassifications	(4,433)	(3,292)
Property, plant and equipment, ending balance	4,065	4,425
Assets in the course of construction | Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	0	0
Exchange adjustments	0	0
Depreciation charge for the year	0	(150)
Disposals	0	150
Reclassifications	0	0
Property, plant and equipment, ending balance	0	0
Motor vehicles and office equipment
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	339
Property, plant and equipment, ending balance	374	339
Motor vehicles and office equipment | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	930	857
Right-of-use assets recognised on transition to IFRS 16			£ 20
Exchange adjustments	33	47
Additions	104	57
Disposals	(65)	(44)
Reclassifications	14	13
Property, plant and equipment, ending balance	1,036	930
Motor vehicles and office equipment | Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(591)	(509)
Exchange adjustments	(20)	(25)
Depreciation charge for the year	(120)	(101)
Disposals	58	44
Reclassifications	11	0
Property, plant and equipment, ending balance	£ (662)	£ (591)

Property, plant and equipment_4

Property, plant and equipment - Disclosure of right-of-use assets (Details) £ in Millions	12 Months Ended
	Mar. 31, 2020GBP (£)
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	£ 684
Additions	84
Depreciation charge for the year	(117)
Interest expense on lease liabilities	(26)
Lease income	35
Expenses relating to low-value leases	(12)
Land and buildings
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	364
Additions	10
Depreciation charge for the year	(29)
Plant and machinery
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	95
Additions	1
Depreciation charge for the year	(16)
Assets in the course of construction
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	0
Additions	0
Depreciation charge for the year	0
Motor vehicles and office equipment
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	225
Additions	73
Depreciation charge for the year	£ (72)

Property, plant and equipment_5

Property, plant and equipment - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Property, plant and equipment [abstract]
Expected future minimum sub lease payments receivable under non-cancellable sub leases	£ 94	£ 86

Property, plant and equipment_6

Property, plant and equipment - Information in relation to property, plant and equipment (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Property, plant and equipment | Cost
Disclosure of detailed information about property, plant and equipment [line items]
Capitalised interest included within cost	£ 2,118	£ 1,995
Trade and other payables
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	84	87
Non-current liabilities
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	428	372
Contract liabilities – current
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	76	61
Contract liabilities – non-current
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	£ 1,082	£ 933

Other non-current assets (Detai

Other non-current assets (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Other receivables	£ 35	£ 28
Non-current tax assets	65	56
Prepayments	19	7
Accrued income	235	173
Other non-current assets	£ 354	£ 264	£ 115	£ 115

Financial and other investmen_3

Financial and other investments - Schedule of financial assets (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
Disclosure of associates [line items]
Debt investments and other at fair value through other comprehensive income, non-current	£ 352	£ 343
Equity investments at fair value through other comprehensive income, non-current	83	93
Investments at fair value through profit and loss, non-current	108	62
Loans to joint ventures, non-current	0	169
Other non-current financial assets	543	667	£ 899	£ 899
Investments at fair value through profit and loss, current	1,278	1,311
Financial assets at amortised cost, current	720	670
Other current financial assets	1,998	1,981	£ 2,694	£ 2,694	£ 8,741
Other financial assets	2,541	2,648
Investments in short-term money funds
Disclosure of associates [line items]
Other financial assets	978	969
Insurance company fund investments
Disclosure of associates [line items]
Other financial assets	300	342
Short term investments, restricted	1	6
Equities
Disclosure of associates [line items]
Other financial assets	83	93
Bonds
Disclosure of associates [line items]
Other financial assets	132	122
Cash surrender value of life insurance policies
Disclosure of associates [line items]
Other financial assets	220	221
Loans to joint ventures and associates
Disclosure of associates [line items]
Other financial assets	0	169
Corporate ventures capital and other
Disclosure of associates [line items]
Other financial assets	108	62
Restricted balances - collateral
Disclosure of associates [line items]
Other financial assets	685	637
Restricted balances - other
Disclosure of associates [line items]
Other financial assets	35	33
U.S. Non-Qualified Plan Investments
Disclosure of associates [line items]
Other financial assets	435	436
Short term investments, restricted	26	22
Unquoted Equity Investments
Disclosure of associates [line items]
Other financial assets	£ 97	£ 51

Investments in joint ventures_3

Investments in joint ventures and associates - Share of net assets, joint ventures and associates (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	£ 608	£ 2,168
Exchange adjustments	32	11
Additions	172	143
Capitalisation of shareholder loan to Nemo Link Limited	176	0
Impairment charge against investment in Quadgas	0	(43)
Transfer of interest in Quadgas to assets held for sale	0	(1,625)
Share of post-tax results for the year	87	78
Share of other comprehensive income of associates, net of tax	1	37
Dividends received	(75)	(68)
Other movements	(6)	(93)
Investments accounted for using equity method, ending balance	995	608
Joint ventures
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	317	361
Exchange adjustments	12	(6)
Additions	156	85
Capitalisation of shareholder loan to Nemo Link Limited	176	0
Impairment charge against investment in Quadgas	0	0
Transfer of interest in Quadgas to assets held for sale	0	0
Share of post-tax results for the year	47	11
Share of other comprehensive income of associates, net of tax	0	0
Dividends received	(34)	(30)
Other movements	(20)	(104)
Investments accounted for using equity method, ending balance	£ 654	317
St William Homes LLP
Disclosure of joint ventures [line items]
Deferred income recognition period remaining	10 years
Associates
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	£ 291	1,807
Exchange adjustments	20	17
Additions	16	58
Capitalisation of shareholder loan to Nemo Link Limited	0	0
Impairment charge against investment in Quadgas	0	(43)
Transfer of interest in Quadgas to assets held for sale	0	(1,625)
Share of post-tax results for the year	40	67
Share of other comprehensive income of associates, net of tax	1	37
Dividends received	(41)	(38)
Other movements	14	11
Investments accounted for using equity method, ending balance	£ 341	£ 291

Investments in joint ventures_4

Investments in joint ventures and associates - Narrative (Details) £ in Millions	12 Months Ended
	Mar. 31, 2020GBP (£)joint_venture	Mar. 31, 2019GBP (£)
Disclosure of joint ventures [line items]
Number of joint ventures | joint_venture	3
Millennium Pipeline Company LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in associate	26.25%
Joint ventures
Disclosure of joint ventures [line items]
Capital commitments | £	£ 240	£ 18
BritNed
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Nemo
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Emerald
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	51.00%

Investments in joint ventures_5

Investments in joint ventures and associates - Summarised financial information, joint venture and associate (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2019	Apr. 01, 2018	Mar. 31, 2017
Disclosure of joint ventures [line items]
Non-current assets	£ 61,288	£ 55,017	£ 52,106		£ 52,106
Cash and cash equivalents	73	252	329		329	£ 1,139
Non-current liabilities	(38,941)	(34,465)	(31,242)		(31,441)
Current liabilities	(8,564)	(9,129)	(8,697)		(8,691)
Net assets (liabilities)	19,584	19,369	18,848	£ 19,369	£ 18,652
Revenue	14,540	14,933	15,250
Other costs	(2,975)	(2,895)	(2,603)
Operating profit/(loss)	2,780	2,870	3,493
Profit before tax	1,754	1,841	2,660
Tax	(480)	(339)	889
Profit/(loss) after tax from continuing operations	1,274	1,502	3,549
Group’s share of profit/(loss)	87	40	£ 49
Millennium Pipeline Company LLC
Disclosure of joint ventures [line items]
Non-current assets	971	937
Cash and cash equivalents	33	35
All other current assets	26	22
Non-current liabilities	(315)	(326)
Current liabilities	(43)	(84)
Net assets (liabilities)	672	584
Group’s ownership interest in joint venture/associate	176	153
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	176	153
Revenue	206	166
Depreciation and amortisation	(46)	(34)
Other costs	(20)	(24)
Operating profit/(loss)	140	108
Net interest expense	(22)	(11)
Profit before tax	118	97
Tax	0	0
Profit/(loss) after tax from continuing operations	118	97
Group’s share of profit/(loss)	31	25
Group adjustment: Tax charge	(9)	0
Group’s share of post-tax results for the year	22	25
BritNed Development Limited
Disclosure of joint ventures [line items]
Non-current assets	399	370
Cash and cash equivalents	54	59
All other current assets	4	2
Non-current liabilities	(45)	(11)
Current liabilities	(16)	(28)
Net assets (liabilities)	396	392
Group’s ownership interest in joint venture/associate	198	196
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	198	196
Revenue	80	87
Depreciation and amortisation	(14)	(13)
Other costs	(10)	(10)
Operating profit/(loss)	56	64
Net interest expense	0	0
Profit before tax	56	64
Tax	(10)	(10)
Profit/(loss) after tax from continuing operations	46	54
Group’s share of profit/(loss)	23	27
Group adjustment: Tax charge	0	0
Group’s share of post-tax results for the year	23	27
Nemo Link Limited
Disclosure of joint ventures [line items]
Non-current assets	582	537
Cash and cash equivalents	26	47
All other current assets	5	3
Non-current liabilities	(29)	2
Current liabilities	(10)	(375)
Net assets (liabilities)	574	214
Group’s ownership interest in joint venture/associate	287	107
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	287	107
Revenue	45	12
Depreciation and amortisation	(23)	(4)
Other costs	(8)	(4)
Operating profit/(loss)	14	4
Net interest expense	0	0
Profit before tax	14	4
Tax	(2)	0
Profit/(loss) after tax from continuing operations	12	4
Group’s share of profit/(loss)	6	2
Group adjustment: Tax charge	0	0
Group’s share of post-tax results for the year	6	£ 2
Emerald Energy Venture LLC
Disclosure of joint ventures [line items]
Non-current assets	435
Cash and cash equivalents	66
All other current assets	6
Non-current liabilities	(232)
Current liabilities	(2)
Net assets (liabilities)	273
Group’s ownership interest in joint venture/associate	139
Group adjustment: elimination of profits on sales to joint venture	(10)
Carrying amount of the Group’s investment	129
Revenue	19
Depreciation and amortisation	(7)
Other costs	(10)
Operating profit/(loss)	2
Net interest expense	(3)
Profit before tax	(1)
Tax	0
Profit/(loss) after tax from continuing operations	(1)
Group’s share of profit/(loss)	(1)
Group adjustment: Tax charge	0
Group’s share of post-tax results for the year	£ (1)

Derivative financial instrume_3

Derivative financial instruments - Derivative financial instruments (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 1,342	£ 1,153
Derivative liabilities	(1,334)	(1,183)
Total	8	(30)
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	1,267	1,052
Derivative liabilities	(1,134)	(1,084)
Total	133	(32)
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	75	101
Derivative liabilities	(200)	(99)
Total	£ (125)	£ 2

Derivative financial instrume_4

Derivative financial instruments - Financing derivatives (Details) £ in Millions, number in Millions	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 1,342	£ 1,153
Derivative liabilities	(1,334)	(1,183)
Total	8	(30)
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	1,267	1,052
Derivative liabilities	(1,134)	(1,084)
Total	£ 133	£ (32)
Derivative notional amount	(15,782)	(17,236)
Interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 556	£ 539
Derivative liabilities	(337)	(384)
Total	£ 219	£ 155
Derivative notional amount	(3,101)	(6,299)
Cross-currency interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 643	£ 470
Derivative liabilities	(514)	(443)
Total	£ 129	£ 27
Derivative notional amount	(8,097)	(6,700)
Foreign exchange forward contracts
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 58	£ 41
Derivative liabilities	(39)	(41)
Total	£ 19	£ 0
Derivative notional amount	(3,284)	(2,937)
Inflation-linked swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 0	£ 0
Derivative liabilities	(234)	(214)
Total	£ (234)	£ (214)
Derivative notional amount	(500)	(500)
Equity options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 10	£ 2
Derivative liabilities	(10)	(2)
Total	£ 0	£ 0
Derivative notional amount	(800)	(800)
Less than 1 year | Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 62	£ 56
Derivative liabilities	(254)	(282)
Total	(192)	(226)
Over 12 months | Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	1,205	996
Derivative liabilities	(880)	(802)
Total	325	194
In 1 to 2 years | Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	480	19
Derivative liabilities	(51)	(193)
Total	429	(174)
In 2 to 3 years | Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	13	416
Derivative liabilities	(5)	(1)
Total	8	415
In 3 to 4 years | Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	20	11
Derivative liabilities	(28)	0
Total	(8)	11
In 4 to 5 years | Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	31	20
Derivative liabilities	(109)	(14)
Total	(78)	6
More than 5 years | Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	661	530
Derivative liabilities	(687)	(594)
Total	(26)	(64)
Capital Expenditure | Foreign exchange forward contracts
Disclosure of detailed information about financial instruments [line items]
Total	£ (3)	£ 32

Derivative financial instrume_5

Derivative financial instruments - Commodity derivatives (Details) £ in Millions, number in Millions	12 Months Ended
	Mar. 31, 2020GBP (£)GW / moGW / hMMBTU	Mar. 31, 2019GBP (£)GW / moGW / hMMBTU
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 1,342	£ 1,153
Derivative liabilities	(1,334)	(1,183)
Total	8	(30)
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	75	101
Derivative liabilities	(200)	(99)
Total	(125)	2
Forward purchases of gas
Disclosure of detailed information about financial instruments [line items]
Derivative assets	64	66
Derivative liabilities	(108)	(78)
Total	£ (44)	£ (12)
Derivative non-monetary notional amount | MMBTU	102	52
Derivative term	4 years	2 years
Derivative contractual amount	128	108
Electricity capacity
Disclosure of detailed information about financial instruments [line items]
Derivative non-monetary notional amount | GW / mo	0	0
Electricity swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 4	£ 29
Derivative liabilities	(83)	(19)
Total	£ (79)	£ 10
Derivative non-monetary notional amount | GW / h	12,836	12,848
Electricity options
Disclosure of detailed information about financial instruments [line items]
Derivative non-monetary notional amount | GW / h	0	10,444
Gas swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 7	£ 5
Derivative liabilities	(8)	(1)
Total	£ (1)	£ 4
Derivative non-monetary notional amount | MMBTU	89	87
Gas options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 0	£ 1
Derivative liabilities	(1)	(1)
Total	£ (1)	£ 0
Derivative non-monetary notional amount | MMBTU	26	34
Less than 1 year | Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 31	£ 52
Derivative liabilities	(126)	(68)
Total	(95)	(16)
Over 12 months | Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	44	49
Derivative liabilities	(74)	(31)
Total	(30)	18
In 1 to 2 years | Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	8	14
Derivative liabilities	(35)	(9)
Total	(27)	5
In 2 to 3 years | Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	9	9
Derivative liabilities	(24)	(8)
Total	(15)	1
In 3 to 4 years | Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	8	6
Derivative liabilities	(12)	(4)
Total	(4)	2
In 4 to 5 years | Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	7	6
Derivative liabilities	(1)	(4)
Total	6	2
More than 5 years | Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	12	14
Derivative liabilities	(2)	(6)
Total	£ 10	£ 8

Inventories and other current_3

Inventories and other current intangibles (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Fuel stocks	£ 151	£ 99
Raw materials and consumables	265	184
Current intangible assets – emission allowances	133	87
Inventories and current intangible assets	549	370
Inventory valuation reserve	£ 21	£ 20

