National Grid (NGG) 20-F 8 Jun 21 2021 FY Annual report (foreign) Financial data

Cover

Cover	12 Months Ended
	Mar. 31, 2021shares
Entity Information [Line Items]
Document Type	20-F
Document Registration Statement	false
Document Annual Report	true
Document Period End Date	Mar. 31, 2021
Current Fiscal Year End Date	--03-31
Document Transition Report	false
Document Shell Company Report	false
Entity File Number	001-14958
Entity Registrant Name	NATIONAL GRID PLC
Entity Incorporation, State or Country Code	X0
Entity Address, Address Line One	1-3 Strand
Entity Address, City or Town	London
Entity Address, Postal Zip Code	WC2N 5EH
Entity Address, Country	GB
Entity Common Stock, Shares Outstanding	3,814,951,606
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Accounting Standard	International Financial Reporting Standards
Entity Shell Company	false
Entity Central Index Key	0001004315
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
Ordinary shares
Entity Information [Line Items]
Title of 12(b) Security	Ordinary Shares of 12 204/473 pence each
Trading Symbol	NG
Security Exchange Name	NYSE
American Depositary Shares
Entity Information [Line Items]
Title of 12(b) Security	American Depositary Shares, each representing five
Trading Symbol	NGG
Security Exchange Name	NYSE
3.90% Series Preferred Stock
Entity Information [Line Items]
Title of 12(b) Security	3.90% Series
Trading Symbol	NMK PR C
Security Exchange Name	NYSE
3.60% Series Preferred Stock
Entity Information [Line Items]
Title of 12(b) Security	3.60% Series
Trading Symbol	NMK PR B
Security Exchange Name	NYSE
Business Contact
Entity Information [Line Items]
Entity Address, Address Line One	1-3 Strand
Entity Address, City or Town	London
Entity Address, Postal Zip Code	WC2N 5EH
Entity Address, Country	GB
Contact Personnel Name	Justine Campbell
Country Region	44
City Area Code	20
Local Phone Number	004 3000
Phone Fax Number Description	011 44 20 7004 3004

Consolidated income statement

Consolidated income statement - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Profit or loss [abstract]
Revenue	£ 14,779	£ 14,540	£ 14,933
Provision for bad and doubtful debts	(326)	(234)	(181)
Other operating costs	(11,558)	(11,526)	(11,882)
Operating profit/(loss)	2,895	2,780	2,870
Finance income	58	54	88
Finance costs	(928)	(1,167)	(1,157)
Share of post-tax results of joint ventures and associates	58	87	40
Profit/(loss) before tax	2,083	1,754	1,841
Tax	(442)	(480)	(339)
Profit/(loss) after tax from continuing operations	1,641	1,274	1,502
Profit/(loss) after tax from discontinued operations		(9)	12
Total profit/(loss) for the year (continuing and discontinued)	1,641	1,265	1,514
Attributable to:
Equity shareholders of the parent	1,640	1,264	1,511
Non-controlling interests from continuing operations	£ 1	£ 1	£ 3
Earnings per share (pence)
Basic earnings per share (continuing) (in GBP per share)	£ 0.466	£ 0.368	£ 0.443
Diluted earnings per share (continuing) (in GBP per share)	0.463	0.366	0.441
Basic earnings per share (continuing and discontinued) (in GBP per share)	0.466	0.365	0.446
Diluted earnings per share (continuing and discontinued) (in GBP per share)	£ 0.463	£ 0.363	£ 0.444

Consolidated statement of compr

Consolidated statement of comprehensive income - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of analysis of other comprehensive income by item [line items]
Profit after tax from continuing operations		£ 1,641	£ 1,274	£ 1,502
Items from continuing operations that will never be reclassified to profit or loss:
Remeasurement gains/(losses) on pension assets and post-retirement benefit obligations		1,408	(724)	68
Net gains/(losses) on equity instruments designated at fair value through other comprehensive income		46	(9)	0
Net (losses)/gains on financial liability designated at fair value through profit and loss attributable to changes in own credit risk		(11)	(3)	7
Net losses in respect of cash flow hedging of capital expenditure		(14)	(17)	(13)
Tax on items that will never be reclassified to profit or loss		(422)	212	(15)
Total items from continuing operations that will never be reclassified to profit or loss		1,007	(541)	47
Items from continuing operations that may be reclassified subsequently to profit or loss:
Exchange adjustments	[1]	(1,347)	561	361
Net gains/(losses) in respect of cash flow hedges		70	(128)	(40)
Net gains/(losses) in respect of cost of hedging		14	(78)	(66)
Net gains/(losses) on investment in debt instruments measured at fair value through other comprehensive income		80	(15)	2
Share of other comprehensive income/(losses) of associates, net of tax		1	(5)	1
Tax on items that may be reclassified subsequently to profit or loss		(8)	35	12
Total items from continuing operations that may be reclassified subsequently to profit or loss		(1,190)	370	270
Other comprehensive (loss)/income for the year, net of tax from continuing operations		(183)	(171)	317
Other comprehensive income for the year, net of tax from discontinued operations	[2]	0	6	36
Other comprehensive (loss)/income for the year, net of tax		(183)	(165)	353
Total comprehensive income for the year from continuing operations		1,458	1,103	1,819
Total comprehensive (loss)/income for the year from discontinued operations		0	(3)	48
Total comprehensive income for the year		1,458	1,100	1,867
Attributable to:
Equity shareholders of the parent		1,459	1,101	1,815
Non-controlling interests		(1)	2	4
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
Items from continuing operations that may be reclassified subsequently to profit or loss:
Total items from continuing operations that may be reclassified subsequently to profit or loss			6	0
Other comprehensive (loss)/income for the year, net of tax			6	36
Total comprehensive income for the year			(3)	48
Attributable to:
Equity shareholders of the parent		0	(3)	48
Aggregate continuing and discontinued operations
Attributable to:
Equity shareholders of the parent		£ 1,459	£ 1,098	£ 1,863
[1]	Comparative amounts have been revised as described in note 1F.
[2]	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 (Previously stated) at Mar. 31, 2018		£ 18,848	£ 18,832	£ 452	£ 1,321	£ 21,599	£ (4,540)		£ 16
Equity, beginning balance (Prior year adjustment) at Mar. 31, 2018	[2]	185	185			185
Equity, beginning balance at Mar. 31, 2018		19,033
Profit for the year		1,514	1,511			1,511	0		3
Other comprehensive income/(loss) for the year		353	352			89	263		1
Total comprehensive income for the year		1,867	1,863			1,600	263		4
Equity dividends		(1,160)	(1,160)			(1,160)
Scrip dividend-related share issue	[3]	(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		19,568	19,548	458	1,314	21,999	(4,223)		20
Profit for the year		1,265	1,264			1,264			1
Other comprehensive income/(loss) for the year		(165)	(166)			(509)	343		1
Total comprehensive income for the year		1,100	1,098			755	343		2
Equity dividends		(892)	(892)			(892)
Scrip dividend-related share issue	[3]	(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		19,793	19,771	470	1,301	21,895	(3,895)		22
Profit for the year		1,641	1,640			1,640	0		1
Other comprehensive income/(loss) for the year		(183)	(181)			1,001	(1,182)		(2)
Total comprehensive income for the year		1,458	1,459			2,641	(1,182)		(1)
Equity dividends		(1,413)	(1,413)			(1,413)
Scrip dividend-related share issue	[3]	(1)	(1)	4	(5)
Issue of treasury shares		17	17			17
Purchase of own shares		(2)	(2)			(2)
Share-based payments		27	27			27
Tax on share-based payments		(2)	(2)			(2)
Cash flow hedges transferred to the statement of financial position, net of tax		(17)	(17)				(17)
Equity, ending balance at Mar. 31, 2021		£ 19,860	£ 19,839	£ 474	£ 1,296	£ 23,163	£ (5,094)		£ 21
[1]	For further details of other equity reserves, see note 28.
[2]	Comparative amounts have been revised as described in note 1F.
[3]	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, 2021		Mar. 31, 2020		Apr. 01, 2019	Mar. 31, 2019		Apr. 01, 2018	Mar. 31, 2018
Non-current assets
Goodwill	£ 4,588	[1]	£ 5,712	[1]		£ 5,372	[1]	£ 4,984	£ 4,984
Other intangible assets	1,443		1,295			1,084		899	899
Property, plant and equipment	47,043	[1]	49,762	[1]	£ 45,327	44,859	[1]	40,730	40,730
Other non-current assets	293		354			264		115	115
Pension assets	1,747		1,849			1,567		1,409	1,409
Financial and other investments	755		543			667		899	899
Investments in joint ventures and associates	867		995			608		2,168	2,168
Derivative financial assets	542		1,249			1,045		1,319	1,319
Total non-current assets	57,278		61,759			55,466		52,523	52,523
Current assets
Inventories and current intangible assets	439		549			370		341	341
Trade and other receivables	2,919		2,986			3,153		2,795	2,798
Current tax assets	67		102			126		114	114
Financial and other investments	2,342		1,998		1,981	1,981		2,694	2,694
Derivative financial assets	457		93			108		405	405
Cash and cash equivalents	157		73		252	252		329	329
Assets held for sale	3,557		0			1,956
Total current assets	9,938		5,801			7,946		6,678	6,681
Total assets	67,216		67,560			63,412		59,201	59,204
Current liabilities
Borrowings	(3,737)		(4,072)			(4,472)		(4,447)	(4,447)
Derivative financial liabilities	(145)		(380)			(350)		(401)	(401)
Trade and other payables	(3,517)		(3,602)		(3,766)	(3,769)		(3,394)	(3,453)
Contract liabilities	(66)		(76)			(61)		(53)	0
Current tax liabilities	(75)		(86)			(161)		(123)	(123)
Provisions	(260)		(348)			(316)		(273)	(273)
Liabilities held for sale	(1,568)		0			0
Total current liabilities	(9,368)		(8,564)			(9,129)		(8,691)	(8,697)
Non-current liabilities
Borrowings	(27,483)		(26,722)			(24,258)		(22,210)	(22,178)
Derivative financial liabilities	(754)		(954)			(833)		(660)	(660)
Other non-current liabilities	(843)		(891)		(805)	(808)		(750)	(1,317)
Contract liabilities	(1,094)		(1,082)			(933)		(813)	0
Deferred tax liabilities	(4,815)	[1]	(4,446)	[1]		(4,215)	[1]	(3,789)	(3,868)
Pensions and other post-retirement benefit obligations	(1,032)		(2,802)			(1,785)		(1,672)	(1,672)
Provisions	(1,967)		(2,306)			(1,883)		(1,779)	(1,779)
Total non-current liabilities	(37,988)		(39,203)			(34,715)		(31,673)	(31,474)
Total liabilities	(47,356)		(47,767)			(43,844)		(40,364)	(40,171)
Net assets	19,860		19,793		19,568	19,568		18,837	19,033
Equity
Share capital	474		470			458		452	452
Share premium account	1,296		1,301			1,314		1,321	1,321
Retained earnings	23,163	[1]	21,895	[1]		21,999	[1]	21,516	21,784
Other equity reserves	(5,094)	[1]	(3,895)	[1]		(4,223)	[1]	(4,468)	(4,540)
Total shareholders’ equity	19,839		19,771			19,548		18,821	19,017
Non-controlling interests	21		22			20		16	16
Total equity	£ 19,860		£ 19,793		£ 19,568	£ 19,568		£ 18,837	£ 19,033
[1]	Comparative amounts have been revised as described in note 1F.

Consolidated cash flow statemen

Consolidated cash flow statement - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Total operating profit from continuing operations	£ 2,895	£ 2,780	£ 2,870
Adjustments for:
Other fair value movements	(22)	0	0
Depreciation, amortisation and impairment	1,672	1,640	1,725
Share-based payments	27	19	27
Changes in working capital	296	394	(36)
Changes in provisions	(195)	198	18
Changes in pensions and other post-retirement benefit obligations	(55)	(117)	(140)
Cash generated from operations – continuing operations	4,618	4,914	4,464
Tax paid	(157)	(199)	(75)
Net cash inflow from operating activities – continuing operations	4,461	4,715	4,389
Net cash used in operating activities – discontinued operations	0	(97)	(71)
Cash flows from investing activities
Acquisition of financial investments	(99)	(108)	(89)
Acquisition of National Grid Renewables (formerly Geronimo) and Emerald	(26)	(139)	0
Investments in joint ventures and associates	(81)	(82)	(143)
Loans to joint ventures and associates	0	0	(31)
Disposal of financial investments	66	63	18
Disposal of interests in Quadgas HoldCo Limited	0	1,965	0
Purchases of intangible assets	(426)	(317)	(306)
Purchases of property, plant and equipment	(4,362)	(4,583)	(3,635)
Disposals of property, plant and equipment	8	68	38
Dividends received from joint ventures and associates	80	75	68
Interest received	16	73	68
Net movements in short-term financial investments	(436)	7	822
Cash inflows on derivatives	225	58	17
Cash outflows on derivatives	(81)	(281)	(429)
Net cash flow used in investing activities – continuing operations	(5,116)	(3,201)	(3,602)
Net cash flow used in investing activities – discontinued operations	0	6	156
Cash flows from financing activities
Proceeds from issue of treasury shares	16	16	17
Purchase of own shares	(2)	(6)	(2)
Proceeds received from loans	5,645	4,218	2,932
Repayment of loans	(1,663)	(3,253)	(1,969)
Payments of lease liabilities	(112)	(121)	(70)
Net movements in short-term borrowings	(759)	(424)	179
Cash inflows on derivatives	58	62	221
Cash outflows on derivatives	(185)	(249)	(186)
Interest paid	(835)	(957)	(914)
Dividends paid to shareholders	(1,413)	(892)	(1,160)
Net cash flow from/(used in) financing activities – continuing operations	750	(1,606)	(952)
Net increase/(decrease) in cash and cash equivalents	95	(183)	(80)
Reclassification to held for sale	(4)	0	0
Exchange movements	(7)	4	3
Cash and cash equivalents, beginning balance	73	252	329
Cash and cash equivalents, ending balance	£ 157	£ 73	£ 252

Post balance sheet events

Post balance sheet events	12 Months Ended
	Mar. 31, 2021
Events After Reporting Period [Abstract]
Post balance sheet events	39. Post balance sheet eventsIn the period between 1 April 2021 and 19 May 2021, there have been no significant post balance sheet events.

Basis of preparation and recent

Basis of preparation and recent accounting developments	12 Months Ended
	Mar. 31, 2021
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
Basis of preparation and recent accounting developments	1. 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 19 May 2021. 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 2021 and in accordance with the Companies Act 2006 applicable to companies reporting under IFRS adopted pursuant to Regulation (EC) No. 1606/2002 as it applies in the European Union. 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 part of the Directors’ consideration of the appropriateness of adopting the going concern basis of accounting in preparing these financial statements, the Directors have considered both the impact of COVID-19 on the Group’s operations alongside the impact of the acquisition of PPL WPD Investments Limited (WPD) (see note 38) and subsequent disposal of The Narragansett Electric Company (NECO) (see note 10) and the expected planned disposal of a majority stake of National Grid Gas plc. The Directors have assessed the principal risks discussed on pages 24 – 27, including by modelling both a base case and a reasonable worst case scenario. Reasonable worst-case: The reasonable worst-case scenario covers the materially adverse cash flow impact associated with a further year of COVID-19 disruption across both the UK and US, with a subsequent phased return to normal operations, increased cash outflows from higher costs (e.g. storms), while still delivering our planned capital investment programme for the year ended 31 March 2022. The continuing economic impact of COVID-19 and the consequential impact on cash collections and capital programmes is the key judgement applied in the analysis. The main cash flow impacts identified in the reasonable worst-case scenario are: • a significant reduction in cash collections 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; and • further increases in other costs such as cleaning, safety equipment and IT; offset by a continued reduction in discretionary spend across all areas (e.g. recruitment, travel and consultancy spend). Impact of WPD acquisition: The cash flows associated with WPD have been based on historic actuals alongside information obtained as part of the financial due diligence process and associated discussions with WPD management. The Directors noted the impact of the transaction on the Group’s financing position as below: • a new bridge facility of £8.25 billion to finance the acquisition, with the first repayment of the bridge expected to be from the proceeds of the announced planned business disposals in 2022; and • c.£1.1 billion of committed facilities to fund WPD working capital. As part of their analysis, the Board also considered the following potential levers at their discretion to improve the position identified by the analysis if the debt capital markets are not accessible: • the payment of dividends to shareholders; • significant changes in the phasing of the Group’s capital programme with elements of non-essential works and programmes delayed; and • a number of further reductions in operating expenditure across the Group primarily related to workforce cost reductions in both the UK and the US. Having considered the reasonable worst-case scenario, the impact of the acquisition of WPD (and any penalties if the transaction did not proceed), the timing of the NECO and National Grid Gas plc transactions, and the 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 c.£5.6 billion debt issuances completed in the period from 1 April 2020 to 31 March 2021 (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 final determinations of the UK RIIO-2 price controls process, the Group’s various ongoing rate case determinations in the 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. 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). D. Disposal of The Narragansett Electric Company As described further in note 10, on 17 March 2021, the Group signed an agreement to sell 100% of the share capital of a wholly owned subsidiary, The Narragansett Electric Company (NECO). The sale is expected to complete in early 2022 once all regulatory approvals are obtained. As the sale is considered highly probable and is expected to complete within a year, the associated assets and liabilities have been presented as held for sale in the consolidated statement of financial position. However, the transaction has not met the criteria for classification as a discontinued operation and therefore its results for the period are not separately disclosed on the face of the income statement. 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 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. The main impact at 31 March 2021 is the consideration of 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), which is an area of estimation uncertainty impacting the Group’s position as at 31 March 2021. 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 the recoverability of customer receivables are included in note 19. 1. Basis of preparation and recent accounting developments continued F. Comparative period revisions During the year, we have revised the comparative balances primarily to reflect adjustments between property, plant and equipment and goodwill related to the accounting performed for acquisitions made by our US business between 2000 and 2007. The adjustments related to the treatment of certain regulatory liabilities recognised under US GAAP on the acquisition balance sheets under UK GAAP and IFRS. This resulted in an overstatement of goodwill and an understatement of property, plant and equipment. The adjustments had a resulting impact on the deferred tax balances that were recognised at the time of the acquisitions and therefore, these have also been updated for all periods presented, also taking into account any subsequent changes in tax rates. The translation reserve on consolidation of these subsidiaries was also updated. There have been no income statement impacts (and therefore no impact on the previously reported earnings per share) for any of the periods presented. Opening retained earnings have increased to correct the income statement impact of amortising the overstated goodwill from the period after acquisition until the adoption of IFRS in 2005 and for the impact on deferred tax of the tax rate changes noted above. Any foreign exchange impacts are recorded within the translation reserve within other equity reserves. Below we set out the impacted line items and the adjustments to our opening statement of financial position as at 1 April 2018. In addition, we set out the adjustments to previously presented balances as at 31 March 2019 and 31 March 2020 (with the only movement each period being as a result of foreign exchange movements): 1 April 2018 31 March 2019 31 March 2020 £m £m £m Goodwill (460) (497) (521) Property, plant and equipment 877 946 992 Deferred tax liability 232 250 262 Retained earnings 185 185 185 Translation reserve — 14 24 G. 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)). H. New IFRS accounting standards and interpretations effective for the year ended 31 March 2021 The UK’s Financial Conduct Authority announced that the London Inter-bank Offered Rate (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 Phase I of Interest Rate Benchmark Reform, which modified certain hedge accounting requirements to allow hedge accounting to continue for affected hedges during the period of uncertainty before the hedged items or hedging instruments were amended 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. Phase II was issued in August 2020 and endorsed in January 2021 for adoption in the EU, resulting in amendments to IFRS 9, IFRS 7 and IFRS 16. The Group has early-adopted these amendments with effect from 1 April 2020 as they enable the Company and its subsidiaries to reflect the effects of transitioning from LIBOR to alternative benchmark interest rates without giving rise to accounting impacts that would not provide useful information to users of the financial statements. There were no transition adjustments on adoption of either phase and the Group has not restated the prior period, but instead has applied the amendments prospectively. Refer to note 32(d) for further details on the contracts to be transitioned to the new alternative benchmark interest rate and for details of our migration project. 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: • amendments to IFRS 16 ‘Leases – COVID-19 Related Rent Concessions’; • amendments to IFRS 3 ‘Business Combinations’; • amendments to IAS 1 and IAS 8 ‘Definition of Material’; and • amendments to the References to the Conceptual Framework. I. 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 IAS 16 ‘Property, Plant and Equipment’; • amendments to IAS 37 ‘Provisions, Contingent Liabilities and Contingent Assets’; • amendments to IAS 1 ‘Presentation of Financial Statements’; • amendments to IAS 8 ‘Accounting Policies, Changes in Accounting Estimates and Errors’; and • annual improvements to IFRS standards 2018-2020. 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, 2021
Operating Segments [Abstract]
Segmental analysis	2. 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 investments in National Grid Renewables (formerly Geronimo) and Emerald Energy Venture LLC (Emerald). 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. (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. 2021 2020 2019 Total £m Sales between segments £m Sales to third parties £m Total Sales Sales Total Sales Sales Operating segments – continuing operations: UK Electricity Transmission 3,992 (10) 3,982 3,702 (8) 3,694 3,351 (20) 3,331 UK Gas Transmission 904 (16) 888 927 (16) 911 896 (12) 884 US Regulated 9,195 — 9,195 9,205 — 9,205 9,846 — 9,846 NGV and Other¹ 715 (1) 714 736 (6) 730 876 (4) 872 Total revenue from continuing operations 14,806 (27) 14,779 14,570 (30) 14,540 14,969 (36) 14,933 Split by geographical areas – continuing operations: UK 5,482 5,282 5,045 US 9,297 9,258 9,888 14,779 14,540 14,933 1. Included within NGV and Other is £636 million (2020: £608 million; 2019: £597 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 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m Operating segments – continuing operations: UK Electricity Transmission 1,034 1,320 1,015 1,027 1,316 778 UK Gas Transmission 342 348 303 337 347 267 US Regulated 1,313 1,397 1,724 1,344 880 1,425 NGV and Other 1 237 242 400 187 237 400 Total operating profit from continuing operations 2,926 3,307 3,442 2,895 2,780 2,870 Split by geographical area – continuing operations: UK 1,612 1,925 1,695 1,550 1,915 1,422 US 1,314 1,382 1,747 1,345 865 1,448 2,926 3,307 3,442 2,895 2,780 2,870 Below we reconcile total operating profit from continuing operations to profit before tax from continuing operations. Total operating exceptional items and remeasurements of £31 million charge (2020: £527 million charge; 2019: £572 million charge) are detailed in note 5. This is comprised of a £7 million charge (2020: £4 million charge; 2019: £237 million charge) attributable to UK Electricity Transmission; £5 million charge (2020: £1 million charge; 2019: £36 million charge) to UK Gas Transmission; £31 million gain (2020: £517 million charge; 2019: £299 million charge) to US Regulated; and £50 million charge (2020: £5 million charge; 2019: £nil) to NGV and Other. Reconciliation to profit before tax: Operating profit from continuing operations 2,926 3,307 3,442 2,895 2,780 2,870 Finance income 35 70 73 58 54 88 Finance costs (977) (1,119) (1,066) (928) (1,167) (1,157) Share of post-tax results of joint ventures and associates 66 88 40 58 87 40 Profit before tax from continuing operations 2,050 2,346 2,489 2,083 1,754 1,841 1. Included within NGV and Other is £298 million (2020: £269 million; 2019: £263 million) of operating profit before exceptional items and remeasurements and £296 million of operating profit after exceptional items and remeasurements (2020: £268 million; 2019: £263 million), relating to NGV. (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. Net book value of property, plant and Capital expenditure Depreciation, amortisation 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Operating segments: UK Electricity Transmission 14,379 13,788 13,288 1,072 1,043 925 (507) (469) (628) UK Gas Transmission 4,531 4,513 4,412 176 249 308 (165) (171) (181) US Regulated 1,2 27,128 30,615 25,488 3,223 3,228 2,650 (888) (855) (700) NGV and Other 2,3 2,448 2,141 2,755 460 559 438 (112) (145) (226) Total from continuing operations 2 48,486 51,057 45,943 4,931 5,079 4,321 (1,672) (1,640) (1,735) Split by geographical area – continuing operations: UK 21,352 20,427 19,343 1,708 1,847 1,584 (783) (784) (931) US 2 27,134 30,630 26,600 3,223 3,232 2,737 (889) (856) (804) Total from continuing operations 2 48,486 51,057 45,943 4,931 5,079 4,321 (1,672) (1,640) (1,735) Asset type: Property, plant and equipment 2 47,043 49,762 44,859 4,510 4,727 4,015 (1,476) (1,464) (1,560) Non-current intangible assets 1,443 1,295 1,084 421 352 306 (196) (176) (175) Total from continuing operations 2 48,486 51,057 45,943 4,931 5,079 4,321 (1,672) (1,640) (1,735) 1. 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. These assets were included within NGV and Other in 2019, and had a net book value of £1,062 million, capital expenditure of £87 million and depreciation, amortisation and impairment of £102 million. 2. Comparative amounts have been revised as described in note 1F. 3. Included within NGV and Other are assets with a net book value of £2,396 million (2020: £2,080 million; 2019: £1,635 million), capital expenditure of £431 million (2020: £550 million; 2019: £317 million) and depreciation, amortisation and impairment of £92 million (2020: £124 million; 2019: £114 million) relating to NGV.

Revenue

Revenue	12 Months Ended
	Mar. 31, 2021
Disclosure of revenue from contracts with customers [Abstract]
Revenue	3. 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 IFRS 16 ‘Leases’ 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. 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 independent 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 our 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 National Grid Electricity Transmission plc and the Scottish and Offshore transmission operators, from users who connect to or use the transmission system. In this context, 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). 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. However, 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. In addition, the transmission operators own and maintain the electricity network and receive direct feedback from electricity suppliers on the quality of the network they provide. As a result, we have concluded that the System Operator 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 as a contract liability and released over the life of the asset. 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. As revenues are received upfront, they are deferred as a contract liability 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 as contract liabilities or customer contributions (where they relate to government entities) and released over the life of the connection. 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 as contract liabilities or customer contributions (where they relate to government entities) and released over the life of the connection. 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 where LIPA receives all of the energy and capacity from the asset until at least 2025. The arrangement is treated as an operating lease 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. Lease payments (capacity payments) are recognised on a straight-line basis and variable lease payments are recognised as the energy is generated. (d) NGV and Other NGV and Other generates revenue from electricity interconnectors, LNG at the Isle of Grain, National Grid Renewables, metering, our UK commercial 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 National Grid Renewables 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 2021 UK Electricity Transmission UK Gas Transmission US Regulated NGV and Other Total Revenue under IFRS 15 Transmission 1,814 603 403 316 3,136 Distribution — — 8,317 — 8,317 System Operator 2,076 240 — — 2,316 Other 67 12 15 302 396 Total IFRS 15 revenue 3,957 855 8,735 618 14,165 Other revenue Generation — — 376 — 376 Other 25 33 84 96 238 Total other revenue 25 33 460 96 614 Total revenue from continuing operations 3,982 888 9,195 714 14,779 Geographical split for the year ended 31 March 2021 UK Electricity Transmission £m UK Gas Transmission £m US Regulated £m NGV and Other £m Total £m Revenue under IFRS 15 UK 3,957 855 — 553 5,365 US — — 8,735 65 8,800 Total IFRS 15 revenue 3,957 855 8,735 618 14,165 Other revenue UK 25 33 — 59 117 US — — 460 37 497 Total other revenue 25 33 460 96 614 Total revenue from continuing operations 3,982 888 9,195 714 14,779 3. Revenue continued (e) Disaggregation of revenue continued 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 Contract liabilities (see note 23) represent revenue to be recognised in future periods relating to contributions in aid of construction of £1,160 million (2020: £1,158 million; 2019: £994 million). 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, 15 years and up to 51 years respectively. The weighted average amortisation period is 19 years. Future revenues in relation to unfulfilled performance obligations not yet received in cash amount to £4.8 billion (2020: £3.1 billion; 2019: £3.5 billion). £1.6 billion (2020: £1.5 billion; 2019: £1.6 billion) relates to connection contracts in UK Electricity Transmission which will be recognised as revenue over 26 years and £3.0 billion (2020: £1.5 billion; 2019: £1.8 billion) relates to revenues to be earned under Grain LNG contracts until 2045. The remaining amount will be recognised as revenue over 9 years.

Operating costs

Operating costs	12 Months Ended
	Mar. 31, 2021
Analysis of income and expense [abstract]
Operating costs	4. 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. 2021 2020 2019 £m £m £m Depreciation, amortisation and impairment 1,672 1,640 1,735 Payroll costs 1,770 1,684 1,852 Purchases of electricity 1,130 1,403 1,454 Purchases of gas 1,250 1,316 1,642 Property and other taxes 1,193 1,191 1,108 Balancing Services Incentive Scheme 1,875 1,317 1,196 Other 2,668 2,975 2,895 Other operating costs 11,558 11,526 11,882 Provision for bad and doubtful debts 326 234 181 Total operating costs 11,884 11,760 12,063 Operating costs include: Inventory consumed 316 328 415 Research and development expenditure 17 14 19 (a) Payroll costs 2021 2020 2019 £m £m £m Wages and salaries¹ 2,282 2,188 2,084 Social security costs 172 168 156 Defined contribution scheme costs 77 75 72 Defined benefit pension costs 136 135 232 Share-based payments 27 19 27 Severance costs (excluding pension costs) 11 1 76 2,705 2,586 2,647 Less: payroll costs capitalised (935) (902) (795) Total payroll costs 1,770 1,684 1,852 1. Included within wages and salaries are US other post-retirement benefit costs of £43 million (2020: £45 million; 2019: £48 million). For further information refer to note 25. (b) Number of employees 31 March 2021 Monthly average 2021 31 March 2020 Monthly average 2020 31 March 2019 Monthly average 2019 UK 6,657 6,517 6,321 6,151 5,962 6,227 US 17,026 16,821 16,748 16,679 16,614 16,669 Total number of employees 23,683 23,338 23,069 22,830 22,576 22,896 4. Operating costs continued (c) Key management compensation 2021 2020 2019 £m £m £m Short-term employee benefits 7 7 7 Compensation for loss of office — 1 — Post-employment benefits 1 1 1 Share-based payments 4 3 3 Total key management compensation 12 12 11 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: 2021 2020 2019 £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 2.5 1.9 1.6 The auditing of accounts of any associate of the Company² 8.1 8.7 8.5 Other services supplied³ 6.4 6.3 5.2 17.0 16.9 15.3 Total other services 4 All other fees: Other assurance services 5 0.8 0.6 1.1 Other non-audit services not covered above 6 2.0 0.5 2.2 2.8 1.1 3.3 Total auditors’ remuneration 19.8 18.0 18.6 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 2021, 2020 and 2019. 2. The 2019 comparative was updated in 2020 following finalisation of the 2019 audit fee with the Audit Committee in 2020. 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 2020, 2019 and 2018 respectively. 4. There were no tax compliance or tax advisory fees and no audit related fees as described in Item 16C(b) of Form 20-F. 5. In all years, principally relates to assurance services provided in relation to comfort letters for debt issuances and, in 2021, also includes amounts related to capacity market auction monitoring services. 6. For 2021, includes the class 1 Circular in respect of the acquisition of WPD announced on 18 March 2021. In 2020, other assurance services include auction monitor work on Contracts for Difference, a review of controls over our data on New York customers and IT project assurance. In 2019, non-audit services primarily related to the UK Commercial 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, 2021
Exceptional Items And Remeasurements [Abstract]
Exceptional items and remeasurements	5. Exceptional items and remeasurements To monitor our segmental performance, we use a profit measure that excludes certain income and expenses. We call that measure ‘adjusted profit’. Adjusted profit (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 adjusted profit 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 adjusted profit. Exceptional items and remeasurements from continuing operations 2021 2020 2019 £m £m £m Included within operating profit Exceptional items: Changes in environmental provisions 14 (402) — New operating model implementation costs (55) — — Transaction costs (24) — — Cost efficiency and restructuring programmes — — (204) Massachusetts Gas labour dispute — — (283) Impairment of nuclear connection development costs — — (137) (65) (402) (624) Remeasurements – commodity contract derivatives 34 (125) 52 (31) (527) (572) 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. 2021 2020 2019 £m £m £m Included within finance income and costs Remeasurements: Net (losses)/gains on financing derivatives (41) 1 (40) Net gains/(losses) on financial assets at fair value through profit and loss 23 (16) 15 Net gains/(losses) on financial liabilities at fair value through profit and loss 90 (49) (51) 72 (64) (76) Included within share of post-tax results of joint ventures and associates Remeasurements: Remeasurements – net losses on financial instruments (8) (1) — Total included within profit before tax 33 (592) (648) Included within tax Exceptional items – movements arising on items not included in profit before tax: Deferred tax charge arising on the reversal of the reduction in UK corporation tax rate — (192) — Tax on exceptional items 8 103 144 Tax on remeasurements (34) 42 5 (26) (47) 149 Total exceptional items and remeasurements after tax 7 (639) (499) Analysis of total exceptional items and remeasurements after tax Exceptional items after tax (57) (491) (480) Remeasurements after tax 64 (148) (19) Total exceptional items and remeasurements after tax 7 (639) (499) 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. 2021 We have considered certain costs incurred in the period against our Exceptional Items Framework, and concluded £55 million of costs associated with the implementation of our new operating model, the £14 million release of environmental provisions for which the original provision was treated as exceptional and the £24 million of transaction costs associated with the acquisition of Western Power Distribution (WPD) and the sale of NECO should be treated as exceptional items in the current year. New operating model implementation costs: The Group incurred £55 million of costs in relation to the design and implementation of our new operating model that is built on a foundation of six business units as described further in the Strategic Review. The costs recognised in the year ended 31 March 2021 primarily relate to professional fees incurred in designing the new operating model, alongside the redundancy provisions accrued in relation to those employees where announcements have been made that they will be leaving the organisation as a result of the changes. Whilst the costs incurred this year do not meet the quantitative threshold to be classified as exceptional on a standalone basis, we have concluded that the costs should be classified as exceptional in line with our exceptional items policy, in order to ensure that the costs are treated in a consistent manner with similar costs incurred previously. The total cash outflow for the year was £33 million. Transaction costs: £24 million of transaction costs were incurred to date in relation to the acquisition of WPD (see note 38) and the sale of NECO (see note 10). The costs relate to legal fees, bankers' fees and professional fees. Whilst the costs incurred in the current year in isolation are not sufficiently material to warrant classification as an exceptional item, we are expecting further costs to be incurred next year, for example, in regards to success fees on completion of the acquisition. When taken in aggregate, the costs incurred over both years will be sufficiently material to be classified as exceptional in line with our policy. The total cash outflow for the year was £14 million. Changes in environmental provision: In the US, the most significant component of our £1.5 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. We have recognised an exceptional gain of £14 million relating to the release of environmental provisions relating to one of our US Superfund sites, for which the original provision was treated as an exceptional item. The reduction in the provision arose as a result of the re-evaluation of the Group’s share of estimated costs following the finalisation of discussions on the scope of certain remediation work with government authorities. The release has been recorded as an exceptional item in line with the treatment of the original provision. 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 ended 31 March 2020 were similarly not 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 were also treated as part of adjusted profit. Changes in environmental provisions: As a result of notices issued by governmental authorities and newly developed cost estimates prepared by third-party engineers in relation to our US Superfund sites, we re-evaluated our estimates of total costs and cost sharing allocations borne by the Company, and accordingly 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 was the £76 million impact of the change in the real discount rate applied to the environmental provisions across the Group, of which £66 million related 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. 5. Exceptional items and remeasurements continued 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. 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). Once the fair value movements are realised (for example, when the derivative matures), the previously recognised fair value movements are then reversed through remeasurements and recognised within earnings before exceptional items and remeasurements. These assets and liabilities include commodity contract derivatives and financing derivatives to the extent that hedge accounting is not available or is not fully effective. The unrealised gains or losses reported in profit and loss on certain additional assets and liabilities 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 adjusted profit. 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 National Grid Renewables (all within NGV and Other). The performance of these assets (including changes in fair value) are included in our assessment of adjusted profit for the relevant business units. Remeasurements excluded from adjusted profit 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 derivatives comprise gains and losses arising on derivative financial instruments used for the 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 comprise 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

Finance income and costs

Finance income and costs	12 Months Ended
	Mar. 31, 2021
Analysis of income and expense [abstract]
Finance income and costs	6. 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 adjusted profit, we adjust net financing costs to exclude any net gains or losses on financial instruments included in remeasurements (see note 5). 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. 2021 2020 2019 Notes £m £m £m Finance income Interest income on financial instruments: Bank deposits and other financial assets 33 48 54 Dividends received on equities held at fair value through other comprehensive income (FVOCI) 2 2 2 Other income — 20 17 35 70 73 Finance costs Net interest on pensions and other post-retirement benefit obligations 25 (38) (23) (22) Interest expense on financial liabilities held at amortised cost: Bank loans and overdrafts (72) (73) (72) Other borrowings¹ (854) (997) (970) Interest expense on financial liabilities held at fair value through profit and loss (FVTPL) (20) (22) (20) Interest on derivatives 7 (39) (43) Unwinding of discount on provisions 26 (78) (77) (74) Other interest (53) (10) — Less: interest capitalised² 131 122 135 (977) (1,119) (1,066) Remeasurements – Finance income Net gains/(losses) on FVTPL financial assets 23 (16) 15 23 (16) 15 Remeasurements – Finance costs Net gains/(losses) on FVTPL financial liabilities 90 (49) (51) Net gains/(losses) on financing derivatives³: Derivatives designated as hedges for hedge accounting 44 (13) (37) Derivatives not designated as hedges for hedge accounting (85) 14 (3) 49 (48) (91) Total remeasurements – Finance income and costs 72 (64) (76) Finance income 58 54 88 Finance costs (928) (1,167) (1,157) Net finance costs from continuing operations (870) (1,113) (1,069) 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 3.1% (2020: 3.6%; 2019: 3.9%). In the UK, capitalised interest qualifies for a current year tax deduction with tax relief claimed of £13 million (2020: £15 million; 2019: £19 million). In the US, capitalised interest is added to the cost of plant and qualifies for tax depreciation allowances.

Tax

Tax	12 Months Ended
	Mar. 31, 2021
Income Taxes [Abstract]
Tax	7. 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 for the year can be analysed as follows: 2021 2020 2019 £m £m £m Current tax: UK corporation tax at 19% (2020: 19%; 2019: 19%) 213 179 132 UK corporation tax adjustment in respect of prior years 23 (4) (12) 236 175 120 Overseas corporation tax 3 (2) 8 Overseas corporation tax adjustment in respect of prior years (15) (41) (40) (12) (43) (32) Total current tax from continuing operations 224 132 88 Deferred tax: UK deferred tax 63 269 27 UK deferred tax adjustment in respect of prior years (26) 6 2 37 275 29 Overseas deferred tax 174 64 208 Overseas deferred tax adjustment in respect of prior years 7 9 14 181 73 222 Total deferred tax from continuing operations 218 348 251 Total tax charge from continuing operations 442 480 339 Tax charged/(credited) to the consolidated statement of comprehensive income and equity 2021 2020 2019 £m £m £m Current tax: Cash flow hedges, cost of hedging and own credit reserve 6 — 3 Deferred tax: Investments at fair value through other comprehensive income 12 (1) — Cash flow hedges, cost of hedging and own credit reserve (2) (40) (12) Remeasurements of pension assets and post-retirement benefit obligations 414 (206) 12 Share-based payments 2 (3) — 432 (250) 3 Total tax recognised in the statements of comprehensive income from continuing operations 430 (247) 3 Total tax relating to share-based payments recognised directly in equity from continuing operations 2 (3) — 432 (250) 3 7. Tax continued The tax charge for the year for the continuing business, is higher (2020: higher tax charge; 2019: lower tax charge) than the standard rate of corporation tax in the UK of 19% (2020: 19%; 2019: 19%): 2021 2020 2019 £m £m £m Profit before tax from continuing operations Before exceptional items and remeasurements 2,050 2,346 2,489 Exceptional items and remeasurements 33 (592) (648) Profit before tax from continuing operations 2,083 1,754 1,841 Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2020: 19%; 2019: 19%) 396 334 350 Effect of: Adjustments in respect of prior years¹ (11) (30) (36) Expenses not deductible for tax purposes 30 29 28 Non-taxable income² (9) (18) (36) Adjustment in respect of foreign tax rates 42 18 56 Deferred tax impact of change in UK tax rate — 192 (3) Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax (12) (17) (8) Other³ 6 (28) (12) Total tax charge from continuing operations 442 480 339 % % % Effective tax rate – continuing operations 21.2 27.4 18.4 1. The prior year adjustments are primarily due to agreement of prior period tax returns. 2. Includes tax on chargeable disposals after the offset of capital losses. 3. Other primarily comprises the movement in the deferred tax asset on previously unrecognised capital losses and claims for land remediation relief. Factors that may affect future tax charges In the Spring Budget 2021, the UK government announced an increase in the main corporation tax rate from 19% to 25% with effect from 1 April 2023. Since this had not been substantively enacted at the balance sheet date, deferred tax balances as at 31 March 2021 have been calculated at the current main UK corporation tax rate of 19%. We expect our future deferred tax liabilities to increase reflecting the impact of the rate change. If the amended tax rate of 25% had been used, the deferred tax liability would have been approximately £560 million higher. US government and US states are also considering changes to federal and state tax rates respectively, but as no changes have been substantively enacted at the balance sheet date deferred tax balances as at 31 March 2021 have been calculated at the prevailing tax rates. 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, from which we do not currently expect there to be a material impact on 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 1 April 2019 2 5,727 (9) (170) 7 (1,340) 4,215 Exchange adjustments and other 2,3 222 (30) (28) (3) (27) 134 Charged/(credited) to income statement 613 (7) 44 (13) (287) 350 (Credited)/charged to other comprehensive income and equity — (2) (206) (46) 1 (253) At 1 April 2020 2 6,562 (48) (360) (55) (1,653) 4,446 Exchange adjustments and other 3 (501) 4 51 4 174 (268) Charged/(credited) to income statement 373 — (12) 1 (147) 215 Charged to other comprehensive income and equity — 2 414 6 — 422 At 31 March 2021 6,434 (42) 93 (44) (1,626) 4,815 1. The deferred tax asset of £1,626 million as at 31 March 2021 (2020: £1,653 million) in respect of other net temporary differences primarily relates to net operating losses of £455 million (2020: £547 million), US environmental provisions of £453 million (2020: £529 million) and US bad debt provision of £184 million (2020: £124 million). 2. Comparative amounts have been revised as described in note 1F. 3. Exchange adjustments and other comprises foreign exchange arising on translation of the US dollar deferred tax balances. In 2020, it also included 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 £4,815 million (2020: £4,446 million). This balance is after offset of a deferred tax asset of £455 million (2020: £547 million) which has been recognised in respect of net operating losses (£440 million) and capital losses (£15 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 total deferred tax assets not recognised are as follows: 2021 2020 £m £m Capital losses 1,620 1,626 Non-trade deficits 1 1 Trading losses 7 6 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.

Earnings per share (EPS)

Earnings per share (EPS)	12 Months Ended
	Mar. 31, 2021
Earnings per share [abstract]
Earnings per share (EPS)	8. Earnings per share (EPS) EPS is the amount of profit after tax attributable to each ordinary share. Basic EPS is calculated on profit after tax 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 adjusted profit 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. (a) Basic EPS Earnings EPS Earnings EPS Earnings EPS 2021 2021 2020 2020 2019 2019 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,633 46.4 1,912 55.2 1,998 59.0 Exceptional items and remeasurements after tax from continuing operations 7 0.2 (639) (18.4) (499) (14.7) Earnings from continuing operations 1,640 46.6 1,273 36.8 1,499 44.3 Adjusted earnings from discontinued operations — — 5 0.2 57 1.7 Exceptional items and remeasurements after tax from discontinued operations — — (14) (0.5) (45) (1.4) Earnings from discontinued operations — — (9) (0.3) 12 0.3 Total adjusted earnings 1,633 46.4 1,917 55.4 2,055 60.7 Total exceptional items and remeasurements after tax (including discontinued operations) 7 0.2 (653) (18.9) (544) (16.1) Total earnings 1,640 46.6 1,264 36.5 1,511 44.6 2021 2020 2019 millions millions millions Weighted average number of ordinary shares – basic 3,523 3,461 3,386 (b) Diluted EPS Earnings EPS Earnings EPS Earnings EPS 2021 2021 2020 2020 2019 2019 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,633 46.1 1,912 55.0 1,998 58.8 Exceptional items and remeasurements after tax from continuing operations 7 0.2 (639) (18.4) (499) (14.7) Earnings from continuing operations 1,640 46.3 1,273 36.6 1,499 44.1 Adjusted earnings from discontinued operations — — 5 0.1 57 1.7 Exceptional items and remeasurements after tax from discontinued operations — — (14) (0.4) (45) (1.4) Earnings from discontinued operations — — (9) (0.3) 12 0.3 Total adjusted earnings 1,633 46.1 1,917 55.1 2,055 60.5 Total exceptional items and remeasurements after tax (including discontinued operations) 7 0.2 (653) (18.8) (544) (16.1) Total earnings 1,640 46.3 1,264 36.3 1,511 44.4 2021 2020 2019 millions millions millions Weighted average number of ordinary shares – diluted 3,540 3,478 3,401 (c) Reconciliation of basic to diluted average number of shares 2021 2020 2019 millions millions millions Weighted average number of ordinary shares – basic 3,523 3,461 3,386 Effect of dilutive potential ordinary shares – employee share plans 17 17 15 Weighted average number of ordinary shares – diluted 3,540 3,478 3,401

Dividends

Dividends	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Dividends	9. Dividends Interim dividends are recognised when they become payable to the Company’s shareholders. Final dividends are recognised when they are approved by shareholders. 2021 2020 2019 Pence per share Cash Scrip dividend £m Pence per share Cash Scrip dividend £m Pence per share Cash Scrip dividend £m Interim dividend in respect of the current year 17.00 348 249 16.57 335 241 16.08 450 94 Final dividend in respect of the prior year 32.00 1,065 54 31.26 557 517 30.44 710 319 49.00 1,413 303 47.83 892 758 46.52 1,160 413

Discontinued operations and ass

Discontinued operations and assets held for sale	12 Months Ended
	Mar. 31, 2021
Non-current Assets Held For Sale And Discontinued Operations [Abstract]
Discontinued operations and assets held for sale	10. 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. The Narragansett Electric Company On 17 March 2021, the Group signed an agreement to sell 100% of the share capital of a wholly owned subsidiary, The Narragansett Electric Company (NECO). NECO is part of our US Regulated segment and is a retail distribution company providing electricity and gas to customers in Rhode Island. The expected sale proceeds are £2.8 billion ($3.8 billion), and the sale is expected to complete in March 2022 once all regulatory approvals are obtained. As the sale is considered highly probable and is expected to complete within a year, the associated assets and liabilities have been presented as held for sale in the consolidated statement of financial position. However, as NECO does not represent a separate major line of business or geographical operations, it has not met the criteria for classification as a discontinued operation and therefore its results for the period are not separately disclosed on the face of the income statement. The following assets and liabilities of NECO were classified as held for sale at 31 March 2021: 2021 £m Goodwill 562 Intangible assets 3 Property, plant and equipment 2,713 Trade and other receivables 237 Cash and cash equivalents 4 Other assets 38 Total assets held for sale 3,557 Borrowings (1,123) Pension liabilities (49) Other liabilities (396) Total liabilities held for sale (1,568) Net assets held for sale 1,989 No impairment losses were recognised upon remeasurement of the assets and liabilities prior to classification as held for sale. NECO generated profit after tax of £104 million (2020: £31 million; 2019: £137 million) for the year ended 31 March 2021. Current and deferred tax balances relating to NECO have not been included as held for sale on the basis that those balances will be retained by National Grid rather than transferring with the other assets and liabilities of NECO. The Group also announced its intention to sell a majority stake in the UK Gas Transmission business. However, as the process is still at an early stage and is not expected to be marketed until later in the year, the business has not been classified as held for sale and has not met the criteria for classification as a discontinued operation as at 31 March 2021. 10. Discontinued operations and assets held for sale continued Quadgas HoldCo Limited 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 classified the various elements of income, expense and cash flows within discontinued operations as set out below. Once the assets were treated as ‘held for sale’, equity accounting ceased 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 £m £m Revenue — — Operating costs¹ (23) (1) Operating loss (23) (1) Net finance income 6 23 Share of post-tax results of joint ventures and associates² — (5) (Loss)/profit before tax from discontinued operations (17) 17 Tax from discontinued operations (1) (5) (Loss)/profit after tax from discontinued operations (18) 12 Gain on disposal 9 — Total (loss)/profit after tax from discontinued operations³ (9) 12 1. Operating costs for the year ended 31 March 2020 related to final transaction costs and other expenses in relation to Quadgas. 2. For the year ended 31 March 2019, the amount presented is the net of £43 million impairment charge against the investment in Quadgas and £38 million share of Quadgas post-tax profits recognised prior to classification as held for sale. 3. For the year ended 31 March 2020, 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 £m £m (Loss)/profit after tax from discontinued operations (9) 12 Other comprehensive income Items that will never be reclassified to profit or loss: Share of other comprehensive income of associate, net of tax — 36 Total items from discontinued operations that will never be reclassified to profit or loss — 36 Items that may be reclassified subsequently to profit or loss: Net gains in respect of cash flow hedges 6 — Total items from discontinued operations that may be reclassified subsequently to profit or loss 6 — Other comprehensive income for the year, net of tax from discontinued operations 6 36 Total comprehensive (loss)/income for the year from discontinued operations (3) 48 The summary cash flows for discontinued operations are as follows: Cash flows used in operating activities of £97 million in 2020 (2019: £71 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. Cash inflows from investing activities of £6 million in 2020 (2019: £156 million) were comprised of dividends received and interest received on the shareholder loan.

