National Grid (NGG) 20-F4 Jun 192019 FY Annual report (foreign)Financial data

Company Profile

Document And Entity Information

Document And Entity Information	12 Months Ended
Document And Entity Information	Mar. 31, 2019shares
Document And Entity Information [Abstract]
Entity Registrant Name	NATIONAL GRID PLC
Entity Central Index Key	0001004315
Current Fiscal Year End Date	--03-31
Document Type	20-F
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	Yes
Entity Common Stock, Shares Outstanding	3,687,483,073
Entity Filer Category	Large Accelerated Filer
Entity Accounting Standard	IFRS
Amendment Flag	false

Consolidated income statement

Consolidated income statement - GBP (£) £ in Millions	12 Months Ended
Consolidated income statement - GBP (£) £ in Millions	Mar. 31, 2019		Mar. 31, 2018		Mar. 31, 2017
Statement [Line Items]
Revenue	£ 14,933		£ 15,250		£ 15,035
Operating costs	(12,063)		(11,757)		(11,827)
Operating profit	2,870		3,493	[1]	3,208
Finance income	88		127		53
Finance costs	(1,157)		(1,009)		(1,140)
Share of post-tax results of joint ventures and associates	40		49		63
Profit before tax	1,841		2,660		2,184
Tax	(339)		889		(374)
Profit after tax from continuing operations	1,502		3,549	[2]	1,810
Profit (loss) after tax from discontinued operations	12		2		5,984
Total profit for the year (continuing and discontinued)	1,514		3,551		7,794
Attributable to:
Equity shareholders of the parent	1,511		3,550		7,795
Non-controlling interests	£ 3	[3]	£ 1	[4]	£ (1)	[5]
Earnings per share (pence)
Basic earnings per share (continuing) (in GBP per share)	£ 0.443		£ 1.025		£ 0.481
Diluted earnings per share (continuing) (in GBP per share)	0.441		1.021		0.479
Basic earnings per share (continuing and discontinued) (in GBP per share)	0.446		1.026		2.071
Diluted earnings per share (continuing and discontinued) (in GBP per share)	£ 0.444		£ 1.021		£ 2.062
Before exceptional items and remeasurements £m
Statement [Line Items]
Revenue	£ 14,933		£ 15,250		£ 15,035
Operating costs	(11,491)		(11,793)		(11,262)
Operating profit	3,442		3,457		3,773
Finance income	73		127		53
Finance costs	(1,066)		(1,128)		(1,082)
Share of post-tax results of joint ventures and associates	40		44		63
Profit before tax	2,489		2,500		2,807
Tax	(488)		(584)		(666)
Profit after tax from continuing operations	2,001		1,916		2,141
Profit (loss) after tax from discontinued operations	57		145		606
Total profit for the year (continuing and discontinued)	2,058		2,061		2,747
Attributable to:
Equity shareholders of the parent	2,055		2,060		2,747
Non-controlling interests	£ 3	[3]	£ 1	[4]	£ 0	[5]
Earnings per share (pence)
Basic earnings per share (continuing) (in GBP per share)	£ 0.590		£ 0.553		£ 0.569
Diluted earnings per share (continuing) (in GBP per share)	0.588		0.551		0.567
Basic earnings per share (continuing and discontinued) (in GBP per share)	0.607		0.595		0.730
Diluted earnings per share (continuing and discontinued) (in GBP per share)	£ 0.605		£ 0.593		£ 0.727
Exceptional items and remeasurements (see note 4) £m
Statement [Line Items]
Revenue	£ 0		£ 0		£ 0
Operating costs	(572)		36		(565)
Operating profit	(572)		36		(565)
Finance income	15		0		0
Finance costs	(91)		119		(58)
Share of post-tax results of joint ventures and associates	0		5		0
Profit before tax	(648)		160		(623)
Tax	149		1,473		292
Profit after tax from continuing operations	(499)		1,633		(331)
Profit (loss) after tax from discontinued operations	(45)		(143)		5,378
Total profit for the year (continuing and discontinued)	(544)		1,490		5,047
Attributable to:
Equity shareholders of the parent	(544)		1,490		5,048
Non-controlling interests	£ 0	[3]	£ 0	[4]	£ (1)	[5]
Earnings per share (pence)
Basic earnings per share (continuing) (in GBP per share)	£ (0.147)		£ 0.472		£ (0.088)
Diluted earnings per share (continuing) (in GBP per share)	(0.147)		0.470		(0.088)
Basic earnings per share (continuing and discontinued) (in GBP per share)	(0.161)		0.431		1.341
Diluted earnings per share (continuing and discontinued) (in GBP per share)	£ (0.161)		£ 0.428		£ 1.335

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[2]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[3]	The non-controlling interests for the year ended 31 March 2019 relate to continuing operations.
[4]	The non-controlling interests for the year ended 31 March 2018 relate to continuing operations.
[5]	The non-controlling interests for the year ended 31 March 2017 relate to discontinued operations.

Consolidated statement of compr

Consolidated statement of comprehensive income - GBP (£)		12 Months Ended
Consolidated statement of comprehensive income - GBP (£)		Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Disclosure of analysis of other comprehensive income by item [line items]
Profit after tax from continuing operations		£ 1,502,000,000	£ 3,549,000,000	[1]	£ 1,810,000,000
Items from continuing operations that will never be reclassified to profit or loss:
Remeasurement gains on pension assets and post-retirement benefit obligations		68,000,000	1,313,000,000	[1]	423,000,000
Net gains on financial liability designated at fair value through profit and loss attributable to changes in own credit risk		7,000,000	0	[1]	0
Net losses in respect of cash flow hedging of capital expenditure		(13,000,000)	0	[1]	0
Tax on items that will never be reclassified to profit or loss		(15,000,000)	(530,000,000)	[1]	(277,000,000)
Total items that will never be reclassified to profit or loss		47,000,000	783,000,000	[1]	146,000,000
Items from continuing operations that may be reclassified subsequently to profit or loss:
Exchange adjustments		347,000,000	(505,000,000)	[1]	346,000,000
Net (losses)/gains in respect of cash flow hedges and cost of hedging		(147,000,000)	19,000,000	[1]	70,000,000
Transferred from/(to) profit or loss in respect of cash flow hedges and cost of hedging		41,000,000	(3,000,000)	[1]	(6,000,000)
Net (losses)/gains on available-for-sale investments		0	(30,000,000)	[1]	81,000,000
Transferred to profit or loss on sale of available-for-sale investments		0	(73,000,000)	[1]	(25,000,000)
Net gains on investment in debt instruments measured at fair value through other comprehensive income		2,000,000	0	[1]	0
Share of other comprehensive income of associates, net of tax		1,000,000	0	[1]	0
Tax on items that may be reclassified subsequently to profit or loss		12,000,000	33,000,000	[1]	(34,000,000)
Total items that may be reclassified subsequently to profit or loss		256,000,000	(559,000,000)	[1]	432,000,000
Other comprehensive income for the year, net of tax from continuing operations		303,000,000	224,000,000	[1]	578,000,000
Other comprehensive income for the year, net of tax from discontinued operations	[2]	36,000,000	147,000,000	[1]	42,000,000
Other comprehensive income for the year, net of tax		339,000,000	371,000,000	[1]	620,000,000
Total comprehensive income for the year from continuing operations		1,805,000,000	3,773,000,000	[1]	2,388,000,000
Total comprehensive income for the year from discontinued operations		48,000,000	149,000,000	[1]	6,026,000,000
Total comprehensive income for the year		1,853,000,000	3,922,000,000	[1]	8,414,000,000
Attributable to:
Comprehensive income, attributable to equity shareholders of the parent		1,849,000,000	3,922,000,000	[1]	8,415,000,000
Comprehensive income, attributable to non-controlling interests		4,000,000	0		(1,000,000)
Net losses in respect of cash flow hedging of capital expenditure		(13,000,000)
Continuing operations
Attributable to:
Comprehensive income, attributable to equity shareholders of the parent		1,801,000,000	3,773,000,000	[1]	2,389,000,000
Comprehensive income, attributable to non-controlling interests		4,000,000	0	[1]	(1,000,000)
Discontinued operations
Items from continuing operations that will never be reclassified to profit or loss:
Remeasurement gains on pension assets and post-retirement benefit obligations		0	0		(75,000,000)
Tax on items that will never be reclassified to profit or loss		0	0		13,000,000
Total items that will never be reclassified to profit or loss		36,000,000	142,000,000		(62,000,000)
Items from continuing operations that may be reclassified subsequently to profit or loss:
Net (losses)/gains in respect of cash flow hedges and cost of hedging		0	0		(106,000,000)
Transferred from/(to) profit or loss in respect of cash flow hedges and cost of hedging		0	0		233,000,000
Share of other comprehensive income of associates, net of tax		0	5,000,000		0
Tax on items that may be reclassified subsequently to profit or loss		0	0		(23,000,000)
Total items that may be reclassified subsequently to profit or loss		0	5,000,000		104,000,000
Other comprehensive income for the year, net of tax		36,000,000	147,000,000		42,000,000
Total comprehensive income for the year		48,000,000	149,000,000		6,026,000,000
Attributable to:
Comprehensive income, attributable to equity shareholders of the parent		48,000,000	149,000,000	[1]	6,026,000,000
UK Gas Distribution (Cadent)
Attributable to:
Other comprehensive income, net of tax, gains (losses) on remeasurements of defined benefit plans		35,000,000	142,000,000		0
Net losses in respect of cash flow hedging of capital expenditure		£ 1,000,000	£ 5,000,000		£ 0

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[2]	The other comprehensive income from discontinued operations relates to the items of other comprehensive income of Cadent (investment through Quadgas HoldCo Limited), comprising mainly £35 million (2018: £142 million; 2017: £nil) remeasurement gains on pension assets and post-retirement benefit obligations and a £1 million (2018: £5 million; 2017: £nil) net gain in respect of cash flow hedges. Both items are shown net of tax.

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, 2016		£ 13,565		£ 13,555	£ 447	£ 1,326	£ 16,305	£ (4,523)		£ 10
Profit for the year		7,794		7,795			7,795	0		(1)
Other comprehensive income for the year		620		620			84	536		0
Total comprehensive income for the year		8,414		8,415			7,879	536		(1)
Equity dividends		(1,463)		(1,463)			(1,463)
Scrip dividend-related share issue	[2]	0		0	2	(2)
Purchase of treasury shares		(189)		(189)			(189)
Issue of treasury shares		18		18			18
Purchase of own shares		(6)		(6)			(6)
Other movements in non-controlling interests		7								7
Share-based payments		35		35			35
Tax on share-based payments		3		3			3
Equity, ending balance at Mar. 31, 2017		20,384		20,368	449	1,324	22,582	(3,987)		16
Profit for the year		3,551		3,550			3,550	0		1
Other comprehensive income for the year		371	[3]	372			925	(553)		(1)
Total comprehensive income for the year		3,922	[3]	3,922			4,475	(553)		0
Equity dividends		(4,487)		(4,487)			(4,487)
Scrip dividend-related share issue	[2]	0		0	3	(3)
Purchase of treasury shares		(1,017)		(1,017)			(1,017)
Issue of treasury shares		33		33			33
Purchase of own shares		(5)		(5)			(5)
Share-based payments		16		16			16
Tax on share-based payments		2		2			2
Equity, ending balance at Mar. 31, 2018		18,848		18,832	452	1,321	21,599	(4,540)		16
Profit for the year		1,514		1,511			1,511	0		3
Other comprehensive income for the year		339		338			89	249		1
Total comprehensive income for the year		1,853		1,849			1,600	249		4
Equity dividends		(1,160)		(1,160)			(1,160)
Scrip dividend-related share issue	[2]	(1)		(1)	6	(7)
Issue of treasury shares		18		18			18
Purchase of own shares		(2)		(2)			(2)
Share-based payments		27		27			27
Cash flow hedges transferred to the statement of financial position, net of tax		(18)		(18)				(18)
Equity, ending balance at Mar. 31, 2019		£ 19,369		£ 19,349	£ 458	£ 1,314	£ 21,814	£ (4,237)		£ 20

[1]	For further details of other equity reserves, see note 28.
[2]	Included within the share premium account are costs associated with scrip dividends.
[3]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Consolidated statement of finan

Consolidated statement of financial position - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018		Mar. 31, 2017		Mar. 31, 2016
Non-current assets
Goodwill	£ 5,869	£ 5,444	£ 5,444
Other intangible assets	1,084	899	899
Property, plant and equipment	43,913	39,853	39,853
Other non-current assets	264	115	115
Pension assets	1,567	1,409	1,409
Financial and other investments	667	899	899
Investments in joint ventures and associates	608	2,168	2,168		£ 2,083
Derivative financial assets	1,045	1,319	1,319
Total non-current assets	55,017	52,106	52,106
Current assets
Inventories and current intangible assets	370	341	341
Trade and other receivables	3,153	2,795	2,798
Current tax assets	126	114	114
Financial and other investments	1,981	2,694	2,694		8,741		£ 2,998
Derivative financial assets	108	405	405
Cash and cash equivalents	252	329	329	[1]	1,139	[1]	124
Assets held for sale	1,956		0
Total current assets	7,946	6,678	6,681
Total assets	62,963	58,784	58,787
Current liabilities
Borrowings	(4,472)	(4,447)	(4,447)
Derivative financial liabilities	(350)	(401)	(401)
Trade and other payables	(3,769)	(3,394)	(3,453)
Contract liabilities	(61)	(53)	0
Current tax liabilities	(161)	(123)	(123)
Provisions	(316)	(273)	(273)
Total current liabilities	(9,129)	(8,691)	(8,697)
Non-current liabilities
Borrowings	(24,258)	(22,210)	(22,178)
Derivative financial liabilities	(833)	(660)	(660)
Other non-current liabilities	(808)	(750)	(1,317)
Contract liabilities	(933)	(813)	0
Deferred tax liabilities	(3,965)	(3,557)	(3,636)
Pensions and other post-retirement benefit obligations	(1,785)	(1,672)	(1,672)
Provisions	(1,883)	(1,779)	(1,779)
Total non-current liabilities	(34,465)	(31,441)	(31,242)
Total liabilities	(43,594)	(40,132)	(39,939)
Net assets	19,369	18,652	18,848
Equity
Share capital	458	452	452
Share premium account	1,314	1,321	1,321
Retained earnings	21,814	21,331	21,599
Other equity reserves	(4,237)	(4,468)	(4,540)		(3,987)		(4,523)
Total shareholders’ equity	19,349	18,636	18,832
Non-controlling interests	20	16	16
Total equity	£ 19,369	£ 18,652	£ 18,848		£ 20,384		£ 13,565

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Consolidated cash flow statemen

Consolidated cash flow statement - GBP (£)		12 Months Ended
Consolidated cash flow statement - GBP (£)		Mar. 31, 2019		Mar. 31, 2018		Mar. 31, 2017
Cash flows from operating activities
Total operating profit from continuing operations		£ 2,870,000,000		£ 3,493,000,000	[1]	£ 3,208,000,000
Adjustments for:
Exceptional items and remeasurements		572,000,000		(36,000,000)	[1]	565,000,000
Depreciation, amortisation and impairment		1,588,000,000		1,530,000,000	[1]	1,481,000,000
Share-based payments		27,000,000		16,000,000	[1]	32,000,000
Changes in working capital		40,000,000		118,000,000	[1]	151,000,000
Changes in provisions		(110,000,000)		(206,000,000)	[1]	(181,000,000)
Changes in pensions and other post-retirement benefit obligations		(123,000,000)		(239,000,000)	[1]	(768,000,000)
Cash flows relating to exceptional items		(400,000,000)		26,000,000	[1]	(36,000,000)
Cash generated from operations – continuing operations		4,464,000,000		4,702,000,000	[1]	4,452,000,000
Tax (paid)/recovered		(75,000,000)		8,000,000	[1]	(132,000,000)
Net cash inflow from operating activities – continuing operations		4,389,000,000		4,710,000,000	[1]	4,320,000,000
Net cash (used in)/inflow from operating activities – discontinued operations		(71,000,000)		(207,000,000)	[1]	909,000,000
Cash flows from investing activities
Acquisition of financial investments		(89,000,000)		(2,000,000)	[1]	0
Investments in joint ventures and associates		(143,000,000)		(129,000,000)	[1]	(76,000,000)
Loans to joint ventures and associates		(31,000,000)		(68,000,000)	[1]	(61,000,000)
Disposal of financial investments		18,000,000		134,000,000	[1]	0
Disposal of 61% interest in UK Gas Distribution		0		(20,000,000)	[1]	5,454,000,000
Purchases of intangible assets		(306,000,000)		(173,000,000)	[1]	(223,000,000)
Purchases of property, plant and equipment		(3,635,000,000)		(3,738,000,000)	[1]	(3,296,000,000)
Disposals of property, plant and equipment		38,000,000		10,000,000	[1]	18,000,000
Dividends received from joint ventures and associates		68,000,000		69,000,000	[1]	99,000,000
Interest received		68,000,000		30,000,000	[1]	51,000,000
Net movements in short-term financial investments		822,000,000		5,953,000,000	[1]	(5,600,000,000)
Net cash flow (used in)/from investing activities – continuing operations		(3,190,000,000)		2,066,000,000	[1]	(3,634,000,000)
Net cash flow from investing activities – discontinued operations	[2]	156,000,000		171,000,000	[1]	(680,000,000)
Cash flows from financing activities
Purchase of treasury shares		0		(1,017,000,000)	[1]	(189,000,000)
Proceeds from issue of treasury shares		17,000,000		33,000,000	[1]	18,000,000
Purchase of own shares		(2,000,000)		(5,000,000)	[1]	(6,000,000)
Proceeds received from loans		2,932,000,000		1,941,000,000	[1]	2,463,000,000
Repayment of loans		(1,969,000,000)		(2,156,000,000)	[1]	(1,616,000,000)
Net movements in short-term borrowings and derivatives		(268,000,000)		(772,000,000)	[1]	90,000,000
Interest paid		(914,000,000)		(853,000,000)	[1]	(839,000,000)
Dividends paid to shareholders		(1,160,000,000)		(4,487,000,000)	[1]	(1,463,000,000)
Net cash flow used in financing activities – continuing operations		(1,364,000,000)		(7,316,000,000)	[1]	(1,542,000,000)
Net cash flow (used in)/from financing activities – discontinued operations		0		(231,000,000)	[1]	1,611,000,000
Net (decrease)/increase in cash and cash equivalents		(80,000,000)		(807,000,000)	[1]	984,000,000
Disposal of bank overdraft in UK Gas Distribution		0		0	[1]	15,000,000
Exchange movements		3,000,000		(3,000,000)	[1]	16,000,000
Cash and cash equivalents, beginning balance		329,000,000	[1]	1,139,000,000	[1]	124,000,000
Cash and cash equivalents, ending balance		252,000,000		329,000,000	[1]	1,139,000,000	[1]
Quadgas HoldCo Limited
Cash flows from investing activities
Investments in joint ventures and associates		(2,000,000,000)		(2,100,000,000)
Cash flows from financing activities
Dividends received from associates		£ 133,000,000		144,000,000
Interest received from associates				£ 23,000,000		£ 27,000,000

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[2]	Receipts of dividends from Quadgas HoldCo Limited of £133 million (2018: £144 million) and interest of £23 million (2018: £27 million).

Basis of preparation and recent

Basis of preparation and recent accounting developments	12 Months Ended
Basis of preparation and recent accounting developments	Mar. 31, 2019
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
Basis of preparation and recent accounting pronouncements	Basis of preparation and recent accounting developments Accounting policies describe our approach to recognising and measuring transactions and balances in the year. The accounting policies applicable across the financial statements are shown below, whereas accounting policies that are specific to a component of the financial statements have been incorporated into the relevant note. This section also shows areas of judgement and key sources of estimation uncertainty in these financial statements. In addition, we have summarised new International Accounting Standards Board (IASB) and EU endorsed accounting standards, amendments and interpretations and whether these are effective for this year end or in later years, explaining how significant changes are expected to affect our reported results. National Grid’s principal activities involve the transmission and distribution of electricity and gas in Great Britain and northeastern US. The Company is a public limited liability company incorporated and domiciled in England and Wales, with its registered office at 1–3 Strand, London WC2N 5EH. The Company, National Grid plc, which is the ultimate parent of the Group, has its primary listing on the London Stock Exchange and is also quoted on the New York Stock Exchange. These consolidated financial statements were approved for issue by the Board on 15 May 2019. These consolidated financial statements have been prepared in accordance with International Accounting Standards (IAS) and International Financial Reporting Standards (IFRS) and related interpretations as issued by the IASB and IFRS as adopted by the EU. They are prepared on the basis of all IFRS accounting standards and interpretations that are mandatory for periods ended 31 March 2019 and in accordance with the Companies Act 2006 applicable to companies reporting under IFRS and Article 4 of the EU IAS Regulation. The comparative financial information has also been prepared on this basis. The consolidated financial statements have been prepared on a historical cost basis, except for the recording of pension assets and liabilities, the revaluation of derivative financial instruments and certain commodity contracts and certain financial assets and liabilities measured at fair value. These consolidated financial statements are presented in pounds sterling, which is also the functional currency of the Company. The notes to the financial statements have been prepared on a continuing basis unless otherwise stated. Our income statement and segmental analysis separately identify financial results before and after exceptional items and remeasurements. We continue to use a columnar presentation as we consider it improves the clarity of the presentation, and is consistent with the way that financial performance is measured by management and reported to the Board and Executive Committee, and assists users of the financial statements to understand the results. The Directors believe that presentation of the results in this way is relevant to an understanding of the Group’s financial performance. Presenting financial results before exceptional items and remeasurements is consistent with the way that financial performance is measured by management and reported to the Board and Executive Committee and aids the comparability of reported financial performance from year to year in this context. The inclusion of total profit for the period from continuing operations before exceptional items and remeasurements forms part of the incentive target set annually for remunerating certain Executive Directors and accordingly we believe it is important for users of the financial statements to understand how this compares to our results on a statutory basis and period on period. A. Going concern The Directors considered it appropriate to prepare the financial statements on a going concern basis, having considered the Company’s cash flow forecasts with respect to business planning and treasury management activities. The going concern basis presumes that the Group has adequate resources to remain in operation, and that the Directors intend it to do so, for at least one year from the date the financial statements are signed. B. Basis of consolidation The consolidated financial statements incorporate the results, assets and liabilities of the Company and its subsidiaries, together with a share of the results, assets and liabilities of joint operations. A subsidiary is defined as an entity controlled by the Group. Control is achieved where the Group is exposed to, or has the rights to, variable returns from its involvement with the entity and has the power to affect those returns through its power over the entity. The Group accounts for joint ventures and associates using the equity method of accounting, where the investment is carried at cost plus post-acquisition changes in the share of net assets of the joint venture or associate, less any provision for impairment. Losses in excess of the consolidated interest in joint ventures and associates are not recognised, except where the Company or its subsidiaries have made a commitment to make good those losses. Where necessary, adjustments are made to bring the accounting policies used in the individual financial statements of the Company, subsidiaries, joint operations, joint ventures and associates into line with those used by the Group in its consolidated financial statements under IFRS. Intercompany transactions are eliminated. The results of subsidiaries, joint operations, joint ventures and associates acquired or disposed of during the year are included in the consolidated income statement from the effective date of acquisition or up to the effective date of disposal, as appropriate. Acquisitions are accounted for using the acquisition method, where the purchase price is allocated to the identifiable assets acquired and liabilities assumed on a fair value basis and the remainder recognised as goodwill. C. Treatment of interests in Quadgas HoldCo Limited (Quadgas) – discontinued operations and held for sale Following the Group’s disposal of a 61% controlling stake in the UK Gas Distribution business on 31 March 2017, we have decided to exercise the options over the retained 39% interest in the business (held through Quadgas) and the sale is expected to complete at the end of June 2019, subject to customary regulatory approvals. Accordingly, our interests have been classified as held for sale with effect from 30 June 2018. The Quadgas disposal group comprises our equity investment in Quadgas, our shareholder loan to Quadgas, the Further Acquisition Agreement (FAA) derivative and the Remaining Acquisition Agreement (RAA) derivative. Refer to note 10 for further details. We have also treated the results of the disposal group as a discontinued operation in the consolidated income statement for the current year and we have restated our prior year comparatives for 2018 on the same basis. The results of the UK Gas Distribution business were already treated as a discontinued operation for the year ended 31 March 2017 with certain true ups (relating to completion accounts) to the disposal of the controlling stake recorded within discontinued operations for the year ended 31 March 2018. The reclassification impacts the consolidated income statement, the consolidated statement of comprehensive income and 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 D. Foreign currencies Transactions in currencies other than the functional currency of the Company or subsidiary concerned are recorded at the rates of exchange prevailing on the dates of the transactions. At each reporting date, monetary assets and liabilities that are denominated in foreign currencies are retranslated at closing exchange rates. Non-monetary assets are not retranslated unless they are carried at fair value. Gains and losses arising on the retranslation of monetary assets and liabilities are included in the income statement, except where the application of hedge accounting requires inclusion in other comprehensive income (see note 32(e)). On consolidation, the assets and liabilities of operations that have a functional currency different from the Company’s functional currency of pounds sterling, principally our US operations that have a functional currency of US dollars, are translated at exchange rates prevailing at the reporting date. Income and expense items are translated at the average exchange rates for the period where these do not differ materially from rates at the date of the transaction. Exchange differences arising are recognised in other comprehensive income and transferred to the consolidated translation reserve within other equity reserves (see note 28). E. Areas of judgement and key sources of estimation uncertainty The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities, and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from these estimates. Information about such judgements and estimations is in the notes to the financial statements, and the key areas are summarised below. Areas of judgement that have the most significant effect on the amounts recognised in the financial statements are as follows: • Categorisation of certain items as exceptional items or remeasurements and the definition of adjusted earnings (see notes 5 and 8). In applying the Group’s exceptional items framework, we have considered a number of key matters, as detailed in note 5. • In addition, we have exercised our judgement in concluding that it is appropriate to classify our investment in and shareholder loan to Quadgas, along with the related Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) derivatives, as held for sale and as a discontinued operation, as detailed in note 10. Key sources of estimation uncertainty that have a significant risk of causing a material adjustment to the carrying amounts of assets and liabilities within the next financial year are as follows: • valuation of liabilities for pensions and other post-retirement benefits (see note 25); and • the cash flows applied in determining the environmental provisions (see note 26). In order to illustrate the impact that changes in assumptions could have on our results and financial position, we have included sensitivity analyses in note 35. F. Accounting policy choices IFRS provides certain options available within accounting standards. Choices we have made, and continue to make, include the following: • Presentational formats: we use the nature of expense method for our income statement and aggregate our statement of financial position to net assets and total equity. In the income statement, we present subtotals of total operating profit, profit before tax and profit after tax from continuing operations, together with additional subtotals excluding exceptional items and remeasurements as a result of the three columnar presentation described earlier. Exceptional items and remeasurements are presented in a separate column on the face of the income statement. • Financial instruments: we normally opt to apply hedge accounting in most circumstances where this is permitted (see note 32(e)). G. New IFRS accounting standards effective for the year ended 31 March 2019 The Group adopted IFRS 9 ‘Financial Instruments’ and IFRS 15 ‘Revenue from Contracts with Customers’ with effect from 1 April 2018. We have applied the modified retrospective approach permitted in the Standards whereby prior year comparatives have not been restated on adoption. Instead, the cumulative transition adjustments are reflected through reserves. Refer to note 37 for full details of the impact and transition adjustments arising on adoption. The Group has also adopted the following amendments to standards, which have had no material impact on the Group’s results or financial statement disclosure: • Annual improvements to IFRSs 2014-2016 Cycle; • Amendments to IFRS 2 ‘Share-based payment’; and • IFRIC 22 ‘Foreign Currency Transactions and Advance Consideration’. 1. Basis of preparation and recent accounting developments continued H. New IFRS accounting standards and interpretations not yet adopted The Group has considered the impact of the following new IFRS standards or interpretations that have not yet been adopted: i) IFRS 16 ‘Leases’ IFRS 16 ‘Leases’ is effective for National Grid for the year ending 31 March 2020. IFRS 16 introduces a single lease accounting model for lessees (rather than the current distinction between operating and finance leases). A contract is, or contains, a lease, if it provides the right to control the use of an identified asset for a specific period of time in exchange for consideration. The new standard will result in our operating leases being accounted for in the consolidated statement of financial position as ‘right-of-use’ assets with corresponding lease liabilities also recognised. It will therefore increase both our assets and liabilities (including net debt). In future periods, this will change the timing and presentation in the consolidated income statement as it will result in an increase in finance costs and depreciation largely offset by a reduction in the previously straight-line operating costs. Transition options We will apply IFRS 16 with effect from 1 April 2019 using the modified retrospective approach. Comparatives will not be restated on adoption. Instead, a cumulative adjustment to our opening consolidated statement of financial position will be reflected in retained earnings as well as recognition of the opening right-of-use assets and additional lease liabilities and associated deferred tax. For short‐term leases (lease term of 12 months or less) and leases of low‐value assets (such as computers), the Group will continue to recognise a lease expense on a straight‐line basis as permitted by IFRS 16. In preparing for the transition, we have elected to apply the practical expedient to grandfather our previous assessments of whether contracts were previously accounted for as a lease, as permitted by the standard, instead of reassessing all significant contracts as at the date of initial application to determine whether they met the IFRS 16 definition of a lease. We have elected to apply the practical expedient on transition, which permits right-of-use assets to be measured at an amount equal to the lease liability on adoption of the standard (adjusted for any prepaid or accrued lease expenses). In addition, we have also elected the option to adjust the carrying amounts of the right-of-use assets as at 1 April 2019 for onerous lease provisions that had been recognised on the Group consolidated statement of financial position as at 31 March 2019, rather than performing impairment assessments on transition. Impact of transition As at the reporting date, the Group has non-cancellable operating lease commitments of £0.3 billion (see note 30), of which the majority are in the US. A further £0.3 billion of lease liabilities is recognised due to the requirement in IFRS 16 to recognise lease liabilities for the term that we are reasonably certain to exercise lease extension or lease termination options for, rather than only for the period of the minimum contractual term that is used in determining our lease liability commitments. This is partially offset by the £0.2 billion impact of discounting our lease liabilities at the incremental borrowing rate for each lease. There are some immaterial short term and low value leases, which will be recognised on a straight-line basis as an expense in profit and loss over the remaining lease term. As a result, the Group expects to recognise additional right-of-use assets and lease liabilities (which are included within net debt) of approximately £0.4 billion at 1 April 2019 with no material additional net deferred tax. This is in addition to the £0.3 billion of finance leases already recognised on the consolidated statement of financial position under IAS 17. There will be no material net impact on net assets. Accordingly, the Group does not expect the impact of IFRS 16 on profit after tax as a result of adopting the new standard to be material. However, it will result in an increase in operating profit due to the operating costs now being replaced with depreciation and interest charges. We expect operating cash flows to increase and financing cash flows to decrease by less than £0.1 billion , because repayment of the principal portion of the lease liabilities will be classified as cash flows from financing activities rather than operating cash flows. ii) Other In addition, the following new accounting standards and amendments to existing standards have been issued but are not yet effective or have not yet been endorsed by the EU: • IFRIC 23 ‘Uncertainty over Income Tax Treatments’; • Amendments to IAS 28 ‘Investments in Associates – Long-term Interests in Associates and Joint Ventures’; • Annual Improvements to IFRS Standards 2015-2017 Cycle; • IFRS 17 ‘Insurance Contracts’; • Amendments to IAS 19 ‘Employee Benefits’; • Amendments to IFRS 3 ‘Business Combinations’; • Amendments to the References to the Conceptual Framework; and • Amendments to IAS 1 and IAS 8: Definition of material. Effective dates remain subject to the EU endorsement process. 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
Segmental analysis	Mar. 31, 2019
Operating Segments [Abstract]
Segmental analysis	Segmental analysis This note sets out the financial performance for the year split into the different parts of the business (operating segments). The performance of these operating segments is monitored and managed on a day-to-day basis. Revenue and the results of the business are analysed by operating segment, based on the information the Board of Directors uses internally for the purposes of evaluating the performance of each operating segment and determining resource allocation between them. The Board is National Grid’s chief operating decision maker (as defined by IFRS 8 ‘Operating Segments’) and assesses the profitability of operations principally on the basis of operating profit before exceptional items and remeasurements (see note 5). As a matter of course, the Board also considers profitability by segment, excluding the effect of timing. However, the measure of profit disclosed in this note is operating profit before exceptional items and remeasurements as this is the measure that is most consistent with the IFRS results reported within these financial statements. The results of our three principal businesses are reported to the Board of Directors and are 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 and Great Britain system operator. UK Gas Transmission The high-pressure gas transmission networks in Great Britain and system operator in Great Britain. US Regulated Gas distribution networks, electricity distribution networks and high-voltage electricity transmission networks in New York and New England and electricity generation facilities in New York. The National Grid Ventures (NGV) operating segment represents our key strategic growth area outside our regulated core business in competitive markets across the US and the UK. The business comprises all commercial operations in metering, LNG at the Isle of Grain in the UK and electricity interconnectors, with a focus on investment and future activities in emerging growth areas. NGV does not currently meet the thresholds set out in IFRS 8 to be identified as a separate reportable segment and therefore its results are not required to be separately presented. However, certain additional disclosure is included in the footnotes below. Other activities that do not form part of any of the segments in the above table or NGV primarily relate to our UK property business together with insurance and corporate activities in the UK and US and the Group’s investments in technology and innovation companies through National Grid Partners. The segmental information is presented in relation to continuing operations only and therefore does not include the profits and losses relating to our interest in Quadgas for 2018 and 2019 or those associated with the UK Gas Distribution business (see note 10). (a) Revenue Revenue primarily represents the sales value derived from the generation, transmission and distribution of energy, together with the sales value derived from the provision of other services to customers. Refer to note 3 for further details. Sales between operating segments are priced considering the regulatory and legal requirements to which the businesses are subject. The analysis of revenue by geographical area is on the basis of destination. There are no material sales between the UK and US geographical areas. 2019 2018 2017 Total £m Sales between segments £m Sales to third parties £m Total Sales Sales Total Sales Sales Operating segments – continuing operations: UK Electricity Transmission 3,351 (20 ) 3,331 4,154 (28) 4,126 4,439 (29) 4,410 UK Gas Transmission 896 (12 ) 884 1,091 (9) 1,082 1,080 (99) 981 US Regulated 9,846 — 9,846 9,272 — 9,272 8,931 — 8,931 NGV and Other 1 876 (4 ) 872 776 (6) 770 713 — 713 Total revenue from continuing operations 14,969 (36 ) 14,933 15,293 (43) 15,250 15,163 (128) 15,035 Split by geographical areas – continuing operations: UK 5,045 5,938 6,064 US 9,888 9,312 8,971 14,933 15,250 15,035 1. Included within NGV and Other is £597 million ( 2018 : £593 million ; 2017 : £604 million ) of revenue relating to NGV. 2. Segmental analysis continued (b) Operating profit A reconciliation of the operating segments’ measure of profit to profit before tax from continuing operations is provided below. Further details of the exceptional items and remeasurements are provided in note 5. Before exceptional items After exceptional items 2019 2018¹ 2017 2019 2018¹ 2017 £m £m £m £m £m £m Operating segments – continuing operations: UK Electricity Transmission 1,015 1,041 1,372 778 1,041 1,361 UK Gas Transmission 303 487 511 267 487 507 US Regulated 1,724 1,698 1,713 1,425 1,734 1,278 NGV and Other 2,3 400 231 177 400 231 62 Total operating profit from continuing operations 3,442 3,457 3,773 2,870 3,493 3,208 Split by geographical area – continuing operations: UK 1,695 1,840 2,118 1,422 1,840 1,988 US 1,747 1,617 1,655 1,448 1,653 1,220 3,442 3,457 3,773 2,870 3,493 3,208 Below we reconcile total operating profit from continuing operations to profit before tax from continuing operations. Operating exceptional items and remeasurements of £237 million charge ( 2018 : £nil ; 2017 : £11 million charge) detailed in note 5 are attributable to UK Electricity Transmission; £36 million charge ( 2018 : £nil ; 2017 : £4 million charge) to UK Gas Transmission; £299 million charge ( 2018 : £36 million gain; 2017 : £435 million charge) to US Regulated; and £nil ( 2018 : £nil ; 2017 : £115 million charge) to NGV and Other. Reconciliation to profit before tax: Operating profit from continuing operations 3,442 3,457 3,773 2,870 3,493 3,208 Finance income 73 127 53 88 127 53 Finance costs (1,066 ) (1,128 ) (1,082 ) (1,157 ) (1,009 ) (1,140 ) Share of post-tax results of joint ventures and associates 40 44 63 40 49 63 Profit before tax from continuing operations 2,489 2,500 2,807 1,841 2,660 2,184 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 2. Included within NGV and Other is £263 million ( 2018 : £234 million ; 2017 : £239 million ) of operating profit (both before and after exceptional items and remeasurements) relating to NGV. Also included in this balance for the year ended 31 March 2019 is £181 million (2018: £84 million ; 2017: £55 million ) of operating profit in relation to the Property business. 3. NGV and Other includes gains of £95 million (2018: £ nil ; 2017: £ nil ) in relation to cash received in respect of two legal settlements. (c) Capital expenditure Net book value of property, plant and Capital expenditure 1 Depreciation, amortisation and impairment 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Operating segments: UK Electricity Transmission 13,288 13,028 12,515 925 999 1,027 (628 ) (475 ) (421 ) UK Gas Transmission 4,412 4,280 4,165 308 310 214 (181 ) (194 ) (186 ) US Regulated 24,542 20,953 21,638 2,650 2,424 2,247 (700 ) (635 ) (642 ) NGV and Other 2 2,755 2,491 2,430 438 341 247 (226 ) (226 ) (232 ) Total from continuing operations 44,997 40,752 40,748 4,321 4,074 3,735 (1,735 ) (1,530 ) (1,481 ) Split by geographical area – continuing operations: UK 19,343 18,772 18,102 1,584 1,527 1,357 (931 ) (804 ) (753 ) US 25,654 21,980 22,646 2,737 2,547 2,378 (804 ) (726 ) (728 ) 44,997 40,752 40,748 4,321 4,074 3,735 (1,735 ) (1,530 ) (1,481 ) Asset type: Property, plant and equipment 43,913 39,853 39,825 4,015 3,901 3,507 (1,560 ) (1,392 ) (1,348 ) Non-current intangible assets 1,084 899 923 306 173 228 (175 ) (138 ) (133 ) Total from continuing operations 44,997 40,752 40,748 4,321 4,074 3,735 (1,735 ) (1,530 ) (1,481 ) 1. Represents additions to property, plant and equipment and non-current intangibles but excludes additional investments in and loans to joint ventures and associates. 2. Included within NGV and Other are assets with a net book value of £1,635 million ( 2018 : £1,454 million ; 2017 : £1,432 million ), capital expenditure of £317 million ( 2018 : £186 million ; 2017 : £98 million ) and depreciation, amortisation and impairment of £114 million ( 2018 : £143 million ; 2017 : £143 million ) relating to NGV. Total non-current assets other than financial instruments and pension assets located in the UK and US were £30,072 million and £21,787 million respectively as at 31 March 2019 ( 31 March 2018 : UK £20,816 million , US £27,663 million ; 31 March 2017 : UK £20,045 million , US £28,951 million ).

Revenue

Revenue	12 Months Ended
Revenue	Mar. 31, 2019
Disclosure of revenue from contracts with customers [Abstract]
Revenue	Revenue Revenue arises in the course of the ordinary activities and principally comprises: • transmission services; • distribution services; and • generation services. Transmission services, distribution services and certain other services (excluding rental income but including metering) fall within the scope of IFRS 15 ‘Revenue from Contracts with Customers’, whereas generation services are accounted for under the leasing standard as rental income, presented within revenue. Revenue is measured based on the consideration specified in a contract with a customer and excludes amounts collected on behalf of third parties and value added tax. The Group recognises revenue when it transfers control over a product or service to a customer. IFRS 15 was effective from 1 April 2018. As explained in note 37, the standard has been applied prospectively and therefore the analysis below is only provided for the current period. The impact of adoption on the opening consolidated statement of financial position and reserves is disclosed in note 37, with the main change to profit being in relation to customer connection income in the UK Electricity Transmission and US Regulated businesses. Note 37 includes the quantification of the impact for the year if revenue were still to have been accounted for under IAS 18, which arises from a change in the recognition of receipts from other UK network owners (and has no impact on profit). The following is a description of principal activities, by reportable segment, from which the Group generates its revenue. For more detailed information about our segments, see note 2. (a) UK Electricity Transmission The UK Electricity Transmission segment principally generates revenue by providing electricity transmission services (both as transmission owner in England and Wales and system operator in Great Britain). Our business operates as a monopoly regulated by Ofgem, which has established price control mechanisms that set the amount of annual allowed returns our business can earn. The IFRS revenues we record are principally a function of volumes and price. Price is determined prior to our financial year end with reference to the regulated allowed returns and estimated annual volumes. Where revenue received or receivable exceeds the maximum amount permitted by regulatory agreement, adjustments will be made to future prices to reflect this over-recovery. No liability is recognised, as such an adjustment to future prices relates to the provision of future services. Similarly no asset is recognised where a regulatory agreement permits adjustments to be made to future prices in respect of an under-recovery. As part of our regulatory agreements we are entitled to recover certain costs directly from customers (pass-through costs). These amounts are included in the overall calculation of allowed revenue as stipulated by regulatory agreements. The transmission of high-voltage electricity encompasses the following principal services: • the supply of high-voltage electricity (including both transmission and system operator charges); and • construction work (principally for connections). For the supply of high-voltage electricity, revenue is recognised based on capacity and volumes. Our performance obligation is satisfied over time as our customers make use of our network. We bill monthly in arrears and our payment terms are up to 60 days. For construction work relating to connections, customers can either pay over the useful life of the connection or upfront. Revenue is recognised over time, as we provide access to our network, and where the customer pays upfront, revenues are deferred and released over the life of the connection. For other construction where there is no consideration for any future services, for example diversions (being the re-routing of network assets at our customers’ request), revenues are recognised as the construction work is completed. (b) UK Gas Transmission The UK Gas Transmission segment of the Group principally generates revenue by providing gas transmission services to our customers (both as transmission owner and as system operator) in Great Britain. Similar to our UK Electricity Transmission business, our business operates as a monopoly regulated by Ofgem. The price control mechanism in place that determines our annual allowances is also similar, as is the way in which revenue is recorded. The transmission of gas encompasses the following principal services: • the supply of high-pressure gas (including both transmission and system operator charges); and • construction work (principally for connections). For the supply of high-pressure gas, revenue is recognised based on capacity and volumes. Our performance obligation is satisfied over time as our customers make use of our network, and we bill monthly in arrears with payment terms of up to 45 days. For construction work relating to connections, customers pay for the connection upfront. Revenue is recognised over time, as we provide access to our network. Where revenues are received upfront, they are deferred and released over the life of the connection. For other construction where there is no consideration for any future services (such as diversions), revenues are recognised when the construction work is completed. 3. Revenue continued (c) US Regulated The US Regulated segments of the Group principally generate revenue by providing gas and electricity distribution services in New York and New England, high voltage electricity transmission services in New York and New England, and electricity generation in New York. Distribution services Provision of gas and electric distribution services in New York and New England. This comprises the following principal services: • Gas and electricity distribution: revenue is recognised based on usage (over time) by customers and billed monthly. Payment terms are 30 days; and • Connections: revenue is recognised over time, as we provide access to our network. Where payments are made upfront, they are deferred over the life of the asset. Transmission services Provision of electricity transmission services to customers and operation of electricity transmission facilities. Our principal services are: • Electricity transmission: revenue is recognised based on usage by customers (over time) and billed monthly. Payment terms are 30 days; and • Connections: revenue is recognised over time, as we provide access to our network. Where payments are made upfront, they are deferred over the life of the asset. Electricity generation Provision of energy services and supply capacity to produce energy for the use of customers of the Long Island Power Authority (LIPA) through a power supply agreement. This falls within the scope of the leasing standard, where we act as lessor with rental income being recorded as other income, which forms part of total revenue. (d) NGV and Other NGV and Other includes electricity interconnectors, LNG at Grain, commercial metering, property sales and rental income, and insurance. The Group recognises revenue from transmission services through interconnectors and from LNG at Grain by means of customers’ use of capacity and volumes. Revenue is recognised over time and is billed monthly. Payment terms are 30 days. Other revenue in the scope of IFRS 15 principally includes revenues from our metering businesses. Revenue is recognised over time and is billed monthly. Payment terms are 30 days. Other revenue, recognised in accordance with standards other than IFRS 15, includes property sales by our UK commercial property business and rental income. Property sales are recorded at a point in time (when the sale is legally completed) and rental income is recorded over time. In the following tables, revenue is disaggregated by primary geographical market and major service lines. The table reconciles disaggregated revenue with the Group’s reportable segments (see note 2). Revenue for the year ended 31 March 2019 UK Electricity Transmission UK Gas Transmission US Regulated NGV and Other Total Revenue under IFRS 15 Transmission 3,325 833 370 313 4,841 Distribution — — 8,941 — 8,941 Other — — — 284 284 Total IFRS 15 revenue 3,325 833 9,311 597 14,066 Other revenue Generation — — 367 — 367 Other 6 51 168 275 500 Total other revenue 6 51 535 275 867 Total revenue from continuing operations 3,331 884 9,846 872 14,933 Geographical split for the year ended 31 March 2019 UK Electricity Transmission £m UK Gas Transmission £m US Regulated £m NGV and Other £m Total £m Revenue under IFRS 15 UK 3,325 833 — 585 4,743 US — — 9,311 12 9,323 Total IFRS 15 revenue 3,325 833 9,311 597 14,066 Other revenue UK 6 51 — 245 302 US — — 535 30 565 Total other revenue 6 51 535 275 867 Total revenue from continuing operations 3,331 884 9,846 872 14,933 Revenue to be recognised in future periods, presented as contract liabilities of £994 million (see note 23), relates to contributions in aid of construction. Revenue is recognised over the life of the asset. The asset lives for connections in UK Electricity Transmission, UK Gas Transmission and US Regulated are 40 years, 36 years (to 2055), and up to 47 years respectively. The weighted average amortisation period is 43 years. Future revenues in relation to unfulfilled performance obligations not yet received in cash amount to £3.5 billion . £1.6 billion relates to connection contracts in UK Electricity Transmission which will be recognised as revenue over 30 years and £1.8 billion relates to revenues to be earned under LNG at Grain contracts over 11 years. The remaining amount will be recognised as revenue over 5 years. The amount of revenue recognised for the year ended 31 March 2019 from performance obligations satisfied (or partially satisfied) in previous periods, mainly due to the changes in the estimate of the stage of completion, is £ nil .

Operating costs

Operating costs	12 Months Ended
Operating costs	Mar. 31, 2019
Analysis of income and expense [abstract]
Operating costs	Operating costs Below we have presented separately certain items included in our operating costs from continuing operations. These include a breakdown of payroll costs (including disclosure of amounts paid to key management personnel) and fees paid to our auditors. Rentals under operating leases are charged to the income statement on a straight-line basis over the term of the relevant lease. Before exceptional items and remeasurements Exceptional items and remeasurements Total 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Depreciation, amortisation and impairment 1,588 1,530 1,481 147 — — 1,735 1,530 1,481 Payroll costs 1,703 1,648 1,578 149 — — 1,852 1,648 1,578 Purchases of electricity 1,504 1,299 1,143 (50 ) (14 ) (46 ) 1,454 1,285 1,097 Purchases of gas 1,644 1,539 1,241 (2 ) 4 (22 ) 1,642 1,543 1,219 Rates and property taxes 1,108 1,057 1,042 — — — 1,108 1,057 1,042 Balancing Services Incentive Scheme 1,196 1,012 1,120 — — — 1,196 1,012 1,120 Payments to other UK network owners 1 — 1,043 1,008 — — — — 1,043 1,008 Other 2,748 2,665 2,649 328 (26 ) 633 3,076 2,639 3,282 11,491 11,793 11,262 572 (36 ) 565 12,063 11,757 11,827 Operating costs include: Inventory consumed 415 367 296 Operating leases 2 46 51 43 Research and development expenditure 19 13 14 1. Under IFRS 15, for 2019 revenue and associated payments to other UK network owners are presented on a net basis. Refer to note 37. 2. Following a review during the year, the comparatives have been refined to provide consistency with the current year. (a) Payroll costs 2019 2018 2017 £m £m £m Wages and salaries 1 2,084 1,998 1,852 Social security costs 156 157 145 Defined contribution scheme costs 72 65 58 Defined benefit pension costs 232 156 151 Share-based payments 27 16 32 Severance costs (excluding pension costs) 76 7 5 2,647 2,399 2,243 Less: payroll costs capitalised (795 ) (751 ) (665 ) Total payroll costs 1,852 1,648 1,578 1. Included within wages and salaries are US other post-retirement benefit costs of £48 million ( 2018 : £46 million ; 2017 : £53 million ). For further information refer to note 25. (b) Number of employees 31 March Monthly 31 March Monthly 31 March Monthly UK 5,962 6,227 6,517 6,431 6,265 6,291 US 16,614 16,669 16,506 16,274 15,867 15,752 Total number of employees 22,576 22,896 23,023 22,705 22,132 22,043 4. Operating costs continued (c) Key management compensation 2019 2018 2017 £m £m £m Short-term employee benefits 7 8 8 Post-employment benefits 1 1 1 Share-based payments 3 3 6 Total key management compensation 11 12 15 Key management compensation relates to the Board, including the Executive Directors and Non-executive Directors for the years presented. (d) Directors’ emoluments Details of Executive Directors’ emoluments are contained in the Remuneration Report on page 79 and those of Non-executive Directors on page 84. (e) Auditors’ remuneration Auditors’ remuneration is presented below in accordance with the requirements of the Companies Act 2006 and the principal accountant fees and services disclosure requirements of Item 16C of Form 20-F: 2019 2018 2017 £m £m £m Audit fees payable to the Parent Company’s auditors and their associates in respect of: 1 Audit of the Parent Company’s individual and consolidated financial statements 2 1.6 2.7 1.5 The auditing of accounts of any associate of the Company 3 7.2 9.3 13.7 Other services supplied 4 5.2 3.9 4.6 14.0 15.9 19.8 Total other services 5 Tax fees: Tax compliance services — 0.3 0.4 Tax advisory services — — 0.1 All other fees: Other assurance services 6 1.1 0.7 4.6 Services relating to corporate finance transactions not covered above 7 — — 5.9 Other non-audit services not covered above 8 2.2 0.9 6.3 3.3 1.9 17.3 Total auditors’ remuneration 17.3 17.8 37.1 1. Deloitte LLP became the Group’s principal auditor for the year ended 31 March 2018. PricewaterhouseCoopers LLP (PwC) was the principal auditor for the year ended 31 March 2017 . 2. Audit fees in each year represent fees for the audit of the Company’s financial statements and regulatory reporting for the years ended 31 March 2019 , 2018 and 2017 . 3. The 2018 comparative has been updated following finalisation of the 2018 audit fee with the Audit Committee. 4. Other services supplied represent fees payable for services in relation to other statutory filings or engagements that are required to be carried out by the auditors. In particular, this includes fees for reports under section 404 of the US Public Company Accounting Reform and Investor Protection Act of 2002 (Sarbanes-Oxley), audit reports on regulatory returns and the review of interim financial statements for the six-month periods ended 30 September 2018, 2017 and 2016 respectively. 5. There were no audit related fees as described in Item 16C(b) of Form 20-F. 6. Principally amounts relating to assurance services provided in relation to comfort letters for debt issuances. In 2017, amounts represented assurance services undertaken by PwC in relation to the sale of UK Gas Distribution and data assurance work in respect of financial information included in US rate filings. 7. Vendor due diligence and other transaction services in relation to the sale of UK Gas Distribution. 8. Fees for other non-audit services – projects including services provided to the UK Property business, relating to evaluating possible options for the use of property assets. In 2017, services related principally to PwC assisting the Company with separation activities in relation to the sale of UK Gas Distribution. The Audit Committee considers and makes recommendations to the Board, to be put to shareholders for approval at each AGM, in relation to the appointment, re-appointment, removal and oversight of the Company’s independent auditors. The Committee also considers and approves the audit fees on behalf of the Board in accordance with the Competition and Market Authority Audit Order 2014. The auditors’ remuneration is then put to shareholders at each AGM. Details of our policies and procedures in relation to non-audit services to be provided by the independent auditors are set out on page 62 of the Corporate Governance Report. Certain services are prohibited from being performed by the external auditors under the Sarbanes-Oxley Act. Of the above services, none were prohibited.

Exceptional items and remeasure

Exceptional items and remeasurements	12 Months Ended
Exceptional items and remeasurements	Mar. 31, 2019
Exceptional Items And Remeasurements [Abstract]
Exceptional items and remeasurements	Exceptional items and remeasurements To monitor our financial performance, we use a profit measure that excludes certain income and expenses. We call that measure ‘business performance’ or ‘adjusted profit’. Business performance (which excludes exceptional items and remeasurements as defined below) is used by management to monitor financial performance as it is considered that it aids the comparability of our reported financial performance from year to year. We exclude items from business performance because, if included, these items could distort understanding of our performance for the year and the comparability between periods. This note analyses these items, which are included in our results for the year but are excluded from business performance. Exceptional items and remeasurements from continuing operations 2019 2018¹ 2017 £m £m £m Included within operating profit Exceptional items: Cost efficiency and restructuring programmes (204 ) — — Massachusetts Gas labour dispute (283 ) — — Impairment of nuclear connection development costs (137 ) — — Final settlement of LIPA MSA Transition — 26 — Environmental charges — — (526 ) Gas holder demolition costs — — (107 ) (624 ) 26 (633 ) Remeasurements – commodity contract derivatives 52 10 68 (572 ) 36 (565 ) Included within finance income and costs Remeasurements: Net (losses)/gains on derivative financial instruments (40 ) 119 (58 ) Net gains on financial assets at fair value through profit and loss 15 — — Net losses on financial liabilities at fair value through profit and loss (51 ) — — (76 ) 119 (58 ) Included within share of post-tax results of joint ventures and associates Deferred tax arising on the reduction in US corporation tax rate — 5 — Total included within profit before tax (648 ) 160 (623 ) Included within tax Exceptional items – credits arising on items not included in profit before tax: Deferred tax arising on the reduction in the UK corporation tax rate — — 94 Deferred tax arising on the reduction in the US corporation tax rate — 1,510 — Tax on exceptional items 144 (9 ) 227 Tax on remeasurements 5 (28 ) (29 ) 149 1,473 292 Total exceptional items and remeasurements after tax (499 ) 1,633 (331 ) Analysis of total exceptional items and remeasurements after tax Exceptional items after tax (480 ) 1,532 (312 ) Remeasurements after tax (19 ) 101 (19 ) Total exceptional items and remeasurements after tax (499 ) 1,633 (331 ) 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 5. Exceptional items and remeasurements continued Exceptional items Management uses an exceptional items framework that has been discussed and approved by the Audit Committee. This follows a three-step process which considers the nature of the event, the financial materiality involved and any particular facts and circumstances. In considering the nature of the event, management focuses on whether the event is within the Group’s control and how frequently such an event typically occurs. In determining the facts and circumstances, management considers factors such as ensuring consistent treatment between favourable and unfavourable transactions, the precedent for similar items, the number of periods over which costs will be spread or gains earned, and the commercial context for the particular transaction. Items of income or expense that are considered by management for designation as exceptional items include significant restructurings, write-downs or impairments of non-current assets, significant changes in environmental or decommissioning provisions, integration of acquired businesses, gains or losses on disposals of businesses or investments and significant debt redemption costs as a consequence of transactions such as significant disposals or issues of equity, and the related tax as well as deferred tax arising on changes to corporation tax rates. Costs arising from restructuring programmes include redundancy costs. Redundancy costs are charged to the consolidated income statement in the year in which a commitment is made to incur the costs and the main features of the restructuring plan have been announced to affected employees. 2019 In assessing certain items of income and expenditure against our exceptional items framework, we have concluded that the costs associated with the Massachusetts Gas labour dispute ( £283 million ), our cost efficiency and restructuring programme ( £204 million ) and impairments relating to two nuclear connection cancellations ( £137 million ) should be treated as exceptional (as described further below). We also considered whether the £95 million income from two legal settlements received in the period should be classified as exceptional. However, we concluded it was appropriate to recognise the income in earnings before exceptional items (within NGV and Other), in line with the treatment of the original costs. Cost efficiency and restructuring programmes: Our UK and US businesses incurred restructuring charges as we reviewed organisational structures, operational activities and relevant roles and responsibilities to ensure we are able to operate more efficiently and to continue to drive outperformance for customers and shareholders. In the UK these reviews were largely completed during the first half of the year, and we reported a £127 million exceptional charge at 30 September 2018, reflecting £100 million in severance and associated planning and support costs. A net charge of £52 million relating to pension costs is recognised within this amount. No significant additional operational costs have been incurred in the UK since 30 September 2018; however, during the second half of the year we commenced an equivalent programme for our US core business, which has resulted in a charge of £68 million , relating to severance and lease terminations following a decision to exit certain of our properties in New York City. The cash outflow for the year was £93 million . Massachusetts Gas labour dispute: On 25 June 2018, National Grid implemented a workforce contingency plan across its Massachusetts Gas business following the expiration of contracts for the 1,250 members of the existing workforce. In early January 2019 we reached agreement with the two unions over employment terms and conditions, with affected staff members returning to work in late January 2019. Throughout the duration of the labour dispute, we employed experienced contractors alongside supervisors and workers from other areas of our business to ensure work continued safely, and external contractor activity returned to normal levels in February 2019. In presenting this year’s financial statements, we have excluded the net incremental cost of £283 million on the basis that this ensures adjusted earnings presents a clear view of the financial performance of the US regulated business had the workforce contingency plan not been implemented. The total cash outflow related to the labour dispute was £320 million for the year. Impairment of nuclear connection development costs: In November 2018, Toshiba announced the cancellation of its NuGen project to build a new nuclear power station at Moorside in Cumbria, and on 23 November 2018, NuGen terminated its connection agreement with UK Electricity Transmission. On 15 February 2019, Hitachi terminated its connection agreements in respect of its Horizon projects at Wylfa and Oldbury. As there is no realistic prospect of these schemes continuing in their present form, we have concluded that it is appropriate to impair the assets we had been developing for over 10 years. After deducting cash inflows relating to termination fees received of £13 million , the net impairment charge was £137 million . 2018 During the year, the Group reached an agreement with LIPA on an amount in final settlement of receivables and payables that arose following the cessation of the Management Services Agreement with LIPA in December 2013. The settlement resulted in a gain of £26 million , which has been recorded as exceptional, consistent with the treatment of gains and losses on the original transaction. 2017 In the US, the Group’s most significant environmental liabilities relate to former manufactured gas plant (MGP) facilities formerly owned or operated by the Group. The sites are subject to both state and federal law in the US. Environmental reserves are re-evaluated at each reporting period. The expenditure is expected to be largely recoverable from rate payers but, under IFRS, no asset can be recorded for this. During 2017, the Group updated its assessment of the gross remediation costs at three key sites in New York, resulting in an increase of £481 million on an undiscounted basis. The charge booked reflects the Group’s best estimate of future cash outflow, based on notices received from state and federal authorities, and plans developed in response, supported by external consultants where appropriate. In some cases, judgement is also required regarding the Group’s share of the estimated cost, principally at sites where other parties are also potentially liable but where no cost sharing agreement exists. Also included within the above are charges relating to the impact of a change in the real discount rate from 2% to 1% on our provisions. A provision of £107 million was made for the demolition of certain non-operational gas holders in the UK. Following the disposal of UK Gas Distribution, the land on which the gas holders are sited was transferred to the Group’s UK property division. The Group’s property division maximises our return from our land portfolio and therefore a constructive obligation exists to demolish the gas holders. 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). Consistent with prior periods, in the current period these assets and liabilities include commodity contract derivatives and financial derivative instruments to the extent that hedge accounting is not achieved or is not effective. Following the adoption of IFRS 9 in the current period, this year we have also classified the unrealised gains or losses reported in profit and loss on certain additional assets and liabilities now treated at FVTPL within remeasurements. These relate to the financial assets (which fail the 'solely payments of principal and interest test' under IFRS 9), the money market fund investments used by Group Treasury for cash management purposes and certain financial liabilities which we elected to designate at FVTPL on transition. In all cases, these fair values increase or decrease because of changes in foreign exchange, commodity or other financial indices over which we have no control. We report unrealised gains or losses relating to certain discrete classes of financial assets accounted for at FVTPL within business performance. These comprise our portfolio of investments made by National Grid Partners, and our investment in Sunrun Neptune 2016 LLC (within NGV and Other). The performance of these assets (including changes in fair value) are included in our assessment of business performance for the relevant business units. Remeasurements excluded from business performance are made up of the following categories: i. Net gains/(losses) on commodity contract derivatives represent mark-to-market movements on certain physical and financial commodity contract obligations in the US. These contracts primarily relate to the forward purchase of energy for supply to customers, or to the economic hedging thereof, that are required to be measured at fair value and that do not qualify for hedge accounting. Under the existing rate plans in the US, commodity costs are recoverable from customers although the timing of recovery may differ from the pattern of costs incurred. ii. Net gains/(losses) on derivative financial instruments comprise gains/(losses) arising on derivative financial instruments reported in the consolidated income statement in relation to our debt financing and foreign exchange hedging of the investment funds held by our insurance captives. These exclude gains and losses for which hedge accounting has been effective, and have been recognised directly in the consolidated statement of other comprehensive income or are offset by adjustments to the carrying value of debt (see notes 17 and 32). iii. Net gains/(losses) on financial assets measured at FVTPL comprise gains/(losses) on the investment funds held by our insurance captives which are categorised as FVTPL (see note 15). iv. Net gains/(losses) on financial liabilities measured at FVTPL comprises the change in the fair value (excluding changes due to own credit risk) of a financial liability that has been designated at FVTPL on transition to IFRS 9 to reduce a measurement mismatch (see note 21). Items included within tax 2018 The Tax Cuts and Jobs Act (Tax Reform), which was enacted on 22 December 2017, reduced the US corporate tax rate from 35% to 21% with effect from 1 January 2018. Deferred taxes at the reporting date have been measured using these enacted tax rates. This resulted in a one-off deferred tax credit in the year ended 31 March 2018. However, as described in note 11, we expect the overall impact of Tax Reform to be economically neutral for the Group. 2017 The Finance Act 2016, which was enacted on 15 September 2016, reduced the main rate of UK corporation tax to 17% with effect from 1 April 2020. Deferred tax balances have been calculated at this rate for the years ended 31 March 2019 and 31 March 2018.

Finance income and costs

Finance income and costs	12 Months Ended
Finance income and costs	Mar. 31, 2019
Analysis of income and expense [abstract]
Finance income and costs	Finance income and costs This note details the interest income generated by our financial assets and interest expense incurred on our financial liabilities, primarily our financing portfolio (including our financing derivatives). It also includes the net interest on our pensions and other post-retirement assets. In reporting business performance, we adjust net financing costs to exclude any net gains or losses on financial instruments included in remeasurements (see note 5). In addition, where debt redemptions relate to exceptional transactions they are typically treated as exceptional. The Group adopted IFRS 9 with effect from 1 April 2018. The comparatives are not required to be restated and are accounted for in accordance with IAS 39. Following the adoption of IFRS 9, finance income and costs remeasurements include unrealised gains and losses on certain assets and liabilities now treated at FVTPL. The interest income, dividends and interest expense on these items are included in finance income and finance costs before remeasurements, respectively. 2019 2018¹ 2017 Notes £m £m £m Finance income Interest income on financial instruments: Bank deposits and other financial assets 54 54 28 Dividends received on equities held at fair value through other comprehensive income 2 — — Gains on disposal of available-for-sale investments — 73 25 Other income 17 — — 73 127 53 Finance costs Net interest on pensions and other post-retirement benefit obligations 25 (22 ) (65 ) (107 ) Interest expense on financial liabilities held at amortised cost: Bank loans and overdrafts (72 ) (87 ) (59 ) Other borrowings (970 ) (1,030 ) (927 ) Interest expense on financial liabilities held at fair value through profit and loss (20 ) — — Derivatives (43 ) 12 (8 ) Unwinding of discount on provisions 26 (74 ) (75 ) (73 ) Other interest — (11 ) (17 ) Less: interest capitalised 2 135 128 109 (1,066 ) (1,128 ) (1,082 ) Remeasurements – Finance income Net gains on financial assets held at fair value through profit and loss 15 — — 15 — — Remeasurements – Finance costs Net losses on financial liabilities held at fair value through profit and loss (51 ) — — Net (losses)/gains on derivative financial instruments 3 : Derivatives designated as hedges for hedge accounting (37 ) 49 81 Derivatives not designated as hedges for hedge accounting (3 ) 70 (139 ) (91 ) 119 (58 ) Total remeasurements – Finance income and costs (76 ) 119 (58 ) Finance income 88 127 53 Finance costs (1,157 ) (1,009 ) (1,140 ) Net finance costs from continuing operations (1,069 ) (882 ) (1,087 ) 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 2. Interest on funding attributable to assets in the course of construction in the current year was capitalised at a rate of 3.9% ( 2018 : 4.1% ; 2017 : 3.4% ). In the UK, capitalised interest qualifies for a current year tax deduction with tax relief claimed of £19 million ( 2018 : £20 million ; 2017 : £18 million ). In the US, capitalised interest is added to the cost of plant and qualifies for tax depreciation allowances. 3. Includes a net foreign exchange gain on financing activities of £264 million ( 2018 : £314 million loss; 2017 : £264 million loss) offset by foreign exchange losses and gains on derivative financial instruments measured at fair value.

Tax

Tax	12 Months Ended
Tax	Mar. 31, 2019
Income Taxes [Abstract]
Tax	Tax Tax is payable in the territories where we operate, mainly the UK and the US. This note gives further details of the total tax charge and tax liabilities, including current and deferred tax. The current tax charge is the tax payable on this year’s taxable profits. Deferred tax is an accounting adjustment to provide for tax that is expected to arise in the future due to differences in the accounting and tax bases. The tax charge for the period is recognised in the income statement, the statement of comprehensive income or directly in equity, according to the accounting treatment of the related transaction. The tax charge comprises both current and deferred tax. Current tax assets and liabilities are measured at the amounts expected to be recovered from or paid to the tax authorities. The tax rates and tax laws used to compute the amounts are those that have been enacted or substantively enacted by the reporting date. The Group operates internationally in territories with different and complex tax codes. Management exercises judgement in relation to the level of provision required for uncertain tax outcomes. There are a number of tax positions not yet agreed with the tax authorities where different interpretations of legislation could lead to a range of outcomes. Judgements are made for each position having regard to particular circumstances and advice obtained. Deferred tax is provided for using the balance sheet liability method, and is recognised on temporary differences between the carrying amount of assets and liabilities in the financial statements and the corresponding tax bases. Deferred tax liabilities are generally recognised on all taxable temporary differences, and deferred tax assets are recognised to the extent that it is probable that taxable profits will be available against which deductible temporary differences can be utilised. However, deferred tax assets and liabilities are not recognised if the temporary differences arise from the initial recognition of goodwill or from the initial recognition of other assets and liabilities in a transaction (other than a business combination) that affects neither the accounting nor the taxable profit or loss. Deferred tax liabilities are recognised on taxable temporary differences arising on investments in subsidiaries and joint arrangements except where the Company is able to control the reversal of the temporary difference and it is probable that the temporary difference will not reverse in the foreseeable future. Deferred tax is calculated at the tax rates that are expected to apply in the period when the liability is settled or the asset is realised, based on the tax rates and tax laws that have been enacted or substantively enacted by the reporting date. The carrying amount of deferred tax assets is reviewed at each reporting date and reduced to the extent that it is no longer probable that sufficient taxable profits will be available to allow all or part of the deferred tax asset to be recovered. Unrecognised deferred tax assets are reassessed at each reporting date and are recognised to the extent that it has become probable that future taxable profits will allow the deferred tax asset to be recovered. Deferred tax assets and liabilities are offset when there is a legally enforceable right to offset current tax assets against current tax liabilities and when they relate to income taxes levied by the same tax authority and the Company and its subsidiaries intend to settle their current tax assets and liabilities on a net basis. Tax charged/(credited) to the consolidated income statement – continuing operations 2019 2018¹ 2017 £m £m £m Tax before exceptional items and remeasurements 488 584 666 Exceptional tax on items not included in profit before tax (see note 5) — (1,510 ) (94 ) Tax on other exceptional items and remeasurements (149 ) 37 (198 ) Tax on total exceptional items and remeasurements (149 ) (1,473 ) (292 ) Total tax charge/(credit) from continuing operations 339 (889 ) 374 Tax as a percentage of profit before tax 2019 2018¹ 2017 % % % Before exceptional items and remeasurements – continuing operations 19.6 23.4 23.7 After exceptional items and remeasurements – continuing operations 18.4 (33.4 ) 17.1 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 7. Tax continued The tax charge for the year can be analysed as follows: 2019 2018¹ 2017 £m £m £m Current tax: UK corporation tax at 19% (2018: 19%; 2017: 20%) 132 200 225 UK corporation tax adjustment in respect of prior years (12 ) (18 ) (47 ) 120 182 178 Overseas corporation tax 8 15 — Overseas corporation tax adjustment in respect of prior years (40 ) (4 ) 1 (32 ) 11 1 Total current tax from continuing operations 88 193 179 Deferred tax: UK deferred tax 27 65 (9 ) UK deferred tax adjustment in respect of prior years 2 (2 ) (18 ) 29 63 (27 ) Overseas deferred tax 208 (1,155 ) 224 Overseas deferred tax adjustment in respect of prior years 14 10 (2 ) 222 (1,145 ) 222 Total deferred tax from continuing operations 251 (1,082 ) 195 Total tax charge/(credit) from continuing operations 339 (889 ) 374 Tax charged/(credited) to the consolidated statement of other comprehensive income and equity 2019 2018¹ 2017 £m £m £m Current tax: Available-for-sale investments — (11 ) 6 Investments at fair value through other comprehensive income — — — Cash flow hedges, Cost of hedging and Own credit reserve 3 — — Share-based payments — (3 ) (4 ) Deferred tax: Available-for-sale investments — (18 ) 8 Investments at fair value through other comprehensive income — — — Cash flow hedges, Cost of hedging and Own credit reserve (12 ) (4 ) 20 Remeasurements of gains of pension assets and post-retirement benefit obligations 2 12 530 277 Share-based payments — 1 1 3 495 308 Total tax recognised in the statements of comprehensive income from continuing operations 3 497 311 Total tax recognised in the statements of comprehensive income from discontinued operations — — 10 Total tax relating to share-based payments recognised directly in equity from continuing operations — (2 ) (3 ) Total tax relating to share-based payments recognised directly in equity from discontinued operations — — — 3 495 318 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 2. Remeasurements of gains on pension assets and post-retirement benefit obligations for the year ended 31 March 2018 includes a deferred tax charge of £281 million arising on the reduction in the US corporation tax rate. 7. Tax continued The tax charge for the year after exceptional items and remeasurements, for the continuing business, is lower ( 2018 : lower tax charge; 2017 : lower tax charge) than the standard rate of corporation tax in the UK of 19% ( 2018 : 19% ; 2017 : 20% ): Before exceptional items and remeasurements After exceptional items and remeasurements Before exceptional items and remeasurements After exceptional items and remeasurements Before exceptional items and remeasurements After exceptional items and remeasurements 2019 2019 2018 2018 2017 2017 £m £m £m £m £m £m Profit before tax from continuing operations Before exceptional items and remeasurements 2,489 2,489 2,500 2,500 2,807 2,807 Exceptional items and remeasurements — (648 ) — 160 — (623 ) Profit before tax from continuing operations 2,489 1,841 2,500 2,660 2,807 2,184 Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2018: 19%; 2017: 20%) 473 350 475 506 561 437 Effect of: Adjustments in respect of prior years 1 (36 ) (36 ) (22 ) (14 ) (67 ) (67 ) Expenses not deductible for tax purposes 2 22 28 20 21 35 442 Non-taxable income 2,3 (36 ) (36 ) (16 ) (26 ) (24 ) (425 ) Adjustment in respect of foreign tax rates 78 56 153 157 180 104 Deferred tax impact of change in UK tax rate (3 ) (3 ) (7 ) (7 ) — (94 ) Deferred tax impact of change in US tax rate due to Tax Reform — — — (1,510 ) — — Other 4 (10 ) (20 ) (19 ) (16 ) (19 ) (23 ) Total tax charge/(credit) from continuing operations 488 339 584 (889 ) 666 374 % % % % % % Effective tax rate – continuing operations 19.6 18.4 23.4 (33.4 ) 23.7 17.1 1. Prior year adjustment is primarily due to agreement of prior period tax returns. 2. For the year ended 31 March 2017, the adjustments after exceptional items and remeasurements primarily represent the impact of the Group’s net investment hedging following significant US dollar currency fluctuations. 3. Includes gains on chargeable disposals which are offset by previously unrecognised capital losses. 4. Other primarily comprises an adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax from continuing operations. Factors that may affect future tax charges The main rate of UK corporation tax is reduced to 17% with effect from 1 April 2020. Deferred tax balances have been calculated at this rate. We will continue to monitor the developments driven by Brexit, the OECD’s Base Erosion and Profit Shifting (BEPS) project and European Commission initiatives including fiscal aid investigations. At this time we do not expect this to have any material impact on our future tax charges. 7. Tax continued Tax included within the statement of financial position The following are the major deferred tax assets and liabilities recognised, and the movements thereon, during the current and prior reporting periods: Accelerated Share- Pensions Financial Other net differences 1 £m Total Deferred tax liabilities/(assets) At 1 April 2017 7,074 (12 ) (747 ) 9 (1,845 ) 4,479 Exchange adjustments and other² (559 ) — 69 1 221 (268 ) (Credited)/charged to income statement (1,641 ) 2 (55 ) 12 598 (1,084 ) Charged/(credited) to other comprehensive income and equity — 1 530 (1 ) (21 ) 509 At 31 March 2018 (as previously reported) 4,874 (9 ) (203 ) 21 (1,047 ) 3,636 Impact of transition to IFRS 9 and IFRS 15 19 — — (5 ) (93 ) (79 ) At 1 April 2018 (as restated) 4,893 (9 ) (203 ) 16 (1,140 ) 3,557 Exchange adjustments and other² 275 — (31 ) (3 ) (76 ) 165 (Credited)/charged to income statement 309 — 52 6 (124 ) 243 Charged/(credited) to other comprehensive income and equity — — 12 (12 ) — — At 31 March 2019 5,477 (9 ) (170 ) 7 (1,340 ) 3,965 1. The deferred tax asset of £1,340 million as at 31 March 2019 (2018: £1,047 million ) in respect of other net temporary differences primarily relates to US net operating losses of £423 million (2018: £390 million ) and environmental provisions of £409 million (2018: £378 million ). 2. Exchange adjustments and other comprises foreign exchange arising on translation of the US dollar deferred tax balances. In the prior period it also included reclassification of £43 million relating to offset of the opening deferred tax balance on US net operating losses against US current tax liabilities. 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 £3,965 million ( 2018 : £3,636 million ). This balance is after offset of a deferred tax asset of £423 million ( 2018 : £390 million ) which has been recognised in respect of net operating losses. In the prior period, the deferred tax credited to the income statement of £1,084 million was after offset of a £293 million deferred tax charge in respect of net operating losses. Deferred tax assets in respect of capital losses, trading losses and non-trade deficits have not been recognised as their future recovery is uncertain or not currently anticipated. The deferred tax assets not recognised are as follows: 2019 2018 £m £m Capital losses 1,470 510 Non-trade deficits 4 4 Trading losses 5 4 The capital losses arose in the UK on disposal of certain businesses or assets, some of which were agreed with HMRC in the current period. They are available to carry forward indefinitely but can only be offset against future capital gains. The UK non-trade deficits arose prior to 1 April 2017 and therefore can only be offset against future non-trade profits. At 31 March 2019 and 31 March 2018, 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
Earnings per share (EPS)	Mar. 31, 2019
Earnings per share [abstract]
Earnings per share (EPS)	Earnings per share (EPS) EPS is the amount of post-tax profit attributable to each ordinary share. Basic EPS is calculated on profit for the year attributable to equity shareholders divided by the weighted average number of shares in issue during the year. Diluted EPS shows what the impact would be if all outstanding share options were exercised and treated as ordinary shares at year end. The weighted average number of shares is increased by additional shares issued as scrip dividends and reduced by shares repurchased by the Company during the year. The earnings per share calculations are based on profit after tax attributable to equity shareholders of the Company which excludes non-controlling interests. Adjusted earnings and EPS, which exclude exceptional items and remeasurements, are provided to reflect the business performance sub-totals used by the Company. We have included reconciliations from this additional EPS measure to earnings for both basic and diluted EPS to provide additional detail for these items. For further details of exceptional items and remeasurements, see note 5. Following the sale of the UK Gas Distribution business on 31 March 2017, National Grid plc returned £3,171 million of proceeds to shareholders through a special dividend, paid on 2 June 2017. In order to maintain the comparability of the Company’s share price before and after the special dividend, this was preceded by a share consolidation undertaken on 22 May 2017, replacing every 12 existing ordinary shares with 11 new ordinary shares. The weighted average number of ordinary shares outstanding for the year ended 31 March 2018 includes the effect of both the share consolidation and the special dividend from the date that the special dividend was paid. The associated share buyback programme which began on 2 June 2017 completed in March 2018. Purchased shares are held as treasury shares. (a) Basic EPS Earnings EPS Earnings EPS Earnings EPS 2019 2019 2018¹ 2018¹ 2017 2017 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,998 59.0 1,915 55.3 2,141 56.9 Exceptional items and remeasurements after tax from continuing operations (499 ) (14.7 ) 1,633 47.2 (331 ) (8.8 ) Earnings from continuing operations 1,499 44.3 3,548 102.5 1,810 48.1 Adjusted earnings from discontinued operations 57 1.7 145 4.2 607 16.1 Exceptional items and remeasurements after tax from discontinued operations (45 ) (1.4 ) (143 ) (4.1 ) 5,378 142.9 Earnings from discontinued operations 12 0.3 2 0.1 5,985 159.0 Total adjusted earnings 2,055 60.7 2,060 59.5 2,748 73.0 Total exceptional items and remeasurements after tax (including discontinued operations) (544 ) (16.1 ) 1,490 43.1 5,047 134.1 Total earnings 1,511 44.6 3,550 102.6 7,795 207.1 2019 2018 2017 millions millions millions Weighted average number of ordinary shares – basic 3,386 3,461 3,763 (b) Diluted EPS Earnings EPS Earnings EPS Earnings EPS 2019 2019 2018¹ 2018¹ 2017 2017 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,998 58.8 1,915 55.1 2,141 56.7 Exceptional items and remeasurements after tax from continuing operations (499 ) (14.7 ) 1,633 47.0 (331 ) (8.8 ) Earnings from continuing operations 1,499 44.1 3,548 102.1 1,810 47.9 Adjusted earnings from discontinued operations 57 1.7 145 4.2 607 16.0 Exceptional items and remeasurements after tax from discontinued operations (45 ) (1.4 ) (143 ) (4.2 ) 5,378 142.3 Earnings from discontinued operations 12 0.3 2 0.0 5,985 158.3 Total adjusted earnings 2,055 60.5 2,060 59.3 2,748 72.7 Total exceptional items and remeasurements after tax (including discontinued operations) (544 ) (16.1 ) 1,490 42.8 5,047 133.5 Total earnings 1,511 44.4 3,550 102.1 7,795 206.2 2019 2018 2017 millions millions millions Weighted average number of ordinary shares – diluted 3,401 3,476 3,780 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 8. Earnings per share (EPS) continued (c) Reconciliation of basic to diluted average number of shares 2019 2018 2017 millions millions millions Weighted average number of ordinary shares – basic 3,386 3,461 3,763 Effect of dilutive potential ordinary shares – employee share plans 15 15 17 Weighted average number of ordinary shares – diluted 3,401 3,476 3,780

Dividends

Dividends	12 Months Ended
Dividends	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Dividends	Dividends Interim dividends are recognised when they become payable to the Company’s shareholders. Final dividends are recognised when they are approved by shareholders. 2019 2018 2017 Pence per share Cash dividend paid £m Scrip dividend £m Pence per share Cash dividend paid £m Scrip dividend £m Pence per share Cash dividend paid £m Scrip dividend £m Interim dividend in respect of the current year 16.08 450 94 15.49 346 176 15.17 540 32 Special dividend — — — 84.375 3,171 — — — — Final dividend in respect of the prior year 30.44 710 319 29.10 970 33 28.34 923 151 46.52 1,160 413 128.965 4,487 209 43.51 1,463 183 The Directors are proposing a final dividend for the year ended 31 March 2019 of 31.26 p per share that will absorb approximately £1,066 million of shareholders’ equity (assuming all amounts are settled in cash). It will be paid on 14 August 2019 to shareholders who are on the register of members at 31 May 2019 (subject to shareholders’ approval at the AGM). A scrip dividend will be offered as an alternative. Following completion of the sale of the majority interest in UK Gas Distribution, the Company paid a special dividend on 2 June 2017 of 84.375 p per existing ordinary share ( $5.4224 per existing American Depositary Share). This returned £3,171 million to shareholders. No scrip dividend was offered as an alternative.