Trade and other receivables - S

Trade and other receivables - Summary of trade and other receivables (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Trade and other receivables [abstract]
Trade receivables	£ 1,551	£ 1,899
Accrued income	869	883
Prepayments	408	237
Other receivables	158	134
Trade and other receivables	£ 2,986	£ 3,153	£ 2,795	£ 2,798

Trade and other receivables - N

Trade and other receivables - Narrative (Details) £ in Millions, $ in Millions	12 Months Ended
	Mar. 31, 2020GBP (£)	Mar. 31, 2020USD ($)	Mar. 31, 2019GBP (£)
Disclosure of financial assets [line items]
Trade receivables	£ 3,266		£ 3,052
Retail customer receivables
Disclosure of financial assets [line items]
Trade receivables	1,806		1,885
Trade receivables
Disclosure of financial assets [line items]
Maximum exposure to credit risk	2,063		2,293
Provision for bad and doubtful debts	234		£ 181
Cessation of customer terminations and collections | Trade receivables
Disclosure of financial assets [line items]
Provision for bad and doubtful debts	117
Bottom of range | Cessation of customer terminations and collections | Trade receivables
Disclosure of financial assets [line items]
Provision for bad and doubtful debts	81	$ 100
Top of range | Cessation of customer terminations and collections | Trade receivables
Disclosure of financial assets [line items]
Provision for bad and doubtful debts	£ 161	$ 200

Trade and other receivables - P

Trade and other receivables - Provision for impairment of receivables (Details) - Trade receivables - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Allowance account for credit losses of financial assets, beginning balance	£ 394	£ 309
Exchange adjustments	20	24
Charge for the year, net of recoveries	234	181
Uncollectible amounts written off	(136)	(120)
Allowance account for credit losses of financial assets, ending balance	£ 512	£ 394

Trade and other receivables - T

Trade and other receivables - Trade receivables, accrued income and provision split by geography (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Disclosure of financial assets [line items]
Trade receivables	£ 3,266	£ 3,052
Accrued income	869	883
UK
Disclosure of financial assets [line items]
Accrued income	461	445
US
Disclosure of financial assets [line items]
Accrued income	408	438
Trade receivables | Gross carrying amount
Disclosure of financial assets [line items]
Trade receivables	2,063	2,293
Trade receivables | Gross carrying amount | UK
Disclosure of financial assets [line items]
Trade receivables	227	313
Trade receivables | Gross carrying amount | US
Disclosure of financial assets [line items]
Trade receivables	1,836	1,980
Trade receivables | Accumulated impairment
Disclosure of financial assets [line items]
Trade receivables	(512)	(394)
Trade receivables | Accumulated impairment | UK
Disclosure of financial assets [line items]
Trade receivables	(40)	(40)
Trade receivables | Accumulated impairment | US
Disclosure of financial assets [line items]
Trade receivables	£ (472)	£ (354)

Trade and other receivables - A

Trade and other receivables - Average expected loss rates and gross balances for the retail customer receivables in our US operations (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Disclosure of financial assets [line items]
Trade receivables	£ 3,266	£ 3,052
Unbilled revenue
Disclosure of financial assets [line items]
Expected credit loss rate	5.00%	0.00%
Trade receivables	£ 395	£ 420
Retail customer receivables
Disclosure of financial assets [line items]
Trade receivables	£ 1,806	£ 1,885
0 – 30 days | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	5.00%	3.00%
Trade receivables	£ 623	£ 736
30 – 60 days | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	14.00%	12.00%
Trade receivables	£ 184	£ 194
60 – 90 days | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	29.00%	20.00%
Trade receivables	£ 105	£ 89
3 – 6 months | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	47.00%	30.00%
Trade receivables	£ 119	£ 109
6 – 12 months | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	63.00%	39.00%
Trade receivables	£ 104	£ 99
Over 12 months | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	79.00%	68.00%
Trade receivables	£ 276	£ 238

Cash and cash equivalents (Deta

Cash and cash equivalents (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
Cash and cash equivalents [abstract]
Cash at bank	£ 73	£ 177
Short-term deposits	0	75
Cash and cash equivalents	£ 73	£ 252	£ 329	£ 329	£ 1,139

Borrowings - Current and non-cu

Borrowings - Current and non-current borrowings (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Current
Bank loans	£ 1,244		£ 641
Bonds	1,446		1,973
Commercial paper	1,269		1,792
Lease liabilities	112	£ 113	65
Other loans	1		1
Current portion of non-current borrowings	4,072		4,472	£ 4,447	£ 4,447
Non-current
Bank loans	2,819		2,599
Bonds	23,094		21,278
Lease liabilities	623	£ 631	205
Other loans	186		176
Non-current portion of non-current borrowings	26,722		24,258	£ 22,210	22,178
Total borrowings	30,794		28,730		£ 26,625
Liability held at fair value through profit and loss	£ 741		£ 667

Borrowings - Borrowings repayme

Borrowings - Borrowings repayment schedule (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 30,794	£ 28,730	£ 26,625
Less than 1 year
Disclosure of detailed information about borrowings [line items]
Borrowings	4,072	4,472
In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Borrowings	2,212	2,393
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Borrowings	1,664	1,990
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Borrowings	757	1,553
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	2,122	714
Borrowings Paid By Instalments | More than 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	870	959
Borrowings Paid By Other Than Instalments | More than 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 19,097	£ 16,649

Borrowings - Narrative (Details

Borrowings - Narrative (Details)	Apr. 30, 2020GBP (£)	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)	Apr. 30, 2020USD ($)	Apr. 01, 2019GBP (£)	Mar. 31, 2018GBP (£)
Disclosure of fair value measurement of liabilities [line items]
Borrowings		£ 30,794,000,000	£ 28,730,000,000			£ 26,625,000,000
Property, plant and equipment pledged as security		84,000,000	81,000,000
Collateral received		785,000,000	558,000,000
Liability held at fair value through profit and loss		741,000,000	667,000,000
Change in fair value		10,000,000	13,000,000
Difference between carrying amount of financial liability and amount contractually required to pay at maturity to holder of obligation		18,000,000	57,000,000
Lease liabilities		735,000,000	270,000,000		£ 744,000,000
IFRS 16
Disclosure of fair value measurement of liabilities [line items]
Lease liabilities					£ 474,000,000
Borrowings
Disclosure of fair value measurement of liabilities [line items]
Notional amount		30,422,000,000	28,417,000,000
At fair value
Disclosure of fair value measurement of liabilities [line items]
Borrowings		34,174,000,000	32,252,000,000
At fair value | Level 1
Disclosure of fair value measurement of liabilities [line items]
Borrowings		14,059,000,000	14,356,000,000
At fair value | Level 2
Disclosure of fair value measurement of liabilities [line items]
Borrowings		20,115,000,000	17,896,000,000
Financial liabilities at fair value through profit and loss
Disclosure of fair value measurement of liabilities [line items]
Borrowings		£ 759,000,000	£ 724,000,000
Borrowings transactions | National Grid Electricity Transmission plc | Fixed interest rate bond, 20-year tenor
Disclosure of fair value measurement of liabilities [line items]
Notional amount	£ 400,000,000
Borrowings Maturity, Term	20 years
Borrowings transactions | Narragansett Electric Company | Fixed interest rate bond, 10-year tenor
Disclosure of fair value measurement of liabilities [line items]
Notional amount	£ 500,000,000			$ 600,000,000
Borrowings Maturity, Term	10 years

Borrowings - Lease obligations

Borrowings - Lease obligations (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Minimum finance lease payments payable	£ 974		£ 310
Less: finance charges allocated to future periods	(239)		(40)
Lease liabilities	735	£ 744	270
Less than 1 year
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Minimum finance lease payments payable	132		65
Lease liabilities	112		65
1 to 5 years
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Minimum finance lease payments payable	361		183
Lease liabilities	297		156
More than 5 years
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Minimum finance lease payments payable	481		62
Lease liabilities	£ 326		£ 49

Trade and other payables (Detai

Trade and other payables (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Trade payables	£ 2,205		£ 2,404
Deferred payables	137		217
Customer contributions	84		87
Social security and other taxes	202		159
Contingent consideration	30		0
Other payables	944		902
Trade and other payables	£ 3,602	£ 3,766	£ 3,769	£ 3,394	£ 3,453

Contract liabilities - Summary

Contract liabilities - Summary of Contract Liabilities (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Contract liabilities [abstract]
Current	£ 76		£ 61	£ 53	£ 0
Non-current	1,082		933	813	£ 0
Total contract liabilities	£ 1,158	£ 994	£ 994	£ 866

Contract liabilities - Signific

Contract liabilities - Significant Changes in Contract Liabilities (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Contract liabilities [abstract]
As at 1 April	£ 994
Exchange adjustments	39	£ 29
Revenue recognised that was included in the contract liability balance at the beginning of the period	(60)	(51)
Increases due to cash received, excluding amounts recognised as revenue during the period	185	155
Changes due to amounts recognised as revenue	0	(5)
At 31 March	£ 1,158	£ 994

Other non-current liabilities_2

Other non-current liabilities (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Deferred income	£ 101		£ 96
Customer contributions	428		372
Contingent consideration	44		0
Other payables	318		340
Other non-current liabilities	£ 891	£ 805	£ 808	£ 750	£ 1,317

Pensions and other post retir_3

Pensions and other post retirement benefits - Narrative (Details)	12 Months Ended
	Mar. 31, 2020GBP (£)plan	Mar. 31, 2019GBP (£)	Mar. 31, 2018GBP (£)	Sep. 30, 2019GBP (£)	Jan. 01, 2017GBP (£)	Mar. 31, 2016GBP (£)
Disclosure of defined benefit plans [line items]
Defined contribution plan, employer matching contribution percent of gross pay	12.00%
Employer contributions	£ 327,000,000	£ 419,000,000	£ 475,000,000
Pensions | NG UKPS
Disclosure of defined benefit plans [line items]
Actuarial loss arising from buy-in arrangement	700,000,000
Pensions | National Grid UK Pension Scheme - Section A
Disclosure of defined benefit plans [line items]
Gilts exchanged for buy-in policy	2,800,000,000
Pensions | National Grid UK Pension Scheme - Section B
Disclosure of defined benefit plans [line items]
Gilts exchanged for buy-in policy	£ 1,600,000,000
US | Pensions
Disclosure of defined benefit plans [line items]
Number of defined benefit plans | plan	4
Employer contributions	£ 153,000,000	231,000,000	208,000,000
Weighted average duration of defined benefit obligation	14 years
US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Employer contributions	£ 18,000,000	14,000,000	117,000,000
Weighted average duration of defined benefit obligation	16 years
UK | Pensions
Disclosure of defined benefit plans [line items]
Employer contributions	£ 156,000,000	£ 174,000,000	£ 150,000,000
Weighted average duration of defined benefit obligation	14 years
UK | Pensions | National Grid UK Pension Scheme - Section A
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings		51.80%
Maximum guarantee payable					£ 1,000,000,000
UK | Pensions | National Grid UK Pension Scheme - Section B
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings		51.40%
Contribution paid				£ 34,000,000
UK | Pensions | National Grid UK Pension Scheme - Section B | Time Period, by September 2020
Disclosure of defined benefit plans [line items]
Additional contribution		£ 32,000,000
UK | Pensions | NGEG of ESPS
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings						40.70%
UK | Pensions | NGEG of ESPS | Time Period, 2016 to 2027
Disclosure of defined benefit plans [line items]
Contributions payable per year						£ 48,000,000
Active members | US | Pensions
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	36.00%	37.00%	38.00%
Active members | US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	35.00%	39.00%	38.00%
Active members | UK | Pensions
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	8.00%	10.00%	10.00%
Deferred members | US | Pensions
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	9.00%	9.00%	8.00%
Deferred members | US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	0.00%	0.00%	0.00%
Deferred members | UK | Pensions
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	14.00%	16.00%	18.00%
Pensioner members | US | Pensions
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	55.00%	54.00%	54.00%
Pensioner members | US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	65.00%	61.00%	62.00%
Pensioner members | UK | Pensions
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	78.00%	74.00%	72.00%

Pensions and other post retir_4

Pensions and other post retirement benefits - Results of the most recent actuarial valuations (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2016
Disclosure of defined benefit plans [line items]
Funding surplus/(deficit)	£ (953)	£ (218)	£ (263)
National Grid UK Pension Scheme - Section A
Disclosure of defined benefit plans [line items]
Fair value of plan assets		6,551
Actuarial value of benefits due to members		£ 6,502
Market value as percentage of benefits		101.00%
Funding surplus/(deficit)		£ 49
Funding surplus/(deficit) net of tax		41
National Grid UK Pension Scheme - Section B
Disclosure of defined benefit plans [line items]
Fair value of plan assets		5,765
Actuarial value of benefits due to members		£ 5,831
Market value as percentage of benefits		99.00%
Funding surplus/(deficit)		£ (66)
Funding surplus/(deficit) net of tax		(55)
NGEG of ESPS
Disclosure of defined benefit plans [line items]
Fair value of plan assets				£ 2,553
Actuarial value of benefits due to members				£ 3,053
Market value as percentage of benefits				84.00%
Funding surplus/(deficit)				£ (500)
Funding surplus/(deficit) net of tax				£ (415)
UK | Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets	14,364	15,507	15,330
Funding surplus/(deficit)	£ 1,520	£ 1,231	£ 1,104

Pensions and other post retir_5

Pensions and other post retirement benefits - Security arrangements (Details) - UK - Pensions - GBP (£)	Apr. 01, 2020	Mar. 31, 2020
National Grid UK Pension Scheme - Section A
Disclosure of defined benefit plans [line items]
Value of security arrangements		£ 315,000,000
Additional amounts payable		72,000,000
National Grid UK Pension Scheme - Section B
Disclosure of defined benefit plans [line items]
Value of security arrangements		180,000,000
Maximum additional amounts payable		280,000,000
NGEG of ESPS
Disclosure of defined benefit plans [line items]
Value of security arrangements		239,000,000
Maximum additional amounts payable		£ 500,000,000
Latest actuarial valuation | National Grid UK Pension Scheme - Section A
Disclosure of defined benefit plans [line items]
Value of security arrangements	£ 186,000,000
Latest actuarial valuation | National Grid UK Pension Scheme - Section B
Disclosure of defined benefit plans [line items]
Value of security arrangements	£ 0

Pensions and other post retir_6

Pensions and other post retirement benefits - Actuarial assumptions (Details) - year	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
UK | Pensions
Disclosure of defined benefit plans [line items]
Discount rate – past service	2.35%	2.40%	2.60%
Discount rate – future service	2.35%	2.45%	2.65%
Salary increases	2.90%	3.50%	3.40%
Rate of increase in RPI – past service	2.65%	3.25%	3.15%
Rate of increase in RPI – future service	2.45%	3.20%	3.10%
Assumed life expectations for a retiree age 65 today: Males	22.1	22	22.3
Assumed life expectations for a retiree age 65 today: Females	23.8	23.6	23.9
Assumed life expectations for a retiree age 65 today: In 20 years: Males	23.3	23.3	23.7
Assumed life expectations for a retiree age 65 today: In 20 years: Females	25.3	25.2	25.5
US | Pensions
Disclosure of defined benefit plans [line items]
Salary increases	3.50%	3.50%	3.50%
Discount rate	3.30%	3.95%	4.00%
Assumed life expectations for a retiree age 65 today: Males	20.9	22.1	22
Assumed life expectations for a retiree age 65 today: Females	23.4	24.2	24.2
Assumed life expectations for a retiree age 65 today: In 20 years: Males	22.5	23.7	23.6
Assumed life expectations for a retiree age 65 today: In 20 years: Females	25.1	25.9	25.8
US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Salary increases	3.50%	3.50%	3.50%
Discount rate	3.30%	3.95%	4.00%
Initial healthcare cost trend rate	7.00%	7.25%	7.50%
Ultimate healthcare cost trend rate	4.50%	4.50%	4.50%