Goodwill

Goodwill	12 Months Ended
	Mar. 31, 2021
Intangible Assets [Abstract]
Goodwill	11. 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 by performing an impairment review annually or more frequently if events or changes in circumstances indicate a potential impairment. 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 acquisition 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 is recognised immediately in the income statement and is not subsequently reversed. 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. Total £m Net book value at 1 April 2019¹ 5,372 Exchange adjustments¹ 259 Acquisition of National Grid Renewables (note 38) 81 Net book value at 1 April 2020 5,712 Exchange adjustments (562) Reclassification to held for sale (note 10) (562) Net book value at 31 March 2021 4,588 1. Comparative amounts have been revised as described in note 1F. There is no significant accumulated impairment charge as at 31 March 2021 or 31 March 2020. The amounts disclosed above as at 31 March 2021 relate to the following cash-generating units: New York £3,004 million (2020: £3,334 million); Massachusetts £963 million (2020: £1,069 million); Rhode Island £nil (2020: £438 million); Federal £544 million (2020: £790 million); and National Grid Renewables £77 million (2020: £81 million). Following the announcement of the sale of NECO (see note 10), goodwill balances relating to the Rhode Island cash generating unit and a portion of the goodwill relating to the Federal cash generating unit were reclassified as held for sale in the period. 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. The projections also take account of the costs associated with our net zero plans and the associated regulatory arrangements. 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% (2020: 2.1%). 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 5.0% (2020: 4.5%). The equivalent pre-tax discount rate is 5.3% (2020: 4.5%). The discount rate represents the estimated weighted average cost of capital of these operations. 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, 2021
Intangible Assets [Abstract]
Other intangible assets	12. Other intangible assets Other intangible assets mainly comprise software which is written down (amortised) over the period we expect to receive a benefit from the asset. An amortisation expense is charged to the income statement to reflect the reduced value of the asset over time. Amortisation 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. 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 other intangible assets are: Years Software 3 to 10 Software £m Assets in the course of construction Total Cost at 1 April 2019 1,784 384 2,168 Exchange adjustments 45 18 63 Additions 38 314 352 Reclassifications 159 (159) — Cost at 1 April 2020 2,026 557 2,583 Exchange adjustments (102) (43) (145) Additions 7 414 421 Disposals (47) (2) (49) Reclassifications¹ 255 (240) 15 Reclassification to held for sale (note 10) (19) — (19) Cost at 31 March 2021 2,120 686 2,806 Accumulated amortisation at 1 April 2019 (1,084) — (1,084) Exchange adjustments (28) — (28) Amortisation charge for the year (176) — (176) Accumulated amortisation at 1 April 2020 (1,288) — (1,288) Exchange adjustments 61 — 61 Amortisation charge for the year (196) — (196) Accumulated amortisation of disposals 44 — 44 Reclassification to held for sale (note 10) 16 — 16 Accumulated amortisation at 31 March 2021 (1,363) — (1,363) Net book value at 31 March 2021² 757 686 1,443 Net book value at 31 March 2020 738 557 1,295 1. Reclassifications includes amounts transferred from property, plant and equipment (see note 13). 2. The Group has capitalised £298 million (2020: £240 million) in relation to the Gas Business Enablement system in the US, of which £82 million (2020: £30 million) is in service and is being amortised over 10 years, with the remainder included within assets in the course of construction. A further £117 million (2020: £59 million) in relation to our new UK general ledger system is also included within assets in the course of construction as at 31 March 2021, and is expected to be amortised over 10 years once it is commissioned in July 2021.

Property, plant and equipment

Property, plant and equipment	12 Months Ended
	Mar. 31, 2021
Property, plant and equipment [abstract]
Property, plant and equipment	13. Property, plant and equipment Property, plant and equipment are 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. 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. (a) Asset useful economic lives 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 to 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 9 Plant and machinery: Electricity transmission plant and wires 15 to 100 45 to 80 30 Electricity distribution plant n/a 35 to 85 33 Electricity generation plant n/a 20 to 93 10 Interconnector plant and other 5 to 60 5 to 50 16 Gas plant – mains, services and regulating equipment 10 to 65 47 to 95 45 Gas plant – storage 5 to 40 12 to 65 12 Gas plant – meters 7 to 30 14 to 40 20 Motor vehicles and office equipment up to 10 up to 26 4 (b) 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 useful economic life of gas mains, services and regulating assets relating to the National Transmission System (NTS) are frequently reviewed throughout the year and subject to a detailed review at the year end. 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. Those reviews considered a number of scenarios, which consider the implications of the UK’s net zero by 2050 legislation for the NTS. Our most recent 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. • 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. We continue to actively engage and support our regulators to enable the clean energy transition in a safe, reliable and affordable way. Asset depreciation lives feed directly into our US regulatory recovery mechanisms, such that any shortening of asset lives and regulatory 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 for the year ended 31 March 2021 Increase in depreciation expense for the year ended 31 March 2020 UK regulated US regulated UK regulated £m US regulated £m UELs limited to 2050 35 160 37 151 UELs limited to 2060 12 70 13 66 UELs limited to 2070 1 28 — 26 Note that this sensitivity calculation excludes any assumptions regarding the residual value for our asset base and the effect shortening asset depreciation lives would be expected to have on our regulatory recovery mechanisms. (c) Analysis of property, plant and equipment Land and buildings £m Plant and machinery £m Assets Motor vehicles and office equipment £m Total £m Cost at 1 April 2019 (before transition to IFRS 16) 1 3,338 53,829 5,049 930 63,146 Right-of-use assets recognised on transition to IFRS 16 2 381 67 — 20 468 Cost at 1 April 2019 (as restated) 3,719 53,896 5,049 950 63,614 Exchange adjustments 1 98 1,484 83 33 1,698 Additions 130 464 4,029 104 4,727 Disposals (79) (486) (9) (65) (639) Reclassifications 3,4 29 4,251 (4,381) 14 (87) Cost at 1 April 2020 3,897 59,609 4,771 1,036 69,313 Exchange adjustments (213) (3,308) (130) (73) (3,724) Additions 89 328 4,023 70 4,510 Disposals (6) (344) (26) (48) (424) Reclassifications 3 96 3,007 (3,243) 77 (63) Reclassification to held for sale (note 10) (111) (3,231) (174) (44) (3,560) Cost at 31 March 2021 3,752 56,061 5,221 1,018 66,052 Accumulated depreciation at 1 April 2019 1 (778) (16,918) — (591) (18,287) Exchange adjustments 1 (16) (329) — (20) (365) Depreciation charge for the year (92) (1,252) — (120) (1,464) Disposals 36 464 — 58 558 Reclassifications 3 3 (7) — 11 7 Accumulated depreciation at 1 April 2020 (847) (18,042) — (662) (19,551) Exchange adjustments 37 698 — 46 781 Depreciation charge for the year (90) (1,270) — (116) (1,476) Disposals — 339 — 48 387 Reclassifications 3 2 (5) — 6 3 Reclassification to held for sale (note 10) 22 798 — 27 847 Accumulated depreciation at 31 March 2021 (876) (17,482) — (651) (19,009) Net book value at 31 March 2021 2,876 38,579 5,221 367 47,043 Net book value at 31 March 2020 3,050 41,567 4,771 374 49,762 1. Comparative amounts have been revised as described in note 1F. 2. On 1 April 2019, £468 million of additional right-of-use assets were recognised on transition to IFRS 16. See note 37 for details. 3. Represents amounts transferred between categories, (to)/from other intangible assets (see note 12), from inventories and reclassifications between cost and accumulated depreciation. 4. In 2020, comprised an £87 million reduction in the 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 were subsequently no longer payable. 2021 2020 £m £m Information in relation to property, plant and equipment Capitalised interest included within cost 2,233 2,118 Contributions to cost of property, plant and equipment included within: Trade and other payables 138 84 Non-current liabilities 400 428 Contract liabilities – current 66 76 Contract liabilities – non-current 1,093 1,082 13. Property, plant and equipment continued (d) 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. The lease payments include fixed payments, any variable lease payments dependent on an index or a rate, and any break fees or renewal option costs that we are reasonably certain to incur. 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 (which is determined based on observable data for borrowing rates for the specific group entity that has entered into the lease, with specific adjustments for the term of the lease and any lease-specific risk premium). 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. The table below shows the net book value of right-of-use assets included within property, plant and equipment at 31 March 2021 and 31 March 2020, split by category. The associated lease liabilities are disclosed in note 21. 31 March 2021 Land and Plant and Assets Motor Total Net book value at 31 March 2021 365 81 — 184 630 Additions 60 6 — 64 130 Depreciation charge for the year (29) (16) — (68) (113) 31 March 2020 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 (29) (16) — (72) (117) The following balances have been included in the income statement for the years ended 31 March 2021 and 31 March 2020 in respect of right-of-use assets: 2021 2020 £m £m Included within net finance income and costs: Interest expense on lease liabilities (21) (26) Included within revenue: Lease income¹ 390 404 Included within operating expenses: Expense relating to short-term and low-value leases (13) (12) 1. Included within lease income is £376 million (2020: £353 million) of variable lease payments, the majority of which relates to the power supply arrangement entered into with LIPA (see note 3). The total of future minimum sublease payments expected to be received under non-cancellable subleases is £104 million (2020: £94 million).

Other non-current assets

Other non-current assets	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Other non-current assets	14. 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 2022. 2021 2020 £m £m Other receivables 45 35 Non-current tax assets 6 65 Prepayments 5 19 Accrued income¹ 237 235 293 354

Financial and other investments

Financial and other investments	12 Months Ended
	Mar. 31, 2021
Disclosure of financial assets [abstract]
Financial and other investments	15. Financial and other investments The Group holds a range of financial and other investments. These investments include short-term money market funds, quoted investments in equities or bonds of other companies, investments in our venture capital portfolio (National Grid Partners), bank deposits with a maturity of greater than three months, and investments that can not be readily used in operations, principally collateral deposited in relation to derivatives. The classification of each investment held by the Group is determined based on two main factors: • its contractual cash flows – whether the assets cash flows are solely payments of the principal and interest on the financial asset on pre-determined dates or whether the cash flows are determined by other factors such as the performance of a company; and • the business model for holding the investments – whether the intention is to hold onto the investment for the longer term (collect the contractual cash flows), or to sell the asset with the intention of managing any gain or loss on sale or to manage any liquidity requirements. The four categories of financial and other investments are as follows: • Financial assets at amortised cost – 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 receivables in relation to deposits and collateral; • FVOCI debt and other investments – debt investments, such as bonds, 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 (FVOCI), with gains or losses recognised in the consolidated statement of comprehensive income instead of through the income statement. On disposal, any gains or losses are recognised within finance income in the income statement (see note 6). Other investments include insurance contracts, measured at fair value, and held to back the present value of unfunded pension liabilities in note 25; • FVOCI equity instruments – the Group has elected to measure equity instruments that are shares held as part of a portfolio of financial instruments which back some long-term employee liabilities at FVOCI on the basis that they are not held for trading and so recognising gains and losses on these investments in the income statement would not be representative of performance in the year. On disposal, any realised gains and losses are transferred to retained earnings (see note 28); and • FVTPL investments – other financial investments are subsequently measured at fair value with any gains or losses recognised in the income statement (FVTPL). 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 using observable market data where possible (see note 32(g) for further details). 15. Financial and other investments continued 2021 2020 £m £m Non-current FVOCI debt and other investments 416 352 FVOCI equity investments 99 83 FVTPL investments 240 108 755 543 Current FVTPL investments 1,768 1,278 Financial assets at amortised cost 574 720 2,342 1,998 3,097 2,541 Financial and other investments include the following: Investments in short-term money market funds 1,412 951 Investments held by National Grid Partners 136 97 Other investments 103 11 Balances that are restricted or not readily used in operations: Collateral 1 540 685 Insurance company and non-qualified plan investments 589 542 Cash surrender value of life insurance policies 283 220 Other investments 34 35 3,097 2,541 1. The collateral balance includes: £480 million (2020: £685 million) of collateral placed with counterparties with whom we have entered into a credit support annex to the International Swaps and Derivatives Association (ISDA) Master Agreement; £42 million (2020: £nil) of collateral paid by operating companies as required security deposits under the Connection and Use of System Code; and £18 million (2020: £nil) of restricted amounts allocated for specific projects within the National Grid Electricity System Operator. FVTPL and FVOCI 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 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 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 FVOCI or amortised cost are therefore considered to have low credit risk and have an immaterial impairment 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 FVOCI 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, 2021
Interests In Other Entities [Abstract]
Investments in joint ventures and associates	16. 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 a share of 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. 2021 2020 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 341 654 995 291 317 608 Exchange adjustments (22) (36) (58) 20 12 32 Additions 6 75 81 16 156 172 Capitalisation of shareholder loan to Nemo Link Limited — — — — 176 176 Share of post-tax results for the year 30 28 58 40 47 87 Share of other comprehensive income of associates, net of tax 1 — 1 1 — 1 Dividends received (31) (49) (80) (41) (34) (75) Other movements¹ (96) (34) (130) 14 (20) (6) Share of net assets at 31 March 229 638 867 341 654 995 1. Within associates, the other movements for the year primarily relates to the reclassification of an investment in an associate to financial investments. 16. Investments in joint ventures and associates continued 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 £141 million (2020: £240 million) in relation to joint ventures. At 31 March 2021, 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 Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m Statement of financial position Non-current assets 409 399 795 910 536 582 559 435 Cash and cash equivalents 47 54 27 33 31 26 112 66 All other current assets 24 4 24 26 8 5 12 6 Non-current liabilities (81) (45) (256) (315) (30) (29) (286) (232) Current liabilities (22) (16) (38) (43) (19) (10) (27) (2) Net assets 377 396 552 611 526 574 370 273 Group’s ownership interest 189 198 145 160 263 287 189 139 Group adjustment: elimination — — — — — — (23) (10) Carrying amount of the Group’s investment 189 198 145 160 263 287 166 129 BritNed Development Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m Income statement Revenue 72 80 199 206 66 45 28 19 Depreciation and amortisation (15) (14) (43) (46) (24) (23) (14) (7) Other costs (15) (10) (21) (20) (6) (8) (22) (10) Operating profit/(loss) 42 56 135 140 36 14 (8) 2 Net interest expense (1) — (18) (22) — — — (3) Profit/(loss) before tax 41 56 117 118 36 14 (8) (1) Income tax expense (11) (10) — — (14) (2) — — Profit/(loss) for the year 30 46 117 118 22 12 (8) (1) Group’s share of profit/(loss) 15 23 31 31 11 6 (4) (1) Group adjustment: tax charge — — (9) (9) — — 1 — Group’s share of post-tax results for the year 15 23 22 22 11 6 (3) (1) 34. 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 2021 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 (US) Investments 2 Limited, National Grid Hong Kong Limited, National Grid Luxembourg SARL 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. All entities incorporated in the United States are taxed in the United States on their worldwide income other than where indicated in the footnotes below. Other entities are tax resident in their jurisdiction of incorporation other than where indicated in the footnotes below. 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 1 NatgridTW1 Limited 1 National Grid Belgium Limited 2 * National Grid Blue Power Limited 2 * 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 2 * National Grid Fourteen Limited 2 * National Grid Gas Holdings Limited National Grid Gas plc National Grid Grain LNG Limited National Grid Holdings Limited 1 National Grid Holdings One plc National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited 1 National Grid Metering Limited National Grid North Sea Link Limited National Grid Offshore Limited National Grid Partners Limited National Grid Plus Limited National Grid Property Holdings Limited National Grid Seventeen Limited 2 * National Grid Smart Limited National Grid Ten National Grid Thirty Five Limited 2 * National Grid Thirty Six Limited National Grid Twelve Limited 1 National Grid Twenty Eight Limited National Grid Twenty-Five Limited 2 * National Grid Twenty Seven Limited National Grid Twenty Three Limited 1 National Grid UK Limited National Grid UK Pension Services Limited National Grid (US) Holdings Limited 1 National Grid (US) Investments 2 Limited 1 National Grid (US) Investments 4 Limited 1 National Grid (US) Partner 1 Limited 1 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 2 * 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%) 3 1. Companies where National Grid plc has issued guarantees over the liabilities of the companies as at 31 March 2021 and for which the companies are taking the exemption from the requirements of an audit for their individual financial statements as permitted by section 479A of the Companies Act. 2. Registered office: c/o KPMG, 15 Canada Square, London E14 5GL, UK. 3. 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). Agave Solar, LLC Altona Solar, LLC Apple River Solar, LLC Apple Solar, LLC Argenta Solar, LLC Armenia Solar, LLC Artemisia Solar, LLC 1 Ashland Solar, LLC Athens Solar, LLC Audubon Wind Farm, LLC Autauga Solar, LLC Baileyville Solar, LLC (previously Ellison Solar, LLC)** Banner Solar, LLC Bazile Creek Wind Farm, LLC Bee Hollow Solar, LLC Bell Plaine Solar, LLC Benevolent Solar, LLC Birdsong Creek Solar, LLC Black Bear Solar, LLC Blackhawk Solar, LLC Blaze Solar, LLC 2 Blevins Solar, LLC Blue Ridge Wind, LLC Blue Spring Solar, LLC Blues Solar, LLC Bluewater Solar, LLC Boone Solar, LLC Boston Gas Company 3 Braeburn Solar, LLC Bridges Solar, LLC Brilliance Solar, LLC British Transco Capital, Inc. 4 British Transco Finance, Inc. 4 Brock Solar, LLC Broken Bridge Corp. 5 Brook Trout Solar, LLC BT Noble Solar, LLC 6 Bullsnake Solar, LLC Burley 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 Cameo Solar, LLC Canary Solar, LLC Canby Solar, LLC Carriere Solar, LLC Cass Wind Farm, LLC Cattle Ridge Wind Farm 2, LLC Cedar Grove Solar, LLC Centennial Solar, LLC Chewelah Solar, LLC Clear Creek Solar, LLC Clermont Solar, LLC Clinton County Solar, LLC Coles Solar, LLC Commonwealth Solar, LLC Compass Prairie Wind, LLC Coneflower Solar, LLC 1 Conestoga Wind, LLC Copperhead Solar, LLC Creekview Solar, LLC Crocker Wind Farm 2, LLC Dahlia Solar, LLC 1 Dakota Hills Wind Farm, LLC Day Lily Solar, LLC 1 Deatsville Solar, LLC Deer Trail Solar, LLC Dodson Creek Solar, LLC 7 Donnellson Solar, LLC East Galesburg Solar, LLC East Macomb Solar, LLC Eastern Hemlock Solar, LLC Eatonville Solar, LLC Elba Solar, LLC Elburn Solar, LLC Eldena Solar, LLC Elk Creek Solar, LLC Elk Creek Solar 2, LLC EUA Energy Investment Corporation 3 Exie Solar, LLC Falls City Solar, LLC Fayette Solar, LLC 8 Firstview Wind Farm, LLC Fish Creek Solar, LLC Forrest Solar, LLC Fort Solar, LLC Fowlkes Solar, LLC Front Range Wind Farm, LLC Fulton Solar, LLC Gala Solar, LLC Galesburg Solar, LLC Gardenia Solar, LLC 1 Genesee Solar Energy, LLC Gillis Solar, LLC Glenwood Solar, LLC Golden Solar, LLC Goldendale Solar, LLC Goldenrod Wind Farm, LLC Goldfinch Solar, LLC Grand Junction Solar, LLC Granite State Power Link LLC 4 Grant Solar, LLC Grant Solar 2, LLC Grayson Solar, LLC Greenbrier Creek Solar, LLC Greensky Solar, LLC Greenwood Solar, LLC Grid NY LLC 9 Grindstone Wind Farm, LLC 10 Hale County Solar, LLC Hale Solar, LLC Hampton Solar, LLC Hansford Energy Storage, LLC Harmony Solar ND, LLC Harmony Solar ND 2, LLC Harrington Solar, LLC Hartley Solar, LLC Hearth Solar, LLC Heyworth Solar, LLC Hill River Solar, LLC Honeybee Solar, LLC Hoosier Solar, LLC Hoskins Solar, LLC Illumination Solar, LLC Innovation Solar, LLC Irwin Solar, LLC Itasca Energy Development, LLC 1 Itasca Energy Services, LLC Jackalope Solar, LLC Jack Rabbit Wind, LLC Jackson County Solar, LLC Jantz Solar, LLC Jonagold Solar, LLC Junction Solar, LLC Kankakee Solar, LLC KeySpan CI Midstream Limited 4 KeySpan Energy Corporation 9 KeySpan Energy Services Inc. 4 KeySpan Gas East Corporation 9 KeySpan International Corporation 4 KeySpan MHK, Inc. 4 KeySpan Midstream Inc. 4 KeySpan Plumbing Solutions, Inc. 9 Kindle Solar, LLC Kingsnake Solar, LLC Knox Solar, LLC KSI Contracting, LLC 4 KSI Electrical, LLC 4 KSI Mechanical, LLC 4 Lake Charlotte Solar, LLC Lake Iris Solar, LLC Lakeside Solar, LLC Lamdin Solar, LLC Land Management & Development, Inc. 9 Landwest, Inc. 9 Lansing Solar, LLC Lawrence Solar, LLC Leola Wind Farm, LLC Liberty Solar, LLC Lilac Solar, LLC 1 Limestone Solar, LLC Lind Solar, LLC Livingston County Solar, LLC Long Mount Solar, LLC 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Incorporated in the US continued Lordsburg Solar, LLC Louisa Solar, LLC Lowlands Solar, LLC Lydia Solar, LLC Macedonia Solar, LLC Madden Creek Solar, LLC Marion County Solar, LLC Massachusetts Electric Company 3 Maverick Wind Farm, LLC Mazon Solar, LLC Mazon Solar 2, LLC McFadden Solar, LLC Meadowlands Solar, LLC Merton Solar, LLC Metrowest Realty LLC 4 Miller Creek Solar, LLC Millers Ferry Solar, LLC Moonrise Solar, LLC Morgan County Solar, LLC Morning Glory Solar, LLC 1 Mountain Laurel Solar, LLC Muddy Creek Solar, LLC Mustang Ridge Wind Farm, LLC Mystic Steamship Corporation 7 Nantucket Electric Company 3 National Grid Algonquin LLC 4 National Grid Connect Inc. 4 National Grid Development Holdings Corp. 4 National Grid Electric Services LLC 9 National Grid Energy Management LLC 4 National Grid Energy Services LLC 4 National Grid Energy Trading Services LLC 9 National Grid Engineering & Survey Inc. 9 National Grid Generation LLC 9 National Grid Generation Ventures LLC 11 National Grid Glenwood Energy Center, LLC 4 National Grid IGTS Corp. 9 National Grid Insurance USA Ltd 12 National Grid Islander East Pipeline LLC 4 National Grid LNG GP LLC 4 National Grid LNG LLC 4 National Grid LNG LP LLC 4 National Grid Millennium LLC 4 National Grid NE Holdings 2 LLC 3 National Grid North America Inc. 4 National Grid North East Ventures Inc. 4 National Grid Partners Inc. 9 National Grid Partners LLC 4 National Grid Port Jefferson Energy Center LLC 4 National Grid Renewables, LLC (previously NGV Emerald Acquisition Co., LLC) 4 National Grid Renewables Development, LLC (previously Geronimo Energy, LLC) National Grid Renewables E Wind, LLC (previously Geronimo E Wind LLC) 1 National Grid Renewables Operations, LLC 4 National Grid Renewables Projects, LLC (previously Geronimo Solar Energy, LLC) 1 National Grid Renewables Stutsman, LLC (previously Geronimo Stutsman Wind Farm, LLC) National Grid Services Inc. 4 National Grid Transmission Services Corporation 3 National Grid US 6 LLC 4,† National Grid US LLC 4 National Grid USA 4 National Grid USA Service Company, Inc. 3 NEES Energy, Inc. 3 New England Electric Transmission Corporation 5 New England Energy Incorporated 3 New England Hydro Finance Company, Inc. (53.704%) 3 New England Hydro-Transmission Corporation (53.704%) 5 New England Hydro-Transmission Electric Company, Inc. (53.704%) 3 New England Power Company 3 Newport America Corporation 13 Newton Solar, LLC NG Renewables Energy Marketing, LLC 4 NG Renewables Energy Services, LLC NGNE LLC 4 NGV Emerald Energy Venture Holdings, LLC 4 NGV OSW Holdings, LLC 4 NGV US Distributed Energy Inc. 4 NGV US, LLC (previously NGV Emerald Holdings, LLC) 4 NGV US Transmission Inc. 4 Niagara Mohawk Energy, Inc. 4 Niagara Mohawk Holdings, Inc. 9 Niagara Mohawk Power Corporation 9 Niobrara Wind, LLC NM Properties, Inc. 9 Noble Storage, LLC Nordic VOS, LLC North Adair Solar, LLC Northeast Renewable Link LLC 4 North East Transmission Co., Inc. 4 North Fork Wind, LLC North Rock Solar, LLC Onton Solar, LLC Opinac North America, Inc. 4 Oreana Solar, LLC Parklawn Solar, LLC Patriotic Solar, LLC Pearl River County Solar, LLC Pennington Solar, LLC Peony Solar, LLC Philadelphia Coke Co., Inc. 4 Pierce County Solar, LLC Pike County Solar, LLC Pinon Pine Solar, LLC Piper Solar, LLC Pipestone Solar, LLC Placedo Solar, LLC Pleasant Plains Solar, LLC Plum Creek Wind Farm, LLC Plum Creek Wind Farm 2, LLC Portage Solar, LLC Port of the Islands North, LLC 9 Prairie Oasis Solar, LLC Prairie Rose Wind 2, LLC 1 Prosperity Wind Farm, LLC Prosperity Wind Farm 2, LLC Radiance Solar, LLC 1 Red Rock Solar SD, LLC Red Wolf Solar, LLC Regal Solar, LLC Regal Solar 2, LLC River North Solar, LLC Robertson Solar, LLC Rochester Solar, LLC 1 Rock Ridge Wind Farm, LLC Rocky Meadow Solar, LLC Rolling Hills Solar, LLC Ross County Solar, LLC 7 Royal Solar, LLC Royal Solar 2, LLC Royerton Solar, LLC Saddle Solar, LLC Saginaw Bay Solar, LLC Sandstone Creek Solar, LLC Sandstone Creek Solar 2, LLC Sapphire Sky Wind Farm, LLC Scorpion Solar, LLC Serenity Solar, LLC 1 Shelby Solar, LLC Sherco Solar, LLC 1 Sherco Solar 2, LLC 1 Silver City Solar, LLC Simpson Solar, LLC (previously Geronimo White Pine Solar, LLC) South Belleville Solar, LLC South Macomb Solar, LLC Spotlight Solar, LLC Spring Brook Solar, LLC Springfield Solar Farm, LLC Spring River Solar, LLC Stockton Solar, LLC Stony Brook Wind, LLC Stony Point Solar, LLC Stove Creek Solar, LLC Sturgis Solar, LLC Summit Lake Solar, LLC Sunbeam Solar, LLC Sunray Solar, LLC Sunrise Solar, LLC Sycamore Creek Solar, LLC Thacker Solar, LLC The Brooklyn Union Gas Company 9 The Narragansett Electric Company 13 Tilton Solar, LLC Torchlight Solar, LLC 1 Transgas Inc. 3 Tri-City Solar, LLC Turquoise Solar, LLC Uintah Solar, LLC Unbridled Solar, LLC (previously Henderson Solar, LLC) Union City Solar, LLC Upper Hudson Development Inc. 9 Valley Appliance and Merchandising Company 13 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Valley Solar, LLC Vermont Green Line Devco, LLC (90%) 4 Vibrant Solar, LLC Virgo Community Solar Gardens, LLC 1 Virtue Solar, LLC Vivid Solar, LLC Wallowa Solar, LLC Wayfinder Group, Inc. 3 Wayside Solar, LLC Western Hemlock Solar, LLC Wheatfield Solar, LLC White Elm Wind Farm, LLC Wild Springs Solar, LLC 1 Wildcat Ridge Wind Farm, LLC Wildhorse Creek Solar, LLC Willard Solar, LLC Williams County Solar, LLC Wiregrass Solar, LLC Wolf River Solar, LLC Wonder Lake Solar, LLC Woodlands Solar, LLC Worthington Solar, LLC Yellowbud Solar, LLC Yellowhammer Solar, LLC Young County Solar, LLC Yucca Solar, LLC 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 LLP, c/o Charles Reagh, Queen’s Marque, 600-1741 Lower Water Street, Halifax, Nova Scotia, B3J 0J2, 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 † 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, JE4 9WG, Jersey, 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 Incorporated in the Netherlands Registered office: Westblaak 89, 3012 KG Rotterdam, PO Box 21153, 3001 AD, Rotterdam, Netherlands British Transco International Finance B.V. Incorporated in the Republic of Ireland Registered office: c/o Moore Stephens Nathans, Third Floor, Ulysses House, 23/24 Foley Street, Dublin, D01 W2T2, Ireland National Grid Company (Ireland) Designated Activity Company* 1. Registered office: National Grid Renewables Development, LLC, 8400 Normandale Lake Blvd. Suite 1200, Bloomington, MN 55437, USA. 2. Registered office: National Registered Agents, Inc., 160 Greentree Drive, Suite 101, Dover DE 19904, USA. 3. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, USA. 4. Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington DE 19808, USA. 5. Registered office: Corporation Service Company, 10 Ferry Street, Suite 313, Concord NH 03301, USA. 6. Registered office: National Registered Agents, Inc., 1999 Bryan St, Bryan Street, Dallas, Dallas County TX 75201, USA. 7. Registered office: The Corporation Trust Company, Corporation Trust Center, 1209 Orange Street, Wilmington, Delaware, 19801, USA. 8. Registered office: 60 Mine Lake Ct, Mine Lake Court, Suite 200, Raleigh, Wake County, NC 27615, USA. 9. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 10. Registered office: National Registered Agents, Inc., 30600 Telegraph Road, Suite 2345, Bingham Farms, MI 48025-5720, USA. 11. Registered office: Corporation Service Company, 84 State Street, Albany NY 12207, USA. 12. Registered office: One MetroTech Center, Brooklyn NY 11201, USA. 13. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, USA. * In liquidation. ** Name change post 31 March 2021. † Entity is tax resident in the United Kingdom. 34. Subsidiary undertakings, joint ventures and associates continued Joint ventures A list of the Group’s joint ventures as at 31 March 2021 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 ** National Places LLP (50%) 2 Nemo Link Limited (50%) NGET/SPT Upgrades Limited (50%) † St William Homes LLP (50%) 3 Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Bight Wind Holdings, LLC (30%) 4 Clean Energy Generation, LLC (50%) Emerald Energy Venture LLC (51%) Island Park Energy Center, LLC (50%) Islander East Pipeline Company, LLC (50%) 4 LI Energy Storage System, LLC (50%) LI Solar Generation, LLC (50%) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, IFA2 SAS (50%) Associates A list of the Group’s associates as at 31 March 2021 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%) 4 Connecticut Yankee Atomic Power Company (19.5%) 5 Direct Global Power, Inc. (26%) 4 Energy Impact Fund LP (9.41%) 6 KHB Venture LLC (33.33%) 7 Maine Yankee Atomic Power Company (24%) 8 Millennium Pipeline Company, LLC (26.25%) 4 New York Transco LLC (28.3%) 9 NYSEARCH RMLD, LLC (22.63%) The Hive IV, LLC (28.2%) 4 Yankee Atomic Electric Company (34.5%) 10 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 2021 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: 80 Cheapside, London, EC2V 6EE, UK. 3. Registered office: Berkeley House, 19 Portsmouth Road, Cobham, Surrey KT11 1JG, UK. 4. Registered office: The Corporation Trust Company, Corporation Trust Center, 1209 Orange Street, Wilmington DE 19801, USA. 5. Registered office: Carla Pizzella, 362 Injun Hollow Road, East Hampton CT 06424-3099, USA. 6. Registered office: Harvard Business Services, Inc., 16192 Coastal Highway, Lewes DE 19958, Sussex County, USA. 7. Registered office: De Maximus Inc., 135 Beaver Street, 4th Floor, Waltham MA 02452, USA. 8. Registered office: Joseph D Fay, 321 Old Ferry Road, Wiscasset ME 04578, USA. 9. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 10. 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. † 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. The following UK subsidiaries will take advantage of the audit exemption set out within section 479A of the Companies Act 2006 for the year ended 31 March 2021: Company name Company number NatGrid One Limited 5521240 Natgrid TW1 Limited 7579324 National Grid Holdings Limited 3096772 National Grid International Limited 2537092 National Grid Twelve Limited 4355616 National Grid Twenty Three Limited 6999009 National Grid (US) Holdings Limited 2630496 National Grid (US) Investments 2 Limited 3784528 National Grid (US) Investments 4 Limited 3867128 National Grid (US) Partner 1 Limited 4314432

Derivative financial instrument

Derivative financial instruments	12 Months Ended
	Mar. 31, 2021
Financial Instruments [Abstract]
Derivative financial instruments	17. 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: These are used to manage 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: These are used to manage our US customers’ exposure to price and supply risks. Some forward contracts for the purchase of commodities meet the definition of derivatives. We also enter into derivative financial instruments linked to commodity prices, including index futures, options and swaps, which 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. 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. The fair value of derivative financial instruments is calculated 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: 2021 2020 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current 457 (145) 312 93 (380) (287) Non-current 542 (754) (212) 1,249 (954) 295 999 (899) 100 1,342 (1,334) 8 Financing derivatives 942 (767) 175 1,267 (1,134) 133 Commodity contract derivatives 57 (132) (75) 75 (200) (125) 999 (899) 100 1,342 (1,334) 8 (a) Financing derivatives The fair values of financing derivatives by type are as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Interest rate swaps 325 (159) 166 556 (337) 219 Cross-currency interest rate swaps 601 (351) 250 643 (514) 129 Foreign exchange forward contracts¹ 16 (74) (58) 58 (39) 19 Inflation-linked swaps — (183) (183) — (234) (234) Equity options — — — 10 (10) — 942 (767) 175 1,267 (1,134) 133 1. Included within the foreign exchange forward contracts balance are £32 million (2020: £3 million) of derivative liabilities in relation to the hedging of capital expenditure and a deal-contingent foreign exchange forward contract liability of £9 million (2020: £nil) in relation to the disposal of NECO (see note 10). 17. Derivative financial instruments continued (a) Financing derivatives continued The maturity profile of financing derivatives is as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total Current Less than 1 year 428 (70) 358 62 (254) (192) 428 (70) 358 62 (254) (192) Non-current In 1 to 2 years 10 (14) (4) 480 (51) 429 In 2 to 3 years 24 (12) 12 13 (5) 8 In 3 to 4 years 62 (80) (18) 20 (28) (8) In 4 to 5 years 4 (42) (38) 31 (109) (78) More than 5 years 414 (549) (135) 661 (687) (26) 514 (697) (183) 1,205 (880) 325 942 (767) 175 1,267 (1,134) 133 The notional contract amounts of financing derivatives by type are as follows: 2021 2020 £m £m Interest rate swaps (2,259) (3,101) Cross-currency interest rate swaps (8,389) (8,097) Foreign exchange forward contracts (4,651) (3,284) Inflation-linked swaps (500) (500) Equity options — (800) (15,799) (15,782) Derivatives with a notional value of £2,810 million, pay or receive cash flows that reference GBP LIBOR of £2,041 million (maturing between 2023 and 2040) or USD LIBOR of £769 million (maturing between 2023 and 2026). LIBOR is being replaced as an interest rate benchmark by alternative reference rates and therefore negotiations are underway to amend these contracts, with any related hedge documentation then being amended. At 31 March 2021, none of the contracts had yet been amended. (b) Commodity contract derivatives The fair values of commodity contract derivatives by type are as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets Liabilities £m Total £m Commodity purchase contracts accounted for as derivative contracts Forward purchases of gas 44 (94) (50) 64 (108) (44) Derivative financial instruments linked to commodity prices Electricity capacity 2 — 2 — — — Electricity swaps 10 (33) (23) 4 (83) (79) Electricity options — (1) (1) — — — Gas swaps 1 (3) (2) 7 (8) (1) Gas options — (1) (1) — (1) (1) 57 (132) (75) 75 (200) (125) 17. Derivative financial instruments continued (b) Commodity contract derivatives continued The maturity profile of commodity contract derivatives is as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than one year 29 (75) (46) 31 (126) (95) 29 (75) (46) 31 (126) (95) Non-current In 1 to 2 years 7 (24) (17) 8 (35) (27) In 2 to 3 years 7 (16) (9) 9 (24) (15) In 3 to 4 years 7 (7) — 8 (12) (4) In 4 to 5 years 6 (5) 1 7 (1) 6 More than 5 years 1 (5) (4) 12 (2) 10 28 (57) (29) 44 (74) (30) 57 (132) (75) 75 (200) (125) The notional quantities of commodity contract derivatives by type are as follows: 2021 2020 Forward purchases of gas 1 36m Dth 102m Dth Electricity swaps 12,321 GWh 12,836 GWh Gas swaps 47m Dth 89m Dth Gas options 40m Dth 26m Dth 1. Forward gas purchases have terms up to five years (2020: four years). The contractual obligations under these contracts are £104 million (2020: £128 million).

Inventories and current intangi

Inventories and current intangible assets	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Inventories and current intangible assets	18. 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. 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. 2021 2020 £m £m Fuel stocks 94 151 Raw materials and consumables 253 265 Current intangible assets – emission allowances 92 133 439 549 There is a provision for obsolescence of £10 million against inventories as at 31 March 2021 (2020: £21 million).

Trade and other receivables

Trade and other receivables	12 Months Ended
	Mar. 31, 2021
Trade and other receivables [abstract]
Trade and other receivables	19. Trade and other receivables Trade and other receivables include amounts which are due from our customers for services we have provided, accrued income which has not yet been billed, prepayments, contract assets where certain milestones are required to be fulfilled and other receivables that are expected to be settled within twelve months. Trade and other receivables are initially recognised at fair value and subsequently measured at amortised cost, less any appropriate allowances for estimated irrecoverable amounts. 2021 2020 £m £m Trade receivables 1,503 1,571 Accrued income 863 849 Prepayments 387 408 Contract assets 13 — Other receivables 153 158 2,919 2,986 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 £2,152 million (2020: £2,063 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. 2021 2020 £m £m At 1 April 512 394 Exchange adjustments (57) 20 Charge for the year, net of recoveries 326 234 Uncollectible amounts written off (59) (136) Reclassification to held for sale (note 10) (50) — At 31 March 672 512 The trade receivables balance, accrued income balance and provisions balance split by geography are as follows: As at 31 March 2021 As at 31 March 2020 UK US Total UK US Total £m £m £m £m £m £m Trade receivables 227 1,925 2,152 227 1,836 2,063 Accrued income 547 339 886 461 408 869 Provision for impairment of receivables and accrued income (23) (649) (672) (40) (472) (512) 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, £1,852 million (2020: £1,852 million) of the trade receivables and accrued income 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 as a result of COVID-19. The Group also ceased customer termination activities as requested by relevant local authorities. Certain collection activities did resume during the year where permitted, but this was a small proportion compared to normal levels. In calculating our provision for impairment of receivables at 31 March 2021, we were able to incorporate the actual cash collection levels experienced since the start of the pandemic to determine the expected loss rates per category of outstanding receivable by operating company, which is summarised in the provision matrix shown below. For the year ended 31 March 2020, there was limited cash collection data available with regards to the impact that COVID-19 would have on collection of receivables. Therefore, in order to reflect the impact of COVID-19 into our calculation of the charge for the year, we 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. 19. Trade and other receivables continued Based on our review of these factors, we concluded that a reasonable range for the provisions recognised in the current year would be £320 million to £342 million ($440 million to $470 million), which considered the continued application of our previous experience regarding debtor recoverability in the aftermath of historical impactful events, as well as the collections experience seen since the start of the pandemic, and concluded that a total charge of £326 million represented our best estimate based on the information available. For the year ended 31 March 2020, we determined that 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), and concluded an additional COVID-19 related 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. The average expected loss rates and gross balances for the retail customer receivables in our US operations are set out below: 2021 2021 2020 2020 % £m % £m Accrued income 7 322 5 395 0 – 30 days past due 7 580 5 651 30 – 60 days past due 24 155 14 194 60 – 90 days past due 36 108 29 109 3 – 6 months past due 52 140 47 121 6 – 12 months past due 66 180 63 105 Over 12 months past due 71 367 79 277 1,852 1,852 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.

Cash and cash equivalents

Cash and cash equivalents	12 Months Ended
	Mar. 31, 2021
Cash and cash equivalents [abstract]
Cash and cash equivalents	20. 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. Bank overdrafts are only shown net within cash and cash equivalents when there is a legal right to offset unconditionally and an intention to settle net has been demonstrated by the physical movement of 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. 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). 2021 2020 £m £m Cash at bank 117 73 Short-term deposits 40 — Cash and cash equivalents 157 73

Borrowings

Borrowings	12 Months Ended
	Mar. 31, 2021
Disclosure of detailed information about borrowings [abstract]
Borrowings	21. 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, inflation rates and foreign exchange. Lease liabilities are also included within borrowings. Our price controls and rate plans require us to fund our networks within a certain ratio of debt to equity or regulatory value 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 measured at amortised cost, with the exception of one current liability which is 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 within equity (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). 2021 2020 £m £m Current Bank loans 1,022 1,244 Bonds¹ 1,987 1,446 Commercial paper 628 1,269 Lease liabilities 99 112 Other loans 1 1 3,737 4,072 Non-current Bank loans 2,532 2,819 Bonds 24,209 23,094 Lease liabilities 586 623 Other loans 156 186 27,483 26,722 Total borrowings 31,220 30,794 1. Includes a liability held at fair value through profit and loss of £682 million (2020: £741 million). 21. Borrowings continued Total borrowings are repayable as follows: 2021 2020 £m £m Less than 1 year 3,737 4,072 In 1 to 2 years 1,745 2,212 In 2 to 3 years 889 1,664 In 3 to 4 years 2,206 757 In 4 to 5 years 1,833 2,122 More than 5 years: By instalments 927 870 Other than by instalments 19,883 19,097 31,220 30,794 The fair value of borrowings at 31 March 2021 was £34,676 million (2020: £34,174 million). Where market values were available, the fair value of borrowings (Level 1) was £20,333 million (2020: £14,059 million). Where market values were not available, fair value of borrowings (Level 2) was £14,343 million (2020: £20,115 million), and calculated by discounting cash flows at prevailing interest rates. The notional amount outstanding of the debt portfolio at 31 March 2021 was £31,010 million (2020: £30,422 million). There have been no new issuances since the year end. In 2020, the assets of the Colonial Gas Company were merged with the Boston Gas Company, and have been ringfenced post-merger. Certain gas distribution assets of NECO are subject to liens and other charges and are provided as collateral over borrowings totalling £67 million at 31 March 2021 (2020: £84 million), all of which have been classified as held for sale as at 31 March 2021 (see note 10). 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 £582 million (2020: £785 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. Certain borrowings, primarily some of our USD denominated bank loans and company car lease contracts, have payments that are linked to LIBOR. LIBOR is being replaced as an interest rate benchmark by alternative reference rates and therefore negotiations are underway to amend these contracts. At 31 March 2021, none of the contracts had yet been amended. £328 million of bank loans affected by GBP LIBOR, £59 million of bank loans affected by USD LIBOR and £173 million of lease liabilities affected by USD LIBOR will be impacted. 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 £682 million (2020: £741 million), which includes cumulative changes in fair value attributable to changes in credit risk recognised in other comprehensive income, post tax of £1 million (2020: £10 million); ii. the amount repayable at maturity in November 2021 is £684 million (2020: £759 million); and iii. the difference between carrying amount and contractual amount at maturity is £2 million (2020: £18 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. 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. 2021 2020 £m £m Gross lease liabilities are repayable as follows: Less than 1 year 114 132 1 to 5 years 321 361 More than 5 years 464 481 899 974 Less: finance charges allocated to future periods (214) (239) 685 735 The present value of lease liabilities are as follows: Less than 1 year 99 112 1 to 5 years 267 297 More than 5 years 319 326 685 735

Trade and other payables

Trade and other payables	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Trade and other payables	22. 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, with the exception of contingent consideration, which is subsequently measured at fair value. 2021 2020 £m £m Trade payables 2,165 2,205 Deferred payables 154 137 Customer contributions¹ 138 84 Social security and other taxes 140 202 Contingent consideration (note 38) 39 30 Other payables 881 944 3,517 3,602 1. Relates to amounts received from government-related entities for connecting to our networks, where we have obligations remaining under the contract.

Contract liabilities

Contract liabilities	12 Months Ended
	Mar. 31, 2021
Contract liabilities [abstract]
Contract liabilities	23. 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. 2021 2020 £m £m Current 66 76 Non-current 1,094 1,082 1,160 1,158 Significant changes in the contract liabilities balances during the period are as follows: 2021 2020 £m £m As at 1 April 1,158 994 Exchange adjustments (65) 39 Revenue recognised that was included in the contract liability balance at the beginning of the period (96) (60) Increases due to cash received, excluding amounts recognised as revenue during the period 262 185 Reclassification to held for sale (note 10) (99) — At 31 March 1,160 1,158