Discontinued operations and ass

Discontinued operations and assets held for sale	12 Months Ended
Discontinued operations and assets held for sale	Mar. 31, 2019
Non-current Assets Held For Sale And Discontinued Operations [Abstract]
Discontinued operations	Discontinued operations and assets held for sale The results and cash flows of significant assets or businesses sold during the year are shown separately from our continuing operations. Assets and businesses are classified as held for sale when their carrying amounts are recovered through sale rather than through continuing use. They only meet the held for sale condition when the assets are ready for immediate sale in their present condition, management is committed to the sale and it is highly probable that the sale will complete within one year. Depreciation ceases on assets and businesses when they are classified as held for sale and the assets and businesses are impaired if the proceeds less sale costs fall short of the carrying value. Following the decision that we will exercise our put option to sell the 39% equity interest we hold in Quadgas, and on the basis that we intend to dispose of our stake by 30 June 2019, we have met the criteria to classify our interests in Quadgas as a disposal group held for sale. The disposal group comprises our equity interests in Quadgas, the shareholder loan to Quadgas and the derivatives arising from the put/call agreements (described further below). The Group has classified the results of the disposal group as a discontinued operation for the year, and therefore they are presented in the income statement as a discontinued operation separately from the results of the rest of our business, in the same way as the results of the UK Gas Distribution business were disclosed following the sale of a 61% controlling stake in the business on 31 March 2017. On 31 March 2017, the Group sold 61% of its UK Gas Distribution business to Quadgas BidCo Limited (the Consortium) and retained 39% of the business. At the same time, we and the Consortium also entered into a Further Acquisition Agreement (FAA), a put/call arrangement, to sell a further 14% of our investment in the business between 1 March 2019 and 30 June 2019 (our put, having given at least six months’ notice) or between 1 July 2019 to 31 October 2019 (the Consortium’s call, having given six months’ notice). On 1 May 2018, we announced that we had entered into a Remaining Acquisition Agreement (RAA) with the Consortium for the remaining 25% stake in the business under an agreement similar to the FAA. The pricing under the RAA is less favourable to the Group than the FAA. However, in all other material aspects, the RAA is similar to the FAA, in particular regarding the windows for the notice to be given and exercise of the put and call options. This resulted in the recognition of a net derivative financial asset with a fair value of £110 million (2018: £110 million ) relating to the FAA. The fair value of this derivative was initially determined by comparing the pricing mechanism within the FAA against that of the agreement concerning our remaining 25% interest. The £110 million gain as at 31 March 2018 reflected the pricing differential between the two contracts. An impairment review of the Group’s interests in Quadgas (comprising the FAA derivative, a 39% equity interest and £0.4 billion in shareholder loans) was undertaken, comparing the aggregated carrying value of these interests against the future dividend income and proceeds we would expect to receive under the FAA and RAA. At 31 March 2018, this resulted in a charge of £213 million , recorded as an impairment against the carrying value of the equity, largely offsetting pension accounting gains, and the recognition of the FAA derivative asset. We have decided to exercise the options over our remaining 39% interest in Quadgas and the sale is expected to complete at the end of June 2019, subject to customary regulatory approvals. The aggregate carrying value of our investment in Quadgas at 31 March 2019 was £2.0 billion (2018: £2.1 billion ), determined with reference to the future proceeds expected to be received under the FAA and RAA. This comprises the carrying value of the Group’s equity interest in Quadgas of £1.5 billion (2018: £1.6 billion ), the shareholder loan to Quadgas of £0.4 billion (2018: £0.4 billion ) and the derivatives described above. Assets held for sale Under IFRS, the reclassification of assets (and any associated liabilities) as ‘held for sale’ can only be triggered once the assets are available for sale in their present condition and the sale is ‘highly probable’. The highly probable criterion is met when the sale is expected to be completed within a year. We have therefore classified our interests in Quadgas as ‘held for sale’ with effect from 30 June 2018, since we expect to exit our investment by 30 June 2019. At 31 March 2018, we had no such expectation of sale completion within a year. The aggregate carrying value of the assets and liabilities we will sell amount to £2.0 billion (2018: £2.1 billion ), reflecting the total proceeds that remain to be received. No discounting has been applied on the basis that the period to exercise is now less than a year. The value allocated to each element of the Quadgas disposal group at 31 March 2019 is as follows: • the shareholder loan receivable is valued at par of £0.4 billion ; • the RAA derivative 1 is valued at £nil ; • the FAA derivative asset 1 is valued at £110 million ; and • the residual balance of £1.5 billion has been allocated to the investment in associate. Treatment as a discontinued operation We consider that the exercise of our put options is the final stage of the plan to dispose of our interest in the UK Gas Distribution business first announced in 2015, and we have accordingly treated the results and cash flows arising from Quadgas as a discontinued operation in the current year on the basis that the sale forms part of a ‘single coordinated plan’ to dispose of UK Gas Distribution. As a consequence, we have classified the various elements of income, expense and cash flows within discontinued operations as set out below, with comparatives also re-presented accordingly. Also included within discontinued operations are the results of the UK Gas Distribution business for the year ended 31 March 2017, following the disposal of our 61% equity interest in the UK Gas Distribution business described above. This principally comprised the Group’s equity and debt interests in National Grid Gas Distribution Limited together with certain other assets (principally property and a 45% interest in Xoserve Limited). The business represented a reportable segment and a separate major line of business and accordingly was presented as a discontinued operation in the consolidated income statement, consolidated statement of comprehensive income and the consolidated cash flow statement in 2017. Further details are included in the Annual Report and Accounts 2016/17. Within the Annual Report and Accounts 2017/18, both the income statement and the cash flow statement for the year ended 31 March 2018 included amounts relating to the transaction within discontinued operations, primarily relating to the completion accounts settlement in November 2017, a cash outflow from operating activities of £207 million related to the utilisation of provisions (mainly relating to payments of professional fees in respect of the disposal of the UK Gas Distribution business), and net cash flows used in financing activities of £231 million for the settlement of RPI swaps (relating to the final stages of the Group-wide liability management programme executed as part of the sale process). 1. The RAA and FAA are both level 3 financial instruments. No sensitivity analysis is provided in respect of the FAA and RAA derivatives. The price at which we will exit our interest in Quadgas is fixed and accordingly reflected in the aggregate carrying value of the disposal group. Any change in the fair value of these derivatives at 31 March would have been offset by equal and opposite adjustments to the carrying value of our equity interest, with nil net impact on profit and loss for the year. The notional value of the FAA was £739 million (2018: £739 million ) and the notional value of the RAA was £1,087 million . 10. Discontinued operations and assets held for sale continued Summary income statement – discontinued operations The summary income statement for discontinued operations is as follows: 2019 2018¹ 2017 £m £m £m Revenue — — 1,887 Operating costs 2 (1 ) (41 ) (993 ) Operating (loss)/profit (1 ) (41 ) 894 Net finance income/(costs) 23 137 (152 ) Share of post-tax results of joint ventures and associates 3 (5 ) (89 ) — Profit before tax from discontinued operations 17 7 742 Tax from discontinued operations (5 ) (5 ) (79 ) Profit after tax from discontinued operations 12 2 663 Gain on disposal of UK Gas Distribution after tax 4 — — 5,321 Total profit after tax from discontinued operations 5 12 2 5,984 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C). 2. Operating costs of £41 million for the year ended 31 March 2018 related to amounts in respect of the disposal of the UK Gas Distribution business, primarily relating to the completion accounts settlement in November 2017. The remainder of the balances relate to the disposal group and have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period. 3. For the year ended 31 March 2019, this is the net of £43 million impairment charge against investment in Quadgas (see note 16) and £38 million share of Quadgas post-tax profits recognised prior to classification as held for sale. 4. The total gain on the disposal after tax of £5,321 million was comprised of total consideration of £7,494 million before transaction costs of £1,837 million and a tax credit of £312 million compared to net assets on disposal of £648 million . 5. Of the total profit after tax from discontinued operations for the year ended 31 March 2019, the £43 million impairment charge against the investment in Quadgas, net operating costs of £1 million and the tax thereon are classified as exceptional items. Statement of comprehensive income – discontinued operations The summary statement of comprehensive income for discontinued operations is as follows: 2019 2018¹ 2017 Notes £m £m £m Profit after tax from discontinued operations 12 2 5,984 Other comprehensive income/(loss) Items that will never be reclassified to profit or loss: Remeasurement losses of pension assets and post-retirement benefit obligations 25 — — (75 ) Share of other comprehensive income of associate, net of tax 36 142 — Tax on items that will never be reclassified to profit or loss — — 13 Total items from discontinued operations that will never be reclassified to profit or loss 36 142 (62 ) Items that may be reclassified subsequently to profit or loss: Net losses in respect of cash flow hedges — — (106 ) Transferred to profit or loss in respect of cash flow hedges — — 233 Share of other comprehensive income of associate, net of tax — 5 — Tax on items that may be reclassified subsequently to profit or loss — — (23 ) Total items from discontinued operations that may be reclassified subsequently to profit or loss — 5 104 Other comprehensive income for the year, net of tax from discontinued operations 36 147 42 Total comprehensive income for the year from discontinued operations 48 149 6,026 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C). Once the assets are treated as ‘held for sale’, equity accounting ceases for our investment in our associate. We therefore ceased to record our share of profits and share of gains/losses recorded within the consolidated statement of other comprehensive income from 30 June 2018. Summary cash flow statement – discontinued operations Cash outflow from operating activities of £71 million (2018: £207 million ) primarily related to the payments to Affordable Warmth and professional fees in respect of the disposal of the UK Gas Distribution business. In 2017, the amount related to outflows of cash by the UK Gas Distribution business itself. Cash inflows from investing activities of £156 million (2018: £171 million ) was comprised of dividends received and interest received on the shareholder loan. In 2017, this represented cash outflows from investments made by UK Gas Distribution. There were no cash flows for financing activities in the year. In 2018, net cash flows used in financing activities were £231 million for the settlement of RPI swaps relating to the final stages of the Group-wide liability management programme executed as part of sale process. In 2017, amounts related to the liability management programme, comprising £4.8 billion of debt issued and term debt raised, offset by £3.2 billion in respect of bond buybacks.

Goodwill

Goodwill	12 Months Ended
Goodwill	Mar. 31, 2019
Intangible Assets [Abstract]
Goodwill	Goodwill Goodwill represents the excess of what we paid to acquire businesses over the fair value of their net assets at the acquisition date. We assess whether goodwill is recoverable each year by performing an impairment review. Goodwill is recognised as an asset and is not amortised, but is tested for impairment annually or more frequently if events or changes in circumstances indicate a potential impairment. Any impairment is recognised immediately in the income statement and is not subsequently reversed. Goodwill and fair value adjustments arising on the acquisition of a foreign entity are treated as assets and liabilities of the foreign entity and translated at the closing exchange rate. Goodwill is allocated to cash-generating units and this allocation is made to those cash-generating units that are expected to benefit from the business combination in which the goodwill arose. Impairment is recognised where there is a difference between the carrying value of the cash-generating unit and the estimated recoverable amount of the cash‑generating unit to which that goodwill has been allocated. Any impairment loss is first allocated to the carrying value of the goodwill and then to the other assets within the cash-generating unit. Recoverable amount is defined as the higher of fair value less costs to sell and estimated value-in-use at the date the impairment review is undertaken. Value-in-use represents the present value of expected future cash flows, discounted using a pre-tax discount rate that reflects current market assessments of the time value of money and the risks specific to the asset for which the estimates of future cash flows have not been adjusted. Impairments are recognised in the income statement and are disclosed separately. Total £m Net book value at 1 April 2017 6,096 Exchange adjustments (652 ) Net book value at 31 March 2018 5,444 Exchange adjustments 425 Net book value at 31 March 2019 5,869 The cost of goodwill at 31 March 2019 was £5,885 million (2018: £5,458 million ) with an accumulated impairment charge of £16 million (2018: £14 million ). The amounts disclosed above as at 31 March 2019 include balances relating to the following cash-generating units: New York £3,382 million (2018: £3,137 million ); Massachusetts £1,264 million (2018: £1,173 million ); Rhode Island £470 million (2018: £436 million ); and Federal £753 million (2018: £698 million ). Goodwill is reviewed annually for impairment and the recoverability of goodwill has been assessed by comparing the carrying amount of our operations described above (our cash-generating units) with the expected recoverable amount on a value-in-use basis. In each assessment, the value-in-use has been calculated based on five-year plan projections that incorporate our best estimates of future cash flows, customer rates, costs (including changes in commodity prices), future prices and growth. Such projections reflect our current regulatory rate plans taking into account regulatory arrangements to allow for future rate plan filings and recovery of investment. Our plans have proved to be reliable guides in the past and the Directors believe the estimates are appropriate. The future economic growth rate used to extrapolate projections beyond five years is 2.2% (2018: 2.3% ). The growth rate has been determined having regard to data on projected growth in US real gross domestic product (GDP). Based on our business’ place in the underlying US economy, it is appropriate for the terminal growth rate to be based upon the overall growth in real GDP and, given the nature of our operations, to extend over a long period of time. Cash flow projections have been discounted to reflect the time value of money, using a post-tax discount rate of 5.3% (2018: 5.3% ). The equivalent pre-tax discount rate is 5.3% (2018: 5.3% ) as tax is assumed to be a pass-through cost to our customers, recoverable under our rate plans. The discount rate represents the estimated weighted average cost of capital of these operations. In reaching this conclusion, the Directors have considered the potential future consequences regarding the manner in which Tax Reform will impact the Group and its future cash flows. In our US business, we are subject to federal and state taxes; however, our regulatory arrangements require us to pass this cost back to our customers. The reduction in the corporation tax rate from 35% to 21% will be reflected through lower bills to customers, reducing our revenues (and tax costs) in future periods. For the purposes of the goodwill impairment exercise, we have reflected the lower billing levels through lower revenue forecasts as well as lower tax charges. Historically, as a result of tax losses arising from claiming accelerated depreciation allowances, we have not paid substantial amounts of tax in the US. Accordingly, for IFRS purposes, we have recognised significant deferred tax liabilities in respect of these accelerated allowances. In accounting terms, Tax Reform triggered the remeasurement of our deferred tax liabilities from 35% to 21% which resulted in the exceptional gain under IFRS for the year ended 31 March 2018 (as disclosed in notes 5 and 7). However, the impact for our US business is that the amounts we have previously received from customers assuming a 35% federal tax rate instead of a 21% federal tax rate must now be returned to customers over a period of up to 50 years. The precise manner and timing over which this occurs remains subject to agreement with our regulators. Offsetting this change will be the additional income we earn, since the rate base will grow faster. (Our rate base is net of deferred tax liabilities, which, as a result of Tax Reform, will now be smaller.) In overall terms we expect the outcome to be economically neutral. In assessing the carrying value of goodwill, we have sensitised our forecasts to factor in a reduction in revenues and lower tax costs into our cash flow forecasts, but we have not reflected the impact of additional rate base growth on future earnings. While it is possible that a key assumption in the calculation could change, the Directors believe that no reasonably foreseeable change would result in an impairment of goodwill, in view of the long-term nature of the key assumptions and the margin by which the estimated value-in-use exceeds the carrying amount.

Other intangible assets

Other intangible assets	12 Months Ended
Other intangible assets	Mar. 31, 2019
Intangible Assets [Abstract]
Other intangible assets	Other intangible assets Other intangible assets include software which is written down (amortised) over the length of period we expect to receive a benefit from the asset. Identifiable intangible assets are recorded at cost less accumulated amortisation and any provision for impairment. Other intangible assets are tested for impairment only if there is an indication that the carrying value of the assets may have been impaired. Impairments of assets are calculated as the difference between the carrying value of the asset and the recoverable amount, if lower. Where such an asset does not generate cash flows that are independent from other assets, the recoverable amount of the cash-generating unit to which that asset belongs is estimated. Impairments are recognised in the income statement and are disclosed separately. Any assets which suffered impairment in a previous period are reviewed for possible reversal of the impairment at each reporting date. Internally generated intangible assets, such as software, are recognised only if: i) an asset is created that can be identified; ii) it is probable that the asset created will generate future economic benefits; and iii) the development cost of the asset can be measured reliably. Where no internally generated intangible asset can be recognised, development expenditure is recorded as an expense in the period in which it is incurred. Other intangible assets are amortised on a straight-line basis over their estimated useful economic lives. Amortisation periods for categories of intangible assets are: Years Software 3 to 10 Software £m Cost at 1 April 2017 1,732 Exchange adjustments (98 ) Additions 173 Disposals (18 ) Reclassifications 1 8 Cost at 31 March 2018 1,797 Exchange adjustments 70 Additions 306 Disposals (15 ) Reclassifications 1 10 Cost at 31 March 2019 2,168 Accumulated amortisation at 1 April 2017 (809 ) Exchange adjustments 43 Amortisation charge for the year (138 ) Accumulated amortisation of disposals 6 Accumulated amortisation at 31 March 2018 (898 ) Exchange adjustments (26 ) Amortisation charge for the year (175 ) Accumulated amortisation of disposals 15 Accumulated amortisation at 31 March 2019 (1,084 ) Net book value at 31 March 2019² 1,084 Net book value at 31 March 2018 899 1. Reclassifications includes amounts transferred (to)/from property, plant and equipment (see note 13). 2. Included in software is £116 million (2018: £160 million ) relating to the US Enterprise Resource Planning system, which still has a remaining amortisation period of four years.

Property, plant and equipment

Property, plant and equipment	12 Months Ended
Property, plant and equipment	Mar. 31, 2019
Property, plant and equipment [abstract]
Property, plant and equipment	Property, plant and equipment The following note shows the physical assets controlled by us. The cost of these assets primarily represents the amount initially paid for them. This includes both their purchase price and the construction and other costs associated with getting them ready for operation. A depreciation expense is charged to the income statement to reflect annual wear and tear and the reduced value of the asset over time. Depreciation is calculated by estimating the number of years we expect the asset to be used (useful economic life) and charging the cost of the asset to the income statement equally over this period. We operate an energy networks business and therefore have a significant physical asset base. We continue to invest in our networks to maintain reliability, create new customer connections and ensure our networks are flexible and resilient. Our business plan envisages these additional investments will be funded through a mixture of cash generated from operations and the issue of new debt. Property, plant and equipment is recorded at cost, less accumulated depreciation and any impairment losses. Cost includes the purchase price of the asset; any payroll and finance costs incurred which are directly attributable to the construction of property, plant and equipment; and the cost of any associated asset retirement obligations. Property, plant and equipment includes assets in which the Group’s interest comprises legally protected statutory or contractual rights of use. Additions represent the purchase or construction of new assets, including capital expenditure for safety and environmental assets, and extensions to, enhancements to, or replacement of, existing assets. All costs associated with projects or activities which have not been fully commissioned at the period end are classified within assets in the course of construction. No depreciation is provided on freehold land or assets in the course of construction. Other items of property, plant and equipment are depreciated, on a straight-line basis, at rates estimated to write off their book values over their estimated useful economic lives. In assessing estimated useful economic lives, consideration is given to any contractual arrangements and operational requirements relating to particular assets. The assessments of estimated useful economic lives and residual values of assets are performed annually. Unless otherwise determined by operational requirements, the depreciation periods for the principal categories of property, plant and equipment are, in general, as shown in the table below: Years Freehold and leasehold buildings up to 103 Plant and machinery: Electricity transmission plant and wires 10 to 100 Electricity distribution plant 29 to 85 Electricity generation plant 15 to 93 Interconnector plant and other 5 to 65 Gas plant – mains, services and regulating equipment 10 to 95 Gas plant – storage 5 to 65 Gas plant – meters 7 to 62 Motor vehicles and office equipment up to 30 Gains and losses on disposals are determined by comparing the proceeds with the carrying amount and are recognised within operating profit in the income statement. 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. Any assets which suffered impairment in a previous period are reviewed for possible reversal of the impairment at each reporting date. 13. Property, plant and equipment continued Land and buildings £m Plant and machinery £m Assets in the course of construction 1 £m Motor vehicles and office equipment £m Total £m Cost at 1 April 2017 2,979 49,231 3,951 834 56,995 Exchange adjustments (169 ) (2,862 ) (89 ) (67 ) (3,187 ) Additions 38 430 3,358 75 3,901 Disposals 2 (16 ) (216 ) (21 ) (34 ) (287 ) Reclassifications 3 98 2,791 (2,926 ) 49 12 Cost at 31 March 2018 2,930 49,374 4,273 857 57,434 Exchange adjustments 114 2,001 70 47 2,232 Additions 34 391 3,533 57 4,015 Disposals 2 (35 ) (357 ) (159 ) (44 ) (595 ) Reclassifications 3 295 2,974 (3,292 ) 13 (10 ) Cost at 31 March 2019 3,338 54,383 4,425 930 63,076 Accumulated depreciation at 1 April 2017 (684 ) (15,996 ) — (490 ) (17,170 ) Exchange adjustments 28 695 — 36 759 Depreciation charge for the year (28 ) (1,276 ) — (88 ) (1,392 ) Disposals 10 199 — 33 242 Reclassifications 3 — (20 ) — — (20 ) Accumulated depreciation at 31 March 2018 (674 ) (16,398 ) — (509 ) (17,581 ) Exchange adjustments (19 ) (501 ) — (25 ) (545 ) Depreciation charge for the year (93 ) (1,229 ) (150 ) (101 ) (1,573 ) Disposals 7 335 150 44 536 Reclassifications 3 1 (1 ) — — — Accumulated depreciation at 31 March 2019 (778 ) (17,794 ) — (591 ) (19,163 ) Net book value at 31 March 2019 2,560 36,589 4,425 339 43,913 Net book value at 31 March 2018 2,256 32,976 4,273 348 39,853 1. Included within disposals are UK nuclear connections development costs of £150 million (before £13 million of termination income) which were written off (2018: £nil ). See note 5 for further details. 2. In 2018, this included the reversal of assets with cost of £51 million and accumulated depreciation of £51 million disposed of in previous years that remain in use in the Group. It also included £334 million of adjustments from accumulated depreciation to cost for historical disposals relating to assets acquired as part of the KeySpan acquisition in 2008 which were disposed of in subsequent periods. Both of these adjustments have a nil net book value impact. 3. Represents amounts transferred between categories, (to)/from other intangible assets (see note 12), reclassifications from inventories and reclassifications between cost and accumulated depreciation. 2019 2018 £m £m Information in relation to property, plant and equipment Capitalised interest included within cost 1,995 1,861 Net book value of assets held under finance leases (all relating to motor vehicles and office equipment) 241 253 Additions to assets held under finance leases (all relating to motor vehicles and office equipment) 38 58 Contributions to cost of property, plant and equipment included within: Trade and other payables 87 85 Non-current liabilities 372 844 Contract liabilities – current 61 — Contract liabilities – non-current 933 —

Other non-current assets

Other non-current assets	12 Months Ended
Other non-current assets	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Other non-current assets	Other non-current assets Other non-current assets include assets that do not fall into any other non-current asset category (such as goodwill or property, plant and equipment) where the benefit to be received from the asset is not due to be received until after 31 March 2020. 2019 2018 £m £m Other receivables 28 36 Non-current tax assets 56 51 Prepayments and accrued income 1 180 28 264 115 1. Includes accrued income in relation to property sales to the St William joint venture.

Financial and other investments

Financial and other investments	12 Months Ended
Financial and other investments	Mar. 31, 2019
Disclosure of financial assets [abstract]
Financial and other investments	Financial and other investments The Group holds a range of financial and other investments. These investments include short-term money funds, quoted investments in equities or bonds of other companies, long-term loans to our associates and joint ventures and other loans and receivables. Other loans and receivables typically includes bank deposits with a maturity of greater than three months, and cash balances that cannot be readily used in operations, principally collateral pledged against derivative holdings. The Group adopted IFRS 9 with effect from 1 April 2018. The comparatives are not required to be restated and are accounted for in accordance with IAS 39. Under IFRS 9, the Group has reported four categories of financial investments, and the classification for each investment is dependent on its contractual cash flows and the business model it is held under and recognised on trade date. Debt instruments that have contractual cash flows that are solely payments of principal and interest, and which are held within a business model whose objective is to collect contractual cash flows, are held at amortised cost. This category includes our long-term loans to joint ventures and associates as well as collateral pledged balances. Debt investments that have contractual cash flows that are solely payments of principal and interest, and which are held within a business model whose objective is both to collect the contractual cash flows and to sell the debt instruments, are measured at fair value through other comprehensive income. On disposal, any realised gains or losses are recycled to the income statement in investment income (see note 6). The Group has elected to measure equity instruments at fair value through other comprehensive income as they are shares held as part of a portfolio of financial instruments which back some long-term employee liabilities. They are not held for trading and so recognising gains and losses on these investments in profit and loss would not be representative of performance in the year. On disposal, any realised gains and losses are transferred to retained profits (see note 28). Other financial investments are subsequently measured at fair value through profit and loss. This primarily comprises our money market funds, insurance company fund investments and corporate venture capital investments held by National Grid Partners. Financial and other investments are initially recognised on trade date. Subsequent to initial recognition, the fair values of financial assets measured at fair value that are quoted in active markets are based on bid prices. When independent prices are not available, fair values are determined by using valuation techniques that are consistent with techniques commonly used by the relevant market. The techniques use observable market data to the extent available. 2018 For 2018, financial and other investments were £3,593 million reported across three categories. Assets classified as available-for-sale typically represent investments in short-term money funds and quoted investments in equities or bonds of other companies. The second category comprises long-term loans to our associates and joint ventures, and the third category is other loans and receivables, which includes bank deposits, collateral pledged against derivative holdings or other restricted deposit balances. Financial assets, liabilities and equity instruments are classified according to the substance of the contractual arrangements entered into, and recognised on trade date. Available-for-sale financial assets are non-derivatives that are either designated in this category or not classified in any other categories. Available-for-sale financial investments are recognised at fair value plus directly related incremental transaction costs, and they are subsequently carried at fair value in the statement of financial position. Changes in the fair value of available-for-sale investments are recognised directly in other comprehensive income, until the investment is disposed of or is determined to be impaired. At this time the cumulative gain or loss previously recognised in equity is included in the income statement for the period. Investment income is recognised using the effective interest method and taken through interest income in the income statement. Loans and other receivables are initially recognised at fair value plus transaction costs and subsequently held at amortised cost using the effective interest method. Interest income, together with gains and losses when the loans and receivables are derecognised or impaired, is recognised in the income statement. 15. Financial and other investments continued 2019 2018 £m £m Non-current Debt investments at fair value through other comprehensive income 343 — Equity investments at fair value through other comprehensive income 93 — Investments at fair value through profit and loss 62 — Available-for-sale investments — 417 Loans to joint ventures and associates 1 169 482 667 899 Current Investments at fair value through profit and loss 1,311 — Available-for-sale investments — 2,304 Other loans and receivables 670 390 1,981 2,694 2,648 3,593 Financial and other investments include the following: Investments in short-term money funds 2 969 1,999 Insurance company fund investments 3 342 301 Equities 4 93 84 Bonds 4 122 145 Cash surrender value of life insurance policies 4 221 198 Loans to joint ventures and associates 169 482 Corporate venture capital and other 62 — Restricted balances: Collateral 5 637 335 Other 33 49 2,648 3,593 1. Comprises a loan to a joint venture. In 2018, £352 million related to a shareholder loan to Quadgas, which has been re-classified to assets held for sale during the period. 2. Includes £6 million ( 2018 : £69 million ) held as insurance company fund investments and £22 million (2018: £ nil ) US non-qualified plan investments, and therefore restricted. 3. Includes restricted amounts of £342 million (2018: £301 million ) held as insurance company fund investments. 4. Primarily includes restricted amounts of £436 million (2018: £411 million ) relating to US non-qualified plan investments. 5. Refers to collateral placed with counterparties with whom we have entered into a credit support annex to the ISDA (International Swaps and Derivatives Association) Master Agreement. Fair value through profit and loss, fair value through other comprehensive income and available-for-sale investments are recorded at fair value. The carrying value of current loans and receivables is approximate to their fair values, due to short-dated maturities. The carrying value of the non-current loans to joint ventures and associates approximates their fair values as at 31 March 2019 and 31 March 2018. The exposure to credit risk at the reporting date is the fair value of the financial investments. For further information on our credit risk, refer to note 32(a). For the purposes of impairment assessment, the investments in bonds are considered to be low risk as they are managed with an investment remit to invest in investment grade securities; life insurance policies are held with regulated insurance companies; and loans to joint ventures are individually assessed based on comparable external credit ratings and a review of forecasts. No balances are more than 30 days past due. All financial assets held at fair value through other comprehensive income or amortised cost are therefore considered to have low credit risk and have a loss allowance equal to 12-month expected credit losses. In determining the expected credit losses for these assets, some or all of the following information has been considered: credit ratings, the financial position of counterparties, the future prospects of the relevant industries and general economic forecasts. No fair value through other comprehensive income or amortised cost financial assets have had modified cash flows during the period. There has been no change in the estimation techniques or significant assumptions made during the year in assessing the loss allowance for these financial assets. There were no significant movements in the gross carrying value of financial assets during the year that contribute to changes in the loss allowance. No collateral is held in respect of any of the financial investments in the above table. No balances were written off during the year.

Investments in joint ventures a

Investments in joint ventures and associates	12 Months Ended
Investments in joint ventures and associates	Mar. 31, 2019
Interests In Other Entities [Abstract]
Investments in joint ventures and associates	Investments in joint ventures and associates Investments in joint ventures and associates represent businesses we do not control but over which we exercise joint control or significant influence. A joint venture is an arrangement established to engage in economic activity, which the Group jointly controls with other parties and has rights to the net assets of the arrangement. An associate is an entity which is neither a subsidiary nor a joint venture, but over which the Group has significant influence. 2019 2018 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 1,807 361 2,168 1,776 307 2,083 Exchange adjustments 17 (6 ) 11 (19 ) 7 (12 ) Additions 58 85 143 65 64 129 Capitalisation of shareholder loan to Quadgas — — — 69 — 69 Impairment charge against investment in Quadgas (43 ) — (43 ) (213 ) — (213 ) Transfer of interest in Quadgas to assets held for sale (1,625 ) — (1,625 ) — — — Share of post-tax results for the year 67 11 78 147 26 173 Share of other comprehensive income of associates, net of tax 37 — 37 147 — 147 Dividends received (38 ) (30 ) (68 ) (170 ) (43 ) (213 ) Other movements 1 11 (104 ) (93 ) 5 — 5 Share of net assets at 31 March 291 317 608 1,807 361 2,168 1. Other movements on joint ventures relate to reducing the carrying value of the investment in St William Homes LLP to reflect deferred income we expect to recognise over the next 10 years . A list of joint ventures and associates including the name and proportion of ownership is provided in note 34. Transactions with and outstanding balances with joint ventures and associates are shown in note 31. Further information on the Group’s interest in Quadgas and the subsequent reclassification of the interest to assets held for sale is provided in note 10. In 2017, the Group first entered into an arrangement with San Francisco-based Sunrun Neptune Investor 2016 LLC, a leading US provider of residential solar energy systems to provide investment capital. In the period to 31 March 2019 , the Group invested £6 million ( 2018 : £38 million ) alongside Sunrun into a newly incorporated partnership vehicle. The investment is measured at fair value. The fair value gain on this investment of £8 million (2018: £7 million ) has been reflected within the share of post-tax results for the year. The joint ventures and associates have no significant contingent liabilities to which the Group is exposed, and the Group has no significant contingent liabilities in relation to its interests in the joint ventures and associates. The Group has capital commitments of £18 million ( 2018 : £120 million ) in relation to joint ventures. At 31 March 2019 , the Group had one material joint venture, being its 50% equity stake in BritNed and one material associate, being its 26.25% investment in Millennium Pipeline Company LLC. The Group’s 39% equity stake in Quadgas is held for sale and therefore all disclosures in relation to Quadgas are included in note 10. BritNed is a joint venture with transmission system operator TenneT and operates the subsea electricity link between Great Britain and the Netherlands, commissioned in 2011. BritNed has a reporting period end of 31 December with monthly management reporting information provided to National Grid. Millennium Pipeline Company LLC is an associate that owns a natural gas pipeline from southern New York to the Lower Hudson Valley. Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Limited Millennium Pipeline Company LLC 2019 2018 2019 2018 £m £m £m £m Statement of financial position Non-current assets 370 390 937 709 Cash and cash equivalents 59 50 35 15 All other current assets 2 4 22 28 Non-current liabilities (11 ) (10 ) (326 ) (331 ) Current liabilities (28 ) (28 ) (84 ) (64 ) Equity 392 406 584 357 Carrying amount of the Group’s investment 196 203 153 94 BritNed Development Limited Millennium Pipeline Company LLC 2019 2018¹ 2019 2018 £m £m £m £m Income statement Revenue 87 121 166 151 Depreciation and amortisation (13 ) (13 ) (34 ) (31 ) Other costs (10 ) (16 ) (35 ) (41 ) Operating profit 64 92 97 79 Income tax expense (10 ) (20 ) — — Profit for the year 54 72 97 79 Group’s share of profit 27 36 25 21 1. Comparatives for revenue and other costs have been re-presented on a net basis in line with current year classification. Subsidiary undertakings, joint ventures and associates While we present consolidated results in these financial statements as if we were one company, our legal structure is such that there are a number of different operating and holding companies that contribute to the overall result. This structure has evolved through acquisitions as well as regulatory requirements to have certain activities within separate legal entities. Subsidiary undertakings A list of the Group’s subsidiaries as at 31 March 2019 is given below. The entire share capital of subsidiaries is held within the Group except where the Group’s ownership percentages are shown. These percentages give the Group’s ultimate interest and therefore allow for the situation where subsidiaries are owned by partly owned intermediate subsidiaries. Where subsidiaries have different classes of shares, this is largely for historical reasons, and the effective percentage holdings given represent both the Group’s voting rights and equity holding. Shares in National Grid (US) Holdings Limited, National Grid Holdings One plc and NGG Finance plc are held directly by National Grid plc. All other holdings in subsidiaries are owned by other subsidiaries within the Group. All subsidiaries are consolidated in the Group’s financial statements. Principal Group companies are identified in bold . These companies are incorporated and principally operate in the countries under which they are shown. Incorporated in England and Wales Registered office: 1 – 3 Strand, London WC2N 5EH, UK (unless stated otherwise in footnotes). Beegas Nominees Limited Birch Sites Limited Carbon Sentinel Limited Droylsden Metering Services Limited Gridcom Limited Icelink Interconnector Limited Landranch Limited Lattice Group Employee Benefit Trust Limited Lattice Group Limited Lattice Group Trustees Limited Natgrid Limited NatGrid One Limited NatgridTW1 Limited National Grid Belgium Limited National Grid Blue Power Limited National Grid Carbon Limited National Grid Commercial Holdings Limited National Grid Distributed Energy Limited National Grid Electricity Group Trustee Limited National Grid Electricity System Operator Limited National Grid Electricity Transmission plc National Grid Energy Metering Limited National Grid Four Limited National Grid Fourteen Limited National Grid Gas Holdings Limited National Grid Gas plc National Grid Grain LNG Limited National Grid Holdings Limited National Grid Holdings One plc National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited National Grid Metering Limited National Grid North Sea Link Limited National Grid Offshore Limited National Grid Partners Limited (previously National Grid Thirty Four Limited) National Grid Property Holdings Limited National Grid Seventeen Limited National Grid Smart Limited National Grid Ten National Grid Thirty Five Limited National Grid Thirty Six Limited National Grid Twelve Limited National Grid Twenty Eight Limited National Grid Twenty-Five Limited National Grid Twenty Seven Limited National Grid Twenty Three Limited National Grid UK Limited National Grid UK Pension Services Limited National Grid (US) Holdings Limited National Grid (US) Investments 2 Limited National Grid (US) Investments 4 Limited National Grid (US) Partner 1 Limited National Grid Ventures Limited National Grid Viking Link Limited National Grid William Limited NG Nominees Limited NG Shetland Link Limited NGC Employee Shares Trustee Limited NGG Finance plc Ngrid Intellectual Property Limited NGT Telecom No. 1 Limited NGT Two Limited Port Greenwich Limited Stargas Nominees Limited Supergrid Electricity Limited Supergrid Energy Transmission Limited Supergrid Limited Thamesport Interchange Limited The National Grid Group Quest Trustee Company Limited The National Grid YouPlan Trustee Limited Transco Limited Warwick Technology Park Management Company (No 2) Limited ( 60.56% ) 1 1. Registered office: Shire Hall, PO Box 9, Warwick CV34 4RL, UK 34. Subsidiary undertakings, joint ventures and associates continued Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, New Castle County, USA (unless stated otherwise in footnotes). Boston Gas Company 1 British Transco Capital Inc. British Transco Finance, Inc. Broken Bridge Corp. 2 Colonial Gas Company 1 EUA Energy Investment Corporation 1 Granite State Power Link LLC GridAmerica Holdings Inc. Grid NY LLC 3 KeySpan CI Midstream Limited KeySpan Energy Corporation 3 KeySpan Energy Services Inc. KeySpan Gas East Corporation 3 KeySpan International Corporation KeySpan MHK, Inc. KeySpan Midstream Inc. KeySpan Plumbing Solutions, Inc. 3 KSI Contracting, LLC KSI Electrical, LLC KSI Mechanical, LLC Land Management & Development, Inc. 3 Landwest, Inc. 3 Massachusetts Electric Company 1 Metro Energy, LLC 3 Metrowest Realty LLC Mystic Steamship Corporation Nantucket Electric Company 1 National Grid Algonquin LLC National Grid Connect Inc. National Grid Development Holdings Corp. National Grid Electric Services, LLC 3 National Grid Energy Management, LLC National Grid Energy Services LLC National Grid Energy Trading Services LLC 3 National Grid Engineering & Survey Inc. 3 National Grid Generation LLC 3 National Grid Generation Ventures LLC 3 National Grid Glenwood Energy Center, LLC National Grid Green Homes Inc. National Grid IGTS Corp. 3 National Grid Insurance USA Ltd 3 National Grid Islander East Pipeline LLC National Grid LNG GP LLC National Grid LNG LLC National Grid LNG LP LLC National Grid Millennium LLC National Grid NE Holdings 2 LLC 1 National Grid North America Inc. National Grid North East Ventures Inc. National Grid Partners Inc. (previously National Grid Technologies Inc.) 3 National Grid Port Jefferson Energy Center LLC National Grid Services Inc. National Grid Transmission Services Corporation 1 National Grid US 6 LLC National Grid US LLC National Grid USA National Grid USA Service Company, Inc. 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 4 NGNE LLC NGV Emerald Acquisition Co. LLC 5 NGV Emerald Holdings LLC 5 Niagara Mohawk Energy, Inc. Niagara Mohawk Holdings, Inc. 3 Niagara Mohawk Power Corporation 3 NM Properties, Inc. 3 Northeast Renewable Link LLC North East Transmission Co., Inc. Opinac North America, Inc. Philadelphia Coke Co., Inc. Port of the Islands North, LLC 3 The Brooklyn Union Gas Company 3 The Narragansett Electric Company 4 Transgas, Inc. 1 Upper Hudson Development Inc. 1 Valley Appliance and Merchandising Company 4 Vermont Green Line Devco, LLC ( 90% ) Wayfinder Group, Inc. 1 Incorporated in Australia Registered office: Level 7, 330 Collins Street, Melbourne, VIC 3000, Australia National Grid Australia Pty Limited Incorporated in Canada Registered office: 1959 Upper Water Street, Suite 800, Halifax NS, B3J 2X2, Canada KeySpan Energy Development Co. Incorporated in the Isle of Man Registered office: Third Floor, St George’s Court, Upper Church Street, Douglas, IM1 1EE, Isle of Man, UK National Grid Insurance Company (Isle of Man) Limited NGT Holding Company (Isle of Man) Limited Incorporated in Jersey Registered office: 44 Esplanade, St Helier, Jersey JE4 9WG, UK National Grid Jersey Investments Limited NG Jersey Limited Incorporated in the Netherlands Registered office: Westblaak 89, 3012 KG Rotterdam, PO Box 21153, 3001 AD, Rotterdam, Netherlands British Transco International Finance B.V. Registered office: Prins Bernhardplein 200, 1097 JB, Amsterdam, Netherlands National Grid Holdings B.V. Incorporated in the Republic of Ireland Registered office: c/o Moore Stephens Nathans, Third Floor, Ulysses House, 23/24 Foley Street, Dublin 1, D01 W2T2, Ireland National Grid Company (Ireland) Designated Activity Company (previously National Grid Insurance Company (Ireland) Designated Activity Company)* 1. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, Suffolk County, USA. 2. Registered office: Corporation Service Company, 10 Ferry Street, Suite 313, Concord NH 03301, Merrimack County, USA. 3. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207-2543, Albany County, USA. 4. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, Kent County, USA. 5. Registered office: 404 Wyman Street, Waltham MA 02451 USA. * In liquidation. 34. Subsidiary undertakings, joint ventures and associates continued Joint ventures A list of the Group’s joint ventures as at 31 March 2019 is given below. All joint ventures are included in the Group’s financial statements using the equity method of accounting. Principal joint ventures are identified in bold . Incorporated in England and Wales Registered office: 1–3 Strand, London WC2N 5EH, UK (unless stated otherwise in footnotes). BritNed Development Limited ( 50% )* Joint Radio Company Limited ( 50% ) 1 Nemo Link Limited ( 50% ) NGET/SPT Upgrades Limited ( 50% ) † St William Homes LLP ( 50% ) 2 Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, New Castle County, USA (unless stated otherwise in footnotes). Clean Energy Generation, LLC ( 50% ) Goldendale Energy Storage LLC ( 50% ) Island Park Energy Center, LLC ( 50% ) Islander East Pipeline Company, LLC ( 50% ) 3 LI Energy Storage System, LLC ( 50% ) LI Solar Generation, LLC ( 50% ) Swan Lake North Holdings LLC ( 50% ) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, Paris La Defense, CEDEX, France IFA2 SAS ( 50% ) Associates A list of the Group’s associates as at 31 March 2019 is given below. Unless otherwise stated, all associates are included in the Group’s financial statements using the equity method of accounting. Principal associates are identified in bold . Incorporated in England and Wales Registered office: Ashbrook Court, Prologis Park, Central Boulevard, Coventry CV7 8PE, UK Quadgas HoldCo Limited ( 39% ) # Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, New Castle County, USA (unless stated otherwise in footnotes). Algonquin Gas Transmission, LLC ( 20% ) 3 Clean Line Energy Partners LLC ( 32% ) 3 Connecticut Yankee Atomic Power Company ( 19.5% ) 4 Direct Global Power, Inc. ( 26% ) 5 Energy Impact Fund LP ( 9.42% ) 6 KHB Venture LLC ( 33% ) 7 Maine Yankee Atomic Power Company ( 24% ) 8 Millennium Pipeline Company, LLC ( 26.25% ) 3 New York Transco LLC ( 28.3% ) 9 Nysearch RMLD, LLC ( 22.63% ) Sunrun Neptune Investor 2016 LLC 3 * 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 2019 is given below. Incorporated in England and Wales Registered office: 1 More London Place, London SE1 2AF, UK Energis plc ( 33.06% ) ‡ 1. Registered office: Friars House, Manor House Drive, Coventry CV1 2TE, UK. 2. Registered office: Berkeley House, 19 Portsmouth Road, Cobham, Surrey KT11 1JG, UK. 3. Registered office: Corporation Trust Company, 1209 Orange, Wilmington DE 19808, New Castle County, USA. 4. Registered office: Carla Pizzella, 362 Injun Hollow Road, East Hampton CT 06424, USA. 5. Registered office: 507 Plum Street, PO Box 5001, Syracuse NY 13250, USA. 6. Registered office: Harvard Business Services, Inc., 16192 Coastal Highway, Lewes DE 19958, Sussex County, USA. 7. Registered office: De Maximus Inc., 135 Beaver Street, 4th Floor, Waltham MA 02452, USA. 8. Registered office: Joseph D Fay, 321 Old Ferry Road, Wiscasset ME 04578, USA. 9. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 10. Registered office: Brian Smith, 49 Yankee Road, Rowe MA 01367, USA. * National Grid Interconnector Holdings Limited owns 284,500,000 €0.20 C Ordinary shares and one £1.00 Ordinary A share. National Grid Gas plc owns all £1.00 A Ordinary shares. * National Grid Green Homes Inc. owns 1,000 Class A Membership Interests. † National Grid Electricity Transmission plc owns 50 £1.00 A Ordinary shares. ‡ In administration. # Quadgas HoldCo Limited is included in the financial statements from 30 June 2018 as an asset held for sale. Our interests and activities are held or operated through the subsidiaries, joint arrangements or associates as disclosed above. These interests and activities (and their branches) are established in – and subject to the laws and regulations of – these jurisdictions.

Derivative financial instrument

Derivative financial instruments	12 Months Ended
Derivative financial instruments	Mar. 31, 2019
Financial Instruments [Abstract]
Derivative financial instruments	Derivative financial instruments Derivatives are financial instruments that derive their value from the price of an underlying item such as interest rates, foreign exchange rates, credit spreads, commodities, equities or other indices. In accordance with Board-approved policies, derivatives are transacted generally to manage exposures to fluctuations in interest rates, foreign exchange rates and commodity prices. Our derivatives balances comprise two broad categories: • financing derivatives managing our exposure to interest rates and foreign exchange rates. Specifically we use these derivatives to manage our financing portfolio, holdings in foreign operations and contractual operational cash flows; and • commodity contract derivatives managing our US customers’ exposure to price and supply risks. Some forward contracts for the purchase of commodities meet the definition of derivatives and are included here. We also enter into derivative financial instruments linked to commodity prices, including index futures, options and swaps. These are used to manage market price volatility. The Group adopted IFRS 9 with effect from 1 April 2018. The comparatives are not required to be restated and are accounted for in accordance with IAS 39. There is no impact on derivatives balances as a result of the transition to IFRS 9. 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 income statement or other comprehensive income as required by IFRS 9. Where the gains or losses recorded in the income statement arise from changes in the fair value of derivatives to the extent that hedge accounting is not applied or is not fully effective, these are recorded as remeasurements, detailed in notes 5 and 6. Where the fair value of a derivative is positive it is carried as a derivative asset, and where negative as a derivative liability. We calculate the fair value of derivative financial instruments by taking the present value of future cash flows, primarily incorporating market observable inputs. The various inputs include foreign exchange spot and forward rates, yield curves of the respective currencies, currency basis spreads between the respective currencies, interest rate and inflation curves, the forward rate curves of underlying commodities, and for those positions that are not fully cash collateralised the credit quality of the counterparties. Certain clauses embedded in non-derivative financial instruments or other contracts are presented as derivatives because they impact the risk profile of their host contracts and they are deemed to have risks or rewards not closely related to those host contracts. Further information on how derivatives are valued and used for risk management purposes is presented in note 32. Information on commodity contracts and other commitments not meeting the definition of derivatives is presented in note 30. The fair values of derivatives by category are as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Financing derivatives 1,052 (1,084 ) (32 ) 1,545 (945 ) 600 Commodity contract derivatives 101 (99 ) 2 69 (116 ) (47 ) Further Acquisition Agreement derivative 1 — — — 110 — 110 1,153 (1,183 ) (30 ) 1,724 (1,061 ) 663 1. The Further Acquisition Agreement derivative is a put/call option over a 14% interest in Quadgas that has been reclassified as held for sale during the period (see note 10). (a) Financing derivatives The fair values of financing derivatives by type are as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Interest rate swaps 539 (384 ) 155 678 (457 ) 221 Cross-currency interest rate swaps 470 (443 ) 27 687 (207 ) 480 Foreign exchange forward contracts 1 41 (41 ) — 174 (2 ) 172 Inflation-linked swaps — (214 ) (214 ) 5 (278 ) (273 ) Equity options 2 (2 ) — 1 (1 ) — 1,052 (1,084 ) (32 ) 1,545 (945 ) 600 1. Included within the foreign exchange forward contracts balance is £32 million ( 2018 : £67 million ) of derivatives in relation to hedging of capital expenditure. 17. Derivative financial instruments continued (a) Financing derivatives continued The maturity profile of financing derivatives is as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total Current Less than 1 year 56 (282 ) (226 ) 375 (325 ) 50 56 (282 ) (226 ) 375 (325 ) 50 Non-current In 1 to 2 years 19 (193 ) (174 ) 83 (88 ) (5 ) In 2 to 3 years 416 (1 ) 415 25 (27 ) (2 ) In 3 to 4 years 11 — 11 418 (5 ) 413 In 4 to 5 years 20 (14 ) 6 12 — 12 More than 5 years 530 (594 ) (64 ) 632 (500 ) 132 996 (802 ) 194 1,170 (620 ) 550 1,052 (1,084 ) (32 ) 1,545 (945 ) 600 The notional contract 1 amounts of financing derivatives by type are as follows: 2019 2018 £m £m Interest rate swaps (6,299 ) (8,390 ) Cross-currency interest rate swaps (6,700 ) (6,925 ) Foreign exchange forward contracts (2,937 ) (5,793 ) Inflation-linked swaps (500 ) (1,191 ) Equity options (800 ) (800 ) (17,236 ) (23,099 ) 1. The notional contract amounts of derivatives indicate the gross nominal value of transactions outstanding at the reporting date. (b) Commodity contract derivatives The fair values of commodity contract derivatives by type are as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets Liabilities £m Total £m Commodity purchase contracts accounted for as derivative contracts Forward purchases of gas 66 (78 ) (12 ) 60 (64 ) (4 ) Derivative financial instruments linked to commodity prices Electricity capacity — — — 1 — 1 Electricity swaps 29 (19 ) 10 7 (46 ) (39 ) Electricity options — — — — (1 ) (1 ) Gas swaps 5 (1 ) 4 1 (4 ) (3 ) Gas options 1 (1 ) — — (1 ) (1 ) 101 (99 ) 2 69 (116 ) (47 ) 17. Derivative financial instruments continued (b) Commodity contract derivatives continued The maturity profile of commodity contract derivatives is as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than one year 52 (68 ) (16 ) 30 (76) (46) 52 (68 ) (16 ) 30 (76) (46) Non-current In 1 to 2 years 14 (9 ) 5 6 (17) (11) In 2 to 3 years 9 (8 ) 1 6 (11) (5) In 3 to 4 years 6 (4 ) 2 6 (3) 3 In 4 to 5 years 6 (4 ) 2 5 (2) 3 More than 5 years 14 (6 ) 8 16 (7) 9 49 (31 ) 18 39 (40) (1) 101 (99 ) 2 69 (116) (47) The notional quantities of commodity contract derivatives by type are as follows: 2019 2018 Forward purchases of gas 1 52m Dth 54m Dth Electricity swaps 12,848 GWh 12,839 GWh Electricity options 10,444 GWh 13,897 GWh Electricity capacity - 0.6 GWm Gas swaps 87m Dth 100m Dth Gas options 34m Dth 7m Dth 1. Forward gas purchases have terms up to two years . The contractual obligations under these contracts are £108 million ( 2018 : £96 million ).

Inventories and other current i

Inventories and other current intangibles	12 Months Ended
Inventories and other current intangibles	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Inventories and current intangible assets	Inventories and current intangible assets Inventories represent assets that we intend to use in order to generate revenue in the short term, either by selling the asset itself (for example, fuel stocks) or by using it to fulfil a service to a customer or to maintain our network (consumables). Inventories are stated at the lower of weighted average cost and net realisable value. Where applicable, cost comprises direct materials and direct labour costs as well as those overheads that have been incurred in bringing the inventories to their present location and condition. Emission allowances, principally relating to the emissions of carbon dioxide in the UK and sulphur and nitrous oxides in the US, are recorded as intangible assets within current assets, and they are initially recorded at cost and subsequently at the lower of cost and net realisable value. A liability is recorded in respect of the obligation to deliver emission allowances, and emission charges are recognised in the income statement in the period in which emissions are made. 2019 2018 £m £m Fuel stocks 99 78 Raw materials and consumables 184 190 Current intangible assets – emission allowances 87 73 370 341 There is a provision for obsolescence of £20 million against inventories as at 31 March 2019 ( 2018 : £18 million ).

Trade and other receivables

Trade and other receivables	12 Months Ended
Trade and other receivables	Mar. 31, 2019
Trade and other receivables [abstract]
Trade and other receivables	Trade and other receivables Trade and other receivables are amounts which are due from our customers for services we have provided. Trade and other receivables are initially recognised at fair value and subsequently measured at amortised cost, less any appropriate allowances for estimated irrecoverable amounts. 2019 2018 £m £m Trade receivables 1,899 1,674 Accrued income 883 817 Prepayments 237 229 Other receivables 134 78 3,153 2,798 Trade receivables are non-interest-bearing and generally have a 30 to 90 days term. Due to their short maturities, the fair value of trade and other receivables approximates their book value. The maximum exposure of trade receivables to credit risk is the gross carrying amount of £2,293 million (2018: £1,983 million ). Provision for impairment of receivables IFRS 9, effective from 1 April 2018, has changed the basis upon which the impairment provision is calculated. Under IFRS 9, a provision is recognised for credit losses at an amount equal to the expected credit losses that will arise over the lifetime of the trade receivables. Under IAS 39, a provision is established for irrecoverable amounts when there is objective evidence that amounts due under the original payment terms will not be collected. Comparative amounts have not been restated, with the 2018 impairment provision being calculated under IAS 39 and the 2019 impairment provision being calculated on the basis of expected losses under IFRS 9. 2019 2018 £m £m At 1 April 309 424 Exchange adjustments 24 (42 ) Charge for the year, net of recoveries 181 36 Uncollectible amounts written off (120 ) (109 ) At 31 March 394 309 The provision for retail customer receivables in the US is calculated based on a series of provision matrices which are prepared by regulated entity and by customer type. The expected loss rates in each provision matrix are based on historical loss rates adjusted for current and forecasted economic conditions at the balance sheet date. The inclusion of forward-looking information in the provision matrix setting process under IFRS 9 resulted in loss rates that reflect expected future economic conditions and the recognition of an expected loss on all debtors even where no loss event has occurred. This had no material impact on the estimation process during the year. The average expected loss rates and balances for the retail customer receivables in our US operations are set out below: 2019 2019 2018 2018 % £m % £m 0 – 30 days 3 736 3 741 30 – 60 days 12 194 8 192 60 – 90 days 20 89 19 97 3 – 6 months 30 109 29 97 6 – 12 months 39 99 39 88 Over 12 months 68 238 69 218 US retail customer receivables are not collateralised. Write-off policies vary as they are aligned with regulatory requirements, which differ between regulators. Receivables are not modified but are written off when regulatory requirements are met. There were no significant amounts written off during the period but still subject to enforcement action. Our internal definition of default is aligned with that of the individual regulators in each jurisdiction. There are no material bad debt provisions in the UK businesses, as they have no retail customer receivables. A provision matrix is not used in the UK as an assessment of expected losses on individual debtors is performed. This is also the case for non-retail US customer receivables. Trade receivables past due 2019 2018 £m £m Up to 3 months past due 295 271 3 to 6 months past due 108 73 Over 6 months past due 160 131 563 475 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
Cash and cash equivalents	Mar. 31, 2019
Cash and cash equivalents [abstract]
Cash and cash equivalents	Cash and cash equivalents Cash and cash equivalents include cash balances, together with short-term investments with an original maturity of less than three months that are readily convertible to cash. Net cash and cash equivalents reflected in the cash flow statement are net of bank overdrafts, which are reported in borrowings. The carrying amounts of cash and cash equivalents and bank overdrafts approximate their fair values. Cash at bank earns interest at floating rates based on daily bank deposit rates. Short-term deposits are made for periods varying between one day and three months, depending on the immediate cash requirements, and earn interest at the respective short-term deposit rates. Net cash and cash equivalents held in currencies other than sterling have been converted into sterling at year-end exchange rates. For further information on currency exposures, refer to note 32. 2019 2018 £m £m Cash at bank 177 54 Short-term deposits 75 275 Cash and cash equivalents 252 329

Borrowings

Borrowings	12 Months Ended
Borrowings	Mar. 31, 2019
Disclosure of detailed information about borrowings [abstract]
Borrowings	Borrowings We borrow money primarily in the form of bonds and bank loans. These are for a fixed term and may have fixed or floating interest rates or are linked to RPI. We use derivatives to manage risks associated with interest rates and foreign exchange. Our price controls and rate plans lead us to fund our networks within a certain ratio of debt to equity and, as a result, we have issued a significant amount of debt. As we continue to invest in our networks, the value of debt is expected to increase over time. To maintain a strong balance sheet and to allow us to access capital markets at commercially acceptable interest rates, we balance the amount of debt we issue with the value of our assets, and we take account of certain other metrics used by credit rating agencies. The Group adopted IFRS 9 with effect from 1 April 2018. The comparatives are not required to be restated and are accounted for in accordance with IAS 39. On adoption of IFRS 9, the Group elected to change the measurement basis of one liability from amortised cost to fair value through profit and loss, in order to eliminate a measurement mismatch. All other borrowings are accounted for at amortised cost. Borrowings, which include interest-bearing and inflation-linked debt and overdrafts, are initially recorded at fair value, which normally reflects the proceeds received, net of direct issue costs less any repayments. Subsequently these are stated either: i) at amortised cost; or ii) at fair value though profit and loss. Where a borrowing is held at amortised cost any difference between the proceeds after direct issue costs and the redemption value is recognised over the term of the borrowing in the income statement using the effective interest method. For the liability held at fair value through profit and loss, the difference between the fair value at the date of reclassification and the redemption value is recognised over the term of the borrowing using the effective interest method. Where a borrowing or liability is held at fair value, changes in the fair value of the borrowing due to changes in the issuer’s credit risk are recorded in the own credit reserve (see note 28). All other changes in the fair value of the liability are recognised in the income statement within remeasurements (see notes 5 and 6). 2018 Under IAS 39, borrowings were all accounted for at amortised cost, using the effective interest method, as described above. 2019 2018 £m £m Current Bank loans 641 2,020 Bonds 1,973 2,156 Commercial paper 1,792 206 Finance leases 65 64 Other loans 1 1 4,472 4,447 Non-current Bank loans 2,599 2,384 Bonds 1 21,278 19,418 Finance leases 205 207 Other loans 176 169 24,258 22,178 Total borrowings 28,730 26,625 1. In 2019 this includes a liability held at fair value through profit and loss of £667 million . 21. Borrowings continued Total borrowings are repayable as follows: 2019 2018 £m £m Less than 1 year 4,472 4,447 In 1 to 2 years 2,393 1,694 In 2 to 3 years 1,990 2,347 In 3 to 4 years 1,553 1,873 In 4 to 5 years 714 1,469 More than 5 years: By instalments 959 1,010 Other than by instalments 16,649 13,785 28,730 26,625 The fair value of borrowings at 31 March 2019 was £32,252 million ( 2018 : £30,164 million ). Where market values were available, fair value of borrowings (Level 1) was £14,356 million ( 2018 : £13,018 million ). Where market values were not available, fair value of borrowings (Level 2) was £17,896 million ( 2018 : £17,146 million ), calculated by discounting cash flows at prevailing interest rates. The notional amount outstanding of the debt portfolio at 31 March 2019 was £28,417 million ( 2018 : £26,363 million ). The assets of the Colonial Gas Company and the Niagara Mohawk Power Corporation and certain gas distribution assets of The Narragansett Electric Company are subject to liens and other charges and are provided as collateral over borrowings totalling £81 million at 31 March 2019 ( 2018 : £392 million ). During 2019, the Niagara Mohawk Power Corporation first mortgage debenture was cancelled; therefore, it is no longer subject to liens and other charges as at 31 March 2019. Collateral is placed with or received from any 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 £558 million ( 2018 : £878 million ) in respect of cash received under collateral agreements. For further details of our borrowing facilities, refer to note 33. For further details of our bonds in issue, please refer to the debt investor section of our website. Unless included herein, the information on our website is unaudited. Financial liability at fair value through profit and loss The financial liability designated at fair value through profit and loss is analysed as follows: i) the fair value of the liability was £667 million , which includes cumulative change in fair value attributable to changes in credit risk recognised in other comprehensive income, post tax of £13 million ; ii) the amount repayable at maturity in November 2021 is £943 million ; and iii) the difference between carrying amount and contractual amount at maturity is £276 million . This liability has been reclassified in order to eliminate a measurement mismatch with derivatives which provide an economic hedge. The associated derivatives are collateralised and do not contain significant exposure to our own credit risk. The presentation of credit risk in other comprehensive income does not, therefore, create or enlarge an accounting mismatch in profit or loss. The change in the fair value attributable to a change in credit risk is calculated as the difference between the total change in the fair value of the liability and the change in the value of the liability due to changes in market risk factors alone. The change in the fair value due to market risk factors was calculated using benchmark yield curves as at the end of the reporting period holding the credit risk margin constant. The fair value of the liability was calculated using observed market prices. 21. Borrowings continued Finance lease obligations Assets held under finance leases are recognised at their fair value or, if lower, the present value of the minimum lease payments on inception. The corresponding liability is recognised as a finance lease obligation within borrowings. Rental payments are apportioned between finance costs and reduction in the finance lease obligation, so as to achieve a constant rate of interest. Assets held under finance leases are depreciated over the shorter of their useful life and the lease term. 2019 2018 £m £m Gross finance lease liabilities are repayable as follows: Less than 1 year 65 64 1 to 5 years 183 177 More than 5 years 62 72 310 313 Less: finance charges allocated to future periods (40 ) (42 ) 270 271 The present value of finance lease liabilities is as follows: Less than 1 year 65 64 1 to 5 years 156 144 More than 5 years 49 63 270 271

Trade and other payables

Trade and other payables	12 Months Ended
Trade and other payables	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Trade and other payables	Trade and other payables Trade and other payables include amounts owed to suppliers, tax authorities and other parties which are due to be settled within 12 months. The total also includes deferred amounts, some of which represent monies received from customers but for which we have not yet delivered the associated service. These amounts are recognised as revenue when the service is provided. Trade and other payables are initially recognised at fair value and subsequently measured at amortised cost. 2019 2018 £m £m Trade payables 2,404 1,977 Deferred payables 217 355 Customer contributions 1 87 85 Social security and other taxes 159 173 Other payables 902 863 3,769 3,453 1. From government-related entities. Due to their short maturities, the fair value of trade payables approximates their book value.

Contract liabilities

Contract liabilities	12 Months Ended
Contract liabilities	Mar. 31, 2019
Contract liabilities [abstract]
Contract liabilities	Contract liabilities Contract liabilities primarily relate to the advance consideration received from customers for construction contracts, mainly in relation to connections, for which revenue is recognised over the life of the asset. The balances have arisen on transition to IFRS 15, which has been applied using the modified retrospective approach and therefore comparatives have not been restated. 2019 2018 £m £m Current 61 — Non-current 933 — 994 — Significant changes in the contract liabilities balances during the period are as follows: 2019 £m As at 1 April 2018 (see note 37) 866 Exchange adjustments 29 Revenue recognised that was included in the contract liability balance at the beginning of the period (51 ) Increases due to cash received, excluding amounts recognised as revenue during the period 155 Changes due to amounts recognised as revenue (5 ) At 31 March 2019 994