Pensions and other post retir_7

Pensions and other post retirement benefits - Amounts recognized in consolidated statement of financial position (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of defined benefit plans [line items]
Funding surplus/(deficit)	£ (953)	£ (218)	£ (263)
Liabilities	(2,802)	(1,785)	(1,672)
Assets	1,849	1,567	1,409
Pensions | Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(24,281)	(24,609)	(23,747)
Fair value of plan assets	23,748	24,793	23,858
Funding surplus/(deficit)	(533)	184	111
Pensions | Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(345)	(330)	(307)
Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Other post-employment liabilities	(75)	(72)	(67)
UK | Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets	14,364	15,507	15,330
Funding surplus/(deficit)	1,520	1,231	1,104
Other post-employment liabilities	0	0	0
Liabilities	(69)	(76)	(74)
Assets	1,589	1,307	1,178
UK | Pensions | Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(12,775)	(14,200)	(14,152)
Fair value of plan assets	14,364	15,507	15,330
Funding surplus/(deficit)	1,589	1,307	1,178
UK | Pensions | Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(69)	(76)	(74)
US | Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets	6,972	6,646	6,030
Funding surplus/(deficit)	(1,113)	(509)	(552)
Other post-employment liabilities	0	0	0
Liabilities	(1,373)	(769)	(783)
Assets	260	260	231
US | Pensions | Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(7,809)	(6,901)	(6,349)
Fair value of plan assets	6,972	6,646	6,030
Funding surplus/(deficit)	(837)	(255)	(319)
US | Pensions | Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(276)	(254)	(233)
US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Fair value of plan assets	2,412	2,640	2,498
Funding surplus/(deficit)	(1,360)	(940)	(815)
Other post-employment liabilities	(75)	(72)	(67)
Liabilities	(1,360)	(940)	(815)
Assets	0	0	0
US | Other post-retirement benefits | Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(3,697)	(3,508)	(3,246)
Fair value of plan assets	2,412	2,640	2,498
Funding surplus/(deficit)	(1,285)	(868)	(748)
US | Other post-retirement benefits | Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	£ 0	£ 0	£ 0

Pensions and other post retir_8

Pensions and other post retirement benefits - Amounts recognised in the income statement and statement of other comprehensive income (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Included within operating costs
Administration costs	£ 16	£ 14	£ 16
Included within payroll costs
Current service cost	178	193	193
Past service cost – augmentations	0	5	1
Past service credit – redundancies	0	(7)	(1)
Special termination benefit cost – redundancies	2	55	9
Past service cost – plan amendments	0	34	0
Total included within payroll costs	180	280	202
Included within finance income and costs
Net interest cost	23	22	65
Total included in income statement	219	316	283
Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations	(724)	68	1,313
Exchange adjustments	(97)	(101)	175
Total included in the statement of other comprehensive income	(821)	(33)	1,488
UK | Pensions
Included within operating costs
Administration costs	9	6	6
Included within payroll costs
Current service cost	33	41	49
Past service cost – augmentations	0	5	1
Past service credit – redundancies	0	(7)	(1)
Special termination benefit cost – redundancies	2	55	9
Past service cost – plan amendments	0	34	0
Total included within payroll costs	35	128	58
Included within finance income and costs
Net interest cost	(31)	(31)	3
Total included in income statement	13	103	67
Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations	143	57	1,177
Exchange adjustments	0	0	0
Total included in the statement of other comprehensive income	143	57	1,177
US | Pensions
Included within operating costs
Administration costs	6	7	9
Included within payroll costs
Current service cost	100	104	98
Past service cost – augmentations	0	0	0
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – plan amendments	0	0	0
Total included within payroll costs	100	104	98
Included within finance income and costs
Net interest cost	21	21	27
Total included in income statement	127	132	134
Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations	(588)	(14)	27
Exchange adjustments	(42)	(42)	75
Total included in the statement of other comprehensive income	(630)	(56)	102
US | Other post-retirement benefits
Included within operating costs
Administration costs	1	1	1
Included within payroll costs
Current service cost	45	48	46
Past service cost – augmentations	0	0	0
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – plan amendments	0	0	0
Total included within payroll costs	45	48	46
Included within finance income and costs
Net interest cost	33	32	35
Total included in income statement	79	81	82
Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations	(279)	25	109
Exchange adjustments	(55)	(59)	100
Total included in the statement of other comprehensive income	(334)	£ (34)	£ 209
NG UKPS | Pensions
Included within finance income and costs
Actuarial loss arising from buy-in arrangement	700
National Grid UK Pension Scheme - Section A
Included within finance income and costs
Cost of equalising for impact of guaranteed minimum pension	17
National Grid UK Pension Scheme - Section B
Included within finance income and costs
Cost of equalising for impact of guaranteed minimum pension	12
NGEG of ESPS
Included within finance income and costs
Cost of equalising for impact of guaranteed minimum pension	£ 5

Pensions and other post retir_9

Pensions and other post retirement benefits - Reconciliation of the net defined benefit liability (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	£ (218)	£ (263)	£ (1,933)
Changes in net defined benefit liability (asset) [abstract]
Cost recognised in the income statement	(219)	(316)	(283)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(821)	(33)	1,488
Employer contributions	327	419	475
Other movements	(22)	(25)	(10)
Net defined benefit (liability) asset, ending balance	(953)	(218)	(263)
UK | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	1,231	1,104	(156)
Changes in net defined benefit liability (asset) [abstract]
Cost recognised in the income statement	(13)	(103)	(67)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	143	57	1,177
Employer contributions	156	174	150
Other movements	3	(1)	0
Net defined benefit (liability) asset, ending balance	1,520	1,231	1,104
US | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	(509)	(552)	(728)
Changes in net defined benefit liability (asset) [abstract]
Cost recognised in the income statement	(127)	(132)	(134)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(630)	(56)	102
Employer contributions	153	231	208
Other movements	0	0	0
Net defined benefit (liability) asset, ending balance	(1,113)	(509)	(552)
US | Other post-retirement benefits
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	(940)	(815)	(1,049)
Changes in net defined benefit liability (asset) [abstract]
Cost recognised in the income statement	(79)	(81)	(82)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(334)	(34)	209
Employer contributions	18	14	117
Other movements	(25)	(24)	(10)
Net defined benefit (liability) asset, ending balance	£ (1,360)	£ (940)	£ (815)

Pensions and other post reti_10

Pensions and other post retirement benefits - Change in the present value of defined benefit obligations (including unfunded obligations) (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of operating segments [line items]
Net defined benefit (liability) asset, beginning balance	£ (218)	£ (263)	£ (1,933)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(178)	(193)	(193)
Net interest cost	(23)	(22)	(65)
Past service credit – redundancies	0	7	1
Special termination benefit cost – redundancies	(2)	(55)	(9)
Past service cost – augmentations	0	(5)	(1)
Past service cost – plan amendments¹	0	(34)	0
Exchange adjustments	(97)	(101)	175
Net defined benefit (liability) asset, ending balance	(953)	(218)	(263)
Present value of defined benefit obligation
Disclosure of operating segments [line items]
Net defined benefit (liability) asset, beginning balance	(24,939)	(24,054)	(26,230)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(178)	(193)	(193)
Net interest cost	(751)	(771)	(775)
Actuarial gains/(losses) – experience	148	(69)	(100)
Actuarial gains – demographic assumptions	452	266	671
Actuarial (losses)/gains – financial assumptions	(84)	(619)	174
Past service credit – redundancies	0	7	1
Special termination benefit cost – redundancies	(2)	(55)	(9)
Past service cost – augmentations	0	(5)	(1)
Past service cost – plan amendments¹	0	(34)	0
Medicare subsidy received	(22)	(19)	(21)
Employee contributions	(1)	(1)	(1)
Benefits paid	1,282	1,376	1,285
Exchange adjustments	(531)	(768)	1,145
Net defined benefit (liability) asset, ending balance	(24,626)	(24,939)	(24,054)
UK | Pensions
Disclosure of operating segments [line items]
Net defined benefit (liability) asset, beginning balance	1,231	1,104	(156)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(33)	(41)	(49)
Net interest cost	31	31	(3)
Past service credit – redundancies	0	7	1
Special termination benefit cost – redundancies	(2)	(55)	(9)
Past service cost – augmentations	0	(5)	(1)
Past service cost – plan amendments¹	0	(34)	0
Exchange adjustments	0	0	0
Net defined benefit (liability) asset, ending balance	1,520	1,231	1,104
UK | Present value of defined benefit obligation | Pensions
Disclosure of operating segments [line items]
Net defined benefit (liability) asset, beginning balance	(14,276)	(14,226)	(15,645)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(33)	(41)	(49)
Net interest cost	(335)	(358)	(366)
Actuarial gains/(losses) – experience	113	(56)	(95)
Actuarial gains – demographic assumptions	140	224	565
Actuarial (losses)/gains – financial assumptions	798	(568)	604
Past service credit – redundancies	0	7	1
Special termination benefit cost – redundancies	(2)	(55)	(9)
Past service cost – augmentations	0	(5)	(1)
Past service cost – plan amendments¹	0	(34)	0
Medicare subsidy received	0	0	0
Employee contributions	(1)	(1)	(1)
Benefits paid	752	837	770
Exchange adjustments	0	0	0
Net defined benefit (liability) asset, ending balance	(12,844)	(14,276)	(14,226)
US | Pensions
Disclosure of operating segments [line items]
Net defined benefit (liability) asset, beginning balance	(509)	(552)	(728)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(100)	(104)	(98)
Net interest cost	(21)	(21)	(27)
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – augmentations	0	0	0
Past service cost – plan amendments¹	0	0	0
Exchange adjustments	(42)	(42)	75
Net defined benefit (liability) asset, ending balance	(1,113)	(509)	(552)
US | Other post-retirement benefits
Disclosure of operating segments [line items]
Net defined benefit (liability) asset, beginning balance	(940)	(815)	(1,049)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(45)	(48)	(46)
Net interest cost	(33)	(32)	(35)
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – augmentations	0	0	0
Past service cost – plan amendments¹	0	0	0
Exchange adjustments	(55)	(59)	100
Net defined benefit (liability) asset, ending balance	(1,360)	(940)	(815)
US | Present value of defined benefit obligation | Pensions
Disclosure of operating segments [line items]
Net defined benefit (liability) asset, beginning balance	(7,155)	(6,582)	(7,050)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(100)	(104)	(98)
Net interest cost	(280)	(277)	(273)
Actuarial gains/(losses) – experience	(45)	(52)	(38)
Actuarial gains – demographic assumptions	78	0	30
Actuarial (losses)/gains – financial assumptions	(595)	(24)	(279)
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – augmentations	0	0	0
Past service cost – plan amendments¹	0	0	0
Medicare subsidy received	0	0	0
Employee contributions	0	0	0
Benefits paid	374	398	362
Exchange adjustments	(362)	(514)	764
Net defined benefit (liability) asset, ending balance	(8,085)	(7,155)	(6,582)
US | Present value of defined benefit obligation | Other post-retirement benefits
Disclosure of operating segments [line items]
Net defined benefit (liability) asset, beginning balance	(3,508)	(3,246)	(3,535)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(45)	(48)	(46)
Net interest cost	(136)	(136)	(136)
Actuarial gains/(losses) – experience	80	39	33
Actuarial gains – demographic assumptions	234	42	76
Actuarial (losses)/gains – financial assumptions	(287)	(27)	(151)
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – augmentations	0	0	0
Past service cost – plan amendments¹	0	0	0
Medicare subsidy received	(22)	(19)	(21)
Employee contributions	0	0	0
Benefits paid	156	141	153
Exchange adjustments	(169)	(254)	381
Net defined benefit (liability) asset, ending balance	£ (3,697)	£ (3,508)	£ (3,246)

Pensions and other post reti_11

Pensions and other post retirement benefits - Change in fair value of plan assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	£ (218)	£ (263)	£ (1,933)
Changes in net defined benefit liability (asset) [abstract]
Interest income	(23)	(22)	(65)
Employer contributions	327	419	475
Exchange adjustments	(97)	(101)	175
Net defined benefit (liability) asset, ending balance	(953)	(218)	(263)
Actual return on plan assets	(512)	1,239	1,278
Expected contributions to plans in the following year	269	307	363
Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	24,793	23,858	24,375
Changes in net defined benefit liability (asset) [abstract]
Interest income	728	749	710
Return on plan assets (less than)/in excess of interest¹	(1,240)	490	568
Administration costs	(16)	(14)	(16)
Employer contributions	327	419	475
Employee contributions	1	1	1
Benefits paid	(1,279)	(1,377)	(1,285)
Exchange adjustments	434	667	(970)
Net defined benefit (liability) asset, ending balance	23,748	24,793	23,858
Pensions | UK
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	1,231	1,104	(156)
Changes in net defined benefit liability (asset) [abstract]
Interest income	31	31	(3)
Employer contributions	156	174	150
Exchange adjustments	0	0	0
Net defined benefit (liability) asset, ending balance	1,520	1,231	1,104
Actual return on plan assets	(542)	846	466
Expected contributions to plans in the following year	137	148	140
Pensions | UK | Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	15,507	15,330	15,489
Changes in net defined benefit liability (asset) [abstract]
Interest income	366	389	363
Return on plan assets (less than)/in excess of interest¹	(908)	457	103
Administration costs	(9)	(6)	(6)
Employer contributions	156	174	150
Employee contributions	1	1	1
Benefits paid	(749)	(838)	(770)
Exchange adjustments	0	0	0
Net defined benefit (liability) asset, ending balance	14,364	15,507	15,330
Pensions | US
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	(509)	(552)	(728)
Changes in net defined benefit liability (asset) [abstract]
Interest income	(21)	(21)	(27)
Employer contributions	153	231	208
Exchange adjustments	(42)	(42)	75
Net defined benefit (liability) asset, ending balance	(1,113)	(509)	(552)
Actual return on plan assets	233	318	560
Expected contributions to plans in the following year	125	150	221
Pensions | US | Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	6,646	6,030	6,322
Changes in net defined benefit liability (asset) [abstract]
Interest income	259	256	246
Return on plan assets (less than)/in excess of interest¹	(26)	62	314
Administration costs	(6)	(7)	(9)
Employer contributions	153	231	208
Employee contributions	0	0	0
Benefits paid	(374)	(398)	(362)
Exchange adjustments	320	472	(689)
Net defined benefit (liability) asset, ending balance	6,972	6,646	6,030
Other post-retirement benefits | US
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	(940)	(815)	(1,049)
Changes in net defined benefit liability (asset) [abstract]
Interest income	(33)	(32)	(35)
Employer contributions	18	14	117
Exchange adjustments	(55)	(59)	100
Net defined benefit (liability) asset, ending balance	(1,360)	(940)	(815)
Actual return on plan assets	(203)	75	252
Expected contributions to plans in the following year	7	9	2
Other post-retirement benefits | US | Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit (liability) asset, beginning balance	2,640	2,498	2,564
Changes in net defined benefit liability (asset) [abstract]
Interest income	103	104	101
Return on plan assets (less than)/in excess of interest¹	(306)	(29)	151
Administration costs	(1)	(1)	(1)
Employer contributions	18	14	117
Employee contributions	0	0	0
Benefits paid	(156)	(141)	(153)
Exchange adjustments	114	195	(281)
Net defined benefit (liability) asset, ending balance	2,412	£ 2,640	£ 2,498
NG UKPS | Pensions
Changes in net defined benefit liability (asset) [abstract]
Actuarial loss arising from buy-in arrangement	£ 700