Other non-current liabilities

Other non-current liabilities	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Other non-current liabilities	24. Other non-current liabilities Other non-current liabilities include deferred income and customer contributions which will not be recognised as income until after 31 March 2022. It also includes contingent consideration and other payables that are not due until after that date. Other non-current liabilities are initially recognised at fair value and subsequently measured at amortised cost, with the exception of contingent consideration, which is subsequently measured at fair value. 2021 2020 £m £m Deferred income¹ 78 101 Customer contributions² 400 428 Contingent consideration (note 38) 18 44 Other payables 347 318 843 891 1. Principally the deferral of profits relating to the sale of property, which we expect to recognise in future years. 2. Relates to amounts received from government-related entities for connecting to our networks, where we have obligations remaining under the contract. 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, 2021
Employee Benefits [Abstract]
Pensions and other post-retirement benefits	25. Pensions and other post-retirement benefits All of our employees are eligible to participate in a pension plan. We have defined contribution (DC) and defined benefit (DB) 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. In March 2021, National Grid announced its intention to move to a new DC plan from 1 April 2021. The National Grid YouPlan (YouPlan) Up until 31 March 2021, YouPlan was the qualifying UK pension plan that was used for automatic enrolment of new hires. National Grid paid contributions into YouPlan to provide DC benefits on behalf of employees, providing 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. National Grid UK Retirement Plan (NGUKRP) The NGUKRP is part of a Master Trust Arrangement managed by Legal & General and is National Grid’s qualifying UK pension plan from 1 April 2021 and is used for the automatic enrolment of new hires. From April 2021, National Grid pays contributions into the NGUKRP to provide DC benefits on behalf of its employees, providing a double match of member contributions up to a maximum Company contribution of 12% of salary. 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 is set with reference to the yield curve on high-quality corporate bonds at the valuation date. 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 asset or 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 COVID-19 pandemic The COVID-19 pandemic has had a global impact on economies, including on equity and bond markets. This directly affects the value of assets held in our pension schemes, as well as the value of National Grid’s DB obligations. Our UK DB plans operate low-risk investment strategies with limited exposure to equities and other return-seeking assets, reducing the impact of investment volatility. Additionally, the large allocation to bonds leads to significant hedging against changes in the value of DB obligations that result from falling bond yields. Our US plans also hedge much of this market risk, however they do have larger asset allocations in return-seeking assets such as equities. Following the start of the pandemic, US equity markets have performed strongly and therefore our US DB plans have remained in a relatively strong funding position. The markets for unquoted investments are illiquid and therefore given the market volatility at 31 March 2020, there was a risk that the valuations provided by fund managers as at 31 March 2020 were based on valuation models that had unobservable inputs, making them subject to additional estimation uncertainty. Such uncertainty has reduced as at 31 March 2021. UK pensions plans 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. National Grid UK Pension Scheme (NGUKPS) NGUKPS consists of two legally and actuarially separate sections: Section A and Section B. This follows the transfer of Section C, a section supported by an unrelated third party, out of NGUKPS in September 2020. The plan closed to new hires on 1 April 2002. 25. Pensions and other post-retirement benefits continued Scheme funding 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 176 for the assumptions used for IAS 19 (revised) purposes. Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Latest full actuarial valuation 31 March 2019 31 March 2019 31 March 2019 Actuary Willis Towers Watson Willis Towers Watson Aon Hewitt Market value of plan assets at latest valuation £6,551 million £5,765 million £3,144 million Actuarial value of benefits due to members £6,502 million £5,831 million £3,381 million Market value as percentage of benefits 101% 99% 93% Funding surplus/(deficit) £49 million (£66 million) (£237 million) 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. Section B The latest full actuarial valuation at 31 March 2019 determined that Section B was in deficit. To recover the deficit, National Grid paid recovery plan payments of approximately £34 million per annum over two years to September 2020. In addition, the employers contribute 51.4% of pensionable salary, less member contributions, in respect of future benefit accrual. Investment de-risking transactions In December 2020, the Trustees of the NGUKPS exchanged £0.8 billion of gilts from Section A for a buy-in transaction with Rothesay Life. This follows two similar arrangements entered into in the previous year. In Section A, £2.8 billion of gilts were exchanged for a buy-in policy with Rothesay Life, and in Section B, £1.6 billion of gilts were exchanged for a buy-in policy with Legal & General. These policies provide bulk annuities in respect of some pensioner and dependant members of NGUKPS and were funded by existing assets. All policies are held by the Trustee. For each transaction, 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 actuarial losses on purchase of £0.1 billion (2020: £0.7 billion), 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. To recover the deficit, National Grid agreed to a payment plan of £54 million per annum over three years to 2022, and a final payment of £26 million in 2023, all adjusted for changes in the Retail Price Index (RPI). In addition, National Grid contributes 44% 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 National Grid pays additional contributions to Section B of NGUKPS and NGEG of ESPS in respect of the costs of plan administration and the Pension Protection Fund (PPF) levies. Section A of NGUKPS will fund these costs from the Section’s assets. 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. 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 2021 £186 million £nil £100 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 1 at 31 March 2021 n/a A maximum of £175 million A maximum of £500 million 1. These amounts are payable if certain trigger events occur which have been individually agreed between the plans and their relevant supporting employers. All of the security is currently provided in the form of surety bonds, but may also be provided as letters of credit or cash. The assets held as 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. In addition, a guarantee of £1 billion has been provided to Section A of NGUKPS, with the payment 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). 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 £110 million (2020: £153 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 £26 million (2020: £18 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 2021 2020 2019 % % % Discount rate – past service 2.00 2.35 2.40 Discount rate – future service 2.15 2.35 2.45 Salary increases 3.40 2.90 3.50 Rate of increase in RPI – past service 3.15 2.65 3.25 Rate of increase in RPI – future service 3.00 2.45 3.20 At 31 March 2021 and 31 March 2020, single equivalent financial assumptions are shown above for presentational purposes, although full yield curves have been used in our calculations. In 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. 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 2021 2020 2019 2021 2020 2019 % % % % % % Discount rate 3.25 3.30 3.95 3.25 3.30 3.95 Salary increases 4.30 3.50 3.50 4.30 3.50 3.50 Initial healthcare cost trend rate n/a n/a n/a 7.10 7.00 7.25 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 (2020: 2030). The table below sets out the projected life expectancies adopted for the UK and US pension arrangements: 2021 2020 2019 UK years US years UK years US years UK years US years Assumed life expectations for a retiree age 65 Males 21.8 21.6 22.1 20.9 22.0 22.1 Females 23.7 24.0 23.8 23.4 23.6 24.2 In 20 years: Males 23.1 23.2 23.3 22.5 23.3 23.7 Females 25.2 25.5 25.3 25.1 25.2 25.9 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 17 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 (2020: 8%; 2019: 10%); 14% deferred members (2020: 14%; 2019: 16%); 78% pensioner members (2020: 78%; 2019: 74%); • US pensions: 35% active members (2020: 36%; 2019: 37%); 9% deferred members (2020: 9%; 2019: 9%); 56% pensioner members (2020: 55%; 2019: 54%); and • US other post-retirement benefits: 34% active members (2020: 35%; 2019: 39%); 66% pensioner members (2020: 65%; 2019: 61%). For sensitivity analysis see note 35. Amounts recognised in the consolidated statement of financial position 2021 2020 2019 £m £m £m Present value of funded obligations (23,283) (24,281) (24,609) Fair value of plan assets 24,388 23,748 24,793 1,105 (533) 184 Present value of unfunded obligations (324) (345) (330) Other post-employment liabilities (66) (75) (72) Net defined benefit asset/(liability) 715 (953) (218) Represented by: Liabilities (1,032) (2,802) (1,785) Assets 1,747 1,849 1,567 715 (953) (218) The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Present value of funded obligations (13,571) (12,775) (14,200) (6,681) (7,809) (6,901) (3,031) (3,697) (3,508) Fair value of plan assets 14,680 14,364 15,507 6,909 6,972 6,646 2,799 2,412 2,640 1,109 1,589 1,307 228 (837) (255) (232) (1,285) (868) Present value of unfunded obligations (74) (69) (76) (250) (276) (254) — — — Other post-employment liabilities — — — — — — (66) (75) (72) Net defined benefit asset/(liability) 1,035 1,520 1,231 (22) (1,113) (509) (298) (1,360) (940) Represented by: Liabilities (74) (69) (76) (393) (1,373) (769) (565) (1,360) (940) Assets 1,109 1,589 1,307 371 260 260 267 — — 1,035 1,520 1,231 (22) (1,113) (509) (298) (1,360) (940) 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 the Niagara Mohawk Plan and the KeySpan Retirement Plan reflects legal and actuarial advice that we have taken regarding recognition of surpluses under IFRIC 14. Similarly on the recognition of US other post-retirement assets in relation to: the Long Island Union Life Insurance plan; the New York Union Health Insurance Plan; the Long Island Union Health Insurance plan; and Retirees Health and Welfare Plan II. 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 2021 2020 2019 £m £m £m Included within operating costs Administration costs 18 16 14 Included within payroll costs Defined benefit plan costs: Current service cost 175 178 193 Past service cost – augmentations — — 5 Past service credit – redundancies (1) — (7) Special termination benefit cost – redundancies 5 2 55 Past service cost – plan amendments¹ — — 34 179 180 280 Included within finance income and costs Net interest cost 38 23 22 Total included in income statement 235 219 316 Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations² 1,408 (724) 68 Exchange adjustments 186 (97) (101) Total included in the statement of other comprehensive income 1,594 (821) (33) 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. This includes actuarial losses from the purchase of buy-in policies of £0.1 billion (2020: £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 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Included within operating costs Administration costs 9 9 6 7 6 7 2 1 1 Included within payroll costs Defined benefit plan costs: Current service cost 28 33 41 104 100 104 43 45 48 Past service cost – augmentations — — 5 — — — — — — Past service credit – redundancies (1) — (7) — — — — — — Special termination benefit cost – redundancies 5 2 55 — — — — — — Past service cost – plan amendments — — 34 — — — — — — 32 35 128 104 100 104 43 45 48 Included within finance income and costs Net interest (income)/cost (38) (31) (31) 35 21 21 41 33 32 Total included in income statement 3 13 103 146 127 132 86 79 81 Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations¹ (622) 143 57 1,017 (588) (14) 1,013 (279) 25 Exchange adjustments — — — 83 (42) (42) 103 (55) (59) Total included in the statement of other comprehensive income (622) 143 57 1,100 (630) (56) 1,116 (334) (34) 1. UK pensions is stated after actuarial losses from the purchase of buy-in policies of £0.1 billion (2020: £0.7 billion). Following a High Court ruling in October 2018, UK pension schemes were required to equalise Guaranteed Minimum Pensions (GMPs). As a result, a past service cost of £34 million was recognised in the year ended 31 March 2019 for the UK DB pension schemes. This reflected the estimated cost of equalising GMPs for current pension scheme members using the most cost-effective permissible methodology. Following the further High Court ruling in December 2020, an additional allowance of £0.4 million, was included for the year ended 31 March 2021, reflecting the associated cost for members who had transferred out of the pension scheme and were therefore not previously in scope. 25. Pensions and other post-retirement benefits continued Reconciliation of the net defined benefit liability 2021 2020 2019 £m £m £m Opening net defined benefit liability (953) (218) (263) Cost recognised in the income statement (235) (219) (316) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income 1,594 (821) (33) Employer contributions 274 327 419 Other movements (14) (22) (25) Reclassification to held for sale (note 10) 49 — — Closing net defined benefit asset/(liability) 715 (953) (218) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Opening net defined benefit asset/(liability) 1,520 1,231 1,104 (1,113) (509) (552) (1,360) (940) (815) Cost recognised in the income statement (3) (13) (103) (146) (127) (132) (86) (79) (81) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (622) 143 57 1,100 (630) (56) 1,116 (334) (34) Employer contributions 138 156 174 110 153 231 26 18 14 Other movements 2 3 (1) — — — (16) (25) (24) Reclassification to held for sale (note 10) — — — 27 — — 22 — — Closing net defined benefit 1,035 1,520 1,231 (22) (1,113) (509) (298) (1,360) (940) Changes in the present value of defined benefit obligations (including unfunded obligations) 2021 2020 2019 £m £m £m Opening defined benefit obligations (24,626) (24,939) (24,054) Current service cost (175) (178) (193) Interest cost (651) (751) (771) Actuarial gains/(losses) – experience 123 148 (69) Actuarial (losses)/gains – demographic assumptions (1) 452 266 Actuarial losses – financial assumptions (1,268) (84) (619) Past service credit – redundancies 1 — 7 Special termination benefit cost – redundancies (5) (2) (55) Past service cost – augmentations — — (5) Past service cost – plan amendments — — (34) Medicare subsidy received (25) (22) (19) Employee contributions (1) (1) (1) Benefits paid 1,246 1,282 1,376 Exchange adjustments 1,166 (531) (768) Reclassification to held for sale (note 10) 609 — — Closing defined benefit obligations (23,607) (24,626) (24,939) 25. Pensions and other post-retirement benefits continued The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Opening defined benefit obligations (12,844) (14,276) (14,226) (8,085) (7,155) (6,582) (3,697) (3,508) (3,246) Current service cost (28) (33) (41) (104) (100) (104) (43) (45) (48) Interest cost (296) (335) (358) (243) (280) (277) (112) (136) (136) Actuarial (losses)/gains – experience (21) 113 (56) (72) (45) (52) 216 80 39 Actuarial (losses)/gains – demographic assumptions (1) 140 224 — 78 — — 234 42 Actuarial (losses)/gains – financial assumptions (1,181) 798 (568) (62) (595) (24) (25) (287) (27) Past service credit – redundancies 1 — 7 — — — — — — Special termination benefit cost – redundancies (5) (2) (55) — — — — — — Past service cost – augmentations — — (5) — — — — — — Past service cost – plan amendments — — (34) — — — — — — Medicare subsidy received — — — — — — (25) (22) (19) Employee contributions (1) (1) (1) — — — — — — Benefits paid 731 752 837 371 374 398 144 156 141 Exchange adjustments — — — 804 (362) (514) 362 (169) (254) Reclassification to held for sale (note 10) — — — 460 — — 149 — — Closing defined benefit obligations (13,645) (12,844) (14,276) (6,931) (8,085) (7,155) (3,031) (3,697) (3,508) Changes in the value of plan assets 2021 2020 2019 £m £m £m Opening fair value of plan assets 23,748 24,793 23,858 Interest income 613 728 749 Return on plan assets in excess of/(less than) interest¹ 2,554 (1,240) 490 Administration costs (18) (16) (14) Employer contributions 274 327 419 Employee contributions 1 1 1 Benefits paid (1,244) (1,279) (1,377) Exchange adjustments (980) 434 667 Reclassification to held for sale (note 10) (560) — — Closing fair value of plan assets 24,388 23,748 24,793 Actual return on plan assets 3,167 (512) 1,239 Expected contributions to plans in the following year 212 269 307 1. This includes actuarial losses from the purchase of buy-in policies of £0.1 billion (2020: £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 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Opening fair value of plan assets 14,364 15,507 15,330 6,972 6,646 6,030 2,412 2,640 2,498 Interest income 334 366 389 208 259 256 71 103 104 Return on plan assets in excess of/ 581 (908) 457 1,151 (26) 62 822 (306) (29) Administration costs (9) (9) (6) (7) (6) (7) (2) (1) (1) Employer contributions 138 156 174 110 153 231 26 18 14 Employee contributions 1 1 1 — — — — — — Benefits paid (729) (749) (838) (371) (374) (398) (144) (156) (141) Exchange adjustments — — — (721) 320 472 (259) 114 195 Reclassification to held for sale (note 10) — — — (433) — — (127) — — Closing fair value of plan assets 14,680 14,364 15,507 6,909 6,972 6,646 2,799 2,412 2,640 Actual return on plan assets 915 (542) 846 1,359 233 318 893 (203) 75 Expected contributions to plans in the following year 93 137 148 113 125 150 6 7 9 1. This includes actuarial losses from the purchase of buy-in policies of £0.1 billion (2020: £0.7 billion). 25. Pensions and other post-retirement benefits continued Main defined benefit 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. The most significant risks associated with the DB plans are: • investment risk – the plans invest in a variety of asset classes, with actual returns likely to differ from the underlying discount rate adopted, impacting the funding position of the plan through the net balance sheet asset or liability. Each plan seeks to balance the level of investment return required with the risk that it can afford to take, to design the most appropriate investment portfolio. Volatility will be controlled through using liability-matching asset strategies including bulk annuities, as well as interest rate hedging and management of foreign exchange exposure, and diversification of the return-seeking assets; • changes in bond yields – liabilities are calculated using discount rates set with reference to the yields on high-quality corporate bonds prevailing in the UK and US debt markets and will fluctuate as yields change; • member longevity – longevity is a key driver of liabilities and changes in life expectancy have a direct impact on liabilities. Improvements in life expectancy will lead to pension payments being paid for longer than expected and benefits ultimately being more expensive. This risk has been partly mitigated by recent scheme investment transactions including a longevity insurance contract (longevity swap) for NGEG of ESPS and three separate buy-in policies for NGUKPS Section A and B; • counterparty risk – is managed by having a diverse range of counterparties and through having a strong collateralisation process (including for the longevity swap held by NGEG of ESPS). Measurement and management of counterparty risk is delegated to the relevant investment managers. For our bulk annuity policies, various termination provisions were introduced in the contracts, managing our exposure to counterparty risk. The insurers’ operational performance and financial strength are monitored on a regular basis; • currency risk – fluctuations in the value of foreign denominated assets due to exposure to currency exchange rates is managed through a combination of segregated currency hedging overlay and currency hedging carried out by some of the investment managers; and • inflation risk – changes in inflation will affect the current and future pensions but are partially mitigated through investing in inflation-matching assets and hedging instruments as well as bulk annuity buy-in policies. Defined benefit investment strategies 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. Where appropriate, the strategies may include interest rate and inflation hedging instruments, and currency hedging to hedge specific risks. 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 positio

Provisions

Provisions	12 Months Ended
	Mar. 31, 2021
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Provisions	26. Provisions Provisions are recognised 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 majority of our provisions relate to environmental remediation, specifically in relation to certain Superfund sites in the US, being sites we own or have owned in the past where hazardous substances are present as a result of the historic operations of manufactured gas plants in Brooklyn, New York. We also recognise provisions for decommissioning costs for various assets we would be required to remove at the end of their lives, the costs associated with restructuring plans and for lease contracts we have entered into that are now loss-making. In determining the quantum of the provision we recognise, we make estimates in relation to management’s best judgement of the evaluation of the likelihood and the probability of exposure to potential loss, and the costs that would be incurred. Should circumstances change following unforeseeable developments, the likelihood or quantum 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. The quantum of the provision recognised for decommissioning, environmental, restructuring and other costs is based on estimated future expenditure, 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. Provisions to decommission significant portions of our regulated transmission and distribution assets are not recognised where no legal obligations exist, and a realistic alternative exists to incurring costs to decommission assets at the end of their life. In any case, even if a legal or constructive obligation did exist, it is not currently determinable when remediation work would take place and therefore no provision would be recorded at this point. 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 Other £m Total provisions £m At 1 April 2019 1,639 188 83 289 2,199 Exchange adjustments 82 5 — 10 97 Additions¹ 437 93 7 52 589 Unused amounts reversed (29) (16) (16) (9) (70) Unwinding of discount 65 5 — 7 77 Utilised (123) (21) (39) (55) (238) At 31 March 2020 2,071 254 35 294 2,654 Exchange adjustments (185) (9) (1) (21) (216) Additions 26 42 11 67 146 Unused amounts reversed (38) (27) — (16) (81) Unwinding of discount 66 7 — 5 78 Utilised (161) (16) (19) (62) (258) Reclassification to held for sale (note 10) (79) (7) — (10) (96) At 31 March 2021 1,700 244 26 257 2,227 2021 2020 £m £m Current 260 348 Non-current 1,967 2,306 2,227 2,654 1. For the year ended 31 March 2020, £402 million of additions related to exceptional environmental provisions, of which £76 million related to the impact of the change in the real discount rate from 1% to 0.5% during the year (see note 5 for details). 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: 2021 2020 Discounted £m Undiscounted £m Real discount rate Discounted £m Undiscounted £m Real discount rate UK sites 167 171 0.5 % 175 184 0.5 % US sites 1,533 1,583 0.5 % 1,896 1,955 0.5 % 1,700 1,754 2,071 2,139 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 15 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 10 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 primarily include £160 million (2020: £174 million) of expenditure relating to asset retirement obligations estimated to be incurred until 2104 and £60 million (2020: £74 million) of expenditure relating to the demolition of gas holders, which is estimated to be incurred until 2026. Restructuring provisions In 2021, we are undertaking the design and implementation of our new operating model in both our UK and US businesses, which resulted in the recognition of a £11 million provision in the year. The income statement expense relating to the provision has been treated as an exceptional item, and details are provided in note 5. Other provisions Included within other provisions at 31 March 2021 are the following amounts: • £166 million (2020: £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 years, but we currently expect that cash flows will be incurred until 2049; • £21 million (2020: £37 million) in respect of legacy provisions recognised following the sale of UK Gas Distribution; • £27 million (2020: £31 million) in respect of onerous lease commitments and rates payable on surplus properties with expenditure expected to be incurred until ###; and • £13 million (2020: £17 million) in respect of emissions provisions.

Share capital

Share capital	12 Months Ended
	Mar. 31, 2021
Share Capital, Reserves And Other Equity Interest [Abstract]
Share capital	27. 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 2019 3,687 458 Issued during the year in lieu of dividends¹ 93 12 At 31 March 2020 3,780 470 Issued during the year in lieu of dividends¹ 35 4 At 31 March 2021 3,815 474 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 2021, the Company held 266 million (2020: 272 million) of its own shares. The market value of these shares as at 31 March 2021 was £2,296 million (2020: £2,574 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 2021: i. During the year, 4 million (2020: 3 million) treasury shares were gifted to National Grid Employee Share Trusts and 2 million (2020: 2 million) treasury shares were re-issued in relation to employee share schemes, in total representing approximately 0.2% (2020: 0.1%) of the ordinary shares in issue as at 31 March 2021. The nominal value of these shares was £1 million (2020: £1 million) and the total proceeds received were £17 million (2020: £17 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 £2 million (2020: £6 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 272 million (2020: 277 million) representing approximately 7.1% (2020: 7.3%) of the ordinary shares in issue as at 31 March 2021 and having a nominal value of £34 million (2020: £34 million).

Other equity reserves

Other equity reserves	12 Months Ended
	Mar. 31, 2021
Disclosure of reserves within equity [abstract]
Other equity reserves	28. 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 or fair value movements on certain financial instruments that the Company holds. Other equity reserves comprise the translation reserve (see accounting policy C in note 1), cash flow hedge reserve and the cost of hedging reserve (see note 32), 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 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 FVOCI equity £m FVOCI Own Capital redemption £m Merger £m Total £m At 1 April 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 adjustments 1,2 360 — — — — — — — — 360 Net (losses)/gains taken to equity — (206) (107) — — 2 7 — — (304) Share of net gains of associates taken to equity — 1 — — — — — — — 1 Transferred to profit or loss — 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 750 61 17 — 34 48 13 19 (5,165) (4,223) Exchange adjustments 1,2 560 — — — — — — — — 560 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 1 April 2020 1,310 (75) (50) — 25 31 10 19 (5,165) (3,895) Exchange adjustments¹ (1,345) — — — — — — — — (1,345) Net gains/(losses) taken to equity — 14 11 — 36 80 (11) — — 130 Share of net gains of associates taken to equity — 1 — — — — — — — 1 Transferred to profit or loss — 56 3 — — — — — — 59 Net losses in respect of cash flow hedging of capital expenditure — (14) — — — — — — — (14) Tax — (13) 8 — (10) — 2 — — (13) Cash flow hedges transferred to the statement of financial position, net of tax — (17) — — — — — — — (17) At 31 March 2021 (35) (48) (28) — 51 111 1 19 (5,165) (5,094) 1. The exchange adjustments recorded in the translation reserve comprise a loss of £1,507 million (2020: gain of £545 million; 2019: gain of £896 million) relating to the translation of foreign operations offset by a gain of £183 million (2020: gain of £5 million; 2019: loss of £550 million) relating to borrowings, cross-currency swaps and foreign exchange forward contracts used to hedge the net investment in non-sterling denominated subsidiaries. 2. Comparative amounts have been revised as described in note 1F.

Net debt

Net debt	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Net debt	29. Net debt We define net debt as the amount of borrowings and overdrafts less cash, current financial investments and related financing derivatives. (a) Composition of net debt Net debt is comprised as follows: 2021 2020 2019 £m £m £m Cash and cash equivalents 157 73 252 Current financial investments 2,342 1,998 1,981 Borrowings (31,220) (30,794) (28,730) Financing derivatives¹ 175 133 (32) (28,546) (28,590) (26,529) 1. The financing derivatives balance included in net debt excludes the commodity derivatives (see note 17). (b) Analysis of changes in net debt Notes Cash and cash equivalents £m Financial investments £m Borrowings £m Financing derivatives £m Total 1 £m At 1 April 2018 329 2,694 (26,625) 600 (23,002) Impact of transition to IFRS 9 37 — — (32) — (32) Cash flow 29(c) (80) (846) (240) 422 (744) Fair value gains and losses — 14 (9) (1,011) (1,006) Foreign exchange movements 3 79 (724) — (642) Interest income/(charges) 6 — 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 37 — — (474) — (474) Cash flow 29(c) (183) (42) 450 450 675 Fair value gains and losses — 1 (57) (246) (302) Foreign exchange movements 4 24 (807) — (779) Interest income/(charges) 6 — 34 (1,092) (39) (1,097) Other non-cash movements — — (84) — (84) At 1 April 2020 73 1,998 (30,794) 133 (28,590) Cash flow 29(c) 95 429 (2,336) 4 (1,808) Fair value gains and losses — 14 159 31 204 Foreign exchange movements (7) (106) 1,710 — 1,597 Interest income/(charges) 6 — 7 (946) 7 (932) Other non-cash movements — — (136) — (136) Reclassification to held for sale 10 (4) — 1,123 — 1,119 At 31 March 2021 157 2,342 (31,220) 175 (28,546) Balances at 31 March 2021 comprise: Non-current assets — — — 514 514 Current assets 157 2,342 — 428 2,927 Current liabilities — — (3,737) (70) (3,807) Non-current liabilities — — (27,483) (697) (28,180) 157 2,342 (31,220) 175 (28,546) 1. Includes accrued interest at 31 March 2021 of £263 million (2020: £246 million; 2019: £223 million). 2. Cash flows on current financial investments are comprised of £7 million (2020: £35 million; 2019: £24 million) of interest received and £436 million of cash inflows (2020: £7 million outflows; 2019: £822 million outflows) of net cash flow movements in short-term financial investments, as presented in the consolidated cash flow statement. 29. Net debt continued (c) Reconciliation of cash flow from liabilities within net debt to cash flow statement 2021 2020 2019 Borrowings and other Financing derivatives Borrowings and other Financing derivatives Borrowings and other Financing derivatives Cash flows per financing activities section of cash flow statement: Proceeds received from loans 5,645 — 4,218 — 2,932 — Repayment of loans (1,663) — (3,253) — (1,969) — Payments of lease liabilities (112) — (121) — (70) — Net movements in short-term borrowings (759) — (424) — 179 — Cash inflows on derivatives — 58 — 62 — 221 Cash outflows on derivatives — (185) — (249) — (186) Interest paid (804) (31) (904) (53) (856) (58) Cash flows per financing activities section of cash flow statement 2,307 (158) (484) (240) 216 (23) Adjustments: Non-net debt-related items 29 — 34 — 24 — Derivative cash inflow in relation to capital expenditure — 10 — 13 — 13 Derivative cash inflows per investing section of cash flow statement — 225 — 58 — 17 Derivative cash outflows per investing section of cash flow statement — (81) — (281) — (429) Cash flows relating to financing liabilities within net debt 2,336 (4) (450) (450) 240 (422) Analysis of changes in net debt: Borrowings 2,336 — (450) — 240 — Financing derivatives — (4) — (450) — (422) Cash flow movements relating to financing liabilities within net debt 2,336 (4) (450) (450) 240 (422) (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. For the purposes of this table, the liabilities arising from financing activities are those for which cash flows were, or future cash flows will be, classified in the consolidated cash flow statement within financing activities. As a result we have separately disclosed the reconciliation below, excluding derivatives associated with our net investment hedges and derivatives associated with the hedging of capital expenditure, given that they are both classified in the consolidated cash flow statement within investing activities. Notes Borrowings £m Financing derivatives £m Total £m At 1 April 2018 (26,625) 553 (26,072) Impact of transition to IFRS 9 37 (32) — (32) Cash flow 29(c) (240) 23 (217) Fair value gains and losses (9) (334) (343) Foreign exchange movements (724) — (724) Interest charges 6 (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 37 (474) — (474) Cash flow 29(c) 450 240 690 Fair value gains and losses (57) (231) (288) Foreign exchange movements (807) — (807) Interest charges 6 (1,092) (9) (1,101) Other non-cash movements (84) — (84) At 1 April 2020 (30,794) 228 (30,566) Cash flow 29(c) (2,336) 158 (2,178) Fair value gains and losses 159 (301) (142) Foreign exchange movements 1,710 — 1,710 Interest charges 6 (946) 11 (935) Other non-cash movements (136) — (136) Reclassification to held for sale 10 1,123 — 1,123 At 31 March 2021 (31,220) 96 (31,124)

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Mar. 31, 2021
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Commitments and contingencies	30. 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. 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. 2021 2020 £m £m Future capital expenditure Contracted for but not provided 2,716 2,629 Energy purchase commitments¹ Less than 1 year 1,255 1,365 In 1 to 2 years 894 890 In 2 to 3 years 975 973 In 3 to 4 years 959 955 In 4 to 5 years 896 861 More than 5 years 10,805 11,314 15,784 16,358 Guarantees² Guarantee of sublease for US property (expires 2040) 149 173 Guarantees of certain obligations of Grain LNG (expire up to 2025) 33 34 Guarantees of certain obligations for construction of HVDC West Coast Link (expected expiry 2059) 85 92 Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates)² 584 683 Guarantees of certain obligations of St William Homes LLP (various expiry dates)³ 53 30 Guarantees of certain obligations of National Grid IFA 2 Limited (expected expiry 2022)² 170 564 Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024) 1,276 1,096 Other guarantees and letters of credit (various expiry dates) 486 150 2,836 2,822 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 £136 million (2020: £358 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, 2021
Related party transactions [abstract]
Related party transactions	31. 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: 2021 2020 2019 £m £m £m Sales: Goods and services supplied to a pension plan 3 5 5 Sales: Goods and services supplied to joint ventures¹ 79 101 151 Sales: Goods and services supplied to associates² 1 33 192 Purchases: Goods and services received from joint ventures³ 35 61 26 Purchases: Goods and services received from associates³ 43 56 141 Receivable from joint ventures 4 263 255 584 Receivable from associates 4 — 1 368 Payable to joint ventures 17 — 8 Payable to associates 3 4 12 Interest income from joint ventures — 2 5 Interest income from associates — 8 23 Dividends received from joint ventures 5 49 34 30 Dividends received from associates 6 32 41 171 1. During the year, £14 million (2020: £38 million; 2019: £139 million) of property sites were sold to St William Homes LLP, £50 million of sales were made to Emerald Energy Venture LLC (2020: £21 million; 2019: £nil) and a further £6 million (2020: £32 million; 2019; £2 million) of sales were made to NGET/SPT Upgrades Limited. 2. In previous years, sales related 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) and included income of £31 million in 2020 and £52 million in 2019 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, £41 million (2020: £31 million; 2019: £30 million) of purchases from Millennium Pipeline Company LLC. The Group also purchased assets of £5 million (2020: £58 million; 2019: £26 million) from NGET/SPT Upgrades Limited (a joint venture). 4. Amounts receivable from joint ventures include £241 million (2020: £242 million; 2019: £325 million) in relation to St William Homes LLP. There are no longer loans receivable from Quadgas (2020: £nil; 2019: £352 million) and Nemo Link (a joint venture) (2020: £nil; 2019: £258 million). 5. Includes dividends of £18 million (2020: £25 million; 2019: £30 million) received from BritNed Development Limited and £25 million (2020: £8 million; 2019:£ nil) from Nemo Link Limited. 6. Includes dividends of £31 million (2020: £32 million; 2019: £24 million) received from Millennium Pipeline Company LLC. Dividends of £133 million were received from Quadgas in 2019.

Financial risk management

Financial risk management	12 Months Ended
	Mar. 31, 2021
Financial Instruments [Abstract]
Financial risk management	32. 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. The categories of hedging entered into 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 on 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 2021, the following limits were in place for investments and derivative financial instruments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 2,259 1,129 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,232 616 Double ‘A+’ G7 sovereign entities (AA+) 2,054 1,027 Double ‘A’ range institutions (AA) 822 to 1,027 411 to 513 Single ‘A’ range institutions (A) 288 to 411 144 to 205 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 2021 and 2020, 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 services have 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. Since 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 (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 would only be reported net in the balance sheet if the transactions were with the same counterparty, a currently enforceable legal right of offset exists, and the cash flows were 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, there are no ‘Gross amounts offset’ under cash pooling arrangements (2020: £23 million). Our UK bank accounts for National Grid subsidiaries previously participated in GBP, EUR and USD Composite Accounting System overdraft facilities subject to offsetting gross and net overdraft limits. EUR and USD offsetting arrangements have been discontinued in the year and GBP offsetting arrangements have no impact as at 31 March 2021. 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 2021 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 942 — 942 (234) (561) 147 Commodity contract derivatives 57 — 57 (8) — 49 999 — 999 (242) (561) 196 Liabilities Financing derivatives (767) — (767) 234 467 (66) Commodity contract derivatives (132) — (132) 8 4 (120) (899) — (899) 242 471 (186) 100 — 100 — (90) 10 Related amounts At 31 March 2020 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 1,267 — 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) 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, restrictions on disposals 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 payment profile of our financial liabilities and derivatives: At 31 March 2021 Less than £m 1 to 2 2 to 3 More than Total Non-derivative financial liabilities Borrowings, excluding lease liabilities (3,350) (1,690) (806) (25,562) (31,408) Interest payments on borrowings¹ (810) (755) (731) (12,018) (14,314) Lease liabilities (118) (108) (90) (599) (915) Other non-interest-bearing liabilities (3,207) (350) — — (3,557) Contingent consideration (40) (24) — — (64) Derivative financial liabilities Financing derivatives – receipts² 3,773 749 451 4,326 9,299 Financing derivatives – payments² (3,899) (877) (533) (5,153) (10,462) Commodity contract derivatives – receipts² 12 — — — 12 Commodity contract derivatives – payments² (83) (23) (14) (12) (132) Derivative financial assets Financing derivatives – receipts² 2,162 926 833 1,789 5,710 Financing derivatives – payments² (1,700) (834) (780) (1,536) (4,850) Commodity contract derivatives – receipts² 21 4 1 1 27 Commodity contract derivatives – payments² (21) (4) (2) — (27) (7,260) (2,986) (1,671) (38,764) (50,681) At 31 March 2020 Less than 1 year £m 1 to 2 2 to 3 years £m More than 3 years £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) 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: 2021 2020 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 63 — 94 — 157 18 — 55 — 73 Financial investments 1,215 — 1,127 — 2,342 813 — 1,185 — 1,998 Borrowings (12,210) (5,351) (12,660) (999) (31,220) (12,407) (4,150) (13,217) (1,020) (30,794) Pre-derivative position (10,932) (5,351) (11,439) (999) (28,721) (11,576) (4,150) (11,977) (1,020) (28,723) Derivative effect (826) 5,459 (5,494) 1,036 175 (1,169) 4,341 (4,214) 1,175 133 Net debt position (11,758) 108 (16,933) 37 (28,546) (12,745) 191 (16,191) 155 (28,590) 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: 2021 2020 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 282 — 1,387 — 1,669 306 — 1,403 — 1,709 Trade and other payables (1,207) — (1,878) — (3,085) (1,177) — (2,002) — (3,179) Other non-current liabilities (77) — (288) — (365) (85) — (277) — (362) 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. 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). Gains and losses arising from 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. 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 will impact the valuations of certain liabilities. We have disclosed our exposure to LIBOR on our derivative portfolio in note 17, on our borrowings in note 21 and on our hedging arrangements in note 32(e). We are managing the risk by planning to replace LIBOR cash flows with alternative reference rates on our affected contracts. The migration project is underway, with all affected contracts expected to be amended by 31 December 2021. As at 31 March 2021 no contracts had yet been amended. The Finance Committee of the Board have delegated to the treasury department the authority to determine which benchmarks are the most appropriate. A combination of LIBOR and the successor benchmarks, primarily GBP Sterling Overnight Index Average (SONIA) and USD Secured Overnight Financing Rate (SOFR) will be used in the portfolio during the migration period. 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: 2021 2020 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 64 67 — 26 157 71 10 — (8) 73 Financial investments — 2,309 — 33 2,342 — 1,966 — 32 1,998 Borrowings (23,163) (1,762) (6,295) — (31,220) (20,969) (3,085) (6,740) — (30,794) Pre-derivative position (23,099) 614 (6,295) 59 (28,721) (20,898) (1,109) (6,740) 24 (28,723) Derivative effect 2,869 (2,511) (183) — 175 2,259 (1,892) (234) — 133 Net debt position (20,230) (1,897) (6,478) 59 (28,546) (18,639) (3,001) (6,974) 24 (28,590) 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 Phase I of IFRS Interest Rate Benchmark Reform amendments related to hedge accounting with effect from 1 April 2019, and Phase II with effect from 1 April 2020. The amendments impact our fair value hedging relationships where derivative cash flows will be transitioned from paying LIBOR to paying an alternative reference rate. The hedged risk must be re-documented to reflect this, and 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 earliest point in time of the Group’s contracts that reference LIBOR being amended, the hedging relationship being formally discontinued or formal market conventions ending uncertainty being 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 7, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Year ended 31 March 2021 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 gains/(losses) in respect of: Cash flow hedges — 14 (14) — Cost of hedging (15) (24) — 50 Transferred to profit or loss in respect of: Cash flow hedges — 56 — — Cost of hedging 1 2 — — Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (30) — 6 Consolidated statement of financial position Derivatives – carrying value of hedging instruments ¹ Assets – current — 10 2 5 Assets – non-current 187 59 1 140 Liabilities – current — (12) (24) (17) Liabilities – non-current (113) (255) (22) — Profiles of the significant timing, price and rate information of hedging instruments Maturity range Jan 2023 – Jan 2043 Sep 2021 – Nov 2040 Apr 2021 – Feb 2027 Mar 2022 – Sep 2027 Spot foreign exchange range: GBP:USD 1.64 1.30 – 1.66 1.31 – 1.41 1.22 – 1.40 GBP:EUR 1.11 – 1.24 1.08 – 1.24 1.04 – 1.29 1.15 – 1.16 EUR:USD 1.13 – 1.17 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+408bps 0.976% – 5.845% n/a n/a USD LIBOR +68bps/+115bps 2.513% – 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 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 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 2021 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 (2,755) 121 (85) 153 (127) 26 1. The carrying value of the hedged borrowings is £2,714 million, of which £nil is current and £2,714 million is non-current. 2. Included within the hedging instrument notional balance is £2,679 million impacted by Interest Rate Benchmark Reform amendments. 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 was £1,883 million, of which £72 million was current and £1,811 million was non-current. 2. Included within the hedging instrument notional balance was £1,675 million impacted by Interest Rate Benchmark Reform amendments. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2021 Balance in cash flow hedge reserve Change in value used for calculating ineffectiveness Hedging instrument noti

Borrowing facilities

Borrowing facilities	12 Months Ended
	Mar. 31, 2021
Disclosure of detailed information about borrowings [abstract]
Borrowing facilities	33. Borrowing facilities To support our liquidity requirements and provide backup to commercial paper and other borrowings, we agree committed credit 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 2021, we had bilateral committed credit facilities of £5,410 million (2020: £5,495 million). In addition, we had committed credit facilities from syndicates of banks of £115 million at 31 March 2021 (2020: £277 million). All committed credit facilities were undrawn in 2021 and 2020. An analysis of the maturity of these undrawn committed facilities is shown below: 2021 2020 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — — In 1 to 2 years 1,668 1,940 In 2 to 3 years 534 1,668 In 3 to 4 years 1,718 277 In 4 to 5 years 1,605 1,887 More than 5 years — — 5,525 5,772 Of the unused facilities at 31 March 2021, £5,410 million (2020: £5,495 million) is available for liquidity purposes, while £115 million (2020: £277 million) is available as backup to specific US borrowings. £1,668 million of the undrawn bilateral facilities due to mature in one to two years, were renegotiated between 1 April 2021 and 19 May 2021, with an uplift in the amount committed to £1,861 million with new expiry dates to May 2024. Of the £534 million of undrawn committed borrowings facilities due to expire within two to three years, £150 million was renegotiated between 1 April 2021 and 19 May 2021, with the expiry extended by a further year to June 2024. £400 million of additional undrawn bilateral facilities were entered into subsequent to the year end with expiry dates in May 2024. In addition, we have the following facilities which are not included in the table above: • for the separately regulated business of National Grid Electricity System Operator Limited, the Group has a facility of £550 million (2020: £550 million). This facility is not available as Group general liquidity support; • the Group has Export Credit Agency (ECA) facilities totalling £1,345 million (2020: £901 million), of which £446 million (2020: £233 million) is undrawn; and • the Group has two new loan facilities in place relating to the acquisition of PPL Western Power Distribution Investments Limited (WPD) (see note 38). A facility of £8,250 million (31 March 2020: £nil) to finance the consideration and a facility of £1,105 million (31 March 2020: £nil) to back up acquired debt which contains change of control provisions, of which £8,250 million and £1,105 million is undrawn. Subsequent to the year end the £1,105 million facility has been cancelled as waivers have been obtained by WPD in relation to the change of control clauses.

Subsidiary undertakings, joint

Subsidiary undertakings, joint ventures and associates	12 Months Ended
	Mar. 31, 2021
Interests In Other Entities [Abstract]
Subsidiary undertakings, joint ventures and associates	16. 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 a share of 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. 2021 2020 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 341 654 995 291 317 608 Exchange adjustments (22) (36) (58) 20 12 32 Additions 6 75 81 16 156 172 Capitalisation of shareholder loan to Nemo Link Limited — — — — 176 176 Share of post-tax results for the year 30 28 58 40 47 87 Share of other comprehensive income of associates, net of tax 1 — 1 1 — 1 Dividends received (31) (49) (80) (41) (34) (75) Other movements¹ (96) (34) (130) 14 (20) (6) Share of net assets at 31 March 229 638 867 341 654 995 1. Within associates, the other movements for the year primarily relates to the reclassification of an investment in an associate to financial investments. 16. Investments in joint ventures and associates continued 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 £141 million (2020: £240 million) in relation to joint ventures. At 31 March 2021, 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 Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m Statement of financial position Non-current assets 409 399 795 910 536 582 559 435 Cash and cash equivalents 47 54 27 33 31 26 112 66 All other current assets 24 4 24 26 8 5 12 6 Non-current liabilities (81) (45) (256) (315) (30) (29) (286) (232) Current liabilities (22) (16) (38) (43) (19) (10) (27) (2) Net assets 377 396 552 611 526 574 370 273 Group’s ownership interest 189 198 145 160 263 287 189 139 Group adjustment: elimination — — — — — — (23) (10) Carrying amount of the Group’s investment 189 198 145 160 263 287 166 129 BritNed Development Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m Income statement Revenue 72 80 199 206 66 45 28 19 Depreciation and amortisation (15) (14) (43) (46) (24) (23) (14) (7) Other costs (15) (10) (21) (20) (6) (8) (22) (10) Operating profit/(loss) 42 56 135 140 36 14 (8) 2 Net interest expense (1) — (18) (22) — — — (3) Profit/(loss) before tax 41 56 117 118 36 14 (8) (1) Income tax expense (11) (10) — — (14) (2) — — Profit/(loss) for the year 30 46 117 118 22 12 (8) (1) Group’s share of profit/(loss) 15 23 31 31 11 6 (4) (1) Group adjustment: tax charge — — (9) (9) — — 1 — Group’s share of post-tax results for the year 15 23 22 22 11 6 (3) (1) 34. 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 2021 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 (US) Investments 2 Limited, National Grid Hong Kong Limited, National Grid Luxembourg SARL 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. All entities incorporated in the United States are taxed in the United States on their worldwide income other than where indicated in the footnotes below. Other entities are tax resident in their jurisdiction of incorporation other than where indicated in the footnotes below. 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 1 NatgridTW1 Limited 1 National Grid Belgium Limited 2 * National Grid Blue Power Limited 2 * 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 2 * National Grid Fourteen Limited 2 * National Grid Gas Holdings Limited National Grid Gas plc National Grid Grain LNG Limited National Grid Holdings Limited 1 National Grid Holdings One plc National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited 1 National Grid Metering Limited National Grid North Sea Link Limited National Grid Offshore Limited National Grid Partners Limited National Grid Plus Limited National Grid Property Holdings Limited National Grid Seventeen Limited 2 * National Grid Smart Limited National Grid Ten National Grid Thirty Five Limited 2 * National Grid Thirty Six Limited National Grid Twelve Limited 1 National Grid Twenty Eight Limited National Grid Twenty-Five Limited 2 * National Grid Twenty Seven Limited National Grid Twenty Three Limited 1 National Grid UK Limited National Grid UK Pension Services Limited National Grid (US) Holdings Limited 1 National Grid (US) Investments 2 Limited 1 National Grid (US) Investments 4 Limited 1 National Grid (US) Partner 1 Limited 1 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 2 * 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%) 3 1. Companies where National Grid plc has issued guarantees over the liabilities of the companies as at 31 March 2021 and for which the companies are taking the exemption from the requirements of an audit for their individual financial statements as permitted by section 479A of the Companies Act. 2. Registered office: c/o KPMG, 15 Canada Square, London E14 5GL, UK. 3. 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). Agave Solar, LLC Altona Solar, LLC Apple River Solar, LLC Apple Solar, LLC Argenta Solar, LLC Armenia Solar, LLC Artemisia Solar, LLC 1 Ashland Solar, LLC Athens Solar, LLC Audubon Wind Farm, LLC Autauga Solar, LLC Baileyville Solar, LLC (previously Ellison Solar, LLC)** Banner Solar, LLC Bazile Creek Wind Farm, LLC Bee Hollow Solar, LLC Bell Plaine Solar, LLC Benevolent Solar, LLC Birdsong Creek Solar, LLC Black Bear Solar, LLC Blackhawk Solar, LLC Blaze Solar, LLC 2 Blevins Solar, LLC Blue Ridge Wind, LLC Blue Spring Solar, LLC Blues Solar, LLC Bluewater Solar, LLC Boone Solar, LLC Boston Gas Company 3 Braeburn Solar, LLC Bridges Solar, LLC Brilliance Solar, LLC British Transco Capital, Inc. 4 British Transco Finance, Inc. 4 Brock Solar, LLC Broken Bridge Corp. 5 Brook Trout Solar, LLC BT Noble Solar, LLC 6 Bullsnake Solar, LLC Burley 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 Cameo Solar, LLC Canary Solar, LLC Canby Solar, LLC Carriere Solar, LLC Cass Wind Farm, LLC Cattle Ridge Wind Farm 2, LLC Cedar Grove Solar, LLC Centennial Solar, LLC Chewelah Solar, LLC Clear Creek Solar, LLC Clermont Solar, LLC Clinton County Solar, LLC Coles Solar, LLC Commonwealth Solar, LLC Compass Prairie Wind, LLC Coneflower Solar, LLC 1 Conestoga Wind, LLC Copperhead Solar, LLC Creekview Solar, LLC Crocker Wind Farm 2, LLC Dahlia Solar, LLC 1 Dakota Hills Wind Farm, LLC Day Lily Solar, LLC 1 Deatsville Solar, LLC Deer Trail Solar, LLC Dodson Creek Solar, LLC 7 Donnellson Solar, LLC East Galesburg Solar, LLC East Macomb Solar, LLC Eastern Hemlock Solar, LLC Eatonville Solar, LLC Elba Solar, LLC Elburn Solar, LLC Eldena Solar, LLC Elk Creek Solar, LLC Elk Creek Solar 2, LLC EUA Energy Investment Corporation 3 Exie Solar, LLC Falls City Solar, LLC Fayette Solar, LLC 8 Firstview Wind Farm, LLC Fish Creek Solar, LLC Forrest Solar, LLC Fort Solar, LLC Fowlkes Solar, LLC Front Range Wind Farm, LLC Fulton Solar, LLC Gala Solar, LLC Galesburg Solar, LLC Gardenia Solar, LLC 1 Genesee Solar Energy, LLC Gillis Solar, LLC Glenwood Solar, LLC Golden Solar, LLC Goldendale Solar, LLC Goldenrod Wind Farm, LLC Goldfinch Solar, LLC Grand Junction Solar, LLC Granite State Power Link LLC 4 Grant Solar, LLC Grant Solar 2, LLC Grayson Solar, LLC Greenbrier Creek Solar, LLC Greensky Solar, LLC Greenwood Solar, LLC Grid NY LLC 9 Grindstone Wind Farm, LLC 10 Hale County Solar, LLC Hale Solar, LLC Hampton Solar, LLC Hansford Energy Storage, LLC Harmony Solar ND, LLC Harmony Solar ND 2, LLC Harrington Solar, LLC Hartley Solar, LLC Hearth Solar, LLC Heyworth Solar, LLC Hill River Solar, LLC Honeybee Solar, LLC Hoosier Solar, LLC Hoskins Solar, LLC Illumination Solar, LLC Innovation Solar, LLC Irwin Solar, LLC Itasca Energy Development, LLC 1 Itasca Energy Services, LLC Jackalope Solar, LLC Jack Rabbit Wind, LLC Jackson County Solar, LLC Jantz Solar, LLC Jonagold Solar, LLC Junction Solar, LLC Kankakee Solar, LLC KeySpan CI Midstream Limited 4 KeySpan Energy Corporation 9 KeySpan Energy Services Inc. 4 KeySpan Gas East Corporation 9 KeySpan International Corporation 4 KeySpan MHK, Inc. 4 KeySpan Midstream Inc. 4 KeySpan Plumbing Solutions, Inc. 9 Kindle Solar, LLC Kingsnake Solar, LLC Knox Solar, LLC KSI Contracting, LLC 4 KSI Electrical, LLC 4 KSI Mechanical, LLC 4 Lake Charlotte Solar, LLC Lake Iris Solar, LLC Lakeside Solar, LLC Lamdin Solar, LLC Land Management & Development, Inc. 9 Landwest, Inc. 9 Lansing Solar, LLC Lawrence Solar, LLC Leola Wind Farm, LLC Liberty Solar, LLC Lilac Solar, LLC 1 Limestone Solar, LLC Lind Solar, LLC Livingston County Solar, LLC Long Mount Solar, LLC 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Incorporated in the US continued Lordsburg Solar, LLC Louisa Solar, LLC Lowlands Solar, LLC Lydia Solar, LLC Macedonia Solar, LLC Madden Creek Solar, LLC Marion County Solar, LLC Massachusetts Electric Company 3 Maverick Wind Farm, LLC Mazon Solar, LLC Mazon Solar 2, LLC McFadden Solar, LLC Meadowlands Solar, LLC Merton Solar, LLC Metrowest Realty LLC 4 Miller Creek Solar, LLC Millers Ferry Solar, LLC Moonrise Solar, LLC Morgan County Solar, LLC Morning Glory Solar, LLC 1 Mountain Laurel Solar, LLC Muddy Creek Solar, LLC Mustang Ridge Wind Farm, LLC Mystic Steamship Corporation 7 Nantucket Electric Company 3 National Grid Algonquin LLC 4 National Grid Connect Inc. 4 National Grid Development Holdings Corp. 4 National Grid Electric Services LLC 9 National Grid Energy Management LLC 4 National Grid Energy Services LLC 4 National Grid Energy Trading Services LLC 9 National Grid Engineering & Survey Inc. 9 National Grid Generation LLC 9 National Grid Generation Ventures LLC 11 National Grid Glenwood Energy Center, LLC 4 National Grid IGTS Corp. 9 National Grid Insurance USA Ltd 12 National Grid Islander East Pipeline LLC 4 National Grid LNG GP LLC 4 National Grid LNG LLC 4 National Grid LNG LP LLC 4 National Grid Millennium LLC 4 National Grid NE Holdings 2 LLC 3 National Grid North America Inc. 4 National Grid North East Ventures Inc. 4 National Grid Partners Inc. 9 National Grid Partners LLC 4 National Grid Port Jefferson Energy Center LLC 4 National Grid Renewables, LLC (previously NGV Emerald Acquisition Co., LLC) 4 National Grid Renewables Development, LLC (previously Geronimo Energy, LLC) National Grid Renewables E Wind, LLC (previously Geronimo E Wind LLC) 1 National Grid Renewables Operations, LLC 4 National Grid Renewables Projects, LLC (previously Geronimo Solar Energy, LLC) 1 National Grid Renewables Stutsman, LLC (previously Geronimo Stutsman Wind Farm, LLC) National Grid Services Inc. 4 National Grid Transmission Services Corporation 3 National Grid US 6 LLC 4,† National Grid US LLC 4 National Grid USA 4 National Grid USA Service Company, Inc. 3 NEES Energy, Inc. 3 New England Electric Transmission Corporation 5 New England Energy Incorporated 3 New England Hydro Finance Company, Inc. (53.704%) 3 New England Hydro-Transmission Corporation (53.704%) 5 New England Hydro-Transmission Electric Company, Inc. (53.704%) 3 New England Power Company 3 Newport America Corporation 13 Newton Solar, LLC NG Renewables Energy Marketing, LLC 4 NG Renewables Energy Services, LLC NGNE LLC 4 NGV Emerald Energy Venture Holdings, LLC 4 NGV OSW Holdings, LLC 4 NGV US Distributed Energy Inc. 4 NGV US, LLC (previously NGV Emerald Holdings, LLC) 4 NGV US Transmission Inc. 4 Niagara Mohawk Energy, Inc. 4 Niagara Mohawk Holdings, Inc. 9 Niagara Mohawk Power Corporation 9 Niobrara Wind, LLC NM Properties, Inc. 9 Noble Storage, LLC Nordic VOS, LLC North Adair Solar, LLC Northeast Renewable Link LLC 4 North East Transmission Co., Inc. 4 North Fork Wind, LLC North Rock Solar, LLC Onton Solar, LLC Opinac North America, Inc. 4 Oreana Solar, LLC Parklawn Solar, LLC Patriotic Solar, LLC Pearl River County Solar, LLC Pennington Solar, LLC Peony Solar, LLC Philadelphia Coke Co., Inc. 4 Pierce County Solar, LLC Pike County Solar, LLC Pinon Pine Solar, LLC Piper Solar, LLC Pipestone Solar, LLC Placedo Solar, LLC Pleasant Plains Solar, LLC Plum Creek Wind Farm, LLC Plum Creek Wind Farm 2, LLC Portage Solar, LLC Port of the Islands North, LLC 9 Prairie Oasis Solar, LLC Prairie Rose Wind 2, LLC 1 Prosperity Wind Farm, LLC Prosperity Wind Farm 2, LLC Radiance Solar, LLC 1 Red Rock Solar SD, LLC Red Wolf Solar, LLC Regal Solar, LLC Regal Solar 2, LLC River North Solar, LLC Robertson Solar, LLC Rochester Solar, LLC 1 Rock Ridge Wind Farm, LLC Rocky Meadow Solar, LLC Rolling Hills Solar, LLC Ross County Solar, LLC 7 Royal Solar, LLC Royal Solar 2, LLC Royerton Solar, LLC Saddle Solar, LLC Saginaw Bay Solar, LLC Sandstone Creek Solar, LLC Sandstone Creek Solar 2, LLC Sapphire Sky Wind Farm, LLC Scorpion Solar, LLC Serenity Solar, LLC 1 Shelby Solar, LLC Sherco Solar, LLC 1 Sherco Solar 2, LLC 1 Silver City Solar, LLC Simpson Solar, LLC (previously Geronimo White Pine Solar, LLC) South Belleville Solar, LLC South Macomb Solar, LLC Spotlight Solar, LLC Spring Brook Solar, LLC Springfield Solar Farm, LLC Spring River Solar, LLC Stockton Solar, LLC Stony Brook Wind, LLC Stony Point Solar, LLC Stove Creek Solar, LLC Sturgis Solar, LLC Summit Lake Solar, LLC Sunbeam Solar, LLC Sunray Solar, LLC Sunrise Solar, LLC Sycamore Creek Solar, LLC Thacker Solar, LLC The Brooklyn Union Gas Company 9 The Narragansett Electric Company 13 Tilton Solar, LLC Torchlight Solar, LLC 1 Transgas Inc. 3 Tri-City Solar, LLC Turquoise Solar, LLC Uintah Solar, LLC Unbridled Solar, LLC (previously Henderson Solar, LLC) Union City Solar, LLC Upper Hudson Development Inc. 9 Valley Appliance and Merchandising Company 13 34. Subsidiary undertakings, joint ventures and associates continued Subsidiary undertakings continued Valley Solar, LLC Vermont Green Line Devco, LLC (90%) 4 Vibrant Solar, LLC Virgo Community Solar Gardens, LLC 1 Virtue Solar, LLC Vivid Solar, LLC Wallowa Solar, LLC Wayfinder Group, Inc. 3 Wayside Solar, LLC Western Hemlock Solar, LLC Wheatfield Solar, LLC White Elm Wind Farm, LLC Wild Springs Solar, LLC 1 Wildcat Ridge Wind Farm, LLC Wildhorse Creek Solar, LLC Willard Solar, LLC Williams County Solar, LLC Wiregrass Solar, LLC Wolf River Solar, LLC Wonder Lake Solar, LLC Woodlands Solar, LLC Worthington Solar, LLC Yellowbud Solar, LLC Yellowhammer Solar, LLC Young County Solar, LLC Yucca Solar, LLC 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 LLP, c/o Charles Reagh, Queen’s Marque, 600-1741 Lower Water Street, Halifax, Nova Scotia, B3J 0J2, 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 † 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, JE4 9WG, Jersey, 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 Incorporated in the Netherlands Registered office: Westblaak 89, 3012 KG Rotterdam, PO Box 21153, 3001 AD, Rotterdam, Netherlands British Transco International Finance B.V. Incorporated in the Republic of Ireland Registered office: c/o Moore Stephens Nathans, Third Floor, Ulysses House, 23/24 Foley Street, Dublin, D01 W2T2, Ireland National Grid Company (Ireland) Designated Activity Company* 1. Registered office: National Grid Renewables Development, LLC, 8400 Normandale Lake Blvd. Suite 1200, Bloomington, MN 55437, USA. 2. Registered office: National Registered Agents, Inc., 160 Greentree Drive, Suite 101, Dover DE 19904, USA. 3. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, USA. 4. Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington DE 19808, USA. 5. Registered office: Corporation Service Company, 10 Ferry Street, Suite 313, Concord NH 03301, USA. 6. Registered office: National Registered Agents, Inc., 1999 Bryan St, Bryan Street, Dallas, Dallas County TX 75201, USA. 7. Registered office: The Corporation Trust Company, Corporation Trust Center, 1209 Orange Street, Wilmington, Delaware, 19801, USA. 8. Registered office: 60 Mine Lake Ct, Mine Lake Court, Suite 200, Raleigh, Wake County, NC 27615, USA. 9. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 10. Registered office: National Registered Agents, Inc., 30600 Telegraph Road, Suite 2345, Bingham Farms, MI 48025-5720, USA. 11. Registered office: Corporation Service Company, 84 State Street, Albany NY 12207, USA. 12. Registered office: One MetroTech Center, Brooklyn NY 11201, USA. 13. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, USA. * In liquidation. ** Name change post 31 March 2021. † Entity is tax resident in the United Kingdom. 34. Subsidiary undertakings, joint ventures and associates continued Joint ventures A list of the Group’s joint ventures as at 31 March 2021 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 ** National Places LLP (50%) 2 Nemo Link Limited (50%) NGET/SPT Upgrades Limited (50%) † St William Homes LLP (50%) 3 Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Bight Wind Holdings, LLC (30%) 4 Clean Energy Generation, LLC (50%) Emerald Energy Venture LLC (51%) Island Park Energy Center, LLC (50%) Islander East Pipeline Company, LLC (50%) 4 LI Energy Storage System, LLC (50%) LI Solar Generation, LLC (50%) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, IFA2 SAS (50%) Associates A list of the Group’s associates as at 31 March 2021 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%) 4 Connecticut Yankee Atomic Power Company (19.5%) 5 Direct Global Power, Inc. (26%) 4 Energy Impact Fund LP (9.41%) 6 KHB Venture LLC (33.33%) 7 Maine Yankee Atomic Power Company (24%) 8 Millennium Pipeline Company, LLC (26.25%) 4 New York Transco LLC (28.3%) 9 NYSEARCH RMLD, LLC (22.63%) The Hive IV, LLC (28.2%) 4 Yankee Atomic Electric Company (34.5%) 10 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 2021 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: 80 Cheapside, London, EC2V 6EE, UK. 3. Registered office: Berkeley House, 19 Portsmouth Road, Cobham, Surrey KT11 1JG, UK. 4. Registered office: The Corporation Trust Company, Corporation Trust Center, 1209 Orange Street, Wilmington DE 19801, USA. 5. Registered office: Carla Pizzella, 362 Injun Hollow Road, East Hampton CT 06424-3099, USA. 6. Registered office: Harvard Business Services, Inc., 16192 Coastal Highway, Lewes DE 19958, Sussex County, USA. 7. Registered office: De Maximus Inc., 135 Beaver Street, 4th Floor, Waltham MA 02452, USA. 8. Registered office: Joseph D Fay, 321 Old Ferry Road, Wiscasset ME 04578, USA. 9. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 10. 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. † 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. The following UK subsidiaries will take advantage of the audit exemption set out within section 479A of the Companies Act 2006 for the year ended 31 March 2021: Company name Company number NatGrid One Limited 5521240 Natgrid TW1 Limited 7579324 National Grid Holdings Limited 3096772 National Grid International Limited 2537092 National Grid Twelve Limited 4355616 National Grid Twenty Three Limited 6999009 National Grid (US) Holdings Limited 2630496 National Grid (US) Investments 2 Limited 3784528 National Grid (US) Investments 4 Limited 3867128 National Grid (US) Partner 1 Limited 4314432