Other non-current liabilities

Other non-current liabilities	12 Months Ended
Other non-current liabilities	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Other non-current liabilities	Other non-current liabilities Other non-current liabilities include deferred income which will not be recognised as income until after 31 March 2020. It also includes payables that are not due until after that date. Non-current liabilities are initially recognised at fair value and subsequently measured at amortised cost. 2019 2018 £m £m Deferred income 1 96 114 Customer contributions 2 372 844 Other payables 340 359 808 1,317 1. Principally the deferral of profits relating to the sale of property, plant and equipment. 2. From government-related entities. 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
Pensions and other post retirement benefits	Mar. 31, 2019
Employee Benefits [Abstract]
Pensions and other post retirement benefits	Pensions and other post-retirement benefits All of our employees are eligible to participate in a pension plan. We have defined benefit (DB) and defined contribution (DC) pension plans. In the US we also provide healthcare and life insurance benefits to eligible employees, post-retirement. The fair value of associated scheme assets and present value of DB obligations are updated annually in accordance with IAS 19 (revised). We separately present our UK and US pension schemes to show geographical split. Below we provide a more detailed analysis of the amounts recorded in the primary financial statements and the actuarial assumptions used to value the DB obligations. Defined contribution plans All of our employees are eligible to participate in a pension plan in the UK or US. These plans are designed to provide members with a pension pot for their retirement. The risks associated with these plans are assumed by the member. Payments to these DC plans are charged as an expense as they fall due. There is no legal or constructive obligation on National Grid to pay additional contributions into a DC plan if the fund has insufficient assets to pay all employees’ benefits relating to employee service in the current and prior periods. Defined benefit schemes The principal UK schemes are the National Grid UK Pension Scheme (NGUKPS) and the National Grid Electricity Group of the Electricity Supply Pension Scheme (NGEG of ESPS). In the US, we have four plans and a number of healthcare and life insurance plans. On retirement, members of DB schemes 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 schemes is calculated separately for each DB scheme by projecting the estimated amount of future benefit payments that employees have earned for their pensionable service in the current and prior periods. These future benefit payments are discounted to determine the present value of the liabilities. Current service cost and any unrecognised past service cost are recognised immediately. The discount rate used is the yield at the valuation date on high-quality corporate bonds. Advice is taken from independent actuaries relating to the appropriateness of the key assumptions applied, including life expectancy, expected salary and pension increases, and inflation. Comparatively small changes in the assumptions used may have a significant effect on the amounts recognised in the consolidated income statement, the consolidated statement of other comprehensive income and the net liability recognised in the consolidated statement of financial position. Remeasurements of pension assets and post-retirement benefit obligations are recognised in full in the period in which they occur in the consolidated statement of other comprehensive income. UK defined benefit plans and Guaranteed Minimum Pension (GMP) equalisation In the UK, GMPs were intended to broadly replace State Earnings Related Pension Scheme (SERPS) benefits for members of contracted-out occupational pension schemes from April 1978 to April 1997. Inequalities in GMP stemmed from the statutory definition of GMP, resulting in benefits accruing at different rates between male and female members. A High Court judgement in October 2018 confirmed that GMP benefits need to be equalised between men and women, and importantly also provided alternative prescribed methods of equalisation. This provides much-needed clarity, as there has been uncertainty in pensions law as it pertains to GMP equalisation. However, schemes cannot directly equalise the GMPs, but need to adjust other benefits in order to achieve this, through correcting the ongoing position and making back-payments to affected members. This is a highly complex issue that will have a significant effect on the eventual cost of providing benefits, as well as significant cost implications in the calculation and implementation of the equalisation method. Under IAS 19 we have estimated the cost of equalising for the impact of GMP under the most cost-effective permissible method to be: • Section A of NGUKPS – £17 million ; • Section B of NGUKPS – £12 million ; and • NGEG of ESPS – £5 million . These amounts have been recognised in the consolidated income statement as past service costs. The key drivers of these costs are the schemes’ benefit structures, the membership profile and retirement choices made by members. National Grid will continue to work closely with the Trustees of NGUKPS and NGEG of ESPS, the actuaries and legal advisors to implement and administer GMP equalisation, which is expected to take some years. Future administration costs related to this process will be expensed as incurred. 25. Pensions and other post-retirement benefits continued UK pension plans Defined contribution The National Grid YouPlan National Grid pays contributions into YouPlan to provide DC benefits on behalf of employees. National Grid provides a double match of member contributions, up to a maximum of 6% of member salary. YouPlan was established in 2013 and is the qualifying scheme that is typically used for automatic enrolment of new hires. Previous DC benefits were transferred to YouPlan in 2013. Defined benefit National Grid’s DB pension arrangements are held in separate Trustee-administered funds. The arrangements are managed by Trustee companies with boards consisting of company- and member-appointed directors. The arrangements are subject to independent actuarial funding valuations at least every three years, and following consultation and agreement with us, the qualified actuary certifies the employers’ contributions, which, together with the specified contributions payable by the employees and proceeds from the plans’ assets, are expected to be sufficient to fund the benefits payable. The results of the most recent actuarial valuations are shown below. See page 147 for the assumptions used for IAS 19 (revised) purposes. Actuarial valuations for all the schemes are currently being performed as at 31 March 2019. Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Latest full actuarial valuation 31 March 2017 31 March 2017 31 March 2016 Actuary Willis Towers Watson Willis Towers Watson Aon Hewitt Market value of scheme assets at latest valuation £6,716m £5,849m £2,553m Actuarial value of benefits due to members £6,627m £6,057m £3,053m Market value as percentage of benefits 101% 97% 84% Funding surplus/(deficit) £89m (£208m) (£500m) Funding surplus/(deficit) net of tax £74m (£173m) (£415m) National Grid UK Pension Scheme NGUKPS consists of three sections, each legally and actuarially separate. Sections A and B are supported by companies within the Group, while Section C is supported by Cadent Gas Limited. The scheme closed to new hires on 1 April 2002. Section A Following the last actuarial valuation, Section A was in surplus, and currently no deficit funding contributions are being made to the section. National Grid and the Trustees have agreed a schedule of contributions whereby the employers will contribute 51.8% of pensionable salary, less member contributions, in respect of ongoing service costs. This rate is deemed to be sufficient to meet the statutory funding objective during the period for which it is in force. As part of the sectionalisation of NGUKPS on 1 January 2017, a guarantee of £1 billion has been provided to Section A. This payment is contingent on insolvency or on failure to pay pension obligations to Section A and can be claimed against National Grid plc, National Grid Holdings One plc or Lattice Group Limited (up to £1 billion in total). Section B The last actuarial valuation determined that Section B was in deficit. National Grid and the Trustees agreed on a schedule of contributions, whereby deficit funding of approximately £32 million is payable by 30 September each year from 2017 until 2022, with an additional £8 million payable by 30 September 2023. All deficit funding amounts due will be adjusted for changes in the Retail Price Index (RPI). The funding shortfall is expected to be eliminated by September 2023. The employer also contributes 51.4% of pensionable salary, less member contributions, in respect of the ongoing service cost. National Grid Electricity Group of the Electricity Supply Pension Scheme The last full actuarial valuation for the NGEG of the ESPS determined that the scheme was in deficit. National Grid and the Trustees agreed on a schedule of contributions, whereby deficit funding of £48 million is payable each year from 2016 to 2027, which should lead to the elimination of the funding shortfall by March 2027. All deficit funding amounts due will be adjusted for changes in the RPI. In addition, National Grid contributes 40.7% of pensionable salary, less member contributions, in respect of the ongoing service cost. The scheme closed to new hires from 1 April 2006. The scheme holds a longevity insurance contract which covers improvements in longevity, providing long-term protection to the scheme, should members live longer than currently expected. National Grid is also responsible for the costs of administration and the Pension Protection Fund (PPF) levies for both Sections A and B of NGUKPS, and NGEG of ESPS. Security arrangements National Grid has also established security arrangements with charges in favour of the Trustees. Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Value of security arrangements at 31 March 2019 £315m £179m £250m Principal supporting employers National Grid plc and National Grid UK Limited National Grid Gas plc (NGG) National Grid Electricity Transmission plc (NGET) Additional amounts payable 1 £72m A maximum of £280m A maximum of £500m 1. These amounts are payable if certain trigger events occur which have been individually agreed between the schemes and their relevant supporting employers. The majority of the security is provided in the form of letters of credit with the remainder in surety bonds. The assets held in security will be paid to the respective section or scheme in the event that the relevant supporting employer is subject to an insolvency event or fails to make the required contributions. The assets will also be paid to the relevant section or scheme where either NGG or NGET loses its licence to operate under relevant legislation. Counter indemnities have also been taken out to ensure the obligations will be fulfilled. 25. Pensions and other post-retirement benefits continued US pension plans National Grid has multiple DC pension plans, primarily comprised of employee savings and Company matching contributions. Non-union employees hired after 1 January 2011, as well as new hires in the majority of represented union employees, receive a core contribution into the DC plan, irrespective of the employee’s contribution into the plan. National Grid also sponsors four non-contributory DB pension plans. The DB plans provide retirement benefits to vested union employees, as well as vested non-union employees hired before 1 January 2011. Benefits under these plans generally reflect age, years of service and compensation and are paid in the form of an annuity or lump sum. An independent actuary performs valuations annually. The Company funds the DB plans by contributing no less than the minimum amount required, but no more than the maximum tax-deductible amount allowed under US Internal Revenue Service regulations. The range of contributions determined under these regulations can vary significantly depending upon the funded status of the plans. At present, there is some flexibility in the amount that is contributed on an annual basis. In general, the Company’s policy for funding the US pension plans is to contribute the amounts collected in rates and capitalised in the rate base during the year, to the extent that the funding is no less than the minimum amount required. For the current financial year, these contributions amounted to approximately £231 million . The assets of the plans are held in trusts and administered by the Retirement Plans Committee comprised of appointed employees of the Company. US retiree healthcare and life insurance plans National Grid provides healthcare and life insurance benefits to eligible employees, post-retirement. Eligibility is based on certain age and length of service requirements, and in most cases retirees contribute to the cost of their healthcare coverage. In the US, there is no governmental requirement to pre-fund post-retirement healthcare and life insurance plans. However, in general, the Company’s policy for funding the US retiree healthcare and life insurance plans is to contribute amounts collected in rates and capitalised in the rate base during the year. For the current financial year, these contributions amounted to £14 million . Actuarial assumptions The Company has applied the following financial assumptions in assessing DB liabilities. UK pensions 2019 2018 2017 % % % Discount rate – past service 2.40 2.60 2.40 Discount rate – future service 2.45 2.65 2.65 Salary increases 3.50 3.40 3.50 Rate of increase in RPI – past service 3.25 3.15 3.20 Rate of increase in RPI – future service 3.20 3.10 3.15 The discount rates for UK pension liabilities have been determined by reference to appropriate yields on high-quality corporate bonds prevailing in the UK debt markets at the reporting date. Since 2018, we have adopted different discount rates for future and past service based on the duration of future and past service plan liabilities. The rate of increase in salaries has been set using a promotional scale where appropriate. The rates of increases stated are not indicative of historical increases awarded or a guarantee of future increase, but merely an appropriate assumption used in assessing DB liabilities. Retail Price Index (RPI) is the key assumption that determines assumed increases in pensions in payment and deferment in the UK only. Consistent with the derivation of the discount rate, the RPI assumption reflects the duration of the active liabilities to be adopted in the calculation of the future service obligations. US pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 % % % % % % Discount rate 3.95 4.00 4.25 3.95 4.00 4.25 Salary increases 3.50 3.50 3.50 3.50 3.50 3.50 Initial healthcare cost trend rate n/a n/a n/a 7.25 7.50 7.00 Ultimate healthcare cost trend rate n/a n/a n/a 4.50 4.50 4.50 Discount rates for US pension liabilities have been determined by reference to appropriate yield on high-quality corporate bonds prevailing in the US debt markets 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 2028 (2018 and 2017: 2028). 2019 2018 2017 UK years US years UK years US years UK years US years Assumed life expectations for a retiree age 65 Males 22.0 22.1 22.3 22.0 22.9 21.9 Females 23.6 24.2 23.9 24.2 24.7 24.1 In 20 years: Males 23.3 23.7 23.7 23.6 25.1 23.6 Females 25.2 25.9 25.5 25.8 27.1 25.7 25. Pensions and other post-retirement benefits continued Maturity profile of DB obligations The weighted average duration of the DB obligation for each category of scheme is 15 years for UK pension schemes; 13 years for US pension schemes and 16 years for US other post-retirement benefits. As at the reporting date, the present value of the funded obligations split according to member status was approximately: • UK pensions: 10% active members (2018: 10% ; 2017: 12% ); 16% deferred members (2018: 18% ; 2017: 19% ); 74% pensioner members (2018: 72% ; 2017: 69% ); • US pensions: 37% active members (2018: 38% ; 2017: 38% ); 9% deferred members (2018: 8% ; 2017: 9% ); 54% pensioner members (2018: 54% ; 2017: 53% ); and • US other post-retirement benefits: 39% active members (2018: 38% ; 2017: 39% ); 0% deferred members (2018: 0% ; 2017: 0% ); 61% pensioner members (2018: 62% ; 2017: 61% ). For sensitivity analysis see note 35. Amounts recognised in the consolidated statement of financial position 2019 2018 2017 £m £m £m Present value of funded obligations (24,609 ) (23,747 ) (25,890 ) Fair value of plan assets 24,793 23,858 24,375 184 111 (1,515 ) Present value of unfunded obligations (330 ) (307 ) (340 ) Other post-employment liabilities (72 ) (67 ) (78 ) Net defined benefit liability (218 ) (263 ) (1,933 ) Represented by: Liabilities (1,785 ) (1,672 ) (2,536 ) Assets 1,567 1,409 603 (218 ) (263 ) (1,933 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Present value of funded obligations (14,200 ) (14,152 ) (15,565 ) (6,901 ) (6,349 ) (6,790 ) (3,508 ) (3,246 ) (3,535 ) Fair value of plan assets 15,507 15,330 15,489 6,646 6,030 6,322 2,640 2,498 2,564 1,307 1,178 (76 ) (255 ) (319 ) (468 ) (868 ) (748 ) (971 ) Present value of unfunded obligations (76 ) (74 ) (80 ) (254 ) (233 ) (260 ) — — — Other post-employment liabilities — — — — — — (72 ) (67 ) (78 ) Net defined benefit asset/(liability) 1,231 1,104 (156 ) (509 ) (552 ) (728 ) (940 ) (815 ) (1,049 ) Represented by: Liabilities (76 ) (74 ) (536 ) (769 ) (783 ) (951 ) (940 ) (815 ) (1,049 ) Assets 1,307 1,178 380 260 231 223 — — — 1,231 1,104 (156 ) (509 ) (552 ) (728 ) (940 ) (815 ) (1,049 ) The recognition of the pension assets in both the UK in relation to the NGUKPS, the NGEG of ESPS and the Niagara Mohawk Plan in the US reflect legal and actuarial advice that we have taken regarding recognition of surpluses under IFRIC 14. In all three cases we have concluded that the Group has an unconditional right to a refund from the individual plans, including from each Section of the NGUKPS and the NGEG of ESPS, in the event of a winding-up. In the UK, the Trustees must seek the agreement of the Company to any benefit augmentation beyond the provisions set out in the Scheme Rules. In the US, the surplus assets may be used to pay benefits under other Plans, thereby allowing the Company to settle other liabilities under other Plans. 25. Pensions and other post-retirement benefits continued Amounts recognised in the income statement and statement of other comprehensive income 2019 2018 2017 £m £m £m Included within operating costs Administration costs 14 16 16 Included within payroll costs Defined benefit scheme costs: Current service cost 193 193 232 Past service cost – augmentations 5 1 1 Past service credit – redundancies (7 ) (1 ) (1 ) Special termination benefit cost – redundancies 55 9 7 Past service cost – plan amendments 34 — — 280 202 239 Included within finance income and costs Net interest cost 22 65 105 Included within gain on disposal of discontinued operations Administration costs — — 5 Disposal of UK Gas Distribution — — 34 — — 39 Total included in income statement 1,2 316 283 399 Remeasurement gains of pension assets and post-retirement benefit obligations 68 1,313 348 Exchange adjustments (101 ) 175 (345 ) Total included in the statement of other comprehensive income 2 (33 ) 1,488 3 1. Amounts recognised in the income statement include operating costs of £nil (2018: £nil ; 2017: £1 million ); payroll costs of £nil (2018: £nil ; 2017: £35 million ); and net interest of £nil (2018: £nil ; 2017: £2 million income) presented within profit from discontinued operations. These amounts all relate to UK pensions. In addition there is a net charge of £52 million (2018: £nil ; 2017: £nil ) relating to redundancy pension costs in respect of the UK cost efficiency and restructuring programme included within exceptional items. 2. Amounts recognised in the statement of other comprehensive income include remeasurements of pension assets and post-retirement benefit obligations of £nil (2018: £nil ; 2017: £75 million loss) presented within discontinued operations. These amounts all relate to UK pensions. The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Included within operating costs Administration costs 6 6 6 7 9 9 1 1 1 Included within payroll costs Defined benefit scheme costs: Current service cost 41 49 76 104 98 103 48 46 53 Past service cost – augmentations 5 1 1 — — — — — — Past service credit – redundancies (7 ) (1 ) (1 ) — — — — — — Special termination benefit cost – redundancies 55 9 7 — — — — — — Past service cost – plan amendments 34 — — — — — — — — 128 58 83 104 98 103 48 46 53 Included within finance income and costs Net interest cost (31 ) 3 — 21 27 43 32 35 62 Included within gain on disposal of discontinued operations Administration costs — — 5 — — — — — — Disposal of UK Gas Distribution — — 34 — — — — — — — — 39 — — — — — — Total included in income statement 103 67 128 132 134 155 81 82 116 Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations 57 1,177 (541 ) (14 ) 27 319 25 109 570 Exchange adjustments — — — (42 ) 75 (140 ) (59 ) 100 (205 ) Total included in the statement of other comprehensive income 57 1,177 (541 ) (56 ) 102 179 (34 ) 209 365 25. Pensions and other post-retirement benefits continued Reconciliation of the net defined benefit liability 2019 2018 2017 £m £m £m Opening net defined benefit liability (263 ) (1,933 ) (2,585 ) Cost recognised in the income statement (316 ) (283 ) (399 ) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (33 ) 1,488 3 Employer contributions 419 475 1,073 Other movements (25 ) (10 ) (25 ) Closing net defined benefit liability (218 ) (263 ) (1,933 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Opening net defined benefit asset/(liability) 1,104 (156 ) (15 ) (552 ) (728 ) (1,009 ) (815 ) (1,049 ) (1,561 ) Cost recognised in the income statement (103 ) (67 ) (128 ) (132 ) (134 ) (155 ) (81 ) (82 ) (116 ) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income 57 1,177 (541 ) (56 ) 102 179 (34 ) 209 365 Employer contributions 174 150 528 231 208 257 14 117 288 Other movements (1 ) — — — — — (24 ) (10 ) (25 ) Closing net defined benefit 1,231 1,104 (156 ) (509 ) (552 ) (728 ) (940 ) (815 ) (1,049 ) 25. Pensions and other post-retirement benefits continued Changes in the present value of defined benefit obligations (including unfunded obligations) 2019 2018 2017 £m £m £m Opening defined benefit obligations (24,054 ) (26,230 ) (28,952 ) Current service cost (193 ) (193 ) (232 ) Interest cost (771 ) (775 ) (1,057 ) Actuarial (losses)/gains – experience (69 ) (100 ) 166 Actuarial gains – demographic assumptions 266 671 225 Actuarial (losses)/gains – financial assumptions (619 ) 174 (3,377 ) Past service credit – redundancies 7 1 1 Special termination benefit cost – redundancies (55 ) (9 ) (7 ) Past service cost – augmentations (5 ) (1 ) (1 ) Past service cost – plan amendments (34 ) — — Medicare subsidy received (19 ) (21 ) (14 ) Obligations transferred on disposal of UK Gas Distribution — — 6,970 Employee contributions (1 ) (1 ) (1 ) Benefits paid 1,376 1,285 1,443 Exchange adjustments (768 ) 1,145 (1,394 ) Closing defined benefit obligations (24,939 ) (24,054 ) (26,230 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Opening defined benefit obligations (14,226 ) (15,645 ) (19,416 ) (6,582 ) (7,050 ) (6,145 ) (3,246 ) (3,535 ) (3,391 ) Current service cost (41 ) (49 ) (76 ) (104 ) (98 ) (103 ) (48 ) (46 ) (53 ) Interest cost (358 ) (366 ) (615 ) (277 ) (273 ) (285 ) (136 ) (136 ) (157 ) Actuarial (losses)/gains – experience (56 ) (95 ) 106 (52 ) (38 ) (2 ) 39 33 62 Actuarial gains – demographic assumptions 224 565 214 — 30 2 42 76 9 Actuarial (losses)/gains – financial assumptions (568 ) 604 (3,751 ) (24 ) (279 ) 37 (27 ) (151 ) 337 Past service credit – redundancies 7 1 1 — — — — — — Special termination benefit cost – redundancies (55 ) (9 ) (7 ) — — — — — — Past service cost – augmentations (5 ) (1 ) (1 ) — — — — — — Past service cost – plan amendments (34 ) — — — — — — — — Medicare subsidy received — — — — — — (19 ) (21 ) (14 ) Obligations transferred on disposal of UK Gas Distribution — — 6,970 — — — — — — Employee contributions (1 ) (1 ) (1 ) — — — — — — Benefits paid 837 770 931 398 362 349 141 153 163 Exchange adjustments — — — (514 ) 764 (903 ) (254 ) 381 (491 ) Closing defined benefit obligations (14,276 ) (14,226 ) (15,645 ) (7,155 ) (6,582 ) (7,050 ) (3,508 ) (3,246 ) (3,535 ) 25. Pensions and other post-retirement benefits continued Changes in the value of plan assets 2019 2018 2017 £m £m £m Opening fair value of plan assets 23,858 24,375 26,434 Interest income 749 710 952 Return on plan assets in excess of interest 490 568 3,334 Administration costs (14 ) (16 ) (21 ) Employer contributions 419 475 1,073 Employee contributions 1 1 1 Benefits paid (1,377 ) (1,285 ) (1,443 ) Exchange adjustments 667 (970 ) 1,049 Assets transferred on disposal of UK Gas Distribution — — (7,004 ) Closing fair value of plan assets 24,793 23,858 24,375 Actual return on plan assets 1,239 1,278 4,286 Expected contributions to plans in the following year 307 363 491 The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Opening fair value of plan assets 15,330 15,489 19,401 6,030 6,322 5,136 2,498 2,564 1,897 Interest income 389 363 615 256 246 242 104 101 95 Return on plan assets in excess 457 103 2,890 62 314 282 (29 ) 151 162 Administration costs (6 ) (6 ) (11 ) (7 ) (9 ) (9 ) (1 ) (1 ) (1 ) Employer contributions 174 150 528 231 208 257 14 117 288 Employee contributions 1 1 1 — — — — — — Benefits paid (838 ) (770 ) (931 ) (398 ) (362 ) (349 ) (141 ) (153 ) (163 ) Exchange adjustments — — — 472 (689 ) 763 195 (281 ) 286 Assets transferred on disposal of UK Gas Distribution — — (7,004 ) — — — — — — Closing fair value of plan assets 15,507 15,330 15,489 6,646 6,030 6,322 2,640 2,498 2,564 Actual return on plan assets 846 466 3,505 318 560 524 75 252 257 Expected contributions to plans in the following year 148 140 128 150 221 229 9 2 134 Asset allocation strategy Each plan’s investment strategy is formulated specifically in order to target specific asset allocations and returns, and to manage risk. The asset allocation of the plans as at 31 March 2019 is as follows: UK pensions US pensions US other post-retirement benefits % % % Equities 12.7 40.8 60.2 Corporate bonds 23.4 26.4 0.7 Government securities 39.4 16.0 20.6 Property 5.5 4.7 — Diversified alternatives 5.0 10.1 12.9 Liability matching assets 11.1 — — Infrastructure — 1.5 — Cash and cash equivalents 1.9 0.3 — Other 1.0 0.2 5.6 100.0 100.0 100.0 25. Pensions and other post-retirement benefits continued Defined benefit investment strategies and risks DB pension schemes can pose a significant risk to future cash flows, as National Grid underwrites the financial and demographic risks associated with these plans. Although the governing bodies have sole responsibility for setting investment strategies and managing risks, National Grid closely works with and supports the governing bodies of each scheme, to assist them in mitigating the risks associated with their schemes and to ensure that the schemes are funded to meet their obligations. In the UK, each scheme has a Trustee that is the governing body. The Trustees’ responsibilities are set out in the Trust Deed and Rules. In the US, the fiduciary committee for all the retirement plans is the Retirement Plan Committee (RPC). The RPC is structured in accordance with US laws governing retirement plans under the Employee Retirement Income Security Act (ERISA). The Trustees and RPC, after taking advice from professional investment advisors and in consultation with National Grid, set the key principles, including expected returns, risk and liquidity requirements. In setting these they take into account expected contributions, maturity of the pension liabilities, and in the UK, the strength of the covenant. The Trustees and RPC formulate an investment strategy to manage risk through diversification, including the use of liability-matching assets, which move in line with the long-term liabilities of the scheme, and return-seeking assets, some of which are designed to mitigate downside risk. Where appropriate, the strategies may include interest rate and inflation hedging instruments, and currency hedging to hedge overseas holdings. Investments are usually grouped into: • Return-seeking assets: equities, property and diversified funds where the objective is to achieve growth within the constraints of the schemes’ risk profiles. These assets should produce returns greater than the liability increase, so improving the funding position, and are assessed by reference to benchmarks and performance targets agreed with the investment managers; and • Liability-matching assets: liability-driven investment (LDI) funds and swaps, where the objective is to secure fixed or inflation-adjusted cash flows in future. These investments are generally expected to match the change in liability valuation, so protecting the funding position. Bonds and securities are also measured against certain market benchmarks. Investments are predominantly made in assets considered to be of investment grade. Where investments are made in non-investment grade assets, the higher volatility involved is carefully judged and balanced against the expected higher returns. Similarly, investments are made predominantly in regulated markets. Where investments are made either in non-investment grade assets or outside of regulated markets, investment levels are kept to prudent levels and subject to agreed control ranges, to control the risk. Should these investments fall outside the pre-agreed ranges, corrective actions and timescales are agreed with the investment manager to remedy the position. The governing bodies ensure that the performance of investment managers is regularly reviewed against measurable objectives, consistent with each scheme’s long-term objectives and accepted risk levels. Where required, the portfolios are amended, or investment managers changed. The Trustees and RPC can generally delegate responsibility for the selection of specific bonds, securities and other investments to appointed investment managers. Investment managers are selected based on the required skills, expertise of those markets, process and financial security to manage the investments. The investment managers use their skill and expertise to manage the investments competently. In some cases they may further delegate this responsibility, through appointing sub-managers. The schemes hold sufficient cash to meet benefit requirements, with other investments being held in liquid or realisable assets to meet unexpected cash flow requirements. The schemes do not borrow money, or act as guarantor, to provide liquidity (unless it is temporary). The NGUKPS Trustee believes that long-term shareholder value and financial success can be protected and enhanced by a responsible environmental, social and corporate governance (ESG) policy. As such, the NGUKPS’ appointed investment managers are expected to be mindful of ESG issues when managing the scheme’s assets. Day-to-day stewardship (voting and engagement) is delegated to the investment managers and they are encouraged to adhere to the UK Stewardship Code. The most significant risks associated with the DB plans are: • Asset volatility – the schemes invest in a variety of asset classes, but principally in equities, government securities, corporate bonds and property. Consequently actual returns will differ from the underlying discount rate adopted, impacting on the funding position of the scheme through the net balance sheet asset or liability. Each scheme seeks to balance the level of investment return required with the risk that it can afford to take, to design the most appropriate investment portfolio. Volatility will be controlled through using liability-matching asset strategies, interest rate hedging and management of foreign exchange exposure, as well as diversification of the return-seeking assets; • Changes

Provisions

Provisions	12 Months Ended
Provisions	Mar. 31, 2019
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Provisions	Provisions We make provisions when an obligation exists resulting from a past event, and it is probable that cash will be paid to settle it, but the exact amount of cash required can only be estimated. The main estimates relate to environmental remediation and decommissioning costs for various sites we own or have owned and other provisions, including restructuring plans and lease contracts we have entered into that are now loss making. The evaluation of the likelihood of the contingent events has required best judgement by management regarding the probability of exposure to potential loss. Should circumstances change following unforeseeable developments, the likelihood could alter. In the current year we recognised a charge to restructuring provisions, reflecting the review and reorganisation of our core regulated businesses in both the UK and US. Provisions are recognised where a legal or constructive obligation exists at the reporting date, as a result of a past event, where the amount of the obligation can be reliably estimated and where the outflow of economic benefit is probable. Provision is made for decommissioning and environmental costs, based on future estimated expenditures, discounted to present values. An initial estimate of decommissioning and environmental costs attributable to property, plant and equipment is recorded as part of the original cost of the related property, plant and equipment. Changes in the provision arising from revised estimates or discount rates or changes in the expected timing of expenditures that relate to property, plant and equipment are recorded as adjustments to their carrying value and depreciated prospectively over their remaining estimated useful economic lives; otherwise such changes are recognised in the income statement. The unwinding of the discount is included within the income statement as finance costs. Environmental £m Decommissioning £m Restructuring £m Emissions £m Other £m Total provisions £m At 1 April 2017 1,721 221 17 32 597 2,588 Exchange adjustments (158 ) (9 ) — (2 ) (26 ) (195 ) Additions 27 2 10 12 23 74 Unused amounts reversed 1 (45 ) (19 ) (6 ) — (37 ) (107 ) Unwinding of discount 61 5 1 — 8 75 Utilised 2 (75 ) (6 ) (7 ) (34 ) (146 ) (268 ) Transfers 3 — — (12 ) — (103 ) (115 ) At 31 March 2018 1,531 194 3 8 316 2,052 Exchange adjustments 103 7 — — 14 124 Additions 32 18 125 16 35 226 Unused amounts reversed 1 (36 ) (10 ) (3 ) (6 ) (10 ) (65 ) Unwinding of discount 62 5 — — 7 74 Utilised 2 (53 ) (26 ) (42 ) (9 ) (79 ) (209 ) Transfers 3 — — — — (3 ) (3 ) At 31 March 2019 1,639 188 83 9 280 2,199 2019 2018 £m £m Current 316 273 Non-current 1,883 1,779 2,199 2,052 1. Unused amounts reversed from other provisions include £ nil (2018: £16 million ) in relation to discontinued operations. 2. Utilised amounts for other provisions include £20 million (2018: £77 million ) in relation to discontinued operations. 3. Represents net amounts transferred to trade and other payables (see note 22) of £3 million ( 2018 : £115 million ). 26. Provisions continued Environmental provisions The environmental provision represents the estimated restoration and remediation costs relating to a number of sites owned and managed by subsidiary undertakings, together with certain US sites that National Grid no longer owns. The environmental provision is as follows: 2019 2018 Discounted £m Undiscounted £m Real discount rate Discounted £m Undiscounted £m Real discount rate UK sites 189 210 1 % 213 235 1 % US sites 1,450 1,555 1 % 1,318 1,410 1 % 1,639 1,765 1,531 1,645 The remediation expenditure in the UK relates to old gas manufacturing sites and also to electricity transmission sites. Cash flows are expected to be incurred until 2076 although the weighted average duration of the cash flows is 12 years . A number of estimation uncertainties affect the calculation of the provision, including the impact of regulation, the accuracy of site surveys, unexpected contaminants, transportation costs, the impact of alternative technologies and changes in the real discount rate. This provision incorporates our best estimate of the financial effect of these uncertainties, but future changes in any of the assumptions could materially impact the calculation of the provision. The undiscounted amount is the undiscounted best estimate of the liability having regard to these uncertainties. The remediation expenditure in the US is expected to be incurred until 2069 . The weighted average duration of the cash flows is nine years . The uncertainties regarding the calculation of this provision are similar to those considered in respect of UK sites. This expenditure is expected to be largely recoverable from ratepayers under the terms of various rate agreements in the US. Decommissioning provisions The decommissioning provision represents £80 million ( 2018 : £71 million ) of expenditure relating to asset retirement obligations estimated to be incurred until 2115 , and £90 million ( 2018 : £104 million ) of expenditure relating to the demolition of gas holders estimated to be incurred until 2026 . It also includes the net present value of the estimated expenditure (discounted at a real rate of 1% ) expected to be incurred until 2044 in respect of the decommissioning of certain US nuclear generating units that National Grid no longer owns. Restructuring provisions During the year, a cost-efficiency and restructuring programme was undertaken in both our UK and US businesses, as detailed in note 5. This resulted in the recognition of a £125 million charge in the year and a closing provision of £83 million . We expect the majority of the provision to be utilised within one year. Other provisions Included within other provisions at 31 March 2019 are the following amounts: • £30 million ( 2018 : £50 million ) in respect of legacy provisions recognised following the sale of UK Gas Distribution; • £29 million ( 2018 : £48 million ) in respect of onerous lease commitments and rates payable on surplus properties with expenditure expected to be incurred until 2039 ; • £164 million ( 2018 : £152 million ) of estimated liabilities in respect of past events insured by insurance subsidiary undertakings, including employer liability claims. In accordance with insurance industry practice, these estimates are based on experience from previous years and there is, therefore, no identifiable payment date; and • £13 million ( 2018 : £13 million ) in respect of obligations associated with investments in joint ventures and associates.

Share capital

Share capital	12 Months Ended
Share capital	Mar. 31, 2019
Share Capital, Reserves And Other Equity Interest [Abstract]
Share capital	Share capital Ordinary share capital represents the total number of shares issued which are publicly traded. We also disclose the number of treasury shares the Company holds, which are shares that the Company has bought itself, predominately to actively manage scrip issuances and settle employee share option and reward plan liabilities. Share capital is accounted for as an equity instrument. An equity instrument is any contract that includes a residual interest in the consolidated assets of the Company after deducting all its liabilities and is recorded at the proceeds received, net of direct issue costs, with an amount equal to the nominal amount of the shares issued included in the share capital account and the balance recorded in the share premium account. Allotted, called-up and fully paid million £m At 1 April 2017 3,943 449 Effect of share consolidation 1 (328 ) — Issued during the year in lieu of dividends 2 23 3 At 31 March 2018 3,638 452 Issued during the year in lieu of dividends 2 49 6 At 31 March 2019 3,687 458 1. On 22 May 2017 the ordinary share capital was consolidated with 11 new ordinary shares of 12 204 / 473 pence nominal value issued for every 12 existing ordinary shares of 11 17 / 43 pence nominal value. This consolidation was completed to maintain the comparability of the Company’s share price before and after the special dividend. 2. The issue of shares under the scrip dividend programme is considered to be a bonus issue under the terms of the Companies Act 2006, and the nominal value of the shares is charged to the share premium account. The share capital of the Company consists of ordinary shares of 12 204 ⁄ 473 pence nominal value each including ADSs. The ordinary shares and ADSs allow holders to receive dividends and vote at general meetings of the Company. The Company holds treasury shares but may not exercise any rights over these shares including the entitlement to vote or receive dividends. There are no restrictions on the transfer or sale of ordinary shares. In line with the provisions of the Companies Act 2006, the Company has amended its Articles of Association and ceased to have authorised share capital. Treasury shares At 31 March 2019 , the Company held 277 million ( 2018 : 283 million ) of its own shares. The market value of these shares as at 31 March 2019 was £2,359 million ( 2018 : £2,270 million ). The Company made the following transactions in respect of its own shares during the year ended 31 March 2019 : i) During the year, 3 million ( 2018 : 3 million ) treasury shares were gifted to National Grid Employee Share Trusts and 3 million ( 2018 : 5 million ) treasury shares were re-issued in relation to employee share schemes, in total representing approximately 0.2% ( 2018 : 0.2% ) of the ordinary shares in issue as at 31 March 2019 . The nominal value of these shares was £1 million ( 2018 : £1 million ) and the total proceeds received were £18 million ( 2018 : £33 million ). ii) During the year, the Company made payments totalling £2 million ( 2018 : £5 million ) to National Grid Employee Share Trusts to enable the trustees to make purchases of National Grid plc shares in order to satisfy the requirements of employee share option and reward plans. During the prior year, the Company completed a share repurchase programme as part of the return of cash to shareholders following the sale of UK Gas Distribution in addition to the management of the dilutive effect of share issuances under the scrip dividend programme. As a result the Company repurchased 114 million ordinary shares for aggregate consideration of £1,017 million including transaction costs. The shares repurchased had a nominal value of £14 million and represented approximately 3.1% of the ordinary shares in issue as at 31 March 2018 . The maximum number of ordinary shares held in treasury during the year was 283 million ( 2018 : 283 million ) representing approximately 7.7% ( 2018 : 7.8% ) of the ordinary shares in issue as at 31 March 2019 and having a nominal value of £35 million ( 2018 : £35 million ).

Other equity reserves

Other equity reserves	12 Months Ended
Other equity reserves	Mar. 31, 2019
Disclosure of reserves within equity [abstract]
Other equity reserves	Other equity reserves Other equity reserves are different categories of equity as required by accounting standards and represent the impact of a number of our historical transactions. Other equity reserves comprise the translation reserve (see accounting policy D in note 1), cash flow hedge reserve and the cost of hedging reserve (see note 32), available-for-sale reserve, debt instruments at fair value through other comprehensive income reserve (FVOCI debt) and equity investments at fair value through other comprehensive income reserve (FVOCI equity) (see note 15), the capital redemption reserve and the merger reserve. The merger reserve arose as a result of the application of merger accounting principles under the then prevailing UK GAAP, which under IFRS 1 was retained for mergers that occurred prior to the IFRS transition date. Under merger accounting principles, the difference between the carrying amount of the capital structure of the acquiring vehicle and that of the acquired business was treated as a merger difference and included within reserves. The cash flow hedge reserve will amortise as the committed future cash flows from borrowings are paid or capitalised in fixed assets (as described in note 32). Cost of hedging, FVOCI debt, and FVOCI equity reserves arose as a result of the adoption of IFRS 9 on 1 April 2018. See note 15 for further detail on FVOCI debt and FVOCI equity reserves and note 32 in respect of cost of hedging reserve. As the amounts included in other equity reserves are not attributable to any of the other classes of equity presented, they have been disclosed as a separate classification of equity. Translation £m Cash flow hedge £m Cost of hedging £m Available- for-sale £m FVOCI equity £m FVOCI debt £m Own credit £m Capital redemption £m Merger £m Total £m At 1 April 2016 548 (45 ) — 120 — — — 19 (5,165 ) (4,523 ) Exchange adjustments 1 346 — — — — — — — — 346 Net (losses)/gains taken to equity — (36 ) — 81 — — — — — 45 Transferred to/(from) profit or loss — 227 — (25 ) — — — — — 202 Tax — (43 ) — (14 ) — — — — — (57 ) At 31 March 2017 894 103 — 162 — — — 19 (5,165 ) (3,987 ) Exchange adjustments 1 (504 ) — — — — — — — — (504 ) Net gains/(losses) taken to equity — 19 — (30 ) — — — — — (11 ) Share of net gains of associates taken to equity — 5 — — — — — — — 5 Transferred from profit or loss — (3 ) — (73 ) — — — — — (76 ) Tax — 4 — 29 — — — — — 33 At 31 March 2018 (as previously reported) 390 128 — 88 — — — 19 (5,165 ) (4,540 ) Transfer on transition to IFRS 9 — (3 ) 76 (88 ) 34 46 7 — — 72 At 1 April 2018 (as restated) 390 125 76 — 34 46 7 19 (5,165 ) (4,468 ) Exchange adjustments 1 346 — — — — — — — — 346 Net (losses)/gains taken to equity — (40 ) (107 ) — — 2 7 — — (138 ) Share of net gains of associates taken to equity — 1 — — — — — — — 1 Transferred to profit or loss — — 41 — — — — — — 41 Net losses in respect of cash flow hedging of capital expenditure — (13 ) — — — — — — — (13 ) Tax — 6 7 — — — (1 ) — — 12 Cash flow hedges transferred to the statement of financial position, net of tax — (18 ) — — — — — — — (18 ) At 31 March 2019 736 61 17 — 34 48 13 19 (5,165 ) (4,237 ) 1. The exchange adjustments recorded in the translation reserve comprise a gain of £896 million ( 2018 : loss of £1,304 million ; 2017 : gain of £1,364 million ) relating to the translation of foreign operations offset by a loss of £550 million ( 2018 : gain of £800 million ; 2017 : loss of £1,018 million ) relating to borrowings, cross-currency swaps and foreign exchange forward contracts used to hedge the net investment in the non-sterling denominated subsidiaries. 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.

Net debt

Net debt	12 Months Ended
Net debt	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Net debt	Net debt Net debt represents the amount of borrowings and overdrafts less cash, current financial investments and related financing derivatives. Funding and liquidity risk management is carried out by the treasury function under policies and guidelines approved by the Finance Committee of the Board. The Finance Committee is responsible for the regular review and monitoring of treasury activity and for the approval of specific transactions, the authority for which fall outside the delegation of authority to management. The primary objective of the treasury function is to manage our funding and liquidity requirements. A further important objective is to manage the associated financial risks, in the form of interest rate risk and foreign exchange risk, to within pre-authorised parameters. Details of the main risks arising from our financing and commodity hedging activities can be found in the risk factors discussion starting on page 212 and in note 32 to the consolidated financial statements. Investment of surplus funds, usually in short-term fixed deposits or placements with money market funds that invest in highly liquid instruments of high credit quality, is subject to our counterparty risk management policy. (a) Reconciliation of net cash flow to movement in net debt 2019 2018 2017 £m £m £m (Decrease)/increase in cash and cash equivalents (80 ) (807 ) 984 (Decrease)/increase in financial investments (822 ) (5,953 ) 5,675 (Increase)/decrease in borrowings and related derivatives 1 (708 ) 1,209 (3,715 ) Net interest paid on the components of net debt 2 866 808 1,955 Change in debt resulting from cash flows (744 ) (4,743 ) 4,899 Changes in fair value of financial assets and liabilities and exchange movements (1,648 ) 2,098 (2,273 ) Net interest charge on the components of net debt (1,076 ) (1,017 ) (2,401 ) Disposal of UK Gas Distribution — — 5,890 Other non-cash movements (27 ) (66 ) (64 ) Movement in net debt (net of related derivative financial instruments) in the year (3,495 ) (3,728 ) 6,051 Net debt (net of related derivative financial instruments) at start of year (23,002 ) (19,274 ) (25,325 ) Impact of transition to IFRS 9 (32 ) — — Net debt (net of related derivative financial instruments) at end of year (26,529 ) (23,002 ) (19,274 ) Composition of net debt Net debt is made up as follows: 2019 2018 2017 £m £m £m Cash, cash equivalents and financial investments 2,233 3,023 9,880 Borrowings and bank overdrafts (28,730 ) (26,625 ) (28,638 ) Financing derivatives 1 (32 ) 600 (516 ) (26,529 ) (23,002 ) (19,274 ) 1. The financing derivatives balance included in net debt excludes the commodity derivatives (see note 17). 2. Excludes £23 million ( 2018 : £27 million ; 2017 : £nil ) cash interest from the Quadgas shareholder loan included within discontinued operations in the cash flow statement. 29. Net debt continued (b) Analysis of changes in net debt Cash and cash equivalents £m Bank overdrafts £m Net cash and cash equivalents £m Financial investments £m Borrowings £m Financing derivatives £m Total 1 £m At 1 April 2016 127 (3 ) 124 2,998 (28,341 ) (106 ) (25,325 ) Cash flow 2 1,001 (17 ) 984 5,624 (2,196 ) 487 4,899 Fair value gains and losses and exchange movements 16 — 16 141 (1,527 ) (903 ) (2,273 ) Interest income/(charges) 3 — — — 53 (2,221 ) (233 ) (2,401 ) Other non-cash movements — — — — (294 ) 230 (64 ) Disposal (5 ) 20 15 (75 ) 5,941 9 5,890 At 1 April 2017 1,139 — 1,139 8,741 (28,638 ) (516 ) (19,274 ) Cash flow 2 (807 ) — (807 ) (5,983 ) 2,108 (61 ) (4,743 ) Fair value gains and losses and exchange movements (3 ) — (3 ) (149 ) 1,088 1,162 2,098 Interest income/(charges) 3 — — — 85 (1,117 ) 15 (1,017 ) Other non-cash movements — — — — (66 ) — (66 ) At 31 March 2018 329 — 329 2,694 (26,625 ) 600 (23,002 ) Impact of transition to IFRS 9 — — — — (32 ) — (32 ) At 1 April 2018 (as restated) 329 — 329 2,694 (26,657 ) 600 (23,034 ) Cash flow 2 (80 ) — (80 ) (846 ) (240 ) 422 (744 ) Fair value gains and losses and exchange movements 3 — 3 93 (733 ) (1,011 ) (1,648 ) Interest income/(charges) 3 — — — 29 (1,062 ) (43 ) (1,076 ) Other non-cash movements — — — 11 (38 ) — (27 ) At 31 March 2019 252 — 252 1,981 (28,730 ) (32 ) (26,529 ) Balances at 31 March 2019 comprise: Non-current assets — — — — — 996 996 Current assets 252 — 252 1,981 — 56 2,289 Current liabilities — — — — (4,472 ) (282 ) (4,754 ) Non-current liabilities — — — — (24,258 ) (802 ) (25,060 ) 252 — 252 1,981 (28,730 ) (32 ) (26,529 ) 1. Includes accrued interest at 31 March 2019 of £223 million ( 2018 : £197 million ; 2017 : £210 million ). 2. Cash flow from financing activities relating to financing liabilities (proceeds and repayment of loans, net movement in short-term borrowings and derivatives and interest paid) includes cash outflow on non-debt-related items of £24 million (2018: £12 million ; 2017: £nil ) and excludes derivative cash inflow in relation to capital expenditure of £13 million (2018: £12 million ; 2017: £18 million ) and items relating to discontinued operations of £nil (2018: £231 million ; 2017: £(1,611) million ). 3. An exceptional income of £nil ( 2018 : £3 million income; 2017 : £1,313 million expense) is included in net interest charge on the components of net debt.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
Commitments and contingencies	Mar. 31, 2019
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Commitments and contingencies	Commitments and contingencies Commitments are those amounts that we are contractually required to pay in the future as long as the other party meets its obligations. These commitments primarily relate to operating lease rentals, 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. 2019 2018 £m £m Future capital expenditure Contracted for but not provided 1,973 1,843 Operating lease commitments 1 Less than 1 year 43 42 In 1 to 2 years 39 37 In 2 to 3 years 34 33 In 3 to 4 years 35 30 In 4 to 5 years 27 28 More than 5 years 123 122 301 292 Energy purchase commitments 2 Less than 1 year 1,353 1,237 In 1 to 2 years 779 700 In 2 to 3 years 651 563 In 3 to 4 years 827 449 In 4 to 5 years 862 410 More than 5 years 11,237 1,969 15,709 5,328 Guarantees 3 Guarantee of sublease for US property (expires 2040) 173 178 Guarantees of certain obligations of Grain LNG (expire up to 2025) 39 46 Guarantees of certain obligations for construction of HVDC West Coast Link (expires 2019) 139 213 Guarantees of certain obligations of Nemo Link Limited (various expiry dates) 19 63 Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates) 3 865 1,009 Guarantees of certain obligations of St William Homes LLP (various expiry dates) 4 22 98 Guarantees of certain obligations for construction of IFA 2 (expected expiry 2021) 3 505 729 Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024) 872 — Other guarantees and letters of credit (various expiry dates) 341 333 2,975 2,669 1. Following a review during the year, the comparatives have been refined to provide consistency with the current year. 2. 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). 3. Included within total guarantees are guarantees to both joint ventures and Engineering, Procurement and Construction contractors regarding the construction of interconnectors of £470 million (2018: £739 million ). 4. Includes guarantees to related parties. The total of future minimum sublease payments expected to be received under non-cancellable sub-leases is £86 million ( 2018 : £42 million ). Through the ordinary course of our operations, we are party to various litigation, claims and investigations. We do not expect the ultimate resolution of any of these proceedings to have a material adverse effect on our results of operations, cash flows or financial position.

Related party transactions

Related party transactions	12 Months Ended
Related party transactions	Mar. 31, 2019
Related party transactions [abstract]
Related party transactions	Related party transactions Related parties include joint ventures, associates, investments and key management personnel. The following significant transactions with related parties were in the normal course of business. Amounts receivable from and payable to related parties are due on normal commercial terms: 2019 2018 2017 £m £m £m Sales: Goods and services supplied to a pension plan 5 3 3 Sales: Goods and services supplied to joint ventures 1 151 14 78 Sales: Goods and services supplied to associates 2 192 220 — Purchases: Goods and services received from joint ventures 3 26 135 168 Purchases: Goods and services received from associates 3 141 160 169 Receivable from joint ventures 4 584 160 64 Receivable from associates 4 368 376 457 Payable to joint ventures 5 8 — 84 Payable to associates 12 17 27 Interest income from joint ventures 5 4 — Interest income from associates 23 27 — Dividends received from joint ventures 6 30 43 75 Dividends received from associates 7 171 170 24 1. During the year, £139 million (2018: £5 million ) of property sites were sold to joint venture St William Homes LLP. 2. Sales in the year relate to transactions with Quadgas. Within this is other income of £52 million (2018: £54 million ) relating to a Transitional Service Agreement following the sale of the UK Gas Distribution business to Quadgas. 3. During the year, the Group received goods and services from a number of US associates, both for the transportation of gas and for pipeline services in the US. Additionally, in 2018, goods and services were received from UK joint ventures for the construction of an electricity transmission link in the UK. 4. Amounts receivable from associates includes a loan receivable balance from Quadgas of £352 million (2018: £352 million ) which is classified as held for sale as at 31 March 2019, a loan receivable balance of £258 million (2018: £130 million ) from Nemo Link Limited (a joint venture) and £325 million (2018: £24 million ) in relation to St William Homes LLP (a joint venture). 5. In previous years the amounts payable to joint ventures include deposits received for National Grid property sites from St William Homes LLP which have been settled during the year. 6. Dividends in respect of joint ventures were received from BritNed Development Limited. 7. Includes £133 million (2018: £144 million ) of dividend income from Quadgas. 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 the Directors' Remuneration Report on pages 69 - 90 and note 4(c).

Financial risk management

Financial risk management	12 Months Ended
Financial risk management	Mar. 31, 2019
Financial Instruments [Abstract]
Financial risk management	Financial risk management Our activities expose us to a variety of financial risks including credit risk, liquidity risk, capital risk, currency risk, interest rate risk, inflation risk and commodity price risk. Our risk management programme focuses on the unpredictability of financial markets and seeks to minimise potential volatility of financial performance from these risks. We use financial instruments, including derivative financial instruments, to manage these risks. Risk management related to financing activities is carried out by a central treasury department under policies approved by the Finance Committee of the Board. The objective of the treasury department is to manage funding and liquidity requirements, including managing associated financial risks, to within acceptable boundaries. The Finance Committee provides written principles for overall risk management, as well as written policies covering specific areas such as 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. Details of key activities in the current year are set out in the Finance Committee report on page 63. We have exposure to the following risks, which are described in more detail below: • credit risk; • liquidity risk; • currency risk; • interest rate risk; • commodity price risk; and • capital risk. Where appropriate, derivatives and other financial instruments used for hedging currency and interest rate risk exposures are formally designated as fair value, cash flow or net investment hedges as defined in IFRS 9. Hedge accounting allows the timing of the profit or loss impact of qualifying hedging instruments to be recognised in the same reporting period as the corresponding impact of hedged exposures. To qualify for hedge accounting, documentation is prepared specifying the risk management objective and strategy, the component transactions and methodology used for measurement of effectiveness. 32. Financial risk management continued Hedge accounting relationships are designated in line with risk management activities further described below. Categories designated at National Grid are as follows: • currency risk arising from our forecasted foreign currency transactions (capital expenditure or revenues) is designated in cash flow hedges; • currency risk arising from our net investments in foreign operations is designated in net investment hedges; and • currency and interest rate risk arising from borrowings are designated in cash flow or fair value hedges. Critical terms of hedging instruments and hedged items are transacted to match on a 1:1 ratio by notional values. Hedge ineffectiveness can nonetheless arise from inherent differences between derivatives and non-derivative instruments and other market factors including credit, correlations, supply and demand, and market volatilities. Ineffectiveness is recognised in the remeasurements component of profit or loss. Hedge accounting is discontinued when a hedging relationship no longer qualifies for hedge accounting. The Group adopted IFRS 9 with effect from 1 April 2018. The comparatives are not required to be restated and are accounted for in accordance with IAS 39. As a result of adoption, certain hedging instrument components are now treated separately as costs of hedging. Cost of hedging gains and losses are deferred in a newly established component of other equity reserves and released systematically into profit or loss to correspond with the timing of hedged exposures. The impact of adopting IFRS 9 is described in note 37. 2018 Under IAS 39, hedging instruments were designated for hedge accounting in their entirety or, where qualifying forward points were excluded from hedging relationships, unrealised gains and losses on excluded components were recognised in the income statement. Refer to sections (c) currency risk and (d) interest rate risk below for further details about hedge accounting. (a) Credit risk We are exposed to the risk of loss resulting from counterparties’ default on their commitments including failure to pay or make a delivery on a contract. This risk is inherent in our commercial business activities. We are exposed to credit risk on our derivative financial instruments, deposits with banks and financial institutions, as well as credit exposures to wholesale and retail customers, primarily trade receivables and committed transactions. Treasury credit risk Counterparty risk arises from the investment of surplus funds and from the use of derivative financial instruments. As at 31 March 2019, the following limits were in place for investments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 1,853 927 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,011 506 Double ‘A+’ G7 sovereign entities (AA+) 1,685 843 Double ‘A’ range institutions (AA) 674 to 843 337 to 421 Single ‘A’ range institutions (A) 236 to 337 118 to 169 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 2019 and 2018, 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. Commodity credit risk The credit policy for US-based commodity transactions is owned by the Finance Committee to the Board, which establishes controls and procedures to determine, monitor and minimise the credit exposure to counterparties. Wholesale and retail credit risk Our principal commercial exposure in the UK is governed by the credit rules within the regulated codes: Uniform Network Code and Connection and Use of System Code. These set out the level of credit relative to the RAV for each credit rating. In the US, we are required to supply electricity and gas under state regulations. Our credit policies and practices are designed to limit credit exposure by collecting security deposits prior to providing utility services, or after utility service has commenced if certain applicable regulatory requirements are met. Collection activities are managed on a daily basis. Sales to retail customers are usually settled in cash, cheques, electronic bank payments or by using major credit cards. We are committed to measuring, monitoring, minimising and recording counterparty credit risk in our wholesale business. The utilisation of credit limits is regularly monitored and collateral is collected against these accounts when necessary. Management does not expect any significant losses of receivables that have not been provided for as shown in note 19. 32. Financial risk management continued (a) Credit risk continued Offsetting financial assets and liabilities The following tables set out our financial assets and liabilities which are subject to offset and to enforceable master netting arrangements or similar agreements. The tables show the amounts which are offset and reported net in the statement of financial position. Amounts which cannot be offset under IFRS, but which could be settled net under terms of master netting arrangements if certain conditions arise, and with collateral received or pledged, are shown to present National Grid’s net exposure. Financial assets and liabilities on different transactions are only reported net if the transactions are with the same counterparty, a currently enforceable legal right of offset exists, and the cash flows are intended to be settled on a net basis. Amounts which do not meet the criteria for offsetting on the statement of financial position, but could be settled net in certain circumstances, principally relate to derivative transactions under ISDA agreements where each party has the option to settle amounts on a net basis in the event of default of the other party. Commodity contract derivatives that have not been offset on the balance sheet may be settled net in certain circumstances under ISDA or North American Energy Standards Board (NAESB) agreements. For bank account balances and bank overdrafts, the ‘Gross amounts offset’ under cash pooling arrangements is £19 million as at 31 March 2019 (2018: £34 million ). Our UK bank accounts for National Grid subsidiaries participate in GBP, EUR and USD Composite Accounting System overdraft facilities subject to offsetting gross and net overdraft limits. In the US, no offsetting arrangements exist, and cash transactions are settled through Service Company bank accounts with subsequent intercompany payables and receivables reported by subsidiaries with the Service Company. The gross amounts offset for trade payables and receivables, which are subject to general terms and conditions, are insignificant. Related amounts At 31 March 2019 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 1,052 — 1,052 (299 ) (551 ) 202 Commodity contract derivatives 101 — 101 29 — 130 1,153 — 1,153 (270 ) (551 ) 332 Liabilities Financing derivatives (1,084 ) — (1,084 ) 299 615 (170 ) Commodity contract derivatives (99 ) — (99 ) (29 ) — (128 ) (1,183 ) — (1,183 ) 270 615 (298 ) (30 ) — (30 ) — 64 34 Related amounts At 31 March 2018 Gross carrying amounts £m Gross amounts offset £m Net amount presented in statement of financial position £m Financial instruments £m Cash collateral received/ pledged £m Net amount £m Assets Financing derivatives 1,545 — 1,545 (523 ) (772 ) 250 Commodity contract derivatives 69 — 69 (16 ) — 53 Further acquisition agreement derivative¹ 110 — 110 — — 110 1,724 — 1,724 (539 ) (772 ) 413 Liabilities Financing derivatives (945 ) — (945 ) 523 326 (96 ) Commodity contract derivatives (116 ) — (116 ) 16 7 (93 ) (1,061 ) — (1,061 ) 539 333 (189 ) 663 — 663 — (439 ) 224 1. The Group is party to the Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) which contain put and call options over 14% and 25% respectively, of the equity and loan balances it holds in Cadent (through its investment in Quadgas). These are classified within the disposal group as at 31 March 2019 (see note 10). 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 financings that we reasonably expect to be able to secure in the future, together with the use of committed facilities if required. Our debt agreements and banking facilities contain covenants, including those relating to the periodic and timely provision of financial information by the issuing entity and financial covenants such as restrictions on the level of subsidiary indebtedness. Failure to comply with these covenants, or to obtain waivers of those requirements, could in some cases trigger a right, at the lender’s discretion, to require repayment of some of our debt and may restrict our ability to draw upon our facilities or access the capital markets. The following is a maturity profile of our financial liabilities and derivatives as at the reporting date: At 31 March 2019 Less than £m 1 to 2 £m 2 to 3 £m More than £m Total £m Non-derivative financial liabilities Borrowings, excluding finance lease liabilities (4,129 ) (2,348 ) (1,998 ) (19,673 ) (28,148 ) Interest payments on borrowings 1 (800 ) (733 ) (721 ) (13,465 ) (15,719 ) Finance lease liabilities (72 ) (63 ) (52 ) (123 ) (310 ) Other non-interest-bearing liabilities (3,306 ) (340 ) — — (3,646 ) Derivative financial liabilities Derivative contracts – receipts 2 3,045 1,703 163 2,560 7,471 Derivative contracts – payments 2 (3,421 ) (2,029 ) (223 ) (3,276 ) (8,949 ) Commodity contract derivatives (73 ) (19 ) (2 ) (1 ) (95 ) Derivative financial assets Derivative contracts – receipts 2 1,928 561 863 1,112 4,464 Derivative contracts – payments 2 (1,251 ) (459 ) (783 ) (875 ) (3,368 ) (8,079 ) (3,727 ) (2,753 ) (33,741 ) (48,300 ) At 31 March 2018³ 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 finance lease liabilities (4,099 ) (1,642 ) (2,325 ) (18,023 ) (26,089 ) Interest payments on borrowings 1 (730 ) (692 ) (629 ) (12,897 ) (14,948 ) Finance lease liabilities (60 ) (60 ) (45 ) (148 ) (313 ) Other non-interest-bearing liabilities (2,840 ) (359 ) — — (3,199 ) Derivative financial liabilities Derivative contracts – receipts 2 1,111 424 441 268 2,244 Derivative contracts – payments 2 (1,468 ) (608 ) (547 ) (704 ) (3,327 ) Commodity contract derivatives (80 ) (33 ) (26 ) 1 (138 ) Derivative financial assets Derivative contracts – receipts 2 6,536 2,225 1,726 3,134 13,621 Derivative contracts – payments 2 (6,000 ) (1,703 ) (1,678 ) (2,977 ) (12,358 ) (7,630 ) (2,448 ) (3,083 ) (31,346 ) (44,507 ) 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 financial derivative payments and receipts include the gross undiscounted cash flows for interest rate and cross currency derivatives. The cash flows for these derivatives are presented as gross payments and receipts where the cash flows are not net settled either due to timing or currency. 3. The comparatives have been refined to provide consistency with the current period. 32. Financial risk management continued (c) Currency risk National Grid operates internationally with mainly the pound sterling as the functional currency for the UK companies and the US dollar as that of 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. During 2019 and 2018, derivative financial instruments were used to manage foreign currency risk as follows: 2019 2018 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 97 2 153 — 252 294 2 33 — 329 Financial investments 965 — 1,016 — 1,981 1,471 69 1,125 29 2,694 Borrowings (10,591 ) (4,787 ) (12,126 ) (1,226 ) (28,730 ) (10,912 ) (3,794 ) (11,068 ) (851 ) (26,625 ) Pre-derivative position (9,529 ) (4,785 ) (10,957 ) (1,226 ) (26,497 ) (9,147 ) (3,723 ) (9,910 ) (822 ) (23,602 ) Derivative effect (1,055 ) 4,803 (5,245 ) 1,465 (32 ) 3,748 3,793 (7,992 ) 1,051 600 Net debt position (10,584 ) 18 (16,202 ) 239 (26,529 ) (5,399 ) 70 (17,902 ) 229 (23,002 ) The exposure to dollars largely relates to our net investment hedge activities; exposure to euros largely relates to hedges for our future non-sterling capital expenditure. The currency exposure on other financial instruments is as follows: 2019 2018 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 398 — 1,635 — 2,033 253 — 1,528 — 1,781 Trade and other payables (1,221 ) — (2,085 ) — (3,306 ) (1,124 ) — (1,793 ) — (2,917 ) Other non-current liabilities (93 ) — (247 ) — (340 ) (144 ) — (254 ) — (398 ) The carrying amounts of other financial instruments are denominated in the above currencies, which in most instances are the functional currency of the respective subsidiaries. Our exposure to dollars is due to activities in our US subsidiaries. We do not have any other significant exposure to currency risk on these balances. Hedge accounting for currency risk Where available, derivatives transacted for hedging are designated for hedge accounting. Economic offset is qualitatively determined because the critical terms (currency and volume) of the hedging instrument match the hedged exposure. If a forecast transaction was no longer expected to occur, the cumulative gain or loss previously reported in equity would be transferred to the income statement. This has not occurred in the current or comparative years. Cash flow hedging of currency risk of capital expenditure and revenues is designated as hedging the exposure to movements in the spot translation rates only; the timing of forecasted transactions is not designated as a hedged risk. Gains and losses on hedging instruments arising from forward points and foreign currency basis spreads are excluded from designation and are recognised immediately in profit or loss, along with any hedge ineffectiveness. On recognition of the hedged purchase or sale in the financial statements, the associated hedge gains and losses, deferred in the cash flow hedge reserve in other equity reserves, are transferred out of reserves and included with the recognition of the underlying transaction. Where a non-financial asset or a non-financial liability results from a forecast transaction or firm commitment being hedged, the amounts deferred in reserves are included directly in the initial measurement of that asset or liability. Net investment hedging is also designated as hedging the exposure to movements in spot translation rates only: spot-related gains and losses on hedging instruments are presented in the cumulative translation reserve within other equity reserves to offset gains or losses on translation of the hedged balance sheet exposure. Any ineffectiveness is recognised immediately in the income statement. Gains and losses arising from forward points and foreign currency basis spreads are excluded from designation and are treated as a cost of hedging, deferred initially in other equity reserves and released into profit or loss over the life of the hedging relationship. Amounts deferred in the cumulative translation reserve with respect to net investment hedges are subsequently recognised in the income statement in the event of disposal of the overseas operations concerned. Any remaining amounts deferred in the cost of hedging reserve are also released to the income statement. Hedges of foreign currency funding are designated as cash flow hedges or fair value hedges of forward exchange risk (hedging both currency and interest rate risk together, where applicable). Hedge accounting for funding is described further in the interest rate risk section below. 32. Financial risk management continued (d) Interest rate risk National Grid’s interest rate risk arises from our long-term borrowings. Our interest rate risk management policy is to seek to minimise total financing costs (being interest costs and changes in the market value of debt). Hedging instruments principally consist of interest rate and cross-currency swaps that are used to translate foreign currency debt into functional currency and to adjust the proportion of fixed-rate and floating-rate in the borrowings portfolio to within a range set by the Finance Committee of the Board. The benchmark interest rates hedged are currently based on Libor. 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. During 2019 and 2018, net debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2019 2018 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 59 104 — 89 252 — 302 — 27 329 Financial investments 6 1,944 — 31 1,981 31 2,625 — 38 2,694 Borrowings (19,043 ) (3,045 ) (6,642 ) — (28,730 ) (16,144 ) (3,191 ) (7,290 ) — (26,625 ) Pre-derivative position (18,978 ) (997 ) (6,642 ) 120 (26,497 ) (16,113 ) (264 ) (7,290 ) 65 (23,602 ) Derivative effect 1,740 (1,559 ) (213 ) — (32 ) 1,735 (1,237 ) 102 — 600 Net debt position (17,238 ) (2,556 ) (6,855 ) 120 (26,529 ) (14,378 ) (1,501 ) (7,188 ) 65 (23,002 ) 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. 32. Financial risk management continued (e) Hedge accounting In accordance with the requirements of IFRS 9, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges — (40 ) (12 ) — Cost of hedging (6 ) (12 ) — (90 ) Transferred to profit or loss in respect of: Cash flow hedges — (1 ) — — Cost of hedging 3 — — 39 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (4 ) — — 32 Consolidated statement of financial position Derivatives – carrying value of hedging instruments 1 Assets – current 17 — 9 — Assets – non-current 168 78 23 — Liabilities – current (9 ) (28 ) (3 ) (43 ) Liabilities – non-current (25 ) (134 ) (4 ) (249 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Nov 2019 – May 2038 Aug 2019 – Feb 2039 Apr 2019 – Dec 2023 Mar 2020 – Jun 2025 Spot foreign exchange range: GBP:USD 1.64 – 1.65 1.52 – 1.66 1.29 – 1.41 1.49 GBP:EUR 1.19 – 1.24 1.14 – 1.24 1.07 – 1.32 1.15 EUR:USD 1.13 – 1.16 1.13 – 1.14 n/a n/a Interest rate range: GBP Libor +30bps/+561bps 1.795% – 5.850% n/a n/a USD Libor -44bps/+115bps 1.103% – 3.864% n/a n/a 1. 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: (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings as at 31 March 2019: Hedge type 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 £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings 1 (1,707 ) 11 (117 ) 11 (6 ) 5 1. The carrying value of the hedged borrowings is £1,810 million , of which £202 million is current and £1,608 million is non-current. (ii) Cash flow hedges of foreign currency and interest rate risk as at 31 March 2019: Hedge type 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 £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings (3,804 ) (17 ) 51 39 (39 ) — Foreign currency risk on forecasted cash flows (697 ) 47 — 12 (12 ) — (iii) Net investment hedges of foreign currency risk as at 31 March 2019: Hedge type Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness £m £m £m £m £m £m Currency risk on foreign operations (2,974 ) (329 ) (2,502 ) 550 (550 ) — (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 recoverable at an amount equal to cost. The timing of recovery of these costs can vary between financial periods leading to an under- or over-recovery within any particular year that can lead to large fluctuations in the income statement. We follow approved policies to manage price and supply risks for our commodity activities. Our energy procurement risk management policy and delegations of authority govern our US commodity trading activities for energy transactions. The purpose of this policy is to ensure we transact within pre-defined risk parameters and only in the physical and financial markets where we or our customers have a physical market requirement. In addition, state regulators require National Grid to manage commodity risk and cost volatility prudently through diversified pricing strategies. In some jurisdictions we are required to file a plan outlining our strategy to be approved by regulators. In certain cases we might receive guidance with regard to specific hedging limits. Energy purchase contracts for the forward purchase of electricity or gas that are used to satisfy physical delivery requirements to customers, or for energy that the Group uses itself, meet the expected purchase or usage requirements of IAS 39 and IFRS 9. They are, therefore, not recognised in the financial statements until they are realised. Disclosure of commitments under such contracts is made in note 30. US states have introduced a variety of legislative requirements with the aim of increasing the proportion of our electricity that is derived from renewable or other forms of clean energy. Annual compliance filings regarding the level of Renewable Energy Certificates (and other similar environmental certificates) are required by the relevant department of utilities. In response to the legislative requirements, National Grid has entered into long-term, typically fixed-price, energy supply contracts to purchase both renewable energy and environmental certificates. We are entitled to recover all costs incurred under these contracts through customer billing. Under IFRS, where these supply contracts are not accounted for as finance leases, they are considered to comprise two components, being a forward purchase of power at spot prices, and a forward purchase of environmental certificates at a variable price (being the contract price less the spot power price). With respect to our current contracts, neither of these components meets the requirement to be accounted for as a derivative. The environmental certificates are currently required for compliance purposes, and at present there are no liquid markets for these attributes. Accordingly, this component meets the expected purchase or usage exemption of IFRS 9/IAS 39. We expect to enter into an increasing number of these contracts, in order to meet our compliance requirements in the short to medium term. It is possible that in future, if and when liquid markets develop, and to the extent that we are in receipt of environmental certificates in excess of our required levels, this exemption may cease to apply and we may be required to account for forward purchase commitments for environmental certificates as derivatives at fair value through profit and loss. 32. Financial risk management continued (g) Fair value analysis Included in the statement of financial position are financial instruments which are measured at fair value. These fair values can be categorised into hierarchy levels that are representative of the inputs used in measuring the fair value. The best evidence of fair value is a quoted price in an actively traded market. In the event that the market for a financial instrument is not active, a valuation technique is used. 2019 2018 Level 1 £m Level 2 £m Level 3 £m Total £m Level 1 £m Level 2 £m Level 3 £m Total £m Assets Available-for-sale investments 1 — — — — 2,406 310 5 2,721 Investments held at FVTPL 1 1,311 — 62 1,373 — — — — Investments held at FVOCI 1 93 343 — 436 — — — — Investments in associates 2 — — 90 90 — — 79 79 Financing derivatives — 1,050 2 1,052 — 1,544 1 1,545 Commodity contract derivatives — 33 68 101 — 8 61 69 Further Ac

Borrowing facilities

Borrowing facilities	12 Months Ended
Borrowing facilities	Mar. 31, 2019
Disclosure of detailed information about borrowings [abstract]
Borrowing facilities	Borrowing facilities To support our liquidity requirements and provide backup to commercial paper and other borrowings, we agree loan facilities with financial institutions over and above the value of borrowings that may be required. These committed credit facilities have never been drawn, and our undrawn amounts are listed below. At 31 March 2019 , we had bilateral committed credit facilities of £5,463 million ( 2018 : £5,438 million ). In addition, we had committed credit facilities from syndicates of banks of £264 million at 31 March 2019 ( 2018 : £245 million ). All committed credit facilities were undrawn in 2019 and 2018 . An analysis of the maturity of these undrawn committed facilities is shown below: 2019 2018 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — — In 1 to 2 years — 3,910 In 2 to 3 years 2,190 — In 3 to 4 years 1,668 — In 4 to 5 years 1,869 1,773 More than 5 years — — 5,727 5,683 Of the unused facilities at 31 March 2019 , £5,463 million ( 2018 : £5,438 million ) is available for liquidity purposes, while £264 million ( 2018 : £245 million ) is available as backup to specific US borrowings. Of the £1,869 million of undrawn committed borrowings facilities due to expire within four to five years, £270 million was renegotiated before 31 March 2019, with the expiry extended by a further year, with effect from 1 June 2019. In addition to the above, the Group has Export Credit Agreements (ECAs) totalling £859 million ( 2018 : £797 million ), of which £510 million ( 2018 : £704 million ) is undrawn. The Group has also negotiated a new facility of £550 million , with effect from 1 April 2019, for the separately regulated business of National Grid Electricity System Operator Limited. This facility is not available as Group general liquidity support.

Subsidiary undertakings, joint

Subsidiary undertakings, joint ventures and associates	12 Months Ended
Subsidiary undertakings, joint ventures and associates	Mar. 31, 2019
Interests In Other Entities [Abstract]
Subsidiary undertakings, joint ventures and associates	Investments in joint ventures and associates Investments in joint ventures and associates represent businesses we do not control but over which we exercise joint control or significant influence. A joint venture is an arrangement established to engage in economic activity, which the Group jointly controls with other parties and has rights to the net assets of the arrangement. An associate is an entity which is neither a subsidiary nor a joint venture, but over which the Group has significant influence. 2019 2018 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 1,807 361 2,168 1,776 307 2,083 Exchange adjustments 17 (6 ) 11 (19 ) 7 (12 ) Additions 58 85 143 65 64 129 Capitalisation of shareholder loan to Quadgas — — — 69 — 69 Impairment charge against investment in Quadgas (43 ) — (43 ) (213 ) — (213 ) Transfer of interest in Quadgas to assets held for sale (1,625 ) — (1,625 ) — — — Share of post-tax results for the year 67 11 78 147 26 173 Share of other comprehensive income of associates, net of tax 37 — 37 147 — 147 Dividends received (38 ) (30 ) (68 ) (170 ) (43 ) (213 ) Other movements 1 11 (104 ) (93 ) 5 — 5 Share of net assets at 31 March 291 317 608 1,807 361 2,168 1. Other movements on joint ventures relate to reducing the carrying value of the investment in St William Homes LLP to reflect deferred income we expect to recognise over the next 10 years . A list of joint ventures and associates including the name and proportion of ownership is provided in note 34. Transactions with and outstanding balances with joint ventures and associates are shown in note 31. Further information on the Group’s interest in Quadgas and the subsequent reclassification of the interest to assets held for sale is provided in note 10. In 2017, the Group first entered into an arrangement with San Francisco-based Sunrun Neptune Investor 2016 LLC, a leading US provider of residential solar energy systems to provide investment capital. In the period to 31 March 2019 , the Group invested £6 million ( 2018 : £38 million ) alongside Sunrun into a newly incorporated partnership vehicle. The investment is measured at fair value. The fair value gain on this investment of £8 million (2018: £7 million ) has been reflected within the share of post-tax results for the year. The joint ventures and associates have no significant contingent liabilities to which the Group is exposed, and the Group has no significant contingent liabilities in relation to its interests in the joint ventures and associates. The Group has capital commitments of £18 million ( 2018 : £120 million ) in relation to joint ventures. At 31 March 2019 , the Group had one material joint venture, being its 50% equity stake in BritNed and one material associate, being its 26.25% investment in Millennium Pipeline Company LLC. The Group’s 39% equity stake in Quadgas is held for sale and therefore all disclosures in relation to Quadgas are included in note 10. BritNed is a joint venture with transmission system operator TenneT and operates the subsea electricity link between Great Britain and the Netherlands, commissioned in 2011. BritNed has a reporting period end of 31 December with monthly management reporting information provided to National Grid. Millennium Pipeline Company LLC is an associate that owns a natural gas pipeline from southern New York to the Lower Hudson Valley. Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Limited Millennium Pipeline Company LLC 2019 2018 2019 2018 £m £m £m £m Statement of financial position Non-current assets 370 390 937 709 Cash and cash equivalents 59 50 35 15 All other current assets 2 4 22 28 Non-current liabilities (11 ) (10 ) (326 ) (331 ) Current liabilities (28 ) (28 ) (84 ) (64 ) Equity 392 406 584 357 Carrying amount of the Group’s investment 196 203 153 94 BritNed Development Limited Millennium Pipeline Company LLC 2019 2018¹ 2019 2018 £m £m £m £m Income statement Revenue 87 121 166 151 Depreciation and amortisation (13 ) (13 ) (34 ) (31 ) Other costs (10 ) (16 ) (35 ) (41 ) Operating profit 64 92 97 79 Income tax expense (10 ) (20 ) — — Profit for the year 54 72 97 79 Group’s share of profit 27 36 25 21 1. Comparatives for revenue and other costs have been re-presented on a net basis in line with current year classification. Subsidiary undertakings, joint ventures and associates While we present consolidated results in these financial statements as if we were one company, our legal structure is such that there are a number of different operating and holding companies that contribute to the overall result. This structure has evolved through acquisitions as well as regulatory requirements to have certain activities within separate legal entities. Subsidiary undertakings A list of the Group’s subsidiaries as at 31 March 2019 is given below. The entire share capital of subsidiaries is held within the Group except where the Group’s ownership percentages are shown. These percentages give the Group’s ultimate interest and therefore allow for the situation where subsidiaries are owned by partly owned intermediate subsidiaries. Where subsidiaries have different classes of shares, this is largely for historical reasons, and the effective percentage holdings given represent both the Group’s voting rights and equity holding. Shares in National Grid (US) Holdings Limited, National Grid Holdings One plc and NGG Finance plc are held directly by National Grid plc. All other holdings in subsidiaries are owned by other subsidiaries within the Group. All subsidiaries are consolidated in the Group’s financial statements. Principal Group companies are identified in bold . These companies are incorporated and principally operate in the countries under which they are shown. Incorporated in England and Wales Registered office: 1 – 3 Strand, London WC2N 5EH, UK (unless stated otherwise in footnotes). Beegas Nominees Limited Birch Sites Limited Carbon Sentinel Limited Droylsden Metering Services Limited Gridcom Limited Icelink Interconnector Limited Landranch Limited Lattice Group Employee Benefit Trust Limited Lattice Group Limited Lattice Group Trustees Limited Natgrid Limited NatGrid One Limited NatgridTW1 Limited National Grid Belgium Limited National Grid Blue Power Limited National Grid Carbon Limited National Grid Commercial Holdings Limited National Grid Distributed Energy Limited National Grid Electricity Group Trustee Limited National Grid Electricity System Operator Limited National Grid Electricity Transmission plc National Grid Energy Metering Limited National Grid Four Limited National Grid Fourteen Limited National Grid Gas Holdings Limited National Grid Gas plc National Grid Grain LNG Limited National Grid Holdings Limited National Grid Holdings One plc National Grid IFA 2 Limited National Grid Interconnector Holdings Limited National Grid Interconnectors Limited National Grid International Limited National Grid Metering Limited National Grid North Sea Link Limited National Grid Offshore Limited National Grid Partners Limited (previously National Grid Thirty Four Limited) National Grid Property Holdings Limited National Grid Seventeen Limited National Grid Smart Limited National Grid Ten National Grid Thirty Five Limited National Grid Thirty Six Limited National Grid Twelve Limited National Grid Twenty Eight Limited National Grid Twenty-Five Limited National Grid Twenty Seven Limited National Grid Twenty Three Limited National Grid UK Limited National Grid UK Pension Services Limited National Grid (US) Holdings Limited National Grid (US) Investments 2 Limited National Grid (US) Investments 4 Limited National Grid (US) Partner 1 Limited National Grid Ventures Limited National Grid Viking Link Limited National Grid William Limited NG Nominees Limited NG Shetland Link Limited NGC Employee Shares Trustee Limited NGG Finance plc Ngrid Intellectual Property Limited NGT Telecom No. 1 Limited NGT Two Limited Port Greenwich Limited Stargas Nominees Limited Supergrid Electricity Limited Supergrid Energy Transmission Limited Supergrid Limited Thamesport Interchange Limited The National Grid Group Quest Trustee Company Limited The National Grid YouPlan Trustee Limited Transco Limited Warwick Technology Park Management Company (No 2) Limited ( 60.56% ) 1 1. Registered office: Shire Hall, PO Box 9, Warwick CV34 4RL, UK 34. Subsidiary undertakings, joint ventures and associates continued Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, New Castle County, USA (unless stated otherwise in footnotes). Boston Gas Company 1 British Transco Capital Inc. British Transco Finance, Inc. Broken Bridge Corp. 2 Colonial Gas Company 1 EUA Energy Investment Corporation 1 Granite State Power Link LLC GridAmerica Holdings Inc. Grid NY LLC 3 KeySpan CI Midstream Limited KeySpan Energy Corporation 3 KeySpan Energy Services Inc. KeySpan Gas East Corporation 3 KeySpan International Corporation KeySpan MHK, Inc. KeySpan Midstream Inc. KeySpan Plumbing Solutions, Inc. 3 KSI Contracting, LLC KSI Electrical, LLC KSI Mechanical, LLC Land Management & Development, Inc. 3 Landwest, Inc. 3 Massachusetts Electric Company 1 Metro Energy, LLC 3 Metrowest Realty LLC Mystic Steamship Corporation Nantucket Electric Company 1 National Grid Algonquin LLC National Grid Connect Inc. National Grid Development Holdings Corp. National Grid Electric Services, LLC 3 National Grid Energy Management, LLC National Grid Energy Services LLC National Grid Energy Trading Services LLC 3 National Grid Engineering & Survey Inc. 3 National Grid Generation LLC 3 National Grid Generation Ventures LLC 3 National Grid Glenwood Energy Center, LLC National Grid Green Homes Inc. National Grid IGTS Corp. 3 National Grid Insurance USA Ltd 3 National Grid Islander East Pipeline LLC National Grid LNG GP LLC National Grid LNG LLC National Grid LNG LP LLC National Grid Millennium LLC National Grid NE Holdings 2 LLC 1 National Grid North America Inc. National Grid North East Ventures Inc. National Grid Partners Inc. (previously National Grid Technologies Inc.) 3 National Grid Port Jefferson Energy Center LLC National Grid Services Inc. National Grid Transmission Services Corporation 1 National Grid US 6 LLC National Grid US LLC National Grid USA National Grid USA Service Company, Inc. 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 4 NGNE LLC NGV Emerald Acquisition Co. LLC 5 NGV Emerald Holdings LLC 5 Niagara Mohawk Energy, Inc. Niagara Mohawk Holdings, Inc. 3 Niagara Mohawk Power Corporation 3 NM Properties, Inc. 3 Northeast Renewable Link LLC North East Transmission Co., Inc. Opinac North America, Inc. Philadelphia Coke Co., Inc. Port of the Islands North, LLC 3 The Brooklyn Union Gas Company 3 The Narragansett Electric Company 4 Transgas, Inc. 1 Upper Hudson Development Inc. 1 Valley Appliance and Merchandising Company 4 Vermont Green Line Devco, LLC ( 90% ) Wayfinder Group, Inc. 1 Incorporated in Australia Registered office: Level 7, 330 Collins Street, Melbourne, VIC 3000, Australia National Grid Australia Pty Limited Incorporated in Canada Registered office: 1959 Upper Water Street, Suite 800, Halifax NS, B3J 2X2, Canada KeySpan Energy Development Co. Incorporated in the Isle of Man Registered office: Third Floor, St George’s Court, Upper Church Street, Douglas, IM1 1EE, Isle of Man, UK National Grid Insurance Company (Isle of Man) Limited NGT Holding Company (Isle of Man) Limited Incorporated in Jersey Registered office: 44 Esplanade, St Helier, Jersey JE4 9WG, UK National Grid Jersey Investments Limited NG Jersey Limited Incorporated in the Netherlands Registered office: Westblaak 89, 3012 KG Rotterdam, PO Box 21153, 3001 AD, Rotterdam, Netherlands British Transco International Finance B.V. Registered office: Prins Bernhardplein 200, 1097 JB, Amsterdam, Netherlands National Grid Holdings B.V. Incorporated in the Republic of Ireland Registered office: c/o Moore Stephens Nathans, Third Floor, Ulysses House, 23/24 Foley Street, Dublin 1, D01 W2T2, Ireland National Grid Company (Ireland) Designated Activity Company (previously National Grid Insurance Company (Ireland) Designated Activity Company)* 1. Registered office: Corporation Service Company, 84 State Street, Boston MA 02109, Suffolk County, USA. 2. Registered office: Corporation Service Company, 10 Ferry Street, Suite 313, Concord NH 03301, Merrimack County, USA. 3. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207-2543, Albany County, USA. 4. Registered office: Corporation Service Company, 222 Jefferson Boulevard, Suite 200, Warwick RI 02888, Kent County, USA. 5. Registered office: 404 Wyman Street, Waltham MA 02451 USA. * In liquidation. 34. Subsidiary undertakings, joint ventures and associates continued Joint ventures A list of the Group’s joint ventures as at 31 March 2019 is given below. All joint ventures are included in the Group’s financial statements using the equity method of accounting. Principal joint ventures are identified in bold . Incorporated in England and Wales Registered office: 1–3 Strand, London WC2N 5EH, UK (unless stated otherwise in footnotes). BritNed Development Limited ( 50% )* Joint Radio Company Limited ( 50% ) 1 Nemo Link Limited ( 50% ) NGET/SPT Upgrades Limited ( 50% ) † St William Homes LLP ( 50% ) 2 Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, New Castle County, USA (unless stated otherwise in footnotes). Clean Energy Generation, LLC ( 50% ) Goldendale Energy Storage LLC ( 50% ) Island Park Energy Center, LLC ( 50% ) Islander East Pipeline Company, LLC ( 50% ) 3 LI Energy Storage System, LLC ( 50% ) LI Solar Generation, LLC ( 50% ) Swan Lake North Holdings LLC ( 50% ) Incorporated in France Registered office: 1 Terrasse Bellini, Tour Initiale, TSA 41000 – 9291, Paris La Defense, CEDEX, France IFA2 SAS ( 50% ) Associates A list of the Group’s associates as at 31 March 2019 is given below. Unless otherwise stated, all associates are included in the Group’s financial statements using the equity method of accounting. Principal associates are identified in bold . Incorporated in England and Wales Registered office: Ashbrook Court, Prologis Park, Central Boulevard, Coventry CV7 8PE, UK Quadgas HoldCo Limited ( 39% ) # Incorporated in the US Registered office: Corporation Service Company, 251 Little Falls Drive, Wilmington, DE 19808, New Castle County, USA (unless stated otherwise in footnotes). Algonquin Gas Transmission, LLC ( 20% ) 3 Clean Line Energy Partners LLC ( 32% ) 3 Connecticut Yankee Atomic Power Company ( 19.5% ) 4 Direct Global Power, Inc. ( 26% ) 5 Energy Impact Fund LP ( 9.42% ) 6 KHB Venture LLC ( 33% ) 7 Maine Yankee Atomic Power Company ( 24% ) 8 Millennium Pipeline Company, LLC ( 26.25% ) 3 New York Transco LLC ( 28.3% ) 9 Nysearch RMLD, LLC ( 22.63% ) Sunrun Neptune Investor 2016 LLC 3 * 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 2019 is given below. Incorporated in England and Wales Registered office: 1 More London Place, London SE1 2AF, UK Energis plc ( 33.06% ) ‡ 1. Registered office: Friars House, Manor House Drive, Coventry CV1 2TE, UK. 2. Registered office: Berkeley House, 19 Portsmouth Road, Cobham, Surrey KT11 1JG, UK. 3. Registered office: Corporation Trust Company, 1209 Orange, Wilmington DE 19808, New Castle County, USA. 4. Registered office: Carla Pizzella, 362 Injun Hollow Road, East Hampton CT 06424, USA. 5. Registered office: 507 Plum Street, PO Box 5001, Syracuse NY 13250, USA. 6. Registered office: Harvard Business Services, Inc., 16192 Coastal Highway, Lewes DE 19958, Sussex County, USA. 7. Registered office: De Maximus Inc., 135 Beaver Street, 4th Floor, Waltham MA 02452, USA. 8. Registered office: Joseph D Fay, 321 Old Ferry Road, Wiscasset ME 04578, USA. 9. Registered office: Corporation Service Company, 80 State Street, Albany NY 12207, USA. 10. Registered office: Brian Smith, 49 Yankee Road, Rowe MA 01367, USA. * National Grid Interconnector Holdings Limited owns 284,500,000 €0.20 C Ordinary shares and one £1.00 Ordinary A share. National Grid Gas plc owns all £1.00 A Ordinary shares. * National Grid Green Homes Inc. owns 1,000 Class A Membership Interests. † National Grid Electricity Transmission plc owns 50 £1.00 A Ordinary shares. ‡ In administration. # Quadgas HoldCo Limited is included in the financial statements from 30 June 2018 as an asset held for sale. 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.