Pensions and other post reti_12

Pensions and other post retirement benefits - Asset allocation strategy (Details)	Mar. 31, 2020	Mar. 31, 2019
UK | Pensions
Disclosure of fair value of plan assets [line items]
Equities	10.20%	12.70%
Property	4.80%	5.50%
Diversified alternatives	6.20%	5.00%
Liability matching assets	34.30%	11.10%
Infrastructure	0.00%	0.00%
Cash and cash equivalents	1.80%	1.90%
Other	1.70%	1.00%
Total	100.00%	100.00%
UK | Corporate bonds | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	26.70%	23.40%
UK | Government securities | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	14.30%	39.40%
US | Pensions
Disclosure of fair value of plan assets [line items]
Equities	36.00%	40.80%
Property	4.40%	4.70%
Diversified alternatives	9.00%	10.10%
Liability matching assets	0.00%	0.00%
Infrastructure	1.70%	1.50%
Cash and cash equivalents	0.30%	0.30%
Other	(0.60%)	0.20%
Total	100.00%	100.00%
US | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Equities	57.60%	60.20%
Property	0.00%	0.00%
Diversified alternatives	13.40%	12.90%
Liability matching assets	0.00%	0.00%
Infrastructure	0.00%	0.00%
Cash and cash equivalents	0.00%	0.00%
Other	5.50%	5.60%
Total	100.00%	100.00%
US | Corporate bonds | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	31.00%	26.40%
US | Corporate bonds | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	0.60%	0.70%
US | Government securities | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	18.20%	16.00%
US | Government securities | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	22.90%	20.60%

Pensions and other post reti_13

Pensions and other post retirement benefits - Asset allocations (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
UK | Pensions
Disclosure of fair value of plan assets [line items]
Equities	£ 1,464	£ 1,965	£ 2,233
Property	688	857	963
Diversified alternatives	893	771	789
Liability-matching assets	4,982	1,751	1,174
Longevity swap	(51)	(35)	0
Cash and cash equivalents	251	299	426
Other	249	160	167
Fair value of plan assets	14,364	15,507	15,330
UK | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Equities	732	1,181	1,420
Property	103	108	129
Diversified alternatives	0	0	99
Liability-matching assets	1,704	1,751	1,174
Longevity swap	0	0	0
Cash and cash equivalents	29	40	211
Other	0	0	0
Fair value of plan assets	8,456	12,819	12,611
UK | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	732	784	813
Property	585	749	834
Diversified alternatives	893	771	690
Liability-matching assets	3,278	0	0
Longevity swap	(51)	(35)	0
Cash and cash equivalents	222	259	215
Other	249	160	167
Fair value of plan assets	5,908	2,688	2,719
UK | Corporate bonds | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	3,837	3,625	3,949
UK | Corporate bonds | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	3,837	3,625	3,949
UK | Corporate bonds | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	0	0	0
UK | Government securities | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	2,051	6,114	5,629
UK | Government securities | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	2,051	6,114	5,629
UK | Government securities | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	0	0	0
US | Pensions
Disclosure of fair value of plan assets [line items]
Equities	2,510	2,711	2,531
Property	307	316	279
Diversified alternatives	626	670	619
Infrastructure	121	99	77
Cash and cash equivalents	24	21	14
Other	(41)	13	33
Fair value of plan assets	6,972	6,646	6,030
US | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Equities	467	533	577
Property	0	0	0
Diversified alternatives	162	183	198
Infrastructure	0	0	0
Cash and cash equivalents	24	21	14
Other	(44)	(8)	6
Fair value of plan assets	2,784	2,480	2,294
US | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	2,043	2,178	1,954
Property	307	316	279
Diversified alternatives	464	487	421
Infrastructure	121	99	77
Cash and cash equivalents	0	0	0
Other	3	21	27
Fair value of plan assets	4,188	4,166	3,736
US | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Equities	1,390	1,588	1,522
Diversified alternatives	323	341	305
Other	132	149	137
Fair value of plan assets	2,412	2,640	2,498
US | Other post-retirement benefits | Quoted
Disclosure of fair value of plan assets [line items]
Equities	353	404	412
Diversified alternatives	162	175	161
Other	0	0	0
Fair value of plan assets	1,081	1,138	1,105
US | Other post-retirement benefits | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	1,037	1,184	1,110
Diversified alternatives	161	166	144
Other	132	149	137
Fair value of plan assets	1,331	1,502	1,393
US | Corporate bonds | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	2,158	1,754	1,498
US | Corporate bonds | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	1,640	1,329	1,085
US | Corporate bonds | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	518	425	413
US | Corporate bonds | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	15	19	24
US | Corporate bonds | Other post-retirement benefits | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	15	19	24
US | Corporate bonds | Other post-retirement benefits | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	0	0	0
US | Government securities | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	1,267	1,062	979
US | Government securities | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	535	422	414
US | Government securities | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	732	640	565
US | Government securities | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	552	543	510
US | Government securities | Other post-retirement benefits | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	551	540	508
US | Government securities | Other post-retirement benefits | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	£ 1	£ 3	£ 2

Provisions - Schedule of change

Provisions - Schedule of changes in provisions (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	£ 2,199	£ 2,052
Exchange adjustments	97	124
Additions	589	226
Unused amounts reversed	(70)	(65)
Unwinding of discount	77	74
Utilised	(238)	(209)
Transfers		(3)
Other provisions, ending balance	2,654	2,199
Environmental
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	1,639	1,531
Exchange adjustments	82	103
Additions	437	32
Unused amounts reversed	(29)	(36)
Unwinding of discount	65	62
Utilised	(123)	(53)
Transfers		0
Other provisions, ending balance	2,071	1,639
Decommissioning
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	188	194
Exchange adjustments	5	7
Additions	93	18
Unused amounts reversed	(16)	(10)
Unwinding of discount	5	5
Utilised	(21)	(26)
Transfers		0
Other provisions, ending balance	254	188
Restructuring
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	83	3
Exchange adjustments	0	0
Additions	7	125
Unused amounts reversed	(16)	(3)
Unwinding of discount	0	0
Utilised	(39)	(42)
Transfers		0
Other provisions, ending balance	35	83
Emissions
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	9	8
Exchange adjustments	1	0
Additions	12	16
Unused amounts reversed	0	(6)
Unwinding of discount	0	0
Utilised	(5)	(9)
Transfers		0
Other provisions, ending balance	17	9
Other
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	280	316
Exchange adjustments	9	14
Additions	40	35
Unused amounts reversed	(9)	(10)
Unwinding of discount	7	7
Utilised	(50)	(79)
Transfers		(3)
Other provisions, ending balance	£ 277	£ 280

Provisions - Current and non-cu

Provisions - Current and non-current provisions (Details) - GBP (£)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Disclosure of other provisions [line items]
Current	£ 348,000,000	£ 316,000,000	£ 273,000,000	£ 273,000,000
Non-current	2,306,000,000	1,883,000,000	£ 1,779,000,000	1,779,000,000
Other provisions	2,654,000,000	2,199,000,000		2,052,000,000
Additions	589,000,000	226,000,000
Utilised	238,000,000	209,000,000
Transferred to trade and other payables	0	3,000,000
Discontinued operations
Disclosure of other provisions [line items]
Additions	15,000,000	0
Utilised	8,000,000	20,000,000
Environmental
Disclosure of other provisions [line items]
Other provisions	2,071,000,000	1,639,000,000		£ 1,531,000,000
Additions	£ 437,000,000	£ 32,000,000
Real discount rate	0.50%	1.00%
Utilised	£ 123,000,000	£ 53,000,000
Environmental | Exceptional items
Disclosure of other provisions [line items]
Additions	402,000,000	£ 0
Environmental | Exceptional items, impact of change in the real discount rate
Disclosure of other provisions [line items]
Additions	£ 76,000,000

Provisions - Environmental prov

Provisions - Environmental provision (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of other provisions [line items]
Discounted	£ 2,654	£ 2,199	£ 2,052
Environmental
Disclosure of other provisions [line items]
Discounted	2,071	1,639	£ 1,531
Undiscounted	£ 2,139	£ 1,765
Real discount rate	0.50%	1.00%
Weighted average duration of cash flows	10 years
Environmental | UK
Disclosure of other provisions [line items]
Discounted	£ 175	£ 189
Undiscounted	£ 184	£ 210
Real discount rate	0.50%	1.00%
Weighted average duration of cash flows	11 years
Environmental | US
Disclosure of other provisions [line items]
Discounted	£ 1,896	£ 1,450
Undiscounted	£ 1,955	£ 1,555
Real discount rate	0.50%	1.00%
Weighted average duration of cash flows	9 years

Provisions - Narrative (Details

Provisions - Narrative (Details) - GBP (£)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of other provisions [line items]
Other provisions	£ 2,654,000,000	£ 2,199,000,000	£ 2,052,000,000
Expense of restructuring activities	589,000,000	226,000,000
Utilised	238,000,000	209,000,000
Decommissioning
Disclosure of other provisions [line items]
Other provisions	254,000,000	188,000,000	194,000,000
Expense of restructuring activities	93,000,000	18,000,000
Utilised	21,000,000	26,000,000
Decommissioning provision, ARO
Disclosure of other provisions [line items]
Other provisions	174,000,000	80,000,000
Provision for decommissioning, demolition of gas holders
Disclosure of other provisions [line items]
Other provisions	74,000,000	90,000,000
Restructuring
Disclosure of other provisions [line items]
Other provisions	35,000,000	83,000,000	3,000,000
Expense of restructuring activities	7,000,000	125,000,000
Utilised	39,000,000	42,000,000
Other
Disclosure of other provisions [line items]
Other provisions	277,000,000	280,000,000	£ 316,000,000
Expense of restructuring activities	40,000,000	35,000,000
Utilised	50,000,000	79,000,000
Business set up and restructuring cost
Disclosure of other provisions [line items]
Other provisions	37,000,000	30,000,000
Onerous lease commitments and rates payable on surplus properties
Disclosure of other provisions [line items]
Other provisions	31,000,000	29,000,000
Liability for claims and claims adjustment
Disclosure of other provisions [line items]
Other provisions	164,000,000	164,000,000
Obligations associated with investments in joint ventures and associates
Disclosure of other provisions [line items]
Other provisions	£ 0	£ 13,000,000

Share capital - Schedule of sha

Share capital - Schedule of share capital (Details) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions		12 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	May 21, 2017
Disclosure of classes of share capital [line items]
Equity, beginning balance		£ 19,369	£ 18,848	£ 20,384
Issued during the year in lieu of dividends	[1]	(1)	(1)	0
Equity, ending balance		£ 19,584	£ 19,369	£ 18,848
Par value per share (GBP per share)					£ 0.1243
Share capital
Disclosure of classes of share capital [line items]
Issued capital (in shares), beginning balance		3,687	3,638
Issued during period, in lieu of dividends (in shares)		93	49
Issued capital (in shares), ending balance		3,780	3,687	3,638
Equity, beginning balance		£ 458	£ 452	£ 449
Issued during the year in lieu of dividends	[1]	12	6	3
Equity, ending balance		£ 470	£ 458	£ 452
[1]	Included within the share premium account are costs associated with scrip dividends.

Share capital - Narrative (Deta

Share capital - Narrative (Details) - GBP (£) £ in Millions, shares in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Share Capital, Reserves And Other Equity Interest [Abstract]
Treasury stock (in shares)	272	277
Treasury shares, market value	£ 2,574	£ 2,359
Treasury shares, gifted (in shares)	3	3
Treasury stock, reissued (in shares)	2	3
Shares reissued to employee share schemes as percent of ordinary shares	0.10%	0.20%
Treasury shares, reissued, nominal value	£ 1	£ 1
Gross proceeds from reissue of treasury shares	17	18
Purchase of own shares, employee share trusts	£ 6	£ 2	£ 5
Maximum number of treasury shares held during the year (in shares)	277	283
Treasury shares as percent of ordinary shares	7.30%	7.70%
Treasury shares, nominal value	£ 34	£ 35

Other equity reserves (Details)

Other equity reserves (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2018
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	£ (4,237)	£ (4,540)	£ (3,987)
Transfer on transition to IFRS 9				£ 72
Exchange adjustments	550	346	(504)
Net gains/(losses) taken to equity	(206)	(304)	266
Share of net gains of associates taken to equity	(5)	1	5
Transferred to (from) profit or loss	(31)	207	(353)
Net losses in respect of cash flow hedging of capital expenditure	(17)	(13)
Tax	42	12	33
Cash flow hedges transferred to the statement of financial position, net of tax	(15)	(18)
Other equity reserves, ending balance	(3,919)	(4,237)	(4,540)
Gains (losses) on exchange adjustments related to the translation of foreign operations	545	896	(1,304)
Gains (losses) on hedges of net investments in foreign subsidiaries	5	(550)	800
Translation
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	736	390	894
Exchange adjustments	550	346	(504)
Other equity reserves, ending balance	1,286	736	390
Cash flow hedge
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	61	128	103
Transfer on transition to IFRS 9				(3)
Net gains/(losses) taken to equity	(142)	(206)	296
Share of net gains of associates taken to equity	(5)	1	5
Transferred to (from) profit or loss	14	166	(280)
Net losses in respect of cash flow hedging of capital expenditure	(17)	(13)
Tax	29	6	4
Cash flow hedges transferred to the statement of financial position, net of tax	(15)	(18)
Other equity reserves, ending balance	(75)	61	128
Cost of hedging
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	17
Transfer on transition to IFRS 9				76
Net gains/(losses) taken to equity	(33)	(107)
Transferred to (from) profit or loss	(45)	41
Tax	11	7
Other equity reserves, ending balance	(50)	17
Available- for-sale
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		88	162
Transfer on transition to IFRS 9				(88)
Net gains/(losses) taken to equity			(30)
Transferred to (from) profit or loss			(73)
Tax			29
Other equity reserves, ending balance	0		88
FVOCI equity
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	34	0
Transfer on transition to IFRS 9				34
Net gains/(losses) taken to equity	(13)
Tax	4
Other equity reserves, ending balance	25	34	0
FVOCI debt
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	48	0
Transfer on transition to IFRS 9				46
Net gains/(losses) taken to equity	(15)	2
Tax	(2)
Other equity reserves, ending balance	31	48	0
Own credit
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	13	0
Transfer on transition to IFRS 9				£ 7
Net gains/(losses) taken to equity	(3)	7
Tax		(1)
Other equity reserves, ending balance	10	13	0
Capital redemption
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	19	19	19
Other equity reserves, ending balance	19	19	19
Merger
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	(5,165)	(5,165)	(5,165)
Other equity reserves, ending balance	£ (5,165)	(5,165)	(5,165)
Change in presentation of spot foreign exchange rate movements on derivatives designated as cash flow hedges of foreign currency risk and interest rates
Disclosure of reserves within equity [line items]
Net gains/(losses) taken to equity		(166)	277
Transferred to (from) profit or loss		£ (166)	£ 277

