National Grid (NGG) 20-F 23 May 24 2024 FY Annual report (foreign) Financial data

Cover

Cover	12 Months Ended
	Mar. 31, 2024 shares
Entity Information [Line Items]
Document Type	20-F
Document Registration Statement	false
Document Annual Report	true
Document Period End Date	Mar. 31, 2024
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	3,967,138,214
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 Financial Statement Error Correction [Flag]	false
Document Accounting Standard	International Financial Reporting Standards
Entity Shell Company	false
Entity Central Index Key	0001004315
Document Fiscal Year Focus	2024
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
5.602% Notes
Entity Information [Line Items]
Title of 12(b) Security	5.602% Notes due 2028
Trading Symbol	NGG28
Security Exchange Name	NYSE
5.809% Notes
Entity Information [Line Items]
Title of 12(b) Security	5.809% Notes due 2033
Trading Symbol	NGG33
Security Exchange Name	NYSE
5.418% Notes
Entity Information [Line Items]
Title of 12(b) Security	5.418% Notes due 2034
Trading Symbol	NGG34
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	7004 3000
Phone Fax Number Description	011 44 20 7004 3004

Audit information

Audit information	12 Months Ended
	Mar. 31, 2024
Auditor Information [Abstract]
Auditor Name	Deloitte LLP
Auditor Location	London, United Kingdom
Auditor Firm ID	1147

Consolidated income statement

Consolidated income statement - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Profit or loss [abstract]
Revenue	£ 19,850	£ 21,659	£ 18,449
Provision for bad and doubtful debts	(179)	(220)	(167)
Other operating costs	(15,208)	(17,549)	(14,139)
Other operating income	12	989	228
Operating profit	4,475	4,879	4,371
Finance income	248	138	50
Finance costs	(1,712)	(1,598)	(1,072)
Share of post-tax results of joint ventures and associates	37	171	92
Profit before tax	3,048	3,590	3,441
Tax	(831)	(876)	(1,258)
Profit after tax from continuing operations	2,217	2,714	2,183
Profit after tax from discontinued operations	74	5,083	171
Total profit for the year (continuing and discontinued)	2,291	7,797	2,354
Attributable to:
Equity shareholders of the parent	2,290	7,797	2,353
Non-controlling interests from continuing operations	£ 1	£ 0	£ 1
Earnings per share (pence)
Basic earnings per share (continuing) (in GBP pence per share)	£ 0.600	£ 0.742	£ 0.606
Diluted earnings per share (continuing) (in GBP pence per share)	0.597	0.738	0.603
Basic earnings per share (continuing and discontinued) (in GBP pence per share)	0.620	2.131	0.654
Diluted earnings per share (continuing and discontinued) (in GBP pence per share)	£ 0.617	£ 2.121	£ 0.650

Consolidated statement of compr

Consolidated statement of comprehensive income - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Statement of comprehensive income [abstract]
Profit after tax from continuing operations	£ 2,217	£ 2,714	£ 2,183
Profit after tax from discontinued operations	74	5,083	171
Items from continuing operations that will never be reclassified to profit or loss:
Remeasurement (losses)/gains on pension assets and post-retirement benefit obligations	(218)	(1,362)	2,172
Net gains on equity instruments designated at fair value through other comprehensive income	0	0	12
Net (losses)/gains in respect of cash flow hedging of capital expenditure	(37)	10	(1)
Tax on items that will never be reclassified to profit or loss	59	341	(496)
Total items from continuing operations that will never be reclassified to profit or loss	(196)	(1,011)	1,687
Items from continuing operations that may be reclassified subsequently to profit or loss:
Retranslation of net assets offset by net investment hedge	(335)	883	630
Exchange differences reclassified to the consolidated income statement on disposal	0	(170)	0
Net gains/(losses) in respect of cash flow hedges	240	0	(57)
Net gains/(losses) in respect of cost of hedging	26	(16)	1
Net gains/(losses) on investment in debt instruments measured at fair value through other comprehensive income	21	(25)	(11)
Share of other comprehensive income of associates, net of tax	0	1	1
Tax on items that may be reclassified subsequently to profit or loss	(66)	11	15
Total items from continuing operations that may be reclassified subsequently to profit or loss	(114)	684	579
Other comprehensive (loss)/income for the year, net of tax from continuing operations	(310)	(327)	2,266
Other comprehensive income/(loss) for the year, net of tax from discontinued operations	10	(227)	211
Other comprehensive (loss)/income for the year, net of tax	(300)	(554)	2,477
Total comprehensive income for the year from continuing operations	1,907	2,387	4,449
Total comprehensive income for the year from discontinued operations	84	4,856	382
Total comprehensive income/(loss) for the year	1,991	7,243	4,831
Attributable to:
Equity shareholders of the parent from continuing operations	1,906	2,386	4,447
Equity shareholders of the parent from discontinued operations	84	4,856	382
Equity shareholders of the parent	1,990	7,242	4,829
Non-controlling interests	£ 1	£ 1	£ 2

Consolidated statement of chang

Consolidated statement of changes in equity - GBP (£) £ in Millions		Total	Total shareholders’ equity	Share capital	Share premium account	Retained earnings	Other equity reserves	[1]	Non-controlling interests
Equity, beginning balance at Mar. 31, 2021		£ 19,860	£ 19,839	£ 474	£ 1,296	£ 23,163	£ (5,094)		£ 21
Profit for the year		2,354	2,353			2,353			1
Other comprehensive income (loss) for the year		2,477	2,476			1,871	605		1
Total comprehensive income/(loss) for the year		4,831	4,829			4,224	605		2
Equity dividends		(922)	(922)			(922)
Scrip dividend-related share issue	[2]	(1)	(1)	11	(12)
Issue of treasury shares		17	17			17
Transactions in own shares		13	13		16	(3)
Share-based payments		43	43			43
Tax on share-based payments		7	7			7
Transfer of accumulated gains and losses on sale of equity investments	[3]	0	0			82	(82)
Cash flow hedges transferred to the statement of financial position, net of tax		8	8				8
Equity, ending balance at Mar. 31, 2022		23,856	23,833	485	1,300	26,611	(4,563)		23
Profit for the year		7,797	7,797			7,797
Other comprehensive income (loss) for the year		(554)	(555)			(1,253)	698		1
Total comprehensive income/(loss) for the year		7,243	7,242			6,544	698		1
Equity dividends		(1,607)	(1,607)			(1,607)
Scrip dividend-related share issue	[2]	0	0	3	(3)
Issue of treasury shares		16	16			16
Transactions in own shares		1	1		5	(4)
Share-based payments		48	48			48
Cash flow hedges transferred to the statement of financial position, net of tax		5	5				5
Equity, ending balance at Mar. 31, 2023		29,562	29,538	488	1,302	31,608	(3,860)		24
Profit for the year		2,291	2,290			2,290			1
Other comprehensive income (loss) for the year		(300)	(300)			(168)	(132)
Total comprehensive income/(loss) for the year		1,991	1,990			2,122	(132)		1
Equity dividends		(1,718)	(1,718)			(1,718)
Scrip dividend-related share issue	[2]	(1)	(1)	5	(6)
Issue of treasury shares		21	21			21
Transactions in own shares		(4)	(4)		2	(6)
Share-based payments		37	37			37
Tax on share-based payments		2	2			2
Cash flow hedges transferred to the statement of financial position, net of tax		2	2				2
Equity, ending balance at Mar. 31, 2024		£ 29,892	£ 29,867	£ 493	£ 1,298	£ 32,066	£ (3,990)		£ 25
[1] For further details of other equity reserves, see note 28 . Included within the share premium account are costs associated with scrip dividends. In the year ended 31 March 2022, the Group disposed of its equity instruments related to shares held as part of a portfolio of financial instruments which back some long‑term employee l iabilities. The equity instruments were previously measured at fair value through other comprehensive income and prior to the disposal the Group recognised a gain of £12 million . The accumulated gain of £82 million recognised in other comprehensive income was transferred to retained earnings on disposal .

Consolidated statement of cha_2

Consolidated statement of changes in equity (Parenthetical) £ in Millions	12 Months Ended
	Mar. 31, 2022 GBP (£)
Gain on disposal of equity instruments measured at FVOCI	£ 12
Retained earnings
Gain on disposal of equity instruments measured at FVOCI	£ 82

Consolidated statement of finan

Consolidated statement of financial position - GBP (£) £ in Millions		Mar. 31, 2024	Mar. 31, 2023
Non-current assets
Goodwill		£ 9,729	£ 9,847
Other intangible assets		3,431	3,604
Property, plant and equipment		68,907	64,433
Other non-current assets	[1]	848	620
Pension assets		2,407	2,645
Financial and other investments		880	859
Investments in joint ventures and associates		1,420	1,300
Derivative financial assets		324	276
Total non-current assets		87,946	83,584
Current assets
Inventories and current intangible assets		828	876
Trade and other receivables	[1]	3,415	3,830
Current tax assets		11	43
Financial and other investments		3,699	2,605
Derivative financial assets		44	153
Cash and cash equivalents		559	163
Assets held for sale		1,823	1,443
Total current assets		10,379	9,113
Total assets		98,325	92,697
Current liabilities
Borrowings		(4,859)	(2,955)
Derivative financial liabilities		(335)	(222)
Trade and other payables		(4,076)	(5,068)
Contract liabilities		(127)	(252)
Current tax liabilities		(220)	(236)
Provisions		(298)	(288)
Liabilities held for sale		(1,474)	(109)
Total current liabilities		(11,389)	(9,130)
Non-current liabilities
Borrowings		(42,213)	(40,030)
Derivative financial liabilities		(909)	(1,071)
Other non-current liabilities		(880)	(921)
Contract liabilities		(2,119)	(1,754)
Deferred tax liabilities		(7,519)	(7,181)
Pensions and other post-retirement benefit obligations		(593)	(694)
Provisions		(2,811)	(2,354)
Total non-current liabilities		(57,044)	(54,005)
Total liabilities		(68,433)	(63,135)
Total assets (liabilities)		29,892	29,562
Equity
Share capital		493	488
Share premium account		1,298	1,302
Retained earnings		32,066	31,608
Other equity reserves		(3,990)	(3,860)
Total shareholders’ equity		29,867	29,538
Non-controlling interests		25	24
Total equity		£ 29,892	£ 29,562
[1] In the year, we have revised our policy in relation to the classification of capital expenditure prepayments between current and non-current in order to align these to the operating cycles of the underlying assets to which they relate. Accordingly, comparative amounts have been re-presented to reflect this change (see notes 14 and 19) .

Consolidated cash flow statemen

Consolidated cash flow statement - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Cash flows from operating activities
Total operating profit from continuing operations		£ 4,475	£ 4,879	£ 4,371
Adjustments for:
Gain on sale of investments		0	(846)	(228)
Other fair value movements		(16)	21	(65)
Depreciation, amortisation and impairment		2,061	1,984	1,830
Share-based payments		37	48	38
Changes in working capital		(147)	547	(223)
Changes in provisions		840	(155)	149
Changes in pensions and other post-retirement benefit obligations		31	(46)	(84)
Cash generated from operations – continuing operations		7,281	6,432	5,788
Tax paid		(342)	(89)	(298)
Net cash inflow from operating activities – continuing operations		6,939	6,343	5,490
Net cash inflow from operating activities – discontinued operations		0	555	782
Cash flows from investing activities
Purchases of intangible assets		(549)	(567)	(446)
Purchases of property, plant and equipment		(6,904)	(6,325)	(5,098)
Disposals of property, plant and equipment		52	87	26
Investments in joint ventures and associates		(332)	(443)	(265)
Dividends received from joint ventures, associates and other investments		176	190	166
Disposal of financial and other investments		102	116	215
Acquisition of financial investments		(81)	(95)	(197)
Net movements in short-term financial investments		(1,141)	586	(781)
Interest received		148	65	40
Cash inflows on derivatives		123	0	17
Cash outflows on derivatives		0	(362)	(122)
Insurance claim from loss of property, plant and equipment		143	79	0
Net cash flow (used in)/from investing activities – continuing operations		(7,601)	804	(13,885)
Net cash flow from/(used in) investing activities – discontinued operations		102	(564)	(125)
Cash flows from financing activities
Proceeds from issue of treasury shares		20	16	33
Transactions in own shares		(4)	1	(3)
Proceeds received from loans		5,563	11,908	12,347
Repayment of loans		(1,701)	(15,260)	(1,261)
Payments of lease liabilities		(118)	(155)	(117)
Net movements in short-term borrowings		544	(511)	(11)
Cash inflows on derivatives		86	190	20
Cash outflows on derivatives		(58)	(118)	(114)
Interest paid		(1,627)	(1,430)	(1,053)
Dividends paid to shareholders		(1,718)	(1,607)	(922)
Net cash flow from/(used in) financing activities – continuing operations		987	(6,966)	8,919
Net cash flow used in financing activities – discontinued operations		0	(207)	(1,150)
Net increase/(decrease) in cash and cash equivalents		427	(35)	31
Supplemental Cash Flow Information Abstract [Abstract]
Reclassification to held for sale		(30)	9	(11)
Exchange movements		(1)	7	5
Cash and cash equivalents at start of year		163	182	157
Cash and cash equivalents at end of year		559	163	182
Millennium Pipeline Company, LLC
Cash flows from investing activities
Disposal of interests in the UK Gas Transmission business, in The Narragansett Electric Company, in Millennium Pipeline Company LLC and in St William Homes LLP		0	497	0
National Grid Electricity Distribution
Cash flows from investing activities
Acquisition of National Grid Electricity Distribution and Contributions to National Grid Renewables and Emerald Energy Venture LLC	[1]	0	0	(7,837)
UK Gas Transmission business
Cash flows from investing activities
Disposal of interests in the UK Gas Transmission business, in The Narragansett Electric Company, in Millennium Pipeline Company LLC and in St William Homes LLP	[2]	681	4,027	0
The Narragansett Electric Company
Cash flows from investing activities
Disposal of interests in the UK Gas Transmission business, in The Narragansett Electric Company, in Millennium Pipeline Company LLC and in St William Homes LLP	[2]	0	2,968	0
St William Homes LLP
Cash flows from investing activities
Disposal of interests in the UK Gas Transmission business, in The Narragansett Electric Company, in Millennium Pipeline Company LLC and in St William Homes LLP		0	0	413
National Grid Renewables and Emerald Energy Venture LLC
Cash flows from investing activities
Acquisition of National Grid Electricity Distribution and Contributions to National Grid Renewables and Emerald Energy Venture LLC		£ (19)	£ (19)	£ (16)
[1] Balance consists of cash consideration paid and cash acquired from National Grid Electricity Distribution (NGED). The balance for the year ended 31 March 2023 consists of cash proceeds received, net of cash disposed .

Basis of preparation and recent

Basis of preparation and recent accounting developments	12 Months Ended
	Mar. 31, 2024
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 in Great Britain and of electricity and gas in 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 22 May 2024 . 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. They are prepared on the basis of all IFRS accounting standards and interpretations that are mandatory for the period ended 31 March 2024 and in accordance with the Companies Act 2006. 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 assessed the principal risks alongside potential downside business cash flow scenarios impacting the Group’s operations. The Directors specifically considered both a base case and reasonable worst-case scenario for business cash flows. As part of the assessment the Directors have included the expected receipt of the fully underwritten Rights Issue. The assessment is prepared on the conservative assumption that the Group has no access to the debt capital markets. The main cash flow impacts identified in the reasonable worst-case scenario are: • the timing of the sale of assets classified as held for sale (see note 10 ); • adverse impacts of inflation and incremental spend on our capital expenditure programme; • adverse impact from timing across the Group (i.e. a net under- recovery of allowed revenues or reductions in over-collections) and slower collections of outstanding receivables; • higher operating and financing costs than expected, including non‑delivery of planned efficiencies across the Group; and • the potential impact of further significant storms in the US. 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 expenditure programme, with elements of non-essential works and programmes delayed; and • a number of further reductions in operating expenditure across the Group. Having considered the reasonable worst-case scenario 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 and extend existing financing was separately included in the analysis, and the Directors noted £5.6 billion of new long-term senior debt issued in the period from 1 April 2023 to 31 March 2024 as evidence of the Group’s ability to continue to have access to the debt capital markets if needed. 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 ability 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 date 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 UK Electricity System Operator (ESO) As described further in note 10 , at the end of October 2023, the legislation required to enable the separation of the ESO and the formation of the National Energy System Operator (NESO) was passed through Parliament. The NESO is expected to be established as an independent Public Corporation this calendar year, with responsibilities across both the electricity and gas systems. As a result, the Group took the judgement to classify the associated assets and liabilities of the ESO as held for sale in the consolidated statement of financial position at the end of October 2023. The ESO has not met the criteria for classification as a discontinued operation and therefore its results have not been separately disclosed on the face of the income statement, and are instead included within the results from continuing operations. E. Disposal of the UK Gas Transmission business Following the Group’s disposal of a 60% controlling stake in the UK Gas Transmission business in the year ended 31 March 2023, the Group completed the sale of a further 20% of its retained interest in the business (held through GasT TopCo Limited) on 11 March 2024. The other 80% of GasT TopCo Limited is owned by Macquarie Infrastructure and Real Assets (MIRA) and British Columbia Investment Management Corporation (BCI) (together, the Consortium). The Group’s remaining 20% interest in GasT TopCo Limited is classified as an investment in an associate on the basis that the Group has a significant influence over the business. The remaining 20% interest is subject to an option agreement with the Consortium, the Remaining Acquisition Agreement (RAA), which on 9 July 2023 replaced the previous Further Acquisition Agreement (FAA) under which the 20% disposal in the year was executed. The RAA option is exercisable, at the Consortium’s option, between 1 May 2024 and 31 July 2024. If the RAA option is partially exercised by the Consortium, the Group will have the right to put the remainder of its interests in GasT TopCo Limited to the Consortium, which can be exercised by the Group between 1 December 2024 and 31 December 2024. Taking into consideration the timing of the RAA exercise window, the Group has continued to classify its remaining interest in GasT TopCo Limited as held for sale and has not equity accounted for its share of the associate’s results. The loss on the 20% disposal of GasT TopCo Limited and the remeasurements in relation to the FAA option and the RAA option have been recorded within discontinued operations. As an associate held for sale, the Group has not recognised any share of results in the year ended 31 March 2024. The classification impacts on the consolidated income statement, the consolidated statement of comprehensive income and the consolidated cash flow statement, as well as earnings per share (EPS) split between continuing and discontinued operations. 1. Basis of preparation and recent accounting developments continued F. 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: • the judgement that it is appropriate to classify our 20% equity investment in GasT TopCo Limited, together with the RAA option, as held for sale, as detailed in note 10 ; and • the judgement that, notwithstanding legislation enacted and targets committing the states of New York and Massachusetts to achieving net zero greenhouse gas emissions by 2050, these do not shorten the remaining useful economic lives (UELs) of our US gas network assets, which we consider will have an expected use and utility beyond 2050 (see key sources of estimation uncertainty below and note 13 ) . 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: • the cash flows and real discount rates applied in determining the US environmental provisions, in particular relating to three Superfund sites and certain other legacy Manufacturing Gas Plant (MGP) sites (see note 26 ); • the estimates made regarding the UELs of our gas network assets due to uncertainty over the pace of delivery of the energy transition and the multiple pathways by which it could be delivered. Our estimates consider anticipated changes in customer behaviour and developments in new technology, the potential to decarbonise fuel through the use of renewable natural gas and green hydrogen, and the feasibility and affordability of increased electrification (see note 13 for details and sensitivity analysis ); and • the valuation of liabilities for pensions and other post-retirement benefits (see note 25 ). 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 analysis in note 35 . G. Impact of climate change and the transition to net zero – areas of judgement and key sources of estimation uncertainty In preparing these financial statements for the year ended 31 March 2024 , management has taken into account the Group’s commitments regarding its transition to net zero and the impact of climate change. The Group has a published climate transition plan which sets out its targets to achieve this commitment by 2050, in line with the Paris Agreement. Management has also identified a number of significant climate-related risks and opportunities. Changes to the Group’s commitments and the impact of climate change may have a material impact on the currently reported amounts of the Group’s assets and liabilities and on similar assets and liabilities that may be recognised in future reporting periods, as set out above with respect to the judgement and key source of estimation uncertainty regarding the UELs of our US gas network assets, and as further detailed below. Repairs to property, plant and equipment and climate adaptation activities The Group’s network assets recorded within property, plant and equipment (PP&E) are at risk of physical impacts from extreme weather events such as major storms which may be accentuated by increased frequency of weather incidents and changing long-term climate trends, thereby leading to asset damage. M ajor storm costs, net of deductibles and disallowances, incurred by the Group are recoverable as revenue in future periods under our rate plans but the associated repair costs are expensed as incurred as other operating costs under IFRS. Impairment of property, plant and equipment and goodwill Included within the Group’s plant and machinery (see note 13 ) are £325 million of oil- and gas-fired electricity generation units with approximately 3,800 MW of electric generation capacity located in Long Island, New York. Whilst the Group retains ownership of these assets, it sells all of the capacity, energy in response to dispatch requests, and any related ancillary services provided by the generating facilities to the Long Island Power Authority (LIPA) via a Power Supply Agreement running until 2028. The maximum UEL for these units ends in 2040, which aligns to the target set by the state of New York to achieve decarbonised power generation by 2040. However, there is a risk that the UEL of certain, or all, of the units may be shortened, depending on the progress of decarbonisation activities in Long Island. The Group believes there are no material accounting judgements in respect of the generation assets and the UELs have not been accelerated in the year. The assets related to the Group’s liquefied natural gas (LNG) storage facility at the Isle of Grain in the UK have a maximum UEL to 2045, which is in line with the current commercial contracts. The UELs of our assets related to our commercial operations in LNG at Providence, Rhode Island are informed by the recovery periods used for ratemaking purposes and the majority of the UELs are covered by fixed price service contracts. The net book value of these assets will be immaterial by 2050. Accordingly, the Group believes there are no material accounting judgements in respect of the UELs of the LNG assets as of 31 March 2024 . 1. Basis of preparation and recent accounting developments continued G. Impact of climate change and the transition to net zero – areas of judgement and key sources of estimation uncertainty continued The net zero pathway may also impact our US gas networks which in turn may affect the recoverable amount of our New York and New England cash-generating units (CGUs). In assessing the recoverability of our CGUs (see note 11 ), we calculate the value-in-use based on projections that incorporate our best estimates of future cash flows and assumptions pertaining to the net zero plans of the jurisdictions that we operate in. In respect of our New York and New England CGUs, our forecast cash flow duration used in our impairment testing is five years . We apply a terminal growth rate informed by expected long-term economic inflation and the discount rate used takes into consideration the potential impact of net zero plans on our gas business. Accordingly, the impact of certain variables that will play out in the medium to long term as a result of the anticipated transition to decarbonised power generation are not anticipated to have an impact on the recoverable amount of our New York and New England CGUs. Decommissioning provisions 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. Included within the Group’s decommissioning provisions as at 31 March 2024 (see note 26 ) is £57 million relating to legal requirements to remove asbestos upon major renovation or demolition of our oil- and gas-fired electricity generation structures and facilities located in Long Island, New York. As noted above, the progress of decarbonisation activities in Long Island may bring forward the decommissioning of these assets, thereby increasing the present value of associated decommissioning provisions. In the current year, there have been no material changes to the expected timing of decommissioning expenditures. Currently, the expected timing of decommissioning expenditures has not materially been brought forward but management will continue to review the facts and circumstances. Sensitivity to commodity contract derivatives The Group has contracts associated with the forward purchase of gas and enters into derivative financial instruments linked to commodity prices, including gas options and swaps which are used to manage market price volatility (see note 17 (b)). As at 31 March 2024 , the Group’s gas commodity contract derivatives are primarily short-term and accordingly we do not anticipate a risk as a result of the transition to net zero. H. 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)). I. New IFRS accounting standards and interpretations effective for the year ended 31 March 2024 The Group adopted the following new standards and amendments to standards which have had no material impact on the Group’s results or financial statement disclosures: • IFRS 17 ‘Insurance Contracts’; • amendments to IAS 1 and IFRS Practice Statement 2 – ‘Making Materiality Judgements’; • amendments to IAS 12 ‘International Tax Reform — Pillar Two Model Rules’; and • amendments to IAS 8 ‘Accounting Policies, Changes in Accounting Estimates and Errors’. In May 2021, the IASB issued amendments to IAS 12 ‘Income Taxes’ in order to narrow the scope of the initial recognition exemption to exclude transactions that give rise to equal and offsetting temporary differences. Following the amendments, the Group recognised separate deferred tax assets in relation to its lease liabilities and decommissioning obligations, and deferred tax liabilities in relation to its right-of-use assets (see note 7 ). As the balances qualify for offset, there is no impact on the consolidated statement of financial position and the opening retained earnings as at 1 April 2023. J. 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: • amendments to IFRS 10 and IAS 28 ‘Sale or Contribution of Assets between an Investor and its Associate or Joint Venture’; • amendments to IAS 1 ‘Classification of Liabilities as Current or Non‑current’; • amendments to IAS 1 ‘Non-current Liabilities with Covenants’; • amendments to IAS 7 and IFRS 7 ‘Supplier Finance Arrangements’; • amendments to IFRS 16 ‘Lease Liability in a Sale and Leaseback’; and • amendments to IAS 21 ‘The Effects of Changes in Foreign Exchange Rates’. 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, 2024
Disclosure of 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 a profit measure that excludes certain income and expenses. We call that measure ‘adjusted profit’. Adjusted profit excludes exceptional items and remeasurements (as defined in note 5 ) and 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. As a matter of course, the Board also considers profitability by segment, excluding the effects of timing, major storm costs and deferred tax in our UK Electricity Transmission and UK Electricity Distribution businesses. 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 six principal businesses are reported to the Board of Directors and are accordingly treated as reportable operating segments. All other operating segments are reported to the Board of Directors on an aggregated basis. 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. This includes our Accelerated Strategic Transmission Investment projects to connect more clean, low-carbon power to the transmission network in England and Wales. UK Electricity Distribution The electricity distribution networks of NGED in the East Midlands, West Midlands and South West of England and South Wales. UK Electricity System Operator The Great Britain system operator. The ESO met the criteria to be classified as held for sale at the end of October 2023 (see note 10). New England Gas distribution networks, electricity distribution networks and high-voltage electricity transmission networks in New England. New York Gas distribution networks, electricity distribution networks and high-voltage electricity transmission networks in New York. National Grid Ventures Comprises all commercial operations in LNG at the Isle of Grain in the UK and Providence, Rhode Island in the US, our electricity generation business in the US, our electricity interconnectors in the UK and our investment in National Grid Renewables Development LLC, our renewables business in the US. Whilst NGV operates outside our regulated core business, the electricity interconnectors in the UK are subject to indirect regulation by Ofgem regarding the level of returns they can earn. Our US LNG operations were reclassified from the New England segment following an internal reorganisation in the year. Other activities that do not form part of any of the segments in the above table 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. (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. 2024 2023 2022 Total sales £m Sales between segments £m Sales to third parties £m Total sales £m Sales between segments £m Sales to third parties £m Total sales £m Sales between segments £m Sales to third parties £m Operating segments – continuing operations: UK Electricity Transmission 2,735 (40) 2,695 1,987 (41) 1,946 2,035 (7) 2,028 UK Electricity Distribution 1,795 (5) 1,790 2,045 (12) 2,033 1,482 (14) 1,468 UK Electricity System Operator 3,788 (35) 3,753 4,690 (31) 4,659 3,455 (18) 3,437 New England 3,948 — 3,948 4,427 — 4,427 4,550 — 4,550 New York 6,094 — 6,094 6,994 — 6,994 5,561 — 5,561 National Grid Ventures 1,389 (57) 1,332 1,341 (58) 1,283 1,024 — 1,024 Other 244 (6) 238 317 — 317 381 — 381 Total revenue from continuing operations 19,993 (143) 19,850 21,801 (142) 21,659 18,488 (39) 18,449 Split by geographical areas – continuing operations: UK 9,063 9,611 7,803 US 10,787 12,048 10,646 Total revenue from continuing operations 19,850 21,659 18,449 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 and remeasurements Exceptional items and remeasurements (see note 5) After exceptional items and remeasurements 2024 2023 2022 2024 2023 2022 2024 2023 2022 £m £m £m £m £m £m £m £m £m Operating segments – continuing operations: UK Electricity Transmission 1,677 995 1,067 (3) (2) (12) 1,674 993 1,055 UK Electricity Distribution 993 1,091 909 (18) (22) — 975 1,069 909 UK Electricity System Operator 880 238 7 (498) (1) (2) 382 237 5 New England 643 708 743 (2) 424 21 641 1,132 764 New York 860 741 780 (498) (200) 315 362 541 1,095 National Grid Ventures 469 490 286 89 467 (3) 558 957 283 Other (60) 31 21 (57) (81) 239 (117) (50) 260 Total operating profit from continuing operations 5,462 4,294 3,813 (987) 585 558 4,475 4,879 4,371 Split by geographical area – continuing operations: UK 3,923 2,825 2,234 (487) 26 224 3,436 2,851 2,458 US 1,539 1,469 1,579 (500) 559 334 1,039 2,028 1,913 Total operating profit from continuing operations 5,462 4,294 3,813 (987) 585 558 4,475 4,879 4,371 Before exceptional items and remeasurements Exceptional items and remeasurements (see note 5) After exceptional items and remeasurements 2024 2023 2022 2024 2023 2022 2024 2023 2022 £m £m £m £m £m £m £m £m £m Reconciliation to profit before tax: Operating profit from continuing operations 5,462 4,294 3,813 (987) 585 558 4,475 4,879 4,371 Share of post-tax results of joint ventures and associates 101 190 148 (64) (19) (56) 37 171 92 Finance income 244 166 65 4 (28) (15) 248 138 50 Finance costs (1,723) (1,680) (1,146) 11 82 74 (1,712) (1,598) (1,072) Profit before tax from continuing operations 4,084 2,970 2,880 (1,036) 620 561 3,048 3,590 3,441 The following items are included in the total operating profit by segment: Depreciation, amortisation and impairment 2024 2023 2022 £m £m £m Operating segments: UK Electricity Transmission (521) (484) (508) UK Electricity Distribution (223) (223) (158) UK Electricity System Operator (61) (101) (83) New England (420) (393) (364) New York (658) (620) (537) National Grid Ventures (166) (149) (156) Other (12) (14) (24) Total (2,061) (1,984) (1,830) Asset type: Property, plant and equipment (1,769) (1,700) (1,544) Non-current intangible assets (292) (284) (286) Total (2,061) (1,984) (1,830) 2. Segmental analysis continued (c) Capital investment Capital investment represents additions to property, plant and equipment, prepayments to suppliers to secure production capacity in relation to our capital projects, non-current intangibles and additional equity investments in joint ventures and associates. Segmental information used for internal decision making was revised in the year to include the capital expenditure prepayments and additional equity investments in joint ventures and associates. Accordingly, comparative information for the year s ended 31 March 2023 and 2022 has been re-presented to reflect the change in the Group’s segmental measure in the year. 2024 2023 1 2022 1 £m £m £m Operating segments: UK Electricity Transmission 1,912 1,301 1,179 UK Electricity Distribution 1,247 1,220 899 UK Electricity System Operator 85 108 108 New England 1,673 1,527 1,478 New York 2,654 2,454 1,960 National Grid Ventures 662 970 989 Other 2 13 10 Total 8,235 7,593 6,623 Asset type: Property, plant and equipment 7,124 6,783 5,622 Non-current intangible assets 481 578 471 Equity investments in joint ventures and associates 2 332 197 461 Capital expenditure prepayments 298 35 69 Total 8,235 7,593 6,623 1. Comparative amounts have been represented to reflect the reclassification of our US LNG operations from New England to NGV following an internal reorganisation in the year and the change in presentation for capital investments. 2. Excludes £nil ( 2023 : £nil , 2022 : £25 million ) equity contribution to the St William Homes LLP joint venture. This was excluded based on the nature of the joint venture arrangement. We typically contributed property assets to the joint venture in exchange for cash and accordingly did not consider these transactions to be in the nature of capital investment. (d) Geographical analysis of non-current assets Non-current assets by geography comprise goodwill, other intangible assets, property, plant and equipment, investments in joint ventures and associates and other non-current assets. 2024 2023 2022 £m £m £m Split by geographical area: UK 40,065 38,043 35,466 US 44,270 41,761 36,411 84,335 79,804 71,877 Reconciliation to total non-current assets: Pension assets 2,407 2,645 3,885 Financial and other investments 880 859 830 Derivative financial assets 324 276 305 Non-current assets 87,946 83,584 76,897

Revenue

Revenue	12 Months Ended
	Mar. 31, 2024
Disclosure of disaggregation 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) fall within the scope of IFRS 15 ‘Revenue from Contracts with Customers’, whereas generation services (which solely relate to the contract with LIPA in the US) are accounted for under IFRS 16 ‘Leases’ as rental income, also presented within revenue. Revenue is recognised to reflect the transfer of goods or services to customers at an amount that reflects the consideration to which the Group expects to be entitled to in exchange for those goods or services 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. Revenue in respect of regulated activities is determined by regulatory agreements that set the price to be charged for services in a given period based on pre-determined allowed revenues. Variances in service usage can result in actual revenue collected exceeding (over-recoveries) or falling short (under-recoveries) of allowed revenues. Where regulatory agreements allow the recovery of under-recoveries or require the return of over-recoveries, the allowed revenue for future periods is typically adjusted. In these instances, no assets or liabilities are recognised for under- or over-recoveries respectively, because the adjustment relates to future customers and services that have not yet been delivered. Revenue in respect of non-regulated activities primarily relates to the sale of capacity on our interconnectors, which is determined at auctions. Capacity is sold in either day, month, quarter or year-ahead tranches. The price charged is determined by market fundamentals rather than regulatory agreement. The interconnectors are subject to indirect regulation with regard to the levels of returns they are allowed to earn. Where amounts fall below this range they receive top-up revenues and where amounts exceed this range they must pass back the excess. In these instances, assets or liabilities are recognised for the top-up or pass-back respectively. 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 in England and Wales. 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 transmission of electricity encompasses the following principal services: • the supply of high-voltage electricity – revenue is recognised based on usage. 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. Price is determined prior to our financial year end with reference to the regulated allowed returns and estimated annual volumes; and • construction work (principally for connections) – revenue is recognised over time, as we provide access to our network. Customers can either pay over the useful life of the connection or upfront. 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), revenues are recognised as the construction work is completed. (b) UK Electricity Distribution The UK Electricity Distribution segment principally generates revenue by providing electricity distribution services in the Midlands and South West of England and South Wales. Similar to UK Electricity Transmission, UK Electricity Distribution operates as a monopoly in the jurisdictions that it operates in and is regulated by Ofgem. The distribution of electricity encompasses the following principal services: • electricity distribution – revenue is recognised based on usage by customers (over time), based upon volumes and price. The price control mechanism that determines our annual allowances is similar to UK Electricity Transmission. Revenues are billed monthly and payment terms are typically within 14 days; and • construction work (principally for connections) – revenue is recognised over time as we provide access to our network. 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, revenues are recognised as the construction work is completed. (c) UK Electricity System Operator The UK Electricity System Operator earns revenue for balancing supply and demand of electricity on Great Britain’s electricity transmission system, where it acts as principal. Balancing services are regulated by Ofgem and revenue, which is payable by generators and suppliers of electricity, is recognised as the service is provided. The UK Electricity 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 (electricity suppliers) who connect to or use the transmission system. As the UK Electricity System Operator acts as an agent in this capacity, it records transmission network revenues net of payments to transmission operators. 3. Revenue continued (d) New England The New England segment principally generates revenue by providing electricity and gas supply and distribution services and high-voltage electricity transmission services in New England. Supply and distribution services are regulated by the Massachusetts Department of Public Utilities (MADPU) and transmission services are regulated by the Federal Energy Regulatory Commission (FERC), both of whom regulate the rates that can be charged to customers. The supply and distribution of electricity and gas and the provision of electricity transmission facilities encompasses the following principal services: • electricity and gas supply and distribution and electricity transmission – revenue is recognised based on usage by customers (over time). Revenues are billed monthly and payment terms are 30 days; and • construction work (principally for connections) – revenue is recognised over time as we provide access to our network. Where the customer pays upfront, revenues are deferred as a contract liability or customer contributions (where they relate to government entities) and released over the life of the connection. (e) New York The New York segment principally generates revenue by providing electricity and gas supply and distribution services and high-voltage electricity transmission services in New York. Supply and distribution services are regulated by the New York Public Service Commission (NYPSC) and transmission services are regulated by the FERC, both of which regulate the rates that can be charged to customers. The supply and distribution of electricity and gas and the provision of electricity transmission facilities encompasses the following principal services: • electricity and gas supply and distribution and electricity transmission – revenue is recognised based on usage by customers (over time). Revenues are billed monthly and payment terms are 30 days; and • construction work (principally for connections) – revenue is recognised over time as we provide access to our network. Where the customer pays upfront, revenues are deferred as a contract liability or customer contributions (where they relate to government entities) and released over the life of the connection. (f) National Grid Ventures National Grid Ventures generates revenue from electricity interconnectors, LNG at the Isle of Grain in the UK and Providence, Rhode Island in the US, National Grid Renewables and rental income. The Group recognises revenue from transmission services through interconnectors and LNG importation at the Isle of Grain and Providence by means of customers’ use of capacity and volumes. Revenue is recognised over time and is billed monthly. Payment terms are up to 60 days. Electricity generation revenue is earned from the provision of energy services and supply capacity to produce energy for the use of customers of LIPA through a power supply agreement, where LIPA receives all of the energy and capacity from the asset until at least 2028. 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 revenue, 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. Other revenue in the scope of IFRS 15 principally includes sales of renewables projects from National Grid Renewables to Emerald Energy Venture LLC (Emerald), which is jointly controlled by National Grid and Washington State Investment Board (WSIB) (see note 16) . National Grid Renewables develops wind and solar generation assets in the US, whilst Emerald has a right of first refusal to buy, build and operate those assets. Revenue is recognised as it is earned. Other revenue, recognised in accordance with standards other than IFRS 15, primarily comprises adjustments in respect of the interconnector cap and floor and Use of Revenue regimes constructed by Ofgem for certain wholly owned interconnector subsidiaries. Under the cap and floor regime, where an interconnector expects to exceed its total five-year cap, a provision and reduction in revenue is recognised in the current reporting period (see note 26 ) . Where an interconnector does not expect to reach its five-year floor, either an asset will be recognised where a future inflow of economic benefits is considered virtually certain, or a contingent asset will be disclosed where the future inflow is concluded to be probable. Under the Use of Revenue framework, any revenues in excess of an agreed incentive level must be passed on as savings to consumers. Where the obligation to transfer excess revenues arises, a payable and reduction in revenue is recognised in the current reporting period. (g) Other Revenue in Other relates to our UK commercial property business and insurance. Revenue is predominantly recognised in accordance with standards other than IFRS 15 and comprises property sales by our UK commercial property business (including sales to the St William joint venture, which was disposed of in the year ended 31 March 2022). Property sales are recorded when the sale is legally completed. 3. Revenue continued (h) Disaggregation of revenue In the following tables, revenue is disaggregated by primary geographical market and major service lines. The table below reconciles disaggregated revenue with the Group’s reportable segments (see note 2 ). Revenue for the year ended 31 March 2024 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 Transmission 1 2,591 — (10) 73 493 869 — 4,016 Distribution — 1,712 — 3,786 5,500 — — 10,998 System Operator — — 3,763 — — — — 3,763 Other 2 25 73 — 8 15 168 4 293 Total IFRS 15 revenue 2,616 1,785 3,753 3,867 6,008 1,037 4 19,070 Other revenue Generation — — — — — 360 — 360 Other 3 79 5 — 81 86 (65) 234 420 Total other revenue 79 5 — 81 86 295 234 780 Total revenue from continuing operations 2,695 1,790 3,753 3,948 6,094 1,332 238 19,850 1. The UK Electricity System Operator transmission revenue in the year represents transmission revenues collected, net of payments made to transmission owners. 2. The UK Electricity Transmission and UK Electricity Distribution other IFRS 15 revenue principally relates to engineering recharges, which are the recovery of costs incurred for construction work requested by customers, such as the rerouting of existing network assets. Within NGV, the other IFRS 15 revenue principally relates to revenue generated from our National Grid Renewables business. 3. Other revenue, recognised in accordance with accounting standards other than IFRS 15, includes property sales by our UK commercial property business, rental income, income arising in connection with the Transition Services Agreements following the sales of NECO and the UK Gas Transmission business in the prior year, and an adjustment to NGV revenue in respect of the interconnector cap and floor and Use of Revenue regimes constructed by Ofgem. Geographical split for the year ended 31 March 2024 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 UK 2,616 1,785 3,753 — — 878 1 9,033 US — — — 3,867 6,008 159 3 10,037 Total IFRS 15 revenue 2,616 1,785 3,753 3,867 6,008 1,037 4 19,070 Other revenue UK 79 5 — — — (76) 22 30 US — — — 81 86 371 212 750 Total other revenue 79 5 — 81 86 295 234 780 Total revenue from continuing operations 2,695 1,790 3,753 3,948 6,094 1,332 238 19,850 Revenue for the year ended 31 March 2023 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 Transmission 1,868 — 126 52 567 791 — 3,404 Distribution — 1,951 — 4,314 6,373 — — 12,638 System Operator — — 4,533 — — — — 4,533 Other 1 31 77 — 8 13 131 — 260 Total IFRS 15 revenue 1,899 2,028 4,659 4,374 6,953 922 — 20,835 Other revenue Generation — — — — — 394 — 394 Other 2 47 5 — 53 41 (33) 317 430 Total other revenue 47 5 — 53 41 361 317 824 Total revenue from continuing operations 1,946 2,033 4,659 4,427 6,994 1,283 317 21,659 1. The UK Electricity Transmission and UK Electricity Distribution other IFRS 15 revenue principally relates to engineering recharges, which are the recovery of costs incurred for construction work requested by customers, such as the rerouting of existing network assets. Within NGV, the other IFRS 15 revenue principally relates to revenue generated from our National Grid Renewables business. 2. Other revenue, recognised in accordance with accounting standards other than IFRS 15, includes property sales by our UK commercial property business, rental income, income arising in connection with the Transition Services Agreements following the sales of NECO and the UK Gas Transmission business, and a provision and adjustment to NGV revenue in respect of the interconnector cap and floor regime constructed by Ofgem. In the year ended 31 March 2023, the Group also recognised other income relating to an insurance claim. 3. Revenue continued (h) Disaggregation of revenue continued Geographical split for the year ended 31 March 2023 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 UK 1,899 2,028 4,659 — — 799 — 9,385 US — — — 4,374 6,953 123 — 11,450 Total IFRS 15 revenue 1,899 2,028 4,659 4,374 6,953 922 — 20,835 Other revenue UK 47 5 — — — (31) 205 226 US — — — 53 41 392 112 598 Total other revenue 47 5 — 53 41 361 317 824 Total revenue from continuing operations 1,946 2,033 4,659 4,427 6,994 1,283 317 21,659 Revenue for the year ended 31 March 2022 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 Transmission 1,983 — — 52 405 627 — 3,067 Distribution — 1,375 — 4,434 5,110 — — 10,919 System Operator — — 3,418 — — — — 3,418 Other¹ 35 89 19 10 10 147 — 310 Total IFRS 15 revenue 2,018 1,464 3,437 4,496 5,525 774 — 17,714 Other revenue Generation — — — — — 373 — 373 Other 2 10 4 — 54 36 (123) 381 362 Total other revenue 10 4 — 54 36 250 381 735 Total revenue from continuing operations 2,028 1,468 3,437 4,550 5,561 1,024 381 18,449 1. The UK Electricity Transmission and UK Electricity Distribution other IFRS 15 revenue principally relates to engineering recharges, which are the recovery of costs incurred for construction work requested by customers, such as the rerouting of existing network assets. UK Electricity System Operator other IFRS 15 revenue reflects the net income from its role as agent in respect of transmission network revenues. Within NGV, the other IFRS 15 revenue principally relates to revenue generated from our National Grid Renewables business. 2. Other revenue, recognised in accordance with accounting standards other than IFRS 15, includes property sales by our UK commercial property business and rental income. Included within NGV is a provision and adjustment to NGV revenue in respect of the interconnector cap and floor regime constructed by Ofgem. Geographical split for the year ended 31 March 2022 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 UK 2,018 1,464 3,437 — — 646 — 7,565 US — — — 4,496 5,525 128 — 10,149 Total IFRS 15 revenue 2,018 1,464 3,437 4,496 5,525 774 — 17,714 Other revenue UK 10 4 — — — (132) 356 238 US — — — 54 36 382 25 497 Total other revenue 10 4 — 54 36 250 381 735 Total revenue from continuing operations 2,028 1,468 3,437 4,550 5,561 1,024 381 18,449 Contract liabilities (see note 23 ) represent revenue to be recognised in future periods relating to contributions in aid of construction of £2,246 million ( 2023 : £2,006 million ; 2022 : £1,472 million ). Revenue is recognised over the life of the asset. The asset lives for connections in UK Electricity Transmission, UK Electricity Distribution, New England and New York are 40 years, 69 years, 51 years and up to 51 years respectively. The weighted average amortisation period is 32 years. Future revenues in relation to unfulfilled performance obligations not yet received in cash amount to £6.1 billion ( 2023 : £5.0 billion ; 2022 : £5.2 billion ). £1.9 billion ( 2023 : £1.8 billion ; 2022 : £1.7 billion ) relates to connection contracts in UK Electricity Transmission which will be recognised as revenue over 24 years and £3.8 billion ( 2023 : £2.7 billion ; 2022 : £3.0 billion ) relates to revenues to be earned under Grain LNG contracts until 2045 . The remaining amount will be recognised as revenue over two years . The amount of revenue recognised for the year ended 31 March 2024 from performance obligations satisfied (or partially satisfied) in previous periods, mainly due to changes in the estimate of the stage of completion, is £nil ( 2023 : £nil ; 2022 : £nil ).

Other operating costs

Other operating costs	12 Months Ended
	Mar. 31, 2024
Analysis of income and expense [abstract]
Other operating costs	4. Other 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. Total 2024 2023 2022 £m £m £m Depreciation, amortisation and impairment 2,061 1,984 1,830 Payroll costs 2,043 1,958 1,794 Purchases of electricity 1,497 2,055 1,280 Purchases of gas 1,289 2,516 1,666 Property and other taxes 1,279 1,302 1,202 UK electricity balancing costs 2,486 4,052 3,152 Other 4,553 3,682 3,215 Other operating costs 15,208 17,549 14,139 Provision for bad and doubtful debts 179 220 167 Total operating costs from continuing operations 15,387 17,769 14,306 Operating costs from continuing operations include: Inventory consumed 408 723 436 Research and development expenditure 32 23 11 (a) Payroll costs 2024 2023 2022 £m £m £m Wages and salaries 1 3,206 2,971 2,563 Social security costs 256 244 201 Defined contribution scheme costs 129 98 81 Defined benefit pension costs 96 121 185 Share-based payments 37 46 38 Severance costs (excluding pension costs) 12 3 5 3,736 3,483 3,073 Less: payroll costs capitalised (1,693) (1,525) (1,279) Total payroll costs from continuing operations 2,043 1,958 1,794 1. Included within wages and salaries are US other post-retirement benefit costs of £26 million ( 2023 : £37 million ; 2022 : £39 million ). For further information, refer to note 25 . (b) Number of employees 31 March 2024 Monthly average 2024 31 March 2023 Monthly average 2023 31 March 2022 Monthly average 2022 UK 13,956 13,439 12,572 12,024 11,960 11,393 US 17,469 17,406 16,878 16,539 17,332 17,314 Total number of employees (continuing operations) 31,425 30,845 29,450 28,563 29,292 28,707 4. Other operating costs continued (c) Key management compensation 2024 2023 2022 £m £m £m Short-term employee benefits 7 7 7 Post-employment benefits — — 1 Share-based payments 5 6 5 Total key management compensation 12 13 13 Key management compensation relates to the Board, including the Executive Directors and Non-executive Directors, for the years presented. (d) Auditor’s remuneration Auditor’s 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: 2024 2023 2022 £m £m £m Audit fees payable to the Parent Company’s auditor and their associates in respect of: Audit of the Parent Company’s individual and consolidated financial statements 1 2.8 2.9 2.7 The auditing of accounts of any associate of the Company 8.8 9.0 8.9 Other services supplied 2 7.3 7.4 7.3 18.9 19.3 18.9 Total other services 3 All other fees: Other assurance services 4 4.0 1.4 0.9 Other non-audit services not covered above — 0.2 0.1 4.0 1.6 1.0 Total auditor’s remuneration 22.9 20.9 19.9 1. Audit fees in each year represent fees for the audit of the Company’s financial statements for the years ended 31 March 2024 , 2023 and 2022 . 2. 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 auditor. 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 Act), audit reports on regulatory returns and the review of interim financial statements for the six-month periods ended 30 September 2023 , 2022 and 2021 respectively. 3. There were no tax compliance or tax advisory fees and no audit-related fees as described in Item 16C(b) of Form 20-F. 4. In all years, principally relates to assurance services provided in relation to comfort letters for debt issuances and reporting accountant services. The Audit & Risk Committee considers and makes recommendations to the Board, to be put to shareholders for approval at each AGM, in relation to the appointment, reappointment, removal and oversight of the Company’s independent auditor. The Committee, under authority granted at the AGM, also considers and approves the audit fees on behalf of the Board in accordance with the Competition and Markets Authority Audit Order 2014. Certain services are prohibited from being performed by the external auditor under the Sarbanes-Oxley Act and the FRC’s 2019 Revised Ethical Standard. Of the above services, none were prohibited.

Exceptional items and remeasure

Exceptional items and remeasurements	12 Months Ended
	Mar. 31, 2024
Exceptional Items And Remeasurements [Abstract]
Exceptional items and remeasurements	5. Exceptional items and remeasurements To monitor our segmental financial performance, we use an adjusted consolidated profit measure that excludes certain income and expenses. 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 2024 2023 2022 £m £m £m Included within operating profit Exceptional items: Transaction, separation and integration costs 1 (44) (117) (223) Cost efficiency programme (65) (100) (42) IFA fire 92 130 — Changes in environmental provisions (496) 176 — Provision for UK electricity balancing costs (498) — — Net gain on disposal of NECO — 511 — Net gain on disposal of Millennium Pipeline Company LLC — 335 — New operating model implementation costs — — (24) Release of St William Homes LLP deferred income — — 189 Net gain on disposal of St William Homes LLP — — 228 Environmental insurance recovery — — 38 (1,011) 935 166 Remeasurements – commodity contract derivatives 24 (350) 392 (987) 585 558 1. Transaction, separation and integration costs represent the aggregate of distinct activities undertaken by the Group in the years presented. Details of remeasurements, tax exceptional items and the tax effect of exceptional items and remeasurements are also provided in this note. 2024 2023 2022 £m £m £m Included within operating profit from continuing operations (987) 585 558 Included within finance income and costs Remeasurements: Net gains/(losses) on financial assets at fair value through profit and loss 4 (28) (15) Net gains on financing derivatives 11 82 74 15 54 59 Included within share of post-tax results of joint ventures and associates Remeasurements: Net losses on financial instruments (64) (19) (56) Total included within profit before tax (1,036) 620 561 Included within tax Exceptional items – movements arising on items not included in profit before tax: Deferred tax charge arising as a result of UK tax rate change — — (458) Tax on exceptional items 159 (316) (28) Tax on remeasurements (7) 75 (103) 152 (241) (589) Total exceptional items and remeasurements after tax (884) 379 (28) Analysis of total exceptional items and remeasurements after tax Exceptional items after tax (852) 619 (320) Remeasurements after tax (32) (240) 292 Total exceptional items and remeasurements after tax (884) 379 (28) 5. Exceptional items and remeasurements continued Exceptional items Management uses an exceptional items framework that has been discussed and approved by the Audit & Risk 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. With respect to restructuring costs, these represent additional expenses incurred that are not related to the normal business and day-to-day activities. These can take place over multiple reporting periods given the scale of the Group, the nature and complexity of the transformation initiatives and due to the impact of strategic transactions. 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. The exceptional items framework was last updated in March 2022. 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 efficiency and transformation 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. 2024 Transaction, separation and integration costs During the year, separation costs of £11 million were incurred in relation to the disposal of NECO, £6 million in relation to the disposal of the UK Gas Transmission business and £27 million in connection with the integration of NGED. The costs incurred primarily relate to professional fees, relocation costs and employee costs. The costs have been classified as exceptional in accordance with our exceptional items policy. Whilst the transaction, separation and integration costs incurred during the period do not meet the quantitative threshold to be classified as exceptional on a standalone basis, when taken in aggregate with the £340 million of costs in previous periods, the costs qualify for exceptional treatment in line with our exceptional items policy. The total cash outflow for the period was £33 million . The Group is entitled to cost recovery in relation to the separation of the ESO. Accordingly, these costs have not been classified as exceptional. Cost efficiency programme During the period, the Group incurred a further £65 million of costs in relation to the major cost efficiency programme announced in November 2021, that targeted at least £400 million savings per annum across the Group by the end of three years . The costs recognised in the period primarily relate to redundancy provisions, employee costs and professional fees incurred in delivering the programme. Whilst the costs incurred during the period do not meet the quantitative threshold to be classified as exceptional on a standalone basis, when taken in aggregate with the £142 million of costs incurred since the announcement of the programme, the costs qualify for exceptional treatment in line with our exceptional items policy. The total cash outflow for the period was £53 million . The cost efficiency programme completed in the year. Fire at IFA converter station In September 2021, a fire at the IFA1 converter station in Sellindge, Kent caused significant damage to infrastructure on site. In the period, the Group recognised net insurance claims of £92 million , which were recognised as exceptional in line with our exceptional items policy and consistent with related claims in the prior year. The total cash inflow in the period in relation to the insurance proceeds was £92 million . Changes in environmental provisions In the US, we recognise environmental provisions related to the remediation of the Gowanus Canal and the former manufacturing gas plant facilities previously owned or operated by the Group or its predecessor companies. The sites are subject to both state and federal environmental remediation laws in the US. 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. During the second half of the financial year, following discussions with the New York State Department of Environmental Conservation and the Environmental Protection Agency on the scope and design of remediation activities related to certain of our responsible sites, we have re-evaluated our estimates of total costs and increased our provision by £496 million (see note 26 ) . Under the terms of our rate plans, we are entitled to recovery of environmental clean-up costs from rate payers in future reporting periods. Such recoveries through overall allowed revenues are not classified as exceptional in the future periods that they occur due to the extended duration over which such costs are recovered and the immateriality of the recoveries in any given year. Provision for UK electricity balancing costs During the year, the ESO’s operating profit increased due to a substantial over-recovery of allowed revenues received under its regulatory framework. As described in note 3 , under IFRS a corresponding liability is not recognised for the return of over-recoveries as this relates to future customers and services that have not yet been delivered. At the end of October 2023, legislation required to enable the separation of the ESO and the formation of the NESO was passed through Parliament and accordingly, the Group took the judgement to classify the assets and liabilities of the ESO as held for sale (see note 10 ). An element of the over-recoveries will now be settled through the sale process and it no longer represents an unrecognised regulatory liability for the Group. Accordingly, a liability has been recognised for the over-recovered revenues which are forecasted to transfer through the disposal. 5. Exceptional items and remeasurements continued Exceptional items continued 2023 Transaction, separation and integration costs Separation costs of £39 million were incurred in relation to the disposal of NECO, £38 million in relation to the disposal of a majority stake in our UK Gas Transmission business and £40 million in connection with the integration of NGED. The costs incurred primarily relate to legal fees, bankers’ fees, professional fees and employee costs. The costs have been classified as exceptional, consistent with similar costs for the years ended 31 March 2022 and 2021, and in line with the exceptional items policy. The total cash outflow for the period was £84 million . Cost efficiency programme The Group incurred a further £100 million of costs in relation to the major cost efficiency programme announced in November 2021. The costs recognised primarily related to property costs, employee costs and professional fees incurred in delivering the programme. Whilst the costs incurred during the period did not meet the quantitative threshold to be classified as exceptional on a standalone basis, when taken in aggregate with the £42 million of costs incurred in the year ended 31 March 2022, the costs qualified for exceptional treatment in line with our exceptional items policy. The total cash outflow for the period was £85 million . Fire at IFA converter station In September 2021, a fire at the IFA1 converter station in Sellindge, Kent caused significant damage to infrastructure on site. In the year, the Group recognised £130 million of insurance claims (net of asset write-offs), which have been recognised as exceptional in line with our exceptional items policy. The total cash inflow for the period was £79 million . Changes in environmental provisions The real discount rate applied to the Group’s environmental provisions was revised to 1.5% ( 2022 : 0.5% ) to reflect the substantial and sustained change in US government bond yield curves (see note 26) . The principal impact of this rate increase was a £165 million decrease in our US environmental provisions and a £11 million decrease in our UK environmental provision. The weighted average remaining duration of our cash flows was around 10.5 years . Net gain on disposal of NECO On 25 May 2022, the Group completed the sale of a wholly owned subsidiary, NECO, to PPL Rhode Island Holdings, LLC for cash consideration of £3.1 billion . As a result, the Group derecognised net assets of £2.7 billion , resulting in a pre-tax gain of £511 million . The receipt of cash was recognised within net cash used in investing activities within the consolidated cash flow statement. Net gain on disposal of Millennium Pipeline Company LLC The Group recognised a gain of £335 million on the disposal of its entire 26.25% equity interest in the Millennium Pipeline Company LLC associate to DT Midstream for cash consideration of £497 million . The receipt of cash was recognised within net cash used in investing activities within the consolidated cash flow statement. 2022 Transaction and separation costs £223 million of transaction and separation costs were incurred in relation to the acquisition of NGED , the disposal of NECO and the disposal of our UK Gas Transmission business . The costs related to legal fees, bankers’ fees and other professional fees. The costs were classified as exceptional, consistent with similar costs for the year ended 31 March 2021. The total cash outflow for the year was £196 million . New operating model implementation costs and cost efficiency programme The Group incurred a further £24 million of costs in relation to the design and implementation of our new operating model and £42 million in relation to the major cost efficiency programme announced in November 2021. The costs recognised primarily related to professional fees incurred and redundancy provisions. Whilst the costs incurred did not meet the quantitative threshold to be classified as exceptional on a standalone basis, when taken in aggregate with the costs expected to be incurred over the duration of the cost efficiency programme, we concluded that the costs should be classified as exceptional in line with our exceptional items policy. The total cash outflow for the period was £48 million . Net gain on disposal of St William Homes LLP and release of deferred income The Group recognised a gain of £228 million on the disposal of its entire 50% equity interest in the St William Homes LLP joint venture to The Berkeley Group plc for cash consideration of £413 million . In connection with the disposal, the Group also released deferred income of £189 million which related to deferred profits from previous property sales to St William Homes LLP. We concluded that the release of the deferred income should be classified as exceptional given the crystallisation event for the release is the sale of the Group’s equity interest in St William Homes LLP. Environmental insurance recovery In the US, the most significant component of our £2.4 billion environmental provision relates to several Superfund sites, and arose from former manufacturing gas plant facilities, previously owned or operated by the Group or its predecessor companies. 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. In the year ended 31 March 2022, we recognised an exceptional gain of £38 million relating to an insurance receivable for site remediation costs included in our Superfund sites environmental provision. The insurance receipts were recorded as an exceptional item in line with the treatment of the related costs. 5. Exceptional items and remeasurements continued Remeasurements Remeasurements comprise unrealised gains or losses recorded in the consolidated income statement arising from changes in the fair value of certain of our financial assets and liabilities accounted for at fair value through profit and loss (FVTPL). 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 the net foreign exchange gains and losses on borrowing activities. These are offset by foreign exchange gains and losses on financing derivatives measured at fair value. 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). The performance of these assets (including changes in fair value) is 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, net of interest accrued, used for the risk management of interest rate and foreign exchange exposures and the offsetting foreign exchange losses and gains on the associated borrowing activities. 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 ) . Net foreign exchange gains and losses on financing derivatives used for the risk management of foreign exchange exposures are offset by foreign exchange losses and gains on borrowing activities; 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 ) ; and iv. Unrealised net gains/(losses) on derivatives and other financial instruments within our joint ventures and associates. Items included within tax 2022 Change in UK corporation tax rate In the Spring Budget 2021, the UK government announced that from 1 April 2023 the UK corporation tax rate would increase to 25% , and this was substantively enacted on 24 May 2021. Deferred tax balances at 31 March 2022 were remeasured at the enacted rate, with £458 million recognised as exceptional, in line with previous periods.