Sensitivites

Sensitivites	12 Months Ended
Sensitivites	Mar. 31, 2019
Disclosure of sensitivity analysis for actuarial assumptions [abstract]
Sensitivities	Financial risk management Our activities expose us to a variety of financial risks including credit risk, liquidity risk, capital risk, currency risk, interest rate risk, inflation risk and commodity price risk. Our risk management programme focuses on the unpredictability of financial markets and seeks to minimise potential volatility of financial performance from these risks. We use financial instruments, including derivative financial instruments, to manage these risks. Risk management related to financing activities is carried out by a central treasury department under policies approved by the Finance Committee of the Board. The objective of the treasury department is to manage funding and liquidity requirements, including managing associated financial risks, to within acceptable boundaries. The Finance Committee provides written principles for overall risk management, as well as written policies covering specific areas such as 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. Details of key activities in the current year are set out in the Finance Committee report on page 63. We have exposure to the following risks, which are described in more detail below: • credit risk; • liquidity risk; • currency risk; • interest rate risk; • commodity price risk; and • capital risk. Where appropriate, derivatives and other financial instruments used for hedging currency and interest rate risk exposures are formally designated as fair value, cash flow or net investment hedges as defined in IFRS 9. Hedge accounting allows the timing of the profit or loss impact of qualifying hedging instruments to be recognised in the same reporting period as the corresponding impact of hedged exposures. To qualify for hedge accounting, documentation is prepared specifying the risk management objective and strategy, the component transactions and methodology used for measurement of effectiveness. 32. Financial risk management continued Hedge accounting relationships are designated in line with risk management activities further described below. Categories designated at National Grid are as follows: • currency risk arising from our forecasted foreign currency transactions (capital expenditure or revenues) is designated in cash flow hedges; • currency risk arising from our net investments in foreign operations is designated in net investment hedges; and • currency and interest rate risk arising from borrowings are designated in cash flow or fair value hedges. Critical terms of hedging instruments and hedged items are transacted to match on a 1:1 ratio by notional values. Hedge ineffectiveness can nonetheless arise from inherent differences between derivatives and non-derivative instruments and other market factors including credit, correlations, supply and demand, and market volatilities. Ineffectiveness is recognised in the remeasurements component of profit or loss. Hedge accounting is discontinued when a hedging relationship no longer qualifies for hedge accounting. The Group adopted IFRS 9 with effect from 1 April 2018. The comparatives are not required to be restated and are accounted for in accordance with IAS 39. As a result of adoption, certain hedging instrument components are now treated separately as costs of hedging. Cost of hedging gains and losses are deferred in a newly established component of other equity reserves and released systematically into profit or loss to correspond with the timing of hedged exposures. The impact of adopting IFRS 9 is described in note 37. 2018 Under IAS 39, hedging instruments were designated for hedge accounting in their entirety or, where qualifying forward points were excluded from hedging relationships, unrealised gains and losses on excluded components were recognised in the income statement. Refer to sections (c) currency risk and (d) interest rate risk below for further details about hedge accounting. (a) Credit risk We are exposed to the risk of loss resulting from counterparties’ default on their commitments including failure to pay or make a delivery on a contract. This risk is inherent in our commercial business activities. We are exposed to credit risk on our derivative financial instruments, deposits with banks and financial institutions, as well as credit exposures to wholesale and retail customers, primarily trade receivables and committed transactions. Treasury credit risk Counterparty risk arises from the investment of surplus funds and from the use of derivative financial instruments. As at 31 March 2019, the following limits were in place for investments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 1,853 927 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,011 506 Double ‘A+’ G7 sovereign entities (AA+) 1,685 843 Double ‘A’ range institutions (AA) 674 to 843 337 to 421 Single ‘A’ range institutions (A) 236 to 337 118 to 169 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 2019 and 2018, 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. Commodity credit risk The credit policy for US-based commodity transactions is owned by the Finance Committee to the Board, which establishes controls and procedures to determine, monitor and minimise the credit exposure to counterparties. Wholesale and retail credit risk Our principal commercial exposure in the UK is governed by the credit rules within the regulated codes: Uniform Network Code and Connection and Use of System Code. These set out the level of credit relative to the RAV for each credit rating. In the US, we are required to supply electricity and gas under state regulations. Our credit policies and practices are designed to limit credit exposure by collecting security deposits prior to providing utility services, or after utility service has commenced if certain applicable regulatory requirements are met. Collection activities are managed on a daily basis. Sales to retail customers are usually settled in cash, cheques, electronic bank payments or by using major credit cards. We are committed to measuring, monitoring, minimising and recording counterparty credit risk in our wholesale business. The utilisation of credit limits is regularly monitored and collateral is collected against these accounts when necessary. Management does not expect any significant losses of receivables that have not been provided for as shown in note 19. 32. Financial risk management continued (a) Credit risk continued Offsetting financial assets and liabilities The following tables set out our financial assets and liabilities which are subject to offset and to enforceable master netting arrangements or similar agreements. The tables show the amounts which are offset and reported net in the statement of financial position. Amounts which cannot be offset under IFRS, but which could be settled net under terms of master netting arrangements if certain conditions arise, and with collateral received or pledged, are shown to present National Grid’s net exposure. Financial assets and liabilities on different transactions are only reported net if the transactions are with the same counterparty, a currently enforceable legal right of offset exists, and the cash flows are intended to be settled on a net basis. Amounts which do not meet the criteria for offsetting on the statement of financial position, but could be settled net in certain circumstances, principally relate to derivative transactions under ISDA agreements where each party has the option to settle amounts on a net basis in the event of default of the other party. Commodity contract derivatives that have not been offset on the balance sheet may be settled net in certain circumstances under ISDA or North American Energy Standards Board (NAESB) agreements. For bank account balances and bank overdrafts, the ‘Gross amounts offset’ under cash pooling arrangements is £19 million as at 31 March 2019 (2018: £34 million ). Our UK bank accounts for National Grid subsidiaries participate in GBP, EUR and USD Composite Accounting System overdraft facilities subject to offsetting gross and net overdraft limits. In the US, no offsetting arrangements exist, and cash transactions are settled through Service Company bank accounts with subsequent intercompany payables and receivables reported by subsidiaries with the Service Company. The gross amounts offset for trade payables and receivables, which are subject to general terms and conditions, are insignificant. Related amounts At 31 March 2019 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 1,052 — 1,052 (299 ) (551 ) 202 Commodity contract derivatives 101 — 101 29 — 130 1,153 — 1,153 (270 ) (551 ) 332 Liabilities Financing derivatives (1,084 ) — (1,084 ) 299 615 (170 ) Commodity contract derivatives (99 ) — (99 ) (29 ) — (128 ) (1,183 ) — (1,183 ) 270 615 (298 ) (30 ) — (30 ) — 64 34 Related amounts At 31 March 2018 Gross carrying amounts £m Gross amounts offset £m Net amount presented in statement of financial position £m Financial instruments £m Cash collateral received/ pledged £m Net amount £m Assets Financing derivatives 1,545 — 1,545 (523 ) (772 ) 250 Commodity contract derivatives 69 — 69 (16 ) — 53 Further acquisition agreement derivative¹ 110 — 110 — — 110 1,724 — 1,724 (539 ) (772 ) 413 Liabilities Financing derivatives (945 ) — (945 ) 523 326 (96 ) Commodity contract derivatives (116 ) — (116 ) 16 7 (93 ) (1,061 ) — (1,061 ) 539 333 (189 ) 663 — 663 — (439 ) 224 1. The Group is party to the Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) which contain put and call options over 14% and 25% respectively, of the equity and loan balances it holds in Cadent (through its investment in Quadgas). These are classified within the disposal group as at 31 March 2019 (see note 10). 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 financings that we reasonably expect to be able to secure in the future, together with the use of committed facilities if required. Our debt agreements and banking facilities contain covenants, including those relating to the periodic and timely provision of financial information by the issuing entity and financial covenants such as restrictions on the level of subsidiary indebtedness. Failure to comply with these covenants, or to obtain waivers of those requirements, could in some cases trigger a right, at the lender’s discretion, to require repayment of some of our debt and may restrict our ability to draw upon our facilities or access the capital markets. The following is a maturity profile of our financial liabilities and derivatives as at the reporting date: At 31 March 2019 Less than £m 1 to 2 £m 2 to 3 £m More than £m Total £m Non-derivative financial liabilities Borrowings, excluding finance lease liabilities (4,129 ) (2,348 ) (1,998 ) (19,673 ) (28,148 ) Interest payments on borrowings 1 (800 ) (733 ) (721 ) (13,465 ) (15,719 ) Finance lease liabilities (72 ) (63 ) (52 ) (123 ) (310 ) Other non-interest-bearing liabilities (3,306 ) (340 ) — — (3,646 ) Derivative financial liabilities Derivative contracts – receipts 2 3,045 1,703 163 2,560 7,471 Derivative contracts – payments 2 (3,421 ) (2,029 ) (223 ) (3,276 ) (8,949 ) Commodity contract derivatives (73 ) (19 ) (2 ) (1 ) (95 ) Derivative financial assets Derivative contracts – receipts 2 1,928 561 863 1,112 4,464 Derivative contracts – payments 2 (1,251 ) (459 ) (783 ) (875 ) (3,368 ) (8,079 ) (3,727 ) (2,753 ) (33,741 ) (48,300 ) At 31 March 2018³ 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 finance lease liabilities (4,099 ) (1,642 ) (2,325 ) (18,023 ) (26,089 ) Interest payments on borrowings 1 (730 ) (692 ) (629 ) (12,897 ) (14,948 ) Finance lease liabilities (60 ) (60 ) (45 ) (148 ) (313 ) Other non-interest-bearing liabilities (2,840 ) (359 ) — — (3,199 ) Derivative financial liabilities Derivative contracts – receipts 2 1,111 424 441 268 2,244 Derivative contracts – payments 2 (1,468 ) (608 ) (547 ) (704 ) (3,327 ) Commodity contract derivatives (80 ) (33 ) (26 ) 1 (138 ) Derivative financial assets Derivative contracts – receipts 2 6,536 2,225 1,726 3,134 13,621 Derivative contracts – payments 2 (6,000 ) (1,703 ) (1,678 ) (2,977 ) (12,358 ) (7,630 ) (2,448 ) (3,083 ) (31,346 ) (44,507 ) 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 financial derivative payments and receipts include the gross undiscounted cash flows for interest rate and cross currency derivatives. The cash flows for these derivatives are presented as gross payments and receipts where the cash flows are not net settled either due to timing or currency. 3. The comparatives have been refined to provide consistency with the current period. 32. Financial risk management continued (c) Currency risk National Grid operates internationally with mainly the pound sterling as the functional currency for the UK companies and the US dollar as that of 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. During 2019 and 2018, derivative financial instruments were used to manage foreign currency risk as follows: 2019 2018 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 97 2 153 — 252 294 2 33 — 329 Financial investments 965 — 1,016 — 1,981 1,471 69 1,125 29 2,694 Borrowings (10,591 ) (4,787 ) (12,126 ) (1,226 ) (28,730 ) (10,912 ) (3,794 ) (11,068 ) (851 ) (26,625 ) Pre-derivative position (9,529 ) (4,785 ) (10,957 ) (1,226 ) (26,497 ) (9,147 ) (3,723 ) (9,910 ) (822 ) (23,602 ) Derivative effect (1,055 ) 4,803 (5,245 ) 1,465 (32 ) 3,748 3,793 (7,992 ) 1,051 600 Net debt position (10,584 ) 18 (16,202 ) 239 (26,529 ) (5,399 ) 70 (17,902 ) 229 (23,002 ) The exposure to dollars largely relates to our net investment hedge activities; exposure to euros largely relates to hedges for our future non-sterling capital expenditure. The currency exposure on other financial instruments is as follows: 2019 2018 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 398 — 1,635 — 2,033 253 — 1,528 — 1,781 Trade and other payables (1,221 ) — (2,085 ) — (3,306 ) (1,124 ) — (1,793 ) — (2,917 ) Other non-current liabilities (93 ) — (247 ) — (340 ) (144 ) — (254 ) — (398 ) The carrying amounts of other financial instruments are denominated in the above currencies, which in most instances are the functional currency of the respective subsidiaries. Our exposure to dollars is due to activities in our US subsidiaries. We do not have any other significant exposure to currency risk on these balances. Hedge accounting for currency risk Where available, derivatives transacted for hedging are designated for hedge accounting. Economic offset is qualitatively determined because the critical terms (currency and volume) of the hedging instrument match the hedged exposure. If a forecast transaction was no longer expected to occur, the cumulative gain or loss previously reported in equity would be transferred to the income statement. This has not occurred in the current or comparative years. Cash flow hedging of currency risk of capital expenditure and revenues is designated as hedging the exposure to movements in the spot translation rates only; the timing of forecasted transactions is not designated as a hedged risk. Gains and losses on hedging instruments arising from forward points and foreign currency basis spreads are excluded from designation and are recognised immediately in profit or loss, along with any hedge ineffectiveness. On recognition of the hedged purchase or sale in the financial statements, the associated hedge gains and losses, deferred in the cash flow hedge reserve in other equity reserves, are transferred out of reserves and included with the recognition of the underlying transaction. Where a non-financial asset or a non-financial liability results from a forecast transaction or firm commitment being hedged, the amounts deferred in reserves are included directly in the initial measurement of that asset or liability. Net investment hedging is also designated as hedging the exposure to movements in spot translation rates only: spot-related gains and losses on hedging instruments are presented in the cumulative translation reserve within other equity reserves to offset gains or losses on translation of the hedged balance sheet exposure. Any ineffectiveness is recognised immediately in the income statement. Gains and losses arising from forward points and foreign currency basis spreads are excluded from designation and are treated as a cost of hedging, deferred initially in other equity reserves and released into profit or loss over the life of the hedging relationship. Amounts deferred in the cumulative translation reserve with respect to net investment hedges are subsequently recognised in the income statement in the event of disposal of the overseas operations concerned. Any remaining amounts deferred in the cost of hedging reserve are also released to the income statement. Hedges of foreign currency funding are designated as cash flow hedges or fair value hedges of forward exchange risk (hedging both currency and interest rate risk together, where applicable). Hedge accounting for funding is described further in the interest rate risk section below. 32. Financial risk management continued (d) Interest rate risk National Grid’s interest rate risk arises from our long-term borrowings. Our interest rate risk management policy is to seek to minimise total financing costs (being interest costs and changes in the market value of debt). Hedging instruments principally consist of interest rate and cross-currency swaps that are used to translate foreign currency debt into functional currency and to adjust the proportion of fixed-rate and floating-rate in the borrowings portfolio to within a range set by the Finance Committee of the Board. The benchmark interest rates hedged are currently based on Libor. 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. During 2019 and 2018, net debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2019 2018 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 59 104 — 89 252 — 302 — 27 329 Financial investments 6 1,944 — 31 1,981 31 2,625 — 38 2,694 Borrowings (19,043 ) (3,045 ) (6,642 ) — (28,730 ) (16,144 ) (3,191 ) (7,290 ) — (26,625 ) Pre-derivative position (18,978 ) (997 ) (6,642 ) 120 (26,497 ) (16,113 ) (264 ) (7,290 ) 65 (23,602 ) Derivative effect 1,740 (1,559 ) (213 ) — (32 ) 1,735 (1,237 ) 102 — 600 Net debt position (17,238 ) (2,556 ) (6,855 ) 120 (26,529 ) (14,378 ) (1,501 ) (7,188 ) 65 (23,002 ) 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. 32. Financial risk management continued (e) Hedge accounting In accordance with the requirements of IFRS 9, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges — (40 ) (12 ) — Cost of hedging (6 ) (12 ) — (90 ) Transferred to profit or loss in respect of: Cash flow hedges — (1 ) — — Cost of hedging 3 — — 39 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (4 ) — — 32 Consolidated statement of financial position Derivatives – carrying value of hedging instruments 1 Assets – current 17 — 9 — Assets – non-current 168 78 23 — Liabilities – current (9 ) (28 ) (3 ) (43 ) Liabilities – non-current (25 ) (134 ) (4 ) (249 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Nov 2019 – May 2038 Aug 2019 – Feb 2039 Apr 2019 – Dec 2023 Mar 2020 – Jun 2025 Spot foreign exchange range: GBP:USD 1.64 – 1.65 1.52 – 1.66 1.29 – 1.41 1.49 GBP:EUR 1.19 – 1.24 1.14 – 1.24 1.07 – 1.32 1.15 EUR:USD 1.13 – 1.16 1.13 – 1.14 n/a n/a Interest rate range: GBP Libor +30bps/+561bps 1.795% – 5.850% n/a n/a USD Libor -44bps/+115bps 1.103% – 3.864% n/a n/a 1. 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: (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings as at 31 March 2019: Hedge type 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 £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings 1 (1,707 ) 11 (117 ) 11 (6 ) 5 1. The carrying value of the hedged borrowings is £1,810 million , of which £202 million is current and £1,608 million is non-current. (ii) Cash flow hedges of foreign currency and interest rate risk as at 31 March 2019: Hedge type 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 £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings (3,804 ) (17 ) 51 39 (39 ) — Foreign currency risk on forecasted cash flows (697 ) 47 — 12 (12 ) — (iii) Net investment hedges of foreign currency risk as at 31 March 2019: Hedge type Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness £m £m £m £m £m £m Currency risk on foreign operations (2,974 ) (329 ) (2,502 ) 550 (550 ) — (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 recoverable at an amount equal to cost. The timing of recovery of these costs can vary between financial periods leading to an under- or over-recovery within any particular year that can lead to large fluctuations in the income statement. We follow approved policies to manage price and supply risks for our commodity activities. Our energy procurement risk management policy and delegations of authority govern our US commodity trading activities for energy transactions. The purpose of this policy is to ensure we transact within pre-defined risk parameters and only in the physical and financial markets where we or our customers have a physical market requirement. In addition, state regulators require National Grid to manage commodity risk and cost volatility prudently through diversified pricing strategies. In some jurisdictions we are required to file a plan outlining our strategy to be approved by regulators. In certain cases we might receive guidance with regard to specific hedging limits. Energy purchase contracts for the forward purchase of electricity or gas that are used to satisfy physical delivery requirements to customers, or for energy that the Group uses itself, meet the expected purchase or usage requirements of IAS 39 and IFRS 9. They are, therefore, not recognised in the financial statements until they are realised. Disclosure of commitments under such contracts is made in note 30. US states have introduced a variety of legislative requirements with the aim of increasing the proportion of our electricity that is derived from renewable or other forms of clean energy. Annual compliance filings regarding the level of Renewable Energy Certificates (and other similar environmental certificates) are required by the relevant department of utilities. In response to the legislative requirements, National Grid has entered into long-term, typically fixed-price, energy supply contracts to purchase both renewable energy and environmental certificates. We are entitled to recover all costs incurred under these contracts through customer billing. Under IFRS, where these supply contracts are not accounted for as finance leases, they are considered to comprise two components, being a forward purchase of power at spot prices, and a forward purchase of environmental certificates at a variable price (being the contract price less the spot power price). With respect to our current contracts, neither of these components meets the requirement to be accounted for as a derivative. The environmental certificates are currently required for compliance purposes, and at present there are no liquid markets for these attributes. Accordingly, this component meets the expected purchase or usage exemption of IFRS 9/IAS 39. We expect to enter into an increasing number of these contracts, in order to meet our compliance requirements in the short to medium term. It is possible that in future, if and when liquid markets develop, and to the extent that we are in receipt of environmental certificates in excess of our required levels, this exemption may cease to apply and we may be required to account for forward purchase commitments for environmental certificates as derivatives at fair value through profit and loss. 32. Financial risk management continued (g) Fair value analysis Included in the statement of financial position are financial instruments which are measured at fair value. These fair values can be categorised into hierarchy levels that are representative of the inputs used in measuring the fair value. The best evidence of fair value is a quoted price in an actively traded market. In the event that the market for a financial instrument is not active, a valuation technique is used. 2019 2018 Level 1 £m Level 2 £m Level 3 £m Total £m Level 1 £m Level 2 £m Level 3 £m Total £m Assets Available-for-sale investments 1 — — — — 2,406 310 5 2,721 Investments held at FVTPL 1 1,311 — 62 1,373 — — — — Investments held at FVOCI 1 93 343 — 436 — — — — Investments in associates 2 — — 90 90 — — 79 79 Financing derivatives — 1,050 2 1,052 — 1,544 1 1,545 Commodity contract derivatives — 33 68 101 — 8 61 69 Further Ac

Additional disclosures in respe

Additional disclosures in respect of guaranteed securities	12 Months Ended
Additional disclosures in respect of guaranteed securities	Mar. 31, 2019
Separate Financial Statements [Abstract]
Additional disclosures in respect of guaranteed securities	Additional disclosures in respect of guaranteed securities We have preferred shares that are listed on a US national securities exchange and are guaranteed by other companies in the Group. These guarantors commit to honour any liabilities should the company issuing the debt have any financial difficulties. In order to provide debt holders with information on the financial stability of the companies providing the guarantees, we are required to disclose individual financial information for these companies. We have chosen to include this information in the Group financial statements rather than submitting separate stand-alone financial statements. The following condensed consolidating financial information, comprising statements of comprehensive income, statements of financial position and cash flow statements, is given in respect of Niagara Mohawk Power Corporation as a result of National Grid plc’s guarantee, dated 29 October 2007, of Niagara Mohawk’s 3.6% and 3.9% issued preferred shares, which amount to £29 million . National Grid plc’s guarantee of Niagara Mohawk Power Corporation’s preferred shares is full and unconditional pursuant to Rule 3-10(i)(8) (i) and (ii) of Regulation S-X. These guarantors commit to honour any liabilities should the company issuing the debt have any financial difficulties. On 1 June 2018, the Group repaid the 6.625% Guaranteed Notes due 2018 that were issued in June 1998 by British Transco Finance Inc., then known as British Gas Finance Inc. (issuer of notes). The following financial information for National Grid plc and Niagara Mohawk Power Corporation on a condensed consolidating basis is intended to provide investors with meaningful and comparable financial information, and is provided pursuant to various rules including Rule 3-10 of Regulation S-X in lieu of the separate financial statements of each subsidiary issuer of public debt securities. This financial information should be read in conjunction with the other disclosures in these financial statements. Summary statements of comprehensive income are presented, on a consolidated basis, for the three years ended 31 March 2019 . Summary statements of comprehensive income of National Grid plc are presented under IFRS measurement principles, as modified by the inclusion of the results of subsidiary undertakings on the basis of equity accounting principles. The summary statements of financial position of National Grid plc include the investments in subsidiaries recorded on the basis of equity accounting principles for the purposes of presenting condensed consolidating financial information under IFRS. The summary statements of financial position present these investments within non-current financial and other investments. The consolidation adjustments column includes the necessary amounts to eliminate the intercompany balances and transactions between National Grid plc, Niagara Mohawk Power Corporation and other subsidiaries. 36. Additional disclosures in respect of guaranteed securities continued Summary statements of comprehensive income for the year ended 31 March 2019 – IFRS Parent guarantor Issuer of notes National Grid plc £m Niagara Mohawk Power Corporation £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Continuing operations Revenue — 2,483 12,450 — 14,933 Operating costs: Depreciation, amortisation and impairment — (216 ) (1,519 ) — (1,735 ) Payroll costs — (360 ) (1,492 ) — (1,852 ) Purchases of electricity — (559 ) (895 ) — (1,454 ) Purchases of gas — (189 ) (1,453 ) — (1,642 ) Rates and property taxes — (200 ) (908 ) — (1,108 ) Balancing Services Incentive Scheme — — (1,196 ) — (1,196 ) Other operating costs — (569 ) (2,507 ) — (3,076 ) — (2,093 ) (9,970 ) — (12,063 ) Total operating profit — 390 2,480 — 2,870 Net finance costs (252 ) (124 ) (693 ) — (1,069 ) Interest in equity accounted affiliates 1,712 — 40 (1,712 ) 40 Profit before tax 1,460 266 1,827 (1,712 ) 1,841 Tax 50 (56 ) (333 ) — (339 ) Profit after tax from discontinued operations — — 12 — 12 Profit for the year 1,510 210 1,506 (1,712 ) 1,514 Amounts recognised in other comprehensive income from continuing operations 1 303 4 (45 ) 41 303 Amounts recognised in other comprehensive income from discontinued operations 1 36 — 36 (36 ) 36 Total comprehensive income for the year 1,849 214 1,497 (1,707 ) 1,853 Attributable to: Equity shareholders 1,849 214 1,493 (1,707 ) 1,849 Non-controlling interests — — 4 — 4 1,849 214 1,497 (1,707 ) 1,853 1. Includes other comprehensive income relating to interest in equity accounted affiliates. 36. Additional disclosures in respect of guaranteed securities continued Summary statements of comprehensive income for the year ended 31 March 2018 1 – IFRS Parent guarantor Issuer of notes Subsidiary guarantor National Grid plc £m Niagara Mohawk Power Corporation £m British Transco Finance Inc. £m National Grid Gas plc £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Continuing operations Revenue — 2,416 — 1,430 11,495 (91 ) 15,250 Operating costs: Depreciation, amortisation and impairment — (190 ) — (245 ) (1,095 ) — (1,530 ) Payroll costs — (318 ) — (122 ) (1,208 ) — (1,648 ) Purchases of electricity — (537 ) — — (748 ) — (1,285 ) Purchases of gas — (166 ) — — (1,377 ) — (1,543 ) Rates and property taxes — (183 ) — (94 ) (780 ) — (1,057 ) Balancing Services Incentive Scheme — — — — (1,012 ) — (1,012 ) Payments to other UK network owners — — — — (1,043 ) — (1,043 ) Other operating costs — (397 ) — (331 ) (2,002 ) 91 (2,639 ) — (1,791 ) — (792 ) (9,265 ) 91 (11,757 ) Total operating profit — 625 — 638 2,230 — 3,493 Net finance income/(costs) 889 (100 ) — (174 ) (1,497 ) — (882 ) Interest in equity accounted affiliates 2,622 — — 8 49 (2,630 ) 49 Profit before tax 3,511 525 — 472 782 (2,630 ) 2,660 Tax 40 321 — (103 ) 631 — 889 Profit after tax from discontinued operations — — — 17 (15 ) — 2 Profit for the year 3,551 846 — 386 1,398 (2,630 ) 3,551 Amounts recognised in other comprehensive income from continuing operations 3 224 1 — 272 457 (730 ) 224 Amounts recognised in other comprehensive income from discontinued operations 3 147 — — — 147 (147 ) 147 Total comprehensive income for the year 3,922 847 — 658 2,002 (3,507 ) 3,922 Attributable to: Equity shareholders 3,922 847 — 658 2,002 (3,507 ) 3,922 Non-controlling interests — — — — — — — 3,922 847 — 658 2,002 (3,507 ) 3,922 1. Comparatives have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 2. Profit for the year for British Transco Finance Inc. is £ nil as interest payable to external bond holders is offset by interest receivable on loans to National Grid Gas plc. 3. Includes other comprehensive income relating to interest in equity accounted affiliates. 36. Additional disclosures in respect of guaranteed securities continued Summary statements of comprehensive income for the year ended 31 March 2017 – IFRS Parent guarantor Issuer of notes Subsidiary guarantor National Grid plc £m Niagara Mohawk Power Corporation £m British Transco Finance Inc. £m National Grid Gas plc re-presented £m Other subsidiaries re-presented £m Consolidation adjustments £m National Grid consolidated £m Continuing operations Revenue — 2,388 — 1,376 11,435 (164 ) 15,035 Operating costs: Depreciation, amortisation and impairment — (193 ) — (256 ) (1,032 ) — (1,481 ) Payroll costs — (326 ) — (114 ) (1,138 ) — (1,578 ) Purchases of electricity — (511 ) — — (586 ) — (1,097 ) Purchases of gas — (140 ) — (67 ) (1,012 ) — (1,219 ) Rates and property taxes — (188 ) — (101 ) (753 ) — (1,042 ) Balancing Services Incentive Scheme — — — — (1,120 ) — (1,120 ) Payments to other UK network owners — — — — (1,008 ) — (1,008 ) Other operating costs — (435 ) — (394 ) (2,617 ) 164 (3,282 ) — (1,793 ) — (932 ) (9,266 ) 164 (11,827 ) Total operating profit — 595 — 444 2,169 — 3,208 Net finance income/(costs) 8,177 (101 ) — (253 ) (8,910 ) — (1,087 ) Dividends receivable — — — — 8,100 (8,100 ) — Interest in equity accounted affiliates (401 ) — — — 63 401 63 Profit before tax 7,776 494 — 191 1,422 (7,699 ) 2,184 Tax 19 (181 ) — 16 (228 ) — (374 ) Profit after tax from discontinued operations — — — 4,633 1,351 — 5,984 Profit for the year 7,795 313 — 4,840 2,545 (7,699 ) 7,794 Amounts recognised in other comprehensive income from continuing operations 2 578 — — 114 177 (291 ) 578 Amounts recognised in other comprehensive income from discontinued operations 2 42 — — 51 (62 ) 11 42 Total comprehensive income for the year 8,415 313 — 5,005 2,660 (7,979 ) 8,414 Attributable to: Equity shareholders 8,415 313 — 5,005 2,661 (7,979 ) 8,415 Non-controlling interests — — — — (1 ) — (1 ) 8,415 313 — 5,005 2,660 (7,979 ) 8,414 1. Profit for the year for British Transco Finance Inc. is £ nil as interest payable to external bond holders is offset by interest receivable on loans to National Grid Gas plc. 2. Includes other comprehensive income relating to interest in equity accounted affiliates. 36. Additional disclosures in respect of guaranteed securities continued Statements of financial position as at 31 March 2019 – IFRS Parent Issuer of notes National Grid plc £m Niagara Mohawk Power Corporation £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Non-current assets Goodwill — 745 5,124 — 5,869 Other intangible assets — 3 1,081 — 1,084 Property, plant and equipment — 6,985 36,928 — 43,913 Other non-current assets — 4 260 — 264 Amounts owed by subsidiary undertakings 358 — 2,073 (2,431 ) — Pension assets — 260 1,307 — 1,567 Financial and other investments 23,573 22 3,434 (25,754 ) 1,275 Derivative financial assets — 9 1,036 — 1,045 Total non-current assets 23,931 8,028 51,243 (28,185 ) 55,017 Current assets Inventories and current intangible assets — 41 329 — 370 Trade and other receivables 1 535 2,617 — 3,153 Current tax assets — — 260 (134 ) 126 Amounts owed by subsidiary undertakings 12,514 476 14,101 (27,091 ) — Financial and other investments 895 13 1,073 — 1,981 Derivative financial assets 110 21 80 (103 ) 108 Cash and cash equivalents 75 12 165 — 252 Assets held for sale — — 1,956 — 1,956 Total current assets 13,595 1,098 20,581 (27,328 ) 7,946 Total assets 37,526 9,126 71,824 (55,513 ) 62,963 Current liabilities Borrowings (1,275 ) (634 ) (2,563 ) — (4,472 ) Derivative financial liabilities (92 ) (15 ) (346 ) 103 (350 ) Trade and other payables (58 ) (413 ) (3,298 ) — (3,769 ) Contract liabilities — (4 ) (57 ) — (61 ) Amounts owed to subsidiary undertakings (14,104 ) — (12,987 ) 27,091 — Current tax liabilities — (148 ) (147 ) 134 (161 ) Provisions — (24 ) (292 ) — (316 ) Total current liabilities (15,529 ) (1,238 ) (19,690 ) 27,328 (9,129 ) Non-current liabilities Borrowings (346 ) (2,048 ) (21,864 ) — (24,258 ) Derivative financial liabilities (228 ) (8 ) (597 ) — (833 ) Other non-current liabilities — (301 ) (507 ) — (808 ) Contract liabilities — (181 ) (752 ) — (933 ) Amounts owed to subsidiary undertakings (2,074 ) — (357 ) 2,431 — Deferred tax liabilities — (678 ) (3,287 ) — (3,965 ) Pensions and other post-retirement benefit obligations — (872 ) (913 ) — (1,785 ) Provisions — (271 ) (1,612 ) — (1,883 ) Total non-current liabilities (2,648 ) (4,359 ) (29,889 ) 2,431 (34,465 ) Total liabilities (18,177 ) (5,597 ) (49,579 ) 29,759 (43,594 ) Net assets 19,349 3,529 22,245 (25,754 ) 19,369 Equity Share capital 458 144 180 (324 ) 458 Share premium account 1,314 2,394 9,032 (11,426 ) 1,314 Retained earnings 21,814 991 13,048 (14,039 ) 21,814 Other equity reserves (4,237 ) — (35 ) 35 (4,237 ) Shareholders’ equity 19,349 3,529 22,225 (25,754 ) 19,349 Non-controlling interests — — 20 — 20 Total equity 19,349 3,529 22,245 (25,754 ) 19,369 36. Additional disclosures in respect of guaranteed securities continued Statements of financial position as at 31 March 2018 – IFRS Parent Issuer of notes Subsidiary guarantor National Grid plc £m Niagara Mohawk Power Corporation £m British Transco Finance Inc. £m National Grid Gas plc £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Non-current assets Goodwill — 691 — — 4,753 — 5,444 Other intangible assets — 3 — 107 789 — 899 Property, plant and equipment — 6,148 — 4,433 29,272 — 39,853 Other non-current assets — 3 — 94 18 — 115 Amounts owed by subsidiary undertakings 350 — — 3,426 2,593 (6,369 ) — Pension assets — 231 — 412 766 — 1,409 Financial and other investments 21,708 30 — 101 12,340 (31,112 ) 3,067 Derivative financial assets 18 2 — 591 708 — 1,319 Total non-current assets 22,076 7,108 — 9,164 51,239 (37,481 ) 52,106 Current assets Inventories and current intangible assets — 36 — 22 283 — 341 Trade and other receivables 1 515 — 276 2,006 — 2,798 Current tax assets — — — — 307 (193 ) 114 Amounts owed by subsidiary undertakings 11,254 130 220 708 11,253 (23,565 ) — Financial and other investments 938 15 — 863 878 — 2,694 Derivative financial assets 308 7 — 46 — 44 405 Cash and cash equivalents — 4 — 271 54 — 329 Total current assets 12,501 707 220 2,186 14,781 (23,714 ) 6,681 Total assets 34,577 7,815 220 11,350 66,020 (61,195 ) 58,787 Current liabilities Borrowings (781 ) (51 ) (218 ) (675 ) (2,722 ) — (4,447 ) Derivative financial liabilities (187 ) (36 ) — (68 ) (66 ) (44 ) (401 ) Trade and other payables (62 ) (318 ) — (347 ) (2,726 ) — (3,453 ) Amounts owed to subsidiary undertakings (11,809 ) — — (624 ) (11,132 ) 23,565 — Current tax liabilities — (202 ) — (26 ) (88 ) 193 (123 ) Provisions — (23 ) — (66 ) (184 ) — (273 ) Total current liabilities (12,839 ) (630 ) (218 ) (1,806 ) (16,918 ) 23,714 (8,697 ) Non-current liabilities Borrowings (773 ) (2,087 ) — (3,635 ) (15,683 ) — (22,178 ) Derivative financial liabilities (41 ) (18 ) — (157 ) (444 ) — (660 ) Other non-current liabilities — (281 ) — (181 ) (855 ) — (1,317 ) Amounts owed to subsidiary undertakings (2,091 ) — — (500 ) (3,778 ) 6,369 — Deferred tax liabilities (1 ) (626 ) — (441 ) (2,568 ) — (3,636 ) Pensions and other post-retirement benefit obligations — (765 ) — — (907 ) — (1,672 ) Provisions — (248 ) — (129 ) (1,402 ) — (1,779 ) Total non-current liabilities (2,906 ) (4,025 ) — (5,043 ) (25,637 ) 6,369 (31,242 ) Total liabilities (15,745 ) (4,655 ) (218 ) (6,849 ) (42,555 ) 30,083 (39,939 ) Net assets 18,832 3,160 2 4,501 23,465 (31,112 ) 18,848 Equity Share capital 452 133 — 45 182 (360 ) 452 Share premium account 1,321 2,194 — 204 9,032 (11,430 ) 1,321 Retained earnings 21,599 830 2 2,929 14,217 (17,978 ) 21,599 Other equity reserves (4,540 ) 3 — 1,323 18 (1,344 ) (4,540 ) Shareholders’ equity 18,832 3,160 2 4,501 23,449 (31,112 ) 18,832 Non-controlling interests — — — — 16 — 16 Total equity 18,832 3,160 2 4,501 23,465 (31,112 ) 18,848 36. Additional disclosures in respect of guaranteed securities continued Cash flow statements Parent Issuer of notes Subsidiary guarantor National Grid plc £m Niagara Mohawk Power Corporation £m British Transco Finance Inc. £m National Grid Gas plc £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Year ended 31 March 2019 Net cash flow from operating activities – continuing operations 33 572 n/a n/a 3,784 — 4,389 Net cash flow used in operating activities – discontinued operations — — n/a n/a (71 ) — (71 ) Net cash flow from/(used in) investing activities – continuing operations 121 (823 ) n/a n/a (3,570 ) 1,082 (3,190 ) Net cash flow from investing activities – discontinued operations — — n/a n/a 156 — 156 Net cash flow (used in)/from financing activities – continuing operations (79 ) 259 n/a n/a (462 ) (1,082 ) (1,364 ) Net cash flow from financing activities – discontinued operations — — n/a n/a — — — Net increase/(decrease) in cash and cash equivalents in the year 75 8 n/a n/a (163 ) — (80 ) Year ended 31 March 2018 Net cash flow from operating activities – continuing operations 35 662 — 888 3,125 — 4,710 Net cash flow used in operating activities – discontinued operations — — — (98 ) (109 ) — (207 ) Net cash flow from/(used in) investing activities – continuing operations 4,660 (473 ) 15 656 (1,930 ) (862 ) 2,066 Net cash flow from investing activities – discontinued operations — — — — 171 — 171 Net cash flow (used in)/from financing activities – continuing operations (5,785 ) (189 ) (15 ) (1,041 ) (1,148 ) 862 (7,316 ) Net cash flow used in financing activities – discontinued operations — — — (125 ) (106 ) — (231 ) Net (decrease)/increase in cash and cash equivalents in the year (1,090 ) — — 280 3 — (807 ) Year ended 31 March 2017 Net cash flow from operating activities – continuing operations 53 757 — 918 2,592 — 4,320 Net cash flow from operating activities – discontinued operations — — — 450 459 — 909 Net cash flow from/(used in) investing activities – continuing operations 4,181 (469 ) 15 215 (1,118 ) (6,458 ) (3,634 ) Net cash flow from/(used in) investing activities – discontinued operations — — — 5,618 (6,298 ) — (680 ) Net cash flow (used in)/from financing activities – continuing operations (3,146 ) (288 ) (15 ) (8,322 ) 3,771 6,458 (1,542 ) Net cash flow from financing activities – discontinued operations — — — 1,120 491 — 1,611 Net increase/(decrease) in cash and cash equivalents in the year 1,088 — — (1 ) (103 ) — 984 Cash dividends were received by National Grid plc from subsidiary undertakings amounting to £ nil during the year ended 31 March 2019 ( 2018 : £950 million ; 2017 : £6,006 million ). Maturity analysis of Parent Company borrowings 2019 2018 £m £m Total borrowings are repayable as follows: Less than 1 year 1,275 781 In 1 to 2 years — 438 In 2 to 3 years 346 — In 3 to 4 years — 335 In 4 to 5 years — — More than 5 years — — 1,621 1,554

Transition to IFRS 9 and IFRS 1

Transition to IFRS 9 and IFRS 15	6 Months Ended
Transition to IFRS 9 and IFRS 15	Sep. 30, 2018
Disclosure of comparative information prepared under previous GAAP [abstract]
Transition to IFRS 9 and IFRS 15	Transition to IFRS 9 and IFRS 15 The Group has adopted IFRS 9 and IFRS 15 with effect from 1 April 2018. The impact of the transition on the opening consolidated statement of financial position is set out in the following table: Impact of transition 31 March 2018 Transition adjustments 1 April 2018 IFRS 9 IFRS 15 £m £m £m £m Non-current assets Goodwill 5,444 — — 5,444 Other intangible assets 899 — — 899 Property, plant and equipment 39,853 — — 39,853 Other non-current assets 115 — — 115 Pension assets 1,409 — — 1,409 Financial and other investments 899 — 1 — 899 Investments in joint ventures and associates 2,168 — — 2,168 Derivative financial assets 1,319 — — 1,319 Total non-current assets 52,106 — — 52,106 Current assets Inventories and current intangible assets 341 — — 341 Trade and other receivables 2,798 — 2 (3 ) 2,795 Current tax assets 114 — — 114 Financial and other investments 2,694 — 1 — 2,694 Derivative financial assets 405 — — 405 Cash and cash equivalents 329 — — 329 Total current assets 6,681 — (3 ) 6,678 Total assets 58,787 — (3 ) 58,784 Current liabilities Borrowings (4,447 ) — — (4,447 ) Derivative financial liabilities (401 ) — — (401 ) Trade and other payables (3,453 ) — 59 7 (3,394 ) Contract liabilities — — (53) 7 (53 ) Current tax liabilities (123 ) — — (123 ) Provisions (273 ) — — (273 ) Total current liabilities (8,697 ) — 6 (8,691 ) Non-current liabilities Borrowings (22,178 ) (32) 3 — (22,210 ) Derivative financial liabilities (660 ) — — (660 ) Other non-current liabilities (1,317 ) — 567 7 (750 ) Contract liabilities — — (813) 7 (813 ) Deferred tax liabilities (3,636 ) 5 4 74 8 (3,557 ) Pensions and other post-retirement benefit obligations (1,672 ) — — (1,672 ) Provisions (1,779 ) — — (1,779 ) Total non-current liabilities (31,242 ) (27 ) (172 ) (31,441 ) Total liabilities (39,939 ) (27 ) (166 ) (40,132 ) Net assets 18,848 (27 ) (169 ) 18,652 Equity Share capital 452 — — 452 Share premium account 1,321 — — 1,321 Retained earnings 21,599 (99) 5 (169) 9 21,331 Other equity reserves (4,540 ) 72 6 — (4,468 ) Total shareholders’ equity 18,832 (27 ) (169 ) 18,636 Non-controlling interests 16 — — 16 Total equity 18,848 (27 ) (169 ) 18,652 37. Transition to IFRS 9 and IFRS 15 continued Both standards were applied using the modified retrospective approach whereby comparative amounts have not been restated on transition, but a cumulative adjustment has been made to retained earnings in the opening consolidated statement of financial position as at 1 April 2018. IFRS 9: Financial Instruments IFRS 9 has changed the rules concerning the classification and measurement of financial instruments, impairment of financial assets, and hedge accounting. Details of the impact of applying IFRS 9 for the year ended 31 March 2019 are set out below. Adjustments arising as a result of the transition to IFRS 9: 1. The available-for-sale category for financial assets has been replaced with investments held at fair value through profit and loss (FVTPL) and investments held at fair value through other comprehensive income (FVOCI). Changes to the classification and measurement of financial assets have not altered the carrying value of any financial assets held by the Group. The net impact to retained earnings of the reclassification on transition was an £8 million gain. As described in note 15, all recognised financial assets that are within the scope of IFRS 9 are initially recorded at fair value and subsequently measured at amortised cost or fair value based on the Group’s business model for managing the financial assets and the contractual cash flow characteristics of the financial assets. Therefore on 1 April 2018, the Group reclassified its investments as follows: • Money market funds and fund investments held by captive insurance companies have been classified as financial assets at FVTPL because their contractual cash flows are not solely payments of principal and interest; • Investments in debt securities that have contractual payments that are solely payments of principal and interest, and which are held as part of the liquidity portfolio or to back employee benefit liabilities, have been classified as financial assets at FVOCI because they are held in a business model whose objective is to collect the contractual cash flows and to sell the debt instruments; • The Group has elected to hold investments in equity securities, which are held to back employee benefit liabilities, as financial assets at FVOCI as the Group does not believe that changes in their fair value is reflective of the financial performance of the Group; and • Loans to joint ventures and associates, cash at bank, and short-term deposits are classified at amortised cost as they have contractual cash flows which are solely payments of principal and interest and the Group holds them to collect contractual cash flows. Aside from derivative financial instruments, which remain classified as FVTPL, the Group did not previously have any financial assets or liabilities classified at FVTPL. The table below illustrates those financial assets and liabilities that have been reclassified at 1 April 2018: Financial asset/liability Note Original measurement category under IAS 39 New measurement category under IFRS 9 Original carrying amount under IAS 39 Change to measurement basis under IFRS 9 New carrying amount under IFRS 9 £m £m £m Money market funds and fund investments in equities and bonds 15 Available-for-sale investments Financial assets at FVTPL 2,294 — 2,294 Cash surrender value of life insurance policies and investments in debt securities 15 Available-for-sale investments Financial assets at FVOCI 343 — 343 Investments in equity securities 15 Available-for-sale investments Financial assets at FVOCI (equity instruments) 84 — 84 Loans to joint ventures and associates and restricted balances 15 Loans and receivables Financial assets at amortised cost 872 — 872 Borrowings 21 Financial liabilities at amortised cost Financial liabilities at fair value through profit and loss (570 ) (32 ) (602 ) Note that the table above does not include derivative assets, derivative liabilities, trade receivables, cash at bank and short-term deposits, borrowings measured at amortised cost or trade payables. This is because neither the classification nor the measurement of these items has changed on transition to IFRS 9. 37. Transition to IFRS 9 and IFRS 15 continued 2. The change from the incurred loss impairment model of IAS 39 to the expected loss model in IFRS 9 has not had a material impact on the Group’s credit loss provision. The Group calculates its impairment provision on trade receivables using a sophisticated provisions matrix. The inclusion of forward-looking information has not had a significant impact on the matrix as the relevant short-term future economic conditions affecting our retail customers in the US are expected to be similar to recent experience. 3. The Group elected to reclassify an existing liability with a carrying value of £570 million from amortised cost to fair value through profit and loss to reduce a measurement mismatch. At transition, the resultant impacts include an increase in the carrying value of the liability of £32 million , a reduction in retained earnings of £40 million and the establishment of an own credit reserve (within other equity reserves) of £7 million . 4. Deferred tax is recognised on the adjustments recorded on the transition to IFRS 9. Reserve impacts are stated net of related deferred tax. 5. Retained earnings includes the impact from adjustments 1, 3 and 6. 6. The Group has adopted the hedge accounting requirements of IFRS 9, which more closely align with the Group’s risk management policies. On transition, it was concluded that all IAS 39 hedge relationships are qualifying IFRS 9 relationships with the treatment of the cost of hedging being the main change. The effect was a reclassification in reserves of a £67 million gain from retained earnings and a £10 million gain from the cash flow hedge reserve, into a new cost of hedging reserve (within other equity reserves). In this reserve, qualifying unrealised gains and losses excluded from hedging relationships are deferred and released systematically into profit or loss to match the timing of hedged items. IFRS 15: Revenue from Contracts with Customers IFRS 15 has primarily changed the accounting for our connection and diversion revenues in our regulated businesses. No practical expedients on transition were applied. The accounting for revenue under IFRS 15 does not represent a substantive change from the Group’s previous practice under IAS 18 for recognising revenue from sales to customers with the exception of the following items: • Certain pass-through revenues (principally revenues collected on behalf of the Scottish and Offshore transmission operators) will be recorded net of operating costs, whereas previously they were recognised gross of operating costs. Had we not adopted IFRS 15, our revenues and operating costs for the year ended 31 March 2019 would have been £1,197 million higher, with no impact to operating profits; • Contributions for capital works relating to connections for our customers are now deferred as contract liabilities on our consolidated statement of financial position and released over the life of the connection assets. This is a change for our US Regulated business and our UK Gas Transmission business, where previously revenues were recorded once the work was completed. Had we not adopted IFRS 15, our revenues and operating profit for the year ended 31 March 2019 would have been £57 million higher; and • In the UK, contributions for capital works relating to diversions are now recognised as the works are completed. This is a change for the UK regulated businesses where revenues were previously deferred over the life of the asset. Had we not adopted IFRS 15, our revenues and operating profit for the year ended 31 March 2019 would have been £26 million and £23 million lower, respectively. Adjustments arising as a result of the transition to IFRS 15: 7. Deferred income from contributions for capital works have now been reclassified to contract liabilities. In addition, these liabilities for capital works relating to connections have increased as these capital contributions for connections are cumulatively adjusted for on 1 April 2018 and are now deferred and released over the life of the connection assets. This is a change for our US Regulated business and our UK Gas Transmission business where previously revenues were recorded once the work was completed. Partially offsetting the increase in contract liabilities for connections is the change in accounting treatment for contributions relating to diversions in our UK businesses. These contributions are recognised as revenue as the works are completed where previously revenue was recognised over the life of the assets. 8. Deferred tax is recorded on the incremental amounts recorded against capital contributions and contract liabilities on the transition to IFRS 15. Deferred tax balances have been calculated at the rate substantially enacted at the balance sheet date. 9. The transition adjustment reflects the net of adjustments 7 and 8 above.

Post balance sheet events

Post balance sheet events	12 Months Ended
Post balance sheet events	Mar. 31, 2019
Events After Reporting Period [Abstract]
Post balance sheet events	Post balance sheet events In March 2019, National Grid Ventures entered into an agreement to acquire 100% of Geronimo Energy, a clean energy developer based in Minneapolis in the United States for $100 million with potential further payments of up to $100 million subject to successful development of the project pipeline. Completion of the acquisition is dependent on the execution of a joint venture agreement with Washington State Investment Board and regulatory approvals being obtained (expected in the summer of 2019).

Basis of preparation and rece_2

Basis of preparation and recent accounting developments (Policies)	12 Months Ended
	Mar. 31, 2019
Accounting Policies, Changes In Accounting Estimates And Errors [Abstract]
Description of accounting policy for basis of preparation	These consolidated financial statements have been prepared in accordance with International Accounting Standards (IAS) and International Financial Reporting Standards (IFRS) and related interpretations as issued by the IASB and IFRS as adopted by the EU. They are prepared on the basis of all IFRS accounting standards and interpretations that are mandatory for periods ended 31 March 2019 and in accordance with the Companies Act 2006 applicable to companies reporting under IFRS and Article 4 of the EU IAS Regulation. The comparative financial information has also been prepared on this basis. The consolidated financial statements have been prepared on a historical cost basis, except for the recording of pension assets and liabilities, the revaluation of derivative financial instruments and certain commodity contracts and certain financial assets and liabilities measured at fair value. These consolidated financial statements are presented in pounds sterling, which is also the functional currency of the Company. The notes to the financial statements have been prepared on a continuing basis unless otherwise stated. Our income statement and segmental analysis separately identify financial results before and after exceptional items and remeasurements. We continue to use a columnar presentation as we consider it improves the clarity of the presentation, and is consistent with the way that financial performance is measured by management and reported to the Board and Executive Committee, and assists users of the financial statements to understand the results. The Directors believe that presentation of the results in this way is relevant to an understanding of the Group’s financial performance. Presenting financial results before exceptional items and remeasurements is consistent with the way that financial performance is measured by management and reported to the Board and Executive Committee and aids the comparability of reported financial performance from year to year in this context. The inclusion of total profit for the period from continuing operations before exceptional items and remeasurements forms part of the incentive target set annually for remunerating certain Executive Directors and accordingly we believe it is important for users of the financial statements to understand how this compares to our results on a statutory basis and period on period.
Going concern	The Directors considered it appropriate to prepare the financial statements on a going concern basis, having considered the Company’s cash flow forecasts with respect to business planning and treasury management activities. The going concern basis presumes that the Group has adequate resources to remain in operation, and that the Directors intend it to do so, for at least one year from the date the financial statements are signed.
Basis of consolidation	The consolidated financial statements incorporate the results, assets and liabilities of the Company and its subsidiaries, together with a share of the results, assets and liabilities of joint operations. A subsidiary is defined as an entity controlled by the Group. Control is achieved where the Group is exposed to, or has the rights to, variable returns from its involvement with the entity and has the power to affect those returns through its power over the entity. The Group accounts for joint ventures and associates using the equity method of accounting, where the investment is carried at cost plus post-acquisition changes in the share of net assets of the joint venture or associate, less any provision for impairment. Losses in excess of the consolidated interest in joint ventures and associates are not recognised, except where the Company or its subsidiaries have made a commitment to make good those losses. Where necessary, adjustments are made to bring the accounting policies used in the individual financial statements of the Company, subsidiaries, joint operations, joint ventures and associates into line with those used by the Group in its consolidated financial statements under IFRS. Intercompany transactions are eliminated. The results of subsidiaries, joint operations, joint ventures and associates acquired or disposed of during the year are included in the consolidated income statement from the effective date of acquisition or up to the effective date of disposal, as appropriate. Acquisitions are accounted for using the acquisition method, where the purchase price is allocated to the identifiable assets acquired and liabilities assumed on a fair value basis and the remainder recognised as goodwill.
Treatment of interests in Quadgas HoldCo Limited (Quadgas) – discontinued operations and held for sale	Following the Group’s disposal of a 61% controlling stake in the UK Gas Distribution business on 31 March 2017, we have decided to exercise the options over the retained 39% interest in the business (held through Quadgas) and the sale is expected to complete at the end of June 2019, subject to customary regulatory approvals. Accordingly, our interests have been classified as held for sale with effect from 30 June 2018. The Quadgas disposal group comprises our equity investment in Quadgas, our shareholder loan to Quadgas, the Further Acquisition Agreement (FAA) derivative and the Remaining Acquisition Agreement (RAA) derivative. Refer to note 10 for further details. We have also treated the results of the disposal group as a discontinued operation in the consolidated income statement for the current year and we have restated our prior year comparatives for 2018 on the same basis. The results of the UK Gas Distribution business were already treated as a discontinued operation for the year ended 31 March 2017 with certain true ups (relating to completion accounts) to the disposal of the controlling stake recorded within discontinued operations for the year ended 31 March 2018. The reclassification impacts the consolidated income statement, the consolidated statement of comprehensive income and 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. Assets and businesses are classified as held for sale when their carrying amounts are recovered through sale rather than through continuing use. They only meet the held for sale condition when the assets are ready for immediate sale in their present condition, management is committed to the sale and it is highly probable that the sale will complete within one year. Depreciation ceases on assets and businesses when they are classified as held for sale and the assets and businesses are impaired if the proceeds less sale costs fall short of the carrying value. Following the decision that we will exercise our put option to sell the 39% equity interest we hold in Quadgas, and on the basis that we intend to dispose of our stake by 30 June 2019, we have met the criteria to classify our interests in Quadgas as a disposal group held for sale. The disposal group comprises our equity interests in Quadgas, the shareholder loan to Quadgas and the derivatives arising from the put/call agreements (described further below). The Group has classified the results of the disposal group as a discontinued operation for the year, and therefore they are presented in the income statement as a discontinued operation separately from the results of the rest of our business, in the same way as the results of the UK Gas Distribution business were disclosed following the sale of a 61% controlling stake in the business on 31 March 2017.
Foreign currencies	Transactions in currencies other than the functional currency of the Company or subsidiary concerned are recorded at the rates of exchange prevailing on the dates of the transactions. At each reporting date, monetary assets and liabilities that are denominated in foreign currencies are retranslated at closing exchange rates. Non-monetary assets are not retranslated unless they are carried at fair value. Gains and losses arising on the retranslation of monetary assets and liabilities are included in the income statement, except where the application of hedge accounting requires inclusion in other comprehensive income (see note 32(e)). On consolidation, the assets and liabilities of operations that have a functional currency different from the Company’s functional currency of pounds sterling, principally our US operations that have a functional currency of US dollars, are translated at exchange rates prevailing at the reporting date. Income and expense items are translated at the average exchange rates for the period where these do not differ materially from rates at the date of the transaction. Exchange differences arising are recognised in other comprehensive income and transferred to the consolidated translation reserve within other equity reserves (see note 28).
Areas of judgement and key sources of estimation uncertainty	The preparation of financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities, and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from these estimates. Information about such judgements and estimations is in the notes to the financial statements, and the key areas are summarised below. Areas of judgement that have the most significant effect on the amounts recognised in the financial statements are as follows: • Categorisation of certain items as exceptional items or remeasurements and the definition of adjusted earnings (see notes 5 and 8). In applying the Group’s exceptional items framework, we have considered a number of key matters, as detailed in note 5. • In addition, we have exercised our judgement in concluding that it is appropriate to classify our investment in and shareholder loan to Quadgas, along with the related Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) derivatives, as held for sale and as a discontinued operation, as detailed in note 10. Key sources of estimation uncertainty that have a significant risk of causing a material adjustment to the carrying amounts of assets and liabilities within the next financial year are as follows: • valuation of liabilities for pensions and other post-retirement benefits (see note 25); and • the cash flows applied in determining the environmental provisions (see note 26). In order to illustrate the impact that changes in assumptions could have on our results and financial position, we have included sensitivity analyses in note 35.
New IFRS accounting standards effective for the year ended 31 March 2019 and New IFRS accounting standards and interpretations not yet adopted	The Group adopted IFRS 9 ‘Financial Instruments’ and IFRS 15 ‘Revenue from Contracts with Customers’ with effect from 1 April 2018. We have applied the modified retrospective approach permitted in the Standards whereby prior year comparatives have not been restated on adoption. Instead, the cumulative transition adjustments are reflected through reserves. Refer to note 37 for full details of the impact and transition adjustments arising on adoption. The Group has also adopted the following amendments to standards, which have had no material impact on the Group’s results or financial statement disclosure: • Annual improvements to IFRSs 2014-2016 Cycle; • Amendments to IFRS 2 ‘Share-based payment’; and • IFRIC 22 ‘Foreign Currency Transactions and Advance Consideration’. The Group has considered the impact of the following new IFRS standards or interpretations that have not yet been adopted: i) IFRS 16 ‘Leases’ IFRS 16 ‘Leases’ is effective for National Grid for the year ending 31 March 2020. IFRS 16 introduces a single lease accounting model for lessees (rather than the current distinction between operating and finance leases). A contract is, or contains, a lease, if it provides the right to control the use of an identified asset for a specific period of time in exchange for consideration. The new standard will result in our operating leases being accounted for in the consolidated statement of financial position as ‘right-of-use’ assets with corresponding lease liabilities also recognised. It will therefore increase both our assets and liabilities (including net debt). In future periods, this will change the timing and presentation in the consolidated income statement as it will result in an increase in finance costs and depreciation largely offset by a reduction in the previously straight-line operating costs. Transition options We will apply IFRS 16 with effect from 1 April 2019 using the modified retrospective approach. Comparatives will not be restated on adoption. Instead, a cumulative adjustment to our opening consolidated statement of financial position will be reflected in retained earnings as well as recognition of the opening right-of-use assets and additional lease liabilities and associated deferred tax. For short‐term leases (lease term of 12 months or less) and leases of low‐value assets (such as computers), the Group will continue to recognise a lease expense on a straight‐line basis as permitted by IFRS 16. In preparing for the transition, we have elected to apply the practical expedient to grandfather our previous assessments of whether contracts were previously accounted for as a lease, as permitted by the standard, instead of reassessing all significant contracts as at the date of initial application to determine whether they met the IFRS 16 definition of a lease. We have elected to apply the practical expedient on transition, which permits right-of-use assets to be measured at an amount equal to the lease liability on adoption of the standard (adjusted for any prepaid or accrued lease expenses). In addition, we have also elected the option to adjust the carrying amounts of the right-of-use assets as at 1 April 2019 for onerous lease provisions that had been recognised on the Group consolidated statement of financial position as at 31 March 2019, rather than performing impairment assessments on transition. Impact of transition As at the reporting date, the Group has non-cancellable operating lease commitments of £0.3 billion (see note 30), of which the majority are in the US. A further £0.3 billion of lease liabilities is recognised due to the requirement in IFRS 16 to recognise lease liabilities for the term that we are reasonably certain to exercise lease extension or lease termination options for, rather than only for the period of the minimum contractual term that is used in determining our lease liability commitments. This is partially offset by the £0.2 billion impact of discounting our lease liabilities at the incremental borrowing rate for each lease. There are some immaterial short term and low value leases, which will be recognised on a straight-line basis as an expense in profit and loss over the remaining lease term. As a result, the Group expects to recognise additional right-of-use assets and lease liabilities (which are included within net debt) of approximately £0.4 billion at 1 April 2019 with no material additional net deferred tax. This is in addition to the £0.3 billion of finance leases already recognised on the consolidated statement of financial position under IAS 17. There will be no material net impact on net assets. Accordingly, the Group does not expect the impact of IFRS 16 on profit after tax as a result of adopting the new standard to be material. However, it will result in an increase in operating profit due to the operating costs now being replaced with depreciation and interest charges. We expect operating cash flows to increase and financing cash flows to decrease by less than £0.1 billion , because repayment of the principal portion of the lease liabilities will be classified as cash flows from financing activities rather than operating cash flows. ii) Other In addition, the following new accounting standards and amendments to existing standards have been issued but are not yet effective or have not yet been endorsed by the EU: • IFRIC 23 ‘Uncertainty over Income Tax Treatments’; • Amendments to IAS 28 ‘Investments in Associates – Long-term Interests in Associates and Joint Ventures’; • Annual Improvements to IFRS Standards 2015-2017 Cycle; • IFRS 17 ‘Insurance Contracts’; • Amendments to IAS 19 ‘Employee Benefits’; • Amendments to IFRS 3 ‘Business Combinations’; • Amendments to the References to the Conceptual Framework; and • Amendments to IAS 1 and IAS 8: Definition of material. Effective dates remain subject to the EU endorsement process. The Group is currently assessing the impact of the above standards, but they are not expected to have a material impact. The Group has not adopted any other standard, amendment or interpretation that has been issued but is not yet effective.
Segmental analysis	This note sets out the financial performance for the year split into the different parts of the business (operating segments). The performance of these operating segments is monitored and managed on a day-to-day basis. Revenue and the results of the business are analysed by operating segment, based on the information the Board of Directors uses internally for the purposes of evaluating the performance of each operating segment and determining resource allocation between them. The Board is National Grid’s chief operating decision maker (as defined by IFRS 8 ‘Operating Segments’) and assesses the profitability of operations principally on the basis of operating profit before exceptional items and remeasurements (see note 5). As a matter of course, the Board also considers profitability by segment, excluding the effect of timing. However, the measure of profit disclosed in this note is operating profit before exceptional items and remeasurements as this is the measure that is most consistent with the IFRS results reported within these financial statements.
Revenue	Revenue arises in the course of the ordinary activities and principally comprises: • transmission services; • distribution services; and • generation services. Transmission services, distribution services and certain other services (excluding rental income but including metering) fall within the scope of IFRS 15 ‘Revenue from Contracts with Customers’, whereas generation services are accounted for under the leasing standard as rental income, presented within revenue. Revenue is measured based on the consideration specified in a contract with a customer and excludes amounts collected on behalf of third parties and value added tax. The Group recognises revenue when it transfers control over a product or service to a customer.
Operating costs	Below we have presented separately certain items included in our operating costs from continuing operations. These include a breakdown of payroll costs (including disclosure of amounts paid to key management personnel) and fees paid to our auditors.
Exceptional items and remeasurements	To monitor our financial performance, we use a profit measure that excludes certain income and expenses. We call that measure ‘business performance’ or ‘adjusted profit’. Business performance (which excludes exceptional items and remeasurements as defined below) is used by management to monitor financial performance as it is considered that it aids the comparability of our reported financial performance from year to year. We exclude items from business performance because, if included, these items could distort understanding of our performance for the year and the comparability between periods. This note analyses these items, which are included in our results for the year but are excluded from business performance.
Finance income and costs	This note details the interest income generated by our financial assets and interest expense incurred on our financial liabilities, primarily our financing portfolio (including our financing derivatives). It also includes the net interest on our pensions and other post-retirement assets. In reporting business performance, we adjust net financing costs to exclude any net gains or losses on financial instruments included in remeasurements (see note 5). In addition, where debt redemptions relate to exceptional transactions they are typically treated as exceptional.
Tax	Tax is payable in the territories where we operate, mainly the UK and the US. This note gives further details of the total tax charge and tax liabilities, including current and deferred tax. The current tax charge is the tax payable on this year’s taxable profits. Deferred tax is an accounting adjustment to provide for tax that is expected to arise in the future due to differences in the accounting and tax bases.
Earnings per share (EPS)	EPS is the amount of post-tax profit attributable to each ordinary share. Basic EPS is calculated on profit for the year attributable to equity shareholders divided by the weighted average number of shares in issue during the year. Diluted EPS shows what the impact would be if all outstanding share options were exercised and treated as ordinary shares at year end. The weighted average number of shares is increased by additional shares issued as scrip dividends and reduced by shares repurchased by the Company during the year. The earnings per share calculations are based on profit after tax attributable to equity shareholders of the Company which excludes non-controlling interests.
Goodwill	Goodwill represents the excess of what we paid to acquire businesses over the fair value of their net assets at the acquisition date. We assess whether goodwill is recoverable each year by performing an impairment review.
Other intangible assets	Other intangible assets include software which is written down (amortised) over the length of period we expect to receive a benefit from the asset.
Property, plant and equipment	The following note shows the physical assets controlled by us. The cost of these assets primarily represents the amount initially paid for them. This includes both their purchase price and the construction and other costs associated with getting them ready for operation. A depreciation expense is charged to the income statement to reflect annual wear and tear and the reduced value of the asset over time. Depreciation is calculated by estimating the number of years we expect the asset to be used (useful economic life) and charging the cost of the asset to the income statement equally over this period. We operate an energy networks business and therefore have a significant physical asset base. We continue to invest in our networks to maintain reliability, create new customer connections and ensure our networks are flexible and resilient. Our business plan envisages these additional investments will be funded through a mixture of cash generated from operations and the issue of new debt.
Other non-current assets	Other non-current assets include assets that do not fall into any other non-current asset category (such as goodwill or property, plant and equipment) where the benefit to be received from the asset is not due to be received until after 31 March 2020.
Financial and other investments	The Group holds a range of financial and other investments. These investments include short-term money funds, quoted investments in equities or bonds of other companies, long-term loans to our associates and joint ventures and other loans and receivables. Other loans and receivables typically includes bank deposits with a maturity of greater than three months, and cash balances that cannot be readily used in operations, principally collateral pledged against derivative holdings.
Investments in joint ventures and associates	Investments in joint ventures and associates represent businesses we do not control but over which we exercise joint control or significant influence. 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 Board-approved policies, derivatives are transacted generally to manage exposures to fluctuations in interest rates, foreign exchange rates and commodity prices. Our derivatives balances comprise two broad categories: • financing derivatives managing our exposure to interest rates and foreign exchange rates. Specifically we use these derivatives to manage our financing portfolio, holdings in foreign operations and contractual operational cash flows; and • commodity contract derivatives managing our US customers’ exposure to price and supply risks. Some forward contracts for the purchase of commodities meet the definition of derivatives and are included here. We also enter into derivative financial instruments linked to commodity prices, including index futures, options and swaps. These are used to manage market price volatility.
Inventories and current intangible assets	Inventories represent assets that we intend to use in order to generate revenue in the short term, either by selling the asset itself (for example, fuel stocks) or by using it to fulfil a service to a customer or to maintain our network (consumables).
Trade and other receivables	Trade and other receivables are amounts which are due from our customers for services we have provided.
Cash and cash equivalents	Cash and cash equivalents include cash balances, together with short-term investments with an original maturity of less than three months that are readily convertible to cash.
Borrowings and Borrowing facilities	We borrow money primarily in the form of bonds and bank loans. These are for a fixed term and may have fixed or floating interest rates or are linked to RPI. We use derivatives to manage risks associated with interest rates and foreign exchange. Our price controls and rate plans lead us to fund our networks within a certain ratio of debt to equity and, as a result, we have issued a significant amount of debt. As we continue to invest in our networks, the value of debt is expected to increase over time. To maintain a strong balance sheet and to allow us to access capital markets at commercially acceptable interest rates, we balance the amount of debt we issue with the value of our assets, and we take account of certain other metrics used by credit rating agencies. To support our liquidity requirements and provide backup to commercial paper and other borrowings, we agree loan facilities with financial institutions over and above the value of borrowings that may be required. These committed credit facilities have never been drawn, and our undrawn amounts are listed below.
Trade and other payables	Trade and other payables include amounts owed to suppliers, tax authorities and other parties which are due to be settled within 12 months. The total also includes deferred amounts, some of which represent monies received from customers but for which we have not yet delivered the associated service. These amounts are recognised as revenue when the service is provided.
Contract liabilities	Contract liabilities primarily relate to the advance consideration received from customers for construction contracts, mainly in relation to connections, for which revenue is recognised over the life of the asset.
Other non-current liabilities	Other non-current liabilities include deferred income which will not be recognised as income until after 31 March 2020. It also includes payables that are not due until after that date.
Pensions and other post-retirement benefits	All of our employees are eligible to participate in a pension plan. We have defined benefit (DB) and defined contribution (DC) pension plans. In the US we also provide healthcare and life insurance benefits to eligible employees, post-retirement. The fair value of associated scheme assets and present value of DB obligations are updated annually in accordance with IAS 19 (revised). We separately present our UK and US pension schemes to show geographical split. Below we provide a more detailed analysis of the amounts recorded in the primary financial statements and the actuarial assumptions used to value the DB obligations.
Provisions	We make provisions when an obligation exists resulting from a past event, and it is probable that cash will be paid to settle it, but the exact amount of cash required can only be estimated. The main estimates relate to environmental remediation and decommissioning costs for various sites we own or have owned and other provisions, including restructuring plans and lease contracts we have entered into that are now loss making. The evaluation of the likelihood of the contingent events has required best judgement by management regarding the probability of exposure to potential loss. Should circumstances change following unforeseeable developments, the likelihood could alter. In the current year we recognised a charge to restructuring provisions, reflecting the review and reorganisation of our core regulated businesses in both the UK and US.
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, predominately to actively manage scrip issuances and settle employee share option and reward plan liabilities.
Other equity reserves	Other equity reserves are different categories of equity as required by accounting standards and represent the impact of a number of our historical transactions.
Net debt	Net debt represents the amount of borrowings and overdrafts less cash, current financial investments and related financing derivatives.
Commitments and contingencies	Commitments are those amounts that we are contractually required to pay in the future as long as the other party meets its obligations. These commitments primarily relate to operating lease rentals, 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.
Sensitivities	In order to give a clearer picture of the impact on our results or financial position of potential changes in significant estimates and assumptions, the following sensitivities are presented. These sensitivities are based on assumptions and conditions prevailing at the year-end and should be used with caution. The effects provided are not necessarily indicative of the actual effects that would be experienced because our actual exposures are constantly changing.
Additional disclosures in respect of guaranteed securities	We have preferred shares that are listed on a US national securities exchange and are guaranteed by other companies in the Group. These guarantors commit to honour any liabilities should the company issuing the debt have any financial difficulties. In order to provide debt holders with information on the financial stability of the companies providing the guarantees, we are required to disclose individual financial information for these companies. We have chosen to include this information in the Group financial statements rather than submitting separate stand-alone financial statements.

Segmental analysis (Tables)

Segmental analysis (Tables)	3 Months Ended	12 Months Ended
Segmental analysis (Tables)	Jun. 30, 2018	Mar. 31, 2019
Operating Segments [Abstract]
Schedule of operating segments	The following table describes the main activities for each reportable operating segment: UK Electricity Transmission The high-voltage electricity transmission networks in England and Wales and Great Britain system operator. UK Gas Transmission The high-pressure gas transmission networks in Great Britain and system operator in Great Britain. US Regulated Gas distribution networks, electricity distribution networks and high-voltage electricity transmission networks in New York and New England and electricity generation facilities in New York.	2019 2018 2017 Total £m Sales between segments £m Sales to third parties £m Total Sales Sales Total Sales Sales Operating segments – continuing operations: UK Electricity Transmission 3,351 (20 ) 3,331 4,154 (28) 4,126 4,439 (29) 4,410 UK Gas Transmission 896 (12 ) 884 1,091 (9) 1,082 1,080 (99) 981 US Regulated 9,846 — 9,846 9,272 — 9,272 8,931 — 8,931 NGV and Other 1 876 (4 ) 872 776 (6) 770 713 — 713 Total revenue from continuing operations 14,969 (36 ) 14,933 15,293 (43) 15,250 15,163 (128) 15,035 Split by geographical areas – continuing operations: UK 5,045 5,938 6,064 US 9,888 9,312 8,971 14,933 15,250 15,035 1. Included within NGV and Other is £597 million ( 2018 : £593 million ; 2017 : £604 million ) of revenue relating to NGV. A reconciliation of the operating segments’ measure of profit to profit before tax from continuing operations is provided below. Further details of the exceptional items and remeasurements are provided in note 5. Before exceptional items After exceptional items 2019 2018¹ 2017 2019 2018¹ 2017 £m £m £m £m £m £m Operating segments – continuing operations: UK Electricity Transmission 1,015 1,041 1,372 778 1,041 1,361 UK Gas Transmission 303 487 511 267 487 507 US Regulated 1,724 1,698 1,713 1,425 1,734 1,278 NGV and Other 2,3 400 231 177 400 231 62 Total operating profit from continuing operations 3,442 3,457 3,773 2,870 3,493 3,208 Split by geographical area – continuing operations: UK 1,695 1,840 2,118 1,422 1,840 1,988 US 1,747 1,617 1,655 1,448 1,653 1,220 3,442 3,457 3,773 2,870 3,493 3,208 Below we reconcile total operating profit from continuing operations to profit before tax from continuing operations. Operating exceptional items and remeasurements of £237 million charge ( 2018 : £nil ; 2017 : £11 million charge) detailed in note 5 are attributable to UK Electricity Transmission; £36 million charge ( 2018 : £nil ; 2017 : £4 million charge) to UK Gas Transmission; £299 million charge ( 2018 : £36 million gain; 2017 : £435 million charge) to US Regulated; and £nil ( 2018 : £nil ; 2017 : £115 million charge) to NGV and Other. Reconciliation to profit before tax: Operating profit from continuing operations 3,442 3,457 3,773 2,870 3,493 3,208 Finance income 73 127 53 88 127 53 Finance costs (1,066 ) (1,128 ) (1,082 ) (1,157 ) (1,009 ) (1,140 ) Share of post-tax results of joint ventures and associates 40 44 63 40 49 63 Profit before tax from continuing operations 2,489 2,500 2,807 1,841 2,660 2,184 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 2. Included within NGV and Other is £263 million ( 2018 : £234 million ; 2017 : £239 million ) of operating profit (both before and after exceptional items and remeasurements) relating to NGV. Also included in this balance for the year ended 31 March 2019 is £181 million (2018: £84 million ; 2017: £55 million ) of operating profit in relation to the Property business. 3. NGV and Other includes gains of £95 million (2018: £ nil ; 2017: £ nil ) in relation to cash received in respect of two legal settlements. (c) Capital expenditure Net book value of property, plant and Capital expenditure 1 Depreciation, amortisation and impairment 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Operating segments: UK Electricity Transmission 13,288 13,028 12,515 925 999 1,027 (628 ) (475 ) (421 ) UK Gas Transmission 4,412 4,280 4,165 308 310 214 (181 ) (194 ) (186 ) US Regulated 24,542 20,953 21,638 2,650 2,424 2,247 (700 ) (635 ) (642 ) NGV and Other 2 2,755 2,491 2,430 438 341 247 (226 ) (226 ) (232 ) Total from continuing operations 44,997 40,752 40,748 4,321 4,074 3,735 (1,735 ) (1,530 ) (1,481 ) Split by geographical area – continuing operations: UK 19,343 18,772 18,102 1,584 1,527 1,357 (931 ) (804 ) (753 ) US 25,654 21,980 22,646 2,737 2,547 2,378 (804 ) (726 ) (728 ) 44,997 40,752 40,748 4,321 4,074 3,735 (1,735 ) (1,530 ) (1,481 ) Asset type: Property, plant and equipment 43,913 39,853 39,825 4,015 3,901 3,507 (1,560 ) (1,392 ) (1,348 ) Non-current intangible assets 1,084 899 923 306 173 228 (175 ) (138 ) (133 ) Total from continuing operations 44,997 40,752 40,748 4,321 4,074 3,735 (1,735 ) (1,530 ) (1,481 ) 1. Represents additions to property, plant and equipment and non-current intangibles but excludes additional investments in and loans to joint ventures and associates. 2. Included within NGV and Other are assets with a net book value of £1,635 million ( 2018 : £1,454 million ; 2017 : £1,432 million ), capital expenditure of £317 million ( 2018 : £186 million ; 2017 : £98 million ) and depreciation, amortisation and impairment of £114 million ( 2018 : £143 million ; 2017 : £143 million ) relating to NGV.