Net debt - Reconciliation of ne

Net debt - Reconciliation of net cash flow to movement in net debt (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2019	Apr. 01, 2018
Subclassifications of assets, liabilities and equities [abstract]
Decrease in cash and cash equivalents	£ (183)	£ (80)	£ (807)
Decrease in financial investments	(7)	(822)	(5,953)
Increase/(decrease) in borrowings and related derivatives	(23)	(708)	1,209
Net interest paid on the components of net debt	888	866	808
Change in debt resulting from cash flows	675	(744)	(4,743)
Changes in fair value of financial assets and liabilities and exchange movements	(1,081)	(1,648)	2,098
Net interest charge on the components of net debt	(1,097)	(1,076)	(1,017)
Other non-cash movements	(84)	(27)	(66)
Movement in net debt (net of related derivative financial instruments) in the year	(1,587)	(3,495)	(3,728)
Net debt (net of related derivative financial instruments) at start of year	(26,529)	(23,002)	(19,274)
Impact of transition to IFRS 16 (2019: IFRS 9)				£ (474)
Impact of transition to IFRS 16 (2019: IFRS 9)					£ (32)
Net debt (net of related derivative financial instruments) at end of year	£ (28,590)	£ (26,529)	£ (23,002)

Net debt - Composition of net d

Net debt - Composition of net debt (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
Subclassifications of assets, liabilities and equities [abstract]
Cash, cash equivalents and financial investments	£ 2,071	£ 2,233		£ 3,023
Borrowings	(30,794)	(28,730)		(26,625)
Financing derivatives	133	(32)	£ 600	600	£ (516)
Net debt position	(28,590)	(26,529)	£ (23,034)	(23,002)	£ (19,274)
Interest shareholder loan	£ 6	£ 23		£ 27

Net debt - Analysis of changes

Net debt - Analysis of changes in net debt (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2019	Apr. 01, 2018
Net cash and cash equivalents
Cash and cash equivalents, beginning balance	£ 252	£ 329	£ 1,139
Cash flow, cash and cash equivalents	(183)	(80)	(807)
Fair value gains and losses and exchange movements, cash and cash equivalents	4	3	(3)
Cash and cash equivalents, ending balance	73	252	329
Financial investments
Financial investments, beginning balance	1,981	2,694	8,741
Cash flow, financial investments	(42)	(846)	(5,983)
Fair value gains and losses and exchange movements, financial investments	25	93	(149)
Interest income/(charges), financial investments	34	29	85
Other non-cash movements, financial Investments		11
Financial investments, ending balance	1,998	1,981	2,694
Borrowings
Borrowings, beginning balance	(28,730)	(26,625)	(28,638)
Cash flow, borrowings	450	(240)	2,108
Fair value gains and losses and exchange movements, borrowings	(864)	(733)	1,088
Interest income/(charges), borrowings	(1,092)	(1,062)	(1,117)
Other non-cash movements, borrowings	(84)	(38)	(66)
Impact of transition to IFRS 9					£ (32)
Impact of transition to IFRS 16				£ (474)
Borrowings, ending balance	(30,794)	(28,730)	(26,625)
Financing derivatives
Financing derivatives, beginning balance	(32)	600	(516)
Financing derivatives	450	422	(61)
Fair value gains and losses and exchange movements, financing derivatives	(246)	(1,011)	1,162
Interest income/(charges), financing derivatives	(39)	(43)	15
Financing derivatives, ending balance	133	(32)	600
Net debt
Net debt (net of related derivative financial instruments) at start of year	(26,529)	(23,002)	(19,274)
Change in debt resulting from cash flows	675	(744)	(4,743)
Changes in fair value of financial assets and liabilities and exchange movements	(1,081)	(1,648)	2,098
Net interest income/(charges) on the components of net debt	(1,097)	(1,076)	(1,017)
Other non-cash movements	(84)	(27)	(66)
Net debt (net of related derivative financial instruments) at end of year	(28,590)	(26,529)	(23,002)
Interest payable	246	£ 223	£ 197
Non-current assets
Financing derivatives
Financing derivatives, ending balance	1,205
Net debt
Net debt (net of related derivative financial instruments) at end of year	1,205
Current assets
Net cash and cash equivalents
Cash and cash equivalents, ending balance	73
Financial investments
Financial investments, ending balance	1,998
Financing derivatives
Financing derivatives, ending balance	62
Net debt
Net debt (net of related derivative financial instruments) at end of year	2,133
Current liabilities
Borrowings
Borrowings, ending balance	(4,072)
Financing derivatives
Financing derivatives, ending balance	(254)
Net debt
Net debt (net of related derivative financial instruments) at end of year	(4,326)
Non-current liabilities
Borrowings
Borrowings, ending balance	(26,722)
Financing derivatives
Financing derivatives, ending balance	(880)
Net debt
Net debt (net of related derivative financial instruments) at end of year	£ (27,602)

Net debt - Reconciliation of ca

Net debt - Reconciliation of cash flow from financing liabilities to cash flow statement (Details) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Proceeds received from loans		£ 4,218	£ 2,932	£ 1,941
Repayment of loans		(3,253)	(1,969)	(2,156)
Payments of lease liabilities		(121)	(70)	(71)
Net movements in short-term borrowings		(424)	179	(764)
Net movements in derivatives¹	[1]	(187)	35	(267)
Interest paid		(957)	(914)	(853)
Cash flows per financing activities section of cash flow statement		(724)	193	(2,170)
Non-net debt-related items		34	24	12
Derivative cash inflow in relation to capital expenditure		13	13	12
Derivative cash flows per investing section of cash flow statement	[1]	(223)	(412)	330
Net cash flow (used in)/from financing activities – discontinued operations		0	0	(231)
Cash flows relating to financing liabilities within net debt		(900)	(182)	(2,047)
Borrowings		(450)	240	(2,108)
Financing derivatives		£ (450)	£ (422)	£ 61
[1]	Certain derivative balances have been represented for all periods presented to reflect a reclassification from financing activities to investing activities to reflect a change in accounting policy (see note 1 for details).

Net debt - Reconciliation of ch

Net debt - Reconciliation of changes in liabilities arising from financing activities (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2019	Apr. 01, 2018
Changes in liabilities arising from financing activities [abstract]
Liabilities arising from financing activities, beginning balance	£ (28,502)	£ (26,072)	£ (28,622)
Impact of transition to IFRS 9					£ (32)
Impact of transition to IFRS 16				£ (474)
Cash flow	690	(217)	2,389
Fair value gains and losses and exchange movements	(1,095)	(1,067)	1,310
Interest income/(charges)	(1,101)	(1,076)	(1,083)
Other non-cash movements	(84)	(38)	(66)
Liabilities arising from financing activities, ending balance	(30,566)	(28,502)	(26,072)
Borrowings
Changes in liabilities arising from financing activities [abstract]
Liabilities arising from financing activities, beginning balance	(28,730)	(26,625)	(28,638)
Impact of transition to IFRS 9					£ (32)
Impact of transition to IFRS 16				£ (474)
Cash flow	450	(240)	2,108
Fair value gains and losses and exchange movements	(864)	(733)	1,088
Interest income/(charges)	(1,092)	(1,062)	(1,117)
Other non-cash movements	(84)	(38)	(66)
Liabilities arising from financing activities, ending balance	(30,794)	(28,730)	(26,625)
Financing derivatives
Changes in liabilities arising from financing activities [abstract]
Liabilities arising from financing activities, beginning balance	228	553	16
Cash flow	240	23	281
Fair value gains and losses and exchange movements	(231)	(334)	222
Interest income/(charges)	(9)	(14)	34
Other non-cash movements	0	0	0
Liabilities arising from financing activities, ending balance	£ 228	£ 228	£ 553

Commitments and contingencies_2

Commitments and contingencies (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Disclosure of contingent liabilities [line items]
Contracted for but not provided	£ 2,629	£ 1,973
Energy purchase commitments	16,358	15,709
Estimated financial effect of contingent liabilities	2,822	2,975
Operating lease commitments		301
Guarantee of sublease for US property (expires 2040)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	173	173
Guarantees of certain obligations of Grain LNG (expire up to 2025)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	34	39
Guarantees of certain obligations for construction of HVDC West Coast Link (expected expiry 2020)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	92	139
Guarantees of certain obligations of Nemo Link Limited (expired 2019)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	0	19
Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	683	865
Guarantees of certain obligations of St William Homes LLP (various expiry dates)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	30	22
Guarantees of certain obligations for construction of IFA 2 (expected expiry 2022)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	564	505
Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	1,096	872
Other guarantees and letters of credit (various expiry dates)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	150	341
Guarantees to both joint ventures and EPC contractors regarding the construction of interconnectors
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	358	470
Less than 1 year
Disclosure of contingent liabilities [line items]
Energy purchase commitments	1,365	1,353
Operating lease commitments		43
In 1 to 2 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	890	779
Operating lease commitments		39
In 2 to 3 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	973	651
Operating lease commitments		34
In 3 to 4 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	955	827
Operating lease commitments		35
In 4 to 5 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	861	862
Operating lease commitments		27
More than 5 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	£ 11,314	11,237
Operating lease commitments		£ 123

Related party transactions - Re

Related party transactions - Related party transactions table (Details) - GBP (£)	1 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
UK Gas Distribution (Cadent)
Disclosure of transactions between related parties [line items]
Proportion of ownership interest disposed	39.00%
Quadgas HoldCo Limited
Disclosure of transactions between related parties [line items]
Proportion of ownership interest disposed	39.00%
Receivables due from associates	£ 352,000,000
Pension plan
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		£ 5,000,000	£ 5,000,000	£ 3,000,000
Joint ventures
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		101,000,000	151,000,000	14,000,000
Purchases of goods and services, related party transactions		61,000,000	26,000,000	135,000,000
Amounts receivable		255,000,000	584,000,000	160,000,000
Amounts payable		72,000,000	8,000,000	0
Interest income		2,000,000	5,000,000	4,000,000
Dividends received		34,000,000	30,000,000	43,000,000
Joint ventures | St William Homes LLP
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		38,000,000	139,000,000
Receivables due from joint ventures		242,000,000	325,000,000
Joint ventures | NGET/SPT Upgrades Limited
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		32,000,000
Purchases of goods and services, related party transactions		58,000,000	26,000,000
Joint ventures | Nemo Link Limited
Disclosure of transactions between related parties [line items]
Receivables due from joint ventures		0	258,000,000
Joint ventures | BritNed Development Limited
Disclosure of transactions between related parties [line items]
Dividends received		25,000,000	30,000,000
Associates
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		33,000,000	192,000,000	220,000,000
Purchases of goods and services, related party transactions		56,000,000	141,000,000	160,000,000
Amounts receivable		1,000,000	368,000,000	376,000,000
Amounts payable		4,000,000	12,000,000	17,000,000
Interest income		8,000,000	23,000,000	27,000,000
Dividends received		41,000,000	171,000,000	£ 170,000,000
Associates | UK Gas Distribution (Cadent)
Disclosure of transactions between related parties [line items]
Proportion of ownership interest disposed	39.00%
Associates | Quadgas HoldCo Limited
Disclosure of transactions between related parties [line items]
Dividends received		0	133,000,000
Other income, sale of UK gas distribution business		31,000,000	52,000,000
Receivables due from associates		0	352,000,000
Associates | Millennium Pipeline Company LLC
Disclosure of transactions between related parties [line items]
Purchases of goods and services, related party transactions		31,000,000	30,000,000
Dividends received		£ 32,000,000	£ 24,000,000

Financial risk management - Nar

Financial risk management - Narrative (Details)	12 Months Ended
	Mar. 31, 2020
Financial Instruments [Abstract]
Hedge ratio	1

Financial risk management - Tre

Financial risk management - Treasury credit risk (Details) £ in Millions	Mar. 31, 2020GBP (£)
Triple ‘A’ G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	£ 2,049
Triple ‘A’ vehicles (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	500
Triple ‘A’ range institutions and non-G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	1,118
Double ‘A’ G7 sovereign entities (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	1,863
Bottom of range | Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	745
Bottom of range | Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	261
Top of range | Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	931
Top of range | Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	373
Long-term limit | Triple ‘A’ G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	1,024
Long-term limit | Triple ‘A’ vehicles (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	0
Long-term limit | Triple ‘A’ range institutions and non-G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	559
Long-term limit | Double ‘A’ G7 sovereign entities (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	931
Long-term limit | Bottom of range | Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	372
Long-term limit | Bottom of range | Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	130
Long-term limit | Top of range | Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	465
Long-term limit | Top of range | Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	£ 186

Financial risk management - Off

Financial risk management - Offsetting financial assets and liabilities (Details) - Credit Risk - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Assets
Gross carrying amounts	£ 1,342	£ 1,153
Gross amounts offset	0	0
Net amount presented in statement of financial position	1,342	1,153
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(356)	(270)
Cash collateral received/ pledged	(697)	(551)
Net amount	289	332
Liabilities
Gross carrying amounts	(1,334)	(1,183)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(1,334)	(1,183)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	356	270
Cash collateral received/ pledged	654	615
Net amount	(324)	(298)
Assets (Liabilities)
Gross carrying amounts	8	(30)
Gross amounts offset	0	0
Net amount presented in statement of financial position	8	(30)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	0	0
Cash collateral received/ pledged	(43)	64
Net amount	(35)	34
Financing derivatives
Liabilities
Gross carrying amounts	(1,134)	(1,084)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(1,134)	(1,084)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	351	299
Cash collateral received/ pledged	646	615
Net amount	(137)	(170)
Commodity contract derivatives
Liabilities
Gross carrying amounts	(200)	(99)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(200)	(99)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	5	(29)
Cash collateral received/ pledged	8	0
Net amount	(187)	(128)
Bank account and bank overdraft
Assets
Gross amounts offset	(23)	(19)
Financing derivatives
Assets
Gross carrying amounts	1,267	1,052
Gross amounts offset	0	0
Net amount presented in statement of financial position	1,267	1,052
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(351)	(299)
Cash collateral received/ pledged	(694)	(551)
Net amount	222	202
Commodity contract derivatives
Assets
Gross carrying amounts	75	101
Gross amounts offset	0	0
Net amount presented in statement of financial position	75	101
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(5)	29
Cash collateral received/ pledged	(3)	0
Net amount	£ 67	£ 130