Finance income and costs

Finance income and costs	12 Months Ended
	Mar. 31, 2024
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. Finance income and costs remeasurements include unrealised gains and losses on certain assets and liabilities treated at FVTPL. The effective interest income and interest expense and dividends on these items are included in finance income and finance costs before remeasurements respectively. 2024 2023 2022 Notes £m £m £m Finance income Net interest income on pensions and other post-retirement benefit obligations 25 100 85 — Interest income on financial instruments: Bank deposits and other financial assets 139 80 32 Dividends received on equities held at fair value through other comprehensive income (FVOCI) 1 1 3 Net gains/(losses) on FVTPL financial assets 4 (28) (15) Other income 4 — 30 248 138 50 Finance costs Interest expense on financial liabilities held at amortised cost: Bank loans and overdrafts (140) (328) (216) Other borrowings 1 (1,424) (1,330) (961) Interest on derivatives (277) (170) (59) Unwinding of discount on provisions 26 (102) (88) (73) Other interest (31) (13) 11 Derivatives designated as hedges for hedge accounting² 13 22 45 Derivatives not designated as hedges for hedge accounting² (2) 60 29 Less: interest capitalised³ 251 249 152 (1,712) (1,598) (1,072) Finance income 248 138 50 Finance costs 4 (1,712) (1,598) (1,072) Net finance costs from continuing operations (1,464) (1,460) (1,022) 1. Includes interest expense on lease liabilities (see note 13 for details) . 2. Includes a net foreign exchange gain on borrowing and investment activities of £271 million ( 2023 : £86 million loss ; 2022 : £110 million gain ) offset by foreign exchange gains and losses on financing derivatives measured at fair value and the impacts of hedge accounting. 3. Interest on funding attributable to assets in the course of construction in the current year was capitalised at a rate of 4.7% ( 2023 : 4.7% ; 2022 : 3.2% ). In the UK, capitalised interest qualifies for a current year tax deduction with tax relief claimed of £39 million ( 2023 : £30 million ; 2022 : £16 million ). In the US, capitalised interest is added to the cost of property, plant and equipment, and qualifies for tax depreciation allowances. 4. Finance costs include principal accretion on inflation-linked liabilities of £208 million ( 2023 : £483 million ; 2022 : £241 million

Tax

Tax	12 Months Ended
	Mar. 31, 2024
Income taxes paid (refund) [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. 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 the statement of changes 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. Where there are tax positions not yet agreed with the tax authorities, 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: 2024 2023 2022 £m £m £m Current tax: UK corporation tax at 25% ( 2023 : 19% ; 2022 : 19% ) 410 161 255 UK corporation tax adjustment in respect of prior years (36) — (9) 374 161 246 Overseas corporation tax 82 225 6 Overseas corporation tax adjustment in respect of prior years (90) (16) (26) (8) 209 (20) Total current tax from continuing operations 366 370 226 Deferred tax: UK deferred tax 388 255 605 UK deferred tax adjustment in respect of prior years 43 13 (5) 431 268 600 Overseas deferred tax (40) 233 425 Overseas deferred tax adjustment in respect of prior years 74 5 7 34 238 432 Total deferred tax from continuing operations 465 506 1,032 Total tax charge from continuing operations 831 876 1,258 Tax (credited)/charged to the consolidated statement of comprehensive income and equity 2024 2023 2022 £m £m £m Current tax: Share-based payments (2) (1) — Deferred tax: Investments at fair value through other comprehensive income 1 (1) — Cash flow hedges, cost of hedging and own credit reserve 56 (7) (12) Remeasurements of pension assets and post-retirement benefit obligations (50) (344) 493 Share-based payments — 1 (4) 5 (352) 477 Total tax recognised in the statements of comprehensive income from continuing operations 7 (352) 481 Total tax relating to share-based payments recognised directly in equity from continuing operations (2) — (4) 5 (352) 477 7. Tax continued The tax charge for the year for continuing operations, is higher ( 2023 : higher tax charge; 2022 : higher tax charge) than the standard rate of corporation tax in the UK of 25% ( 2023 : 19% ; 2022 : 19% ): 2024 2023 2022 £m £m £m Profit before tax from continuing operations 3,048 3,590 3,441 Profit before tax from continuing operations multiplied by UK corporation tax rate of 25% ( 2023 : 19% ; 2022 : 19% ) 762 682 654 Effect of: Adjustments in respect of prior years 1 (9) 2 (33) Expenses not deductible for tax purposes 155 92 47 Non-taxable income 2 (43) (75) (49) Adjustment in respect of foreign tax rates 3 (20) 147 170 Deferred tax impact of change in UK tax rate — 66 501 Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax (9) (27) (17) Other 4 (5) (11) (15) Total tax charge from continuing operations 831 876 1,258 % % % Effective tax rate – continuing operations 27.3 24.4 36.6 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. Included in the prior year are remeasurements of US closing state deferred tax balances as a result of an expected increase in the blended state tax rate following the disposal of NECO. 4. Other primarily comprises the movement in the deferred tax asset on previously unrecognised capital losses, claims for land remediation relief and claims for Research & Development credit. Factors that may affect future tax charges The main UK corporation tax rate is 25% with effect from 1 April 2023. Deferred tax balances as at 31 March 2024 have been calculated at 25%. The US government continues to consider changes to federal tax legislation, but as no changes have been substantively enacted at the balance sheet date, deferred tax balances as at 31 March 2024 have been calculated at the prevailing tax rates based on the current tax laws. The legislation implementing the Organisation for Economic Co-operation and Development’s (OECD) proposals for a global minimum corporation tax rate (Pillar Two) was enacted into UK law on 11 July 2023. The legislation includes an income inclusion rule and a domestic minimum tax, which together are designed to ensure a minimum effective tax rate of 15% in each country in which the Group operates. Similar legislation is being enacted by other governments around the world. The legislation is effective for National Grid from 1 April 2024 and therefore the rules do not impact the Group’s consolidated financial statements for year ended 31 March 2024. The Group has applied the mandatory exception in the UK to recognising and disclosing information about the deferred tax assets and liabilities related to Pillar Two income taxes in accordance with the amendments to IAS 12 published by the IASB on 23 May 2023. The Group does not 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: Regulatory licences £m Accelerated tax depreciation £m Share- based payments £m Pensions and other post- retirement benefits £m Financial instruments £m Other net temporary differences 1 £m Total £m Deferred tax liabilities/(assets) At 1 April 2022 429 7,710 (18) 775 (301) (1,830) 6,765 Exchange adjustments and other 2 — 357 (2) 8 8 (116) 255 Charged/(credited) to income statement — 145 (2) 51 (71) 386 509 Charged/(credited) to other comprehensive income and equity — — 1 (344) (6) — (349) Disposals — 1 — — — — 1 At 1 April 2023 (as previously reported) 429 8,213 (21) 490 (370) (1,560) 7,181 Impact of IAS 12 amendment 3 — 29 — — — (29) — At 1 April 2023 (as restated) 429 8,242 (21) 490 (370) (1,589) 7,181 Exchange adjustments and other 2 — (132) — (1) 23 (110) Charged/(credited) to income statement — 720 (5) 26 38 (312) 467 (Credited)/charged to other comprehensive income and equity — — — (50) 57 — 7 Disposals — (2) — — — (2) Reclassification to held for sale (note 10) — (12) 1 (4) — (9) (24) At 31 March 2024 429 8,816 (25) 461 (275) (1,887) 7,519 1. The deferred tax asset of £1,887 million as at 31 March 2024 ( 2023 : £1,560 million ) in respect of other net temporary differences primarily relates to losses of £184 million ( 2023 : £47 million ), US contract and lease liabilities of £575 million ( 2023 : £511 million ), US environmental provisions of £646 million ( 2023 : £503 million ) and US bad debt provision of £150 million ( 2023 : £148 million ). 2. Exchange adjustments and other primarily comprises foreign exchange arising on translation of the US dollar deferred tax balances. 3. In May 2021, the IASB issued amendments to IAS 12 resulting in the recognition of separate deferred tax assets and deferred tax liabilities (see note 1 ). 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 £7,519 million ( 2023 : £7,181 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: 2024 2023 £m £m Capital losses 2,483 2,367 Trading losses 4 4 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. At 31 March 2024 and 31 March 2023 , there were no recognised deferred tax liabilities for taxes that would be payable on the unremitted earnings of the Group’s subsidiaries or its associates as there are no significant corporation tax consequences of the Group’s UK, US or overseas subsidiaries or associates paying dividends to their parent companies. There are also no significant income tax consequences for the Group from the payment of dividends by the Group to its shareholders.

Earnings per share (EPS)

Earnings per share (EPS)	12 Months Ended
	Mar. 31, 2024
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. (a) Basic EPS Earnings EPS Earnings EPS Earnings EPS 2024 2024 2023 2023 2022 2022 £m pence £m pence £m pence Earnings from continuing operations 2,216 60.0 2,714 74.2 2,182 60.6 Earnings from discontinued operations 74 2.0 5,083 138.9 171 4.8 Total earnings 2,290 62.0 7,797 213.1 2,353 65.4 2024 2023 2022 millions millions millions Weighted average number of ordinary shares – basic 3,692 3,659 3,599 (b) Diluted EPS Earnings EPS Earnings EPS Earnings EPS 2024 2024 2023 2023 2022 2022 £m pence £m pence £m pence Earnings from continuing operations 2,216 59.7 2,714 73.8 2,182 60.3 Earnings from discontinued operations 74 2.0 5,083 138.3 171 4.7 Total earnings 2,290 61.7 7,797 212.1 2,353 65.0 2024 2023 2022 millions millions millions Weighted average number of ordinary shares – diluted 3,709 3,676 3,616 (c) Reconciliation of basic to diluted average number of shares 2024 2023 2022 millions millions millions Weighted average number of ordinary shares – basic 3,692 3,659 3,599 Effect of dilutive potential ordinary shares – employee share plans 17 17 17 Weighted average number of ordinary shares – diluted 3,709 3,676 3,616

Dividends

Dividends	12 Months Ended
	Mar. 31, 2024
Dividend [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. 2024 2023 2022 Pence per share Cash dividend £m Scrip dividend £m Pence per share Cash dividend £m Scrip dividend £m Pence per share Cash dividend £m Scrip dividend £m Interim dividend in respect of the current year 19.40 393 320 17.84 488 163 17.21 339 282 Final dividend in respect of the prior year 37.60 1,325 56 33.76 1,119 114 32.16 583 562 57.00 1,718 376 51.60 1,607 277 49.37 922 844 The Directors are proposing a final dividend for the year ended 31 March 2024 of 39.12p per share that would absorb approximately £1,455 million of shareholders’ equity (assuming all amounts are settled in cash). It will be paid on 19 July 2024 to shareholders who are on the register of members at 7 June 2024 (subject to shareholders’ approval at the AGM). A scrip dividend will be offered as an alternative

Assets held for sale and discon

Assets held for sale and discontinued operations	12 Months Ended
	Mar. 31, 2024
Non-current assets or disposal groups classified as held for sale or as held for distribution to owners [abstract]
Assets held for sale and discontinued operations	10. Assets held for sale and discontinued operations 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 expected to be 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. (a) Assets held for sale The following assets and liabilities were classified as held for sale: 2024 2023 Total assets held for sale £m Total liabilities held for sale £m Net assets held for sale £m Total assets held for sale £m Total liabilities held for sale £m Net assets held for sale £m UK Electricity System Operator 1,134 (1,427) (293) — — — Investment in GasT TopCo Limited 689 — 689 1,443 — 1,443 FAA option — — — — (109) (109) RAA option — (47) (47) — — — Net assets held for sale 1,823 (1,474) 349 1,443 (109) 1,334 UK Electricity System Operator At the end of October 2023, legislation required to enable the separation of the ESO and the formation of the NESO was passed through Parliament. The NESO is expected to be established as a Public Corporation this calendar year, with responsibilities across both the electricity and gas systems. The assets and liabilities are consequently presented as held for sale in the consolidated financial statements for the year ended 31 March 2024 . Based on the scale and pass-through nature of the ESO, it is not considered a separate major line of business or geographic operation under IFRS 5 for treatment as a discontinued operation, and its disposal is not part of a single coordinated plan being undertaken by the Group. Accordingly, the results of the ESO have not been separately disclosed on the face of the income statement. The following assets and liabilities of the ESO were classified as held for sale at 31 March 2024 . £m Intangible assets 405 Property, plant and equipment 113 Trade and other receivables 563 Pension asset 17 Cash and cash equivalents 30 Financing derivatives 6 Total assets 1,134 Borrowings (13) Other liabilities (916) Provision for UK electricity balancing costs (498) Total liabilities (1,427) Net liabilities (293) No impairment losses were recognised on reclassification of the ESO assets and liabilities classified to held for sale. The ESO generated profit after tax of £178 million for the year ended 31 March 2024 ( 2023 : £182 million profit; 2022 : £12 million loss). 10. Assets held for sale and discontinued operations continued (a) Assets held for sale continued The UK Gas Transmission business On 31 January 2023, the Group disposed of 100% of the UK Gas Transmission business for cash consideration of £4.0 billion and a 40% interest in a newly incorporated UK limited company, GasT TopCo Limited. The other 60% was purchased by MIRA and BCI (together, the Consortium). On disposal, the Group recognised an investment in GasT TopCo Limited of £1.4 billion . As a result, the Group derecognised net assets of £0.6 billion and the gain on disposal, after transaction costs, was £4.8 billion . The Group also entered into a Further Acquisition Agreement (the FAA option) with the Consortium over its remaining 40% interest. Both the investment in GasT TopCo Limited and the FAA option were immediately classified as held for sale. The Group has not applied equity accounting in relation to its investment in GasT TopCo Limited. On 11 March 2024, the FAA option was partially exercised by the Consortium and the Group disposed of 20% of the 40% interest in GasT TopCo Limited that was acquired on 31 January 2023. The total sales proceeds were £681 million and the loss on disposal, after transaction costs, was £4 million . As part of the transaction, the Group also entered into a new option agreement with the Consortium, the Remaining Acquisition Agreement (the RAA option), to replace the FAA option for the potential sale of all or part of the remaining 20% equity interest in GasT TopCo Limited. The RAA option is exercisable, at the Consortium’s option, between 1 May 2024 and 31 July 2024. If the RAA option is partially exercised by the Consortium, the Group will have the right to put the remainder of its interests in GasT TopCo Limited to the Consortium, which can be exercised by the Group between 1 December 2024 and 31 December 2024. The RAA option is a Level 3 derivative, which is accounted for at fair value, and the assumptions which are used to determine fair value are specific to the contract and not readily observable in active markets. Significant unobservable inputs include the valuation and volatility of GasT TopCo Limited’s unlisted equity. These inputs are used as part of a Black-Scholes option pricing model to provide the reported fair values. The fair value of the option as at 31 March 2024 is £47 million . The RAA option will be extinguished when the option is either exercised or lapses. The option cannot be cash settled. (b) Discontinued operations UK Gas Transmission The disposal of the Group’s interests in GasT TopCo Limited is considered to be the final stage of the plan to dispose of the UK Gas Transmission business which was first announced in 2021. As a discontinued operation, the results of the business prior to the recognition of the associate and any remeasurements pertaining to the financial derivatives noted above are shown separately from the continuing business for all periods presented on the face of the income statement. This is also reflected in the statement of comprehensive income, as well as EPS being shown split between continuing and discontinued operations. The summary income statements for the years ended 31 March 2024 , 2023 and 2022 are as follows: Total 2024 2023 2022 £m £m £m Discontinued operations Revenue — 1,604 1,362 Other operating costs — (889) (725) Operating profit — 715 637 Finance income 17 21 — Finance costs 1 62 (363) (230) Profit before tax 79 373 407 Tax 2 (1) (93) (236) Profit after tax from discontinued operations 78 280 171 (Loss)/gain on disposal (4) 4,803 — Total profit after tax from discontinued operations 74 5,083 171 1. Finance costs include the remeasurement of the FAA and RAA options. 2. Of the £236 million tax charge in the year ended 31 March 2022, £145 million related to an increase in deferred tax liability due to the change in the UK corporation tax rate. 10. Assets held for sale and discontinued operations continued (b) Discontinued operations continued The summary statements of comprehensive income for discontinued operations for the years ended 31 March 2024 , 2023 and 2022 are as follows: 2024 2023 2022 £m £m £m Profit after tax from discontinued operations 74 5,083 171 Other comprehensive (loss)/income from discontinued operations Items from discontinued operations that will never be reclassified to profit or loss: Remeasurement (losses)/gains on pension assets and post-retirement benefit obligations — (313) 309 Net losses on financial liability designated at fair value through profit and loss attributable to changes in own credit risk — — (1) Tax on items that will never be reclassified to profit or loss — 78 (94) Total (losses)/gains from discontinued operations that will never be reclassified to profit or loss — (235) 214 Items from discontinued operations that may be reclassified subsequently to profit or loss: Net gains in respect of cash flow hedges — 6 1 Net gains/(losses) in respect of cost of hedging — 4 (4) Net gains on investments in debt instruments measured at fair value through other comprehensive income 13 — — Tax on items that may be reclassified subsequently to profit or loss (3) (2) — Total gains/(losses) from discontinued operations that may be reclassified subsequently to profit or loss 10 8 (3) Other comprehensive income/(loss) for the year, net of tax from discontinued operations 10 (227) 211 Total comprehensive income for the year from discontinued operations 84 4,856 382 Details of the cash flows relating to discontinued operations are set out within the consolidated cash flow statement. Cash inflows from investing activities in the year comprised dividends received from GasT TopCo Limited of £102 million

Goodwill

Goodwill	12 Months Ended
	Mar. 31, 2024
Intangible assets and goodwill [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 CGUs and this allocation is made to those CGUs 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 CGU and the estimated recoverable amount of the CGU 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 CGU. 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 2022 9,532 Exchange adjustments 315 Net book value at 1 April 2023 9,847 Exchange adjustments (118) Net book value at 31 March 2024 9,729 There was no significant accumulated impairment charge as at 31 March 2024 or 31 March 2023 . Impairment review of goodwill and indefinite-lived intangibles Goodwill and indefinite-lived intangibles (see note 12 ) are reviewed annually for impairment and the recoverability is assessed by comparing the carrying amount of our operations with the expected recoverable amount on a value-in-use basis which uses pre-financing and pre-tax cash flow projections based on the Group’s financial plans, approved by the Directors, as a starting point. See below for a summary of which operations our goodwill and indefinite-lived intangibles are allocated to: 2024 2023 CGU or group of CGUs £m £m Goodwill: National Grid Ventures – US 188 163 New England 1,541 1,609 New York 3,279 3,354 UK Electricity Distribution 1 4,721 4,721 Total goodwill 9,729 9,847 Indefinite-lived intangibles (regulatory licences related to UK Electricity Distribution): West Midlands 518 518 East Midlands 519 519 South Wales 257 257 South West 420 420 Total indefinite-lived intangibles 1,714 1,714 1. This is a combination of the West Midlands, East Midlands, South Wales and South West CGUs, reflecting the level at which the goodwill is monitored. In each assessment, the value-in-use has been calculated assuming a stable regulatory framework and is based on projections that incorporate our best estimates of future cash flows, including costs, changes in commodity prices, future rates and growth. Such projections reflect our current regulatory agreements and allow for future agreements and recovery of investment, including those related to achieving the net zero plans of the jurisdictions that we operate in. Our plans have proved to be reliable guides in the past and the Directors believe the estimates are appropriate. 11. Goodwill continued (a) Cash flow periods, terminal value and discount rate assumptions We select cash flow durations longer than five years, when our forecasts are considered reliable. The cash flow durations selected reflect our knowledge and understanding of the regulatory environments in which we operate, and most significantly, where markets have legislated decarbonisation commitments by 2050, we may utilise longer cash flow forecasts that reflect the investment required to deliver those commitments before applying a terminal value at the point those commitments are due to be fulfilled and market growth is expected to stabilise. For our regulated UK ED operations, we consider cash flow durations that run until 2050, reflecting the expected investment required in the network, in excess of economy‑wide long-term growth rates in order to deliver the energy transition. Total expenditure forecasts, comprising capital and operating expenditure, are estimated with reference to the Group’s strategic modelling and expectations around a reasonable energy transition based upon the policies and commitments in place today. Cash flows related to uncommitted future restructurings and enhancement capital expenditure (beyond activity to reinforce the network and build new connections) are excluded from the projections. For our regulated US operations (New York and New England CGUs), we use a five-year cash flow forecast. For our National Grid Ventures operations, we typically model cash flows extending out to the end of each project’s operational life based on the long-term horizon of our projects. For our UK ED business, a nominal terminal growth rate of 2.3% ( 2023 : 2.6% ) is assumed upon the terminal year cash flows, reflecting management’s best view, based on market and operational experience, of the expected long-term growth in the relevant market. For our regulated US operations we apply a growth rate of 2.4% ( 2023 : 2.5% ). This has been determined with regard to data on industry growth projections, specifically related to the energy transition, and projected growth in real Gross Domestic Product (GDP) for the territory within which the CGU is based. Pre-tax cash flows are discounted by applying a pre-tax discount rate reflecting the time value of money and the risks specific to the group of assets. In practice, the post-tax discount rate for the group of assets in question is derived from a post-tax weighted average cost of capital. The assumptions used in the calculation of the weighted average cost of capital are benchmarked to externally available data. The determined discount rate is independent of the entity’s capital structure and reflects a market participant’s view of a risk adjusted discount rate specific to the CGU or group of CGUs. The post-tax discount rate is then grossed up to a pre-tax discount rate that is applied to pre-tax cash flows. The pre-tax discount rates used for the year ended 31 March 2024 were as follows: UK ED Group 5.0% ( 2023 : 5.6% ); UK ED distribution network operators 5.0% ( 2023 : 5.6% ); New York 6.2% ( 2023 : 6.4% ); New England 6.1% ( 2023 : 6.6% ); and National Grid Ventures – US 7.2% ( 2023 : 8.6% ). (b) Key inputs and sensitivity analysis In assessing the carrying value of goodwill and licences, we have sensitised our forecasts to factor in adjustments to key inputs to each model. Whilst regulatory licences are tested for impairment before we test goodwill, we consider the sensitivity for goodwill attributable to UK ED and our regulated US operations and those related to licences separately below. Goodwill – UK ED, regulated US operations (New York and New England) and National Grid Ventures – US While key assumptions underpinning the goodwill valuations will change over time, the Directors consider that no reasonably foreseeable change would result in an impairment of goodwill. This is in view of the long-term nature of the key assumptions, including those used in determining an appropriate discount rate, and specifically the risk-free rate and total market return, the margin by which the estimated value-in-use exceeds the carrying amount and the nature of the regulatory regimes that UK ED and our regulated US businesses operate under. No reasonably possible changes to inputs to the impairment test performed over goodwill attributable to National Grid Ventures – US were identified as resulting in an impairment. Indefinite-lived regulatory licences – UK ED No reasonably possible changes to inputs to the impairment test performed over the South West, East Midlands, West Midlands and South Wales Distribution Network Operator licences were identified as resulting in an impairment.

Other intangible assets

Other intangible assets	12 Months Ended
	Mar. 31, 2024
Intangible assets other than goodwill [abstract]
Other intangible assets	12. Other intangible assets Other intangible assets are the software assets controlled by us and the electricity distribution licences which provide us with the right to operate and invest in the relevant network that operates as a monopoly in the licensed geographical area. The regulatory licences were acquired following the Group’s acquisition of NGED. Our electricity distribution licences are indefinite-lived intangible assets for which there is no foreseeable limit to the period over which they are expected to generate net cash inflows. Once granted by Ofgem, the licence is issued to a licensee on the basis that it remains active into perpetuity. On that basis, the value attributed to the electricity distribution network licence assets is considered to have an indefinite useful life. The regulatory licence assets are subject to a review for impairment annually, or more frequently if events or circumstances indicate a potential impairment (see note 11 for details of impairment tests performed over indefinite-lived intangible assets). Any impairment is charged to the income statement as it arises. Software is recorded at cost less accumulated amortisation and any provision for impairment. Our software assets are tested for impairment only if there is an indication that their carrying values 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 CGU to which that asset belongs is estimated. Impairments are recognised in the consolidated income statement within other operating costs. 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 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. Cloud computing arrangements are reviewed to determine if the Group has control of the software intangible asset. Control is considered to exist where the Group has the right to take possession of the software and run it on its own or a third party’s computer infrastructure or if the Group has exclusive rights to use the software such that the supplier is unable to make the software available to other customers. Costs relating to configuring or customising the software in a cloud computing arrangement are assessed to determine if there is a separate intangible asset over which the Group has control. If an asset is identified, it is capitalised and amortised over the useful economic life of the asset. To the extent that no separate intangible asset is identified, then the costs are either expensed when incurred or recognised as a prepayment and spread over the term of the arrangement if the costs are concluded to not be distinct. (a) Analysis of other intangible assets Regulatory licences £m Software £m Assets in the course of construction £m Total £m Cost at 1 April 2022 1,714 2,075 870 4,659 Exchange adjustments — 79 32 111 Additions — 34 544 578 Disposals — (17) — (17) Reclassifications 1 — 895 (885) 10 Cost at 1 April 2023 1,714 3,066 561 5,341 Exchange adjustments — (45) (6) (51) Additions — 17 464 481 Disposals — (23) — (23) Reclassifications¹ — 598 (436) 162 Reclassification to held for sale (note 10) — (520) (191) (711) Cost at 31 March 2024 1,714 3,093 392 5,199 Accumulated amortisation at 1 April 2022 — (1,377) (10) (1,387) Exchange adjustments — (51) — (51) Amortisation charge for the year — (291) — (291) Accumulated amortisation of disposals — 15 — 15 Reclassifications¹ — (23) — (23) Accumulated amortisation at 1 April 2023 — (1,727) (10) (1,737) Exchange adjustments — 23 — 23 Amortisation charge for the year — (301) — (301) Accumulated amortisation of disposals — 23 — 23 Reclassifications¹ — (161) — (161) Reclassification to held for sale (note 10) — 385 — 385 Accumulated amortisation at 31 March 2024 — (1,758) (10) (1,768) Net book value at 31 March 2024² 1,714 1,335 382 3,431 Net book value at 31 March 2023 1,714 1,339 551 3,604 1. Reclassifications includes amounts transferred to property, plant and equipment (see note 13 ). 2. The Group has capitalised £320 million ( 2023 : £370 million ) in relation to the Gas Business Enablement system in the US, of which £320 million ( 2023 : £369 million ) is in service and is being amortised over 10 years , with the remainder included within assets in the course of construction. A further £81 million ( 2023 : £87 million ) relates to our UK general ledger system within software and is being amortised over 10 years . 12. Other intangible assets continued (b) Asset useful economic lives No amortisation is provided on regulatory licences. Software is 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 (its useful economic life or UEL) and charging the cost of the asset to the income statement equally over this period. Years Software 3 to 10 Regulatory licences Indefinite

Property, plant and equipment

Property, plant and equipment	12 Months Ended
	Mar. 31, 2024
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 Group’s interest comprises legally protected statutory or contractual rights of use. Property, plant and equipment is recorded at cost, less accumulated depreciation and any impairment losses. The cost of property, plant and equipment primarily represents the amount initially paid or the fair value on the date of acquisition of a business. 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 together with an appropriate portion of overheads which are directly linked to the capital work performed; and the cost of any associated asset retirement obligations. 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. 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 (its useful economic life or UEL) and charging the cost of the asset to the income statement equally over this period. 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. 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, resilient and prepared for the transition to net zero. Our business plan envisages these additional investments will be funded through a mixture of cash generated from operations and the issue of new debt and equity. 13. Property, plant and equipment continued (a) Analysis of property, plant and equipment Land and buildings £m Plant and machinery £m Assets in the course of construction £m Motor vehicles and office equipment £m Total £m Cost at 1 April 2022 3,659 63,022 5,587 1,072 73,340 Exchange adjustments 126 2,073 156 50 2,405 Additions 158 1,196 5,345 154 6,853 Disposals (163) (331) (4) (156) (654) Adjustment for change in discount rate on decommissioning provisions (note 26) — (36) (12) — (48) Reclassifications 1 286 3,841 (4,312) 102 (83) Cost at 1 April 2023 4,066 69,765 6,760 1,222 81,813 Exchange adjustments (49) (841) (67) (19) (976) Additions 59 1,157 5,754 197 7,167 Disposals (55) (271) (5) (134) (465) Adjustment for change in discount rate on decommissioning provisions (note 26) — 29 — — 29 Reclassifications 1 277 4,725 (5,389) 218 (169) Reclassification to held for sale (note 10) (88) (13) (31) (134) (266) Cost at 31 March 2024 4,210 74,551 7,022 1,350 87,133 Accumulated depreciation at 1 April 2022 (773) (14,441) (60) (534) (15,808) Exchange adjustments (30) (444) — (32) (506) Depreciation charge for the year² (122) (1,459) (1) (183) (1,765) Disposals 127 311 2 152 592 Reclassifications 1 4 107 4 (8) 107 Accumulated depreciation at 1 April 2023 (794) (15,926) (55) (605) (17,380) Exchange adjustments 10 177 — 12 199 Depreciation charge for the year² (80) (1,515) (20) (189) (1,804) Disposals 50 252 2 134 438 Reclassifications 1 (3) 281 — (112) 166 Reclassification to held for sale (note 10) 59 1 6 89 155 Accumulated depreciation at 31 March 2024 (758) (16,730) (67) (671) (18,226) Net book value at 31 March 2024 3,452 57,821 6,955 679 68,907 Net book value at 31 March 2023 3,272 53,839 6,705 617 64,433 1. Represents amounts transferred between categories, (to)/from other intangible assets (see note 12 ) , (to)/from inventories. 2. Depreciation of assets in the course of construction relates to impairment provision adjustments. (b) 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 UELs. In assessing UELs, consideration is given to any contractual arrangements and operational requirements relating to particular assets. The assessments of estimated UELs and residual values of assets are performed annually. Certain network assets are depreciated using the group method of depreciation, in which a single composite depreciation rate is applied to a particular class of property, plant and equipment. This method pools similar assets together, and then depreciates each group as a whole over their respective useful lives. In the US, the Company conducts independent depreciation studies on a periodic basis as part of the regulatory ratemaking process to estimate group depreciation rates. These depreciation studies are subject to review and approval by the US state and federal regulators, with the depreciation expense recovered through rates charged to customers. Likewise in the UK, the composite depreciation rates are benchmarked to internal engineering studies and known asset performance lives. Depreciation expense includes a component for the original cost of assets and a component for estimated cost of future removal, net of any salvage value at retirement. Upon retirement of components of the Company’s network assets, the original cost of the retired assets, net of salvage value, is charged against accumulated depreciation, with no gain or loss recognised. Unless otherwise determined by operational requirements, the depreciation periods for the principal categories of property, plant and equipment are shown in the table that follows 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). 13. Property, plant and equipment continued (b) Asset useful economic lives continued Years UK US Weighted average remaining UEL Freehold and leasehold buildings up to 60 up to 100 38 Plant and machinery: Electricity transmission plant and wires up to 100 10 to 85 32 Electricity distribution plant 14 to 99 5 to 85 46 Electricity generation plant n/a 10 to 93 10 Interconnector plant and other 5 to 70 5 to 37 31 Gas plant – mains, services and regulating equipment n/a 25 to 95 53 Gas plant – storage 5 to 20 20 to 60 18 Gas plant – meters n/a 14 to 45 24 Motor vehicles and office equipment up to 50 up to 26 3 (c) Gas asset lives The role that our US 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. Policymakers in New York and Massachusetts continue to indicate an increase in electrification to meet their respective decarbonisation targets, whilst as a Group we are committed in our transition to net zero. As a result, there is a risk that the UELs of certain elements of our gas networks may be shortened in line with future policy, regulatory frameworks and planning systems aimed to support the decarbonisation of the energy sector. In the US, our gas distribution 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. The weighted average remaining UEL for our US gas distribution fixed asset base is circa 53 years ; however, a sizeable proportion of our assets are assumed to have UELs which extend beyond 2080. In assessing these UELs, we consider a range of different pathways related to our gas assets. These pathways factor in the net zero ambitions of the Group and the jurisdictions that we operate in, anticipated changes in customer behaviour, developments in new technology, the feasibility and affordability of electrification, and the ability to decarbonise fuel through the use of renewable natural gas (RNG) and green hydrogen. On balance of the different pathways considered, we continue to believe the lives identified by rate proceedings are the best estimate of the assets’ UELs given the need to provide safe, affordable and reliable heating services. We keep this assumption under review and we continue to actively engage and support our regulators to enable the clean energy transition. 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. Given the uncertainty described relating to the UELs of our gas assets, below we provide a sensitivity analysis for the depreciation charge for our New York and New England segments were a shorter UEL presumed. It should be noted that the net zero pathways which we consider probable all suggest some role for gas in heating buildings beyond 2050, so our sensitivity analysis for 2050 illustrates an unlikely worst-case scenario. Increase in depreciation expense for the year ended 31 March 2024 Increase in depreciation expense for the year ended 31 March 2023 New York £m New England £m New York £m New England £m UELs limited to 2050 208 66 185 54 UELs limited to 2060 100 26 90 21 UELs limited to 2070 46 6 42 3 Note that this sensitivity calculation excludes any assumptions regarding the residual value for our asset base and the effect that shortening asset depreciation lives would be expected to have on our regulatory recovery mechanisms. In the event that any of the US gas distribution assets are stranded, the Group would expect to recover the associated costs. While recovery is not guaranteed and is determined by regulators in the US, there are precedents for stranded asset cost recovery for US utility companies. (d) Right-of-use assets The Group leases various properties, land, equipment and cars. 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. 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, the incremental rate of borrowing for a similar term and similar security. This 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 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 that follows shows the movements in the net book value of right-of-use assets included within property, plant and equipment at 31 March 2024 and 31 March 2023 , split by category. The associated lease liabilities are disclosed in note 21 . 13. Property, plant and equipment continued (d) Right-of-use assets continued Land and buildings £m Plant and machinery £m Assets in the course of construction £m Motor vehicles and office equipment £m Total £m Net book value at 1 April 2022 225 70 — 210 505 Exchange adjustments 10 1 — 13 24 Additions 101 97 — 88 286 Disposals (13) — — (1) (14) Depreciation charge for the year (42) (18) — (70) (130) Net book value at 31 March 2023 281 150 — 240 671 Exchange adjustments (5) (2) — (5) (12) Additions 52 2 — 146 200 Reclassifications — (5) — 5 — Reclassification to held for sale (note 10) (12) — — (1) (13) Disposals (1) — — (2) (3) Depreciation charge for the year (22) (17) — (76) (115) Net book value at 31 March 2024 293 128 — 307 728 The following balances have been included in the income statement for the years ended 31 March 2024 and 31 March 2023 in respect of right-of- use assets: 2024 2023 £m £m Included within net finance income and costs: Interest expense on lease liabilities (69) (24) Included within revenue: Lease income 1 384 409 Included within operating expenses: Expense relating to short-term and low-value leases (20) (19) 1. Included within lease income is £360 million ( 2023 : £394 million ) of variable lease payments, the majority of which relates to the power supply arrangement entered into with LIPA (see note 3

Other non-current assets

Other non-current assets	12 Months Ended
	Mar. 31, 2024
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 specific non-current asset categories (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 2025. 2024 2023 £m £m Other receivables¹ 458 496 Prepayments² 390 124 848 620 1. Primarily comprises amounts due in relation to property sales to The Berkeley Group. These amounts will be fully received by 2031. 2. Included within prepayments are capital expenditure prepayments made to suppliers to secure production capacity for certain of our capital projects. In the year, we have also revised our policy in relation to the classification of capital expenditure prepayments between current and non-current in order to align these to the operating cycles of the underlying assets to which they relate. Accordingly, prior year non-current prepayments have increased by £53 million to reflect this change, with a corresponding reduction in current prepayments (note 19 ).

Financial and other investments

Financial and other investments	12 Months Ended
	Mar. 31, 2024
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 cannot 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 asset’s 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 three 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 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 which are held to back the present value of unfunded pension liabilities (see note 25 ); 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 by applying valuation techniques used by the relevant markets, including observable market data where possible (see note 32 (g) for further details). 15. Financial and other investments continued 2024 2023 £m £m Non-current FVOCI debt and other investments 397 407 FVTPL investments 483 452 880 859 Current FVTPL investments 3,084 1,764 Financial assets at amortised cost 615 841 3,699 2,605 4,579 3,464 Financial and other investments include the following: Investments in short-term money market funds 2,668 1,449 Investments held by National Grid Partners 375 346 Investments in Sunrun 108 106 Balances that are restricted or not readily used in operations: Collateral 1 496 764 Insurance company and non-qualified plan investments 578 490 Cash surrender value of life insurance policies 235 232 Other investments 119 77 4,579 3,464 1. The collateral balance includes £466 million ( 2023 : £734 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, £24 million ( 2023 : £25 million ) of restricted amounts allocated for specific projects within National Grid Electricity System Operator and National Grid Electricity Transmission plc and £6 million ( 2023 : £5 million ) insurance captive letters of credit. 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 have an average credit rating on a weighted basis of AA or better at all times based on investment policy. 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, 2024
Investments accounted for using equity method [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. 2024 2023 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 154 1,146 1,300 277 961 1,238 Exchange adjustments (3) (28) (31) 20 52 72 Additions 13 319 332 40 157 197 Share of post-tax results for the year 9 28 37 9 162 171 Share of other comprehensive income of associates, net of tax — — — 1 — 1 Dividends received (15) (152) (167) (30) (152) (182) Disposals¹ (1) — (1) (167) — (167) Other movements² 1 (51) (50) 4 (34) (30) Share of net assets at 31 March 158 1,262 1,420 154 1,146 1,300 1. Disposals in the prior year included the sale of the Group’s 26.25% minority ownership interest in the Millennium Pipeline Company LLC. 2. Other movements relate to tax liabilities for US and certain UK associates and joint ventures which are borne by the Group and the elimination of profits arising from sales to the Group’s share of joint ventures. 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 in relation to its joint ventures and associates of £1,286 million ( 2023 : £412 million ), which primarily relate to the funding of new capital investment projects. The following table describes the Group’s material joint ventures and associates at 31 March 2024 : Joint venture 1 % stake BritNed Development Limited 50% BritNed is a joint venture with the Dutch transmission system operator, TenneT, and operates the subsea electricity interconnector between Great Britain and the Netherlands, commissioned in 2011. Nemo Link Limited 50% Nemo is a joint venture with the Belgian transmission operator, Elia, and is a subsea electricity interconnector between Great Britain and Belgium, which became operational on 31 January 2019. Emerald Energy Venture, LLC 51% Emerald is a joint venture with Washington State Investment Board which builds and operates wind and solar assets. Emerald was acquired on 11 July 2019. Community Offshore Wind, LLC 27.3% Community Offshore Wind is a joint venture with RWE Renewables. The joint venture owns six seabed leases in the northeastern US and is developing an offshore wind project which will play a key role in supplying clean energy to customers in New York. 1. The joint ventures have reporting periods ending on 31 December with monthly management reporting information provided to the Group. 16. Investments in joint ventures and associates continued Summarised financial information as at 31 March, together with the carrying amount of material investments, is as follows: BritNed Development Limited Nemo Link Limited Emerald Energy Venture LLC Community Offshore Wind LLC 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Statement of financial position Non-current assets 376 397 478 514 2,171 1,598 1,005 925 Cash and cash equivalents 69 208 46 77 206 169 40 19 All other current assets 36 29 6 8 16 14 42 — Non-current liabilities (57) (55) (3) (3) (249) (244) (20) (19) Non-current financial liabilities (31) (31) (32) (32) (643) (398) — — Current liabilities (39) (34) (55) (131) (217) (131) (1) (3) Current financial liabilities — — — — (10) (95) — — Net assets 354 514 440 433 1,274 913 1,066 922 Group’s ownership interest in joint venture/associate 177 257 220 217 650 466 291 251 Group adjustment: elimination of profits on sales to joint venture — — — — (123) (85) — — Carrying amount of the Group’s investment 177 257 220 217 527 381 291 251 BritNed Development Limited Nemo Link Limited Emerald Energy Venture LLC Community Offshore Wind LLC 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Income statement Revenue 158 358 109 88 87 75 — — Depreciation and amortisation (16) (16) (23) (23) (38) (29) — — Other (costs)/income (25) 22 (15) (1) (152) (46) — 1 Operating profit/(loss) 117 364 71 64 (103) — — 1 Net interest expense (2) (2) — (7) (9) (6) — — Profit/(loss) before tax 115 362 71 57 (112) (6) — 1 Income tax expense (31) (82) (17) (11) — — — — Profit/(loss) for the year 84 280 54 46 (112) (6) — 1 Group’s share of profit/(loss) 42 140 27 23 (57) (3) — — Group adjustment: tax credit — — — — 15 1 — — Group’s share of post-tax results for the year 42 140 27 23 (42) (2) — — 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 2024 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. The Group does not have any branches. 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 US are taxed in the US 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). Birch Sites Limited Carbon Sentinel Limited Central Networks Trustees Limited 1 Hyder Profit Sharing Trustees Limited 1 Icelink Interconnector Limited Kelston Properties 2 Limited 1 Lattice Group Employee Benefit Trust Limited Lattice Group Limited Lattice Group Trustees Limited NatGrid One Limited 2 * NatgridTW1 Limited National Energy System Operator Limited National Grid (US) Holdings Limited 3 National Grid (US) Investments 2 Limited 2 * National Grid (US) Investments 4 Limited 3 National Grid (US) Partner 1 Limited 3 National Grid Carbon Limited National Grid Commercial Holdings Limited National Grid Continental Limited National Grid Distributed Energy Limited National Grid Electricity Distribution (East Midlands) plc 1 National Grid Electricity Distribution (South Wales) plc 1 National Grid Electricity Distribution (South West) plc 1 National Grid Electricity Distribution (West Midlands) plc 1 National Grid Electricity Distribution Generation Limited 1 National Grid Electricity Distribution Holdings Limited 1 National Grid Electricity Distribution Investments Limited 1 National Grid Electricity Distribution Midlands Limited 1 National Grid Electricity Distribution Network Holdings Limited 1 National Grid Electricity Distribution plc 1 National Grid Electricity Distribution Property Investments Limited 1 National Grid Electricity Group Trustee Limited National Grid Electricity System Operator Limited National Grid Electricity Transmission plc National Grid Energy Metering Limited National Grid Grain LNG Limited National Grid Helicopters Limited 1 National Grid Holdings Limited 3 National Grid Holdings One plc National Grid Hydrogen Limited National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited 3 National Grid Lion Link Limited National Grid Nautilus Limited National Grid North Sea Link Limited National Grid Partners Limited National Grid Plus Limited National Grid Property Holdings Limited National Grid Telecoms Limited 1 National Grid Twelve Limited National Grid Twenty Eight Limited National Grid Twenty Seven Limited National Grid Twenty Three Limited 2 * National Grid UK Limited National Grid UK Pension Services Limited 2 * National Grid Ventures Limited National Grid Viking Link Limited National Grid William Limited NG Nominees Limited 3 NGC Employee Shares Trustee Limited NGG Finance plc Ngrid Intellectual Property Limited Port Greenwich Limited Sheet Road Management Company Limited ( 51% ) 4 South Wales Electricity Share Scheme Trustees Limited 1 Thamesport Interchange Limited The National Grid Group Quest Trustee Company Limited Warwick Technology Park Management Company (No 2) Limited ( 60.56% ) 5 Western Power Pension Trustee Limited 1 WPD Share Scheme Trustees Limited 1 WPD WEM Holdings Limited 1 WPD WEM Limited 1 WW Share Scheme Trustees Limited 1 1. Registered office: Avonbank, Feeder Road, Bristol, Avon, BS2 0TB, UK. 2. Registered office: C/o Interpath Limited, 10 Fleet Place, London, EC4M 7RB, UK. 3. Companies where National Grid plc has issued guarantees over the liabilities of the companies as at 31 March 2024 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. 4. Registered office: Netley Old Hall Farm, Dorrington, Shrewsbury, SY5 7JY, UK. 5. Registered office: Shire Hall, PO Box 9, Warwick, CV34 4RL, UK. * In liquidation. Incorporated in the US Registered office: National Registered Agents, Inc., 1209 Orange Street, Wilmington, DE 19801, USA (unless stated otherwise in footnotes). Apple River Solar, LLC Armenia Solar, LLC Ashland Solar, LLC Athens Solar, LLC Autauga Solar, LLC Bazile Creek Wind Farm, LLC Bee Hollow Solar, LLC Belle Plaine Solar, LLC Benevolent Solar, LLC Blaze Solar, LLC Blevins Storage, LLC Blue Ridge Wind, LLC Blue Spring Solar, LLC Blues Solar, LLC Boone Solar, LLC Boston Gas Company 1 Brock Solar, LLC Broken Bridge Corp. 2 Brook Trout Solar, LLC Burley Solar, LLC Burr Ridge Wind, LLC Cage Ranch Solar II, LLC Cage Ranch Solar III, LLC Cage Ranch Solar, LLC Caldwell Solar II, LLC Caldwell Solar, LLC Camp Creek Wind Farm, LLC Carnation Solar, LLC Cattle Ridge Wind Farm 2, LLC Cedar Grove Solar, LLC Charter Oak Solar, LLC Charter Oak Storage, LLC Clay Boswell Solar, LLC Clermont Solar, LLC Coles Solar, LLC Compass Prairie Wind, LLC Conestoga Wind, LLC Creekview Solar, LLC Crocker Wind Farm 2, LLC Dakota Hills Wind Farm, LLC Deatsville Solar, LLC Donnellson Solar, LLC Doorstep Community LLC 3 Elburn Solar, LLC Eldena Solar, LLC Elk Creek Solar 2, LLC Elk Creek Solar, LLC EUA Energy Investment Corporation 1 Exie Solar, LLC Falls City Solar, LLC Firstview Wind Farm, LLC Fort Solar, LLC Front Range Wind Farm, LLC Galaxy Solar, LLC Golden Solar, LLC Goldendale Solar, LLC Goldenrod Wind Farm, LLC Goldfinch Solar, LLC Granite State Power Link LLC 3 Grant Solar 2, LLC Grant Solar, LLC Grayson Solar, LLC Greenbrier Creek Solar, LLC Greenwood Solar, LLC Grid NY LLC 4 Grindstone Wind Farm, LLC 5 Hale County Solar, LLC Hansford Energy Storage, LLC Harmony Solar ND 2, LLC Harmony Solar ND, LLC Harrington Solar, LLC Hartley Solar, LLC Hearth Solar, LLC High View Property, LLC Honeybee Solar, LLC Hoosier Solar, LLC Hoskins Solar, LLC Illumination Solar, LLC Itasca Energy Development, LLC 6 Itasca Energy Services, LLC Jack Rabbit Wind, LLC Jackson County Solar, LLC KeySpan CI Midstream Limited 3 KeySpan Energy Corporation 4 KeySpan Energy Services Inc. 3 KeySpan Gas East Corporation 4 KeySpan International Corporation 3 KeySpan MHK, Inc. 3 KeySpan Midstream, Inc. 3 KeySpan Plumbing Solutions, Inc. 4 Kit Carson Wind, LLC Kit Fox Storage, LLC Knox Solar, LLC Kota Storage, LLC KSI Contracting, LLC 3 KSI Electrical, LLC 3 KSI Mechanical, LLC 3 Lake Charlotte Solar, LLC Lakeside Solar, LLC Land Management & Development, Inc. 4 Landwest, Inc. 4 Lansing Solar, LLC Las Moras Storage, LLC Leola Wind Farm, LLC Liberty Solar, LLC Livingston County Solar, LLC Long Mount Storage, LLC Lordsburg Solar, LLC Louisa Solar, LLC Lowlands Solar, LLC Lydia Solar, LLC Massachusetts Electric Company 1 Maverick Wind Farm, LLC Meadowlands Solar, LLC Mentha Solar, LLC Metrowest Realty LLC 3 Millers Ferry Solar, LLC Morgan County Solar, LLC Morning Glory Solar, LLC 6 Muddy Creek Solar, LLC Mustang Ridge Wind Farm, LLC Mystic Steamship Corporation 7 Nantucket Electric Company 1 National Grid Development Holdings Corp. 3 National Grid Electric Services LLC 4 National Grid Energy Trading Services LLC 4 National Grid Engineering & Survey Inc. 4 National Grid Generation LLC 4 National Grid Generation Ventures LLC 4 National Grid Glenwood Energy Center LLC 3 National Grid IGTS Corp. 4 National Grid Insurance USA Ltd 8 National Grid LNG LLC 3 National Grid NE Holdings 2 LLC 1 National Grid North America Inc. 3 National Grid Partners Inc. 4 National Grid Partners LLC 3 National Grid Port Jefferson Energy Center LLC 3 National Grid Renewables Development, LLC National Grid Renewables E Wind, LLC 9 National Grid Renewables Operations, LLC 3 National Grid Renewables Projects, LLC 6 National Grid Renewables Stutsman, LLC National Grid Renewables, LLC 3 National Grid Services Inc. 3 National Grid US LLC 3 National Grid USA Service Company, Inc. 1 National Grid USA 3 NEES Energy, Inc. 1 New England Electric Transmission Corporation 2 New England Energy Incorporated 1 New England Hydro Finance Company, Inc. ( 53.704% ) 1 New England Hydro-Transmission Corporation ( 53.704% ) 2 New England Hydro-Transmission Electric Company, Inc. ( 53.704% ) 1 New England Power Company 1 Newport America Corporation 10 Newton Solar, LLC NG Renewables Energy Marketing, LLC 3 NG Renewables Energy Services, LLC NG Renewables Remote Operations Center, LLC NGNE LLC 3 NGV Emerald Energy Venture Holdings, LLC 3 NGV H2 Holdings LLC 3 NGV LNG Holdings LLC 3 NGV OSW Holdings, LLC 3 NGV US Distributed Energy Inc. 3 NGV US Transmission Inc. 3 NGV US, LLC 3 Niagara Mohawk Energy, Inc. 3 Niagara Mohawk Holdings, Inc. 4 Niagara Mohawk Power Corporation 4 Niobrara Wind, LLC NM Properties, Inc. 4 Noble Solar, LLC 11 Nordic VOS, LLC North East Transmission Co., Inc. 3 North Fork Wind, LLC Northeast Renewable Link LLC 3 Opinac North America, Inc. 3 Peony Solar, LLC Philadelphia Coke Co., Inc. 3 Pike County Solar, LLC Pipestone Solar, LLC Plum Creek Wind Farm 2, LLC Plum Creek Wind Farm, LLC Port of the Islands North, LLC 4 Portage Solar, LLC Prairie Oasis Solar, LLC Prairie Rose Wind 2, LLC 6 Prosperity Wind Farm 2, LLC Prosperity Wind Farm, LLC Red Rock Solar SD, LLC Regal Solar 2, LLC Regal Solar, LLC Reunion Solar, LLC River North Solar, LLC Robertson Solar, LLC Rock Ridge Wind Farm, LLC Rolling Hills Solar, LLC Royal Solar 2, LLC Royal Solar, LLC Royerton Solar, LLC Saginaw Bay Solar, LLC Saltillo Storage, LLC Sandstone Creek Solar 2, LLC Sandstone Creek Solar, LLC Sapphire Sky Wind Farm, LLC Sherco Solar 2, LLC 6 Sherco Solar 3, LLC Silver City Solar, LLC Simpson Solar, LLC Spring Brook Solar, LLC Spring River Solar, LLC Stony Brook Wind, LLC Stony Point Solar, LLC Stove Creek Solar, LLC Summit Lake Solar, LLC Sunbeam Solar, LLC Sunrise Solar, LLC Sycamore Creek Solar, LLC Tejano Storage, LLC Thacker Solar, LLC The Brooklyn Union Gas Company 4 Torchlight Solar, LLC 6 Transgas Inc. 1 Tri-City Solar, LLC Uintah Solar, LLC Upper Hudson Development, Inc. 4 Valley Solar, LLC Vermont Green Line Devco, LLC ( 90% ) 3 Violet Storage, LLC Virgo Community Solar Gardens, LLC 6 Virtue Solar, LLC Vivid Solar, LLC Wallowa Solar, LLC Wayfinder Group, Inc. 1 White Elm Wind Farm, LLC Wildcat Ridge Wind Farm, LLC Wilder Solar, LLC Wildhorse Creek Solar, LLC Willard Solar, LLC Williams County Solar, LLC Wiregrass Solar, LLC Woodlands Solar, LLC Worthington Solar, LLC Young County Solar, LLC Incorporated in Guernsey Registered office: 1st & 2nd Floors Elizabeth House, Les Ruettes Brayes, St Peter Port, GY1 1EW, Guernsey, Channel Islands NG Electricity Distribution Limited † Incorporated in Hong Kong Registered office: 5/F, Manulife Place, 348 Kwun Tong Road, Kowloon, 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 Incorporated in Luxembourg Registered office: 412F, Route d’Esch, L-2086, Luxembourg, Grand Duchy of Luxembourg National Grid Luxembourg SARL 1. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, USA. 2. Registered office: Corporation Service Company, 10 Ferry Street, Suite 313, Concord NH 03301, USA. 3. Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington DE 19808, USA. 4. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 5. Registered office: National Registered Agents Inc., 30600 Telegraph Road, Suite 2345, Bingham Farms MI 48025-5720, USA. 6. Registered office: 8400 Normandale Lake Blvd., Suite 1200, Bloomington MN 55437, USA. 7. Registered office: Corporation Trust Company, 1209 Orange Street, Wilmington DE 19801, USA. 8. Registered office: 100 Bank Street, Suite 630, Burlington, Chittenden County VT 05401, USA. 9. Registered office: National Registered Agents, Inc., 301 S. Bedford Street, Suite 1, Madison WI 5, USA. 10. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, USA. 11. Registered office: National Registered Agents, Inc., 1999 Bryan Street, Dallas TX 75201, USA. * In liquidation. † Entity is tax resident in the UK. A list of the Group’s joint ventures as at 31 March 2024 is given below. All joint ventures are included in the Group’s Financial statements using the equity method of accounting. Incorporated in England and Wales Registered office: 1–3 Strand, London, WC2N 5EH, UK (unless stated otherwise in footnotes). BritNed Development Limited ( 50% )** National Places LLP ( 50% ) 1 Nemo Link Limited ( 50% ) Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Community Offshore Wind, LLC (previously Bight Wind Holdings LLC) ( 27.27% ) 2 Clean Energy Storage Systems LLC ( 50% ) Emerald Energy Venture, LLC ( 51% ) Island Park Energy Center, LLC ( 50% ) LI Energy Storage System, LLC ( 50% ) LI Solar Generation, LLC ( 50% ) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, Paris La Defense, CEDEX, France IFA2 ( 50% )* Joint operations A list of the Group’s incorporated joint operations as at 31 March 2024 is given below. All joint operations are included in the Group’s financial statements under IFRS 11 Joint arrangements. Incorporated in England and Wales Registered office: 1–3 Strand, London, WC2N 5EH, UK (unless stated otherwise in footnotes). Eastern Green Link 1 Limited ( 50% ) Eastern Green Link 2 Limited ( 50% ) 3 NGET/SPT Upgrades Limited ( 50% ) † A list of the Group’s associates as at 31 March 2024 is given below. Unless otherwise stated, all associates are included in the Group’s financial statements using the equity method of accounting. Incorporated in England and Wales Registered office: National Grid House, Warwick Technology Park, Gallows Hill, Warwick, CV34 6DA GasT TopCo Limited ( 20% ) Joint Radio Company Limited ( 25% ) 4 *** 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% ) 2 Connecticut Yankee Atomic Power Company ( 19.5% ) 5 Direct Global Power Inc. ( 26% ) 2 Energy Impact Fund LP ( 9.41% ) 6 KHB Venture LLC ( 33.33% ) 7 Maine Yankee Atomic Power Company ( 24% ) 8 New York Transco LLC ( 28.3% ) 9 NYSEARCH RMLD, LLC ( 22.63% ) The Hive IV, LLC ( 28.2% ) 2 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 2024 is given below. Incorporated in England and Wales Registered office: 1 More London Place, London SE1 2AF, UK Energis plc ( 33.06% ) ‡ Registered office: Third Floor, Northumberland House, 303–306 High Holborn, London, WC1V 7JZ Electralink Limited ( 27.04% ) 1. Registered office: 80 Cheapside, London, EC2V 6EE, UK. 2. Registered office: The Corporation Trust Company, Corporation Trust Center, 1209 Orange Street, Wilmington DE 19801, USA. 3. Registered office: No.1 Forbury Place, 43 Forbury Road, Reading, RG1 3JH, UK. 4. Registered office: Friars House, Manor House Drive, Coventry, CV1 2TE, UK. 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, USA. 7. Registered office: c/o de maximis, 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. * In liquidation. ** National Grid Interconnector Holdings Limited owns 284,500,000 €0.20 C Ordinary shares and one £1.00 Ordinary A share. *** National Grid Electricity Transmission plc owns one £0.50 A Ordinary share. † 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 supported by guarantees issued by National Grid plc over their liabilities for the year ended 31 March 2024 : Company name Company number National Grid Holdings Limited 3096772 National Grid International Limited 2537092 National Grid (US) Holdings Limited 2630496 National Grid (US) Investments 4 Limited 3867128 National Grid (US) Partner 1 Limited 4314432 NG Nominees Limited 2489329

Derivative financial instrument

Derivative financial instruments	12 Months Ended
	Mar. 31, 2024
Disclosure of detailed information about 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 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: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current 44 (335) (291) 153 (222) (69) Non-current 324 (909) (585) 276 (1,071) (795) 368 (1,244) (876) 429 (1,293) (864) Financing derivatives 333 (1,126) (793) 363 (1,119) (756) Commodity contract derivatives 35 (118) (83) 66 (174) (108) 368 (1,244) (876) 429 (1,293) (864) (a) Financing derivatives The fair values of financing derivatives by type are as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Interest rate swaps 43 (110) (67) 49 (98) (49) Cross-currency interest rate swaps 234 (844) (610) 192 (888) (696) Foreign exchange forward contracts¹ 16 (68) (52) 100 (11) 89 Inflation-linked swaps 40 (104) (64) 22 (122) (100) 333 (1,126) (793) 363 (1,119) (756) 1. Included within the foreign exchange forward contracts balance are £36 million ( 2023 : £4 million ) of derivative liabilities in relation to the hedging of capital expenditure . 17. Derivative financial instruments continued (a) Financing derivatives continued The maturity profile of financing derivatives is as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than 1 year 18 (249) (231) 100 (93) 7 18 (249) (231) 100 (93) 7 Non-current In 1 to 2 years 6 (80) (74) 13 (100) (87) In 2 to 3 years 31 (44) (13) 15 (96) (81) In 3 to 4 years 32 (74) (42) 32 (11) 21 In 4 to 5 years 49 (83) (34) 14 (107) (93) More than 5 years 197 (596) (399) 189 (712) (523) 315 (877) (562) 263 (1,026) (763) 333 (1,126) (793) 363 (1,119) (756) The notional contract amounts of financing derivatives by type are as follows: 2024 2023 £m £m Interest rate swaps (2,175) (1,727) Cross-currency interest rate swaps (15,602) (15,025) Foreign exchange forward contracts (7,675) (5,263) Inflation-linked swaps (3,190) (2,387) (28,642) (24,402) (b) Commodity contract derivatives The fair values of commodity contract derivatives by type are as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Commodity purchase contracts accounted for as derivative contracts Forward purchases of gas — (3) (3) 2 (6) (4) Derivative financial instruments linked to commodity prices Electricity capacity — — — 1 — 1 Electricity swaps 33 (82) (49) 53 (92) (39) Electricity options — (1) (1) — (3) (3) Gas swaps 2 (22) (20) 9 (42) (33) Gas options — (10) (10) 1 (31) (30) 35 (118) (83) 66 (174) (108) 17. Derivative financial instruments continued (b) Commodity contract derivatives continued The maturity profile of commodity contract derivatives is as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than one year 26 (86) (60) 53 (129) (76) 26 (86) (60) 53 (129) (76) Non-current In 1 to 2 years 3 (28) (25) 11 (29) (18) In 2 to 3 years 5 (4) 1 2 (15) (13) In 3 to 4 years 1 — 1 — (1) (1) 9 (32) (23) 13 (45) (32) 35 (118) (83) 66 (174) (108) The notional quantities of commodity contract derivatives by type are as follows: 2024 2023 Forward purchases of gas 1 38m Dth 22m Dth Electricity swaps 14,128 GWh 14,076 GWh Gas swaps 44m Dth 50m Dth Gas options 78m Dth 57m Dth 1. Forward gas purchases have terms up to one year ( 2023 : one year ). The contractual obligations under these contracts are £14 million ( 2023 : £24 million ) .

Inventories and current intangi

Inventories and current intangible assets	12 Months Ended
	Mar. 31, 2024
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 directly 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. 2024 2023 £m £m Fuel stocks 188 280 Raw materials and consumables 542 460 Current intangible assets – emission allowances 98 136 828 876 There is a provision for obsolescence of £4 million against inventories as at 31 March 2024 ( 2023 : £6 million ).

Trade and other receivables

Trade and other receivables	12 Months Ended
	Mar. 31, 2024
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 12 months. Trade and other receivables are initially recognised at fair value, except for trade receivables that do not have a significant financing component which are measured at transaction price, and are subsequently measured at amortised cost, less any appropriate allowances for estimated irrecoverable amounts. 2024 2023 £m £m Trade receivables 2,501 2,583 Accrued income 885 1,126 Provision for impairment of receivables and accrued income (559) (560) Trade receivables and accrued income, net 2,827 3,149 Prepayments¹ 385 389 Contract assets 76 49 Other receivables 127 243 3,415 3,830 1. In the year, we have revised our policy in relation to the classification of capital expenditure prepayments between current and non-current in order to align these to the operating cycles of the underlying assets to which they relate. Accordingly, prior year current prepayments have decreased by £53 million to reflect this change, with a corresponding increase in non-current prepayments (note 14 ). Trade receivables are non-interest-bearing and generally have a term of up to 60 days. Due to their short maturities, the fair value of trade and other receivables approximates their carrying value. The maximum exposure of trade and other receivables to credit risk is the carrying amount reported on the balance sheet. 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. 2024 2023 £m £m At 1 April 560 741 Exchange adjustments (12) 51 Charge for the year, net of recoveries 179 220 Uncollectible amounts written off (163) (452) Reclassification to held for sale (note 10) (5) — At 31 March 559 560 The trade receivables balance, accrued income balance and provisions balance split by geography are as follows: As at 31 March 2024 As at 31 March 2023 UK US Total UK US Total £m £m £m £m £m £m Trade receivables 162 2,339 2,501 223 2,360 2,583 Accrued income 337 548 885 650 476 1,126 Provision for impairment of receivables and accrued income (3) (556) (559) (11) (549) (560) 496 2,331 2,827 862 2,287 3,149 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, £2,437 million ( 2023 : £2,325 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 forecast economic conditions at the balance sheet date. The inclusion of forward-looking information in the provision matrix-setting process under IFRS 9 results 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 business temporarily 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. Customer termination activities also ceased in line with requests by relevant local authorities and this resulted in the recognition of additional expected credit losses, although cash collection and customer termination activities have subsequently resumed in both New England and New York. In the years ended 31 March 2024 and 2023 , the Group’s US distribution businesses have been supported by certain government and state COVID-19 funding programmes, including the Arrears Management Program in New York, aimed to provide low-income customers with COVID-19 relief via one-time bill credits. In the prior year, the Group wrote off £270 million ( $333 million ) of COVID-19-related trade receivables in connection with the Arrears Management Program, which was funded via the receipt of £44 million ( $51 million ) of government funding. 19. Trade and other receivables continued Provision for impairment of receivables continued In calculating our provision for impairment of receivables at 31 March 2024 , we incorporate actual cash collection levels experienced over a three -year period to determine the expected loss rates per category of outstanding receivable by operating company. These are benchmarked against provision matrices run on pre‑COVID-19 behaviour and data. Factored into our analysis are expected cash collections based on the resumed collection activities in New England and New York, as well as the impacts of government and state funding programmes and the outlook for the wider macroeconomic environment. The resulting rates are summarised in the provision matrix shown below. Based on our review, we recognised a charge of £176 million ( 2023 : £215 million ), which represents our best estimate based on the information available. We based our review on certain macroeconomic factors, including unemployment levels, inflation, average commodity rate changes and our experience regarding debtor recoverability. In performing our review of actual cash collection levels, we also factor in the impacts of government and state COVID-19 funding programmes in order to reflect an expected collection rate. The average expected loss rates and gross balances for the retail customer receivables in our US operations are set out below. Loss rates have decreased across the majority of our ageing categories, primarily due to the impact of ongoing cash collection activities. 2024 2023 % £m % £m Accrued income 3 533 3 462 0 – 30 days past due 3 822 3 838 30 – 60 days past due 14 219 13 235 60 – 90 days past due 21 125 23 139 3 – 6 months past due 27 173 32 189 6 – 12 months past due 34 191 43 178 Over 12 months past due 73 374 88 284 2,437 2,325 US retail customer receivables are not collateralised. Trade receivables are written off when regulatory requirements are met. Write-off policies vary between jurisdictions as they are aligned with the local regulatory requirements, which differ between regulators. There were no significant amounts written off during the period that were still subject to enforcement action. Our internal definition of default is aligned with that of the individual regulators in each jurisdiction. For further information on our wholesale and retail credit risk, refer to note 32 (a).

Cash and cash equivalents

Cash and cash equivalents	12 Months Ended
	Mar. 31, 2024
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. 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). Cash and cash equivalents at 31 March 2024 include £11 million ( 2023 : £37 million ) that is restricted. The restricted cash balances include amounts required to be maintained for insurance purposes and cash balances that can only be used for low-carbon network fund projects. 2024 2023 £m £m Cash at bank 259 163 Short-term deposits 300 — Cash and cash equivalents 559 163

Borrowings

Borrowings	12 Months Ended
	Mar. 31, 2024
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 inflation indices. 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 lead us to fund our networks within a certain ratio of debt to equity or regulatory asset 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. Borrowings, which include interest-bearing 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. 2024 2023 £m £m Current Bank loans 460 381 Bonds 2,841 1,638 Commercial paper 1,444 840 Lease liabilities 114 96 4,859 2,955 Non-current Bank loans 2,434 2,557 Bonds 39,114 36,855 Lease liabilities 665 618 42,213 40,030 Total borrowings 47,072 42,985 Total borrowings are repayable as follows: 2024 2023 £m £m Less than 1 year 4,859 2,955 In 1 to 2 years 2,706 2,799 In 2 to 3 years 3,134 2,689 In 3 to 4 years 2,948 3,129 In 4 to 5 years 4,375 2,505 More than 5 years: By instalments 736 922 Other than by instalments 28,314 27,986 47,072 42,985 The fair value of borrowings, excluding lease liabilities, at 31 March 2024 was £42,617 million ( 2023 : £38,219 million ). Where market values were available, the fair value of borrowings (Level 1) was £34,281 million ( 2023 : £31,710 million ). Where market values were not available, the fair value of borrowings (Level 2) was £8,336 million ( 2023 : £6,509 million ) and calculated by discounting cash flows at prevailing interest rates. The notional amount outstanding of the debt portfolio at 31 March 2024 was £46,141 million ( 2023 : £42,353 million ). There have been no new issuances since the year end. 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 £72 million ( 2023 : £111 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. 21. Borrowings continued Lease liabilities 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, 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 as well as 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. 2024 2023 £m £m Gross lease liabilities are repayable as follows: Less than 1 year 133 118 1 to 5 years 370 318 More than 5 years 507 480 1,010 916 Less: finance charges allocated to future periods (231) (202) 779 714 The present value of lease liabilities are as follows: Less than 1 year 114 96 1 to 5 years 300 269 More than 5 years 365 349 779 714 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 are undrawn. An analysis of the maturity of our undrawn committed facilities as at 31 March 2024 is shown below: 2024 2023 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — 42 In 1 to 2 years — 4,361 In 2 to 3 years 195 2,100 In 3 to 4 years 5,859 — In 4 to 5 years 106 — More than 5 years 1,745 — 7,905 6,503 Of the unused facilities at 31 March 2024 , £7,864 million ( 2023 : £6,461 million ) is available for liquidity purposes, while £41 million ( 2023 : £42 million )

Trade and other payables

Trade and other payables	12 Months Ended
	Mar. 31, 2024
Trade and other payables [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. 2024 2023 £m £m Trade payables 2,786 3,249 Deferred payables 327 404 Customer contributions 1 34 171 Social security and other taxes — 240 Contingent consideration — 19 Other payables² 929 985 4,076 5,068 1. Relates to amounts received from government-related entities for connecting to our networks, where we have obligations remaining under the contract. 2. Included within other payables are payments due in respect of interconnector excess revenues in accordance with the cap and floor regime constructed by Ofgem (see note 3 ). Due to their short maturities, the fair value of trade and other payables approximates their carrying value.