Revenue (Tables)

Revenue (Tables)	12 Months Ended
Revenue (Tables)	Mar. 31, 2019
Disclosure of revenue from contracts with customers [Abstract]
Disclosure of disaggregation of revenue from contracts with customers	In the following tables, revenue is disaggregated by primary geographical market and major service lines. The table reconciles disaggregated revenue with the Group’s reportable segments (see note 2). Revenue for the year ended 31 March 2019 UK Electricity Transmission UK Gas Transmission US Regulated NGV and Other Total Revenue under IFRS 15 Transmission 3,325 833 370 313 4,841 Distribution — — 8,941 — 8,941 Other — — — 284 284 Total IFRS 15 revenue 3,325 833 9,311 597 14,066 Other revenue Generation — — 367 — 367 Other 6 51 168 275 500 Total other revenue 6 51 535 275 867 Total revenue from continuing operations 3,331 884 9,846 872 14,933 Geographical split for the year ended 31 March 2019 UK Electricity Transmission £m UK Gas Transmission £m US Regulated £m NGV and Other £m Total £m Revenue under IFRS 15 UK 3,325 833 — 585 4,743 US — — 9,311 12 9,323 Total IFRS 15 revenue 3,325 833 9,311 597 14,066 Other revenue UK 6 51 — 245 302 US — — 535 30 565 Total other revenue 6 51 535 275 867 Total revenue from continuing operations 3,331 884 9,846 872 14,933

Operating costs (Tables)

Operating costs (Tables)	12 Months Ended
Operating costs (Tables)	Mar. 31, 2019
Analysis of income and expense [abstract]
Schedule of expenses by nature	Before exceptional items and remeasurements Exceptional items and remeasurements Total 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Depreciation, amortisation and impairment 1,588 1,530 1,481 147 — — 1,735 1,530 1,481 Payroll costs 1,703 1,648 1,578 149 — — 1,852 1,648 1,578 Purchases of electricity 1,504 1,299 1,143 (50 ) (14 ) (46 ) 1,454 1,285 1,097 Purchases of gas 1,644 1,539 1,241 (2 ) 4 (22 ) 1,642 1,543 1,219 Rates and property taxes 1,108 1,057 1,042 — — — 1,108 1,057 1,042 Balancing Services Incentive Scheme 1,196 1,012 1,120 — — — 1,196 1,012 1,120 Payments to other UK network owners 1 — 1,043 1,008 — — — — 1,043 1,008 Other 2,748 2,665 2,649 328 (26 ) 633 3,076 2,639 3,282 11,491 11,793 11,262 572 (36 ) 565 12,063 11,757 11,827 Operating costs include: Inventory consumed 415 367 296 Operating leases 2 46 51 43 Research and development expenditure 19 13 14 1. Under IFRS 15, for 2019 revenue and associated payments to other UK network owners are presented on a net basis. Refer to note 37. 2. Following a review during the year, the comparatives have been refined to provide consistency with the current year. (a) Payroll costs 2019 2018 2017 £m £m £m Wages and salaries 1 2,084 1,998 1,852 Social security costs 156 157 145 Defined contribution scheme costs 72 65 58 Defined benefit pension costs 232 156 151 Share-based payments 27 16 32 Severance costs (excluding pension costs) 76 7 5 2,647 2,399 2,243 Less: payroll costs capitalised (795 ) (751 ) (665 ) Total payroll costs 1,852 1,648 1,578 1. Included within wages and salaries are US other post-retirement benefit costs of £48 million ( 2018 : £46 million ; 2017 : £53 million ). For further information refer to note 25.
Schedule of additional information	(e) Auditors’ remuneration Auditors’ remuneration is presented below in accordance with the requirements of the Companies Act 2006 and the principal accountant fees and services disclosure requirements of Item 16C of Form 20-F: 2019 2018 2017 £m £m £m Audit fees payable to the Parent Company’s auditors and their associates in respect of: 1 Audit of the Parent Company’s individual and consolidated financial statements 2 1.6 2.7 1.5 The auditing of accounts of any associate of the Company 3 7.2 9.3 13.7 Other services supplied 4 5.2 3.9 4.6 14.0 15.9 19.8 Total other services 5 Tax fees: Tax compliance services — 0.3 0.4 Tax advisory services — — 0.1 All other fees: Other assurance services 6 1.1 0.7 4.6 Services relating to corporate finance transactions not covered above 7 — — 5.9 Other non-audit services not covered above 8 2.2 0.9 6.3 3.3 1.9 17.3 Total auditors’ remuneration 17.3 17.8 37.1 1. Deloitte LLP became the Group’s principal auditor for the year ended 31 March 2018. PricewaterhouseCoopers LLP (PwC) was the principal auditor for the year ended 31 March 2017 . 2. Audit fees in each year represent fees for the audit of the Company’s financial statements and regulatory reporting for the years ended 31 March 2019 , 2018 and 2017 . 3. The 2018 comparative has been updated following finalisation of the 2018 audit fee with the Audit Committee. 4. Other services supplied represent fees payable for services in relation to other statutory filings or engagements that are required to be carried out by the auditors. In particular, this includes fees for reports under section 404 of the US Public Company Accounting Reform and Investor Protection Act of 2002 (Sarbanes-Oxley), audit reports on regulatory returns and the review of interim financial statements for the six-month periods ended 30 September 2018, 2017 and 2016 respectively. 5. There were no audit related fees as described in Item 16C(b) of Form 20-F. 6. Principally amounts relating to assurance services provided in relation to comfort letters for debt issuances. In 2017, amounts represented assurance services undertaken by PwC in relation to the sale of UK Gas Distribution and data assurance work in respect of financial information included in US rate filings. 7. Vendor due diligence and other transaction services in relation to the sale of UK Gas Distribution. 8. Fees for other non-audit services – projects including services provided to the UK Property business, relating to evaluating possible options for the use of property assets. In 2017, services related principally to PwC assisting the Company with separation activities in relation to the sale of UK Gas Distribution. (b) Number of employees 31 March Monthly 31 March Monthly 31 March Monthly UK 5,962 6,227 6,517 6,431 6,265 6,291 US 16,614 16,669 16,506 16,274 15,867 15,752 Total number of employees 22,576 22,896 23,023 22,705 22,132 22,043 4. Operating costs continued (c) Key management compensation 2019 2018 2017 £m £m £m Short-term employee benefits 7 8 8 Post-employment benefits 1 1 1 Share-based payments 3 3 6 Total key management compensation 11 12 15

Exceptional items and remeasu_2

Exceptional items and remeasurements (Tables)	12 Months Ended
Exceptional items and remeasurements (Tables)	Mar. 31, 2019
Exceptional Items And Remeasurements [Abstract]
Schedule of exceptional items and remeasurements from continuing operations	Exceptional items and remeasurements from continuing operations 2019 2018¹ 2017 £m £m £m Included within operating profit Exceptional items: Cost efficiency and restructuring programmes (204 ) — — Massachusetts Gas labour dispute (283 ) — — Impairment of nuclear connection development costs (137 ) — — Final settlement of LIPA MSA Transition — 26 — Environmental charges — — (526 ) Gas holder demolition costs — — (107 ) (624 ) 26 (633 ) Remeasurements – commodity contract derivatives 52 10 68 (572 ) 36 (565 ) Included within finance income and costs Remeasurements: Net (losses)/gains on derivative financial instruments (40 ) 119 (58 ) Net gains on financial assets at fair value through profit and loss 15 — — Net losses on financial liabilities at fair value through profit and loss (51 ) — — (76 ) 119 (58 ) Included within share of post-tax results of joint ventures and associates Deferred tax arising on the reduction in US corporation tax rate — 5 — Total included within profit before tax (648 ) 160 (623 ) Included within tax Exceptional items – credits arising on items not included in profit before tax: Deferred tax arising on the reduction in the UK corporation tax rate — — 94 Deferred tax arising on the reduction in the US corporation tax rate — 1,510 — Tax on exceptional items 144 (9 ) 227 Tax on remeasurements 5 (28 ) (29 ) 149 1,473 292 Total exceptional items and remeasurements after tax (499 ) 1,633 (331 ) Analysis of total exceptional items and remeasurements after tax Exceptional items after tax (480 ) 1,532 (312 ) Remeasurements after tax (19 ) 101 (19 ) Total exceptional items and remeasurements after tax (499 ) 1,633 (331 ) 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10).

Finance income and costs (Table

Finance income and costs (Tables)	12 Months Ended
Finance income and costs (Tables)	Mar. 31, 2019
Analysis of income and expense [abstract]
Schedule of finance income and costs	2019 2018¹ 2017 Notes £m £m £m Finance income Interest income on financial instruments: Bank deposits and other financial assets 54 54 28 Dividends received on equities held at fair value through other comprehensive income 2 — — Gains on disposal of available-for-sale investments — 73 25 Other income 17 — — 73 127 53 Finance costs Net interest on pensions and other post-retirement benefit obligations 25 (22 ) (65 ) (107 ) Interest expense on financial liabilities held at amortised cost: Bank loans and overdrafts (72 ) (87 ) (59 ) Other borrowings (970 ) (1,030 ) (927 ) Interest expense on financial liabilities held at fair value through profit and loss (20 ) — — Derivatives (43 ) 12 (8 ) Unwinding of discount on provisions 26 (74 ) (75 ) (73 ) Other interest — (11 ) (17 ) Less: interest capitalised 2 135 128 109 (1,066 ) (1,128 ) (1,082 ) Remeasurements – Finance income Net gains on financial assets held at fair value through profit and loss 15 — — 15 — — Remeasurements – Finance costs Net losses on financial liabilities held at fair value through profit and loss (51 ) — — Net (losses)/gains on derivative financial instruments 3 : Derivatives designated as hedges for hedge accounting (37 ) 49 81 Derivatives not designated as hedges for hedge accounting (3 ) 70 (139 ) (91 ) 119 (58 ) Total remeasurements – Finance income and costs (76 ) 119 (58 ) Finance income 88 127 53 Finance costs (1,157 ) (1,009 ) (1,140 ) Net finance costs from continuing operations (1,069 ) (882 ) (1,087 ) 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 2. Interest on funding attributable to assets in the course of construction in the current year was capitalised at a rate of 3.9% ( 2018 : 4.1% ; 2017 : 3.4% ). In the UK, capitalised interest qualifies for a current year tax deduction with tax relief claimed of £19 million ( 2018 : £20 million ; 2017 : £18 million ). In the US, capitalised interest is added to the cost of plant and qualifies for tax depreciation allowances. 3. Includes a net foreign exchange gain on financing activities of £264 million ( 2018 : £314 million loss; 2017 : £264 million loss) offset by foreign exchange losses and gains on derivative financial instruments measured at fair value.

Tax (Tables)

Tax (Tables)	12 Months Ended
Tax (Tables)	Mar. 31, 2019
Income Taxes [Abstract]
Disclosure of major components of tax expense (income)	Tax charged/(credited) to the consolidated income statement – continuing operations 2019 2018¹ 2017 £m £m £m Tax before exceptional items and remeasurements 488 584 666 Exceptional tax on items not included in profit before tax (see note 5) — (1,510 ) (94 ) Tax on other exceptional items and remeasurements (149 ) 37 (198 ) Tax on total exceptional items and remeasurements (149 ) (1,473 ) (292 ) Total tax charge/(credit) from continuing operations 339 (889 ) 374 The tax charge for the year can be analysed as follows: 2019 2018¹ 2017 £m £m £m Current tax: UK corporation tax at 19% (2018: 19%; 2017: 20%) 132 200 225 UK corporation tax adjustment in respect of prior years (12 ) (18 ) (47 ) 120 182 178 Overseas corporation tax 8 15 — Overseas corporation tax adjustment in respect of prior years (40 ) (4 ) 1 (32 ) 11 1 Total current tax from continuing operations 88 193 179 Deferred tax: UK deferred tax 27 65 (9 ) UK deferred tax adjustment in respect of prior years 2 (2 ) (18 ) 29 63 (27 ) Overseas deferred tax 208 (1,155 ) 224 Overseas deferred tax adjustment in respect of prior years 14 10 (2 ) 222 (1,145 ) 222 Total deferred tax from continuing operations 251 (1,082 ) 195 Total tax charge/(credit) from continuing operations 339 (889 ) 374
Disclosure of effective applicable tax rate	Tax as a percentage of profit before tax 2019 2018¹ 2017 % % % Before exceptional items and remeasurements – continuing operations 19.6 23.4 23.7 After exceptional items and remeasurements – continuing operations 18.4 (33.4 ) 17.1 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10).
Disclosure of income tax relating to components of other comprehensive income and items credited (charged) directly to equity	Tax charged/(credited) to the consolidated statement of other comprehensive income and equity 2019 2018¹ 2017 £m £m £m Current tax: Available-for-sale investments — (11 ) 6 Investments at fair value through other comprehensive income — — — Cash flow hedges, Cost of hedging and Own credit reserve 3 — — Share-based payments — (3 ) (4 ) Deferred tax: Available-for-sale investments — (18 ) 8 Investments at fair value through other comprehensive income — — — Cash flow hedges, Cost of hedging and Own credit reserve (12 ) (4 ) 20 Remeasurements of gains of pension assets and post-retirement benefit obligations 2 12 530 277 Share-based payments — 1 1 3 495 308 Total tax recognised in the statements of comprehensive income from continuing operations 3 497 311 Total tax recognised in the statements of comprehensive income from discontinued operations — — 10 Total tax relating to share-based payments recognised directly in equity from continuing operations — (2 ) (3 ) Total tax relating to share-based payments recognised directly in equity from discontinued operations — — — 3 495 318 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 2. Remeasurements of gains on pension assets and post-retirement benefit obligations for the year ended 31 March 2018 includes a deferred tax charge of £281 million arising on the reduction in the US corporation tax rate.
Disclosure of reconciliation of accounting profit multiplied by applicable tax rates and average effective tax rate	The tax charge for the year after exceptional items and remeasurements, for the continuing business, is lower ( 2018 : lower tax charge; 2017 : lower tax charge) than the standard rate of corporation tax in the UK of 19% ( 2018 : 19% ; 2017 : 20% ): Before exceptional items and remeasurements After exceptional items and remeasurements Before exceptional items and remeasurements After exceptional items and remeasurements Before exceptional items and remeasurements After exceptional items and remeasurements 2019 2019 2018 2018 2017 2017 £m £m £m £m £m £m Profit before tax from continuing operations Before exceptional items and remeasurements 2,489 2,489 2,500 2,500 2,807 2,807 Exceptional items and remeasurements — (648 ) — 160 — (623 ) Profit before tax from continuing operations 2,489 1,841 2,500 2,660 2,807 2,184 Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2018: 19%; 2017: 20%) 473 350 475 506 561 437 Effect of: Adjustments in respect of prior years 1 (36 ) (36 ) (22 ) (14 ) (67 ) (67 ) Expenses not deductible for tax purposes 2 22 28 20 21 35 442 Non-taxable income 2,3 (36 ) (36 ) (16 ) (26 ) (24 ) (425 ) Adjustment in respect of foreign tax rates 78 56 153 157 180 104 Deferred tax impact of change in UK tax rate (3 ) (3 ) (7 ) (7 ) — (94 ) Deferred tax impact of change in US tax rate due to Tax Reform — — — (1,510 ) — — Other 4 (10 ) (20 ) (19 ) (16 ) (19 ) (23 ) Total tax charge/(credit) from continuing operations 488 339 584 (889 ) 666 374 % % % % % % Effective tax rate – continuing operations 19.6 18.4 23.4 (33.4 ) 23.7 17.1 1. Prior year adjustment is primarily due to agreement of prior period tax returns. 2. For the year ended 31 March 2017, the adjustments after exceptional items and remeasurements primarily represent the impact of the Group’s net investment hedging following significant US dollar currency fluctuations. 3. Includes gains on chargeable disposals which are offset by previously unrecognised capital losses. 4. Other primarily comprises an adjustment in respect of post-tax profits of joint ventures and associates included within profit before tax from continuing operations.
Disclosure of temporary difference, unused tax losses and unused tax credits	Deferred tax assets in respect of capital losses, trading losses and non-trade deficits have not been recognised as their future recovery is uncertain or not currently anticipated. The deferred tax assets not recognised are as follows: 2019 2018 £m £m Capital losses 1,470 510 Non-trade deficits 4 4 Trading losses 5 4 The following are the major deferred tax assets and liabilities recognised, and the movements thereon, during the current and prior reporting periods: Accelerated Share- Pensions Financial Other net differences 1 £m Total Deferred tax liabilities/(assets) At 1 April 2017 7,074 (12 ) (747 ) 9 (1,845 ) 4,479 Exchange adjustments and other² (559 ) — 69 1 221 (268 ) (Credited)/charged to income statement (1,641 ) 2 (55 ) 12 598 (1,084 ) Charged/(credited) to other comprehensive income and equity — 1 530 (1 ) (21 ) 509 At 31 March 2018 (as previously reported) 4,874 (9 ) (203 ) 21 (1,047 ) 3,636 Impact of transition to IFRS 9 and IFRS 15 19 — — (5 ) (93 ) (79 ) At 1 April 2018 (as restated) 4,893 (9 ) (203 ) 16 (1,140 ) 3,557 Exchange adjustments and other² 275 — (31 ) (3 ) (76 ) 165 (Credited)/charged to income statement 309 — 52 6 (124 ) 243 Charged/(credited) to other comprehensive income and equity — — 12 (12 ) — — At 31 March 2019 5,477 (9 ) (170 ) 7 (1,340 ) 3,965 1. The deferred tax asset of £1,340 million as at 31 March 2019 (2018: £1,047 million ) in respect of other net temporary differences primarily relates to US net operating losses of £423 million (2018: £390 million ) and environmental provisions of £409 million (2018: £378 million ). 2. Exchange adjustments and other comprises foreign exchange arising on translation of the US dollar deferred tax balances. In the prior period it also included reclassification of £43 million relating to offset of the opening deferred tax balance on US net operating losses against US current tax liabilities.

Earnings per share (EPS) (Table

Earnings per share (EPS) (Tables)	12 Months Ended
Earnings per share (EPS) (Tables)	Mar. 31, 2019
Earnings per share [abstract]
Schedule of earnings per share	(c) Reconciliation of basic to diluted average number of shares 2019 2018 2017 millions millions millions Weighted average number of ordinary shares – basic 3,386 3,461 3,763 Effect of dilutive potential ordinary shares – employee share plans 15 15 17 Weighted average number of ordinary shares – diluted 3,401 3,476 3,780 (a) Basic EPS Earnings EPS Earnings EPS Earnings EPS 2019 2019 2018¹ 2018¹ 2017 2017 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,998 59.0 1,915 55.3 2,141 56.9 Exceptional items and remeasurements after tax from continuing operations (499 ) (14.7 ) 1,633 47.2 (331 ) (8.8 ) Earnings from continuing operations 1,499 44.3 3,548 102.5 1,810 48.1 Adjusted earnings from discontinued operations 57 1.7 145 4.2 607 16.1 Exceptional items and remeasurements after tax from discontinued operations (45 ) (1.4 ) (143 ) (4.1 ) 5,378 142.9 Earnings from discontinued operations 12 0.3 2 0.1 5,985 159.0 Total adjusted earnings 2,055 60.7 2,060 59.5 2,748 73.0 Total exceptional items and remeasurements after tax (including discontinued operations) (544 ) (16.1 ) 1,490 43.1 5,047 134.1 Total earnings 1,511 44.6 3,550 102.6 7,795 207.1 2019 2018 2017 millions millions millions Weighted average number of ordinary shares – basic 3,386 3,461 3,763 (b) Diluted EPS Earnings EPS Earnings EPS Earnings EPS 2019 2019 2018¹ 2018¹ 2017 2017 £m pence £m pence £m pence Adjusted earnings from continuing operations 1,998 58.8 1,915 55.1 2,141 56.7 Exceptional items and remeasurements after tax from continuing operations (499 ) (14.7 ) 1,633 47.0 (331 ) (8.8 ) Earnings from continuing operations 1,499 44.1 3,548 102.1 1,810 47.9 Adjusted earnings from discontinued operations 57 1.7 145 4.2 607 16.0 Exceptional items and remeasurements after tax from discontinued operations (45 ) (1.4 ) (143 ) (4.2 ) 5,378 142.3 Earnings from discontinued operations 12 0.3 2 0.0 5,985 158.3 Total adjusted earnings 2,055 60.5 2,060 59.3 2,748 72.7 Total exceptional items and remeasurements after tax (including discontinued operations) (544 ) (16.1 ) 1,490 42.8 5,047 133.5 Total earnings 1,511 44.4 3,550 102.1 7,795 206.2 2019 2018 2017 millions millions millions Weighted average number of ordinary shares – diluted 3,401 3,476 3,780 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10).

Dividends (Tables)

Dividends (Tables)	12 Months Ended
Dividends (Tables)	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Schedule of Dividends to Shareholders	2019 2018 2017 Pence per share Cash dividend paid £m Scrip dividend £m Pence per share Cash dividend paid £m Scrip dividend £m Pence per share Cash dividend paid £m Scrip dividend £m Interim dividend in respect of the current year 16.08 450 94 15.49 346 176 15.17 540 32 Special dividend — — — 84.375 3,171 — — — — Final dividend in respect of the prior year 30.44 710 319 29.10 970 33 28.34 923 151 46.52 1,160 413 128.965 4,487 209 43.51 1,463 183

Discontinued operations and a_2

Discontinued operations and assets held for sale (Tables)	12 Months Ended
Discontinued operations and assets held for sale (Tables)	Mar. 31, 2019
Non-current Assets Held For Sale And Discontinued Operations [Abstract]
Schedule of discontinued operations	The summary statement of comprehensive income for discontinued operations is as follows: 2019 2018¹ 2017 Notes £m £m £m Profit after tax from discontinued operations 12 2 5,984 Other comprehensive income/(loss) Items that will never be reclassified to profit or loss: Remeasurement losses of pension assets and post-retirement benefit obligations 25 — — (75 ) Share of other comprehensive income of associate, net of tax 36 142 — Tax on items that will never be reclassified to profit or loss — — 13 Total items from discontinued operations that will never be reclassified to profit or loss 36 142 (62 ) Items that may be reclassified subsequently to profit or loss: Net losses in respect of cash flow hedges — — (106 ) Transferred to profit or loss in respect of cash flow hedges — — 233 Share of other comprehensive income of associate, net of tax — 5 — Tax on items that may be reclassified subsequently to profit or loss — — (23 ) Total items from discontinued operations that may be reclassified subsequently to profit or loss — 5 104 Other comprehensive income for the year, net of tax from discontinued operations 36 147 42 Total comprehensive income for the year from discontinued operations 48 149 6,026 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C). The summary income statement for discontinued operations is as follows: 2019 2018¹ 2017 £m £m £m Revenue — — 1,887 Operating costs 2 (1 ) (41 ) (993 ) Operating (loss)/profit (1 ) (41 ) 894 Net finance income/(costs) 23 137 (152 ) Share of post-tax results of joint ventures and associates 3 (5 ) (89 ) — Profit before tax from discontinued operations 17 7 742 Tax from discontinued operations (5 ) (5 ) (79 ) Profit after tax from discontinued operations 12 2 663 Gain on disposal of UK Gas Distribution after tax 4 — — 5,321 Total profit after tax from discontinued operations 5 12 2 5,984 1. Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C). 2. Operating costs of £41 million for the year ended 31 March 2018 related to amounts in respect of the disposal of the UK Gas Distribution business, primarily relating to the completion accounts settlement in November 2017. The remainder of the balances relate to the disposal group and have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period. 3. For the year ended 31 March 2019, this is the net of £43 million impairment charge against investment in Quadgas (see note 16) and £38 million share of Quadgas post-tax profits recognised prior to classification as held for sale. 4. The total gain on the disposal after tax of £5,321 million was comprised of total consideration of £7,494 million before transaction costs of £1,837 million and a tax credit of £312 million compared to net assets on disposal of £648 million . 5. Of the total profit after tax from discontinued operations for the year ended 31 March 2019, the £43 million impairment charge against the investment in Quadgas, net operating costs of £1 million and the tax thereon are classified as exceptional items.

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
Goodwill (Tables)	Mar. 31, 2019
Intangible Assets [Abstract]
Schedule of changes in intangible assets and goodwill	Impairments are recognised in the income statement and are disclosed separately. Total £m Net book value at 1 April 2017 6,096 Exchange adjustments (652 ) Net book value at 31 March 2018 5,444 Exchange adjustments 425 Net book value at 31 March 2019 5,869

Other intangible assets (Tables

Other intangible assets (Tables)	12 Months Ended
Other intangible assets (Tables)	Mar. 31, 2019
Intangible Assets [Abstract]
Schedule of intangible assets	Other intangible assets are amortised on a straight-line basis over their estimated useful economic lives. Amortisation periods for categories of intangible assets are: Years Software 3 to 10 Software £m Cost at 1 April 2017 1,732 Exchange adjustments (98 ) Additions 173 Disposals (18 ) Reclassifications 1 8 Cost at 31 March 2018 1,797 Exchange adjustments 70 Additions 306 Disposals (15 ) Reclassifications 1 10 Cost at 31 March 2019 2,168 Accumulated amortisation at 1 April 2017 (809 ) Exchange adjustments 43 Amortisation charge for the year (138 ) Accumulated amortisation of disposals 6 Accumulated amortisation at 31 March 2018 (898 ) Exchange adjustments (26 ) Amortisation charge for the year (175 ) Accumulated amortisation of disposals 15 Accumulated amortisation at 31 March 2019 (1,084 ) Net book value at 31 March 2019² 1,084 Net book value at 31 March 2018 899 1. Reclassifications includes amounts transferred (to)/from property, plant and equipment (see note 13). 2. Included in software is £116 million (2018: £160 million ) relating to the US Enterprise Resource Planning system, which still has a remaining amortisation period of four years.

Property, plant and equipment (

Property, plant and equipment (Tables)	12 Months Ended
Property, plant and equipment (Tables)	Mar. 31, 2019
Property, plant and equipment [abstract]
Schedule of property, plant and equipment	Land and buildings £m Plant and machinery £m Assets in the course of construction 1 £m Motor vehicles and office equipment £m Total £m Cost at 1 April 2017 2,979 49,231 3,951 834 56,995 Exchange adjustments (169 ) (2,862 ) (89 ) (67 ) (3,187 ) Additions 38 430 3,358 75 3,901 Disposals 2 (16 ) (216 ) (21 ) (34 ) (287 ) Reclassifications 3 98 2,791 (2,926 ) 49 12 Cost at 31 March 2018 2,930 49,374 4,273 857 57,434 Exchange adjustments 114 2,001 70 47 2,232 Additions 34 391 3,533 57 4,015 Disposals 2 (35 ) (357 ) (159 ) (44 ) (595 ) Reclassifications 3 295 2,974 (3,292 ) 13 (10 ) Cost at 31 March 2019 3,338 54,383 4,425 930 63,076 Accumulated depreciation at 1 April 2017 (684 ) (15,996 ) — (490 ) (17,170 ) Exchange adjustments 28 695 — 36 759 Depreciation charge for the year (28 ) (1,276 ) — (88 ) (1,392 ) Disposals 10 199 — 33 242 Reclassifications 3 — (20 ) — — (20 ) Accumulated depreciation at 31 March 2018 (674 ) (16,398 ) — (509 ) (17,581 ) Exchange adjustments (19 ) (501 ) — (25 ) (545 ) Depreciation charge for the year (93 ) (1,229 ) (150 ) (101 ) (1,573 ) Disposals 7 335 150 44 536 Reclassifications 3 1 (1 ) — — — Accumulated depreciation at 31 March 2019 (778 ) (17,794 ) — (591 ) (19,163 ) Net book value at 31 March 2019 2,560 36,589 4,425 339 43,913 Net book value at 31 March 2018 2,256 32,976 4,273 348 39,853 1. Included within disposals are UK nuclear connections development costs of £150 million (before £13 million of termination income) which were written off (2018: £nil ). See note 5 for further details. 2. In 2018, this included the reversal of assets with cost of £51 million and accumulated depreciation of £51 million disposed of in previous years that remain in use in the Group. It also included £334 million of adjustments from accumulated depreciation to cost for historical disposals relating to assets acquired as part of the KeySpan acquisition in 2008 which were disposed of in subsequent periods. Both of these adjustments have a nil net book value impact. 3. Represents amounts transferred between categories, (to)/from other intangible assets (see note 12), reclassifications from inventories and reclassifications between cost and accumulated depreciation. 2019 2018 £m £m Information in relation to property, plant and equipment Capitalised interest included within cost 1,995 1,861 Net book value of assets held under finance leases (all relating to motor vehicles and office equipment) 241 253 Additions to assets held under finance leases (all relating to motor vehicles and office equipment) 38 58 Contributions to cost of property, plant and equipment included within: Trade and other payables 87 85 Non-current liabilities 372 844 Contract liabilities – current 61 — Contract liabilities – non-current 933 — Unless otherwise determined by operational requirements, the depreciation periods for the principal categories of property, plant and equipment are, in general, as shown in the table below: Years Freehold and leasehold buildings up to 103 Plant and machinery: Electricity transmission plant and wires 10 to 100 Electricity distribution plant 29 to 85 Electricity generation plant 15 to 93 Interconnector plant and other 5 to 65 Gas plant – mains, services and regulating equipment 10 to 95 Gas plant – storage 5 to 65 Gas plant – meters 7 to 62 Motor vehicles and office equipment up to 30

Other non-current assets (Table

Other non-current assets (Tables)	12 Months Ended
Other non-current assets (Tables)	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Schedule of other non current assets	2019 2018 £m £m Other receivables 28 36 Non-current tax assets 56 51 Prepayments and accrued income 1 180 28 264 115 1. Includes accrued income in relation to property sales to the St William joint venture.

Financial and other investmen_2

Financial and other investments (Tables)	12 Months Ended
Financial and other investments (Tables)	Mar. 31, 2019
Disclosure of financial assets [abstract]
Schedule of financial assets	2019 2018 £m £m Non-current Debt investments at fair value through other comprehensive income 343 — Equity investments at fair value through other comprehensive income 93 — Investments at fair value through profit and loss 62 — Available-for-sale investments — 417 Loans to joint ventures and associates 1 169 482 667 899 Current Investments at fair value through profit and loss 1,311 — Available-for-sale investments — 2,304 Other loans and receivables 670 390 1,981 2,694 2,648 3,593 Financial and other investments include the following: Investments in short-term money funds 2 969 1,999 Insurance company fund investments 3 342 301 Equities 4 93 84 Bonds 4 122 145 Cash surrender value of life insurance policies 4 221 198 Loans to joint ventures and associates 169 482 Corporate venture capital and other 62 — Restricted balances: Collateral 5 637 335 Other 33 49 2,648 3,593 1. Comprises a loan to a joint venture. In 2018, £352 million related to a shareholder loan to Quadgas, which has been re-classified to assets held for sale during the period. 2. Includes £6 million ( 2018 : £69 million ) held as insurance company fund investments and £22 million (2018: £ nil ) US non-qualified plan investments, and therefore restricted. 3. Includes restricted amounts of £342 million (2018: £301 million ) held as insurance company fund investments. 4. Primarily includes restricted amounts of £436 million (2018: £411 million ) relating to US non-qualified plan investments. 5. Refers to collateral placed with counterparties with whom we have entered into a credit support annex to the ISDA (International Swaps and Derivatives Association) Master Agreement.

Investments in joint ventures_2

Investments in joint ventures and associates (Tables)	12 Months Ended
Investments in joint ventures and associates (Tables)	Mar. 31, 2019
Interests In Other Entities [Abstract]
Disclosure of joint ventures	Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Limited Millennium Pipeline Company LLC 2019 2018 2019 2018 £m £m £m £m Statement of financial position Non-current assets 370 390 937 709 Cash and cash equivalents 59 50 35 15 All other current assets 2 4 22 28 Non-current liabilities (11 ) (10 ) (326 ) (331 ) Current liabilities (28 ) (28 ) (84 ) (64 ) Equity 392 406 584 357 Carrying amount of the Group’s investment 196 203 153 94 BritNed Development Limited Millennium Pipeline Company LLC 2019 2018¹ 2019 2018 £m £m £m £m Income statement Revenue 87 121 166 151 Depreciation and amortisation (13 ) (13 ) (34 ) (31 ) Other costs (10 ) (16 ) (35 ) (41 ) Operating profit 64 92 97 79 Income tax expense (10 ) (20 ) — — Profit for the year 54 72 97 79 Group’s share of profit 27 36 25 21 1. Comparatives for revenue and other costs have been re-presented on a net basis in line with current year classification. 2019 2018 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 1,807 361 2,168 1,776 307 2,083 Exchange adjustments 17 (6 ) 11 (19 ) 7 (12 ) Additions 58 85 143 65 64 129 Capitalisation of shareholder loan to Quadgas — — — 69 — 69 Impairment charge against investment in Quadgas (43 ) — (43 ) (213 ) — (213 ) Transfer of interest in Quadgas to assets held for sale (1,625 ) — (1,625 ) — — — Share of post-tax results for the year 67 11 78 147 26 173 Share of other comprehensive income of associates, net of tax 37 — 37 147 — 147 Dividends received (38 ) (30 ) (68 ) (170 ) (43 ) (213 ) Other movements 1 11 (104 ) (93 ) 5 — 5 Share of net assets at 31 March 291 317 608 1,807 361 2,168 1. Other movements on joint ventures relate to reducing the carrying value of the investment in St William Homes LLP to reflect deferred income we expect to recognise over the next 10 years .
Disclosure of associates	A joint venture is an arrangement established to engage in economic activity, which the Group jointly controls with other parties and has rights to the net assets of the arrangement. An associate is an entity which is neither a subsidiary nor a joint venture, but over which the Group has significant influence. 2019 2018 Associates £m Joint ventures £m Total £m Associates £m Joint ventures £m Total £m Share of net assets at 1 April 1,807 361 2,168 1,776 307 2,083 Exchange adjustments 17 (6 ) 11 (19 ) 7 (12 ) Additions 58 85 143 65 64 129 Capitalisation of shareholder loan to Quadgas — — — 69 — 69 Impairment charge against investment in Quadgas (43 ) — (43 ) (213 ) — (213 ) Transfer of interest in Quadgas to assets held for sale (1,625 ) — (1,625 ) — — — Share of post-tax results for the year 67 11 78 147 26 173 Share of other comprehensive income of associates, net of tax 37 — 37 147 — 147 Dividends received (38 ) (30 ) (68 ) (170 ) (43 ) (213 ) Other movements 1 11 (104 ) (93 ) 5 — 5 Share of net assets at 31 March 291 317 608 1,807 361 2,168 1. Other movements on joint ventures relate to reducing the carrying value of the investment in St William Homes LLP to reflect deferred income we expect to recognise over the next 10 years . Summarised financial information as at 31 March, together with the carrying amount of the investments, is as follows: BritNed Development Limited Millennium Pipeline Company LLC 2019 2018 2019 2018 £m £m £m £m Statement of financial position Non-current assets 370 390 937 709 Cash and cash equivalents 59 50 35 15 All other current assets 2 4 22 28 Non-current liabilities (11 ) (10 ) (326 ) (331 ) Current liabilities (28 ) (28 ) (84 ) (64 ) Equity 392 406 584 357 Carrying amount of the Group’s investment 196 203 153 94 BritNed Development Limited Millennium Pipeline Company LLC 2019 2018¹ 2019 2018 £m £m £m £m Income statement Revenue 87 121 166 151 Depreciation and amortisation (13 ) (13 ) (34 ) (31 ) Other costs (10 ) (16 ) (35 ) (41 ) Operating profit 64 92 97 79 Income tax expense (10 ) (20 ) — — Profit for the year 54 72 97 79 Group’s share of profit 27 36 25 21 1. Comparatives for revenue and other costs have been re-presented on a net basis in line with current year classification.

Derivative financial instrume_2

Derivative financial instruments (Tables)	12 Months Ended
Derivative financial instruments (Tables)	Mar. 31, 2019
Financial Instruments [Abstract]
Disclosure of detailed information about derivative financial instruments	The notional contract 1 amounts of financing derivatives by type are as follows: 2019 2018 £m £m Interest rate swaps (6,299 ) (8,390 ) Cross-currency interest rate swaps (6,700 ) (6,925 ) Foreign exchange forward contracts (2,937 ) (5,793 ) Inflation-linked swaps (500 ) (1,191 ) Equity options (800 ) (800 ) (17,236 ) (23,099 ) 1. The notional contract amounts of derivatives indicate the gross nominal value of transactions outstanding at the reporting date. The fair values of financing derivatives by type are as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Interest rate swaps 539 (384 ) 155 678 (457 ) 221 Cross-currency interest rate swaps 470 (443 ) 27 687 (207 ) 480 Foreign exchange forward contracts 1 41 (41 ) — 174 (2 ) 172 Inflation-linked swaps — (214 ) (214 ) 5 (278 ) (273 ) Equity options 2 (2 ) — 1 (1 ) — 1,052 (1,084 ) (32 ) 1,545 (945 ) 600 1. Included within the foreign exchange forward contracts balance is £32 million ( 2018 : £67 million ) of derivatives in relation to hedging of capital expenditure. The notional quantities of commodity contract derivatives by type are as follows: 2019 2018 Forward purchases of gas 1 52m Dth 54m Dth Electricity swaps 12,848 GWh 12,839 GWh Electricity options 10,444 GWh 13,897 GWh Electricity capacity - 0.6 GWm Gas swaps 87m Dth 100m Dth Gas options 34m Dth 7m Dth 1. Forward gas purchases have terms up to two years . The contractual obligations under these contracts are £108 million ( 2018 : £96 million ). The fair values of derivatives by category are as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Financing derivatives 1,052 (1,084 ) (32 ) 1,545 (945 ) 600 Commodity contract derivatives 101 (99 ) 2 69 (116 ) (47 ) Further Acquisition Agreement derivative 1 — — — 110 — 110 1,153 (1,183 ) (30 ) 1,724 (1,061 ) 663 1. The Further Acquisition Agreement derivative is a put/call option over a 14% interest in Quadgas that has been reclassified as held for sale during the period (see note 10). The fair values of commodity contract derivatives by type are as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets Liabilities £m Total £m Commodity purchase contracts accounted for as derivative contracts Forward purchases of gas 66 (78 ) (12 ) 60 (64 ) (4 ) Derivative financial instruments linked to commodity prices Electricity capacity — — — 1 — 1 Electricity swaps 29 (19 ) 10 7 (46 ) (39 ) Electricity options — — — — (1 ) (1 ) Gas swaps 5 (1 ) 4 1 (4 ) (3 ) Gas options 1 (1 ) — — (1 ) (1 ) 101 (99 ) 2 69 (116 ) (47 )
Disclosure of maturity analysis for derivative financial liabilities	The maturity profile of commodity contract derivatives is as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total £m Current Less than one year 52 (68 ) (16 ) 30 (76) (46) 52 (68 ) (16 ) 30 (76) (46) Non-current In 1 to 2 years 14 (9 ) 5 6 (17) (11) In 2 to 3 years 9 (8 ) 1 6 (11) (5) In 3 to 4 years 6 (4 ) 2 6 (3) 3 In 4 to 5 years 6 (4 ) 2 5 (2) 3 More than 5 years 14 (6 ) 8 16 (7) 9 49 (31 ) 18 39 (40) (1) 101 (99 ) 2 69 (116) (47) The maturity profile of financing derivatives is as follows: 2019 2018 Assets £m Liabilities £m Total £m Assets £m Liabilities £m Total Current Less than 1 year 56 (282 ) (226 ) 375 (325 ) 50 56 (282 ) (226 ) 375 (325 ) 50 Non-current In 1 to 2 years 19 (193 ) (174 ) 83 (88 ) (5 ) In 2 to 3 years 416 (1 ) 415 25 (27 ) (2 ) In 3 to 4 years 11 — 11 418 (5 ) 413 In 4 to 5 years 20 (14 ) 6 12 — 12 More than 5 years 530 (594 ) (64 ) 632 (500 ) 132 996 (802 ) 194 1,170 (620 ) 550 1,052 (1,084 ) (32 ) 1,545 (945 ) 600

Inventories and other current_2

Inventories and other current intangibles (Tables)	12 Months Ended
Inventories and other current intangibles (Tables)	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Schedule of inventories	2019 2018 £m £m Fuel stocks 99 78 Raw materials and consumables 184 190 Current intangible assets – emission allowances 87 73 370 341

Trade and other receivables (Ta

Trade and other receivables (Tables)	12 Months Ended
Trade and other receivables (Tables)	Mar. 31, 2019
Trade and other receivables [abstract]
Schedule of trade and other receivables	2019 2018 £m £m Trade receivables 1,899 1,674 Accrued income 883 817 Prepayments 237 229 Other receivables 134 78 3,153 2,798
Schedule of reconciliation of changes in allowance account for credit losses	2019 2018 £m £m At 1 April 309 424 Exchange adjustments 24 (42 ) Charge for the year, net of recoveries 181 36 Uncollectible amounts written off (120 ) (109 ) At 31 March 394 309
Schedule of average expected loss rates and balances	The average expected loss rates and balances for the retail customer receivables in our US operations are set out below: 2019 2019 2018 2018 % £m % £m 0 – 30 days 3 736 3 741 30 – 60 days 12 194 8 192 60 – 90 days 20 89 19 97 3 – 6 months 30 109 29 97 6 – 12 months 39 99 39 88 Over 12 months 68 238 69 218
Schedule of financial assets that are either past due or impaired	Trade receivables past due 2019 2018 £m £m Up to 3 months past due 295 271 3 to 6 months past due 108 73 Over 6 months past due 160 131 563 475

Cash and cash equivalents (Tabl

Cash and cash equivalents (Tables)	12 Months Ended
Cash and cash equivalents (Tables)	Mar. 31, 2019
Cash and cash equivalents [abstract]
Schedule of cash and cash equivalents	2019 2018 £m £m Cash at bank 177 54 Short-term deposits 75 275 Cash and cash equivalents 252 329

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
Borrowings (Tables)	Mar. 31, 2019
Disclosure of detailed information about borrowings [abstract]
Schedule of borrowings	Total borrowings are repayable as follows: 2019 2018 £m £m Less than 1 year 4,472 4,447 In 1 to 2 years 2,393 1,694 In 2 to 3 years 1,990 2,347 In 3 to 4 years 1,553 1,873 In 4 to 5 years 714 1,469 More than 5 years: By instalments 959 1,010 Other than by instalments 16,649 13,785 28,730 26,625 2019 2018 £m £m Current Bank loans 641 2,020 Bonds 1,973 2,156 Commercial paper 1,792 206 Finance leases 65 64 Other loans 1 1 4,472 4,447 Non-current Bank loans 2,599 2,384 Bonds 1 21,278 19,418 Finance leases 205 207 Other loans 176 169 24,258 22,178 Total borrowings 28,730 26,625 1. In 2019 this includes a liability held at fair value through profit and loss of £667 million . Maturity analysis of Parent Company borrowings 2019 2018 £m £m Total borrowings are repayable as follows: Less than 1 year 1,275 781 In 1 to 2 years — 438 In 2 to 3 years 346 — In 3 to 4 years — 335 In 4 to 5 years — — More than 5 years — — 1,621 1,554
Schedule of finance lease obligations	2019 2018 £m £m Gross finance lease liabilities are repayable as follows: Less than 1 year 65 64 1 to 5 years 183 177 More than 5 years 62 72 310 313 Less: finance charges allocated to future periods (40 ) (42 ) 270 271 The present value of finance lease liabilities is as follows: Less than 1 year 65 64 1 to 5 years 156 144 More than 5 years 49 63 270 271

Trade and other payables (Table

Trade and other payables (Tables)	12 Months Ended
Trade and other payables (Tables)	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Schedule of trade and other payables	2019 2018 £m £m Trade payables 2,404 1,977 Deferred payables 217 355 Customer contributions 1 87 85 Social security and other taxes 159 173 Other payables 902 863 3,769 3,453 1. From government-related entities.

Contract liabilities (Tables)

Contract liabilities (Tables)	12 Months Ended
Contract liabilities (Tables)	Mar. 31, 2019
Contract liabilities [abstract]
Summary of contract liabilities	2019 2018 £m £m Current 61 — Non-current 933 — 994 —
Explanation of significant changes in contract assets and contract liabilities	Significant changes in the contract liabilities balances during the period are as follows: 2019 £m As at 1 April 2018 (see note 37) 866 Exchange adjustments 29 Revenue recognised that was included in the contract liability balance at the beginning of the period (51 ) Increases due to cash received, excluding amounts recognised as revenue during the period 155 Changes due to amounts recognised as revenue (5 ) At 31 March 2019 994

Other non-current liabilities (

Other non-current liabilities (Tables)	12 Months Ended
Other non-current liabilities (Tables)	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Schedule of other non current liabilities	2019 2018 £m £m Deferred income 1 96 114 Customer contributions 2 372 844 Other payables 340 359 808 1,317 1. Principally the deferral of profits relating to the sale of property, plant and equipment. 2. From government-related entities.

Pensions and other post retir_2

Pensions and other post retirement benefits (Tables)	12 Months Ended
Pensions and other post retirement benefits (Tables)	Mar. 31, 2019
Employee Benefits [Abstract]
Schedule of results of most recent actuarial valuations	The results of the most recent actuarial valuations are shown below. See page 147 for the assumptions used for IAS 19 (revised) purposes. Actuarial valuations for all the schemes are currently being performed as at 31 March 2019. Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Latest full actuarial valuation 31 March 2017 31 March 2017 31 March 2016 Actuary Willis Towers Watson Willis Towers Watson Aon Hewitt Market value of scheme assets at latest valuation £6,716m £5,849m £2,553m Actuarial value of benefits due to members £6,627m £6,057m £3,053m Market value as percentage of benefits 101% 97% 84% Funding surplus/(deficit) £89m (£208m) (£500m) Funding surplus/(deficit) net of tax £74m (£173m) (£415m)
Schedule of security agreements	Section A of NGUKPS Section B of NGUKPS NGEG of ESPS Value of security arrangements at 31 March 2019 £315m £179m £250m Principal supporting employers National Grid plc and National Grid UK Limited National Grid Gas plc (NGG) National Grid Electricity Transmission plc (NGET) Additional amounts payable 1 £72m A maximum of £280m A maximum of £500m 1. These amounts are payable if certain trigger events occur which have been individually agreed between the schemes and their relevant supporting employers.
Disclosure of actuarial assumptions	2019 2018 2017 UK years US years UK years US years UK years US years Assumed life expectations for a retiree age 65 Males 22.0 22.1 22.3 22.0 22.9 21.9 Females 23.6 24.2 23.9 24.2 24.7 24.1 In 20 years: Males 23.3 23.7 23.7 23.6 25.1 23.6 Females 25.2 25.9 25.5 25.8 27.1 25.7 The Company has applied the following financial assumptions in assessing DB liabilities. UK pensions 2019 2018 2017 % % % Discount rate – past service 2.40 2.60 2.40 Discount rate – future service 2.45 2.65 2.65 Salary increases 3.50 3.40 3.50 Rate of increase in RPI – past service 3.25 3.15 3.20 Rate of increase in RPI – future service 3.20 3.10 3.15 US pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 % % % % % % Discount rate 3.95 4.00 4.25 3.95 4.00 4.25 Salary increases 3.50 3.50 3.50 3.50 3.50 3.50 Initial healthcare cost trend rate n/a n/a n/a 7.25 7.50 7.00 Ultimate healthcare cost trend rate n/a n/a n/a 4.50 4.50 4.50
Amounts recognised in the statement of financial position	Amounts recognised in the consolidated statement of financial position 2019 2018 2017 £m £m £m Present value of funded obligations (24,609 ) (23,747 ) (25,890 ) Fair value of plan assets 24,793 23,858 24,375 184 111 (1,515 ) Present value of unfunded obligations (330 ) (307 ) (340 ) Other post-employment liabilities (72 ) (67 ) (78 ) Net defined benefit liability (218 ) (263 ) (1,933 ) Represented by: Liabilities (1,785 ) (1,672 ) (2,536 ) Assets 1,567 1,409 603 (218 ) (263 ) (1,933 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Present value of funded obligations (14,200 ) (14,152 ) (15,565 ) (6,901 ) (6,349 ) (6,790 ) (3,508 ) (3,246 ) (3,535 ) Fair value of plan assets 15,507 15,330 15,489 6,646 6,030 6,322 2,640 2,498 2,564 1,307 1,178 (76 ) (255 ) (319 ) (468 ) (868 ) (748 ) (971 ) Present value of unfunded obligations (76 ) (74 ) (80 ) (254 ) (233 ) (260 ) — — — Other post-employment liabilities — — — — — — (72 ) (67 ) (78 ) Net defined benefit asset/(liability) 1,231 1,104 (156 ) (509 ) (552 ) (728 ) (940 ) (815 ) (1,049 ) Represented by: Liabilities (76 ) (74 ) (536 ) (769 ) (783 ) (951 ) (940 ) (815 ) (1,049 ) Assets 1,307 1,178 380 260 231 223 — — — 1,231 1,104 (156 ) (509 ) (552 ) (728 ) (940 ) (815 ) (1,049 )
Amounts recognised in the income statement and statement of other comprehensive income	Amounts recognised in the income statement and statement of other comprehensive income 2019 2018 2017 £m £m £m Included within operating costs Administration costs 14 16 16 Included within payroll costs Defined benefit scheme costs: Current service cost 193 193 232 Past service cost – augmentations 5 1 1 Past service credit – redundancies (7 ) (1 ) (1 ) Special termination benefit cost – redundancies 55 9 7 Past service cost – plan amendments 34 — — 280 202 239 Included within finance income and costs Net interest cost 22 65 105 Included within gain on disposal of discontinued operations Administration costs — — 5 Disposal of UK Gas Distribution — — 34 — — 39 Total included in income statement 1,2 316 283 399 Remeasurement gains of pension assets and post-retirement benefit obligations 68 1,313 348 Exchange adjustments (101 ) 175 (345 ) Total included in the statement of other comprehensive income 2 (33 ) 1,488 3 1. Amounts recognised in the income statement include operating costs of £nil (2018: £nil ; 2017: £1 million ); payroll costs of £nil (2018: £nil ; 2017: £35 million ); and net interest of £nil (2018: £nil ; 2017: £2 million income) presented within profit from discontinued operations. These amounts all relate to UK pensions. In addition there is a net charge of £52 million (2018: £nil ; 2017: £nil ) relating to redundancy pension costs in respect of the UK cost efficiency and restructuring programme included within exceptional items. 2. Amounts recognised in the statement of other comprehensive income include remeasurements of pension assets and post-retirement benefit obligations of £nil (2018: £nil ; 2017: £75 million loss) presented within discontinued operations. These amounts all relate to UK pensions. The geographical split of pensions and other post-retirement benefits is as shown below: UK Pensions US Pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Included within operating costs Administration costs 6 6 6 7 9 9 1 1 1 Included within payroll costs Defined benefit scheme costs: Current service cost 41 49 76 104 98 103 48 46 53 Past service cost – augmentations 5 1 1 — — — — — — Past service credit – redundancies (7 ) (1 ) (1 ) — — — — — — Special termination benefit cost – redundancies 55 9 7 — — — — — — Past service cost – plan amendments 34 — — — — — — — — 128 58 83 104 98 103 48 46 53 Included within finance income and costs Net interest cost (31 ) 3 — 21 27 43 32 35 62 Included within gain on disposal of discontinued operations Administration costs — — 5 — — — — — — Disposal of UK Gas Distribution — — 34 — — — — — — — — 39 — — — — — — Total included in income statement 103 67 128 132 134 155 81 82 116 Remeasurement gains/(losses) of pension assets and post-retirement benefit obligations 57 1,177 (541 ) (14 ) 27 319 25 109 570 Exchange adjustments — — — (42 ) 75 (140 ) (59 ) 100 (205 ) Total included in the statement of other comprehensive income 57 1,177 (541 ) (56 ) 102 179 (34 ) 209 365
Disclosure of reconciliation of the net defined benefit liability	Reconciliation of the net defined benefit liability 2019 2018 2017 £m £m £m Opening net defined benefit liability (263 ) (1,933 ) (2,585 ) Cost recognised in the income statement (316 ) (283 ) (399 ) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (33 ) 1,488 3 Employer contributions 419 475 1,073 Other movements (25 ) (10 ) (25 ) Closing net defined benefit liability (218 ) (263 ) (1,933 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Opening net defined benefit asset/(liability) 1,104 (156 ) (15 ) (552 ) (728 ) (1,009 ) (815 ) (1,049 ) (1,561 ) Cost recognised in the income statement (103 ) (67 ) (128 ) (132 ) (134 ) (155 ) (81 ) (82 ) (116 ) Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income 57 1,177 (541 ) (56 ) 102 179 (34 ) 209 365 Employer contributions 174 150 528 231 208 257 14 117 288 Other movements (1 ) — — — — — (24 ) (10 ) (25 ) Closing net defined benefit 1,231 1,104 (156 ) (509 ) (552 ) (728 ) (940 ) (815 ) (1,049 ) 25. Pensions and other post-retirement benefits continued Changes in the present value of defined benefit obligations (including unfunded obligations) 2019 2018 2017 £m £m £m Opening defined benefit obligations (24,054 ) (26,230 ) (28,952 ) Current service cost (193 ) (193 ) (232 ) Interest cost (771 ) (775 ) (1,057 ) Actuarial (losses)/gains – experience (69 ) (100 ) 166 Actuarial gains – demographic assumptions 266 671 225 Actuarial (losses)/gains – financial assumptions (619 ) 174 (3,377 ) Past service credit – redundancies 7 1 1 Special termination benefit cost – redundancies (55 ) (9 ) (7 ) Past service cost – augmentations (5 ) (1 ) (1 ) Past service cost – plan amendments (34 ) — — Medicare subsidy received (19 ) (21 ) (14 ) Obligations transferred on disposal of UK Gas Distribution — — 6,970 Employee contributions (1 ) (1 ) (1 ) Benefits paid 1,376 1,285 1,443 Exchange adjustments (768 ) 1,145 (1,394 ) Closing defined benefit obligations (24,939 ) (24,054 ) (26,230 ) The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Opening defined benefit obligations (14,226 ) (15,645 ) (19,416 ) (6,582 ) (7,050 ) (6,145 ) (3,246 ) (3,535 ) (3,391 ) Current service cost (41 ) (49 ) (76 ) (104 ) (98 ) (103 ) (48 ) (46 ) (53 ) Interest cost (358 ) (366 ) (615 ) (277 ) (273 ) (285 ) (136 ) (136 ) (157 ) Actuarial (losses)/gains – experience (56 ) (95 ) 106 (52 ) (38 ) (2 ) 39 33 62 Actuarial gains – demographic assumptions 224 565 214 — 30 2 42 76 9 Actuarial (losses)/gains – financial assumptions (568 ) 604 (3,751 ) (24 ) (279 ) 37 (27 ) (151 ) 337 Past service credit – redundancies 7 1 1 — — — — — — Special termination benefit cost – redundancies (55 ) (9 ) (7 ) — — — — — — Past service cost – augmentations (5 ) (1 ) (1 ) — — — — — — Past service cost – plan amendments (34 ) — — — — — — — — Medicare subsidy received — — — — — — (19 ) (21 ) (14 ) Obligations transferred on disposal of UK Gas Distribution — — 6,970 — — — — — — Employee contributions (1 ) (1 ) (1 ) — — — — — — Benefits paid 837 770 931 398 362 349 141 153 163 Exchange adjustments — — — (514 ) 764 (903 ) (254 ) 381 (491 ) Closing defined benefit obligations (14,276 ) (14,226 ) (15,645 ) (7,155 ) (6,582 ) (7,050 ) (3,508 ) (3,246 ) (3,535 ) 25. Pensions and other post-retirement benefits continued Changes in the value of plan assets 2019 2018 2017 £m £m £m Opening fair value of plan assets 23,858 24,375 26,434 Interest income 749 710 952 Return on plan assets in excess of interest 490 568 3,334 Administration costs (14 ) (16 ) (21 ) Employer contributions 419 475 1,073 Employee contributions 1 1 1 Benefits paid (1,377 ) (1,285 ) (1,443 ) Exchange adjustments 667 (970 ) 1,049 Assets transferred on disposal of UK Gas Distribution — — (7,004 ) Closing fair value of plan assets 24,793 23,858 24,375 Actual return on plan assets 1,239 1,278 4,286 Expected contributions to plans in the following year 307 363 491 The geographical split of pensions and other post-retirement benefits is as shown below: UK pensions US pensions US other post-retirement benefits 2019 2018 2017 2019 2018 2017 2019 2018 2017 £m £m £m £m £m £m £m £m £m Opening fair value of plan assets 15,330 15,489 19,401 6,030 6,322 5,136 2,498 2,564 1,897 Interest income 389 363 615 256 246 242 104 101 95 Return on plan assets in excess 457 103 2,890 62 314 282 (29 ) 151 162 Administration costs (6 ) (6 ) (11 ) (7 ) (9 ) (9 ) (1 ) (1 ) (1 ) Employer contributions 174 150 528 231 208 257 14 117 288 Employee contributions 1 1 1 — — — — — — Benefits paid (838 ) (770 ) (931 ) (398 ) (362 ) (349 ) (141 ) (153 ) (163 ) Exchange adjustments — — — 472 (689 ) 763 195 (281 ) 286 Assets transferred on disposal of UK Gas Distribution — — (7,004 ) — — — — — — Closing fair value of plan assets 15,507 15,330 15,489 6,646 6,030 6,322 2,640 2,498 2,564 Actual return on plan assets 846 466 3,505 318 560 524 75 252 257 Expected contributions to plans in the following year 148 140 128 150 221 229 9 2 134
Disclosure of asset allocations	Asset allocations Within the asset allocations below, there is significant diversification across regions, asset managers, currencies and bond categories. UK pensions 2019 2018 2017 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 1 1,181 784 1,965 1,420 813 2,233 2,624 596 3,220 Corporate bonds 3,625 — 3,625 3,949 — 3,949 3,526 — 3,526 Government securities 6,114 — 6,114 5,629 — 5,629 5,406 — 5,406 Property 108 749 857 129 834 963 90 708 798 Diversified alternatives — 771 771 99 690 789 250 628 878 Liability-matching assets 1,751 (35 )² 1,716 1,174 — 1,174 1,162 — 1,162 Cash and cash equivalents 40 259 299 211 215 426 211 412 623 Other (including net current assets and liabilities) — 160 160 — 167 167 (148 ) 24 (124 ) 12,819 2,688 15,507 12,611 2,719 15,330 13,121 2,368 15,489 1. Included within equities at 31 March 2019 were ordinary shares of National Grid plc with a value of £nil ( 2018 : £ nil ; 2017 : £2 million ). 2. Comprises the longevity insurance contract within the NGEG of the ESPS. US pensions 2019 2018 2017 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 533 2,178 2,711 577 1,954 2,531 698 1,915 2,613 Corporate bonds 1,329 425 1,754 1,085 413 1,498 1,130 537 1,667 Government securities 422 640 1,062 414 565 979 872 71 943 Property — 316 316 — 279 279 — 335 335 Diversified alternatives 183 487 670 198 421 619 209 433 642 Infrastructure — 99 99 — 77 77 — 79 79 Cash and cash equivalents 21 — 21 14 — 14 28 — 28 Other (including net current assets and liabilities) (8 ) 21 13 6 27 33 3 12 15 2,480 4,166 6,646 2,294 3,736 6,030 2,940 3,382 6,322 US other post-retirement benefits 2019 2018 2017 Quoted Unquoted Total Quoted Unquoted Total Quoted Unquoted Total £m £m £m £m £m £m £m £m £m Equities 404 1,184 1,588 412 1,110 1,522 405 1,162 1,567 Corporate bonds 19 — 19 24 — 24 19 — 19 Government securities 540 3 543 508 2 510 520 1 521 Diversified alternatives 175 166 341 161 144 305 166 149 315 Other 1 — 149 149 — 137 137 — 142 142 1,138 1,502 2,640 1,105 1,393 2,498 1,110 1,454 2,564 1. Other primarily comprises insurance contracts. Asset allocation strategy Each plan’s investment strategy is formulated specifically in order to target specific asset allocations and returns, and to manage risk. The asset allocation of the plans as at 31 March 2019 is as follows: UK pensions US pensions US other post-retirement benefits % % % Equities 12.7 40.8 60.2 Corporate bonds 23.4 26.4 0.7 Government securities 39.4 16.0 20.6 Property 5.5 4.7 — Diversified alternatives 5.0 10.1 12.9 Liability matching assets 11.1 — — Infrastructure — 1.5 — Cash and cash equivalents 1.9 0.3 — Other 1.0 0.2 5.6 100.0 100.0 100.0

Provisions (Tables)

Provisions (Tables)	12 Months Ended
Provisions (Tables)	Mar. 31, 2019
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Schedule of provisions	Environmental £m Decommissioning £m Restructuring £m Emissions £m Other £m Total provisions £m At 1 April 2017 1,721 221 17 32 597 2,588 Exchange adjustments (158 ) (9 ) — (2 ) (26 ) (195 ) Additions 27 2 10 12 23 74 Unused amounts reversed 1 (45 ) (19 ) (6 ) — (37 ) (107 ) Unwinding of discount 61 5 1 — 8 75 Utilised 2 (75 ) (6 ) (7 ) (34 ) (146 ) (268 ) Transfers 3 — — (12 ) — (103 ) (115 ) At 31 March 2018 1,531 194 3 8 316 2,052 Exchange adjustments 103 7 — — 14 124 Additions 32 18 125 16 35 226 Unused amounts reversed 1 (36 ) (10 ) (3 ) (6 ) (10 ) (65 ) Unwinding of discount 62 5 — — 7 74 Utilised 2 (53 ) (26 ) (42 ) (9 ) (79 ) (209 ) Transfers 3 — — — — (3 ) (3 ) At 31 March 2019 1,639 188 83 9 280 2,199 2019 2018 £m £m Current 316 273 Non-current 1,883 1,779 2,199 2,052 1. Unused amounts reversed from other provisions include £ nil (2018: £16 million ) in relation to discontinued operations. 2. Utilised amounts for other provisions include £20 million (2018: £77 million ) in relation to discontinued operations. 3. Represents net amounts transferred to trade and other payables (see note 22) of £3 million ( 2018 : £115 million ).
Schedule of environmental provision	The environmental provision is as follows: 2019 2018 Discounted £m Undiscounted £m Real discount rate Discounted £m Undiscounted £m Real discount rate UK sites 189 210 1 % 213 235 1 % US sites 1,450 1,555 1 % 1,318 1,410 1 % 1,639 1,765 1,531 1,645

Share capital (Tables)

Share capital (Tables)	12 Months Ended
Share capital (Tables)	Mar. 31, 2019
Share Capital, Reserves And Other Equity Interest [Abstract]
Schedule of share capital	Allotted, called-up and fully paid million £m At 1 April 2017 3,943 449 Effect of share consolidation 1 (328 ) — Issued during the year in lieu of dividends 2 23 3 At 31 March 2018 3,638 452 Issued during the year in lieu of dividends 2 49 6 At 31 March 2019 3,687 458 1. On 22 May 2017 the ordinary share capital was consolidated with 11 new ordinary shares of 12 204 / 473 pence nominal value issued for every 12 existing ordinary shares of 11 17 / 43 pence nominal value. This consolidation was completed to maintain the comparability of the Company’s share price before and after the special dividend. 2. 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
Other equity reserves (Tables)	Mar. 31, 2019
Disclosure of reserves within equity [abstract]
Schedule of reserves within equity	Translation £m Cash flow hedge £m Cost of hedging £m Available- for-sale £m FVOCI equity £m FVOCI debt £m Own credit £m Capital redemption £m Merger £m Total £m At 1 April 2016 548 (45 ) — 120 — — — 19 (5,165 ) (4,523 ) Exchange adjustments 1 346 — — — — — — — — 346 Net (losses)/gains taken to equity — (36 ) — 81 — — — — — 45 Transferred to/(from) profit or loss — 227 — (25 ) — — — — — 202 Tax — (43 ) — (14 ) — — — — — (57 ) At 31 March 2017 894 103 — 162 — — — 19 (5,165 ) (3,987 ) Exchange adjustments 1 (504 ) — — — — — — — — (504 ) Net gains/(losses) taken to equity — 19 — (30 ) — — — — — (11 ) Share of net gains of associates taken to equity — 5 — — — — — — — 5 Transferred from profit or loss — (3 ) — (73 ) — — — — — (76 ) Tax — 4 — 29 — — — — — 33 At 31 March 2018 (as previously reported) 390 128 — 88 — — — 19 (5,165 ) (4,540 ) Transfer on transition to IFRS 9 — (3 ) 76 (88 ) 34 46 7 — — 72 At 1 April 2018 (as restated) 390 125 76 — 34 46 7 19 (5,165 ) (4,468 ) Exchange adjustments 1 346 — — — — — — — — 346 Net (losses)/gains taken to equity — (40 ) (107 ) — — 2 7 — — (138 ) Share of net gains of associates taken to equity — 1 — — — — — — — 1 Transferred to profit or loss — — 41 — — — — — — 41 Net losses in respect of cash flow hedging of capital expenditure — (13 ) — — — — — — — (13 ) Tax — 6 7 — — — (1 ) — — 12 Cash flow hedges transferred to the statement of financial position, net of tax — (18 ) — — — — — — — (18 ) At 31 March 2019 736 61 17 — 34 48 13 19 (5,165 ) (4,237 ) 1. The exchange adjustments recorded in the translation reserve comprise a gain of £896 million ( 2018 : loss of £1,304 million ; 2017 : gain of £1,364 million ) relating to the translation of foreign operations offset by a loss of £550 million ( 2018 : gain of £800 million ; 2017 : loss of £1,018 million ) relating to borrowings, cross-currency swaps and foreign exchange forward contracts used to hedge the net investment in the non-sterling denominated subsidiaries.

Net debt (Tables)

Net debt (Tables)	12 Months Ended
Net debt (Tables)	Mar. 31, 2019
Subclassifications of assets, liabilities and equities [abstract]
Reconciliation of net cash flow to movement in net debt	Reconciliation of net cash flow to movement in net debt 2019 2018 2017 £m £m £m (Decrease)/increase in cash and cash equivalents (80 ) (807 ) 984 (Decrease)/increase in financial investments (822 ) (5,953 ) 5,675 (Increase)/decrease in borrowings and related derivatives 1 (708 ) 1,209 (3,715 ) Net interest paid on the components of net debt 2 866 808 1,955 Change in debt resulting from cash flows (744 ) (4,743 ) 4,899 Changes in fair value of financial assets and liabilities and exchange movements (1,648 ) 2,098 (2,273 ) Net interest charge on the components of net debt (1,076 ) (1,017 ) (2,401 ) Disposal of UK Gas Distribution — — 5,890 Other non-cash movements (27 ) (66 ) (64 ) Movement in net debt (net of related derivative financial instruments) in the year (3,495 ) (3,728 ) 6,051 Net debt (net of related derivative financial instruments) at start of year (23,002 ) (19,274 ) (25,325 ) Impact of transition to IFRS 9 (32 ) — — Net debt (net of related derivative financial instruments) at end of year (26,529 ) (23,002 ) (19,274 )
Schedule of components of net debt	Net debt is made up as follows: 2019 2018 2017 £m £m £m Cash, cash equivalents and financial investments 2,233 3,023 9,880 Borrowings and bank overdrafts (28,730 ) (26,625 ) (28,638 ) Financing derivatives 1 (32 ) 600 (516 ) (26,529 ) (23,002 ) (19,274 ) 1. The financing derivatives balance included in net debt excludes the commodity derivatives (see note 17). 2. Excludes £23 million ( 2018 : £27 million ; 2017 : £nil ) cash interest from the Quadgas shareholder loan included within discontinued operations in the cash flow statement.
Schedule of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments	Analysis of changes in net debt Cash and cash equivalents £m Bank overdrafts £m Net cash and cash equivalents £m Financial investments £m Borrowings £m Financing derivatives £m Total 1 £m At 1 April 2016 127 (3 ) 124 2,998 (28,341 ) (106 ) (25,325 ) Cash flow 2 1,001 (17 ) 984 5,624 (2,196 ) 487 4,899 Fair value gains and losses and exchange movements 16 — 16 141 (1,527 ) (903 ) (2,273 ) Interest income/(charges) 3 — — — 53 (2,221 ) (233 ) (2,401 ) Other non-cash movements — — — — (294 ) 230 (64 ) Disposal (5 ) 20 15 (75 ) 5,941 9 5,890 At 1 April 2017 1,139 — 1,139 8,741 (28,638 ) (516 ) (19,274 ) Cash flow 2 (807 ) — (807 ) (5,983 ) 2,108 (61 ) (4,743 ) Fair value gains and losses and exchange movements (3 ) — (3 ) (149 ) 1,088 1,162 2,098 Interest income/(charges) 3 — — — 85 (1,117 ) 15 (1,017 ) Other non-cash movements — — — — (66 ) — (66 ) At 31 March 2018 329 — 329 2,694 (26,625 ) 600 (23,002 ) Impact of transition to IFRS 9 — — — — (32 ) — (32 ) At 1 April 2018 (as restated) 329 — 329 2,694 (26,657 ) 600 (23,034 ) Cash flow 2 (80 ) — (80 ) (846 ) (240 ) 422 (744 ) Fair value gains and losses and exchange movements 3 — 3 93 (733 ) (1,011 ) (1,648 ) Interest income/(charges) 3 — — — 29 (1,062 ) (43 ) (1,076 ) Other non-cash movements — — — 11 (38 ) — (27 ) At 31 March 2019 252 — 252 1,981 (28,730 ) (32 ) (26,529 ) Balances at 31 March 2019 comprise: Non-current assets — — — — — 996 996 Current assets 252 — 252 1,981 — 56 2,289 Current liabilities — — — — (4,472 ) (282 ) (4,754 ) Non-current liabilities — — — — (24,258 ) (802 ) (25,060 ) 252 — 252 1,981 (28,730 ) (32 ) (26,529 ) 1. Includes accrued interest at 31 March 2019 of £223 million ( 2018 : £197 million ; 2017 : £210 million ). 2. Cash flow from financing activities relating to financing liabilities (proceeds and repayment of loans, net movement in short-term borrowings and derivatives and interest paid) includes cash outflow on non-debt-related items of £24 million (2018: £12 million ; 2017: £nil ) and excludes derivative cash inflow in relation to capital expenditure of £13 million (2018: £12 million ; 2017: £18 million ) and items relating to discontinued operations of £nil (2018: £231 million ; 2017: £(1,611) million ). 3. An exceptional income of £nil ( 2018 : £3 million income; 2017 : £1,313 million expense) is included in net interest charge on the components of net debt.

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
Commitments and contingencies (Tables)	Mar. 31, 2019
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]
Schedule of capital commitments and contingent liabilities	2019 2018 £m £m Future capital expenditure Contracted for but not provided 1,973 1,843 Operating lease commitments 1 Less than 1 year 43 42 In 1 to 2 years 39 37 In 2 to 3 years 34 33 In 3 to 4 years 35 30 In 4 to 5 years 27 28 More than 5 years 123 122 301 292 Energy purchase commitments 2 Less than 1 year 1,353 1,237 In 1 to 2 years 779 700 In 2 to 3 years 651 563 In 3 to 4 years 827 449 In 4 to 5 years 862 410 More than 5 years 11,237 1,969 15,709 5,328 Guarantees 3 Guarantee of sublease for US property (expires 2040) 173 178 Guarantees of certain obligations of Grain LNG (expire up to 2025) 39 46 Guarantees of certain obligations for construction of HVDC West Coast Link (expires 2019) 139 213 Guarantees of certain obligations of Nemo Link Limited (various expiry dates) 19 63 Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates) 3 865 1,009 Guarantees of certain obligations of St William Homes LLP (various expiry dates) 4 22 98 Guarantees of certain obligations for construction of IFA 2 (expected expiry 2021) 3 505 729 Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024) 872 — Other guarantees and letters of credit (various expiry dates) 341 333 2,975 2,669 1. Following a review during the year, the comparatives have been refined to provide consistency with the current year. 2. 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). 3. Included within total guarantees are guarantees to both joint ventures and Engineering, Procurement and Construction contractors regarding the construction of interconnectors of £470 million (2018: £739 million ). 4. Includes guarantees to related parties.

Related party transactions (Tab

Related party transactions (Tables)	12 Months Ended
Related party transactions (Tables)	Mar. 31, 2019
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: 2019 2018 2017 £m £m £m Sales: Goods and services supplied to a pension plan 5 3 3 Sales: Goods and services supplied to joint ventures 1 151 14 78 Sales: Goods and services supplied to associates 2 192 220 — Purchases: Goods and services received from joint ventures 3 26 135 168 Purchases: Goods and services received from associates 3 141 160 169 Receivable from joint ventures 4 584 160 64 Receivable from associates 4 368 376 457 Payable to joint ventures 5 8 — 84 Payable to associates 12 17 27 Interest income from joint ventures 5 4 — Interest income from associates 23 27 — Dividends received from joint ventures 6 30 43 75 Dividends received from associates 7 171 170 24 1. During the year, £139 million (2018: £5 million ) of property sites were sold to joint venture St William Homes LLP. 2. Sales in the year relate to transactions with Quadgas. Within this is other income of £52 million (2018: £54 million ) relating to a Transitional Service Agreement following the sale of the UK Gas Distribution business to Quadgas. 3. During the year, the Group received goods and services from a number of US associates, both for the transportation of gas and for pipeline services in the US. Additionally, in 2018, goods and services were received from UK joint ventures for the construction of an electricity transmission link in the UK. 4. Amounts receivable from associates includes a loan receivable balance from Quadgas of £352 million (2018: £352 million ) which is classified as held for sale as at 31 March 2019, a loan receivable balance of £258 million (2018: £130 million ) from Nemo Link Limited (a joint venture) and £325 million (2018: £24 million ) in relation to St William Homes LLP (a joint venture). 5. In previous years the amounts payable to joint ventures include deposits received for National Grid property sites from St William Homes LLP which have been settled during the year. 6. Dividends in respect of joint ventures were received from BritNed Development Limited. 7. Includes £133 million (2018: £144 million ) of dividend income from Quadgas.