Financial risk management - Liq

Financial risk management - Liquidity risk (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Non-derivative financial liabilities
Lease liabilities	£ (974)	£ (310)
Less than 1 year
Non-derivative financial liabilities
Lease liabilities	(132)	(65)
Liquidity risk
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(29,647)	(28,148)
Interest payments on borrowings	(14,231)	(15,719)
Lease liabilities	(974)	(310)
Other non-interest-bearing liabilities	(3,467)	(3,646)
Contingent consideration	(96)
Derivative financial assets
Financial liabilities	(48,679)	(48,300)
Liquidity risk | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	5,877	4,464
Liquidity risk | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(4,651)	(3,368)
Liquidity risk | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	22	34
Liquidity risk | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(21)	(6)
Liquidity risk | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	7,953	7,471
Liquidity risk | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(9,248)	(8,949)
Liquidity risk | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	6	6
Liquidity risk | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(202)	(129)
Liquidity risk | Less than 1 year
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(3,672)	(4,129)
Interest payments on borrowings	(765)	(800)
Lease liabilities	(132)	(72)
Other non-interest-bearing liabilities	(3,149)	(3,306)
Contingent consideration	(32)
Derivative financial assets
Financial liabilities	(7,998)	(8,079)
Liquidity risk | Less than 1 year | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	2,469	1,928
Liquidity risk | Less than 1 year | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(2,271)	(1,251)
Liquidity risk | Less than 1 year | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	20	23
Liquidity risk | Less than 1 year | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(21)	0
Liquidity risk | Less than 1 year | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	2,249	3,045
Liquidity risk | Less than 1 year | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(2,582)	(3,421)
Liquidity risk | Less than 1 year | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	4	2
Liquidity risk | Less than 1 year | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(116)	(98)
Liquidity risk | In 1 to 2 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(2,150)	(2,348)
Interest payments on borrowings	(750)	(733)
Lease liabilities	(114)	(63)
Other non-interest-bearing liabilities	(318)	(340)
Contingent consideration	(16)
Derivative financial assets
Financial liabilities	(3,009)	(3,727)
Liquidity risk | In 1 to 2 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	1,063	561
Liquidity risk | In 1 to 2 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(527)	(459)
Liquidity risk | In 1 to 2 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	1	9
Liquidity risk | In 1 to 2 years | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	0	(5)
Liquidity risk | In 1 to 2 years | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	986	1,703
Liquidity risk | In 1 to 2 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(1,136)	(2,029)
Liquidity risk | In 1 to 2 years | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	2	3
Liquidity risk | In 1 to 2 years | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(50)	(26)
Liquidity risk | In 2 to 3 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(1,611)	(1,998)
Interest payments on borrowings	(714)	(721)
Lease liabilities	(99)	(52)
Other non-interest-bearing liabilities	0	0
Contingent consideration	(32)
Derivative financial assets
Financial liabilities	(2,539)	(2,753)
Liquidity risk | In 2 to 3 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	570	863
Liquidity risk | In 2 to 3 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(375)	(783)
Liquidity risk | In 2 to 3 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	1	2
Liquidity risk | In 2 to 3 years | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	0	(1)
Liquidity risk | In 2 to 3 years | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	1,208	163
Liquidity risk | In 2 to 3 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(1,463)	(223)
Liquidity risk | In 2 to 3 years | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	0	1
Liquidity risk | In 2 to 3 years | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(24)	(4)
Liquidity risk | More than 3 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(22,214)	(19,673)
Interest payments on borrowings	(12,002)	(13,465)
Lease liabilities	(629)	(123)
Other non-interest-bearing liabilities	0	0
Contingent consideration	(16)
Derivative financial assets
Financial liabilities	(35,133)	(33,741)
Liquidity risk | More than 3 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	1,775	1,112
Liquidity risk | More than 3 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(1,478)	(875)
Liquidity risk | More than 3 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	0	0
Liquidity risk | More than 3 years | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	0	0
Liquidity risk | More than 3 years | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	3,510	2,560
Liquidity risk | More than 3 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(4,067)	(3,276)
Liquidity risk | More than 3 years | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	0	0
Liquidity risk | More than 3 years | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	£ (12)	£ (1)

Financial risk management - Cur

Financial risk management - Currency risk (Details) - Currency risk - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	£ (28,590)	£ (26,529)
Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	73	252
Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,998	1,981
Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(30,794)	(28,730)
Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(28,723)	(26,497)
Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	133	(32)
Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,709	2,033
Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(3,179)	(3,306)
Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(362)	(340)
Sterling
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(12,745)	(10,584)
Sterling | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	18	97
Sterling | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	813	965
Sterling | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(12,407)	(10,591)
Sterling | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(11,576)	(9,529)
Sterling | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,169)	(1,055)
Sterling | Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	306	398
Sterling | Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,177)	(1,221)
Sterling | Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(85)	(93)
Euro
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	191	18
Euro | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	2
Euro | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Euro | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(4,150)	(4,787)
Euro | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(4,150)	(4,785)
Euro | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	4,341	4,803
Euro | Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Euro | Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Euro | Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Dollar
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(16,191)	(16,202)
Dollar | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	55	153
Dollar | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,185	1,016
Dollar | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(13,217)	(12,126)
Dollar | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(11,977)	(10,957)
Dollar | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(4,214)	(5,245)
Dollar | Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,403	1,635
Dollar | Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(2,002)	(2,085)
Dollar | Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(277)	(247)
Other
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	155	239
Other | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,020)	(1,226)
Other | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,020)	(1,226)
Other | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,175	1,465
Other | Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other | Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other | Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	£ 0	£ 0

Financial risk management - Int

Financial risk management - Interest rate risk (Details) - Interest rate risk - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	£ (28,590)	£ (26,529)
Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(18,639)	(17,238)
Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(3,001)	(2,556)
Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,974)	(6,855)
Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	24	120
Cash and cash equivalents
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	73	252
Cash and cash equivalents | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	71	59
Cash and cash equivalents | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	10	104
Cash and cash equivalents | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Cash and cash equivalents | Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(8)	89
Financial investments
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	1,998	1,981
Financial investments | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	0	6
Financial investments | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	1,966	1,944
Financial investments | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Financial investments | Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	32	31
Borrowings
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(30,794)	(28,730)
Borrowings | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(20,969)	(19,043)
Borrowings | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(3,085)	(3,045)
Borrowings | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,740)	(6,642)
Borrowings | Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Pre-derivative position
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(28,723)	(26,497)
Pre-derivative position | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(20,898)	(18,978)
Pre-derivative position | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(1,109)	(997)
Pre-derivative position | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,740)	(6,642)
Pre-derivative position | Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	24	120
Derivative effect
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	133	(32)
Derivative effect | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	2,259	1,740
Derivative effect | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(1,892)	(1,559)
Derivative effect | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(234)	(213)
Derivative effect | Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	£ 0	£ 0

Financial risk management - Imp

Financial risk management - Impact of hedge accounting in the primary financial statements (Details) £ in Millions	12 Months Ended
	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)	Mar. 31, 2020	Mar. 31, 2020£ / $	Mar. 31, 2020€ / $	Mar. 31, 2020£ / €	Mar. 31, 2019	Mar. 31, 2019£ / $	Mar. 31, 2019€ / $	Mar. 31, 2019£ / €	Apr. 01, 2018GBP (£)	Mar. 31, 2018GBP (£)	Mar. 31, 2017GBP (£)
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	£ (3,919)	£ (4,237)									£ (4,468)	£ (4,540)	£ (3,987)
Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	(50)	17									£ 76
Fair value hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Net gains (losses) in respect of cost of hedging	5	(6)
Transferred to profit or loss in respect of cost of hedging	1	3
Closing foreign exchange rate | £ / $				1.64
Fair value hedges | Cost of hedging | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	2	(4)
Fair value hedges | Bottom of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate					1.13	1.19		1.64	1.13	1.19
Fair value hedges | Top of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate					1.17	1.24		1.65	1.16	1.24
Fair value hedges | GBP | Libor | Bottom of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis			0.30%				0.30%
Fair value hedges | GBP | Libor | Top of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis			4.08%				5.61%
Fair value hedges | USD | Libor | Bottom of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis			(0.44%)				(0.44%)
Fair value hedges | USD | Libor | Top of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis			1.15%				1.15%
Cash flow hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Net gains (losses) in respect of cash flow hedges	(143)	(206)
Net gains (losses) in respect of cost of hedging	(7)	(12)
Transferred to profit or loss in respect of cash flow hedges	14	166
Transferred to profit or loss in respect of cost of hedging	(1)	0
Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Net gains (losses) in respect of cash flow hedges	(17)	(12)
Net gains (losses) in respect of cost of hedging	0	0
Transferred to profit or loss in respect of cash flow hedges	0	0
Transferred to profit or loss in respect of cost of hedging	0	0
Cash flow hedges | Cost of hedging | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	(8)	0
Cash flow hedges | Cost of hedging | Currency risk
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	0	0
Cash flow hedges | Bottom of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.30	1.13	1.10		1.52	1.13	1.14
Cash flow hedges | Bottom of range | Currency risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.24		1.04		1.29		1.07
Cash flow hedges | Top of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.66	1.14	1.24		1.66	1.14	1.24
Cash flow hedges | Top of range | Currency risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.41		1.30		1.41		1.32
Cash flow hedges | GBP | Bottom of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate			1.331%				1.795%
Cash flow hedges | GBP | Top of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate			5.85%				5.85%
Cash flow hedges | USD | Bottom of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate			1.103%				1.103%
Cash flow hedges | USD | Top of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate			3.864%				3.864%
Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Net gains (losses) in respect of cost of hedging	(30)	(90)
Transferred to profit or loss in respect of cost of hedging	(45)	39
Closing foreign exchange rate						1.14		1.49		1.15
Net investment hedges | Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	(43)	32
Net investment hedges | Bottom of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate | £ / $				1.21
Net investment hedges | Top of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate | £ / $				1.49
Derivative assets - current | Fair value hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	1	17
Derivative assets - current | Cash flow hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0	0
Derivative assets - current | Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	4	9
Derivative assets - current | Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	9	0
Derivative assets - non-current | Fair value hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	247	168
Derivative assets - non-current | Cash flow hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	106	78
Derivative assets - non-current | Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	8	23
Derivative assets - non-current | Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0	0
Derivative liabilities - current | Fair value hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(1)	(9)
Derivative liabilities - current | Cash flow hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(105)	(28)
Derivative liabilities - current | Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(8)	(3)
Derivative liabilities - current | Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(82)	(43)
Derivative liabilities - non-current | Fair value hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(39)	(25)
Derivative liabilities - non-current | Cash flow hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(264)	(134)
Derivative liabilities - non-current | Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(12)	(4)
Derivative liabilities - non-current | Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	£ (19)	(249)
Change in presentation of spot foreign exchange rate movements on derivatives designated as cash flow hedges of foreign currency risk and interest rates | Cash flow hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Net gains (losses) in respect of cash flow hedges		(166)
Transferred to profit or loss in respect of cash flow hedges		£ 166

Financial risk management - Eff

Financial risk management - Effects of hedge accounting on financial position and performance for each type of hedge (Details) £ in Millions	12 Months Ended
	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)
Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(1,751,000,000)	(1,707,000,000)
Balance of fair value hedge adjustments in borrowings, Continuing hedges	£ (31)	£ 11
Balance of fair value hedge adjustments in borrowings, Discontinued hedges	(95)	(117)
Change in value used for calculating ineffectiveness, Hedged item	(42)	15
Change in value used for calculating ineffectiveness, Hedging instrument	48	(10)
Hedge ineffectiveness	£ 6	£ 5
Foreign currency and interest rate risk | Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(4,127,000,000)	(3,804,000,000)
Balance in cash flow hedge reserve, Continuing hedges	£ (69)	£ (17)
Balance in cash flow hedge reserve, Discontinued hedges	(22)	51
Change in value used for calculating ineffectiveness, Hedged item	142	206
Change in value used for calculating ineffectiveness, Hedging instrument	(143)	(206)
Hedge ineffectiveness	£ (1)	£ 0
Currency risk | Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(794,000,000)	(697,000,000)
Balance in cash flow hedge reserve, Continuing hedges	£ 8	£ 45
Balance in cash flow hedge reserve, Discontinued hedges	0	0
Change in value used for calculating ineffectiveness, Hedged item	17	12
Change in value used for calculating ineffectiveness, Hedging instrument	(17)	(12)
Hedge ineffectiveness	£ 0	£ 0
Currency risk | Net investment hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(3,064,000,000)	(2,974,000,000)
Balance in translation reserve, Continuing hedges	£ 45	£ (329)
Balance in translation reserve, Discontinued hedges	(2,871)	(2,502)
Change in value used for calculating ineffectiveness, Hedged item	(6)	550
Change in value used for calculating ineffectiveness, Hedging instrument	6	(550)
Hedge ineffectiveness	0	0
Borrowings | Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	1,883	1,810
Current liabilities | Borrowings | Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	72	202
Non-current liabilities | Borrowings | Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	£ 1,811	1,608
Impacted by Interest Rate Benchmark Reform amendments | Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(1,675,000,000)
Impacted by Interest Rate Benchmark Reform amendments | Foreign currency and interest rate risk | Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(176,000,000)
Impacted by Interest Rate Benchmark Reform amendments | Currency risk | Net investment hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	0
Change in presentation of spot foreign exchange rate movements on derivatives designated as cash flow hedges of foreign currency risk and interest rates | Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Change in value used for calculating ineffectiveness, Hedged item		4
Change in value used for calculating ineffectiveness, Hedging instrument		(4)
Change in presentation of spot foreign exchange rate movements on derivatives designated as cash flow hedges of foreign currency risk and interest rates | Foreign currency and interest rate risk | Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Change in value used for calculating ineffectiveness, Hedged item		167
Change in value used for calculating ineffectiveness, Hedging instrument		£ (167)

Financial risk management - Fai

Financial risk management - Fair value analysis (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 3,266	£ 3,052
Liabilities	(2,149)	(1,850)
Financial Assets (Liabilities)	1,117	1,202
Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,361	1,404
Liabilities	(741)	(667)
Financial Assets (Liabilities)	620	737
Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,618	1,426
Liabilities	(1,025)	(900)
Financial Assets (Liabilities)	593	526
Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	287	222
Liabilities	(383)	(283)
Financial Assets (Liabilities)	(96)	(61)	£ (26)
Financing derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(1,134)	(1,084)
Financing derivatives | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	0
Financing derivatives | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(889)	(868)
Financing derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(245)	(216)
Commodity contract derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(200)	(99)
Commodity contract derivatives | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	0
Commodity contract derivatives | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(136)	(32)
Commodity contract derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(64)	(67)
Liabilities held at fair value
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(741)	(667)
Liabilities held at fair value | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(741)	(667)
Liabilities held at fair value | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	0
Liabilities held at fair value | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	0
Contingent consideration
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(74)	0
Contingent consideration | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	0
Contingent consideration | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	0
Contingent consideration | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(74)	0
Investments held at FVTPL
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,386	1,373
Investments held at FVTPL | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,278	1,311
Investments held at FVTPL | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Investments held at FVTPL | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	108	62
Investments held at FVOCI
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	435	436
Investments held at FVOCI | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	83	93
Investments held at FVOCI | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	352	343
Investments held at FVOCI | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Investments in associates
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	103	90
Investments in associates | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Investments in associates | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Investments in associates | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	103	90
Financing derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,267	1,052
Financing derivatives | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Financing derivatives | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,257	1,050
Financing derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	10	2
Commodity contract derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	75	101
Commodity contract derivatives | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Commodity contract derivatives | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	9	33
Commodity contract derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 66	£ 68