Sensitivites

Sensitivites	12 Months Ended
	Mar. 31, 2021
Disclosure of sensitivity analysis for actuarial assumptions [abstract]
Sensitivities	32. 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. The categories of hedging entered into 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 on 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 2021, the following limits were in place for investments and derivative financial instruments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 2,259 1,129 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,232 616 Double ‘A+’ G7 sovereign entities (AA+) 2,054 1,027 Double ‘A’ range institutions (AA) 822 to 1,027 411 to 513 Single ‘A’ range institutions (A) 288 to 411 144 to 205 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 2021 and 2020, 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 services have 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. Since 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 (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 would only be reported net in the balance sheet if the transactions were with the same counterparty, a currently enforceable legal right of offset exists, and the cash flows were 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, there are no ‘Gross amounts offset’ under cash pooling arrangements (2020: £23 million). Our UK bank accounts for National Grid subsidiaries previously participated in GBP, EUR and USD Composite Accounting System overdraft facilities subject to offsetting gross and net overdraft limits. EUR and USD offsetting arrangements have been discontinued in the year and GBP offsetting arrangements have no impact as at 31 March 2021. 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 2021 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 942 — 942 (234) (561) 147 Commodity contract derivatives 57 — 57 (8) — 49 999 — 999 (242) (561) 196 Liabilities Financing derivatives (767) — (767) 234 467 (66) Commodity contract derivatives (132) — (132) 8 4 (120) (899) — (899) 242 471 (186) 100 — 100 — (90) 10 Related amounts At 31 March 2020 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 1,267 — 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) 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, restrictions on disposals 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 payment profile of our financial liabilities and derivatives: At 31 March 2021 Less than £m 1 to 2 2 to 3 More than Total Non-derivative financial liabilities Borrowings, excluding lease liabilities (3,350) (1,690) (806) (25,562) (31,408) Interest payments on borrowings¹ (810) (755) (731) (12,018) (14,314) Lease liabilities (118) (108) (90) (599) (915) Other non-interest-bearing liabilities (3,207) (350) — — (3,557) Contingent consideration (40) (24) — — (64) Derivative financial liabilities Financing derivatives – receipts² 3,773 749 451 4,326 9,299 Financing derivatives – payments² (3,899) (877) (533) (5,153) (10,462) Commodity contract derivatives – receipts² 12 — — — 12 Commodity contract derivatives – payments² (83) (23) (14) (12) (132) Derivative financial assets Financing derivatives – receipts² 2,162 926 833 1,789 5,710 Financing derivatives – payments² (1,700) (834) (780) (1,536) (4,850) Commodity contract derivatives – receipts² 21 4 1 1 27 Commodity contract derivatives – payments² (21) (4) (2) — (27) (7,260) (2,986) (1,671) (38,764) (50,681) At 31 March 2020 Less than 1 year £m 1 to 2 2 to 3 years £m More than 3 years £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) 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: 2021 2020 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 63 — 94 — 157 18 — 55 — 73 Financial investments 1,215 — 1,127 — 2,342 813 — 1,185 — 1,998 Borrowings (12,210) (5,351) (12,660) (999) (31,220) (12,407) (4,150) (13,217) (1,020) (30,794) Pre-derivative position (10,932) (5,351) (11,439) (999) (28,721) (11,576) (4,150) (11,977) (1,020) (28,723) Derivative effect (826) 5,459 (5,494) 1,036 175 (1,169) 4,341 (4,214) 1,175 133 Net debt position (11,758) 108 (16,933) 37 (28,546) (12,745) 191 (16,191) 155 (28,590) 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: 2021 2020 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 282 — 1,387 — 1,669 306 — 1,403 — 1,709 Trade and other payables (1,207) — (1,878) — (3,085) (1,177) — (2,002) — (3,179) Other non-current liabilities (77) — (288) — (365) (85) — (277) — (362) 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. 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). Gains and losses arising from 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. 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 will impact the valuations of certain liabilities. We have disclosed our exposure to LIBOR on our derivative portfolio in note 17, on our borrowings in note 21 and on our hedging arrangements in note 32(e). We are managing the risk by planning to replace LIBOR cash flows with alternative reference rates on our affected contracts. The migration project is underway, with all affected contracts expected to be amended by 31 December 2021. As at 31 March 2021 no contracts had yet been amended. The Finance Committee of the Board have delegated to the treasury department the authority to determine which benchmarks are the most appropriate. A combination of LIBOR and the successor benchmarks, primarily GBP Sterling Overnight Index Average (SONIA) and USD Secured Overnight Financing Rate (SOFR) will be used in the portfolio during the migration period. 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: 2021 2020 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 64 67 — 26 157 71 10 — (8) 73 Financial investments — 2,309 — 33 2,342 — 1,966 — 32 1,998 Borrowings (23,163) (1,762) (6,295) — (31,220) (20,969) (3,085) (6,740) — (30,794) Pre-derivative position (23,099) 614 (6,295) 59 (28,721) (20,898) (1,109) (6,740) 24 (28,723) Derivative effect 2,869 (2,511) (183) — 175 2,259 (1,892) (234) — 133 Net debt position (20,230) (1,897) (6,478) 59 (28,546) (18,639) (3,001) (6,974) 24 (28,590) 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 Phase I of IFRS Interest Rate Benchmark Reform amendments related to hedge accounting with effect from 1 April 2019, and Phase II with effect from 1 April 2020. The amendments impact our fair value hedging relationships where derivative cash flows will be transitioned from paying LIBOR to paying an alternative reference rate. The hedged risk must be re-documented to reflect this, and 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 earliest point in time of the Group’s contracts that reference LIBOR being amended, the hedging relationship being formally discontinued or formal market conventions ending uncertainty being 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 7, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Year ended 31 March 2021 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 gains/(losses) in respect of: Cash flow hedges — 14 (14) — Cost of hedging (15) (24) — 50 Transferred to profit or loss in respect of: Cash flow hedges — 56 — — Cost of hedging 1 2 — — Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (30) — 6 Consolidated statement of financial position Derivatives – carrying value of hedging instruments ¹ Assets – current — 10 2 5 Assets – non-current 187 59 1 140 Liabilities – current — (12) (24) (17) Liabilities – non-current (113) (255) (22) — Profiles of the significant timing, price and rate information of hedging instruments Maturity range Jan 2023 – Jan 2043 Sep 2021 – Nov 2040 Apr 2021 – Feb 2027 Mar 2022 – Sep 2027 Spot foreign exchange range: GBP:USD 1.64 1.30 – 1.66 1.31 – 1.41 1.22 – 1.40 GBP:EUR 1.11 – 1.24 1.08 – 1.24 1.04 – 1.29 1.15 – 1.16 EUR:USD 1.13 – 1.17 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+408bps 0.976% – 5.845% n/a n/a USD LIBOR +68bps/+115bps 2.513% – 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 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 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 2021 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 (2,755) 121 (85) 153 (127) 26 1. The carrying value of the hedged borrowings is £2,714 million, of which £nil is current and £2,714 million is non-current. 2. Included within the hedging instrument notional balance is £2,679 million impacted by Interest Rate Benchmark Reform amendments. 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 was £1,883 million, of which £72 million was current and £1,811 million was non-current. 2. Included within the hedging instrument notional balance was £1,675 million impacted by Interest Rate Benchmark Reform amendments. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2021 Balance in cash flow hedge reserve Change in value used for calculating ineffectiveness Hedging instrument noti

Additional disclosures in respe

Additional disclosures in respect of guaranteed securities	12 Months Ended
	Mar. 31, 2021
Separate Financial Statements [Abstract]
Additional disclosures in respect of guaranteed securities	36. Additional disclosures in respect of guaranteed securities We have preferred shares that are listed on a US national securities exchange and are guaranteed by a company in the Group. This guarantor commits 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 company providing the guarantee, we are required to disclose individual financial information for this company. 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 2021. 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 2021 – IFRS National Grid plc and Niagara Mohawk Power Corporation combined £m Combined statement of financial position Non-current loans to other subsidiaries — Non-current assets 8,940 Current loans to other subsidiaries 20,692 Current assets 1,553 Current loans from other subsidiaries (17,589) Current liabilities (1,342) Non-current loans from other subsidiaries (2,059) Non-current liabilities (6,363) Net assets ¹ 3,832 Equity 3,832 Combined income statement – continuing operations Revenue 2,462 Operating costs (4,562) Operating profit (2,100) Other income from other subsidiaries 9,978 Other income and costs, including taxation (182) Profit after tax 7,696 1. Excluded from net assets above are investments in other consolidated subsidiaries with a carrying value of £14,415 million.

Transition to new accounting st

Transition to new accounting standards	12 Months Ended
	Mar. 31, 2021
Disclosure of initial application of standards or interpretations [abstract]
Transition to new accounting standards	37. Transition to new accounting standards (a) Transition to IFRS 16 The Group adopted IFRS 16 ‘Leases’, with effect from 1 April 2019. IFRS 16 introduced a single lease accounting model for lessees (rather than the previous 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 resulted 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 increased both our assets and liabilities (including net debt). It also changed the timing and presentation in the consolidated income statement as it resulted in an increase in finance costs and depreciation largely offset by a reduction in the previously straight-line operating costs. Transition options We applied IFRS 16 using the modified retrospective approach. Comparatives were not 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 were 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 elected to apply the practical expedient on transition, which permitted 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 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 were recognised on a straight-line basis as an expense in the consolidated income statement over the remaining lease term. As a result, the Group 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 was recognised. The transition adjustment was in addition to the £270 million of finance leases already recognised on the consolidated statement of financial position under IAS 17. There was 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 (before the impact of IFRS 16) 1 £m IFRS 16 1 April 2019 As restated £m Property, plant and equipment – Right-of-use assets Land and buildings 2,560 381 2,941 Plant and machinery 36,911 67 36,978 Assets in the course of construction 5,049 — 5,049 Motor vehicles and office equipment 339 20 359 Total property, plant and equipment 44,859 468 45,327 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 19,568 — 19,568 Equity Total equity 19,568 — 19,568 1. Comparative amounts have been revised as described in note 1F. The impact of IFRS 16 on profit after tax as a result of adopting the new standard was not material. However, it 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 was also not material, although there was 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 (Before the impact of transition adjustments)* Transition adjustments 1 April 2018 IFRS 9 IFRS 15 £m £m £m £m Non-current assets Goodwill 4,984 — — 4,984 Other intangible assets 899 — — 899 Property, plant and equipment 40,730 — — 40,730 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 52,523 — — 52,523 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 59,204 — (3) 59,201 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 (3,868) 5 4 74 8 (3,789) Pensions and other post-retirement benefit obligations (1,672) — — (1,672) Provisions (1,779) — — (1,779) Total non-current liabilities (31,474) (27) (172) (31,673) Total liabilities (40,171) (27) (166) (40,364) Net assets 19,033 (27) (169) 18,837 Equity Share capital 452 — — 452 Share premium account 1,321 — — 1,321 Retained earnings 21,784 (99) 5 (169) 9 21,516 Other equity reserves (4,540) 72 6 — (4,468) Total shareholders’ equity 19,017 (27) (169) 18,821 Non-controlling interests 16 — — 16 Total equity 19,033 (27) (169) 18,837 *Comparative amounts have been revised as described in note 1F. 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 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 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 substantively enacted at the balance sheet date. 9. The transition adjustment reflected the net of adjustments 7 and 8 above.

Acquisitions

Acquisitions	12 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Acquisitions	38. Acquisitions This note outlines the acquisition announced during the year and the acquisition made in the prior year. Acquisition of PPL Western Power Distribution Investments Limited On 17 March 2021, National Grid plc entered into an agreement to acquire 100% of the share capital of PPL WPD Investments Limited (WPD), the holding company of Western Power Distribution plc, which is the UK’s largest electricity distribution network operator. The total consideration for the transaction is £7.8 billion. The transaction is expected to complete in July 2021. Acquisition of Geronimo Energy LLC and Emerald Energy Venture LLC On 11 July 2019, National Grid Ventures acquired 100% of the share capital of National Grid Renewables (formerly known as Geronimo Energy LLC) and 51% of Emerald Energy Venture LLC (Emerald), which is jointly controlled by National Grid and Washington State Investment Board (WSIB). National Grid Renewables Development LLC 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 National Grid Renewables 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 was 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 was 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 National Grid Renewables over the relevant period.The contingent consideration will be payable over a number of years. The fair values of the assets and liabilities recognised at the acquisition date for both the acquisition of the subsidiary, National Grid Renewables, 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 – National Grid Renewables 70 Cash consideration – National Grid Renewables 49 Cash consideration – Emerald 90 209 The goodwill arising from the acquisition comprised the value associated with the potential future projects that will be developed by National Grid Renewables as well as the expertise of the management team that was acquired, neither of which qualify for recognition as tangible or intangible assets. At the acquisition date, there were no material contingent liabilities. Total acquisition-related costs of £3 million were recognised within operating costs within the consolidated income statement, of which £1 million was recognised in the year ended 31 March 2020.

Basis of preparation and rece_2

Basis of preparation and recent accounting developments (Policies)	12 Months Ended
	Mar. 31, 2021
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 2021 and in accordance with the Companies Act 2006 applicable to companies reporting under IFRS adopted pursuant to Regulation (EC) No. 1606/2002 as it applies in the European Union. 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 part of the Directors’ consideration of the appropriateness of adopting the going concern basis of accounting in preparing these financial statements, the Directors have considered both the impact of COVID-19 on the Group’s operations alongside the impact of the acquisition of PPL WPD Investments Limited (WPD) (see note 38) and subsequent disposal of The Narragansett Electric Company (NECO) (see note 10) and the expected planned disposal of a majority stake of National Grid Gas plc. The Directors have assessed the principal risks discussed on pages 24 – 27, including by modelling both a base case and a reasonable worst case scenario. Reasonable worst-case: The reasonable worst-case scenario covers the materially adverse cash flow impact associated with a further year of COVID-19 disruption across both the UK and US, with a subsequent phased return to normal operations, increased cash outflows from higher costs (e.g. storms), while still delivering our planned capital investment programme for the year ended 31 March 2022. The continuing economic impact of COVID-19 and the consequential impact on cash collections and capital programmes is the key judgement applied in the analysis. The main cash flow impacts identified in the reasonable worst-case scenario are: • a significant reduction in cash collections 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; and • further increases in other costs such as cleaning, safety equipment and IT; offset by a continued reduction in discretionary spend across all areas (e.g. recruitment, travel and consultancy spend). Impact of WPD acquisition: The cash flows associated with WPD have been based on historic actuals alongside information obtained as part of the financial due diligence process and associated discussions with WPD management. The Directors noted the impact of the transaction on the Group’s financing position as below: • a new bridge facility of £8.25 billion to finance the acquisition, with the first repayment of the bridge expected to be from the proceeds of the announced planned business disposals in 2022; and • c.£1.1 billion of committed facilities to fund WPD working capital. As part of their analysis, the Board also considered the following potential levers at their discretion to improve the position identified by the analysis if the debt capital markets are not accessible: • the payment of dividends to shareholders; • significant changes in the phasing of the Group’s capital programme with elements of non-essential works and programmes delayed; and • a number of further reductions in operating expenditure across the Group primarily related to workforce cost reductions in both the UK and the US. Having considered the reasonable worst-case scenario, the impact of the acquisition of WPD (and any penalties if the transaction did not proceed), the timing of the NECO and National Grid Gas plc transactions, and the 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 c.£5.6 billion debt issuances completed in the period from 1 April 2020 to 31 March 2021 (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 final determinations of the UK RIIO-2 price controls process, the Group’s various ongoing rate case determinations in the 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.
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).
Disposal of The Naragansett Electric Company	Disposal of The Narragansett Electric CompanyAs described further in note 10, on 17 March 2021, the Group signed an agreement to sell 100% of the share capital of a wholly owned subsidiary, The Narragansett Electric Company (NECO). The sale is expected to complete in early 2022 once all regulatory approvals are obtained. As the sale is considered highly probable and is expected to complete within a year, the associated assets and liabilities have been presented as held for sale in the consolidated statement of financial position. However, the transaction has not met the criteria for classification as a discontinued operation and therefore its results for the period are not separately disclosed on the face of the income statement.
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 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. The main impact at 31 March 2021 is the consideration of 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), which is an area of estimation uncertainty impacting the Group’s position as at 31 March 2021. 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).
Comparative period revisions	During the year, we have revised the comparative balances primarily to reflect adjustments between property, plant and equipment and goodwill related to the accounting performed for acquisitions made by our US business between 2000 and 2007. The adjustments related to the treatment of certain regulatory liabilities recognised under US GAAP on the acquisition balance sheets under UK GAAP and IFRS. This resulted in an overstatement of goodwill and an understatement of property, plant and equipment. The adjustments had a resulting impact on the deferred tax balances that were recognised at the time of the acquisitions and therefore, these have also been updated for all periods presented, also taking into account any subsequent changes in tax rates. The translation reserve on consolidation of these subsidiaries was also updated. There have been no income statement impacts (and therefore no impact on the previously reported earnings per share) for any of the periods presented. Opening retained earnings have increased to correct the income statement impact of amortising the overstated goodwill from the period after acquisition until the adoption of IFRS in 2005 and for the impact on deferred tax of the tax rate changes noted above. Any foreign exchange impacts are recorded within the translation reserve within other equity reserves. Below we set out the impacted line items and the adjustments to our opening statement of financial position as at 1 April 2018. In addition, we set out the adjustments to previously presented balances as at 31 March 2019 and 31 March 2020 (with the only movement each period being as a result of foreign exchange movements): 1 April 2018 31 March 2019 31 March 2020 £m £m £m Goodwill (460) (497) (521) Property, plant and equipment 877 946 992 Deferred tax liability 232 250 262 Retained earnings 185 185 185 Translation reserve — 14 24
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)).
New IFRS accounting standards and interpretations effective for the year ended 31 March 2021 and New IFRS accounting standards and interpretations not yet adopted	The UK’s Financial Conduct Authority announced that the London Inter-bank Offered Rate (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 Phase I of Interest Rate Benchmark Reform, which modified certain hedge accounting requirements to allow hedge accounting to continue for affected hedges during the period of uncertainty before the hedged items or hedging instruments were amended 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. Phase II was issued in August 2020 and endorsed in January 2021 for adoption in the EU, resulting in amendments to IFRS 9, IFRS 7 and IFRS 16. The Group has early-adopted these amendments with effect from 1 April 2020 as they enable the Company and its subsidiaries to reflect the effects of transitioning from LIBOR to alternative benchmark interest rates without giving rise to accounting impacts that would not provide useful information to users of the financial statements. There were no transition adjustments on adoption of either phase and the Group has not restated the prior period, but instead has applied the amendments prospectively. Refer to note 32(d) for further details on the contracts to be transitioned to the new alternative benchmark interest rate and for details of our migration project. 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: • amendments to IFRS 16 ‘Leases – COVID-19 Related Rent Concessions’; • amendments to IFRS 3 ‘Business Combinations’; • amendments to IAS 1 and IAS 8 ‘Definition of Material’; and 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 IAS 16 ‘Property, Plant and Equipment’; • amendments to IAS 37 ‘Provisions, Contingent Liabilities and Contingent Assets’; • amendments to IAS 1 ‘Presentation of Financial Statements’; • amendments to IAS 8 ‘Accounting Policies, Changes in Accounting Estimates and Errors’; and • annual improvements to IFRS standards 2018-2020. 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	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 IFRS 16 ‘Leases’ 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 performance, we use a profit measure that excludes certain income and expenses. We call that measure ‘adjusted profit’. Adjusted profit (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 adjusted profit 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 adjusted profit.
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 adjusted profit, we adjust net financing costs to exclude any net gains or losses on financial instruments included in remeasurements (see note 5).
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 profit after tax attributable to each ordinary share. Basic EPS is calculated on profit after tax 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.
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.
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 by performing an impairment review annually or more frequently if events or changes in circumstances indicate a potential impairment.
Other intangible assets	Other intangible assets mainly comprise software which is written down (amortised) over the period we expect to receive a benefit from the asset. An amortisation expense is charged to the income statement to reflect the reduced value of the asset over time. Amortisation 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.
Property, plant and equipment	Property, plant and equipment are 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 2022.
Financial and other investments	The Group holds a range of financial and other investments. These investments include short-term money market funds, quoted investments in equities or bonds of other companies, investments in our venture capital portfolio (National Grid Partners), bank deposits with a maturity of greater than three months, and investments that can not be readily used in operations, principally collateral deposited in relation to derivatives.
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 a share of 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: These are used to manage 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: These are used to manage our US customers’ exposure to price and supply risks. Some forward contracts for the purchase of commodities meet the definition of derivatives. We also enter into derivative financial instruments linked to commodity prices, including index futures, options and swaps, which 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 include amounts which are due from our customers for services we have provided, accrued income which has not yet been billed, prepayments, contract assets where certain milestones are required to be fulfilled and other receivables that are expected to be settled within twelve months.
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. Bank overdrafts are only shown net within cash and cash equivalents when there is a legal right to offset unconditionally and an intention to settle net has been demonstrated by the physical movement of cash.
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, inflation rates and foreign exchange. Lease liabilities are also included within borrowings. Our price controls and rate plans require us to fund our networks within a certain ratio of debt to equity or regulatory value 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 committed credit 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 and customer contributions which will not be recognised as income until after 31 March 2022. It also includes contingent consideration and other 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 contribution (DC) and defined benefit (DB) 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	Provisions are recognised 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 majority of our provisions relate to environmental remediation, specifically in relation to certain Superfund sites in the US, being sites we own or have owned in the past where hazardous substances are present as a result of the historic operations of manufactured gas plants in Brooklyn, New York. We also recognise provisions for decommissioning costs for various assets we would be required to remove at the end of their lives, the costs associated with restructuring plans and for lease contracts we have entered into that are now loss-making. In determining the quantum of the provision we recognise, we make estimates in relation to management’s best judgement of the evaluation of the likelihood and the probability of exposure to potential loss, and the costs that would be incurred. Should circumstances change following unforeseeable developments, the likelihood or quantum 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 or fair value movements on certain financial instruments that the Company holds.
Net debt	We define net debt as 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. 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.
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, inflation rates and foreign exchange. Lease liabilities are also included within borrowings. Our price controls and rate plans require us to fund our networks within a certain ratio of debt to equity or regulatory value 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 committed credit 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.
Subsidiary undertakings, 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 a share of 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.
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 a company in the Group. This guarantor commits 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 company providing the guarantee, we are required to disclose individual financial information for this company. We have chosen to include this information in the Group financial statements rather than submitting separate stand-alone financial statements.

Basis of preparation and rece_3

Basis of preparation and recent accounting developments (Tables)	12 Months Ended
	Mar. 31, 2021
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
Disclosure of adjustments to balance sheet items for foreign exchange movements	Below we set out the impacted line items and the adjustments to our opening statement of financial position as at 1 April 2018. In addition, we set out the adjustments to previously presented balances as at 31 March 2019 and 31 March 2020 (with the only movement each period being as a result of foreign exchange movements): 1 April 2018 31 March 2019 31 March 2020 £m £m £m Goodwill (460) (497) (521) Property, plant and equipment 877 946 992 Deferred tax liability 232 250 262 Retained earnings 185 185 185 Translation reserve — 14 24

Segmental analysis (Tables)

Segmental analysis (Tables)	12 Months Ended
	Mar. 31, 2021
Operating Segments [Abstract]
Schedule of 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. 2021 2020 2019 Total £m Sales between segments £m Sales to third parties £m Total Sales Sales Total Sales Sales Operating segments – continuing operations: UK Electricity Transmission 3,992 (10) 3,982 3,702 (8) 3,694 3,351 (20) 3,331 UK Gas Transmission 904 (16) 888 927 (16) 911 896 (12) 884 US Regulated 9,195 — 9,195 9,205 — 9,205 9,846 — 9,846 NGV and Other¹ 715 (1) 714 736 (6) 730 876 (4) 872 Total revenue from continuing operations 14,806 (27) 14,779 14,570 (30) 14,540 14,969 (36) 14,933 Split by geographical areas – continuing operations: UK 5,482 5,282 5,045 US 9,297 9,258 9,888 14,779 14,540 14,933 1. Included within NGV and Other is £636 million (2020: £608 million; 2019: £597 million) of revenue relating to NGV. 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 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m Operating segments – continuing operations: UK Electricity Transmission 1,034 1,320 1,015 1,027 1,316 778 UK Gas Transmission 342 348 303 337 347 267 US Regulated 1,313 1,397 1,724 1,344 880 1,425 NGV and Other 1 237 242 400 187 237 400 Total operating profit from continuing operations 2,926 3,307 3,442 2,895 2,780 2,870 Split by geographical area – continuing operations: UK 1,612 1,925 1,695 1,550 1,915 1,422 US 1,314 1,382 1,747 1,345 865 1,448 2,926 3,307 3,442 2,895 2,780 2,870 Below we reconcile total operating profit from continuing operations to profit before tax from continuing operations. Total operating exceptional items and remeasurements of £31 million charge (2020: £527 million charge; 2019: £572 million charge) are detailed in note 5. This is comprised of a £7 million charge (2020: £4 million charge; 2019: £237 million charge) attributable to UK Electricity Transmission; £5 million charge (2020: £1 million charge; 2019: £36 million charge) to UK Gas Transmission; £31 million gain (2020: £517 million charge; 2019: £299 million charge) to US Regulated; and £50 million charge (2020: £5 million charge; 2019: £nil) to NGV and Other. Reconciliation to profit before tax: Operating profit from continuing operations 2,926 3,307 3,442 2,895 2,780 2,870 Finance income 35 70 73 58 54 88 Finance costs (977) (1,119) (1,066) (928) (1,167) (1,157) Share of post-tax results of joint ventures and associates 66 88 40 58 87 40 Profit before tax from continuing operations 2,050 2,346 2,489 2,083 1,754 1,841 1. Included within NGV and Other is £298 million (2020: £269 million; 2019: £263 million) of operating profit before exceptional items and remeasurements and £296 million of operating profit after exceptional items and remeasurements (2020: £268 million; 2019: £263 million), relating to NGV. 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. Net book value of property, plant and Capital expenditure Depreciation, amortisation 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Operating segments: UK Electricity Transmission 14,379 13,788 13,288 1,072 1,043 925 (507) (469) (628) UK Gas Transmission 4,531 4,513 4,412 176 249 308 (165) (171) (181) US Regulated 1,2 27,128 30,615 25,488 3,223 3,228 2,650 (888) (855) (700) NGV and Other 2,3 2,448 2,141 2,755 460 559 438 (112) (145) (226) Total from continuing operations 2 48,486 51,057 45,943 4,931 5,079 4,321 (1,672) (1,640) (1,735) Split by geographical area – continuing operations: UK 21,352 20,427 19,343 1,708 1,847 1,584 (783) (784) (931) US 2 27,134 30,630 26,600 3,223 3,232 2,737 (889) (856) (804) Total from continuing operations 2 48,486 51,057 45,943 4,931 5,079 4,321 (1,672) (1,640) (1,735) Asset type: Property, plant and equipment 2 47,043 49,762 44,859 4,510 4,727 4,015 (1,476) (1,464) (1,560) Non-current intangible assets 1,443 1,295 1,084 421 352 306 (196) (176) (175) Total from continuing operations 2 48,486 51,057 45,943 4,931 5,079 4,321 (1,672) (1,640) (1,735) 1. 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. These assets were included within NGV and Other in 2019, and had a net book value of £1,062 million, capital expenditure of £87 million and depreciation, amortisation and impairment of £102 million. 2. Comparative amounts have been revised as described in note 1F. 3. Included within NGV and Other are assets with a net book value of £2,396 million (2020: £2,080 million; 2019: £1,635 million), capital expenditure of £431 million (2020: £550 million; 2019: £317 million) and depreciation, amortisation and impairment of £92 million (2020: £124 million; 2019: £114 million) relating to NGV.

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Mar. 31, 2021
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 2021 UK Electricity Transmission UK Gas Transmission US Regulated NGV and Other Total Revenue under IFRS 15 Transmission 1,814 603 403 316 3,136 Distribution — — 8,317 — 8,317 System Operator 2,076 240 — — 2,316 Other 67 12 15 302 396 Total IFRS 15 revenue 3,957 855 8,735 618 14,165 Other revenue Generation — — 376 — 376 Other 25 33 84 96 238 Total other revenue 25 33 460 96 614 Total revenue from continuing operations 3,982 888 9,195 714 14,779 Geographical split for the year ended 31 March 2021 UK Electricity Transmission £m UK Gas Transmission £m US Regulated £m NGV and Other £m Total £m Revenue under IFRS 15 UK 3,957 855 — 553 5,365 US — — 8,735 65 8,800 Total IFRS 15 revenue 3,957 855 8,735 618 14,165 Other revenue UK 25 33 — 59 117 US — — 460 37 497 Total other revenue 25 33 460 96 614 Total revenue from continuing operations 3,982 888 9,195 714 14,779 3. Revenue continued (e) Disaggregation of revenue continued 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, 2021
Analysis of income and expense [abstract]
Schedule of expenses by nature	2021 2020 2019 £m £m £m Depreciation, amortisation and impairment 1,672 1,640 1,735 Payroll costs 1,770 1,684 1,852 Purchases of electricity 1,130 1,403 1,454 Purchases of gas 1,250 1,316 1,642 Property and other taxes 1,193 1,191 1,108 Balancing Services Incentive Scheme 1,875 1,317 1,196 Other 2,668 2,975 2,895 Other operating costs 11,558 11,526 11,882 Provision for bad and doubtful debts 326 234 181 Total operating costs 11,884 11,760 12,063 Operating costs include: Inventory consumed 316 328 415 Research and development expenditure 17 14 19 (a) Payroll costs 2021 2020 2019 £m £m £m Wages and salaries¹ 2,282 2,188 2,084 Social security costs 172 168 156 Defined contribution scheme costs 77 75 72 Defined benefit pension costs 136 135 232 Share-based payments 27 19 27 Severance costs (excluding pension costs) 11 1 76 2,705 2,586 2,647 Less: payroll costs capitalised (935) (902) (795) Total payroll costs 1,770 1,684 1,852 1. Included within wages and salaries are US other post-retirement benefit costs of £43 million (2020: £45 million; 2019: £48 million). For further information refer to note 25.
Schedule of additional information	(b) Number of employees 31 March 2021 Monthly average 2021 31 March 2020 Monthly average 2020 31 March 2019 Monthly average 2019 UK 6,657 6,517 6,321 6,151 5,962 6,227 US 17,026 16,821 16,748 16,679 16,614 16,669 Total number of employees 23,683 23,338 23,069 22,830 22,576 22,896 4. Operating costs continued (c) Key management compensation 2021 2020 2019 £m £m £m Short-term employee benefits 7 7 7 Compensation for loss of office — 1 — Post-employment benefits 1 1 1 Share-based payments 4 3 3 Total key management compensation 12 12 11 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: 2021 2020 2019 £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 2.5 1.9 1.6 The auditing of accounts of any associate of the Company² 8.1 8.7 8.5 Other services supplied³ 6.4 6.3 5.2 17.0 16.9 15.3 Total other services 4 All other fees: Other assurance services 5 0.8 0.6 1.1 Other non-audit services not covered above 6 2.0 0.5 2.2 2.8 1.1 3.3 Total auditors’ remuneration 19.8 18.0 18.6 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 2021, 2020 and 2019. 2. The 2019 comparative was updated in 2020 following finalisation of the 2019 audit fee with the Audit Committee in 2020. 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 2020, 2019 and 2018 respectively. 4. There were no tax compliance or tax advisory fees and no audit related fees as described in Item 16C(b) of Form 20-F. 5. In all years, principally relates to assurance services provided in relation to comfort letters for debt issuances and, in 2021, also includes amounts related to capacity market auction monitoring services. 6. For 2021, includes the class 1 Circular in respect of the acquisition of WPD announced on 18 March 2021. In 2020, other assurance services include auction monitor work on Contracts for Difference, a review of controls over our data on New York customers and IT project assurance. In 2019, non-audit services primarily related to the UK Commercial Property business in respect of the evaluation of possible options for the use of property assets.

Exceptional items and remeasu_2

Exceptional items and remeasurements (Tables)	12 Months Ended
	Mar. 31, 2021
Exceptional Items And Remeasurements [Abstract]
Schedule of exceptional items and remeasurements from continuing operations	Exceptional items and remeasurements from continuing operations 2021 2020 2019 £m £m £m Included within operating profit Exceptional items: Changes in environmental provisions 14 (402) — New operating model implementation costs (55) — — Transaction costs (24) — — Cost efficiency and restructuring programmes — — (204) Massachusetts Gas labour dispute — — (283) Impairment of nuclear connection development costs — — (137) (65) (402) (624) Remeasurements – commodity contract derivatives 34 (125) 52 (31) (527) (572) 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. 2021 2020 2019 £m £m £m Included within finance income and costs Remeasurements: Net (losses)/gains on financing derivatives (41) 1 (40) Net gains/(losses) on financial assets at fair value through profit and loss 23 (16) 15 Net gains/(losses) on financial liabilities at fair value through profit and loss 90 (49) (51) 72 (64) (76) Included within share of post-tax results of joint ventures and associates Remeasurements: Remeasurements – net losses on financial instruments (8) (1) — Total included within profit before tax 33 (592) (648) Included within tax Exceptional items – movements arising on items not included in profit before tax: Deferred tax charge arising on the reversal of the reduction in UK corporation tax rate — (192) — Tax on exceptional items 8 103 144 Tax on remeasurements (34) 42 5 (26) (47) 149 Total exceptional items and remeasurements after tax 7 (639) (499) Analysis of total exceptional items and remeasurements after tax Exceptional items after tax (57) (491) (480) Remeasurements after tax 64 (148) (19) Total exceptional items and remeasurements after tax 7 (639) (499)

Finance income and costs (Table

Finance income and costs (Tables)	12 Months Ended
	Mar. 31, 2021
Analysis of income and expense [abstract]
Schedule of finance income and costs	2021 2020 2019 Notes £m £m £m Finance income Interest income on financial instruments: Bank deposits and other financial assets 33 48 54 Dividends received on equities held at fair value through other comprehensive income (FVOCI) 2 2 2 Other income — 20 17 35 70 73 Finance costs Net interest on pensions and other post-retirement benefit obligations 25 (38) (23) (22) Interest expense on financial liabilities held at amortised cost: Bank loans and overdrafts (72) (73) (72) Other borrowings¹ (854) (997) (970) Interest expense on financial liabilities held at fair value through profit and loss (FVTPL) (20) (22) (20) Interest on derivatives 7 (39) (43) Unwinding of discount on provisions 26 (78) (77) (74) Other interest (53) (10) — Less: interest capitalised² 131 122 135 (977) (1,119) (1,066) Remeasurements – Finance income Net gains/(losses) on FVTPL financial assets 23 (16) 15 23 (16) 15 Remeasurements – Finance costs Net gains/(losses) on FVTPL financial liabilities 90 (49) (51) Net gains/(losses) on financing derivatives³: Derivatives designated as hedges for hedge accounting 44 (13) (37) Derivatives not designated as hedges for hedge accounting (85) 14 (3) 49 (48) (91) Total remeasurements – Finance income and costs 72 (64) (76) Finance income 58 54 88 Finance costs (928) (1,167) (1,157) Net finance costs from continuing operations (870) (1,113) (1,069) 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 3.1% (2020: 3.6%; 2019: 3.9%). In the UK, capitalised interest qualifies for a current year tax deduction with tax relief claimed of £13 million (2020: £15 million; 2019: £19 million). In the US, capitalised interest is added to the cost of plant and qualifies for tax depreciation allowances.

Tax (Tables)

Tax (Tables)	12 Months Ended
	Mar. 31, 2021
Income Taxes [Abstract]
Disclosure of major components of tax expense (income)	The tax charge for the year can be analysed as follows: 2021 2020 2019 £m £m £m Current tax: UK corporation tax at 19% (2020: 19%; 2019: 19%) 213 179 132 UK corporation tax adjustment in respect of prior years 23 (4) (12) 236 175 120 Overseas corporation tax 3 (2) 8 Overseas corporation tax adjustment in respect of prior years (15) (41) (40) (12) (43) (32) Total current tax from continuing operations 224 132 88 Deferred tax: UK deferred tax 63 269 27 UK deferred tax adjustment in respect of prior years (26) 6 2 37 275 29 Overseas deferred tax 174 64 208 Overseas deferred tax adjustment in respect of prior years 7 9 14 181 73 222 Total deferred tax from continuing operations 218 348 251 Total tax charge from continuing operations 442 480 339
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 2021 2020 2019 £m £m £m Current tax: Cash flow hedges, cost of hedging and own credit reserve 6 — 3 Deferred tax: Investments at fair value through other comprehensive income 12 (1) — Cash flow hedges, cost of hedging and own credit reserve (2) (40) (12) Remeasurements of pension assets and post-retirement benefit obligations 414 (206) 12 Share-based payments 2 (3) — 432 (250) 3 Total tax recognised in the statements of comprehensive income from continuing operations 430 (247) 3 Total tax relating to share-based payments recognised directly in equity from continuing operations 2 (3) — 432 (250) 3
Disclosure of reconciliation of accounting profit multiplied by applicable tax rates and average effective tax rate	The tax charge for the year for the continuing business, is higher (2020: higher tax charge; 2019: lower tax charge) than the standard rate of corporation tax in the UK of 19% (2020: 19%; 2019: 19%): 2021 2020 2019 £m £m £m Profit before tax from continuing operations Before exceptional items and remeasurements 2,050 2,346 2,489 Exceptional items and remeasurements 33 (592) (648) Profit before tax from continuing operations 2,083 1,754 1,841 Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2020: 19%; 2019: 19%) 396 334 350 Effect of: Adjustments in respect of prior years¹ (11) (30) (36) Expenses not deductible for tax purposes 30 29 28 Non-taxable income² (9) (18) (36) Adjustment in respect of foreign tax rates 42 18 56 Deferred tax impact of change in UK tax rate — 192 (3) Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax (12) (17) (8) Other³ 6 (28) (12) Total tax charge from continuing operations 442 480 339 % % % Effective tax rate – continuing operations 21.2 27.4 18.4 1. The prior year adjustments are primarily due to agreement of prior period tax returns. 2. Includes tax on chargeable disposals after the offset of capital losses. 3. Other primarily comprises the movement in the deferred tax asset 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 1 April 2019 2 5,727 (9) (170) 7 (1,340) 4,215 Exchange adjustments and other 2,3 222 (30) (28) (3) (27) 134 Charged/(credited) to income statement 613 (7) 44 (13) (287) 350 (Credited)/charged to other comprehensive income and equity — (2) (206) (46) 1 (253) At 1 April 2020 2 6,562 (48) (360) (55) (1,653) 4,446 Exchange adjustments and other 3 (501) 4 51 4 174 (268) Charged/(credited) to income statement 373 — (12) 1 (147) 215 Charged to other comprehensive income and equity — 2 414 6 — 422 At 31 March 2021 6,434 (42) 93 (44) (1,626) 4,815 1. The deferred tax asset of £1,626 million as at 31 March 2021 (2020: £1,653 million) in respect of other net temporary differences primarily relates to net operating losses of £455 million (2020: £547 million), US environmental provisions of £453 million (2020: £529 million) and US bad debt provision of £184 million (2020: £124 million). 2. Comparative amounts have been revised as described in note 1F. 3. Exchange adjustments and other comprises foreign exchange arising on translation of the US dollar deferred tax balances. In 2020, it also included 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 total deferred tax assets not recognised are as follows: 2021 2020 £m £m Capital losses 1,620 1,626 Non-trade deficits 1 1 Trading losses 7 6

Earnings per share (EPS) (Table

Earnings per share (EPS) (Tables)	12 Months Ended
	Mar. 31, 2021
Earnings per share [abstract]
Schedule of earnings per share	(a) Basic EPS Earnings EPS Earnings EPS Earnings EPS 2021 2021 2020 2020 2019 2019 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,633 46.4 1,912 55.2 1,998 59.0 Exceptional items and remeasurements after tax from continuing operations 7 0.2 (639) (18.4) (499) (14.7) Earnings from continuing operations 1,640 46.6 1,273 36.8 1,499 44.3 Adjusted earnings from discontinued operations — — 5 0.2 57 1.7 Exceptional items and remeasurements after tax from discontinued operations — — (14) (0.5) (45) (1.4) Earnings from discontinued operations — — (9) (0.3) 12 0.3 Total adjusted earnings 1,633 46.4 1,917 55.4 2,055 60.7 Total exceptional items and remeasurements after tax (including discontinued operations) 7 0.2 (653) (18.9) (544) (16.1) Total earnings 1,640 46.6 1,264 36.5 1,511 44.6 2021 2020 2019 millions millions millions Weighted average number of ordinary shares – basic 3,523 3,461 3,386 (b) Diluted EPS Earnings EPS Earnings EPS Earnings EPS 2021 2021 2020 2020 2019 2019 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,633 46.1 1,912 55.0 1,998 58.8 Exceptional items and remeasurements after tax from continuing operations 7 0.2 (639) (18.4) (499) (14.7) Earnings from continuing operations 1,640 46.3 1,273 36.6 1,499 44.1 Adjusted earnings from discontinued operations — — 5 0.1 57 1.7 Exceptional items and remeasurements after tax from discontinued operations — — (14) (0.4) (45) (1.4) Earnings from discontinued operations — — (9) (0.3) 12 0.3 Total adjusted earnings 1,633 46.1 1,917 55.1 2,055 60.5 Total exceptional items and remeasurements after tax (including discontinued operations) 7 0.2 (653) (18.8) (544) (16.1) Total earnings 1,640 46.3 1,264 36.3 1,511 44.4 2021 2020 2019 millions millions millions Weighted average number of ordinary shares – diluted 3,540 3,478 3,401 (c) Reconciliation of basic to diluted average number of shares 2021 2020 2019 millions millions millions Weighted average number of ordinary shares – basic 3,523 3,461 3,386 Effect of dilutive potential ordinary shares – employee share plans 17 17 15 Weighted average number of ordinary shares – diluted 3,540 3,478 3,401

Dividends (Tables)

Dividends (Tables)	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Schedule of dividends to shareholders	2021 2020 2019 Pence per share Cash Scrip dividend £m Pence per share Cash Scrip dividend £m Pence per share Cash Scrip dividend £m Interim dividend in respect of the current year 17.00 348 249 16.57 335 241 16.08 450 94 Final dividend in respect of the prior year 32.00 1,065 54 31.26 557 517 30.44 710 319 49.00 1,413 303 47.83 892 758 46.52 1,160 413

Discontinued operations and a_2

Discontinued operations and assets held for sale (Tables)	12 Months Ended
	Mar. 31, 2021
Non-current Assets Held For Sale And Discontinued Operations [Abstract]
Schedule of discontinued operations	The following assets and liabilities of NECO were classified as held for sale at 31 March 2021: 2021 £m Goodwill 562 Intangible assets 3 Property, plant and equipment 2,713 Trade and other receivables 237 Cash and cash equivalents 4 Other assets 38 Total assets held for sale 3,557 Borrowings (1,123) Pension liabilities (49) Other liabilities (396) Total liabilities held for sale (1,568) Net assets held for sale 1,989 The summary income statement for discontinued operations is as follows: 2020 2019 £m £m Revenue — — Operating costs¹ (23) (1) Operating loss (23) (1) Net finance income 6 23 Share of post-tax results of joint ventures and associates² — (5) (Loss)/profit before tax from discontinued operations (17) 17 Tax from discontinued operations (1) (5) (Loss)/profit after tax from discontinued operations (18) 12 Gain on disposal 9 — Total (loss)/profit after tax from discontinued operations³ (9) 12 1. Operating costs for the year ended 31 March 2020 related to final transaction costs and other expenses in relation to Quadgas. 2. For the year ended 31 March 2019, the amount presented is the net of £43 million impairment charge against the investment in Quadgas and £38 million share of Quadgas post-tax profits recognised prior to classification as held for sale. 3. For the year ended 31 March 2020, 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 £m £m (Loss)/profit after tax from discontinued operations (9) 12 Other comprehensive income Items that will never be reclassified to profit or loss: Share of other comprehensive income of associate, net of tax — 36 Total items from discontinued operations that will never be reclassified to profit or loss — 36 Items that may be reclassified subsequently to profit or loss: Net gains in respect of cash flow hedges 6 — Total items from discontinued operations that may be reclassified subsequently to profit or loss 6 — Other comprehensive income for the year, net of tax from discontinued operations 6 36 Total comprehensive (loss)/income for the year from discontinued operations (3) 48

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Mar. 31, 2021
Intangible Assets [Abstract]
Schedule of changes in intangible assets and goodwill	Total £m Net book value at 1 April 2019¹ 5,372 Exchange adjustments¹ 259 Acquisition of National Grid Renewables (note 38) 81 Net book value at 1 April 2020 5,712 Exchange adjustments (562) Reclassification to held for sale (note 10) (562) Net book value at 31 March 2021 4,588 1. Comparative amounts have been revised as described in note 1F.

Other intangible assets (Tables

Other intangible assets (Tables)	12 Months Ended
	Mar. 31, 2021
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 other intangible assets are: Years Software 3 to 10 Software £m Assets in the course of construction Total Cost at 1 April 2019 1,784 384 2,168 Exchange adjustments 45 18 63 Additions 38 314 352 Reclassifications 159 (159) — Cost at 1 April 2020 2,026 557 2,583 Exchange adjustments (102) (43) (145) Additions 7 414 421 Disposals (47) (2) (49) Reclassifications¹ 255 (240) 15 Reclassification to held for sale (note 10) (19) — (19) Cost at 31 March 2021 2,120 686 2,806 Accumulated amortisation at 1 April 2019 (1,084) — (1,084) Exchange adjustments (28) — (28) Amortisation charge for the year (176) — (176) Accumulated amortisation at 1 April 2020 (1,288) — (1,288) Exchange adjustments 61 — 61 Amortisation charge for the year (196) — (196) Accumulated amortisation of disposals 44 — 44 Reclassification to held for sale (note 10) 16 — 16 Accumulated amortisation at 31 March 2021 (1,363) — (1,363) Net book value at 31 March 2021² 757 686 1,443 Net book value at 31 March 2020 738 557 1,295 1. Reclassifications includes amounts transferred from property, plant and equipment (see note 13). 2. The Group has capitalised £298 million (2020: £240 million) in relation to the Gas Business Enablement system in the US, of which £82 million (2020: £30 million) is in service and is being amortised over 10 years, with the remainder included within assets in the course of construction. A further £117 million (2020: £59 million) in relation to our new UK general ledger system is also included within assets in the course of construction as at 31 March 2021, and is expected to be amortised over 10 years once it is commissioned in July 2021.