Contract liabilities

Contract liabilities	12 Months Ended
	Mar. 31, 2024
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. 2024 2023 £m £m Current 127 252 Non-current 2,119 1,754 2,246 2,006 Significant changes in the contract liabilities balances during the period are as follows: 2024 2023 £m £m As at 1 April 2,006 1,472 Exchange adjustments (27) 54 Revenue recognised that was included in the contract liability balance at the beginning of the period (252) (292) Increases due to cash received, excluding amounts recognised as revenue during the period 519 772 At 31 March 2,246 2,006

Other non-current liabilities

Other non-current liabilities	12 Months Ended
	Mar. 31, 2024
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 2025 . 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. 2024 2023 £m £m Deferred income 11 84 Customer contributions 1 411 421 Other payables² 458 416 880 921 1. Relates to amounts received from government-related entities for connecting to our networks, where we have obligations remaining under the contract. 2. Included within other payables are payments due in respect of the IFA1 interconnector in accordance with the Use of Revenue regime constructed by Ofgem. 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, 2024
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 ‘Employee Benefits’. We separately present our UK and US pension plans to show the 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. UK pension plans Defined contribution plan UK employees are eligible to join the National Grid UK Retirement Plan (NGUKRP), a section of a Master Trust arrangement managed by Legal & General. During the year, ongoing DC pension provision for NGED employees was transferred from the Western Power Pension Scheme (WPPS) to the NGUKRP to align benefit provision across the UK. National Grid pays contributions into the NGUKRP to provide DC benefits on behalf of its employees, generally providing a double match of member contributions up to a maximum Company contribution of 12% of salary. Investment risks are borne by the member and there is no legal or constructive obligation on National Grid to pay additional contributions in the instance that investment performance is poor. Payments to these DC plans are charged as an expense as they fall due. Defined benefit plans National Grid operates various DB pension arrangements in the UK. These include Section A of the National Grid UK Pension Scheme (Section A of NGUKPS), three sections of the industry-wide Electricity Supply Pension Scheme (ESPS), a legacy scheme (WPUPS), a DB section within WPPS and some unfunded pension obligations. Each of these plans holds assets in separate Trustee administered funds. The arrangements are managed by Trustee companies with boards consisting of company and member appointed Directors. These plans are all closed to new members, except for the ESPS schemes in very rare circumstances. The ESO is expected to transfer out of the Group, with business separation expected to take place in the summer of 2024. As a result, the ESO’s share of pension assets and liabilities has been reallocated as held for sale (see note 10 ). The arrangements are subject to independent actuarial funding valuations carried out by the Trustees every three years . Following consultation and agreement with the Company, 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 latest full actuarial valuations for each of the DB plans were carried out at 31 March 2022, with three of the plans showing a funding shortfall at the valuation date. These shortfalls were funded via recovery plan payments from the Company totalling approximately £100 million , with £12 million of those still due to be paid as at 31 March 2024. The Company also funds the cost of future benefit accrual (over and above member contributions) for each of the DB plans, with the aggregate level of ongoing contributions (excluding recovery plan payments) over the year to 31 March 2024 totalling £95 million ( 2023 : £74 million ). For some of the DB plans, the Company also pays contributions in respect of the costs of plan administration and the Pension Protection Fund (PPF) levies. The Company has also established security arrangements with some of the DB plans. This includes contingent security provided to National Grid Electricity Group (NGEG) of ESPS in the form of surety bonds, letters of credit or cash payments which are implemented if certain trigger events occur in respect of National Grid Electricity Transmission plc. The security, which is currently capped at £180 million , would then become payable to NGEG on certain company-related events, such as loss of licence or insolvency. In respect of Section A of NGUKPS, there is a guarantee in place which is enforceable 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. US pension plans The US pension plans are governed by the Retirement Plan Committee (RPC), a fiduciary committee. The RPC is structured in accordance with US laws governing retirement plans under the Employee Retirement Income Security Act (ERISA) and comprises appointed employees of the Company. Defined contribution plan National Grid has a DC pension plan which allows employee as well as Company contributions. Non-union employees hired after 1 January 2011, as well as most new hire union employees, receive a core contribution into the DC plan ranging from 3% to 9% of salary, irrespective of the employee’s contribution into the plan. Most employees also receive a matching contribution that varies between 25% and 50% of employee contributions up to a maximum Company contribution of 8% . The assets of the plans are held in trusts and administered by the RPC. 25. Pensions and other post-retirement benefits continued US pension plans continued Defined benefit plans National Grid sponsors four non-contributory qualified DB pension plans, which provide vested non-union employees hired before 1 January 2011, and vested eligible union employees, 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 closed group of current and former employees with designated company investments set aside to fund these obligations. 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. 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 £26 million ( 2023 : £76 million ). In both the current and prior year, some of our US DB pension plans undertook annuity buyout transactions in which a portion of existing retiree pension payments were transferred to a reputable insurance company in exchange for single bulk premium payments. As a result, all associated financial, governance and administrative responsibilities for those payments were transferred to the selected insurer. US other post-retirement benefits National Grid provides post-retirement healthcare and life insurance benefits to eligible employees. 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 £21 million ( 2023 : £11 million ). In the prior year, several post-retirement benefit plans were consolidated in an effort to simplify the plan and trust structure. This consolidation did not impact the benefits or plan obligations. Actuarial assumptions 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. 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. The sensitivities to significant risks are disclosed in note 35 . 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 Company has applied the following financial assumptions in assessing DB liabilities: UK pensions US pensions US other post-retirement benefits 2024 2023 2022 2024 2023 2022 2024 2023 2022 % % % % % % % % % Discount rate – past service 4.87 4.80 2.78 5.15 4.85 3.65 5.15 4.85 3.65 Discount rate – future service 4.92 4.80 2.85 5.15 4.85 3.65 5.15 4.85 3.65 Rate of increase in RPI – past service 3.05 3.17 3.60 n/a n/a n/a n/a n/a n/a Rate of increase in RPI – future service 2.92 3.07 3.33 n/a n/a n/a n/a n/a n/a Salary increases 3.10 3.11 3.47 4.50 4.50 4.60 4.50 4.50 4.60 Initial healthcare cost trend rate n/a n/a n/a n/a n/a n/a 7.10 6.80 6.80 Ultimate healthcare cost trend rate n/a n/a n/a n/a n/a n/a 4.50 4.50 4.50 For UK pensions, single equivalent financial assumptions are shown above for presentational purposes, although full yield curves have been used in our calculations. 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. Our DB plans in the UK provide for pension increases that are generally linked to Retail Price Index (RPI), subject to relevant caps and floors. 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 2033 ( 2023 : 2031 ). 25. Pensions and other post-retirement benefits continued Actuarial assumptions continued The table below sets out the projected life expectancies adopted for the UK and US pension arrangements: UK pensions US pensions 2024 2023 2022 2024 2023 2022 years years years years years years Assumed life expectations for a retiree age 65 Males 21.5 21.9 22.0 21.6 21.6 21.4 Females 23.5 23.7 23.8 23.9 23.8 23.6 In 20 years: Males 22.6 23.0 23.2 23.3 23.2 23.1 Females 24.9 25.1 25.2 25.5 25.4 25.3 The weighted average duration of the DB obligation for each category of plan is 11 years for UK pension plans, 11 years for US pension plans and 12 years for US other post-retirement benefit plans. The table below summarises the split of DB obligations by status for each category of plan: UK pensions US pensions US other post-retirement benefits 2024 2023 2024 2023 2024 2023 % % % % % % Active members 14 14 37 37 29 33 Deferred members 8 9 10 9 — — Pensioner members 78 77 53 54 71 67 Amounts recognised in the consolidated statement of financial position 2024 2023 £m £m Present value of funded obligations (17,601) (18,934) Fair value of plan assets 19,733 21,246 2,132 2,312 Present value of unfunded obligations (266) (292) Other post-employment liabilities (52) (69) Net defined benefit asset 1,814 1,951 Represented by: Liabilities (593) (694) Assets 2,407 2,645 1,814 1,951 The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Present value of funded obligations (10,465) (10,906) (4,702) (5,502) (2,434) (2,526) (17,601) (18,934) Fair value of plan assets 11,782 12,578 5,320 6,060 2,631 2,608 19,733 21,246 1,317 1,672 618 558 197 82 2,132 2,312 Present value of unfunded obligations (56) (58) (210) (234) — — (266) (292) Other post-employment liabilities — — — — (52) (69) (52) (69) Net defined benefit asset 1,261 1,614 408 324 145 13 1,814 1,951 Represented by: Liabilities (56) (58) (210) (234) (327) (402) (593) (694) Assets 1,317 1,672 618 558 472 415 2,407 2,645 1,261 1,614 408 324 145 13 1,814 1,951 The recognition of the pension assets in the UK and in the US reflects legal and actuarial advice that we have taken regarding recognition of surpluses under IFRIC 14. In the UK, the Group has an unconditional right to a refund in the event of a winding up. In the US, surplus assets of a plan may be used to pay for future benefits expected to be earned under that plan. 25. Pensions and other post-retirement benefits continued Amounts recognised in the income statement and statement of other comprehensive income The expense or income arising from all Group retirement benefit arrangements recognised in the Group income statements is shown below: 2024 2023 2022 £m £m £m Included within operating costs Administration costs 22 19 20 Included within payroll costs Defined benefit plan costs: Current service cost 143 194 223 Past service cost – augmentations and redundancies 9 8 11 Gains on settlement (30) (45) — 122 157 234 Included within finance income and costs Net interest income (100) (85) (2) Total included in income statement 1 44 91 252 Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations (218) (1,364) 2,481 Exchange adjustments (6) 41 7 Total included in the statement of other comprehensive income² (224) (1,323) 2,488 1. Amounts shown in the table above include operating costs of £nil ( 2023 : £nil ; 2022 : £4 million ); payroll costs of £nil ( 2023 : £nil ; 2022 : £10 million ); and net interest income of £nil ( 2023 : £nil ; 2022 : £2 million ) presented within profit from discontinued operations. These amounts all relate to UK pensions. 2. Amounts shown in the table above include remeasurements of pension assets and post-retirement benefit obligations of £nil ( 2023 : £nil ; 2022 : £309 million gain ) presented within discontinued operations. These amounts all relate to UK pensions. The geographical split of pensions and other post-retirement benefits is shown below: UK pensions US pensions US other post-retirement benefits 2024 2023 2022 2024 2023 2022 2024 2023 2022 £m £m £m £m £m £m £m £m £m Included within operating costs Administration costs 13 9 11 7 8 7 2 2 2 Included within payroll costs Defined benefit plan costs: Current service cost 45 69 83 72 88 101 26 37 39 Past service cost – augmentations and redundancies 9 8 11 — — — — — — Gains on settlement — — — (30) (45) — — — — 54 77 94 42 43 101 26 37 39 Included within finance income and costs Net interest (income)/cost (84) (64) (7) (13) (21) — (3) — 5 Total included in income statement (17) 22 98 36 30 108 25 39 46 Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations (474) (1,183) 1,577 99 (242) 532 157 61 372 Exchange adjustments — — — (5) 36 11 (1) 5 (4) Total included in the statement of other comprehensive income (474) (1,183) 1,577 94 (206) 543 156 66 368 25. Pensions and other post-retirement benefits continued Reconciliation of the net defined benefit asset UK pensions US pensions US other post-retirement benefits Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Opening net defined benefit asset 1,614 2,590 324 484 13 1 1,951 3,075 Income/(cost) recognised in the income statement (including discontinued operations) 17 (22) (36) (30) (25) (39) (44) (91) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (474) (1,183) 94 (206) 156 66 (224) (1,323) Employer contributions 118 197 26 76 21 11 165 284 Other movements 3 2 — — (20) (26) (17) (24) Reclassification to held for sale (note 10) (17) 30 — — — — (17) 30 Closing net defined benefit asset 1,261 1,614 408 324 145 13 1,814 1,951 Changes in the present value of defined benefit obligations (including unfunded obligations) The table below shows the movement in defined benefit obligations across our DB plans over the year. UK pensions US pensions US other post-retirement benefits Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Opening defined benefit obligations (10,964) (14,275) (5,736) (6,779) (2,526) (2,813) (19,226) (23,867) Current service cost (45) (69) (72) (88) (26) (37) (143) (194) Interest cost (536) (334) (258) (252) (117) (111) (911) (697) Actuarial (losses)/gains – experience (2) (235) (34) (17) 73 48 37 (204) Actuarial gains/(losses) – demographic assumptions 98 135 12 5 (4) 10 106 150 Actuarial gains/(losses) – financial assumptions 165 3,167 190 818 (7) 443 348 4,428 Past service cost – augmentations and redundancies (9) (8) — — — — (9) (8) Liabilities extinguished on settlements — — 543 616 — — 543 616 Medicare subsidy received — — — — (26) (28) (26) (28) Employee contributions (10) (10) — — — — (10) (10) Benefits paid 710 711 312 426 152 153 1,174 1,290 Exchange adjustments — — 131 (465) 58 (191) 189 (656) Reclassification from other post-employment liabilities — — — — (11) — (11) — Reclassification to held for sale (note 10) 72 (46) — — — — 72 (46) Closing defined benefit obligations (10,521) (10,964) (4,912) (5,736) (2,434) (2,526) (17,867) (19,226) Changes in the value of plan assets The table below shows the movement in pension assets across our DB plans over the year. UK pensions US pensions US other post-retirement benefits Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Opening fair value of plan assets 12,578 16,865 6,060 7,263 2,608 2,885 21,246 27,013 Interest income 620 398 271 273 120 111 1,011 782 Return on plan assets (less than)/in excess of interest (735) (4,250) (69) (1,048) 95 (440) (709) (5,738) Administration costs (13) (9) (7) (8) (2) (2) (22) (19) Assets distributed on settlements — — (513) (571) — — (513) (571) Employer contributions 118 197 26 76 21 11 165 284 Employee contributions 10 10 — — — — 10 10 Benefits paid (707) (709) (312) (426) (152) (153) (1,171) (1,288) Exchange adjustments — — (136) 501 (59) 196 (195) 697 Reclassification to held for sale (note 10) (89) 76 — — — — (89) 76 Closing fair value of plan assets 11,782 12,578 5,320 6,060 2,631 2,608 19,733 21,246 Actual return on plan assets (115) (3,852) 202 (775) 215 (329) 302 (4,956) Expected contributions to plans in the following year 108 99 28 36 15 14 151 149 25. Pensions and other post-retirement benefits continued Asset allocations The allocation of assets by asset class is set out below. Within these asset allocations there is significant diversification across regions, asset managers, currencies and bond categories. UK pensions 2024 2023¹ 2022¹ Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 576 153 729 475 179 654 1,458 324 1,782 Corporate bonds 1,910 — 1,910 1,892 — 1,892 2,741 — 2,741 Government securities and liability- driven investments — 5,259 5,259 2 762 4,906 5,668 2,3 786 5,768 6,554 2,3 Property — 679 4 679 23 860 4 883 122 1,002 4 1,124 Diversified alternatives 669 572 1,241 708 680 1,388 1,334 582 1,916 Buy-in/bulk annuity policies — 2,060 2,060 — 2,126 2,126 5 78 2,706 2,784 5 Longevity swap — (94) (94) — (88) (88) — (80) (80) Cash and cash equivalents 3 — 3 8 — 8 38 — 38 Other (including net current assets and liabilities) — (5) (5) 59 (12) 47 16 (10) 6 3,158 8,624 11,782 6 3,927 8,651 12,578 6 6,573 10,292 16,865 6 1. Comparative amounts have been represented to reflect the reclassification of assets associated with liability driven investment strategies as unquoted following an internal asset categorisation review. 2. Included within government securities and liability-driven investments above is £2.7 billion ( 2023 : £3.4 billion ; 2022 : £6.1 billion ) of repurchase agreements. These are used to increase the market exposure of the liability-matching portfolios. 3. This asset class has been redefined to include liability driven investments totalling £4,906 million ( 2022 : £5,857 million ). These were previously allocated in other asset classes, primarily buy-in/bulk annuity policies. 4. Includes £288 million ( 2023 : £304 million ; 2022 : £283 million ) of investments in forestry funds. 5. This asset class has been redefined to only include the value of buy-in/bulk annuities and therefore has been restated to exclude the value of liability-driven investments. 6. The fair value of plan assets includes employer-related investment exposure of £44 million ( 2023 : £23 million ; 2022 : £32 million ). US pensions 2024 2023¹ 2022¹ Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 99 1,224 1,323 154 1,346 1,500 272 1,904 2,176 Corporate bonds 1,987 403 2,390 2,147 528 2,675 2,311 697 3,008 Government securities 360 444 804 410 514 924 335 715 1,050 Property — 237 237 — 299 299 — 295 295 Diversified alternatives 54 502 556 85 550 635 142 546 688 Cash and cash equivalents 9 — 9 16 — 16 31 — 31 Other (including net current assets and liabilities) 1 — 1 7 4 11 12 3 15 2,510 2,810 5,320 2,819 3,241 6,060 3,103 4,160 7,263 1. Comparative amounts have been represented to reflect the reclassification of infrastructure assets following an internal asset categorisation review. US other post-retirement benefits 2024 2023 2022 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 37 524 561 74 510 584 185 1,013 1,198 Corporate bonds 1,351 46 1,397 1,332 2 1,334 723 2 725 Government securities 410 1 411 431 2 433 511 2 513 Diversified alternatives 92 9 101 100 9 109 144 120 264 Other 1 — 161 161 1 147 148 — 185 185 1,890 741 2,631 1,938 670 2,608 1,563 1,322 2,885 1. Other primarily comprises insurance contracts. Main defined benefit risks National Grid underwrites the financial and demographic risks associated with the Group’s DB 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. 25. Pensions and other post-retirement benefits continued Main defined benefit risks continued The most significant risks associated with the DB plans are as follows: Main risks Description and mitigation Investment risk The plans invest in a variety of asset classes, with actual returns likely to differ from the underlying discount rate adopted, impacting on 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. Changes in bond yields Liabilities will fluctuate as yields change. Volatility of the net balance sheet asset or liability is controlled through liability- matching strategies. The investment strategies allow for the use of synthetic as well as physical assets to be used to hedge interest rate risk. Inflation risk Changes in inflation will affect 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. The investment strategies allow for the use of synthetic as well as physical assets to be used to hedge inflation risk. Member longevity 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 scheme investment transactions including a longevity insurance contract (longevity swap) for NGEG of ESPS and two buy-in policies for Section A of NGUKPS. Counterparty risk This 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. Default risk Debt investments are predominantly made in regulated markets in assets considered to be of investment grade. Where investments are made either in non-investment grade assets or outside of regulated markets, investment levels are kept to prudent levels and subject to agreed ranges, to control the risk. Liquidity risk The pension plans hold sufficient cash to meet benefit requirements, with other investments being held in liquid or realisable assets to meet unexpected cash flow requirements. These could include collateral calls relating to the plans’ liability- matching assets which could result from extreme market movements. Should the plans not have sufficient liquidity to meet cash flow requirements, they could be forced to take sub-optimal investment decisions such as selling assets at a reduced price. The plans do not borrow money, or act as guarantor, to provide liquidity to other parties (unless it is temporary). Currency risk Fluctuations in the value of foreign denominated assets due to exposure to currency exchange rates are managed through currency hedging overlay and currency hedging carried out by some of the investment managers. In June 2023, the UK High Court issued a ruling in the case of Virgin Media Limited versus NTL Pension Trustees II Limited and others relating to the validity of certain historical pension changes. This case may have implications for other defined benefit schemes in the UK, although it is subject to possible appeal in 2024. The Group has performed an initial review of past significant changes made to its pension arrangements. Based on this initial review, there is no financial impact from the ruling of the case, although the Group will monitor the impact of future developments. Investment strategies The Trustees and RPC, after taking advice from professional investment advisors and in consultation with National Grid, set their key principles, including expected returns, risk and liquidity requirements. They formulate an investment strategy to manage risk through diversification, taking into account expected contributions, maturity of the pension liabilities and, in the UK, the strength of the covenant. These strategies allocate investments between return-seeking assets such as equities and property, and liability-matching assets such as buy-in policies, government securities and corporate bonds which are intended to protect the funding position. The approximate investment allocations for our plans at 31 March 2024 are as follows: UK pensions US pensions US other post- retirement benefits % % % Return-seeking assets 22 40 31 Liability-matching assets 78 60 69 The governing bodies generally delegate responsibility for the selection of specific bonds, securities and other investments to appointed investment managers, who are selected based on the required skills, expertise in those markets, process and financial security to manage the investments. Their performance is regularly reviewed against measurable objectives, consistent with each pension plan’s long-term objectives and accepted risk levels. In the UK, each of our pension plans has Responsible Investment (RI) Policies, which consider ESG factors and generally incorporate the six UN‑backed Principles for Responsible Investment (UNPRI). While each Trustee board understands its fiduciary responsibility to maximise return on investments based on an appropriate level of risk, they each also recognise that ESG factors can be material to financial outcomes and can have a potential impact on the quality and sustainability of long-term investment returns. The principal defined contribution arrangement in the UK embeds ESG factors in the investment options offered to members. As well as offering a range of self‑select ethical funds, it directly incorporates its Climate Impact Pledge into the default investment option, which acts to align the fund to a carbon net zero future. Whilst in the US there is no regulatory requirement to have ESG-specific principles embedded in investment policies, our investment managers often utilise ESG principles to inform their decision-making process.

Provisions

Provisions	12 Months Ended
	Mar. 31, 2024
Other provisions [abstract]
Provisions	26. Provisions Provisions are recognised where a legal or constructive obligation exists at the reporting date, as a result of a past event, where the outflow of economic benefit is probable and where the amount of the obligation can be reliably estimated. Provisions are recognised for the costs of environmental remediation; decommissioning costs for certain assets that we are required to remove at the end of their useful economic lives; restructuring costs; and for certain other situations where the above thresholds are met. Long-term provisions are measured based on management’s best estimates of the likely cash flows, discounted at an appropriate discount rate. The unwinding of the discount is included within the income statement within finance costs. Short-term provisions are measured at the expected cash outflow and are not discounted. Environmental £m Decommissioning £m Other £m Total provisions £m At 1 April 2022 1,877 258 404 2,539 Exchange adjustments 114 5 12 131 Additions 142 91 222 455 Unused amounts reversed (38) (10) (14) (62) Adjustment for change in discount rate¹ (176) (48) — (224) Unwinding of discount 72 10 6 88 Utilised (100) (9) (176) (285) At 31 March 2023 1,891 297 454 2,642 Exchange adjustments (37) (2) (8) (47) Additions² 600 34 138 772 Unused amounts reversed (18) (7) (100) (125) Adjustment for change in discount rate 4 29 — 33 Unwinding of discount 85 11 6 102 Utilised (107) (9) (149) (265) Reclassification to held for sale (note 10) — — (3) (3) At 31 March 2024 2,418 353 338 3,109 2024 2023 £m £m Current 298 288 Non-current 2,811 2,354 3,109 2,642 1. In the prior year, environmental provisions in the US and the UK decreased by £176 million as a result of the change in the real discount rate from 0.5% to 1.5% . The impact of the change in discount rate to the decommissioning provisions was recognised against the carrying amount of property, plant and equipment (see note 13 ). 2. Included within additions is a £496 million increase in provision related to changes in the scope of work required on the Group’s clean-up operations on the Gowanus Canal and nearby legacy MGP sites in Brooklyn, New York. These arose from remediation design changes as communicated in the year by US environmental agencies. 26. Provisions continued Environmental provisions We recognise environmental provisions for 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: 2024 2023 Discounted £m Real undiscounted £m Real discount rate Discounted £m Real undiscounted £m Real discount rate UK sites 108 118 1.0 % 123 138 1.5 % US sites 2,310 2,579 1.5 % 1,768 2,006 1.5 % 2,418 2,697 1,891 2,144 Remediation expenditure in the US is expected to be incurred until 2071 , of which the majority relates to three Superfund sites (being sites where hazardous substances are present as a result of the historical operations of manufacturing gas plants previously owned or operated by the Group or its predecessor companies in Brooklyn, New York). The weighted average duration of the forecasted cash flows is 10 years . Under the terms of our rate plans, we are entitled to recovery of environmental clean-up costs from rate payers. 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 2070 . The real undiscounted amount is management’s best estimate of the actual cash flows that will be required. The provisions are calculated based on these cash flows discounted at the appropriate real discount rate for the jurisdiction, which is determined using the relevant government bond yield curve and the weighted average life of the provisions. Numerous estimation uncertainties affect the calculation of these provisions, including the impact of and possibility of changes to regulatory requirements, the accuracy of site surveys, unexpected contaminants, the scope of remediation work, transportation costs, the impact of alternative technologies, the expected timing, cost and duration of cash flows, and changes in the real discount rate. These provisions incorporate 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. Changes in the provision arising from revised estimates, discount rates or changes in the expected timing of expenditure are recognised in the income statement. A sensitivity of the impact of changes to the US environmental provision real discount rate and changes in estimated future cash flows is shown in note 35 . The facts and circumstances relating to particular cases are evaluated regularly in determining whether an environmental provision should be revised (see note 30 ). Decommissioning provisions We recognise provisions for decommissioning costs for various assets we are required to remove at the end of their lives, including the safe removal of asbestos for certain of our generation units and the restoration of seabeds in respect of our interconnectors. Provisions to decommission significant portions of our regulated transmission and distribution assets are not recognised where no legal obligations exist and where a realistic alternative exists to incurring costs to decommission the assets at the end of their lives. An initial estimate of decommissioning costs attributable to property, plant and equipment is recorded as part of the cost of the related property, plant and equipment. Changes in the provision arising from revised estimates, discount rates or changes in the expected timing of expenditure that relates to property, plant and equipment are recorded as adjustments to their carrying value and depreciated prospectively over their remaining estimated useful economic lives. Expenditure is expected to be incurred until 2108 . Other provisions Included within other provisions at 31 March 2024 are the following amounts: • £170 million ( 2023 : £182 million ) of estimated liabilities in respect of past events insured by subsidiary undertakings and policy excesses incurred by operating companies. Estimates are based on experience from previous years. We expect that cash flows will be incurred until 2040; and • £76 million ( 2023 : £108 million ) of estimated liabilities in respect of interconnector excess revenues which will be repayable in future reporting periods in accordance with the cap and floor regime agreed with Ofgem (see note 3 ). These estimates are based on the respective interconnectors’ performance against their cumulative caps and cash outflows will be required to settle these liabilities by the financial year ending 31 March 2028.

Share capital

Share capital	12 Months Ended
	Mar. 31, 2024
Disclosure of classes of share capital [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 Shares million Nominal value £m At 1 April 2022 3,904 485 Issued during the year in lieu of dividends 1 26 3 At 31 March 2023 3,930 488 Issued during the year in lieu of dividends 1 37 5 At 31 March 2024 3,967 493 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 (each of which represents five ordinary shares) 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. The Company conducts a share forfeiture programme following the completion of a tracing and notification exercise to any shareholders who have not had contact with the Company over the past 12 years, in accordance with the provisions set out in the Company’s Articles of Association. Under the share forfeiture programme, the shares and dividends associated with shares of untraced members have been forfeited, with the resulting proceeds transferred to the Company to use in line with the Company’s strategy in relation to corporate responsibility. During the financial year, the Company received £2 million ( 2023 : £5 million ) of proceeds from the sale of untraced shares and derecognised £5 million ( 2023 : £5 million ) of liabilities related to unclaimed dividends, which are reflected in share premium and the income statement respectively. Treasury shares At 31 March 2024 , the Company held 247 million ( 2023 : 254 million ) of its own shares. The market value of these shares as at 31 March 2024 was £2,637 million ( 2023 : £2,783 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 2024 : i. 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. During the year, 4 million ( 2023 : 3 million ) treasury shares were gifted to National Grid Employee Share Trusts and 3 million ( 2023 : 2 million ) treasury shares were reissued in relation to employee share schemes, in total representing 0.2% ( 2023 : 0.1% ) of the ordinary shares in issue as at 31 March 2024 . The nominal value of these shares was £1 million ( 2023 : £1 million ) and the total proceeds received were £21 million ( 2023 : £16 million ). ii. During the year, the Company made payments totalling £6 million ( 2023 : £4 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 254 million ( 2023 : 259 million ), representing 6.4% ( 2023 : 6.6% ) of the ordinary shares in issue as at 31 March 2024 and having a nominal value of £32 million ( 2023 : £32 million ).

Other equity reserves

Other equity reserves	12 Months Ended
	Mar. 31, 2024
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 note 1 C), 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 ). 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 FVOCI equity £m FVOCI debt £m Own credit £m Capital redemption £m Merger £m Total £m At 1 April 2021 (35) (48) (28) 51 111 1 19 (5,165) (5,094) Exchange adjustments 1 629 — — — — — — — 629 Net losses taken to equity 2 — (96) (2) (70) (11) (1) — — (180) Share of net gains of associates taken to equity — 1 — — — — — — 1 Transferred to profit or loss — 40 (1) — — — — — 39 Net losses in respect of cash flow hedging of capital expenditure — (1) — — — — — — (1) Tax — 11 2 19 3 — — — 35 Cash flow hedges transferred to the statement of financial position, net of tax — 8 — — — — — — 8 At 1 April 2022 594 (85) (29) — 103 — 19 (5,165) (4,563) Exchange adjustments 1 882 — — — — — — — 882 Exchange differences reclassified to the consolidated income statement on disposal (170) — — — — — — — (170) Net gains/(losses) taken to equity — 142 (12) — (25) — — — 105 Share of net gains of associates taken to equity — 1 — — — — — — 1 Transferred to profit or loss — (136) — — — — — — (136) Net gains in respect of cash flow hedging of capital expenditure — 10 — — — — — — 10 Tax — 2 3 — 1 — — — 6 Cash flow hedges transferred to the statement of financial position, net of tax — 5 — — — — — — 5 At 1 April 2023 1,306 (61) (38) — 79 — 19 (5,165) (3,860) Exchange adjustments¹ (335) — — — — — — — (335) Net gains/(losses) taken to equity — 16 37 — 34 — — — 87 Transferred to profit or loss — 224 (11) — — — — — 213 Net losses in respect of cash flow hedging of capital expenditure — (37) — — — — — — (37) Tax — (50) (6) — (4) — — — (60) Cash flow hedges transferred to the statement of financial position, net of tax — 2 — — — — — — 2 At 31 March 2024 971 94 (18) — 109 — 19 (5,165) (3,990) 1. The exchange adjustments recorded in the translation reserve comprise a loss of £397 million ( 2023 : gain of £1,080 million ; 2022 : gain of £754 million ) relating to the translation of foreign operations, offset by a gain of £62 million ( 2023 : loss of £198 million ; 2022 : loss of £125 million ) relating to borrowings, cross-currency swaps and foreign exchange forward contracts used to hedge the net investment in non-sterling denominated subsidiaries. 2. In the year ended 31 March 2022, the Group disposed of its equity instruments related to shares held as part of a portfolio of financial instruments which back some long‑term employee liabilities. The equity instruments were previously measured at FVOCI and, prior to the disposal, the Group recognised a gain of £12 million . The accumulated gain of £82 million recognised in other comprehensive income in the year ended 31 March 2022 was transferred to retained earnings on disposal.

Net debt

Net debt	12 Months Ended
	Mar. 31, 2024
Subclassifications of assets, liabilities and equities [abstract]
Net debt	29. Net debt We define net debt as the amount of borrowings and financing derivatives less cash and current financial investments. (a) Composition of net debt Net debt is comprised as follows: 2024 2023 2022 £m £m £m Cash and cash equivalents (see note 20) 559 163 204 Current financial investments (see note 15) 3,699 2,605 3,145 Borrowings (see note 21) (47,072) (42,985) (45,465) Financing derivatives 1 (see note 17) (793) (756) (693) (43,607) (40,973) (42,809) 1. The financing derivatives balance included in net debt excludes the commodity derivatives (see note 17 ). (b) Analysis of changes in net debt Notes Borrowings £m Financing derivatives used to hedge debt £m Total liabilities from financing activities £m Cash and cash equivalents £m Financial investments £m Other financing derivatives £m Total 1 £m At 1 April 2023 (42,985) (793) (43,778) 163 2,605 37 (40,973) Net increase in cash and cash equivalents — — — 427 — — 427 Included within financing cash flows: Proceeds received from loans (5,563) — (5,563) — — — (5,563) Repayment of loans 1,701 — 1,701 — — — 1,701 Payments of lease liabilities 118 — 118 — — — 118 Net movements in short-term borrowings (544) — (544) — — — (544) Cash inflows on derivatives — (86) (86) — — — (86) Cash outflows on derivatives — 58 58 — — — 58 Interest paid 1,330 297 1,627 — — — 1,627 Non-net debt financing cash flows (18) — (18) — — — (18) Included within investing cash flows: Net movements in short-term financial investments — — — — 1,141 — 1,141 Cash inflows on derivatives — — — — — (123) (123) Cash outflows on derivatives — — — — — — — Derivative cash flows included in capital expenditure — — — — — 5 5 Interest received — — — — (148) — (148) Derivative cash flows included in revenue — — — — — (11) (11) Fair value gains and losses (69) 40 (29) — 4 60 35 Foreign exchange movements 718 — 718 (1) (49) — 668 Interest (charges)/income 6 (1,564) (284) (1,848) — 152 7 (1,689) Other non-cash movements (209) 4 (205) — — (4) (209) Reclassification to held for sale 2 10 13 — 13 (30) (6) — (23) At 31 March 2024 (47,072) (764) (47,836) 559 3,699 (29) (43,607) Balances at 31 March 2024 comprise: Non-current assets — 310 310 — — 5 315 Current assets — 1 1 559 3,699 17 4,276 Current liabilities (4,859) (231) (5,090) — — (18) (5,108) Non-current liabilities (42,213) (844) (43,057) — — (33) (43,090) (47,072) (764) (47,836) 559 3,699 (29) (43,607) 1. Includes accrued interest of £490 million . 2. Reclassification to held for sale represents the closing net debt position of the ESO (see note 10 ). 29. Net debt continued Notes Borrowings £m Financing derivatives used to hedge debt £m Total liabilities from financing activities £m Cash and cash equivalents 1 £m Financial investments £m Other financing derivatives £m Total² £m At 1 April 2022 (45,465) (750) (46,215) 204 3,145 57 (42,809) Net decrease in cash and cash equivalents — — — (48) — — (48) Included within financing cash flows: Proceeds received from loans (11,908) — (11,908) — — — (11,908) Repayment of loans 15,260 — 15,260 — — — 15,260 Payments of lease liabilities 155 — 155 — — — 155 Net movements in short-term borrowings 511 — 511 — — — 511 Cash inflows on derivatives — (190) (190) — — — (190) Cash outflows on derivatives — 118 118 — — — 118 Interest paid 1,277 153 1,430 — — 1,430 Non-net debt financing cash flows (27) — (27) — — — (27) Included within investing cash flows: Net movements in short-term financial investments — — — — (586) — (586) Cash outflows on derivatives — — — — — 362 362 Derivative cash outflow in relation to capital expenditure — — — — — 12 12 Interest received — — — — (65) (65) Fair value gains and losses 367 46 413 — (18) (394) 1 Foreign exchange movements (1,311) — (1,311) 7 61 — (1,243) Interest (charges)/income 6 (1,658) (170) (1,828) — 73 — (1,755) Other non-cash movements (283) — (283) — — — (283) Reclassification to held for sale 3 97 — 97 — (5) — 92 At 31 March 2023 (42,985) (793) (43,778) 163 2,605 37 (40,973) 1. Cash and cash equivalents at the start of year exclude the Group’s bank overdraft as at 1 April 2022 of £22 million . 2. Includes accrued interest of £401 million . 3. Reclassification to held for sale represented the disposal of NECO, which was not classified as a discontinued operation. Notes Borrowings £m Financing derivatives used to hedge debt £m Total liabilities from financing activities £m Cash and cash equivalents 1 £m Financial investments £m Other financing derivatives £m Total² £m At 1 April 2021 (31,220) 96 (31,124) 157 2,342 79 (28,546) Net increase in cash and cash equivalents — — — 9 — — 9 Included within financing cash flows: Proceeds received from loans (12,347) — (12,347) — — — (12,347) Repayment of loans 1,261 — 1,261 — — — 1,261 Payments of lease liabilities 117 — 117 — — — 117 Net movements in short-term borrowings 11 — 11 — — — 11 Cash inflows on derivatives — (20) (20) — — — (20) Cash outflows on derivatives — 114 114 — — — 114 Interest paid 998 55 1,053 — — — 1,053 Non-net debt financing cash flows (33) — (33) — — — (33) Included within investing cash flows: Net movements in short-term financial investments — — — — 781 — 781 Cash inflows on derivatives — — — — — (17) (17) Cash outflows on derivatives — — — — — 122 122 Derivative cash outflow in relation to capital expenditure — — — — — 8 8 Interest received — — — — (40) — (40) Fair value gains and losses 286 (472) (186) — (12) (132) (330) Foreign exchange movements (652) — (652) 5 53 — (594) Interest (charges)/income 6 (1,177) (54) (1,231) — 54 (5) (1,182) Other non-cash movements 34 — 34 — (15) — 19 Acquisition of NGED (8,286) 26 (8,260) 44 69 — (8,147) Reclassification to held for sale 3 5,543 (495) 5,048 (11) (87) 2 4,952 At 31 March 2022 (45,465) (750) (46,215) 204 3,145 57 (42,809) 1. Cash and cash equivalents at the end of year exclude the Group’s bank overdraft as at 31 March 2022 of £22 million . 2. Includes accrued interest of £351 million . 3. Reclassification to held for sale represented the opening net debt position of the UK Gas Transmission business.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Mar. 31, 2024
Disclosure of contingent liabilities [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. Contingent assets are disclosed where the Group concludes that an inflow of economic benefits is probable. 2024 2023 £m £m Future capital expenditure Contracted for but not provided 3,329 3,035 Energy purchase commitments 1 Less than 1 year 1,244 1,391 In 1 to 2 years 982 985 In 2 to 3 years 1,062 1,057 In 3 to 4 years 941 912 In 4 to 5 years 866 929 More than 5 years 9,080 13,920 14,175 19,194 Guarantees Guarantee of subleases for US properties (expire up to 2040) 67 219 Guarantees of certain obligations of Eastern Green Link Joint Operations (various expiry dates) 2,465 — Guarantees of certain obligations of Grain LNG (expire up to 2025) 32 32 Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates) 271 281 Guarantees of certain obligations of St William Homes LLP (various expiry dates) 44 44 Guarantees of certain obligations of National Grid IFA 2 Limited (expected expiry 2024) 121 144 Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024) 243 1,185 Other guarantees and letters of credit (various expiry dates) 123 321 3,366 2,226 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). 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. Contingent liabilities The Group is subject to national and local laws governing the clean-up of sites used previously in its operations. These laws and associated regulations require the Group to take future actions to remediate the effects on the environment of the release of chemicals and other substances. Such contingencies may exist for various sites, including manufacturing gas plants, power stations and water courses that were impacted by those activities. The ultimate costs of these clean-ups involve estimation uncertainty as work may be impacted by changing regulations and additional work may be required once sites have been fully surveyed. The estimated clean-up costs have been provided for in note 26 based upon management’s best estimate of the likely future cash flows. Whilst the amounts of future possible costs that are not provided for could be material to the Group’s results in the period when they are recognised, it is not possible to reliably estimate the amounts involved at this time. As environmental remediation costs are recoverable through the Group’s rate-setting processes, the Group does not expect these costs to have a material impact on its liquidity.

Related party transactions

Related party transactions	12 Months Ended
	Mar. 31, 2024
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. 2024 2023 2022 £m £m £m Sales: Goods and services supplied to a pension plan — — 3 Sales: Goods and services supplied to joint ventures 1 221 100 284 Sales: Goods and services supplied to associates 1 1 — Sales: Goods and services supplied to subsidiary of an associate 1 70 6 — Purchases: Goods and services received from joint ventures 2 6 — 19 Purchases: Goods and services received from associates 2 4 31 41 Purchases: Goods and services received from subsidiaries of an associate 1 — — Receivables from joint ventures 3 80 58 43 Receivables from associates — — 1 Receivables from subsidiaries of an associate 8 8 — Payables to joint ventures 4 — 19 247 Payables to associates 1 1 4 Dividends received from joint ventures 5 152 150 123 Dividends received from associates 6 117 32 35 1. During the year, £126 million of sales were made to Emerald Energy Venture LLC ( 2023 : £76 million ; 2022 : £74 million ), £71 million ( 2023 : £ nil ; 2022 : £ nil ) of sales were made to Nemo Link Limited and £70 million ( 2023 : £ nil ) of sales were made to National Gas Transmission Plc after becoming a related party to the Group from 31 January 2023 following the sale of the UK Gas Transmission business. In the year ended 31 March 2022, £202 million of property sites were sold to St William Homes LLP prior to the Group’s disposal. 2. During the prior 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 £22 million ( 2022 : £38 million ) of purchases were made from Millennium Pipeline Company LLC in the period up until disposal on 7 October 2022. In the year ended 31 March 2022, the Group purchased assets of £18 million from BritNed Development Limited. 3. Amounts receivable from joint ventures include £77 million ( 2023 : £55 million ; 2022 : £33 million ) from Emerald Energy Venture LLC. 4. Amounts payable to joint ventures in the year ended 31 March 2022 included £223 million due to Community Offshore Wind, LLC, NGV’s joint venture with RWE Renewables, in respect of a capital call to NGV following the successful auction of six seabed leases in New York. This was settled in the year ended 31 March 2023. 5. Includes dividends of £116 million ( 2023 : £84 million ; 2022 : £39 million ) received from BritNed Development Limited and £17 million ( 2023 : £47 million ; 2022 : £77 million ) from Nemo Link Limited. 6. Includes dividends received in the year of £102 million from GasT TopCo Limited (see note 10) and £12 million ( 2023 : £12 million ; 2022 : £2 million ) from New York Transco LLC. During the prior year, £16 million ( 2022 : £34 million ) was received from Millennium Pipeline Company LLC in the period up until disposal on 7 October 2022. Details of investments in principal subsidiary undertakings, joint ventures and associates are disclosed in note 34 , and information relating to pension fund arrangements is disclosed in note 25 . For details of Directors’ and key management remuneration, refer to note 4 (c).

Financial risk management

Financial risk management	12 Months Ended
	Mar. 31, 2024
Financial Risk Management [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; • valuation 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 forecast 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 2024 , the following limits were in place for investments and derivative financial instruments held with banks and financial institutions: Maximum limit £m Utilisation of maximum limit £m Long-term limit £m Utilisation of long-term limit £m Triple ‘A’ G7 sovereign entities (AAA) 2,818 — 2,114 — Triple ‘A’ vehicles (AAA) 500 460 — — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 2,562 — 1,922 — Double ‘A+’ G7 sovereign entities (AA+) 2,562 — 1,922 — Double ‘A’ range institutions (AA) 1,537 to 2,050 0 to 316 1,153 to 1,537 0 to 311 Single ‘A’ range institutions (A) 512 to 1,025 0 to 542 384 to 769 0 to 376 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 2024 and 2023 , 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. Investments associated with insurance and employee benefit trusts, such as the investments held at FVOCI, sit outside of treasury credit risk and are managed to individual mandates aligned to their regulated purpose. 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 code: Connection and Use of System Code. This sets 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. In March 2020, the Group’s US distribution business temporarily 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. Customer termination activities also ceased in line with requests by relevant local authorities and this resulted in the recognition of additional expected credit losses, although cash collection and customer termination activities have subsequently resumed in both New England and New York. In the years ended 31 March 2024 and 2023, the Group’s US distribution business has also been supported by certain government and state COVID-19 funding programmes, which has been factored into the assessment of expected credit losses for the year (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 presented to show 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. The Group has no offsetting arrangements in relation to bank account balances and bank overdrafts as at 31 March 2024 ( 2023 : £nil ). The gross amounts offset for trade payables and receivables, which are subject to general terms and conditions, are insignificant. Related amounts available to be offset but not offset in statement of financial position At 31 March 2024 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 333 — 333 (246) (28) 59 Commodity contract derivatives 35 — 35 (27) — 8 368 — 368 (273) (28) 67 Liabilities Financing derivatives (1,126) — (1,126) 246 441 (439) Commodity contract derivatives (118) — (118) 27 11 (80) (1,244) — (1,244) 273 452 (519) (876) — (876) — 424 (452) Related amounts available to be offset but not offset in statement of financial position At 31 March 2023 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 363 — 363 (204) (76) 83 Commodity contract derivatives 66 — 66 (28) — 38 429 — 429 (232) (76) 121 Liabilities Financing derivatives (1,119) — (1,119) 204 681 (234) Commodity contract derivatives (174) — (174) 28 19 (127) (1,293) — (1,293) 232 700 (361) (864) — (864) — 624 (240) 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 2024 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (4,480) (2,627) (3,036) (35,243) (45,386) Interest payments on borrowings 1 (1,505) (1,442) (1,386) (17,247) (21,580) Lease liabilities (133) (118) (97) (662) (1,010) Other non-interest-bearing liabilities (3,715) (458) — — (4,173) Contingent consideration — — — — — Derivative financial liabilities Financing derivatives – receipts 2 5,583 2,993 2,672 5,246 16,494 Financing derivatives – payments 2 (6,068) (3,496) (2,909) (5,756) (18,229) Commodity contract derivatives – receipts 2 8 3 — — 11 Commodity contract derivatives – payments 2 (79) (24) (7) — (110) Derivative financial assets Financing derivatives – receipts 2 1,927 311 3,993 2,485 8,716 Financing derivatives – payments 2 (1,884) (312) (3,935) (2,305) (8,436) Commodity contract derivatives – receipts 2 23 8 1 — 32 Commodity contract derivatives – payments 2 (9) (5) (1) — (15) (10,332) (5,167) (4,705) (53,482) (73,686) At 31 March 2023 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (2,433) (2,722) (2,614) (33,866) (41,635) Interest payments on borrowings 1 (1,220) (1,244) (1,148) (15,301) (18,913) Lease liabilities (118) (102) (86) (610) (916) Other non-interest-bearing liabilities (4,232) (416) — — (4,648) Contingent consideration (19) — — — (19) Derivative financial liabilities Financing derivatives – receipts 2 1,174 2,154 2,381 7,364 13,073 Financing derivatives – payments 2 (1,461) (2,483) (2,705) (8,335) (14,984) Commodity contract derivatives – receipts 2 11 9 1 — 21 Commodity contract derivatives – payments 2 (126) (35) (11) (1) (173) Derivative financial assets Financing derivatives – receipts 2 4,757 701 745 3,299 9,502 Financing derivatives – payments 2 (4,679) (676) (719) (3,183) (9,257) Commodity contract derivatives – receipts 2 48 11 — — 59 Commodity contract derivatives – payments 2 (11) (6) (3) — (20) (8,309) (4,809) (4,159) (50,633) (67,910) 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 pound sterling as the functional currency for the UK companies and 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. D erivative financial instruments were used to manage foreign currency risk as follows: 2024 2023 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 402 — 157 — 559 96 14 53 — 163 Financial investments 1,514 — 2,185 — 3,699 1,031 — 1,574 — 2,605 Borrowings (14,498) (11,936) (18,938) (1,700) (47,072) (14,473) (11,045) (15,741) (1,726) (42,985) Pre-derivative position (12,582) (11,936) (16,596) (1,700) (42,814) (13,346) (11,031) (14,114) (1,726) (40,217) Derivative effect (9,102) 12,976 (6,625) 1,958 (793) (6,751) 10,733 (6,476) 1,738 (756) Net debt position (21,684) 1,040 (23,221) 258 (43,607) (20,097) (298) (20,590) 12 (40,973) The exposure to dollars largely relates to our net investment hedge activities and exposure to euros largely relates to hedges for our future non‑sterling capital expenditure and associated revenues. The currency exposure on other financial instruments is as follows: 2024 2023 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 280 — 1,878 — 2,158 448 — 1,881 — 2,329 Trade and other payables (1,330) — (2,385) — (3,715) (1,624) — (2,629) — (4,253) Other non-current liabilities (169) — (289) — (458) (147) — (269) — (416) 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 revenue are designated as either hedging the exposure to movements in the spot or forward translation risk. Gains and losses on hedging instruments arising from undesignated 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 that follows. 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 Secured Overnight Financing Rate (SOFR) for USD and Sterling Overnight Index Average (SONIA) for GBP. 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. N et debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2024 2023 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 157 402 — — 559 53 110 — — 163 Financial investments — 3,640 — 59 3,699 — 2,569 — 36 2,605 Borrowings (39,948) (2,378) (4,746) — (47,072) (36,631) (1,744) (4,610) — (42,985) Pre-derivative position (39,791) 1,664 (4,746) 59 (42,814) (36,578) 935 (4,610) 36 (40,217) Derivative effect 5,034 (5,763) (64) — (793) 4,213 (4,869) (100) — (756) Net debt position (34,757) (4,099) (4,810) 59 (43,607) (32,365) (3,934) (4,710) 36 (40,973) 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. 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 2024 Fair value hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency risk £m Net investment hedges £m Consolidated statement of comprehensive income Net gains/(losses) in respect of: Cash flow hedges — 5 (26) — Cost of hedging — (1) — 38 Net investment hedges — — — 62 Transferred to profit or loss in respect of: Cash flow hedges — 220 4 — Cost of hedging 1 (4) — (8) Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (16) — 3 Consolidated statement of financial position Borrowings – carrying value of hedging instruments Liabilities – non-current — — — (1,768) Derivatives – carrying value of hedging instruments 1 Assets – current — — 5 11 Assets – non-current 33 161 1 — Liabilities – current (96) (112) (4) (8) Liabilities – non-current (499) (164) (32) — Profiles of the significant timing, price and rate information of hedging instruments Maturity range Jul 2024 – Sep 2044 Jul 2024 – Nov 2040 Apr 2024 – Feb 2030 Apr 2024 – Jan 2034 Spot foreign exchange range: GBP:USD n/a 1.30 – 1.66 1.23 – 1.27 1.22 – 1.29 GBP:EUR 1.11 – 1.24 1.08 – 1.19 1.11 – 1.18 1.17 – 1.17 EUR:USD 1.07 – 1.15 1.07 – 1.15 n/a n/a Interest rate range: GBP SONIA + 56 bps/+ 374 bps 0.976% – 7.410% n/a n/a USD SOFR + 83 bps/+ 223 bps 2.095% – 5.989% 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 2023 Fair value hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency risk £m Net investment hedges £m Consolidated statement of comprehensive income Net gains/(losses) in respect of: Cash flow hedges — 136 10 — Cost of hedging 4 4 — (24) Net investment hedges — — — (198) Transferred to profit or loss in respect of: Cash flow hedges — (136) — — Cost of hedging — — — 1 Reclassification of foreign currency translation reserve 1 — — — 373 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (12) — (27) Consolidated statement of financial position Derivatives – carrying value of hedging instruments 2 Assets – current — — 6 52 Assets – non-current 25 166 1 — Liabilities – current (43) (39) (6) — Liabilities – non-current (559) (248) (1) (15) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Aug 2023 – Sep 2044 Jul 2024 – Nov 2040 Apr 2023 – May 2029 Jun 2023 – Sep 2027 Spot foreign exchange range: GBP:USD n/a 1.30 – 1.66 1.20 – 1.36 1.18 – 1.22 GBP:EUR 1.11 – 1.20 1.08 – 1.24 1.10 – 1.20 1.12 – 1.13 EUR:USD 1.13 – 1.17 1.13 – 1.15 n/a n/a Interest rate range: GBP SONIA + 84 bps/+ 374 bps 0.976% – 7.410% n/a n/a USD LIBOR + 68 bps/ SOFR + 126 bps 2.095% – 3.864% n/a n/a 1. The reclassification of the net investment hedge on the disposals of NECO and Millennium Pipeline Company LLC were included within Other operating income. 2. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. 32. Financial risk management continued (e) Hedge accounting continued The following tables show the effects of hedge accounting on financial position and year-to-date performance for each type of hedge. These tables also present the notional values of hedging instruments (and equal hedged exposures) which were impacted by IFRS 9 Interest Rate Benchmark Reform amendments in the prior year. (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2024 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 (5,096) 720 (35) 40 (22) 18 1. The carrying value of the hedged borrowings is £4,364 million , of which £271 million is current and £4,093 million is non-current. As at 31 March 2023 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 (4,779) 789 (43) 398 (351) 47 1. The carrying value of the hedged borrowings was £4,042 million , of which £511 million was current and £3,531 million was non-current. 2. Included within the hedging instrument notional balance was £859 million impacted by Interest Rate Benchmark Reform amendments which were still to be transitioned. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2024 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 and forecast cash flows (9,892) 154 — (18) 3 (15) Foreign currency risk on forecast cash flows (2,039) (31) — 28 (28) — As at 31 March 2023 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 (9,357) (73) — 149 (154) (5) Foreign currency risk on forecast cash flows (537) (3) — (35) 35 — (iii) Net investment hedges of foreign currency risk: As at 31 March 2024 Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Currency risk on foreign operations (2,999) 40 (2,564) (62) 62 — As at 31 March 2023 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 (3,095) (129) (2,457) 198 (198) — 32. Financial risk management continued (f) Commodity price risk We purchase electricity and gas to supply our customers in the US and to meet our own energy needs. Substantially all our costs of purchasing electricity and gas for supply to customers are recovera

Borrowing facilities

Borrowing facilities	12 Months Ended
	Mar. 31, 2024
Disclosure of detailed information about borrowings [abstract]
Borrowing facilities	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 inflation indices. 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 lead us to fund our networks within a certain ratio of debt to equity or regulatory asset 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. Borrowings, which include interest-bearing 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. 2024 2023 £m £m Current Bank loans 460 381 Bonds 2,841 1,638 Commercial paper 1,444 840 Lease liabilities 114 96 4,859 2,955 Non-current Bank loans 2,434 2,557 Bonds 39,114 36,855 Lease liabilities 665 618 42,213 40,030 Total borrowings 47,072 42,985 Total borrowings are repayable as follows: 2024 2023 £m £m Less than 1 year 4,859 2,955 In 1 to 2 years 2,706 2,799 In 2 to 3 years 3,134 2,689 In 3 to 4 years 2,948 3,129 In 4 to 5 years 4,375 2,505 More than 5 years: By instalments 736 922 Other than by instalments 28,314 27,986 47,072 42,985 The fair value of borrowings, excluding lease liabilities, at 31 March 2024 was £42,617 million ( 2023 : £38,219 million ). Where market values were available, the fair value of borrowings (Level 1) was £34,281 million ( 2023 : £31,710 million ). Where market values were not available, the fair value of borrowings (Level 2) was £8,336 million ( 2023 : £6,509 million ) and calculated by discounting cash flows at prevailing interest rates. The notional amount outstanding of the debt portfolio at 31 March 2024 was £46,141 million ( 2023 : £42,353 million ). There have been no new issuances since the year end. 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 £72 million ( 2023 : £111 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. 21. Borrowings continued Lease liabilities 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, 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 as well as 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. 2024 2023 £m £m Gross lease liabilities are repayable as follows: Less than 1 year 133 118 1 to 5 years 370 318 More than 5 years 507 480 1,010 916 Less: finance charges allocated to future periods (231) (202) 779 714 The present value of lease liabilities are as follows: Less than 1 year 114 96 1 to 5 years 300 269 More than 5 years 365 349 779 714 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 are undrawn. An analysis of the maturity of our undrawn committed facilities as at 31 March 2024 is shown below: 2024 2023 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — 42 In 1 to 2 years — 4,361 In 2 to 3 years 195 2,100 In 3 to 4 years 5,859 — In 4 to 5 years 106 — More than 5 years 1,745 — 7,905 6,503 Of the unused facilities at 31 March 2024 , £7,864 million ( 2023 : £6,461 million ) is available for liquidity purposes, while £41 million ( 2023 : £42 million )