Financial risk management - Cha

Financial risk management - Changes in level 3 financial instruments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	£ 1,202
Ending balance	1,117	£ 1,202
Derivative assets	1,342	1,153
Financing derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Derivative assets	1,267	1,052
Commodity contract derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Derivative assets	75	101
Level 3
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	(61)	(26)
Net (losses)/gains for the year	12	3
Purchases	77	101
Acquisition of Geronimo	(74)	0
Settlements	(50)	(29)
Reclassification to held for sale	0	(110)
Ending balance	(96)	(61)
Level 3 | Financing derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	(214)	(219)
Net (losses)/gains for the year	(20)	4
Purchases	0	0
Acquisition of Geronimo	0	0
Settlements	(1)	1
Reclassification to held for sale	0	0
Ending balance	(235)	(214)
Gains (losses) on assets held at end of year	(20)	4
Level 3 | Commodity contract derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	1	(1)
Net (losses)/gains for the year	6	(16)
Purchases	26	44
Acquisition of Geronimo	0	0
Settlements	(31)	(26)
Reclassification to held for sale	0	0
Ending balance	2	1
Gains (losses) on assets held at end of year	(17)	(21)
Level 3 | Other
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	152	194
Net (losses)/gains for the year	26	15
Purchases	51	57
Acquisition of Geronimo	(74)	0
Settlements	(18)	(4)
Reclassification to held for sale	0	(110)
Ending balance	£ 137	£ 152

Financial risk management - I_2

Financial risk management - Impacts of reasonably possible changes in significant level 3 assumptions (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Financing derivatives | Plus 20 basis points change in Limited Price Inflation (LPI) market curve
Disclosure of detailed information about financial instruments [line items]
20 basis points change in Limited Price Inflation (LPI) market curve	£ (95)	£ (88)
Financing derivatives | Minus 20 basis points change in LPI market curve
Disclosure of detailed information about financial instruments [line items]
–20 basis points change in LPI market curve	90	83
Commodity contract derivatives | 10% increase in commodity prices
Disclosure of detailed information about financial instruments [line items]
10% increase in commodity prices	2	(1)
Commodity contract derivatives | 10% decrease in commodity prices
Disclosure of detailed information about financial instruments [line items]
10% decrease in commodity prices	0	2
Commodity contract derivatives | Plus 10% market area price change
Disclosure of detailed information about financial instruments [line items]
10% market area price change	(4)	(10)
Commodity contract derivatives | Minus 10% market area price change
Disclosure of detailed information about financial instruments [line items]
-10% market area price change	4	10
Other | Plus 50 basis points change in discount rate
Disclosure of detailed information about financial instruments [line items]
50 basis points change in discount rate	(3)	(3)
Other | Minus 50 basis points change in discount rate
Disclosure of detailed information about financial instruments [line items]
-50 basis points change in discount rate	£ 4	£ 3

Financial risk management - Cap

Financial risk management - Capital risk management (Details)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financial Instruments [Abstract]
Retained cash flow ratio	9.20%	9.40%
Gearing ratio	63.00%	66.00%
Interest cover ratio	4.1	4.4

Borrowing facilities - Narrativ

Borrowing facilities - Narrative (Details) - GBP (£) £ in Millions	Jun. 17, 2020	Apr. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities			£ 5,772	£ 5,727
Borrowings			30,794	28,730	£ 26,625
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities			1,887	1,869
Borrowings			2,122	714
More than 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities			0	0
Renegotiated undrawn borrowing facilities			110
Borrowings transactions | In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Renegotiated undrawn borrowing facilities	£ 1,923
Bilateral Committed Credit Facilities
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity			5,495	5,463
Credit Facilities From Syndicates Of Banks
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity			277	264
Facilities Held As Backup To Commercial Paper And Similar Borrowings
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities			5,495	5,463
Facilities Available As Backup To Specific US Borrowings
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities			277	264
2019 Export Credit Agreements
Disclosure of detailed information about borrowings [line items]
Borrowings			550	550
Export Credit Agreements
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities			233	510
Borrowings			£ 901	£ 859
2020 Export Credit Agreements | Borrowings transactions
Disclosure of detailed information about borrowings [line items]
Borrowings		£ 598

Borrowing facilities - Schedule

Borrowing facilities - Schedule of Undrawn Committed Borrowing Facilities (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Mar. 31, 2019
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 5,772	£ 5,727
Less than 1 year
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	0	0
In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	1,940	0
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	1,668	2,190
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	277	1,668
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	1,887	1,869
More than 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 0	£ 0

Subsidiary undertakings, join_2

Subsidiary undertakings, joint ventures and associates - Subsidiaries (Details)	12 Months Ended
	Mar. 31, 2020
Warwick Technology Park Management Company (No 2) Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	60.56%
New England Hydro Finance Company, Inc.
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	53.704%
New England Hydro-Transmission Corporation
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	53.704%
New England Hydro-Transmission Electric Company Inc.
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	53.704%
Vermont Green Line Devco, LLC
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	90.00%

Subsidiary undertakings, join_3

Subsidiary undertakings, joint ventures and associates - Joint ventures (Details)	12 Months Ended
	Mar. 31, 2020£ / sharesshares	Mar. 31, 2020€ / sharesshares	May 21, 2017£ / shares
Disclosure of joint ventures [line items]
Par value per share (GBP/EUR per share) | £ / shares			£ 0.1243
BritNed Development Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Joint Radio Company Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Nemo Link Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
NGET/SPT Upgrades Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
St William Homes LLP
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Clean Energy Generation, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Emerald Energy Venture LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	51.00%
Goldendale Energy Storage LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Island Park Energy Center, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Islander East Pipeline Company, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
LI Energy Storage System, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
LI Solar Generation, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
Swan Lake North Holdings LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
IFA2 SAS
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%
C Ordinary shares
Disclosure of joint ventures [line items]
Par value per share (GBP/EUR per share) | € / shares		€ 0.20
A Ordinary shares
Disclosure of joint ventures [line items]
Par value per share (GBP/EUR per share) | £ / shares	£ 1
National Grid Interconnector Holdings Limited | C Ordinary shares | BritNed Development Limited
Disclosure of joint ventures [line items]
Number of shares held in joint venture (in shares)	284,500,000	284,500,000
National Grid Interconnector Holdings Limited | A Ordinary shares | BritNed Development Limited
Disclosure of joint ventures [line items]
Number of shares held in joint venture (in shares)	1	1
National Grid Electricity Transmission plc | A Ordinary shares | NGET/SPT Upgrades Limited
Disclosure of joint ventures [line items]
Number of shares held in joint venture (in shares)	50	50

Subsidiary undertakings, join_4

Subsidiary undertakings, joint ventures and associates - Associates (Details)	12 Months Ended
	Mar. 31, 2020shares
Clean Line Energy Partners LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate	32.00%
Connecticut Yankee Atomic Power Company
Disclosure of associates [line items]
Proportion of ownership interest in associate	19.50%
Direct Global Power, Inc.
Disclosure of associates [line items]
Proportion of ownership interest in associate	26.00%
Energy Impact Fund LP
Disclosure of associates [line items]
Proportion of ownership interest in associate	9.42%
Greeneru, Inc.
Disclosure of associates [line items]
Proportion of ownership interest in associate	21.60%
KHB Venture LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate	33.00%
Maine Yankee Atomic Power Company
Disclosure of associates [line items]
Proportion of ownership interest in associate	24.00%
Millennium Pipeline Company LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate	26.25%
New York Transco LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate	28.30%
Nysearch RMLD, LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate	22.63%
Yankee Atomic Electric Company
Disclosure of associates [line items]
Proportion of ownership interest in associate	34.50%
Coreso SA
Disclosure of associates [line items]
Proportion of ownership interest in associate	15.84%
Energis plc
Disclosure of associates [line items]
Proportion of ownership interest in associate	33.06%
Class A Membership Interests | NGV US Distributed Energy Inc. | Sunrun Neptune Investor 2016 LLC
Disclosure of associates [line items]
Number of shares held in associate (in shares)	1,000

Sensitivities - Sensitivities o

Sensitivities - Sensitivities on areas of estimation uncertainty (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Other environment related provision | Estimated future cash flows change
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, percent	10.00%
Change in risk variable, impact on income statement	£ 210	£ 165
Change in risk variable, impact on net assets	£ 210	165
Pensions | Plan assets | Unquoted equities change
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, percent	10.00%
Change in risk variable, impact on income statement	£ 0	0
Change in risk variable, impact on net assets	£ 381	415
Pensions | Plan assets | Unquoted properties change
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, percent	10.00%
Change in risk variable, impact on income statement	£ 0	0
Change in risk variable, impact on net assets	£ 89	107
Pensions | Plan assets | Unquoted diversified alternatives change
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, percent	10.00%
Change in risk variable, impact on income statement	£ 0	0
Change in risk variable, impact on net assets	152	142
UK | Actuarial assumption of discount rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	6	6
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	877	1,064
UK | Actuarial assumption of expected rates of inflation
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	4	4
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	670	908
UK | Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase in actuarial assumption	1	1
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption	39	56
UK | Actuarial assumption of life expectancy after retirement
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	1	1
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	545	610
UK | Pensions | Value of buy-in policies offset to actuarial assumption of discount rate
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on net assets	(205)
UK | Pensions | Value of buy-in policies offset to actuarial assumption of expected rates of inflation
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on net assets	(152)
UK | Pensions | Value of buy-in policies and longevity swap offset to actuarial assumption of life expectancy after retirement
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on net assets	£ (223)
UK | Pensions | Actuarial assumption of discount rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in actuarial assumption, percent	0.50%
UK | Pensions | Actuarial assumption of expected rates of inflation
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in actuarial assumption, percent	0.50%
UK | Pensions | Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase in actuarial assumption, percent	0.50%
UK | Pensions | Actuarial assumption of life expectancy after retirement
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase in actuarial assumption, years	1 year
US | Actuarial assumption of discount rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	£ 10	16
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	514	688
US | Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase in actuarial assumption	2	2
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption	47	46
US | Actuarial assumption of life expectancy after retirement
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	4	4
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	456	406
US | US Healthcare Cost
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	31	32
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 507	£ 503
US | Pensions | Actuarial assumption of discount rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in actuarial assumption, percent	0.50%
US | Pensions | Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase in actuarial assumption, percent	0.50%
US | Pensions | Actuarial assumption of life expectancy after retirement
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase in actuarial assumption, years	1 year
US | Pensions | US Healthcare Cost
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in actuarial assumption, percent	1.00%

Sensitivities - Sensitivities_2

Sensitivities - Sensitivities on financial instruments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair value change | Derivative financial instruments
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	10.00%
Change in risk variable, impact on income statement	£ 12	£ (3)
Change in risk variable, impact on net assets	£ 12	(3)
Fair value change | Commodity contract derivative liabilities
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	10.00%
Change in risk variable, impact on income statement	£ 9	0
Change in risk variable, impact on net assets	£ 9	0
Inflation, UK RPI change | UK
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	0.50%
Change in risk variable, impact on income statement	£ 27	27
Change in risk variable, impact on other equity reserves	£ 0	0
Interest rate risk | UK
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	0.50%
Change in risk variable, impact on income statement	£ 14	16
Change in risk variable, impact on other equity reserves	£ 47	13
Interest rate risk | US
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	0.50%
Change in risk variable, impact on income statement	£ 5	11
Change in risk variable, impact on other equity reserves	£ 27	44
Currency risk
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	10.00%
Change in risk variable, impact on income statement	£ 49	53
Change in risk variable, impact on other equity reserves	216	246
Change in risk variable, impact on net assets	£ 1,319	1,119
Commodity price risk
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	10.00%
Increase in risk variable, impact on earnings	£ 26	26
Decrease in risk variable, impact on earnings	(27)	(27)
Increase in risk variable, impact on net assets	26	26
Decrease in risk variable, impact on net assets	£ (27)	£ (27)

Additional disclosures in res_3

Additional disclosures in respect of guaranteed securities - Narrative (Details) - GBP (£) £ in Millions	Oct. 29, 2007	Mar. 31, 2020
National Grid Gas plc
Disclosure of detailed information about borrowings [line items]
Preferred shares issuance rate	3.60%
British Transco Finance Inc. £m
Disclosure of detailed information about borrowings [line items]
Preferred shares issuance rate	3.90%
British Transco Finance Inc. £m
Disclosure of detailed information about borrowings [line items]
Proceeds from issuing shares		£ 29

Additional disclosures in res_4

Additional disclosures in respect of guaranteed securities - Combined Statement of financial position and income statement (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2019	Apr. 01, 2018	Mar. 31, 2017
Disclosure of information about consolidated structured entities [line items]
Non-current assets	£ 61,288	£ 55,017	£ 52,106		£ 52,106
Total current assets	5,801	7,946	6,681		6,678
Total current liabilities	(8,564)	(9,129)	(8,697)		(8,691)
Total non-current liabilities	(38,941)	(34,465)	(31,242)		(31,441)
Net assets (liabilities)	19,584	19,369	18,848	£ 19,369	18,652
Equity	19,584	19,369	18,848	£ 19,369	£ 18,652	£ 20,384
Revenue	14,540	14,933	15,250
Operating costs	(11,760)	(12,063)	(11,757)
Operating profit/(loss)	2,780	2,870	3,493
Profit/(loss) after tax from continuing operations	1,274	£ 1,502	£ 3,549
National Grid plc and Niagara Mohawk Power Corporation combined
Disclosure of information about consolidated structured entities [line items]
Non-current assets	8,939
Total current assets	1,378
Total current liabilities	(1,648)
Total non-current liabilities	(5,460)
Net assets (liabilities)	(2,324)
Equity	(2,324)
Revenue	2,365
Operating costs	(2,131)
Operating profit/(loss)	234
Other income and costs, including taxation	(428)
Profit/(loss) after tax from continuing operations	3,694
Other subsidiaries
Disclosure of information about consolidated structured entities [line items]
Investments in subsidiaries	14,362
Other subsidiaries | National Grid plc and Niagara Mohawk Power Corporation combined
Disclosure of information about consolidated structured entities [line items]
Non-current assets	363
Total current assets	12,435
Total current liabilities	(16,226)
Total non-current liabilities	(2,105)
Other income	£ 3,888

Transition to new accounting _3

Transition to new accounting standards - Narrative (Details) - GBP (£)	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2019	Apr. 01, 2018
Disclosure of initial application of standards or interpretations [line items]
Operating lease commitments		£ 301,000,000
Lease liabilities	£ 974,000,000	310,000,000
Lease liabilities, impact of discounting	239,000,000	40,000,000
Weighted average lessee's incremental borrowing rate applied to lease liabilities recognised at date of initial application of IFRS 16				2.80%
Right-of-use assets	684,000,000
Lease liabilities	735,000,000	270,000,000		£ 744,000,000
Higher (lower) revenue	13,910,000,000	14,066,000,000
Higher (lower) operating costs	11,760,000,000	12,063,000,000	£ 11,757,000,000
Operating profit from continuing operations	£ 2,780,000,000	2,870,000,000	£ 3,493,000,000
IFRS 16
Disclosure of initial application of standards or interpretations [line items]
Lease liabilities				400,000,000
Lease liabilities, impact of discounting				200,000,000
Right-of-use assets				468,000,000
Lease liabilities				474,000,000
Financial assets at fair value through profit or loss and through other comprehensive income | Retained earnings
Disclosure of initial application of standards or interpretations [line items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9					£ 8,000,000
Financial liabilities at fair value through profit and loss
Disclosure of initial application of standards or interpretations [line items]
Financial liability previously designated at amortised cost reclassified to FVTPL, Initial application of IFRS 9		570,000,000
Increase (decrease) in financial liabilities on basis of measurement category, initial application of IFRS 9		32,000,000
Financial liabilities at fair value through profit and loss | Retained earnings
Disclosure of initial application of standards or interpretations [line items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9		(40,000,000)
Cost of hedging | Retained earnings
Disclosure of initial application of standards or interpretations [line items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9		(67,000,000)
Cost of hedging | Cash flow hedge
Disclosure of initial application of standards or interpretations [line items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9		(10,000,000)
Own credit | Financial liabilities at fair value through profit and loss | Other equity reserves
Disclosure of initial application of standards or interpretations [line items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9		7,000,000
Scenario, Adjustment | IFRS 15
Disclosure of initial application of standards or interpretations [line items]
Higher (lower) revenue		(1,197,000,000)
Higher (lower) operating costs		(1,197,000,000)
Operating profit from continuing operations		0
Scenario, Adjustment | IFRS 16
Disclosure of initial application of standards or interpretations [line items]
Lease liabilities				£ 474,000,000
Scenario, Adjustment | US Regulated and UK Gas Transmission | IFRS 15
Disclosure of initial application of standards or interpretations [line items]
Higher (lower) revenue		(57,000,000)
Operating profit from continuing operations		(57,000,000)
Scenario, Adjustment | UK Regulated | IFRS 15
Disclosure of initial application of standards or interpretations [line items]
Higher (lower) revenue		26,000,000
Operating profit from continuing operations		£ 23,000,000