Property, plant and equipment (

Property, plant and equipment (Tables)	12 Months Ended
	Mar. 31, 2021
Property, plant and equipment [abstract]
Schedule of property, plant and equipment	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 to 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 9 Plant and machinery: Electricity transmission plant and wires 15 to 100 45 to 80 30 Electricity distribution plant n/a 35 to 85 33 Electricity generation plant n/a 20 to 93 10 Interconnector plant and other 5 to 60 5 to 50 16 Gas plant – mains, services and regulating equipment 10 to 65 47 to 95 45 Gas plant – storage 5 to 40 12 to 65 12 Gas plant – meters 7 to 30 14 to 40 20 Motor vehicles and office equipment up to 10 up to 26 4 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 for the year ended 31 March 2021 Increase in depreciation expense for the year ended 31 March 2020 UK regulated US regulated UK regulated £m US regulated £m UELs limited to 2050 35 160 37 151 UELs limited to 2060 12 70 13 66 UELs limited to 2070 1 28 — 26 Land and buildings £m Plant and machinery £m Assets Motor vehicles and office equipment £m Total £m Cost at 1 April 2019 (before transition to IFRS 16) 1 3,338 53,829 5,049 930 63,146 Right-of-use assets recognised on transition to IFRS 16 2 381 67 — 20 468 Cost at 1 April 2019 (as restated) 3,719 53,896 5,049 950 63,614 Exchange adjustments 1 98 1,484 83 33 1,698 Additions 130 464 4,029 104 4,727 Disposals (79) (486) (9) (65) (639) Reclassifications 3,4 29 4,251 (4,381) 14 (87) Cost at 1 April 2020 3,897 59,609 4,771 1,036 69,313 Exchange adjustments (213) (3,308) (130) (73) (3,724) Additions 89 328 4,023 70 4,510 Disposals (6) (344) (26) (48) (424) Reclassifications 3 96 3,007 (3,243) 77 (63) Reclassification to held for sale (note 10) (111) (3,231) (174) (44) (3,560) Cost at 31 March 2021 3,752 56,061 5,221 1,018 66,052 Accumulated depreciation at 1 April 2019 1 (778) (16,918) — (591) (18,287) Exchange adjustments 1 (16) (329) — (20) (365) Depreciation charge for the year (92) (1,252) — (120) (1,464) Disposals 36 464 — 58 558 Reclassifications 3 3 (7) — 11 7 Accumulated depreciation at 1 April 2020 (847) (18,042) — (662) (19,551) Exchange adjustments 37 698 — 46 781 Depreciation charge for the year (90) (1,270) — (116) (1,476) Disposals — 339 — 48 387 Reclassifications 3 2 (5) — 6 3 Reclassification to held for sale (note 10) 22 798 — 27 847 Accumulated depreciation at 31 March 2021 (876) (17,482) — (651) (19,009) Net book value at 31 March 2021 2,876 38,579 5,221 367 47,043 Net book value at 31 March 2020 3,050 41,567 4,771 374 49,762 1. Comparative amounts have been revised as described in note 1F. 2. On 1 April 2019, £468 million of additional right-of-use assets were recognised on transition to IFRS 16. See note 37 for details. 3. Represents amounts transferred between categories, (to)/from other intangible assets (see note 12), from inventories and reclassifications between cost and accumulated depreciation. 2021 2020 £m £m Information in relation to property, plant and equipment Capitalised interest included within cost 2,233 2,118 Contributions to cost of property, plant and equipment included within: Trade and other payables 138 84 Non-current liabilities 400 428 Contract liabilities – current 66 76 Contract liabilities – non-current 1,093 1,082
Schedule of information about right-of-use assets	The table below shows the net book value of right-of-use assets included within property, plant and equipment at 31 March 2021 and 31 March 2020, split by category. The associated lease liabilities are disclosed in note 21. 31 March 2021 Land and Plant and Assets Motor Total Net book value at 31 March 2021 365 81 — 184 630 Additions 60 6 — 64 130 Depreciation charge for the year (29) (16) — (68) (113) 31 March 2020 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 (29) (16) — (72) (117) The following balances have been included in the income statement for the years ended 31 March 2021 and 31 March 2020 in respect of right-of-use assets: 2021 2020 £m £m Included within net finance income and costs: Interest expense on lease liabilities (21) (26) Included within revenue: Lease income¹ 390 404 Included within operating expenses: Expense relating to short-term and low-value leases (13) (12)

Other non-current assets (Table

Other non-current assets (Tables)	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Schedule of other non current assets	2021 2020 £m £m Other receivables 45 35 Non-current tax assets 6 65 Prepayments 5 19 Accrued income¹ 237 235 293 354

Financial and other investmen_2

Financial and other investments (Tables)	12 Months Ended
	Mar. 31, 2021
Disclosure of financial assets [abstract]
Schedule of financial assets	2021 2020 £m £m Non-current FVOCI debt and other investments 416 352 FVOCI equity investments 99 83 FVTPL investments 240 108 755 543 Current FVTPL investments 1,768 1,278 Financial assets at amortised cost 574 720 2,342 1,998 3,097 2,541 Financial and other investments include the following: Investments in short-term money market funds 1,412 951 Investments held by National Grid Partners 136 97 Other investments 103 11 Balances that are restricted or not readily used in operations: Collateral 1 540 685 Insurance company and non-qualified plan investments 589 542 Cash surrender value of life insurance policies 283 220 Other investments 34 35 3,097 2,541 1. The collateral balance includes: £480 million (2020: £685 million) of collateral placed with counterparties with whom we have entered into a credit support annex to the International Swaps and Derivatives Association (ISDA) Master Agreement; £42 million (2020: £nil) of collateral paid by operating companies as required security deposits under the Connection and Use of System Code; and £18 million (2020: £nil) of restricted amounts allocated for specific projects within the National Grid Electricity System Operator.

Investments in joint ventures_2

Investments in joint ventures and associates (Tables)	12 Months Ended
	Mar. 31, 2021
Interests In Other Entities [Abstract]
Disclosure of joint ventures	2021 2020 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 341 654 995 291 317 608 Exchange adjustments (22) (36) (58) 20 12 32 Additions 6 75 81 16 156 172 Capitalisation of shareholder loan to Nemo Link Limited — — — — 176 176 Share of post-tax results for the year 30 28 58 40 47 87 Share of other comprehensive income of associates, net of tax 1 — 1 1 — 1 Dividends received (31) (49) (80) (41) (34) (75) Other movements¹ (96) (34) (130) 14 (20) (6) Share of net assets at 31 March 229 638 867 341 654 995 1. Within associates, the other movements for the year primarily relates to the reclassification of an investment in an associate to financial investments. Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m Statement of financial position Non-current assets 409 399 795 910 536 582 559 435 Cash and cash equivalents 47 54 27 33 31 26 112 66 All other current assets 24 4 24 26 8 5 12 6 Non-current liabilities (81) (45) (256) (315) (30) (29) (286) (232) Current liabilities (22) (16) (38) (43) (19) (10) (27) (2) Net assets 377 396 552 611 526 574 370 273 Group’s ownership interest 189 198 145 160 263 287 189 139 Group adjustment: elimination — — — — — — (23) (10) Carrying amount of the Group’s investment 189 198 145 160 263 287 166 129 BritNed Development Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m Income statement Revenue 72 80 199 206 66 45 28 19 Depreciation and amortisation (15) (14) (43) (46) (24) (23) (14) (7) Other costs (15) (10) (21) (20) (6) (8) (22) (10) Operating profit/(loss) 42 56 135 140 36 14 (8) 2 Net interest expense (1) — (18) (22) — — — (3) Profit/(loss) before tax 41 56 117 118 36 14 (8) (1) Income tax expense (11) (10) — — (14) (2) — — Profit/(loss) for the year 30 46 117 118 22 12 (8) (1) Group’s share of profit/(loss) 15 23 31 31 11 6 (4) (1) Group adjustment: tax charge — — (9) (9) — — 1 — Group’s share of post-tax results for the year 15 23 22 22 11 6 (3) (1)
Disclosure of associates	2021 2020 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 341 654 995 291 317 608 Exchange adjustments (22) (36) (58) 20 12 32 Additions 6 75 81 16 156 172 Capitalisation of shareholder loan to Nemo Link Limited — — — — 176 176 Share of post-tax results for the year 30 28 58 40 47 87 Share of other comprehensive income of associates, net of tax 1 — 1 1 — 1 Dividends received (31) (49) (80) (41) (34) (75) Other movements¹ (96) (34) (130) 14 (20) (6) Share of net assets at 31 March 229 638 867 341 654 995 1. Within associates, the other movements for the year primarily relates to the reclassification of an investment in an associate to financial investments. Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m Statement of financial position Non-current assets 409 399 795 910 536 582 559 435 Cash and cash equivalents 47 54 27 33 31 26 112 66 All other current assets 24 4 24 26 8 5 12 6 Non-current liabilities (81) (45) (256) (315) (30) (29) (286) (232) Current liabilities (22) (16) (38) (43) (19) (10) (27) (2) Net assets 377 396 552 611 526 574 370 273 Group’s ownership interest 189 198 145 160 263 287 189 139 Group adjustment: elimination — — — — — — (23) (10) Carrying amount of the Group’s investment 189 198 145 160 263 287 166 129 BritNed Development Millennium Pipeline Company LLC Nemo Link Limited Emerald Energy 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m Income statement Revenue 72 80 199 206 66 45 28 19 Depreciation and amortisation (15) (14) (43) (46) (24) (23) (14) (7) Other costs (15) (10) (21) (20) (6) (8) (22) (10) Operating profit/(loss) 42 56 135 140 36 14 (8) 2 Net interest expense (1) — (18) (22) — — — (3) Profit/(loss) before tax 41 56 117 118 36 14 (8) (1) Income tax expense (11) (10) — — (14) (2) — — Profit/(loss) for the year 30 46 117 118 22 12 (8) (1) Group’s share of profit/(loss) 15 23 31 31 11 6 (4) (1) Group adjustment: tax charge — — (9) (9) — — 1 — Group’s share of post-tax results for the year 15 23 22 22 11 6 (3) (1)

Derivative financial instrume_2

Derivative financial instruments (Tables)	12 Months Ended
	Mar. 31, 2021
Financial Instruments [Abstract]
Disclosure of detailed information about derivative financial instruments	The fair values of derivatives by category are as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current 457 (145) 312 93 (380) (287) Non-current 542 (754) (212) 1,249 (954) 295 999 (899) 100 1,342 (1,334) 8 Financing derivatives 942 (767) 175 1,267 (1,134) 133 Commodity contract derivatives 57 (132) (75) 75 (200) (125) 999 (899) 100 1,342 (1,334) 8 The fair values of financing derivatives by type are as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Interest rate swaps 325 (159) 166 556 (337) 219 Cross-currency interest rate swaps 601 (351) 250 643 (514) 129 Foreign exchange forward contracts¹ 16 (74) (58) 58 (39) 19 Inflation-linked swaps — (183) (183) — (234) (234) Equity options — — — 10 (10) — 942 (767) 175 1,267 (1,134) 133 1. Included within the foreign exchange forward contracts balance are £32 million (2020: £3 million) of derivative liabilities in relation to the hedging of capital expenditure and a deal-contingent foreign exchange forward contract liability of £9 million (2020: £nil) in relation to the disposal of NECO (see note 10). The notional contract amounts of financing derivatives by type are as follows: 2021 2020 £m £m Interest rate swaps (2,259) (3,101) Cross-currency interest rate swaps (8,389) (8,097) Foreign exchange forward contracts (4,651) (3,284) Inflation-linked swaps (500) (500) Equity options — (800) (15,799) (15,782) The fair values of commodity contract derivatives by type are as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets Liabilities £m Total £m Commodity purchase contracts accounted for as derivative contracts Forward purchases of gas 44 (94) (50) 64 (108) (44) Derivative financial instruments linked to commodity prices Electricity capacity 2 — 2 — — — Electricity swaps 10 (33) (23) 4 (83) (79) Electricity options — (1) (1) — — — Gas swaps 1 (3) (2) 7 (8) (1) Gas options — (1) (1) — (1) (1) 57 (132) (75) 75 (200) (125) The notional quantities of commodity contract derivatives by type are as follows: 2021 2020 Forward purchases of gas 1 36m Dth 102m Dth Electricity swaps 12,321 GWh 12,836 GWh Gas swaps 47m Dth 89m Dth Gas options 40m Dth 26m Dth 1. Forward gas purchases have terms up to five years (2020: four years). The contractual obligations under these contracts are £104 million (2020: £128 million).
Disclosure of maturity analysis for derivative financial liabilities	The maturity profile of financing derivatives is as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total Current Less than 1 year 428 (70) 358 62 (254) (192) 428 (70) 358 62 (254) (192) Non-current In 1 to 2 years 10 (14) (4) 480 (51) 429 In 2 to 3 years 24 (12) 12 13 (5) 8 In 3 to 4 years 62 (80) (18) 20 (28) (8) In 4 to 5 years 4 (42) (38) 31 (109) (78) More than 5 years 414 (549) (135) 661 (687) (26) 514 (697) (183) 1,205 (880) 325 942 (767) 175 1,267 (1,134) 133 The maturity profile of commodity contract derivatives is as follows: 2021 2020 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than one year 29 (75) (46) 31 (126) (95) 29 (75) (46) 31 (126) (95) Non-current In 1 to 2 years 7 (24) (17) 8 (35) (27) In 2 to 3 years 7 (16) (9) 9 (24) (15) In 3 to 4 years 7 (7) — 8 (12) (4) In 4 to 5 years 6 (5) 1 7 (1) 6 More than 5 years 1 (5) (4) 12 (2) 10 28 (57) (29) 44 (74) (30) 57 (132) (75) 75 (200) (125)

Inventories and current intan_2

Inventories and current intangible assets (Tables)	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Schedule of inventories and current intangible assets	2021 2020 £m £m Fuel stocks 94 151 Raw materials and consumables 253 265 Current intangible assets – emission allowances 92 133 439 549

Trade and other receivables (Ta

Trade and other receivables (Tables)	12 Months Ended
	Mar. 31, 2021
Trade and other receivables [abstract]
Schedule of trade and other receivables	2021 2020 £m £m Trade receivables 1,503 1,571 Accrued income 863 849 Prepayments 387 408 Contract assets 13 — Other receivables 153 158 2,919 2,986
Schedule of reconciliation of changes in allowance account for credit losses	2021 2020 £m £m At 1 April 512 394 Exchange adjustments (57) 20 Charge for the year, net of recoveries 326 234 Uncollectible amounts written off (59) (136) Reclassification to held for sale (note 10) (50) — At 31 March 672 512
Schedule of receivables by geographical area	The trade receivables balance, accrued income balance and provisions balance split by geography are as follows: As at 31 March 2021 As at 31 March 2020 UK US Total UK US Total £m £m £m £m £m £m Trade receivables 227 1,925 2,152 227 1,836 2,063 Accrued income 547 339 886 461 408 869 Provision for impairment of receivables and accrued income (23) (649) (672) (40) (472) (512)
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: 2021 2021 2020 2020 % £m % £m Accrued income 7 322 5 395 0 – 30 days past due 7 580 5 651 30 – 60 days past due 24 155 14 194 60 – 90 days past due 36 108 29 109 3 – 6 months past due 52 140 47 121 6 – 12 months past due 66 180 63 105 Over 12 months past due 71 367 79 277 1,852 1,852

Cash and cash equivalents (Tabl

Cash and cash equivalents (Tables)	12 Months Ended
	Mar. 31, 2021
Cash and cash equivalents [abstract]
Schedule of cash and cash equivalents	2021 2020 £m £m Cash at bank 117 73 Short-term deposits 40 — Cash and cash equivalents 157 73

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Mar. 31, 2021
Disclosure of detailed information about borrowings [abstract]
Schedule of borrowings	2021 2020 £m £m Current Bank loans 1,022 1,244 Bonds¹ 1,987 1,446 Commercial paper 628 1,269 Lease liabilities 99 112 Other loans 1 1 3,737 4,072 Non-current Bank loans 2,532 2,819 Bonds 24,209 23,094 Lease liabilities 586 623 Other loans 156 186 27,483 26,722 Total borrowings 31,220 30,794 1. Includes a liability held at fair value through profit and loss of £682 million (2020: £741 million). Total borrowings are repayable as follows: 2021 2020 £m £m Less than 1 year 3,737 4,072 In 1 to 2 years 1,745 2,212 In 2 to 3 years 889 1,664 In 3 to 4 years 2,206 757 In 4 to 5 years 1,833 2,122 More than 5 years: By instalments 927 870 Other than by instalments 19,883 19,097 31,220 30,794
Schedule of lease obligations	2021 2020 £m £m Gross lease liabilities are repayable as follows: Less than 1 year 114 132 1 to 5 years 321 361 More than 5 years 464 481 899 974 Less: finance charges allocated to future periods (214) (239) 685 735 The present value of lease liabilities are as follows: Less than 1 year 99 112 1 to 5 years 267 297 More than 5 years 319 326 685 735

Trade and other payables (Table

Trade and other payables (Tables)	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Schedule of trade and other payables	2021 2020 £m £m Trade payables 2,165 2,205 Deferred payables 154 137 Customer contributions¹ 138 84 Social security and other taxes 140 202 Contingent consideration (note 38) 39 30 Other payables 881 944 3,517 3,602 1. Relates to amounts received from government-related entities for connecting to our networks, where we have obligations remaining under the contract.

Contract liabilities (Tables)

Contract liabilities (Tables)	12 Months Ended
	Mar. 31, 2021
Contract liabilities [abstract]
Summary of contract liabilities	2021 2020 £m £m Current 66 76 Non-current 1,094 1,082 1,160 1,158
Explanation of significant changes in contract assets and contract liabilities	Significant changes in the contract liabilities balances during the period are as follows: 2021 2020 £m £m As at 1 April 1,158 994 Exchange adjustments (65) 39 Revenue recognised that was included in the contract liability balance at the beginning of the period (96) (60) Increases due to cash received, excluding amounts recognised as revenue during the period 262 185 Reclassification to held for sale (note 10) (99) — At 31 March 1,160 1,158

Other non-current liabilities (

Other non-current liabilities (Tables)	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Schedule of other non current liabilities	2021 2020 £m £m Deferred income¹ 78 101 Customer contributions² 400 428 Contingent consideration (note 38) 18 44 Other payables 347 318 843 891 1. Principally the deferral of profits relating to the sale of property, which we expect to recognise in future years. 2. Relates to amounts received from government-related entities for connecting to our networks, where we have obligations remaining under the contract.

Pensions and other post-retir_2

Pensions and other post-retirement benefits (Tables)	12 Months Ended
	Mar. 31, 2021
Employee Benefits [Abstract]
Schedule of results of most recent actuarial valuations	The results of the most recent actuarial valuations are shown below. See page 176 for the assumptions used for IAS 19 (revised) purposes. Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Latest full actuarial valuation 31 March 2019 31 March 2019 31 March 2019 Actuary Willis Towers Watson Willis Towers Watson Aon Hewitt Market value of plan assets at latest valuation £6,551 million £5,765 million £3,144 million Actuarial value of benefits due to members £6,502 million £5,831 million £3,381 million Market value as percentage of benefits 101% 99% 93% Funding surplus/(deficit) £49 million (£66 million) (£237 million)
Schedule of security agreements	Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Value of security arrangements at 31 March 2021 £186 million £nil £100 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 1 at 31 March 2021 n/a A maximum of £175 million A maximum of £500 million 1. 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 2021 2020 2019 % % % Discount rate – past service 2.00 2.35 2.40 Discount rate – future service 2.15 2.35 2.45 Salary increases 3.40 2.90 3.50 Rate of increase in RPI – past service 3.15 2.65 3.25 Rate of increase in RPI – future service 3.00 2.45 3.20 US pensions US other post-retirement benefits 2021 2020 2019 2021 2020 2019 % % % % % % Discount rate 3.25 3.30 3.95 3.25 3.30 3.95 Salary increases 4.30 3.50 3.50 4.30 3.50 3.50 Initial healthcare cost trend rate n/a n/a n/a 7.10 7.00 7.25 Ultimate healthcare cost trend rate n/a n/a n/a 4.50 4.50 4.50 2021 2020 2019 UK years US years UK years US years UK years US years Assumed life expectations for a retiree age 65 Males 21.8 21.6 22.1 20.9 22.0 22.1 Females 23.7 24.0 23.8 23.4 23.6 24.2 In 20 years: Males 23.1 23.2 23.3 22.5 23.3 23.7 Females 25.2 25.5 25.3 25.1 25.2 25.9
Amounts recognised in the statement of financial position	Amounts recognised in the consolidated statement of financial position 2021 2020 2019 £m £m £m Present value of funded obligations (23,283) (24,281) (24,609) Fair value of plan assets 24,388 23,748 24,793 1,105 (533) 184 Present value of unfunded obligations (324) (345) (330) Other post-employment liabilities (66) (75) (72) Net defined benefit asset/(liability) 715 (953) (218) Represented by: Liabilities (1,032) (2,802) (1,785) Assets 1,747 1,849 1,567 715 (953) (218) The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Present value of funded obligations (13,571) (12,775) (14,200) (6,681) (7,809) (6,901) (3,031) (3,697) (3,508) Fair value of plan assets 14,680 14,364 15,507 6,909 6,972 6,646 2,799 2,412 2,640 1,109 1,589 1,307 228 (837) (255) (232) (1,285) (868) Present value of unfunded obligations (74) (69) (76) (250) (276) (254) — — — Other post-employment liabilities — — — — — — (66) (75) (72) Net defined benefit asset/(liability) 1,035 1,520 1,231 (22) (1,113) (509) (298) (1,360) (940) Represented by: Liabilities (74) (69) (76) (393) (1,373) (769) (565) (1,360) (940) Assets 1,109 1,589 1,307 371 260 260 267 — — 1,035 1,520 1,231 (22) (1,113) (509) (298) (1,360) (940)
Amounts recognised in the income statement and statement of other comprehensive income	Amounts recognised in the income statement and statement of other comprehensive income 2021 2020 2019 £m £m £m Included within operating costs Administration costs 18 16 14 Included within payroll costs Defined benefit plan costs: Current service cost 175 178 193 Past service cost – augmentations — — 5 Past service credit – redundancies (1) — (7) Special termination benefit cost – redundancies 5 2 55 Past service cost – plan amendments¹ — — 34 179 180 280 Included within finance income and costs Net interest cost 38 23 22 Total included in income statement 235 219 316 Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations² 1,408 (724) 68 Exchange adjustments 186 (97) (101) Total included in the statement of other comprehensive income 1,594 (821) (33) 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. This includes actuarial losses from the purchase of buy-in policies of £0.1 billion (2020: £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 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Included within operating costs Administration costs 9 9 6 7 6 7 2 1 1 Included within payroll costs Defined benefit plan costs: Current service cost 28 33 41 104 100 104 43 45 48 Past service cost – augmentations — — 5 — — — — — — Past service credit – redundancies (1) — (7) — — — — — — Special termination benefit cost – redundancies 5 2 55 — — — — — — Past service cost – plan amendments — — 34 — — — — — — 32 35 128 104 100 104 43 45 48 Included within finance income and costs Net interest (income)/cost (38) (31) (31) 35 21 21 41 33 32 Total included in income statement 3 13 103 146 127 132 86 79 81 Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations¹ (622) 143 57 1,017 (588) (14) 1,013 (279) 25 Exchange adjustments — — — 83 (42) (42) 103 (55) (59) Total included in the statement of other comprehensive income (622) 143 57 1,100 (630) (56) 1,116 (334) (34) 1. UK pensions is stated after actuarial losses from the purchase of buy-in policies of £0.1 billion (2020: £0.7 billion).
Disclosure of reconciliation of the net defined benefit liability	Reconciliation of the net defined benefit liability 2021 2020 2019 £m £m £m Opening net defined benefit liability (953) (218) (263) Cost recognised in the income statement (235) (219) (316) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income 1,594 (821) (33) Employer contributions 274 327 419 Other movements (14) (22) (25) Reclassification to held for sale (note 10) 49 — — Closing net defined benefit asset/(liability) 715 (953) (218) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Opening net defined benefit asset/(liability) 1,520 1,231 1,104 (1,113) (509) (552) (1,360) (940) (815) Cost recognised in the income statement (3) (13) (103) (146) (127) (132) (86) (79) (81) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (622) 143 57 1,100 (630) (56) 1,116 (334) (34) Employer contributions 138 156 174 110 153 231 26 18 14 Other movements 2 3 (1) — — — (16) (25) (24) Reclassification to held for sale (note 10) — — — 27 — — 22 — — Closing net defined benefit 1,035 1,520 1,231 (22) (1,113) (509) (298) (1,360) (940) Changes in the present value of defined benefit obligations (including unfunded obligations) 2021 2020 2019 £m £m £m Opening defined benefit obligations (24,626) (24,939) (24,054) Current service cost (175) (178) (193) Interest cost (651) (751) (771) Actuarial gains/(losses) – experience 123 148 (69) Actuarial (losses)/gains – demographic assumptions (1) 452 266 Actuarial losses – financial assumptions (1,268) (84) (619) Past service credit – redundancies 1 — 7 Special termination benefit cost – redundancies (5) (2) (55) Past service cost – augmentations — — (5) Past service cost – plan amendments — — (34) Medicare subsidy received (25) (22) (19) Employee contributions (1) (1) (1) Benefits paid 1,246 1,282 1,376 Exchange adjustments 1,166 (531) (768) Reclassification to held for sale (note 10) 609 — — Closing defined benefit obligations (23,607) (24,626) (24,939) 25. Pensions and other post-retirement benefits continued The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Opening defined benefit obligations (12,844) (14,276) (14,226) (8,085) (7,155) (6,582) (3,697) (3,508) (3,246) Current service cost (28) (33) (41) (104) (100) (104) (43) (45) (48) Interest cost (296) (335) (358) (243) (280) (277) (112) (136) (136) Actuarial (losses)/gains – experience (21) 113 (56) (72) (45) (52) 216 80 39 Actuarial (losses)/gains – demographic assumptions (1) 140 224 — 78 — — 234 42 Actuarial (losses)/gains – financial assumptions (1,181) 798 (568) (62) (595) (24) (25) (287) (27) Past service credit – redundancies 1 — 7 — — — — — — Special termination benefit cost – redundancies (5) (2) (55) — — — — — — Past service cost – augmentations — — (5) — — — — — — Past service cost – plan amendments — — (34) — — — — — — Medicare subsidy received — — — — — — (25) (22) (19) Employee contributions (1) (1) (1) — — — — — — Benefits paid 731 752 837 371 374 398 144 156 141 Exchange adjustments — — — 804 (362) (514) 362 (169) (254) Reclassification to held for sale (note 10) — — — 460 — — 149 — — Closing defined benefit obligations (13,645) (12,844) (14,276) (6,931) (8,085) (7,155) (3,031) (3,697) (3,508) Changes in the value of plan assets 2021 2020 2019 £m £m £m Opening fair value of plan assets 23,748 24,793 23,858 Interest income 613 728 749 Return on plan assets in excess of/(less than) interest¹ 2,554 (1,240) 490 Administration costs (18) (16) (14) Employer contributions 274 327 419 Employee contributions 1 1 1 Benefits paid (1,244) (1,279) (1,377) Exchange adjustments (980) 434 667 Reclassification to held for sale (note 10) (560) — — Closing fair value of plan assets 24,388 23,748 24,793 Actual return on plan assets 3,167 (512) 1,239 Expected contributions to plans in the following year 212 269 307 1. This includes actuarial losses from the purchase of buy-in policies of £0.1 billion (2020: £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 2021 2020 2019 2021 2020 2019 2021 2020 2019 £m £m £m £m £m £m £m £m £m Opening fair value of plan assets 14,364 15,507 15,330 6,972 6,646 6,030 2,412 2,640 2,498 Interest income 334 366 389 208 259 256 71 103 104 Return on plan assets in excess of/ 581 (908) 457 1,151 (26) 62 822 (306) (29) Administration costs (9) (9) (6) (7) (6) (7) (2) (1) (1) Employer contributions 138 156 174 110 153 231 26 18 14 Employee contributions 1 1 1 — — — — — — Benefits paid (729) (749) (838) (371) (374) (398) (144) (156) (141) Exchange adjustments — — — (721) 320 472 (259) 114 195 Reclassification to held for sale (note 10) — — — (433) — — (127) — — Closing fair value of plan assets 14,680 14,364 15,507 6,909 6,972 6,646 2,799 2,412 2,640 Actual return on plan assets 915 (542) 846 1,359 233 318 893 (203) 75 Expected contributions to plans in the following year 93 137 148 113 125 150 6 7 9 1. This includes actuarial losses from the purchase of buy-in policies of £0.1 billion (2020: £0.7 billion).
Disclosure of asset allocations	The approximate investment allocations for our plans is as follows: 2021 2020 2019 UK pensions US pensions US other post-retirement benefits UK pensions US pensions US other post-retirement benefits UK pensions US pensions US other post-retirement benefits % % % % % % % % % Return-seeking assets 18 55 74 21 49 71 23 56 73 Liability-matching assets 82 45 26 79 51 29 77 44 27 Asset allocations Within the asset allocations below, there is significant diversification across regions, asset managers, currencies and bond categories. UK pensions 2021 2020 2019 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 555 801 1,356 732 732 1,464 1,181 784 1,965 Corporate bonds 3,730 37 3,767 3,837 — 3,837 3,625 — 3,625 Government securities 1,836 — 1,836 2,051 — 2,051 6,114 — 6,114 Property 104 565 669 103 585 688 108 749 857 Diversified alternatives — 712 712 — 893 893 — 771 771 Liability-matching assets 1,731 ¹ 4,133 ² 5,864 1,704 ¹ 3,278 ² 4,982 1,751 ¹ — 1,751 Longevity swap — (64) (64) — (51) (51) — (35) (35) Cash and cash equivalents 34 250 284 29 222 251 40 259 299 Other (including net current assets and liabilities) — 256 256 — 249 249 — 160 160 7,990 6,690 14,680 8,456 5,908 14,364 12,819 2,688 15,507 1. Consists of pooled funds which invests mainly in fixed interest securities. 2. Comprises the buy-in policies held by NGUKPS. US pensions 2021 2020 2019 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 560 2,359 2,919 467 2,043 2,510 533 2,178 2,711 Corporate bonds 1,547 507 2,054 1,640 518 2,158 1,329 425 1,754 Government securities 354 527 881 535 732 1,267 422 640 1,062 Property — 264 264 — 307 307 — 316 316 Diversified alternatives 167 458 625 162 464 626 183 487 670 Infrastructure — 130 130 — 121 121 — 99 99 Cash and cash equivalents 24 — 24 24 — 24 21 — 21 Other (including net current assets and liabilities) 12 — 12 (44) 3 (41) (8) 21 13 2,664 4,245 6,909 2,784 4,188 6,972 2,480 4,166 6,646 US other post-retirement benefits 2021 2020 2019 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 419 1,303 1,722 353 1,037 1,390 404 1,184 1,588 Corporate bonds 13 — 13 15 — 15 19 — 19 Government securities 533 3 536 551 1 552 540 3 543 Diversified alternatives 185 172 357 162 161 323 175 166 341 Other¹ — 171 171 — 132 132 — 149 149 1,150 1,649 2,799 1,081 1,331 2,412 1,138 1,502 2,640 1. Other primarily comprises insurance contracts.

Provisions (Tables)

Provisions (Tables)	12 Months Ended
	Mar. 31, 2021
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Schedule of provisions	Environmental £m Decommissioning £m Restructuring £m Other £m Total provisions £m At 1 April 2019 1,639 188 83 289 2,199 Exchange adjustments 82 5 — 10 97 Additions¹ 437 93 7 52 589 Unused amounts reversed (29) (16) (16) (9) (70) Unwinding of discount 65 5 — 7 77 Utilised (123) (21) (39) (55) (238) At 31 March 2020 2,071 254 35 294 2,654 Exchange adjustments (185) (9) (1) (21) (216) Additions 26 42 11 67 146 Unused amounts reversed (38) (27) — (16) (81) Unwinding of discount 66 7 — 5 78 Utilised (161) (16) (19) (62) (258) Reclassification to held for sale (note 10) (79) (7) — (10) (96) At 31 March 2021 1,700 244 26 257 2,227 2021 2020 £m £m Current 260 348 Non-current 1,967 2,306 2,227 2,654
Schedule of environmental provision	The environmental provision is as follows: 2021 2020 Discounted £m Undiscounted £m Real discount rate Discounted £m Undiscounted £m Real discount rate UK sites 167 171 0.5 % 175 184 0.5 % US sites 1,533 1,583 0.5 % 1,896 1,955 0.5 % 1,700 1,754 2,071 2,139

Share capital (Tables)

Share capital (Tables)	12 Months Ended
	Mar. 31, 2021
Share Capital, Reserves And Other Equity Interest [Abstract]
Schedule of share capital	Allotted, called-up and fully paid million £m At 1 April 2019 3,687 458 Issued during the year in lieu of dividends¹ 93 12 At 31 March 2020 3,780 470 Issued during the year in lieu of dividends¹ 35 4 At 31 March 2021 3,815 474 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, 2021
Disclosure of reserves within equity [abstract]
Schedule of reserves within equity	Translation £m Cash flow hedge £m Cost of hedging £m Available-for-sale FVOCI equity £m FVOCI Own Capital redemption £m Merger £m Total £m At 1 April 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 adjustments 1,2 360 — — — — — — — — 360 Net (losses)/gains taken to equity — (206) (107) — — 2 7 — — (304) Share of net gains of associates taken to equity — 1 — — — — — — — 1 Transferred to profit or loss — 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 750 61 17 — 34 48 13 19 (5,165) (4,223) Exchange adjustments 1,2 560 — — — — — — — — 560 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 1 April 2020 1,310 (75) (50) — 25 31 10 19 (5,165) (3,895) Exchange adjustments¹ (1,345) — — — — — — — — (1,345) Net gains/(losses) taken to equity — 14 11 — 36 80 (11) — — 130 Share of net gains of associates taken to equity — 1 — — — — — — — 1 Transferred to profit or loss — 56 3 — — — — — — 59 Net losses in respect of cash flow hedging of capital expenditure — (14) — — — — — — — (14) Tax — (13) 8 — (10) — 2 — — (13) Cash flow hedges transferred to the statement of financial position, net of tax — (17) — — — — — — — (17) At 31 March 2021 (35) (48) (28) — 51 111 1 19 (5,165) (5,094) 1. The exchange adjustments recorded in the translation reserve comprise a loss of £1,507 million (2020: gain of £545 million; 2019: gain of £896 million) relating to the translation of foreign operations offset by a gain of £183 million (2020: gain of £5 million; 2019: loss of £550 million) relating to borrowings, cross-currency swaps and foreign exchange forward contracts used to hedge the net investment in non-sterling denominated subsidiaries. 2. Comparative amounts have been revised as described in note 1F.

Net debt (Tables)

Net debt (Tables)	12 Months Ended
	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Schedule of components of net debt	Composition of net debt Net debt is comprised as follows: 2021 2020 2019 £m £m £m Cash and cash equivalents 157 73 252 Current financial investments 2,342 1,998 1,981 Borrowings (31,220) (30,794) (28,730) Financing derivatives¹ 175 133 (32) (28,546) (28,590) (26,529) 1. The financing derivatives balance included in net debt excludes the commodity derivatives (see note 17).
Schedule of changes in net debt	Analysis of changes in net debt Notes Cash and cash equivalents £m Financial investments £m Borrowings £m Financing derivatives £m Total 1 £m At 1 April 2018 329 2,694 (26,625) 600 (23,002) Impact of transition to IFRS 9 37 — — (32) — (32) Cash flow 29(c) (80) (846) (240) 422 (744) Fair value gains and losses — 14 (9) (1,011) (1,006) Foreign exchange movements 3 79 (724) — (642) Interest income/(charges) 6 — 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 37 — — (474) — (474) Cash flow 29(c) (183) (42) 450 450 675 Fair value gains and losses — 1 (57) (246) (302) Foreign exchange movements 4 24 (807) — (779) Interest income/(charges) 6 — 34 (1,092) (39) (1,097) Other non-cash movements — — (84) — (84) At 1 April 2020 73 1,998 (30,794) 133 (28,590) Cash flow 29(c) 95 429 (2,336) 4 (1,808) Fair value gains and losses — 14 159 31 204 Foreign exchange movements (7) (106) 1,710 — 1,597 Interest income/(charges) 6 — 7 (946) 7 (932) Other non-cash movements — — (136) — (136) Reclassification to held for sale 10 (4) — 1,123 — 1,119 At 31 March 2021 157 2,342 (31,220) 175 (28,546) Balances at 31 March 2021 comprise: Non-current assets — — — 514 514 Current assets 157 2,342 — 428 2,927 Current liabilities — — (3,737) (70) (3,807) Non-current liabilities — — (27,483) (697) (28,180) 157 2,342 (31,220) 175 (28,546) 1. Includes accrued interest at 31 March 2021 of £263 million (2020: £246 million; 2019: £223 million).
Reconciliation of cash flow from financing liabilities to cash flow statement	Reconciliation of cash flow from liabilities within net debt to cash flow statement 2021 2020 2019 Borrowings and other Financing derivatives Borrowings and other Financing derivatives Borrowings and other Financing derivatives Cash flows per financing activities section of cash flow statement: Proceeds received from loans 5,645 — 4,218 — 2,932 — Repayment of loans (1,663) — (3,253) — (1,969) — Payments of lease liabilities (112) — (121) — (70) — Net movements in short-term borrowings (759) — (424) — 179 — Cash inflows on derivatives — 58 — 62 — 221 Cash outflows on derivatives — (185) — (249) — (186) Interest paid (804) (31) (904) (53) (856) (58) Cash flows per financing activities section of cash flow statement 2,307 (158) (484) (240) 216 (23) Adjustments: Non-net debt-related items 29 — 34 — 24 — Derivative cash inflow in relation to capital expenditure — 10 — 13 — 13 Derivative cash inflows per investing section of cash flow statement — 225 — 58 — 17 Derivative cash outflows per investing section of cash flow statement — (81) — (281) — (429) Cash flows relating to financing liabilities within net debt 2,336 (4) (450) (450) 240 (422) Analysis of changes in net debt: Borrowings 2,336 — (450) — 240 — Financing derivatives — (4) — (450) — (422) Cash flow movements relating to financing liabilities within net debt 2,336 (4) (450) (450) 240 (422)
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. For the purposes of this table, the liabilities arising from financing activities are those for which cash flows were, or future cash flows will be, classified in the consolidated cash flow statement within financing activities. As a result we have separately disclosed the reconciliation below, excluding derivatives associated with our net investment hedges and derivatives associated with the hedging of capital expenditure, given that they are both classified in the consolidated cash flow statement within investing activities. Notes Borrowings £m Financing derivatives £m Total £m At 1 April 2018 (26,625) 553 (26,072) Impact of transition to IFRS 9 37 (32) — (32) Cash flow 29(c) (240) 23 (217) Fair value gains and losses (9) (334) (343) Foreign exchange movements (724) — (724) Interest charges 6 (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 37 (474) — (474) Cash flow 29(c) 450 240 690 Fair value gains and losses (57) (231) (288) Foreign exchange movements (807) — (807) Interest charges 6 (1,092) (9) (1,101) Other non-cash movements (84) — (84) At 1 April 2020 (30,794) 228 (30,566) Cash flow 29(c) (2,336) 158 (2,178) Fair value gains and losses 159 (301) (142) Foreign exchange movements 1,710 — 1,710 Interest charges 6 (946) 11 (935) Other non-cash movements (136) — (136) Reclassification to held for sale 10 1,123 — 1,123 At 31 March 2021 (31,220) 96 (31,124)

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Mar. 31, 2021
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Schedule of capital commitments and contingent liabilities	2021 2020 £m £m Future capital expenditure Contracted for but not provided 2,716 2,629 Energy purchase commitments¹ Less than 1 year 1,255 1,365 In 1 to 2 years 894 890 In 2 to 3 years 975 973 In 3 to 4 years 959 955 In 4 to 5 years 896 861 More than 5 years 10,805 11,314 15,784 16,358 Guarantees² Guarantee of sublease for US property (expires 2040) 149 173 Guarantees of certain obligations of Grain LNG (expire up to 2025) 33 34 Guarantees of certain obligations for construction of HVDC West Coast Link (expected expiry 2059) 85 92 Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates)² 584 683 Guarantees of certain obligations of St William Homes LLP (various expiry dates)³ 53 30 Guarantees of certain obligations of National Grid IFA 2 Limited (expected expiry 2022)² 170 564 Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024) 1,276 1,096 Other guarantees and letters of credit (various expiry dates) 486 150 2,836 2,822 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 £136 million (2020: £358 million). 3. Includes guarantees to related parties.

Related party transactions (Tab

Related party transactions (Tables)	12 Months Ended
	Mar. 31, 2021
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: 2021 2020 2019 £m £m £m Sales: Goods and services supplied to a pension plan 3 5 5 Sales: Goods and services supplied to joint ventures¹ 79 101 151 Sales: Goods and services supplied to associates² 1 33 192 Purchases: Goods and services received from joint ventures³ 35 61 26 Purchases: Goods and services received from associates³ 43 56 141 Receivable from joint ventures 4 263 255 584 Receivable from associates 4 — 1 368 Payable to joint ventures 17 — 8 Payable to associates 3 4 12 Interest income from joint ventures — 2 5 Interest income from associates — 8 23 Dividends received from joint ventures 5 49 34 30 Dividends received from associates 6 32 41 171 1. During the year, £14 million (2020: £38 million; 2019: £139 million) of property sites were sold to St William Homes LLP, £50 million of sales were made to Emerald Energy Venture LLC (2020: £21 million; 2019: £nil) and a further £6 million (2020: £32 million; 2019; £2 million) of sales were made to NGET/SPT Upgrades Limited. 2. In previous years, sales related 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) and included income of £31 million in 2020 and £52 million in 2019 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, £41 million (2020: £31 million; 2019: £30 million) of purchases from Millennium Pipeline Company LLC. The Group also purchased assets of £5 million (2020: £58 million; 2019: £26 million) from NGET/SPT Upgrades Limited (a joint venture). 4. Amounts receivable from joint ventures include £241 million (2020: £242 million; 2019: £325 million) in relation to St William Homes LLP. There are no longer loans receivable from Quadgas (2020: £nil; 2019: £352 million) and Nemo Link (a joint venture) (2020: £nil; 2019: £258 million). 5. Includes dividends of £18 million (2020: £25 million; 2019: £30 million) received from BritNed Development Limited and £25 million (2020: £8 million; 2019:£ nil) from Nemo Link Limited. 6. Includes dividends of £31 million (2020: £32 million; 2019: £24 million) received from Millennium Pipeline Company LLC. Dividends of £133 million were received from Quadgas in 2019.

Financial risk management (Tabl

Financial risk management (Tables)	12 Months Ended
	Mar. 31, 2021
Financial Instruments [Abstract]
Disclosure of treasury credit risk	As at 31 March 2021, the following limits were in place for investments and derivative financial instruments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 2,259 1,129 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,232 616 Double ‘A+’ G7 sovereign entities (AA+) 2,054 1,027 Double ‘A’ range institutions (AA) 822 to 1,027 411 to 513 Single ‘A’ range institutions (A) 288 to 411 144 to 205
Disclosure of offsetting of financial assets and financial liabilities	Related amounts At 31 March 2021 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 942 — 942 (234) (561) 147 Commodity contract derivatives 57 — 57 (8) — 49 999 — 999 (242) (561) 196 Liabilities Financing derivatives (767) — (767) 234 467 (66) Commodity contract derivatives (132) — (132) 8 4 (120) (899) — (899) 242 471 (186) 100 — 100 — (90) 10 Related amounts At 31 March 2020 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 1,267 — 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)
Disclosure of maturity analysis for financial liabilities and derivatives	The following is a payment profile of our financial liabilities and derivatives: At 31 March 2021 Less than £m 1 to 2 2 to 3 More than Total Non-derivative financial liabilities Borrowings, excluding lease liabilities (3,350) (1,690) (806) (25,562) (31,408) Interest payments on borrowings¹ (810) (755) (731) (12,018) (14,314) Lease liabilities (118) (108) (90) (599) (915) Other non-interest-bearing liabilities (3,207) (350) — — (3,557) Contingent consideration (40) (24) — — (64) Derivative financial liabilities Financing derivatives – receipts² 3,773 749 451 4,326 9,299 Financing derivatives – payments² (3,899) (877) (533) (5,153) (10,462) Commodity contract derivatives – receipts² 12 — — — 12 Commodity contract derivatives – payments² (83) (23) (14) (12) (132) Derivative financial assets Financing derivatives – receipts² 2,162 926 833 1,789 5,710 Financing derivatives – payments² (1,700) (834) (780) (1,536) (4,850) Commodity contract derivatives – receipts² 21 4 1 1 27 Commodity contract derivatives – payments² (21) (4) (2) — (27) (7,260) (2,986) (1,671) (38,764) (50,681) At 31 March 2020 Less than 1 year £m 1 to 2 2 to 3 years £m More than 3 years £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) 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: 2021 2020 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 63 — 94 — 157 18 — 55 — 73 Financial investments 1,215 — 1,127 — 2,342 813 — 1,185 — 1,998 Borrowings (12,210) (5,351) (12,660) (999) (31,220) (12,407) (4,150) (13,217) (1,020) (30,794) Pre-derivative position (10,932) (5,351) (11,439) (999) (28,721) (11,576) (4,150) (11,977) (1,020) (28,723) Derivative effect (826) 5,459 (5,494) 1,036 175 (1,169) 4,341 (4,214) 1,175 133 Net debt position (11,758) 108 (16,933) 37 (28,546) (12,745) 191 (16,191) 155 (28,590) The currency exposure on other financial instruments is as follows: 2021 2020 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 282 — 1,387 — 1,669 306 — 1,403 — 1,709 Trade and other payables (1,207) — (1,878) — (3,085) (1,177) — (2,002) — (3,179) Other non-current liabilities (77) — (288) — (365) (85) — (277) — (362) 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. 2021 2020 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 4 952 6 877 US discount rate change of 0.5%² 17 730 10 514 UK RPI rate change of 0.5%³ 3 723 4 670 UK long-term rate of increase in salaries change of 0.5% 1 42 1 39 US long-term rate of increase in salaries change of 0.5% 3 42 2 47 UK change of one year to life expectancy at age 65 4 1 612 1 545 US change of one year to life expectancy at age 65 4 429 4 456 Assumed US healthcare cost trend rates change of 1% 26 437 31 507 Environmental provision: 10% change in estimated future cash flows 170 170 210 210 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 £257 million (2020: £205 million) net assets offset from the buy-in policies, 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 would have a £190 million (2020: £152 million) net assets offset to the above. 4. In the UK, the buy-in policies and the longevity swap entered into, would have a £183 million (2020: £223 million) net assets offset to the above. 2021 2020 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 25 — 27 — UK interest rates change of 0.5% 12 98 14 47 US interest rates change of 0.5% 6 22 5 27 US dollar exchange rate change of 10%² 44 285 49 216 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 £1,425 million (2020: £1,319 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: 2021 2020 Income statement £m Net assets £m Income statement £m Net assets £m Commodity price risk (post-tax): 10% increase in commodity prices 20 20 26 26 10% decrease in commodity prices (21) (21) (27) (27) Assets and liabilities carried at fair value (post-tax): 10% fair value change in derivative financial instruments¹ 14 14 12 12 10% fair value change in commodity contract derivative liabilities 6 6 9 9 1. The effect of a 10% change in fair value assumes no hedge accounting.
Disclosure of financial instruments by type of interest rate	Net debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2021 2020 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 64 67 — 26 157 71 10 — (8) 73 Financial investments — 2,309 — 33 2,342 — 1,966 — 32 1,998 Borrowings (23,163) (1,762) (6,295) — (31,220) (20,969) (3,085) (6,740) — (30,794) Pre-derivative position (23,099) 614 (6,295) 59 (28,721) (20,898) (1,109) (6,740) 24 (28,723) Derivative effect 2,869 (2,511) (183) — 175 2,259 (1,892) (234) — 133 Net debt position (20,230) (1,897) (6,478) 59 (28,546) (18,639) (3,001) (6,974) 24 (28,590) 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	In accordance with the requirements of IFRS 7, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Year ended 31 March 2021 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 gains/(losses) in respect of: Cash flow hedges — 14 (14) — Cost of hedging (15) (24) — 50 Transferred to profit or loss in respect of: Cash flow hedges — 56 — — Cost of hedging 1 2 — — Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (30) — 6 Consolidated statement of financial position Derivatives – carrying value of hedging instruments ¹ Assets – current — 10 2 5 Assets – non-current 187 59 1 140 Liabilities – current — (12) (24) (17) Liabilities – non-current (113) (255) (22) — Profiles of the significant timing, price and rate information of hedging instruments Maturity range Jan 2023 – Jan 2043 Sep 2021 – Nov 2040 Apr 2021 – Feb 2027 Mar 2022 – Sep 2027 Spot foreign exchange range: GBP:USD 1.64 1.30 – 1.66 1.31 – 1.41 1.22 – 1.40 GBP:EUR 1.11 – 1.24 1.08 – 1.24 1.04 – 1.29 1.15 – 1.16 EUR:USD 1.13 – 1.17 1.13 – 1.14 n/a n/a Interest rate range: GBP LIBOR +30bps/+408bps 0.976% – 5.845% n/a n/a USD LIBOR +68bps/+115bps 2.513% – 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. 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. (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2021 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 (2,755) 121 (85) 153 (127) 26 1. The carrying value of the hedged borrowings is £2,714 million, of which £nil is current and £2,714 million is non-current. 2. Included within the hedging instrument notional balance is £2,679 million impacted by Interest Rate Benchmark Reform amendments. 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 was £1,883 million, of which £72 million was current and £1,811 million was non-current. 2. Included within the hedging instrument notional balance was £1,675 million impacted by Interest Rate Benchmark Reform amendments. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2021 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 borrowings ¹ (4,884) (11) (6) (16) 16 — Foreign currency risk on forecasted cash flows (988) (31) 3 17 (17) — 1. Included within the hedging instrument notional balance is £176 million impacted by Interest Rate Benchmark Reform amendments. 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 borrowings ¹ (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 was £176 million impacted by Interest Rate Benchmark Reform amendments. (iii) Net investment hedges of foreign currency risk: As at 31 March 2021 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 ¹ (2,786) 183 (2,826) (183) 183 — 1. Included within the hedging instrument notional balance is £nil impacted by Interest Rate Benchmark Reform amendments. 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 was £nil impacted by Interest Rate Benchmark Reform amendments.
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 2021 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 (2,755) 121 (85) 153 (127) 26 1. The carrying value of the hedged borrowings is £2,714 million, of which £nil is current and £2,714 million is non-current. 2. Included within the hedging instrument notional balance is £2,679 million impacted by Interest Rate Benchmark Reform amendments. 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 was £1,883 million, of which £72 million was current and £1,811 million was non-current. 2. Included within the hedging instrument notional balance was £1,675 million impacted by Interest Rate Benchmark Reform amendments. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2021 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 borrowings ¹ (4,884) (11) (6) (16) 16 — Foreign currency risk on forecasted cash flows (988) (31) 3 17 (17) — 1. Included within the hedging instrument notional balance is £176 million impacted by Interest Rate Benchmark Reform amendments. 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 borrowings ¹ (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 was £176 million impacted by Interest Rate Benchmark Reform amendments. (iii) Net investment hedges of foreign currency risk: As at 31 March 2021 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 ¹ (2,786) 183 (2,826) (183) 183 — 1. Included within the hedging instrument notional balance is £nil impacted by Interest Rate Benchmark Reform amendments. 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 was £nil impacted by Interest Rate Benchmark Reform amendments.
Disclosure of fair value measurement of assets	2021 2020 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 1,768 — 240 2,008 1,278 — 108 1,386 Investments held at FVOCI 99 416 — 515 83 352 — 435 Investments in associates — — — — — — 103 103 Financing derivatives — 942 — 942 — 1,257 10 1,267 Commodity contract derivatives — 12 45 57 — 9 66 75 1,867 1,370 285 3,522 1,361 1,618 287 3,266 Liabilities Financing derivatives — (584) (183) (767) — (889) (245) (1,134) Commodity contract derivatives — (75) (57) (132) — (136) (64) (200) Liabilities held at fair value (682) — — (682) (741) — — (741) Contingent consideration 1 — — (57) (57) — — (74) (74) (682) (659) (297) (1,638) (741) (1,025) (383) (2,149) 1,185 711 (12) 1,884 620 593 (96) 1,117 1. Contingent consideration relates to the acquisition of National Grid Renewables (see note 38). The changes in value of our Level 3 financial instruments are as follows: Financing derivatives Commodity contract derivatives Other 3 Total 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m At 1 April (235) (214) 2 1 137 152 (96) (61) Net gains/(losses) for the year 1,2 51 (20) (16) 6 (2) 26 33 12 Purchases — — (1) 26 32 51 31 77 Acquisition of National Grid Renewables — — — — — (74) — (74) Settlements 1 (1) (1) (31) 16 (18) 16 (50) Reclassification to held for sale (note 10) — — 4 — — — 4 — At 31 March (183) (235) (12) 2 183 137 (12) (96) 1. Gain of £51 million (2020: £20 million loss) 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 £46 million (2020: £17 million loss) is attributable to commodity contract derivative financial instruments held at the end of the reporting period. 3. Other comprises our investments in Sunrun Neptune 2016 LLC 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 National Grid Renewables (see note 38).
Disclosure of fair value measurement of liabilities	2021 2020 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 1,768 — 240 2,008 1,278 — 108 1,386 Investments held at FVOCI 99 416 — 515 83 352 — 435 Investments in associates — — — — — — 103 103 Financing derivatives — 942 — 942 — 1,257 10 1,267 Commodity contract derivatives — 12 45 57 — 9 66 75 1,867 1,370 285 3,522 1,361 1,618 287 3,266 Liabilities Financing derivatives — (584) (183) (767) — (889) (245) (1,134) Commodity contract derivatives — (75) (57) (132) — (136) (64) (200) Liabilities held at fair value (682) — — (682) (741) — — (741) Contingent consideration 1 — — (57) (57) — — (74) (74) (682) (659) (297) (1,638) (741) (1,025) (383) (2,149) 1,185 711 (12) 1,884 620 593 (96) 1,117 1. Contingent consideration relates to the acquisition of National Grid Renewables (see note 38). The changes in value of our Level 3 financial instruments are as follows: Financing derivatives Commodity contract derivatives Other 3 Total 2021 2020 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m £m £m At 1 April (235) (214) 2 1 137 152 (96) (61) Net gains/(losses) for the year 1,2 51 (20) (16) 6 (2) 26 33 12 Purchases — — (1) 26 32 51 31 77 Acquisition of National Grid Renewables — — — — — (74) — (74) Settlements 1 (1) (1) (31) 16 (18) 16 (50) Reclassification to held for sale (note 10) — — 4 — — — 4 — At 31 March (183) (235) (12) 2 183 137 (12) (96) 1. Gain of £51 million (2020: £20 million loss) 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 £46 million (2020: £17 million loss) is attributable to commodity contract derivative financial instruments held at the end of the reporting period. 3. Other comprises our investments in Sunrun Neptune 2016 LLC 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 National Grid Renewables (see note 38).
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 2021 2020 2021 2020 2021 2020 £m £m £m £m £m £m 10% increase in commodity prices¹ — — 3 2 — — 10% decrease in commodity prices¹ — — (1) — — — +10% market area price change — — (4) (4) — — -10% market area price change — — 7 4 — — +20 basis points change in Limited Price Inflation (LPI) market curve² (83) (95) — — — — -20 basis points change in LPI market curve² 83 90 — — — — +50 basis points change in discount rate — — — — (5) (3) -50 basis points change in discount rate — — — — 5 4 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 2021.