Subsidiary undertakings, joint

Subsidiary undertakings, joint ventures and associates	12 Months Ended
	Mar. 31, 2024
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. 2024 2023 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 154 1,146 1,300 277 961 1,238 Exchange adjustments (3) (28) (31) 20 52 72 Additions 13 319 332 40 157 197 Share of post-tax results for the year 9 28 37 9 162 171 Share of other comprehensive income of associates, net of tax — — — 1 — 1 Dividends received (15) (152) (167) (30) (152) (182) Disposals¹ (1) — (1) (167) — (167) Other movements² 1 (51) (50) 4 (34) (30) Share of net assets at 31 March 158 1,262 1,420 154 1,146 1,300 1. Disposals in the prior year included the sale of the Group’s 26.25% minority ownership interest in the Millennium Pipeline Company LLC. 2. Other movements relate to tax liabilities for US and certain UK associates and joint ventures which are borne by the Group and the elimination of profits arising from sales to the Group’s share of joint ventures. 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 in relation to its joint ventures and associates of £1,286 million ( 2023 : £412 million ), which primarily relate to the funding of new capital investment projects. The following table describes the Group’s material joint ventures and associates at 31 March 2024 : Joint venture 1 % stake BritNed Development Limited 50% BritNed is a joint venture with the Dutch transmission system operator, TenneT, and operates the subsea electricity interconnector between Great Britain and the Netherlands, commissioned in 2011. Nemo Link Limited 50% Nemo is a joint venture with the Belgian transmission operator, Elia, and is a subsea electricity interconnector between Great Britain and Belgium, which became operational on 31 January 2019. Emerald Energy Venture, LLC 51% Emerald is a joint venture with Washington State Investment Board which builds and operates wind and solar assets. Emerald was acquired on 11 July 2019. Community Offshore Wind, LLC 27.3% Community Offshore Wind is a joint venture with RWE Renewables. The joint venture owns six seabed leases in the northeastern US and is developing an offshore wind project which will play a key role in supplying clean energy to customers in New York. 1. The joint ventures have reporting periods ending on 31 December with monthly management reporting information provided to the Group. 16. Investments in joint ventures and associates continued Summarised financial information as at 31 March, together with the carrying amount of material investments, is as follows: BritNed Development Limited Nemo Link Limited Emerald Energy Venture LLC Community Offshore Wind LLC 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Statement of financial position Non-current assets 376 397 478 514 2,171 1,598 1,005 925 Cash and cash equivalents 69 208 46 77 206 169 40 19 All other current assets 36 29 6 8 16 14 42 — Non-current liabilities (57) (55) (3) (3) (249) (244) (20) (19) Non-current financial liabilities (31) (31) (32) (32) (643) (398) — — Current liabilities (39) (34) (55) (131) (217) (131) (1) (3) Current financial liabilities — — — — (10) (95) — — Net assets 354 514 440 433 1,274 913 1,066 922 Group’s ownership interest in joint venture/associate 177 257 220 217 650 466 291 251 Group adjustment: elimination of profits on sales to joint venture — — — — (123) (85) — — Carrying amount of the Group’s investment 177 257 220 217 527 381 291 251 BritNed Development Limited Nemo Link Limited Emerald Energy Venture LLC Community Offshore Wind LLC 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Income statement Revenue 158 358 109 88 87 75 — — Depreciation and amortisation (16) (16) (23) (23) (38) (29) — — Other (costs)/income (25) 22 (15) (1) (152) (46) — 1 Operating profit/(loss) 117 364 71 64 (103) — — 1 Net interest expense (2) (2) — (7) (9) (6) — — Profit/(loss) before tax 115 362 71 57 (112) (6) — 1 Income tax expense (31) (82) (17) (11) — — — — Profit/(loss) for the year 84 280 54 46 (112) (6) — 1 Group’s share of profit/(loss) 42 140 27 23 (57) (3) — — Group adjustment: tax credit — — — — 15 1 — — Group’s share of post-tax results for the year 42 140 27 23 (42) (2) — — 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 2024 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. The Group does not have any branches. 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 US are taxed in the US 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). Birch Sites Limited Carbon Sentinel Limited Central Networks Trustees Limited 1 Hyder Profit Sharing Trustees Limited 1 Icelink Interconnector Limited Kelston Properties 2 Limited 1 Lattice Group Employee Benefit Trust Limited Lattice Group Limited Lattice Group Trustees Limited NatGrid One Limited 2 * NatgridTW1 Limited National Energy System Operator Limited National Grid (US) Holdings Limited 3 National Grid (US) Investments 2 Limited 2 * National Grid (US) Investments 4 Limited 3 National Grid (US) Partner 1 Limited 3 National Grid Carbon Limited National Grid Commercial Holdings Limited National Grid Continental Limited National Grid Distributed Energy Limited National Grid Electricity Distribution (East Midlands) plc 1 National Grid Electricity Distribution (South Wales) plc 1 National Grid Electricity Distribution (South West) plc 1 National Grid Electricity Distribution (West Midlands) plc 1 National Grid Electricity Distribution Generation Limited 1 National Grid Electricity Distribution Holdings Limited 1 National Grid Electricity Distribution Investments Limited 1 National Grid Electricity Distribution Midlands Limited 1 National Grid Electricity Distribution Network Holdings Limited 1 National Grid Electricity Distribution plc 1 National Grid Electricity Distribution Property Investments Limited 1 National Grid Electricity Group Trustee Limited National Grid Electricity System Operator Limited National Grid Electricity Transmission plc National Grid Energy Metering Limited National Grid Grain LNG Limited National Grid Helicopters Limited 1 National Grid Holdings Limited 3 National Grid Holdings One plc National Grid Hydrogen Limited National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited 3 National Grid Lion Link Limited National Grid Nautilus Limited National Grid North Sea Link Limited National Grid Partners Limited National Grid Plus Limited National Grid Property Holdings Limited National Grid Telecoms Limited 1 National Grid Twelve Limited National Grid Twenty Eight Limited National Grid Twenty Seven Limited National Grid Twenty Three Limited 2 * National Grid UK Limited National Grid UK Pension Services Limited 2 * National Grid Ventures Limited National Grid Viking Link Limited National Grid William Limited NG Nominees Limited 3 NGC Employee Shares Trustee Limited NGG Finance plc Ngrid Intellectual Property Limited Port Greenwich Limited Sheet Road Management Company Limited ( 51% ) 4 South Wales Electricity Share Scheme Trustees Limited 1 Thamesport Interchange Limited The National Grid Group Quest Trustee Company Limited Warwick Technology Park Management Company (No 2) Limited ( 60.56% ) 5 Western Power Pension Trustee Limited 1 WPD Share Scheme Trustees Limited 1 WPD WEM Holdings Limited 1 WPD WEM Limited 1 WW Share Scheme Trustees Limited 1 1. Registered office: Avonbank, Feeder Road, Bristol, Avon, BS2 0TB, UK. 2. Registered office: C/o Interpath Limited, 10 Fleet Place, London, EC4M 7RB, UK. 3. Companies where National Grid plc has issued guarantees over the liabilities of the companies as at 31 March 2024 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. 4. Registered office: Netley Old Hall Farm, Dorrington, Shrewsbury, SY5 7JY, UK. 5. Registered office: Shire Hall, PO Box 9, Warwick, CV34 4RL, UK. * In liquidation. Incorporated in the US Registered office: National Registered Agents, Inc., 1209 Orange Street, Wilmington, DE 19801, USA (unless stated otherwise in footnotes). Apple River Solar, LLC Armenia Solar, LLC Ashland Solar, LLC Athens Solar, LLC Autauga Solar, LLC Bazile Creek Wind Farm, LLC Bee Hollow Solar, LLC Belle Plaine Solar, LLC Benevolent Solar, LLC Blaze Solar, LLC Blevins Storage, LLC Blue Ridge Wind, LLC Blue Spring Solar, LLC Blues Solar, LLC Boone Solar, LLC Boston Gas Company 1 Brock Solar, LLC Broken Bridge Corp. 2 Brook Trout Solar, LLC Burley Solar, LLC Burr Ridge Wind, LLC Cage Ranch Solar II, LLC Cage Ranch Solar III, LLC Cage Ranch Solar, LLC Caldwell Solar II, LLC Caldwell Solar, LLC Camp Creek Wind Farm, LLC Carnation Solar, LLC Cattle Ridge Wind Farm 2, LLC Cedar Grove Solar, LLC Charter Oak Solar, LLC Charter Oak Storage, LLC Clay Boswell Solar, LLC Clermont Solar, LLC Coles Solar, LLC Compass Prairie Wind, LLC Conestoga Wind, LLC Creekview Solar, LLC Crocker Wind Farm 2, LLC Dakota Hills Wind Farm, LLC Deatsville Solar, LLC Donnellson Solar, LLC Doorstep Community LLC 3 Elburn Solar, LLC Eldena Solar, LLC Elk Creek Solar 2, LLC Elk Creek Solar, LLC EUA Energy Investment Corporation 1 Exie Solar, LLC Falls City Solar, LLC Firstview Wind Farm, LLC Fort Solar, LLC Front Range Wind Farm, LLC Galaxy Solar, LLC Golden Solar, LLC Goldendale Solar, LLC Goldenrod Wind Farm, LLC Goldfinch Solar, LLC Granite State Power Link LLC 3 Grant Solar 2, LLC Grant Solar, LLC Grayson Solar, LLC Greenbrier Creek Solar, LLC Greenwood Solar, LLC Grid NY LLC 4 Grindstone Wind Farm, LLC 5 Hale County Solar, LLC Hansford Energy Storage, LLC Harmony Solar ND 2, LLC Harmony Solar ND, LLC Harrington Solar, LLC Hartley Solar, LLC Hearth Solar, LLC High View Property, LLC Honeybee Solar, LLC Hoosier Solar, LLC Hoskins Solar, LLC Illumination Solar, LLC Itasca Energy Development, LLC 6 Itasca Energy Services, LLC Jack Rabbit Wind, LLC Jackson County Solar, LLC KeySpan CI Midstream Limited 3 KeySpan Energy Corporation 4 KeySpan Energy Services Inc. 3 KeySpan Gas East Corporation 4 KeySpan International Corporation 3 KeySpan MHK, Inc. 3 KeySpan Midstream, Inc. 3 KeySpan Plumbing Solutions, Inc. 4 Kit Carson Wind, LLC Kit Fox Storage, LLC Knox Solar, LLC Kota Storage, LLC KSI Contracting, LLC 3 KSI Electrical, LLC 3 KSI Mechanical, LLC 3 Lake Charlotte Solar, LLC Lakeside Solar, LLC Land Management & Development, Inc. 4 Landwest, Inc. 4 Lansing Solar, LLC Las Moras Storage, LLC Leola Wind Farm, LLC Liberty Solar, LLC Livingston County Solar, LLC Long Mount Storage, LLC Lordsburg Solar, LLC Louisa Solar, LLC Lowlands Solar, LLC Lydia Solar, LLC Massachusetts Electric Company 1 Maverick Wind Farm, LLC Meadowlands Solar, LLC Mentha Solar, LLC Metrowest Realty LLC 3 Millers Ferry Solar, LLC Morgan County Solar, LLC Morning Glory Solar, LLC 6 Muddy Creek Solar, LLC Mustang Ridge Wind Farm, LLC Mystic Steamship Corporation 7 Nantucket Electric Company 1 National Grid Development Holdings Corp. 3 National Grid Electric Services LLC 4 National Grid Energy Trading Services LLC 4 National Grid Engineering & Survey Inc. 4 National Grid Generation LLC 4 National Grid Generation Ventures LLC 4 National Grid Glenwood Energy Center LLC 3 National Grid IGTS Corp. 4 National Grid Insurance USA Ltd 8 National Grid LNG LLC 3 National Grid NE Holdings 2 LLC 1 National Grid North America Inc. 3 National Grid Partners Inc. 4 National Grid Partners LLC 3 National Grid Port Jefferson Energy Center LLC 3 National Grid Renewables Development, LLC National Grid Renewables E Wind, LLC 9 National Grid Renewables Operations, LLC 3 National Grid Renewables Projects, LLC 6 National Grid Renewables Stutsman, LLC National Grid Renewables, LLC 3 National Grid Services Inc. 3 National Grid US LLC 3 National Grid USA Service Company, Inc. 1 National Grid USA 3 NEES Energy, Inc. 1 New England Electric Transmission Corporation 2 New England Energy Incorporated 1 New England Hydro Finance Company, Inc. ( 53.704% ) 1 New England Hydro-Transmission Corporation ( 53.704% ) 2 New England Hydro-Transmission Electric Company, Inc. ( 53.704% ) 1 New England Power Company 1 Newport America Corporation 10 Newton Solar, LLC NG Renewables Energy Marketing, LLC 3 NG Renewables Energy Services, LLC NG Renewables Remote Operations Center, LLC NGNE LLC 3 NGV Emerald Energy Venture Holdings, LLC 3 NGV H2 Holdings LLC 3 NGV LNG Holdings LLC 3 NGV OSW Holdings, LLC 3 NGV US Distributed Energy Inc. 3 NGV US Transmission Inc. 3 NGV US, LLC 3 Niagara Mohawk Energy, Inc. 3 Niagara Mohawk Holdings, Inc. 4 Niagara Mohawk Power Corporation 4 Niobrara Wind, LLC NM Properties, Inc. 4 Noble Solar, LLC 11 Nordic VOS, LLC North East Transmission Co., Inc. 3 North Fork Wind, LLC Northeast Renewable Link LLC 3 Opinac North America, Inc. 3 Peony Solar, LLC Philadelphia Coke Co., Inc. 3 Pike County Solar, LLC Pipestone Solar, LLC Plum Creek Wind Farm 2, LLC Plum Creek Wind Farm, LLC Port of the Islands North, LLC 4 Portage Solar, LLC Prairie Oasis Solar, LLC Prairie Rose Wind 2, LLC 6 Prosperity Wind Farm 2, LLC Prosperity Wind Farm, LLC Red Rock Solar SD, LLC Regal Solar 2, LLC Regal Solar, LLC Reunion Solar, LLC River North Solar, LLC Robertson Solar, LLC Rock Ridge Wind Farm, LLC Rolling Hills Solar, LLC Royal Solar 2, LLC Royal Solar, LLC Royerton Solar, LLC Saginaw Bay Solar, LLC Saltillo Storage, LLC Sandstone Creek Solar 2, LLC Sandstone Creek Solar, LLC Sapphire Sky Wind Farm, LLC Sherco Solar 2, LLC 6 Sherco Solar 3, LLC Silver City Solar, LLC Simpson Solar, LLC Spring Brook Solar, LLC Spring River Solar, LLC Stony Brook Wind, LLC Stony Point Solar, LLC Stove Creek Solar, LLC Summit Lake Solar, LLC Sunbeam Solar, LLC Sunrise Solar, LLC Sycamore Creek Solar, LLC Tejano Storage, LLC Thacker Solar, LLC The Brooklyn Union Gas Company 4 Torchlight Solar, LLC 6 Transgas Inc. 1 Tri-City Solar, LLC Uintah Solar, LLC Upper Hudson Development, Inc. 4 Valley Solar, LLC Vermont Green Line Devco, LLC ( 90% ) 3 Violet Storage, LLC Virgo Community Solar Gardens, LLC 6 Virtue Solar, LLC Vivid Solar, LLC Wallowa Solar, LLC Wayfinder Group, Inc. 1 White Elm Wind Farm, LLC Wildcat Ridge Wind Farm, LLC Wilder Solar, LLC Wildhorse Creek Solar, LLC Willard Solar, LLC Williams County Solar, LLC Wiregrass Solar, LLC Woodlands Solar, LLC Worthington Solar, LLC Young County Solar, LLC Incorporated in Guernsey Registered office: 1st & 2nd Floors Elizabeth House, Les Ruettes Brayes, St Peter Port, GY1 1EW, Guernsey, Channel Islands NG Electricity Distribution Limited † Incorporated in Hong Kong Registered office: 5/F, Manulife Place, 348 Kwun Tong Road, Kowloon, 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 Incorporated in Luxembourg Registered office: 412F, Route d’Esch, L-2086, Luxembourg, Grand Duchy of Luxembourg National Grid Luxembourg SARL 1. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, USA. 2. Registered office: Corporation Service Company, 10 Ferry Street, Suite 313, Concord NH 03301, USA. 3. Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington DE 19808, USA. 4. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 5. Registered office: National Registered Agents Inc., 30600 Telegraph Road, Suite 2345, Bingham Farms MI 48025-5720, USA. 6. Registered office: 8400 Normandale Lake Blvd., Suite 1200, Bloomington MN 55437, USA. 7. Registered office: Corporation Trust Company, 1209 Orange Street, Wilmington DE 19801, USA. 8. Registered office: 100 Bank Street, Suite 630, Burlington, Chittenden County VT 05401, USA. 9. Registered office: National Registered Agents, Inc., 301 S. Bedford Street, Suite 1, Madison WI 5, USA. 10. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, USA. 11. Registered office: National Registered Agents, Inc., 1999 Bryan Street, Dallas TX 75201, USA. * In liquidation. † Entity is tax resident in the UK. A list of the Group’s joint ventures as at 31 March 2024 is given below. All joint ventures are included in the Group’s Financial statements using the equity method of accounting. Incorporated in England and Wales Registered office: 1–3 Strand, London, WC2N 5EH, UK (unless stated otherwise in footnotes). BritNed Development Limited ( 50% )** National Places LLP ( 50% ) 1 Nemo Link Limited ( 50% ) Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Community Offshore Wind, LLC (previously Bight Wind Holdings LLC) ( 27.27% ) 2 Clean Energy Storage Systems LLC ( 50% ) Emerald Energy Venture, LLC ( 51% ) Island Park Energy Center, LLC ( 50% ) LI Energy Storage System, LLC ( 50% ) LI Solar Generation, LLC ( 50% ) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, Paris La Defense, CEDEX, France IFA2 ( 50% )* Joint operations A list of the Group’s incorporated joint operations as at 31 March 2024 is given below. All joint operations are included in the Group’s financial statements under IFRS 11 Joint arrangements. Incorporated in England and Wales Registered office: 1–3 Strand, London, WC2N 5EH, UK (unless stated otherwise in footnotes). Eastern Green Link 1 Limited ( 50% ) Eastern Green Link 2 Limited ( 50% ) 3 NGET/SPT Upgrades Limited ( 50% ) † A list of the Group’s associates as at 31 March 2024 is given below. Unless otherwise stated, all associates are included in the Group’s financial statements using the equity method of accounting. Incorporated in England and Wales Registered office: National Grid House, Warwick Technology Park, Gallows Hill, Warwick, CV34 6DA GasT TopCo Limited ( 20% ) Joint Radio Company Limited ( 25% ) 4 *** 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% ) 2 Connecticut Yankee Atomic Power Company ( 19.5% ) 5 Direct Global Power Inc. ( 26% ) 2 Energy Impact Fund LP ( 9.41% ) 6 KHB Venture LLC ( 33.33% ) 7 Maine Yankee Atomic Power Company ( 24% ) 8 New York Transco LLC ( 28.3% ) 9 NYSEARCH RMLD, LLC ( 22.63% ) The Hive IV, LLC ( 28.2% ) 2 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 2024 is given below. Incorporated in England and Wales Registered office: 1 More London Place, London SE1 2AF, UK Energis plc ( 33.06% ) ‡ Registered office: Third Floor, Northumberland House, 303–306 High Holborn, London, WC1V 7JZ Electralink Limited ( 27.04% ) 1. Registered office: 80 Cheapside, London, EC2V 6EE, UK. 2. Registered office: The Corporation Trust Company, Corporation Trust Center, 1209 Orange Street, Wilmington DE 19801, USA. 3. Registered office: No.1 Forbury Place, 43 Forbury Road, Reading, RG1 3JH, UK. 4. Registered office: Friars House, Manor House Drive, Coventry, CV1 2TE, UK. 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, USA. 7. Registered office: c/o de maximis, 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. * In liquidation. ** National Grid Interconnector Holdings Limited owns 284,500,000 €0.20 C Ordinary shares and one £1.00 Ordinary A share. *** National Grid Electricity Transmission plc owns one £0.50 A Ordinary share. † 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 supported by guarantees issued by National Grid plc over their liabilities for the year ended 31 March 2024 : Company name Company number National Grid Holdings Limited 3096772 National Grid International Limited 2537092 National Grid (US) Holdings Limited 2630496 National Grid (US) Investments 4 Limited 3867128 National Grid (US) Partner 1 Limited 4314432 NG Nominees Limited 2489329

Sensitivities

Sensitivities	12 Months Ended
	Mar. 31, 2024
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; • valuation 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 forecast 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 2024 , the following limits were in place for investments and derivative financial instruments held with banks and financial institutions: Maximum limit £m Utilisation of maximum limit £m Long-term limit £m Utilisation of long-term limit £m Triple ‘A’ G7 sovereign entities (AAA) 2,818 — 2,114 — Triple ‘A’ vehicles (AAA) 500 460 — — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 2,562 — 1,922 — Double ‘A+’ G7 sovereign entities (AA+) 2,562 — 1,922 — Double ‘A’ range institutions (AA) 1,537 to 2,050 0 to 316 1,153 to 1,537 0 to 311 Single ‘A’ range institutions (A) 512 to 1,025 0 to 542 384 to 769 0 to 376 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 2024 and 2023 , 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. Investments associated with insurance and employee benefit trusts, such as the investments held at FVOCI, sit outside of treasury credit risk and are managed to individual mandates aligned to their regulated purpose. 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 code: Connection and Use of System Code. This sets 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. In March 2020, the Group’s US distribution business temporarily 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. Customer termination activities also ceased in line with requests by relevant local authorities and this resulted in the recognition of additional expected credit losses, although cash collection and customer termination activities have subsequently resumed in both New England and New York. In the years ended 31 March 2024 and 2023, the Group’s US distribution business has also been supported by certain government and state COVID-19 funding programmes, which has been factored into the assessment of expected credit losses for the year (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 presented to show 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. The Group has no offsetting arrangements in relation to bank account balances and bank overdrafts as at 31 March 2024 ( 2023 : £nil ). The gross amounts offset for trade payables and receivables, which are subject to general terms and conditions, are insignificant. Related amounts available to be offset but not offset in statement of financial position At 31 March 2024 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 333 — 333 (246) (28) 59 Commodity contract derivatives 35 — 35 (27) — 8 368 — 368 (273) (28) 67 Liabilities Financing derivatives (1,126) — (1,126) 246 441 (439) Commodity contract derivatives (118) — (118) 27 11 (80) (1,244) — (1,244) 273 452 (519) (876) — (876) — 424 (452) Related amounts available to be offset but not offset in statement of financial position At 31 March 2023 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 363 — 363 (204) (76) 83 Commodity contract derivatives 66 — 66 (28) — 38 429 — 429 (232) (76) 121 Liabilities Financing derivatives (1,119) — (1,119) 204 681 (234) Commodity contract derivatives (174) — (174) 28 19 (127) (1,293) — (1,293) 232 700 (361) (864) — (864) — 624 (240) 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 2024 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (4,480) (2,627) (3,036) (35,243) (45,386) Interest payments on borrowings 1 (1,505) (1,442) (1,386) (17,247) (21,580) Lease liabilities (133) (118) (97) (662) (1,010) Other non-interest-bearing liabilities (3,715) (458) — — (4,173) Contingent consideration — — — — — Derivative financial liabilities Financing derivatives – receipts 2 5,583 2,993 2,672 5,246 16,494 Financing derivatives – payments 2 (6,068) (3,496) (2,909) (5,756) (18,229) Commodity contract derivatives – receipts 2 8 3 — — 11 Commodity contract derivatives – payments 2 (79) (24) (7) — (110) Derivative financial assets Financing derivatives – receipts 2 1,927 311 3,993 2,485 8,716 Financing derivatives – payments 2 (1,884) (312) (3,935) (2,305) (8,436) Commodity contract derivatives – receipts 2 23 8 1 — 32 Commodity contract derivatives – payments 2 (9) (5) (1) — (15) (10,332) (5,167) (4,705) (53,482) (73,686) At 31 March 2023 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (2,433) (2,722) (2,614) (33,866) (41,635) Interest payments on borrowings 1 (1,220) (1,244) (1,148) (15,301) (18,913) Lease liabilities (118) (102) (86) (610) (916) Other non-interest-bearing liabilities (4,232) (416) — — (4,648) Contingent consideration (19) — — — (19) Derivative financial liabilities Financing derivatives – receipts 2 1,174 2,154 2,381 7,364 13,073 Financing derivatives – payments 2 (1,461) (2,483) (2,705) (8,335) (14,984) Commodity contract derivatives – receipts 2 11 9 1 — 21 Commodity contract derivatives – payments 2 (126) (35) (11) (1) (173) Derivative financial assets Financing derivatives – receipts 2 4,757 701 745 3,299 9,502 Financing derivatives – payments 2 (4,679) (676) (719) (3,183) (9,257) Commodity contract derivatives – receipts 2 48 11 — — 59 Commodity contract derivatives – payments 2 (11) (6) (3) — (20) (8,309) (4,809) (4,159) (50,633) (67,910) 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 pound sterling as the functional currency for the UK companies and 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. D erivative financial instruments were used to manage foreign currency risk as follows: 2024 2023 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 402 — 157 — 559 96 14 53 — 163 Financial investments 1,514 — 2,185 — 3,699 1,031 — 1,574 — 2,605 Borrowings (14,498) (11,936) (18,938) (1,700) (47,072) (14,473) (11,045) (15,741) (1,726) (42,985) Pre-derivative position (12,582) (11,936) (16,596) (1,700) (42,814) (13,346) (11,031) (14,114) (1,726) (40,217) Derivative effect (9,102) 12,976 (6,625) 1,958 (793) (6,751) 10,733 (6,476) 1,738 (756) Net debt position (21,684) 1,040 (23,221) 258 (43,607) (20,097) (298) (20,590) 12 (40,973) The exposure to dollars largely relates to our net investment hedge activities and exposure to euros largely relates to hedges for our future non‑sterling capital expenditure and associated revenues. The currency exposure on other financial instruments is as follows: 2024 2023 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 280 — 1,878 — 2,158 448 — 1,881 — 2,329 Trade and other payables (1,330) — (2,385) — (3,715) (1,624) — (2,629) — (4,253) Other non-current liabilities (169) — (289) — (458) (147) — (269) — (416) 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 revenue are designated as either hedging the exposure to movements in the spot or forward translation risk. Gains and losses on hedging instruments arising from undesignated 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 that follows. 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 Secured Overnight Financing Rate (SOFR) for USD and Sterling Overnight Index Average (SONIA) for GBP. 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. N et debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2024 2023 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 157 402 — — 559 53 110 — — 163 Financial investments — 3,640 — 59 3,699 — 2,569 — 36 2,605 Borrowings (39,948) (2,378) (4,746) — (47,072) (36,631) (1,744) (4,610) — (42,985) Pre-derivative position (39,791) 1,664 (4,746) 59 (42,814) (36,578) 935 (4,610) 36 (40,217) Derivative effect 5,034 (5,763) (64) — (793) 4,213 (4,869) (100) — (756) Net debt position (34,757) (4,099) (4,810) 59 (43,607) (32,365) (3,934) (4,710) 36 (40,973) 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. 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 2024 Fair value hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency risk £m Net investment hedges £m Consolidated statement of comprehensive income Net gains/(losses) in respect of: Cash flow hedges — 5 (26) — Cost of hedging — (1) — 38 Net investment hedges — — — 62 Transferred to profit or loss in respect of: Cash flow hedges — 220 4 — Cost of hedging 1 (4) — (8) Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (16) — 3 Consolidated statement of financial position Borrowings – carrying value of hedging instruments Liabilities – non-current — — — (1,768) Derivatives – carrying value of hedging instruments 1 Assets – current — — 5 11 Assets – non-current 33 161 1 — Liabilities – current (96) (112) (4) (8) Liabilities – non-current (499) (164) (32) — Profiles of the significant timing, price and rate information of hedging instruments Maturity range Jul 2024 – Sep 2044 Jul 2024 – Nov 2040 Apr 2024 – Feb 2030 Apr 2024 – Jan 2034 Spot foreign exchange range: GBP:USD n/a 1.30 – 1.66 1.23 – 1.27 1.22 – 1.29 GBP:EUR 1.11 – 1.24 1.08 – 1.19 1.11 – 1.18 1.17 – 1.17 EUR:USD 1.07 – 1.15 1.07 – 1.15 n/a n/a Interest rate range: GBP SONIA + 56 bps/+ 374 bps 0.976% – 7.410% n/a n/a USD SOFR + 83 bps/+ 223 bps 2.095% – 5.989% 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 2023 Fair value hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency risk £m Net investment hedges £m Consolidated statement of comprehensive income Net gains/(losses) in respect of: Cash flow hedges — 136 10 — Cost of hedging 4 4 — (24) Net investment hedges — — — (198) Transferred to profit or loss in respect of: Cash flow hedges — (136) — — Cost of hedging — — — 1 Reclassification of foreign currency translation reserve 1 — — — 373 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (12) — (27) Consolidated statement of financial position Derivatives – carrying value of hedging instruments 2 Assets – current — — 6 52 Assets – non-current 25 166 1 — Liabilities – current (43) (39) (6) — Liabilities – non-current (559) (248) (1) (15) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Aug 2023 – Sep 2044 Jul 2024 – Nov 2040 Apr 2023 – May 2029 Jun 2023 – Sep 2027 Spot foreign exchange range: GBP:USD n/a 1.30 – 1.66 1.20 – 1.36 1.18 – 1.22 GBP:EUR 1.11 – 1.20 1.08 – 1.24 1.10 – 1.20 1.12 – 1.13 EUR:USD 1.13 – 1.17 1.13 – 1.15 n/a n/a Interest rate range: GBP SONIA + 84 bps/+ 374 bps 0.976% – 7.410% n/a n/a USD LIBOR + 68 bps/ SOFR + 126 bps 2.095% – 3.864% n/a n/a 1. The reclassification of the net investment hedge on the disposals of NECO and Millennium Pipeline Company LLC were included within Other operating income. 2. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. 32. Financial risk management continued (e) Hedge accounting continued The following tables show the effects of hedge accounting on financial position and year-to-date performance for each type of hedge. These tables also present the notional values of hedging instruments (and equal hedged exposures) which were impacted by IFRS 9 Interest Rate Benchmark Reform amendments in the prior year. (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2024 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 (5,096) 720 (35) 40 (22) 18 1. The carrying value of the hedged borrowings is £4,364 million , of which £271 million is current and £4,093 million is non-current. As at 31 March 2023 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 (4,779) 789 (43) 398 (351) 47 1. The carrying value of the hedged borrowings was £4,042 million , of which £511 million was current and £3,531 million was non-current. 2. Included within the hedging instrument notional balance was £859 million impacted by Interest Rate Benchmark Reform amendments which were still to be transitioned. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2024 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 and forecast cash flows (9,892) 154 — (18) 3 (15) Foreign currency risk on forecast cash flows (2,039) (31) — 28 (28) — As at 31 March 2023 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 (9,357) (73) — 149 (154) (5) Foreign currency risk on forecast cash flows (537) (3) — (35) 35 — (iii) Net investment hedges of foreign currency risk: As at 31 March 2024 Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Currency risk on foreign operations (2,999) 40 (2,564) (62) 62 — As at 31 March 2023 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 (3,095) (129) (2,457) 198 (198) — 32. Financial risk management continued (f) Commodity price risk We purchase electricity and gas to supply our customers in the US and to meet our own energy needs. Substantially all our costs of purchasing electricity and gas for supply to customers are recovera

Post balance sheet events

Post balance sheet events	12 Months Ended
	Mar. 31, 2024
Disclosure of non-adjusting events after reporting period [abstract]
Post balance sheet events	36. Post balance sheet events On 22 May 2024 , the Board resolved to offer a fully underwritten Rights Issue to raise gross proceeds of £7 billion .

Insider Trading Policies and Pr

Insider Trading Policies and Procedures	12 Months Ended
	Mar. 31, 2024
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Basis of preparation and rece_2

Basis of preparation and recent accounting developments (Policies)	12 Months Ended
	Mar. 31, 2024
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
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. They are prepared on the basis of all IFRS accounting standards and interpretations that are mandatory for the period ended 31 March 2024 and in accordance with the Companies Act 2006. 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	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 assessed the principal risks alongside potential downside business cash flow scenarios impacting the Group’s operations. The Directors specifically considered both a base case and reasonable worst-case scenario for business cash flows. As part of the assessment the Directors have included the expected receipt of the fully underwritten Rights Issue. The assessment is prepared on the conservative assumption that the Group has no access to the debt capital markets. The main cash flow impacts identified in the reasonable worst-case scenario are: • the timing of the sale of assets classified as held for sale (see note 10 ); • adverse impacts of inflation and incremental spend on our capital expenditure programme; • adverse impact from timing across the Group (i.e. a net under- recovery of allowed revenues or reductions in over-collections) and slower collections of outstanding receivables; • higher operating and financing costs than expected, including non‑delivery of planned efficiencies across the Group; and • the potential impact of further significant storms in the US. 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 expenditure programme, with elements of non-essential works and programmes delayed; and • a number of further reductions in operating expenditure across the Group. Having considered the reasonable worst-case scenario 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 and extend existing financing was separately included in the analysis, and the Directors noted £5.6 billion of new long-term senior debt issued in the period from 1 April 2023 to 31 March 2024 as evidence of the Group’s ability to continue to have access to the debt capital markets if needed. 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	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 ability 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	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 date 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 ).
Disposals of the UK Electricity System Operator (ESO), and disposals of the UK Gas Transmission business	D. Disposal of the UK Electricity System Operator (ESO) As described further in note 10 , at the end of October 2023, the legislation required to enable the separation of the ESO and the formation of the National Energy System Operator (NESO) was passed through Parliament. The NESO is expected to be established as an independent Public Corporation this calendar year, with responsibilities across both the electricity and gas systems. As a result, the Group took the judgement to classify the associated assets and liabilities of the ESO as held for sale in the consolidated statement of financial position at the end of October 2023. The ESO has not met the criteria for classification as a discontinued operation and therefore its results have not been separately disclosed on the face of the income statement, and are instead included within the results from continuing operations. E. Disposal of the UK Gas Transmission business Following the Group’s disposal of a 60% controlling stake in the UK Gas Transmission business in the year ended 31 March 2023, the Group completed the sale of a further 20% of its retained interest in the business (held through GasT TopCo Limited) on 11 March 2024. The other 80% of GasT TopCo Limited is owned by Macquarie Infrastructure and Real Assets (MIRA) and British Columbia Investment Management Corporation (BCI) (together, the Consortium). The Group’s remaining 20% interest in GasT TopCo Limited is classified as an investment in an associate on the basis that the Group has a significant influence over the business. The remaining 20% interest is subject to an option agreement with the Consortium, the Remaining Acquisition Agreement (RAA), which on 9 July 2023 replaced the previous Further Acquisition Agreement (FAA) under which the 20% disposal in the year was executed. The RAA option is exercisable, at the Consortium’s option, between 1 May 2024 and 31 July 2024. If the RAA option is partially exercised by the Consortium, the Group will have the right to put the remainder of its interests in GasT TopCo Limited to the Consortium, which can be exercised by the Group between 1 December 2024 and 31 December 2024. Taking into consideration the timing of the RAA exercise window, the Group has continued to classify its remaining interest in GasT TopCo Limited as held for sale and has not equity accounted for its share of the associate’s results. The loss on the 20% disposal of GasT TopCo Limited and the remeasurements in relation to the FAA option and the RAA option have been recorded within discontinued operations. As an associate held for sale, the Group has not recognised any share of results in the year ended 31 March 2024. The classification impacts on the consolidated income statement, the consolidated statement of comprehensive income and the consolidated cash flow statement, as well as earnings per share (EPS) split between continuing and discontinued operations. 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 expected to be 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.
Areas of judgement and key sources of estimation uncertainty	F. 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: • the judgement that it is appropriate to classify our 20% equity investment in GasT TopCo Limited, together with the RAA option, as held for sale, as detailed in note 10 ; and • the judgement that, notwithstanding legislation enacted and targets committing the states of New York and Massachusetts to achieving net zero greenhouse gas emissions by 2050, these do not shorten the remaining useful economic lives (UELs) of our US gas network assets, which we consider will have an expected use and utility beyond 2050 (see key sources of estimation uncertainty below and note 13 ) . 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: • the cash flows and real discount rates applied in determining the US environmental provisions, in particular relating to three Superfund sites and certain other legacy Manufacturing Gas Plant (MGP) sites (see note 26 ); • the estimates made regarding the UELs of our gas network assets due to uncertainty over the pace of delivery of the energy transition and the multiple pathways by which it could be delivered. Our estimates consider anticipated changes in customer behaviour and developments in new technology, the potential to decarbonise fuel through the use of renewable natural gas and green hydrogen, and the feasibility and affordability of increased electrification (see note 13 for details and sensitivity analysis ); and • the valuation of liabilities for pensions and other post-retirement benefits (see note 25 ). 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 analysis in note 35
Impact of climate change and the transition to net zero – areas of judgement and key sources of estimation uncertainty	G. Impact of climate change and the transition to net zero – areas of judgement and key sources of estimation uncertainty In preparing these financial statements for the year ended 31 March 2024 , management has taken into account the Group’s commitments regarding its transition to net zero and the impact of climate change. The Group has a published climate transition plan which sets out its targets to achieve this commitment by 2050, in line with the Paris Agreement. Management has also identified a number of significant climate-related risks and opportunities. Changes to the Group’s commitments and the impact of climate change may have a material impact on the currently reported amounts of the Group’s assets and liabilities and on similar assets and liabilities that may be recognised in future reporting periods, as set out above with respect to the judgement and key source of estimation uncertainty regarding the UELs of our US gas network assets, and as further detailed below. Repairs to property, plant and equipment and climate adaptation activities The Group’s network assets recorded within property, plant and equipment (PP&E) are at risk of physical impacts from extreme weather events such as major storms which may be accentuated by increased frequency of weather incidents and changing long-term climate trends, thereby leading to asset damage. M ajor storm costs, net of deductibles and disallowances, incurred by the Group are recoverable as revenue in future periods under our rate plans but the associated repair costs are expensed as incurred as other operating costs under IFRS. Impairment of property, plant and equipment and goodwill Included within the Group’s plant and machinery (see note 13 ) are £325 million of oil- and gas-fired electricity generation units with approximately 3,800 MW of electric generation capacity located in Long Island, New York. Whilst the Group retains ownership of these assets, it sells all of the capacity, energy in response to dispatch requests, and any related ancillary services provided by the generating facilities to the Long Island Power Authority (LIPA) via a Power Supply Agreement running until 2028. The maximum UEL for these units ends in 2040, which aligns to the target set by the state of New York to achieve decarbonised power generation by 2040. However, there is a risk that the UEL of certain, or all, of the units may be shortened, depending on the progress of decarbonisation activities in Long Island. The Group believes there are no material accounting judgements in respect of the generation assets and the UELs have not been accelerated in the year. The assets related to the Group’s liquefied natural gas (LNG) storage facility at the Isle of Grain in the UK have a maximum UEL to 2045, which is in line with the current commercial contracts. The UELs of our assets related to our commercial operations in LNG at Providence, Rhode Island are informed by the recovery periods used for ratemaking purposes and the majority of the UELs are covered by fixed price service contracts. The net book value of these assets will be immaterial by 2050. Accordingly, the Group believes there are no material accounting judgements in respect of the UELs of the LNG assets as of 31 March 2024 . 1. Basis of preparation and recent accounting developments continued G. Impact of climate change and the transition to net zero – areas of judgement and key sources of estimation uncertainty continued The net zero pathway may also impact our US gas networks which in turn may affect the recoverable amount of our New York and New England cash-generating units (CGUs). In assessing the recoverability of our CGUs (see note 11 ), we calculate the value-in-use based on projections that incorporate our best estimates of future cash flows and assumptions pertaining to the net zero plans of the jurisdictions that we operate in. In respect of our New York and New England CGUs, our forecast cash flow duration used in our impairment testing is five years . We apply a terminal growth rate informed by expected long-term economic inflation and the discount rate used takes into consideration the potential impact of net zero plans on our gas business. Accordingly, the impact of certain variables that will play out in the medium to long term as a result of the anticipated transition to decarbonised power generation are not anticipated to have an impact on the recoverable amount of our New York and New England CGUs. Decommissioning provisions 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. Included within the Group’s decommissioning provisions as at 31 March 2024 (see note 26 ) is £57 million relating to legal requirements to remove asbestos upon major renovation or demolition of our oil- and gas-fired electricity generation structures and facilities located in Long Island, New York. As noted above, the progress of decarbonisation activities in Long Island may bring forward the decommissioning of these assets, thereby increasing the present value of associated decommissioning provisions. In the current year, there have been no material changes to the expected timing of decommissioning expenditures. Currently, the expected timing of decommissioning expenditures has not materially been brought forward but management will continue to review the facts and circumstances. Sensitivity to commodity contract derivatives The Group has contracts associated with the forward purchase of gas and enters into derivative financial instruments linked to commodity prices, including gas options and swaps which are used to manage market price volatility (see note 17 (b)). As at 31 March 2024 , the Group’s gas commodity contract derivatives are primarily short-term and accordingly we do not anticipate a risk as a result of the transition
Accounting policy choices	H. 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 2024	I. New IFRS accounting standards and interpretations effective for the year ended 31 March 2024 The Group adopted the following new standards and amendments to standards which have had no material impact on the Group’s results or financial statement disclosures: • IFRS 17 ‘Insurance Contracts’; • amendments to IAS 1 and IFRS Practice Statement 2 – ‘Making Materiality Judgements’; • amendments to IAS 12 ‘International Tax Reform — Pillar Two Model Rules’; and • amendments to IAS 8 ‘Accounting Policies, Changes in Accounting Estimates and Errors’. In May 2021, the IASB issued amendments to IAS 12 ‘Income Taxes’ in order to narrow the scope of the initial recognition exemption to exclude transactions that give rise to equal and offsetting temporary differences. Following the amendments, the Group recognised separate deferred tax assets in relation to its lease liabilities and decommissioning obligations, and deferred tax liabilities in relation to its right-of-use assets (see note 7 ). As the balances qualify for offset, there is no impact on the consolidated statement of financial position and the opening retained earnings as at 1 April 2023.
New IFRS accounting standards and interpretations not yet adopted	J. 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: • amendments to IFRS 10 and IAS 28 ‘Sale or Contribution of Assets between an Investor and its Associate or Joint Venture’; • amendments to IAS 1 ‘Classification of Liabilities as Current or Non‑current’; • amendments to IAS 1 ‘Non-current Liabilities with Covenants’; • amendments to IAS 7 and IFRS 7 ‘Supplier Finance Arrangements’; • amendments to IFRS 16 ‘Lease Liability in a Sale and Leaseback’; and • amendments to IAS 21 ‘The Effects of Changes in Foreign Exchange Rates’. 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 a profit measure that excludes certain income and expenses. We call that measure ‘adjusted profit’. Adjusted profit excludes exceptional items and remeasurements (as defined in note 5 ) and 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. As a matter of course, the Board also considers profitability by segment, excluding the effects of timing, major storm costs and deferred tax in our UK Electricity Transmission and UK Electricity Distribution businesses. 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) fall within the scope of IFRS 15 ‘Revenue from Contracts with Customers’, whereas generation services (which solely relate to the contract with LIPA in the US) are accounted for under IFRS 16 ‘Leases’ as rental income, also presented within revenue. Revenue is recognised to reflect the transfer of goods or services to customers at an amount that reflects the consideration to which the Group expects to be entitled to in exchange for those goods or services 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. Revenue in respect of regulated activities is determined by regulatory agreements that set the price to be charged for services in a given period based on pre-determined allowed revenues. Variances in service usage can result in actual revenue collected exceeding (over-recoveries) or falling short (under-recoveries) of allowed revenues. Where regulatory agreements allow the recovery of under-recoveries or require the return of over-recoveries, the allowed revenue for future periods is typically adjusted. In these instances, no assets or liabilities are recognised for under- or over-recoveries respectively, because the adjustment relates to future customers and services that have not yet been delivered. Revenue in respect of non-regulated activities primarily relates to the sale of capacity on our interconnectors, which is determined at auctions. Capacity is sold in either day, month, quarter or year-ahead tranches. The price charged is determined by market fundamentals rather than regulatory agreement. The interconnectors are subject to indirect regulation with regard to the levels of returns they are allowed to earn. Where amounts fall below this range they receive top-up revenues and where amounts exceed this range they must pass back the excess. In these instances, assets or liabilities are recognised for the top-up or pass-back respectively.
Other operating costs	Below we have presented separately certain items included in our operating costs from continuing operations. These include a breakdown
Exceptional items and remeasurements	To monitor our segmental financial performance, we use an adjusted consolidated profit measure that excludes certain income and expenses. 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.
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. 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.
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 are the software assets controlled by us and the electricity distribution licences which provide us with the right to operate and invest in the relevant network that operates as a monopoly in the licensed geographical area. The regulatory licences were acquired following the Group’s acquisition of NGED.
Property, plant and equipment	Property, plant and equipment are the physical assets controlled by us. The Group’s interest comprises legally protected statutory or contractual
Other non-current assets	Other non-current assets include assets that do not fall into specific non-current asset categories (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 2025.
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 cannot be readily used in operations, principally collateral deposited in relation to derivatives.
Subsidiaries	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.
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 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 12 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
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 inflation indices. 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 lead us to fund our networks within a certain ratio of debt to equity or regulatory asset 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 are undrawn.
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 2025 . 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 ‘Employee Benefits’. We separately present our UK and US pension plans to show the 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.
Provisions	Provisions are recognised where a legal or constructive obligation exists at the reporting date, as a result of a past event, where the outflow
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 financing derivatives less cash and current financial investments.
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.
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.

Segmental analysis (Tables)

Segmental analysis (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of operating segments [abstract]
Schedule of main activities, revenue, operating profit and capital investment by 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. This includes our Accelerated Strategic Transmission Investment projects to connect more clean, low-carbon power to the transmission network in England and Wales. UK Electricity Distribution The electricity distribution networks of NGED in the East Midlands, West Midlands and South West of England and South Wales. UK Electricity System Operator The Great Britain system operator. The ESO met the criteria to be classified as held for sale at the end of October 2023 (see note 10). New England Gas distribution networks, electricity distribution networks and high-voltage electricity transmission networks in New England. New York Gas distribution networks, electricity distribution networks and high-voltage electricity transmission networks in New York. National Grid Ventures Comprises all commercial operations in LNG at the Isle of Grain in the UK and Providence, Rhode Island in the US, our electricity generation business in the US, our electricity interconnectors in the UK and our investment in National Grid Renewables Development LLC, our renewables business in the US. Whilst NGV operates outside our regulated core business, the electricity interconnectors in the UK are subject to indirect regulation by Ofgem regarding the level of returns they can earn. Our US LNG operations were reclassified from the New England segment following an internal reorganisation in the year. 2024 2023 2022 Total sales £m Sales between segments £m Sales to third parties £m Total sales £m Sales between segments £m Sales to third parties £m Total sales £m Sales between segments £m Sales to third parties £m Operating segments – continuing operations: UK Electricity Transmission 2,735 (40) 2,695 1,987 (41) 1,946 2,035 (7) 2,028 UK Electricity Distribution 1,795 (5) 1,790 2,045 (12) 2,033 1,482 (14) 1,468 UK Electricity System Operator 3,788 (35) 3,753 4,690 (31) 4,659 3,455 (18) 3,437 New England 3,948 — 3,948 4,427 — 4,427 4,550 — 4,550 New York 6,094 — 6,094 6,994 — 6,994 5,561 — 5,561 National Grid Ventures 1,389 (57) 1,332 1,341 (58) 1,283 1,024 — 1,024 Other 244 (6) 238 317 — 317 381 — 381 Total revenue from continuing operations 19,993 (143) 19,850 21,801 (142) 21,659 18,488 (39) 18,449 Split by geographical areas – continuing operations: UK 9,063 9,611 7,803 US 10,787 12,048 10,646 Total revenue from continuing operations 19,850 21,659 18,449 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 and remeasurements Exceptional items and remeasurements (see note 5) After exceptional items and remeasurements 2024 2023 2022 2024 2023 2022 2024 2023 2022 £m £m £m £m £m £m £m £m £m Operating segments – continuing operations: UK Electricity Transmission 1,677 995 1,067 (3) (2) (12) 1,674 993 1,055 UK Electricity Distribution 993 1,091 909 (18) (22) — 975 1,069 909 UK Electricity System Operator 880 238 7 (498) (1) (2) 382 237 5 New England 643 708 743 (2) 424 21 641 1,132 764 New York 860 741 780 (498) (200) 315 362 541 1,095 National Grid Ventures 469 490 286 89 467 (3) 558 957 283 Other (60) 31 21 (57) (81) 239 (117) (50) 260 Total operating profit from continuing operations 5,462 4,294 3,813 (987) 585 558 4,475 4,879 4,371 Split by geographical area – continuing operations: UK 3,923 2,825 2,234 (487) 26 224 3,436 2,851 2,458 US 1,539 1,469 1,579 (500) 559 334 1,039 2,028 1,913 Total operating profit from continuing operations 5,462 4,294 3,813 (987) 585 558 4,475 4,879 4,371 Before exceptional items and remeasurements Exceptional items and remeasurements (see note 5) After exceptional items and remeasurements 2024 2023 2022 2024 2023 2022 2024 2023 2022 £m £m £m £m £m £m £m £m £m Reconciliation to profit before tax: Operating profit from continuing operations 5,462 4,294 3,813 (987) 585 558 4,475 4,879 4,371 Share of post-tax results of joint ventures and associates 101 190 148 (64) (19) (56) 37 171 92 Finance income 244 166 65 4 (28) (15) 248 138 50 Finance costs (1,723) (1,680) (1,146) 11 82 74 (1,712) (1,598) (1,072) Profit before tax from continuing operations 4,084 2,970 2,880 (1,036) 620 561 3,048 3,590 3,441 The following items are included in the total operating profit by segment: Depreciation, amortisation and impairment 2024 2023 2022 £m £m £m Operating segments: UK Electricity Transmission (521) (484) (508) UK Electricity Distribution (223) (223) (158) UK Electricity System Operator (61) (101) (83) New England (420) (393) (364) New York (658) (620) (537) National Grid Ventures (166) (149) (156) Other (12) (14) (24) Total (2,061) (1,984) (1,830) Asset type: Property, plant and equipment (1,769) (1,700) (1,544) Non-current intangible assets (292) (284) (286) Total (2,061) (1,984) (1,830) 2024 2023 1 2022 1 £m £m £m Operating segments: UK Electricity Transmission 1,912 1,301 1,179 UK Electricity Distribution 1,247 1,220 899 UK Electricity System Operator 85 108 108 New England 1,673 1,527 1,478 New York 2,654 2,454 1,960 National Grid Ventures 662 970 989 Other 2 13 10 Total 8,235 7,593 6,623 Asset type: Property, plant and equipment 7,124 6,783 5,622 Non-current intangible assets 481 578 471 Equity investments in joint ventures and associates 2 332 197 461 Capital expenditure prepayments 298 35 69 Total 8,235 7,593 6,623 1. Comparative amounts have been represented to reflect the reclassification of our US LNG operations from New England to NGV following an internal reorganisation in the year and the change in presentation for capital investments. 2. Excludes £nil ( 2023 : £nil , 2022 : £25 million ) equity contribution to the St William Homes LLP joint venture. This was excluded based on the nature of the joint venture arrangement. We typically contributed property assets to the joint venture in exchange for cash and accordingly did not consider these transactions to be in the nature of capital investment.
Schedule of geographical analysis of non-current assets	2024 2023 2022 £m £m £m Split by geographical area: UK 40,065 38,043 35,466 US 44,270 41,761 36,411 84,335 79,804 71,877 Reconciliation to total non-current assets: Pension assets 2,407 2,645 3,885 Financial and other investments 880 859 830 Derivative financial assets 324 276 305 Non-current assets 87,946 83,584 76,897 The trade receivables balance, accrued income balance and provisions balance split by geography are as follows: As at 31 March 2024 As at 31 March 2023 UK US Total UK US Total £m £m £m £m £m £m Trade receivables 162 2,339 2,501 223 2,360 2,583 Accrued income 337 548 885 650 476 1,126 Provision for impairment of receivables and accrued income (3) (556) (559) (11) (549) (560) 496 2,331 2,827 862 2,287 3,149

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of disaggregation of revenue from contracts with customers [abstract]
Disclosure of disaggregation of revenue by primary geographical market and major service lines	3. Revenue continued (h) Disaggregation of revenue In the following tables, revenue is disaggregated by primary geographical market and major service lines. The table below reconciles disaggregated revenue with the Group’s reportable segments (see note 2 ). Revenue for the year ended 31 March 2024 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 Transmission 1 2,591 — (10) 73 493 869 — 4,016 Distribution — 1,712 — 3,786 5,500 — — 10,998 System Operator — — 3,763 — — — — 3,763 Other 2 25 73 — 8 15 168 4 293 Total IFRS 15 revenue 2,616 1,785 3,753 3,867 6,008 1,037 4 19,070 Other revenue Generation — — — — — 360 — 360 Other 3 79 5 — 81 86 (65) 234 420 Total other revenue 79 5 — 81 86 295 234 780 Total revenue from continuing operations 2,695 1,790 3,753 3,948 6,094 1,332 238 19,850 1. The UK Electricity System Operator transmission revenue in the year represents transmission revenues collected, net of payments made to transmission owners. 2. The UK Electricity Transmission and UK Electricity Distribution other IFRS 15 revenue principally relates to engineering recharges, which are the recovery of costs incurred for construction work requested by customers, such as the rerouting of existing network assets. Within NGV, the other IFRS 15 revenue principally relates to revenue generated from our National Grid Renewables business. 3. Other revenue, recognised in accordance with accounting standards other than IFRS 15, includes property sales by our UK commercial property business, rental income, income arising in connection with the Transition Services Agreements following the sales of NECO and the UK Gas Transmission business in the prior year, and an adjustment to NGV revenue in respect of the interconnector cap and floor and Use of Revenue regimes constructed by Ofgem. Geographical split for the year ended 31 March 2024 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 UK 2,616 1,785 3,753 — — 878 1 9,033 US — — — 3,867 6,008 159 3 10,037 Total IFRS 15 revenue 2,616 1,785 3,753 3,867 6,008 1,037 4 19,070 Other revenue UK 79 5 — — — (76) 22 30 US — — — 81 86 371 212 750 Total other revenue 79 5 — 81 86 295 234 780 Total revenue from continuing operations 2,695 1,790 3,753 3,948 6,094 1,332 238 19,850 Revenue for the year ended 31 March 2023 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 Transmission 1,868 — 126 52 567 791 — 3,404 Distribution — 1,951 — 4,314 6,373 — — 12,638 System Operator — — 4,533 — — — — 4,533 Other 1 31 77 — 8 13 131 — 260 Total IFRS 15 revenue 1,899 2,028 4,659 4,374 6,953 922 — 20,835 Other revenue Generation — — — — — 394 — 394 Other 2 47 5 — 53 41 (33) 317 430 Total other revenue 47 5 — 53 41 361 317 824 Total revenue from continuing operations 1,946 2,033 4,659 4,427 6,994 1,283 317 21,659 1. The UK Electricity Transmission and UK Electricity Distribution other IFRS 15 revenue principally relates to engineering recharges, which are the recovery of costs incurred for construction work requested by customers, such as the rerouting of existing network assets. Within NGV, the other IFRS 15 revenue principally relates to revenue generated from our National Grid Renewables business. 2. Other revenue, recognised in accordance with accounting standards other than IFRS 15, includes property sales by our UK commercial property business, rental income, income arising in connection with the Transition Services Agreements following the sales of NECO and the UK Gas Transmission business, and a provision and adjustment to NGV revenue in respect of the interconnector cap and floor regime constructed by Ofgem. In the year ended 31 March 2023, the Group also recognised other income relating to an insurance claim. 3. Revenue continued (h) Disaggregation of revenue continued Geographical split for the year ended 31 March 2023 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 UK 1,899 2,028 4,659 — — 799 — 9,385 US — — — 4,374 6,953 123 — 11,450 Total IFRS 15 revenue 1,899 2,028 4,659 4,374 6,953 922 — 20,835 Other revenue UK 47 5 — — — (31) 205 226 US — — — 53 41 392 112 598 Total other revenue 47 5 — 53 41 361 317 824 Total revenue from continuing operations 1,946 2,033 4,659 4,427 6,994 1,283 317 21,659 Revenue for the year ended 31 March 2022 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 Transmission 1,983 — — 52 405 627 — 3,067 Distribution — 1,375 — 4,434 5,110 — — 10,919 System Operator — — 3,418 — — — — 3,418 Other¹ 35 89 19 10 10 147 — 310 Total IFRS 15 revenue 2,018 1,464 3,437 4,496 5,525 774 — 17,714 Other revenue Generation — — — — — 373 — 373 Other 2 10 4 — 54 36 (123) 381 362 Total other revenue 10 4 — 54 36 250 381 735 Total revenue from continuing operations 2,028 1,468 3,437 4,550 5,561 1,024 381 18,449 1. The UK Electricity Transmission and UK Electricity Distribution other IFRS 15 revenue principally relates to engineering recharges, which are the recovery of costs incurred for construction work requested by customers, such as the rerouting of existing network assets. UK Electricity System Operator other IFRS 15 revenue reflects the net income from its role as agent in respect of transmission network revenues. Within NGV, the other IFRS 15 revenue principally relates to revenue generated from our National Grid Renewables business. 2. Other revenue, recognised in accordance with accounting standards other than IFRS 15, includes property sales by our UK commercial property business and rental income. Included within NGV is a provision and adjustment to NGV revenue in respect of the interconnector cap and floor regime constructed by Ofgem. Geographical split for the year ended 31 March 2022 UK Electricity Transmission £m UK Electricity Distribution £m UK Electricity System Operator £m New England £m New York £m National Grid Ventures £m Other £m Total £m Revenue under IFRS 15 UK 2,018 1,464 3,437 — — 646 — 7,565 US — — — 4,496 5,525 128 — 10,149 Total IFRS 15 revenue 2,018 1,464 3,437 4,496 5,525 774 — 17,714 Other revenue UK 10 4 — — — (132) 356 238 US — — — 54 36 382 25 497 Total other revenue 10 4 — 54 36 250 381 735 Total revenue from continuing operations 2,028 1,468 3,437 4,550 5,561 1,024 381 18,449

Other operating costs (Tables)

Other operating costs (Tables)	12 Months Ended
	Mar. 31, 2024
Analysis of income and expense [abstract]
Schedule of analysis of expenses by nature and payroll costs	Total 2024 2023 2022 £m £m £m Depreciation, amortisation and impairment 2,061 1,984 1,830 Payroll costs 2,043 1,958 1,794 Purchases of electricity 1,497 2,055 1,280 Purchases of gas 1,289 2,516 1,666 Property and other taxes 1,279 1,302 1,202 UK electricity balancing costs 2,486 4,052 3,152 Other 4,553 3,682 3,215 Other operating costs 15,208 17,549 14,139 Provision for bad and doubtful debts 179 220 167 Total operating costs from continuing operations 15,387 17,769 14,306 Operating costs from continuing operations include: Inventory consumed 408 723 436 Research and development expenditure 32 23 11 (a) Payroll costs 2024 2023 2022 £m £m £m Wages and salaries 1 3,206 2,971 2,563 Social security costs 256 244 201 Defined contribution scheme costs 129 98 81 Defined benefit pension costs 96 121 185 Share-based payments 37 46 38 Severance costs (excluding pension costs) 12 3 5 3,736 3,483 3,073 Less: payroll costs capitalised (1,693) (1,525) (1,279) Total payroll costs from continuing operations 2,043 1,958 1,794 1. Included within wages and salaries are US other post-retirement benefit costs of £26 million ( 2023 : £37 million ; 2022 : £39 million ). For further information, refer to note 25 .
Schedule of additional information about employee, key management personnel and auditors' remuneration	(b) Number of employees 31 March 2024 Monthly average 2024 31 March 2023 Monthly average 2023 31 March 2022 Monthly average 2022 UK 13,956 13,439 12,572 12,024 11,960 11,393 US 17,469 17,406 16,878 16,539 17,332 17,314 Total number of employees (continuing operations) 31,425 30,845 29,450 28,563 29,292 28,707 4. Other operating costs continued (c) Key management compensation 2024 2023 2022 £m £m £m Short-term employee benefits 7 7 7 Post-employment benefits — — 1 Share-based payments 5 6 5 Total key management compensation 12 13 13 Auditor’s 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: 2024 2023 2022 £m £m £m Audit fees payable to the Parent Company’s auditor and their associates in respect of: Audit of the Parent Company’s individual and consolidated financial statements 1 2.8 2.9 2.7 The auditing of accounts of any associate of the Company 8.8 9.0 8.9 Other services supplied 2 7.3 7.4 7.3 18.9 19.3 18.9 Total other services 3 All other fees: Other assurance services 4 4.0 1.4 0.9 Other non-audit services not covered above — 0.2 0.1 4.0 1.6 1.0 Total auditor’s remuneration 22.9 20.9 19.9 1. Audit fees in each year represent fees for the audit of the Company’s financial statements for the years ended 31 March 2024 , 2023 and 2022 . 2. 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 auditor. 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 Act), audit reports on regulatory returns and the review of interim financial statements for the six-month periods ended 30 September 2023 , 2022 and 2021 respectively. 3. There were no tax compliance or tax advisory fees and no audit-related fees as described in Item 16C(b) of Form 20-F. 4. In all years, principally relates to assurance services provided in relation to comfort letters for debt issuances and reporting accountant services.

Exceptional items and remeasu_2

Exceptional items and remeasurements (Tables)	12 Months Ended
	Mar. 31, 2024
Exceptional Items And Remeasurements [Abstract]
Schedule of exceptional items and remeasurements from continuing operations	Exceptional items and remeasurements from continuing operations 2024 2023 2022 £m £m £m Included within operating profit Exceptional items: Transaction, separation and integration costs 1 (44) (117) (223) Cost efficiency programme (65) (100) (42) IFA fire 92 130 — Changes in environmental provisions (496) 176 — Provision for UK electricity balancing costs (498) — — Net gain on disposal of NECO — 511 — Net gain on disposal of Millennium Pipeline Company LLC — 335 — New operating model implementation costs — — (24) Release of St William Homes LLP deferred income — — 189 Net gain on disposal of St William Homes LLP — — 228 Environmental insurance recovery — — 38 (1,011) 935 166 Remeasurements – commodity contract derivatives 24 (350) 392 (987) 585 558 1. Transaction, separation and integration costs represent the aggregate of distinct activities undertaken by the Group in the years presented. Details of remeasurements, tax exceptional items and the tax effect of exceptional items and remeasurements are also provided in this note. 2024 2023 2022 £m £m £m Included within operating profit from continuing operations (987) 585 558 Included within finance income and costs Remeasurements: Net gains/(losses) on financial assets at fair value through profit and loss 4 (28) (15) Net gains on financing derivatives 11 82 74 15 54 59 Included within share of post-tax results of joint ventures and associates Remeasurements: Net losses on financial instruments (64) (19) (56) Total included within profit before tax (1,036) 620 561 Included within tax Exceptional items – movements arising on items not included in profit before tax: Deferred tax charge arising as a result of UK tax rate change — — (458) Tax on exceptional items 159 (316) (28) Tax on remeasurements (7) 75 (103) 152 (241) (589) Total exceptional items and remeasurements after tax (884) 379 (28) Analysis of total exceptional items and remeasurements after tax Exceptional items after tax (852) 619 (320) Remeasurements after tax (32) (240) 292 Total exceptional items and remeasurements after tax (884) 379 (28)

Finance income and costs (Table

Finance income and costs (Tables)	12 Months Ended
	Mar. 31, 2024
Analysis of income and expense [abstract]
Schedule of finance income and costs	Finance income and costs remeasurements include unrealised gains and losses on certain assets and liabilities treated at FVTPL. The effective interest income and interest expense and dividends on these items are included in finance income and finance costs before remeasurements respectively. 2024 2023 2022 Notes £m £m £m Finance income Net interest income on pensions and other post-retirement benefit obligations 25 100 85 — Interest income on financial instruments: Bank deposits and other financial assets 139 80 32 Dividends received on equities held at fair value through other comprehensive income (FVOCI) 1 1 3 Net gains/(losses) on FVTPL financial assets 4 (28) (15) Other income 4 — 30 248 138 50 Finance costs Interest expense on financial liabilities held at amortised cost: Bank loans and overdrafts (140) (328) (216) Other borrowings 1 (1,424) (1,330) (961) Interest on derivatives (277) (170) (59) Unwinding of discount on provisions 26 (102) (88) (73) Other interest (31) (13) 11 Derivatives designated as hedges for hedge accounting² 13 22 45 Derivatives not designated as hedges for hedge accounting² (2) 60 29 Less: interest capitalised³ 251 249 152 (1,712) (1,598) (1,072) Finance income 248 138 50 Finance costs 4 (1,712) (1,598) (1,072) Net finance costs from continuing operations (1,464) (1,460) (1,022) 1. Includes interest expense on lease liabilities (see note 13 for details) . 2. Includes a net foreign exchange gain on borrowing and investment activities of £271 million ( 2023 : £86 million loss ; 2022 : £110 million gain ) offset by foreign exchange gains and losses on financing derivatives measured at fair value and the impacts of hedge accounting. 3. Interest on funding attributable to assets in the course of construction in the current year was capitalised at a rate of 4.7% ( 2023 : 4.7% ; 2022 : 3.2% ). In the UK, capitalised interest qualifies for a current year tax deduction with tax relief claimed of £39 million ( 2023 : £30 million ; 2022 : £16 million ). In the US, capitalised interest is added to the cost of property, plant and equipment, and qualifies for tax depreciation allowances. 4. Finance costs include principal accretion on inflation-linked liabilities of £208 million ( 2023 : £483 million ; 2022 : £241 million

Tax (Tables)

Tax (Tables)	12 Months Ended
	Mar. 31, 2024
Income taxes paid (refund) [abstract]
Schedule of tax charged to the consolidated income statement for continuing operations and components of tax expense	The tax charge for the year can be analysed as follows: 2024 2023 2022 £m £m £m Current tax: UK corporation tax at 25% ( 2023 : 19% ; 2022 : 19% ) 410 161 255 UK corporation tax adjustment in respect of prior years (36) — (9) 374 161 246 Overseas corporation tax 82 225 6 Overseas corporation tax adjustment in respect of prior years (90) (16) (26) (8) 209 (20) Total current tax from continuing operations 366 370 226 Deferred tax: UK deferred tax 388 255 605 UK deferred tax adjustment in respect of prior years 43 13 (5) 431 268 600 Overseas deferred tax (40) 233 425 Overseas deferred tax adjustment in respect of prior years 74 5 7 34 238 432 Total deferred tax from continuing operations 465 506 1,032 Total tax charge from continuing operations 831 876 1,258
Disclosure of tax (credited)/charged to the consolidated statement of comprehensive income and equity	Tax (credited)/charged to the consolidated statement of comprehensive income and equity 2024 2023 2022 £m £m £m Current tax: Share-based payments (2) (1) — Deferred tax: Investments at fair value through other comprehensive income 1 (1) — Cash flow hedges, cost of hedging and own credit reserve 56 (7) (12) Remeasurements of pension assets and post-retirement benefit obligations (50) (344) 493 Share-based payments — 1 (4) 5 (352) 477 Total tax recognised in the statements of comprehensive income from continuing operations 7 (352) 481 Total tax relating to share-based payments recognised directly in equity from continuing operations (2) — (4) 5 (352) 477
Schedule of effective tax rate reconciliation	The tax charge for the year for continuing operations, is higher ( 2023 : higher tax charge; 2022 : higher tax charge) than the standard rate of corporation tax in the UK of 25% ( 2023 : 19% ; 2022 : 19% ): 2024 2023 2022 £m £m £m Profit before tax from continuing operations 3,048 3,590 3,441 Profit before tax from continuing operations multiplied by UK corporation tax rate of 25% ( 2023 : 19% ; 2022 : 19% ) 762 682 654 Effect of: Adjustments in respect of prior years 1 (9) 2 (33) Expenses not deductible for tax purposes 155 92 47 Non-taxable income 2 (43) (75) (49) Adjustment in respect of foreign tax rates 3 (20) 147 170 Deferred tax impact of change in UK tax rate — 66 501 Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax (9) (27) (17) Other 4 (5) (11) (15) Total tax charge from continuing operations 831 876 1,258 % % % Effective tax rate – continuing operations 27.3 24.4 36.6 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. Included in the prior year are remeasurements of US closing state deferred tax balances as a result of an expected increase in the blended state tax rate following the disposal of NECO. 4. Other primarily comprises the movement in the deferred tax asset on previously unrecognised capital losses, claims for land remediation relief and claims for Research & Development credit.
Schedule of tax included within the statement of financial position and deferred tax assets not recognised	The following are the major deferred tax assets and liabilities recognised, and the movements thereon, during the current and prior reporting periods: Regulatory licences £m Accelerated tax depreciation £m Share- based payments £m Pensions and other post- retirement benefits £m Financial instruments £m Other net temporary differences 1 £m Total £m Deferred tax liabilities/(assets) At 1 April 2022 429 7,710 (18) 775 (301) (1,830) 6,765 Exchange adjustments and other 2 — 357 (2) 8 8 (116) 255 Charged/(credited) to income statement — 145 (2) 51 (71) 386 509 Charged/(credited) to other comprehensive income and equity — — 1 (344) (6) — (349) Disposals — 1 — — — — 1 At 1 April 2023 (as previously reported) 429 8,213 (21) 490 (370) (1,560) 7,181 Impact of IAS 12 amendment 3 — 29 — — — (29) — At 1 April 2023 (as restated) 429 8,242 (21) 490 (370) (1,589) 7,181 Exchange adjustments and other 2 — (132) — (1) 23 (110) Charged/(credited) to income statement — 720 (5) 26 38 (312) 467 (Credited)/charged to other comprehensive income and equity — — — (50) 57 — 7 Disposals — (2) — — — (2) Reclassification to held for sale (note 10) — (12) 1 (4) — (9) (24) At 31 March 2024 429 8,816 (25) 461 (275) (1,887) 7,519 1. The deferred tax asset of £1,887 million as at 31 March 2024 ( 2023 : £1,560 million ) in respect of other net temporary differences primarily relates to losses of £184 million ( 2023 : £47 million ), US contract and lease liabilities of £575 million ( 2023 : £511 million ), US environmental provisions of £646 million ( 2023 : £503 million ) and US bad debt provision of £150 million ( 2023 : £148 million ). 2. Exchange adjustments and other primarily comprises foreign exchange arising on translation of the US dollar deferred tax balances. 3. In May 2021, the IASB issued amendments to IAS 12 resulting in the recognition of separate deferred tax assets and deferred tax liabilities (see note 1 ). The total deferred tax assets not recognised are as follows: 2024 2023 £m £m Capital losses 2,483 2,367 Trading losses 4 4

Earnings per share (EPS) (Table

Earnings per share (EPS) (Tables)	12 Months Ended
	Mar. 31, 2024
Earnings per share [abstract]
Schedule of earnings per share	(a) Basic EPS Earnings EPS Earnings EPS Earnings EPS 2024 2024 2023 2023 2022 2022 £m pence £m pence £m pence Earnings from continuing operations 2,216 60.0 2,714 74.2 2,182 60.6 Earnings from discontinued operations 74 2.0 5,083 138.9 171 4.8 Total earnings 2,290 62.0 7,797 213.1 2,353 65.4 2024 2023 2022 millions millions millions Weighted average number of ordinary shares – basic 3,692 3,659 3,599 (b) Diluted EPS Earnings EPS Earnings EPS Earnings EPS 2024 2024 2023 2023 2022 2022 £m pence £m pence £m pence Earnings from continuing operations 2,216 59.7 2,714 73.8 2,182 60.3 Earnings from discontinued operations 74 2.0 5,083 138.3 171 4.7 Total earnings 2,290 61.7 7,797 212.1 2,353 65.0 2024 2023 2022 millions millions millions Weighted average number of ordinary shares – diluted 3,709 3,676 3,616 (c) Reconciliation of basic to diluted average number of shares 2024 2023 2022 millions millions millions Weighted average number of ordinary shares – basic 3,692 3,659 3,599 Effect of dilutive potential ordinary shares – employee share plans 17 17 17 Weighted average number of ordinary shares – diluted 3,709 3,676 3,616

Dividends (Tables)

Dividends (Tables)	12 Months Ended
	Mar. 31, 2024
Dividend [Abstract]
Schedule of dividends to shareholders	Interim dividends are recognised when they become payable to the Company’s shareholders. Final dividends are recognised when they are approved by shareholders. 2024 2023 2022 Pence per share Cash dividend £m Scrip dividend £m Pence per share Cash dividend £m Scrip dividend £m Pence per share Cash dividend £m Scrip dividend £m Interim dividend in respect of the current year 19.40 393 320 17.84 488 163 17.21 339 282 Final dividend in respect of the prior year 37.60 1,325 56 33.76 1,119 114 32.16 583 562 57.00 1,718 376 51.60 1,607 277 49.37 922 844

Assets held for sale and disc_2

Assets held for sale and discontinued operations (Tables)	12 Months Ended
	Mar. 31, 2024
Non-current assets or disposal groups classified as held for sale or as held for distribution to owners [abstract]
Schedule of assets and liabilities classified as held for sale	The following assets and liabilities were classified as held for sale: 2024 2023 Total assets held for sale £m Total liabilities held for sale £m Net assets held for sale £m Total assets held for sale £m Total liabilities held for sale £m Net assets held for sale £m UK Electricity System Operator 1,134 (1,427) (293) — — — Investment in GasT TopCo Limited 689 — 689 1,443 — 1,443 FAA option — — — — (109) (109) RAA option — (47) (47) — — — Net assets held for sale 1,823 (1,474) 349 1,443 (109) 1,334 The following assets and liabilities of the ESO were classified as held for sale at 31 March 2024 . £m Intangible assets 405 Property, plant and equipment 113 Trade and other receivables 563 Pension asset 17 Cash and cash equivalents 30 Financing derivatives 6 Total assets 1,134 Borrowings (13) Other liabilities (916) Provision for UK electricity balancing costs (498) Total liabilities (1,427) Net liabilities (293)
Schedule of statements for discontinued operations	The summary income statements for the years ended 31 March 2024 , 2023 and 2022 are as follows: Total 2024 2023 2022 £m £m £m Discontinued operations Revenue — 1,604 1,362 Other operating costs — (889) (725) Operating profit — 715 637 Finance income 17 21 — Finance costs 1 62 (363) (230) Profit before tax 79 373 407 Tax 2 (1) (93) (236) Profit after tax from discontinued operations 78 280 171 (Loss)/gain on disposal (4) 4,803 — Total profit after tax from discontinued operations 74 5,083 171 1. Finance costs include the remeasurement of the FAA and RAA options. 2. Of the £236 million tax charge in the year ended 31 March 2022, £145 million related to an increase in deferred tax liability due to the change in the UK corporation tax rate. 10. Assets held for sale and discontinued operations continued (b) Discontinued operations continued The summary statements of comprehensive income for discontinued operations for the years ended 31 March 2024 , 2023 and 2022 are as follows: 2024 2023 2022 £m £m £m Profit after tax from discontinued operations 74 5,083 171 Other comprehensive (loss)/income from discontinued operations Items from discontinued operations that will never be reclassified to profit or loss: Remeasurement (losses)/gains on pension assets and post-retirement benefit obligations — (313) 309 Net losses on financial liability designated at fair value through profit and loss attributable to changes in own credit risk — — (1) Tax on items that will never be reclassified to profit or loss — 78 (94) Total (losses)/gains from discontinued operations that will never be reclassified to profit or loss — (235) 214 Items from discontinued operations that may be reclassified subsequently to profit or loss: Net gains in respect of cash flow hedges — 6 1 Net gains/(losses) in respect of cost of hedging — 4 (4) Net gains on investments in debt instruments measured at fair value through other comprehensive income 13 — — Tax on items that may be reclassified subsequently to profit or loss (3) (2) — Total gains/(losses) from discontinued operations that may be reclassified subsequently to profit or loss 10 8 (3) Other comprehensive income/(loss) for the year, net of tax from discontinued operations 10 (227) 211 Total comprehensive income for the year from discontinued operations 84 4,856 382

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Mar. 31, 2024
Intangible assets and goodwill [abstract]
Schedule of changes in intangible assets and goodwill	Total £m Net book value at 1 April 2022 9,532 Exchange adjustments 315 Net book value at 1 April 2023 9,847 Exchange adjustments (118) Net book value at 31 March 2024 9,729
Schedule of allocation of goodwill by operations	See below for a summary of which operations our goodwill and indefinite-lived intangibles are allocated to: 2024 2023 CGU or group of CGUs £m £m Goodwill: National Grid Ventures – US 188 163 New England 1,541 1,609 New York 3,279 3,354 UK Electricity Distribution 1 4,721 4,721 Total goodwill 9,729 9,847 Indefinite-lived intangibles (regulatory licences related to UK Electricity Distribution): West Midlands 518 518 East Midlands 519 519 South Wales 257 257 South West 420 420 Total indefinite-lived intangibles 1,714 1,714 1. This is a combination of the West Midlands, East Midlands, South Wales and South West CGUs, reflecting the level at which the goodwill is monitored.