Transition to new accounting _4

Transition to new accounting standards - IFRS 16: Impact of transition (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
Property, plant and equipment – Right-of-use assets
Land and buildings		£ 2,941	£ 2,560
Plant and machinery		36,656	36,589
Assets in the course of construction		4,425	4,425
Motor vehicles and office equipment		359	339
Total property, plant and equipment	£ 48,770	44,381	43,913	£ 39,853	£ 39,853
Borrowings – Lease liabilities
Current	(112)	(113)	(65)
Non-current	(623)	(631)	(205)
Total lease liabilities	(735)	(744)	(270)
Other liabilities
Trade and other payables	(3,602)	(3,766)	(3,769)	(3,394)	(3,453)
Other non-current liabilities	(891)	(805)	(808)	(750)	(1,317)
Net assets	19,584	19,369	19,369	18,652	18,848
Equity
Total equity	£ 19,584	19,369	£ 19,369	£ 18,652	£ 18,848	£ 20,384
IFRS 16
Borrowings – Lease liabilities
Total lease liabilities		(474)
IFRS 16 | Scenario, Adjustment
Property, plant and equipment – Right-of-use assets
Land and buildings		381
Plant and machinery		67
Assets in the course of construction		0
Motor vehicles and office equipment		20
Total property, plant and equipment		468
Borrowings – Lease liabilities
Current		(48)
Non-current		(426)
Total lease liabilities		(474)
Other liabilities
Trade and other payables		3
Other non-current liabilities		3
Net assets		0
Equity
Total equity		£ 0

Transition to new accounting _5

Transition to new accounting standards - IFRS 9 and IFRS 15: Impact of transition (Details) - GBP (£) £ in Millions	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
Non-current assets
Goodwill	£ 6,233		£ 5,869	£ 5,444	£ 5,444
Other intangible assets	1,295		1,084	899	899
Property, plant and equipment	48,770	£ 44,381	43,913	39,853	39,853
Other non-current assets	354		264	115	115
Pension assets	1,849		1,567	1,409	1,409
Financial and other investments	543		667	899	899
Investments in joint ventures and associates	995		608	2,168	2,168
Derivative financial assets	1,249		1,045	1,319	1,319
Total non-current assets	61,288		55,017	52,106	52,106
Current assets
Inventories and current intangible assets	549		370	341	341
Trade and other receivables	2,986		3,153	2,795	2,798
Current tax assets	102		126	114	114
Financial and other investments	1,998		1,981	2,694	2,694	£ 8,741
Derivative financial assets	93		108	405	405
Cash and cash equivalents	73		252	329	329	1,139
Total current assets	5,801		7,946	6,678	6,681
Total assets	67,089		62,963	58,784	58,787
Current liabilities
Borrowings	(4,072)		(4,472)	(4,447)	(4,447)
Derivative financial liabilities	(380)		(350)	(401)	(401)
Trade and other payables	(3,602)	(3,766)	(3,769)	(3,394)	(3,453)
Contract liabilities	(76)		(61)	(53)	0
Current tax liabilities	(86)		(161)	(123)	(123)
Provisions	(348)		(316)	(273)	(273)
Total current liabilities	(8,564)		(9,129)	(8,691)	(8,697)
Non-current liabilities
Borrowings	(26,722)		(24,258)	(22,210)	(22,178)
Derivative financial liabilities	(954)		(833)	(660)	(660)
Other non-current liabilities	(891)	(805)	(808)	(750)	(1,317)
Contract liabilities	(1,082)		(933)	(813)	0
Deferred tax liabilities	(4,184)		(3,965)	(3,557)	(3,636)
Pensions and other post-retirement benefit obligations	(2,802)		(1,785)	(1,672)	(1,672)
Provisions	(2,306)		(1,883)	(1,779)	(1,779)
Total non-current liabilities	(38,941)		(34,465)	(31,441)	(31,242)
Total liabilities	(47,505)		(43,594)	(40,132)	(39,939)
Net assets (liabilities)	19,584	19,369	19,369	18,652	18,848
Equity
Share capital	470		458	452	452
Share premium account	1,301		1,314	1,321	1,321
Retained earnings	21,710		21,814	21,331	21,599
Other equity reserves	(3,919)		(4,237)	(4,468)	(4,540)	(3,987)
Total shareholders’ equity	19,562		19,349	18,636	18,832
Non-controlling interests	22		20	16	16
Total equity	£ 19,584	£ 19,369	£ 19,369	18,652	£ 18,848	£ 20,384
IFRS 9 | Scenario, Adjustment
Non-current assets
Goodwill				0
Other intangible assets				0
Property, plant and equipment				0
Other non-current assets				0
Pension assets				0
Financial and other investments				0
Investments in joint ventures and associates				0
Derivative financial assets				0
Total non-current assets				0
Current assets
Inventories and current intangible assets				0
Trade and other receivables				0
Current tax assets				0
Financial and other investments				0
Derivative financial assets				0
Cash and cash equivalents				0
Total current assets				0
Total assets				0
Current liabilities
Borrowings				0
Derivative financial liabilities				0
Trade and other payables				0
Contract liabilities				0
Current tax liabilities				0
Provisions				0
Total current liabilities				0
Non-current liabilities
Borrowings				(32)
Derivative financial liabilities				0
Other non-current liabilities				0
Contract liabilities				0
Deferred tax liabilities				5
Pensions and other post-retirement benefit obligations				0
Provisions				0
Total non-current liabilities				(27)
Total liabilities				(27)
Net assets (liabilities)				(27)
Equity
Share capital				0
Share premium account				0
Retained earnings				(99)
Other equity reserves				72
Total shareholders’ equity				(27)
Non-controlling interests				0
Total equity				(27)
IFRS 15 | Scenario, Adjustment
Non-current assets
Goodwill				0
Other intangible assets				0
Property, plant and equipment				0
Other non-current assets				0
Pension assets				0
Financial and other investments				0
Investments in joint ventures and associates				0
Derivative financial assets				0
Total non-current assets				0
Current assets
Inventories and current intangible assets				0
Trade and other receivables				(3)
Current tax assets				0
Financial and other investments				0
Derivative financial assets				0
Cash and cash equivalents				0
Total current assets				(3)
Total assets				(3)
Current liabilities
Borrowings				0
Derivative financial liabilities				0
Trade and other payables				59
Contract liabilities				(53)
Current tax liabilities				0
Provisions				0
Total current liabilities				6
Non-current liabilities
Borrowings				0
Derivative financial liabilities				0
Other non-current liabilities				567
Contract liabilities				(813)
Deferred tax liabilities				74
Pensions and other post-retirement benefit obligations				0
Provisions				0
Total non-current liabilities				(172)
Total liabilities				(166)
Net assets (liabilities)				(169)
Equity
Share capital				0
Share premium account				0
Retained earnings				(169)
Other equity reserves				0
Total shareholders’ equity				(169)
Non-controlling interests				0
Total equity				£ (169)

Transition to new accounting _6

Transition to new accounting standards - IFRS 9: Financial Instruments (Details) £ in Millions	Apr. 01, 2018GBP (£)
Borrowings
Disclosure of financial liabilities at date of initial application of IFRS 9 [line items]
Change to measurement basis under IFRS 9, Financial liabilities	£ (32)
Borrowings | Financial liabilities at amortised cost
Disclosure of financial liabilities at date of initial application of IFRS 9 [line items]
Original carrying amount under IAS 39, Financial liabilities	(570)
Borrowings | Financial liabilities at fair value through profit and loss
Disclosure of financial liabilities at date of initial application of IFRS 9 [line items]
New carrying amount under IFRS 9, Financial liabilities	(602)
Money market funds and fund investments in equities and bonds
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Change to measurement basis under IFRS 9, Financial assets	0
Money market funds and fund investments in equities and bonds | Available-for-sale investments
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Original carrying amount under IAS 39, Financial assets	2,294
Money market funds and fund investments in equities and bonds | Financial assets at FVTPL
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
New carrying amount under IFRS 9, Financial assets	2,294
Cash surrender value of life insurance policies and investments in debt securities
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Change to measurement basis under IFRS 9, Financial assets	0
Cash surrender value of life insurance policies and investments in debt securities | Available-for-sale investments
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Original carrying amount under IAS 39, Financial assets	343
Cash surrender value of life insurance policies and investments in debt securities | Financial assets at FVOCI
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
New carrying amount under IFRS 9, Financial assets	343
Investments in equity securities
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Change to measurement basis under IFRS 9, Financial assets	0
Investments in equity securities | Available-for-sale investments
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Original carrying amount under IAS 39, Financial assets	84
Investments in equity securities | Financial assets at FVOCI
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
New carrying amount under IFRS 9, Financial assets	84
Loans to joint ventures and associates and restricted balances
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Change to measurement basis under IFRS 9, Financial assets	0
Loans to joint ventures and associates and restricted balances | Loans and receivables
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
Original carrying amount under IAS 39, Financial assets	872
Loans to joint ventures and associates and restricted balances | Financial assets at amortised cost
Disclosure of financial assets at date of initial application of IFRS 9 [line items]
New carrying amount under IFRS 9, Financial assets	£ 872

Acquisition of Geronimo Energ_3

Acquisition of Geronimo Energy LLC and Emerald Energy Venture LLC - Fair values of the assets and liabilities recognised (Details) £ in Millions	Jul. 11, 2019GBP (£)
Geronimo and Emerald
Disclosure of detailed information about business combination [line items]
Intangible assets	£ 5
Property, plant and equipment	1
Cash	2
Other identifiable assets and liabilities	30
Total identifiable assets	128
Goodwill	81
Total consideration transferred	209
Emerald
Disclosure of detailed information about business combination [line items]
Investment in joint venture – Emerald	90
Cash consideration	90
Geronimo
Disclosure of detailed information about business combination [line items]
Contingent consideration – Geronimo	70
Cash consideration	£ 49

Acquisition of Geronimo Energ_4

Acquisition of Geronimo Energy LLC and Emerald Energy Venture LLC - Narrative (Details) - GBP (£) £ in Millions	9 Months Ended	12 Months Ended	24 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Mar. 31, 2020	Jul. 11, 2019
Geronimo
Disclosure of detailed information about business combination [line items]
Percentage of share capital acquired				100.00%
Emerald
Disclosure of detailed information about business combination [line items]
Percentage of share capital acquired				51.00%
Geronimo and Emerald
Disclosure of detailed information about business combination [line items]
Total consideration				£ 209
Acquisition-related costs recognised		£ 1	£ 3
Emerald
Disclosure of detailed information about business combination [line items]
Capital contribution to joint venture	£ 50

Uncategorized Items - nggtf-202

Label	Element	Value
Liabilities arising from financing activities	ifrs-full_LiabilitiesArisingFromFinancingActivities	£ 26,104,000,000
Borrowings, Excluding Bank Overdrafts	nggtf_BorrowingsExcludingBankOverdrafts	26,657,000,000
Capital redemption reserve [member]
Other reserves	ifrs-full_OtherReserves	19,000,000
Reserve Of Gains and Losses On Financial Liabilities Measured At Fair Value Through Other Comprehensive Income [Member]
Other reserves	ifrs-full_OtherReserves	46,000,000
Reserve of change in fair value of financial liability attributable to change in credit risk of liability [member]
Other reserves	ifrs-full_OtherReserves	7,000,000
Reserve of gains and losses from investments in equity instruments [member]
Other reserves	ifrs-full_OtherReserves	34,000,000
Reserve of exchange differences on translation [member]
Other reserves	ifrs-full_OtherReserves	390,000,000
Reserve of cash flow hedges [member]
Other reserves	ifrs-full_OtherReserves	125,000,000
Reserve of gains and losses on remeasuring available-for-sale financial assets [member]
Other reserves	ifrs-full_OtherReserves	0
Merger reserve [member]
Other reserves	ifrs-full_OtherReserves	(5,165,000,000)
IFRS 9 and 15 [Member]
Equity	ifrs-full_Equity	(196,000,000)
Borrowings [Member]
Liabilities arising from financing activities	ifrs-full_LiabilitiesArisingFromFinancingActivities	26,657,000,000
Financing Derivatives [Member]
Liabilities arising from financing activities	ifrs-full_LiabilitiesArisingFromFinancingActivities	(553,000,000)
Share premium [member]
Equity	ifrs-full_Equity	1,321,000,000
Equity attributable to owners of parent [member]
Equity	ifrs-full_Equity	18,636,000,000
Equity attributable to owners of parent [member] | IFRS 9 and 15 [Member]
Equity	ifrs-full_Equity	(196,000,000)
Retained earnings [member]
Equity	ifrs-full_Equity	21,331,000,000
Retained earnings [member] | IFRS 9 and 15 [Member]
Equity	ifrs-full_Equity	(268,000,000)
Other Equity Reserves [Member]
Equity	ifrs-full_Equity	(4,468,000,000)	[1]
Other Equity Reserves [Member] | IFRS 9 and 15 [Member]
Equity	ifrs-full_Equity	72,000,000	[1]
Issued capital [member]
Equity	ifrs-full_Equity	452,000,000
Non-controlling interests [member]
Equity	ifrs-full_Equity	16,000,000
Gross carrying amount [member]
Property, plant and equipment	ifrs-full_PropertyPlantAndEquipment	63,544,000,000
Gross carrying amount [member] | Plant And Machinery [Member]
Property, plant and equipment	ifrs-full_PropertyPlantAndEquipment	54,450,000,000
Gross carrying amount [member] | Motor Vehicles And Office Equipment [Member]
Property, plant and equipment	ifrs-full_PropertyPlantAndEquipment	950,000,000
Gross carrying amount [member] | Land and buildings [member]
Property, plant and equipment	ifrs-full_PropertyPlantAndEquipment	3,719,000,000
Gross carrying amount [member] | Construction in progress [member]
Property, plant and equipment	ifrs-full_PropertyPlantAndEquipment	£ 4,425,000,000
[1]	For further details of other equity reserves, see note 28.