Borrowing facilities (Tables)

Borrowing facilities (Tables)	12 Months Ended
	Mar. 31, 2021
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: 2021 2020 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — — In 1 to 2 years 1,668 1,940 In 2 to 3 years 534 1,668 In 3 to 4 years 1,718 277 In 4 to 5 years 1,605 1,887 More than 5 years — — 5,525 5,772

Subsidiary undertakings, join_2

Subsidiary undertakings, joint ventures and associates (Tables)	12 Months Ended
	Mar. 31, 2021
Interests In Other Entities [Abstract]
Disclosure of subsidiaries taking advantage of audit exemption under section 479A of Companies Act 2006	The following UK subsidiaries will take advantage of the audit exemption set out within section 479A of the Companies Act 2006 for the year ended 31 March 2021: Company name Company number NatGrid One Limited 5521240 Natgrid TW1 Limited 7579324 National Grid Holdings Limited 3096772 National Grid International Limited 2537092 National Grid Twelve Limited 4355616 National Grid Twenty Three Limited 6999009 National Grid (US) Holdings Limited 2630496 National Grid (US) Investments 2 Limited 3784528 National Grid (US) Investments 4 Limited 3867128 National Grid (US) Partner 1 Limited 4314432

Sensitivites (Tables)

Sensitivites (Tables)	12 Months Ended
	Mar. 31, 2021
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: 2021 2020 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 63 — 94 — 157 18 — 55 — 73 Financial investments 1,215 — 1,127 — 2,342 813 — 1,185 — 1,998 Borrowings (12,210) (5,351) (12,660) (999) (31,220) (12,407) (4,150) (13,217) (1,020) (30,794) Pre-derivative position (10,932) (5,351) (11,439) (999) (28,721) (11,576) (4,150) (11,977) (1,020) (28,723) Derivative effect (826) 5,459 (5,494) 1,036 175 (1,169) 4,341 (4,214) 1,175 133 Net debt position (11,758) 108 (16,933) 37 (28,546) (12,745) 191 (16,191) 155 (28,590) The currency exposure on other financial instruments is as follows: 2021 2020 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 282 — 1,387 — 1,669 306 — 1,403 — 1,709 Trade and other payables (1,207) — (1,878) — (3,085) (1,177) — (2,002) — (3,179) Other non-current liabilities (77) — (288) — (365) (85) — (277) — (362) 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. 2021 2020 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 4 952 6 877 US discount rate change of 0.5%² 17 730 10 514 UK RPI rate change of 0.5%³ 3 723 4 670 UK long-term rate of increase in salaries change of 0.5% 1 42 1 39 US long-term rate of increase in salaries change of 0.5% 3 42 2 47 UK change of one year to life expectancy at age 65 4 1 612 1 545 US change of one year to life expectancy at age 65 4 429 4 456 Assumed US healthcare cost trend rates change of 1% 26 437 31 507 Environmental provision: 10% change in estimated future cash flows 170 170 210 210 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 £257 million (2020: £205 million) net assets offset from the buy-in policies, 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 would have a £190 million (2020: £152 million) net assets offset to the above. 4. In the UK, the buy-in policies and the longevity swap entered into, would have a £183 million (2020: £223 million) net assets offset to the above. 2021 2020 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 25 — 27 — UK interest rates change of 0.5% 12 98 14 47 US interest rates change of 0.5% 6 22 5 27 US dollar exchange rate change of 10%² 44 285 49 216 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 £1,425 million (2020: £1,319 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: 2021 2020 Income statement £m Net assets £m Income statement £m Net assets £m Commodity price risk (post-tax): 10% increase in commodity prices 20 20 26 26 10% decrease in commodity prices (21) (21) (27) (27) Assets and liabilities carried at fair value (post-tax): 10% fair value change in derivative financial instruments¹ 14 14 12 12 10% fair value change in commodity contract derivative liabilities 6 6 9 9 1. The effect of a 10% change in fair value assumes no hedge accounting.

Additional disclosures in res_2

Additional disclosures in respect of guaranteed securities (Tables)	12 Months Ended
	Mar. 31, 2021
Separate Financial Statements [Abstract]
Disclosure of Condensed Balance Sheet	Summarised financial information for the year ended 31 March 2021 – IFRS National Grid plc and Niagara Mohawk Power Corporation combined £m Combined statement of financial position Non-current loans to other subsidiaries — Non-current assets 8,940 Current loans to other subsidiaries 20,692 Current assets 1,553 Current loans from other subsidiaries (17,589) Current liabilities (1,342) Non-current loans from other subsidiaries (2,059) Non-current liabilities (6,363) Net assets ¹ 3,832 Equity 3,832 Combined income statement – continuing operations Revenue 2,462 Operating costs (4,562) Operating profit (2,100) Other income from other subsidiaries 9,978 Other income and costs, including taxation (182) Profit after tax 7,696 1. Excluded from net assets above are investments in other consolidated subsidiaries with a carrying value of £14,415 million.
Disclosure of Condensed Income Statement	Summarised financial information for the year ended 31 March 2021 – IFRS National Grid plc and Niagara Mohawk Power Corporation combined £m Combined statement of financial position Non-current loans to other subsidiaries — Non-current assets 8,940 Current loans to other subsidiaries 20,692 Current assets 1,553 Current loans from other subsidiaries (17,589) Current liabilities (1,342) Non-current loans from other subsidiaries (2,059) Non-current liabilities (6,363) Net assets ¹ 3,832 Equity 3,832 Combined income statement – continuing operations Revenue 2,462 Operating costs (4,562) Operating profit (2,100) Other income from other subsidiaries 9,978 Other income and costs, including taxation (182) Profit after tax 7,696 1. Excluded from net assets above are investments in other consolidated subsidiaries with a carrying value of £14,415 million.

Transition to new accounting _2

Transition to new accounting standards (Tables)	12 Months Ended
	Mar. 31, 2021
Disclosure of initial application of standards or interpretations [abstract]
Disclosure of impact of transition to new accounting standards	Impact of transition 31 March 2019 (before the impact of IFRS 16) 1 £m IFRS 16 1 April 2019 As restated £m Property, plant and equipment – Right-of-use assets Land and buildings 2,560 381 2,941 Plant and machinery 36,911 67 36,978 Assets in the course of construction 5,049 — 5,049 Motor vehicles and office equipment 339 20 359 Total property, plant and equipment 44,859 468 45,327 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 19,568 — 19,568 Equity Total equity 19,568 — 19,568 1. Comparative amounts have been revised as described in note 1F. Impact of transition 31 March 2018 (Before the impact of transition adjustments)* Transition adjustments 1 April 2018 IFRS 9 IFRS 15 £m £m £m £m Non-current assets Goodwill 4,984 — — 4,984 Other intangible assets 899 — — 899 Property, plant and equipment 40,730 — — 40,730 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 52,523 — — 52,523 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 59,204 — (3) 59,201 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 (3,868) 5 4 74 8 (3,789) Pensions and other post-retirement benefit obligations (1,672) — — (1,672) Provisions (1,779) — — (1,779) Total non-current liabilities (31,474) (27) (172) (31,673) Total liabilities (40,171) (27) (166) (40,364) Net assets 19,033 (27) (169) 18,837 Equity Share capital 452 — — 452 Share premium account 1,321 — — 1,321 Retained earnings 21,784 (99) 5 (169) 9 21,516 Other equity reserves (4,540) 72 6 — (4,468) Total shareholders’ equity 19,017 (27) (169) 18,821 Non-controlling interests 16 — — 16 Total equity 19,033 (27) (169) 18,837 *Comparative amounts have been revised as described in note 1F.
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 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 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)

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Schedule of fair values of the assets and liabilities recognised	The fair values of the assets and liabilities recognised at the acquisition date for both the acquisition of the subsidiary, National Grid Renewables, 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 – National Grid Renewables 70 Cash consideration – National Grid Renewables 49 Cash consideration – Emerald 90 209

Basis of preparation and rece_4

Basis of preparation and recent accounting developments - Going concern (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Fixed interest rate bonds
Disclosure of detailed information about borrowings [line items]
Notional amount	£ 5,600
Facilities To Finance The Acquisition
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity	8,250	£ 0
Facilities To Backup Acquired Debt
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity	£ 1,105	£ 0

Basis of preparation and rece_5

Basis of preparation and recent accounting developments - Narratives (Details)	Mar. 17, 2021
Narragansett Electric Company
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary, sold	100.00%

Basis of preparation and rece_6

Basis of preparation and recent accounting developments - Comparative period revisions (Details) - GBP (£) £ in Millions	Mar. 31, 2021	[1]	Mar. 31, 2020		Apr. 01, 2019	Mar. 31, 2019		Apr. 01, 2018	Mar. 31, 2018
Disclosure of adjustments made to previously presented financial statements concepts [Line Items]
Goodwill	£ 4,588		£ 5,712	[1]		£ 5,372	[1]	£ 4,984	£ 4,984
Property, plant and equipment	47,043		49,762	[1]	£ 45,327	44,859	[1]	40,730	40,730
Deferred tax liability	4,815		4,446	[1]		4,215	[1]	3,789	3,868
Retained earnings	£ 23,163		21,895	[1]		21,999	[1]	£ 21,516	21,784
Prior year adjustment
Disclosure of adjustments made to previously presented financial statements concepts [Line Items]
Goodwill			(521)			(497)			(460)
Property, plant and equipment			992			946			877
Deferred tax liability			262			250			232
Retained earnings			185			185			185
Translation reserve			£ 24			£ 14			£ 0
[1]	Comparative amounts have been revised as described in note 1F.

Segmental analysis - Narrative

Segmental analysis - Narrative (Details) £ in Millions	12 Months Ended
	Mar. 31, 2021GBP (£)segment	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)
Disclosure of operating segments [line items]
Number of operating segments | segment	3
Operating profit/(loss) from continuing operations	£ 2,895	£ 2,780	£ 2,870
UK
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	1,550	1,915	1,422
US
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	1,345	865	1,448
UK Electricity Transmission | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	1,027	1,316	778
UK Gas Transmission | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	337	347	267
US Regulated | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	1,344	880	1,425
NG Ventures and Other | Unallocated amounts
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	187	237	400
Exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	(31)	(527)	(572)
Exceptional items and remeasurements | UK Electricity Transmission | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	(7)	(4)	(237)
Exceptional items and remeasurements | UK Gas Transmission | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	(5)	(1)	(36)
Exceptional items and remeasurements | US Regulated | Operating segments
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	31	(517)	(299)
Exceptional items and remeasurements | NG Ventures and Other | Unallocated amounts
Disclosure of operating segments [line items]
Operating profit/(loss) from continuing operations	£ (50)	£ (5)	£ 0

Segmental analysis - Revenue (D

Segmental analysis - Revenue (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of operating segments [line items]
Revenue	£ 14,779	£ 14,540	£ 14,933
UK
Disclosure of operating segments [line items]
Revenue	5,482	5,282	5,045
US
Disclosure of operating segments [line items]
Revenue	9,297	9,258	9,888
UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	3,982	3,694	3,331
UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	888	911	884
US Regulated
Disclosure of operating segments [line items]
Revenue	9,195	9,205	9,846
NG Ventures and Other
Disclosure of operating segments [line items]
Revenue	714	730	872
Operating Segments And Unallocated Amounts
Disclosure of operating segments [line items]
Revenue	14,806	14,570	14,969
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	3,992	3,702	3,351
Operating segments | UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	904	927	896
Operating segments | US Regulated
Disclosure of operating segments [line items]
Revenue	9,195	9,205	9,846
Unallocated amounts | NG Ventures and Other
Disclosure of operating segments [line items]
Revenue	715	736	876
Unallocated amounts | NG Ventures
Disclosure of operating segments [line items]
Revenue	636	608	597
Sales between segments
Disclosure of operating segments [line items]
Revenue	(27)	(30)	(36)
Sales between segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	(10)	(8)	(20)
Sales between segments | UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	(16)	(16)	(12)
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	£ (1)	£ (6)	£ (4)

Segmental analysis - Operating

Segmental analysis - Operating profit from continuing operations (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 2,895	£ 2,780	£ 2,870
Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	2,926	3,307	3,442
UK
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,550	1,915	1,422
UK | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,612	1,925	1,695
US
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,345	865	1,448
US | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,314	1,382	1,747
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,027	1,316	778
Operating segments | UK Electricity Transmission | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,034	1,320	1,015
Operating segments | UK Gas Transmission
Disclosure of operating segments [line items]
Operating profit from continuing operations	337	347	267
Operating segments | UK Gas Transmission | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	342	348	303
Operating segments | US Regulated
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,344	880	1,425
Operating segments | US Regulated | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,313	1,397	1,724
Unallocated amounts | NG Ventures and Other
Disclosure of operating segments [line items]
Operating profit from continuing operations	187	237	400
Unallocated amounts | NG Ventures and Other | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	237	242	400
Unallocated amounts | NG Ventures
Disclosure of operating segments [line items]
Operating profit from continuing operations	296	268	263
Unallocated amounts | NG Ventures | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 298	£ 269	£ 263

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, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 2,895	£ 2,780	£ 2,870
Finance income	58	54	88
Finance costs	(928)	(1,167)	(1,157)
Share of post-tax results of joint ventures and associates	58	87	40
Profit/(loss) before tax	2,083	1,754	1,841
Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	2,926	3,307	3,442
Finance income	35	70	73
Finance costs	(977)	(1,119)	(1,066)
Share of post-tax results of joint ventures and associates	66	88	40
Profit/(loss) before tax	£ 2,050	£ 2,346	£ 2,489

Segmental analysis - Capital ex

Segmental analysis - Capital expenditure (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	£ 48,486	£ 51,057	£ 45,943
Capital expenditure	4,931	5,079	4,321
Depreciation, amortisation and impairment	(1,672)	(1,640)	(1,735)
Property, plant and equipment
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	47,043	49,762	44,859
Capital expenditure	4,510	4,727	4,015
Depreciation, amortisation and impairment	(1,476)	(1,464)	(1,560)
Non-current intangible assets
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	1,443	1,295	1,084
Capital expenditure	421	352	306
Depreciation, amortisation and impairment	(196)	(176)	(175)
UK
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	21,352	20,427	19,343
Capital expenditure	1,708	1,847	1,584
Depreciation, amortisation and impairment	(783)	(784)	(931)
US
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	27,134	30,630	26,600
Capital expenditure	3,223	3,232	2,737
Depreciation, amortisation and impairment	(889)	(856)	(804)
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	14,379	13,788	13,288
Capital expenditure	1,072	1,043	925
Depreciation, amortisation and impairment	(507)	(469)	(628)
Operating segments | UK Gas Transmission
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	4,531	4,513	4,412
Capital expenditure	176	249	308
Depreciation, amortisation and impairment	(165)	(171)	(181)
Operating segments | US Regulated
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	27,128	30,615	25,488
Capital expenditure	3,223	3,228	2,650
Depreciation, amortisation and impairment	(888)	(855)	(700)
Unallocated amounts | NG Ventures and Other
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	2,448	2,141	2,755
Capital expenditure	460	559	438
Depreciation, amortisation and impairment	(112)	(145)	(226)
Unallocated amounts | NG Ventures
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	2,396	2,080	1,635
Capital expenditure	431	550	317
Depreciation, amortisation and impairment	£ 92	£ (124)	(114)
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
Capital expenditure			87
Depreciation, amortisation and impairment			£ (102)

Revenue - Disaggregation of rev

Revenue - Disaggregation of revenue (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	£ 14,165	£ 13,910	£ 14,066
Other revenue	614	630	867
Revenue	14,779	14,540	14,933
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,957	3,671	3,325
Other revenue	25	23	6
Revenue	3,982	3,694	3,331
UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	855	878	833
Other revenue	33	33	51
Revenue	888	911	884
US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,735	8,756	9,311
Other revenue	460	449	535
Revenue	9,195	9,205	9,846
NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	618	605	597
Other revenue	96	125	275
Revenue	714	730	872
UK
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	5,365	5,116	4,743
Other revenue	117	166	302
Revenue	5,482	5,282	5,045
UK | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,957	3,671	3,325
Other revenue	25	23	6
UK | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	855	878	833
Other revenue	33	33	51
UK | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0	0
Other revenue	0	0	0
UK | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	553	567	585
Other revenue	59	110	245
US
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,800	8,794	9,323
Other revenue	497	464	565
US | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0	0
Other revenue	0	0	0
US | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0	0
Other revenue	0	0	0
US | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,735	8,756	9,311
Other revenue	460	449	535
US | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	65	38	12
Other revenue	37	15	30
Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,136	3,375	3,253
Transmission | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	1,814	1,992	1,909
Transmission | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	603	649	661
Transmission | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	403	425	370
Transmission | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	316	309	313
Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,317	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	0
Distribution | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0	0
Distribution | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,317	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	0
System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	2,316	1,824	1,588
System Operator | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	2,076	1,610	1,416
System Operator | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	240	214	172
System Operator | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0	0
System Operator | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0	0	0
Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	396	392	284
Other revenue	238	261	500
Other | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	67	69	0
Other revenue	25	23	6
Other | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	12	15	0
Other revenue	33	33	51
Other | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	15	12	0
Other revenue	84	80	168
Other | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	302	296	284
Other revenue	96	125	275
Generation
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	376	369	367
Generation | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	0	0	0
Generation | UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	0	0	0
Generation | US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	376	369	367
Generation | NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	£ 0	£ 0	£ 0

Revenue - Narrative (Details)

Revenue - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contract liabilities	£ 1,160	£ 1,158	£ 994
Future revenues in relation to unfulfilled performance obligations	£ 4,800	3,100	3,500
Remaining performance obligation, expected timing of satisfaction, period (years)	9 years
Revenue from performance obligations satisfied or partially satisfied in previous periods	£ 0	0	0
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 1,600	1,500	1,600
Remaining performance obligation, expected timing of satisfaction, period (years)	26 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	£ 3,000	£ 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	19 years

Operating costs - Analysis of e

Operating costs - Analysis of expenses by nature (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Analysis of income and expense [abstract]
Depreciation, amortisation and impairment	£ 1,672	£ 1,640	£ 1,735
Payroll costs	1,770	1,684	1,852
Purchases of electricity	1,130	1,403	1,454
Purchases of gas	1,250	1,316	1,642
Property and other taxes	1,193	1,191	1,108
Balancing Services Incentive Scheme	1,875	1,317	1,196
Other	2,668	2,975	2,895
Other operating costs	11,558	11,526	11,882
Provision for bad and doubtful debts	326	234	181
Total operating costs	11,884	11,760	12,063
Inventory consumed	316	328	415
Research and development expenditure	£ 17	£ 14	£ 19

Operating costs - Payroll costs

Operating costs - Payroll costs (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Analysis of income and expense [abstract]
Wages and salaries	£ 2,282	£ 2,188	£ 2,084
Social security costs	172	168	156
Defined contribution scheme costs	77	75	72
Defined benefit pension costs	136	135	232
Share-based payments	27	19	27
Severance costs (excluding pension costs)	11	1	76
Payroll costs including capitalised costs	2,705	2,586	2,647
Less: payroll costs capitalised	(935)	(902)	(795)
Total payroll costs	1,770	1,684	1,852
US other post retirement benefit costs	£ 43	£ 45	£ 48

Operating costs - Number of emp

Operating costs - Number of employees (Details) - employee	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of operating segments [line items]
Number of employees, year end	23,683	23,069	22,576
Average number of employees	23,338	22,830	22,896
UK
Disclosure of operating segments [line items]
Number of employees, year end	6,657	6,321	5,962
Average number of employees	6,517	6,151	6,227
US
Disclosure of operating segments [line items]
Number of employees, year end	17,026	16,748	16,614
Average number of employees	16,821	16,679	16,669

Operating costs - Key managemen

Operating costs - Key management personnel (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Analysis of income and expense [abstract]
Short-term employee benefits	£ 7	£ 7	£ 7
Compensation for loss of office	0	1	0
Post-employment benefits	1	1	1
Share-based payments	4	3	3
Total key management compensation	£ 12	£ 12	£ 11

Operating costs - Auditors remu

Operating costs - Auditors remuneration (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Analysis of income and expense [abstract]
Audit of the Parent Company’s individual and consolidated financial statements	£ 2.5	£ 1.9	£ 1.6
The auditing of accounts of any associate of the Company	8.1	8.7	8.5
Other services supplied	6.4	6.3	5.2
Auditor's remuneration for audit services	17	16.9	15.3
Other assurance services	0.8	0.6	1.1
Other non-audit services not covered above	2	0.5	2.2
Auditor's remuneration for tax and other services	2.8	1.1	3.3
Total auditors’ remuneration	19.8	£ 18	£ 18.6
Tax compliance services	0
Tax advisory services	£ 0

Exceptional items and remeasu_3

Exceptional items and remeasurements (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of associates [line items]
Massachusetts Gas labour dispute	£ (1,770)	£ (1,684)	£ (1,852)
Operating profit/(loss)	2,895	2,780	2,870
Finance income and costs	(870)	(1,113)	(1,069)
Profit/(loss) before tax	2,083	1,754	1,841
Tax expense (income) on exceptional items and remeasurements	(442)	(480)	(339)
Profit/(loss) after tax from continuing operations	1,641	1,274	1,502
Exceptional items and remeasurements
Disclosure of associates [line items]
Operating profit/(loss)	(31)	(527)	(572)
Profit/(loss) before tax	33	(592)	(648)
Tax expense (income) on exceptional items and remeasurements	(26)	(47)	149
Profit/(loss) after tax from continuing operations	7	(639)	(499)
Exceptional items
Disclosure of associates [line items]
Changes in environmental provisions	14	(402)	0
Cost efficiency and restructuring programmes	(55)	0	(204)
Transaction costs	(24)	0	0
Massachusetts Gas labour dispute	0	0	(283)
Impairment of nuclear connection development costs	0	0	(137)
Operating profit/(loss)	(65)	(402)	(624)
Tax expense (income) on exceptional items and remeasurements	8	103	144
Profit/(loss) after tax from continuing operations	(57)	(491)	(480)
Remeasurements
Disclosure of associates [line items]
Net (losses)/gains on financing derivatives	(41)	1	(40)
Net gains/(losses) on financial assets at fair value through profit and loss	23	(16)	15
Net gains/(losses) on financial liabilities at fair value through profit and loss	90	(49)	(51)
Finance income and costs	72	(64)	(76)
Remeasurements – net losses on financial instruments	(8)	(1)	0
Tax expense (income) on exceptional items and remeasurements	(34)	42	5
Profit/(loss) after tax from continuing operations	64	(148)	(19)
Remeasurements | Commodity contract derivatives
Disclosure of associates [line items]
Operating profit/(loss)	34	(125)	52
UK | Exceptional items
Disclosure of associates [line items]
Deferred tax charge arising on the reversal of the reduction in UK corporation tax rate	£ 0	£ (192)	£ 0

Exceptional items and remeasu_4

Exceptional items and remeasurements - Narrative (Details) £ in Millions	12 Months Ended
	Mar. 31, 2021GBP (£)numberOfBusinessUnits	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)settlementcancellation	Mar. 31, 2017GBP (£)	May 31, 2018employee
Disclosure of other provisions [line items]
Number of business units | numberOfBusinessUnits	6
Other provisions	£ 2,227	£ 2,654	£ 2,199
COVID-19 related costs		10
Additions	146	589
Massachusetts Gas work continuation	1,770	1,684	1,852
Cash received from legal settlements			£ 95
Number of legal settlements | settlement			2
Environmental
Disclosure of other provisions [line items]
Other provisions	1,700	2,071	£ 1,639
Additions	26	£ 437
Real discount rate		0.50%
Weighted average duration of cash flows		10 years
Exceptional items
Disclosure of other provisions [line items]
Cost efficiency and restructuring programmes	55	£ 0	204
Environmental charges	(14)	402	0
Transaction costs	(24)	0	0
Payments related to restructuring activities	33
Payments related to transaction costs	14
Massachusetts Gas work continuation	0	0	£ 283
Number of nuclear connection cancellations (cancellation) | cancellation			2
Impairment of nuclear connection development costs	0	0	£ 137
Cash outflow for cost efficiency and restructuring programmes			93
Payments related to work continuation			£ 320
Development period of assets (over) (in years)			10 years
Proceeds from termination fees received			£ 13
Deferred tax expense arising from reduction in UK tax rate				£ 94
Exceptional items | Environmental
Disclosure of other provisions [line items]
Additions		402
Exceptional items, change in estimate of total cost and cost sharing | Environmental
Disclosure of other provisions [line items]
Additions		326
Exceptional items, impact of change in the real discount rate | Environmental
Disclosure of other provisions [line items]
Additions		76
US | Environmental
Disclosure of other provisions [line items]
Other provisions	£ 1,533	1,896
Additions		£ 66
Real discount rate	0.50%	0.50%
Weighted average duration of cash flows	10 years
UK
Disclosure of other provisions [line items]
Deferred tax expense due to change in substantively enacted UK Corporation tax rate		£ 192
UK | Environmental
Disclosure of other provisions [line items]
Other provisions	£ 167	175
Additions		£ 10
Real discount rate	0.50%	0.50%
Weighted average duration of cash flows	15 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, 2021	Mar. 31, 2020	Mar. 31, 2019
Finance Income And Costs [Line Items]
Finance income	£ 58	£ 54	£ 88
Finance costs	(928)	(1,167)	(1,157)
Finance income and costs	(870)	(1,113)	(1,069)
Before exceptional items and remeasurements
Finance Income And Costs [Line Items]
Bank deposits and other financial assets	33	48	54
Dividends received on equities held at fair value through other comprehensive income (FVOCI)	2	2	2
Other income	0	20	17
Finance income	35	70	73
Net interest on pensions and other post-retirement benefit obligations	(38)	(23)	(22)
Bank loans and overdrafts	(72)	(73)	(72)
Other borrowings	(854)	(997)	(970)
Interest expense on financial liabilities held at fair value through profit and loss (FVTPL)	(20)	(22)	(20)
Interest on derivatives	7	(39)	(43)
Unwinding of discount on provisions	(78)	(77)	(74)
Other interest	(53)	(10)	0
Less: interest capitalised	131	122	135
Finance costs	£ (977)	£ (1,119)	£ (1,066)
Capitalisation rate of borrowing costs eligible for capitalisation	3.10%	3.60%	3.90%
Tax relief on capitalised interest	£ 13	£ 15	£ 19
Remeasurements
Finance Income And Costs [Line Items]
Finance income	23	(16)	15
Finance costs	49	(48)	(91)
Net gains/(losses) on FVTPL financial assets	23	(16)	15
Net gains/(losses) on FVTPL financial liabilities	90	(49)	(51)
Derivatives designated as hedges for hedge accounting	44	(13)	(37)
Derivatives not designated as hedges for hedge accounting	(85)	14	(3)
Finance income and costs	72	(64)	(76)
Net foreign exchange gain (loss) on financing activities	£ 172	£ 66	£ 264

Tax - Tax charges (Details)

Tax - Tax charges (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Current tax:
Total current tax from continuing operations	£ 224	£ 132	£ 88
Deferred tax:
Total deferred tax from continuing operations	218	348	251
Total tax charge from continuing operations	442	480	339
UK
Current tax:
Corporation tax	213	179	132
Corporate tax adjustment in respect of prior years	23	(4)	(12)
Total current tax from continuing operations	236	175	120
Deferred tax:
Deferred tax	63	269	27
Deferred tax adjustment in respect of prior years	(26)	6	2
Total deferred tax from continuing operations	37	275	29
Overseas
Current tax:
Corporation tax	3	(2)	8
Corporate tax adjustment in respect of prior years	(15)	(41)	(40)
Total current tax from continuing operations	(12)	(43)	(32)
Deferred tax:
Deferred tax	174	64	208
Deferred tax adjustment in respect of prior years	7	9	14
Total deferred tax from continuing operations	£ 181	£ 73	£ 222

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, 2021	Mar. 31, 2020	Mar. 31, 2019
Current tax:
Cash flow hedges, cost of hedging and own credit reserve	£ 6	£ 0	£ 3
Deferred tax:
Investments at fair value through other comprehensive income	12	(1)	0
Cash flow hedges, cost of hedging and own credit reserve	(2)	(40)	(12)
Remeasurements of pension assets and post-retirement benefit obligations	414	(206)	12
Share-based payments	2	(3)	0
Tax charged/(credited) to other comprehensive income and equity	432	(250)	3
Total tax recognised in the statements of comprehensive income from continuing operations	430	(247)	3
Total tax relating to share-based payments recognised directly in equity from continuing operations	£ 2	£ (3)	£ 0

Tax - Effective tax rate reconc

Tax - Effective tax rate reconciliation (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure Of Income Taxes [Line Items]
Profit before tax from continuing operations	£ 2,083	£ 1,754	£ 1,841
Profit before tax from continuing operations multiplied by UK corporation tax rate of 19%	396	334	350
Adjustments in respect of prior years	(11)	(30)	(36)
Expenses not deductible for tax purposes	30	29	28
Non-taxable income	(9)	(18)	(36)
Adjustment in respect of foreign tax rates	42	18	56
Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax	(12)	(17)	(8)
Other	6	(28)	(12)
Total tax charge from continuing operations	£ 442	£ 480	£ 339
Effective tax rate – continuing operations	21.20%	27.40%	18.40%
Before exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Profit before tax from continuing operations	£ 2,050	£ 2,346	£ 2,489
Exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Profit before tax from continuing operations	33	(592)	(648)
Total tax charge from continuing operations	26	47	(149)
UK
Disclosure Of Income Taxes [Line Items]
Deferred tax impact of change in UK tax rate	£ 0	£ 192	£ (3)

Tax - Narrative (Details)

Tax - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure Of Income Taxes [Line Items]
Net deferred tax liabilities	£ 4,815	£ 4,446	£ 4,215
Deferred tax assets	455	547
Net operating losses
Disclosure Of Income Taxes [Line Items]
Net deferred tax liabilities	(455)	(547)
Deferred tax assets	440
Capital losses
Disclosure Of Income Taxes [Line Items]
Deferred tax assets	15
Share- based payments
Disclosure Of Income Taxes [Line Items]
Net deferred tax liabilities	(42)	£ (48)	£ (9)
Forecast | Changes in tax rates or tax laws enacted or announced
Disclosure Of Income Taxes [Line Items]
Increase in deferred tax liability	£ 560

Tax - Tax included within the s

Tax - Tax included within the statement of financial position (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	£ 4,446	£ 4,215
Exchange adjustments and other	(268)	134
Charged/(credited) to income statement	215	350
(Credited)/charged to other comprehensive income and equity	422	(253)
Deferred tax liability (asset) end of period	4,815	4,446
Accelerated tax depreciation
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	6,562	5,727
Exchange adjustments and other	(501)	222
Charged/(credited) to income statement	373	613
(Credited)/charged to other comprehensive income and equity	0	0
Deferred tax liability (asset) end of period	6,434	6,562
Share- based payments
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(48)	(9)
Exchange adjustments and other	4	(30)
Charged/(credited) to income statement	0	(7)
(Credited)/charged to other comprehensive income and equity	2	(2)
Deferred tax liability (asset) end of period	(42)	(48)
Share- based payments | Reclassification from other temporary differences to share-based payments
Reconciliation of changes in deferred tax liability (asset) [abstract]
Exchange adjustments and other	(29)
Pensions and other post- retirement benefits
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(360)	(170)
Exchange adjustments and other	51	(28)
Charged/(credited) to income statement	(12)	44
(Credited)/charged to other comprehensive income and equity	414	(206)
Deferred tax liability (asset) end of period	93	(360)
Financial instruments
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(55)	7
Exchange adjustments and other	4	(3)
Charged/(credited) to income statement	1	(13)
(Credited)/charged to other comprehensive income and equity	6	(46)
Deferred tax liability (asset) end of period	(44)	(55)
Other net temporary differences
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(1,653)	(1,340)
Exchange adjustments and other	174	(27)
Charged/(credited) to income statement	(147)	(287)
(Credited)/charged to other comprehensive income and equity	0	1
Deferred tax liability (asset) end of period	(1,626)	(1,653)
Net operating losses
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(547)
Deferred tax liability (asset) end of period	(455)	(547)
Environmental provisions
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(529)
Deferred tax liability (asset) end of period	(453)	(529)
Allowance for credit losses
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(124)
Deferred tax liability (asset) end of period	£ (184)	£ (124)

Tax - Deferred tax assets not r

Tax - Deferred tax assets not recognised (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
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	£ 1,620	£ 1,626
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	1
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	£ 7	£ 6

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, 2021	Mar. 31, 2020	Mar. 31, 2019
Basic EPS
Basic earnings from continuing operations	£ 1,640	£ 1,273	£ 1,499
Basic earnings from discontinued operations	0	(9)	12
Basic total earnings	£ 1,640	£ 1,264	£ 1,511
Basic EPS (continuing) (in GBP per share)	£ 0.466	£ 0.368	£ 0.443
Basic EPS (discontinuing) (in GBP per share)	0	(0.003)	0.003
Total basic earnings per share (in GBP per share)	£ 0.466	£ 0.365	£ 0.446
Weighted average number of shares – basic (in shares)	3,523	3,461	3,386
Diluted EPS
Diluted earnings from continuing operations	£ 1,640	£ 1,273	£ 1,499
Diluted earnings from discontinued operations	0	(9)	12
Diluted total earnings	£ 1,640	£ 1,264	£ 1,511
Diluted EPS (continuing) (in GBP per share)	£ 0.463	£ 0.366	£ 0.441
Diluted EPS (discontinuing) (in GBP per share)	0	(0.003)	0.003
Diluted EPS (in GBP per share)	£ 0.463	£ 0.363	£ 0.444
Weighted average number of shares – diluted (in shares)	3,540	3,478	3,401
Reconciliation of basic to diluted average number of shares
Weighted average number of shares – basic (in shares)	3,523	3,461	3,386
Effect of dilutive potential ordinary shares – employee share plans (in shares)	17	17	15
Weighted average number of shares – diluted (in shares)	3,540	3,478	3,401
Before exceptional items and remeasurements
Basic EPS
Basic earnings from continuing operations	£ 1,633	£ 1,912	£ 1,998
Basic earnings from discontinued operations	0	5	57
Basic total earnings	£ 1,633	£ 1,917	£ 2,055
Basic EPS (continuing) (in GBP per share)	£ 0.464	£ 0.552	£ 0.590
Basic EPS (discontinuing) (in GBP per share)	0	0.002	0.017
Total basic earnings per share (in GBP per share)	£ 0.464	£ 0.554	£ 0.607
Diluted EPS
Diluted earnings from continuing operations	£ 1,633	£ 1,912	£ 1,998
Diluted earnings from discontinued operations	0	5	57
Diluted total earnings	£ 1,633	£ 1,917	£ 2,055
Diluted EPS (continuing) (in GBP per share)	£ 0.461	£ 0.550	£ 0.588
Diluted EPS (discontinuing) (in GBP per share)	0	0.001	0.017
Diluted EPS (in GBP per share)	£ 0.461	£ 0.551	£ 0.605
Exceptional items and remeasurements
Basic EPS
Basic earnings from continuing operations	£ 7	£ (639)	£ (499)
Basic earnings from discontinued operations	0	(14)	(45)
Basic total earnings	£ 7	£ (653)	£ (544)
Basic EPS (continuing) (in GBP per share)	£ 0.002	£ (0.184)	£ (0.147)
Basic EPS (discontinuing) (in GBP per share)	0	(0.005)	(0.014)
Total basic earnings per share (in GBP per share)	£ 0.002	£ (0.189)	£ (0.161)
Diluted EPS
Diluted earnings from continuing operations	£ 7	£ (639)	£ (499)
Diluted earnings from discontinued operations	0	(14)	(45)
Diluted total earnings	£ 7	£ (653)	£ (544)
Diluted EPS (continuing) (in GBP per share)	£ 0.002	£ (0.184)	£ (0.147)
Diluted EPS (discontinuing) (in GBP per share)	0	(0.004)	(0.014)
Diluted EPS (in GBP per share)	£ 0.002	£ (0.188)	£ (0.161)

Dividends (Details)

Dividends (Details) - GBP (£) £ / shares in Units, £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)	£ 0.4900	£ 0.4783	£ 0.4652
Dividends paid	£ 1,413	£ 892	£ 1,160
Scrip dividend	£ 303	£ 758	£ 413
Interim dividend in respect of the current year
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)	£ 0.1700	£ 0.1657	£ 0.1608
Dividends paid	£ 348	£ 335	£ 450
Scrip dividend	£ 249	£ 241	£ 94
Final dividend in respect of the prior year
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)	£ 0.3200	£ 0.3126	£ 0.3044
Dividends paid	£ 1,065	£ 557	£ 710
Scrip dividend	£ 54	£ 517	£ 319

Dividends - Narrative (Details)

Dividends - Narrative (Details) £ / shares in Units, £ in Millions	12 Months Ended
	Mar. 31, 2021GBP (£)£ / shares
Summary Of Dividends [Line Items]
Dividends declared before financial statements authorised for issue (GBP per share) | £ / shares	£ 0.3216
Dividends declared before financial statements authorised for issue | £	£ 1,141

Discontinued operations and a_3

Discontinued operations and assets held for sale - Narrative (Details) $ in Billions	Mar. 17, 2021	Mar. 31, 2022GBP (£)	Mar. 31, 2022USD ($)	Jun. 30, 2019GBP (£)	Mar. 31, 2021GBP (£)	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)
Disclosure of subsidiaries [line items]
Profit after tax					£ 1,641,000,000	£ 1,265,000,000	£ 1,514,000,000
Purchase of interests in investments accounted for using equity method					81,000,000	82,000,000	143,000,000
Derivative assets					999,000,000	1,342,000,000
Net cash outflow from operating activities – discontinued operations					0	97,000,000	71,000,000
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					0	6,000,000	156,000,000
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				9,000,000		9,000,000	0
Net cash flow (used in)/from financing activities – discontinued operations						0	0
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
The Narragansett Electric Company
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed	100.00%
Profit after tax					£ 104,000,000	£ 31,000,000	£ 137,000,000
The Narragansett Electric Company | Forecast
Disclosure of subsidiaries [line items]
Consideration received		£ 2,800,000,000	$ 3.8

Discontinued operations and a_4

Discontinued operations and assets held for sale - Assets and Liabilities Classified as Held-For-Sale (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Summary income statement and comprehensive income, discontinued operations [line items]
Assets held for sale	£ 3,557	£ 0	£ 1,956
Liabilities held for sale	(1,568)	£ 0	£ 0
Assets and liabilities classified as held for sale
Summary income statement and comprehensive income, discontinued operations [line items]
Assets held for sale	3,557
Liabilities held for sale	(1,568)
Net assets held for sale	1,989
Assets and liabilities classified as held for sale | Borrowings
Summary income statement and comprehensive income, discontinued operations [line items]
Liabilities held for sale	(1,123)
Assets and liabilities classified as held for sale | Pension liabilities
Summary income statement and comprehensive income, discontinued operations [line items]
Liabilities held for sale	(49)
Assets and liabilities classified as held for sale | Other liabilities
Summary income statement and comprehensive income, discontinued operations [line items]
Liabilities held for sale	(396)
Assets and liabilities classified as held for sale | Goodwill
Summary income statement and comprehensive income, discontinued operations [line items]
Assets held for sale	562
Assets and liabilities classified as held for sale | Intangible assets
Summary income statement and comprehensive income, discontinued operations [line items]
Assets held for sale	3
Assets and liabilities classified as held for sale | Property, plant and equipment
Summary income statement and comprehensive income, discontinued operations [line items]
Assets held for sale	2,713
Assets and liabilities classified as held for sale | Trade and other receivables
Summary income statement and comprehensive income, discontinued operations [line items]
Assets held for sale	237
Assets and liabilities classified as held for sale | Cash and cash equivalents
Summary income statement and comprehensive income, discontinued operations [line items]
Assets held for sale	4
Assets and liabilities classified as held for sale | Other assets
Summary income statement and comprehensive income, discontinued operations [line items]
Assets held for sale	£ 38

Discontinued operations and a_5

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, 2021	Mar. 31, 2020	Mar. 31, 2019
Summary income statement and comprehensive income, discontinued operations [line items]
Revenue		£ 14,779	£ 14,540	£ 14,933
Operating costs		(11,884)	(11,760)	(12,063)
Operating profit/(loss)		2,895	2,780	2,870
Net finance income		(870)	(1,113)	(1,069)
Share of post-tax results of joint ventures and associates		58	87	40
Profit/(loss) before tax		2,083	1,754	1,841
Total (loss)/profit after tax from discontinued operations			(9)	12
Items that will never be reclassified to profit or loss:
Total items from continuing operations that will never be reclassified to profit or loss		1,007	(541)	47
Items that may be reclassified subsequently to profit or loss:
Total items from continuing operations that may be reclassified subsequently to profit or loss		(1,190)	370	270
Other comprehensive income for the year, net of tax from discontinued operations		(183)	(165)	353
Total comprehensive income for the year		£ 1,458	1,100	1,867
Discontinued operations
Summary income statement and comprehensive income, discontinued operations [line items]
Revenue			0	0
Operating costs			(23)	(1)
Operating profit/(loss)			(23)	(1)
Net finance income			6	23
Share of post-tax results of joint ventures and associates			0	(5)
Profit/(loss) before tax			(17)	17
Tax from discontinued operations			(1)	(5)
(Loss)/profit after tax from discontinued operations			(18)	12
Gain on disposal	£ 9		9	0
Total (loss)/profit after tax from discontinued operations			(9)	12
Items that will never be reclassified to profit or loss:
Share of other comprehensive income of associate, net of tax			0	36
Total items from continuing operations that will never be reclassified to profit or loss			0	36
Items that may be reclassified subsequently to profit or loss:
Net gains in respect of cash flow hedges			6	0
Total items from continuing operations that may be reclassified subsequently to profit or loss			6	0
Other comprehensive income for the year, net of tax from discontinued operations			6	36
Total comprehensive income for the year			£ (3)	48
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, 2021	Mar. 31, 2020
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill, beginning balance	£ 5,712	£ 5,372
Exchange adjustments	(562)	259
Acquisition of National Grid Renewables (note 38)		81
Reclassification to held for sale (note 10)	(562)
Goodwill, ending balance	£ 4,588	£ 5,712

Goodwill - Narrative (Details)

Goodwill - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of reconciliation of changes in goodwill [line items]
Growth rate used to extrapolate cash flow projections	2.10%	2.10%
Discount rate applied to cash flow projections	5.00%	4.50%
Pre-tax discount rate applied to cash flow projections	5.30%	4.50%
Goodwill
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	£ 4,588	£ 5,712	£ 5,372
Goodwill | Accumulated impairment
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	0	0
Goodwill | New York | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	3,004	3,334
Goodwill | Massachusetts | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	963	1,069
Goodwill | Rhode Island | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	0	438
Goodwill | Federal | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	544	790
Goodwill | National Grid Renewables | Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	£ 77	£ 81

Other intangible assets (Detail

Other intangible assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	£ 1,295	£ 1,084
Intangible assets other than goodwill, ending balance	1,443	1,295
Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	738
Intangible assets other than goodwill, ending balance	757	738
Assets in the course of construction
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	557
Intangible assets other than goodwill, ending balance	£ 686	557
Gas Business Enablement System
Changes in intangible assets other than goodwill [abstract]
Amortised period	10 years
Intangible assets other than goodwill, beginning balance	£ 240
Intangible assets other than goodwill, ending balance	298	240
Intangible assets other than goodwill, in service amount	82	30
UK General Ledger System
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	59
Intangible assets other than goodwill, ending balance	117	59
Gross carrying amount
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	2,583	2,168
Exchange adjustments	(145)	63
Additions	421	352
Disposals	(49)
Reclassifications	15	0
Reclassification to held for sale (note 10)	(19)
Intangible assets other than goodwill, ending balance	2,806	2,583
Gross carrying amount | Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	2,026	1,784
Exchange adjustments	(102)	45
Additions	7	38
Disposals	(47)
Reclassifications	255	159
Reclassification to held for sale (note 10)	(19)
Intangible assets other than goodwill, ending balance	2,120	2,026
Gross carrying amount | Assets in the course of construction
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	557	384
Exchange adjustments	(43)	18
Additions	414	314
Disposals	(2)
Reclassifications	(240)	(159)
Reclassification to held for sale (note 10)	0
Intangible assets other than goodwill, ending balance	686	557
Accumulated depreciation/amortisation
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	(1,288)	(1,084)
Exchange adjustments	61	(28)
Disposals	44
Reclassification to held for sale (note 10)	16
Amortisation charge for the year	(196)	176
Intangible assets other than goodwill, ending balance	(1,363)	(1,288)
Accumulated depreciation/amortisation | Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	(1,288)	(1,084)
Exchange adjustments	61	(28)
Disposals	44
Reclassification to held for sale (note 10)	16
Amortisation charge for the year	(196)	176
Intangible assets other than goodwill, ending balance	(1,363)	(1,288)
Accumulated depreciation/amortisation | Assets in the course of construction
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	0	0
Exchange adjustments	0	0
Disposals	0
Reclassification to held for sale (note 10)	0
Amortisation charge for the year	0	0
Intangible assets other than goodwill, ending balance	£ 0	£ 0
Bottom of range | Software
Changes in intangible assets other than goodwill [abstract]
Amortised period	3 years
Top of range | Software
Changes in intangible assets other than goodwill [abstract]
Amortised period	10 years

Property, plant and equipment -

Property, plant and equipment - Useful economic lives (Details)	12 Months Ended
	Mar. 31, 2021
Weighted average | Freehold and leasehold buildings
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	9 years
Weighted average | Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	30 years
Weighted average | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	33 years
Weighted average | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	10 years
Weighted average | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	16 years
Weighted average | Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	45 years
Weighted average | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	12 years
Weighted average | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	20 years
Weighted average | Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life	4 years
UK | Bottom of range | Electricity transmission plant and wires
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 | 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	5 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	40 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) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
UK Regulated
Disclosure of operating segments [line items]
UELs limited to 2050, impact on depreciation expense	£ 35	£ 37
UELs limited to 2060, impact on depreciation expense	12	13
UELs limited to 2070, impact on depreciation expense	1	0
US Regulated
Disclosure of operating segments [line items]
UELs limited to 2050, impact on depreciation expense	160	151
UELs limited to 2060, impact on depreciation expense	70	66
UELs limited to 2070, impact on depreciation expense	£ 28	£ 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, 2021	Mar. 31, 2020	Apr. 01, 2019
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	[1]	£ 49,762	£ 44,859
Property, plant and equipment, ending balance	[1]	47,043	49,762
Right-of-use assets		630	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		69,313	63,614
Exchange adjustments		(3,724)	1,698
Additions		4,510	4,727
Disposals		(424)	(639)
Reclassifications		(63)	(87)
Reclassification to held for sale (note 10)		(3,560)
Property, plant and equipment, ending balance		66,052	69,313
Cost | Previously stated
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			63,146
Cost | IFRS 16
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			468
Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		(19,551)	(18,287)
Exchange adjustments		781	(365)
Depreciation charge for the year		(1,476)	(1,464)
Disposals		387	558
Reclassifications		3	7
Reclassification to held for sale (note 10)		847
Property, plant and equipment, ending balance		(19,009)	(19,551)
Land and buildings
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		3,050
Property, plant and equipment, ending balance		2,876	3,050
Land and buildings | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		3,897	3,719
Exchange adjustments		(213)	98
Additions		89	130
Disposals		(6)	(79)
Reclassifications		96	29
Reclassification to held for sale (note 10)		(111)
Property, plant and equipment, ending balance		3,752	3,897
Land and buildings | Cost | Previously stated
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			3,338
Land and buildings | Cost | IFRS 16
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			381
Land and buildings | Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		(847)	(778)
Exchange adjustments		37	(16)
Depreciation charge for the year		(90)	(92)
Disposals		0	36
Reclassifications		2	3
Reclassification to held for sale (note 10)		22
Property, plant and equipment, ending balance		(876)	(847)
Plant and machinery
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		41,567
Property, plant and equipment, ending balance		38,579	41,567
Plant and machinery | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		59,609	53,896
Exchange adjustments		(3,308)	1,484
Additions		328	464
Disposals		(344)	(486)
Reclassifications		3,007	4,251
Reclassification to held for sale (note 10)		(3,231)
Property, plant and equipment, ending balance		56,061	59,609
Plant and machinery | Cost | Previously stated
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			53,829
Plant and machinery | Cost | IFRS 16
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			67
Plant and machinery | Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		(18,042)	(16,918)
Exchange adjustments		698	(329)
Depreciation charge for the year		(1,270)	(1,252)
Disposals		339	464
Reclassifications		(5)	(7)
Reclassification to held for sale (note 10)		798
Property, plant and equipment, ending balance		(17,482)	(18,042)
Assets in the course of construction
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		4,771
Property, plant and equipment, ending balance		5,221	4,771
Assets in the course of construction | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		4,771	5,049
Exchange adjustments		(130)	83
Additions		4,023	4,029
Disposals		(26)	(9)
Reclassifications		(3,243)	(4,381)
Reclassification to held for sale (note 10)		(174)
Property, plant and equipment, ending balance		5,221	4,771
Assets in the course of construction | Cost | Previously stated
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			5,049
Assets in the course of construction | Cost | IFRS 16
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			0
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	0
Disposals		0	0
Reclassifications		0	0
Reclassification to held for sale (note 10)		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		374
Property, plant and equipment, ending balance		367	374
Motor vehicles and office equipment | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		1,036	950
Exchange adjustments		(73)	33
Additions		70	104
Disposals		(48)	(65)
Reclassifications		77	14
Reclassification to held for sale (note 10)		(44)
Property, plant and equipment, ending balance		1,018	1,036
Motor vehicles and office equipment | Cost | Previously stated
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			930
Motor vehicles and office equipment | Cost | IFRS 16
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance			20
Motor vehicles and office equipment | Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance		(662)	(591)
Exchange adjustments		46	(20)
Depreciation charge for the year		(116)	(120)
Disposals		48	58
Reclassifications		6	11
Reclassification to held for sale (note 10)		27
Property, plant and equipment, ending balance		£ (651)	£ (662)
[1]	Comparative amounts have been revised as described in note 1F.