Other intangible assets (Tables

Other intangible assets (Tables)	12 Months Ended
	Mar. 31, 2024
Intangible assets other than goodwill [abstract]
Schedule of intangible assets	Regulatory licences £m Software £m Assets in the course of construction £m Total £m Cost at 1 April 2022 1,714 2,075 870 4,659 Exchange adjustments — 79 32 111 Additions — 34 544 578 Disposals — (17) — (17) Reclassifications 1 — 895 (885) 10 Cost at 1 April 2023 1,714 3,066 561 5,341 Exchange adjustments — (45) (6) (51) Additions — 17 464 481 Disposals — (23) — (23) Reclassifications¹ — 598 (436) 162 Reclassification to held for sale (note 10) — (520) (191) (711) Cost at 31 March 2024 1,714 3,093 392 5,199 Accumulated amortisation at 1 April 2022 — (1,377) (10) (1,387) Exchange adjustments — (51) — (51) Amortisation charge for the year — (291) — (291) Accumulated amortisation of disposals — 15 — 15 Reclassifications¹ — (23) — (23) Accumulated amortisation at 1 April 2023 — (1,727) (10) (1,737) Exchange adjustments — 23 — 23 Amortisation charge for the year — (301) — (301) Accumulated amortisation of disposals — 23 — 23 Reclassifications¹ — (161) — (161) Reclassification to held for sale (note 10) — 385 — 385 Accumulated amortisation at 31 March 2024 — (1,758) (10) (1,768) Net book value at 31 March 2024² 1,714 1,335 382 3,431 Net book value at 31 March 2023 1,714 1,339 551 3,604 1. Reclassifications includes amounts transferred to property, plant and equipment (see note 13 ). 2. The Group has capitalised £320 million ( 2023 : £370 million ) in relation to the Gas Business Enablement system in the US, of which £320 million ( 2023 : £369 million ) is in service and is being amortised over 10 years , with the remainder included within assets in the course of construction. A further £81 million ( 2023 : £87 million ) relates to our UK general ledger system within software and is being amortised over 10 years . Years Software 3 to 10 Regulatory licences Indefinite

Property, plant and equipment (

Property, plant and equipment (Tables)	12 Months Ended
	Mar. 31, 2024
Property, plant and equipment [abstract]
Disclosure of detailed information about property, plant and equipment	Land and buildings £m Plant and machinery £m Assets in the course of construction £m Motor vehicles and office equipment £m Total £m Cost at 1 April 2022 3,659 63,022 5,587 1,072 73,340 Exchange adjustments 126 2,073 156 50 2,405 Additions 158 1,196 5,345 154 6,853 Disposals (163) (331) (4) (156) (654) Adjustment for change in discount rate on decommissioning provisions (note 26) — (36) (12) — (48) Reclassifications 1 286 3,841 (4,312) 102 (83) Cost at 1 April 2023 4,066 69,765 6,760 1,222 81,813 Exchange adjustments (49) (841) (67) (19) (976) Additions 59 1,157 5,754 197 7,167 Disposals (55) (271) (5) (134) (465) Adjustment for change in discount rate on decommissioning provisions (note 26) — 29 — — 29 Reclassifications 1 277 4,725 (5,389) 218 (169) Reclassification to held for sale (note 10) (88) (13) (31) (134) (266) Cost at 31 March 2024 4,210 74,551 7,022 1,350 87,133 Accumulated depreciation at 1 April 2022 (773) (14,441) (60) (534) (15,808) Exchange adjustments (30) (444) — (32) (506) Depreciation charge for the year² (122) (1,459) (1) (183) (1,765) Disposals 127 311 2 152 592 Reclassifications 1 4 107 4 (8) 107 Accumulated depreciation at 1 April 2023 (794) (15,926) (55) (605) (17,380) Exchange adjustments 10 177 — 12 199 Depreciation charge for the year² (80) (1,515) (20) (189) (1,804) Disposals 50 252 2 134 438 Reclassifications 1 (3) 281 — (112) 166 Reclassification to held for sale (note 10) 59 1 6 89 155 Accumulated depreciation at 31 March 2024 (758) (16,730) (67) (671) (18,226) Net book value at 31 March 2024 3,452 57,821 6,955 679 68,907 Net book value at 31 March 2023 3,272 53,839 6,705 617 64,433 1. Represents amounts transferred between categories, (to)/from other intangible assets (see note 12 ) , (to)/from inventories. 2. Depreciation of assets in the course of construction relates to impairment provision adjustments. Years UK US Weighted average remaining UEL Freehold and leasehold buildings up to 60 up to 100 38 Plant and machinery: Electricity transmission plant and wires up to 100 10 to 85 32 Electricity distribution plant 14 to 99 5 to 85 46 Electricity generation plant n/a 10 to 93 10 Interconnector plant and other 5 to 70 5 to 37 31 Gas plant – mains, services and regulating equipment n/a 25 to 95 53 Gas plant – storage 5 to 20 20 to 60 18 Gas plant – meters n/a 14 to 45 24 Motor vehicles and office equipment up to 50 up to 26 3 Increase in depreciation expense for the year ended 31 March 2024 Increase in depreciation expense for the year ended 31 March 2023 New York £m New England £m New York £m New England £m UELs limited to 2050 208 66 185 54 UELs limited to 2060 100 26 90 21 UELs limited to 2070 46 6 42 3
Disclosure of detailed information about right-of-use assets	The table that follows shows the movements in the net book value of right-of-use assets included within property, plant and equipment at 31 March 2024 and 31 March 2023 , split by category. The associated lease liabilities are disclosed in note 21 . 13. Property, plant and equipment continued (d) Right-of-use assets continued Land and buildings £m Plant and machinery £m Assets in the course of construction £m Motor vehicles and office equipment £m Total £m Net book value at 1 April 2022 225 70 — 210 505 Exchange adjustments 10 1 — 13 24 Additions 101 97 — 88 286 Disposals (13) — — (1) (14) Depreciation charge for the year (42) (18) — (70) (130) Net book value at 31 March 2023 281 150 — 240 671 Exchange adjustments (5) (2) — (5) (12) Additions 52 2 — 146 200 Reclassifications — (5) — 5 — Reclassification to held for sale (note 10) (12) — — (1) (13) Disposals (1) — — (2) (3) Depreciation charge for the year (22) (17) — (76) (115) Net book value at 31 March 2024 293 128 — 307 728 The following balances have been included in the income statement for the years ended 31 March 2024 and 31 March 2023 in respect of right-of- use assets: 2024 2023 £m £m Included within net finance income and costs: Interest expense on lease liabilities (69) (24) Included within revenue: Lease income 1 384 409 Included within operating expenses: Expense relating to short-term and low-value leases (20) (19) 1. Included within lease income is £360 million ( 2023 : £394 million ) of variable lease payments, the majority of which relates to the power supply arrangement entered into with LIPA (see note 3

Other non-current assets (Table

Other non-current assets (Tables)	12 Months Ended
	Mar. 31, 2024
Subclassifications of assets, liabilities and equities [abstract]
Schedule of other non-current assets	2024 2023 £m £m Other receivables¹ 458 496 Prepayments² 390 124 848 620 1. Primarily comprises amounts due in relation to property sales to The Berkeley Group. These amounts will be fully received by 2031. 2. Included within prepayments are capital expenditure prepayments made to suppliers to secure production capacity for certain of our capital projects. In the year, we have also revised our policy in relation to the classification of capital expenditure prepayments between current and non-current in order to align these to the operating cycles of the underlying assets to which they relate. Accordingly, prior year non-current prepayments have increased by £53 million to reflect this change, with a corresponding reduction in current prepayments (note 19 ).

Financial and other investmen_2

Financial and other investments (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of financial assets [abstract]
Schedule of financial assets	2024 2023 £m £m Non-current FVOCI debt and other investments 397 407 FVTPL investments 483 452 880 859 Current FVTPL investments 3,084 1,764 Financial assets at amortised cost 615 841 3,699 2,605 4,579 3,464 Financial and other investments include the following: Investments in short-term money market funds 2,668 1,449 Investments held by National Grid Partners 375 346 Investments in Sunrun 108 106 Balances that are restricted or not readily used in operations: Collateral 1 496 764 Insurance company and non-qualified plan investments 578 490 Cash surrender value of life insurance policies 235 232 Other investments 119 77 4,579 3,464 1. The collateral balance includes £466 million ( 2023 : £734 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, £24 million ( 2023 : £25 million ) of restricted amounts allocated for specific projects within National Grid Electricity System Operator and National Grid Electricity Transmission plc and £6 million ( 2023 : £5 million

Investments in joint ventures_2

Investments in joint ventures and associates (Tables)	12 Months Ended
	Mar. 31, 2024
Investments accounted for using equity method [abstract]
Disclosure of joint ventures	2024 2023 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 154 1,146 1,300 277 961 1,238 Exchange adjustments (3) (28) (31) 20 52 72 Additions 13 319 332 40 157 197 Share of post-tax results for the year 9 28 37 9 162 171 Share of other comprehensive income of associates, net of tax — — — 1 — 1 Dividends received (15) (152) (167) (30) (152) (182) Disposals¹ (1) — (1) (167) — (167) Other movements² 1 (51) (50) 4 (34) (30) Share of net assets at 31 March 158 1,262 1,420 154 1,146 1,300 1. Disposals in the prior year included the sale of the Group’s 26.25% minority ownership interest in the Millennium Pipeline Company LLC. 2. Other movements relate to tax liabilities for US and certain UK associates and joint ventures which are borne by the Group and the elimination of profits arising from sales to the Group’s share of joint ventures. The following table describes the Group’s material joint ventures and associates at 31 March 2024 : Joint venture 1 % stake BritNed Development Limited 50% BritNed is a joint venture with the Dutch transmission system operator, TenneT, and operates the subsea electricity interconnector between Great Britain and the Netherlands, commissioned in 2011. Nemo Link Limited 50% Nemo is a joint venture with the Belgian transmission operator, Elia, and is a subsea electricity interconnector between Great Britain and Belgium, which became operational on 31 January 2019. Emerald Energy Venture, LLC 51% Emerald is a joint venture with Washington State Investment Board which builds and operates wind and solar assets. Emerald was acquired on 11 July 2019. Community Offshore Wind, LLC 27.3% Community Offshore Wind is a joint venture with RWE Renewables. The joint venture owns six seabed leases in the northeastern US and is developing an offshore wind project which will play a key role in supplying clean energy to customers in New York. 1. The joint ventures have reporting periods ending on 31 December with monthly management reporting information provided to the Group. Summarised financial information as at 31 March, together with the carrying amount of material investments, is as follows: BritNed Development Limited Nemo Link Limited Emerald Energy Venture LLC Community Offshore Wind LLC 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Statement of financial position Non-current assets 376 397 478 514 2,171 1,598 1,005 925 Cash and cash equivalents 69 208 46 77 206 169 40 19 All other current assets 36 29 6 8 16 14 42 — Non-current liabilities (57) (55) (3) (3) (249) (244) (20) (19) Non-current financial liabilities (31) (31) (32) (32) (643) (398) — — Current liabilities (39) (34) (55) (131) (217) (131) (1) (3) Current financial liabilities — — — — (10) (95) — — Net assets 354 514 440 433 1,274 913 1,066 922 Group’s ownership interest in joint venture/associate 177 257 220 217 650 466 291 251 Group adjustment: elimination of profits on sales to joint venture — — — — (123) (85) — — Carrying amount of the Group’s investment 177 257 220 217 527 381 291 251 BritNed Development Limited Nemo Link Limited Emerald Energy Venture LLC Community Offshore Wind LLC 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Income statement Revenue 158 358 109 88 87 75 — — Depreciation and amortisation (16) (16) (23) (23) (38) (29) — — Other (costs)/income (25) 22 (15) (1) (152) (46) — 1 Operating profit/(loss) 117 364 71 64 (103) — — 1 Net interest expense (2) (2) — (7) (9) (6) — — Profit/(loss) before tax 115 362 71 57 (112) (6) — 1 Income tax expense (31) (82) (17) (11) — — — — Profit/(loss) for the year 84 280 54 46 (112) (6) — 1 Group’s share of profit/(loss) 42 140 27 23 (57) (3) — — Group adjustment: tax credit — — — — 15 1 — — Group’s share of post-tax results for the year 42 140 27 23 (42) (2) — —
Disclosure of associates	2024 2023 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 154 1,146 1,300 277 961 1,238 Exchange adjustments (3) (28) (31) 20 52 72 Additions 13 319 332 40 157 197 Share of post-tax results for the year 9 28 37 9 162 171 Share of other comprehensive income of associates, net of tax — — — 1 — 1 Dividends received (15) (152) (167) (30) (152) (182) Disposals¹ (1) — (1) (167) — (167) Other movements² 1 (51) (50) 4 (34) (30) Share of net assets at 31 March 158 1,262 1,420 154 1,146 1,300 1. Disposals in the prior year included the sale of the Group’s 26.25% minority ownership interest in the Millennium Pipeline Company LLC. 2. Other movements relate to tax liabilities for US and certain UK associates and joint ventures which are borne by the Group and the elimination of profits arising from sales to the Group’s share of joint ventures. The following table describes the Group’s material joint ventures and associates at 31 March 2024 : Joint venture 1 % stake BritNed Development Limited 50% BritNed is a joint venture with the Dutch transmission system operator, TenneT, and operates the subsea electricity interconnector between Great Britain and the Netherlands, commissioned in 2011. Nemo Link Limited 50% Nemo is a joint venture with the Belgian transmission operator, Elia, and is a subsea electricity interconnector between Great Britain and Belgium, which became operational on 31 January 2019. Emerald Energy Venture, LLC 51% Emerald is a joint venture with Washington State Investment Board which builds and operates wind and solar assets. Emerald was acquired on 11 July 2019. Community Offshore Wind, LLC 27.3% Community Offshore Wind is a joint venture with RWE Renewables. The joint venture owns six seabed leases in the northeastern US and is developing an offshore wind project which will play a key role in supplying clean energy to customers in New York. 1. The joint ventures have reporting periods ending on 31 December with monthly management reporting information provided to the Group. Summarised financial information as at 31 March, together with the carrying amount of material investments, is as follows: BritNed Development Limited Nemo Link Limited Emerald Energy Venture LLC Community Offshore Wind LLC 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Statement of financial position Non-current assets 376 397 478 514 2,171 1,598 1,005 925 Cash and cash equivalents 69 208 46 77 206 169 40 19 All other current assets 36 29 6 8 16 14 42 — Non-current liabilities (57) (55) (3) (3) (249) (244) (20) (19) Non-current financial liabilities (31) (31) (32) (32) (643) (398) — — Current liabilities (39) (34) (55) (131) (217) (131) (1) (3) Current financial liabilities — — — — (10) (95) — — Net assets 354 514 440 433 1,274 913 1,066 922 Group’s ownership interest in joint venture/associate 177 257 220 217 650 466 291 251 Group adjustment: elimination of profits on sales to joint venture — — — — (123) (85) — — Carrying amount of the Group’s investment 177 257 220 217 527 381 291 251 BritNed Development Limited Nemo Link Limited Emerald Energy Venture LLC Community Offshore Wind LLC 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Income statement Revenue 158 358 109 88 87 75 — — Depreciation and amortisation (16) (16) (23) (23) (38) (29) — — Other (costs)/income (25) 22 (15) (1) (152) (46) — 1 Operating profit/(loss) 117 364 71 64 (103) — — 1 Net interest expense (2) (2) — (7) (9) (6) — — Profit/(loss) before tax 115 362 71 57 (112) (6) — 1 Income tax expense (31) (82) (17) (11) — — — — Profit/(loss) for the year 84 280 54 46 (112) (6) — 1 Group’s share of profit/(loss) 42 140 27 23 (57) (3) — — Group adjustment: tax credit — — — — 15 1 — — Group’s share of post-tax results for the year 42 140 27 23 (42) (2) — —

Derivative financial instrume_2

Derivative financial instruments (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of detailed information about financial instruments [abstract]
Disclosure of detailed information about derivative financial instruments	The fair values of derivatives by category are as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current 44 (335) (291) 153 (222) (69) Non-current 324 (909) (585) 276 (1,071) (795) 368 (1,244) (876) 429 (1,293) (864) Financing derivatives 333 (1,126) (793) 363 (1,119) (756) Commodity contract derivatives 35 (118) (83) 66 (174) (108) 368 (1,244) (876) 429 (1,293) (864) The fair values of financing derivatives by type are as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Interest rate swaps 43 (110) (67) 49 (98) (49) Cross-currency interest rate swaps 234 (844) (610) 192 (888) (696) Foreign exchange forward contracts¹ 16 (68) (52) 100 (11) 89 Inflation-linked swaps 40 (104) (64) 22 (122) (100) 333 (1,126) (793) 363 (1,119) (756) 1. Included within the foreign exchange forward contracts balance are £36 million ( 2023 : £4 million ) of derivative liabilities in relation to the hedging of capital expenditure The notional contract amounts of financing derivatives by type are as follows: 2024 2023 £m £m Interest rate swaps (2,175) (1,727) Cross-currency interest rate swaps (15,602) (15,025) Foreign exchange forward contracts (7,675) (5,263) Inflation-linked swaps (3,190) (2,387) (28,642) (24,402) The fair values of commodity contract derivatives by type are as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Commodity purchase contracts accounted for as derivative contracts Forward purchases of gas — (3) (3) 2 (6) (4) Derivative financial instruments linked to commodity prices Electricity capacity — — — 1 — 1 Electricity swaps 33 (82) (49) 53 (92) (39) Electricity options — (1) (1) — (3) (3) Gas swaps 2 (22) (20) 9 (42) (33) Gas options — (10) (10) 1 (31) (30) 35 (118) (83) 66 (174) (108) The notional quantities of commodity contract derivatives by type are as follows: 2024 2023 Forward purchases of gas 1 38m Dth 22m Dth Electricity swaps 14,128 GWh 14,076 GWh Gas swaps 44m Dth 50m Dth Gas options 78m Dth 57m Dth 1. Forward gas purchases have terms up to one year ( 2023 : one year ). The contractual obligations under these contracts are £14 million ( 2023 : £24 million )
Disclosure of maturity analysis for derivative financial liabilities	The maturity profile of financing derivatives is as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than 1 year 18 (249) (231) 100 (93) 7 18 (249) (231) 100 (93) 7 Non-current In 1 to 2 years 6 (80) (74) 13 (100) (87) In 2 to 3 years 31 (44) (13) 15 (96) (81) In 3 to 4 years 32 (74) (42) 32 (11) 21 In 4 to 5 years 49 (83) (34) 14 (107) (93) More than 5 years 197 (596) (399) 189 (712) (523) 315 (877) (562) 263 (1,026) (763) 333 (1,126) (793) 363 (1,119) (756) The maturity profile of commodity contract derivatives is as follows: 2024 2023 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than one year 26 (86) (60) 53 (129) (76) 26 (86) (60) 53 (129) (76) Non-current In 1 to 2 years 3 (28) (25) 11 (29) (18) In 2 to 3 years 5 (4) 1 2 (15) (13) In 3 to 4 years 1 — 1 — (1) (1) 9 (32) (23) 13 (45) (32) 35 (118) (83) 66 (174) (108)

Inventories and current intan_2

Inventories and current intangible assets (Tables)	12 Months Ended
	Mar. 31, 2024
Subclassifications of assets, liabilities and equities [abstract]
Schedule of inventories and current intangible assets	2024 2023 £m £m Fuel stocks 188 280 Raw materials and consumables 542 460 Current intangible assets – emission allowances 98 136 828 876

Trade and other receivables (Ta

Trade and other receivables (Tables)	12 Months Ended
	Mar. 31, 2024
Trade and other receivables [abstract]
Schedule of trade and other receivables	Trade and other receivables are initially recognised at fair value, except for trade receivables that do not have a significant financing component which are measured at transaction price, and are subsequently measured at amortised cost, less any appropriate allowances for estimated irrecoverable amounts. 2024 2023 £m £m Trade receivables 2,501 2,583 Accrued income 885 1,126 Provision for impairment of receivables and accrued income (559) (560) Trade receivables and accrued income, net 2,827 3,149 Prepayments¹ 385 389 Contract assets 76 49 Other receivables 127 243 3,415 3,830 1. In the year, we have revised our policy in relation to the classification of capital expenditure prepayments between current and non-current in order to align these to the operating cycles of the underlying assets to which they relate. Accordingly, prior year current prepayments have decreased by £53 million to reflect this change, with a corresponding increase in non-current prepayments (note 14 ).
Schedule of reconciliation of changes in allowance account for credit losses	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. 2024 2023 £m £m At 1 April 560 741 Exchange adjustments (12) 51 Charge for the year, net of recoveries 179 220 Uncollectible amounts written off (163) (452) Reclassification to held for sale (note 10) (5) — At 31 March 559 560
Schedule of receivables by geographical area	2024 2023 2022 £m £m £m Split by geographical area: UK 40,065 38,043 35,466 US 44,270 41,761 36,411 84,335 79,804 71,877 Reconciliation to total non-current assets: Pension assets 2,407 2,645 3,885 Financial and other investments 880 859 830 Derivative financial assets 324 276 305 Non-current assets 87,946 83,584 76,897 The trade receivables balance, accrued income balance and provisions balance split by geography are as follows: As at 31 March 2024 As at 31 March 2023 UK US Total UK US Total £m £m £m £m £m £m Trade receivables 162 2,339 2,501 223 2,360 2,583 Accrued income 337 548 885 650 476 1,126 Provision for impairment of receivables and accrued income (3) (556) (559) (11) (549) (560) 496 2,331 2,827 862 2,287 3,149
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. Loss rates have decreased across the majority of our ageing categories, primarily due to the impact of ongoing cash collection activities. 2024 2023 % £m % £m Accrued income 3 533 3 462 0 – 30 days past due 3 822 3 838 30 – 60 days past due 14 219 13 235 60 – 90 days past due 21 125 23 139 3 – 6 months past due 27 173 32 189 6 – 12 months past due 34 191 43 178 Over 12 months past due 73 374 88 284 2,437 2,325

Cash and cash equivalents (Tabl

Cash and cash equivalents (Tables)	12 Months Ended
	Mar. 31, 2024
Cash and cash equivalents [abstract]
Schedule of cash and cash equivalents	2024 2023 £m £m Cash at bank 259 163 Short-term deposits 300 — Cash and cash equivalents 559 163

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of detailed information about borrowings [abstract]
Schedule of borrowings	2024 2023 £m £m Current Bank loans 460 381 Bonds 2,841 1,638 Commercial paper 1,444 840 Lease liabilities 114 96 4,859 2,955 Non-current Bank loans 2,434 2,557 Bonds 39,114 36,855 Lease liabilities 665 618 42,213 40,030 Total borrowings 47,072 42,985 Total borrowings are repayable as follows: 2024 2023 £m £m Less than 1 year 4,859 2,955 In 1 to 2 years 2,706 2,799 In 2 to 3 years 3,134 2,689 In 3 to 4 years 2,948 3,129 In 4 to 5 years 4,375 2,505 More than 5 years: By instalments 736 922 Other than by instalments 28,314 27,986 47,072 42,985
Schedule of lease obligations	2024 2023 £m £m Gross lease liabilities are repayable as follows: Less than 1 year 133 118 1 to 5 years 370 318 More than 5 years 507 480 1,010 916 Less: finance charges allocated to future periods (231) (202) 779 714 The present value of lease liabilities are as follows: Less than 1 year 114 96 1 to 5 years 300 269 More than 5 years 365 349 779 714

Trade and other payables (Table

Trade and other payables (Tables)	12 Months Ended
	Mar. 31, 2024
Trade and other payables [abstract]
Schedule of trade and other payables	2024 2023 £m £m Trade payables 2,786 3,249 Deferred payables 327 404 Customer contributions 1 34 171 Social security and other taxes — 240 Contingent consideration — 19 Other payables² 929 985 4,076 5,068 1. Relates to amounts received from government-related entities for connecting to our networks, where we have obligations remaining under the contract. 2. Included within other payables are payments due in respect of interconnector excess revenues in accordance with the cap and floor regime constructed by Ofgem (see note 3 ).

Contract liabilities (Tables)

Contract liabilities (Tables)	12 Months Ended
	Mar. 31, 2024
Contract liabilities [abstract]
Summary of contract liabilities	2024 2023 £m £m Current 127 252 Non-current 2,119 1,754 2,246 2,006
Schedule of significant changes in contract assets and contract liabilities	Significant changes in the contract liabilities balances during the period are as follows: 2024 2023 £m £m As at 1 April 2,006 1,472 Exchange adjustments (27) 54 Revenue recognised that was included in the contract liability balance at the beginning of the period (252) (292) Increases due to cash received, excluding amounts recognised as revenue during the period 519 772 At 31 March 2,246 2,006

Other non-current liabilities (

Other non-current liabilities (Tables)	12 Months Ended
	Mar. 31, 2024
Subclassifications of assets, liabilities and equities [abstract]
Schedule of other non-current liabilities	Other non-current liabilities are initially recognised at fair value and subsequently measured at amortised cost. 2024 2023 £m £m Deferred income 11 84 Customer contributions 1 411 421 Other payables² 458 416 880 921 1. Relates to amounts received from government-related entities for connecting to our networks, where we have obligations remaining under the contract. 2. Included within other payables are payments due in respect of the IFA1 interconnector in accordance with the Use of Revenue regime constructed by Ofgem.

Pensions and other post-retir_2

Pensions and other post-retirement benefits (Tables)	12 Months Ended
	Mar. 31, 2024
Employee Benefits [Abstract]
Disclosure of actuarial assumptions	The Company has applied the following financial assumptions in assessing DB liabilities: UK pensions US pensions US other post-retirement benefits 2024 2023 2022 2024 2023 2022 2024 2023 2022 % % % % % % % % % Discount rate – past service 4.87 4.80 2.78 5.15 4.85 3.65 5.15 4.85 3.65 Discount rate – future service 4.92 4.80 2.85 5.15 4.85 3.65 5.15 4.85 3.65 Rate of increase in RPI – past service 3.05 3.17 3.60 n/a n/a n/a n/a n/a n/a Rate of increase in RPI – future service 2.92 3.07 3.33 n/a n/a n/a n/a n/a n/a Salary increases 3.10 3.11 3.47 4.50 4.50 4.60 4.50 4.50 4.60 Initial healthcare cost trend rate n/a n/a n/a n/a n/a n/a 7.10 6.80 6.80 Ultimate healthcare cost trend rate n/a n/a n/a n/a n/a n/a 4.50 4.50 4.50 The table below sets out the projected life expectancies adopted for the UK and US pension arrangements: UK pensions US pensions 2024 2023 2022 2024 2023 2022 years years years years years years Assumed life expectations for a retiree age 65 Males 21.5 21.9 22.0 21.6 21.6 21.4 Females 23.5 23.7 23.8 23.9 23.8 23.6 In 20 years: Males 22.6 23.0 23.2 23.3 23.2 23.1 Females 24.9 25.1 25.2 25.5 25.4 25.3 The table below summarises the split of DB obligations by status for each category of plan: UK pensions US pensions US other post-retirement benefits 2024 2023 2024 2023 2024 2023 % % % % % % Active members 14 14 37 37 29 33 Deferred members 8 9 10 9 — — Pensioner members 78 77 53 54 71 67
Disclosure of amounts recognised in the statement of financial position	Amounts recognised in the consolidated statement of financial position 2024 2023 £m £m Present value of funded obligations (17,601) (18,934) Fair value of plan assets 19,733 21,246 2,132 2,312 Present value of unfunded obligations (266) (292) Other post-employment liabilities (52) (69) Net defined benefit asset 1,814 1,951 Represented by: Liabilities (593) (694) Assets 2,407 2,645 1,814 1,951 The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Present value of funded obligations (10,465) (10,906) (4,702) (5,502) (2,434) (2,526) (17,601) (18,934) Fair value of plan assets 11,782 12,578 5,320 6,060 2,631 2,608 19,733 21,246 1,317 1,672 618 558 197 82 2,132 2,312 Present value of unfunded obligations (56) (58) (210) (234) — — (266) (292) Other post-employment liabilities — — — — (52) (69) (52) (69) Net defined benefit asset 1,261 1,614 408 324 145 13 1,814 1,951 Represented by: Liabilities (56) (58) (210) (234) (327) (402) (593) (694) Assets 1,317 1,672 618 558 472 415 2,407 2,645 1,261 1,614 408 324 145 13 1,814 1,951
Disclosure of amounts recognised in the income statement and statement of other comprehensive income	Amounts recognised in the income statement and statement of other comprehensive income The expense or income arising from all Group retirement benefit arrangements recognised in the Group income statements is shown below: 2024 2023 2022 £m £m £m Included within operating costs Administration costs 22 19 20 Included within payroll costs Defined benefit plan costs: Current service cost 143 194 223 Past service cost – augmentations and redundancies 9 8 11 Gains on settlement (30) (45) — 122 157 234 Included within finance income and costs Net interest income (100) (85) (2) Total included in income statement 1 44 91 252 Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations (218) (1,364) 2,481 Exchange adjustments (6) 41 7 Total included in the statement of other comprehensive income² (224) (1,323) 2,488 1. Amounts shown in the table above include operating costs of £nil ( 2023 : £nil ; 2022 : £4 million ); payroll costs of £nil ( 2023 : £nil ; 2022 : £10 million ); and net interest income of £nil ( 2023 : £nil ; 2022 : £2 million ) presented within profit from discontinued operations. These amounts all relate to UK pensions. 2. Amounts shown in the table above include remeasurements of pension assets and post-retirement benefit obligations of £nil ( 2023 : £nil ; 2022 : £309 million gain ) presented within discontinued operations. These amounts all relate to UK pensions. The geographical split of pensions and other post-retirement benefits is shown below: UK pensions US pensions US other post-retirement benefits 2024 2023 2022 2024 2023 2022 2024 2023 2022 £m £m £m £m £m £m £m £m £m Included within operating costs Administration costs 13 9 11 7 8 7 2 2 2 Included within payroll costs Defined benefit plan costs: Current service cost 45 69 83 72 88 101 26 37 39 Past service cost – augmentations and redundancies 9 8 11 — — — — — — Gains on settlement — — — (30) (45) — — — — 54 77 94 42 43 101 26 37 39 Included within finance income and costs Net interest (income)/cost (84) (64) (7) (13) (21) — (3) — 5 Total included in income statement (17) 22 98 36 30 108 25 39 46 Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations (474) (1,183) 1,577 99 (242) 532 157 61 372 Exchange adjustments — — — (5) 36 11 (1) 5 (4) Total included in the statement of other comprehensive income (474) (1,183) 1,577 94 (206) 543 156 66 368
Schedule of reconciliation of the net defined benefit asset (liability)	Reconciliation of the net defined benefit asset UK pensions US pensions US other post-retirement benefits Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Opening net defined benefit asset 1,614 2,590 324 484 13 1 1,951 3,075 Income/(cost) recognised in the income statement (including discontinued operations) 17 (22) (36) (30) (25) (39) (44) (91) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (474) (1,183) 94 (206) 156 66 (224) (1,323) Employer contributions 118 197 26 76 21 11 165 284 Other movements 3 2 — — (20) (26) (17) (24) Reclassification to held for sale (note 10) (17) 30 — — — — (17) 30 Closing net defined benefit asset 1,261 1,614 408 324 145 13 1,814 1,951 Changes in the present value of defined benefit obligations (including unfunded obligations) The table below shows the movement in defined benefit obligations across our DB plans over the year. UK pensions US pensions US other post-retirement benefits Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Opening defined benefit obligations (10,964) (14,275) (5,736) (6,779) (2,526) (2,813) (19,226) (23,867) Current service cost (45) (69) (72) (88) (26) (37) (143) (194) Interest cost (536) (334) (258) (252) (117) (111) (911) (697) Actuarial (losses)/gains – experience (2) (235) (34) (17) 73 48 37 (204) Actuarial gains/(losses) – demographic assumptions 98 135 12 5 (4) 10 106 150 Actuarial gains/(losses) – financial assumptions 165 3,167 190 818 (7) 443 348 4,428 Past service cost – augmentations and redundancies (9) (8) — — — — (9) (8) Liabilities extinguished on settlements — — 543 616 — — 543 616 Medicare subsidy received — — — — (26) (28) (26) (28) Employee contributions (10) (10) — — — — (10) (10) Benefits paid 710 711 312 426 152 153 1,174 1,290 Exchange adjustments — — 131 (465) 58 (191) 189 (656) Reclassification from other post-employment liabilities — — — — (11) — (11) — Reclassification to held for sale (note 10) 72 (46) — — — — 72 (46) Closing defined benefit obligations (10,521) (10,964) (4,912) (5,736) (2,434) (2,526) (17,867) (19,226) Changes in the value of plan assets The table below shows the movement in pension assets across our DB plans over the year. UK pensions US pensions US other post-retirement benefits Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m Opening fair value of plan assets 12,578 16,865 6,060 7,263 2,608 2,885 21,246 27,013 Interest income 620 398 271 273 120 111 1,011 782 Return on plan assets (less than)/in excess of interest (735) (4,250) (69) (1,048) 95 (440) (709) (5,738) Administration costs (13) (9) (7) (8) (2) (2) (22) (19) Assets distributed on settlements — — (513) (571) — — (513) (571) Employer contributions 118 197 26 76 21 11 165 284 Employee contributions 10 10 — — — — 10 10 Benefits paid (707) (709) (312) (426) (152) (153) (1,171) (1,288) Exchange adjustments — — (136) 501 (59) 196 (195) 697 Reclassification to held for sale (note 10) (89) 76 — — — — (89) 76 Closing fair value of plan assets 11,782 12,578 5,320 6,060 2,631 2,608 19,733 21,246 Actual return on plan assets (115) (3,852) 202 (775) 215 (329) 302 (4,956) Expected contributions to plans in the following year 108 99 28 36 15 14 151 149
Disclosure of asset allocations	The allocation of assets by asset class is set out below. Within these asset allocations there is significant diversification across regions, asset managers, currencies and bond categories. UK pensions 2024 2023¹ 2022¹ Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 576 153 729 475 179 654 1,458 324 1,782 Corporate bonds 1,910 — 1,910 1,892 — 1,892 2,741 — 2,741 Government securities and liability- driven investments — 5,259 5,259 2 762 4,906 5,668 2,3 786 5,768 6,554 2,3 Property — 679 4 679 23 860 4 883 122 1,002 4 1,124 Diversified alternatives 669 572 1,241 708 680 1,388 1,334 582 1,916 Buy-in/bulk annuity policies — 2,060 2,060 — 2,126 2,126 5 78 2,706 2,784 5 Longevity swap — (94) (94) — (88) (88) — (80) (80) Cash and cash equivalents 3 — 3 8 — 8 38 — 38 Other (including net current assets and liabilities) — (5) (5) 59 (12) 47 16 (10) 6 3,158 8,624 11,782 6 3,927 8,651 12,578 6 6,573 10,292 16,865 6 1. Comparative amounts have been represented to reflect the reclassification of assets associated with liability driven investment strategies as unquoted following an internal asset categorisation review. 2. Included within government securities and liability-driven investments above is £2.7 billion ( 2023 : £3.4 billion ; 2022 : £6.1 billion ) of repurchase agreements. These are used to increase the market exposure of the liability-matching portfolios. 3. This asset class has been redefined to include liability driven investments totalling £4,906 million ( 2022 : £5,857 million ). These were previously allocated in other asset classes, primarily buy-in/bulk annuity policies. 4. Includes £288 million ( 2023 : £304 million ; 2022 : £283 million ) of investments in forestry funds. 5. This asset class has been redefined to only include the value of buy-in/bulk annuities and therefore has been restated to exclude the value of liability-driven investments. 6. The fair value of plan assets includes employer-related investment exposure of £44 million ( 2023 : £23 million ; 2022 : £32 million ). US pensions 2024 2023¹ 2022¹ Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 99 1,224 1,323 154 1,346 1,500 272 1,904 2,176 Corporate bonds 1,987 403 2,390 2,147 528 2,675 2,311 697 3,008 Government securities 360 444 804 410 514 924 335 715 1,050 Property — 237 237 — 299 299 — 295 295 Diversified alternatives 54 502 556 85 550 635 142 546 688 Cash and cash equivalents 9 — 9 16 — 16 31 — 31 Other (including net current assets and liabilities) 1 — 1 7 4 11 12 3 15 2,510 2,810 5,320 2,819 3,241 6,060 3,103 4,160 7,263 1. Comparative amounts have been represented to reflect the reclassification of infrastructure assets following an internal asset categorisation review. US other post-retirement benefits 2024 2023 2022 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 37 524 561 74 510 584 185 1,013 1,198 Corporate bonds 1,351 46 1,397 1,332 2 1,334 723 2 725 Government securities 410 1 411 431 2 433 511 2 513 Diversified alternatives 92 9 101 100 9 109 144 120 264 Other 1 — 161 161 1 147 148 — 185 185 1,890 741 2,631 1,938 670 2,608 1,563 1,322 2,885 1. Other primarily comprises insurance contracts. The approximate investment allocations for our plans at 31 March 2024 are as follows: UK pensions US pensions US other post- retirement benefits % % % Return-seeking assets 22 40 31 Liability-matching assets 78 60 69
Disclosure of most significant risks associated with DB plans	The most significant risks associated with the DB plans are as follows: Main risks Description and mitigation Investment risk The plans invest in a variety of asset classes, with actual returns likely to differ from the underlying discount rate adopted, impacting on 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. Changes in bond yields Liabilities will fluctuate as yields change. Volatility of the net balance sheet asset or liability is controlled through liability- matching strategies. The investment strategies allow for the use of synthetic as well as physical assets to be used to hedge interest rate risk. Inflation risk Changes in inflation will affect 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. The investment strategies allow for the use of synthetic as well as physical assets to be used to hedge inflation risk. Member longevity 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 scheme investment transactions including a longevity insurance contract (longevity swap) for NGEG of ESPS and two buy-in policies for Section A of NGUKPS. Counterparty risk This 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. Default risk Debt investments are predominantly made in regulated markets in assets considered to be of investment grade. Where investments are made either in non-investment grade assets or outside of regulated markets, investment levels are kept to prudent levels and subject to agreed ranges, to control the risk. Liquidity risk The pension plans hold sufficient cash to meet benefit requirements, with other investments being held in liquid or realisable assets to meet unexpected cash flow requirements. These could include collateral calls relating to the plans’ liability- matching assets which could result from extreme market movements. Should the plans not have sufficient liquidity to meet cash flow requirements, they could be forced to take sub-optimal investment decisions such as selling assets at a reduced price. The plans do not borrow money, or act as guarantor, to provide liquidity to other parties (unless it is temporary). Currency risk Fluctuations in the value of foreign denominated assets due to exposure to currency exchange rates are managed through currency hedging overlay and currency hedging carried out by some of the investment managers.

Provisions (Tables)

Provisions (Tables)	12 Months Ended
	Mar. 31, 2024
Other provisions [abstract]
Schedule of provisions	Environmental £m Decommissioning £m Other £m Total provisions £m At 1 April 2022 1,877 258 404 2,539 Exchange adjustments 114 5 12 131 Additions 142 91 222 455 Unused amounts reversed (38) (10) (14) (62) Adjustment for change in discount rate¹ (176) (48) — (224) Unwinding of discount 72 10 6 88 Utilised (100) (9) (176) (285) At 31 March 2023 1,891 297 454 2,642 Exchange adjustments (37) (2) (8) (47) Additions² 600 34 138 772 Unused amounts reversed (18) (7) (100) (125) Adjustment for change in discount rate 4 29 — 33 Unwinding of discount 85 11 6 102 Utilised (107) (9) (149) (265) Reclassification to held for sale (note 10) — — (3) (3) At 31 March 2024 2,418 353 338 3,109 2024 2023 £m £m Current 298 288 Non-current 2,811 2,354 3,109 2,642 1. In the prior year, environmental provisions in the US and the UK decreased by £176 million as a result of the change in the real discount rate from 0.5% to 1.5% . The impact of the change in discount rate to the decommissioning provisions was recognised against the carrying amount of property, plant and equipment (see note 13 ). 2. Included within additions is a £496 million increase in provision related to changes in the scope of work required on the Group’s clean-up operations on the Gowanus Canal and nearby
Schedule of environmental provision	The environmental provision is as follows: 2024 2023 Discounted £m Real undiscounted £m Real discount rate Discounted £m Real undiscounted £m Real discount rate UK sites 108 118 1.0 % 123 138 1.5 % US sites 2,310 2,579 1.5 % 1,768 2,006 1.5 % 2,418 2,697 1,891 2,144

Share capital (Tables)

Share capital (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of classes of share capital [abstract]
Schedule of share capital	Allotted, called-up and fully paid Shares million Nominal value £m At 1 April 2022 3,904 485 Issued during the year in lieu of dividends 1 26 3 At 31 March 2023 3,930 488 Issued during the year in lieu of dividends 1 37 5 At 31 March 2024 3,967 493 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, 2024
Disclosure of reserves within equity [abstract]
Schedule of reserves within equity	Translation £m Cash flow hedge £m Cost of hedging £m FVOCI equity £m FVOCI debt £m Own credit £m Capital redemption £m Merger £m Total £m At 1 April 2021 (35) (48) (28) 51 111 1 19 (5,165) (5,094) Exchange adjustments 1 629 — — — — — — — 629 Net losses taken to equity 2 — (96) (2) (70) (11) (1) — — (180) Share of net gains of associates taken to equity — 1 — — — — — — 1 Transferred to profit or loss — 40 (1) — — — — — 39 Net losses in respect of cash flow hedging of capital expenditure — (1) — — — — — — (1) Tax — 11 2 19 3 — — — 35 Cash flow hedges transferred to the statement of financial position, net of tax — 8 — — — — — — 8 At 1 April 2022 594 (85) (29) — 103 — 19 (5,165) (4,563) Exchange adjustments 1 882 — — — — — — — 882 Exchange differences reclassified to the consolidated income statement on disposal (170) — — — — — — — (170) Net gains/(losses) taken to equity — 142 (12) — (25) — — — 105 Share of net gains of associates taken to equity — 1 — — — — — — 1 Transferred to profit or loss — (136) — — — — — — (136) Net gains in respect of cash flow hedging of capital expenditure — 10 — — — — — — 10 Tax — 2 3 — 1 — — — 6 Cash flow hedges transferred to the statement of financial position, net of tax — 5 — — — — — — 5 At 1 April 2023 1,306 (61) (38) — 79 — 19 (5,165) (3,860) Exchange adjustments¹ (335) — — — — — — — (335) Net gains/(losses) taken to equity — 16 37 — 34 — — — 87 Transferred to profit or loss — 224 (11) — — — — — 213 Net losses in respect of cash flow hedging of capital expenditure — (37) — — — — — — (37) Tax — (50) (6) — (4) — — — (60) Cash flow hedges transferred to the statement of financial position, net of tax — 2 — — — — — — 2 At 31 March 2024 971 94 (18) — 109 — 19 (5,165) (3,990) 1. The exchange adjustments recorded in the translation reserve comprise a loss of £397 million ( 2023 : gain of £1,080 million ; 2022 : gain of £754 million ) relating to the translation of foreign operations, offset by a gain of £62 million ( 2023 : loss of £198 million ; 2022 : loss of £125 million ) relating to borrowings, cross-currency swaps and foreign exchange forward contracts used to hedge the net investment in non-sterling denominated subsidiaries. 2. In the year ended 31 March 2022, the Group disposed of its equity instruments related to shares held as part of a portfolio of financial instruments which back some long‑term employee liabilities. The equity instruments were previously measured at FVOCI and, prior to the disposal, the Group recognised a gain of £12 million . The accumulated gain of £82 million recognised in other comprehensive income in the year ended 31 March 2022 was transferred to retained earnings on disposal.

Net debt (Tables)

Net debt (Tables)	12 Months Ended
	Mar. 31, 2024
Subclassifications of assets, liabilities and equities [abstract]
Schedule of components of net debt	Net debt is comprised as follows: 2024 2023 2022 £m £m £m Cash and cash equivalents (see note 20) 559 163 204 Current financial investments (see note 15) 3,699 2,605 3,145 Borrowings (see note 21) (47,072) (42,985) (45,465) Financing derivatives 1 (see note 17) (793) (756) (693) (43,607) (40,973) (42,809) 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 Borrowings £m Financing derivatives used to hedge debt £m Total liabilities from financing activities £m Cash and cash equivalents £m Financial investments £m Other financing derivatives £m Total 1 £m At 1 April 2023 (42,985) (793) (43,778) 163 2,605 37 (40,973) Net increase in cash and cash equivalents — — — 427 — — 427 Included within financing cash flows: Proceeds received from loans (5,563) — (5,563) — — — (5,563) Repayment of loans 1,701 — 1,701 — — — 1,701 Payments of lease liabilities 118 — 118 — — — 118 Net movements in short-term borrowings (544) — (544) — — — (544) Cash inflows on derivatives — (86) (86) — — — (86) Cash outflows on derivatives — 58 58 — — — 58 Interest paid 1,330 297 1,627 — — — 1,627 Non-net debt financing cash flows (18) — (18) — — — (18) Included within investing cash flows: Net movements in short-term financial investments — — — — 1,141 — 1,141 Cash inflows on derivatives — — — — — (123) (123) Cash outflows on derivatives — — — — — — — Derivative cash flows included in capital expenditure — — — — — 5 5 Interest received — — — — (148) — (148) Derivative cash flows included in revenue — — — — — (11) (11) Fair value gains and losses (69) 40 (29) — 4 60 35 Foreign exchange movements 718 — 718 (1) (49) — 668 Interest (charges)/income 6 (1,564) (284) (1,848) — 152 7 (1,689) Other non-cash movements (209) 4 (205) — — (4) (209) Reclassification to held for sale 2 10 13 — 13 (30) (6) — (23) At 31 March 2024 (47,072) (764) (47,836) 559 3,699 (29) (43,607) Balances at 31 March 2024 comprise: Non-current assets — 310 310 — — 5 315 Current assets — 1 1 559 3,699 17 4,276 Current liabilities (4,859) (231) (5,090) — — (18) (5,108) Non-current liabilities (42,213) (844) (43,057) — — (33) (43,090) (47,072) (764) (47,836) 559 3,699 (29) (43,607) 1. Includes accrued interest of £490 million . 2. Reclassification to held for sale represents the closing net debt position of the ESO (see note 10 ). 29. Net debt continued Notes Borrowings £m Financing derivatives used to hedge debt £m Total liabilities from financing activities £m Cash and cash equivalents 1 £m Financial investments £m Other financing derivatives £m Total² £m At 1 April 2022 (45,465) (750) (46,215) 204 3,145 57 (42,809) Net decrease in cash and cash equivalents — — — (48) — — (48) Included within financing cash flows: Proceeds received from loans (11,908) — (11,908) — — — (11,908) Repayment of loans 15,260 — 15,260 — — — 15,260 Payments of lease liabilities 155 — 155 — — — 155 Net movements in short-term borrowings 511 — 511 — — — 511 Cash inflows on derivatives — (190) (190) — — — (190) Cash outflows on derivatives — 118 118 — — — 118 Interest paid 1,277 153 1,430 — — 1,430 Non-net debt financing cash flows (27) — (27) — — — (27) Included within investing cash flows: Net movements in short-term financial investments — — — — (586) — (586) Cash outflows on derivatives — — — — — 362 362 Derivative cash outflow in relation to capital expenditure — — — — — 12 12 Interest received — — — — (65) (65) Fair value gains and losses 367 46 413 — (18) (394) 1 Foreign exchange movements (1,311) — (1,311) 7 61 — (1,243) Interest (charges)/income 6 (1,658) (170) (1,828) — 73 — (1,755) Other non-cash movements (283) — (283) — — — (283) Reclassification to held for sale 3 97 — 97 — (5) — 92 At 31 March 2023 (42,985) (793) (43,778) 163 2,605 37 (40,973) 1. Cash and cash equivalents at the start of year exclude the Group’s bank overdraft as at 1 April 2022 of £22 million . 2. Includes accrued interest of £401 million . 3. Reclassification to held for sale represented the disposal of NECO, which was not classified as a discontinued operation. Notes Borrowings £m Financing derivatives used to hedge debt £m Total liabilities from financing activities £m Cash and cash equivalents 1 £m Financial investments £m Other financing derivatives £m Total² £m At 1 April 2021 (31,220) 96 (31,124) 157 2,342 79 (28,546) Net increase in cash and cash equivalents — — — 9 — — 9 Included within financing cash flows: Proceeds received from loans (12,347) — (12,347) — — — (12,347) Repayment of loans 1,261 — 1,261 — — — 1,261 Payments of lease liabilities 117 — 117 — — — 117 Net movements in short-term borrowings 11 — 11 — — — 11 Cash inflows on derivatives — (20) (20) — — — (20) Cash outflows on derivatives — 114 114 — — — 114 Interest paid 998 55 1,053 — — — 1,053 Non-net debt financing cash flows (33) — (33) — — — (33) Included within investing cash flows: Net movements in short-term financial investments — — — — 781 — 781 Cash inflows on derivatives — — — — — (17) (17) Cash outflows on derivatives — — — — — 122 122 Derivative cash outflow in relation to capital expenditure — — — — — 8 8 Interest received — — — — (40) — (40) Fair value gains and losses 286 (472) (186) — (12) (132) (330) Foreign exchange movements (652) — (652) 5 53 — (594) Interest (charges)/income 6 (1,177) (54) (1,231) — 54 (5) (1,182) Other non-cash movements 34 — 34 — (15) — 19 Acquisition of NGED (8,286) 26 (8,260) 44 69 — (8,147) Reclassification to held for sale 3 5,543 (495) 5,048 (11) (87) 2 4,952 At 31 March 2022 (45,465) (750) (46,215) 204 3,145 57 (42,809) 1. Cash and cash equivalents at the end of year exclude the Group’s bank overdraft as at 31 March 2022 of £22 million . 2. Includes accrued interest of £351 million . 3. Reclassification to held for sale represented the opening net debt position of the UK Gas Transmission business.

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of contingent liabilities [abstract]
Schedule of capital commitments and contingent liabilities	2024 2023 £m £m Future capital expenditure Contracted for but not provided 3,329 3,035 Energy purchase commitments 1 Less than 1 year 1,244 1,391 In 1 to 2 years 982 985 In 2 to 3 years 1,062 1,057 In 3 to 4 years 941 912 In 4 to 5 years 866 929 More than 5 years 9,080 13,920 14,175 19,194 Guarantees Guarantee of subleases for US properties (expire up to 2040) 67 219 Guarantees of certain obligations of Eastern Green Link Joint Operations (various expiry dates) 2,465 — Guarantees of certain obligations of Grain LNG (expire up to 2025) 32 32 Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates) 271 281 Guarantees of certain obligations of St William Homes LLP (various expiry dates) 44 44 Guarantees of certain obligations of National Grid IFA 2 Limited (expected expiry 2024) 121 144 Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024) 243 1,185 Other guarantees and letters of credit (various expiry dates) 123 321 3,366 2,226 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).

Related party transactions (Tab

Related party transactions (Tables)	12 Months Ended
	Mar. 31, 2024
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. 2024 2023 2022 £m £m £m Sales: Goods and services supplied to a pension plan — — 3 Sales: Goods and services supplied to joint ventures 1 221 100 284 Sales: Goods and services supplied to associates 1 1 — Sales: Goods and services supplied to subsidiary of an associate 1 70 6 — Purchases: Goods and services received from joint ventures 2 6 — 19 Purchases: Goods and services received from associates 2 4 31 41 Purchases: Goods and services received from subsidiaries of an associate 1 — — Receivables from joint ventures 3 80 58 43 Receivables from associates — — 1 Receivables from subsidiaries of an associate 8 8 — Payables to joint ventures 4 — 19 247 Payables to associates 1 1 4 Dividends received from joint ventures 5 152 150 123 Dividends received from associates 6 117 32 35 1. During the year, £126 million of sales were made to Emerald Energy Venture LLC ( 2023 : £76 million ; 2022 : £74 million ), £71 million ( 2023 : £ nil ; 2022 : £ nil ) of sales were made to Nemo Link Limited and £70 million ( 2023 : £ nil ) of sales were made to National Gas Transmission Plc after becoming a related party to the Group from 31 January 2023 following the sale of the UK Gas Transmission business. In the year ended 31 March 2022, £202 million of property sites were sold to St William Homes LLP prior to the Group’s disposal. 2. During the prior 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 £22 million ( 2022 : £38 million ) of purchases were made from Millennium Pipeline Company LLC in the period up until disposal on 7 October 2022. In the year ended 31 March 2022, the Group purchased assets of £18 million from BritNed Development Limited. 3. Amounts receivable from joint ventures include £77 million ( 2023 : £55 million ; 2022 : £33 million ) from Emerald Energy Venture LLC. 4. Amounts payable to joint ventures in the year ended 31 March 2022 included £223 million due to Community Offshore Wind, LLC, NGV’s joint venture with RWE Renewables, in respect of a capital call to NGV following the successful auction of six seabed leases in New York. This was settled in the year ended 31 March 2023. 5. Includes dividends of £116 million ( 2023 : £84 million ; 2022 : £39 million ) received from BritNed Development Limited and £17 million ( 2023 : £47 million ; 2022 : £77 million ) from Nemo Link Limited. 6. Includes dividends received in the year of £102 million from GasT TopCo Limited (see note 10) and £12 million ( 2023 : £12 million ; 2022 : £2 million ) from New York Transco LLC. During the prior year, £16 million ( 2022 : £34 million ) was received from Millennium Pipeline Company LLC in the period up until disposal on 7 October 2022.