Financial risk management (Tabl

Financial risk management (Tables)	12 Months Ended
Financial risk management (Tables)	Mar. 31, 2019
Financial Instruments [Abstract]
Disclosure of treasury credit risk	As at 31 March 2019, the following limits were in place for investments held with banks and financial institutions: Maximum limit Long-term limit Triple ‘A’ G7 sovereign entities (AAA) 1,853 927 Triple ‘A’ vehicles (AAA) 500 — Triple ‘A’ range institutions and non-G7 sovereign entities (AAA) 1,011 506 Double ‘A+’ G7 sovereign entities (AA+) 1,685 843 Double ‘A’ range institutions (AA) 674 to 843 337 to 421 Single ‘A’ range institutions (A) 236 to 337 118 to 169
Disclosure of offsetting of financial assets and financial liabilities	Related amounts At 31 March 2019 Gross £m Gross £m Net amount £m Financial instruments £m Cash £m Net amount £m Assets Financing derivatives 1,052 — 1,052 (299 ) (551 ) 202 Commodity contract derivatives 101 — 101 29 — 130 1,153 — 1,153 (270 ) (551 ) 332 Liabilities Financing derivatives (1,084 ) — (1,084 ) 299 615 (170 ) Commodity contract derivatives (99 ) — (99 ) (29 ) — (128 ) (1,183 ) — (1,183 ) 270 615 (298 ) (30 ) — (30 ) — 64 34 Related amounts At 31 March 2018 Gross carrying amounts £m Gross amounts offset £m Net amount presented in statement of financial position £m Financial instruments £m Cash collateral received/ pledged £m Net amount £m Assets Financing derivatives 1,545 — 1,545 (523 ) (772 ) 250 Commodity contract derivatives 69 — 69 (16 ) — 53 Further acquisition agreement derivative¹ 110 — 110 — — 110 1,724 — 1,724 (539 ) (772 ) 413 Liabilities Financing derivatives (945 ) — (945 ) 523 326 (96 ) Commodity contract derivatives (116 ) — (116 ) 16 7 (93 ) (1,061 ) — (1,061 ) 539 333 (189 ) 663 — 663 — (439 ) 224 1. The Group is party to the Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) which contain put and call options over 14% and 25% respectively, of the equity and loan balances it holds in Cadent (through its investment in Quadgas). These are classified within the disposal group as at 31 March 2019 (see note 10).
Disclosure of maturity analysis for financial liabilities	The following is a maturity profile of our financial liabilities and derivatives as at the reporting date: At 31 March 2019 Less than £m 1 to 2 £m 2 to 3 £m More than £m Total £m Non-derivative financial liabilities Borrowings, excluding finance lease liabilities (4,129 ) (2,348 ) (1,998 ) (19,673 ) (28,148 ) Interest payments on borrowings 1 (800 ) (733 ) (721 ) (13,465 ) (15,719 ) Finance lease liabilities (72 ) (63 ) (52 ) (123 ) (310 ) Other non-interest-bearing liabilities (3,306 ) (340 ) — — (3,646 ) Derivative financial liabilities Derivative contracts – receipts 2 3,045 1,703 163 2,560 7,471 Derivative contracts – payments 2 (3,421 ) (2,029 ) (223 ) (3,276 ) (8,949 ) Commodity contract derivatives (73 ) (19 ) (2 ) (1 ) (95 ) Derivative financial assets Derivative contracts – receipts 2 1,928 561 863 1,112 4,464 Derivative contracts – payments 2 (1,251 ) (459 ) (783 ) (875 ) (3,368 ) (8,079 ) (3,727 ) (2,753 ) (33,741 ) (48,300 ) At 31 March 2018³ 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 finance lease liabilities (4,099 ) (1,642 ) (2,325 ) (18,023 ) (26,089 ) Interest payments on borrowings 1 (730 ) (692 ) (629 ) (12,897 ) (14,948 ) Finance lease liabilities (60 ) (60 ) (45 ) (148 ) (313 ) Other non-interest-bearing liabilities (2,840 ) (359 ) — — (3,199 ) Derivative financial liabilities Derivative contracts – receipts 2 1,111 424 441 268 2,244 Derivative contracts – payments 2 (1,468 ) (608 ) (547 ) (704 ) (3,327 ) Commodity contract derivatives (80 ) (33 ) (26 ) 1 (138 ) Derivative financial assets Derivative contracts – receipts 2 6,536 2,225 1,726 3,134 13,621 Derivative contracts – payments 2 (6,000 ) (1,703 ) (1,678 ) (2,977 ) (12,358 ) (7,630 ) (2,448 ) (3,083 ) (31,346 ) (44,507 ) 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 financial derivative payments and receipts include the gross undiscounted cash flows for interest rate and cross currency derivatives. The cash flows for these derivatives are presented as gross payments and receipts where the cash flows are not net settled either due to timing or currency. 3. The comparatives have been refined to provide consistency with the current period.
Disclosure of nature and extent of risks arising from financial instruments	During 2019 and 2018, derivative financial instruments were used to manage foreign currency risk as follows: 2019 2018 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 97 2 153 — 252 294 2 33 — 329 Financial investments 965 — 1,016 — 1,981 1,471 69 1,125 29 2,694 Borrowings (10,591 ) (4,787 ) (12,126 ) (1,226 ) (28,730 ) (10,912 ) (3,794 ) (11,068 ) (851 ) (26,625 ) Pre-derivative position (9,529 ) (4,785 ) (10,957 ) (1,226 ) (26,497 ) (9,147 ) (3,723 ) (9,910 ) (822 ) (23,602 ) Derivative effect (1,055 ) 4,803 (5,245 ) 1,465 (32 ) 3,748 3,793 (7,992 ) 1,051 600 Net debt position (10,584 ) 18 (16,202 ) 239 (26,529 ) (5,399 ) 70 (17,902 ) 229 (23,002 ) The currency exposure on other financial instruments is as follows: 2019 2018 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 398 — 1,635 — 2,033 253 — 1,528 — 1,781 Trade and other payables (1,221 ) — (2,085 ) — (3,306 ) (1,124 ) — (1,793 ) — (2,917 ) Other non-current liabilities (93 ) — (247 ) — (340 ) (144 ) — (254 ) — (398 ) 2019 2018 Income statement £m Other equity reserves £m Income statement £m Other equity reserves £m Financial risk (post-tax): UK RPI change of 0.5% 1 27 — 30 — UK interest rates change of 0.5% 16 13 43 26 US interest rates change of 0.5% 11 44 39 17 US dollar exchange rate change of 10% 2 53 246 48 479 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 £1,119 million ( 2018 : £1,040 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: 2019 2018 Income statement £m Net assets £m Income statement £m Net assets £m Commodity price risk (post-tax): 10% increase in commodity prices 26 26 23 23 10% decrease in commodity prices (27 ) (27 ) (23 ) (23 ) Assets and liabilities carried at fair value (pre-tax): 1 10% fair value change in derivative financial instruments 2 (3 ) (3 ) 60 60 10% fair value change in commodity contract derivative liabilities — — (5 ) (5 ) 1. Excludes sensitivities to the Further Acquisition Agreement derivative. These were classified to held for sale as at 31 March 2019 (see note 10). 2. The effect of a 10% change in fair value assumes no hedge accounting. The table below sets out the sensitivity analysis for each of the areas of estimation uncertainty set out in note 1E. These estimates are those that have a significant risk of resulting in a material adjustment to the carrying values of assets and liabilities in the next year. 2019 2018 Income statement £m Net assets £m Income statement £m Net assets £m Pensions and other post-retirement benefits (pre-tax): 1 UK discount rate change of 0.5% 2 6 1,064 8 1,075 US discount rate change of 0.5% 2 16 688 15 623 UK RPI rate change of 0.5% 3 4 908 5 965 UK long-term rate of increase in salaries change of 0.5% 4 1 56 — 61 US long-term rate of increase in salaries change of 0.5% 4 2 46 3 44 UK change of one year to life expectancy at age 65 1 610 2 588 US change of one year to life expectancy at age 65 4 406 4 359 Assumed US healthcare cost trend rates change of 1% 32 503 31 448 Environmental provision: 10% change in estimated future cash flows 165 165 154 154 1. The changes shown are a change in the annual pension or other post-retirement benefit service charge and change in the defined benefit obligations. 2. A change in the discount rate is likely to occur as a result of changes in bond yields and as such would be expected to be offset to a significant degree by a change in the value of the bond assets held by the plans. 3. The projected impact resulting from a change in RPI reflects the underlying effect on pensions in payment, pensions in deferment and resultant increases in salary assumptions. 4. This change has been applied to both the pre 1 April 2014 and post 1 April 2014 rate of increase in salary assumption.
Disclosure of financial instruments by type of interest rate	During 2019 and 2018, net debt was managed using derivative financial instruments to hedge interest rate risk as follows: 2019 2018 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 59 104 — 89 252 — 302 — 27 329 Financial investments 6 1,944 — 31 1,981 31 2,625 — 38 2,694 Borrowings (19,043 ) (3,045 ) (6,642 ) — (28,730 ) (16,144 ) (3,191 ) (7,290 ) — (26,625 ) Pre-derivative position (18,978 ) (997 ) (6,642 ) 120 (26,497 ) (16,113 ) (264 ) (7,290 ) 65 (23,602 ) Derivative effect 1,740 (1,559 ) (213 ) — (32 ) 1,735 (1,237 ) 102 — 600 Net debt position (17,238 ) (2,556 ) (6,855 ) 120 (26,529 ) (14,378 ) (1,501 ) (7,188 ) 65 (23,002 ) 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 hedged items	(i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings as at 31 March 2019: Hedge type 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 £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings 1 (1,707 ) 11 (117 ) 11 (6 ) 5 1. The carrying value of the hedged borrowings is £1,810 million , of which £202 million is current and £1,608 million is non-current. (ii) Cash flow hedges of foreign currency and interest rate risk as at 31 March 2019: Hedge type 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 £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings (3,804 ) (17 ) 51 39 (39 ) — Foreign currency risk on forecasted cash flows (697 ) 47 — 12 (12 ) — (iii) Net investment hedges of foreign currency risk as at 31 March 2019: Hedge type Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness £m £m £m £m £m £m Currency risk on foreign operations (2,974 ) (329 ) (2,502 ) 550 (550 ) —
Disclosure of detailed information about hedging instruments	In accordance with the requirements of IFRS 9, certain additional information about hedge accounting is disaggregated by risk type and hedge designation type in the tables below: Fair value hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency and interest rate risk Cash flow hedges of foreign currency risk Net investment hedges £m £m £m £m Consolidated statement of comprehensive income Net losses in respect of: Cash flow hedges — (40 ) (12 ) — Cost of hedging (6 ) (12 ) — (90 ) Transferred to profit or loss in respect of: Cash flow hedges — (1 ) — — Cost of hedging 3 — — 39 Consolidated statement of changes in equity Other equity reserves – cost of hedging balances (4 ) — — 32 Consolidated statement of financial position Derivatives – carrying value of hedging instruments 1 Assets – current 17 — 9 — Assets – non-current 168 78 23 — Liabilities – current (9 ) (28 ) (3 ) (43 ) Liabilities – non-current (25 ) (134 ) (4 ) (249 ) Profiles of the significant timing, price and rate information of hedging instruments Maturity range Nov 2019 – May 2038 Aug 2019 – Feb 2039 Apr 2019 – Dec 2023 Mar 2020 – Jun 2025 Spot foreign exchange range: GBP:USD 1.64 – 1.65 1.52 – 1.66 1.29 – 1.41 1.49 GBP:EUR 1.19 – 1.24 1.14 – 1.24 1.07 – 1.32 1.15 EUR:USD 1.13 – 1.16 1.13 – 1.14 n/a n/a Interest rate range: GBP Libor +30bps/+561bps 1.795% – 5.850% n/a n/a USD Libor -44bps/+115bps 1.103% – 3.864% n/a n/a 1. The use of derivatives may entail a derivative transaction qualifying for more than one hedge type designation under IFRS 9. Therefore, the derivative amounts in the table above are grossed up by hedge type, whereas they are presented net at an instrument level in the statement of financial position. (i) Fair value hedges of foreign currency and interest rate risk on recognised borrowings as at 31 March 2019: Hedge type 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 £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings 1 (1,707 ) 11 (117 ) 11 (6 ) 5 1. The carrying value of the hedged borrowings is £1,810 million , of which £202 million is current and £1,608 million is non-current. (ii) Cash flow hedges of foreign currency and interest rate risk as at 31 March 2019: Hedge type 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 £m £m £m £m £m £m Foreign currency and interest rate risk on borrowings (3,804 ) (17 ) 51 39 (39 ) — Foreign currency risk on forecasted cash flows (697 ) 47 — 12 (12 ) — (iii) Net investment hedges of foreign currency risk as at 31 March 2019: Hedge type Balance in translation reserve Change in value used for calculating ineffectiveness Hedging instrument notional Continuing hedges Discontinued hedges Hedged item Hedging instrument Hedge ineffectiveness £m £m £m £m £m £m Currency risk on foreign operations (2,974 ) (329 ) (2,502 ) 550 (550 ) —
Disclosure of fair value measurement of assets	The changes in value of our Level 3 financial instruments are as follows: Financing derivatives Commodity contract derivatives Other 3,4 Total 2019 2018 2019 2018 2019 2018 2019 2018 £m £m £m £m £m £m £m £m At 1 April (219 ) (465 ) (1 ) (16 ) 194 46 (26 ) (435 ) Net gains/(losses) for the year 1,2 4 15 (16 ) 8 15 110 3 133 Purchases — — 44 27 57 41 101 68 Settlements 1 231 (26 ) (20 ) (4 ) (3 ) (29 ) 208 Reclassification to held for sale 3 — — — — (110 ) — (110 ) — At 31 March (214 ) (219 ) 1 (1 ) 152 194 (61 ) (26 ) 1. Gain of £4 million ( 2018 : £15 million gain) is attributable to derivative financial instruments held at the end of the reporting period and has been recognised in finance costs in the income statement. 2. Loss of £21 million ( 2018 : £35 million gain) is attributable to commodity contract derivative financial instruments held at the end of the reporting period. 3. The Group is party to the Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) which contain put and call options over 14% and 25% respectively, of the equity and loan balances it holds in Cadent (through its investment in Quadgas). These were classified to held for sale as at 31 March 2019 (see note 10). The fair value was £110 million as at 31 March 2018. 4. Other comprises our investments in Sunrun Neptune 2016 LLC and the investments made by the National Grid Partners accounted for at fair value through profit and loss. 2019 2018 Level 1 £m Level 2 £m Level 3 £m Total £m Level 1 £m Level 2 £m Level 3 £m Total £m Assets Available-for-sale investments 1 — — — — 2,406 310 5 2,721 Investments held at FVTPL 1 1,311 — 62 1,373 — — — — Investments held at FVOCI 1 93 343 — 436 — — — — Investments in associates 2 — — 90 90 — — 79 79 Financing derivatives — 1,050 2 1,052 — 1,544 1 1,545 Commodity contract derivatives — 33 68 101 — 8 61 69 Further Acquisition Agreement derivative 3 — — — — — — 110 110 1,404 1,426 222 3,052 2,406 1,862 256 4,524 Liabilities Financing derivatives — (868 ) (216 ) (1,084 ) — (725 ) (220 ) (945 ) Commodity contract derivatives — (32 ) (67 ) (99 ) — (54 ) (62 ) (116 ) Liabilities held at fair value 4 (667 ) — — (667 ) — — — — (667 ) (900 ) (283 ) (1,850 ) — (779 ) (282 ) (1,061 ) 737 526 (61 ) 1,202 2,406 1,083 (26 ) 3,463 1. The available-for-sale investments have been reclassified, with the adoption of IFRS 9 (see notes 15 and 37). 2. Our Level 3 investments include investments relating to Sunrun Neptune 2016 LLC accounted for at fair value. 3. The Group is party to the Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) which contain put and call options over the equity and loan balances it holds in Cadent (through its investment in Quadgas). These are classified within the disposal group as at 31 March 2019 (see note 10). 4. On adoption of IFRS 9 the Group elected to change the measurement basis to fair value through profit and loss (see notes 21 and 37).
Disclosure of fair value measurement of liabilities	The changes in value of our Level 3 financial instruments are as follows: Financing derivatives Commodity contract derivatives Other 3,4 Total 2019 2018 2019 2018 2019 2018 2019 2018 £m £m £m £m £m £m £m £m At 1 April (219 ) (465 ) (1 ) (16 ) 194 46 (26 ) (435 ) Net gains/(losses) for the year 1,2 4 15 (16 ) 8 15 110 3 133 Purchases — — 44 27 57 41 101 68 Settlements 1 231 (26 ) (20 ) (4 ) (3 ) (29 ) 208 Reclassification to held for sale 3 — — — — (110 ) — (110 ) — At 31 March (214 ) (219 ) 1 (1 ) 152 194 (61 ) (26 ) 1. Gain of £4 million ( 2018 : £15 million gain) is attributable to derivative financial instruments held at the end of the reporting period and has been recognised in finance costs in the income statement. 2. Loss of £21 million ( 2018 : £35 million gain) is attributable to commodity contract derivative financial instruments held at the end of the reporting period. 3. The Group is party to the Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) which contain put and call options over 14% and 25% respectively, of the equity and loan balances it holds in Cadent (through its investment in Quadgas). These were classified to held for sale as at 31 March 2019 (see note 10). The fair value was £110 million as at 31 March 2018. 4. Other comprises our investments in Sunrun Neptune 2016 LLC and the investments made by the National Grid Partners accounted for at fair value through profit and loss. 2019 2018 Level 1 £m Level 2 £m Level 3 £m Total £m Level 1 £m Level 2 £m Level 3 £m Total £m Assets Available-for-sale investments 1 — — — — 2,406 310 5 2,721 Investments held at FVTPL 1 1,311 — 62 1,373 — — — — Investments held at FVOCI 1 93 343 — 436 — — — — Investments in associates 2 — — 90 90 — — 79 79 Financing derivatives — 1,050 2 1,052 — 1,544 1 1,545 Commodity contract derivatives — 33 68 101 — 8 61 69 Further Acquisition Agreement derivative 3 — — — — — — 110 110 1,404 1,426 222 3,052 2,406 1,862 256 4,524 Liabilities Financing derivatives — (868 ) (216 ) (1,084 ) — (725 ) (220 ) (945 ) Commodity contract derivatives — (32 ) (67 ) (99 ) — (54 ) (62 ) (116 ) Liabilities held at fair value 4 (667 ) — — (667 ) — — — — (667 ) (900 ) (283 ) (1,850 ) — (779 ) (282 ) (1,061 ) 737 526 (61 ) 1,202 2,406 1,083 (26 ) 3,463 1. The available-for-sale investments have been reclassified, with the adoption of IFRS 9 (see notes 15 and 37). 2. Our Level 3 investments include investments relating to Sunrun Neptune 2016 LLC accounted for at fair value. 3. The Group is party to the Further Acquisition Agreement (FAA) and Remaining Acquisition Agreement (RAA) which contain put and call options over the equity and loan balances it holds in Cadent (through its investment in Quadgas). These are classified within the disposal group as at 31 March 2019 (see note 10). 4. On adoption of IFRS 9 the Group elected to change the measurement basis to fair value through profit and loss (see notes 21 and 37).
Sensitivity analysis for types of market risk	The impacts on a post-tax basis of reasonably possible changes in significant Level 3 assumptions are as follows: Financing derivatives Commodity contract derivatives Other 3 2019 2018 2019 2018 2019 2018 £m £m £m £m £m £m 10% increase in commodity prices 1 — — (1 ) (1 ) — — 10% decrease in commodity prices 1 — — 2 3 — — +10% market area price change — — (10 ) (6 ) — — -10% market area price change — — 10 5 — — +20 basis points change in Limited Price Inflation (LPI) market curve 2 (88 ) (84 ) — — — — -20 basis points change in LPI market curve 2 83 82 — — — — +50 basis points change in discount rate — — — — (3 ) (5 ) -50 basis points change in discount rate — — — — 3 6 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 2019 .

Borrowing facilities (Tables)

Borrowing facilities (Tables)	12 Months Ended
Borrowing facilities (Tables)	Mar. 31, 2019
Disclosure of detailed information about borrowings [abstract]
Schedule of undrawn committed borrowing facilities	An analysis of the maturity of these undrawn committed facilities is shown below: 2019 2018 £m £m Undrawn committed borrowing facilities expiring: Less than 1 year — — In 1 to 2 years — 3,910 In 2 to 3 years 2,190 — In 3 to 4 years 1,668 — In 4 to 5 years 1,869 1,773 More than 5 years — — 5,727 5,683

Sensitivites (Tables)

Sensitivites (Tables)	12 Months Ended
Sensitivites (Tables)	Mar. 31, 2019
Disclosure of sensitivity analysis for actuarial assumptions [abstract]
Schedule of sensitivity analysis for actuarial assumptions	During 2019 and 2018, derivative financial instruments were used to manage foreign currency risk as follows: 2019 2018 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Cash and cash equivalents 97 2 153 — 252 294 2 33 — 329 Financial investments 965 — 1,016 — 1,981 1,471 69 1,125 29 2,694 Borrowings (10,591 ) (4,787 ) (12,126 ) (1,226 ) (28,730 ) (10,912 ) (3,794 ) (11,068 ) (851 ) (26,625 ) Pre-derivative position (9,529 ) (4,785 ) (10,957 ) (1,226 ) (26,497 ) (9,147 ) (3,723 ) (9,910 ) (822 ) (23,602 ) Derivative effect (1,055 ) 4,803 (5,245 ) 1,465 (32 ) 3,748 3,793 (7,992 ) 1,051 600 Net debt position (10,584 ) 18 (16,202 ) 239 (26,529 ) (5,399 ) 70 (17,902 ) 229 (23,002 ) The currency exposure on other financial instruments is as follows: 2019 2018 Sterling £m Euro £m Dollar £m Other £m Total £m Sterling £m Euro £m Dollar £m Other £m Total £m Trade and other receivables 398 — 1,635 — 2,033 253 — 1,528 — 1,781 Trade and other payables (1,221 ) — (2,085 ) — (3,306 ) (1,124 ) — (1,793 ) — (2,917 ) Other non-current liabilities (93 ) — (247 ) — (340 ) (144 ) — (254 ) — (398 ) 2019 2018 Income statement £m Other equity reserves £m Income statement £m Other equity reserves £m Financial risk (post-tax): UK RPI change of 0.5% 1 27 — 30 — UK interest rates change of 0.5% 16 13 43 26 US interest rates change of 0.5% 11 44 39 17 US dollar exchange rate change of 10% 2 53 246 48 479 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 £1,119 million ( 2018 : £1,040 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: 2019 2018 Income statement £m Net assets £m Income statement £m Net assets £m Commodity price risk (post-tax): 10% increase in commodity prices 26 26 23 23 10% decrease in commodity prices (27 ) (27 ) (23 ) (23 ) Assets and liabilities carried at fair value (pre-tax): 1 10% fair value change in derivative financial instruments 2 (3 ) (3 ) 60 60 10% fair value change in commodity contract derivative liabilities — — (5 ) (5 ) 1. Excludes sensitivities to the Further Acquisition Agreement derivative. These were classified to held for sale as at 31 March 2019 (see note 10). 2. The effect of a 10% change in fair value assumes no hedge accounting. The table below sets out the sensitivity analysis for each of the areas of estimation uncertainty set out in note 1E. These estimates are those that have a significant risk of resulting in a material adjustment to the carrying values of assets and liabilities in the next year. 2019 2018 Income statement £m Net assets £m Income statement £m Net assets £m Pensions and other post-retirement benefits (pre-tax): 1 UK discount rate change of 0.5% 2 6 1,064 8 1,075 US discount rate change of 0.5% 2 16 688 15 623 UK RPI rate change of 0.5% 3 4 908 5 965 UK long-term rate of increase in salaries change of 0.5% 4 1 56 — 61 US long-term rate of increase in salaries change of 0.5% 4 2 46 3 44 UK change of one year to life expectancy at age 65 1 610 2 588 US change of one year to life expectancy at age 65 4 406 4 359 Assumed US healthcare cost trend rates change of 1% 32 503 31 448 Environmental provision: 10% change in estimated future cash flows 165 165 154 154 1. The changes shown are a change in the annual pension or other post-retirement benefit service charge and change in the defined benefit obligations. 2. A change in the discount rate is likely to occur as a result of changes in bond yields and as such would be expected to be offset to a significant degree by a change in the value of the bond assets held by the plans. 3. The projected impact resulting from a change in RPI reflects the underlying effect on pensions in payment, pensions in deferment and resultant increases in salary assumptions. 4. This change has been applied to both the pre 1 April 2014 and post 1 April 2014 rate of increase in salary assumption.

Additional disclosures in res_2

Additional disclosures in respect of guaranteed securities (Tables)	12 Months Ended
	Mar. 31, 2019
Separate Financial Statements [Abstract]
Disclosure of Condensed Income Statement	Summary statements of comprehensive income for the year ended 31 March 2019 – IFRS Parent guarantor Issuer of notes National Grid plc £m Niagara Mohawk Power Corporation £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Continuing operations Revenue — 2,483 12,450 — 14,933 Operating costs: Depreciation, amortisation and impairment — (216 ) (1,519 ) — (1,735 ) Payroll costs — (360 ) (1,492 ) — (1,852 ) Purchases of electricity — (559 ) (895 ) — (1,454 ) Purchases of gas — (189 ) (1,453 ) — (1,642 ) Rates and property taxes — (200 ) (908 ) — (1,108 ) Balancing Services Incentive Scheme — — (1,196 ) — (1,196 ) Other operating costs — (569 ) (2,507 ) — (3,076 ) — (2,093 ) (9,970 ) — (12,063 ) Total operating profit — 390 2,480 — 2,870 Net finance costs (252 ) (124 ) (693 ) — (1,069 ) Interest in equity accounted affiliates 1,712 — 40 (1,712 ) 40 Profit before tax 1,460 266 1,827 (1,712 ) 1,841 Tax 50 (56 ) (333 ) — (339 ) Profit after tax from discontinued operations — — 12 — 12 Profit for the year 1,510 210 1,506 (1,712 ) 1,514 Amounts recognised in other comprehensive income from continuing operations 1 303 4 (45 ) 41 303 Amounts recognised in other comprehensive income from discontinued operations 1 36 — 36 (36 ) 36 Total comprehensive income for the year 1,849 214 1,497 (1,707 ) 1,853 Attributable to: Equity shareholders 1,849 214 1,493 (1,707 ) 1,849 Non-controlling interests — — 4 — 4 1,849 214 1,497 (1,707 ) 1,853 1. Includes other comprehensive income relating to interest in equity accounted affiliates. 36. Additional disclosures in respect of guaranteed securities continued Summary statements of comprehensive income for the year ended 31 March 2018 1 – IFRS Parent guarantor Issuer of notes Subsidiary guarantor National Grid plc £m Niagara Mohawk Power Corporation £m British Transco Finance Inc. £m National Grid Gas plc £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Continuing operations Revenue — 2,416 — 1,430 11,495 (91 ) 15,250 Operating costs: Depreciation, amortisation and impairment — (190 ) — (245 ) (1,095 ) — (1,530 ) Payroll costs — (318 ) — (122 ) (1,208 ) — (1,648 ) Purchases of electricity — (537 ) — — (748 ) — (1,285 ) Purchases of gas — (166 ) — — (1,377 ) — (1,543 ) Rates and property taxes — (183 ) — (94 ) (780 ) — (1,057 ) Balancing Services Incentive Scheme — — — — (1,012 ) — (1,012 ) Payments to other UK network owners — — — — (1,043 ) — (1,043 ) Other operating costs — (397 ) — (331 ) (2,002 ) 91 (2,639 ) — (1,791 ) — (792 ) (9,265 ) 91 (11,757 ) Total operating profit — 625 — 638 2,230 — 3,493 Net finance income/(costs) 889 (100 ) — (174 ) (1,497 ) — (882 ) Interest in equity accounted affiliates 2,622 — — 8 49 (2,630 ) 49 Profit before tax 3,511 525 — 472 782 (2,630 ) 2,660 Tax 40 321 — (103 ) 631 — 889 Profit after tax from discontinued operations — — — 17 (15 ) — 2 Profit for the year 3,551 846 — 386 1,398 (2,630 ) 3,551 Amounts recognised in other comprehensive income from continuing operations 3 224 1 — 272 457 (730 ) 224 Amounts recognised in other comprehensive income from discontinued operations 3 147 — — — 147 (147 ) 147 Total comprehensive income for the year 3,922 847 — 658 2,002 (3,507 ) 3,922 Attributable to: Equity shareholders 3,922 847 — 658 2,002 (3,507 ) 3,922 Non-controlling interests — — — — — — — 3,922 847 — 658 2,002 (3,507 ) 3,922 1. Comparatives have been re-presented to reflect the classification of our retained interest in Quadgas as a discontinued operation in the current period (see note 1C and note 10). 2. Profit for the year for British Transco Finance Inc. is £ nil as interest payable to external bond holders is offset by interest receivable on loans to National Grid Gas plc. 3. Includes other comprehensive income relating to interest in equity accounted affiliates. 36. Additional disclosures in respect of guaranteed securities continued Summary statements of comprehensive income for the year ended 31 March 2017 – IFRS Parent guarantor Issuer of notes Subsidiary guarantor National Grid plc £m Niagara Mohawk Power Corporation £m British Transco Finance Inc. £m National Grid Gas plc re-presented £m Other subsidiaries re-presented £m Consolidation adjustments £m National Grid consolidated £m Continuing operations Revenue — 2,388 — 1,376 11,435 (164 ) 15,035 Operating costs: Depreciation, amortisation and impairment — (193 ) — (256 ) (1,032 ) — (1,481 ) Payroll costs — (326 ) — (114 ) (1,138 ) — (1,578 ) Purchases of electricity — (511 ) — — (586 ) — (1,097 ) Purchases of gas — (140 ) — (67 ) (1,012 ) — (1,219 ) Rates and property taxes — (188 ) — (101 ) (753 ) — (1,042 ) Balancing Services Incentive Scheme — — — — (1,120 ) — (1,120 ) Payments to other UK network owners — — — — (1,008 ) — (1,008 ) Other operating costs — (435 ) — (394 ) (2,617 ) 164 (3,282 ) — (1,793 ) — (932 ) (9,266 ) 164 (11,827 ) Total operating profit — 595 — 444 2,169 — 3,208 Net finance income/(costs) 8,177 (101 ) — (253 ) (8,910 ) — (1,087 ) Dividends receivable — — — — 8,100 (8,100 ) — Interest in equity accounted affiliates (401 ) — — — 63 401 63 Profit before tax 7,776 494 — 191 1,422 (7,699 ) 2,184 Tax 19 (181 ) — 16 (228 ) — (374 ) Profit after tax from discontinued operations — — — 4,633 1,351 — 5,984 Profit for the year 7,795 313 — 4,840 2,545 (7,699 ) 7,794 Amounts recognised in other comprehensive income from continuing operations 2 578 — — 114 177 (291 ) 578 Amounts recognised in other comprehensive income from discontinued operations 2 42 — — 51 (62 ) 11 42 Total comprehensive income for the year 8,415 313 — 5,005 2,660 (7,979 ) 8,414 Attributable to: Equity shareholders 8,415 313 — 5,005 2,661 (7,979 ) 8,415 Non-controlling interests — — — — (1 ) — (1 ) 8,415 313 — 5,005 2,660 (7,979 ) 8,414 1. Profit for the year for British Transco Finance Inc. is £ nil as interest payable to external bond holders is offset by interest receivable on loans to National Grid Gas plc. 2. Includes other comprehensive income relating to interest in equity accounted affiliates.
Disclosure of Condensed Balance Sheet	Statements of financial position as at 31 March 2019 – IFRS Parent Issuer of notes National Grid plc £m Niagara Mohawk Power Corporation £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Non-current assets Goodwill — 745 5,124 — 5,869 Other intangible assets — 3 1,081 — 1,084 Property, plant and equipment — 6,985 36,928 — 43,913 Other non-current assets — 4 260 — 264 Amounts owed by subsidiary undertakings 358 — 2,073 (2,431 ) — Pension assets — 260 1,307 — 1,567 Financial and other investments 23,573 22 3,434 (25,754 ) 1,275 Derivative financial assets — 9 1,036 — 1,045 Total non-current assets 23,931 8,028 51,243 (28,185 ) 55,017 Current assets Inventories and current intangible assets — 41 329 — 370 Trade and other receivables 1 535 2,617 — 3,153 Current tax assets — — 260 (134 ) 126 Amounts owed by subsidiary undertakings 12,514 476 14,101 (27,091 ) — Financial and other investments 895 13 1,073 — 1,981 Derivative financial assets 110 21 80 (103 ) 108 Cash and cash equivalents 75 12 165 — 252 Assets held for sale — — 1,956 — 1,956 Total current assets 13,595 1,098 20,581 (27,328 ) 7,946 Total assets 37,526 9,126 71,824 (55,513 ) 62,963 Current liabilities Borrowings (1,275 ) (634 ) (2,563 ) — (4,472 ) Derivative financial liabilities (92 ) (15 ) (346 ) 103 (350 ) Trade and other payables (58 ) (413 ) (3,298 ) — (3,769 ) Contract liabilities — (4 ) (57 ) — (61 ) Amounts owed to subsidiary undertakings (14,104 ) — (12,987 ) 27,091 — Current tax liabilities — (148 ) (147 ) 134 (161 ) Provisions — (24 ) (292 ) — (316 ) Total current liabilities (15,529 ) (1,238 ) (19,690 ) 27,328 (9,129 ) Non-current liabilities Borrowings (346 ) (2,048 ) (21,864 ) — (24,258 ) Derivative financial liabilities (228 ) (8 ) (597 ) — (833 ) Other non-current liabilities — (301 ) (507 ) — (808 ) Contract liabilities — (181 ) (752 ) — (933 ) Amounts owed to subsidiary undertakings (2,074 ) — (357 ) 2,431 — Deferred tax liabilities — (678 ) (3,287 ) — (3,965 ) Pensions and other post-retirement benefit obligations — (872 ) (913 ) — (1,785 ) Provisions — (271 ) (1,612 ) — (1,883 ) Total non-current liabilities (2,648 ) (4,359 ) (29,889 ) 2,431 (34,465 ) Total liabilities (18,177 ) (5,597 ) (49,579 ) 29,759 (43,594 ) Net assets 19,349 3,529 22,245 (25,754 ) 19,369 Equity Share capital 458 144 180 (324 ) 458 Share premium account 1,314 2,394 9,032 (11,426 ) 1,314 Retained earnings 21,814 991 13,048 (14,039 ) 21,814 Other equity reserves (4,237 ) — (35 ) 35 (4,237 ) Shareholders’ equity 19,349 3,529 22,225 (25,754 ) 19,349 Non-controlling interests — — 20 — 20 Total equity 19,349 3,529 22,245 (25,754 ) 19,369 36. Additional disclosures in respect of guaranteed securities continued Statements of financial position as at 31 March 2018 – IFRS Parent Issuer of notes Subsidiary guarantor National Grid plc £m Niagara Mohawk Power Corporation £m British Transco Finance Inc. £m National Grid Gas plc £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Non-current assets Goodwill — 691 — — 4,753 — 5,444 Other intangible assets — 3 — 107 789 — 899 Property, plant and equipment — 6,148 — 4,433 29,272 — 39,853 Other non-current assets — 3 — 94 18 — 115 Amounts owed by subsidiary undertakings 350 — — 3,426 2,593 (6,369 ) — Pension assets — 231 — 412 766 — 1,409 Financial and other investments 21,708 30 — 101 12,340 (31,112 ) 3,067 Derivative financial assets 18 2 — 591 708 — 1,319 Total non-current assets 22,076 7,108 — 9,164 51,239 (37,481 ) 52,106 Current assets Inventories and current intangible assets — 36 — 22 283 — 341 Trade and other receivables 1 515 — 276 2,006 — 2,798 Current tax assets — — — — 307 (193 ) 114 Amounts owed by subsidiary undertakings 11,254 130 220 708 11,253 (23,565 ) — Financial and other investments 938 15 — 863 878 — 2,694 Derivative financial assets 308 7 — 46 — 44 405 Cash and cash equivalents — 4 — 271 54 — 329 Total current assets 12,501 707 220 2,186 14,781 (23,714 ) 6,681 Total assets 34,577 7,815 220 11,350 66,020 (61,195 ) 58,787 Current liabilities Borrowings (781 ) (51 ) (218 ) (675 ) (2,722 ) — (4,447 ) Derivative financial liabilities (187 ) (36 ) — (68 ) (66 ) (44 ) (401 ) Trade and other payables (62 ) (318 ) — (347 ) (2,726 ) — (3,453 ) Amounts owed to subsidiary undertakings (11,809 ) — — (624 ) (11,132 ) 23,565 — Current tax liabilities — (202 ) — (26 ) (88 ) 193 (123 ) Provisions — (23 ) — (66 ) (184 ) — (273 ) Total current liabilities (12,839 ) (630 ) (218 ) (1,806 ) (16,918 ) 23,714 (8,697 ) Non-current liabilities Borrowings (773 ) (2,087 ) — (3,635 ) (15,683 ) — (22,178 ) Derivative financial liabilities (41 ) (18 ) — (157 ) (444 ) — (660 ) Other non-current liabilities — (281 ) — (181 ) (855 ) — (1,317 ) Amounts owed to subsidiary undertakings (2,091 ) — — (500 ) (3,778 ) 6,369 — Deferred tax liabilities (1 ) (626 ) — (441 ) (2,568 ) — (3,636 ) Pensions and other post-retirement benefit obligations — (765 ) — — (907 ) — (1,672 ) Provisions — (248 ) — (129 ) (1,402 ) — (1,779 ) Total non-current liabilities (2,906 ) (4,025 ) — (5,043 ) (25,637 ) 6,369 (31,242 ) Total liabilities (15,745 ) (4,655 ) (218 ) (6,849 ) (42,555 ) 30,083 (39,939 ) Net assets 18,832 3,160 2 4,501 23,465 (31,112 ) 18,848 Equity Share capital 452 133 — 45 182 (360 ) 452 Share premium account 1,321 2,194 — 204 9,032 (11,430 ) 1,321 Retained earnings 21,599 830 2 2,929 14,217 (17,978 ) 21,599 Other equity reserves (4,540 ) 3 — 1,323 18 (1,344 ) (4,540 ) Shareholders’ equity 18,832 3,160 2 4,501 23,449 (31,112 ) 18,832 Non-controlling interests — — — — 16 — 16 Total equity 18,832 3,160 2 4,501 23,465 (31,112 ) 18,848
Disclosure Of Condensed Cash Flow Statement	Cash flow statements Parent Issuer of notes Subsidiary guarantor National Grid plc £m Niagara Mohawk Power Corporation £m British Transco Finance Inc. £m National Grid Gas plc £m Other subsidiaries £m Consolidation adjustments £m National Grid consolidated £m Year ended 31 March 2019 Net cash flow from operating activities – continuing operations 33 572 n/a n/a 3,784 — 4,389 Net cash flow used in operating activities – discontinued operations — — n/a n/a (71 ) — (71 ) Net cash flow from/(used in) investing activities – continuing operations 121 (823 ) n/a n/a (3,570 ) 1,082 (3,190 ) Net cash flow from investing activities – discontinued operations — — n/a n/a 156 — 156 Net cash flow (used in)/from financing activities – continuing operations (79 ) 259 n/a n/a (462 ) (1,082 ) (1,364 ) Net cash flow from financing activities – discontinued operations — — n/a n/a — — — Net increase/(decrease) in cash and cash equivalents in the year 75 8 n/a n/a (163 ) — (80 ) Year ended 31 March 2018 Net cash flow from operating activities – continuing operations 35 662 — 888 3,125 — 4,710 Net cash flow used in operating activities – discontinued operations — — — (98 ) (109 ) — (207 ) Net cash flow from/(used in) investing activities – continuing operations 4,660 (473 ) 15 656 (1,930 ) (862 ) 2,066 Net cash flow from investing activities – discontinued operations — — — — 171 — 171 Net cash flow (used in)/from financing activities – continuing operations (5,785 ) (189 ) (15 ) (1,041 ) (1,148 ) 862 (7,316 ) Net cash flow used in financing activities – discontinued operations — — — (125 ) (106 ) — (231 ) Net (decrease)/increase in cash and cash equivalents in the year (1,090 ) — — 280 3 — (807 ) Year ended 31 March 2017 Net cash flow from operating activities – continuing operations 53 757 — 918 2,592 — 4,320 Net cash flow from operating activities – discontinued operations — — — 450 459 — 909 Net cash flow from/(used in) investing activities – continuing operations 4,181 (469 ) 15 215 (1,118 ) (6,458 ) (3,634 ) Net cash flow from/(used in) investing activities – discontinued operations — — — 5,618 (6,298 ) — (680 ) Net cash flow (used in)/from financing activities – continuing operations (3,146 ) (288 ) (15 ) (8,322 ) 3,771 6,458 (1,542 ) Net cash flow from financing activities – discontinued operations — — — 1,120 491 — 1,611 Net increase/(decrease) in cash and cash equivalents in the year 1,088 — — (1 ) (103 ) — 984
Schedule of borrowings	Total borrowings are repayable as follows: 2019 2018 £m £m Less than 1 year 4,472 4,447 In 1 to 2 years 2,393 1,694 In 2 to 3 years 1,990 2,347 In 3 to 4 years 1,553 1,873 In 4 to 5 years 714 1,469 More than 5 years: By instalments 959 1,010 Other than by instalments 16,649 13,785 28,730 26,625 2019 2018 £m £m Current Bank loans 641 2,020 Bonds 1,973 2,156 Commercial paper 1,792 206 Finance leases 65 64 Other loans 1 1 4,472 4,447 Non-current Bank loans 2,599 2,384 Bonds 1 21,278 19,418 Finance leases 205 207 Other loans 176 169 24,258 22,178 Total borrowings 28,730 26,625 1. In 2019 this includes a liability held at fair value through profit and loss of £667 million . Maturity analysis of Parent Company borrowings 2019 2018 £m £m Total borrowings are repayable as follows: Less than 1 year 1,275 781 In 1 to 2 years — 438 In 2 to 3 years 346 — In 3 to 4 years — 335 In 4 to 5 years — — More than 5 years — — 1,621 1,554

Transition to IFRS 9 and IFRS_2

Transition to IFRS 9 and IFRS 15 (Tables)	6 Months Ended	12 Months Ended
Transition to IFRS 9 and IFRS 15 (Tables)	Sep. 30, 2018	Mar. 31, 2019
Disclosure of comparative information prepared under previous GAAP [abstract]
Disclosure of comparative information prepared under previous GAAP	The impact of the transition on the opening consolidated statement of financial position is set out in the following table: Impact of transition 31 March 2018 Transition adjustments 1 April 2018 IFRS 9 IFRS 15 £m £m £m £m Non-current assets Goodwill 5,444 — — 5,444 Other intangible assets 899 — — 899 Property, plant and equipment 39,853 — — 39,853 Other non-current assets 115 — — 115 Pension assets 1,409 — — 1,409 Financial and other investments 899 — 1 — 899 Investments in joint ventures and associates 2,168 — — 2,168 Derivative financial assets 1,319 — — 1,319 Total non-current assets 52,106 — — 52,106 Current assets Inventories and current intangible assets 341 — — 341 Trade and other receivables 2,798 — 2 (3 ) 2,795 Current tax assets 114 — — 114 Financial and other investments 2,694 — 1 — 2,694 Derivative financial assets 405 — — 405 Cash and cash equivalents 329 — — 329 Total current assets 6,681 — (3 ) 6,678 Total assets 58,787 — (3 ) 58,784 Current liabilities Borrowings (4,447 ) — — (4,447 ) Derivative financial liabilities (401 ) — — (401 ) Trade and other payables (3,453 ) — 59 7 (3,394 ) Contract liabilities — — (53) 7 (53 ) Current tax liabilities (123 ) — — (123 ) Provisions (273 ) — — (273 ) Total current liabilities (8,697 ) — 6 (8,691 ) Non-current liabilities Borrowings (22,178 ) (32) 3 — (22,210 ) Derivative financial liabilities (660 ) — — (660 ) Other non-current liabilities (1,317 ) — 567 7 (750 ) Contract liabilities — — (813) 7 (813 ) Deferred tax liabilities (3,636 ) 5 4 74 8 (3,557 ) Pensions and other post-retirement benefit obligations (1,672 ) — — (1,672 ) Provisions (1,779 ) — — (1,779 ) Total non-current liabilities (31,242 ) (27 ) (172 ) (31,441 ) Total liabilities (39,939 ) (27 ) (166 ) (40,132 ) Net assets 18,848 (27 ) (169 ) 18,652 Equity Share capital 452 — — 452 Share premium account 1,321 — — 1,321 Retained earnings 21,599 (99) 5 (169) 9 21,331 Other equity reserves (4,540 ) 72 6 — (4,468 ) Total shareholders’ equity 18,832 (27 ) (169 ) 18,636 Non-controlling interests 16 — — 16 Total equity 18,848 (27 ) (169 ) 18,652
Disclosure of financial assets at date of initial application of IFRS 9		The table below illustrates those financial assets and liabilities that have been reclassified at 1 April 2018: Financial asset/liability Note Original measurement category under IAS 39 New measurement category under IFRS 9 Original carrying amount under IAS 39 Change to measurement basis under IFRS 9 New carrying amount under IFRS 9 £m £m £m Money market funds and fund investments in equities and bonds 15 Available-for-sale investments Financial assets at FVTPL 2,294 — 2,294 Cash surrender value of life insurance policies and investments in debt securities 15 Available-for-sale investments Financial assets at FVOCI 343 — 343 Investments in equity securities 15 Available-for-sale investments Financial assets at FVOCI (equity instruments) 84 — 84 Loans to joint ventures and associates and restricted balances 15 Loans and receivables Financial assets at amortised cost 872 — 872 Borrowings 21 Financial liabilities at amortised cost Financial liabilities at fair value through profit and loss (570 ) (32 ) (602 )
Disclosure of financial liabilities at date of initial application of IFRS 9		The table below illustrates those financial assets and liabilities that have been reclassified at 1 April 2018: Financial asset/liability Note Original measurement category under IAS 39 New measurement category under IFRS 9 Original carrying amount under IAS 39 Change to measurement basis under IFRS 9 New carrying amount under IFRS 9 £m £m £m Money market funds and fund investments in equities and bonds 15 Available-for-sale investments Financial assets at FVTPL 2,294 — 2,294 Cash surrender value of life insurance policies and investments in debt securities 15 Available-for-sale investments Financial assets at FVOCI 343 — 343 Investments in equity securities 15 Available-for-sale investments Financial assets at FVOCI (equity instruments) 84 — 84 Loans to joint ventures and associates and restricted balances 15 Loans and receivables Financial assets at amortised cost 872 — 872 Borrowings 21 Financial liabilities at amortised cost Financial liabilities at fair value through profit and loss (570 ) (32 ) (602 )

Basis of preparation and rece_3

Basis of preparation and recent accounting developments - Disposal of UK Gas Distribution (Details) - UK Gas Distribution (Cadent)	Mar. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed	61.00%		61.00%
Proportion of ownership interest in associate	39.00%	39.00%

Basis of preparation and rece_4

Basis of preparation and recent accounting developments - Impact of new IFRS accounting standards (Details) - GBP (£) £ in Millions	Apr. 01, 2019	Mar. 31, 2019	Mar. 31, 2018
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Operating lease commitments		£ 301	£ 292
Operating lease commitments, undiscounted excess amount		200
Finance lease liabilities		300
IFRS 16
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Lease liabilities		£ 300
Scenario, Forecast \| IFRS 16
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Lease liabilities	£ 400
Right-of-use assets	400
Increase in operating cash flows	100
Decrease in financing cash flows	£ 100

Segmental analysis - Revenue (D

Segmental analysis - Revenue (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of operating segments [line items]
Revenue	£ 14,933	£ 15,250	£ 15,035
UK
Disclosure of operating segments [line items]
Revenue	5,045	5,938	6,064
US
Disclosure of operating segments [line items]
Revenue	9,888	9,312	8,971
UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	3,331	4,126	4,410
UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	884	1,082	981
US Regulated
Disclosure of operating segments [line items]
Revenue	9,846	9,272	8,931
NG Ventures and Other
Disclosure of operating segments [line items]
Revenue	872	770	713
Operating Segments And Unallocated Amounts
Disclosure of operating segments [line items]
Revenue	14,969	15,293	15,163
Operating segments \| UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	3,351	4,154	4,439
Operating segments \| UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	896	1,091	1,080
Operating segments \| US Regulated
Disclosure of operating segments [line items]
Revenue	9,846	9,272	8,931
Unallocated amounts \| NG Ventures and Other
Disclosure of operating segments [line items]
Revenue	876	776	713
Unallocated amounts \| NG Ventures
Disclosure of operating segments [line items]
Revenue	597	593	604
Sales between segments
Disclosure of operating segments [line items]
Revenue	(36)	(43)	(128)
Sales between segments \| UK Electricity Transmission
Disclosure of operating segments [line items]
Revenue	(20)	(28)	(29)
Sales between segments \| UK Gas Transmission
Disclosure of operating segments [line items]
Revenue	(12)	(9)	(99)
Sales between segments \| US Regulated
Disclosure of operating segments [line items]
Revenue	0	0	0
Sales between segments \| NG Ventures and Other
Disclosure of operating segments [line items]
Revenue	£ (4)	£ (6)	£ 0

Segmental analysis - Operating

Segmental analysis - Operating profit from continuing operations (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 2,870	£ 3,493	[1]	£ 3,208
Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	3,442	3,457		3,773
UK
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,422	1,840		1,988
UK \| Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,695	1,840		2,118
US
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,448	1,653		1,220
US \| Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,747	1,617		1,655
Operating segments \| UK Electricity Transmission
Disclosure of operating segments [line items]
Operating profit from continuing operations	778	1,041		1,361
Operating segments \| UK Electricity Transmission \| Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,015	1,041		1,372
Operating segments \| UK Gas Transmission
Disclosure of operating segments [line items]
Operating profit from continuing operations	267	487		507
Operating segments \| UK Gas Transmission \| Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	303	487		511
Operating segments \| US Regulated
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,425	1,734		1,278
Operating segments \| US Regulated \| Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	1,724	1,698		1,713
Unallocated amounts \| NG Ventures and Other
Disclosure of operating segments [line items]
Operating profit from continuing operations	400	231		62
Unallocated amounts \| NG Ventures and Other \| Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 400	£ 231		£ 177

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Segmental analysis - Reconcile

Segmental analysis - Reconcile total operating profit to profit before tax from continuing operations (Details)	12 Months Ended
	Mar. 31, 2019GBP (£)settlement	Mar. 31, 2018GBP (£)		Mar. 31, 2017GBP (£)
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 2,870,000,000	£ 3,493,000,000	[1]	£ 3,208,000,000
Finance income	88,000,000	127,000,000		53,000,000
Finance costs	(1,157,000,000)	(1,009,000,000)		(1,140,000,000)
Share of post-tax results of joint ventures and associates	40,000,000	49,000,000		63,000,000
Profit before tax	1,841,000,000	2,660,000,000		2,184,000,000
Cash received from legal settlements	£ 95,000,000
Number of legal settlements \| settlement	2
Before exceptional items and remeasurements
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 3,442,000,000	3,457,000,000		3,773,000,000
Finance income	73,000,000	127,000,000		53,000,000
Finance costs	(1,066,000,000)	(1,128,000,000)		(1,082,000,000)
Share of post-tax results of joint ventures and associates	40,000,000	44,000,000		63,000,000
Profit before tax	2,489,000,000	2,500,000,000		2,807,000,000
Unallocated amounts \| NG Ventures and Other
Disclosure of operating segments [line items]
Operating profit from continuing operations	400,000,000	231,000,000		62,000,000
Cash received from legal settlements	£ 95,000,000	0		0
Number of legal settlements \| settlement	2
Unallocated amounts \| NG Ventures
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 263,000,000	234,000,000		239,000,000
Unallocated amounts \| UK Property Development
Disclosure of operating segments [line items]
Operating profit from continuing operations	181,000,000	84,000,000		55,000,000
Unallocated amounts \| Before exceptional items and remeasurements \| NG Ventures and Other
Disclosure of operating segments [line items]
Operating profit from continuing operations	£ 400,000,000	£ 231,000,000		£ 177,000,000

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Segmental analysis - Capital ex

Segmental analysis - Capital expenditure (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	£ 44,997	£ 40,752	£ 40,748
Capital expenditure	4,321	4,074	3,735
Depreciation, amortisation and impairment	(1,735)	(1,530)	(1,481)
Property, plant and equipment
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	43,913	39,853	39,825
Capital expenditure	4,015	3,901	3,507
Depreciation, amortisation and impairment	(1,560)	(1,392)	(1,348)
Non-current intangible assets
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	1,084	899	923
Capital expenditure	306	173	228
Depreciation, amortisation and impairment	(175)	(138)	(133)
UK
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	19,343	18,772	18,102
Capital expenditure	1,584	1,527	1,357
Depreciation, amortisation and impairment	(931)	(804)	(753)
US
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	25,654	21,980	22,646
Capital expenditure	2,737	2,547	2,378
Depreciation, amortisation and impairment	(804)	(726)	(728)
NG Ventures
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	1,635	1,454	1,432
Capital expenditure	317	186	98
Depreciation, amortisation and impairment	(114)	(143)	(143)
Operating segments \| UK Electricity Transmission
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	13,288	13,028	12,515
Capital expenditure	925	999	1,027
Depreciation, amortisation and impairment	(628)	(475)	(421)
Operating segments \| UK Gas Transmission
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	4,412	4,280	4,165
Capital expenditure	308	310	214
Depreciation, amortisation and impairment	(181)	(194)	(186)
Operating segments \| US Regulated
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	24,542	20,953	21,638
Capital expenditure	2,650	2,424	2,247
Depreciation, amortisation and impairment	(700)	(635)	(642)
Unallocated amounts \| NG Ventures and Other
Disclosure of operating segments [line items]
Net book value of property, plant and equipment and other intangible assets	2,755	2,491	2,430
Capital expenditure	438	341	247
Depreciation, amortisation and impairment	£ (226)	£ (226)	£ (232)

Segmental analysis - Narrative

Segmental analysis - Narrative (Details)	12 Months Ended
Segmental analysis - Narrative (Details)	Mar. 31, 2019GBP (£)segment	Mar. 31, 2018GBP (£)	Mar. 31, 2017GBP (£)
Disclosure of operating segments [line items]
Number of operating segments \| segment	3
UK
Disclosure of operating segments [line items]
Total non-current assets other than financial instruments and pension assets	£ 30,072,000,000	£ 20,816,000,000	£ 20,045,000,000
US
Disclosure of operating segments [line items]
Total non-current assets other than financial instruments and pension assets	21,787,000,000	27,663,000,000	28,951,000,000
Operating segments \| UK Electricity Transmission
Disclosure of operating segments [line items]
Operating exceptional items and remeasurements credit (debit)	237,000,000	0	11,000,000
Operating segments \| UK Gas Transmission
Disclosure of operating segments [line items]
Operating exceptional items and remeasurements credit (debit)	36,000,000	0	4,000,000
Operating segments \| US Regulated
Disclosure of operating segments [line items]
Operating exceptional items and remeasurements credit (debit)	299,000,000	36,000,000	435,000,000
Unallocated amounts \| NG Ventures and Other
Disclosure of operating segments [line items]
Operating exceptional items and remeasurements credit (debit)	£ 0	£ 0	£ 115,000,000

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	£ 14,066
Other revenue	867
Revenue	14,933	£ 15,250	£ 15,035
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,325
Other revenue	6
Revenue	3,331	4,126	4,410
UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	833
Other revenue	51
Revenue	884	1,082	981
US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	9,311
Other revenue	535
Revenue	9,846	9,272	8,931
NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	597
Other revenue	275
Revenue	872
UK
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	4,743
Other revenue	302
Revenue	5,045	£ 5,938	£ 6,064
UK \| UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,325
Other revenue	6
UK \| UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	833
Other revenue	51
UK \| US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Other revenue	0
UK \| NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	585
Other revenue	245
US
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	9,323
Other revenue	565
US \| UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Other revenue	0
US \| UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Other revenue	0
US \| US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	9,311
Other revenue	535
US \| NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	12
Other revenue	30
Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	4,841
Transmission \| UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	3,325
Transmission \| UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	833
Transmission \| US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	370
Transmission \| NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	313
Distribution
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,941
Distribution \| UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Distribution \| UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Distribution \| US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	8,941
Distribution \| NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	284
Other revenue	500
Other \| UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Other revenue	6
Other \| UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Other revenue	51
Other \| US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	0
Other revenue	168
Other \| NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue under IFRS 15	284
Other revenue	275
Generation
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	367
Generation \| UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	0
Generation \| UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	0
Generation \| US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	367
Generation \| NGV and Other
Disclosure of disaggregation of revenue from contracts with customers [line items]
Other revenue	£ 0

Revenue - Narrative (Details)

Revenue - Narrative (Details) - GBP (£)	12 Months Ended
Revenue - Narrative (Details) - GBP (£)	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contract liabilities	£ 994,000,000	£ 866,000,000	£ 0
Weighted average amortisation period	43 years
Future revenues in relation to unfulfilled performance obligations	£ 3,500,000,000
Remaining performance obligation, expected timing of satisfaction, period (years)	5 years
Revenue from performance obligations satisfied or partially satisfied in previous periods	£ 0
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	40 years
Future revenues in relation to unfulfilled performance obligations	£ 1,600,000,000
Remaining performance obligation, expected timing of satisfaction, period (years)	30 years
UK Gas Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	36 years
US Regulated
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	47 years
National Grid Grain LNG Limited
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 1,800,000,000
Remaining performance obligation, expected timing of satisfaction, period (years)	11 years

Operating costs - Analysis of e

Operating costs - Analysis of expenses by nature (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Operating Costs [Line Items]
Depreciation, amortisation and impairment	£ 1,735	£ 1,530	£ 1,481
Payroll costs	1,852	1,648	1,578
Purchases of electricity	1,454	1,285	1,097
Purchases of gas	1,642	1,543	1,219
Rates and property taxes	1,108	1,057	1,042
Balancing Services Incentive Scheme	1,196	1,012	1,120
Payments to other UK network owners	0	1,043	1,008
Other	3,076	2,639	3,282
Operating expense	12,063	11,757	11,827
Inventory consumed	415	367	296
Operating leases	46	51	43
Research and development expenditure	19	13	14
Before exceptional items and remeasurements
Operating Costs [Line Items]
Depreciation, amortisation and impairment	1,588	1,530	1,481
Payroll costs	1,703	1,648	1,578
Purchases of electricity	1,504	1,299	1,143
Purchases of gas	1,644	1,539	1,241
Rates and property taxes	1,108	1,057	1,042
Balancing Services Incentive Scheme	1,196	1,012	1,120
Payments to other UK network owners	0	1,043	1,008
Other	2,748	2,665	2,649
Operating expense	11,491	11,793	11,262
Exceptional items and remeasurements
Operating Costs [Line Items]
Depreciation, amortisation and impairment	147	0	0
Payroll costs	149	0	0
Purchases of electricity	(50)	(14)	(46)
Purchases of gas	(2)	4	(22)
Rates and property taxes	0	0	0
Balancing Services Incentive Scheme	0	0	0
Payments to other UK network owners	0	0	0
Other	328	(26)	633
Operating expense	£ 572	£ (36)	£ 565

Operating costs - Payroll costs

Operating costs - Payroll costs (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Analysis of income and expense [abstract]
Wages and salaries	£ 2,084	£ 1,998	£ 1,852
Social security costs	156	157	145
Defined contribution scheme costs	72	65	58
Defined benefit pension costs	232	156	151
Share-based payments	27	16	32
Severance costs (excluding pension costs)	76	7	5
Payroll costs including capitalised costs	2,647	2,399	2,243
Less: payroll costs capitalised	(795)	(751)	(665)
Total payroll costs	1,852	1,648	1,578
US other post retirement benefit costs	£ 48	£ 46	£ 53

Operating costs - Number of emp

Operating costs - Number of employees (Details) - employee	12 Months Ended
Operating costs - Number of employees (Details) - employee	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of operating segments [line items]
Number of employees, year end	22,576	23,023	22,132
Average number of employees	22,896	22,705	22,043
UK
Disclosure of operating segments [line items]
Number of employees, year end	5,962	6,517	6,265
Average number of employees	6,227	6,431	6,291
US
Disclosure of operating segments [line items]
Number of employees, year end	16,614	16,506	15,867
Average number of employees	16,669	16,274	15,752

Operating costs - Key managemen

Operating costs - Key management personnel (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Analysis of income and expense [abstract]
Short-term employee benefits	£ 7	£ 8	£ 8
Post-employment benefits	1	1	1
Share-based payments	3	3	6
Total key management compensation	£ 11	£ 12	£ 15

Operating costs - Auditors remu

Operating costs - Auditors remuneration (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Analysis of income and expense [abstract]
Audit of the Parent Company’s individual and consolidated financial statements	£ 1.6	£ 2.7	£ 1.5
The auditing of accounts of any associate of the Company	7.2	9.3	13.7
Other services supplied	5.2	3.9	4.6
Auditor's remuneration for audit services	14	15.9	19.8
Tax compliance services	0	0.3	0.4
Tax advisory services	0	0	0.1
Other assurance services	1.1	0.7	4.6
Services relating to corporate finance transactions not covered above	0	0	5.9
Other non-audit services not covered above	2.2	0.9	6.3
Auditor's remuneration for tax and other services	3.3	1.9	17.3
Total auditors’ remuneration	£ 17.3	£ 17.8	£ 37.1

Exceptional items and remeasu_3

Exceptional items and remeasurements (Details) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
	Sep. 30, 2018	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Disclosure of associates [line items]
Massachusetts Gas labour dispute		£ (1,852)	£ (1,648)		£ (1,578)
Operating profit		2,870	3,493	[1]	3,208
Finance income and costs		(1,069)	(882)		(1,087)
Profit before tax		1,841	2,660		2,184
Tax expense (income) on exceptional items and remeasurements		(339)	889		(374)
Profit after tax from continuing operations		1,502	3,549	[2]	1,810
Exceptional items and remeasurements
Disclosure of associates [line items]
Massachusetts Gas labour dispute		(149)	0		0
Operating profit		(572)	36		(565)
Net (losses)/gains on derivative financial instruments		(40)	119		(58)
Net gains on financial assets at fair value through profit and loss		15	0		0
Net losses on financial liabilities at fair value through profit and loss		(51)	0		0
Finance income and costs		(76)	119		(58)
Deferred tax arising on the reduction in US corporation tax rate		0	5		0
Profit before tax		(648)	160		(623)
Tax expense (income) on exceptional items and remeasurements		149	1,473		292
Profit after tax from continuing operations		(499)	1,633		(331)
Exceptional items
Disclosure of associates [line items]
Cost efficiency and restructuring programmes	£ (127)	(204)	0		0
Massachusetts Gas labour dispute		(283)	0		0
Impairment of nuclear connection development costs		(137)	0		0
Final settlement of LIPA MSA Transition		0	26		0
Environmental charges		0	0		(526)
Gas holder demolition costs		0	0		(107)
Operating profit		(624)	26		(633)
Deferred tax expense arising from reduction in UK tax rate		0	0		94
Deferred tax expense arising from reduction in US tax rate		0	1,510		0
Tax expense (income) on exceptional items and remeasurements		144	(9)		227
Profit after tax from continuing operations		(480)	1,532		(312)
Remeasurements
Disclosure of associates [line items]
Net gains on financial assets at fair value through profit and loss		15	0		0
Net losses on financial liabilities at fair value through profit and loss		(51)	0		0
Finance income and costs		(76)	119		(58)
Tax expense (income) on exceptional items and remeasurements		5	(28)		(29)
Profit after tax from continuing operations		(19)	101		(19)
Remeasurements \| Commodity contract derivatives
Disclosure of associates [line items]
Operating profit		£ 52	£ 10		£ 68

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[2]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Exceptional items and remeasu_4

Exceptional items and remeasurements - Narrative (Details)	1 Months Ended	6 Months Ended		12 Months Ended
Exceptional items and remeasurements - Narrative (Details)	Jan. 31, 2019union	Mar. 31, 2019GBP (£)	Sep. 30, 2018GBP (£)	Mar. 31, 2019GBP (£)settlementcancellation	Mar. 31, 2018GBP (£)	Mar. 31, 2017GBP (£)	Jun. 25, 2018employee
Disclosure of other provisions [line items]
Massachusetts Gas work continuation				£ 1,852,000,000	£ 1,648,000,000	£ 1,578,000,000
Impairment of nuclear connection development costs				19,000,000	£ 13,000,000	14,000,000
Cash received from legal settlements				£ 95,000,000
Number of legal settlements \| settlement				2
Number of employees (employee) \| employee							1,250
Number of unions (union) \| union	2
Remediation costs gross undiscounted						£ 481,000,000
Real discount rate					1.00%	2.00%
Other provisions		£ 2,199,000,000		£ 2,199,000,000	£ 2,052,000,000	£ 2,588,000,000
Provision for decommissioning, demolition of gas holders
Disclosure of other provisions [line items]
Other provisions		90,000,000		90,000,000	104,000,000	107,000,000
Exceptional items
Disclosure of other provisions [line items]
Massachusetts Gas work continuation				283,000,000	0	0
Cost efficiency and restructuring programmes			£ 127,000,000	£ 204,000,000	0	0
Number of nuclear connection cancellations (cancellation) \| cancellation				2
Impairment of nuclear connection development costs				£ 137,000,000
Pension costs			52,000,000	52,000,000	0	0
Payments for restructuring				93,000,000
Payments related to work continuation				£ 320,000,000
Development period of assets (over) (in years)				10 years
Proceeds from termination fees received				£ 13,000,000
Impairment of nuclear connection development costs				137,000,000	0	0
Final settlement of LIPA MSA Transition				£ 0	£ 26,000,000	£ 0
Severance \| Exceptional items
Disclosure of other provisions [line items]
Cost efficiency and restructuring programmes			£ 100,000,000
Severance and lease termination \| Exceptional items
Disclosure of other provisions [line items]
Cost efficiency and restructuring programmes		£ 68,000,000

Finance income and costs - (Det

Finance income and costs - (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Finance Income And Costs [Line Items]
Finance income	£ 88	£ 127	£ 53
Finance costs	(1,157)	(1,009)	(1,140)
Finance income and costs	£ (1,069)	£ (882)	£ (1,087)
Capitalisation rate of borrowing costs eligible for capitalisation	3.90%	4.10%	3.40%
Tax relief on capitalised interest	£ 19	£ 20	£ 18
Net foreign exchange gain (loss) on financing activities	264	(314)	(264)
Before exceptional items and remeasurements
Finance Income And Costs [Line Items]
Bank deposits and other financial assets	54	54	28
Dividends received on equities held at fair value through other comprehensive income	2	0	0
Gains on disposal of available-for-sale investments	0	73	25
Other income	17	0	0
Finance income	73	127	53
Net interest on pensions and other post-retirement benefit obligations	(22)	(65)	(107)
Bank loans and overdrafts	(72)	(87)	(59)
Other borrowings	(970)	(1,030)	(927)
Interest expense on financial liabilities held at fair value through profit and loss	(20)	0	0
Derivatives	(43)	12	(8)
Unwinding of discount on provisions	(74)	(75)	(73)
Other interest	0	(11)	(17)
Less: interest capitalised	135	128	109
Finance costs	(1,066)	(1,128)	(1,082)
Remeasurements
Finance Income And Costs [Line Items]
Finance income	15	0	0
Finance costs	(91)	119	(58)
Net gains on financial assets at fair value through profit and loss	15	0	0
Net losses on financial liabilities held at fair value through profit and loss	(51)	0	0
Derivative designated as hedges for hedge accounting	(37)	49	81
Derivatives not designated as hedges for hedge accounting	(3)	70	(139)
Finance income and costs	£ (76)	£ 119	£ (58)

Tax - Tax charged_(credited) to

Tax - Tax charged/(credited) to the consolidated income statement - continuing operations (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Income Taxes [Line Items]
Tax expense (income), continuing operations	£ 339	£ (889)	£ 374
Before exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Tax expense (income), continuing operations	488	584	666
Exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Tax expense (income), continuing operations	(149)	(1,473)	(292)
Exceptional tax on items not included in profit before tax
Disclosure Of Income Taxes [Line Items]
Tax expense (income), continuing operations	0	(1,510)	(94)
Tax on other exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Tax expense (income), continuing operations	£ (149)	£ 37	£ (198)

Tax - Tax as a percentage of pr

Tax - Tax as a percentage of profit before tax (Details)	12 Months Ended
Tax - Tax as a percentage of profit before tax (Details)	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Income Taxes [Line Items]
Effective tax rate – continuing operations	18.40%	(33.40%)	17.10%
Before exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Effective tax rate – continuing operations	19.60%	23.40%	23.70%

Tax - Tax charges (Details)

Tax - Tax charges (Details) - GBP (£) £ in Millions	12 Months Ended
Tax - Tax charges (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Current tax:
Total current tax from continuing operations	£ 88	£ 193	£ 179
Deferred tax:
Total deferred tax from continuing operations	251	(1,082)	195
Total tax charge/(credit) from continuing operations	339	(889)	374
UK
Current tax:
Corporation tax	132	200	225
Corporate tax adjustment in respect of prior years	(12)	(18)	(47)
Total current tax from continuing operations	120	182	178
Deferred tax:
Deferred tax	27	65	(9)
Deferred tax adjustment in respect of prior years	2	(2)	(18)
Total deferred tax from continuing operations	29	63	(27)
Overseas
Current tax:
Corporation tax	8	15	0
Corporate tax adjustment in respect of prior years	(40)	(4)	1
Total current tax from continuing operations	(32)	11	1
Deferred tax:
Deferred tax	208	(1,155)	224
Deferred tax adjustment in respect of prior years	14	10	(2)
Total deferred tax from continuing operations	£ 222	£ (1,145)	£ 222

Tax - Tax charged_(credited) _2

Tax - Tax charged/(credited) to the consolidated statement of other comprehensive income and equity (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Deferred tax:
Tax charged/(credited) to other comprehensive income and equity	£ 3	£ 495	£ 318
Continuing operations
Current tax:
Available-for-sale investments	0	(11)	6
Investments at fair value through other comprehensive income	0	0	0
Cash flow hedges, Cost of hedging and Own credit reserve	3	0	0
Share-based payments	0	(3)	(4)
Deferred tax:
Available-for-sale investments	0	(18)	8
Investments at fair value through other comprehensive income	0	0	0
Cash flow hedges, Cost of hedging and Own credit reserve	(12)	(4)	20
Remeasurements of gains of pension assets and post-retirement benefit obligations	12	530	277
Share-based payments	0	1	1
Tax charged/(credited) to other comprehensive income and equity	3	495	308
Total tax recognised in the statements of comprehensive income	3	497	311
Total tax relating to share based payments recognised directly in equity	0	(2)	(3)
Discontinued operations
Deferred tax:
Total tax recognised in the statements of comprehensive income	0	0	10
Total tax relating to share based payments recognised directly in equity	£ 0	0	£ 0
Internal Revenue Service (IRS)
Deferred tax:
Remeasurements of gains of pension assets and post-retirement benefit obligations		£ 281

Tax - Effective tax rate reconc

Tax - Effective tax rate reconciliation (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Income Taxes [Line Items]
Applicable tax rate	19.00%	19.00%	20.00%
Profit before tax from continuing operations	£ 1,841	£ 2,660	£ 2,184
Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2018: 19%; 2017: 20%)	350	506	437
Effect of:
Adjustments in respect of prior years	(36)	(14)	(67)
Expenses not deductible for tax purposes	28	21	442
Non-taxable income	(36)	(26)	(425)
Adjustment in respect of foreign tax rates	56	157	104
Other	(20)	(16)	(23)
Total tax charge/(credit) from continuing operations	£ 339	£ (889)	£ 374
Effective tax rate – continuing operations	18.40%	(33.40%)	17.10%
Before exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Profit before tax from continuing operations	£ 2,489	£ 2,500	£ 2,807
Profit before tax from continuing operations multiplied by UK corporation tax rate of 19% (2018: 19%; 2017: 20%)	473	475	561
Effect of:
Adjustments in respect of prior years	(36)	(22)	(67)
Expenses not deductible for tax purposes	22	20	35
Non-taxable income	(36)	(16)	(24)
Adjustment in respect of foreign tax rates	78	153	180
Other	(10)	(19)	(19)
Total tax charge/(credit) from continuing operations	£ 488	£ 584	£ 666
Effective tax rate – continuing operations	19.60%	23.40%	23.70%
Exceptional items and remeasurements
Disclosure Of Income Taxes [Line Items]
Profit before tax from continuing operations	£ (648)	£ 160	£ (623)
Effect of:
Total tax charge/(credit) from continuing operations	(149)	(1,473)	(292)
UK
Effect of:
Deferred tax impact of change in tax rate	(3)	(7)	(94)
UK \| Before exceptional items and remeasurements
Effect of:
Deferred tax impact of change in tax rate	(3)	(7)	0
US
Effect of:
Deferred tax impact of change in tax rate	0	(1,510)	0
US \| Before exceptional items and remeasurements
Effect of:
Deferred tax impact of change in tax rate	£ 0	£ 0	£ 0

Tax - Tax included within the s

Tax - Tax included within the statement of financial position (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2018
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	£ 3,636	£ 4,479
Exchange adjustments and other	165	(268)
(Credited)/charged to income statement	243	(1,084)
Charged/(credited) to other comprehensive income and equity	0	509
Impact of transition to IFRS 9 and IFRS 15			£ (79)
Deferred tax liability (asset) end of period	3,965	3,636
Accelerated tax depreciation £m
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	4,874	7,074
Exchange adjustments and other	275	(559)
(Credited)/charged to income statement	309	(1,641)
Charged/(credited) to other comprehensive income and equity	0	0
Impact of transition to IFRS 9 and IFRS 15			19
Deferred tax liability (asset) end of period	5,477	4,874
Share- based payments £m
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(9)	(12)
Exchange adjustments and other	0	0
(Credited)/charged to income statement	0	2
Charged/(credited) to other comprehensive income and equity	0	1
Impact of transition to IFRS 9 and IFRS 15			0
Deferred tax liability (asset) end of period	(9)	(9)
Pensions and other post- retirement benefits £m
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(203)	(747)
Exchange adjustments and other	(31)	69
(Credited)/charged to income statement	52	(55)
Charged/(credited) to other comprehensive income and equity	12	530
Impact of transition to IFRS 9 and IFRS 15			0
Deferred tax liability (asset) end of period	(170)	(203)
Financial instruments £m
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	21	9
Exchange adjustments and other	(3)	1
(Credited)/charged to income statement	6	12
Charged/(credited) to other comprehensive income and equity	(12)	(1)
Impact of transition to IFRS 9 and IFRS 15			(5)
Deferred tax liability (asset) end of period	7	21
Other net temporary differences
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(1,047)	(1,845)
Exchange adjustments and other	(76)	221
(Credited)/charged to income statement	(124)	598
Charged/(credited) to other comprehensive income and equity	0	(21)
Impact of transition to IFRS 9 and IFRS 15			£ (93)
Deferred tax liability (asset) end of period	(1,340)	(1,047)
Net operating losses
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(390)
(Credited)/charged to income statement		293
Deferred tax liability (asset) end of period	(423)	(390)
Environmental provisions
Reconciliation of changes in deferred tax liability (asset) [abstract]
Deferred tax liability (asset) beginning of period	(378)
Deferred tax liability (asset) end of period	£ (409)	(378)
Internal Revenue Service (IRS) \| Other net temporary differences
Reconciliation of changes in deferred tax liability (asset) [abstract]
Exchange adjustments and other		£ 43

Tax - Narrative (Details)

Tax - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
Tax - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2018	Mar. 31, 2017
Disclosure Of Income Taxes [Line Items]
Deferred tax liability (asset)	£ 3,965	£ 3,636	£ 3,557	£ 4,479
Deferred tax assets	423	390
(Credited)/charged to income statement	243	(1,084)
Net operating losses
Disclosure Of Income Taxes [Line Items]
Deferred tax liability (asset)	£ (423)	(390)
(Credited)/charged to income statement		£ 293

Tax - Deferred tax assets not r

Tax - Deferred tax assets not recognised (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Capital losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused tax losses for which no deferred tax asset recognised	£ 1,470	£ 510
Non-trade deficits
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused tax losses for which no deferred tax asset recognised	4	4
Trading losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Unused tax losses for which no deferred tax asset recognised	£ 5	£ 4

Earnings per share (EPS) - Narr

Earnings per share (EPS) - Narrative (Details) £ in Millions	Jun. 02, 2017GBP (£)	May 22, 2017	Mar. 31, 2019GBP (£)	Mar. 31, 2018GBP (£)	Mar. 31, 2017GBP (£)
Summary Of Dividends [Line Items]
Dividends paid			£ 1,160	£ 4,487	£ 1,463
Stock consolidation ratio		0.9167
Special dividend
Summary Of Dividends [Line Items]
Dividends paid	£ 3,171		£ 0	£ 3,171	£ 0

Earnings per share (EPS) - Sche

Earnings per share (EPS) - Schedule of earnings per share (Details) - GBP (£) £ / shares in Units, £ in Millions, shares in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Earnings per share [line items]
Basic earnings from continuing operations	£ 1,499	£ 3,548	£ 1,810
Basic earnings from discontinued operations	12	2	5,985
Basic total earnings	£ 1,511	£ 3,550	£ 7,795
Basic EPS (continuing) (in GBP per share)	£ 0.443	£ 1.025	£ 0.481
Basic EPS (discontinuing) (in GBP per share)	0.003	0.001	1.590
Total basic earnings per share (in GBP per share)	£ 0.446	£ 1.026	£ 2.071
Weighted average number of shares – basic (in shares)	3,386	3,461	3,763
Diluted earnings from continuing operations	£ 1,499	£ 3,548	£ 1,810
Diluted earnings from discontinued operations	12	2	5,985
Diluted total earnings	£ 1,511	£ 3,550	£ 7,795
Diluted EPS (continuing) (in GBP per share)	£ 0.441	£ 1.021	£ 0.479
Diluted EPS (discontinuing) (in GBP per share)	0.003	0	1.583
Diluted EPS (in GBP per share)	£ 0.444	£ 1.021	£ 2.062
Weighted average number of shares – diluted (in shares)	3,401	3,476	3,780
Weighted average number of shares – basic (in shares)	3,386	3,461	3,763
Effect of dilutive potential ordinary shares – employee share plans (in shares)	15	15	17
Weighted average number of shares – diluted (in shares)	3,401	3,476	3,780
Before exceptional items and remeasurements
Earnings per share [line items]
Basic earnings from continuing operations	£ 1,998	£ 1,915	£ 2,141
Basic earnings from discontinued operations	57	145	607
Basic total earnings	£ 2,055	£ 2,060	£ 2,748
Basic EPS (continuing) (in GBP per share)	£ 0.590	£ 0.553	£ 0.569
Basic EPS (discontinuing) (in GBP per share)	0.017	0.042	0.161
Total basic earnings per share (in GBP per share)	£ 0.607	£ 0.595	£ 0.730
Diluted earnings from continuing operations	£ 1,998	£ 1,915	£ 2,141
Diluted earnings from discontinued operations	57	145	607
Diluted total earnings	£ 2,055	£ 2,060	£ 2,748
Diluted EPS (continuing) (in GBP per share)	£ 0.588	£ 0.551	£ 0.567
Diluted EPS (discontinuing) (in GBP per share)	0.017	0.042	0.160
Diluted EPS (in GBP per share)	£ 0.605	£ 0.593	£ 0.727
Exceptional items and remeasurements
Earnings per share [line items]
Basic earnings from continuing operations	£ (499)	£ 1,633	£ (331)
Basic earnings from discontinued operations	(45)	(143)	5,378
Basic total earnings	£ (544)	£ 1,490	£ 5,047
Basic EPS (continuing) (in GBP per share)	£ (0.147)	£ 0.472	£ (0.088)
Basic EPS (discontinuing) (in GBP per share)	(0.014)	(0.041)	1.429
Total basic earnings per share (in GBP per share)	£ (0.161)	£ 0.431	£ 1.341
Diluted earnings from continuing operations	£ (499)	£ 1,633	£ (331)
Diluted earnings from discontinued operations	(45)	(143)	5,378
Diluted total earnings	£ (544)	£ 1,490	£ 5,047
Diluted EPS (continuing) (in GBP per share)	£ (0.147)	£ 0.470	£ (0.088)
Diluted EPS (discontinuing) (in GBP per share)	(0.014)	(0.042)	1.423
Diluted EPS (in GBP per share)	£ (0.161)	£ 0.428	£ 1.335

Dividends (Details)

Dividends (Details) - GBP (£) £ / shares in Units, £ in Millions	Jun. 02, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)		£ 0.4652	£ 1.28965	£ 0.4351
Dividends paid		£ 1,160	£ 4,487	£ 1,463
Scrip dividend		£ 413	£ 209	£ 183
Interim dividend in respect of the current year
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)		£ 0.1608	£ 0.1549	£ 0.1517
Dividends paid		£ 450	£ 346	£ 540
Scrip dividend		£ 94	£ 176	£ 32
Special dividend
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)	£ 0.84375	£ 0	£ 0.84375	£ 0
Dividends paid	£ 3,171	£ 0	£ 3,171	£ 0
Scrip dividend		£ 0	£ 0	£ 0
Final dividend in respect of the prior year
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share)		£ 0.3044	£ 0.2910	£ 0.2834
Dividends paid		£ 710	£ 970	£ 923
Scrip dividend		£ 319	£ 33	£ 151

Dividends - Narrative (Details)

Dividends - Narrative (Details) £ / shares in Units, £ in Millions	Jun. 02, 2017GBP (£)£ / shares	Jun. 02, 2017$ / shares	Mar. 31, 2019GBP (£)£ / shares	Mar. 31, 2018GBP (£)£ / shares	Mar. 31, 2017GBP (£)£ / shares
Summary Of Dividends [Line Items]
Dividends declared before financial statements authorised for issue (GBP per share) \| £ / shares			£ 0.3126
Dividends declared before financial statements authorised for issue \| £			£ 1,066
Cash dividends paid (GBP per share) \| £ / shares			£ 0.4652	£ 1.28965	£ 0.4351
Cash dividends paid, special dividend \| £			£ 1,160	£ 4,487	£ 1,463
Special dividend
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share) \| £ / shares	£ 0.84375		£ 0	£ 0.84375	£ 0
Cash dividends paid, special dividend \| £	£ 3,171		£ 0	£ 3,171	£ 0
Special dividend - American Depositary Share
Summary Of Dividends [Line Items]
Cash dividends paid (GBP per share) \| $ / shares		$ 5.4224

Discontinued operations and a_3

Discontinued operations and assets held for sale - Narrative (Details) - GBP (£)		Mar. 31, 2019	May 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Disclosure of subsidiaries [line items]
Derivative assets		£ 1,153,000,000		£ 1,724,000,000		£ 1,153,000,000	£ 1,724,000,000
Impairment charge against investment in Quadgas						43,000,000	213,000,000
Purchase of interests in investments accounted for using equity method						143,000,000	129,000,000	[1]	£ 76,000,000
Net cash (used in)/inflow from operating activities – discontinued operations						(71,000,000)	(207,000,000)	[1]	909,000,000
Net cash flow from investing activities – discontinued operations	[2]					156,000,000	171,000,000	[1]	(680,000,000)
Net cash flow (used in)/from financing activities – discontinued operations						0	(231,000,000)	[1]	1,611,000,000
Proceeds from borrowings						2,932,000,000	1,941,000,000	[1]	2,463,000,000
Repayments of borrowings						£ 1,969,000,000	£ 2,156,000,000	[1]	1,616,000,000
UK Gas Distribution (Cadent)
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed					61.00%		61.00%
Proportion of ownership interest in associate					39.00%	39.00%
Proportion of ownership interest in associate, put/call option equity interest					14.00%
Proportion of ownership interest in associate, excluding put/call option equity interest			25.00%			25.00%
Quadgas HoldCo Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest in associate		39.00%				39.00%
Proportion of ownership interest in associate, put/call option equity interest						14.00%	14.00%
Proportion of ownership interest in associate, excluding put/call option equity interest						25.00%
Receivables due from associates		£ 352,000,000		352,000,000		£ 352,000,000	£ 352,000,000
Impairment charge against investment in Quadgas				213,000,000		43,000,000
Purchase of interests in investments accounted for using equity method						2,000,000,000	2,100,000,000
Investments in associates		1,500,000,000		1,600,000,000		1,500,000,000	£ 1,600,000,000
Xoserve Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest disposed							45.00%
Discontinued operations
Disclosure of subsidiaries [line items]
Net cash flow from investing activities – discontinued operations						156,000,000	£ 171,000,000
Net cash flow (used in)/from financing activities – discontinued operations							231,000,000
Proceeds from borrowings									4,800,000,000
Repayments of borrowings									£ 3,200,000,000
Discontinued operations \| UK Gas Distribution
Disclosure of subsidiaries [line items]
Net cash (used in)/inflow from operating activities – discontinued operations						(71,000,000)	(207,000,000)
Put, Call Option, Derivatives, RAA And FAA
Disclosure of subsidiaries [line items]
Derivative assets		110,000,000		110,000,000		110,000,000	110,000,000
RAA derivative
Disclosure of subsidiaries [line items]
Derivative assets		0				0
Notional amount		1,087,000,000				1,087,000,000
FAA derivative
Disclosure of subsidiaries [line items]
Derivative assets		110,000,000				110,000,000
Notional amount		£ 739,000,000		£ 739,000,000		£ 739,000,000	£ 739,000,000

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[2]	Receipts of dividends from Quadgas HoldCo Limited of £133 million (2018: £144 million) and interest of £23 million (2018: £27 million).