Property, plant and equipment_4

Property, plant and equipment - Information in relation to property, plant and equipment (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Property, plant and equipment | Cost
Disclosure of detailed information about property, plant and equipment [line items]
Capitalised interest included within cost	£ 2,233	£ 2,118
Trade and other payables
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	138	84
Non-current liabilities
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	400	428
Contract liabilities – current
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	66	76
Contract liabilities – non-current
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	£ 1,093	£ 1,082

Property, plant and equipment_5

Property, plant and equipment - Disclosure of right-of-use assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	£ 630	£ 684
Additions	130	84
Depreciation charge for the year	(113)	(117)
Interest expense on lease liabilities	(21)	(26)
Lease income	390	404
Expense relating to short-term and low-value leases	(13)	(12)
Variable lease payments included in lease income	376	353
Land and buildings
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	365	364
Additions	60	10
Depreciation charge for the year	(29)	(29)
Plant and machinery
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	81	95
Additions	6	1
Depreciation charge for the year	(16)	(16)
Assets in the course of construction
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	0	0
Additions	0	0
Depreciation charge for the year	0	0
Motor vehicles and office equipment
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	184	225
Additions	64	73
Depreciation charge for the year	£ (68)	£ (72)

Property, plant and equipment_6

Property, plant and equipment - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Property, plant and equipment [abstract]
Expected future minimum sub lease payments receivable under non-cancellable sub leases	£ 104	£ 94

Other non-current assets (Detai

Other non-current assets (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Other receivables	£ 45	£ 35
Non-current tax assets	6	65
Prepayments	5	19
Accrued income	237	235
Other non-current assets	£ 293	£ 354	£ 264	£ 115	£ 115

Financial and other investmen_3

Financial and other investments - Schedule of financial assets (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Disclosure of associates [line items]
FVOCI debt and other investments	£ 416	£ 352
FVOCI equity investments	99	83
FVTPL investments	240	108
Other non-current financial assets	755	543		£ 667	£ 899	£ 899
FVTPL investments	1,768	1,278
Financial assets at amortised cost	574	720
Other current financial assets	2,342	1,998	£ 1,981	£ 1,981	£ 2,694	£ 2,694
Other financial assets	3,097	2,541
Investments in short-term money market funds
Disclosure of associates [line items]
Other financial assets	1,412	951
Investments held by National Grid Partners
Disclosure of associates [line items]
Other financial assets	136	97
Other investments
Disclosure of associates [line items]
Other financial assets	103	11
Collateral
Disclosure of associates [line items]
Other financial assets	540	685
Insurance company and non-qualified plan investments
Disclosure of associates [line items]
Other financial assets	589	542
Short term investments, restricted	42	0
Cash surrender value of life insurance policies
Disclosure of associates [line items]
Other financial assets	283	220
Other investments
Disclosure of associates [line items]
Other financial assets	34	35
Insurance company fund investments
Disclosure of associates [line items]
Other financial assets	18	0
Short term investments, restricted	£ 480	£ 685

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, 2021	Mar. 31, 2020
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	£ 995	£ 608
Exchange adjustments	(58)	32
Additions	81	172
Capitalisation of shareholder loan to Nemo Link Limited	0	176
Share of post-tax results for the year	58	87
Share of other comprehensive income of associates, net of tax	1	1
Dividends received	(80)	(75)
Other movements	(130)	(6)
Investments accounted for using equity method, ending balance	867	995
Joint ventures
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	654	317
Exchange adjustments	(36)	12
Additions	75	156
Capitalisation of shareholder loan to Nemo Link Limited	0	176
Share of post-tax results for the year	28	47
Share of other comprehensive income of associates, net of tax	0	0
Dividends received	(49)	(34)
Other movements	(34)	(20)
Investments accounted for using equity method, ending balance	638	654
Associates
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	341	291
Exchange adjustments	(22)	20
Additions	6	16
Capitalisation of shareholder loan to Nemo Link Limited	0	0
Share of post-tax results for the year	30	40
Share of other comprehensive income of associates, net of tax	1	1
Dividends received	(31)	(41)
Other movements	(96)	14
Investments accounted for using equity method, ending balance	£ 229	£ 341

Investments in joint ventures_4

Investments in joint ventures and associates - Narrative (Details) £ in Millions	12 Months Ended
	Mar. 31, 2021GBP (£)joint_venture	Mar. 31, 2020GBP (£)
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 | £	£ 141	£ 240
BritNed
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, 2021	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2019	Apr. 01, 2018	Mar. 31, 2018
Disclosure of joint ventures [line items]
Non-current assets	£ 57,278	£ 61,759	£ 55,466		£ 52,523	£ 52,523
Cash and cash equivalents	157	73	252	£ 252	329	329
Non-current liabilities	(37,988)	(39,203)	(34,715)		(31,673)	(31,474)
Current liabilities	(9,368)	(8,564)	(9,129)		(8,691)	(8,697)
Net assets	19,860	19,793	19,568	£ 19,568	£ 18,837	£ 19,033
Revenue	14,779	14,540	14,933
Other costs	(2,668)	(2,975)	(2,895)
Operating profit/(loss)	2,895	2,780	2,870
Profit/(loss) before tax	2,083	1,754	1,841
Tax	(442)	(480)	(339)
Profit/(loss) after tax from continuing operations	1,641	1,274	1,502
Group’s share of profit/(loss)	58	87	£ 40
Millennium Pipeline Company LLC
Disclosure of joint ventures [line items]
Non-current assets	795	910
Cash and cash equivalents	27	33
All other current assets	24	26
Non-current liabilities	(256)	(315)
Current liabilities	(38)	(43)
Net assets	552	611
Group’s ownership interest in joint venture/associate	145	160
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	145	160
Revenue	199	206
Depreciation and amortisation	(43)	(46)
Other costs	(21)	(20)
Operating profit/(loss)	135	140
Net interest expense	(18)	(22)
Profit/(loss) before tax	117	118
Tax	0	0
Profit/(loss) after tax from continuing operations	117	118
Group’s share of profit/(loss)	31	31
Group adjustment: tax charge	(9)	(9)
Group’s share of post-tax results for the year	22	22
BritNed Development Limited
Disclosure of joint ventures [line items]
Non-current assets	409	399
Cash and cash equivalents	47	54
All other current assets	24	4
Non-current liabilities	(81)	(45)
Current liabilities	(22)	(16)
Net assets	377	396
Group’s ownership interest in joint venture/associate	189	198
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	189	198
Revenue	72	80
Depreciation and amortisation	(15)	(14)
Other costs	(15)	(10)
Operating profit/(loss)	42	56
Net interest expense	(1)	0
Profit/(loss) before tax	41	56
Tax	(11)	(10)
Profit/(loss) after tax from continuing operations	30	46
Group’s share of profit/(loss)	15	23
Group adjustment: tax charge	0	0
Group’s share of post-tax results for the year	15	23
Nemo Link Limited
Disclosure of joint ventures [line items]
Non-current assets	536	582
Cash and cash equivalents	31	26
All other current assets	8	5
Non-current liabilities	(30)	(29)
Current liabilities	(19)	(10)
Net assets	526	574
Group’s ownership interest in joint venture/associate	263	287
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	263	287
Revenue	66	45
Depreciation and amortisation	(24)	(23)
Other costs	(6)	(8)
Operating profit/(loss)	36	14
Net interest expense	0	0
Profit/(loss) before tax	36	14
Tax	(14)	(2)
Profit/(loss) after tax from continuing operations	22	12
Group’s share of profit/(loss)	11	6
Group adjustment: tax charge	0	0
Group’s share of post-tax results for the year	11	6
Emerald Energy Venture LLC
Disclosure of joint ventures [line items]
Non-current assets	559	435
Cash and cash equivalents	112	66
All other current assets	12	6
Non-current liabilities	(286)	(232)
Current liabilities	(27)	(2)
Net assets	370	273
Group’s ownership interest in joint venture/associate	189	139
Group adjustment: elimination of profits on sales to joint venture	(23)	(10)
Carrying amount of the Group’s investment	166	129
Revenue	28	19
Depreciation and amortisation	(14)	(7)
Other costs	(22)	(10)
Operating profit/(loss)	(8)	2
Net interest expense	0	(3)
Profit/(loss) before tax	(8)	(1)
Tax	0	0
Profit/(loss) after tax from continuing operations	(8)	(1)
Group’s share of profit/(loss)	(4)	(1)
Group adjustment: tax charge	1	0
Group’s share of post-tax results for the year	£ (3)	£ (1)

Derivative financial instrume_3

Derivative financial instruments - Derivative financial instruments (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 999	£ 1,342
Derivative liabilities	(899)	(1,334)
Total	100	8
Derivative assets - current
Disclosure of detailed information about financial instruments [line items]
Derivative assets	457	93
Derivative liabilities - current
Disclosure of detailed information about financial instruments [line items]
Derivative liabilities	(145)	(380)
Total	312	(287)
Derivative assets - non-current
Disclosure of detailed information about financial instruments [line items]
Derivative assets	542	1,249
Derivative liabilities - non-current
Disclosure of detailed information about financial instruments [line items]
Derivative liabilities	(754)	(954)
Total	(212)	295
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	942	1,267
Derivative liabilities	(767)	(1,134)
Total	175	133
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	57	75
Derivative liabilities	(132)	(200)
Total	£ (75)	£ (125)

Derivative financial instrume_4

Derivative financial instruments - Financing derivatives (Details) £ in Millions, number in Millions	Mar. 31, 2021GBP (£)	Mar. 31, 2020GBP (£)
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 999	£ 1,342
Derivative liabilities	(899)	(1,334)
Total	100	8
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	942	1,267
Derivative liabilities	(767)	(1,134)
Total	£ 175	£ 133
Derivative notional amount	(15,799)	(15,782)
Financing derivatives | LIBOR
Disclosure of detailed information about financial instruments [line items]
Notional amount	£ 2,810
Financing derivatives | GBP LIBOR
Disclosure of detailed information about financial instruments [line items]
Notional amount	2,041
Financing derivatives | USD LIBOR
Disclosure of detailed information about financial instruments [line items]
Notional amount	769
Financing derivatives | Less than 1 year
Disclosure of detailed information about financial instruments [line items]
Derivative assets	428	£ 62
Derivative liabilities	(70)	(254)
Total	358	(192)
Financing derivatives | Over 12 months past due
Disclosure of detailed information about financial instruments [line items]
Derivative assets	514	1,205
Derivative liabilities	(697)	(880)
Total	(183)	325
Financing derivatives | In 1 to 2 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	10	480
Derivative liabilities	(14)	(51)
Total	(4)	429
Financing derivatives | In 2 to 3 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	24	13
Derivative liabilities	(12)	(5)
Total	12	8
Financing derivatives | In 3 to 4 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	62	20
Derivative liabilities	(80)	(28)
Total	(18)	(8)
Financing derivatives | In 4 to 5 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	4	31
Derivative liabilities	(42)	(109)
Total	(38)	(78)
Financing derivatives | More than 5 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	414	661
Derivative liabilities	(549)	(687)
Total	(135)	(26)
Interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	325	556
Derivative liabilities	(159)	(337)
Total	£ 166	£ 219
Derivative notional amount	(2,259)	(3,101)
Cross-currency interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 601	£ 643
Derivative liabilities	(351)	(514)
Total	£ 250	£ 129
Derivative notional amount	(8,389)	(8,097)
Foreign exchange forward contracts
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 16	£ 58
Derivative liabilities	(74)	(39)
Total	£ (58)	£ 19
Derivative notional amount	(4,651)	(3,284)
Foreign exchange forward contracts | Capital Expenditure
Disclosure of detailed information about financial instruments [line items]
Total	£ (32)	£ (3)
Inflation-linked swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	0	0
Derivative liabilities	(183)	(234)
Total	£ (183)	£ (234)
Derivative notional amount	(500)	(500)
Equity options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 0	£ 10
Derivative liabilities	0	(10)
Total	£ 0	£ 0
Derivative notional amount	0	(800)
Deal contingent foreign exchange forward contracts
Disclosure of detailed information about financial instruments [line items]
Total	£ (9)	£ 0

Derivative financial instrume_5

Derivative financial instruments - Commodity derivatives (Details) £ in Millions, number in Millions	12 Months Ended
	Mar. 31, 2021GBP (£)MMBTUGWh	Mar. 31, 2020GBP (£)MMBTUGWh
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 999	£ 1,342
Derivative liabilities	(899)	(1,334)
Total	100	8
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	57	75
Derivative liabilities	(132)	(200)
Total	(75)	(125)
Commodity contract derivatives | Less than 1 year
Disclosure of detailed information about financial instruments [line items]
Derivative assets	29	31
Derivative liabilities	(75)	(126)
Total	(46)	(95)
Commodity contract derivatives | Over 12 months past due
Disclosure of detailed information about financial instruments [line items]
Derivative assets	28	44
Derivative liabilities	(57)	(74)
Total	(29)	(30)
Commodity contract derivatives | In 1 to 2 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	7	8
Derivative liabilities	(24)	(35)
Total	(17)	(27)
Commodity contract derivatives | In 2 to 3 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	7	9
Derivative liabilities	(16)	(24)
Total	(9)	(15)
Commodity contract derivatives | In 3 to 4 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	7	8
Derivative liabilities	(7)	(12)
Total	0	(4)
Commodity contract derivatives | In 4 to 5 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	6	7
Derivative liabilities	(5)	(1)
Total	1	6
Commodity contract derivatives | More than 5 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	1	12
Derivative liabilities	(5)	(2)
Total	(4)	10
Forward purchases of gas
Disclosure of detailed information about financial instruments [line items]
Derivative assets	44	64
Derivative liabilities	(94)	(108)
Total	£ (50)	£ (44)
Derivative non-monetary notional amount | MMBTU	36	102
Derivative term	5 years	4 years
Derivative contractual amount	104	128
Electricity capacity
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 2
Total	2
Electricity swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	10	£ 4
Derivative liabilities	(33)	(83)
Total	£ (23)	£ (79)
Derivative non-monetary notional amount | GWh	12,321	12,836
Electricity options
Disclosure of detailed information about financial instruments [line items]
Derivative liabilities	£ (1)
Total	(1)
Gas swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	1	£ 7
Derivative liabilities	(3)	(8)
Total	£ (2)	£ (1)
Derivative non-monetary notional amount | MMBTU	47	89
Gas options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 0	£ 0
Derivative liabilities	(1)	(1)
Total	£ (1)	£ (1)
Derivative non-monetary notional amount | MMBTU	40	26

Inventories and current intan_3

Inventories and current intangible assets (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Subclassifications of assets, liabilities and equities [abstract]
Fuel stocks	£ 94	£ 151
Raw materials and consumables	253	265
Current intangible assets – emission allowances	92	133
Inventories and current intangible assets	439	549
Inventory valuation reserve	£ 10	£ 21

Trade and other receivables - S

Trade and other receivables - Summary of trade and other receivables (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Trade and other receivables [abstract]
Trade receivables	£ 1,503	£ 1,571
Accrued income	863	849
Prepayments	387	408
Contract assets	13	0
Other receivables	153	158
Trade and other receivables	£ 2,919	£ 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, 2021GBP (£)	Mar. 31, 2021USD ($)	Mar. 31, 2020GBP (£)	Mar. 31, 2020USD ($)
Disclosure of financial assets [line items]
Trade receivables	£ 3,522		£ 3,266
Retail customer receivables
Disclosure of financial assets [line items]
Trade receivables	1,852		1,852
Trade and other receivables
Disclosure of financial assets [line items]
Maximum exposure to credit risk	2,152		2,063
Provision for bad and doubtful debts	326		234
Impact of COVID-19 | Trade and other receivables
Disclosure of financial assets [line items]
Provision for bad and doubtful debts			117
Bottom of range | Trade and other receivables
Disclosure of financial assets [line items]
Provision for bad and doubtful debts	320	$ 440
Bottom of range | Cessation of customer terminations and collections | Trade and other receivables
Disclosure of financial assets [line items]
Provision for bad and doubtful debts			81	$ 100
Top of range | Trade and other receivables
Disclosure of financial assets [line items]
Provision for bad and doubtful debts	£ 342	$ 470
Top of range | Cessation of customer terminations and collections | Trade and other 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 and other receivables - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Allowance account for credit losses of financial assets, beginning balance	£ 512	£ 394
Exchange adjustments	(57)	20
Charge for the year, net of recoveries	326	234
Uncollectible amounts written off	(59)	(136)
Reclassification to held for sale (note 10)	(50)	0
Allowance account for credit losses of financial assets, ending balance	£ 672	£ 512

Trade and other receivables - T

Trade and other receivables - Trade receivables, accrued income and provision split by geography (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Disclosure of financial assets [line items]
Trade receivables	£ 3,522	£ 3,266
Accrued income	863	849
Gross carrying amount
Disclosure of financial assets [line items]
Accrued income	886	869
Gross carrying amount | UK
Disclosure of financial assets [line items]
Accrued income	547	461
Gross carrying amount | US
Disclosure of financial assets [line items]
Accrued income	339	408
Trade and other receivables | Gross carrying amount
Disclosure of financial assets [line items]
Trade receivables	2,152	2,063
Trade and other receivables | Gross carrying amount | UK
Disclosure of financial assets [line items]
Trade receivables	227	227
Trade and other receivables | Gross carrying amount | US
Disclosure of financial assets [line items]
Trade receivables	1,925	1,836
Trade and other receivables | Accumulated impairment
Disclosure of financial assets [line items]
Trade receivables	(672)	(512)
Trade and other receivables | Accumulated impairment | UK
Disclosure of financial assets [line items]
Trade receivables	(23)	(40)
Trade and other receivables | Accumulated impairment | US
Disclosure of financial assets [line items]
Trade receivables	£ (649)	£ (472)

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, 2021	Mar. 31, 2020
Disclosure of financial assets [line items]
Trade receivables	£ 3,522	£ 3,266
Accrued income
Disclosure of financial assets [line items]
Expected credit loss rate	7.00%	5.00%
Trade receivables	£ 322	£ 395
Retail customer receivables
Disclosure of financial assets [line items]
Trade receivables	£ 1,852	£ 1,852
0 – 30 days past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	7.00%	5.00%
Trade receivables	£ 580	£ 651
30 – 60 days past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	24.00%	14.00%
Trade receivables	£ 155	£ 194
60 – 90 days past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	36.00%	29.00%
Trade receivables	£ 108	£ 109
3 – 6 months past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	52.00%	47.00%
Trade receivables	£ 140	£ 121
6 – 12 months past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	66.00%	63.00%
Trade receivables	£ 180	£ 105
Over 12 months past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	71.00%	79.00%
Trade receivables	£ 367	£ 277

Cash and cash equivalents (Deta

Cash and cash equivalents (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Cash and cash equivalents [abstract]
Cash at bank	£ 117	£ 73
Short-term deposits	40	0
Cash and cash equivalents	£ 157	£ 73	£ 252	£ 252	£ 329	£ 329

Borrowings - Current and non-cu

Borrowings - Current and non-current borrowings (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Current
Bank loans	£ 1,022	£ 1,244
Bonds	1,987	1,446
Commercial paper	628	1,269
Lease liabilities	99	112	£ 113	£ 65
Other loans	1	1
Current portion of non-current borrowings	3,737	4,072		4,472	£ 4,447	£ 4,447
Non-current
Bank loans	2,532	2,819
Bonds	24,209	23,094
Lease liabilities	586	623	£ 631	205
Other loans	156	186
Non-current portion of non-current borrowings	27,483	26,722		24,258	£ 22,210	£ 22,178
Total borrowings	31,220	30,794		£ 28,730
Liability held at fair value through profit and loss	£ 682	£ 741

Borrowings - Borrowings repayme

Borrowings - Borrowings repayment schedule (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 31,220	£ 30,794	£ 28,730
Less than 1 year
Disclosure of detailed information about borrowings [line items]
Borrowings	3,737	4,072
In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Borrowings	1,745	2,212
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Borrowings	889	1,664
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Borrowings	2,206	757
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	1,833	2,122
Borrowings Paid By Instalments | More than 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	927	870
Borrowings Paid By Other Than Instalments | More than 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 19,883	£ 19,097

Borrowings - Narrative (Details

Borrowings - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019
Disclosure of fair value measurement of liabilities [line items]
Borrowings	£ 31,220	£ 30,794		£ 28,730
Property, plant and equipment pledged as security	67	84
Collateral received	582	785
Lease liabilities	685	735	£ 744	£ 270
Liability held at fair value through profit and loss	682	741
Change in fair value	1	10
Difference between carrying amount of financial liability and amount contractually required to pay at maturity to holder of obligation	2	18
GBP LIBOR
Disclosure of fair value measurement of liabilities [line items]
Borrowings	328
USD LIBOR
Disclosure of fair value measurement of liabilities [line items]
Borrowings	59
Lease liabilities	173
IFRS 16
Disclosure of fair value measurement of liabilities [line items]
Lease liabilities			£ 474
Borrowings
Disclosure of fair value measurement of liabilities [line items]
Notional amount	31,010	30,422
At fair value
Disclosure of fair value measurement of liabilities [line items]
Borrowings	34,676	34,174
At fair value | Level 1
Disclosure of fair value measurement of liabilities [line items]
Borrowings	20,333	14,059
At fair value | Level 2
Disclosure of fair value measurement of liabilities [line items]
Borrowings	14,343	20,115
Financial liabilities at fair value through profit and loss
Disclosure of fair value measurement of liabilities [line items]
Borrowings	£ 684	£ 759

Borrowings - Lease obligations

Borrowings - Lease obligations (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Gross lease liabilities	£ 899	£ 974
Less: finance charges allocated to future periods	(214)	(239)
Lease liabilities	685	735	£ 744	£ 270
Less than 1 year
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Gross lease liabilities	114	132
Lease liabilities	99	112
1 to 5 years
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Gross lease liabilities	321	361
Lease liabilities	267	297
More than 5 years
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Gross lease liabilities	464	481
Lease liabilities	£ 319	£ 326

Trade and other payables (Detai

Trade and other payables (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Trade payables	£ 2,165	£ 2,205
Deferred payables	154	137
Customer contributions	138	84
Social security and other taxes	140	202
Contingent consideration	39	30
Other payables	881	944
Trade and other payables	£ 3,517	£ 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, 2021	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Contract liabilities [abstract]
Current	£ 66	£ 76	£ 61	£ 53	£ 0
Non-current	1,094	1,082	933	£ 813	£ 0
Total contract liabilities	£ 1,160	£ 1,158	£ 994

Contract liabilities - Signific

Contract liabilities - Significant Changes in Contract Liabilities (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Increase (Decrease) in Contract Liabilities [Roll Forward]
As at 1 April	£ 1,158	£ 994
Exchange adjustments	(65)	39
Revenue recognised that was included in the contract liability balance at the beginning of the period	(96)	(60)
Increases due to cash received, excluding amounts recognised as revenue during the period	262	185
Reclassification to held for sale (note 10)	(99)	0
At 31 March	£ 1,160	£ 1,158

Other non-current liabilities_2

Other non-current liabilities (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Deferred income	£ 78	£ 101
Customer contributions	400	428
Contingent consideration (note 38)	18	44
Other payables	347	318
Other non-current liabilities	£ 843	£ 891	£ 805	£ 808	£ 750	£ 1,317

Pensions and other post-retir_3

Pensions and other post-retirement benefits - Narrative (Details) £ in Millions	12 Months Ended
	Mar. 31, 2021GBP (£)plan	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)	Dec. 31, 2020GBP (£)
Disclosure of defined benefit plans [line items]
Employer contributions	£ 274	£ 327	£ 419
Past service cost – plan amendments	£ 0	0	34
Pensions | US
Disclosure of defined benefit plans [line items]
Number of defined benefit plans | plan	4
Employer contributions	£ 110	153	231
Weighted average duration of defined benefit obligation	14 years
Past service cost – plan amendments	£ 0	£ 0	£ 0
Pensions | US | Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	35.00%	36.00%	37.00%
Pensions | US | Deferred members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	9.00%	9.00%	9.00%
Pensions | US | Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	56.00%	55.00%	54.00%
Pensions | UK
Disclosure of defined benefit plans [line items]
Employer contributions	£ 138	£ 156	£ 174
Weighted average duration of defined benefit obligation	14 years
Past service cost – plan amendments	£ 0.4	£ 0	£ 34
Pensions | UK | Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	8.00%	8.00%	10.00%
Pensions | UK | Deferred members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	14.00%	14.00%	16.00%
Pensions | UK | Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	78.00%	78.00%	74.00%
Other post-retirement benefits | US
Disclosure of defined benefit plans [line items]
Employer contributions	£ 26	£ 18	£ 14
Weighted average duration of defined benefit obligation	17 years
Past service cost – plan amendments	£ 0	£ 0	£ 0
Other post-retirement benefits | US | Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	34.00%	35.00%	39.00%
Other post-retirement benefits | US | Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	66.00%	65.00%	61.00%
The National Grid YouPlan (YouPlan)
Disclosure of defined benefit plans [line items]
Defined contribution plan, employer matching contribution percent of gross pay	12.00%
National Grid UK Retirement Plan (NGUKRP)
Disclosure of defined benefit plans [line items]
Defined contribution plan, employer matching contribution percent of gross pay	12.00%
NG UKPS | Pensions
Disclosure of defined benefit plans [line items]
Actuarial loss arising from buy-in arrangement	£ (100)	£ (700)
Section A of NGUKPS | UK
Disclosure of defined benefit plans [line items]
Maximum guarantee payable	£ 1,000
Section A of NGUKPS | Pensions
Disclosure of defined benefit plans [line items]
Gilts exchanged for buy-in policy		2,800		£ 800
Section A of NGUKPS | Pensions | UK
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings			51.80%
Section B of NGUKPS | Pensions
Disclosure of defined benefit plans [line items]
Gilts exchanged for buy-in policy		£ 1,600
Section B of NGUKPS | Pensions | UK
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings			51.40%
Contribution paid			£ 34
NGEG of ESPS | Pensions | UK
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings	44.00%
NGEG of ESPS | Pensions | UK | Time Period, 2020 to 2022
Disclosure of defined benefit plans [line items]
Contributions payable per year	£ 54
NGEG of ESPS | Pensions | UK | Time Period, 2023
Disclosure of defined benefit plans [line items]
Contributions payable per year	£ 26

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, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of defined benefit plans [line items]
Funding surplus/(deficit)	£ 715	£ (953)	£ (218)
Section A of NGUKPS
Disclosure of defined benefit plans [line items]
Market value of plan assets at latest valuation			6,551
Actuarial value of benefits due to members			£ 6,502
Market value as percentage of benefits			101.00%
Funding surplus/(deficit)			£ 49
Section B of NGUKPS
Disclosure of defined benefit plans [line items]
Market value of plan assets at latest valuation			5,765
Actuarial value of benefits due to members			£ 5,831
Market value as percentage of benefits			99.00%
Funding surplus/(deficit)			£ (66)
NGEG of ESPS
Disclosure of defined benefit plans [line items]
Market value of plan assets at latest valuation			3,144
Actuarial value of benefits due to members			£ 3,381
Market value as percentage of benefits			93.00%
Funding surplus/(deficit)			£ (237)

Pensions and other post-retir_5

Pensions and other post-retirement benefits - Security arrangements (Details) - UK - Pensions £ in Millions	Mar. 31, 2021GBP (£)
Section A of NGUKPS
Disclosure of defined benefit plans [line items]
Value of security arrangements	£ 186
Section B of NGUKPS
Disclosure of defined benefit plans [line items]
Value of security arrangements	0
Maximum additional amounts payable	175
NGEG of ESPS
Disclosure of defined benefit plans [line items]
Value of security arrangements	100
Maximum additional amounts payable	£ 500

Pensions and other post-retir_6

Pensions and other post-retirement benefits - Actuarial assumptions (Details) - year	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
UK | Pensions
Disclosure of defined benefit plans [line items]
Discount rate – past service	2.00%	2.35%	2.40%
Discount rate – future service	2.15%	2.35%	2.45%
Salary increases	3.40%	2.90%	3.50%
Rate of increase in RPI – past service	3.15%	2.65%	3.25%
Rate of increase in RPI – future service	3.00%	2.45%	3.20%
Assumed life expectations for a retiree age 65 today: Males	21.8	22.1	22
Assumed life expectations for a retiree age 65 today: Females	23.7	23.8	23.6
Assumed life expectations for a retiree age 65 today: In 20 years: Males	23.1	23.3	23.3
Assumed life expectations for a retiree age 65 today: In 20 years: Females	25.2	25.3	25.2
US | Pensions
Disclosure of defined benefit plans [line items]
Salary increases	4.30%	3.50%	3.50%
Discount rate	3.25%	3.30%	3.95%
Assumed life expectations for a retiree age 65 today: Males	21.6	20.9	22.1
Assumed life expectations for a retiree age 65 today: Females	24	23.4	24.2
Assumed life expectations for a retiree age 65 today: In 20 years: Males	23.2	22.5	23.7
Assumed life expectations for a retiree age 65 today: In 20 years: Females	25.5	25.1	25.9
US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Salary increases	4.30%	3.50%	3.50%
Discount rate	3.25%	3.30%	3.95%
Initial healthcare cost trend rate	7.10%	7.00%	7.25%
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, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of defined benefit plans [line items]
Funding surplus/(deficit)	£ 715	£ (953)	£ (218)
Liabilities	(1,032)	(2,802)	(1,785)
Assets	1,747	1,849	1,567
Pensions | Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(23,283)	(24,281)	(24,609)
Fair value of plan assets	24,388	23,748	24,793
Funding surplus/(deficit)	1,105	(533)	184
Pensions | Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(324)	(345)	(330)
Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Other post-employment liabilities	(66)	(75)	(72)
UK | Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets	14,680	14,364	15,507
Funding surplus/(deficit)	1,035	1,520	1,231
Other post-employment liabilities	0	0	0
Liabilities	(74)	(69)	(76)
Assets	1,109	1,589	1,307
UK | Pensions | Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(13,571)	(12,775)	(14,200)
Fair value of plan assets	14,680	14,364	15,507
Funding surplus/(deficit)	1,109	1,589	1,307
UK | Pensions | Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(74)	(69)	(76)
US | Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets	6,909	6,972	6,646
Funding surplus/(deficit)	(22)	(1,113)	(509)
Other post-employment liabilities	0	0	0
Liabilities	(393)	(1,373)	(769)
Assets	371	260	260
US | Pensions | Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(6,681)	(7,809)	(6,901)
Fair value of plan assets	6,909	6,972	6,646
Funding surplus/(deficit)	228	(837)	(255)
US | Pensions | Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(250)	(276)	(254)
US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Fair value of plan assets	2,799	2,412	2,640
Funding surplus/(deficit)	(298)	(1,360)	(940)
Other post-employment liabilities	(66)	(75)	(72)
Liabilities	(565)	(1,360)	(940)
Assets	267	0	0
US | Other post-retirement benefits | Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(3,031)	(3,697)	(3,508)
Fair value of plan assets	2,799	2,412	2,640
Funding surplus/(deficit)	(232)	(1,285)	(868)
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, 2021	Mar. 31, 2020	Mar. 31, 2019
Included within operating costs
Administration costs	£ 18	£ 16	£ 14
Defined benefit plan costs:
Current service cost	175	178	193
Past service cost – augmentations	0	0	5
Past service credit – redundancies	(1)	0	(7)
Special termination benefit cost – redundancies	5	2	55
Past service cost – plan amendments	0	0	34
Total included within payroll costs	179	180	280
Included within finance income and costs
Net interest (income)/cost	38	23	22
Total included in income statement	235	219	316
Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations	1,408	(724)	68
Exchange adjustments	186	(97)	(101)
Total included in the statement of other comprehensive income	1,594	(821)	(33)
UK | Pensions
Included within operating costs
Administration costs	9	9	6
Defined benefit plan costs:
Current service cost	28	33	41
Past service cost – augmentations	0	0	5
Past service credit – redundancies	(1)	0	(7)
Special termination benefit cost – redundancies	5	2	55
Past service cost – plan amendments	0.4	0	34
Total included within payroll costs	32	35	128
Included within finance income and costs
Net interest (income)/cost	(38)	(31)	(31)
Total included in income statement	3	13	103
Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations	(622)	143	57
Exchange adjustments	0	0	0
Total included in the statement of other comprehensive income	(622)	143	57
US | Pensions
Included within operating costs
Administration costs	7	6	7
Defined benefit plan costs:
Current service cost	104	100	104
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	104	100	104
Included within finance income and costs
Net interest (income)/cost	35	21	21
Total included in income statement	146	127	132
Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations	1,017	(588)	(14)
Exchange adjustments	83	(42)	(42)
Total included in the statement of other comprehensive income	1,100	(630)	(56)
US | Other post-retirement benefits
Included within operating costs
Administration costs	2	1	1
Defined benefit plan costs:
Current service cost	43	45	48
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	43	45	48
Included within finance income and costs
Net interest (income)/cost	41	33	32
Total included in income statement	86	79	81
Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations	1,013	(279)	25
Exchange adjustments	103	(55)	(59)
Total included in the statement of other comprehensive income	1,116	(334)	(34)
NG UKPS | Pensions
Included within finance income and costs
Actuarial loss arising from buy-in arrangement	£ (100)	£ (700)
Section A of NGUKPS
Included within finance income and costs
Cost of equalising for impact of guaranteed minimum pension			17
Section B of NGUKPS
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, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	£ (953)	£ (218)	£ (263)
Cost recognised in the income statement	(235)	(219)	(316)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	1,594	(821)	(33)
Employer contributions	274	327	419
Other movements	(14)	(22)	(25)
Reclassification to held for sale (note 10)	49	0	0
Closing net defined benefit asset/(liability)	715	(953)	(218)
UK | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	1,520	1,231	1,104
Cost recognised in the income statement	(3)	(13)	(103)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(622)	143	57
Employer contributions	138	156	174
Other movements	2	3	(1)
Reclassification to held for sale (note 10)	0	0	0
Closing net defined benefit asset/(liability)	1,035	1,520	1,231
US | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	(1,113)	(509)	(552)
Cost recognised in the income statement	(146)	(127)	(132)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	1,100	(630)	(56)
Employer contributions	110	153	231
Other movements	0	0	0
Reclassification to held for sale (note 10)	27	0	0
Closing net defined benefit asset/(liability)	(22)	(1,113)	(509)
US | Other post-retirement benefits
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	(1,360)	(940)	(815)
Cost recognised in the income statement	(86)	(79)	(81)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	1,116	(334)	(34)
Employer contributions	26	18	14
Other movements	(16)	(25)	(24)
Reclassification to held for sale (note 10)	22	0	0
Closing net defined benefit asset/(liability)	£ (298)	£ (1,360)	£ (940)

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, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of operating segments [line items]
Opening net defined benefit liability	£ (953)	£ (218)	£ (263)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(175)	(178)	(193)
Interest cost	(38)	(23)	(22)
Past service credit – redundancies	1	0	7
Special termination benefit cost – redundancies	(5)	(2)	(55)
Past service cost – augmentations	0	0	(5)
Past service cost – plan amendments	0	0	(34)
Exchange adjustments	186	(97)	(101)
Reclassification to held for sale (note 10)	49	0	0
Closing net defined benefit asset/(liability)	715	(953)	(218)
Present value of defined benefit obligation
Disclosure of operating segments [line items]
Opening net defined benefit liability	(24,626)	(24,939)	(24,054)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(175)	(178)	(193)
Interest cost	(651)	(751)	(771)
Actuarial gains/(losses) – experience	123	148	(69)
Actuarial (losses)/gains – demographic assumptions	(1)	452	266
Actuarial (losses)/gains – financial assumptions	(1,268)	(84)	(619)
Past service credit – redundancies	1	0	7
Special termination benefit cost – redundancies	(5)	(2)	(55)
Past service cost – augmentations	0	0	(5)
Past service cost – plan amendments	0	0	(34)
Medicare subsidy received	(25)	(22)	(19)
Employee contributions	(1)	(1)	(1)
Benefits paid	1,246	1,282	1,376
Exchange adjustments	1,166	(531)	(768)
Reclassification to held for sale (note 10)	609	0	0
Closing net defined benefit asset/(liability)	(23,607)	(24,626)	(24,939)
UK | Pensions
Disclosure of operating segments [line items]
Opening net defined benefit liability	1,520	1,231	1,104
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(28)	(33)	(41)
Interest cost	38	31	31
Past service credit – redundancies	1	0	7
Special termination benefit cost – redundancies	(5)	(2)	(55)
Past service cost – augmentations	0	0	(5)
Past service cost – plan amendments	(0.4)	0	(34)
Exchange adjustments	0	0	0
Reclassification to held for sale (note 10)	0	0	0
Closing net defined benefit asset/(liability)	1,035	1,520	1,231
UK | Present value of defined benefit obligation | Pensions
Disclosure of operating segments [line items]
Opening net defined benefit liability	(12,844)	(14,276)	(14,226)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(28)	(33)	(41)
Interest cost	(296)	(335)	(358)
Actuarial gains/(losses) – experience	(21)	113	(56)
Actuarial (losses)/gains – demographic assumptions	(1)	140	224
Actuarial (losses)/gains – financial assumptions	(1,181)	798	(568)
Past service credit – redundancies	1	0	7
Special termination benefit cost – redundancies	(5)	(2)	(55)
Past service cost – augmentations	0	0	(5)
Past service cost – plan amendments	0	0	(34)
Medicare subsidy received	0	0	0
Employee contributions	(1)	(1)	(1)
Benefits paid	731	752	837
Exchange adjustments	0	0	0
Reclassification to held for sale (note 10)	0	0	0
Closing net defined benefit asset/(liability)	(13,645)	(12,844)	(14,276)
US | Pensions
Disclosure of operating segments [line items]
Opening net defined benefit liability	(1,113)	(509)	(552)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(104)	(100)	(104)
Interest cost	(35)	(21)	(21)
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 amendments	0	0	0
Exchange adjustments	83	(42)	(42)
Reclassification to held for sale (note 10)	27	0	0
Closing net defined benefit asset/(liability)	(22)	(1,113)	(509)
US | Other post-retirement benefits
Disclosure of operating segments [line items]
Opening net defined benefit liability	(1,360)	(940)	(815)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(43)	(45)	(48)
Interest cost	(41)	(33)	(32)
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 amendments	0	0	0
Exchange adjustments	103	(55)	(59)
Reclassification to held for sale (note 10)	22	0	0
Closing net defined benefit asset/(liability)	(298)	(1,360)	(940)
US | Present value of defined benefit obligation | Pensions
Disclosure of operating segments [line items]
Opening net defined benefit liability	(8,085)	(7,155)	(6,582)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(104)	(100)	(104)
Interest cost	(243)	(280)	(277)
Actuarial gains/(losses) – experience	(72)	(45)	(52)
Actuarial (losses)/gains – demographic assumptions	0	78	0
Actuarial (losses)/gains – financial assumptions	(62)	(595)	(24)
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 amendments	0	0	0
Medicare subsidy received	0	0	0
Employee contributions	0	0	0
Benefits paid	371	374	398
Exchange adjustments	804	(362)	(514)
Reclassification to held for sale (note 10)	460	0	0
Closing net defined benefit asset/(liability)	(6,931)	(8,085)	(7,155)
US | Present value of defined benefit obligation | Other post-retirement benefits
Disclosure of operating segments [line items]
Opening net defined benefit liability	(3,697)	(3,508)	(3,246)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(43)	(45)	(48)
Interest cost	(112)	(136)	(136)
Actuarial gains/(losses) – experience	216	80	39
Actuarial (losses)/gains – demographic assumptions	0	234	42
Actuarial (losses)/gains – financial assumptions	(25)	(287)	(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 amendments	0	0	0
Medicare subsidy received	(25)	(22)	(19)
Employee contributions	0	0	0
Benefits paid	144	156	141
Exchange adjustments	362	(169)	(254)
Reclassification to held for sale (note 10)	149	0	0
Closing net defined benefit asset/(liability)	£ (3,031)	£ (3,697)	£ (3,508)

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, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	£ (953)	£ (218)	£ (263)
Changes in net defined benefit liability (asset) [abstract]
Interest income	(38)	(23)	(22)
Employer contributions	274	327	419
Exchange adjustments	186	(97)	(101)
Reclassification to held for sale (note 10)	49	0	0
Closing net defined benefit asset/(liability)	715	(953)	(218)
Actual return on plan assets	3,167	(512)	1,239
Expected contributions to plans in the following year	212	269	307
Pensions | UK
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	1,520	1,231	1,104
Changes in net defined benefit liability (asset) [abstract]
Interest income	38	31	31
Employer contributions	138	156	174
Exchange adjustments	0	0	0
Reclassification to held for sale (note 10)	0	0	0
Closing net defined benefit asset/(liability)	1,035	1,520	1,231
Actual return on plan assets	915	(542)	846
Expected contributions to plans in the following year	93	137	148
Pensions | US
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	(1,113)	(509)	(552)
Changes in net defined benefit liability (asset) [abstract]
Interest income	(35)	(21)	(21)
Employer contributions	110	153	231
Exchange adjustments	83	(42)	(42)
Reclassification to held for sale (note 10)	27	0	0
Closing net defined benefit asset/(liability)	(22)	(1,113)	(509)
Actual return on plan assets	1,359	233	318
Expected contributions to plans in the following year	113	125	150
Other post-retirement benefits | US
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	(1,360)	(940)	(815)
Changes in net defined benefit liability (asset) [abstract]
Interest income	(41)	(33)	(32)
Employer contributions	26	18	14
Exchange adjustments	103	(55)	(59)
Reclassification to held for sale (note 10)	22	0	0
Closing net defined benefit asset/(liability)	(298)	(1,360)	(940)
Actual return on plan assets	893	(203)	75
Expected contributions to plans in the following year	6	7	9
NG UKPS | Pensions
Changes in net defined benefit liability (asset) [abstract]
Actuarial loss arising from buy-in arrangement	(100)	(700)
Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	23,748	24,793	23,858
Changes in net defined benefit liability (asset) [abstract]
Interest income	613	728	749
Return on plan assets in excess of/ (less than) interest	2,554	(1,240)	490
Administration costs	(18)	(16)	(14)
Employer contributions	274	327	419
Employee contributions	1	1	1
Benefits paid	(1,244)	(1,279)	(1,377)
Exchange adjustments	(980)	434	667
Reclassification to held for sale (note 10)	(560)	0	0
Closing net defined benefit asset/(liability)	24,388	23,748	24,793
Plan assets | Pensions | UK
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	14,364	15,507	15,330
Changes in net defined benefit liability (asset) [abstract]
Interest income	334	366	389
Return on plan assets in excess of/ (less than) interest	581	(908)	457
Administration costs	(9)	(9)	(6)
Employer contributions	138	156	174
Employee contributions	1	1	1
Benefits paid	(729)	(749)	(838)
Exchange adjustments	0	0	0
Reclassification to held for sale (note 10)	0	0	0
Closing net defined benefit asset/(liability)	14,680	14,364	15,507
Plan assets | Pensions | US
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	6,972	6,646	6,030
Changes in net defined benefit liability (asset) [abstract]
Interest income	208	259	256
Return on plan assets in excess of/ (less than) interest	1,151	(26)	62
Administration costs	(7)	(6)	(7)
Employer contributions	110	153	231
Employee contributions	0	0	0
Benefits paid	(371)	(374)	(398)
Exchange adjustments	(721)	320	472
Reclassification to held for sale (note 10)	(433)	0	0
Closing net defined benefit asset/(liability)	6,909	6,972	6,646
Plan assets | Other post-retirement benefits | US
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit liability	2,412	2,640	2,498
Changes in net defined benefit liability (asset) [abstract]
Interest income	71	103	104
Return on plan assets in excess of/ (less than) interest	822	(306)	(29)
Administration costs	(2)	(1)	(1)
Employer contributions	26	18	14
Employee contributions	0	0	0
Benefits paid	(144)	(156)	(141)
Exchange adjustments	(259)	114	195
Reclassification to held for sale (note 10)	(127)	0	0
Closing net defined benefit asset/(liability)	£ 2,799	£ 2,412	£ 2,640

Pensions and other post-reti_12

Pensions and other post-retirement benefits - Asset allocation strategy (Details)	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
UK | Pensions
Disclosure of fair value of plan assets [line items]
Return-seeking assets	18.00%	21.00%	23.00%
Liability-matching assets	82.00%	79.00%	77.00%
US | Pensions
Disclosure of fair value of plan assets [line items]
Return-seeking assets	55.00%	49.00%	56.00%
Liability-matching assets	45.00%	51.00%	44.00%
US | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Return-seeking assets	74.00%	71.00%	73.00%
Liability-matching assets	26.00%	29.00%	27.00%

Pensions and other post-reti_13

Pensions and other post-retirement benefits - Asset allocations (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
UK | Pensions
Disclosure of fair value of plan assets [line items]
Equities	£ 1,356	£ 1,464	£ 1,965
Property	669	688	857
Diversified alternatives	712	893	771
Liability-matching assets	5,864	4,982	1,751
Longevity swap	(64)	(51)	(35)
Cash and cash equivalents	284	251	299
Other (including net current assets and liabilities)	256	249	160
Fair value of plan assets	14,680	14,364	15,507
UK | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Equities	555	732	1,181
Property	104	103	108
Diversified alternatives	0	0	0
Liability-matching assets	1,731	1,704	1,751
Longevity swap	0	0	0
Cash and cash equivalents	34	29	40
Other (including net current assets and liabilities)	0	0	0
Fair value of plan assets	7,990	8,456	12,819
UK | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	801	732	784
Property	565	585	749
Diversified alternatives	712	893	771
Liability-matching assets	4,133	3,278	0
Longevity swap	(64)	(51)	(35)
Cash and cash equivalents	250	222	259
Other (including net current assets and liabilities)	256	249	160
Fair value of plan assets	6,690	5,908	2,688
UK | Corporate bonds | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	3,767	3,837	3,625
UK | Corporate bonds | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	3,730	3,837	3,625
UK | Corporate bonds | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	37	0	0
UK | Government securities | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	1,836	2,051	6,114
UK | Government securities | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	1,836	2,051	6,114
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	2,919	2,510	2,711
Property	264	307	316
Diversified alternatives	625	626	670
Infrastructure	130	121	99
Cash and cash equivalents	24	24	21
Other (including net current assets and liabilities)	12	(41)	13
Fair value of plan assets	6,909	6,972	6,646
US | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Equities	560	467	533
Property	0	0	0
Diversified alternatives	167	162	183
Infrastructure	0	0	0
Cash and cash equivalents	24	24	21
Other (including net current assets and liabilities)	12	(44)	(8)
Fair value of plan assets	2,664	2,784	2,480
US | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	2,359	2,043	2,178
Property	264	307	316
Diversified alternatives	458	464	487
Infrastructure	130	121	99
Cash and cash equivalents	0	0	0
Other (including net current assets and liabilities)	0	3	21
Fair value of plan assets	4,245	4,188	4,166
US | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Equities	1,722	1,390	1,588
Diversified alternatives	357	323	341
Other (including net current assets and liabilities)	171	132	149
Fair value of plan assets	2,799	2,412	2,640
US | Other post-retirement benefits | Quoted
Disclosure of fair value of plan assets [line items]
Equities	419	353	404
Diversified alternatives	185	162	175
Other (including net current assets and liabilities)	0	0	0
Fair value of plan assets	1,150	1,081	1,138
US | Other post-retirement benefits | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	1,303	1,037	1,184
Diversified alternatives	172	161	166
Other (including net current assets and liabilities)	171	132	149
Fair value of plan assets	1,649	1,331	1,502
US | Corporate bonds | Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	2,054	2,158	1,754
US | Corporate bonds | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	1,547	1,640	1,329
US | Corporate bonds | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	507	518	425
US | Corporate bonds | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	13	15	19
US | Corporate bonds | Other post-retirement benefits | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	13	15	19
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	881	1,267	1,062
US | Government securities | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	354	535	422
US | Government securities | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	527	732	640
US | Government securities | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	536	552	543
US | Government securities | Other post-retirement benefits | Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	533	551	540
US | Government securities | Other post-retirement benefits | Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	£ 3	£ 1	£ 3

Provisions - Schedule of change

Provisions - Schedule of changes in provisions (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	£ 2,654	£ 2,199
Exchange adjustments	(216)	97
Additions	146	589
Unused amounts reversed	(81)	(70)
Unwinding of discount	78	77
Utilised	(258)	(238)
Reclassification to held for sale (note 10)	(96)
Other provisions, ending balance	2,227	2,654
Environmental
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	2,071	1,639
Exchange adjustments	(185)	82
Additions	26	437
Unused amounts reversed	(38)	(29)
Unwinding of discount	66	65
Utilised	(161)	(123)
Reclassification to held for sale (note 10)	(79)
Other provisions, ending balance	1,700	2,071
Decommissioning
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	254	188
Exchange adjustments	(9)	5
Additions	42	93
Unused amounts reversed	(27)	(16)
Unwinding of discount	7	5
Utilised	(16)	(21)
Reclassification to held for sale (note 10)	(7)
Other provisions, ending balance	244	254
Restructuring
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	35	83
Exchange adjustments	(1)	0
Additions	11	7
Unused amounts reversed	0	(16)
Unwinding of discount	0	0
Utilised	(19)	(39)
Reclassification to held for sale (note 10)	0
Other provisions, ending balance	26	35
Other
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	294	289
Exchange adjustments	(21)	10
Additions	67	52
Unused amounts reversed	(16)	(9)
Unwinding of discount	5	7
Utilised	(62)	(55)
Reclassification to held for sale (note 10)	(10)
Other provisions, ending balance	£ 257	£ 294

Provisions - Current and non-cu

Provisions - Current and non-current provisions (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Disclosure of other provisions [line items]
Current	£ 260	£ 348	£ 316	£ 273	£ 273
Non-current	1,967	2,306	1,883	£ 1,779	£ 1,779
Other provisions	2,227	2,654	2,199
Additions	146	589
Environmental
Disclosure of other provisions [line items]
Other provisions	1,700	2,071	£ 1,639
Additions	£ 26	£ 437
Real discount rate		0.50%
Environmental | Exceptional items
Disclosure of other provisions [line items]
Additions		£ 402
Environmental | Exceptional items, impact of change in the real discount rate
Disclosure of other provisions [line items]
Additions		£ 76

Provisions - Environmental prov

Provisions - Environmental provision (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of other provisions [line items]
Discounted	£ 2,227	£ 2,654	£ 2,199
Environmental
Disclosure of other provisions [line items]
Discounted	1,700	2,071	£ 1,639
Undiscounted	1,754	£ 2,139
Real discount rate		0.50%
Weighted average duration of cash flows		10 years
Environmental | UK
Disclosure of other provisions [line items]
Discounted	167	£ 175
Undiscounted	£ 171	£ 184
Real discount rate	0.50%	0.50%
Weighted average duration of cash flows	15 years
Environmental | US
Disclosure of other provisions [line items]
Discounted	£ 1,533	£ 1,896
Undiscounted	£ 1,583	£ 1,955
Real discount rate	0.50%	0.50%
Weighted average duration of cash flows	10 years

Provisions - Narrative (Details

Provisions - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of other provisions [line items]
Other provisions	£ 2,227	£ 2,654	£ 2,199
Expense of restructuring activities	146	589
Decommissioning
Disclosure of other provisions [line items]
Other provisions	244	254	188
Expense of restructuring activities	42	93
Decommissioning provision, ARO
Disclosure of other provisions [line items]
Other provisions	160	174
Provision for decommissioning, demolition of gas holders
Disclosure of other provisions [line items]
Other provisions	60	74
Restructuring
Disclosure of other provisions [line items]
Other provisions	26	35	83
Expense of restructuring activities	11	7
Other
Disclosure of other provisions [line items]
Other provisions	257	294	£ 289
Expense of restructuring activities	67	52
Liability for claims and claims adjustment
Disclosure of other provisions [line items]
Other provisions	166	164
Business set up and restructuring cost
Disclosure of other provisions [line items]
Other provisions	21	37
Onerous lease commitments and rates payable on surplus properties
Disclosure of other provisions [line items]
Other provisions	27	31
Emissions
Disclosure of other provisions [line items]
Other provisions	£ 13	£ 17

Share capital - Schedule of sha

Share capital - Schedule of share capital (Details) - GBP (£) £ in Millions, shares in Millions		12 Months Ended
		Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of classes of share capital [line items]
Equity, beginning balance		£ 19,793	£ 19,568	£ 19,033
Issued during the year in lieu of dividends	[1]	(1)	(1)	(1)
Equity, ending balance		£ 19,860	£ 19,793	£ 19,568
Share capital
Disclosure of classes of share capital [line items]
Issued capital (in shares), beginning balance		3,780	3,687
Issued during the year in lieu of dividends (in shares)		35	93
Issued capital (in shares), ending balance		3,815	3,780	3,687
Equity, beginning balance		£ 470	£ 458
Issued during the year in lieu of dividends	[1]	4	12	£ 6
Equity, ending balance		£ 474	£ 470	£ 458
[1]	Included within the share premium account are costs associated with scrip dividends.