Financial risk management (Tabl

Financial risk management (Tables)	12 Months Ended
	Mar. 31, 2024
Financial Risk Management [Abstract]
Disclosure of treasury credit risk	As at 31 March 2024 , the following limits were in place for investments and derivative financial instruments held with banks and financial institutions: Maximum limit £m Utilisation of maximum limit £m Long-term limit £m Utilisation of long-term limit £m Triple ‘A’ G7 sovereign entities (AAA) 2,818 — 2,114 — Triple ‘A’ vehicles (AAA) 500 460 — — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 2,562 — 1,922 — Double ‘A+’ G7 sovereign entities (AA+) 2,562 — 1,922 — Double ‘A’ range institutions (AA) 1,537 to 2,050 0 to 316 1,153 to 1,537 0 to 311 Single ‘A’ range institutions (A) 512 to 1,025 0 to 542 384 to 769 0 to 376
Disclosure of offsetting of financial assets and financial liabilities	Related amounts available to be offset but not offset in statement of financial position At 31 March 2024 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 333 — 333 (246) (28) 59 Commodity contract derivatives 35 — 35 (27) — 8 368 — 368 (273) (28) 67 Liabilities Financing derivatives (1,126) — (1,126) 246 441 (439) Commodity contract derivatives (118) — (118) 27 11 (80) (1,244) — (1,244) 273 452 (519) (876) — (876) — 424 (452) Related amounts available to be offset but not offset in statement of financial position At 31 March 2023 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 363 — 363 (204) (76) 83 Commodity contract derivatives 66 — 66 (28) — 38 429 — 429 (232) (76) 121 Liabilities Financing derivatives (1,119) — (1,119) 204 681 (234) Commodity contract derivatives (174) — (174) 28 19 (127) (1,293) — (1,293) 232 700 (361) (864) — (864) — 624 (240)
Disclosure of maturity analysis for financial liabilities and derivatives	The following is a payment profile of our financial liabilities and derivatives: At 31 March 2024 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (4,480) (2,627) (3,036) (35,243) (45,386) Interest payments on borrowings 1 (1,505) (1,442) (1,386) (17,247) (21,580) Lease liabilities (133) (118) (97) (662) (1,010) Other non-interest-bearing liabilities (3,715) (458) — — (4,173) Contingent consideration — — — — — Derivative financial liabilities Financing derivatives – receipts 2 5,583 2,993 2,672 5,246 16,494 Financing derivatives – payments 2 (6,068) (3,496) (2,909) (5,756) (18,229) Commodity contract derivatives – receipts 2 8 3 — — 11 Commodity contract derivatives – payments 2 (79) (24) (7) — (110) Derivative financial assets Financing derivatives – receipts 2 1,927 311 3,993 2,485 8,716 Financing derivatives – payments 2 (1,884) (312) (3,935) (2,305) (8,436) Commodity contract derivatives – receipts 2 23 8 1 — 32 Commodity contract derivatives – payments 2 (9) (5) (1) — (15) (10,332) (5,167) (4,705) (53,482) (73,686) At 31 March 2023 Less than 1 year £m 1 to 2 years £m 2 to 3 years £m More than 3 years £m Total £m Non-derivative financial liabilities Borrowings, excluding lease liabilities (2,433) (2,722) (2,614) (33,866) (41,635) Interest payments on borrowings 1 (1,220) (1,244) (1,148) (15,301) (18,913) Lease liabilities (118) (102) (86) (610) (916) Other non-interest-bearing liabilities (4,232) (416) — — (4,648) Contingent consideration (19) — — — (19) Derivative financial liabilities Financing derivatives – receipts 2 1,174 2,154 2,381 7,364 13,073 Financing derivatives – payments 2 (1,461) (2,483) (2,705) (8,335) (14,984) Commodity contract derivatives – receipts 2 11 9 1 — 21 Commodity contract derivatives – payments 2 (126) (35) (11) (1) (173) Derivative financial assets Financing derivatives – receipts 2 4,757 701 745 3,299 9,502 Financing derivatives – payments 2 (4,679) (676) (719) (3,183) (9,257) Commodity contract derivatives – receipts 2 48 11 — — 59 Commodity contract derivatives – payments 2 (11) (6) (3) — (20) (8,309) (4,809) (4,159) (50,633) (67,910) 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	D erivative financial instruments were used to manage foreign currency risk as follows: 2024 2023 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 402 — 157 — 559 96 14 53 — 163 Financial investments 1,514 — 2,185 — 3,699 1,031 — 1,574 — 2,605 Borrowings (14,498) (11,936) (18,938) (1,700) (47,072) (14,473) (11,045) (15,741) (1,726) (42,985) Pre-derivative position (12,582) (11,936) (16,596) (1,700) (42,814) (13,346) (11,031) (14,114) (1,726) (40,217) Derivative effect (9,102) 12,976 (6,625) 1,958 (793) (6,751) 10,733 (6,476) 1,738 (756) Net debt position (21,684) 1,040 (23,221) 258 (43,607) (20,097) (298) (20,590) 12 (40,973) The currency exposure on other financial instruments is as follows: 2024 2023 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 280 — 1,878 — 2,158 448 — 1,881 — 2,329 Trade and other payables (1,330) — (2,385) — (3,715) (1,624) — (2,629) — (4,253) Other non-current liabilities (169) — (289) — (458) (147) — (269) — (416) The table below sets out the sensitivity analysis for certain areas of estimation uncertainty set out in note 1 F. 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. This includes the impact of changes in assumptions on the net assets recognised at the balance sheet date and the amount charged to the income statement for the following year. Note that the sensitivity analysis for the useful economic lives of our gas network assets is included in note 13 . 2024 2023 Assumptions used Income statement £m Net assets £m Assumptions used Income statement £m Net assets £m Pensions and other post-retirement benefit liabilities (pre-tax): UK discount rate change¹ 1% 22 1,147 1% 29 1,264 US discount rate change¹ 1% 18 801 1% 26 977 UK inflation rate change² 1% 8 902 1% 8 933 UK long-term rate of increase in salaries change 1% 4 81 1% 4 50 US long-term rate of increase in salaries change 1% 2 37 1% 4 57 UK change to life expectancy at age 65 3 one year 2 402 one year 2 441 US change to life expectancy at age 65 one year 2 288 one year 3 344 Assumed US healthcare cost trend rates change 1% 18 276 1% 24 324 US environmental provision 4 : Change in the real discount rate 1% 173 173 1% 150 150 Change in estimated future cash flows 20% 462 462 20% 354 354 1. A change in the discount rate is likely to be driven by 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 £171 million ( 2023 : £188 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. 2. The projected impact resulting from a change in RPI reflects the associated effect on escalation rates for pensions in payment and in deferment and future salary increases. The buy‑in policies would have a £150 million ( 2023 : £164 million ) net assets offset to the above. 3. In the UK, the buy-in policies and the longevity swap entered into would have a £126 million ( 2023 : £136 million ) net assets offset to the above. 4. In the prior year, our sensitivity analysis included our UK environmental provisions, which are not considered to be a key source of estimation uncertainty in the current year. Accordingly, comparatives have been restated in line with current year disclosure. As a result of this change, the change in the real discount rate decreased by £9 million and the change in the estimated future cash flows decreased by £24 million . 2024 2023 Assumptions used Income statement £m Other equity reserves £m Assumptions used Income statement £m Other equity reserves £m Financial risk (post tax): UK inflation change¹ 1% 36 — 1% 35 — UK interest rates change 1% 24 304 1% 34 361 US interest rates change 1% 5 39 1% 14 50 US dollar exchange rate change² 10% 58 268 10% 51 291 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 £1,680 million ( 2023 : £1,680 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: 2024 2023 Assumptions used Income statement £m Net assets £m Assumptions used Income statement £m Net assets £m Commodity price risk (post tax): Increase in commodity prices 10% 43 43 10% 49 49 Decrease in commodity prices 10% (43) (43) 10% (40) (40) Assets and liabilities carried at fair value (post tax): Fair value change in derivative financial instruments¹ 10% (59) (59) 10% (60) (60) Fair value change in commodity contract derivative liabilities 10% (6) (6) 10% (8) (8) 1. The effect of a 10% change in fair value assumes no hedge accounting
Disclosure of financial instruments by type of interest rate	N et debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2024 2023 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 157 402 — — 559 53 110 — — 163 Financial investments — 3,640 — 59 3,699 — 2,569 — 36 2,605 Borrowings (39,948) (2,378) (4,746) — (47,072) (36,631) (1,744) (4,610) — (42,985) Pre-derivative position (39,791) 1,664 (4,746) 59 (42,814) (36,578) 935 (4,610) 36 (40,217) Derivative effect 5,034 (5,763) (64) — (793) 4,213 (4,869) (100) — (756) Net debt position (34,757) (4,099) (4,810) 59 (43,607) (32,365) (3,934) (4,710) 36 (40,973) 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 2024 Fair value hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency risk £m Net investment hedges £m Consolidated statement of comprehensive income Net gains/(losses) in respect of: Cash flow hedges — 5 (26) — Cost of hedging — (1) — 38 Net investment hedges — — — 62 Transferred to profit or loss in respect of: Cash flow hedges — 220 4 — Cost of hedging 1 (4) — (8) Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (16) — 3 Consolidated statement of financial position Borrowings – carrying value of hedging instruments Liabilities – non-current — — — (1,768) Derivatives – carrying value of hedging instruments 1 Assets – current — — 5 11 Assets – non-current 33 161 1 — Liabilities – current (96) (112) (4) (8) Liabilities – non-current (499) (164) (32) — Profiles of the significant timing, price and rate information of hedging instruments Maturity range Jul 2024 – Sep 2044 Jul 2024 – Nov 2040 Apr 2024 – Feb 2030 Apr 2024 – Jan 2034 Spot foreign exchange range: GBP:USD n/a 1.30 – 1.66 1.23 – 1.27 1.22 – 1.29 GBP:EUR 1.11 – 1.24 1.08 – 1.19 1.11 – 1.18 1.17 – 1.17 EUR:USD 1.07 – 1.15 1.07 – 1.15 n/a n/a Interest rate range: GBP SONIA + 56 bps/+ 374 bps 0.976% – 7.410% n/a n/a USD SOFR + 83 bps/+ 223 bps 2.095% – 5.989% 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 2023 Fair value hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency and/or interest rate risk £m Cash flow hedges of foreign currency risk £m Net investment hedges £m Consolidated statement of comprehensive income Net gains/(losses) in respect of: Cash flow hedges — 136 10 — Cost of hedging 4 4 — (24) Net investment hedges — — — (198) Transferred to profit or loss in respect of: Cash flow hedges — (136) — — Cost of hedging — — — 1 Reclassification of foreign currency translation reserve 1 — — — 373 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (11) (12) — (27) Consolidated statement of financial position Derivatives – carrying value of hedging instruments 2 Assets – current — — 6 52 Assets – non-current 25 166 1 — Liabilities – current (43) (39) (6) — Liabilities – non-current (559) (248) (1) (15) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Aug 2023 – Sep 2044 Jul 2024 – Nov 2040 Apr 2023 – May 2029 Jun 2023 – Sep 2027 Spot foreign exchange range: GBP:USD n/a 1.30 – 1.66 1.20 – 1.36 1.18 – 1.22 GBP:EUR 1.11 – 1.20 1.08 – 1.24 1.10 – 1.20 1.12 – 1.13 EUR:USD 1.13 – 1.17 1.13 – 1.15 n/a n/a Interest rate range: GBP SONIA + 84 bps/+ 374 bps 0.976% – 7.410% n/a n/a USD LIBOR + 68 bps/ SOFR + 126 bps 2.095% – 3.864% n/a n/a 1. The reclassification of the net investment hedge on the disposals of NECO and Millennium Pipeline Company LLC were included within Other operating income. 2. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. 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 the notional values of hedging instruments (and equal hedged exposures) which were impacted by IFRS 9 Interest Rate Benchmark Reform amendments in the prior year. (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2024 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 (5,096) 720 (35) 40 (22) 18 1. The carrying value of the hedged borrowings is £4,364 million , of which £271 million is current and £4,093 million is non-current. As at 31 March 2023 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 (4,779) 789 (43) 398 (351) 47 1. The carrying value of the hedged borrowings was £4,042 million , of which £511 million was current and £3,531 million was non-current. 2. Included within the hedging instrument notional balance was £859 million impacted by Interest Rate Benchmark Reform amendments which were still to be transitioned. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2024 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 and forecast cash flows (9,892) 154 — (18) 3 (15) Foreign currency risk on forecast cash flows (2,039) (31) — 28 (28) — As at 31 March 2023 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 (9,357) (73) — 149 (154) (5) Foreign currency risk on forecast cash flows (537) (3) — (35) 35 — (iii) Net investment hedges of foreign currency risk: As at 31 March 2024 Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Currency risk on foreign operations (2,999) 40 (2,564) (62) 62 — As at 31 March 2023 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 (3,095) (129) (2,457) 198 (198) —
Disclosure of detailed information about hedged items	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 the notional values of hedging instruments (and equal hedged exposures) which were impacted by IFRS 9 Interest Rate Benchmark Reform amendments in the prior year. (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings: As at 31 March 2024 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 (5,096) 720 (35) 40 (22) 18 1. The carrying value of the hedged borrowings is £4,364 million , of which £271 million is current and £4,093 million is non-current. As at 31 March 2023 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 (4,779) 789 (43) 398 (351) 47 1. The carrying value of the hedged borrowings was £4,042 million , of which £511 million was current and £3,531 million was non-current. 2. Included within the hedging instrument notional balance was £859 million impacted by Interest Rate Benchmark Reform amendments which were still to be transitioned. (ii) Cash flow hedges of foreign currency and interest rate risk: As at 31 March 2024 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 and forecast cash flows (9,892) 154 — (18) 3 (15) Foreign currency risk on forecast cash flows (2,039) (31) — 28 (28) — As at 31 March 2023 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 (9,357) (73) — 149 (154) (5) Foreign currency risk on forecast cash flows (537) (3) — (35) 35 — (iii) Net investment hedges of foreign currency risk: As at 31 March 2024 Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness Hedge type £m £m £m £m £m £m Currency risk on foreign operations (2,999) 40 (2,564) (62) 62 — As at 31 March 2023 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 (3,095) (129) (2,457) 198 (198) —
Disclosure of fair value measurement of assets	2024 2023 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 3,084 — 483 3,567 1,764 — 452 2,216 Investments held at FVOCI 1 — 397 — 397 — 407 — 407 Financing derivatives — 293 40 333 — 341 22 363 Commodity contract derivatives — 35 — 35 — 62 4 66 3,084 725 523 4,332 1,764 810 478 3,052 Liabilities Financing derivatives — (1,022) (104) (1,126) — (997) (122) (1,119) Commodity contract derivatives — (105) (13) (118) — (134) (40) (174) Contingent consideration 2 — — — — — — (19) (19) — (1,127) (117) (1,244) — (1,131) (181) (1,312) 3,084 (402) 406 3,088 1,764 (321) 297 1,740 1. Investments held includes instruments which meet the criteria of IFRS 9 or IAS 19. 2. Contingent consideration relates to the acquisition of National Grid Renewables. he changes in value of our Level 3 financial instruments are as follows: Financing derivatives Commodity contract derivatives Other 3 Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m At 1 April (100) (187) (36) 44 433 376 297 233 Net gains/(losses) for the year 1,2 36 87 — (18) 6 (2) 42 67 Purchases — — (16) (56) 35 59 19 3 Settlements — — 39 (6) 9 — 48 (6) At 31 March (64) (100) (13) (36) 483 433 406 297 1. Gain of £36 million ( 2023 : £87 million gain ) is attributable to derivative financial instruments held at the end of the reporting period and has been recognised in finance costs in the consolidated income statement. 2. Includes a loss of £18 million ( 2023 : £41 million loss ) attributable to commodity contract derivative financial instruments held at the end of the reporting period and has been recognised in other operating costs in the consolidated income statement. 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. In March 2023 this also included the contingent consideration arising from the acquisition of National Grid Renewables now settled. Net gains and losses are recognised within finance income and costs in the consolidated income statement.
Disclosure of fair value measurement of liabilities	2024 2023 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 3,084 — 483 3,567 1,764 — 452 2,216 Investments held at FVOCI 1 — 397 — 397 — 407 — 407 Financing derivatives — 293 40 333 — 341 22 363 Commodity contract derivatives — 35 — 35 — 62 4 66 3,084 725 523 4,332 1,764 810 478 3,052 Liabilities Financing derivatives — (1,022) (104) (1,126) — (997) (122) (1,119) Commodity contract derivatives — (105) (13) (118) — (134) (40) (174) Contingent consideration 2 — — — — — — (19) (19) — (1,127) (117) (1,244) — (1,131) (181) (1,312) 3,084 (402) 406 3,088 1,764 (321) 297 1,740 1. Investments held includes instruments which meet the criteria of IFRS 9 or IAS 19. 2. Contingent consideration relates to the acquisition of National Grid Renewables. he changes in value of our Level 3 financial instruments are as follows: Financing derivatives Commodity contract derivatives Other 3 Total 2024 2023 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m £m £m At 1 April (100) (187) (36) 44 433 376 297 233 Net gains/(losses) for the year 1,2 36 87 — (18) 6 (2) 42 67 Purchases — — (16) (56) 35 59 19 3 Settlements — — 39 (6) 9 — 48 (6) At 31 March (64) (100) (13) (36) 483 433 406 297 1. Gain of £36 million ( 2023 : £87 million gain ) is attributable to derivative financial instruments held at the end of the reporting period and has been recognised in finance costs in the consolidated income statement. 2. Includes a loss of £18 million ( 2023 : £41 million loss ) attributable to commodity contract derivative financial instruments held at the end of the reporting period and has been recognised in other operating costs in the consolidated income statement. 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. In March 2023 this also included the contingent consideration arising from the acquisition of National Grid Renewables now settled. Net gains and losses are recognised within finance income and costs in the consolidated income statement.
Schedule of impacts of reasonably possible changes in significant level 3 assumptions	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 2024 2023 2024 2023 2024 2023 £m £m £m £m £m £m 10% increase in commodity prices 1 — — 4 5 — — 10% decrease in commodity prices 1 — — (4) (6) — — +20 basis points change in Limited Price Inflation (LPI) market curve² (41) (53) — — — — -20 basis points change in LPI market curve² 41 51 — — — — +20 basis points increase between RPI and Consumer Price Index (CPI) 37 43 — — — — -20 basis points decrease between RPI and CPI (34) (38) — — — — +100 basis points change in discount rate — — — — (7) (9) -100 basis points change in discount rate — — — — 9 10 +10% change in venture capital price — — — — 28 28 -10% change in venture capital price — — — — (28) (28) 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 2024 .

Borrowing facilities (Tables)

Borrowing facilities (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of detailed information about borrowings [abstract]
Schedule of undrawn committed borrowing facilities	An analysis of the maturity of our undrawn committed facilities as at 31 March 2024 is shown below: 2024 2023 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — 42 In 1 to 2 years — 4,361 In 2 to 3 years 195 2,100 In 3 to 4 years 5,859 — In 4 to 5 years 106 — More than 5 years 1,745 — 7,905 6,503

Subsidiary undertakings, join_2

Subsidiary undertakings, joint ventures and associates (Tables)	12 Months Ended
	Mar. 31, 2024
Interests In Other Entities [Abstract]
Disclosure of interests in subsidiaries, joint ventures and associates	Incorporated in England and Wales Registered office: 1–3 Strand, London, WC2N 5EH, UK (unless stated otherwise in footnotes). Birch Sites Limited Carbon Sentinel Limited Central Networks Trustees Limited 1 Hyder Profit Sharing Trustees Limited 1 Icelink Interconnector Limited Kelston Properties 2 Limited 1 Lattice Group Employee Benefit Trust Limited Lattice Group Limited Lattice Group Trustees Limited NatGrid One Limited 2 * NatgridTW1 Limited National Energy System Operator Limited National Grid (US) Holdings Limited 3 National Grid (US) Investments 2 Limited 2 * National Grid (US) Investments 4 Limited 3 National Grid (US) Partner 1 Limited 3 National Grid Carbon Limited National Grid Commercial Holdings Limited National Grid Continental Limited National Grid Distributed Energy Limited National Grid Electricity Distribution (East Midlands) plc 1 National Grid Electricity Distribution (South Wales) plc 1 National Grid Electricity Distribution (South West) plc 1 National Grid Electricity Distribution (West Midlands) plc 1 National Grid Electricity Distribution Generation Limited 1 National Grid Electricity Distribution Holdings Limited 1 National Grid Electricity Distribution Investments Limited 1 National Grid Electricity Distribution Midlands Limited 1 National Grid Electricity Distribution Network Holdings Limited 1 National Grid Electricity Distribution plc 1 National Grid Electricity Distribution Property Investments Limited 1 National Grid Electricity Group Trustee Limited National Grid Electricity System Operator Limited National Grid Electricity Transmission plc National Grid Energy Metering Limited National Grid Grain LNG Limited National Grid Helicopters Limited 1 National Grid Holdings Limited 3 National Grid Holdings One plc National Grid Hydrogen Limited National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited 3 National Grid Lion Link Limited National Grid Nautilus Limited National Grid North Sea Link Limited National Grid Partners Limited National Grid Plus Limited National Grid Property Holdings Limited National Grid Telecoms Limited 1 National Grid Twelve Limited National Grid Twenty Eight Limited National Grid Twenty Seven Limited National Grid Twenty Three Limited 2 * National Grid UK Limited National Grid UK Pension Services Limited 2 * National Grid Ventures Limited National Grid Viking Link Limited National Grid William Limited NG Nominees Limited 3 NGC Employee Shares Trustee Limited NGG Finance plc Ngrid Intellectual Property Limited Port Greenwich Limited Sheet Road Management Company Limited ( 51% ) 4 South Wales Electricity Share Scheme Trustees Limited 1 Thamesport Interchange Limited The National Grid Group Quest Trustee Company Limited Warwick Technology Park Management Company (No 2) Limited ( 60.56% ) 5 Western Power Pension Trustee Limited 1 WPD Share Scheme Trustees Limited 1 WPD WEM Holdings Limited 1 WPD WEM Limited 1 WW Share Scheme Trustees Limited 1 1. Registered office: Avonbank, Feeder Road, Bristol, Avon, BS2 0TB, UK. 2. Registered office: C/o Interpath Limited, 10 Fleet Place, London, EC4M 7RB, UK. 3. Companies where National Grid plc has issued guarantees over the liabilities of the companies as at 31 March 2024 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. 4. Registered office: Netley Old Hall Farm, Dorrington, Shrewsbury, SY5 7JY, UK. 5. Registered office: Shire Hall, PO Box 9, Warwick, CV34 4RL, UK. * In liquidation. Incorporated in the US Registered office: National Registered Agents, Inc., 1209 Orange Street, Wilmington, DE 19801, USA (unless stated otherwise in footnotes). Apple River Solar, LLC Armenia Solar, LLC Ashland Solar, LLC Athens Solar, LLC Autauga Solar, LLC Bazile Creek Wind Farm, LLC Bee Hollow Solar, LLC Belle Plaine Solar, LLC Benevolent Solar, LLC Blaze Solar, LLC Blevins Storage, LLC Blue Ridge Wind, LLC Blue Spring Solar, LLC Blues Solar, LLC Boone Solar, LLC Boston Gas Company 1 Brock Solar, LLC Broken Bridge Corp. 2 Brook Trout Solar, LLC Burley Solar, LLC Burr Ridge Wind, LLC Cage Ranch Solar II, LLC Cage Ranch Solar III, LLC Cage Ranch Solar, LLC Caldwell Solar II, LLC Caldwell Solar, LLC Camp Creek Wind Farm, LLC Carnation Solar, LLC Cattle Ridge Wind Farm 2, LLC Cedar Grove Solar, LLC Charter Oak Solar, LLC Charter Oak Storage, LLC Clay Boswell Solar, LLC Clermont Solar, LLC Coles Solar, LLC Compass Prairie Wind, LLC Conestoga Wind, LLC Creekview Solar, LLC Crocker Wind Farm 2, LLC Dakota Hills Wind Farm, LLC Deatsville Solar, LLC Donnellson Solar, LLC Doorstep Community LLC 3 Elburn Solar, LLC Eldena Solar, LLC Elk Creek Solar 2, LLC Elk Creek Solar, LLC EUA Energy Investment Corporation 1 Exie Solar, LLC Falls City Solar, LLC Firstview Wind Farm, LLC Fort Solar, LLC Front Range Wind Farm, LLC Galaxy Solar, LLC Golden Solar, LLC Goldendale Solar, LLC Goldenrod Wind Farm, LLC Goldfinch Solar, LLC Granite State Power Link LLC 3 Grant Solar 2, LLC Grant Solar, LLC Grayson Solar, LLC Greenbrier Creek Solar, LLC Greenwood Solar, LLC Grid NY LLC 4 Grindstone Wind Farm, LLC 5 Hale County Solar, LLC Hansford Energy Storage, LLC Harmony Solar ND 2, LLC Harmony Solar ND, LLC Harrington Solar, LLC Hartley Solar, LLC Hearth Solar, LLC High View Property, LLC Honeybee Solar, LLC Hoosier Solar, LLC Hoskins Solar, LLC Illumination Solar, LLC Itasca Energy Development, LLC 6 Itasca Energy Services, LLC Jack Rabbit Wind, LLC Jackson County Solar, LLC KeySpan CI Midstream Limited 3 KeySpan Energy Corporation 4 KeySpan Energy Services Inc. 3 KeySpan Gas East Corporation 4 KeySpan International Corporation 3 KeySpan MHK, Inc. 3 KeySpan Midstream, Inc. 3 KeySpan Plumbing Solutions, Inc. 4 Kit Carson Wind, LLC Kit Fox Storage, LLC Knox Solar, LLC Kota Storage, LLC KSI Contracting, LLC 3 KSI Electrical, LLC 3 KSI Mechanical, LLC 3 Lake Charlotte Solar, LLC Lakeside Solar, LLC Land Management & Development, Inc. 4 Landwest, Inc. 4 Lansing Solar, LLC Las Moras Storage, LLC Leola Wind Farm, LLC Liberty Solar, LLC Livingston County Solar, LLC Long Mount Storage, LLC Lordsburg Solar, LLC Louisa Solar, LLC Lowlands Solar, LLC Lydia Solar, LLC Massachusetts Electric Company 1 Maverick Wind Farm, LLC Meadowlands Solar, LLC Mentha Solar, LLC Metrowest Realty LLC 3 Millers Ferry Solar, LLC Morgan County Solar, LLC Morning Glory Solar, LLC 6 Muddy Creek Solar, LLC Mustang Ridge Wind Farm, LLC Mystic Steamship Corporation 7 Nantucket Electric Company 1 National Grid Development Holdings Corp. 3 National Grid Electric Services LLC 4 National Grid Energy Trading Services LLC 4 National Grid Engineering & Survey Inc. 4 National Grid Generation LLC 4 National Grid Generation Ventures LLC 4 National Grid Glenwood Energy Center LLC 3 National Grid IGTS Corp. 4 National Grid Insurance USA Ltd 8 National Grid LNG LLC 3 National Grid NE Holdings 2 LLC 1 National Grid North America Inc. 3 National Grid Partners Inc. 4 National Grid Partners LLC 3 National Grid Port Jefferson Energy Center LLC 3 National Grid Renewables Development, LLC National Grid Renewables E Wind, LLC 9 National Grid Renewables Operations, LLC 3 National Grid Renewables Projects, LLC 6 National Grid Renewables Stutsman, LLC National Grid Renewables, LLC 3 National Grid Services Inc. 3 National Grid US LLC 3 National Grid USA Service Company, Inc. 1 National Grid USA 3 NEES Energy, Inc. 1 New England Electric Transmission Corporation 2 New England Energy Incorporated 1 New England Hydro Finance Company, Inc. ( 53.704% ) 1 New England Hydro-Transmission Corporation ( 53.704% ) 2 New England Hydro-Transmission Electric Company, Inc. ( 53.704% ) 1 New England Power Company 1 Newport America Corporation 10 Newton Solar, LLC NG Renewables Energy Marketing, LLC 3 NG Renewables Energy Services, LLC NG Renewables Remote Operations Center, LLC NGNE LLC 3 NGV Emerald Energy Venture Holdings, LLC 3 NGV H2 Holdings LLC 3 NGV LNG Holdings LLC 3 NGV OSW Holdings, LLC 3 NGV US Distributed Energy Inc. 3 NGV US Transmission Inc. 3 NGV US, LLC 3 Niagara Mohawk Energy, Inc. 3 Niagara Mohawk Holdings, Inc. 4 Niagara Mohawk Power Corporation 4 Niobrara Wind, LLC NM Properties, Inc. 4 Noble Solar, LLC 11 Nordic VOS, LLC North East Transmission Co., Inc. 3 North Fork Wind, LLC Northeast Renewable Link LLC 3 Opinac North America, Inc. 3 Peony Solar, LLC Philadelphia Coke Co., Inc. 3 Pike County Solar, LLC Pipestone Solar, LLC Plum Creek Wind Farm 2, LLC Plum Creek Wind Farm, LLC Port of the Islands North, LLC 4 Portage Solar, LLC Prairie Oasis Solar, LLC Prairie Rose Wind 2, LLC 6 Prosperity Wind Farm 2, LLC Prosperity Wind Farm, LLC Red Rock Solar SD, LLC Regal Solar 2, LLC Regal Solar, LLC Reunion Solar, LLC River North Solar, LLC Robertson Solar, LLC Rock Ridge Wind Farm, LLC Rolling Hills Solar, LLC Royal Solar 2, LLC Royal Solar, LLC Royerton Solar, LLC Saginaw Bay Solar, LLC Saltillo Storage, LLC Sandstone Creek Solar 2, LLC Sandstone Creek Solar, LLC Sapphire Sky Wind Farm, LLC Sherco Solar 2, LLC 6 Sherco Solar 3, LLC Silver City Solar, LLC Simpson Solar, LLC Spring Brook Solar, LLC Spring River Solar, LLC Stony Brook Wind, LLC Stony Point Solar, LLC Stove Creek Solar, LLC Summit Lake Solar, LLC Sunbeam Solar, LLC Sunrise Solar, LLC Sycamore Creek Solar, LLC Tejano Storage, LLC Thacker Solar, LLC The Brooklyn Union Gas Company 4 Torchlight Solar, LLC 6 Transgas Inc. 1 Tri-City Solar, LLC Uintah Solar, LLC Upper Hudson Development, Inc. 4 Valley Solar, LLC Vermont Green Line Devco, LLC ( 90% ) 3 Violet Storage, LLC Virgo Community Solar Gardens, LLC 6 Virtue Solar, LLC Vivid Solar, LLC Wallowa Solar, LLC Wayfinder Group, Inc. 1 White Elm Wind Farm, LLC Wildcat Ridge Wind Farm, LLC Wilder Solar, LLC Wildhorse Creek Solar, LLC Willard Solar, LLC Williams County Solar, LLC Wiregrass Solar, LLC Woodlands Solar, LLC Worthington Solar, LLC Young County Solar, LLC Incorporated in Guernsey Registered office: 1st & 2nd Floors Elizabeth House, Les Ruettes Brayes, St Peter Port, GY1 1EW, Guernsey, Channel Islands NG Electricity Distribution Limited † Incorporated in Hong Kong Registered office: 5/F, Manulife Place, 348 Kwun Tong Road, Kowloon, 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 Incorporated in Luxembourg Registered office: 412F, Route d’Esch, L-2086, Luxembourg, Grand Duchy of Luxembourg National Grid Luxembourg SARL 1. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, USA. 2. Registered office: Corporation Service Company, 10 Ferry Street, Suite 313, Concord NH 03301, USA. 3. Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington DE 19808, USA. 4. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 5. Registered office: National Registered Agents Inc., 30600 Telegraph Road, Suite 2345, Bingham Farms MI 48025-5720, USA. 6. Registered office: 8400 Normandale Lake Blvd., Suite 1200, Bloomington MN 55437, USA. 7. Registered office: Corporation Trust Company, 1209 Orange Street, Wilmington DE 19801, USA. 8. Registered office: 100 Bank Street, Suite 630, Burlington, Chittenden County VT 05401, USA. 9. Registered office: National Registered Agents, Inc., 301 S. Bedford Street, Suite 1, Madison WI 5, USA. 10. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, USA. 11. Registered office: National Registered Agents, Inc., 1999 Bryan Street, Dallas TX 75201, USA. * In liquidation. † Entity is tax resident in the UK. A list of the Group’s joint ventures as at 31 March 2024 is given below. All joint ventures are included in the Group’s Financial statements using the equity method of accounting. Incorporated in England and Wales Registered office: 1–3 Strand, London, WC2N 5EH, UK (unless stated otherwise in footnotes). BritNed Development Limited ( 50% )** National Places LLP ( 50% ) 1 Nemo Link Limited ( 50% ) Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, USA (unless stated otherwise in footnotes). Community Offshore Wind, LLC (previously Bight Wind Holdings LLC) ( 27.27% ) 2 Clean Energy Storage Systems LLC ( 50% ) Emerald Energy Venture, LLC ( 51% ) Island Park Energy Center, LLC ( 50% ) LI Energy Storage System, LLC ( 50% ) LI Solar Generation, LLC ( 50% ) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, Paris La Defense, CEDEX, France IFA2 ( 50% )* Joint operations A list of the Group’s incorporated joint operations as at 31 March 2024 is given below. All joint operations are included in the Group’s financial statements under IFRS 11 Joint arrangements. Incorporated in England and Wales Registered office: 1–3 Strand, London, WC2N 5EH, UK (unless stated otherwise in footnotes). Eastern Green Link 1 Limited ( 50% ) Eastern Green Link 2 Limited ( 50% ) 3 NGET/SPT Upgrades Limited ( 50% ) † A list of the Group’s associates as at 31 March 2024 is given below. Unless otherwise stated, all associates are included in the Group’s financial statements using the equity method of accounting. Incorporated in England and Wales Registered office: National Grid House, Warwick Technology Park, Gallows Hill, Warwick, CV34 6DA GasT TopCo Limited ( 20% ) Joint Radio Company Limited ( 25% ) 4 *** 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% ) 2 Connecticut Yankee Atomic Power Company ( 19.5% ) 5 Direct Global Power Inc. ( 26% ) 2 Energy Impact Fund LP ( 9.41% ) 6 KHB Venture LLC ( 33.33% ) 7 Maine Yankee Atomic Power Company ( 24% ) 8 New York Transco LLC ( 28.3% ) 9 NYSEARCH RMLD, LLC ( 22.63% ) The Hive IV, LLC ( 28.2% ) 2 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 2024 is given below. Incorporated in England and Wales Registered office: 1 More London Place, London SE1 2AF, UK Energis plc ( 33.06% ) ‡ Registered office: Third Floor, Northumberland House, 303–306 High Holborn, London, WC1V 7JZ Electralink Limited ( 27.04% ) 1. Registered office: 80 Cheapside, London, EC2V 6EE, UK. 2. Registered office: The Corporation Trust Company, Corporation Trust Center, 1209 Orange Street, Wilmington DE 19801, USA. 3. Registered office: No.1 Forbury Place, 43 Forbury Road, Reading, RG1 3JH, UK. 4. Registered office: Friars House, Manor House Drive, Coventry, CV1 2TE, UK. 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, USA. 7. Registered office: c/o de maximis, 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. * In liquidation. ** National Grid Interconnector Holdings Limited owns 284,500,000 €0.20 C Ordinary shares and one £1.00 Ordinary A share. *** National Grid Electricity Transmission plc owns one £0.50 A Ordinary share. † National Grid Electricity Transmission plc owns 50 £1.00 A Ordinary shares. ‡ In administration.
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 supported by guarantees issued by National Grid plc over their liabilities for the year ended 31 March 2024 : Company name Company number National Grid Holdings Limited 3096772 National Grid International Limited 2537092 National Grid (US) Holdings Limited 2630496 National Grid (US) Investments 4 Limited 3867128 National Grid (US) Partner 1 Limited 4314432 NG Nominees Limited 2489329

Sensitivities (Tables)

Sensitivities (Tables)	12 Months Ended
	Mar. 31, 2024
Disclosure of sensitivity analysis for actuarial assumptions [abstract]
Schedule of sensitivities on areas of estimation uncertainty and on financial instruments	D erivative financial instruments were used to manage foreign currency risk as follows: 2024 2023 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 402 — 157 — 559 96 14 53 — 163 Financial investments 1,514 — 2,185 — 3,699 1,031 — 1,574 — 2,605 Borrowings (14,498) (11,936) (18,938) (1,700) (47,072) (14,473) (11,045) (15,741) (1,726) (42,985) Pre-derivative position (12,582) (11,936) (16,596) (1,700) (42,814) (13,346) (11,031) (14,114) (1,726) (40,217) Derivative effect (9,102) 12,976 (6,625) 1,958 (793) (6,751) 10,733 (6,476) 1,738 (756) Net debt position (21,684) 1,040 (23,221) 258 (43,607) (20,097) (298) (20,590) 12 (40,973) The currency exposure on other financial instruments is as follows: 2024 2023 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 280 — 1,878 — 2,158 448 — 1,881 — 2,329 Trade and other payables (1,330) — (2,385) — (3,715) (1,624) — (2,629) — (4,253) Other non-current liabilities (169) — (289) — (458) (147) — (269) — (416) The table below sets out the sensitivity analysis for certain areas of estimation uncertainty set out in note 1 F. 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. This includes the impact of changes in assumptions on the net assets recognised at the balance sheet date and the amount charged to the income statement for the following year. Note that the sensitivity analysis for the useful economic lives of our gas network assets is included in note 13 . 2024 2023 Assumptions used Income statement £m Net assets £m Assumptions used Income statement £m Net assets £m Pensions and other post-retirement benefit liabilities (pre-tax): UK discount rate change¹ 1% 22 1,147 1% 29 1,264 US discount rate change¹ 1% 18 801 1% 26 977 UK inflation rate change² 1% 8 902 1% 8 933 UK long-term rate of increase in salaries change 1% 4 81 1% 4 50 US long-term rate of increase in salaries change 1% 2 37 1% 4 57 UK change to life expectancy at age 65 3 one year 2 402 one year 2 441 US change to life expectancy at age 65 one year 2 288 one year 3 344 Assumed US healthcare cost trend rates change 1% 18 276 1% 24 324 US environmental provision 4 : Change in the real discount rate 1% 173 173 1% 150 150 Change in estimated future cash flows 20% 462 462 20% 354 354 1. A change in the discount rate is likely to be driven by 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 £171 million ( 2023 : £188 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. 2. The projected impact resulting from a change in RPI reflects the associated effect on escalation rates for pensions in payment and in deferment and future salary increases. The buy‑in policies would have a £150 million ( 2023 : £164 million ) net assets offset to the above. 3. In the UK, the buy-in policies and the longevity swap entered into would have a £126 million ( 2023 : £136 million ) net assets offset to the above. 4. In the prior year, our sensitivity analysis included our UK environmental provisions, which are not considered to be a key source of estimation uncertainty in the current year. Accordingly, comparatives have been restated in line with current year disclosure. As a result of this change, the change in the real discount rate decreased by £9 million and the change in the estimated future cash flows decreased by £24 million . 2024 2023 Assumptions used Income statement £m Other equity reserves £m Assumptions used Income statement £m Other equity reserves £m Financial risk (post tax): UK inflation change¹ 1% 36 — 1% 35 — UK interest rates change 1% 24 304 1% 34 361 US interest rates change 1% 5 39 1% 14 50 US dollar exchange rate change² 10% 58 268 10% 51 291 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 £1,680 million ( 2023 : £1,680 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: 2024 2023 Assumptions used Income statement £m Net assets £m Assumptions used Income statement £m Net assets £m Commodity price risk (post tax): Increase in commodity prices 10% 43 43 10% 49 49 Decrease in commodity prices 10% (43) (43) 10% (40) (40) Assets and liabilities carried at fair value (post tax): Fair value change in derivative financial instruments¹ 10% (59) (59) 10% (60) (60) Fair value change in commodity contract derivative liabilities 10% (6) (6) 10% (8) (8) 1. The effect of a 10% change in fair value assumes no hedge accounting

Basis of preparation and rece_3

Basis of preparation and recent accounting developments (Details) £ in Millions				12 Months Ended
	Mar. 31, 2024 GBP (£) MW site	Mar. 11, 2024	Jan. 31, 2023	Mar. 31, 2024 GBP (£) MW site	Mar. 31, 2023 GBP (£)	Mar. 31, 2050 GBP (£)	Mar. 31, 2022 GBP (£)
Disclosure of subsidiaries [line items]
Number of US Superfund sites | site	3			3
Property, plant and equipment	£ 68,907			£ 68,907	£ 64,433
Other provisions	3,109			3,109	£ 2,642		£ 2,539
Decommissioning provision, ARO
Disclosure of subsidiaries [line items]
Other provisions	57			£ 57
New York
Disclosure of subsidiaries [line items]
Cash flow projection, forecast period				5 years
New England
Disclosure of subsidiaries [line items]
Cash flow projection, forecast period				5 years
Electricity generation plant
Disclosure of subsidiaries [line items]
Property, plant and equipment	£ 325			£ 325
Property, plant and equipment, capacity | MW	3,800			3,800
Liquefied natural gas | Forecast
Disclosure of subsidiaries [line items]
Property, plant and equipment						£ 0
GasT TopCo Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed		20%
Proportion of ownership interest in associate	20%	20%	40%	20%
GasT TopCo Limited | The Consortium
Disclosure of subsidiaries [line items]
Proportion of ownership interest in associate		80%
UK Gas Transmission business
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed			100%		60%
Minimum | Fixed interest rate bonds
Disclosure of subsidiaries [line items]
Notional amount	£ 5,600			£ 5,600

Segmental analysis - Narrative

Segmental analysis - Narrative (Details)	Mar. 31, 2024 business_unit
Disclosure of operating segments [abstract]
Number of operating business units	6

Segmental analysis - Schedule o

Segmental analysis - Schedule of revenue by operating segments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of operating segments [line items]
Revenue	£ 19,850	£ 21,659	£ 18,449
UK
Disclosure of operating segments [line items]
Revenue	9,063	9,611	7,803
US
Disclosure of operating segments [line items]
Revenue	10,787	12,048	10,646
UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	2,695	1,946	2,028
UK Electricity Distribution
Disclosure of operating segments [line items]
Revenue	1,790	2,033	1,468
UK Electricity System Operator
Disclosure of operating segments [line items]
Revenue	3,753	4,659	3,437
New England
Disclosure of operating segments [line items]
Revenue	3,948	4,427	4,550
New York
Disclosure of operating segments [line items]
Revenue	6,094	6,994	5,561
National Grid Ventures
Disclosure of operating segments [line items]
Revenue	1,332	1,283	1,024
Other
Disclosure of operating segments [line items]
Revenue	238	317	381
Operating segments
Disclosure of operating segments [line items]
Revenue	19,993	21,801	18,488
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	2,735	1,987	2,035
Operating segments | UK Electricity Distribution
Disclosure of operating segments [line items]
Revenue	1,795	2,045	1,482
Operating segments | UK Electricity System Operator
Disclosure of operating segments [line items]
Revenue	3,788	4,690	3,455
Operating segments | New England
Disclosure of operating segments [line items]
Revenue	3,948	4,427	4,550
Operating segments | New York
Disclosure of operating segments [line items]
Revenue	6,094	6,994	5,561
Operating segments | National Grid Ventures
Disclosure of operating segments [line items]
Revenue	1,389	1,341	1,024
Operating segments | Other
Disclosure of operating segments [line items]
Revenue	244	317	381
Sales between segments
Disclosure of operating segments [line items]
Revenue	(143)	(142)	(39)
Sales between segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	(40)	(41)	(7)
Sales between segments | UK Electricity Distribution
Disclosure of operating segments [line items]
Revenue	(5)	(12)	(14)
Sales between segments | UK Electricity System Operator
Disclosure of operating segments [line items]
Revenue	(35)	(31)	(18)
Sales between segments | New England
Disclosure of operating segments [line items]
Revenue	0	0	0
Sales between segments | New York
Disclosure of operating segments [line items]
Revenue	0	0	0
Sales between segments | National Grid Ventures
Disclosure of operating segments [line items]
Revenue	(57)	(58)	0
Sales between segments | Other
Disclosure of operating segments [line items]
Revenue	£ (6)	£ 0	£ 0

Segmental analysis - Schedule_2

Segmental analysis - Schedule of operating profit by operating segments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of operating segments [line items]
Total operating profit from continuing operations	£ 4,475	£ 4,879	£ 4,371
Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	5,462	4,294	3,813
Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(987)	585	558
UK
Disclosure of operating segments [line items]
Total operating profit from continuing operations	3,436	2,851	2,458
UK | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	3,923	2,825	2,234
UK | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(487)	26	224
US
Disclosure of operating segments [line items]
Total operating profit from continuing operations	1,039	2,028	1,913
US | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	1,539	1,469	1,579
US | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(500)	559	334
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Total operating profit from continuing operations	1,674	993	1,055
Operating segments | UK Electricity Transmission | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	1,677	995	1,067
Operating segments | UK Electricity Transmission | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(3)	(2)	(12)
Operating segments | UK Electricity Distribution
Disclosure of operating segments [line items]
Total operating profit from continuing operations	975	1,069	909
Operating segments | UK Electricity Distribution | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	993	1,091	909
Operating segments | UK Electricity Distribution | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(18)	(22)	0
Operating segments | UK Electricity System Operator
Disclosure of operating segments [line items]
Total operating profit from continuing operations	382	237	5
Operating segments | UK Electricity System Operator | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	880	238	7
Operating segments | UK Electricity System Operator | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(498)	(1)	(2)
Operating segments | New England
Disclosure of operating segments [line items]
Total operating profit from continuing operations	641	1,132	764
Operating segments | New England | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	643	708	743
Operating segments | New England | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(2)	424	21
Operating segments | New York
Disclosure of operating segments [line items]
Total operating profit from continuing operations	362	541	1,095
Operating segments | New York | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	860	741	780
Operating segments | New York | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(498)	(200)	315
Operating segments | National Grid Ventures
Disclosure of operating segments [line items]
Total operating profit from continuing operations	558	957	283
Operating segments | National Grid Ventures | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	469	490	286
Operating segments | National Grid Ventures | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	89	467	(3)
Operating segments | Other
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(117)	(50)	260
Operating segments | Other | Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Total operating profit from continuing operations	(60)	31	21
Operating segments | Other | Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Total operating profit from continuing operations	£ (57)	£ (81)	£ 239

Segmental analysis - Schedule_3

Segmental analysis - Schedule of reconciliation of total operating profit to profit before tax from continuing operations (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 4,475	£ 4,879	£ 4,371
Share of post-tax results of joint ventures and associates	37	171	92
Finance income	248	138	50
Finance costs	(1,712)	(1,598)	(1,072)
Profit before tax	3,048	3,590	3,441
Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	5,462	4,294	3,813
Share of post-tax results of joint ventures and associates	101	190	148
Finance income	244	166	65
Finance costs	(1,723)	(1,680)	(1,146)
Profit before tax	4,084	2,970	2,880
Exceptional items and remeasurements (see note 5)
Disclosure of operating segments [line items]
Operating profit from continuing operations	(987)	585	558
Share of post-tax results of joint ventures and associates	(64)	(19)	(56)
Finance income	4	(28)	(15)
Finance costs	11	82	74
Profit before tax	£ (1,036)	£ 620	£ 561

Segmental analysis - Schedule_4

Segmental analysis - Schedule of depreciation, amortisation and impairment by operating segments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	£ (2,061)	£ (1,984)	£ (1,830)
Property, plant and equipment
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	(1,769)	(1,700)	(1,544)
Non-current intangible assets
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	(292)	(284)	(286)
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	(521)	(484)	(508)
Operating segments | UK Electricity Distribution
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	(223)	(223)	(158)
Operating segments | UK Electricity System Operator
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	(61)	(101)	(83)
Operating segments | New England
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	(420)	(393)	(364)
Operating segments | New York
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	(658)	(620)	(537)
Operating segments | National Grid Ventures
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	(166)	(149)	(156)
Operating segments | Other
Disclosure of operating segments [line items]
Depreciation, amortisation and impairment	£ (12)	£ (14)	£ (24)

Segmental analysis - Schedule_5

Segmental analysis - Schedule of capital investment by operating segments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of operating segments [line items]
Capital investment	£ 8,235	£ 7,593	£ 6,623
Revenue	19,850	21,659	18,449
St William Homes LLP
Disclosure of operating segments [line items]
Investments to joint ventures	0	0	25
Property, plant and equipment
Disclosure of operating segments [line items]
Capital investment	7,124	6,783	5,622
Non-current intangible assets
Disclosure of operating segments [line items]
Capital investment	481	578	471
Equity investments to joint ventures and associates
Disclosure of operating segments [line items]
Capital investment	332	197	461
Capital expenditure prepayments
Disclosure of operating segments [line items]
Capital investment	298	35	69
UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	2,695	1,946	2,028
UK Electricity Distribution
Disclosure of operating segments [line items]
Revenue	1,790	2,033	1,468
UK Electricity System Operator
Disclosure of operating segments [line items]
Revenue	3,753	4,659	3,437
New England
Disclosure of operating segments [line items]
Revenue	3,948	4,427	4,550
New York
Disclosure of operating segments [line items]
Revenue	6,094	6,994	5,561
National Grid Ventures
Disclosure of operating segments [line items]
Revenue	1,332	1,283	1,024
Other
Disclosure of operating segments [line items]
Revenue	238	317	381
Operating segments
Disclosure of operating segments [line items]
Revenue	19,993	21,801	18,488
Operating segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Capital investment	1,912	1,301	1,179
Revenue	2,735	1,987	2,035
Operating segments | UK Electricity Distribution
Disclosure of operating segments [line items]
Capital investment	1,247	1,220	899
Revenue	1,795	2,045	1,482
Operating segments | UK Electricity System Operator
Disclosure of operating segments [line items]
Capital investment	85	108	108
Revenue	3,788	4,690	3,455
Operating segments | New England
Disclosure of operating segments [line items]
Capital investment	1,673	1,527	1,478
Revenue	3,948	4,427	4,550
Operating segments | New York
Disclosure of operating segments [line items]
Capital investment	2,654	2,454	1,960
Revenue	6,094	6,994	5,561
Operating segments | National Grid Ventures
Disclosure of operating segments [line items]
Capital investment	662	970	989
Revenue	1,389	1,341	1,024
Operating segments | Other
Disclosure of operating segments [line items]
Capital investment	2	13	10
Revenue	244	317	381
Sales between segments
Disclosure of operating segments [line items]
Revenue	(143)	(142)	(39)
Sales between segments | UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	(40)	(41)	(7)
Sales between segments | UK Electricity Distribution
Disclosure of operating segments [line items]
Revenue	(5)	(12)	(14)
Sales between segments | UK Electricity System Operator
Disclosure of operating segments [line items]
Revenue	(35)	(31)	(18)
Sales between segments | New England
Disclosure of operating segments [line items]
Revenue	0	0	0
Sales between segments | New York
Disclosure of operating segments [line items]
Revenue	0	0	0
Sales between segments | National Grid Ventures
Disclosure of operating segments [line items]
Revenue	(57)	(58)	0
Sales between segments | Other
Disclosure of operating segments [line items]
Revenue	£ (6)	£ 0	£ 0

Segmental analysis - Schedule_6

Segmental analysis - Schedule of geographical analysis of non-current assets (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of other provisions [line items]
Non-current assets other than financial instruments and pension assets	£ 84,335	£ 79,804	£ 71,877
Pension assets	2,407	2,645	3,885
Financial and other investments	880	859	830
Derivative financial assets	324	276	305
Total non-current assets	87,946	83,584	76,897
UK
Disclosure of other provisions [line items]
Non-current assets other than financial instruments and pension assets	40,065	38,043	35,466
US
Disclosure of other provisions [line items]
Non-current assets other than financial instruments and pension assets	£ 44,270	£ 41,761	£ 36,411

Revenue - Disclosure of disaggr

Revenue - Disclosure of disaggregation of revenue by primary geographical market and major service lines (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	£ 19,070	£ 20,835	£ 17,714
Total other revenue	780	824	735
Total revenue from continuing operations	19,850	21,659	18,449
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	2,616	1,899	2,018
Total other revenue	79	47	10
Total revenue from continuing operations	2,695	1,946	2,028
UK Electricity Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	1,785	2,028	1,464
Total other revenue	5	5	4
Total revenue from continuing operations	1,790	2,033	1,468
UK Electricity System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	3,753	4,659	3,437
Total other revenue	0	0	0
Total revenue from continuing operations	3,753	4,659	3,437
New England
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	3,867	4,374	4,496
Total other revenue	81	53	54
Total revenue from continuing operations	3,948	4,427	4,550
New York
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	6,008	6,953	5,525
Total other revenue	86	41	36
Total revenue from continuing operations	6,094	6,994	5,561
National Grid Ventures
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	1,037	922	774
Total other revenue	295	361	250
Total revenue from continuing operations	1,332	1,283	1,024
Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	4	0	0
Total other revenue	234	317	381
Total revenue from continuing operations	238	317	381
UK
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	9,033	9,385	7,565
Total other revenue	30	226	238
Total revenue from continuing operations	9,063	9,611	7,803
UK | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	2,616	1,899	2,018
Total other revenue	79	47	10
UK | UK Electricity Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	1,785	2,028	1,464
Total other revenue	5	5	4
UK | UK Electricity System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	3,753	4,659	3,437
Total other revenue	0	0	0
UK | New England
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Total other revenue	0	0	0
UK | New York
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Total other revenue	0	0	0
UK | National Grid Ventures
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	878	799	646
Total other revenue	(76)	(31)	(132)
UK | Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	1	0	0
Total other revenue	22	205	356
US
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	10,037	11,450	10,149
Total other revenue	750	598	497
Total revenue from continuing operations	10,787	12,048	10,646
US | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Total other revenue	0	0	0
US | UK Electricity Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Total other revenue	0	0	0
US | UK Electricity System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Total other revenue	0	0	0
US | New England
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	3,867	4,374	4,496
Total other revenue	81	53	54
US | New York
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	6,008	6,953	5,525
Total other revenue	86	41	36
US | National Grid Ventures
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	159	123	128
Total other revenue	371	392	382
US | Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	3	0	0
Total other revenue	212	112	25
Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	4,016	3,404	3,067
Transmission | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	2,591	1,868	1,983
Transmission | UK Electricity Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Transmission | UK Electricity System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	(10)	126	0
Transmission | New England
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	73	52	52
Transmission | New York
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	493	567	405
Transmission | National Grid Ventures
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	869	791	627
Transmission | Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	10,998	12,638	10,919
Distribution | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Distribution | UK Electricity Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	1,712	1,951	1,375
Distribution | UK Electricity System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Distribution | New England
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	3,786	4,314	4,434
Distribution | New York
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	5,500	6,373	5,110
Distribution | National Grid Ventures
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Distribution | Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	3,763	4,533	3,418
System Operator | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
System Operator | UK Electricity Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
System Operator | UK Electricity System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	3,763	4,533	3,418
System Operator | New England
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
System Operator | New York
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
System Operator | National Grid Ventures
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
System Operator | Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	0
Generation
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total other revenue	360	394	373
Generation | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total other revenue	0	0	0
Generation | UK Electricity Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total other revenue	0	0	0
Generation | UK Electricity System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total other revenue	0	0	0
Generation | New England
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total other revenue	0	0	0
Generation | New York
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total other revenue	0	0	0
Generation | National Grid Ventures
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total other revenue	360	394	373
Generation | Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total other revenue	0	0	0
Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	293	260	310
Total other revenue	420	430	362
Other | UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	25	31	35
Total other revenue	79	47	10
Other | UK Electricity Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	73	77	89
Total other revenue	5	5	4
Other | UK Electricity System Operator
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	0	0	19
Total other revenue	0	0	0
Other | New England
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	8	8	10
Total other revenue	81	53	54
Other | New York
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	15	13	10
Total other revenue	86	41	36
Other | National Grid Ventures
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	168	131	147
Total other revenue	(65)	(33)	(123)
Other | Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Total IFRS 15 revenue	4	0	0
Total other revenue	£ 234	£ 317	£ 381

Revenue - Narrative (Details)

Revenue - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contract liabilities	£ 2,246	£ 2,006	£ 1,472
Future revenues in relation to unfulfilled performance obligations	£ 6,100	5,000	5,200
Remaining performance obligation, expected timing of satisfaction, period	2 years
Revenue from performance obligations satisfied or partially satisfied in previous periods	£ 0	0	0
National Grid Grain LNG Limited
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 3,800	2,700	3,000
Connections | Weighted average
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	32 years
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 1,900	£ 1,800	£ 1,700
Remaining performance obligation, expected timing of satisfaction, period	24 years
UK Electricity Transmission | Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	40 years
UK Electricity Distribution | Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	69 years
New England | Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	51 years
New York | Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	51 years

Other operating costs - Schedul

Other operating costs - Schedule of analysis of expenses by nature (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure Of Operating Expenses [Line Items]
Depreciation, amortisation and impairment	£ 2,061	£ 1,984	£ 1,830
Payroll costs	2,043	1,958	1,794
Purchases of electricity	1,497	2,055	1,280
Purchases of gas	1,289	2,516	1,666
Property and other taxes	1,279	1,302	1,202
UK electricity balancing costs	2,486	4,052	3,152
Other	4,553	3,682	3,215
Other operating costs	15,208	17,549	14,139
Provision for bad and doubtful debts	179	220	167
Total operating costs from continuing operations	15,387	17,769	14,306
Operating costs from continuing operations include:
Inventory consumed	408	723	436
Research and development expenditure	£ 32	£ 23	£ 11

Other operating costs - Sched_2

Other operating costs - Schedule of payroll costs (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Analysis of income and expense [abstract]
Wages and salaries	£ 3,206	£ 2,971	£ 2,563
Social security costs	256	244	201
Defined contribution scheme costs	129	98	81
Defined benefit pension costs	96	121	185
Share-based payments	37	46	38
Severance costs (excluding pension costs)	12	3	5
Payroll costs including capitalised costs	3,736	3,483	3,073
Less: payroll costs capitalised	(1,693)	(1,525)	(1,279)
Total payroll costs from continuing operations	2,043	1,958	1,794
US other post retirement benefit costs	£ 26	£ 37	£ 39

Other operating costs - Summary

Other operating costs - Summary of number of employees (Details) - employee	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of operating segments [line items]
Number of employees, year end	31,425	29,450	29,292
Average number of employees	30,845	28,563	28,707
UK
Disclosure of operating segments [line items]
Number of employees, year end	13,956	12,572	11,960
Average number of employees	13,439	12,024	11,393
US
Disclosure of operating segments [line items]
Number of employees, year end	17,469	16,878	17,332
Average number of employees	17,406	16,539	17,314

Other operating costs - Sched_3

Other operating costs - Schedule of key management personnel (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Analysis of income and expense [abstract]
Short-term employee benefits	£ 7	£ 7	£ 7
Post-employment benefits	0	0	1
Share-based payments	5	6	5
Total key management compensation	£ 12	£ 13	£ 13

Other operating costs - Sched_4

Other operating costs - Schedule of auditors' remuneration (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Audit fees payable to the Parent Company’s auditor and their associates in respect of:
Audit of the Parent Company’s individual and consolidated financial statements	£ 2.8	£ 2.9	£ 2.7
The auditing of accounts of any associate of the Company	8.8	9	8.9
Other services supplied	7.3	7.4	7.3
Audit fees payable to the Parent Company’s auditors and their associates	18.9	19.3	18.9
All other fees:
Other assurance services	4	1.4	0.9
Other non-audit services not covered above	0	0.2	0.1
Total other services	4	1.6	1
Total auditor’s remuneration	22.9	£ 20.9	£ 19.9
Tax compliance services	0
Tax advisory services	£ 0

Exceptional items and remeasu_3

Exceptional items and remeasurements - Schedule of exceptional items and remeasurements from continuing operations (Details) - GBP (£) £ in Millions	12 Months Ended			17 Months Ended	24 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2023
Included within operating profit
Release of St William Homes LLP deferred income	£ 19,850	£ 21,659	£ 18,449
Operating profit	4,475	4,879	4,371
Included within finance income and costs
Net gains/(losses) on financial assets at fair value through profit and loss	4	(28)	(15)
Finance income and costs	(1,464)	(1,460)	(1,022)
Included within share of post-tax results of joint ventures and associates
Profit before tax	3,048	3,590	3,441
Included within tax
Tax on exceptional items and remeasurements	(831)	(876)	(1,258)
Analysis Of Exceptional Items And Remeasurements After Tax [Abstract]
Profit after tax from continuing operations	2,217	2,714	2,183
Exceptional items and remeasurements (see note 5)
Included within operating profit
Operating profit	(987)	585	558
Included within share of post-tax results of joint ventures and associates
Profit before tax	(1,036)	620	561
Included within tax
Tax on exceptional items and remeasurements	152	(241)	(589)
Analysis Of Exceptional Items And Remeasurements After Tax [Abstract]
Profit after tax from continuing operations	(884)	379	(28)
Exceptional items
Included within operating profit
Transaction, separation and integration costs	(44)	(117)	(223)		£ (340)
Cost efficiency programme	(65)	(100)	(42)	£ (142)
IFA fire	92	130	0
Changes in environmental provisions	(496)	176	0
Provision for UK electricity balancing costs	(498)	0	0
New operating model implementation costs	0	0	(24)
Environmental insurance recovery	0	0	38
Operating profit	(1,011)	935	166
Included within tax
Tax on exceptional items and remeasurements	159	(316)	(28)
Analysis Of Exceptional Items And Remeasurements After Tax [Abstract]
Profit after tax from continuing operations	(852)	619	(320)
Exceptional items | UK
Included within tax
Deferred tax expense (income) relating to tax rate changes or imposition of new taxes	0	0	(458)
Remeasurements
Included within finance income and costs
Net gains/(losses) on financial assets at fair value through profit and loss	4	(28)	(15)
Net gains on financing derivatives	11	82	74
Finance income and costs	15	54	59
Included within share of post-tax results of joint ventures and associates
Net losses on financial instruments	(64)	(19)	(56)
Included within tax
Tax on exceptional items and remeasurements	(7)	75	(103)
Analysis Of Exceptional Items And Remeasurements After Tax [Abstract]
Profit after tax from continuing operations	(32)	(240)	292
Remeasurements | Commodity contract derivatives
Included within operating profit
Operating profit	24	(350)	392
St William Homes LLP | Exceptional items
Included within operating profit
Net gain on disposal	0	0	228
Release of St William Homes LLP deferred income	0	0	189
Millennium Pipeline Company, LLC | Exceptional items
Included within operating profit
Net gain on disposal	0	335	0
The Narragansett Electric Company | Exceptional items
Included within operating profit
Transaction, separation and integration costs	(11)	(39)
Net gain on disposal	£ 0	£ 511	£ 0

Exceptional items and remeasu_4

Exceptional items and remeasurements - Narrative (Details) - GBP (£) £ in Millions						1 Months Ended	12 Months Ended			17 Months Ended	24 Months Ended
	Jan. 31, 2023	Oct. 07, 2022	May 25, 2022	Mar. 31, 2022	Mar. 15, 2022	Nov. 30, 2021	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2023
Disclosure Of Exceptional Items [Line Items]
Cash outflow for transaction and separation costs							£ 33
Cost efficiency programme, annual savings, target						£ 400
Cost efficiency programme, period						3 years
Cash outflows relating to restructuring activities, operating activities							53	£ 85
Cash inflows relating to insurance recovery							92	79
Net assets							29,892	29,562		£ 29,562	£ 29,562
Revenue							19,850	21,659	£ 18,449
Other provisions				£ 2,539			3,109	2,642	2,539	2,642	2,642
St William Homes LLP
Disclosure Of Exceptional Items [Line Items]
Proportion of ownership interest disposed					50%
Cash proceeds					£ 413
Millennium Pipeline Company, LLC
Disclosure Of Exceptional Items [Line Items]
Consideration received		£ 497
Proportion of ownership interest disposed		26.25%
US
Disclosure Of Exceptional Items [Line Items]
Revenue							10,787	£ 12,048	£ 10,646
Other environment related provision
Disclosure Of Exceptional Items [Line Items]
Real discount rate (in percent)								1.50%	0.50%
Weighted average duration of cash flows								10 years 6 months
Other provisions				1,877			£ 2,418	£ 1,891	£ 1,877	1,891	1,891
Other environment related provision | US
Disclosure Of Exceptional Items [Line Items]
Real discount rate (in percent)							1.50%	1.50%
Weighted average duration of cash flows							10 years
Other provisions							£ 2,310	£ 1,768		1,768	1,768
Other environment related provision | UK
Disclosure Of Exceptional Items [Line Items]
Real discount rate (in percent)							1%	1.50%
Other provisions							£ 108	£ 123		123	123
The Narragansett Electric Company
Disclosure Of Exceptional Items [Line Items]
Consideration received			£ 3,100
Net assets			£ 2,700
UK Gas Transmission business
Disclosure Of Exceptional Items [Line Items]
Proportion of ownership interest disposed	100%							60%
Cash proceeds	£ 4,000
Exceptional items
Disclosure Of Exceptional Items [Line Items]
Transaction, separation and integration costs							44	£ 117	223		£ 340
Cash outflow for transaction and separation costs								84	196
Cost efficiency programme							65	100	42	£ 142
Income from reimbursements under insurance policies							92	130	0
Changes in environmental provisions							(496)	176	0
New operating model implementation costs							0	0	24
Cash outflow for new operating model implementation costs and cost efficiency programme									48
Environmental insurance recovery							0	0	38
Exceptional items | St William Homes LLP
Disclosure Of Exceptional Items [Line Items]
Net gain on disposal							0	0	228
Revenue							0	0	189
Exceptional items | Millennium Pipeline Company, LLC
Disclosure Of Exceptional Items [Line Items]
Net gain on disposal							0	335	0
Proportion of ownership interest disposed		26.25%
Exceptional items | UK
Disclosure Of Exceptional Items [Line Items]
Deferred tax expense (income) relating to tax rate changes or imposition of new taxes				£ 458
Exceptional items | Other environment related provision | US
Disclosure Of Exceptional Items [Line Items]
Changes in environmental provisions								165
Exceptional items | Other environment related provision | UK
Disclosure Of Exceptional Items [Line Items]
Changes in environmental provisions								11
Exceptional items | The Narragansett Electric Company
Disclosure Of Exceptional Items [Line Items]
Transaction, separation and integration costs							11	39
Net gain on disposal							0	511	£ 0
Exceptional items | UK Gas Transmission business
Disclosure Of Exceptional Items [Line Items]
Transaction, separation and integration costs							6	38
Exceptional items | National Grid Electricity Distribution
Disclosure Of Exceptional Items [Line Items]
Transaction, separation and integration costs							£ 27	£ 40

Finance income and costs (Detai

Finance income and costs (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Finance income
Net interest income on pensions and other post-retirement benefit obligations	£ 100	£ 85	£ 0
Interest income on financial instruments:
Bank deposits and other financial assets	139	80	32
Dividends received on equities held at fair value through other comprehensive income (FVOCI)	1	1	3
Net gains/(losses) on FVTPL financial assets	4	(28)	(15)
Other income	4	0	30
Finance income	248	138	50
Interest expense on financial liabilities held at amortised cost:
Bank loans and overdrafts	(140)	(328)	(216)
Other borrowings	(1,424)	(1,330)	(961)
Interest on derivatives	(277)	(170)	(59)
Unwinding of discount on provisions	(102)	(88)	(73)
Other interest	(31)	(13)	11
Derivatives designated as hedges for hedge accounting²	13	22	45
Derivatives not designated as hedges for hedge accounting	(2)	60	29
Less: interest capitalised	251	249	152
Finance costs	(1,712)	(1,598)	(1,072)
Finance income and costs	(1,464)	(1,460)	(1,022)
Net finance costs from continuing operations	£ 271	£ (86)	£ 110
Capitalisation rate of borrowing costs eligible for capitalisation	4.70%	4.70%	3.20%
Tax relief on capitalised interest	£ 39	£ 30	£ 16
Amount of accretion on inflation linked liabilities	£ 208	£ 483	£ 241

Tax - Schedule of components of

Tax - Schedule of components of tax expense (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Current tax:
Total current tax from continuing operations	£ 366	£ 370	£ 226
Deferred tax:
Total deferred tax from continuing operations	465	506	1,032
Total tax charge from continuing operations	831	876	1,258
UK
Current tax:
Corporation tax	410	161	255
Corporate tax adjustment in respect of prior years	(36)	0	(9)
Total current tax from continuing operations	374	161	246
Deferred tax:
Deferred tax	388	255	605
Deferred tax adjustment in respect of prior years	43	13	(5)
Total deferred tax from continuing operations	431	268	600
Overseas
Current tax:
Corporation tax	82	225	6
Corporate tax adjustment in respect of prior years	(90)	(16)	(26)
Total current tax from continuing operations	(8)	209	(20)
Deferred tax:
Deferred tax	(40)	233	425
Deferred tax adjustment in respect of prior years	74	5	7
Total deferred tax from continuing operations	£ 34	£ 238	£ 432

Tax - Disclosure of tax (credit

Tax - Disclosure of tax (credited)/charged to the consolidated statement of comprehensive income and equity (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Current tax:
Share-based payments	£ (2)	£ (1)	£ 0
Deferred tax:
Investments at fair value through other comprehensive income	1	(1)	0
Cash flow hedges, cost of hedging and own credit reserve	56	(7)	(12)
Remeasurements of pension assets and post-retirement benefit obligations	(50)	(344)	493
Share-based payments	0	1	(4)
Tax charged/(credited) to other comprehensive income and equity	5	(352)	477
Total tax recognised in the statements of comprehensive income from continuing operations	7	(352)	481
Total tax relating to share-based payments recognised directly in equity from continuing operations	£ (2)	£ 0	£ (4)