Discontinued operations and a_4

Discontinued operations and assets held for sale - Summary income statement (Details) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Summary income statement and comprehensive income, discontinued operations [line items]
Share of post-tax results of joint ventures and associates		£ 40	£ 49		£ 63
Gain on disposal of UK Gas Distribution after tax					5,321
Total profit after tax from discontinued operations		12	2		5,984
Items that will never be reclassified to profit or loss:
Remeasurement losses on pension assets and post-retirement benefit obligations		68	1,313	[1]	423
Tax on items that will never be reclassified to profit or loss		(15)	(530)	[1]	(277)
Total items that will never be reclassified to profit or loss		47	783	[1]	146
Items that may be reclassified subsequently to profit or loss:
Net losses in respect of cash flow hedges		(147)	19	[1]	70
Transferred to profit or loss in respect of cash flow hedges		41	(3)	[1]	(6)
Share of other comprehensive income of associates, net of tax		1	0	[1]	0
Tax on items that may be reclassified subsequently to profit or loss		12	33	[1]	(34)
Total items from discontinued operations that may be reclassified subsequently to profit or loss		256	(559)	[1]	432
Other comprehensive income for the year, net of tax		339	371	[1]	620
Total comprehensive income for the year		1,853	3,922	[1]	8,414
Impairment charge against investment in Quadgas		43	213
Sales price consideration					7,494
Transaction costs					1,837
Tax credit					312
Net assets on disposal					648
Discontinued operations
Summary income statement and comprehensive income, discontinued operations [line items]
Revenue		0	0		1,887
Operating costs		(1)	(41)		(993)
Operating (loss)/profit		(1)	(41)		894
Net finance income/(costs)		23	137		(152)
Share of post-tax results of joint ventures and associates		(5)	(89)		0
Profit before tax from discontinued operations		17	7		742
Tax from discontinued operations		(5)	(5)		(79)
Profit after tax from discontinued operations		12	2		663
Gain on disposal of UK Gas Distribution after tax		0	0		5,321
Total profit after tax from discontinued operations		12	2		5,984
Items that will never be reclassified to profit or loss:
Remeasurement losses on pension assets and post-retirement benefit obligations		0	0		(75)
Share of other comprehensive income of associate, net of tax		36	142		0
Tax on items that will never be reclassified to profit or loss		0	0		13
Total items that will never be reclassified to profit or loss		36	142		(62)
Items that may be reclassified subsequently to profit or loss:
Net losses in respect of cash flow hedges		0	0		(106)
Transferred to profit or loss in respect of cash flow hedges		0	0		233
Share of other comprehensive income of associates, net of tax		0	5		0
Tax on items that may be reclassified subsequently to profit or loss		0	0		(23)
Total items from discontinued operations that may be reclassified subsequently to profit or loss		0	5		104
Other comprehensive income for the year, net of tax		36	147		42
Total comprehensive income for the year		48	149		£ 6,026
UK Gas Distribution \| Discontinued operations
Summary income statement and comprehensive income, discontinued operations [line items]
Operating costs			£ (41)
Quadgas HoldCo Limited
Items that may be reclassified subsequently to profit or loss:
Impairment charge against investment in Quadgas	£ 213	43
Share of post-tax results of associates		£ 38

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Goodwill - Disclosure of goodwi

Goodwill - Disclosure of goodwill (Details) - Goodwill - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure of reconciliation of changes in intangible assets and goodwill [line items]
Goodwill, beginning balance	£ 5,444	£ 6,096
Exchange adjustments	425	(652)
Goodwill, ending balance	£ 5,869	£ 5,444

Goodwill - Narrative (Details)

Goodwill - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of reconciliation of changes in goodwill [line items]
Growth rate used to extrapolate cash flow projections	2.20%	2.30%
Discount rate applied to cash flow projections	5.30%	5.30%
Goodwill
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	£ 5,869	£ 5,444	£ 6,096
Goodwill \| Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	5,885	5,458
Goodwill \| Accumulated impairment
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	16	14
Goodwill \| New York \| Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	3,382	3,137
Goodwill \| Massachusetts \| Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	1,264	1,173
Goodwill \| Rhode Island \| Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	470	436
Goodwill \| Federal \| Gross carrying amount
Disclosure of reconciliation of changes in goodwill [line items]
Goodwill	£ 753	£ 698

Other intangible assets (Detail

Other intangible assets (Details) - GBP (£) £ in Millions	12 Months Ended
Other intangible assets (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	£ 899
Intangible assets other than goodwill, ending balance	1,084	£ 899
Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	899
Intangible assets other than goodwill, ending balance	£ 1,084	899
US ERP System
Disclosure of detailed information about intangible assets [line items]
Useful lives or amortisation rates, Intangible assets other than goodwill, period	4 years
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	£ 160
Intangible assets other than goodwill, ending balance	116	160
Gross carrying amount \| Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	1,797	1,732
Exchange adjustments	70	(98)
Additions	306	173
Disposals	(15)	(18)
Reclassifications	10	8
Intangible assets other than goodwill, ending balance	2,168	1,797
Accumulated depreciation/amortisation \| Software
Changes in intangible assets other than goodwill [abstract]
Intangible assets other than goodwill, beginning balance	(898)	(809)
Exchange adjustments	(26)	43
Disposals	15	6
Amortisation charge for the year	(175)	(138)
Intangible assets other than goodwill, ending balance	£ (1,084)	£ (898)
Bottom of range \| Software
Disclosure of detailed information about intangible assets [line items]
Useful lives or amortisation rates, Intangible assets other than goodwill, period	3 years
Top of range \| Software
Disclosure of detailed information about intangible assets [line items]
Useful lives or amortisation rates, Intangible assets other than goodwill, period	10 years

Property, plant and equipment -

Property, plant and equipment - Disclosure of property plant and equipment (Details) - GBP (£)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	£ 39,853,000,000
Property, plant and equipment, ending balance	43,913,000,000	£ 39,853,000,000
Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	57,434,000,000	56,995,000,000
Exchange adjustments	2,232,000,000	(3,187,000,000)
Additions	4,015,000,000	3,901,000,000
Disposals	(595,000,000)	(287,000,000)
Reclassifications	(10,000,000)	12,000,000
Property, plant and equipment, ending balance	63,076,000,000	57,434,000,000
Property, plant and equipment, assets retired from active use and not classified as held for sale		51,000,000
Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(17,581,000,000)	(17,170,000,000)
Exchange adjustments	(545,000,000)	759,000,000
Disposals	536,000,000	242,000,000
Reclassifications	0	(20,000,000)
Depreciation charge for the year	(1,573,000,000)	(1,392,000,000)
Property, plant and equipment, ending balance	(19,163,000,000)	(17,581,000,000)
Property, plant and equipment, assets retired from active use and not classified as held for sale		51,000,000
Land and buildings
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	2,256,000,000
Property, plant and equipment, ending balance	2,560,000,000	2,256,000,000
Land and buildings \| Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	2,930,000,000	2,979,000,000
Exchange adjustments	114,000,000	(169,000,000)
Additions	34,000,000	38,000,000
Disposals	(35,000,000)	(16,000,000)
Reclassifications	295,000,000	98,000,000
Property, plant and equipment, ending balance	3,338,000,000	2,930,000,000
Land and buildings \| Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(674,000,000)	(684,000,000)
Exchange adjustments	(19,000,000)	28,000,000
Disposals	7,000,000	10,000,000
Reclassifications	1,000,000	0
Depreciation charge for the year	(93,000,000)	(28,000,000)
Property, plant and equipment, ending balance	(778,000,000)	(674,000,000)
Plant and machinery
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	32,976,000,000
Property, plant and equipment, ending balance	36,589,000,000	32,976,000,000
Plant and machinery \| Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	49,374,000,000	49,231,000,000
Exchange adjustments	2,001,000,000	(2,862,000,000)
Additions	391,000,000	430,000,000
Disposals	(357,000,000)	(216,000,000)
Reclassifications	2,974,000,000	2,791,000,000
Property, plant and equipment, ending balance	54,383,000,000	49,374,000,000
Plant and machinery \| Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(16,398,000,000)	(15,996,000,000)
Exchange adjustments	(501,000,000)	695,000,000
Disposals	335,000,000	199,000,000
Reclassifications	(1,000,000)	(20,000,000)
Depreciation charge for the year	(1,229,000,000)	(1,276,000,000)
Property, plant and equipment, ending balance	(17,794,000,000)	(16,398,000,000)
Assets in the course of construction
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	4,273,000,000
Property, plant and equipment, ending balance	4,425,000,000	4,273,000,000
Property, plant and equipment, expenditures recognised in course of its construction	150,000,000	0
Proceeds from termination fees received	13,000,000
Assets in the course of construction \| Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	4,273,000,000	3,951,000,000
Exchange adjustments	70,000,000	(89,000,000)
Additions	3,533,000,000	3,358,000,000
Disposals	(159,000,000)	(21,000,000)
Reclassifications	(3,292,000,000)	(2,926,000,000)
Property, plant and equipment, ending balance	4,425,000,000	4,273,000,000
Assets in the course of construction \| Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	0	0
Exchange adjustments	0	0
Disposals	150,000,000	0
Reclassifications	0	0
Depreciation charge for the year	(150,000,000)	0
Property, plant and equipment, ending balance	0	0
Motor vehicles and office equipment
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	348,000,000
Property, plant and equipment, ending balance	339,000,000	348,000,000
Motor vehicles and office equipment \| Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	857,000,000	834,000,000
Exchange adjustments	47,000,000	(67,000,000)
Additions	57,000,000	75,000,000
Disposals	(44,000,000)	(34,000,000)
Reclassifications	13,000,000	49,000,000
Property, plant and equipment, ending balance	930,000,000	857,000,000
Motor vehicles and office equipment \| Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(509,000,000)	(490,000,000)
Exchange adjustments	(25,000,000)	36,000,000
Disposals	44,000,000	33,000,000
Reclassifications	0	0
Depreciation charge for the year	(101,000,000)	(88,000,000)
Property, plant and equipment, ending balance	£ (591,000,000)	(509,000,000)
KeySpan \| Cost
Changes in property, plant and equipment [abstract]
Disposals		(334,000,000)
KeySpan \| Accumulated depreciation/amortisation
Changes in property, plant and equipment [abstract]
Disposals		£ (334,000,000)

Property, plant and equipment_2

Property, plant and equipment - Other Disclosures (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Recognised finance lease as assets	£ 241	£ 253
Additions to recognised finance lease as assets	£ 38	58
Bottom of range \| Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	10 years
Bottom of range \| Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	29 years
Bottom of range \| Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	15 years
Bottom of range \| Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	5 years
Bottom of range \| Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	10 years
Bottom of range \| Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	5 years
Bottom of range \| Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	7 years
Top of range \| Land and buildings
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	103 years
Top of range \| Motor vehicles and office equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	30 years
Top of range \| Electricity transmission plant and wires
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	100 years
Top of range \| Electricity distribution plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	85 years
Top of range \| Electricity generation plant
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	93 years
Top of range \| Interconnector plant and other
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	65 years
Top of range \| Gas plant – mains, services and regulating equipment
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	95 years
Top of range \| Gas plant – storage
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	65 years
Top of range \| Gas plant – meters
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment, period	62 years
Property, plant and equipment \| Cost
Disclosure of detailed information about property, plant and equipment [line items]
Interest costs capitalised	£ 1,995	1,861
Trade and other payables
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	87	85
Non-current liabilities
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	372	844
Contract liabilities – current
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	61	0
Contract liabilities – non-current
Disclosure of detailed information about property, plant and equipment [line items]
Contributions to cost of property, plant and equipment	£ 933	£ 0

Other non-current assets (Detai

Other non-current assets (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Other receivables	£ 28		£ 36
Non-current tax assets	56		51
Prepayments and accrued income	180		28
Other non-current assets	£ 264	£ 115	£ 115

Financial and other investmen_3

Financial and other investments - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Disclosure of financial assets [abstract]
Financial and other investments	£ 2,648	£ 3,593

Financial and other investmen_4

Financial and other investments - Schedule of financial assets (Details) - GBP (£)	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of associates [line items]
Debt investments at fair value through other comprehensive income	£ 343,000,000		£ 0
Equity investments at fair value through other comprehensive income	93,000,000		0
Investments at fair value through profit and loss, non-current	62,000,000		0
Available-for-sale investments, non-current	0		417,000,000
Loans to joint ventures and associates, non-current	169,000,000		482,000,000
Other non-current financial assets	667,000,000	£ 899,000,000	899,000,000
Investments at fair value through profit and loss, current	1,311,000,000		0
Available-for-sale investments, current	0		2,304,000,000
Other loans and receivables, current	670,000,000		390,000,000
Other current financial assets	1,981,000,000	£ 2,694,000,000	2,694,000,000	£ 8,741,000,000	£ 2,998,000,000
Other financial assets	2,648,000,000		3,593,000,000
Managed investments in equity and bonds, restricted	342,000,000		301,000,000
Managed investments in equity and bonds, US non-qualified plan	436,000,000		411,000,000
Quadgas HoldCo Limited
Disclosure of associates [line items]
Receivables due from associates	352,000,000		352,000,000
Investments in short-term money funds
Disclosure of associates [line items]
Other financial assets	969,000,000		1,999,000,000
Insurance company fund investments
Disclosure of associates [line items]
Other financial assets	342,000,000		301,000,000
Short term investments, restricted	6,000,000		69,000,000
Equities
Disclosure of associates [line items]
Other financial assets	93,000,000		84,000,000
Bonds
Disclosure of associates [line items]
Other financial assets	122,000,000		145,000,000
Cash surrender value of life insurance policies
Disclosure of associates [line items]
Other financial assets	221,000,000		198,000,000
Loans to joint ventures and associates
Disclosure of associates [line items]
Other financial assets	169,000,000		482,000,000
Corporate ventures capital and other
Disclosure of associates [line items]
Other financial assets	62,000,000		0
Restricted balances - collateral
Disclosure of associates [line items]
Other financial assets	637,000,000		335,000,000
Restricted balances - other
Disclosure of associates [line items]
Other financial assets	33,000,000		49,000,000
U.S. Non-Qualified Plan Investments
Disclosure of associates [line items]
Short term investments, restricted	£ 22,000,000		£ 0

Investments in joint ventures_3

Investments in joint ventures and associates - Share of net assets, joint ventures and associates (Details) - GBP (£) £ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	£ 608	£ 2,168	£ 2,083
Exchange adjustments		11	(12)
Additions		143	129
Capitalisation of shareholder loan to Quadgas		0	69
Impairment charge against investment in Quadgas		(43)	(213)
Transfer of interest in Quadgas to assets held for sale		(1,625)	0
Share of post-tax results for the year		78	173
Share of other comprehensive income of associates, net of tax		37	147
Dividends received		(68)	(213)
Other movements		(93)	5
Investments accounted for using equity method, ending balance		608	2,168
Joint ventures
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	£ 317	361	307
Exchange adjustments		(6)	7
Additions		85	64
Capitalisation of shareholder loan to Quadgas		0	0
Impairment charge against investment in Quadgas		0	0
Transfer of interest in Quadgas to assets held for sale		0	0
Share of post-tax results for the year		11	26
Share of other comprehensive income of associates, net of tax		0	0
Dividends received		(30)	(43)
Other movements		(104)	0
Investments accounted for using equity method, ending balance		317	361
St William Homes LLP
Disclosure of joint ventures [line items]
Deferred income recognition period remaining	10 years
Associates
Disclosure of joint ventures [line items]
Investments accounted for using equity method, beginning balance	£ 291	1,807	1,776
Exchange adjustments		17	(19)
Additions		58	65
Capitalisation of shareholder loan to Quadgas		0	69
Impairment charge against investment in Quadgas		(43)	(213)
Transfer of interest in Quadgas to assets held for sale		(1,625)	0
Share of post-tax results for the year		67	147
Share of other comprehensive income of associates, net of tax		37	147
Dividends received		(38)	(170)
Other movements		11	5
Investments accounted for using equity method, ending balance		£ 291	£ 1,807

Investments in joint ventures_4

Investments in joint ventures and associates - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Disclosure of joint ventures [line items]
Purchase of interests in investments accounted for using equity method		£ 143	£ 129	[1]	£ 76
Share of post-tax results of joint ventures and associates		40	49		£ 63
Joint ventures
Disclosure of joint ventures [line items]
Capital commitments	£ 18	18	120
BritNed Development Limited
Disclosure of joint ventures [line items]
Share of post-tax results of joint ventures and associates		£ 27	36
Proportion of ownership interest in joint venture	50.00%	50.00%
Partnership Vehicle with Sunrun
Disclosure of joint ventures [line items]
Purchase of interests in investments accounted for using equity method		£ 6	38
Share of post-tax results of joint ventures and associates		8	7
Millennium Pipeline Company LLC
Disclosure of joint ventures [line items]
Share of post-tax results of joint ventures and associates		£ 25	21
Proportion of ownership interest in associate	26.25%	26.25%
Quadgas HoldCo Limited
Disclosure of joint ventures [line items]
Purchase of interests in investments accounted for using equity method		£ 2,000	£ 2,100
Proportion of ownership interest in associate	39.00%	39.00%

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Investments in joint ventures_5

Investments in joint ventures and associates - Summarised financial information, joint venture and associate (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017		Apr. 01, 2018	Mar. 31, 2016
Disclosure of joint ventures [line items]
Non-current assets	£ 55,017	£ 52,106				£ 52,106
Cash and cash equivalents	252	329	[1]	£ 1,139	[1]	329	£ 124
Non-current liabilities	(34,465)	(31,242)				(31,441)
Current liabilities	(9,129)	(8,697)				(8,691)
Net assets	19,369	18,848				£ 18,652
Revenue	14,933	15,250		15,035
Other costs	(3,076)	(2,639)		(3,282)
Operating profit	2,870	3,493	[1]	3,208
Tax	(339)	889		(374)
Profit after tax from continuing operations	1,502	3,549	[2]	1,810
Group’s share of profit	40	49		£ 63
Millennium Pipeline Company LLC
Disclosure of joint ventures [line items]
Non-current assets	937	709
Cash and cash equivalents	35	15
All other current assets	22	28
Non-current liabilities	(326)	(331)
Current liabilities	(84)	(64)
Net assets	584	357
Carrying amount of the Group’s investment	153	94
Revenue	166	151
Depreciation and amortisation	(34)	(31)
Other costs	(35)	(41)
Operating profit	97	79
Tax	0	0
Profit after tax from continuing operations	97	79
Group’s share of profit	25	21
BritNed Development Limited
Disclosure of joint ventures [line items]
Non-current assets	370	390
Cash and cash equivalents	59	50
All other current assets	2	4
Non-current liabilities	(11)	(10)
Current liabilities	(28)	(28)
Net assets	392	406
Carrying amount of the Group’s investment	196	203
Revenue	87	121
Depreciation and amortisation	(13)	(13)
Other costs	(10)	(16)
Operating profit	64	92
Tax	(10)	(20)
Profit after tax from continuing operations	54	72
Group’s share of profit	£ 27	£ 36

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[2]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Derivative financial instrume_3

Derivative financial instruments - Derivative financial instruments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 1,153	£ 1,724
Derivative liabilities	(1,183)	(1,061)
Total	(30)	663
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	1,052	1,545
Derivative liabilities	(1,084)	(945)
Total	(32)	600
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	101	69
Derivative liabilities	(99)	(116)
Total	2	(47)
Further Acquisition Agreement derivative
Disclosure of detailed information about financial instruments [line items]
Derivative assets	0	110
Derivative liabilities	0	0
Total	£ 0	£ 110
Quadgas HoldCo Limited
Disclosure of detailed information about financial instruments [line items]
Proportion of ownership interest in associate, put/call option equity interest	14.00%	14.00%

Derivative financial instrume_4

Derivative financial instruments - Financing derivatives (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 1,153	£ 1,724
Derivative liabilities	(1,183)	(1,061)
Total	(30)	663
Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	1,052	1,545
Derivative liabilities	(1,084)	(945)
Total	(32)	600
Derivative notional amount	(17,236)	(23,099)
Interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	539	678
Derivative liabilities	(384)	(457)
Total	155	221
Derivative notional amount	(6,299)	(8,390)
Cross-currency interest rate swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	470	687
Derivative liabilities	(443)	(207)
Total	27	480
Derivative notional amount	(6,700)	(6,925)
Foreign exchange forward contracts
Disclosure of detailed information about financial instruments [line items]
Derivative assets	41	174
Derivative liabilities	(41)	(2)
Total	0	172
Derivative notional amount	(2,937)	(5,793)
Inflation-linked swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	0	5
Derivative liabilities	(214)	(278)
Total	(214)	(273)
Derivative notional amount	(500)	(1,191)
Equity options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	2	1
Derivative liabilities	(2)	(1)
Total	0	0
Derivative notional amount	(800)	(800)
Less than 1 year \| Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	56	375
Derivative liabilities	(282)	(325)
Total	(226)	50
Later than one year \| Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	996	1,170
Derivative liabilities	(802)	(620)
Total	194	550
In 1 to 2 years \| Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	19	83
Derivative liabilities	(193)	(88)
Total	(174)	(5)
In 2 to 3 years \| Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	416	25
Derivative liabilities	(1)	(27)
Total	415	(2)
In 3 to 4 years \| Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	11	418
Derivative liabilities	0	(5)
Total	11	413
In 4 to 5 years \| Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	20	12
Derivative liabilities	(14)	0
Total	6	12
More than 5 years \| Financing derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	530	632
Derivative liabilities	(594)	(500)
Total	(64)	132
Capital Expenditure \| Foreign exchange forward contracts
Disclosure of detailed information about financial instruments [line items]
Total	£ 32	£ 67

Derivative financial instrume_5

Derivative financial instruments - Commodity derivatives (Details) £ in Millions	12 Months Ended
	Mar. 31, 2019GBP (£)GW / moGW / hMMBTU	Mar. 31, 2018GBP (£)GW / moGW / hMMBTU
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 1,153	£ 1,724
Derivative liabilities	(1,183)	(1,061)
Total	(30)	663
Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	101	69
Derivative liabilities	(99)	(116)
Total	2	(47)
Forward purchases of gas
Disclosure of detailed information about financial instruments [line items]
Derivative assets	66	60
Derivative liabilities	(78)	(64)
Total	£ (12)	£ (4)
Derivative non-monetary notional amount \| MMBTU	52	54
Derivative term	2 years
Derivative contractual amount	£ 108	£ 96
Electricity capacity
Disclosure of detailed information about financial instruments [line items]
Derivative assets	0	1
Derivative liabilities	0	0
Total	£ 0	£ 1
Derivative non-monetary notional amount \| GW / mo	0	0.6
Electricity swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 29	£ 7
Derivative liabilities	(19)	(46)
Total	£ 10	£ (39)
Derivative non-monetary notional amount \| GW / h	12,848	12,839
Electricity options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 0	£ 0
Derivative liabilities	0	(1)
Total	£ 0	£ (1)
Derivative non-monetary notional amount \| GW / h	10,444	13,897
Gas swaps
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 5	£ 1
Derivative liabilities	(1)	(4)
Total	£ 4	£ (3)
Derivative non-monetary notional amount \| MMBTU	87	100
Gas options
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 1	£ 0
Derivative liabilities	(1)	(1)
Total	£ 0	£ (1)
Derivative non-monetary notional amount \| MMBTU	34	7
Less than 1 year \| Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	£ 52	£ 30
Derivative liabilities	(68)	(76)
Total	(16)	(46)
Later than one year \| Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	49	39
Derivative liabilities	(31)	(40)
Total	18	(1)
In 1 to 2 years \| Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	14	6
Derivative liabilities	(9)	(17)
Total	5	(11)
In 2 to 3 years \| Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	9	6
Derivative liabilities	(8)	(11)
Total	1	(5)
In 3 to 4 years \| Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	6	6
Derivative liabilities	(4)	(3)
Total	2	3
In 4 to 5 years \| Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	6	5
Derivative liabilities	(4)	(2)
Total	2	3
More than 5 years \| Commodity contract derivatives
Disclosure of detailed information about financial instruments [line items]
Derivative assets	14	16
Derivative liabilities	(6)	(7)
Total	£ 8	£ 9

Inventories and other current_3

Inventories and other current intangibles (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Fuel stocks	£ 99	£ 78
Raw materials and consumables	184	190
Current intangible assets – emission allowances	87	73
Inventories and current intangible assets	370	341
Inventory valuation reserve	£ 20	£ 18

Trade and other receivables (De

Trade and other receivables (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2018
Disclosure of trade and other receivables [line items]
Trade receivables	£ 1,899	£ 1,674
Accrued income	883	817
Prepayments	237	229
Other receivables	134	78
Trade and other current receivables	3,153	2,798	£ 2,795
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Trade receivables	£ 3,052	£ 4,524
Retail customer receivables \| 0 – 30 days
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Expected credit loss rate	3.00%	3.00%
Trade receivables	£ 736	£ 741
Retail customer receivables \| 30 – 60 days
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Expected credit loss rate	12.00%	8.00%
Trade receivables	£ 194	£ 192
Retail customer receivables \| 60 – 90 days
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Expected credit loss rate	20.00%	19.00%
Trade receivables	£ 89	£ 97
Retail customer receivables \| 3 to 6 months past due
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Expected credit loss rate	30.00%	29.00%
Trade receivables	£ 109	£ 97
Retail customer receivables \| 6 – 12 months
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Expected credit loss rate	39.00%	39.00%
Trade receivables	£ 99	£ 88
Retail customer receivables \| Over 12 months
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Expected credit loss rate	68.00%	69.00%
Trade receivables	£ 238	£ 218
Trade receivables
Disclosure of trade and other receivables [line items]
Maximum exposure to credit risk	2,293	1,983
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Allowance account for credit losses of financial assets, beginning balance	309	424
Exchange adjustments	24	(42)
Charge for the year, net of recoveries	181	36
Uncollectible amounts written off	(120)	(109)
Allowance account for credit losses of financial assets, ending balance	394	309
Trade receivables \| Financial assets past due but not impaired
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Trade receivables	563	475
Trade receivables \| Financial assets past due but not impaired \| Up to 3 months past due
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Trade receivables	295	271
Trade receivables \| Financial assets past due but not impaired \| 3 to 6 months past due
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Trade receivables	108	73
Trade receivables \| Financial assets past due but not impaired \| Over 6 months past due
Reconciliation of changes in allowance account for credit losses of financial assets [abstract]
Trade receivables	£ 160	£ 131

Cash and cash equivalents (Deta

Cash and cash equivalents (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018		Mar. 31, 2017	[1]	Mar. 31, 2016
Cash and cash equivalents [abstract]
Cash at bank	£ 177		£ 54
Short-term deposits	75		275
Cash and cash equivalents	£ 252	£ 329	£ 329	[1]	£ 1,139		£ 124

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Borrowings - Current and non-cu

Borrowings - Current and non-current borrowings (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017
Current
Bank loans	£ 641		£ 2,020
Bonds	1,973		2,156
Commercial paper	1,792		206
Finance leases	65		64
Other loans	1		1
Current portion of non-current borrowings	4,472	£ 4,447	4,447
Non-current
Bank loans	2,599		2,384
Bonds	21,278		19,418
Finance leases	205		207
Other loans	176		169
Non-current portion of non-current borrowings	24,258	£ 22,210	22,178
Liability held at fair value through profit and loss	667
Total borrowings	£ 28,730		£ 26,625	£ 28,638

Borrowings - Borrowings repayme

Borrowings - Borrowings repayment schedule (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 28,730	£ 26,625	£ 28,638
Less than 1 year
Disclosure of detailed information about borrowings [line items]
Borrowings	4,472	4,447
In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Borrowings	2,393	1,694
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Borrowings	1,990	2,347
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Borrowings	1,553	1,873
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	714	1,469
Borrowings Paid By Instalments \| More than 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	959	1,010
Borrowings Paid By Other Than Instalments \| More than 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 16,649	£ 13,785

Borrowings - Finance lease obli

Borrowings - Finance lease obligations (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Disclosure of finance lease and operating lease by lessee [line items]
Minimum finance lease payments payable	£ 310	£ 313
Less: finance charges allocated to future periods	(40)	(42)
Minimum finance lease payments payable, at present value	270	271
Less than 1 year
Disclosure of finance lease and operating lease by lessee [line items]
Minimum finance lease payments payable	65	64
Minimum finance lease payments payable, at present value	65	64
1 to 5 years
Disclosure of finance lease and operating lease by lessee [line items]
Minimum finance lease payments payable	183	177
Minimum finance lease payments payable, at present value	156	144
More than 5 years
Disclosure of finance lease and operating lease by lessee [line items]
Minimum finance lease payments payable	62	72
Minimum finance lease payments payable, at present value	£ 49	£ 63

Borrowings - Narrative (Details

Borrowings - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
Borrowings - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of fair value measurement of liabilities [line items]
Borrowings	£ 28,730	£ 26,625	£ 28,638
Property, plant and equipment pledged as security	81	392
Collateral received	558	878
Liability held at fair value through profit and loss	667
Change in fair value	13
Difference between carrying amount of financial liability and amount contractually required to pay at maturity to holder of obligation	276
Borrowings
Disclosure of fair value measurement of liabilities [line items]
Notional amount	28,417	26,363
At fair value
Disclosure of fair value measurement of liabilities [line items]
Borrowings	32,252	30,164
At fair value \| Level 1
Disclosure of fair value measurement of liabilities [line items]
Borrowings	14,356	13,018
At fair value \| Level 2
Disclosure of fair value measurement of liabilities [line items]
Borrowings	17,896	£ 17,146
Financial liabilities at fair value through profit and loss
Disclosure of fair value measurement of liabilities [line items]
Borrowings	£ 943

Trade and other payables (Detai

Trade and other payables (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Trade payables	£ 2,404		£ 1,977
Deferred payables	217		355
Customer contributions	87		85
Social security and other taxes	159		173
Other payables	902		863
Trade and other payables	£ 3,769	£ 3,394	£ 3,453

Contract liabilities - Summary

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

Contract liabilities - Signific

Contract liabilities - Significant Changes in Contract Liabilities (Details) £ in Millions	12 Months Ended
	Mar. 31, 2019GBP (£)
Increase (Decrease) in Contract Liabilities [Roll Forward]
As at 1 April 2018 (see note 37)	£ 0
Exchange adjustments	29
Revenue recognised that was included in the contract liability balance at the beginning of the period	(51)
Increases due to cash received, excluding amounts recognised as revenue during the period	155
Changes due to amounts recognised as revenue	(5)
At 31 March 2019	£ 994

Other non-current liabilities_2

Other non-current liabilities (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
Subclassifications of assets, liabilities and equities [abstract]
Deferred income	£ 96		£ 114
Customer contributions	372		844
Other payables	340		359
Other non-current liabilities	£ 808	£ 750	£ 1,317

Pensions and other post retir_3

Pensions and other post retirement benefits - Narrative (Details)	12 Months Ended
	Mar. 31, 2019GBP (£)plan	Mar. 31, 2018GBP (£)	Mar. 31, 2017GBP (£)	Jan. 01, 2017GBP (£)	Mar. 31, 2016GBP (£)
Disclosure of defined benefit plans [line items]
Defined contribution plan, employer matching contribution percent of gross pay	6.00%
Employer contributions	£ 419,000,000	£ 475,000,000	£ 1,073,000,000
US Pensions
Disclosure of defined benefit plans [line items]
Number of defined benefit plans \| plan	4
Employer contributions	£ 231,000,000	208,000,000	257,000,000
UK Pensions
Disclosure of defined benefit plans [line items]
Employer contributions	174,000,000	150,000,000	528,000,000
US other post-retirement benefits
Disclosure of defined benefit plans [line items]
Employer contributions	14,000,000	£ 117,000,000	£ 288,000,000
National Grid UK Pension Scheme - Section A
Disclosure of defined benefit plans [line items]
Cost of equalising for impact of guaranteed minimum pension	17,000,000
National Grid UK Pension Scheme - Section A \| UK Pensions
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings			51.80%
Maximum guarantee payable				£ 1,000,000,000
National Grid UK Pension Scheme - Section B
Disclosure of defined benefit plans [line items]
Cost of equalising for impact of guaranteed minimum pension	12,000,000
National Grid UK Pension Scheme - Section B \| UK Pensions
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings			51.40%
National Grid UK Pension Scheme - Section B \| UK Pensions \| Time Period, 30 September 2017 - 30 September 2022
Disclosure of defined benefit plans [line items]
Contributions payable per year			£ 32,000,000
National Grid UK Pension Scheme - Section B \| UK Pensions \| Time Period, 30 September 2023
Disclosure of defined benefit plans [line items]
Contributions payable per year			£ 8,000,000
NGEG of ESPS
Disclosure of defined benefit plans [line items]
Cost of equalising for impact of guaranteed minimum pension	£ 5,000,000
NGEG of ESPS \| UK Pensions
Disclosure of defined benefit plans [line items]
Contribution rate to meet future benefit accrual, percentage of pensionable earnings					40.70%
NGEG of ESPS \| UK Pensions \| Time Period 2016/17 - 31 March 2027
Disclosure of defined benefit plans [line items]
Contributions payable per year					£ 48,000,000

Pensions and other post retir_4

Pensions and other post retirement benefits - Results of the most recent actuarial valuations (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of defined benefit plans [line items]
Funding surplus/(deficit)	£ (218)	£ (263)	£ (1,933)
UK Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets	15,507	15,330	15,489
Funding surplus/(deficit)	£ 1,231	£ 1,104	(156)
National Grid UK Pension Scheme - Section A \| UK Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets			6,716
Market value of scheme assets at latest valuation			£ 6,627
Market value as percentage of benefits			101.00%
Funding surplus/(deficit)			£ 89
Funding surplus/(deficit) net of tax			74
National Grid UK Pension Scheme - Section B \| UK Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets			5,849
Market value of scheme assets at latest valuation			£ 6,057
Market value as percentage of benefits			97.00%
Funding surplus/(deficit)			£ (208)
Funding surplus/(deficit) net of tax			£ (173)
NGEG of ESPS \| UK Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets				£ 2,553
Market value of scheme assets at latest valuation				£ 3,053
Market value as percentage of benefits				84.00%
Funding surplus/(deficit)				£ (500)
Funding surplus/(deficit) net of tax				£ (415)

Pensions and other post retir_5

Pensions and other post retirement benefits - Security arrangements (Details) - UK Pensions £ in Millions	Mar. 31, 2019GBP (£)
National Grid UK Pension Scheme - Section A
Disclosure of defined benefit plans [line items]
Value of security arrangements	£ 315
Additional amounts payable	72
National Grid UK Pension Scheme - Section B
Disclosure of defined benefit plans [line items]
Value of security arrangements	179
Maximum additional amounts payable	280
NGEG of ESPS
Disclosure of defined benefit plans [line items]
Value of security arrangements	250
Maximum additional amounts payable	£ 500

Pensions and other post retir_6

Pensions and other post retirement benefits - Actuarial assumptions (Details) - year	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
UK Pensions
Disclosure of defined benefit plans [line items]
Discount rate - past service	2.40%	2.60%	2.40%
Discount rate - future service	2.45%	2.65%	2.65%
Rate of increase in salaries	3.50%	3.40%	3.50%
Rate of increase in RPI, past service	3.25%	3.15%	3.20%
Rate of increase in RPI, future service	3.20%	3.10%	3.15%
Assumed life expectations for a retiree age 65 today: Males	22	22.3	22.9
Assumed life expectations for a retiree age 65 today: Females	23.6	23.9	24.7
Assumed life expectations for a retiree age 65 today: In 20 years: Males	23.3	23.7	25.1
Assumed life expectations for a retiree age 65 today: In 20 years: Females	25.2	25.5	27.1
Weighted average duration of defined benefit obligation	15
US Pensions
Disclosure of defined benefit plans [line items]
Rate of increase in salaries	3.50%	3.50%	3.50%
Discount rate	3.95%	4.00%	4.25%
Assumed life expectations for a retiree age 65 today: Males	22.1	22	21.9
Assumed life expectations for a retiree age 65 today: Females	24.2	24.2	24.1
Assumed life expectations for a retiree age 65 today: In 20 years: Males	23.7	23.6	23.6
Assumed life expectations for a retiree age 65 today: In 20 years: Females	25.9	25.8	25.7
Weighted average duration of defined benefit obligation	13
US other post-retirement benefits
Disclosure of defined benefit plans [line items]
Rate of increase in salaries	3.50%	3.50%	3.50%
Discount rate	3.95%	4.00%	4.25%
Initial healthcare cost trend rate	7.25%	7.50%	7.00%
Ultimate healthcare cost trend rate	4.50%	4.50%	4.50%
Weighted average duration of defined benefit obligation	16

Pensions and other post retir_7

Pensions and other post retirement benefits - Amounts recognized in consolidated statement of financial position (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of defined benefit plans [line items]
Funding surplus/(deficit)	£ (218)	£ (263)	£ (1,933)
Liabilities	(1,785)	(1,672)	(2,536)
Assets	1,567	1,409	603
Pensions \| Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(24,609)	(23,747)	(25,890)
Fair value of plan assets	24,793	23,858	24,375
Funding surplus/(deficit)	184	111	(1,515)
Pensions \| Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(330)	(307)	(340)
UK Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets	15,507	15,330	15,489
Funding surplus/(deficit)	1,231	1,104	(156)
Liabilities	(76)	(74)	(536)
Assets	1,307	1,178	380
UK Pensions \| Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(14,200)	(14,152)	(15,565)
Fair value of plan assets	15,507	15,330	15,489
Funding surplus/(deficit)	1,307	1,178	(76)
UK Pensions \| Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(76)	(74)	(80)
Other post-employment liabilities	£ 0	£ 0	£ 0
UK Pensions \| Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	10.00%	10.00%	12.00%
UK Pensions \| Deferred members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	16.00%	18.00%	19.00%
UK Pensions \| Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	74.00%	72.00%	69.00%
US Pensions
Disclosure of defined benefit plans [line items]
Fair value of plan assets	£ 6,646	£ 6,030	£ 6,322
Funding surplus/(deficit)	(509)	(552)	(728)
Liabilities	(769)	(783)	(951)
Assets	260	231	223
US Pensions \| Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(6,901)	(6,349)	(6,790)
Fair value of plan assets	6,646	6,030	6,322
Funding surplus/(deficit)	(255)	(319)	(468)
US Pensions \| Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(254)	(233)	(260)
Other post-employment liabilities	£ 0	£ 0	£ 0
US Pensions \| Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	37.00%	38.00%	38.00%
US Pensions \| Deferred members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	9.00%	8.00%	9.00%
US Pensions \| Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	54.00%	54.00%	53.00%
US other post-retirement benefits
Disclosure of defined benefit plans [line items]
Fair value of plan assets	£ 2,640	£ 2,498	£ 2,564
Funding surplus/(deficit)	(940)	(815)	(1,049)
Other post-employment liabilities	(72)	(67)	(78)
Liabilities	(940)	(815)	(1,049)
Assets	0	0	0
US other post-retirement benefits \| Funded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	(3,508)	(3,246)	(3,535)
Fair value of plan assets	2,640	2,498	2,564
Funding surplus/(deficit)	(868)	(748)	(971)
US other post-retirement benefits \| Unfunded obligations
Disclosure of defined benefit plans [line items]
Defined benefit obligation, at present value	£ 0	£ 0	£ 0
US other post-retirement benefits \| Active members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	39.00%	38.00%	39.00%
US other post-retirement benefits \| Deferred members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	0.00%	0.00%	0.00%
US other post-retirement benefits \| Pensioner members
Disclosure of defined benefit plans [line items]
Defined benefit obligation, member concentration percentage	61.00%	62.00%	61.00%

Pensions and other post retir_8

Pensions and other post retirement benefits - Amounts recognised in the income statement and statement of other comprehensive income (Details) - GBP (£)	6 Months Ended	12 Months Ended
	Sep. 30, 2018	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Included within operating costs
Administration costs		£ 14,000,000	£ 16,000,000	£ 16,000,000
Included within payroll costs
Current service cost		193,000,000	193,000,000	232,000,000
Past service cost – augmentations		5,000,000	1,000,000	1,000,000
Past service credit – redundancies		(7,000,000)	(1,000,000)	(1,000,000)
Special termination benefit cost – redundancies		55,000,000	9,000,000	7,000,000
Past service cost – plan amendments		34,000,000	0	0
Total included within payroll costs		280,000,000	202,000,000	239,000,000
Included within finance income and costs
Net interest cost		22,000,000	65,000,000	105,000,000
Included within gain on disposal of discontinued operations
Administration costs		0	0	5,000,000
Disposal of UK Gas Distribution		0	0	34,000,000
Total included within gain on disposal of discontinued operations		0	0	39,000,000
Total included in income statement		316,000,000	283,000,000	399,000,000
Remeasurement gains of pension assets and post-retirement benefit obligations		68,000,000	1,313,000,000	348,000,000
Exchange adjustments		(101,000,000)	175,000,000	(345,000,000)
Total included in the statement of other comprehensive income		(33,000,000)	1,488,000,000	3,000,000
UK Pensions
Included within operating costs
Administration costs		6,000,000	6,000,000	6,000,000
Included within payroll costs
Current service cost		41,000,000	49,000,000	76,000,000
Past service cost – augmentations		5,000,000	1,000,000	1,000,000
Past service credit – redundancies		(7,000,000)	(1,000,000)	(1,000,000)
Special termination benefit cost – redundancies		55,000,000	9,000,000	7,000,000
Past service cost – plan amendments		34,000,000	0	0
Total included within payroll costs		128,000,000	58,000,000	83,000,000
Included within finance income and costs
Net interest cost		(31,000,000)	3,000,000	0
Included within gain on disposal of discontinued operations
Administration costs		0	0	5,000,000
Disposal of UK Gas Distribution		0	0	34,000,000
Total included within gain on disposal of discontinued operations		0	0	39,000,000
Total included in income statement		103,000,000	67,000,000	128,000,000
Remeasurement gains of pension assets and post-retirement benefit obligations		57,000,000	1,177,000,000	(541,000,000)
Exchange adjustments		0	0	0
Total included in the statement of other comprehensive income		57,000,000	1,177,000,000	(541,000,000)
UK Pensions \| Discontinued operations
Included within operating costs
Administration costs		0	0	(1,000,000)
Included within payroll costs
Total included within payroll costs		0	0	35,000,000
Included within finance income and costs
Net interest cost		0	0	(2,000,000)
Included within gain on disposal of discontinued operations
Remeasurement gains of pension assets and post-retirement benefit obligations		0	0	75,000,000
US Pensions
Included within operating costs
Administration costs		7,000,000	9,000,000	9,000,000
Included within payroll costs
Current service cost		104,000,000	98,000,000	103,000,000
Past service cost – augmentations		0	0	0
Past service credit – redundancies		0	0	0
Special termination benefit cost – redundancies		0	0	0
Past service cost – plan amendments		0	0	0
Total included within payroll costs		104,000,000	98,000,000	103,000,000
Included within finance income and costs
Net interest cost		21,000,000	27,000,000	43,000,000
Included within gain on disposal of discontinued operations
Administration costs		0	0	0
Disposal of UK Gas Distribution		0	0	0
Total included within gain on disposal of discontinued operations		0	0	0
Total included in income statement		132,000,000	134,000,000	155,000,000
Remeasurement gains of pension assets and post-retirement benefit obligations		(14,000,000)	27,000,000	319,000,000
Exchange adjustments		(42,000,000)	75,000,000	(140,000,000)
Total included in the statement of other comprehensive income		(56,000,000)	102,000,000	179,000,000
US other post-retirement benefits
Included within operating costs
Administration costs		1,000,000	1,000,000	1,000,000
Included within payroll costs
Current service cost		48,000,000	46,000,000	53,000,000
Past service cost – augmentations		0	0	0
Past service credit – redundancies		0	0	0
Special termination benefit cost – redundancies		0	0	0
Past service cost – plan amendments		0	0	0
Total included within payroll costs		48,000,000	46,000,000	53,000,000
Included within finance income and costs
Net interest cost		32,000,000	35,000,000	62,000,000
Included within gain on disposal of discontinued operations
Administration costs		0	0	0
Disposal of UK Gas Distribution		0	0	0
Total included within gain on disposal of discontinued operations		0	0	0
Total included in income statement		81,000,000	82,000,000	116,000,000
Remeasurement gains of pension assets and post-retirement benefit obligations		25,000,000	109,000,000	570,000,000
Exchange adjustments		(59,000,000)	100,000,000	(205,000,000)
Total included in the statement of other comprehensive income		(34,000,000)	209,000,000	365,000,000
Exceptional items
Included within gain on disposal of discontinued operations
Redundancy pension costs	£ 52,000,000	£ 52,000,000	£ 0	£ 0

Pensions and other post retir_9

Pensions and other post retirement benefits - Reconciliation of the net defined benefit liability (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	£ (263)	£ (1,933)	£ (2,585)
Changes in net defined benefit liability (asset) [abstract]
Cost recognised in the income statement	(316)	(283)	(399)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(33)	1,488	3
Employer contributions	419	475	1,073
Other movements	(25)	(10)	(25)
Net defined benefit liability (asset), ending balance	(218)	(263)	(1,933)
UK Pensions
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	1,104	(156)	(15)
Changes in net defined benefit liability (asset) [abstract]
Cost recognised in the income statement	(103)	(67)	(128)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	57	1,177	(541)
Employer contributions	174	150	528
Other movements	(1)	0	0
Net defined benefit liability (asset), ending balance	1,231	1,104	(156)
US Pensions
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	(552)	(728)	(1,009)
Changes in net defined benefit liability (asset) [abstract]
Cost recognised in the income statement	(132)	(134)	(155)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(56)	102	179
Employer contributions	231	208	257
Other movements	0	0	0
Net defined benefit liability (asset), ending balance	(509)	(552)	(728)
US other post-retirement benefits
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	(815)	(1,049)	(1,561)
Changes in net defined benefit liability (asset) [abstract]
Cost recognised in the income statement	(81)	(82)	(116)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income	(34)	209	365
Employer contributions	14	117	288
Other movements	(24)	(10)	(25)
Net defined benefit liability (asset), ending balance	£ (940)	£ (815)	£ (1,049)

Pensions and other post reti_10

Pensions and other post retirement benefits - Change in the present value of defined benefit obligations (including unfunded obligations) (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of operating segments [line items]
Net defined benefit liability (asset), beginning balance	£ (263)	£ (1,933)	£ (2,585)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	193	193	232
Net interest cost	22	65	105
Past service credit – redundancies	(7)	(1)	(1)
Special termination benefit cost – redundancies	55	9	7
Past service cost – augmentations	5	1	1
Past service cost – plan amendments	34	0	0
Disposal of UK Gas Distribution	0	0	34
Exchange adjustments	(101)	175	(345)
Net defined benefit liability (asset), ending balance	(218)	(263)	(1,933)
UK Pensions
Disclosure of operating segments [line items]
Net defined benefit liability (asset), beginning balance	1,104	(156)	(15)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	41	49	76
Net interest cost	(31)	3	0
Past service credit – redundancies	(7)	(1)	(1)
Special termination benefit cost – redundancies	55	9	7
Past service cost – augmentations	5	1	1
Past service cost – plan amendments	34	0	0
Disposal of UK Gas Distribution	0	0	34
Exchange adjustments	0	0	0
Net defined benefit liability (asset), ending balance	1,231	1,104	(156)
US Pensions
Disclosure of operating segments [line items]
Net defined benefit liability (asset), beginning balance	(552)	(728)	(1,009)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	104	98	103
Net interest cost	21	27	43
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – augmentations	0	0	0
Past service cost – plan amendments	0	0	0
Disposal of UK Gas Distribution	0	0	0
Exchange adjustments	(42)	75	(140)
Net defined benefit liability (asset), ending balance	(509)	(552)	(728)
US other post-retirement benefits
Disclosure of operating segments [line items]
Net defined benefit liability (asset), beginning balance	(815)	(1,049)	(1,561)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	48	46	53
Net interest cost	32	35	62
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – augmentations	0	0	0
Past service cost – plan amendments	0	0	0
Disposal of UK Gas Distribution	0	0	0
Exchange adjustments	(59)	100	(205)
Net defined benefit liability (asset), ending balance	(940)	(815)	(1,049)
Present value of defined benefit obligation
Disclosure of operating segments [line items]
Net defined benefit liability (asset), beginning balance	(24,054)	(26,230)	(28,952)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(193)	(193)	(232)
Net interest cost	(771)	(775)	(1,057)
Actuarial (losses)/gains – experience	(69)	(100)	166
Actuarial gains – demographic assumptions	266	671	225
Actuarial (losses)/gains – financial assumptions	(619)	174	(3,377)
Past service credit – redundancies	7	1	1
Special termination benefit cost – redundancies	(55)	(9)	(7)
Past service cost – augmentations	(5)	(1)	(1)
Past service cost – plan amendments	(34)	0	0
Medicare subsidy received	(19)	(21)	(14)
Disposal of UK Gas Distribution	0	0	6,970
Employee contributions	(1)	(1)	(1)
Benefits paid	1,376	1,285	1,443
Exchange adjustments	(768)	1,145	(1,394)
Net defined benefit liability (asset), ending balance	(24,939)	(24,054)	(26,230)
Present value of defined benefit obligation \| UK Pensions
Disclosure of operating segments [line items]
Net defined benefit liability (asset), beginning balance	(14,226)	(15,645)	(19,416)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(41)	(49)	(76)
Net interest cost	(358)	(366)	(615)
Actuarial (losses)/gains – experience	(56)	(95)	106
Actuarial gains – demographic assumptions	224	565	214
Actuarial (losses)/gains – financial assumptions	(568)	604	(3,751)
Past service credit – redundancies	7	1	1
Special termination benefit cost – redundancies	(55)	(9)	(7)
Past service cost – augmentations	(5)	(1)	(1)
Past service cost – plan amendments	(34)	0	0
Medicare subsidy received	0	0	0
Disposal of UK Gas Distribution	0	0	6,970
Employee contributions	(1)	(1)	(1)
Benefits paid	837	770	931
Exchange adjustments	0	0	0
Net defined benefit liability (asset), ending balance	(14,276)	(14,226)	(15,645)
Present value of defined benefit obligation \| US Pensions
Disclosure of operating segments [line items]
Net defined benefit liability (asset), beginning balance	(6,582)	(7,050)	(6,145)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(104)	(98)	(103)
Net interest cost	(277)	(273)	(285)
Actuarial (losses)/gains – experience	(52)	(38)	(2)
Actuarial gains – demographic assumptions	0	30	2
Actuarial (losses)/gains – financial assumptions	(24)	(279)	37
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – augmentations	0	0	0
Past service cost – plan amendments	0	0	0
Medicare subsidy received	0	0	0
Disposal of UK Gas Distribution	0	0	0
Employee contributions	0	0	0
Benefits paid	398	362	349
Exchange adjustments	(514)	764	(903)
Net defined benefit liability (asset), ending balance	(7,155)	(6,582)	(7,050)
Present value of defined benefit obligation \| US other post-retirement benefits
Disclosure of operating segments [line items]
Net defined benefit liability (asset), beginning balance	(3,246)	(3,535)	(3,391)
Changes in net defined benefit liability (asset) [abstract]
Current service cost	(48)	(46)	(53)
Net interest cost	(136)	(136)	(157)
Actuarial (losses)/gains – experience	39	33	62
Actuarial gains – demographic assumptions	42	76	9
Actuarial (losses)/gains – financial assumptions	(27)	(151)	337
Past service credit – redundancies	0	0	0
Special termination benefit cost – redundancies	0	0	0
Past service cost – augmentations	0	0	0
Past service cost – plan amendments	0	0	0
Medicare subsidy received	(19)	(21)	(14)
Disposal of UK Gas Distribution	0	0	0
Employee contributions	0	0	0
Benefits paid	141	153	163
Exchange adjustments	(254)	381	(491)
Net defined benefit liability (asset), ending balance	£ (3,508)	£ (3,246)	£ (3,535)

Pensions and other post reti_11

Pensions and other post retirement benefits - Change in fair value of plan assets (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	£ (263)	£ (1,933)	£ (2,585)
Changes in net defined benefit liability (asset) [abstract]
Interest income	22	65	105
Employer contributions	419	475	1,073
Exchange adjustments	(101)	175	(345)
Assets transferred on disposal of UK Gas Distribution	0	0	34
Net defined benefit liability (asset), ending balance	(218)	(263)	(1,933)
Actual return on plan assets	1,239	1,278	4,286
Expected contributions to plans in the following year	307	363	491
Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	23,858	24,375	26,434
Changes in net defined benefit liability (asset) [abstract]
Interest income	749	710	952
Return on plan assets in excess of interest	490	568	3,334
Administration costs	(14)	(16)	(21)
Employer contributions	419	475	1,073
Employee contributions	1	1	1
Benefits paid	(1,377)	(1,285)	(1,443)
Exchange adjustments	667	(970)	1,049
Assets transferred on disposal of UK Gas Distribution	0	0	(7,004)
Net defined benefit liability (asset), ending balance	24,793	23,858	24,375
UK Pensions
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	1,104	(156)	(15)
Changes in net defined benefit liability (asset) [abstract]
Interest income	(31)	3	0
Employer contributions	174	150	528
Exchange adjustments	0	0	0
Assets transferred on disposal of UK Gas Distribution	0	0	34
Net defined benefit liability (asset), ending balance	1,231	1,104	(156)
Actual return on plan assets	846	466	3,505
Expected contributions to plans in the following year	148	140	128
UK Pensions \| Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	15,330	15,489	19,401
Changes in net defined benefit liability (asset) [abstract]
Interest income	389	363	615
Return on plan assets in excess of interest	457	103	2,890
Administration costs	(6)	(6)	(11)
Employer contributions	174	150	528
Employee contributions	1	1	1
Benefits paid	(838)	(770)	(931)
Exchange adjustments	0	0	0
Assets transferred on disposal of UK Gas Distribution	0	0	(7,004)
Net defined benefit liability (asset), ending balance	15,507	15,330	15,489
US Pensions
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	(552)	(728)	(1,009)
Changes in net defined benefit liability (asset) [abstract]
Interest income	21	27	43
Employer contributions	231	208	257
Exchange adjustments	(42)	75	(140)
Assets transferred on disposal of UK Gas Distribution	0	0	0
Net defined benefit liability (asset), ending balance	(509)	(552)	(728)
Actual return on plan assets	318	560	524
Expected contributions to plans in the following year	150	221	229
US Pensions \| Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	6,030	6,322	5,136
Changes in net defined benefit liability (asset) [abstract]
Interest income	256	246	242
Return on plan assets in excess of interest	62	314	282
Administration costs	(7)	(9)	(9)
Employer contributions	231	208	257
Employee contributions	0	0	0
Benefits paid	(398)	(362)	(349)
Exchange adjustments	472	(689)	763
Assets transferred on disposal of UK Gas Distribution	0	0	0
Net defined benefit liability (asset), ending balance	6,646	6,030	6,322
US other post-retirement benefits
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	(815)	(1,049)	(1,561)
Changes in net defined benefit liability (asset) [abstract]
Interest income	32	35	62
Employer contributions	14	117	288
Exchange adjustments	(59)	100	(205)
Assets transferred on disposal of UK Gas Distribution	0	0	0
Net defined benefit liability (asset), ending balance	(940)	(815)	(1,049)
Actual return on plan assets	75	252	257
Expected contributions to plans in the following year	9	2	134
US other post-retirement benefits \| Plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net defined benefit liability (asset), beginning balance	2,498	2,564	1,897
Changes in net defined benefit liability (asset) [abstract]
Interest income	104	101	95
Return on plan assets in excess of interest	(29)	151	162
Administration costs	(1)	(1)	(1)
Employer contributions	14	117	288
Employee contributions	0	0	0
Benefits paid	(141)	(153)	(163)
Exchange adjustments	195	(281)	286
Assets transferred on disposal of UK Gas Distribution	0	0	0
Net defined benefit liability (asset), ending balance	£ 2,640	£ 2,498	£ 2,564

Pensions and other post reti_12

Pensions and other post retirement benefits - Asset allocation percentages (Details)	Mar. 31, 2019
UK \| UK Pensions
Disclosure of fair value of plan assets [line items]
Equities	12.70%
Property	5.50%
Diversified alternatives	5.00%
Liability matching assets	11.10%
Infrastructure	0.00%
Cash and cash equivalents	1.90%
Other	1.00%
Total	100.00%
UK \| Corporate bonds \| UK Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	23.40%
UK \| Government securities \| UK Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	39.40%
US \| US Pensions
Disclosure of fair value of plan assets [line items]
Equities	40.80%
Property	4.70%
Diversified alternatives	10.10%
Liability matching assets	0.00%
Infrastructure	1.50%
Cash and cash equivalents	0.30%
Other	0.20%
Total	100.00%
US \| US other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Equities	60.20%
Property	0.00%
Diversified alternatives	12.90%
Liability matching assets	0.00%
Infrastructure	0.00%
Cash and cash equivalents	0.00%
Other	5.60%
Total	100.00%
US \| Corporate bonds \| US Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	26.40%
US \| Corporate bonds \| US other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	0.70%
US \| Government securities \| US Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	16.00%
US \| Government securities \| US other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	20.60%

Pensions and other post reti_13

Pensions and other post retirement benefits - Asset allocations (Details) - GBP (£)	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
UK Pensions
Disclosure of fair value of plan assets [line items]
Equities	£ 1,965,000,000	£ 2,233,000,000	£ 3,220,000,000
Property	857,000,000	963,000,000	798,000,000
Diversified alternatives	771,000,000	789,000,000	878,000,000
Liability-matching assets	1,716,000,000	1,174,000,000	1,162,000,000
Cash and cash equivalents	299,000,000	426,000,000	623,000,000
Other	160,000,000	167,000,000	(124,000,000)
Fair value of plan assets	15,507,000,000	15,330,000,000	15,489,000,000
Ordinary shares of National Grid including in fair value of plan assets	0	0	2,000,000
UK Pensions \| Quoted
Disclosure of fair value of plan assets [line items]
Equities	1,181,000,000	1,420,000,000	2,624,000,000
Property	108,000,000	129,000,000	90,000,000
Diversified alternatives	0	99,000,000	250,000,000
Liability-matching assets	1,751,000,000	1,174,000,000	1,162,000,000
Cash and cash equivalents	40,000,000	211,000,000	211,000,000
Other	0	0	(148,000,000)
Fair value of plan assets	12,819,000,000	12,611,000,000	13,121,000,000
UK Pensions \| Unquoted
Disclosure of fair value of plan assets [line items]
Equities	784,000,000	813,000,000	596,000,000
Property	749,000,000	834,000,000	708,000,000
Diversified alternatives	771,000,000	690,000,000	628,000,000
Liability-matching assets	(35,000,000)	0	0
Cash and cash equivalents	259,000,000	215,000,000	412,000,000
Other	160,000,000	167,000,000	24,000,000
Fair value of plan assets	2,688,000,000	2,719,000,000	2,368,000,000
US Pensions
Disclosure of fair value of plan assets [line items]
Equities	2,711,000,000	2,531,000,000	2,613,000,000
Property	316,000,000	279,000,000	335,000,000
Diversified alternatives	670,000,000	619,000,000	642,000,000
Infrastructure	99,000,000	77,000,000	79,000,000
Cash and cash equivalents	21,000,000	14,000,000	28,000,000
Other	13,000,000	33,000,000	15,000,000
Fair value of plan assets	6,646,000,000	6,030,000,000	6,322,000,000
US Pensions \| Quoted
Disclosure of fair value of plan assets [line items]
Equities	533,000,000	577,000,000	698,000,000
Property	0	0	0
Diversified alternatives	183,000,000	198,000,000	209,000,000
Infrastructure	0	0	0
Cash and cash equivalents	21,000,000	14,000,000	28,000,000
Other	(8,000,000)	6,000,000	3,000,000
Fair value of plan assets	2,480,000,000	2,294,000,000	2,940,000,000
US Pensions \| Unquoted
Disclosure of fair value of plan assets [line items]
Equities	2,178,000,000	1,954,000,000	1,915,000,000
Property	316,000,000	279,000,000	335,000,000
Diversified alternatives	487,000,000	421,000,000	433,000,000
Infrastructure	99,000,000	77,000,000	79,000,000
Cash and cash equivalents	0	0	0
Other	21,000,000	27,000,000	12,000,000
Fair value of plan assets	4,166,000,000	3,736,000,000	3,382,000,000
US other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Equities	1,588,000,000	1,522,000,000	1,567,000,000
Diversified alternatives	341,000,000	305,000,000	315,000,000
Other	149,000,000	137,000,000	142,000,000
Fair value of plan assets	2,640,000,000	2,498,000,000	2,564,000,000
US other post-retirement benefits \| Quoted
Disclosure of fair value of plan assets [line items]
Equities	404,000,000	412,000,000	405,000,000
Diversified alternatives	175,000,000	161,000,000	166,000,000
Other	0	0	0
Fair value of plan assets	1,138,000,000	1,105,000,000	1,110,000,000
US other post-retirement benefits \| Unquoted
Disclosure of fair value of plan assets [line items]
Equities	1,184,000,000	1,110,000,000	1,162,000,000
Diversified alternatives	166,000,000	144,000,000	149,000,000
Other	149,000,000	137,000,000	142,000,000
Fair value of plan assets	1,502,000,000	1,393,000,000	1,454,000,000
Corporate bonds \| UK Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	3,625,000,000	3,949,000,000	3,526,000,000
Corporate bonds \| UK Pensions \| Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	3,625,000,000	3,949,000,000	3,526,000,000
Corporate bonds \| UK Pensions \| Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	0	0	0
Corporate bonds \| US Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	1,754,000,000	1,498,000,000	1,667,000,000
Corporate bonds \| US Pensions \| Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	1,329,000,000	1,085,000,000	1,130,000,000
Corporate bonds \| US Pensions \| Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	425,000,000	413,000,000	537,000,000
Corporate bonds \| US other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	19,000,000	24,000,000	19,000,000
Corporate bonds \| US other post-retirement benefits \| Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	19,000,000	24,000,000	19,000,000
Corporate bonds \| US other post-retirement benefits \| Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	0	0	0
Government securities \| UK Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	6,114,000,000	5,629,000,000	5,406,000,000
Government securities \| UK Pensions \| Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	6,114,000,000	5,629,000,000	5,406,000,000
Government securities \| UK Pensions \| Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	0	0	0
Government securities \| US Pensions
Disclosure of fair value of plan assets [line items]
Debt instruments	1,062,000,000	979,000,000	943,000,000
Government securities \| US Pensions \| Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	422,000,000	414,000,000	872,000,000
Government securities \| US Pensions \| Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	640,000,000	565,000,000	71,000,000
Government securities \| US other post-retirement benefits
Disclosure of fair value of plan assets [line items]
Debt instruments	543,000,000	510,000,000	521,000,000
Government securities \| US other post-retirement benefits \| Quoted
Disclosure of fair value of plan assets [line items]
Debt instruments	540,000,000	508,000,000	520,000,000
Government securities \| US other post-retirement benefits \| Unquoted
Disclosure of fair value of plan assets [line items]
Debt instruments	£ 3,000,000	£ 2,000,000	£ 1,000,000

Provisions - Schedule of change

Provisions - Schedule of changes in provisions (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure of other provisions [line items]
Other provisions, beginning balance	£ 2,052	£ 2,588
Exchange adjustments	124	(195)
Additions	226	74
Unused amounts reversed1	(65)	(107)
Unwinding of discount	74	75
Utilised	(209)	(268)
Transfers	(3)	(115)
Other provisions, ending balance	2,199	2,052
Environmental
Disclosure of other provisions [line items]
Other provisions, beginning balance	1,531	1,721
Exchange adjustments	103	(158)
Additions	32	27
Unused amounts reversed1	(36)	(45)
Unwinding of discount	62	61
Utilised	(53)	(75)
Transfers	0	0
Other provisions, ending balance	1,639	1,531
Decommissioning
Disclosure of other provisions [line items]
Other provisions, beginning balance	194	221
Exchange adjustments	7	(9)
Additions	18	2
Unused amounts reversed1	(10)	(19)
Unwinding of discount	5	5
Utilised	(26)	(6)
Transfers	0	0
Other provisions, ending balance	188	194
Restructuring
Disclosure of other provisions [line items]
Other provisions, beginning balance	3	17
Exchange adjustments	0	0
Additions	125	10
Unused amounts reversed1	(3)	(6)
Unwinding of discount	0	1
Utilised	(42)	(7)
Transfers	0	(12)
Other provisions, ending balance	83	3
Emissions
Disclosure of other provisions [line items]
Other provisions, beginning balance	8	32
Exchange adjustments	0	(2)
Additions	16	12
Unused amounts reversed1	(6)	0
Unwinding of discount	0	0
Utilised	(9)	(34)
Transfers	0	0
Other provisions, ending balance	9	8
Other
Disclosure of other provisions [line items]
Other provisions, beginning balance	316	597
Exchange adjustments	14	(26)
Additions	35	23
Unused amounts reversed1	(10)	(37)
Unwinding of discount	7	8
Utilised	(79)	(146)
Transfers	(3)	(103)
Other provisions, ending balance	£ 280	£ 316

Provisions - Current and non-cu

Provisions - Current and non-current provisions (Details) - GBP (£)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Apr. 01, 2018	Mar. 31, 2017
Disclosure of other provisions [line items]
Current	£ 316,000,000	£ 273,000,000	£ 273,000,000
Non-current	1,883,000,000	1,779,000,000	£ 1,779,000,000
Other provisions	2,199,000,000	2,052,000,000		£ 2,588,000,000
Unused amounts reversed	65,000,000	107,000,000
Utilised	209,000,000	268,000,000
Transferred to trade and other payables	3,000,000	115,000,000
Discontinued operations
Disclosure of other provisions [line items]
Unused amounts reversed	0	16,000,000
Utilised	£ 20,000,000	£ 77,000,000

Provisions - Environmental prov

Provisions - Environmental provision (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of other provisions [line items]
Discounted	£ 2,199	£ 2,052	£ 2,588
Real discount rate		1.00%	2.00%
Environmental
Disclosure of other provisions [line items]
Discounted	1,639	£ 1,531	£ 1,721
Undiscounted	1,765	1,645
Environmental \| UK
Disclosure of other provisions [line items]
Discounted	189	213
Undiscounted	£ 210	£ 235
Real discount rate	1.00%	1.00%
Weighted average duration of cash flows	12 years
Environmental \| US
Disclosure of other provisions [line items]
Discounted	£ 1,450	£ 1,318
Undiscounted	£ 1,555	£ 1,410
Real discount rate	1.00%	1.00%
Weighted average duration of cash flows	9 years

Provisions - Narrative (Details

Provisions - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
Provisions - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of other provisions [line items]
Other provisions	£ 2,199	£ 2,052	£ 2,588
Real discount rate		1.00%	2.00%
Expense of restructuring activities	226	£ 74
Decommissioning
Disclosure of other provisions [line items]
Other provisions	£ 188	194	£ 221
Real discount rate	1.00%
Expense of restructuring activities	£ 18	2
Decommissioning provision, ARO
Disclosure of other provisions [line items]
Other provisions	80	71
Provision for decommissioning, demolition of gas holders
Disclosure of other provisions [line items]
Other provisions	90	104	107
Restructuring
Disclosure of other provisions [line items]
Other provisions	83	3	17
Expense of restructuring activities	125	10
Other
Disclosure of other provisions [line items]
Other provisions	280	316	£ 597
Expense of restructuring activities	35	23
Business set up and restructuring cost
Disclosure of other provisions [line items]
Other provisions	30	50
Onerous lease commitments and rates payable on surplus properties
Disclosure of other provisions [line items]
Other provisions	29	48
Liability for claims and claims adjustment
Disclosure of other provisions [line items]
Other provisions	164	152
Obligations associated with investments in joint ventures and associates
Disclosure of other provisions [line items]
Other provisions	£ 13	£ 13

Share capital - Schedule of sha

Share capital - Schedule of share capital (Details) £ / shares in Units, £ in Millions, shares in Millions		May 22, 2017£ / shares	Mar. 31, 2019GBP (£)shares	Mar. 31, 2018GBP (£)shares	Mar. 31, 2017GBP (£)shares	May 21, 2017£ / shares
Disclosure of classes of share capital [line items]
Equity, beginning balance			£ 18,848	£ 20,384	£ 13,565
Issued during the year in lieu of dividends	[1]		(1)	0	0
Equity, ending balance			£ 19,369	£ 18,848	£ 20,384
Share consolidation ratio		0.9167
Par value per share (per share) \| £ / shares		£ 0.1140				£ 0.1243
Share capital
Disclosure of classes of share capital [line items]
Issued capital (in shares), beginning balance \| shares			3,638	3,943
Effect of share consolidation (in shares) \| shares				(328)
Issued during period, in lieu of dividends (in shares) \| shares			49	23
Issued capital (in shares), ending balance \| shares			3,687	3,638	3,943
Equity, beginning balance			£ 452	£ 449	£ 447
Issued during the year in lieu of dividends	[1]		6	3	2
Equity, ending balance			£ 458	£ 452	£ 449

[1]	Included within the share premium account are costs associated with scrip dividends.