Share capital - Narrative (Deta

Share capital - Narrative (Details) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Share Capital, Reserves And Other Equity Interest [Abstract]
Par value per share (GBP per share)	£ 0.1243129
Treasury stock (in shares)	266	272
Treasury shares, market value	£ 2,296	£ 2,574
Treasury shares, gifted (in shares)	4	3
Treasury stock, reissued (in shares)	2	2
Shares reissued to employee share schemes as percent of ordinary shares	0.20%	0.10%
Treasury shares, reissued, nominal value	£ 1	£ 1
Gross proceeds from reissue of treasury shares	17	17
Purchase of own shares, employee share trusts	£ 2	£ 6	£ 2
Maximum number of treasury shares held during the year (in shares)	272	277
Treasury shares as percent of ordinary shares	7.10%	7.30%
Treasury shares, nominal value	£ 34	£ 34

Other equity reserves (Details)

Other equity reserves (Details) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2021		Mar. 31, 2020		Mar. 31, 2019
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		£ (3,895)	[1]	£ (4,223)	[1]	£ (4,540)
Exchange adjustments		(1,345)		560		360
Net (losses)/gains taken to equity		130		(206)		(304)
Share of net gains/ (losses) of associates taken to equity		1		(5)		1
Transferred to profit or loss		59		(31)		207
Net losses in respect of cash flow hedging of capital expenditure		(14)		(17)		(13)
Tax		(13)		42		12
Cash flow hedges transferred to the statement of financial position, net of tax		(17)		(15)		(18)
Other equity reserves, ending balance	[1]	(5,094)		(3,895)		(4,223)
(Losses)/ gains on exchange adjustments related to the translation of foreign operations		1,507		(545)		(896)
Gains (losses) on hedges of net investments in foreign subsidiaries		183		5		(550)
Previously reported
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance						(4,540)
Translation
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		1,310		750
Exchange adjustments		(1,345)		560		360
Other equity reserves, ending balance		(35)		1,310		750
Translation | Previously reported
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance						390
Cash flow hedge
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		(75)		61
Net (losses)/gains taken to equity		14		(142)		(206)
Share of net gains/ (losses) of associates taken to equity		1		(5)		1
Transferred to profit or loss		56		14		166
Net losses in respect of cash flow hedging of capital expenditure		(14)		(17)		(13)
Tax		(13)		29		6
Cash flow hedges transferred to the statement of financial position, net of tax		(17)		(15)		(18)
Other equity reserves, ending balance		(48)		(75)		61
Cash flow hedge | Previously reported
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance						128
Cost of hedging
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		(50)		17
Net (losses)/gains taken to equity		11		(33)		(107)
Transferred to profit or loss		3		(45)		41
Tax		8		11		7
Other equity reserves, ending balance		(28)		(50)		17
Available- for-sale | Previously reported
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance				0		88
Other equity reserves, ending balance						0
FVOCI equity
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		25		34
Net (losses)/gains taken to equity		36		(13)
Tax		(10)		4
Other equity reserves, ending balance		51		25		34
FVOCI debt
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		31		48
Net (losses)/gains taken to equity		80		(15)		2
Tax				(2)
Other equity reserves, ending balance		111		31		48
Own credit
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		10		13
Net (losses)/gains taken to equity		(11)		(3)		7
Tax		2		0		(1)
Other equity reserves, ending balance		1		10		13
Capital redemption
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		19		19
Other equity reserves, ending balance		19		19		19
Capital redemption | Previously reported
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance						19
Merger
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance		(5,165)		(5,165)
Other equity reserves, ending balance		£ (5,165)		£ (5,165)		(5,165)
Merger | Previously reported
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance						£ (5,165)
[1]	Comparative amounts have been revised as described in note 1F.

Net debt - Composition of net d

Net debt - Composition of net debt (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Cash and cash equivalents	£ 157	£ 73	£ 252	£ 252	£ 329	£ 329
Current financial investments	2,342	1,998	1,981	1,981	2,694	£ 2,694
Borrowings	(31,220)	(30,794)		(28,730)
Financing derivatives	175	133	(32)	(32)	600
Net debt position	£ (28,546)	£ (28,590)	£ (26,529)	£ (26,529)	£ (23,002)

Net debt - Analysis of changes

Net debt - Analysis of changes in net debt (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2019	Apr. 01, 2018
Net cash and cash equivalents
Cash and cash equivalents, beginning balance	£ 73	£ 252	£ 329
Cash flow, cash and cash equivalents	95	(183)	(80)
Foreign exchange movements, cash and cash equivalents	(7)	4	3
Reclassification to held for sale, cash and cash equivalents	(4)
Cash and cash equivalents, ending balance	157	73	252
Financial investments
Financial investments, beginning balance	1,998	1,981	2,694
Cash flow, financial investments	429	(42)	(846)
Fair value gains and losses, financial investments	14	1	14
Foreign exchange movements, financial investments	(106)	24	79
Interest income/(charges), financial investments	7	34	29
Other non-cash movements, financial Investments		0	11
Financial investments, ending balance	2,342	1,998	1,981
Borrowings
Borrowings, beginning balance	(30,794)
Impact of transition to IFRS 9, borrowings					£ (32)
Impact of transition to IFRS 16, borrowings				£ (474)
Cash flow, borrowings	(2,336)	450	(240)
Fair value gains and losses, borrowings	159	(57)	(9)
Foreign exchange movements, borrowings	1,710	(807)	(724)
Interest income/(charges), borrowings	(946)	(1,092)	(1,062)
Other non-cash movements, borrowings	(136)	(84)	(38)
Reclassification to held for sale, borrowings	1,123
Borrowings, ending balance	(31,220)	(30,794)
Financing derivatives
Financing derivatives, beginning balance	133	(32)
Cash flow, financing derivatives	4	450	422
Fair value gains and losses, financing derivatives	31	(246)	(1,011)
Interest income/(charges), financing derivatives	7	(39)	(43)
Financing derivatives, ending balance	175	133	(32)
Net debt
Net debt	(28,590)	(26,529)
Impact of transition to IFRS 9, net debt					£ (32)
Impact of transition to IFRS 16, net debt				£ (474)
Cash flows, net debt	(1,808)	675	(744)
Fair value gains and losses, net debt	204	(302)	(1,006)
Foreign exchange movements, net debt	1,597	(779)	(642)
Interest income/(charges), net debt	(932)	(1,097)	(1,076)
Other non-cash movements, net debt	(136)	(84)	(27)
Reclassification to held for sale, net debt	1,119
Net debt	(28,546)	(28,590)	(26,529)
Interest payable	263	246	223
Interest received	7	35	24
Cash flows from (used in) decrease (increase) in short-term deposits and investments	(436)	£ 7	£ 822
Non-current assets
Financing derivatives
Financing derivatives, ending balance	514
Net debt
Net debt	514
Current assets
Net cash and cash equivalents
Cash and cash equivalents, ending balance	157
Financial investments
Financial investments, ending balance	2,342
Financing derivatives
Financing derivatives, ending balance	428
Net debt
Net debt	2,927
Current liabilities
Borrowings
Borrowings, ending balance	(3,737)
Financing derivatives
Financing derivatives, ending balance	(70)
Net debt
Net debt	(3,807)
Non-current liabilities
Borrowings
Borrowings, ending balance	(27,483)
Financing derivatives
Financing derivatives, ending balance	(697)
Net debt
Net debt	£ (28,180)

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, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Proceeds received from loans	£ 5,645	£ 4,218	£ 2,932
Repayment of loans	(1,663)	(3,253)	(1,969)
Payments of lease liabilities	(112)	(121)	(70)
Net movements in short-term borrowings	(759)	(424)	179
Interest paid	(835)	(957)	(914)
Borrowings
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Proceeds received from loans	5,645	4,218	2,932
Repayment of loans	(1,663)	(3,253)	(1,969)
Payments of lease liabilities	(112)	(121)	(70)
Net movements in short-term borrowings	(759)	(424)	179
Interest paid	(804)	(904)	(856)
Cash flows per financing activities section of cash flow statement	2,307	(484)	216
Non-net debt-related items	29	34	24
Cash flows relating to financing liabilities within net debt	2,336	(450)	240
Borrowings	2,336	(450)	240
Financing derivatives
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Cash inflows on derivatives	58	62	221
Cash outflows on derivatives	(185)	(249)	(186)
Interest paid	(31)	(53)	(58)
Cash flows per financing activities section of cash flow statement	(158)	(240)	(23)
Derivative cash inflow in relation to capital expenditure	10	13	13
Derivative cash inflows per investing section of cash flow statement	225	58	17
Derivative cash outflows per investing section of cash flow statement	(81)	(281)	(429)
Cash flows relating to financing liabilities within net debt	(4)	(450)	(422)
Financing derivatives	£ (4)	£ (450)	£ (422)

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, 2021	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Changes in liabilities arising from financing activities [abstract]
Liabilities arising from financing activities, beginning balance	£ (30,566)	£ (28,502)	£ (26,072)
Impact of transition to IFRS 9				£ (32)
Impact of transition to IFRS 16			(474)
Cash flow	(2,178)	690	(217)
Fair value gains and losses	(142)	(288)	(343)
Foreign exchange movements	1,710	(807)	(724)
Interest charges	(935)	(1,101)	(1,076)
Other non-cash movements	(136)	(84)	(38)
Reclassification to held for sale	1,123
Liabilities arising from financing activities, ending balance	(31,124)	(30,566)	(28,502)
Borrowings
Changes in liabilities arising from financing activities [abstract]
Liabilities arising from financing activities, beginning balance	(30,794)	(28,730)	(26,625)
Impact of transition to IFRS 9				(32)
Impact of transition to IFRS 16			(474)
Cash flow	(2,336)	450	(240)
Fair value gains and losses	159	(57)	(9)
Foreign exchange movements	1,710	(807)	(724)
Interest charges	(946)	(1,092)	(1,062)
Other non-cash movements	(136)	(84)	(38)
Reclassification to held for sale	1,123
Liabilities arising from financing activities, ending balance	(31,220)	(30,794)	(28,730)
Financing derivatives
Changes in liabilities arising from financing activities [abstract]
Liabilities arising from financing activities, beginning balance	228	228	553
Impact of transition to IFRS 9				£ 0
Impact of transition to IFRS 16			0
Cash flow	158	240	23
Fair value gains and losses	(301)	(231)	(334)
Foreign exchange movements	0	0	0
Interest charges	11	(9)	(14)
Other non-cash movements	0	0	0
Reclassification to held for sale	0
Liabilities arising from financing activities, ending balance	£ 96	£ 228	£ 228

Commitments and contingencies_2

Commitments and contingencies (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Disclosure of contingent liabilities [line items]
Contracted for but not provided	£ 2,716	£ 2,629
Energy purchase commitments	15,784	16,358
Estimated financial effect of contingent liabilities	2,836	2,822
Guarantee of sublease for US property (expires 2040)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	149	173
Guarantees of certain obligations of Grain LNG (expire up to 2025)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	33	34
Guarantees of certain obligations for construction of HVDC West Coast Link (expected expiry 2059)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	85	92
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	584	683
Guarantees of certain obligations of St William Homes LLP (various expiry dates)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	53	30
Guarantees of certain obligations of National Grid IFA 2 Limited (expected expiry 2022)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	170	564
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	1,276	1,096
Other guarantees and letters of credit (various expiry dates)
Disclosure of contingent liabilities [line items]
Estimated financial effect of contingent liabilities	486	150
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	136	358
Less than 1 year
Disclosure of contingent liabilities [line items]
Energy purchase commitments	1,255	1,365
In 1 to 2 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	894	890
In 2 to 3 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	975	973
In 3 to 4 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	959	955
In 4 to 5 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	896	861
More than 5 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	£ 10,805	£ 11,314

Related party transactions - Re

Related party transactions - Related party transactions table (Details) - GBP (£)	1 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
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		£ 3,000,000	£ 5,000,000	£ 5,000,000
Joint ventures
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		79,000,000	101,000,000	151,000,000
Purchases of goods and services, related party transactions		35,000,000	61,000,000	26,000,000
Amounts receivable		263,000,000	255,000,000	584,000,000
Amounts payable		17,000,000	0	8,000,000
Interest income		0	2,000,000	5,000,000
Dividends received		49,000,000	34,000,000	30,000,000
Joint ventures | St William Homes LLP
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		14,000,000	38,000,000	139,000,000
Receivables due from joint ventures		241,000,000	242,000,000	325,000,000
Joint ventures | Emerald Energy Venture LLC
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		50,000,000	21,000,000	0
Joint ventures | NGET/SPT Upgrades Limited
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		6,000,000	32,000,000	2,000,000
Purchases of goods and services, related party transactions		5,000,000	58,000,000	26,000,000
Joint ventures | Nemo Link Limited
Disclosure of transactions between related parties [line items]
Dividends received		25,000,000	8,000,000	0
Receivables due from joint ventures		0	0	258,000,000
Joint ventures | BritNed Development Limited
Disclosure of transactions between related parties [line items]
Dividends received		18,000,000	25,000,000	30,000,000
Joint ventures | Quadgas HoldCo Limited
Disclosure of transactions between related parties [line items]
Receivables due from joint ventures		0
Associates
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		1,000,000	33,000,000	192,000,000
Purchases of goods and services, related party transactions		43,000,000	56,000,000	141,000,000
Amounts receivable		0	1,000,000	368,000,000
Amounts payable		3,000,000	4,000,000	12,000,000
Interest income		0	8,000,000	23,000,000
Dividends received		32,000,000	41,000,000	171,000,000
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				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		41,000,000	31,000,000	30,000,000
Dividends received		£ 31,000,000	£ 32,000,000	£ 24,000,000

Financial risk management - Nar

Financial risk management - Narrative (Details)	12 Months Ended
	Mar. 31, 2021
Financial Instruments [Abstract]
Hedge ratio	1

Financial risk management - Tre

Financial risk management - Treasury credit risk (Details) £ in Millions	Mar. 31, 2021GBP (£)
Triple ‘A’ G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	£ 2,259
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	1,232
Double ‘A+’ G7 sovereign entities (AA+)
Disclosure of credit risk exposure [line items]
Maximum limit	2,054
Bottom of range | Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	822
Bottom of range | Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	288
Top of range | Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	1,027
Top of range | Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	411
Long-term limit | Triple ‘A’ G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	1,129
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	616
Long-term limit | Double ‘A+’ G7 sovereign entities (AA+)
Disclosure of credit risk exposure [line items]
Maximum limit	1,027
Long-term limit | Bottom of range | Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	411
Long-term limit | Bottom of range | Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	144
Long-term limit | Top of range | Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	513
Long-term limit | Top of range | Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	£ 205

Financial risk management - Off

Financial risk management - Offsetting financial assets and liabilities (Details) - Credit Risk - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Assets
Gross carrying amounts	£ 999	£ 1,342
Gross amounts offset	0	0
Net amount presented in statement of financial position	999	1,342
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(242)	(356)
Cash collateral received/ pledged	(561)	(697)
Net amount	196	289
Liabilities
Gross carrying amounts	(899)	(1,334)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(899)	(1,334)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	242	356
Cash collateral received/ pledged	471	654
Net amount	(186)	(324)
Assets (Liabilities)
Gross carrying amounts	100	8
Gross amounts offset	0	0
Net amount presented in statement of financial position	100	8
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	0	0
Cash collateral received/ pledged	(90)	(43)
Net amount	10	(35)
Financing derivatives
Liabilities
Gross carrying amounts	(767)	(1,134)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(767)	(1,134)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	234	351
Cash collateral received/ pledged	467	646
Net amount	(66)	(137)
Commodity contract derivatives
Liabilities
Gross carrying amounts	(132)	(200)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(132)	(200)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	8	5
Cash collateral received/ pledged	4	8
Net amount	(120)	(187)
Bank account and bank overdraft
Assets
Gross amounts offset	0	(23)
Financing derivatives
Assets
Gross carrying amounts	942	1,267
Gross amounts offset	0	0
Net amount presented in statement of financial position	942	1,267
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(234)	(351)
Cash collateral received/ pledged	(561)	(694)
Net amount	147	222
Commodity contract derivatives
Assets
Gross carrying amounts	57	75
Gross amounts offset	0	0
Net amount presented in statement of financial position	57	75
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(8)	(5)
Cash collateral received/ pledged	0	(3)
Net amount	£ 49	£ 67

Financial risk management - Liq

Financial risk management - Liquidity risk (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Non-derivative financial liabilities
Lease liabilities	£ (899)	£ (974)
Less than 1 year
Non-derivative financial liabilities
Lease liabilities	(114)	(132)
Liquidity risk
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(31,408)	(29,647)
Interest payments on borrowings	(14,314)	(14,231)
Lease liabilities	(915)	(974)
Other non-interest-bearing liabilities	(3,557)	(3,467)
Contingent consideration	(64)	(96)
Derivative financial assets
Financial liabilities	(50,681)	(48,679)
Liquidity risk | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	5,710	5,877
Liquidity risk | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(4,850)	(4,651)
Liquidity risk | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	27	22
Liquidity risk | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(27)	(21)
Liquidity risk | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	9,299	7,953
Liquidity risk | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(10,462)	(9,248)
Liquidity risk | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	12	6
Liquidity risk | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(132)	(202)
Liquidity risk | Less than 1 year
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(3,350)	(3,672)
Interest payments on borrowings	(810)	(765)
Lease liabilities	(118)	(132)
Other non-interest-bearing liabilities	(3,207)	(3,149)
Contingent consideration	(40)	(32)
Derivative financial assets
Financial liabilities	(7,260)	(7,998)
Liquidity risk | Less than 1 year | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	2,162	2,469
Liquidity risk | Less than 1 year | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(1,700)	(2,271)
Liquidity risk | Less than 1 year | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	21	20
Liquidity risk | Less than 1 year | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(21)	(21)
Liquidity risk | Less than 1 year | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	3,773	2,249
Liquidity risk | Less than 1 year | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(3,899)	(2,582)
Liquidity risk | Less than 1 year | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	12	4
Liquidity risk | Less than 1 year | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(83)	(116)
Liquidity risk | In 1 to 2 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(1,690)	(2,150)
Interest payments on borrowings	(755)	(750)
Lease liabilities	(108)	(114)
Other non-interest-bearing liabilities	(350)	(318)
Contingent consideration	(24)	(16)
Derivative financial assets
Financial liabilities	(2,986)	(3,009)
Liquidity risk | In 1 to 2 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	926	1,063
Liquidity risk | In 1 to 2 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(834)	(527)
Liquidity risk | In 1 to 2 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	4	1
Liquidity risk | In 1 to 2 years | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(4)	0
Liquidity risk | In 1 to 2 years | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	749	986
Liquidity risk | In 1 to 2 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(877)	(1,136)
Liquidity risk | In 1 to 2 years | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	0	2
Liquidity risk | In 1 to 2 years | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(23)	(50)
Liquidity risk | In 2 to 3 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(806)	(1,611)
Interest payments on borrowings	(731)	(714)
Lease liabilities	(90)	(99)
Other non-interest-bearing liabilities	0	0
Contingent consideration	0	(32)
Derivative financial assets
Financial liabilities	(1,671)	(2,539)
Liquidity risk | In 2 to 3 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	833	570
Liquidity risk | In 2 to 3 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(780)	(375)
Liquidity risk | In 2 to 3 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	1	1
Liquidity risk | In 2 to 3 years | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(2)	0
Liquidity risk | In 2 to 3 years | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	451	1,208
Liquidity risk | In 2 to 3 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(533)	(1,463)
Liquidity risk | In 2 to 3 years | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	0	0
Liquidity risk | In 2 to 3 years | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(14)	(24)
Liquidity risk | More than 3 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(25,562)	(22,214)
Interest payments on borrowings	(12,018)	(12,002)
Lease liabilities	(599)	(629)
Other non-interest-bearing liabilities	0	0
Contingent consideration	0	(16)
Derivative financial assets
Financial liabilities	(38,764)	(35,133)
Liquidity risk | More than 3 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	1,789	1,775
Liquidity risk | More than 3 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(1,536)	(1,478)
Liquidity risk | More than 3 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	1	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	4,326	3,510
Liquidity risk | More than 3 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(5,153)	(4,067)
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)	£ (12)

Financial risk management - Cur

Financial risk management - Currency risk (Details) - Currency risk - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	£ (28,546)	£ (28,590)
Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	157	73
Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	2,342	1,998
Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(31,220)	(30,794)
Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(28,721)	(28,723)
Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	175	133
Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,669	1,709
Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(3,085)	(3,179)
Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(365)	(362)
Sterling
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(11,758)	(12,745)
Sterling | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	63	18
Sterling | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,215	813
Sterling | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(12,210)	(12,407)
Sterling | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(10,932)	(11,576)
Sterling | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(826)	(1,169)
Sterling | Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	282	306
Sterling | Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,207)	(1,177)
Sterling | Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(77)	(85)
Euro
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	108	191
Euro | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
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	(5,351)	(4,150)
Euro | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(5,351)	(4,150)
Euro | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	5,459	4,341
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	(16,933)	(16,191)
Dollar | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	94	55
Dollar | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,127	1,185
Dollar | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(12,660)	(13,217)
Dollar | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(11,439)	(11,977)
Dollar | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(5,494)	(4,214)
Dollar | Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,387	1,403
Dollar | Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,878)	(2,002)
Dollar | Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(288)	(277)
Other
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	37	155
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	(999)	(1,020)
Other | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(999)	(1,020)
Other | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,036	1,175
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, 2021	Mar. 31, 2020
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	£ (28,546)	£ (28,590)
Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(20,230)	(18,639)
Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(1,897)	(3,001)
Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,478)	(6,974)
Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	59	24
Cash and cash equivalents
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	157	73
Cash and cash equivalents | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	64	71
Cash and cash equivalents | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	67	10
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	26	(8)
Financial investments
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	2,342	1,998
Financial investments | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Financial investments | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	2,309	1,966
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	33	32
Borrowings
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(31,220)	(30,794)
Borrowings | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(23,163)	(20,969)
Borrowings | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(1,762)	(3,085)
Borrowings | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,295)	(6,740)
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	(28,721)	(28,723)
Pre-derivative position | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(23,099)	(20,898)
Pre-derivative position | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	614	(1,109)
Pre-derivative position | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,295)	(6,740)
Pre-derivative position | Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	59	24
Derivative effect
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	175	133
Derivative effect | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	2,869	2,259
Derivative effect | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(2,511)	(1,892)
Derivative effect | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(183)	(234)
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, 2021GBP (£)		Mar. 31, 2020GBP (£)		Mar. 31, 2021£ / $	Mar. 31, 2021£ / €	Mar. 31, 2021€ / $	Mar. 31, 2021	Mar. 31, 2020£ / $	Mar. 31, 2020£ / €	Mar. 31, 2020€ / $	Mar. 31, 2020	Mar. 31, 2019GBP (£)		Apr. 01, 2018GBP (£)	Mar. 31, 2018GBP (£)
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	£ (5,094)	[1]	£ (3,895)	[1]									£ (4,223)	[1]	£ (4,468)	£ (4,540)
Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	(28)		(50)										£ 17		£ 76
Fair value hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Net losses in respect of cost of hedging	(15)		5
Transferred to profit or loss in respect of cost of hedging	1		1
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	(11)		2
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						1.11	1.13		1.64	1.19	1.13
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						1.24	1.17			1.24	1.17
Fair value hedges | Sterling | Bottom of range | Foreign currency and interest rate risk | LIBOR
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis								0.30%				0.30%
Fair value hedges | Sterling | Top of range | Foreign currency and interest rate risk | LIBOR
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis								4.08%				4.08%
Fair value hedges | Dollar | Bottom of range | Foreign currency and interest rate risk | LIBOR
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis								0.68%				(0.44%)
Fair value hedges | Dollar | Top of range | Foreign currency and interest rate risk | LIBOR
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 in respect of cash flow hedges	14		(143)
Net losses in respect of cost of hedging	(24)		(7)
Transferred to profit or loss in respect of cash flow hedges	56		14
Transferred to profit or loss in respect of cost of hedging	2		(1)
Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Net gains in respect of cash flow hedges	(14)		(17)
Net 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	(30)		(8)
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	1.08	1.13		1.30	1.10	1.13
Cash flow hedges | Bottom of range | Currency risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate					1.31	1.04			1.24	1.04
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	1.24	1.14		1.66	1.24	1.14
Cash flow hedges | Top of range | Currency risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate					1.41	1.29			1.41	1.30
Cash flow hedges | Sterling | Bottom of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate								0.976%				1.331%
Cash flow hedges | Sterling | Top of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate								5.845%				5.85%
Cash flow hedges | Dollar | Bottom of range | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate								2.513%				1.103%
Cash flow hedges | Dollar | 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 losses in respect of cost of hedging	50		(30)
Transferred to profit or loss in respect of cost of hedging	0		(45)
Closing foreign exchange rate | £ / €										1.14
Net investment hedges | Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	6		(43)
Net investment hedges | Bottom of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate					1.22	1.15			1.21
Net investment hedges | Top of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate					1.40	1.16			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	0		1
Derivative assets - current | Cash flow hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	10		0
Derivative assets - current | Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	2		4
Derivative assets - current | Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	5		9
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	187		247
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	59		106
Derivative assets - non-current | Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	1		8
Derivative assets - non-current | Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	140		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	0		(1)
Derivative liabilities - current | Cash flow hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(12)		(105)
Derivative liabilities - current | Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(24)		(8)
Derivative liabilities - current | Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(17)		(82)
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	(113)		(39)
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	(255)		(264)
Derivative liabilities - non-current | Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(22)		(12)
Derivative liabilities - non-current | Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	£ 0		£ (19)
[1]	Comparative amounts have been revised as described in note 1F.

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, 2021GBP (£)	Mar. 31, 2020GBP (£)
Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(2,755,000,000)	(1,751,000,000)
Balance of fair value hedge adjustments in borrowings, Continuing hedges	£ 121	£ (31)
Balance of fair value hedge adjustments in borrowings, Discontinued hedges	(85)	(95)
Change in value used for calculating ineffectiveness, Hedged item	153	(42)
Change in value used for calculating ineffectiveness, Hedging instrument	(127)	48
Hedge ineffectiveness	£ 26	£ 6
Foreign currency and interest rate risk | Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(4,884,000,000)	(4,127,000,000)
Balance in cash flow hedge reserve, Continuing hedges	£ (11)	£ (69)
Balance in cash flow hedge reserve, Discontinued hedges	(6)	(22)
Change in value used for calculating ineffectiveness, Hedged item	(16)	142
Change in value used for calculating ineffectiveness, Hedging instrument	16	(143)
Hedge ineffectiveness	£ 0	£ (1)
Currency risk | Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(988,000,000)	(794,000,000)
Balance in cash flow hedge reserve, Continuing hedges	£ (31)	£ 8
Balance in cash flow hedge reserve, Discontinued hedges	3	0
Change in value used for calculating ineffectiveness, Hedged item	17	17
Change in value used for calculating ineffectiveness, Hedging instrument	(17)	(17)
Hedge ineffectiveness	£ 0	£ 0
Currency risk | Net investment hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(2,786,000,000)	(3,064,000,000)
Balance in translation reserve, Continuing hedges	£ 183	£ 45
Balance in translation reserve, Discontinued hedges	(2,826)	(2,871)
Change in value used for calculating ineffectiveness, Hedged item	(183)	(6)
Change in value used for calculating ineffectiveness, Hedging instrument	183	6
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	2,714	1,883
Current liabilities | Borrowings | Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	0	72
Non-current liabilities | Borrowings | Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	£ 2,714	£ 1,811
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	(2,679,000,000)	(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)	(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	0

Financial risk management - Fai

Financial risk management - Fair value analysis (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 3,522	£ 3,266
Liabilities	(1,638)	(2,149)
Financial Assets (Liabilities)	1,884	1,117
Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,867	1,361
Liabilities	(682)	(741)
Financial Assets (Liabilities)	1,185	620
Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,370	1,618
Liabilities	(659)	(1,025)
Financial Assets (Liabilities)	711	593
Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	285	287
Liabilities	(297)	(383)
Financial Assets (Liabilities)	(12)	(96)	£ (61)
Financing derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(767)	(1,134)
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	(584)	(889)
Financing derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(183)	(245)
Commodity contract derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(132)	(200)
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	(75)	(136)
Commodity contract derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(57)	(64)
Liabilities held at fair value
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(682)	(741)
Liabilities held at fair value | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(682)	(741)
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	(57)	(74)
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	(57)	(74)
Investments held at FVTPL
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	2,008	1,386
Investments held at FVTPL | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,768	1,278
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	240	108
Investments held at FVOCI
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	515	435
Investments held at FVOCI | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	99	83
Investments held at FVOCI | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	416	352
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	0	103
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	0	103
Financing derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	942	1,267
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	942	1,257
Financing derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	10
Commodity contract derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	57	75
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	12	9
Commodity contract derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 45	£ 66

Financial risk management - Cha

Financial risk management - Changes in level 3 financial instruments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	£ 1,117
Ending balance	1,884	£ 1,117
Level 3
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	(96)	(61)
Net gains/(losses) for the year	33	12
Purchases	31	77
Acquisition of National Grid Renewables	0	(74)
Settlements	16	(50)
Reclassification to held for sale (note 10)	4	0
Ending balance	(12)	(96)
Level 3 | Financing derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	(235)	(214)
Net gains/(losses) for the year	51	(20)
Purchases	0	0
Acquisition of National Grid Renewables	0	0
Settlements	1	(1)
Reclassification to held for sale (note 10)	0	0
Ending balance	(183)	(235)
Gains (losses) on assets held at end of year	51	(20)
Level 3 | Commodity contract derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	2	1
Net gains/(losses) for the year	(16)	6
Purchases	(1)	26
Acquisition of National Grid Renewables	0	0
Settlements	(1)	(31)
Reclassification to held for sale (note 10)	4	0
Ending balance	(12)	2
Gains (losses) on assets held at end of year	(46)	(17)
Level 3 | Other
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	137	152
Net gains/(losses) for the year	(2)	26
Purchases	32	51
Acquisition of National Grid Renewables	0	(74)
Settlements	16	(18)
Reclassification to held for sale (note 10)	0	0
Ending balance	£ 183	£ 137

Financial risk management - I_2

Financial risk management - Impacts of reasonably possible changes in significant level 3 assumptions (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Financing derivatives | + 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	£ (83)	£ (95)
Financing derivatives | - 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	83	90
Commodity contract derivatives | 10% increase in commodity prices
Disclosure of detailed information about financial instruments [line items]
10% increase in commodity prices	3	2
Commodity contract derivatives | 10% decrease in commodity prices
Disclosure of detailed information about financial instruments [line items]
10% decrease in commodity prices	(1)	0
Commodity contract derivatives | +10% market area price change
Disclosure of detailed information about financial instruments [line items]
+10% market area price change	(4)	(4)
Commodity contract derivatives | -10% market area price change
Disclosure of detailed information about financial instruments [line items]
-10% market area price change	7	4
Other | +50 basis points change in discount rate
Disclosure of detailed information about financial instruments [line items]
+50 basis points change in discount rate	(5)	(3)
Other | -50 basis points change in discount rate
Disclosure of detailed information about financial instruments [line items]
-50 basis points change in discount rate	£ 5	£ 4

Financial risk management - Cap

Financial risk management - Capital risk management (Details)	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financial Instruments [Abstract]
Retained cash flow ratio	6.60%	9.20%
Gearing ratio	65.00%	63.00%
Interest cover ratio	4.5	4.1

Borrowing facilities - Narrativ

Borrowing facilities - Narrative (Details) £ in Millions	May 31, 2024GBP (£)	Mar. 31, 2021GBP (£)numberOfLoan	Mar. 31, 2020GBP (£)	Mar. 31, 2019GBP (£)
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		£ 5,525	£ 5,772
Borrowings		£ 31,220	30,794	£ 28,730
Number of loan facilities | numberOfLoan		2
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		£ 1,718	277
Additional undrawn borrowing facilities		1,861
Borrowings		2,206	757
More than 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		0	0
Renegotiated undrawn borrowing facilities		150
Bilateral Committed Credit Facilities
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity		5,410	5,495
Bilateral Committed Credit Facilities | In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity	£ 400
Credit Facilities From Syndicates Of Banks
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity		115	277
Facilities Held As Backup To Commercial Paper And Similar Borrowings
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		5,410	5,495
Facilities Available As Backup To Specific US Borrowings
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		115	277
2019 Export Credit Agreements
Disclosure of detailed information about borrowings [line items]
Borrowings		550	550
Export Credit Agency
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		446	233
Borrowings		1,345	901
Facilities To Finance The Acquisition
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity		8,250	0
Undrawn borrowing facilities		8,250
Facilities To Backup Acquired Debt
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity		1,105	£ 0
Undrawn borrowing facilities		1,105
Facilities Cancelled As Waivers Obtained
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity		£ 1,105

Borrowing facilities - Schedule

Borrowing facilities - Schedule of undrawn committed borrowing facilities (Details) - GBP (£) £ in Millions	Mar. 31, 2021	Mar. 31, 2020
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 5,525	£ 5,772
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	1,668	1,940
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	534	1,668
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	1,718	277
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	1,605	1,887
More than 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 0	£ 0

Subsidiary undertakings, join_3

Subsidiary undertakings, joint ventures and associates - Subsidiaries (Details)	12 Months Ended
	Mar. 31, 2021
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_4

Subsidiary undertakings, joint ventures and associates - Joint ventures (Details)	12 Months Ended
	Mar. 31, 2021£ / sharesshares	Mar. 31, 2021€ / sharesshares
Disclosure of joint ventures [line items]
Par value per share (GBP/EUR per share) | £ / shares	£ 0.1243129
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%
National Places LLP
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%
Bight Wind Holdings LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	30.00%
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%
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%
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_5

Subsidiary undertakings, joint ventures and associates - Associates (Details)	12 Months Ended
	Mar. 31, 2021
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	9.41%
KHB Venture LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate	33.33%
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%
The Hive IV, LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate	28.20%
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%

Sensitivites - Sensitivities on

Sensitivites - Sensitivities on areas of estimation uncertainty (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
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	£ 170	£ 210
Change in risk variable, impact on net assets	170	210
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	4	6
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	952	877
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	3	4
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	723	670
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	42	39
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	612	545
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	(257)	(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	(190)	(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	£ (183)	(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	£ 17	10
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	730	514
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	3	2
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption	42	47
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	429	456
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	26	31
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 437	£ 507
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%

Sensitivites - Sensitivities _2

Sensitivites - Sensitivities on financial instruments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
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	£ 14	£ 12
Change in risk variable, impact on net assets	£ 14	12
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	£ 6	9
Change in risk variable, impact on net assets	£ 6	9
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	£ 25	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	£ 12	14
Change in risk variable, impact on other equity reserves	£ 98	47
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	£ 6	5
Change in risk variable, impact on other equity reserves	£ 22	27
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	£ 44	49
Change in risk variable, impact on other equity reserves	285	216
Change in risk variable, impact on net assets	£ 1,425	1,319
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	£ 20	26
Decrease in risk variable, impact on earnings	(21)	(27)
Increase in risk variable, impact on net assets	20	26
Decrease in risk variable, impact on net assets	£ (21)	£ (27)

Additional disclosures in res_3

Additional disclosures in respect of guaranteed securities - Narrative (Details) - GBP (£) £ in Millions	Oct. 29, 2007	Mar. 31, 2021
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, 2021	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2019	Apr. 01, 2018	Mar. 31, 2018
Disclosure of information about consolidated structured entities [line items]
Non-current assets	£ 57,278	£ 61,759	£ 55,466		£ 52,523	£ 52,523
Total current assets	9,938	5,801	7,946		6,678	6,681
Total current liabilities	(9,368)	(8,564)	(9,129)		(8,691)	(8,697)
Total non-current liabilities	(37,988)	(39,203)	(34,715)		(31,673)	(31,474)
Net assets	19,860	19,793	19,568	£ 19,568	18,837	19,033
Equity	19,860	19,793	19,568	£ 19,568	£ 18,837	£ 19,033
Revenue	14,779	14,540	14,933
Operating costs	(11,884)	(11,760)	(12,063)
Operating profit/(loss)	2,895	2,780	2,870
Profit/(loss) after tax from continuing operations	1,641	£ 1,274	£ 1,502
Other subsidiaries
Disclosure of information about consolidated structured entities [line items]
Non-current assets	0
Total current assets	20,692
Total current liabilities	(17,589)
Total non-current liabilities	(2,059)
Other income from other subsidiaries	9,978
Investments in subsidiaries	14,415
National Grid plc and Niagara Mohawk Power Corporation combined
Disclosure of information about consolidated structured entities [line items]
Non-current assets	8,940
Total current assets	1,553
Total current liabilities	(1,342)
Total non-current liabilities	(6,363)
Net assets	3,832
Equity	3,832
Revenue	2,462
Operating costs	(4,562)
Operating profit/(loss)	(2,100)
Other income and costs, including taxation	(182)
Profit/(loss) after tax from continuing operations	£ 7,696

Transition to new accounting _3

Transition to new accounting standards - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Apr. 01, 2019	Mar. 31, 2018
Disclosure of initial application of standards or interpretations [line items]
Operating lease commitments			£ 300
Lease liabilities	£ 899	£ 974
Lease liabilities, impact of discounting	214	239
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	630	684
Lease liabilities	685	735	£ 270	£ 744
Revenue	14,165	13,910	14,066
Operating costs	11,884	11,760	12,063
Operating profit from continuing operations	£ 2,895	£ 2,780	2,870
IFRS 16
Disclosure of initial application of standards or interpretations [line items]
Lease liabilities			400
Lease liabilities, impact of discounting			200
Right-of-use assets				468
Lease liabilities				£ 474
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
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
Increase (decrease) in financial liabilities on basis of measurement category, initial application of IFRS 9			32
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)
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)
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)
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
Increase (decrease) due to application of IFRS 15 | Previous GAAP
Disclosure of initial application of standards or interpretations [line items]
Revenue			1,197
Operating costs			1,197
Operating profit from continuing operations			0
US Regulated and UK Gas Transmission | Increase (decrease) due to application of IFRS 15 | Previous GAAP
Disclosure of initial application of standards or interpretations [line items]
Revenue			57
Operating profit from continuing operations			57
UK Regulated | Increase (decrease) due to application of IFRS 15 | Previous GAAP
Disclosure of initial application of standards or interpretations [line items]
Revenue			26
Operating profit from continuing operations			£ 23

Transition to new accounting _4

Transition to new accounting standards - IFRS 16: Impact of transition (Details) - GBP (£) £ in Millions	Mar. 31, 2021		Mar. 31, 2020		Apr. 01, 2019	Mar. 31, 2019		Apr. 01, 2018	Mar. 31, 2018
Property, plant and equipment – Right-of-use assets
Land and buildings					£ 2,941	£ 2,560
Plant and machinery					36,978	36,911
Assets in the course of construction					5,049	5,049
Motor vehicles and office equipment					359	339
Total property, plant and equipment	£ 47,043	[1]	£ 49,762	[1]	45,327	44,859	[1]	£ 40,730	£ 40,730
Borrowings – Lease liabilities
Current	(99)		(112)		(113)	(65)
Non-current	(586)		(623)		(631)	(205)
Total lease liabilities	(685)		(735)		(744)	(270)
Other liabilities
Trade and other payables	(3,517)		(3,602)		(3,766)	(3,769)		(3,394)	(3,453)
Other non-current liabilities	(843)		(891)		(805)	(808)		(750)	(1,317)
Net assets	19,860		19,793		19,568	19,568		18,837	19,033
Equity
Total equity	£ 19,860		£ 19,793		19,568	£ 19,568		£ 18,837	£ 19,033
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
[1]	Comparative amounts have been revised as described in note 1F.

Transition to new accounting _5

Transition to new accounting standards - IFRS 9 and IFRS 15: Impact of transition (Details) - GBP (£) £ in Millions	Mar. 31, 2021		Mar. 31, 2020		Apr. 01, 2019	Mar. 31, 2019		Apr. 01, 2018	Mar. 31, 2018
Non-current assets
Goodwill	£ 4,588	[1]	£ 5,712	[1]		£ 5,372	[1]	£ 4,984	£ 4,984
Other intangible assets	1,443		1,295			1,084		899	899
Property, plant and equipment	47,043	[1]	49,762	[1]	£ 45,327	44,859	[1]	40,730	40,730
Other non-current assets	293		354			264		115	115
Pension assets	1,747		1,849			1,567		1,409	1,409
Financial and other investments	755		543			667		899	899
Investments in joint ventures and associates	867		995			608		2,168	2,168
Derivative financial assets	542		1,249			1,045		1,319	1,319
Total non-current assets	57,278		61,759			55,466		52,523	52,523
Current assets
Inventories and current intangible assets	439		549			370		341	341
Trade and other receivables	2,919		2,986			3,153		2,795	2,798
Current tax assets	67		102			126		114	114
Financial and other investments	2,342		1,998		1,981	1,981		2,694	2,694
Derivative financial assets	457		93			108		405	405
Cash and cash equivalents	157		73		252	252		329	329
Total current assets	9,938		5,801			7,946		6,678	6,681
Total assets	67,216		67,560			63,412		59,201	59,204
Current liabilities
Borrowings	(3,737)		(4,072)			(4,472)		(4,447)	(4,447)
Derivative financial liabilities	(145)		(380)			(350)		(401)	(401)
Trade and other payables	(3,517)		(3,602)		(3,766)	(3,769)		(3,394)	(3,453)
Contract liabilities	(66)		(76)			(61)		(53)	0
Current tax liabilities	(75)		(86)			(161)		(123)	(123)
Provisions	(260)		(348)			(316)		(273)	(273)
Total current liabilities	(9,368)		(8,564)			(9,129)		(8,691)	(8,697)
Non-current liabilities
Borrowings	(27,483)		(26,722)			(24,258)		(22,210)	(22,178)
Derivative financial liabilities	(754)		(954)			(833)		(660)	(660)
Other non-current liabilities	(843)		(891)		(805)	(808)		(750)	(1,317)
Contract liabilities	(1,094)		(1,082)			(933)		(813)	0
Deferred tax liabilities	(4,815)	[1]	(4,446)	[1]		(4,215)	[1]	(3,789)	(3,868)
Pensions and other post-retirement benefit obligations	(1,032)		(2,802)			(1,785)		(1,672)	(1,672)
Provisions	(1,967)		(2,306)			(1,883)		(1,779)	(1,779)
Total non-current liabilities	(37,988)		(39,203)			(34,715)		(31,673)	(31,474)
Total liabilities	(47,356)		(47,767)			(43,844)		(40,364)	(40,171)
Net assets	19,860		19,793		19,568	19,568		18,837	19,033
Equity
Share capital	474		470			458		452	452
Share premium account	1,296		1,301			1,314		1,321	1,321
Retained earnings	23,163	[1]	21,895	[1]		21,999	[1]	21,516	21,784
Other equity reserves	(5,094)	[1]	(3,895)	[1]		(4,223)	[1]	(4,468)	(4,540)
Total shareholders’ equity	19,839		19,771			19,548		18,821	19,017
Non-controlling interests	21		22			20		16	16
Total equity	£ 19,860		£ 19,793		£ 19,568	£ 19,568		18,837	£ 19,033
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)
Deferred tax liabilities								5
Total non-current liabilities								(27)
Total liabilities								(27)
Net assets								(27)
Equity
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
Other non-current liabilities								567
Contract liabilities								(813)
Deferred tax liabilities								74
Total non-current liabilities								(172)
Total liabilities								(166)
Net assets								(169)
Equity
Retained earnings								(169)
Total shareholders’ equity								(169)
Non-controlling interests								0
Total equity								£ (169)
[1]	Comparative amounts have been revised as described in note 1F.

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

Acquisitions - Narrative (Detai

Acquisitions - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended	24 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Mar. 17, 2021	Jul. 11, 2019
PPL Western Power Distribution Investments Limited
Disclosure of detailed information about business combination [line items]
Percentage of share capital acquired			100.00%
Total consideration			£ 7,800
National Grid Renewables
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%
National Grid Renewables And Emerald Energy Venture LLC
Disclosure of detailed information about business combination [line items]
Total consideration				£ 209
Acquisition-related costs recognised	£ 1	£ 3

Acquisitions (Details)

Acquisitions (Details) £ in Millions	Jul. 11, 2019GBP (£)
National Grid Renewables
Disclosure of detailed information about business combination [line items]
Contingent consideration – National Grid Renewables	£ 70
Cash consideration	49
Emerald
Disclosure of detailed information about business combination [line items]
Investment in joint venture – Emerald	90
Cash consideration	90
National Grid Renewables And Emerald Energy Venture LLC
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

Uncategorized Items - nggtf-202

Label	Element	Value
Borrowings, Excluding Bank Overdrafts	nggtf_BorrowingsExcludingBankOverdrafts	£ 26,625,000,000
Borrowings, Excluding Bank Overdrafts	nggtf_BorrowingsExcludingBankOverdrafts	28,730,000,000
Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Equity	ifrs-full_Equity	(196,000,000)
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 cash flow hedges [member]
Other reserves	ifrs-full_OtherReserves	125,000,000
Reserve of gains and losses from investments in equity instruments [member]
Other reserves	ifrs-full_OtherReserves	34,000,000
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
Capital redemption reserve [member]
Other reserves	ifrs-full_OtherReserves	19,000,000
Reserve of exchange differences on translation [member]
Other reserves	ifrs-full_OtherReserves	390,000,000
Merger reserve [member]
Other reserves	ifrs-full_OtherReserves	(5,165,000,000)
IFRS 9 [Member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Other reserves	ifrs-full_OtherReserves	72,000,000
IFRS 9 [Member] | Reserve Of Gains and Losses On Financial Liabilities Measured At Fair Value Through Other Comprehensive Income [Member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Other reserves	ifrs-full_OtherReserves	46,000,000
IFRS 9 [Member] | Reserve Of Cost Of Hedging [Member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Other reserves	ifrs-full_OtherReserves	76,000,000
IFRS 9 [Member] | Reserve of cash flow hedges [member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Other reserves	ifrs-full_OtherReserves	(3,000,000)
IFRS 9 [Member] | Reserve of gains and losses from investments in equity instruments [member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Other reserves	ifrs-full_OtherReserves	34,000,000
IFRS 9 [Member] | Reserve of change in fair value of financial liability attributable to change in credit risk of liability [member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Other reserves	ifrs-full_OtherReserves	7,000,000
IFRS 9 [Member] | Reserve of gains and losses on remeasuring available-for-sale financial assets [member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Other reserves	ifrs-full_OtherReserves	(88,000,000)
Other Equity Reserves [Member]
Equity	ifrs-full_Equity	(4,468,000,000)	[1]
Other Equity Reserves [Member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Equity	ifrs-full_Equity	72,000,000	[1]
Share premium [member]
Equity	ifrs-full_Equity	1,321,000,000
Non-controlling interests [member]
Equity	ifrs-full_Equity	16,000,000
Issued capital [member]
Equity	ifrs-full_Equity	452,000,000
Equity attributable to owners of parent [member]
Equity	ifrs-full_Equity	18,821,000,000
Equity attributable to owners of parent [member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Equity	ifrs-full_Equity	(196,000,000)
Retained earnings [member]
Equity	ifrs-full_Equity	21,516,000,000
Retained earnings [member] | Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Equity	ifrs-full_Equity	£ (268,000,000)
[1]	For further details of other equity reserves, see note 28.