Tax - Schedule of effective tax

Tax - Schedule of effective tax rate reconciliation (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure Of Income Taxes [Line Items]
Profit before tax from continuing operations	£ 3,048	£ 3,590	£ 3,441
Profit before tax from continuing operations multiplied by UK corporation tax rate of 25% (2023: 19%; 2022: 19%)	762	682	654
Adjustments in respect of prior years	(9)	2	(33)
Expenses not deductible for tax purposes	155	92	47
Non-taxable income	(43)	(75)	(49)
Adjustment in respect of foreign tax rates	(20)	147	170
Deferred tax impact of change in UK tax rate	0	66	501
Adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax	(9)	(27)	(17)
Other	(5)	(11)	(15)
Total tax charge from continuing operations	£ 831	£ 876	£ 1,258
Effective tax rate – continuing operations	27.30%	24.40%	36.60%

Tax - Schedule of tax included

Tax - Schedule of tax included within the statement of financial position (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	£ 7,181	£ 6,765
Exchange adjustments and other	(110)	255
Charged/(credited) to income statement	467	509
Charged/(credited) to other comprehensive income and equity	7	(349)
Disposals	(2)	1
Reclassification to held for sale	(24)
Deferred tax liability (asset) end of period	7,519	7,181
Impact of IAS 12 amendment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	0
Deferred tax liability (asset) end of period		0
Opening balance after adjustment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	7,181
Deferred tax liability (asset) end of period		7,181
Regulatory licenses
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	429	429
Exchange adjustments and other	0	0
Charged/(credited) to income statement	0	0
Charged/(credited) to other comprehensive income and equity	0	0
Disposals	0	0
Reclassification to held for sale	0
Deferred tax liability (asset) end of period	429	429
Regulatory licenses | Impact of IAS 12 amendment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	0
Deferred tax liability (asset) end of period		0
Regulatory licenses | Opening balance after adjustment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	429
Deferred tax liability (asset) end of period		429
Accelerated tax depreciation
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	8,213	7,710
Exchange adjustments and other	(132)	357
Charged/(credited) to income statement	720	145
Charged/(credited) to other comprehensive income and equity	0	0
Disposals	(2)	1
Reclassification to held for sale	(12)
Deferred tax liability (asset) end of period	8,816	8,213
Accelerated tax depreciation | Impact of IAS 12 amendment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	29
Deferred tax liability (asset) end of period		29
Accelerated tax depreciation | Opening balance after adjustment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	8,242
Deferred tax liability (asset) end of period		8,242
Share- based payments
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(21)	(18)
Exchange adjustments and other	0	(2)
Charged/(credited) to income statement	(5)	(2)
Charged/(credited) to other comprehensive income and equity	0	1
Disposals	0	0
Reclassification to held for sale	1
Deferred tax liability (asset) end of period	(25)	(21)
Share- based payments | Impact of IAS 12 amendment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	0
Deferred tax liability (asset) end of period		0
Share- based payments | Opening balance after adjustment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(21)
Deferred tax liability (asset) end of period		(21)
Pensions and other post- retirement benefits
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	490	775
Exchange adjustments and other	(1)	8
Charged/(credited) to income statement	26	51
Charged/(credited) to other comprehensive income and equity	(50)	(344)
Disposals	0	0
Reclassification to held for sale	(4)
Deferred tax liability (asset) end of period	461	490
Pensions and other post- retirement benefits | Impact of IAS 12 amendment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	0
Deferred tax liability (asset) end of period		0
Pensions and other post- retirement benefits | Opening balance after adjustment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	490
Deferred tax liability (asset) end of period		490
Financial instruments
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(370)	(301)
Exchange adjustments and other		8
Charged/(credited) to income statement	38	(71)
Charged/(credited) to other comprehensive income and equity	57	(6)
Disposals		0
Reclassification to held for sale	0
Deferred tax liability (asset) end of period	(275)	(370)
Financial instruments | Impact of IAS 12 amendment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	0
Deferred tax liability (asset) end of period		0
Financial instruments | Opening balance after adjustment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(370)
Deferred tax liability (asset) end of period		(370)
Other net temporary differences
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(1,560)	(1,830)
Exchange adjustments and other	23	(116)
Charged/(credited) to income statement	(312)	386
Charged/(credited) to other comprehensive income and equity	0	0
Disposals	0	0
Reclassification to held for sale	(9)
Deferred tax liability (asset) end of period	(1,887)	(1,560)
Deferred tax assets	1,887	1,560
Other net temporary differences | Impact of IAS 12 amendment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(29)
Deferred tax liability (asset) end of period		(29)
Other net temporary differences | Opening balance after adjustment
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(1,589)
Deferred tax liability (asset) end of period		(1,589)
Net operating losses
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax assets	184	47
Lease liabilities
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax assets	575	511
Environmental provisions
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax assets	646	503
Allowance for credit losses
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax assets	£ 150	£ 148

Tax - Narrative (Details)

Tax - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Income taxes paid (refund) [abstract]
Deferred tax liability	£ 7,519	£ 7,181	£ 6,765

Tax - Schedule of deferred tax

Tax - Schedule of deferred tax assets not recognised (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Capital losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax assets not recognised	£ 2,483	£ 2,367
Trading losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax assets not recognised	£ 4	£ 4

Earnings per share (EPS) (Detai

Earnings per share (EPS) (Details) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Basic EPS
Basic earnings from continuing operations	£ 2,216	£ 2,714	£ 2,182
Basic earnings from discontinued operations	74	5,083	171
Basic total earnings	£ 2,290	£ 7,797	£ 2,353
Basic EPS (continuing) (in GBP per share)	£ 0.600	£ 0.742	£ 0.606
Basic EPS (discontinuing) (in GBP per share)	0.020	1.389	0.048
Total basic earnings per share (in GBP per share)	£ 0.620	£ 2.131	£ 0.654
Weighted average number of shares – basic (in shares)	3,692	3,659	3,599
Diluted EPS
Diluted earnings from continuing operations	£ 2,216	£ 2,714	£ 2,182
Diluted earnings from discontinued operations	74	5,083	171
Diluted total earnings	£ 2,290	£ 7,797	£ 2,353
Diluted EPS (continuing) (in GBP per share)	£ 0.597	£ 0.738	£ 0.603
Diluted EPS (discontinuing) (in GBP per share)	0.020	1.383	0.047
Diluted EPS (in GBP per share)	£ 0.617	£ 2.121	£ 0.650
Weighted average number of shares – diluted (in shares)	3,709	3,676	3,616
Reconciliation of basic to diluted average number of shares
Weighted average number of shares – basic (in shares)	3,692	3,659	3,599
Effect of dilutive potential ordinary shares – employee share plans (in shares)	17	17	17
Weighted average number of shares – diluted (in shares)	3,709	3,676	3,616

Dividends - Schedule of dividen

Dividends - Schedule of dividends to shareholders (Details) - GBP (£) £ / shares in Units, £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)	£ 0.5700	£ 0.5160	£ 0.4937
Cash dividend	£ 1,718	£ 1,607	£ 922
Scrip dividend	£ 376	£ 277	£ 844
Interim dividend in respect of the current year
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)	£ 0.1940	£ 0.1784	£ 0.1721
Cash dividend	£ 393	£ 488	£ 339
Scrip dividend	£ 320	£ 163	£ 282
Final dividend in respect of the prior year
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)	£ 0.3760	£ 0.3376	£ 0.3216
Cash dividend	£ 1,325	£ 1,119	£ 583
Scrip dividend	£ 56	£ 114	£ 562

Dividends - Narrative (Details)

Dividends - Narrative (Details) £ / shares in Units, £ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£) £ / shares
Summary Of Dividends [Line Items]
Dividends declared before financial statements authorised for issue (GBP per share) | £ / shares	£ 0.3912
Dividends declared before financial statements authorised for issue | £	£ 1,455

Assets held for sale and disc_3

Assets held for sale and discontinued operations - Schedule of assets and liabilities classified as held for sale (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure Of Detailed Information About Assets Held For Sale [Line Items]
Total assets held for sale	£ 1,823	£ 1,443
Total liabilities held for sale	(1,474)	(109)
Assets and liabilities classified as held for sale
Disclosure Of Detailed Information About Assets Held For Sale [Line Items]
Total assets held for sale	1,823	1,443
Total liabilities held for sale	(1,474)	(109)
Net assets held for sale	349	1,334
Assets and liabilities classified as held for sale | UK Electricity System Operator
Disclosure Of Detailed Information About Assets Held For Sale [Line Items]
Total assets held for sale	1,134	0
Total liabilities held for sale	(1,427)	0
Net assets held for sale	(293)	0
Assets and liabilities classified as held for sale | FAA option
Disclosure Of Detailed Information About Assets Held For Sale [Line Items]
Total assets held for sale	0	0
Total liabilities held for sale	0	(109)
Net assets held for sale	0	(109)
Assets and liabilities classified as held for sale | RAA option
Disclosure Of Detailed Information About Assets Held For Sale [Line Items]
Total assets held for sale	0	0
Total liabilities held for sale	(47)	0
Net assets held for sale	(47)	0
Assets and liabilities classified as held for sale | GasT TopCo Limited
Disclosure Of Detailed Information About Assets Held For Sale [Line Items]
Total assets held for sale	689	1,443
Total liabilities held for sale	0	0
Net assets held for sale	£ 689	£ 1,443

Assets held for sale and disc_4

Assets held for sale and discontinued operations - Schedule of assets and liabilities classified as held for sale, ESO (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Disclosure Of Detailed Information About Assets Held For Sale [Line Items]
Intangible assets	£ 3,431	£ 3,604
Property, plant and equipment	68,907	64,433
Pension asset	2,407	2,645
Cash and cash equivalents	559	163	£ 204	£ 157
Financing derivatives	368	429
Total assets	98,325	92,697
Borrowings	(47,072)	(42,985)	£ (45,465)
Total liabilities	(68,433)	(63,135)
Total assets (liabilities)	29,892	£ 29,562
Assets and liabilities classified as held for sale | UK Electricity System Operator
Disclosure Of Detailed Information About Assets Held For Sale [Line Items]
Intangible assets	405
Property, plant and equipment	113
Trade and other receivables	563
Pension asset	17
Cash and cash equivalents	30
Financing derivatives	6
Total assets	1,134
Borrowings	(13)
Other liabilities	(916)
Provision for UK electricity balancing costs	(498)
Total liabilities	(1,427)
Total assets (liabilities)	£ (293)

Assets held for sale and disc_5

Assets held for sale and discontinued operations - Narrative (Details) - GBP (£) £ in Millions				12 Months Ended
	Mar. 31, 2024	Mar. 11, 2024	Jan. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of subsidiaries [line items]
Profit after tax				£ 2,291	£ 7,797	£ 2,354
Total identifiable net assets	£ 29,892			29,892	29,562
Assets and liabilities classified as held for sale
Disclosure of subsidiaries [line items]
Net assets held for sale	349			349	1,334
UK Electricity System Operator
Disclosure of subsidiaries [line items]
Profit after tax				178	182	£ (12)
UK Electricity System Operator | Assets and liabilities classified as held for sale
Disclosure of subsidiaries [line items]
Total identifiable net assets	(293)			(293)
Net assets held for sale	(293)			(293)	0
RAA option | Assets and liabilities classified as held for sale
Disclosure of subsidiaries [line items]
Net assets held for sale	£ (47)			£ (47)	0
GasT TopCo Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed		20%
Cash proceeds		£ 681
Proportion of ownership interest in associate	20%	20%	40%	20%
Gain on disposal		£ (4)
GasT TopCo Limited | Discontinued operations
Disclosure of subsidiaries [line items]
Dividends received from associates				£ 102
GasT TopCo Limited | Assets and liabilities classified as held for sale
Disclosure of subsidiaries [line items]
Net assets held for sale	£ 689			£ 689	£ 1,443
UK Gas Transmission business
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed			100%		60%
Cash proceeds			£ 4,000
Portion of consideration received consisting of shareholding in acquirer			40%
Associate at fair value			£ 1,400
Gain on disposal			4,800
UK Gas Transmission business | Disposal groups classified as held for sale
Disclosure of subsidiaries [line items]
Total identifiable net assets			£ 600
Macquarie Infrastructure and Real Assets (MIRA) and British Columbia Investment Management Corporation (BCI) | GasT TopCo Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest in associate			60%

Assets held for sale and disc_6

Assets held for sale and discontinued operations - Summary of Income Statement for discontinued operations (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of analysis of other comprehensive income by item [line items]
Revenue	£ 19,850	£ 21,659	£ 18,449
Operating profit	4,475	4,879	4,371
Finance income	248	138	50
Finance costs	(1,712)	(1,598)	(1,072)
Profit before tax	3,048	3,590	3,441
Total profit after tax from discontinued operations	74	5,083	171
Discontinued operations
Disclosure of analysis of other comprehensive income by item [line items]
Revenue	0	1,604	1,362
Other operating costs	0	(889)	(725)
Operating profit	0	715	637
Finance income	17	21	0
Finance costs	62	(363)	(230)
Profit before tax	79	373	407
Tax	(1)	(93)	(236)
Profit after tax from discontinued operations	78	280	171
(Loss)/gain on disposal	(4)	4,803	0
Total profit after tax from discontinued operations	£ 74	£ 5,083	171
Discontinued operations | UK
Disclosure of analysis of other comprehensive income by item [line items]
Deferred tax expense (income) relating to tax rate changes or imposition of new taxes			£ 145

Assets held for sale and disc_7

Assets held for sale and discontinued operations - Summary of Statement of Comprehensive Income for discontinued operations (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of analysis of other comprehensive income by item [line items]
Profit after tax from discontinued operations	£ 74	£ 5,083	£ 171
Items from discontinued operations that will never be reclassified to profit or loss:
Remeasurement (losses)/gains on pension assets and post-retirement benefit obligations	(218)	(1,362)	2,172
Tax on items that will never be reclassified to profit or loss	59	341	(496)
Total items from continuing operations that will never be reclassified to profit or loss	(196)	(1,011)	1,687
Items from discontinued operations that may be reclassified subsequently to profit or loss:
Net gains in respect of cash flow hedges	240	0	(57)
Net gains/(losses) in respect of cost of hedging	26	(16)	1
Net gains on investments in debt instruments measured at fair value through other comprehensive income	21	(25)	(11)
Tax on items that may be reclassified subsequently to profit or loss	(66)	11	15
Total items from continuing operations that may be reclassified subsequently to profit or loss	(114)	684	579
Other comprehensive income (loss) for the year	(300)	(554)	2,477
Total comprehensive income/(loss) for the year	1,991	7,243	4,831
Discontinued operations
Disclosure of analysis of other comprehensive income by item [line items]
Profit after tax from discontinued operations	74	5,083	171
Items from discontinued operations that will never be reclassified to profit or loss:
Remeasurement (losses)/gains on pension assets and post-retirement benefit obligations	0	(313)	309
Net losses on financial liability designated at fair value through profit and loss attributable to changes in own credit risk	0	0	(1)
Tax on items that will never be reclassified to profit or loss	0	78	(94)
Total items from continuing operations that will never be reclassified to profit or loss	0	(235)	214
Items from discontinued operations that may be reclassified subsequently to profit or loss:
Net gains in respect of cash flow hedges	0	6	1
Net gains/(losses) in respect of cost of hedging	0	4	(4)
Net gains on investments in debt instruments measured at fair value through other comprehensive income	13	0	0
Tax on items that may be reclassified subsequently to profit or loss	(3)	(2)	0
Total items from continuing operations that may be reclassified subsequently to profit or loss	10	8	(3)
Other comprehensive income (loss) for the year	10	(227)	211
Total comprehensive income/(loss) for the year	£ 84	£ 4,856	£ 382

Goodwill - Schedule of changes

Goodwill - Schedule of changes in intangible assets and goodwill (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Reconciliation of changes in goodwill [abstract]
Goodwill at beginning of period	£ 9,847	£ 9,532
Exchange adjustments	(118)	315
Goodwill at end of period	£ 9,729	£ 9,847

Goodwill - Narrative (Details)

Goodwill - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
US Regulated
Disclosure of reconciliation of changes in goodwill [line items]
Growth rate used to extrapolate cash flow projections	2.40%	2.50%
UK Electricity Distribution
Disclosure of reconciliation of changes in goodwill [line items]
Growth rate used to extrapolate cash flow projections	2.30%	2.60%
UK Electricity Distribution Group
Disclosure of reconciliation of changes in goodwill [line items]
Discount rate applied to cash flow projections	5%	5.60%
UK Electricity Distribution DNO
Disclosure of reconciliation of changes in goodwill [line items]
Discount rate applied to cash flow projections	5%	5.60%
New York
Disclosure of reconciliation of changes in goodwill [line items]
Discount rate applied to cash flow projections	6.20%	6.40%
New England
Disclosure of reconciliation of changes in goodwill [line items]
Discount rate applied to cash flow projections	6.10%	6.60%
National Grid Ventures – US
Disclosure of reconciliation of changes in goodwill [line items]
Discount rate applied to cash flow projections	7.20%	8.60%
Accumulated impairment | Goodwill
Disclosure of reconciliation of changes in goodwill [line items]
Intangible assets and goodwill	£ 0	£ 0

Goodwill - Schedule of allocati

Goodwill - Schedule of allocation of goodwill by operations (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill	£ 9,729	£ 9,847	£ 9,532
Other intangible assets	3,431	3,604
Regulatory licenses
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Other intangible assets	1,714	1,714
National Grid Ventures – US
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill	188	163
New England
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill	1,541	1,609
New York
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill	3,279	3,354
UK Electricity Distribution
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill	4,721	4,721
West Midlands | Regulatory licenses
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Other intangible assets	518	518
East Midlands | Regulatory licenses
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Other intangible assets	519	519
South Wales | Regulatory licenses
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Other intangible assets	257	257
South West | Regulatory licenses
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Other intangible assets	£ 420	£ 420

Other intangible assets - Sched

Other intangible assets - Schedule of analysis of other intangible assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	£ 3,604
Intangible assets other than goodwill, ending balance	3,431	£ 3,604
Regulatory licenses
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	1,714
Intangible assets other than goodwill, ending balance	1,714	1,714
Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	1,339
Intangible assets other than goodwill, ending balance	1,335	1,339
Assets in the course of construction
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	551
Intangible assets other than goodwill, ending balance	382	551
Gas Business Enablement system
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	370
Intangible assets other than goodwill, ending balance	320	370
Intangible assets other than goodwill, in service amount	£ 320	369
Amortised period (in years)	10 years
UK General Ledger system
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	£ 87
Intangible assets other than goodwill, ending balance	£ 81	87
Amortised period (in years)	10 years
Gross carrying amount
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	£ 5,341	4,659
Exchange adjustments	(51)	111
Additions	481	578
Disposals	(23)	(17)
Reclassifications	162	10
Reclassification to held for sale (note 10)	(711)
Intangible assets other than goodwill, ending balance	5,199	5,341
Gross carrying amount | Regulatory licenses
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	1,714	1,714
Exchange adjustments	0	0
Additions	0	0
Disposals	0	0
Reclassifications	0	0
Reclassification to held for sale (note 10)	0
Intangible assets other than goodwill, ending balance	1,714	1,714
Gross carrying amount | Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	3,066	2,075
Exchange adjustments	(45)	79
Additions	17	34
Disposals	(23)	(17)
Reclassifications	598	895
Reclassification to held for sale (note 10)	(520)
Intangible assets other than goodwill, ending balance	3,093	3,066
Gross carrying amount | Assets in the course of construction
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	561	870
Exchange adjustments	(6)	32
Additions	464	544
Disposals	0	0
Reclassifications	(436)	(885)
Reclassification to held for sale (note 10)	(191)
Intangible assets other than goodwill, ending balance	392	561
Accumulated amortisation
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	(1,737)	(1,387)
Exchange adjustments	23	(51)
Amortisation charge for the year	(301)	(291)
Disposals	23	15
Reclassifications	(161)	(23)
Reclassification to held for sale (note 10)	385
Intangible assets other than goodwill, ending balance	(1,768)	(1,737)
Accumulated amortisation | Regulatory licenses
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	0	0
Exchange adjustments	0	0
Amortisation charge for the year	0	0
Disposals	0	0
Reclassifications	0	0
Reclassification to held for sale (note 10)	0
Intangible assets other than goodwill, ending balance	0	0
Accumulated amortisation | Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	(1,727)	(1,377)
Exchange adjustments	23	(51)
Amortisation charge for the year	(301)	(291)
Disposals	23	15
Reclassifications	(161)	(23)
Reclassification to held for sale (note 10)	385
Intangible assets other than goodwill, ending balance	(1,758)	(1,727)
Accumulated amortisation | Assets in the course of construction
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	(10)	(10)
Exchange adjustments	0	0
Amortisation charge for the year	0	0
Disposals	0	0
Reclassifications	0	0
Reclassification to held for sale (note 10)	0
Intangible assets other than goodwill, ending balance	£ (10)	£ (10)

Other intangible assets - Sch_2

Other intangible assets - Schedule of asset useful economic lives (Details) - Software	12 Months Ended
	Mar. 31, 2024
Bottom of range
Disclosure of detailed information about intangible assets [line items]
Amortised period (in years)	3 years
Top of range
Disclosure of detailed information about intangible assets [line items]
Amortised period (in years)	10 years

Property, plant and equipment -

Property, plant and equipment - Disclosure of analysis of property, plant and equipment (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	£ 64,433
Property, plant and equipment, ending balance	68,907	£ 64,433
Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	81,813	73,340
Exchange adjustments	(976)	2,405
Additions	7,167	6,853
Disposals	(465)	(654)
Adjustment for change in discount rate on decommissioning provisions	29	(48)
Reclassifications	(169)	(83)
Reclassification to held for sale	(266)
Property, plant and equipment, ending balance	87,133	81,813
Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(17,380)	(15,808)
Exchange adjustments	199	(506)
Depreciation charge for the year	(1,804)	(1,765)
Disposals	438	592
Reclassifications	166	107
Reclassification to held for sale	155
Property, plant and equipment, ending balance	(18,226)	(17,380)
Land and buildings
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	3,272
Property, plant and equipment, ending balance	3,452	3,272
Land and buildings | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	4,066	3,659
Exchange adjustments	(49)	126
Additions	59	158
Disposals	(55)	(163)
Adjustment for change in discount rate on decommissioning provisions	0	0
Reclassifications	277	286
Reclassification to held for sale	(88)
Property, plant and equipment, ending balance	4,210	4,066
Land and buildings | Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(794)	(773)
Exchange adjustments	10	(30)
Depreciation charge for the year	(80)	(122)
Disposals	50	127
Reclassifications	(3)	4
Reclassification to held for sale	59
Property, plant and equipment, ending balance	(758)	(794)
Plant and machinery
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	53,839
Property, plant and equipment, ending balance	57,821	53,839
Plant and machinery | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	69,765	63,022
Exchange adjustments	(841)	2,073
Additions	1,157	1,196
Disposals	(271)	(331)
Adjustment for change in discount rate on decommissioning provisions	29	(36)
Reclassifications	4,725	3,841
Reclassification to held for sale	(13)
Property, plant and equipment, ending balance	74,551	69,765
Plant and machinery | Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(15,926)	(14,441)
Exchange adjustments	177	(444)
Depreciation charge for the year	(1,515)	(1,459)
Disposals	252	311
Reclassifications	281	107
Reclassification to held for sale	1
Property, plant and equipment, ending balance	(16,730)	(15,926)
Assets in the course of construction
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	6,705
Property, plant and equipment, ending balance	6,955	6,705
Assets in the course of construction | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	6,760	5,587
Exchange adjustments	(67)	156
Additions	5,754	5,345
Disposals	(5)	(4)
Adjustment for change in discount rate on decommissioning provisions	0	(12)
Reclassifications	(5,389)	(4,312)
Reclassification to held for sale	(31)
Property, plant and equipment, ending balance	7,022	6,760
Assets in the course of construction | Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(55)	(60)
Exchange adjustments	0	0
Depreciation charge for the year	(20)	(1)
Disposals	2	2
Reclassifications	0	4
Reclassification to held for sale	6
Property, plant and equipment, ending balance	(67)	(55)
Motor vehicles and office equipment
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	617
Property, plant and equipment, ending balance	679	617
Motor vehicles and office equipment | Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	1,222	1,072
Exchange adjustments	(19)	50
Additions	197	154
Disposals	(134)	(156)
Adjustment for change in discount rate on decommissioning provisions	0	0
Reclassifications	218	102
Reclassification to held for sale	(134)
Property, plant and equipment, ending balance	1,350	1,222
Motor vehicles and office equipment | Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(605)	(534)
Exchange adjustments	12	(32)
Depreciation charge for the year	(189)	(183)
Disposals	134	152
Reclassifications	(112)	(8)
Reclassification to held for sale	89
Property, plant and equipment, ending balance	£ (671)	£ (605)

Property, plant and equipment_2

Property, plant and equipment - Disclosure of useful economic lives of property, plant and equipment (Details)	12 Months Ended
	Mar. 31, 2024
Weighted average | Freehold and leasehold buildings
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	38 years
Weighted average | Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	32 years
Weighted average | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	46 years
Weighted average | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	10 years
Weighted average | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	31 years
Weighted average | Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	53 years
Weighted average | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	18 years
Weighted average | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	24 years
Weighted average | Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	3 years
UK | Bottom of range | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	14 years
UK | Bottom of range | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	5 years
UK | Bottom of range | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	5 years
UK | Top of range | Freehold and leasehold buildings
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	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, property, plant and equipment	100 years
UK | Top of range | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	99 years
UK | Top of range | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	70 years
UK | Top of range | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	20 years
UK | Top of range | Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	50 years
US | Bottom of range | Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	10 years
US | Bottom of range | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	5 years
US | Bottom of range | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	10 years
US | Bottom of range | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	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, property, plant and equipment	25 years
US | Bottom of range | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	20 years
US | Bottom of range | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	14 years
US | Top of range | Freehold and leasehold buildings
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	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, property, plant and equipment	85 years
US | Top of range | Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	85 years
US | Top of range | Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	93 years
US | Top of range | Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	37 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, property, plant and equipment	95 years
US | Top of range | Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	60 years
US | Top of range | Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	45 years
US | Top of range | Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	26 years

Property, plant and equipment_3

Property, plant and equipment - Narrative (Details)	12 Months Ended
	Mar. 31, 2024
Gas distribution | Weighted average | US
Disclosure of detailed information about property, plant and equipment [line items]
Useful economic life, property, plant and equipment	53 years

Property, plant and equipment_4

Property, plant and equipment - Disclosure of sensitivity of gas assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
New York
Disclosure of operating segments [line items]
UELs limited to 2050, impact on depreciation expense	£ 208	£ 185
UELs limited to 2060, impact on depreciation expense	100	90
UELs limited to 2070, impact on depreciation expense	46	42
New England
Disclosure of operating segments [line items]
UELs limited to 2050, impact on depreciation expense	66	54
UELs limited to 2060, impact on depreciation expense	26	21
UELs limited to 2070, impact on depreciation expense	£ 6	£ 3

Property, plant and equipment_5

Property, plant and equipment - Disclosure of movements of right-of-use assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets, beginning balance	£ 671	£ 505
Exchange adjustments	(12)	24
Additions	200	286
Reclassifications	0
Reclassification to held for sale	(13)
Disposals	(3)	(14)
Depreciation charge for the year	(115)	(130)
Right-of-use assets, ending balance	728	671
Land and buildings
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets, beginning balance	281	225
Exchange adjustments	(5)	10
Additions	52	101
Reclassifications	0
Reclassification to held for sale	(12)
Disposals	(1)	(13)
Depreciation charge for the year	(22)	(42)
Right-of-use assets, ending balance	293	281
Plant and machinery
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets, beginning balance	150	70
Exchange adjustments	(2)	1
Additions	2	97
Reclassifications	(5)
Reclassification to held for sale	0
Disposals	0	0
Depreciation charge for the year	(17)	(18)
Right-of-use assets, ending balance	128	150
Assets in the course of construction
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets, beginning balance	0	0
Exchange adjustments	0	0
Additions	0	0
Reclassifications	0
Reclassification to held for sale	0
Disposals	0	0
Depreciation charge for the year	0	0
Right-of-use assets, ending balance	0	0
Motor vehicles and office equipment
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets, beginning balance	240	210
Exchange adjustments	(5)	13
Additions	146	88
Reclassifications	5
Reclassification to held for sale	(1)
Disposals	(2)	(1)
Depreciation charge for the year	(76)	(70)
Right-of-use assets, ending balance	£ 307	£ 240

Property, plant and equipment_6

Property, plant and equipment - Disclosure of information in relation to right-of-use assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Property, plant and equipment [abstract]
Interest expense on lease liabilities	£ (69)	£ (24)
Lease income	384	409
Expense relating to short-term and low-value leases	(20)	(19)
Variable lease payments included in lease income	£ 360	£ 394

Other non-current assets (Detai

Other non-current assets (Details) - GBP (£) £ in Millions		Mar. 31, 2024	Mar. 31, 2023
Disclosure Of Other Non-Current Assets [Line Items]
Other receivables		£ 458	£ 496
Prepayments		390	124
Other non-current assets	[1]	848	620
Current prepayments		£ (385)	(389)
Increase (decrease) due to voluntary changes in accounting policy
Disclosure Of Other Non-Current Assets [Line Items]
Prepayments			53
Current prepayments			£ 53
[1] In the year, we have revised our policy in relation to the classification of capital expenditure prepayments between current and non-current in order to align these to the operating cycles of the underlying assets to which they relate. Accordingly, comparative amounts have been re-presented to reflect this change (see notes 14 and 19) .

Financial and other investmen_3

Financial and other investments - Narrative (Details)	12 Months Ended
	Mar. 31, 2024 category
Disclosure of financial assets [abstract]
Number of different categories of financial and other investments	3

Financial and other investmen_4

Financial and other investments - Schedule of financial assets (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Non-current
FVOCI debt and other investments	£ 397	£ 407
FVTPL investments	483	452
Other non-current financial assets	880	859	£ 830
Current
FVTPL investments	3,084	1,764
Financial assets at amortised cost	615	841
Other current financial assets	3,699	2,605	£ 3,145	£ 2,342
Other financial assets	4,579	3,464
Investments in short-term money market funds
Current
Other financial assets	2,668	1,449
Investments held by National Grid Partners
Current
Other financial assets	375	346
Investments in Sunrun
Current
Other financial assets	108	106
Collateral
Current
Other financial assets	496	764
Insurance company fund investments
Current
Short term investments, restricted	466	734
Specific project
Current
Short term investments, restricted	24	25
Letter of credit
Current
Short term investments, restricted	6	5
Insurance company and non-qualified plan investments
Current
Other financial assets	578	490
Cash surrender value of life insurance policies
Current
Other financial assets	235	232
Other investments
Current
Other financial assets	£ 119	£ 77

Investments in joint ventures_3

Investments in joint ventures and associates - Disclosure of share of net assets, joint ventures and associates (Details) - GBP (£) £ in Millions		12 Months Ended
	Oct. 07, 2022	Mar. 31, 2024	Mar. 31, 2023
Disclosure of joint ventures [line items]
Share of net assets, beginning balance		£ 1,300	£ 1,238
Exchange adjustments		(31)	72
Additions		332	197
Share of post-tax results for the year		37	171
Share of other comprehensive income of associates, net of tax		0	1
Dividends received		(167)	(182)
Disposals		(1)	(167)
Other movements		(50)	(30)
Share of net assets, ending balance		1,420	1,300
Joint ventures
Disclosure of joint ventures [line items]
Share of net assets, beginning balance		1,146	961
Exchange adjustments		(28)	52
Additions		319	157
Share of post-tax results for the year		28	162
Share of other comprehensive income of associates, net of tax		0	0
Dividends received		(152)	(152)
Disposals		0	0
Other movements		(51)	(34)
Share of net assets, ending balance		1,262	1,146
Associates
Disclosure of joint ventures [line items]
Share of net assets, beginning balance		154	277
Exchange adjustments		(3)	20
Additions		13	40
Share of post-tax results for the year		9	9
Share of other comprehensive income of associates, net of tax		0	1
Dividends received		(15)	(30)
Disposals		(1)	(167)
Other movements		1	4
Share of net assets, ending balance		£ 158	£ 154
Millennium Pipeline Company, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest disposed	26.25%

Investments in joint ventures_4

Investments in joint ventures and associates - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Joint Ventures and Associates
Disclosure of associates [line items]
Capital commitments	£ 1,286	£ 412

Investments in joint ventures_5

Investments in joint ventures and associates - Disclosure of material interest in joint ventures and associates (Details) - lease	12 Months Ended
	Mar. 31, 2024	Feb. 25, 2022
BritNed Development Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
Nemo Link Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
Emerald Energy Venture LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	51%
Community Offshore Wind LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	27.27%
Community Offshore Wind LLC | Joint ventures
Disclosure of joint ventures [line items]
Number of leases won		6

Investments in joint ventures_6

Investments in joint ventures and associates - Disclosure of detailed information about joint ventures and associates (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Statement of financial position
Non-current assets	£ 87,946	£ 83,584	£ 76,897
Cash and cash equivalents	559	163	204	£ 157
Non-current liabilities	(57,044)	(54,005)
Current liabilities	(11,389)	(9,130)
Total assets (liabilities)	29,892	29,562
Income statement
Revenue	19,850	21,659	18,449
Operating profit	4,475	4,879	4,371
Profit before tax	3,048	3,590	3,441
Tax	(831)	(876)	(1,258)
Profit after tax from continuing operations	2,217	2,714	2,183
Group’s share of profit/(loss)	37	171	£ 92
BritNed Development Limited
Statement of financial position
Non-current assets	376	397
Cash and cash equivalents	69	208
All other current assets	36	29
Non-current liabilities	(57)	(55)
Non-current financial liabilities	(31)	(31)
Current liabilities	(39)	(34)
Current financial liabilities	0	0
Total assets (liabilities)	354	514
Group’s ownership interest in joint venture/associate	177	257
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	177	257
Income statement
Revenue	158	358
Depreciation and amortisation	(16)	(16)
Other (costs)/income	(25)	22
Operating profit	117	364
Net interest expense	(2)	(2)
Profit before tax	115	362
Tax	(31)	(82)
Profit after tax from continuing operations	84	280
Group’s share of profit/(loss)	42	140
Group adjustment: tax credit	0	0
Group’s share of post-tax results for the year	42	140
Nemo Link Limited
Statement of financial position
Non-current assets	478	514
Cash and cash equivalents	46	77
All other current assets	6	8
Non-current liabilities	(3)	(3)
Non-current financial liabilities	(32)	(32)
Current liabilities	(55)	(131)
Current financial liabilities	0	0
Total assets (liabilities)	440	433
Group’s ownership interest in joint venture/associate	220	217
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	220	217
Income statement
Revenue	109	88
Depreciation and amortisation	(23)	(23)
Other (costs)/income	(15)	(1)
Operating profit	71	64
Net interest expense	0	(7)
Profit before tax	71	57
Tax	(17)	(11)
Profit after tax from continuing operations	54	46
Group’s share of profit/(loss)	27	23
Group adjustment: tax credit	0	0
Group’s share of post-tax results for the year	27	23
Emerald Energy Venture LLC
Statement of financial position
Non-current assets	2,171	1,598
Cash and cash equivalents	206	169
All other current assets	16	14
Non-current liabilities	(249)	(244)
Non-current financial liabilities	(643)	(398)
Current liabilities	(217)	(131)
Current financial liabilities	(10)	(95)
Total assets (liabilities)	1,274	913
Group’s ownership interest in joint venture/associate	650	466
Group adjustment: elimination of profits on sales to joint venture	(123)	(85)
Carrying amount of the Group’s investment	527	381
Income statement
Revenue	87	75
Depreciation and amortisation	(38)	(29)
Other (costs)/income	(152)	(46)
Operating profit	(103)	0
Net interest expense	(9)	(6)
Profit before tax	(112)	(6)
Tax	0	0
Profit after tax from continuing operations	(112)	(6)
Group’s share of profit/(loss)	(57)	(3)
Group adjustment: tax credit	15	1
Group’s share of post-tax results for the year	(42)	(2)
Community Offshore Wind LLC
Statement of financial position
Non-current assets	1,005	925
Cash and cash equivalents	40	19
All other current assets	42	0
Non-current liabilities	(20)	(19)
Non-current financial liabilities	0	0
Current liabilities	(1)	(3)
Current financial liabilities	0	0
Total assets (liabilities)	1,066	922
Group’s ownership interest in joint venture/associate	291	251
Group adjustment: elimination of profits on sales to joint venture	0	0
Carrying amount of the Group’s investment	291	251
Income statement
Revenue	0	0
Depreciation and amortisation	0	0
Other (costs)/income	0	1
Operating profit	0	1
Net interest expense	0	0
Profit before tax	0	1
Tax	0	0
Profit after tax from continuing operations	0	1
Group’s share of profit/(loss)	0	0
Group adjustment: tax credit	0	0
Group’s share of post-tax results for the year	£ 0	£ 0

Derivative financial instrume_3

Derivative financial instruments - Schedule of fair values of derivatives by category (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 368	£ 429
Derivative liabilities	(1,244)	(1,293)
Total	(876)	(864)
Current
Disclosure of detailed information about financial instruments [line items]
Derivative assets	44	153
Derivative liabilities	(335)	(222)
Total	(291)	(69)
Non-current
Disclosure of detailed information about financial instruments [line items]
Derivative assets	324	276
Derivative liabilities	(909)	(1,071)
Total	(585)	(795)
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	333	363
Derivative liabilities	(1,126)	(1,119)
Total	(793)	(756)
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	35	66
Derivative liabilities	(118)	(174)
Total	£ (83)	£ (108)

Derivative financial instrume_4

Derivative financial instruments - Schedule of fair values of financing derivatives by type (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 368	£ 429
Derivative liabilities	(1,244)	(1,293)
Total	(876)	(864)
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	333	363
Derivative liabilities	(1,126)	(1,119)
Total	(793)	(756)
Interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	43	49
Derivative liabilities	(110)	(98)
Total	(67)	(49)
Cross-currency interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	234	192
Derivative liabilities	(844)	(888)
Total	(610)	(696)
Foreign exchange forward contracts
Disclosure of detailed information about financial instruments [line items]
Derivative assets	16	100
Derivative liabilities	(68)	(11)
Total	(52)	89
Foreign exchange forward contracts | Capital expenditure
Disclosure of detailed information about financial instruments [line items]
Total	(36)	(4)
Inflation-linked swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	40	22
Derivative liabilities	(104)	(122)
Total	£ (64)	£ (100)

Derivative financial instrume_5

Derivative financial instruments - Schedule of maturity profile of financing derivatives (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 368	£ 429
Derivative liabilities	(1,244)	(1,293)
Total	(876)	(864)
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	333	363
Derivative liabilities	(1,126)	(1,119)
Total	(793)	(756)
Financing derivatives | Less than 1 year
Disclosure of detailed information about financial instruments [line items]
Derivative assets	18	100
Derivative liabilities	(249)	(93)
Total	(231)	7
Financing derivatives | Over 12 months past due
Disclosure of detailed information about financial instruments [line items]
Derivative assets	315	263
Derivative liabilities	(877)	(1,026)
Total	(562)	(763)
Financing derivatives | In 1 to 2 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	6	13
Derivative liabilities	(80)	(100)
Total	(74)	(87)
Financing derivatives | In 2 to 3 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	31	15
Derivative liabilities	(44)	(96)
Total	(13)	(81)
Financing derivatives | In 3 to 4 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	32	32
Derivative liabilities	(74)	(11)
Total	(42)	21
Financing derivatives | In 4 to 5 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	49	14
Derivative liabilities	(83)	(107)
Total	(34)	(93)
Financing derivatives | More than 5 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	197	189
Derivative liabilities	(596)	(712)
Total	£ (399)	£ (523)

Derivative financial instrume_6

Derivative financial instruments - Schedule of notional contract amounts of financing derivatives by type (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative notional amount	£ (28,642)	£ (24,402)
Interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative notional amount	(2,175)	(1,727)
Cross-currency interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative notional amount	(15,602)	(15,025)
Foreign exchange forward contracts
Disclosure of detailed information about financial instruments [line items]
Derivative notional amount	(7,675)	(5,263)
Inflation-linked swaps
Disclosure of detailed information about financial instruments [line items]
Derivative notional amount	£ (3,190)	£ (2,387)

Derivative financial instrume_7

Derivative financial instruments - Schedule of fair values of commodity contract derivatives by type (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 368	£ 429
Derivative liabilities	(1,244)	(1,293)
Total	(876)	(864)
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	35	66
Derivative liabilities	(118)	(174)
Total	(83)	(108)
Forward purchases of gas
Disclosure of detailed information about financial instruments [line items]
Derivative assets	0	2
Derivative liabilities	(3)	(6)
Total	(3)	(4)
Electricity capacity
Disclosure of detailed information about financial instruments [line items]
Derivative assets	0	1
Derivative liabilities	0	0
Total	0	1
Electricity swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	33	53
Derivative liabilities	(82)	(92)
Total	(49)	(39)
Electricity options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	0	0
Derivative liabilities	(1)	(3)
Total	(1)	(3)
Gas swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	2	9
Derivative liabilities	(22)	(42)
Total	(20)	(33)
Gas options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	0	1
Derivative liabilities	(10)	(31)
Total	£ (10)	£ (30)

Derivative financial instrume_8

Derivative financial instruments - Schedule of maturity profile of commodity contract derivatives (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 368	£ 429
Derivative liabilities	(1,244)	(1,293)
Total	(876)	(864)
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	35	66
Derivative liabilities	(118)	(174)
Total	(83)	(108)
Commodity contract derivatives | Less than 1 year
Disclosure of detailed information about financial instruments [line items]
Derivative assets	26	53
Derivative liabilities	(86)	(129)
Total	(60)	(76)
Commodity contract derivatives | Over 12 months past due
Disclosure of detailed information about financial instruments [line items]
Derivative assets	9	13
Derivative liabilities	(32)	(45)
Total	(23)	(32)
Commodity contract derivatives | In 1 to 2 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	3	11
Derivative liabilities	(28)	(29)
Total	(25)	(18)
Commodity contract derivatives | In 2 to 3 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	5	2
Derivative liabilities	(4)	(15)
Total	1	(13)
Commodity contract derivatives | In 3 to 4 years
Disclosure of detailed information about financial instruments [line items]
Derivative assets	1	0
Derivative liabilities	0	(1)
Total	£ 1	£ (1)

Derivative financial instrume_9

Derivative financial instruments - Schedule of notional quantities of commodity contract derivatives by type (Details) £ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£) GWh MMBTU	Mar. 31, 2023 GBP (£) MMBTU GWh
Forward purchases of gas
Disclosure of detailed information about financial instruments [line items]
Derivative non-monetary notional amount	38,000,000	22
Derivative term	1 year	1 year
Derivative contractual amount | £	£ 14	£ 24
Electricity swaps
Disclosure of detailed information about financial instruments [line items]
Derivative non-monetary notional amount | GWh	14,128,000,000	14,076
Gas swaps
Disclosure of detailed information about financial instruments [line items]
Derivative non-monetary notional amount	44,000,000	50
Gas options
Disclosure of detailed information about financial instruments [line items]
Derivative non-monetary notional amount	78,000,000	57

Inventories and current intan_3

Inventories and current intangible assets - Schedule of inventories and current intangible assets (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Subclassifications of assets, liabilities and equities [abstract]
Fuel stocks	£ 188	£ 280
Raw materials and consumables	542	460
Current intangible assets – emission allowances	98	136
Inventories and current intangible assets	£ 828	£ 876

Inventories and current intan_4

Inventories and current intangible assets - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Subclassifications of assets, liabilities and equities [abstract]
Inventory valuation reserve	£ 4	£ 6

Trade and other receivables - S

Trade and other receivables - Schedule of trade and other receivables (Details) - GBP (£) £ in Millions		Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure Of Trade And Other Receivables [Line Items]
Accrued income		£ 885	£ 1,126
Trade receivables		4,332	3,052
Trade receivables and accrued income, net		2,827	3,149
Prepayments		385	389
Contract assets		76	49
Other receivables		127	243
Trade and other receivables	[1]	3,415	3,830
Non-current prepayments		390	124
Gross carrying amount
Disclosure Of Trade And Other Receivables [Line Items]
Trade receivables		2,501	2,583
Accrued income		885	1,126
Gross carrying amount | Trade receivables
Disclosure Of Trade And Other Receivables [Line Items]
Trade receivables		2,501	2,583
Accumulated impairment
Disclosure Of Trade And Other Receivables [Line Items]
Trade receivables		(559)	(560)
Accumulated impairment | Trade receivables
Disclosure Of Trade And Other Receivables [Line Items]
Trade receivables		£ (559)	(560)	£ (741)
Increase (decrease) due to voluntary changes in accounting policy
Disclosure Of Trade And Other Receivables [Line Items]
Prepayments			(53)
Non-current prepayments			£ 53
[1] In the year, we have revised our policy in relation to the classification of capital expenditure prepayments between current and non-current in order to align these to the operating cycles of the underlying assets to which they relate. Accordingly, comparative amounts have been re-presented to reflect this change (see notes 14 and 19) .

Trade and other receivables -_2

Trade and other receivables - Schedule of reconciliation of changes in allowance account for credit losses (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Provision for credit losses of financial assets, beginning balance	£ (3,052)
Provision for credit losses of financial assets, ending balance	(4,332)	£ (3,052)
Trade receivables | Accumulated impairment
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Provision for credit losses of financial assets, beginning balance	560	741
Exchange adjustments	(12)	51
Charge for the year, net of recoveries	179	220
Uncollectible amounts written off	(163)	(452)
Reclassification to held for sale (note 10)	(5)	0
Provision for credit losses of financial assets, ending balance	£ 559	£ 560

Trade and other receivables -_3

Trade and other receivables - Schedule of receivables by geographical area (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of financial assets [line items]
Trade receivables	£ 4,332	£ 3,052
Accrued income	885	1,126
Trade receivables and accrued income, net	2,827	3,149
UK
Disclosure of financial assets [line items]
Trade receivables and accrued income, net	496	862
US
Disclosure of financial assets [line items]
Trade receivables and accrued income, net	2,331	2,287
Gross carrying amount
Disclosure of financial assets [line items]
Accrued income	885	1,126
Gross carrying amount | UK
Disclosure of financial assets [line items]
Accrued income	337	650
Gross carrying amount | US
Disclosure of financial assets [line items]
Accrued income	548	476
Trade receivables | Gross carrying amount
Disclosure of financial assets [line items]
Trade receivables	2,501	2,583
Trade receivables | Gross carrying amount | UK
Disclosure of financial assets [line items]
Trade receivables	162	223
Trade receivables | Gross carrying amount | US
Disclosure of financial assets [line items]
Trade receivables	2,339	2,360
Trade receivables | Accumulated impairment
Disclosure of financial assets [line items]
Trade receivables	(559)	(560)	£ (741)
Trade receivables | Accumulated impairment | UK
Disclosure of financial assets [line items]
Trade receivables	(3)	(11)
Trade receivables | Accumulated impairment | US
Disclosure of financial assets [line items]
Trade receivables	£ (556)	£ (549)

Trade and other receivables - N

Trade and other receivables - Narrative (Details) £ in Millions, $ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£)	Mar. 31, 2023 GBP (£)	Mar. 31, 2023 USD ($)	Mar. 31, 2022 GBP (£)
Disclosure of financial assets [line items]
Trade receivables	£ 4,332	£ 3,052
Provision for impairment of receivables, period	3 years
Trade receivables | Accumulated impairment
Disclosure of financial assets [line items]
Trade receivables	£ (559)	(560)		£ (741)
Uncollectible amounts written off	163	452
Impairment loss (reversal of impairment loss) recognised in profit or loss, trade receivables	(179)	(220)
Arrears Management Program | Trade receivables
Disclosure of financial assets [line items]
Government funding programmes, amount received		44	$ 51
Arrears Management Program | Trade receivables | Accumulated impairment
Disclosure of financial assets [line items]
Uncollectible amounts written off		270	$ 333
Before exceptional items and remeasurements | Trade receivables | Accumulated impairment
Disclosure of financial assets [line items]
Impairment loss (reversal of impairment loss) recognised in profit or loss, trade receivables	176	215
Retail customer receivables
Disclosure of financial assets [line items]
Trade receivables	£ 2,437	£ 2,325

Trade and other receivables -_4

Trade and other receivables - Schedule of average expected loss rates and balances (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of financial assets [line items]
Trade receivables	£ 4,332	£ 3,052
Accrued income
Disclosure of financial assets [line items]
Expected credit loss rate	3%	3%
Trade receivables	£ 533	£ 462
Retail customer receivables
Disclosure of financial assets [line items]
Trade receivables	£ 2,437	£ 2,325
0 – 30 days past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	3%	3%
Trade receivables	£ 822	£ 838
30 – 60 days past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	14%	13%
Trade receivables	£ 219	£ 235
60 – 90 days past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	21%	23%
Trade receivables	£ 125	£ 139
3 – 6 months past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	27%	32%
Trade receivables	£ 173	£ 189
6 – 12 months past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	34%	43%
Trade receivables	£ 191	£ 178
Over 12 months past due | Retail customer receivables
Disclosure of financial assets [line items]
Expected credit loss rate	73%	88%
Trade receivables	£ 374	£ 284

Cash and cash equivalents - Nar

Cash and cash equivalents - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Cash and cash equivalents [abstract]
Restricted cash and cash equivalents	£ 11	£ 37

Cash and cash equivalents - Sch

Cash and cash equivalents - Schedule of cash and cash equivalents (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Cash and cash equivalents [abstract]
Cash at bank	£ 259	£ 163
Short-term deposits	300	0
Cash and cash equivalents	£ 559	£ 163	£ 204	£ 157

Borrowings - Schedule of curren

Borrowings - Schedule of current and non-current borrowings (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Current
Bank loans	£ 460	£ 381
Bonds	2,841	1,638
Commercial paper	1,444	840
Lease liabilities	114	96
Current portion of non-current borrowings	4,859	2,955
Non-current
Bank loans	2,434	2,557
Bonds	39,114	36,855
Lease liabilities	665	618
Non-current portion of non-current borrowings	42,213	40,030
Total borrowings	£ 47,072	£ 42,985	£ 45,465

Borrowings - Schedule of borrow

Borrowings - Schedule of borrowings repayment schedule (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 47,072	£ 42,985	£ 45,465
Less than 1 year
Disclosure of detailed information about borrowings [line items]
Borrowings	4,859	2,955
In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Borrowings	2,706	2,799
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Borrowings	3,134	2,689
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Borrowings	2,948	3,129
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	4,375	2,505
More than 5 years | By instalments
Disclosure of detailed information about borrowings [line items]
Borrowings	736	922
More than 5 years | Other than by instalments
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 28,314	£ 27,986

Borrowings - Narrative (Details

Borrowings - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of fair value measurement of liabilities [line items]
Borrowings	£ 47,072	£ 42,985	£ 45,465
Collateral received	72	111
Borrowings
Disclosure of fair value measurement of liabilities [line items]
Notional amount	46,141	42,353
At fair value
Disclosure of fair value measurement of liabilities [line items]
Borrowings	42,617	38,219
At fair value | Level 1
Disclosure of fair value measurement of liabilities [line items]
Borrowings	34,281	31,710
At fair value | Level 2
Disclosure of fair value measurement of liabilities [line items]
Borrowings	£ 8,336	£ 6,509

Borrowings - Schedule of lease

Borrowings - Schedule of lease obligations (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Gross lease liabilities	£ 1,010	£ 916
Less: finance charges allocated to future periods	(231)	(202)
Lease liabilities	779	714
Less than 1 year
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Gross lease liabilities	133	118
Lease liabilities	114	96
1 to 5 years
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Gross lease liabilities	370	318
Lease liabilities	300	269
More than 5 years
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Gross lease liabilities	507	480
Lease liabilities	£ 365	£ 349

Trade and other payables (Detai

Trade and other payables (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Trade and other payables [abstract]
Trade payables	£ 2,786	£ 3,249
Deferred payables	327	404
Customer contributions	34	171
Social security and other taxes	0	240
Contingent consideration	0	19
Other payables	929	985
Trade and other payables	£ 4,076	£ 5,068

Contract liabilities - Summary

Contract liabilities - Summary of contract liabilities (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Contract liabilities [abstract]
Current	£ 127	£ 252
Non-current	2,119	1,754
Total contract liabilities	£ 2,246	£ 2,006	£ 1,472

Contract liabilities - Schedule

Contract liabilities - Schedule of significant changes in contract assets and contract liabilities (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Increase (Decrease) in Contract Liabilities [Roll Forward]
As at 1 April	£ 2,006	£ 1,472
Exchange adjustments	(27)	54
Revenue recognised that was included in the contract liability balance at the beginning of the period	(252)	(292)
Increases due to cash received, excluding amounts recognised as revenue during the period	519	772
At 31 March	£ 2,246	£ 2,006

Other non-current liabilities_2

Other non-current liabilities (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Subclassifications of assets, liabilities and equities [abstract]
Deferred income	£ 11	£ 84
Customer contributions	411	421
Other payables	458	416
Other non-current liabilities	£ 880	£ 921

Pensions and other post-retir_3

Pensions and other post-retirement benefits - Narrative (Details) £ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£) plan	Mar. 31, 2023 GBP (£)	Mar. 31, 2022 GBP (£)
Disclosure of defined benefit plans [line items]
Independent actuarial funding valuation, period	3 years
Number of plans showing funding shortfall | plan	3
Recovery plan payment amount			£ 100
Employer contributions	£ 165	£ 284
Plan assets
Disclosure of defined benefit plans [line items]
Employer contributions	165	284
UK | Pensions
Disclosure of defined benefit plans [line items]
Recovery plan payments to be paid	12
Employer contributions, excluding recovery plan payments	95	74
Employer contributions	£ 118	197
Weighted average duration of defined benefit obligation	11 years
UK | Pensions | Maximum
Disclosure of defined benefit plans [line items]
Value of security arrangements	£ 180
UK | Pensions | Plan assets
Disclosure of defined benefit plans [line items]
Employer contributions	£ 118	197
US
Disclosure of defined benefit plans [line items]
Defined contribution plan, employer matching contribution percent of gross pay	8%
US | Pensions
Disclosure of defined benefit plans [line items]
Number of defined benefit plans | plan	4
Employer contributions	£ 26	76
Weighted average duration of defined benefit obligation	11 years
US | Pensions | Plan assets
Disclosure of defined benefit plans [line items]
Employer contributions	£ 26	76
US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Employer contributions	£ 21	11
Weighted average duration of defined benefit obligation	12 years
US | Other post-retirement benefits | Plan assets
Disclosure of defined benefit plans [line items]
Employer contributions	£ 21	£ 11
Top of range | UK | National Grid UK Retirement Plan (NGUKRP)
Disclosure of defined benefit plans [line items]
Defined contribution plan, employer matching contribution percent of gross pay	12%
Top of range | US
Disclosure of defined benefit plans [line items]
Defined contribution plan, employer core contribution as a percent of salary	9%
Defined contribution plan, employer matching contribution, percent of match	50%
Bottom of range | US
Disclosure of defined benefit plans [line items]
Defined contribution plan, employer core contribution as a percent of salary	3%
Defined contribution plan, employer matching contribution, percent of match	25%

Pensions and other post-retir_4

Pensions and other post-retirement benefits - Disclosure of actuarial assumptions (Details)	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
UK | Pensions
Disclosure of defined benefit plans [line items]
Discount rate – past service	4.87%	4.80%	2.78%
Discount rate – future service	4.92%	4.80%	2.85%
Rate of increase in RPI – past service	3.05%	3.17%	3.60%
Rate of increase in RPI – future service	2.92%	3.07%	3.33%
Salary increases	3.10%	3.11%	3.47%
Assumed life expectations for a retiree age 65 today: Males	21 years 6 months	21 years 10 months 24 days	22 years
Assumed life expectations for a retiree age 65 today: Females	23 years 6 months	23 years 8 months 12 days	23 years 9 months 18 days
Assumed life expectations for a retiree age 65 today: In 20 years: Males	22 years 7 months 6 days	23 years	23 years 2 months 12 days
Assumed life expectations for a retiree age 65 today: In 20 years: Females	24 years 10 months 24 days	25 years 1 month 6 days	25 years 2 months 12 days
UK | Pensions | Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	14%	14%
UK | Pensions | Deferred members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	8%	9%
UK | Pensions | Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	78%	77%
US | Pensions
Disclosure of defined benefit plans [line items]
Discount rate – past service	5.15%	4.85%	3.65%
Discount rate – future service	5.15%	4.85%	3.65%
Salary increases	4.50%	4.50%	4.60%
Assumed life expectations for a retiree age 65 today: Males	21 years 7 months 6 days	21 years 7 months 6 days	21 years 4 months 24 days
Assumed life expectations for a retiree age 65 today: Females	23 years 10 months 24 days	23 years 9 months 18 days	23 years 7 months 6 days
Assumed life expectations for a retiree age 65 today: In 20 years: Males	23 years 3 months 18 days	23 years 2 months 12 days	23 years 1 month 6 days
Assumed life expectations for a retiree age 65 today: In 20 years: Females	25 years 6 months	25 years 4 months 24 days	25 years 3 months 18 days
US | Pensions | Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	37%	37%
US | Pensions | Deferred members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	10%	9%
US | Pensions | Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	53%	54%
US | Other post-retirement benefits
Disclosure of defined benefit plans [line items]
Discount rate – past service	5.15%	4.85%	3.65%
Discount rate – future service	5.15%	4.85%	3.65%
Salary increases	4.50%	4.50%	4.60%
Initial healthcare cost trend rate	7.10%	6.80%	6.80%
Ultimate healthcare cost trend rate	4.50%	4.50%	4.50%
US | Other post-retirement benefits | Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	29%	33%
US | Other post-retirement benefits | Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	71%	67%

Pensions and other post-retir_5

Pensions and other post-retirement benefits - Disclosure of amounts recognised in the statement of financial position (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of defined benefit plans [line items]
Other post-employment liabilities	£ (52)	£ (69)
Net defined benefit asset	1,814	1,951	£ 3,075
Liabilities	(593)	(694)
Assets	2,407	2,645
Funded obligations
Disclosure of defined benefit plans [line items]
Present value of funded obligations	(17,601)	(18,934)
Fair value of plan assets	19,733	21,246
Funding surplus/(deficit)	2,132	2,312
Unfunded obligations
Disclosure of defined benefit plans [line items]
Present value of funded obligations	(266)	(292)
Pensions | UK
Disclosure of defined benefit plans [line items]
Fair value of plan assets	11,782	12,578	16,865
Other post-employment liabilities	0	0
Net defined benefit asset	1,261	1,614	2,590
Liabilities	(56)	(58)
Assets	1,317	1,672
Pensions | US
Disclosure of defined benefit plans [line items]
Fair value of plan assets	5,320	6,060	7,263
Other post-employment liabilities	0	0
Net defined benefit asset	408	324	484
Liabilities	(210)	(234)
Assets	618	558
Pensions | Funded obligations | UK
Disclosure of defined benefit plans [line items]
Present value of funded obligations	(10,465)	(10,906)
Fair value of plan assets	11,782	12,578
Funding surplus/(deficit)	1,317	1,672
Pensions | Funded obligations | US
Disclosure of defined benefit plans [line items]
Present value of funded obligations	(4,702)	(5,502)
Fair value of plan assets	5,320	6,060
Funding surplus/(deficit)	618	558
Pensions | Unfunded obligations | UK
Disclosure of defined benefit plans [line items]
Present value of funded obligations	(56)	(58)
Pensions | Unfunded obligations | US
Disclosure of defined benefit plans [line items]
Present value of funded obligations	(210)	(234)
Other post-retirement benefits | US
Disclosure of defined benefit plans [line items]
Fair value of plan assets	2,631	2,608	2,885
Other post-employment liabilities	(52)	(69)
Net defined benefit asset	145	13	£ 1
Liabilities	(327)	(402)
Assets	472	415
Other post-retirement benefits | Funded obligations | US
Disclosure of defined benefit plans [line items]
Present value of funded obligations	(2,434)	(2,526)
Fair value of plan assets	2,631	2,608
Funding surplus/(deficit)	197	82
Other post-retirement benefits | Unfunded obligations | US
Disclosure of defined benefit plans [line items]
Present value of funded obligations	£ 0	£ 0

Pensions and other post-retir_6

Pensions and other post-retirement benefits - Disclosure of amounts recognised in the income statement and statement of other comprehensive income (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Included within operating costs
Administration costs	£ 22	£ 19	£ 20
Defined benefit plan costs:
Current service cost	143	194	223
Past service cost – augmentations and redundancies	9	8	11
Gains on settlement	(30)	(45)	0
Post-employment benefit expense, payroll cost, defined benefit plans	122	157	234
Included within finance income and costs
Net interest (income)/cost	(100)	(85)	(2)
Total included in income statement	44	91	252
Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations	(218)	(1,364)	2,481
Exchange adjustments	(6)	41	7
Total included in the statement of other comprehensive income	(224)	(1,323)	2,488
Discontinued operations
Included within operating costs
Administration costs	0	0	4
Included within finance income and costs
Net interest (income)/cost	0	0	(2)
Total included in income statement	0	0	10
Total included in the statement of other comprehensive income	0	0	309
Pensions | UK
Included within operating costs
Administration costs	13	9	11
Defined benefit plan costs:
Current service cost	45	69	83
Past service cost – augmentations and redundancies	9	8	11
Gains on settlement	0	0	0
Post-employment benefit expense, payroll cost, defined benefit plans	54	77	94
Included within finance income and costs
Net interest (income)/cost	(84)	(64)	(7)
Total included in income statement	(17)	22	98
Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations	(474)	(1,183)	1,577
Exchange adjustments	0	0	0
Total included in the statement of other comprehensive income	(474)	(1,183)	1,577
Pensions | US
Included within operating costs
Administration costs	7	8	7
Defined benefit plan costs:
Current service cost	72	88	101
Past service cost – augmentations and redundancies	0	0	0
Gains on settlement	(30)	(45)	0
Post-employment benefit expense, payroll cost, defined benefit plans	42	43	101
Included within finance income and costs
Net interest (income)/cost	(13)	(21)	0
Total included in income statement	36	30	108
Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations	99	(242)	532
Exchange adjustments	(5)	36	11
Total included in the statement of other comprehensive income	94	(206)	543
Other post-retirement benefits | US
Included within operating costs
Administration costs	2	2	2
Defined benefit plan costs:
Current service cost	26	37	39
Past service cost – augmentations and redundancies	0	0	0
Gains on settlement	0	0	0
Post-employment benefit expense, payroll cost, defined benefit plans	26	37	39
Included within finance income and costs
Net interest (income)/cost	(3)	0	5
Total included in income statement	25	39	46
Remeasurement (losses)/gains of pension assets and post-retirement benefit obligations	157	61	372
Exchange adjustments	(1)	5	(4)
Total included in the statement of other comprehensive income	£ 156	£ 66	£ 368

Pensions and other post-retir_7

Pensions and other post-retirement benefits - Schedule of reconciliation of the net defined benefit asset (liability) (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	£ 1,951	£ 3,075
Changes in net defined benefit liability (asset) [abstract]
Income/(cost) recognised in the income statement (including discontinued operations)	(44)	(91)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(224)	(1,323)
Employer contributions	165	284
Other movements	(17)	(24)
Reclassification to held for sale (note 10)	(17)	30
Closing net defined benefit asset	1,814	1,951
UK | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	1,614	2,590
Changes in net defined benefit liability (asset) [abstract]
Income/(cost) recognised in the income statement (including discontinued operations)	17	(22)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(474)	(1,183)
Employer contributions	118	197
Other movements	3	2
Reclassification to held for sale (note 10)	(17)	30
Closing net defined benefit asset	1,261	1,614
US | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	324	484
Changes in net defined benefit liability (asset) [abstract]
Income/(cost) recognised in the income statement (including discontinued operations)	(36)	(30)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	94	(206)
Employer contributions	26	76
Other movements	0	0
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	408	324
US | Other post-retirement benefits
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	13	1
Changes in net defined benefit liability (asset) [abstract]
Income/(cost) recognised in the income statement (including discontinued operations)	(25)	(39)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	156	66
Employer contributions	21	11
Other movements	(20)	(26)
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	£ 145	£ 13

Pensions and other post-retir_8

Pensions and other post-retirement benefits - Schedule of reconciliation of changes in the present value of defined benefit obligations (including unfunded obligations) (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disclosure of operating segments [line items]
Opening net defined benefit asset	£ 1,951	£ 3,075
Changes in net defined benefit liability (asset) [abstract]
Reclassification to held for sale (note 10)	(17)	30
Closing net defined benefit asset	1,814	1,951
UK | Pensions
Disclosure of operating segments [line items]
Opening net defined benefit asset	1,614	2,590
Changes in net defined benefit liability (asset) [abstract]
Reclassification to held for sale (note 10)	(17)	30
Closing net defined benefit asset	1,261	1,614
US | Pensions
Disclosure of operating segments [line items]
Opening net defined benefit asset	324	484
Changes in net defined benefit liability (asset) [abstract]
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	408	324
US | Other post-retirement benefits
Disclosure of operating segments [line items]
Opening net defined benefit asset	13	1
Changes in net defined benefit liability (asset) [abstract]
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	145	13
Present value of defined benefit obligation
Disclosure of operating segments [line items]
Opening net defined benefit asset	(19,226)	(23,867)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(143)	(194)
Interest cost	(911)	(697)
Actuarial (losses)/gains – experience	37	(204)
Actuarial gains/(losses) – demographic assumptions	106	150
Actuarial gains/(losses) – financial assumptions	348	4,428
Past service cost – augmentations and redundancies	(9)	(8)
Liabilities extinguished on settlements	543	616
Medicare subsidy received	(26)	(28)
Employee contributions	(10)	(10)
Benefits paid	1,174	1,290
Exchange adjustments	189	(656)
Reclassification from other post-employment liabilities	(11)	0
Reclassification to held for sale (note 10)	72	(46)
Closing net defined benefit asset	(17,867)	(19,226)
Present value of defined benefit obligation | UK | Pensions
Disclosure of operating segments [line items]
Opening net defined benefit asset	(10,964)	(14,275)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(45)	(69)
Interest cost	(536)	(334)
Actuarial (losses)/gains – experience	(2)	(235)
Actuarial gains/(losses) – demographic assumptions	98	135
Actuarial gains/(losses) – financial assumptions	165	3,167
Past service cost – augmentations and redundancies	(9)	(8)
Liabilities extinguished on settlements	0	0
Medicare subsidy received	0	0
Employee contributions	(10)	(10)
Benefits paid	710	711
Exchange adjustments	0	0
Reclassification from other post-employment liabilities	0	0
Reclassification to held for sale (note 10)	72	(46)
Closing net defined benefit asset	(10,521)	(10,964)
Present value of defined benefit obligation | US | Pensions
Disclosure of operating segments [line items]
Opening net defined benefit asset	(5,736)	(6,779)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(72)	(88)
Interest cost	(258)	(252)
Actuarial (losses)/gains – experience	(34)	(17)
Actuarial gains/(losses) – demographic assumptions	12	5
Actuarial gains/(losses) – financial assumptions	190	818
Past service cost – augmentations and redundancies	0	0
Liabilities extinguished on settlements	543	616
Medicare subsidy received	0	0
Employee contributions	0	0
Benefits paid	312	426
Exchange adjustments	131	(465)
Reclassification from other post-employment liabilities	0	0
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	(4,912)	(5,736)
Present value of defined benefit obligation | US | Other post-retirement benefits
Disclosure of operating segments [line items]
Opening net defined benefit asset	(2,526)	(2,813)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(26)	(37)
Interest cost	(117)	(111)
Actuarial (losses)/gains – experience	73	48
Actuarial gains/(losses) – demographic assumptions	(4)	10
Actuarial gains/(losses) – financial assumptions	(7)	443
Past service cost – augmentations and redundancies	0	0
Liabilities extinguished on settlements	0	0
Medicare subsidy received	(26)	(28)
Employee contributions	0	0
Benefits paid	152	153
Exchange adjustments	58	(191)
Reclassification from other post-employment liabilities	(11)	0
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	£ (2,434)	£ (2,526)

Pensions and other post-retir_9

Pensions and other post-retirement benefits - Schedule of reconciliation of changes in fair value of plan assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	£ 1,951	£ 3,075
Changes in net defined benefit liability (asset) [abstract]
Employer contributions	165	284
Reclassification to held for sale (note 10)	(17)	30
Closing net defined benefit asset	1,814	1,951
Actual return on plan assets	302	(4,956)
Expected contributions to plans in the following year	151	149
UK | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	1,614	2,590
Changes in net defined benefit liability (asset) [abstract]
Employer contributions	118	197
Reclassification to held for sale (note 10)	(17)	30
Closing net defined benefit asset	1,261	1,614
Actual return on plan assets	(115)	(3,852)
Expected contributions to plans in the following year	108	99
US | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	324	484
Changes in net defined benefit liability (asset) [abstract]
Employer contributions	26	76
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	408	324
Actual return on plan assets	202	(775)
Expected contributions to plans in the following year	28	36
US | Other post-retirement benefits
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	13	1
Changes in net defined benefit liability (asset) [abstract]
Employer contributions	21	11
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	145	13
Actual return on plan assets	215	(329)
Expected contributions to plans in the following year	15	14
Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	21,246	27,013
Changes in net defined benefit liability (asset) [abstract]
Interest income	1,011	782
Return on plan assets (less than)/in excess of interest	(709)	(5,738)
Administration costs	(22)	(19)
Assets distributed on settlements	(513)	(571)
Employer contributions	165	284
Employee contributions	10	10
Benefits paid	(1,171)	(1,288)
Exchange adjustments	(195)	697
Reclassification to held for sale (note 10)	(89)	76
Closing net defined benefit asset	19,733	21,246
Plan assets | UK | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	12,578	16,865
Changes in net defined benefit liability (asset) [abstract]
Interest income	620	398
Return on plan assets (less than)/in excess of interest	(735)	(4,250)
Administration costs	(13)	(9)
Assets distributed on settlements	0	0
Employer contributions	118	197
Employee contributions	10	10
Benefits paid	(707)	(709)
Exchange adjustments	0	0
Reclassification to held for sale (note 10)	(89)	76
Closing net defined benefit asset	11,782	12,578
Plan assets | US | Pensions
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	6,060	7,263
Changes in net defined benefit liability (asset) [abstract]
Interest income	271	273
Return on plan assets (less than)/in excess of interest	(69)	(1,048)
Administration costs	(7)	(8)
Assets distributed on settlements	(513)	(571)
Employer contributions	26	76
Employee contributions	0	0
Benefits paid	(312)	(426)
Exchange adjustments	(136)	501
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	5,320	6,060
Plan assets | US | Other post-retirement benefits
Disclosure of net defined benefit liability (asset) [line items]
Opening net defined benefit asset	2,608	2,885
Changes in net defined benefit liability (asset) [abstract]
Interest income	120	111
Return on plan assets (less than)/in excess of interest	95	(440)
Administration costs	(2)	(2)
Assets distributed on settlements	0	0
Employer contributions	21	11
Employee contributions	0	0
Benefits paid	(152)	(153)
Exchange adjustments	(59)	196
Reclassification to held for sale (note 10)	0	0
Closing net defined benefit asset	£ 2,631	£ 2,608

Pensions and other post-reti_10

Pensions and other post-retirement benefits - Disclosure of asset allocations (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
UK | Pensions
Disclosure of fair value of plan assets [line items]
Equities	£ 729	£ 654	£ 1,782
Property	679	883	1,124
Diversified alternatives	1,241	1,388	1,916
Buy-in/bulk annuity policies	2,060	2,126	2,784
Longevity swap	(94)	(88)	(80)
Cash and cash equivalents	3	8	38
Other (including net current assets and liabilities)	(5)	47	6
Fair value of plan assets	11,782	12,578	16,865
Repurchase agreements	2,700	3,400	6,100
Pension fund investments in employer issued securities	44	23	32
UK | Pensions | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	1,910	1,892	2,741
UK | Pensions | Government securities and liability-driven investments
Disclosure of fair value of plan assets [line items]
Debt instruments	5,259	5,668	6,554
UK | Pensions | Liability driven investment
Disclosure of fair value of plan assets [line items]
Debt instruments		4,906	5,857
UK | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Equities	576	475	1,458
Property	0	23	122
Diversified alternatives	669	708	1,334
Buy-in/bulk annuity policies	0	0	78
Longevity swap	0	0	0
Cash and cash equivalents	3	8	38
Other (including net current assets and liabilities)	0	59	16
Fair value of plan assets	3,158	3,927	6,573
UK | Pensions | Quoted | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	1,910	1,892	2,741
UK | Pensions | Quoted | Government securities and liability-driven investments
Disclosure of fair value of plan assets [line items]
Debt instruments	0	762	786
UK | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	153	179	324
Property	679	860	1,002
Diversified alternatives	572	680	582
Buy-in/bulk annuity policies	2,060	2,126	2,706
Longevity swap	(94)	(88)	(80)
Cash and cash equivalents	0	0	0
Other (including net current assets and liabilities)	(5)	(12)	(10)
Fair value of plan assets	8,624	8,651	10,292
Investments in forestry funds	288	304	283
UK | Pensions | Unquoted | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	0	0	0
UK | Pensions | Unquoted | Government securities and liability-driven investments
Disclosure of fair value of plan assets [line items]
Debt instruments	5,259	4,906	5,768
US | Pensions
Disclosure of fair value of plan assets [line items]
Equities	1,323	1,500	2,176
Property	237	299	295
Diversified alternatives	556	635	688
Cash and cash equivalents	9	16	31
Other (including net current assets and liabilities)	1	11	15
Fair value of plan assets	5,320	6,060	7,263
US | Pensions | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	2,390	2,675	3,008
US | Pensions | Government securities
Disclosure of fair value of plan assets [line items]
Debt instruments	804	924	1,050
US | Pensions | Quoted
Disclosure of fair value of plan assets [line items]
Equities	99	154	272
Property	0	0	0
Diversified alternatives	54	85	142
Cash and cash equivalents	9	16	31
Other (including net current assets and liabilities)	1	7	12
Fair value of plan assets	2,510	2,819	3,103
US | Pensions | Quoted | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	1,987	2,147	2,311
US | Pensions | Quoted | Government securities
Disclosure of fair value of plan assets [line items]
Debt instruments	360	410	335
US | Pensions | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	1,224	1,346	1,904
Property	237	299	295
Diversified alternatives	502	550	546
Cash and cash equivalents	0	0	0
Other (including net current assets and liabilities)	0	4	3
Fair value of plan assets	2,810	3,241	4,160
US | Pensions | Unquoted | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	403	528	697
US | Pensions | Unquoted | Government securities
Disclosure of fair value of plan assets [line items]
Debt instruments	444	514	715
US | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Equities	561	584	1,198
Diversified alternatives	101	109	264
Other (including net current assets and liabilities)	161	148	185
Fair value of plan assets	2,631	2,608	2,885
US | Other post-retirement benefits | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	1,397	1,334	725
US | Other post-retirement benefits | Government securities
Disclosure of fair value of plan assets [line items]
Debt instruments	411	433	513
US | Other post-retirement benefits | Quoted
Disclosure of fair value of plan assets [line items]
Equities	37	74	185
Diversified alternatives	92	100	144
Other (including net current assets and liabilities)	0	1	0
Fair value of plan assets	1,890	1,938	1,563
US | Other post-retirement benefits | Quoted | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	1,351	1,332	723
US | Other post-retirement benefits | Quoted | Government securities
Disclosure of fair value of plan assets [line items]
Debt instruments	410	431	511
US | Other post-retirement benefits | Unquoted
Disclosure of fair value of plan assets [line items]
Equities	524	510	1,013
Diversified alternatives	9	9	120
Other (including net current assets and liabilities)	161	147	185
Fair value of plan assets	741	670	1,322
US | Other post-retirement benefits | Unquoted | Corporate bonds
Disclosure of fair value of plan assets [line items]
Debt instruments	46	2	2
US | Other post-retirement benefits | Unquoted | Government securities
Disclosure of fair value of plan assets [line items]
Debt instruments	£ 1	£ 2	£ 2

Pensions and other post-reti_11

Pensions and other post-retirement benefits - Disclosure of asset allocation strategy (Details)	Mar. 31, 2024
UK | Pensions
Disclosure of fair value of plan assets [line items]
Return-seeking assets	22%
Liability-matching assets	78%
US | Pensions
Disclosure of fair value of plan assets [line items]
Return-seeking assets	40%
Liability-matching assets	60%
US | Other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Return-seeking assets	31%
Liability-matching assets	69%

Provisions - Schedule of change

Provisions - Schedule of changes in provisions (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	£ 2,642	£ 2,539
Exchange adjustments	(47)	131
Additions	772	455
Unused amounts reversed	(125)	(62)
Adjustment for change in discount rate	33	(224)
Unwinding of discount	102	88
Utilised	(265)	(285)
Reclassification to held for sale (note 10)	(3)
Other provisions, ending balance	3,109	2,642	£ 2,539
Exceptional items
Reconciliation of changes in other provisions [abstract]
Changes in environmental provisions	(496)	176	0
Environmental
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	1,891	1,877
Exchange adjustments	(37)	114
Additions	600	142
Unused amounts reversed	(18)	(38)
Adjustment for change in discount rate	4	(176)
Unwinding of discount	85	72
Utilised	(107)	(100)
Reclassification to held for sale (note 10)	0
Other provisions, ending balance	2,418	£ 1,891	£ 1,877
Real discount rate (in percent)		1.50%	0.50%
Decommissioning
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	297	£ 258
Exchange adjustments	(2)	5
Additions	34	91
Unused amounts reversed	(7)	(10)
Adjustment for change in discount rate	29	(48)
Unwinding of discount	11	10
Utilised	(9)	(9)
Reclassification to held for sale (note 10)	0
Other provisions, ending balance	353	297	£ 258
Other
Reconciliation of changes in other provisions [abstract]
Other provisions, beginning balance	454	404
Exchange adjustments	(8)	12
Additions	138	222
Unused amounts reversed	(100)	(14)
Adjustment for change in discount rate	0	0
Unwinding of discount	6	6
Utilised	(149)	(176)
Reclassification to held for sale (note 10)	(3)
Other provisions, ending balance	£ 338	£ 454	£ 404

Provisions - Schedule of curren

Provisions - Schedule of current and non-current provisions (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Other provisions [abstract]
Current	£ 298	£ 288
Non-current	2,811	2,354
Other provisions	£ 3,109	£ 2,642	£ 2,539

Provisions - Schedule of enviro

Provisions - Schedule of environmental provision (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of other provisions [line items]
Discounted	£ 3,109	£ 2,642	£ 2,539
Environmental
Disclosure of other provisions [line items]
Discounted	2,418	1,891	£ 1,877
Real undiscounted	2,697	£ 2,144
Real discount rate (in percent)		1.50%	0.50%
Environmental | UK
Disclosure of other provisions [line items]
Discounted	108	£ 123
Real undiscounted	£ 118	£ 138
Real discount rate (in percent)	1%	1.50%
Environmental | US
Disclosure of other provisions [line items]
Discounted	£ 2,310	£ 1,768
Real undiscounted	£ 2,579	£ 2,006
Real discount rate (in percent)	1.50%	1.50%

Provisions - Narrative (Details

Provisions - Narrative (Details) £ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£) site	Mar. 31, 2023 GBP (£)	Mar. 31, 2022 GBP (£)
Disclosure of other provisions [line items]
Other provisions	£ 3,109	£ 2,642	£ 2,539
Other environment related provision
Disclosure of other provisions [line items]
Weighted average duration of cash flows		10 years 6 months
Other provisions	£ 2,418	£ 1,891	£ 1,877
Other environment related provision | US
Disclosure of other provisions [line items]
Number of Superfund sites | site	3
Weighted average duration of cash flows	10 years
Other provisions	£ 2,310	1,768
Liability for claims and claims adjustment
Disclosure of other provisions [line items]
Other provisions	170	182
Liability for interconnector excess revenues
Disclosure of other provisions [line items]
Other provisions	£ 76	£ 108

Share capital - Schedule of sha

Share capital - Schedule of share capital (Details) - GBP (£) £ in Millions, shares in Millions		12 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of classes of share capital [line items]
Equity, beginning balance		£ 29,562	£ 23,856	£ 19,860
Issued during the year in lieu of dividends	[1]	(1)	0	(1)
Equity, ending balance		£ 29,892	£ 29,562	£ 23,856
Share capital
Disclosure of classes of share capital [line items]
Issued capital beginning balance (in shares)		3,930	3,904
Issued during the year in lieu of dividends (in shares)		37	26
Issued capital ending balance (in shares)		3,967	3,930	3,904
Equity, beginning balance		£ 488	£ 485	£ 474
Issued during the year in lieu of dividends	[1]	5	3	11
Equity, ending balance		£ 493	£ 488	£ 485
[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	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disclosure of classes of share capital [abstract]
Par value per share (GBP per share)	£ 0.1243129
Number of ordinary shares per ADS (in shares)	5
Proceeds from issuing shares	£ 2	£ 5
Amount of unclaimed dividends derecognised	£ 5	£ 5
Treasury stock (in shares)	247,000,000	254,000,000
Treasury shares, market value	£ 2,637	£ 2,783
Treasury shares, gifted (in shares)	4,000,000	3,000,000
Treasury stock, reissued (in shares)	3,000,000	2,000,000
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	21	16
Purchase of own shares, employee share trusts	£ 6	£ 4
Maximum number of treasury shares held during the year (in shares)	254,000,000	259,000,000
Treasury shares as percent of ordinary shares	6.40%	6.60%
Treasury shares, nominal value	£ 32	£ 32

Other equity reserves (Details)

Other equity reserves (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	£ (3,860)	£ (4,563)	£ (5,094)
Exchange adjustments	(335)	882	629
Exchange differences reclassified to the consolidated income statement on disposal	0	(170)	0
Net (losses) gains taken to equity	87	105	(180)
Share of net gains of associates taken to equity		1	1
Transferred to profit or loss	213	(136)	39
Net (losses) gains in respect of cash flow hedging of capital expenditure	(37)	10	(1)
Tax	(60)	6	35
Cash flow hedges transferred to the statement of financial position, net of tax	2	5	8
Other equity reserves, ending balance	(3,990)	(3,860)	(4,563)
Retranslation of net assets offset by net investment hedge	(397)	1,080	754
Net gains (losses) in respect of net investment hedges	(62)	198	125
Gain on disposal of equity instruments measured at FVOCI			12
Retained earnings
Disclosure of reserves within equity [line items]
Gain on disposal of equity instruments measured at FVOCI			82
Translation
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	1,306	594	(35)
Exchange adjustments	(335)	882	629
Exchange differences reclassified to the consolidated income statement on disposal		(170)
Other equity reserves, ending balance	971	1,306	594
Cash flow hedge
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	(61)	(85)	(48)
Net (losses) gains taken to equity	16	142	(96)
Share of net gains of associates taken to equity		1	1
Transferred to profit or loss	224	(136)	40
Net (losses) gains in respect of cash flow hedging of capital expenditure	(37)	10	(1)
Tax	(50)	2	11
Cash flow hedges transferred to the statement of financial position, net of tax	2	5	8
Other equity reserves, ending balance	94	(61)	(85)
Cost of hedging
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	(38)	(29)	(28)
Net (losses) gains taken to equity	37	(12)	(2)
Transferred to profit or loss	(11)		(1)
Tax	(6)	3	2
Other equity reserves, ending balance	(18)	(38)	(29)
FVOCI equity
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	0	0	51
Net (losses) gains taken to equity			(70)
Tax			19
Other equity reserves, ending balance	0	0	0
FVOCI debt
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	79	103	111
Net (losses) gains taken to equity	34	(25)	(11)
Tax	(4)	1	3
Other equity reserves, ending balance	109	79	103
Own credit
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	0	0	1
Net (losses) gains taken to equity			(1)
Other equity reserves, ending balance	0	0	0
Capital redemption
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	19	19	19
Other equity reserves, ending balance	19	19	19
Merger
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	(5,165)	(5,165)	(5,165)
Other equity reserves, ending balance	£ (5,165)	£ (5,165)	£ (5,165)

Net debt - Schedule of componen

Net debt - Schedule of components of net debt (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Subclassifications of assets, liabilities and equities [abstract]
Cash and cash equivalents	£ 559	£ 163	£ 204	£ 157
Current financial investments	3,699	2,605	3,145	2,342
Borrowings	(47,072)	(42,985)	(45,465)
Financing derivatives	(793)	(756)	(693)
Net debt position	£ (43,607)	£ (40,973)	£ (42,809)	£ (28,546)

Net debt - Schedule of changes

Net debt - Schedule of changes in net debt (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Liabilities from financing activities
Liabilities arising from financing activities at start of year	£ (43,778)	£ (46,215)	£ (31,124)
Proceeds received from loans	(5,563)	(11,908)	(12,347)
Repayment of loans	1,701	15,260	1,261
Payments of lease liabilities	118	155	117
Net movements in short-term borrowings	(544)	511	11
Cash inflows on derivatives	(86)	(190)	(20)
Cash outflows on derivatives	58	118	114
Interest paid	1,627	1,430	1,053
Non-net debt financing cash flows	(18)	(27)	(33)
Fair value gains and losses	(29)	413	(186)
Foreign exchange movements	718	(1,311)	(652)
Interest (charges)/income	(1,848)	(1,828)	(1,231)
Other non-cash movements	(205)	(283)	34
Acquisition of NGED			(8,260)
Reclassification to held for sale	13	97	5,048
Liabilities arising from financing activities at end of year	(47,836)	(43,778)	(46,215)
Cash and cash equivalents
Cash and cash equivalents at start of year	163	204	157
Net increase (decrease) in cash and cash equivalents	427	(48)	9
Foreign exchange movements	(1)	7	5
Acquisition of NGED			44
Reclassification to held for sale	(30)	9	(11)
Cash and cash equivalents at end of year	559	163	204
Financial investments
Financial investments at start of year	2,605	3,145	2,342
Net movements in short-term financial investments	1,141	(586)	781
Interest received	(148)	(65)	(40)
Fair value gains and losses	4	(18)	(12)
Foreign exchange movements	(49)	61	53
Interest (charges)/income	152	73	54
Other non-cash movements			(15)
Acquisition of NGED			69
Reclassification to held for sale	(6)	(5)	(87)
Financial investments at end of year	3,699	2,605	3,145
Other financing derivatives
Other financing derivatives at start of year	37	57	79
Cash inflows on derivatives	(123)	0	(17)
Cash outflows on derivatives	0	362	122
Derivative cash flows included in capital expenditure	5	12	8
Derivative cash flows included in revenue	(11)
Fair value gains and losses	60	(394)	(132)
Interest (charges)/income	7		(5)
Other non-cash movements	(4)
Reclassification to held for sale			2
Other financing derivatives at end of year	(29)	37	57
Net debt
Net debt at start of year	(40,973)	(42,809)	(28,546)
Net increase (decrease) in cash and cash equivalents	427	(48)	9
Proceeds received from loans	(5,563)	(11,908)	(12,347)
Repayment of loans	1,701	15,260	1,261
Payments of lease liabilities	118	155	117
Net movements in short-term borrowings	(544)	511	11
Cash inflows on derivatives	(86)	(190)	(20)
Cash outflows on derivatives	58	118	114
Interest paid	1,627	1,430	1,053
Non-net debt financing cash flows	(18)	(27)	(33)
Net movements in short-term financial investments	1,141	(586)	781
Cash inflows on derivatives	(123)	0	(17)
Cash outflows on derivatives	0	362	122
Derivative cash flows included in capital expenditure	5	12	8
Interest received	(148)	(65)	(40)
Derivative cash flows included in revenue	(11)
Fair value gains and losses	35	1	(330)
Foreign exchange movements	668	(1,243)	(594)
Interest (charges)/income	(1,689)	(1,755)	(1,182)
Other non-cash movements	(209)	(283)	19
Acquisition of NGED			(8,147)
Reclassification to held for sale	(23)	92	4,952
Net debt at end of year	(43,607)	(40,973)	(42,809)
Interest payable	490	401	351
Bank overdrafts			22
Borrowings
Liabilities from financing activities
Liabilities arising from financing activities at start of year	(42,985)	(45,465)	(31,220)
Proceeds received from loans	(5,563)	(11,908)	(12,347)
Repayment of loans	1,701	15,260	1,261
Payments of lease liabilities	118	155	117
Net movements in short-term borrowings	(544)	511	11
Interest paid	1,330	1,277	998
Non-net debt financing cash flows	(18)	(27)	(33)
Fair value gains and losses	(69)	367	286
Foreign exchange movements	718	(1,311)	(652)
Interest (charges)/income	(1,564)	(1,658)	(1,177)
Other non-cash movements	(209)	(283)	34
Acquisition of NGED			(8,286)
Reclassification to held for sale	13	97	5,543
Liabilities arising from financing activities at end of year	(47,072)	(42,985)	(45,465)
Net debt
Proceeds received from loans	(5,563)	(11,908)	(12,347)
Repayment of loans	1,701	15,260	1,261
Payments of lease liabilities	118	155	117
Net movements in short-term borrowings	(544)	511	11
Interest paid	1,330	1,277	998
Non-net debt financing cash flows	(18)	(27)	(33)
Financing derivatives used to hedge debt
Liabilities from financing activities
Liabilities arising from financing activities at start of year	(793)	(750)	96
Cash inflows on derivatives	(86)	(190)	(20)
Cash outflows on derivatives	58	118	114
Interest paid	297	153	55
Fair value gains and losses	40	46	(472)
Interest (charges)/income	(284)	(170)	(54)
Other non-cash movements	4
Acquisition of NGED			26
Reclassification to held for sale			(495)
Liabilities arising from financing activities at end of year	(764)	(793)	(750)
Net debt
Cash inflows on derivatives	(86)	(190)	(20)
Cash outflows on derivatives	58	118	114
Interest paid	297	£ 153	£ 55
Non-current assets
Liabilities from financing activities
Liabilities arising from financing activities at end of year	310
Other financing derivatives
Other financing derivatives at end of year	5
Net debt
Net debt at end of year	315
Non-current assets | Financing derivatives used to hedge debt
Liabilities from financing activities
Liabilities arising from financing activities at end of year	310
Current assets
Liabilities from financing activities
Liabilities arising from financing activities at end of year	1
Cash and cash equivalents
Cash and cash equivalents at end of year	559
Financial investments
Financial investments at end of year	3,699
Other financing derivatives
Other financing derivatives at end of year	17
Net debt
Net debt at end of year	4,276
Current assets | Financing derivatives used to hedge debt
Liabilities from financing activities
Liabilities arising from financing activities at end of year	1
Current liabilities
Liabilities from financing activities
Liabilities arising from financing activities at end of year	(5,090)
Other financing derivatives
Other financing derivatives at end of year	(18)
Net debt
Net debt at end of year	(5,108)
Current liabilities | Borrowings
Liabilities from financing activities
Liabilities arising from financing activities at end of year	(4,859)
Current liabilities | Financing derivatives used to hedge debt
Liabilities from financing activities
Liabilities arising from financing activities at end of year	(231)
Non-current liabilities
Liabilities from financing activities
Liabilities arising from financing activities at end of year	(43,057)
Other financing derivatives
Other financing derivatives at end of year	(33)
Net debt
Net debt at end of year	(43,090)
Non-current liabilities | Borrowings
Liabilities from financing activities
Liabilities arising from financing activities at end of year	(42,213)
Non-current liabilities | Financing derivatives used to hedge debt
Liabilities from financing activities
Liabilities arising from financing activities at end of year	£ (844)

Commitments and contingencies_2

Commitments and contingencies (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of contingent liabilities [line items]
Contracted for but not provided	£ 3,329	£ 3,035
Energy purchase commitments	14,175	19,194
Guarantees	3,366	2,226
Guarantee of subleases for US properties (expire up to 2040)
Disclosure of contingent liabilities [line items]
Guarantees	67	219
Guarantees of certain obligations of Eastern Green Link Joint Operations (various expiry dates)
Disclosure of contingent liabilities [line items]
Guarantees	2,465	0
Guarantees of certain obligations of Grain LNG (expire up to 2025)
Disclosure of contingent liabilities [line items]
Guarantees	32	32
Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates)
Disclosure of contingent liabilities [line items]
Guarantees	271	281
Guarantees of certain obligations of St William Homes LLP (various expiry dates)
Disclosure of contingent liabilities [line items]
Guarantees	44	44
Guarantees of certain obligations of National Grid IFA 2 Limited (expected expiry 2024)
Disclosure of contingent liabilities [line items]
Guarantees	121	144
Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024)
Disclosure of contingent liabilities [line items]
Guarantees	243	1,185
Other guarantees and letters of credit (various expiry dates)
Disclosure of contingent liabilities [line items]
Guarantees	123	321
Less than 1 year
Disclosure of contingent liabilities [line items]
Energy purchase commitments	1,244	1,391
In 1 to 2 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	982	985
In 2 to 3 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	1,062	1,057
In 3 to 4 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	941	912
In 4 to 5 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	866	929
More than 5 years
Disclosure of contingent liabilities [line items]
Energy purchase commitments	£ 9,080	£ 13,920

Related party transactions (Det

Related party transactions (Details) £ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£)	Mar. 31, 2023 GBP (£)	Mar. 31, 2022 GBP (£) lease	Feb. 25, 2022 lease
New York
Disclosure of transactions between related parties [line items]
Number of leases won | lease			6
Pension plan
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions	£ 0	£ 0	£ 3
Joint ventures
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions	221	100	284
Purchases of goods and services, related party transactions	6	0	19
Amounts receivable	80	58	43
Amounts payable	0	19	247
Dividends received	152	150	123
Joint ventures | Emerald Energy Venture LLC
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions	126	76	74
Receivables due from joint ventures	77	55	33
Joint ventures | Nemo Link Limited
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions	71	0	0
Dividends received	17	47	77
Joint ventures | St William Homes LLP
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions			202
Joint ventures | BritNed Development Limited
Disclosure of transactions between related parties [line items]
Dividends received	116	84	39
Purchases of property and other assets, related party transactions			18
Joint ventures | Community Offshore Wind LLC
Disclosure of transactions between related parties [line items]
Amounts payable			223
Number of leases won | lease				6
Associates
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions	1	1	0
Purchases of goods and services, related party transactions	4	31	41
Amounts receivable	0	0	1
Amounts payable	1	1	4
Dividends received	117	32	35
Associates | Millennium Pipeline Company, LLC
Disclosure of transactions between related parties [line items]
Purchases of goods and services, related party transactions		22	38
Dividends received		16	34
Associates | GasT TopCo Limited
Disclosure of transactions between related parties [line items]
Dividends received	102
Associates | New York Transco LLC
Disclosure of transactions between related parties [line items]
Dividends received	12	12	2
Subsidiaries of an associate
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions	70	6	0
Purchases of goods and services, related party transactions	1	0	0
Amounts receivable	8	8	£ 0
Subsidiaries of an associate | National Gas Transmission Plc
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions	£ 70	£ 0

Financial risk management - Nar

Financial risk management - Narrative (Details)	12 Months Ended
	Mar. 31, 2024
Financial Risk Management [Abstract]
Hedge ratio	1

Financial risk management - Dis

Financial risk management - Disclosure of treasury credit risk (Details) £ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£)
Triple ‘A’ G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	£ 2,818
Triple ‘A’ G7 sovereign entities (AAA) | Long-term limit
Disclosure of credit risk exposure [line items]
Maximum limit	2,114
Triple ‘A’ vehicles (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	500
Maximum limit, utilisation	460
Triple ‘A’ range institutions and non-G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	2,562
Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) | Long-term limit
Disclosure of credit risk exposure [line items]
Maximum limit	1,922
Double ‘A+’ G7 sovereign entities (AA+)
Disclosure of credit risk exposure [line items]
Maximum limit	2,562
Double ‘A+’ G7 sovereign entities (AA+) | Long-term limit
Disclosure of credit risk exposure [line items]
Maximum limit	1,922
Double ‘A’ range institutions (AA) | Bottom of range
Disclosure of credit risk exposure [line items]
Maximum limit	1,537
Maximum limit, utilisation	0
Double ‘A’ range institutions (AA) | Top of range
Disclosure of credit risk exposure [line items]
Maximum limit	2,050
Maximum limit, utilisation	316
Double ‘A’ range institutions (AA) | Long-term limit | Bottom of range
Disclosure of credit risk exposure [line items]
Maximum limit	1,153
Maximum limit, utilisation	0
Double ‘A’ range institutions (AA) | Long-term limit | Top of range
Disclosure of credit risk exposure [line items]
Maximum limit	1,537
Maximum limit, utilisation	311
Single ‘A’ range institutions (A) | Bottom of range
Disclosure of credit risk exposure [line items]
Maximum limit	512
Maximum limit, utilisation	0
Single ‘A’ range institutions (A) | Top of range
Disclosure of credit risk exposure [line items]
Maximum limit	1,025
Maximum limit, utilisation	542
Single ‘A’ range institutions (A) | Long-term limit | Bottom of range
Disclosure of credit risk exposure [line items]
Maximum limit	384
Maximum limit, utilisation	0
Single ‘A’ range institutions (A) | Long-term limit | Top of range
Disclosure of credit risk exposure [line items]
Maximum limit	769
Maximum limit, utilisation	£ 376

Financial risk management - Cre

Financial risk management - Credit risk, narrative (Details) - Credit risk - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about financial instruments [line items]
Gross amounts offset	£ 0	£ 0
Bank account and bank overdraft
Disclosure of detailed information about financial instruments [line items]
Gross amounts offset	£ 0	£ 0

Financial risk management - D_2

Financial risk management - Disclosure of offsetting of financial assets and financial liabilities (Details) - Credit Risk - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Assets
Gross carrying amounts	£ 368	£ 429
Gross amounts offset	0	0
Net amount presented in statement of financial position	368	429
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(273)	(232)
Cash collateral received/ pledged	(28)	(76)
Net amount	67	121
Liabilities
Gross carrying amounts	(1,244)	(1,293)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(1,244)	(1,293)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	273	232
Cash collateral received/ pledged	452	700
Net amount	(519)	(361)
Assets (Liabilities)
Gross carrying amounts	(876)	(864)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(876)	(864)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	0	0
Cash collateral received/ pledged	424	624
Net amount	(452)	(240)
Financing derivatives
Liabilities
Gross carrying amounts	(1,126)	(1,119)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(1,126)	(1,119)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	246	204
Cash collateral received/ pledged	441	681
Net amount	(439)	(234)
Commodity contract derivatives
Liabilities
Gross carrying amounts	(118)	(174)
Gross amounts offset	0	0
Net amount presented in statement of financial position	(118)	(174)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	27	28
Cash collateral received/ pledged	11	19
Net amount	(80)	(127)
Financing derivatives
Assets
Gross carrying amounts	333	363
Gross amounts offset	0	0
Net amount presented in statement of financial position	333	363
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(246)	(204)
Cash collateral received/ pledged	(28)	(76)
Net amount	59	83
Commodity contract derivatives
Assets
Gross carrying amounts	35	66
Gross amounts offset	0	0
Net amount presented in statement of financial position	35	66
Related amounts available to be offset but not offset in statement of financial position
Financial instruments	(27)	(28)
Cash collateral received/ pledged	0	0
Net amount	£ 8	£ 38

Financial risk management - D_3

Financial risk management - Disclosure of maturity analysis for financial liabilities and derivatives (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Non-derivative financial liabilities
Lease liabilities	£ (1,010)	£ (916)
Less than 1 year
Non-derivative financial liabilities
Lease liabilities	(133)	(118)
Liquidity risk
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(45,386)	(41,635)
Interest payments on borrowings	(21,580)	(18,913)
Lease liabilities	(1,010)	(916)
Other non-interest-bearing liabilities	(4,173)	(4,648)
Contingent consideration	0	(19)
Derivative financial assets
Financial liabilities	(73,686)	(67,910)
Liquidity risk | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	8,716	9,502
Liquidity risk | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(8,436)	(9,257)
Liquidity risk | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	32	59
Liquidity risk | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(15)	(20)
Liquidity risk | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	16,494	13,073
Liquidity risk | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(18,229)	(14,984)
Liquidity risk | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	11	21
Liquidity risk | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(110)	(173)
Liquidity risk | Less than 1 year
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(4,480)	(2,433)
Interest payments on borrowings	(1,505)	(1,220)
Lease liabilities	(133)	(118)
Other non-interest-bearing liabilities	(3,715)	(4,232)
Contingent consideration	0	(19)
Derivative financial assets
Financial liabilities	(10,332)	(8,309)
Liquidity risk | Less than 1 year | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	1,927	4,757
Liquidity risk | Less than 1 year | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(1,884)	(4,679)
Liquidity risk | Less than 1 year | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	23	48
Liquidity risk | Less than 1 year | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(9)	(11)
Liquidity risk | Less than 1 year | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	5,583	1,174
Liquidity risk | Less than 1 year | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(6,068)	(1,461)
Liquidity risk | Less than 1 year | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	8	11
Liquidity risk | Less than 1 year | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(79)	(126)
Liquidity risk | In 1 to 2 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(2,627)	(2,722)
Interest payments on borrowings	(1,442)	(1,244)
Lease liabilities	(118)	(102)
Other non-interest-bearing liabilities	(458)	(416)
Contingent consideration	0	0
Derivative financial assets
Financial liabilities	(5,167)	(4,809)
Liquidity risk | In 1 to 2 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	311	701
Liquidity risk | In 1 to 2 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(312)	(676)
Liquidity risk | In 1 to 2 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	8	11
Liquidity risk | In 1 to 2 years | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(5)	(6)
Liquidity risk | In 1 to 2 years | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	2,993	2,154
Liquidity risk | In 1 to 2 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(3,496)	(2,483)
Liquidity risk | In 1 to 2 years | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	3	9
Liquidity risk | In 1 to 2 years | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(24)	(35)
Liquidity risk | In 2 to 3 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(3,036)	(2,614)
Interest payments on borrowings	(1,386)	(1,148)
Lease liabilities	(97)	(86)
Other non-interest-bearing liabilities	0	0
Contingent consideration	0	0
Derivative financial assets
Financial liabilities	(4,705)	(4,159)
Liquidity risk | In 2 to 3 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	3,993	745
Liquidity risk | In 2 to 3 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(3,935)	(719)
Liquidity risk | In 2 to 3 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	1	0
Liquidity risk | In 2 to 3 years | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	(1)	(3)
Liquidity risk | In 2 to 3 years | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	2,672	2,381
Liquidity risk | In 2 to 3 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(2,909)	(2,705)
Liquidity risk | In 2 to 3 years | Commodity derivatives - receipts
Derivative financial liabilities
Derivative financial liabilities	0	1
Liquidity risk | In 2 to 3 years | Commodity derivatives - payments
Derivative financial liabilities
Derivative financial liabilities	(7)	(11)
Liquidity risk | More than 3 years
Non-derivative financial liabilities
Borrowings, excluding lease liabilities	(35,243)	(33,866)
Interest payments on borrowings	(17,247)	(15,301)
Lease liabilities	(662)	(610)
Other non-interest-bearing liabilities	0	0
Contingent consideration	0	0
Derivative financial assets
Financial liabilities	(53,482)	(50,633)
Liquidity risk | More than 3 years | Derivative contracts – receipts
Derivative financial assets
Derivative financial assets	2,485	3,299
Liquidity risk | More than 3 years | Derivative contracts – payments
Derivative financial assets
Derivative financial assets	(2,305)	(3,183)
Liquidity risk | More than 3 years | Commodity derivatives - receipts
Derivative financial assets
Derivative financial assets	0	0
Liquidity risk | More than 3 years | Commodity derivatives - payments
Derivative financial assets
Derivative financial assets	0	0
Liquidity risk | More than 3 years | Derivative contracts – receipts
Derivative financial liabilities
Derivative financial liabilities	5,246	7,364
Liquidity risk | More than 3 years | Derivative contracts – payments
Derivative financial liabilities
Derivative financial liabilities	(5,756)	(8,335)
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	£ 0	£ (1)

Financial risk management - D_4

Financial risk management - Disclosure of nature and extent of risks arising from financial instruments (Details) - Currency risk - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	£ (43,607)	£ (40,973)
Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	559	163
Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	3,699	2,605
Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(47,072)	(42,985)
Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(42,814)	(40,217)
Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(793)	(756)
Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	2,158	2,329
Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(3,715)	(4,253)
Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(458)	(416)
GBP
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(21,684)	(20,097)
GBP | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	402	96
GBP | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,514	1,031
GBP | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(14,498)	(14,473)
GBP | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(12,582)	(13,346)
GBP | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(9,102)	(6,751)
GBP | Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	280	448
GBP | Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,330)	(1,624)
GBP | Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(169)	(147)
Euro
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,040	(298)
Euro | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	14
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	(11,936)	(11,045)
Euro | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(11,936)	(11,031)
Euro | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	12,976	10,733
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
USD
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(23,221)	(20,590)
USD | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	157	53
USD | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	2,185	1,574
USD | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(18,938)	(15,741)
USD | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(16,596)	(14,114)
USD | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(6,625)	(6,476)
USD | Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,878	1,881
USD | Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(2,385)	(2,629)
USD | Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(289)	(269)
Other
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	258	12
Other | Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other | Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other | Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,700)	(1,726)
Other | Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,700)	(1,726)
Other | Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,958	1,738
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 - D_5

Financial risk management - Disclosure of financial instruments by type of interest rate (Details) - Interest rate risk - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	£ (43,607)	£ (40,973)
Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(34,757)	(32,365)
Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(4,099)	(3,934)
Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(4,810)	(4,710)
Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	59	36
Cash and cash equivalents
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	559	163
Cash and cash equivalents | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	157	53
Cash and cash equivalents | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	402	110
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	0	0
Financial investments
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	3,699	2,605
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	3,640	2,569
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	59	36
Borrowings
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(47,072)	(42,985)
Borrowings | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(39,948)	(36,631)
Borrowings | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(2,378)	(1,744)
Borrowings | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(4,746)	(4,610)
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	(42,814)	(40,217)
Pre-derivative position | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(39,791)	(36,578)
Pre-derivative position | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	1,664	935
Pre-derivative position | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(4,746)	(4,610)
Pre-derivative position | Other
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	59	36
Derivative effect
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(793)	(756)
Derivative effect | Fixed rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	5,034	4,213
Derivative effect | Floating rate
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(5,763)	(4,869)
Derivative effect | Inflation linked
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(64)	(100)
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 - D_6

Financial risk management - Disclosure of detailed information about hedging instruments (Details) £ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£)	Mar. 31, 2023 GBP (£)	Mar. 31, 2022 GBP (£)	Mar. 31, 2024 $ / £	Mar. 31, 2024 € / £	Mar. 31, 2024 $ / €	Mar. 31, 2024	Mar. 31, 2023 $ / £	Mar. 31, 2023 € / £	Mar. 31, 2023 $ / €	Mar. 31, 2023	Mar. 31, 2021 GBP (£)
Disclosure of detailed information about financial instruments [line items]
Net gains in respect of cash flow hedges	£ 240	£ 0	£ (57)
Net gains/(losses) in respect of cost of hedging	26	(16)	1
Net gains (losses) in respect of net investment hedges	62	(198)	(125)
Other equity reserves – cost of hedging balances	(3,990)	(3,860)	(4,563)									£ (5,094)
Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	(18)	(38)	£ (29)									£ (28)
Fair value hedges | Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Net gains in respect of cash flow hedges	0	0
Net gains/(losses) in respect of cost of hedging	0	4
Net gains (losses) in respect of net investment hedges	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	1	0
Reclassification of foreign currency translation reserve		0
Fair value hedges | Foreign currency and interest rate risk | Bottom of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate					1.11	1.07			1.11	1.13
Fair value hedges | Foreign currency and interest rate risk | Bottom of range | GBP | SONIA
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis							0.56%				0.84%
Fair value hedges | Foreign currency and interest rate risk | Bottom of range | USD | LIBOR
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis											0.68%
Fair value hedges | Foreign currency and interest rate risk | Bottom of range | USD | SOFR
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis							0.83%
Fair value hedges | Foreign currency and interest rate risk | Top of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate					1.24	1.15			1.20	1.17
Fair value hedges | Foreign currency and interest rate risk | Top of range | GBP | SONIA
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis							3.74%				3.74%
Fair value hedges | Foreign currency and interest rate risk | Top of range | USD | SOFR
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis							2.23%				1.26%
Fair value hedges | Foreign currency and interest rate risk | Liabilities – non-current | Non-derivatives hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	0
Fair value hedges | Foreign currency and interest rate risk | Current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets		0
Fair value hedges | Foreign currency and interest rate risk | Current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0
Fair value hedges | Foreign currency and interest rate risk | Non-current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets		25
Fair value hedges | Foreign currency and interest rate risk | Non-current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	33
Fair value hedges | Foreign currency and interest rate risk | Derivative liabilities - current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities		(43)
Fair value hedges | Foreign currency and interest rate risk | Derivative liabilities - current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(96)
Fair value hedges | Foreign currency and interest rate risk | Derivative liabilities - non-current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities		(559)
Fair value hedges | Foreign currency and interest rate risk | Derivative liabilities - non-current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(499)
Fair value hedges | Foreign currency and interest rate risk | Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	(11)	(11)
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	5	136
Net gains/(losses) in respect of cost of hedging	(1)	4
Net gains (losses) in respect of net investment hedges	0	0
Transferred to profit or loss in respect of cash flow hedges	220	(136)
Transferred to profit or loss in respect of cost of hedging	(4)	0
Reclassification of foreign currency translation reserve		0
Cash flow hedges | Foreign currency and interest rate risk | Bottom of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.30	1.08	1.07		1.30	1.08	1.13
Cash flow hedges | Foreign currency and interest rate risk | Bottom of range | GBP
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate							0.976%				0.976%
Cash flow hedges | Foreign currency and interest rate risk | Bottom of range | USD
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate							2.095%				2.095%
Cash flow hedges | Foreign currency and interest rate risk | Top of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.66	1.19	1.15		1.66	1.24	1.15
Cash flow hedges | Foreign currency and interest rate risk | Top of range | GBP
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate							7.41%				7.41%
Cash flow hedges | Foreign currency and interest rate risk | Top of range | USD
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate							5.989%				3.864%
Cash flow hedges | Foreign currency and interest rate risk | Liabilities – non-current | Non-derivatives hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	0
Cash flow hedges | Foreign currency and interest rate risk | Current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets		0
Cash flow hedges | Foreign currency and interest rate risk | Current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0
Cash flow hedges | Foreign currency and interest rate risk | Non-current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets		166
Cash flow hedges | Foreign currency and interest rate risk | Non-current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	161
Cash flow hedges | Foreign currency and interest rate risk | Derivative liabilities - current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities		(39)
Cash flow hedges | Foreign currency and interest rate risk | Derivative liabilities - current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(112)
Cash flow hedges | Foreign currency and interest rate risk | Derivative liabilities - non-current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities		(248)
Cash flow hedges | Foreign currency and interest rate risk | Derivative liabilities - non-current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(164)
Cash flow hedges | Foreign currency and interest rate risk | Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	(16)	(12)
Cash flow hedges | Currency risk
Disclosure of detailed information about financial instruments [line items]
Net gains in respect of cash flow hedges	(26)	10
Net gains/(losses) in respect of cost of hedging	0	0
Net gains (losses) in respect of net investment hedges	0	0
Transferred to profit or loss in respect of cash flow hedges	4	0
Transferred to profit or loss in respect of cost of hedging	0	0
Reclassification of foreign currency translation reserve		0
Cash flow hedges | Currency risk | Bottom of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.23	1.11			1.20	1.10
Cash flow hedges | Currency risk | Top of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.27	1.18			1.36	1.20
Cash flow hedges | Currency risk | Liabilities – non-current | Non-derivatives hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	0
Cash flow hedges | Currency risk | Current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets		6
Cash flow hedges | Currency risk | Current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	5
Cash flow hedges | Currency risk | Non-current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets		1
Cash flow hedges | Currency risk | Non-current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	1
Cash flow hedges | Currency risk | Derivative liabilities - current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities		(6)
Cash flow hedges | Currency risk | Derivative liabilities - current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(4)
Cash flow hedges | Currency risk | Derivative liabilities - non-current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities		(1)
Cash flow hedges | Currency risk | Derivative liabilities - non-current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(32)
Cash flow hedges | Currency risk | Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	0	0
Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Net gains in respect of cash flow hedges	0	0
Net gains/(losses) in respect of cost of hedging	38	(24)
Net gains (losses) in respect of net investment hedges	62	(198)
Transferred to profit or loss in respect of cash flow hedges	0	0
Transferred to profit or loss in respect of cost of hedging	(8)	1
Reclassification of foreign currency translation reserve		373
Net investment hedges | Bottom of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.22	1.17			1.18	1.12
Net investment hedges | Top of range
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate				1.29	1.17			1.22	1.13
Net investment hedges | Liabilities – non-current | Non-derivatives hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(1,768)
Net investment hedges | Current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets		52
Net investment hedges | Current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	11
Net investment hedges | Non-current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets		0
Net investment hedges | Non-current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0
Net investment hedges | Derivative liabilities - current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities		0
Net investment hedges | Derivative liabilities - current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(8)
Net investment hedges | Derivative liabilities - non-current
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities		(15)
Net investment hedges | Derivative liabilities - non-current | Derivative hedging instrument
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	0
Net investment hedges | Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves – cost of hedging balances	£ 3	£ (27)

Financial risk management - D_7

Financial risk management - Disclosure of effects of hedge accounting on financial position and year-to-date performance for each type of hedge (Details) £ in Millions	12 Months Ended
	Mar. 31, 2024 GBP (£)	Mar. 31, 2023 GBP (£)
Foreign currency and interest rate risk | Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(5,096)	(4,779)
Balance of fair value hedge adjustments in borrowings, Continuing hedges	£ 720	£ 789
Balance of fair value hedge adjustments in borrowings, Discontinued hedges	(35)	(43)
Change in value used for calculating ineffectiveness, Hedged item	40	398
Change in value used for calculating ineffectiveness, Hedging instrument	(22)	(351)
Hedge ineffectiveness	18	47
Foreign currency and interest rate risk | Fair value hedges | Impacted by Interest Rate Benchmark Reform amendments
Disclosure of detailed information about hedging instruments [line items]
Nominal amount of hedging instruments in hedging relationships to which amendments for interest rate benchmark reform are applied		859
Foreign currency and interest rate risk | Fair value hedges | Borrowings
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	4,364	4,042
Foreign currency and interest rate risk | Fair value hedges | Borrowings | Current liabilities
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	271	511
Foreign currency and interest rate risk | Fair value hedges | Borrowings | Non-current liabilities
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	£ 4,093	£ 3,531
Foreign currency and interest rate risk | Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(9,892)	(9,357)
Balance in cash flow hedge reserve, Continuing hedges	£ 154	£ (73)
Balance in cash flow hedge reserve, Discontinued hedges	0	0
Change in value used for calculating ineffectiveness, Hedged item	(18)	149
Change in value used for calculating ineffectiveness, Hedging instrument	3	(154)
Hedge ineffectiveness	£ (15)	£ (5)
Currency risk | Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(2,039)	(537)
Balance in cash flow hedge reserve, Continuing hedges	£ (31)	£ (3)
Balance in cash flow hedge reserve, Discontinued hedges	0	0
Change in value used for calculating ineffectiveness, Hedged item	28	(35)
Change in value used for calculating ineffectiveness, Hedging instrument	(28)	35
Hedge ineffectiveness	£ 0	£ 0
Currency risk | Net investment hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(2,999)	(3,095)
Balance in translation reserve, Continuing hedges	£ 40	£ (129)
Balance in translation reserve, Discontinued hedges	(2,564)	(2,457)
Change in value used for calculating ineffectiveness, Hedged item	(62)	198
Change in value used for calculating ineffectiveness, Hedging instrument	62	(198)
Hedge ineffectiveness	£ 0	£ 0

Financial risk management - Sch

Financial risk management - Schedule of fair value analysis (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 4,332	£ 3,052
Liabilities	(1,244)	(1,312)
Financial assets (liabilities)	3,088	1,740
Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	3,084	1,764
Liabilities	0	0
Financial assets (liabilities)	3,084	1,764
Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	725	810
Liabilities	(1,127)	(1,131)
Financial assets (liabilities)	(402)	(321)
Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	523	478
Liabilities	(117)	(181)
Financial assets (liabilities)	406	297	£ 233
Financing derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(1,126)	(1,119)
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	(1,022)	(997)
Financing derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(104)	(122)
Commodity contract derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(118)	(174)
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	(105)	(134)
Commodity contract derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(13)	(40)
Contingent consideration
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	(19)
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	0	(19)
Investments held at FVTPL
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	3,567	2,216
Investments held at FVTPL | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	3,084	1,764
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	483	452
Investments held at FVOCI
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	397	407
Investments held at FVOCI | Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Investments held at FVOCI | Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	397	407
Investments held at FVOCI | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Financing derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	333	363
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	293	341
Financing derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	40	22
Commodity contract derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	35	66
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	35	62
Commodity contract derivatives | Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 0	£ 4

Financial risk management - Fai

Financial risk management - Fair value analysis, narrative (Details)	Mar. 31, 2024 investment
Financial Risk Management [Abstract]
Number of equity investments valued based on latest transaction price	23
Number of equity investments	38
Number of investments held at cost	2
Number of equity investments valued based on internal valuation process	13

Financial risk management - S_2

Financial risk management - Schedule of changes in level 3 financial instruments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Financial assets (liabilities) at beginning of period	£ 1,740
Financial assets (liabilities) at end of period	3,088	£ 1,740
Level 3
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Financial assets (liabilities) at beginning of period	297	233
Net gains/(losses) for the year	42	67
Purchases	19	3
Settlements	48	(6)
Financial assets (liabilities) at end of period	406	297
Level 3 | Financing derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Financial assets (liabilities) at beginning of period	(100)	(187)
Net gains/(losses) for the year	36	87
Purchases	0	0
Settlements	0	0
Financial assets (liabilities) at end of period	(64)	(100)
Gain (loss) on assets held at end of year	36	87
Level 3 | Commodity contract derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Financial assets (liabilities) at beginning of period	(36)	44
Net gains/(losses) for the year	0	(18)
Purchases	(16)	(56)
Settlements	39	(6)
Financial assets (liabilities) at end of period	(13)	(36)
Gain (loss) on assets held at end of year	(18)	(41)
Level 3 | Other
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Financial assets (liabilities) at beginning of period	433	376
Net gains/(losses) for the year	6	(2)
Purchases	35	59
Settlements	9	0
Financial assets (liabilities) at end of period	£ 483	£ 433

Financial risk management - S_3

Financial risk management - Schedule of impacts of reasonably possible changes in significant level 3 assumptions (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
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	£ (41)	£ (53)
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	41	51
Financing derivatives | +20 basis points increase between RPI and Consumer Price Index (CPI)
Disclosure of detailed information about financial instruments [line items]
+20 basis points increase between RPI and Consumer Price Index (CPI)	37	43
Financing derivatives | -20 basis points decrease between RPI and CPI
Disclosure of detailed information about financial instruments [line items]
-20 basis points decrease between RPI and CPI	(34)	(38)
Commodity contract derivatives | 10% increase in commodity prices
Disclosure of detailed information about financial instruments [line items]
10% increase in commodity prices	4	5
Commodity contract derivatives | 10% decrease in commodity prices
Disclosure of detailed information about financial instruments [line items]
10% decrease in commodity prices	(4)	(6)
Other | +100 basis points change in discount rate
Disclosure of detailed information about financial instruments [line items]
+100 basis points change in discount rate	(7)	(9)
Other | -100 basis points change in discount rate
Disclosure of detailed information about financial instruments [line items]
-100 basis points change in discount rate	9	10
Other | +10% change in venture capital price
Disclosure of detailed information about financial instruments [line items]
+10% change in venture capital price	28	28
Other | -10% change in venture capital price
Disclosure of detailed information about financial instruments [line items]
-10% change in venture capital price	£ (28)	£ (28)

Financial risk management - Cap

Financial risk management - Capital risk management (Details) £ in Billions, $ in Billions	12 Months Ended
	Mar. 31, 2024 GBP (£)	Mar. 31, 2023	Mar. 31, 2024 USD ($)
Disclosure of credit risk exposure [line items]
Retained cash flow ratio	9.20%	9.30%
Gearing ratio	69%	71%
Interest cover ratio	3.9	3.8
Debt covenants, borrowings excluding cash and short term investments	£ 55
Debt covenants, borrowings excluding cash and short term investments, headroom	10
Non-US Subsidiaries
Disclosure of credit risk exposure [line items]
Debt covenants, total debt	35
US Subsidiaries
Disclosure of credit risk exposure [line items]
Debt covenants, total debt | $			$ 35
US And Non-US subsidiaries
Disclosure of credit risk exposure [line items]
Debt covenants, total debt, headroom	£ 10
National Grid Electricity Distribution
Disclosure of credit risk exposure [line items]
Net debt to RAV gearing covenants	0.85		0.85
Debt covenants, impacted companies	20%		20%
National Grid Electricity Distribution | Minimum
Disclosure of credit risk exposure [line items]
Net debt to RAV gearing covenants	0.85		0.85

Borrowing facilities - Narrativ

Borrowing facilities - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 7,905	£ 6,503
Facilities held as backup to commercial paper and similar borrowings
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	7,864	6,461
Facilities available as backup to specific US borrowings
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 41	£ 42

Borrowing facilities - Schedule

Borrowing facilities - Schedule of undrawn committed borrowing facilities (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 7,905	£ 6,503
Less than 1 year
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	0	42
In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	0	4,361
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	195	2,100
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	5,859	0
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	106	0
More than 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 1,745	£ 0

Subsidiary undertakings, join_3

Subsidiary undertakings, joint ventures and associates - Disclosure of interests in subsidiaries (Details)	12 Months Ended
	Mar. 31, 2024
Sheet Road Management Company Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	51%
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%

Subsidiary undertakings, join_4

Subsidiary undertakings, joint ventures and associates - Disclosure of interests in joint ventures (Details)	12 Months Ended
	Mar. 31, 2024 £ / shares shares	Mar. 31, 2024 € / shares shares
Disclosure of joint ventures [line items]
Par value per share (EUR/GBP per share) | £ / shares	£ 0.1243129
BritNed Development Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
BritNed Development Limited | National Grid Interconnector Holdings Limited | C Ordinary shares
Disclosure of joint ventures [line items]
Number of shares held in joint venture (in shares) | shares	284,500,000	284,500,000
Par value per share (EUR/GBP per share) | € / shares		€ 0.20
BritNed Development Limited | National Grid Interconnector Holdings Limited | A Ordinary shares
Disclosure of joint ventures [line items]
Number of shares held in joint venture (in shares) | shares	1	1
Par value per share (EUR/GBP per share) | £ / shares	£ 1
National Places LLP
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
Nemo Link Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
Community Offshore Wind LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	27.27%
Clean Energy Storage Systems, LLC (previously Clean Energy Generation, LLC)
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
Emerald Energy Venture LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	51%
Island Park Energy Center, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
LI Energy Storage System, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
LI Solar Generation, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%
IFA2 SAS
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50%

Subsidiary undertakings, join_5

Subsidiary undertakings, joint ventures and associates - Disclosure of interests in joint operations (Details)	12 Months Ended
	Mar. 31, 2024 £ / shares shares
Disclosure of joint operations [line items]
Par value per share (EUR/GBP per share)	£ 0.1243129
Eastern Green Link 1 Limited
Disclosure of joint operations [line items]
Proportion of ownership interest in joint operation	50%
Eastern Green Link 2 Limited
Disclosure of joint operations [line items]
Proportion of ownership interest in joint operation	50%
NGET/SPT Upgrades Limited
Disclosure of joint operations [line items]
Proportion of ownership interest in joint operation	50%
National Grid Electricity Transmission plc | A Ordinary shares | NGET/SPT Upgrades Limited
Disclosure of joint operations [line items]
Number of shares held in joint operation (in shares) | shares	50
Par value per share (EUR/GBP per share)	£ 1

Subsidiary undertakings, join_6

Subsidiary undertakings, joint ventures and associates - Disclosure of interests in associates (Details) - £ / shares				12 Months Ended
	Mar. 31, 2024	Mar. 11, 2024	Jan. 31, 2023	Mar. 31, 2024
Disclosure of associates [line items]
Par value per share (GBP per share)	£ 0.1243129			£ 0.1243129
GasT TopCo Limited
Disclosure of associates [line items]
Proportion of ownership interest in associate	20%	20%	40%	20%
Joint Radio Company Limited
Disclosure of associates [line items]
Proportion of ownership interest in associate				25%
Joint Radio Company Limited | A Ordinary shares | National Grid Electricity Transmission plc
Disclosure of associates [line items]
Number of shares held in joint venture (in shares)	1			1
Par value per share (GBP per share)	£ 0.50			£ 0.50
Clean Line Energy Partners LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate				32%
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%
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%
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%
Electralink Limited
Disclosure of associates [line items]
Proportion of ownership interest in associate				27.04%

Sensitivities - Schedule of sen

Sensitivities - Schedule of sensitivities on areas of estimation uncertainty (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Other environment related provision | Change in the real discount rate
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, percent	1%	1%
Change in risk variable, impact on income statement	£ 173	£ 150
Change in risk variable, impact on net assets	£ 173	150
Other environment related provision | Change in the real discount rate | Increase (decrease) due to voluntary changes in accounting policy
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on income statement		(9)
Change in risk variable, impact on net assets		£ (24)
Other environment related provision | Change in estimated future cash flows
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, percent	20%	20%
Change in risk variable, impact on income statement	£ 462	£ 354
Change in risk variable, impact on net assets	462	354
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	22	29
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	1,147	1,264
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	8	8
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	902	933
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	4	4
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption	81	50
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	2	2
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	402	441
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	(171)	(188)
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	(150)	(164)
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	£ (126)	£ (136)
UK | Pensions | Actuarial assumption of discount rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in actuarial assumption, percent	1%	1%
UK | Pensions | Actuarial assumption of expected rates of inflation
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in actuarial assumption, percent	1%	1%
UK | Pensions | Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase in actuarial assumption, percent	1%	1%
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	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	£ 18	£ 26
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	801	977
US | Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase in actuarial assumption	2	4
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption	37	57
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	2	3
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	288	344
US | Assumed US healthcare cost trend rates change
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	18	24
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 276	£ 324
US | Pensions | Actuarial assumption of discount rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in actuarial assumption, percent	1%	1%
US | Pensions | Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase in actuarial assumption, percent	1%	1%
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	1 year
US | Pensions | Assumed US healthcare cost trend rates change
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in actuarial assumption, percent	1%	1%

Sensitivities - Schedule of s_2

Sensitivities - Schedule of sensitivities on financial instruments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
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%	10%
Change in risk variable, impact on income statement	£ (59)	£ (60)
Change in risk variable, impact on net assets	£ (59)	£ (60)
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%	10%
Change in risk variable, impact on income statement	£ (6)	£ (8)
Change in risk variable, impact on net assets	£ (6)	£ (8)
Inflation, UK RPI change | UK
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	1%	1%
Change in risk variable, impact on income statement	£ 36	£ 35
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	1%	1%
Change in risk variable, impact on income statement	£ 24	£ 34
Change in risk variable, impact on other equity reserves	£ 304	£ 361
Interest rate risk | US
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	1%	1%
Change in risk variable, impact on income statement	£ 5	£ 14
Change in risk variable, impact on other equity reserves	39	50
Currency risk
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, impact on net assets	£ 1,680	£ 1,680
Currency risk | US
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	10%	10%
Change in risk variable, impact on income statement	£ 58	£ 51
Change in risk variable, impact on other equity reserves	£ 268	£ 291
Commodity price risk
Disclosure of nature and extent of risks arising from financial instruments [line items]
Change in risk variable, percent	10%	10%
Increase in risk variable, impact on earnings	£ 43	£ 49
Increase in risk variable, impact on net assets	43	49
Decrease in risk variable, impact on earnings	(43)	(40)
Decrease in risk variable, impact on net assets	£ (43)	£ (40)

Post balance sheet events (Deta

Post balance sheet events (Details) £ in Billions	May 22, 2024 GBP (£)
Major ordinary share transactions
Disclosure of non-adjusting events after reporting period [line items]
Approved equity for issue	£ 7