Share capital - Narrative (Deta

Share capital - Narrative (Details) - GBP (£) £ in Millions, shares in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Share Capital, Reserves And Other Equity Interest [Abstract]
Treasury stock (in shares)	277	283
Treasury shares, market value	£ 2,359	£ 2,270
Treasury shares, gifted (in shares)	3	3
Treasury stock, reissued (in shares)	3	5
Shares reissued to employee share schemes as percent of ordinary shares	0.20%	0.20%
Treasury shares, reissued, nominal value	£ 1	£ 1
Gross proceeds from reissue of treasury shares	18	33
Purchase of own shares, employee share trusts	£ 2	£ 5	[1]	£ 6
Treasury stock acquired (in shares)		114
Purchase of treasury shares		£ 1,017		£ 189
Purchase of treasury shares, nominal value		£ 14
Shares repurchased as percent of ordinary shares		3.10%
Maximum number of treasury shares held during the year (in shares)	283	283
Treasury shares as percent of ordinary shares	7.70%	7.80%
Treasury shares, nominal value	£ 35	£ 35

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Other equity reserves (Details)

Other equity reserves (Details) - GBP (£) £ in Millions	12 Months Ended
Other equity reserves (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Apr. 01, 2018
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	£ (4,540)	£ (3,987)	£ (4,523)
Exchange adjustments	346	(504)	346
Net (losses)/gains taken to equity	(138)	(11)	45
Share of net gains of associates taken to equity	1	5
Transferred to/(from) profit or loss	41	(76)	202
Net losses in respect of cash flow hedging of capital expenditure	(13)
Tax	12	33	(57)
Cash flow hedges transferred to the statement of financial position, net of tax	(18)
Transfer on transition to IFRS 9				£ 72
Other equity reserves, ending balance	(4,237)	(4,540)	(3,987)
Gains (losses) on exchange adjustments related to the translation of foreign operations	896	(1,304)	1,364
Gains (losses) on hedges of net investments in foreign subsidiaries	(550)	800	(1,018)
Translation
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	390	894	548
Exchange adjustments	346	(504)	346
Other equity reserves, ending balance	736	390	894
Cash flow hedge
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	128	103	(45)
Net (losses)/gains taken to equity	(40)	19	(36)
Share of net gains of associates taken to equity	1	5
Transferred to/(from) profit or loss		(3)	227
Net losses in respect of cash flow hedging of capital expenditure	(13)
Tax	6	4	(43)
Cash flow hedges transferred to the statement of financial position, net of tax	(18)
Transfer on transition to IFRS 9				(3)
Other equity reserves, ending balance	61	128	103
Cost of hedging
Disclosure of reserves within equity [line items]
Net (losses)/gains taken to equity	(107)
Transferred to/(from) profit or loss	41
Tax	7
Transfer on transition to IFRS 9				76
Other equity reserves, ending balance	17
Available- for-sale
Disclosure of reserves within equity [line items]
Other equity reserves, beginning balance	88	162	120
Net (losses)/gains taken to equity		(30)	81
Transferred to/(from) profit or loss		(73)	(25)
Tax		29	(14)
Transfer on transition to IFRS 9				(88)
Other equity reserves, ending balance	0	88	162
Reserve of gains and losses from investments in equity instruments [member]
Disclosure of reserves within equity [line items]
Transfer on transition to IFRS 9				34
Other equity reserves, ending balance	34
FVOCI equity
Disclosure of reserves within equity [line items]
Net (losses)/gains taken to equity	2
Transfer on transition to IFRS 9				46
Other equity reserves, ending balance	48
Own credit
Disclosure of reserves within equity [line items]
Net (losses)/gains taken to equity	7
Tax	(1)
Transfer on transition to IFRS 9				£ 7
Other equity reserves, ending balance	13
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 - Reconciliation of ne

Net debt - Reconciliation of net cash flow to movement in net debt (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017	Mar. 31, 2016
Subclassifications of assets, liabilities and equities [abstract]
(Decrease)/increase in cash and cash equivalents	£ (80)	£ (807)	[1]	£ 984
(Decrease)/increase in financial investments	(822)	(5,953)		5,675
(Increase)/decrease in borrowings and related derivatives	(708)	1,209		(3,715)
Net interest paid on the components of net debt2	866	808		1,955
Change in debt resulting from cash flows	(744)	(4,743)		4,899
Changes in fair value of financial assets and liabilities and exchange movements	(1,648)	2,098		(2,273)
Net interest charge on the components of net debt	(1,076)	(1,017)		(2,401)
Disposal of UK Gas Distribution	0	0		5,890
Other non-cash movements	(27)	(66)		(64)
Movement in net debt (net of related derivative financial instruments) in the year	(3,495)	(3,728)		6,051
Net debt (net of related derivative financial instruments) at start of year	(23,002)	(19,274)		(25,325)
Impact of transition to IFRS 9		(32)		0	£ 0
Net debt (net of related derivative financial instruments) at end of year	£ (26,529)	£ (23,002)		£ (19,274)

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Net debt - Composition of net d

Net debt - Composition of net debt (Details) - GBP (£)	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Subclassifications of assets, liabilities and equities [abstract]
Cash, cash equivalents and financial investments	£ 2,233,000,000		£ 3,023,000,000	£ 9,880,000,000
Borrowings and bank overdrafts	(28,730,000,000)		(26,625,000,000)	(28,638,000,000)
Financing derivatives	(32,000,000)	£ 600,000,000	600,000,000	(516,000,000)	£ (106,000,000)
Net debt position	(26,529,000,000)	£ (23,034,000,000)	(23,002,000,000)	(19,274,000,000)	£ (25,325,000,000)
Interest shareholder loan	£ 23,000,000		£ 27,000,000	£ 0

Net debt - Analysis of changes

Net debt - Analysis of changes in net debt (Details) - GBP (£)	12 Months Ended
	Mar. 31, 2019		Mar. 31, 2018		Mar. 31, 2017		Mar. 31, 2016
Cash and cash equivalents
Cash and cash equivalents excluding bank overdrafts, beginning balance	£ 329,000,000		£ 1,139,000,000		£ 127,000,000
Cash flow, cash and cash equivalents	(80,000,000)		(807,000,000)		1,001,000,000
Fair value gains and losses and exchange movements, cash and cash equivalents	3,000,000		(3,000,000)		16,000,000
Disposal, cash and cash equivalents					(5,000,000)
Cash and cash equivalents excluding bank overdrafts, ending balance	252,000,000		329,000,000		1,139,000,000
Bank overdrafts
Bank overdrafts, beginning balance	0		0		(3,000,000)
Cash flow, bank overdrafts					(17,000,000)
Disposal, bank overdrafts					20,000,000
Bank overdrafts, ending balance	0		0		0
Net cash and cash equivalents
Cash and cash equivalents, beginning balance	329,000,000	[1]	1,139,000,000	[1]	124,000,000
Net (decrease)/increase in cash and cash equivalents	(80,000,000)		(807,000,000)	[1]	984,000,000
Fair value gains and losses and exchange movements, net cash and cash equivalents	3,000,000		(3,000,000)	[1]	16,000,000
Disposal, Net cash and cash equivalents					15,000,000
Cash and cash equivalents, ending balance	252,000,000		329,000,000	[1]	1,139,000,000	[1]
Financial investments
Financial investments, beginning balance	2,694,000,000		8,741,000,000		2,998,000,000
Cash flow, financial investments	(846,000,000)		(5,983,000,000)		5,624,000,000
Fair value gains and losses and exchange movements, financial investments	93,000,000		(149,000,000)		141,000,000
Interest income/(charges), financial investments	29,000,000		85,000,000		53,000,000
Other non-cash movements, financial investments	11,000,000
Disposal, financial investments					(75,000,000)
Financial investments, ending balance	1,981,000,000		2,694,000,000		8,741,000,000
Borrowings
Borrowings, beginning balance	(26,625,000,000)		(28,638,000,000)		(28,341,000,000)
Cash flow, borrowings	(240,000,000)		2,108,000,000		(2,196,000,000)
Fair value gains and losses and exchange movements, borrowings	(733,000,000)		1,088,000,000		(1,527,000,000)
Interest income/(charges), borrowings	(1,062,000,000)		(1,117,000,000)		(2,221,000,000)
Other non-cash movements, borrowings	(38,000,000)		(66,000,000)		(294,000,000)
Disposal, borrowings					5,941,000,000
Impact of transition to IFRS 9			(32,000,000)		0		£ 0
Borrowings, ending balance	(28,730,000,000)		(26,625,000,000)		(28,638,000,000)
Financing derivatives
Financing derivatives, beginning balance	600,000,000		(516,000,000)		(106,000,000)
Cash flow, financing derivatives	422,000,000		(61,000,000)		487,000,000
Fair value gains and losses and exchange movements, financing derivatives	(1,011,000,000)		1,162,000,000		(903,000,000)
Interest income/(charges), financing derivatives	(43,000,000)		15,000,000		(233,000,000)
Other non-cash movements, financing derivatives					230,000,000
Disposal, financing derivatives					9,000,000
Financing derivatives, ending balance	(32,000,000)		600,000,000		(516,000,000)
Net debt
Net debt (net of related derivative financial instruments) at start of year	(23,002,000,000)		(19,274,000,000)		(25,325,000,000)
Change in debt resulting from cash flows	(744,000,000)		(4,743,000,000)		4,899,000,000
Changes in fair value of financial assets and liabilities and exchange movements	(1,648,000,000)		2,098,000,000		(2,273,000,000)
Net interest charge on the components of net debt	(1,076,000,000)		(1,017,000,000)		(2,401,000,000)
Other non-cash movements	(27,000,000)		(66,000,000)		(64,000,000)
Disposal	0		0		5,890,000,000
Net debt (net of related derivative financial instruments) at end of year	(26,529,000,000)		(23,002,000,000)		(19,274,000,000)
Interest payable	223,000,000		197,000,000		210,000,000
Cash outflow on non debt related items	24,000,000		12,000,000		0
Derivative cash inflow in relation to capital expenditure	13,000,000		12,000,000		18,000,000
Cash flow (used in)/from financing activities, discontinued operations	0		231,000,000	[1]	(1,611,000,000)
Exceptional items
Net debt
Net interest charge on the components of net debt	0		£ (3,000,000)		£ (1,313,000,000)
Non-current assets
Financing derivatives
Financing derivatives, ending balance	996,000,000
Net debt
Net debt (net of related derivative financial instruments) at end of year	996,000,000
Current assets
Cash and cash equivalents
Cash and cash equivalents excluding bank overdrafts, ending balance	252,000,000
Net cash and cash equivalents
Cash and cash equivalents, ending balance	252,000,000
Financial investments
Financial investments, ending balance	1,981,000,000
Financing derivatives
Financing derivatives, ending balance	56,000,000
Net debt
Net debt (net of related derivative financial instruments) at end of year	2,289,000,000
Current liabilities
Borrowings
Borrowings, ending balance	(4,472,000,000)
Financing derivatives
Financing derivatives, ending balance	(282,000,000)
Net debt
Net debt (net of related derivative financial instruments) at end of year	(4,754,000,000)
Non-current liabilities
Borrowings
Borrowings, ending balance	(24,258,000,000)
Financing derivatives
Financing derivatives, ending balance	(802,000,000)
Net debt
Net debt (net of related derivative financial instruments) at end of year	£ (25,060,000,000)

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Commitments and contingencies_2

Commitments and contingencies (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Disclosure of finance lease and operating lease by lessee [line items]
Contracted for but not provided	£ 1,973	£ 1,843
Operating lease commitments	301	292
Energy purchase commitments	15,709	5,328
Estimated financial effect of contingent liabilities	2,975	2,669
Expected future minimum sublease payments receivable under non-cancellable sub-leases	86	42
Less than 1 year
Disclosure of finance lease and operating lease by lessee [line items]
Operating lease commitments	43	42
Energy purchase commitments	1,353	1,237
In 1 to 2 years
Disclosure of finance lease and operating lease by lessee [line items]
Operating lease commitments	39	37
Energy purchase commitments	779	700
In 2 to 3 years
Disclosure of finance lease and operating lease by lessee [line items]
Operating lease commitments	34	33
Energy purchase commitments	651	563
In 3 to 4 years
Disclosure of finance lease and operating lease by lessee [line items]
Operating lease commitments	35	30
Energy purchase commitments	827	449
In 4 to 5 years
Disclosure of finance lease and operating lease by lessee [line items]
Operating lease commitments	27	28
Energy purchase commitments	862	410
More than 5 years
Disclosure of finance lease and operating lease by lessee [line items]
Operating lease commitments	123	122
Energy purchase commitments	11,237	1,969
Guarantee of sublease for US property (expires 2040)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	173	178
Guarantees of certain obligations of Grain LNG (expire up to 2025)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	39	46
Guarantees of certain obligations for construction of HVDC West Coast Link (expires 2019)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	139	213
Guarantees of certain obligations of Nemo Link Limited (various expiry dates)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	19	63
Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	865	1,009
Guarantees of certain obligations of St William Homes LLP (various expiry dates)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	22	98
Guarantees of certain obligations for construction of IFA 2 (expected expiry 2021)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	505	729
Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	872	0
Other guarantees and letters of credit (various expiry dates)
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	341	333
Guarantees to both joint ventures and EPC contractors regarding the construction of interconnectors
Disclosure of finance lease and operating lease by lessee [line items]
Estimated financial effect of contingent liabilities	£ 470	£ 739

Related party transactions - Re

Related party transactions - Related party transactions table (Details) - GBP (£) £ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Pension plan
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		£ 5	£ 3	£ 3
Joint ventures
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		151	14	78
Purchases of goods and services, related party transactions		26	135	168
Amounts receivable	£ 160	584	160	64
Amounts payable	0	8	0	84
Interest income		5	4	0
Dividends received		30	43	75
Associates
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		192	220	0
Purchases of goods and services, related party transactions		141	160	169
Amounts receivable	376	368	376	457
Amounts payable	17	12	17	27
Interest income		23	27	0
Dividends received		171	170	£ 24
Quadgas HoldCo Limited
Disclosure of transactions between related parties [line items]
Other income, sale of UK gas distribution business	54	52
Receivables due from associates	352	352	352
Quadgas HoldCo Limited \| Associates
Disclosure of transactions between related parties [line items]
Dividends received		133	144
St William Homes LLP
Disclosure of transactions between related parties [line items]
Revenue from sale of goods and services, related party transactions		139	5
Receivables due from joint ventures	24	325	24
Nemo Link Limited
Disclosure of transactions between related parties [line items]
Receivables due from joint ventures	£ 130	£ 258	£ 130

Financial risk management - Tre

Financial risk management - Treasury credit risk (Details) £ in Millions	Mar. 31, 2019GBP (£)
Triple ‘A’ G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	£ 1,853
Triple ‘A’ vehicles (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	500
Triple ‘A’ range institutions and non-G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	1,011
Double ‘A’ G7 sovereign entities (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	1,685
Bottom of range \| Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	674
Bottom of range \| Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	236
Top of range \| Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	843
Top of range \| Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	337
Long-term limit £m \| Triple ‘A’ G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	927
Long-term limit £m \| Triple ‘A’ vehicles (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	0
Long-term limit £m \| Triple ‘A’ range institutions and non-G7 sovereign entities (AAA)
Disclosure of credit risk exposure [line items]
Maximum limit	506
Long-term limit £m \| Double ‘A’ G7 sovereign entities (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	843
Long-term limit £m \| Bottom of range \| Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	337
Long-term limit £m \| Bottom of range \| Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	118
Long-term limit £m \| Top of range \| Double ‘A’ range institutions (AA)
Disclosure of credit risk exposure [line items]
Maximum limit	421
Long-term limit £m \| Top of range \| Single ‘A’ range institutions (A)
Disclosure of credit risk exposure [line items]
Maximum limit	£ 169

Financial risk management - Off

Financial risk management - Offsetting financial assets and liabilities (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Related amounts available to be offset but not offset in statement of financial position
Derivative assets	£ 1,153	£ 1,724
Credit Risk
Assets
Gross carrying amounts £m	1,153	1,724
Gross amounts offset £m	0	0
Net amount presented in statement of financial position £m	1,153	1,724
Related amounts available to be offset but not offset in statement of financial position
Financial instruments £m	(270)	(539)
Cash collateral received/ pledged £m	(551)	(772)
Net amount £m	332	413
Liabilities
Gross carrying amounts £m	(1,183)	(1,061)
Gross amounts offset £m	0	0
Net amount presented in statement of financial position £m	(1,183)	(1,061)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments £m	270	539
Cash collateral received/ pledged £m	615	333
Net amount £m	(298)	(189)
Assets (Liabilities)
Gross carrying amounts £m	(30)	663
Gross amounts offset £m	0	0
Net amount presented in statement of financial position £m	(30)	663
Related amounts available to be offset but not offset in statement of financial position
Financial instruments £m	0	0
Cash collateral received/ pledged £m	64	(439)
Net amount £m	34	224
Credit Risk \| Financing derivatives
Liabilities
Gross carrying amounts £m	(1,084)	(945)
Gross amounts offset £m	0	0
Net amount presented in statement of financial position £m	(1,084)	(945)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments £m	299	523
Cash collateral received/ pledged £m	615	326
Net amount £m	(170)	(96)
Credit Risk \| Commodity contract derivatives
Liabilities
Gross carrying amounts £m	(99)	(116)
Gross amounts offset £m	0	0
Net amount presented in statement of financial position £m	(99)	(116)
Related amounts available to be offset but not offset in statement of financial position
Financial instruments £m	(29)	16
Cash collateral received/ pledged £m	0	7
Net amount £m	(128)	(93)
Credit Risk \| Bank account and bank overdraft
Assets
Gross amounts offset £m	(19)	(34)
Credit Risk \| Financing derivatives
Assets
Gross carrying amounts £m	1,052	1,545
Gross amounts offset £m	0	0
Net amount presented in statement of financial position £m	1,052	1,545
Related amounts available to be offset but not offset in statement of financial position
Financial instruments £m	(299)	(523)
Cash collateral received/ pledged £m	(551)	(772)
Net amount £m	202	250
Credit Risk \| Commodity contract derivatives
Assets
Gross carrying amounts £m	101	69
Gross amounts offset £m	0	0
Net amount presented in statement of financial position £m	101	69
Related amounts available to be offset but not offset in statement of financial position
Financial instruments £m	29	(16)
Cash collateral received/ pledged £m	0	0
Net amount £m	£ 130	53
Credit Risk \| Further acquisition agreement derivative
Assets
Gross carrying amounts £m		110
Gross amounts offset £m		0
Net amount presented in statement of financial position £m		110
Related amounts available to be offset but not offset in statement of financial position
Financial instruments £m		0
Cash collateral received/ pledged £m		0
Net amount £m		£ 110
Quadgas HoldCo Limited
Related amounts available to be offset but not offset in statement of financial position
Proportion of ownership interest in associate, put/call option equity interest	14.00%	14.00%
Proportion of ownership interest in associate, excluding put/call option equity interest	25.00%

Financial risk management - Liq

Financial risk management - Liquidity risk (Details) - Liquidity risk - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Non-derivative financial liabilities
Borrowings, excluding finance lease liabilities	£ (28,148)	£ (26,089)
Interest payments on borrowings	(15,719)	(14,948)
Finance lease liabilities	(310)	(313)
Other non-interest-bearing liabilities	(3,646)	(3,199)
Derivative financial assets
Financial liabilities	(48,300)	(44,507)
Derivative contracts – receipts
Derivative financial assets
Derivative contracts – receipts/payments	4,464	13,621
Derivative contracts – payments
Derivative financial assets
Derivative contracts – receipts/payments	(3,368)	(12,358)
Derivative contracts – receipts
Derivative financial liabilities
Derivative contracts – receipts/payments	7,471	2,244
Derivative contracts – payments
Derivative financial liabilities
Derivative contracts – receipts/payments	(8,949)	(3,327)
Commodity contract derivatives
Derivative financial liabilities
Commodity contract derivatives	(95)	(138)
Less than 1 year
Non-derivative financial liabilities
Borrowings, excluding finance lease liabilities	(4,129)	(4,099)
Interest payments on borrowings	(800)	(730)
Finance lease liabilities	(72)	(60)
Other non-interest-bearing liabilities	(3,306)	(2,840)
Derivative financial assets
Financial liabilities	(8,079)	(7,630)
Less than 1 year \| Derivative contracts – receipts
Derivative financial assets
Derivative contracts – receipts/payments	1,928	6,536
Less than 1 year \| Derivative contracts – payments
Derivative financial assets
Derivative contracts – receipts/payments	(1,251)	(6,000)
Less than 1 year \| Derivative contracts – receipts
Derivative financial liabilities
Derivative contracts – receipts/payments	3,045	1,111
Less than 1 year \| Derivative contracts – payments
Derivative financial liabilities
Derivative contracts – receipts/payments	(3,421)	(1,468)
Less than 1 year \| Commodity contract derivatives
Derivative financial liabilities
Commodity contract derivatives	(73)	(80)
In 1 to 2 years
Non-derivative financial liabilities
Borrowings, excluding finance lease liabilities	(2,348)	(1,642)
Interest payments on borrowings	(733)	(692)
Finance lease liabilities	(63)	(60)
Other non-interest-bearing liabilities	(340)	(359)
Derivative financial assets
Financial liabilities	(3,727)	(2,448)
In 1 to 2 years \| Derivative contracts – receipts
Derivative financial assets
Derivative contracts – receipts/payments	561	2,225
In 1 to 2 years \| Derivative contracts – payments
Derivative financial assets
Derivative contracts – receipts/payments	(459)	(1,703)
In 1 to 2 years \| Derivative contracts – receipts
Derivative financial liabilities
Derivative contracts – receipts/payments	1,703	424
In 1 to 2 years \| Derivative contracts – payments
Derivative financial liabilities
Derivative contracts – receipts/payments	(2,029)	(608)
In 1 to 2 years \| Commodity contract derivatives
Derivative financial liabilities
Commodity contract derivatives	(19)	(33)
In 2 to 3 years
Non-derivative financial liabilities
Borrowings, excluding finance lease liabilities	(1,998)	(2,325)
Interest payments on borrowings	(721)	(629)
Finance lease liabilities	(52)	(45)
Other non-interest-bearing liabilities	0	0
Derivative financial assets
Financial liabilities	(2,753)	(3,083)
In 2 to 3 years \| Derivative contracts – receipts
Derivative financial assets
Derivative contracts – receipts/payments	863	1,726
In 2 to 3 years \| Derivative contracts – payments
Derivative financial assets
Derivative contracts – receipts/payments	(783)	(1,678)
In 2 to 3 years \| Derivative contracts – receipts
Derivative financial liabilities
Derivative contracts – receipts/payments	163	441
In 2 to 3 years \| Derivative contracts – payments
Derivative financial liabilities
Derivative contracts – receipts/payments	(223)	(547)
In 2 to 3 years \| Commodity contract derivatives
Derivative financial liabilities
Commodity contract derivatives	(2)	(26)
More than 3 years
Non-derivative financial liabilities
Borrowings, excluding finance lease liabilities	(19,673)	(18,023)
Interest payments on borrowings	(13,465)	(12,897)
Finance lease liabilities	(123)	(148)
Other non-interest-bearing liabilities	0	0
Derivative financial assets
Financial liabilities	(33,741)	(31,346)
More than 3 years \| Derivative contracts – receipts
Derivative financial assets
Derivative contracts – receipts/payments	1,112	3,134
More than 3 years \| Derivative contracts – payments
Derivative financial assets
Derivative contracts – receipts/payments	(875)	(2,977)
More than 3 years \| Derivative contracts – receipts
Derivative financial liabilities
Derivative contracts – receipts/payments	2,560	268
More than 3 years \| Derivative contracts – payments
Derivative financial liabilities
Derivative contracts – receipts/payments	(3,276)	(704)
More than 3 years \| Commodity contract derivatives
Derivative financial liabilities
Commodity contract derivatives	£ (1)	£ 1

Financial risk management - Cur

Financial risk management - Currency risk (Details) - Currency risk - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	£ (26,529)	£ (23,002)
Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	252	329
Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,981	2,694
Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(28,730)	(26,625)
Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(26,497)	(23,602)
Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(32)	600
Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	2,033	1,781
Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(3,306)	(2,917)
Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(340)	(398)
Sterling £m
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(10,584)	(5,399)
Sterling £m \| Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	97	294
Sterling £m \| Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	965	1,471
Sterling £m \| Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(10,591)	(10,912)
Sterling £m \| Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(9,529)	(9,147)
Sterling £m \| Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,055)	3,748
Sterling £m \| Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	398	253
Sterling £m \| Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,221)	(1,124)
Sterling £m \| Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(93)	(144)
Euro £m
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	18	70
Euro £m \| Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	2	2
Euro £m \| Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	69
Euro £m \| Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(4,787)	(3,794)
Euro £m \| Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(4,785)	(3,723)
Euro £m \| Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	4,803	3,793
Euro £m \| Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Euro £m \| Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Euro £m \| Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Dollar £m
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(16,202)	(17,902)
Dollar £m \| Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	153	33
Dollar £m \| Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,016	1,125
Dollar £m \| Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(12,126)	(11,068)
Dollar £m \| Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(10,957)	(9,910)
Dollar £m \| Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(5,245)	(7,992)
Dollar £m \| Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,635	1,528
Dollar £m \| Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(2,085)	(1,793)
Dollar £m \| Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(247)	(254)
Other £m
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	239	229
Other £m \| Cash and cash equivalents
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other £m \| Financial investments
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	29
Other £m \| Borrowings
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,226)	(851)
Other £m \| Pre-derivative position
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	(1,226)	(822)
Other £m \| Derivative effect
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	1,465	1,051
Other £m \| Trade and other receivables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other £m \| Trade and other payables
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Other £m \| Other non-current liabilities
Disclosure of detailed information about financial instruments [line items]
Risk exposure associated with instruments sharing characteristic	£ 0	£ 0

Financial risk management - Int

Financial risk management - Interest rate risk (Details) - Interest rate risk - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	£ (26,529)	£ (23,002)
Fixed rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(17,238)	(14,378)
Floating rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(2,556)	(1,501)
Inflation linked £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,855)	(7,188)
Other £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	120	65
Cash and cash equivalents
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	252	329
Cash and cash equivalents \| Fixed rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	59	0
Cash and cash equivalents \| Floating rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	104	302
Cash and cash equivalents \| Inflation linked £m
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 £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	89	27
Financial investments
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	1,981	2,694
Financial investments \| Fixed rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	6	31
Financial investments \| Floating rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	1,944	2,625
Financial investments \| Inflation linked £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	0	0
Financial investments \| Other £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	31	38
Borrowings
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(28,730)	(26,625)
Borrowings \| Fixed rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(19,043)	(16,144)
Borrowings \| Floating rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(3,045)	(3,191)
Borrowings \| Inflation linked £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,642)	(7,290)
Borrowings \| Other £m
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	(26,497)	(23,602)
Pre-derivative position \| Fixed rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(18,978)	(16,113)
Pre-derivative position \| Floating rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(997)	(264)
Pre-derivative position \| Inflation linked £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(6,642)	(7,290)
Pre-derivative position \| Other £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	120	65
Derivative effect
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(32)	600
Derivative effect \| Fixed rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	1,740	1,735
Derivative effect \| Floating rate £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(1,559)	(1,237)
Derivative effect \| Inflation linked £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	(213)	102
Derivative effect \| Other £m
Disclosure of financial instruments by type of interest rate [line items]
Risk exposure associated with instruments sharing characteristic	£ 0	£ 0

Financial risk management - Imp

Financial risk management - Impact of hedge accounting in the primary financial statements (Details) £ in Millions	12 Months Ended
	Mar. 31, 2019GBP (£)	Mar. 31, 2019	Mar. 31, 2019£ / $	Mar. 31, 2019€ / $	Mar. 31, 2019£ / €	Apr. 01, 2018GBP (£)	Mar. 31, 2018GBP (£)	Mar. 31, 2017GBP (£)	Mar. 31, 2016GBP (£)
Disclosure of detailed information about financial instruments [line items]
Net losses in respect of cash flow hedges	£ (13)
Other equity reserves	(4,237)					£ (4,468)	£ (4,540)	£ (3,987)	£ (4,523)
Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves	17					£ 76
Fair value hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Net losses in respect of cost of hedging	(6)
Transferred to profit or loss in respect of cost of hedging	3
Fair value hedges \| Cost of hedging \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Other equity reserves	(4)
Fair value hedges \| Bottom of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate			1.64	1.13	1.19
Fair value hedges \| Top of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate			1.65	1.16	1.24
Fair value hedges \| GBP \| Libor \| Bottom of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis		0.30%
Fair value hedges \| GBP \| Libor \| Top of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis		5.61%
Fair value hedges \| USD \| Libor \| Bottom of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis		(0.44%)
Fair value hedges \| USD \| Libor \| Top of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, adjustment to interest rate basis		1.15%
Cash flow hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Net losses in respect of cash flow hedges	(40)
Net losses in respect of cost of hedging	(12)
Transferred to profit or loss in respect of cash flow hedges	(1)
Transferred to profit or loss in respect of cost of hedging	0
Cash flow hedges \| Currency risk
Disclosure of detailed information about financial instruments [line items]
Net losses in respect of cash flow hedges	(12)
Net losses in respect of cost of hedging	0
Transferred to profit or loss in respect of cash flow hedges	0
Transferred to profit or loss in respect of cost of hedging	0
Cash flow hedges \| Cost of hedging \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Other equity reserves	0
Cash flow hedges \| Cost of hedging \| Currency risk
Disclosure of detailed information about financial instruments [line items]
Other equity reserves	0
Cash flow hedges \| Bottom of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate			1.52	1.13	1.14
Cash flow hedges \| Bottom of range \| Currency risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate			1.29		1.07
Cash flow hedges \| Top of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate			1.66	1.14	1.24
Cash flow hedges \| Top of range \| Currency risk
Disclosure of detailed information about financial instruments [line items]
Closing foreign exchange rate			1.41		1.32
Cash flow hedges \| GBP \| Bottom of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate		1.795%
Cash flow hedges \| GBP \| Top of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate		5.85%
Cash flow hedges \| USD \| Bottom of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate		1.103%
Cash flow hedges \| USD \| Top of range \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Borrowings, interest rate		3.864%
Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Net losses in respect of cost of hedging	(90)
Transferred to profit or loss in respect of cost of hedging	39
Closing foreign exchange rate			1.49		1.15
Net investment hedges \| Cost of hedging
Disclosure of detailed information about financial instruments [line items]
Other equity reserves	32
Derivative assets - current \| Fair value hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	17
Derivative assets - current \| Cash flow hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0
Derivative assets - current \| Cash flow hedges \| Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	9
Derivative assets - current \| Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0
Derivative assets - non-current \| Fair value hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	168
Derivative assets - non-current \| Cash flow hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	78
Derivative assets - non-current \| Cash flow hedges \| Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	23
Derivative assets - non-current \| Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, assets	0
Derivative liabilities - current \| Fair value hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(9)
Derivative liabilities - current \| Cash flow hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(28)
Derivative liabilities - current \| Cash flow hedges \| Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(3)
Derivative liabilities - current \| Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(43)
Derivative liabilities - non-current \| Fair value hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(25)
Derivative liabilities - non-current \| Cash flow hedges \| Foreign currency and interest rate risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(134)
Derivative liabilities - non-current \| Cash flow hedges \| Currency risk
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	(4)
Derivative liabilities - non-current \| Net investment hedges
Disclosure of detailed information about financial instruments [line items]
Hedging instrument, liabilities	£ (249)

Financial risk management - Eff

Financial risk management - Effects of hedge accounting on financial position and performance for each type of hedge (Details) £ in Millions	12 Months Ended
	Mar. 31, 2019GBP (£)
Foreign currency and interest rate risk \| Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	£ (1,707)
Balance of fair value hedge adjustments in borrowings, Continuing hedges	11
Balance of fair value hedge adjustments in borrowings, Discontinued hedges	(117)
Change in value used for calculating ineffectiveness, Hedged item	11
Change in value used for calculating ineffectiveness, Hedging instrument	(6)
Hedge ineffectiveness	5
Foreign currency and interest rate risk \| Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(3,804)
Balance in cash flow hedge reserve, Continuing hedges	(17)
Balance in cash flow hedge reserve, Discontinued hedges	51
Change in value used for calculating ineffectiveness, Hedged item	39
Change in value used for calculating ineffectiveness, Hedging instrument	(39)
Hedge ineffectiveness	0
Currency risk \| Cash flow hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(697)
Balance in cash flow hedge reserve, Continuing hedges	47
Balance in cash flow hedge reserve, Discontinued hedges	0
Change in value used for calculating ineffectiveness, Hedged item	12
Change in value used for calculating ineffectiveness, Hedging instrument	(12)
Hedge ineffectiveness	0
Currency risk \| Net investment hedges
Disclosure of detailed information about hedging instruments [line items]
Hedging instrument notional	(2,974)
Balance in translation reserve, Continuing hedges	(329)
Balance in translation reserve, Discontinued hedges	(2,502)
Change in value used for calculating ineffectiveness, Hedged item	550
Change in value used for calculating ineffectiveness, Hedging instrument	(550)
Hedge ineffectiveness	0
Borrowings \| Foreign currency and interest rate risk \| Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	1,810
Current liabilities \| Borrowings \| Foreign currency and interest rate risk \| Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	202
Non-current liabilities \| Borrowings \| Foreign currency and interest rate risk \| Fair value hedges
Disclosure of detailed information about hedging instruments [line items]
Hedged borrowings	£ 1,608

Financial risk management - Fai

Financial risk management - Fair value analysis (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 3,052	£ 4,524
Liabilities	(1,850)	(1,061)
Financial Assets (Liabilities)	1,202	3,463
Derivative assets	£ 1,153	1,724
Minimum deviation of growth curve to be considered observable for fair value measurement	5.00%
Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 1,404	2,406
Liabilities	(667)	0
Financial Assets (Liabilities)	737	2,406
Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,426	1,862
Liabilities	(900)	(779)
Financial Assets (Liabilities)	526	1,083
Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	222	256
Liabilities	(283)	(282)
Financial Assets (Liabilities)	(61)	(26)	£ (435)
Financing derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(1,084)	(945)
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	(868)	(725)
Financing derivatives \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(216)	(220)
Commodity contract derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(99)	(116)
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	(32)	(54)
Commodity contract derivatives \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(67)	(62)
Liabilities held at fair value
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(667)	0
Liabilities held at fair value \| Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	(667)	0
Liabilities held at fair value \| Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	0
Liabilities held at fair value \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Liabilities	0	0
Available-for-sale investments
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	2,721
Available-for-sale investments \| Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	2,406
Available-for-sale investments \| Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	310
Available-for-sale investments \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	5
Investments held at FVTPL
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,373	0
Investments held at FVTPL \| Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,311	0
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	62	0
Investments held at FVOCI
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	436	0
Investments held at FVOCI \| Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	93	0
Investments held at FVOCI \| Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	343	0
Investments held at FVOCI \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Investments in associates
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	90	79
Investments in associates \| Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Investments in associates \| Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Investments in associates \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	90	79
Financing derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,052	1,545
Financing derivatives \| Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
Financing derivatives \| Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	1,050	1,544
Financing derivatives \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	2	1
Commodity contract derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	101	69
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	33	8
Commodity contract derivatives \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	68	61
FAA derivative
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	110
FAA derivative \| Level 1
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
FAA derivative \| Level 2
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	0	0
FAA derivative \| Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Assets	£ 0	£ 110
Quadgas HoldCo Limited
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Proportion of ownership interest in associate, put/call option equity interest	14.00%	14.00%
Proportion of ownership interest in associate, excluding put/call option equity interest	25.00%

Financial risk management - Cha

Financial risk management - Changes in level 3 financial instruments (Details) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	£ 3,463
Ending balance	1,202	£ 3,463
Derivative assets	1,153	1,724
Financing derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Derivative assets	1,052	1,545
Commodity contract derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Derivative assets	101	69
Level 3
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	(26)	(435)
Net gains/(losses) for the year	3	133
Purchases	101	68
Settlements	(29)	208
Reclassification to held for sale	(110)	0
Ending balance	(61)	(26)
Level 3 \| Financing derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	(219)	(465)
Net gains/(losses) for the year	4	15
Purchases	0	0
Settlements	1	231
Reclassification to held for sale	0	0
Ending balance	(214)	(219)
Gains (losses) on assets held at end of year	4	15
Level 3 \| Commodity contract derivatives
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	(1)	(16)
Net gains/(losses) for the year	(16)	8
Purchases	44	27
Settlements	(26)	(20)
Reclassification to held for sale	0	0
Ending balance	1	(1)
Gains (losses) on assets held at end of year	(21)	35
Level 3 \| Other
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Beginning balance	194	46
Net gains/(losses) for the year	15	110
Purchases	57	41
Settlements	(4)	(3)
Reclassification to held for sale	(110)	0
Ending balance	£ 152	194
FAA derivative \| Level 3
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Derivative assets		£ 110
Quadgas HoldCo Limited
Changes In Fair Value Measurement, Assets (Liabilities) [Roll Forward]
Proportion of ownership interest in associate, put/call option equity interest	14.00%	14.00%
Proportion of ownership interest in associate, excluding put/call option equity interest	25.00%

Financial risk management - I_2

Financial risk management - Impacts of reasonably possible changes in significant level 3 assumptions (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Financing derivatives \| Plus 20 basis points change in Limited Price Inflation (LPI) market curve
Disclosure of detailed information about financial instruments [line items]
20 basis points change in Limited Price Inflation (LPI) market curve	£ (88)	£ (84)
Financing derivatives \| Minus 20 basis points change in LPI market curve
Disclosure of detailed information about financial instruments [line items]
–20 basis points change in LPI market curve	83	82
Commodity contract derivatives \| 10% increase in commodity prices
Disclosure of detailed information about financial instruments [line items]
10% increase in commodity prices	(1)	(1)
Commodity contract derivatives \| 10% decrease in commodity prices
Disclosure of detailed information about financial instruments [line items]
10% decrease in commodity prices	2	3
Commodity contract derivatives \| Plus 10% market area price change
Disclosure of detailed information about financial instruments [line items]
10% market area price change	(10)	(6)
Commodity contract derivatives \| Minus 10% market area price change
Disclosure of detailed information about financial instruments [line items]
–10% market area price change	10	5
Other \| Plus 50 basis points change in discount rate
Disclosure of detailed information about financial instruments [line items]
50 basis points change in discount rate	(3)	(5)
Other \| Minus 50 basis points change in discount rate
Disclosure of detailed information about financial instruments [line items]
- 50 basis points change in discount rate	£ 3	£ 6

Financial risk management - Cap

Financial risk management - Capital risk management (Details)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Financial Instruments [Abstract]
Retained cash flow ratio	9.40%	9.70%
Gearing ratio	66.00%	64.00%
Interest cover ratio	4.4	4.4

Borrowing facilities (Details)

Borrowing facilities (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 5,727	£ 5,683
Less than 1 year
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	0	0
In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	0	3,910
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	2,190	0
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	1,668	0
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	1,869	1,773
More than 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities	£ 0	£ 0

Borrowing facilities - Narrativ

Borrowing facilities - Narrative (Details) - GBP (£) £ in Millions	Apr. 01, 2019	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		£ 5,727	£ 5,683
Borrowings		28,730	26,625	£ 28,638
Bilateral Committed Credit Facilities
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity		5,463	5,438
Credit Facilities From Syndicates Of Banks
Disclosure of detailed information about borrowings [line items]
Line of credit facility, maximum borrowing capacity		264	245
Facilities Held As Backup To Commercial Paper And Similar Borrowings
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		5,463	5,438
Facilities Available As Backup To Specific US Borrowings
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		264	245
Export Credit Agreements
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		510	704
Borrowings		859	797
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		1,869	1,773
Borrowings		714	1,469
More than 5 years
Disclosure of detailed information about borrowings [line items]
Undrawn borrowing facilities		0	£ 0
Renegotiated undrawn borrowing facilities		£ 270
Subsequent event \| 2019 Export Credit Agreements
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 550

Subsidiary undertakings, join_2

Subsidiary undertakings, joint ventures and associates - Subsidiaries (Details)	12 Months Ended
	Mar. 31, 2019
Warwick Technology Park Management Company (No 2) Limited
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	60.56%
New England Hydro Finance Company, Inc.
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	53.704%
New England Hydro-Transmission Corporation
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	53.704%
New England Hydro-Transmission Electric Company Inc.
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	53.704%
Vermont Green Line Devco, LLC
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	90.00%

Subsidiary undertakings, join_3

Subsidiary undertakings, joint ventures and associates - Joint ventures (Details)	Mar. 31, 2019	Mar. 31, 2019
BritNed Development Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture	50.00%	50.00%
Joint Radio Company Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
Nemo Link Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
NGET/SPT Upgrades Limited
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
St William Homes LLP
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
Clean Energy Generation, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
Goldendale Energy Storage LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
Island Park Energy Center, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
Islander East Pipeline Company, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
LI Energy Storage System, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
LI Solar Generation, LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
Swan Lake North Holdings LLC
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%
IFA2 SAS
Disclosure of joint ventures [line items]
Proportion of ownership interest in joint venture		50.00%

Subsidiary undertakings, join_4

Subsidiary undertakings, joint ventures and associates - Associates (Details)	Mar. 31, 2019	Mar. 31, 2019
Quadgas HoldCo Limited
Disclosure of associates [line items]
Proportion of ownership interest in associate	39.00%	39.00%
Algonquin Gas Transmission, LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate		20.00%
Clean Line Energy Partners LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate		32.00%
Connecticut Yankee Atomic Power Company
Disclosure of associates [line items]
Proportion of ownership interest in associate		19.50%
Direct Global Power, Inc.
Disclosure of associates [line items]
Proportion of ownership interest in associate		26.00%
Energy Impact Fund LP
Disclosure of associates [line items]
Proportion of ownership interest in associate		9.42%
KHB Venture LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate		33.00%
Maine Yankee Atomic Power Company
Disclosure of associates [line items]
Proportion of ownership interest in associate		24.00%
Millennium Pipeline Company LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate	26.25%	26.25%
New York Transco LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate		28.30%
Nysearch RMLD, LLC
Disclosure of associates [line items]
Proportion of ownership interest in associate		22.63%
Yankee Atomic Electric Company
Disclosure of associates [line items]
Proportion of ownership interest in associate		34.50%
Coreso SA
Disclosure of associates [line items]
Proportion of ownership interest in associate		15.84%
Energis plc
Disclosure of associates [line items]
Proportion of ownership interest in associate		33.06%

Sensitivites (Details)

Sensitivites (Details) - GBP (£) £ in Millions	12 Months Ended
Sensitivites (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018
UK Pensions \| Actuarial assumption of discount rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	£ 6	£ 8
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 1,064	1,075
Change in actuarial assumption, percent	0.50%
UK Pensions \| Actuarial assumption of expected rates of inflation
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	£ 4	5
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 908	965
Change in actuarial assumption, percent	0.50%
UK Pensions \| Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase in actuarial assumption	£ 1	0
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption	£ 56	61
Increase in actuarial assumption, percent	0.50%
UK Pensions \| Actuarial assumption of life expectancy after retirement
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	£ 1	2
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 610	588
Increase in actuarial assumption, years	1 year
US Pensions \| 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	£ 16	15
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 688	623
Change in actuarial assumption, percent	0.50%
US Pensions \| Actuarial assumption of expected rates of salary increases
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase in actuarial assumption	£ 2	3
Increase (decrease) in defined benefit obligation due to reasonably possible increase in actuarial assumption	£ 46	44
Increase in actuarial assumption, percent	0.50%
US Pensions \| Actuarial assumption of life expectancy after retirement
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	£ 4	4
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 406	359
Increase in actuarial assumption, years	1 year
US Pensions \| US Healthcare Cost
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase (decrease) in defined benefit plan expense due to reasonably possible increase (decrease) in actuarial assumption	£ 32	31
Increase (decrease) in defined benefit obligation due to reasonably possible increase (decrease) in actuarial assumption	£ 503	448
Change in actuarial assumption, percent	1.00%
Commodity price risk
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, percent	10.00%
Increase in risk variable, impact on earnings	£ 26	23
Increase in risk variable, impact on other equity reserves	26	23
Decrease in risk variable, impact on earnings	(27)	(23)
Decrease in risk variable, impact on other equity reserves	(27)	(23)
Inflation, UK RPI change
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on earnings	27	30
Change in risk variable, impact on other equity reserves	£ 0	0
Change in risk variable, percent	0.50%
Currency risk
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on earnings	£ 53	48
Change in risk variable, impact on other equity reserves	246	479
Change in risk variable, impact on net assets	£ 1,119	1,040
Change in risk variable, percent	10.00%
Country of domicile \| Interest rate risk
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on earnings	£ 16	43
Change in risk variable, impact on other equity reserves	£ 13	26
Change in risk variable, percent	0.50%
Foreign countries \| Interest rate risk
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on earnings	£ 11	39
Change in risk variable, impact on other equity reserves	£ 44	17
Change in risk variable, percent	0.50%
Fair Value Change \| Derivative Financial Instruments
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on earnings	£ (3)	60
Change in risk variable, impact on other equity reserves	£ (3)	60
Change in risk variable, percent	10.00%
Fair Value Change \| Commodity Contract Derivative Liabilities
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on earnings	£ 0	(5)
Change in risk variable, impact on other equity reserves	£ 0	(5)
Change in risk variable, percent	10.00%
Other environment related provision \| Actuarial assumption of discount rates
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, percent	0.50%
Other environment related provision \| Estimated Future Cash Flows Change
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Change in risk variable, impact on earnings	£ 165	154
Change in risk variable, impact on other equity reserves	£ 165	£ 154
Change in risk variable, percent	10.00%

Additional disclosures in res_3

Additional disclosures in respect of guaranteed securities - Narrative (Details) - GBP (£)	Oct. 29, 2007	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Jun. 01, 2018
Disclosure of detailed information about borrowings [line items]
Profit (loss)		£ 1,514,000,000	£ 3,551,000,000	£ 7,794,000,000
National Grid Gas plc
Disclosure of detailed information about borrowings [line items]
Preferred shares issuance rate	3.60%
British Transco Finance Inc. £m
Disclosure of detailed information about borrowings [line items]
Preferred shares issuance rate	3.90%
Borrowings, interest rate					6.625%
British Transco Finance Inc. £m
Disclosure of detailed information about borrowings [line items]
Proceeds from issuing shares		£ 29,000,000
Profit (loss)			£ 0	£ 0

Additional disclosures in res_4

Additional disclosures in respect of guaranteed securities - Summary statements of comprehensive income (Details) - GBP (£)		12 Months Ended
		Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Continuing Operations [Abstract]
Revenue		£ 14,933,000,000	£ 15,250,000,000		£ 15,035,000,000
Operating Costs [Abstract]
Depreciation, amortisation and impairment		(1,735,000,000)	(1,530,000,000)		(1,481,000,000)
Payroll costs		(1,852,000,000)	(1,648,000,000)		(1,578,000,000)
Purchases of electricity		(1,454,000,000)	(1,285,000,000)		(1,097,000,000)
Purchases of gas		(1,642,000,000)	(1,543,000,000)		(1,219,000,000)
Rates and property taxes		(1,108,000,000)	(1,057,000,000)		(1,042,000,000)
Balancing Services Incentive Scheme		(1,196,000,000)	(1,012,000,000)		(1,120,000,000)
Payments to other UK network owners		0	(1,043,000,000)		(1,008,000,000)
Other operating costs		(3,076,000,000)	(2,639,000,000)		(3,282,000,000)
Operating costs		(12,063,000,000)	(11,757,000,000)		(11,827,000,000)
Operating profit		2,870,000,000	3,493,000,000	[1]	3,208,000,000
Net finance costs		(1,069,000,000)	(882,000,000)		(1,087,000,000)
Dividends receivable					0
Share of post-tax results of joint ventures and associates		40,000,000	49,000,000		63,000,000
Profit before tax		1,841,000,000	2,660,000,000		2,184,000,000
Tax		(339,000,000)	889,000,000		(374,000,000)
Profit (loss) after tax from discontinued operations		12,000,000	2,000,000		5,984,000,000
Total profit for the year (continuing and discontinued)		1,514,000,000	3,551,000,000		7,794,000,000
Amounts recognised in other comprehensive income from continuing operations		303,000,000	224,000,000	[2]	578,000,000
Amounts recognised in other comprehensive income from discontinued operations	[3]	36,000,000	147,000,000	[2]	42,000,000
Total comprehensive income for the year		1,853,000,000	3,922,000,000	[2]	8,414,000,000
Comprehensive income, attributable to owners of parent		1,849,000,000	3,922,000,000	[2]	8,415,000,000
Comprehensive income, attributable to non-controlling interests		4,000,000	0		(1,000,000)
National Grid plc
Continuing Operations [Abstract]
Revenue		0	0		0
Operating Costs [Abstract]
Depreciation, amortisation and impairment		0	0		0
Payroll costs		0	0		0
Purchases of electricity		0	0		0
Purchases of gas		0	0		0
Rates and property taxes		0	0		0
Balancing Services Incentive Scheme		0	0		0
Payments to other UK network owners			0		0
Other operating costs		0	0		0
Operating costs		0	0		0
Operating profit		0	0		0
Net finance costs		(252,000,000)	889,000,000		8,177,000,000
Dividends receivable					0
Share of post-tax results of joint ventures and associates		1,712,000,000	2,622,000,000		(401,000,000)
Profit before tax		1,460,000,000	3,511,000,000		7,776,000,000
Tax		50,000,000	40,000,000		19,000,000
Profit (loss) after tax from discontinued operations		0	0		0
Total profit for the year (continuing and discontinued)		1,510,000,000	3,551,000,000		7,795,000,000
Amounts recognised in other comprehensive income from continuing operations		303,000,000	224,000,000		578,000,000
Amounts recognised in other comprehensive income from discontinued operations		36,000,000	147,000,000		42,000,000
Total comprehensive income for the year		1,849,000,000	3,922,000,000		8,415,000,000
Comprehensive income, attributable to owners of parent		1,849,000,000	3,922,000,000		8,415,000,000
Comprehensive income, attributable to non-controlling interests		0	0		0
Niagara Mohawk Power Corporation
Continuing Operations [Abstract]
Revenue		2,483,000,000	2,416,000,000		2,388,000,000
Operating Costs [Abstract]
Depreciation, amortisation and impairment		(216,000,000)	(190,000,000)		(193,000,000)
Payroll costs		(360,000,000)	(318,000,000)		(326,000,000)
Purchases of electricity		(559,000,000)	(537,000,000)		(511,000,000)
Purchases of gas		(189,000,000)	(166,000,000)		(140,000,000)
Rates and property taxes		(200,000,000)	(183,000,000)		(188,000,000)
Balancing Services Incentive Scheme		0	0		0
Payments to other UK network owners			0		0
Other operating costs		(569,000,000)	(397,000,000)		(435,000,000)
Operating costs		(2,093,000,000)	(1,791,000,000)		(1,793,000,000)
Operating profit		390,000,000	625,000,000		595,000,000
Net finance costs		(124,000,000)	(100,000,000)		(101,000,000)
Dividends receivable					0
Share of post-tax results of joint ventures and associates		0	0		0
Profit before tax		266,000,000	525,000,000		494,000,000
Tax		(56,000,000)	321,000,000		(181,000,000)
Profit (loss) after tax from discontinued operations		0	0		0
Total profit for the year (continuing and discontinued)		210,000,000	846,000,000		313,000,000
Amounts recognised in other comprehensive income from continuing operations		4,000,000	1,000,000		0
Amounts recognised in other comprehensive income from discontinued operations		0	0		0
Total comprehensive income for the year		214,000,000	847,000,000		313,000,000
Comprehensive income, attributable to owners of parent		214,000,000	847,000,000		313,000,000
Comprehensive income, attributable to non-controlling interests		0	0		0
British Transco Finance Inc.
Continuing Operations [Abstract]
Revenue			0		0
Operating Costs [Abstract]
Depreciation, amortisation and impairment			0		0
Payroll costs			0		0
Purchases of electricity			0		0
Purchases of gas			0		0
Rates and property taxes			0		0
Balancing Services Incentive Scheme			0		0
Payments to other UK network owners			0		0
Other operating costs			0		0
Operating costs			0		0
Operating profit			0		0
Net finance costs			0		0
Dividends receivable					0
Share of post-tax results of joint ventures and associates			0		0
Profit before tax			0		0
Tax			0		0
Profit (loss) after tax from discontinued operations			0		0
Total profit for the year (continuing and discontinued)			0		0
Amounts recognised in other comprehensive income from continuing operations			0		0
Amounts recognised in other comprehensive income from discontinued operations			0		0
Total comprehensive income for the year			0		0
Comprehensive income, attributable to owners of parent			0		0
Comprehensive income, attributable to non-controlling interests			0		0
National Grid Gas plc
Continuing Operations [Abstract]
Revenue			1,430,000,000		1,376,000,000
Operating Costs [Abstract]
Depreciation, amortisation and impairment			(245,000,000)		(256,000,000)
Payroll costs			(122,000,000)		(114,000,000)
Purchases of electricity			0		0
Purchases of gas			0		(67,000,000)
Rates and property taxes			(94,000,000)		(101,000,000)
Balancing Services Incentive Scheme			0		0
Payments to other UK network owners			0		0
Other operating costs			(331,000,000)		(394,000,000)
Operating costs			(792,000,000)		(932,000,000)
Operating profit			638,000,000		444,000,000
Net finance costs			(174,000,000)		(253,000,000)
Dividends receivable					0
Share of post-tax results of joint ventures and associates			8,000,000		0
Profit before tax			472,000,000		191,000,000
Tax			(103,000,000)		16,000,000
Profit (loss) after tax from discontinued operations			17,000,000		4,633,000,000
Total profit for the year (continuing and discontinued)			386,000,000		4,840,000,000
Amounts recognised in other comprehensive income from continuing operations			272,000,000		114,000,000
Amounts recognised in other comprehensive income from discontinued operations			0		51,000,000
Total comprehensive income for the year			658,000,000		5,005,000,000
Comprehensive income, attributable to owners of parent			658,000,000		5,005,000,000
Comprehensive income, attributable to non-controlling interests			0		0
Other subsidiaries
Continuing Operations [Abstract]
Revenue		12,450,000,000	11,495,000,000		11,435,000,000
Operating Costs [Abstract]
Depreciation, amortisation and impairment		(1,519,000,000)	(1,095,000,000)		(1,032,000,000)
Payroll costs		(1,492,000,000)	(1,208,000,000)		(1,138,000,000)
Purchases of electricity		(895,000,000)	(748,000,000)		(586,000,000)
Purchases of gas		(1,453,000,000)	(1,377,000,000)		(1,012,000,000)
Rates and property taxes		(908,000,000)	(780,000,000)		(753,000,000)
Balancing Services Incentive Scheme		(1,196,000,000)	(1,012,000,000)		(1,120,000,000)
Payments to other UK network owners			(1,043,000,000)		(1,008,000,000)
Other operating costs		(2,507,000,000)	(2,002,000,000)		(2,617,000,000)
Operating costs		(9,970,000,000)	(9,265,000,000)		(9,266,000,000)
Operating profit		2,480,000,000	2,230,000,000		2,169,000,000
Net finance costs		(693,000,000)	(1,497,000,000)		(8,910,000,000)
Dividends receivable					8,100,000,000
Share of post-tax results of joint ventures and associates		40,000,000	49,000,000		63,000,000
Profit before tax		1,827,000,000	782,000,000		1,422,000,000
Tax		(333,000,000)	631,000,000		(228,000,000)
Profit (loss) after tax from discontinued operations		12,000,000	(15,000,000)		1,351,000,000
Total profit for the year (continuing and discontinued)		1,506,000,000	1,398,000,000		2,545,000,000
Amounts recognised in other comprehensive income from continuing operations		(45,000,000)	457,000,000		177,000,000
Amounts recognised in other comprehensive income from discontinued operations		36,000,000	147,000,000		(62,000,000)
Total comprehensive income for the year		1,497,000,000	2,002,000,000		2,660,000,000
Comprehensive income, attributable to owners of parent		1,493,000,000	2,002,000,000		2,661,000,000
Comprehensive income, attributable to non-controlling interests		4,000,000	0		(1,000,000)
Consolidation adjustments
Continuing Operations [Abstract]
Revenue		0	(91,000,000)		(164,000,000)
Operating Costs [Abstract]
Depreciation, amortisation and impairment		0	0		0
Payroll costs		0	0		0
Purchases of electricity		0	0		0
Purchases of gas		0	0		0
Rates and property taxes		0	0		0
Balancing Services Incentive Scheme		0	0		0
Payments to other UK network owners			0		0
Other operating costs		0	91,000,000		164,000,000
Operating costs		0	91,000,000		164,000,000
Operating profit		0	0		0
Net finance costs		0	0		0
Dividends receivable					(8,100,000,000)
Share of post-tax results of joint ventures and associates		(1,712,000,000)	(2,630,000,000)		401,000,000
Profit before tax		(1,712,000,000)	(2,630,000,000)		(7,699,000,000)
Tax		0	0		0
Profit (loss) after tax from discontinued operations		0	0		0
Total profit for the year (continuing and discontinued)		(1,712,000,000)	(2,630,000,000)		(7,699,000,000)
Amounts recognised in other comprehensive income from continuing operations		41,000,000	(730,000,000)		(291,000,000)
Amounts recognised in other comprehensive income from discontinued operations		(36,000,000)	(147,000,000)		11,000,000
Total comprehensive income for the year		(1,707,000,000)	(3,507,000,000)		(7,979,000,000)
Comprehensive income, attributable to owners of parent		(1,707,000,000)	(3,507,000,000)		(7,979,000,000)
Comprehensive income, attributable to non-controlling interests		£ 0	£ 0		£ 0

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[2]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[3]	The other comprehensive income from discontinued operations relates to the items of other comprehensive income of Cadent (investment through Quadgas HoldCo Limited), comprising mainly £35 million (2018: £142 million; 2017: £nil) remeasurement gains on pension assets and post-retirement benefit obligations and a £1 million (2018: £5 million; 2017: £nil) net gain in respect of cash flow hedges. Both items are shown net of tax.

Additional disclosures in res_5

Additional disclosures in respect of guaranteed securities - Statements of financial position (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018		Mar. 31, 2017		Mar. 31, 2016
Non-current assets
Goodwill	£ 5,869	£ 5,444	£ 5,444
Other intangible assets	1,084	899	899
Property, plant and equipment	43,913	39,853	39,853
Other non-current assets	264	115	115
Amounts owed by subsidiary undertakings	0		0
Pension assets	1,567	1,409	1,409
Financial and other investments	1,275		3,067
Derivative financial assets	1,045	1,319	1,319
Total non-current assets	55,017	52,106	52,106
Current assets
Inventories and current intangible assets	370	341	341
Trade and other receivables	3,153	2,795	2,798
Current tax assets	126	114	114
Amounts owed by subsidiary undertakings	0		0
Financial and other investments	1,981	2,694	2,694		£ 8,741		£ 2,998
Derivative financial assets	108	405	405
Cash and cash equivalents	252	329	329	[1]	1,139	[1]	124
Assets held for sale	1,956		0
Total current assets	7,946	6,678	6,681
Total assets	62,963	58,784	58,787
Current liabilities
Borrowings	(4,472)	(4,447)	(4,447)
Derivative financial liabilities	(350)	(401)	(401)
Trade and other payables	(3,769)	(3,394)	(3,453)
Contract liabilities	(61)	(53)	0
Amounts owed to subsidiary undertakings	0		0
Current tax liabilities	(161)	(123)	(123)
Provisions	(316)	(273)	(273)
Total current liabilities	(9,129)	(8,691)	(8,697)
Non-current liabilities
Borrowings	(24,258)	(22,210)	(22,178)
Derivative financial liabilities	(833)	(660)	(660)
Other non-current liabilities	(808)	(750)	(1,317)
Contract liabilities	(933)	(813)	0
Amounts owed to subsidiary undertakings	0		0
Deferred tax liabilities	(3,965)	(3,557)	(3,636)
Pensions and other post-retirement benefit obligations	(1,785)	(1,672)	(1,672)
Provisions	(1,883)	(1,779)	(1,779)
Total non-current liabilities	(34,465)	(31,441)	(31,242)
Total liabilities	(43,594)	(40,132)	(39,939)
Net assets	19,369	18,652	18,848
Equity
Share capital	458	452	452
Share premium account	1,314	1,321	1,321
Retained earnings	21,814	21,331	21,599
Other equity reserves	(4,237)	(4,468)	(4,540)		(3,987)		(4,523)
Total shareholders’ equity	19,349	18,636	18,832
Non-controlling interests	20	16	16
Equity	19,369	£ 18,652	18,848		£ 20,384		£ 13,565
National Grid plc
Non-current assets
Goodwill	0		0
Other intangible assets	0		0
Property, plant and equipment	0		0
Other non-current assets	0		0
Amounts owed by subsidiary undertakings	358		350
Pension assets	0		0
Financial and other investments	23,573		21,708
Derivative financial assets	0		18
Total non-current assets	23,931		22,076
Current assets
Inventories and current intangible assets	0		0
Trade and other receivables	1		1
Current tax assets	0		0
Amounts owed by subsidiary undertakings	12,514		11,254
Financial and other investments	895		938
Derivative financial assets	110		308
Cash and cash equivalents	75		0
Assets held for sale	0
Total current assets	13,595		12,501
Total assets	37,526		34,577
Current liabilities
Borrowings	(1,275)		(781)
Derivative financial liabilities	(92)		(187)
Trade and other payables	(58)		(62)
Contract liabilities	0
Amounts owed to subsidiary undertakings	(14,104)		(11,809)
Current tax liabilities	0		0
Provisions	0		0
Total current liabilities	(15,529)		(12,839)
Non-current liabilities
Borrowings	(346)		(773)
Derivative financial liabilities	(228)		(41)
Other non-current liabilities	0		0
Contract liabilities	0
Amounts owed to subsidiary undertakings	(2,074)		(2,091)
Deferred tax liabilities	0		(1)
Pensions and other post-retirement benefit obligations	0		0
Provisions	0		0
Total non-current liabilities	(2,648)		(2,906)
Total liabilities	(18,177)		(15,745)
Net assets	19,349		18,832
Equity
Share capital	458		452
Share premium account	1,314		1,321
Retained earnings	21,814		21,599
Other equity reserves	(4,237)		(4,540)
Total shareholders’ equity	19,349		18,832
Non-controlling interests	0		0
Equity	19,349		18,832
Niagara Mohawk Power Corporation
Non-current assets
Goodwill	745		691
Other intangible assets	3		3
Property, plant and equipment	6,985		6,148
Other non-current assets	4		3
Amounts owed by subsidiary undertakings	0		0
Pension assets	260		231
Financial and other investments	22		30
Derivative financial assets	9		2
Total non-current assets	8,028		7,108
Current assets
Inventories and current intangible assets	41		36
Trade and other receivables	535		515
Current tax assets	0		0
Amounts owed by subsidiary undertakings	476		130
Financial and other investments	13		15
Derivative financial assets	21		7
Cash and cash equivalents	12		4
Assets held for sale	0
Total current assets	1,098		707
Total assets	9,126		7,815
Current liabilities
Borrowings	(634)		(51)
Derivative financial liabilities	(15)		(36)
Trade and other payables	(413)		(318)
Contract liabilities	(4)
Amounts owed to subsidiary undertakings	0		0
Current tax liabilities	(148)		(202)
Provisions	(24)		(23)
Total current liabilities	(1,238)		(630)
Non-current liabilities
Borrowings	(2,048)		(2,087)
Derivative financial liabilities	(8)		(18)
Other non-current liabilities	(301)		(281)
Contract liabilities	(181)
Amounts owed to subsidiary undertakings	0		0
Deferred tax liabilities	(678)		(626)
Pensions and other post-retirement benefit obligations	(872)		(765)
Provisions	(271)		(248)
Total non-current liabilities	(4,359)		(4,025)
Total liabilities	(5,597)		(4,655)
Net assets	3,529		3,160
Equity
Share capital	144		133
Share premium account	2,394		2,194
Retained earnings	991		830
Other equity reserves	0		3
Total shareholders’ equity	3,529		3,160
Non-controlling interests	0		0
Equity	3,529		3,160
British Transco Finance Inc.
Non-current assets
Goodwill			0
Other intangible assets			0
Property, plant and equipment			0
Other non-current assets			0
Amounts owed by subsidiary undertakings			0
Pension assets			0
Financial and other investments			0
Derivative financial assets			0
Total non-current assets			0
Current assets
Inventories and current intangible assets			0
Trade and other receivables			0
Current tax assets			0
Amounts owed by subsidiary undertakings			220
Financial and other investments			0
Derivative financial assets			0
Cash and cash equivalents			0
Total current assets			220
Total assets			220
Current liabilities
Borrowings			(218)
Derivative financial liabilities			0
Trade and other payables			0
Amounts owed to subsidiary undertakings			0
Current tax liabilities			0
Provisions			0
Total current liabilities			(218)
Non-current liabilities
Borrowings			0
Derivative financial liabilities			0
Other non-current liabilities			0
Amounts owed to subsidiary undertakings			0
Deferred tax liabilities			0
Pensions and other post-retirement benefit obligations			0
Provisions			0
Total non-current liabilities			0
Total liabilities			(218)
Net assets			2
Equity
Share capital			0
Share premium account			0
Retained earnings			2
Other equity reserves			0
Total shareholders’ equity			2
Non-controlling interests			0
Equity			2
National Grid Gas plc
Non-current assets
Goodwill			0
Other intangible assets			107
Property, plant and equipment			4,433
Other non-current assets			94
Amounts owed by subsidiary undertakings			3,426
Pension assets			412
Financial and other investments			101
Derivative financial assets			591
Total non-current assets			9,164
Current assets
Inventories and current intangible assets			22
Trade and other receivables			276
Current tax assets			0
Amounts owed by subsidiary undertakings			708
Financial and other investments			863
Derivative financial assets			46
Cash and cash equivalents			271
Total current assets			2,186
Total assets			11,350
Current liabilities
Borrowings			(675)
Derivative financial liabilities			(68)
Trade and other payables			(347)
Amounts owed to subsidiary undertakings			(624)
Current tax liabilities			(26)
Provisions			(66)
Total current liabilities			(1,806)
Non-current liabilities
Borrowings			(3,635)
Derivative financial liabilities			(157)
Other non-current liabilities			(181)
Amounts owed to subsidiary undertakings			(500)
Deferred tax liabilities			(441)
Pensions and other post-retirement benefit obligations			0
Provisions			(129)
Total non-current liabilities			(5,043)
Total liabilities			(6,849)
Net assets			4,501
Equity
Share capital			45
Share premium account			204
Retained earnings			2,929
Other equity reserves			1,323
Total shareholders’ equity			4,501
Non-controlling interests			0
Equity			4,501
Other subsidiaries
Non-current assets
Goodwill	5,124		4,753
Other intangible assets	1,081		789
Property, plant and equipment	36,928		29,272
Other non-current assets	260		18
Amounts owed by subsidiary undertakings	2,073		2,593
Pension assets	1,307		766
Financial and other investments	3,434		12,340
Derivative financial assets	1,036		708
Total non-current assets	51,243		51,239
Current assets
Inventories and current intangible assets	329		283
Trade and other receivables	2,617		2,006
Current tax assets	260		307
Amounts owed by subsidiary undertakings	14,101		11,253
Financial and other investments	1,073		878
Derivative financial assets	80		0
Cash and cash equivalents	165		54
Assets held for sale	1,956
Total current assets	20,581		14,781
Total assets	71,824		66,020
Current liabilities
Borrowings	(2,563)		(2,722)
Derivative financial liabilities	(346)		(66)
Trade and other payables	(3,298)		(2,726)
Contract liabilities	(57)
Amounts owed to subsidiary undertakings	(12,987)		(11,132)
Current tax liabilities	(147)		(88)
Provisions	(292)		(184)
Total current liabilities	(19,690)		(16,918)
Non-current liabilities
Borrowings	(21,864)		(15,683)
Derivative financial liabilities	(597)		(444)
Other non-current liabilities	(507)		(855)
Contract liabilities	(752)
Amounts owed to subsidiary undertakings	(357)		(3,778)
Deferred tax liabilities	(3,287)		(2,568)
Pensions and other post-retirement benefit obligations	(913)		(907)
Provisions	(1,612)		(1,402)
Total non-current liabilities	(29,889)		(25,637)
Total liabilities	(49,579)		(42,555)
Net assets	22,245		23,465
Equity
Share capital	180		182
Share premium account	9,032		9,032
Retained earnings	13,048		14,217
Other equity reserves	(35)		18
Total shareholders’ equity	22,225		23,449
Non-controlling interests	20		16
Equity	22,245		23,465
Consolidation adjustments
Non-current assets
Goodwill	0		0
Other intangible assets	0		0
Property, plant and equipment	0		0
Other non-current assets	0		0
Amounts owed by subsidiary undertakings	(2,431)		(6,369)
Pension assets	0		0
Financial and other investments	(25,754)		(31,112)
Derivative financial assets	0		0
Total non-current assets	(28,185)		(37,481)
Current assets
Inventories and current intangible assets	0		0
Trade and other receivables	0		0
Current tax assets	(134)		(193)
Amounts owed by subsidiary undertakings	(27,091)		(23,565)
Financial and other investments	0		0
Derivative financial assets	(103)		44
Cash and cash equivalents	0		0
Assets held for sale	0
Total current assets	(27,328)		(23,714)
Total assets	(55,513)		(61,195)
Current liabilities
Borrowings	0		0
Derivative financial liabilities	103		(44)
Trade and other payables	0		0
Contract liabilities	0
Amounts owed to subsidiary undertakings	27,091		23,565
Current tax liabilities	134		193
Provisions	0		0
Total current liabilities	27,328		23,714
Non-current liabilities
Borrowings	0		0
Derivative financial liabilities	0		0
Other non-current liabilities	0		0
Contract liabilities	0
Amounts owed to subsidiary undertakings	2,431		6,369
Deferred tax liabilities	0		0
Pensions and other post-retirement benefit obligations	0		0
Provisions	0		0
Total non-current liabilities	2,431		6,369
Total liabilities	29,759		30,083
Net assets	(25,754)		(31,112)
Equity
Share capital	(324)		(360)
Share premium account	(11,426)		(11,430)
Retained earnings	(14,039)		(17,978)
Other equity reserves	35		(1,344)
Total shareholders’ equity	(25,754)		(31,112)
Non-controlling interests	0		0
Equity	£ (25,754)		£ (31,112)

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Additional disclosures in res_6

Additional disclosures in respect of guaranteed securities - Cash flow statements (Details) - GBP (£)		12 Months Ended
		Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Disclosure of information about consolidated structured entities [line items]
Net cash flow from operating activities – continuing operations		£ 4,389,000,000	£ 4,710,000,000	[1]	£ 4,320,000,000
Net cash (used in)/inflow from operating activities – discontinued operations		(71,000,000)	(207,000,000)	[1]	909,000,000
Net cash flow from/(used in) investing activities – continuing operations		(3,190,000,000)	2,066,000,000	[1]	(3,634,000,000)
Net cash flow from/(used in) investing activities – discontinued operations	[2]	156,000,000	171,000,000	[1]	(680,000,000)
Net cash flow (used in)/from financing activities – continuing operations		(1,364,000,000)	(7,316,000,000)	[1]	(1,542,000,000)
Net cash flow (used in)/from financing activities – discontinued operations		0	(231,000,000)	[1]	1,611,000,000
Net (decrease)/increase in cash and cash equivalents		(80,000,000)	(807,000,000)	[1]	984,000,000
National Grid plc
Disclosure of information about consolidated structured entities [line items]
Net cash flow from operating activities – continuing operations		33,000,000	35,000,000		53,000,000
Net cash (used in)/inflow from operating activities – discontinued operations		0	0		0
Net cash flow from/(used in) investing activities – continuing operations		121,000,000	4,660,000,000		4,181,000,000
Net cash flow from/(used in) investing activities – discontinued operations		0	0		0
Net cash flow (used in)/from financing activities – continuing operations		(79,000,000)	(5,785,000,000)		(3,146,000,000)
Net cash flow (used in)/from financing activities – discontinued operations		0	0		0
Net (decrease)/increase in cash and cash equivalents		75,000,000	(1,090,000,000)		1,088,000,000
Niagara Mohawk Power Corporation
Disclosure of information about consolidated structured entities [line items]
Net cash flow from operating activities – continuing operations		572,000,000	662,000,000		757,000,000
Net cash (used in)/inflow from operating activities – discontinued operations		0	0		0
Net cash flow from/(used in) investing activities – continuing operations		(823,000,000)	(473,000,000)		(469,000,000)
Net cash flow from/(used in) investing activities – discontinued operations		0	0		0
Net cash flow (used in)/from financing activities – continuing operations		259,000,000	(189,000,000)		(288,000,000)
Net cash flow (used in)/from financing activities – discontinued operations		0	0		0
Net (decrease)/increase in cash and cash equivalents		8,000,000	0		0
British Transco Finance Inc.
Disclosure of information about consolidated structured entities [line items]
Net cash flow from operating activities – continuing operations			0		0
Net cash (used in)/inflow from operating activities – discontinued operations			0		0
Net cash flow from/(used in) investing activities – continuing operations			15,000,000		15,000,000
Net cash flow from/(used in) investing activities – discontinued operations			0		0
Net cash flow (used in)/from financing activities – continuing operations			(15,000,000)		(15,000,000)
Net cash flow (used in)/from financing activities – discontinued operations			0		0
Net (decrease)/increase in cash and cash equivalents			0		0
National Grid Gas plc
Disclosure of information about consolidated structured entities [line items]
Net cash flow from operating activities – continuing operations			888,000,000		918,000,000
Net cash (used in)/inflow from operating activities – discontinued operations			(98,000,000)		450,000,000
Net cash flow from/(used in) investing activities – continuing operations			656,000,000		215,000,000
Net cash flow from/(used in) investing activities – discontinued operations			0		5,618,000,000
Net cash flow (used in)/from financing activities – continuing operations			(1,041,000,000)		(8,322,000,000)
Net cash flow (used in)/from financing activities – discontinued operations			(125,000,000)		1,120,000,000
Net (decrease)/increase in cash and cash equivalents			280,000,000		(1,000,000)
Other subsidiaries
Disclosure of information about consolidated structured entities [line items]
Net cash flow from operating activities – continuing operations		3,784,000,000	3,125,000,000		2,592,000,000
Net cash (used in)/inflow from operating activities – discontinued operations		(71,000,000)	(109,000,000)		459,000,000
Net cash flow from/(used in) investing activities – continuing operations		(3,570,000,000)	(1,930,000,000)		(1,118,000,000)
Net cash flow from/(used in) investing activities – discontinued operations		156,000,000	171,000,000		(6,298,000,000)
Net cash flow (used in)/from financing activities – continuing operations		(462,000,000)	(1,148,000,000)		3,771,000,000
Net cash flow (used in)/from financing activities – discontinued operations		0	(106,000,000)		491,000,000
Net (decrease)/increase in cash and cash equivalents		(163,000,000)	3,000,000		(103,000,000)
Consolidation adjustments
Disclosure of information about consolidated structured entities [line items]
Net cash flow from operating activities – continuing operations		0	0		0
Net cash (used in)/inflow from operating activities – discontinued operations		0	0		0
Net cash flow from/(used in) investing activities – continuing operations		1,082,000,000	(862,000,000)		(6,458,000,000)
Net cash flow from/(used in) investing activities – discontinued operations		0	0		0
Net cash flow (used in)/from financing activities – continuing operations		(1,082,000,000)	862,000,000		6,458,000,000
Net cash flow (used in)/from financing activities – discontinued operations		0	0		0
Net (decrease)/increase in cash and cash equivalents		0	0		0
Subsidiary Undertaking
Disclosure of information about consolidated structured entities [line items]
Dividends received		£ 0	£ 950,000,000		£ 6,006,000,000

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).
[2]	Receipts of dividends from Quadgas HoldCo Limited of £133 million (2018: £144 million) and interest of £23 million (2018: £27 million).

Additional disclosures in res_7

Additional disclosures in respect of guaranteed securities - Maturity analysis of Parent Company borrowings (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 28,730	£ 26,625	£ 28,638
Less than 1 year
Disclosure of detailed information about borrowings [line items]
Borrowings	4,472	4,447
In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Borrowings	2,393	1,694
In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Borrowings	1,990	2,347
In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Borrowings	1,553	1,873
In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	714	1,469
National Grid plc
Disclosure of detailed information about borrowings [line items]
Borrowings	1,621	1,554
National Grid plc \| Less than 1 year
Disclosure of detailed information about borrowings [line items]
Borrowings	1,275	781
National Grid plc \| In 1 to 2 years
Disclosure of detailed information about borrowings [line items]
Borrowings	0	438
National Grid plc \| In 2 to 3 years
Disclosure of detailed information about borrowings [line items]
Borrowings	346	0
National Grid plc \| In 3 to 4 years
Disclosure of detailed information about borrowings [line items]
Borrowings	0	335
National Grid plc \| In 4 to 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	0	0
National Grid plc \| More than 5 years
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 0	£ 0

Transition to IFRS 9 and IFRS_3

Transition to IFRS 9 and IFRS 15 - Impact of IFRS 9 and IFRS 15 (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018		Mar. 31, 2017		Mar. 31, 2016
Non-current assets
Goodwill	£ 5,869	£ 5,444	£ 5,444
Other intangible assets	1,084	899	899
Property, plant and equipment	43,913	39,853	39,853
Other non-current assets	264	115	115
Pension assets	1,567	1,409	1,409
Financial and other investments	667	899	899
Investments in joint ventures and associates	608	2,168	2,168		£ 2,083
Derivative financial assets	1,045	1,319	1,319
Total non-current assets	55,017	52,106	52,106
Current assets
Inventories and current intangible assets	370	341	341
Trade and other receivables	3,153	2,795	2,798
Current tax assets	126	114	114
Financial and other investments	1,981	2,694	2,694		8,741		£ 2,998
Derivative financial assets	108	405	405
Cash and cash equivalents	252	329	329	[1]	1,139	[1]	124
Total current assets	7,946	6,678	6,681
Total assets	62,963	58,784	58,787
Current liabilities
Borrowings	(4,472)	(4,447)	(4,447)
Derivative financial liabilities	(350)	(401)	(401)
Trade and other payables	(3,769)	(3,394)	(3,453)
Contract liabilities	(61)	(53)	0
Current tax liabilities	(161)	(123)	(123)
Provisions	(316)	(273)	(273)
Total current liabilities	(9,129)	(8,691)	(8,697)
Non-current liabilities
Borrowings	(24,258)	(22,210)	(22,178)
Derivative financial liabilities	(833)	(660)	(660)
Other non-current liabilities	(808)	(750)	(1,317)
Contract liabilities	(933)	(813)	0
Deferred tax liabilities	(3,965)	(3,557)	(3,636)
Pensions and other post-retirement benefit obligations	(1,785)	(1,672)	(1,672)
Provisions	(1,883)	(1,779)	(1,779)
Total non-current liabilities	(34,465)	(31,441)	(31,242)
Total liabilities	(43,594)	(40,132)	(39,939)
Net assets	19,369	18,652	18,848
Equity
Share capital	458	452	452
Share premium account	1,314	1,321	1,321
Retained earnings	21,814	21,331	21,599
Other equity reserves	(4,237)	(4,468)	(4,540)		(3,987)		(4,523)
Total shareholders’ equity	19,349	18,636	18,832
Non-controlling interests	20	16	16
Total equity	£ 19,369	£ 18,652	18,848		£ 20,384		£ 13,565
Previously stated
Non-current assets
Goodwill			5,444
Other intangible assets			899
Property, plant and equipment			39,853
Other non-current assets			115
Pension assets			1,409
Financial and other investments			899
Investments in joint ventures and associates			2,168
Derivative financial assets			1,319
Total non-current assets			52,106
Current assets
Inventories and current intangible assets			341
Trade and other receivables			2,798
Current tax assets			114
Financial and other investments			2,694
Derivative financial assets			405
Cash and cash equivalents			329
Total current assets			6,681
Total assets			58,787
Current liabilities
Borrowings			(4,447)
Derivative financial liabilities			(401)
Trade and other payables			(3,453)
Contract liabilities			0
Current tax liabilities			(123)
Provisions			(273)
Total current liabilities			(8,697)
Non-current liabilities
Borrowings			(22,178)
Derivative financial liabilities			(660)
Other non-current liabilities			(1,317)
Contract liabilities			0
Deferred tax liabilities			(3,636)
Pensions and other post-retirement benefit obligations			(1,672)
Provisions			(1,779)
Total non-current liabilities			(31,242)
Total liabilities			(39,939)
Net assets			18,848
Equity
Share capital			452
Share premium account			1,321
Retained earnings			21,599
Other equity reserves			(4,540)
Total shareholders’ equity			18,832
Non-controlling interests			16
Total equity			18,848
Transition adjustments - IFRS 9
Non-current assets
Goodwill			0
Other intangible assets			0
Property, plant and equipment			0
Other non-current assets			0
Pension assets			0
Financial and other investments			0
Investments in joint ventures and associates			0
Derivative financial assets			0
Total non-current assets			0
Current assets
Inventories and current intangible assets			0
Trade and other receivables			0
Current tax assets			0
Financial and other investments			0
Derivative financial assets			0
Cash and cash equivalents			0
Total current assets			0
Total assets			0
Current liabilities
Borrowings			0
Derivative financial liabilities			0
Trade and other payables			0
Contract liabilities			0
Current tax liabilities			0
Provisions			0
Total current liabilities			0
Non-current liabilities
Borrowings			(32)
Derivative financial liabilities			0
Other non-current liabilities			0
Contract liabilities			0
Deferred tax liabilities			5
Pensions and other post-retirement benefit obligations			0
Provisions			0
Total non-current liabilities			(27)
Total liabilities			(27)
Net assets			(27)
Equity
Share capital			0
Share premium account			0
Retained earnings			(99)
Other equity reserves			72
Total shareholders’ equity			(27)
Non-controlling interests			0
Total equity			(27)
Transition adjustments - IFRS 15
Non-current assets
Goodwill			0
Other intangible assets			0
Property, plant and equipment			0
Other non-current assets			0
Pension assets			0
Financial and other investments			0
Investments in joint ventures and associates			0
Derivative financial assets			0
Total non-current assets			0
Current assets
Inventories and current intangible assets			0
Trade and other receivables			(3)
Current tax assets			0
Financial and other investments			0
Derivative financial assets			0
Cash and cash equivalents			0
Total current assets			(3)
Total assets			(3)
Current liabilities
Borrowings			0
Derivative financial liabilities			0
Trade and other payables			59
Contract liabilities			(53)
Current tax liabilities			0
Provisions			0
Total current liabilities			6
Non-current liabilities
Borrowings			0
Derivative financial liabilities			0
Other non-current liabilities			567
Contract liabilities			(813)
Deferred tax liabilities			74
Pensions and other post-retirement benefit obligations			0
Provisions			0
Total non-current liabilities			(172)
Total liabilities			(166)
Net assets			(169)
Equity
Share capital			0
Share premium account			0
Retained earnings			(169)
Other equity reserves			0
Total shareholders’ equity			(169)
Non-controlling interests			0
Total equity			£ (169)

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Transition to IFRS 9 and IFRS_4

Transition to IFRS 9 and IFRS 15 - IFRS 9: Financial instruments (Details) £ in Millions	Apr. 01, 2018GBP (£)
Borrowings
Disclosure of comparative information prepared under previous GAAP [line items]
Change in measurement basis under IFRS 9, Financial liabilities	£ (32)
Financial liabilities at amortised cost \| Borrowings
Disclosure of comparative information prepared under previous GAAP [line items]
Original carrying amount under IAS 39, Financial liabilities	(570)
Financial liabilities at fair value through profit and loss \| Borrowings
Disclosure of comparative information prepared under previous GAAP [line items]
New carrying amount under IFRS 9, Financial liabilities	(602)
Money market funds and fund investments in equities and bonds
Disclosure of comparative information prepared under previous GAAP [line items]
Change in measurement basis under IFRS 9, Financial assets	0
Money market funds and fund investments in equities and bonds \| Available-for-sale investments
Disclosure of comparative information prepared under previous GAAP [line items]
Original carrying amount under IAS 39, Financial assets	2,294
Money market funds and fund investments in equities and bonds \| Financial assets at FVTPL
Disclosure of comparative information prepared under previous GAAP [line items]
New carrying amount under IFRS 9, Financial assets	2,294
Cash surrender value of life insurance policies and investments in debt securities
Disclosure of comparative information prepared under previous GAAP [line items]
Change in measurement basis under IFRS 9, Financial assets	0
Cash surrender value of life insurance policies and investments in debt securities \| Available-for-sale investments
Disclosure of comparative information prepared under previous GAAP [line items]
Original carrying amount under IAS 39, Financial assets	343
Cash surrender value of life insurance policies and investments in debt securities \| Financial assets at FVOCI
Disclosure of comparative information prepared under previous GAAP [line items]
New carrying amount under IFRS 9, Financial assets	343
Investments in equity securities
Disclosure of comparative information prepared under previous GAAP [line items]
Change in measurement basis under IFRS 9, Financial assets	0
Investments in equity securities \| Available-for-sale investments
Disclosure of comparative information prepared under previous GAAP [line items]
Original carrying amount under IAS 39, Financial assets	84
Investments in equity securities \| Financial assets at FVOCI
Disclosure of comparative information prepared under previous GAAP [line items]
New carrying amount under IFRS 9, Financial assets	84
Loans to joint ventures and associates and restricted balances
Disclosure of comparative information prepared under previous GAAP [line items]
Change in measurement basis under IFRS 9, Financial assets	0
Loans to joint ventures and associates and restricted balances \| Loans and receivables
Disclosure of comparative information prepared under previous GAAP [line items]
Original carrying amount under IAS 39, Financial assets	872
Loans to joint ventures and associates and restricted balances \| Financial assets at amortised cost
Disclosure of comparative information prepared under previous GAAP [line items]
New carrying amount under IFRS 9, Financial assets	£ 872

Transition to IFRS 9 and IFRS_5

Transition to IFRS 9 and IFRS 15 - IFRS 9: Financial Instruments - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2019	Apr. 01, 2018
Financial liabilities at fair value through profit and loss
IFRS 9 Reclassification Category [Line Items]
Financial liability previously designated at amortised cost reclassified to FVTPL, Initial application of IFRS 9	£ 570
Increase in financial liability on basis of measurement category, initial application of IFRS 9	32
Cash flow hedges reserve \| Cost of hedging
IFRS 9 Reclassification Category [Line Items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9	(10)
Retained earnings \| Financial assets at fair value through profit or loss and through other comprehensive income
IFRS 9 Reclassification Category [Line Items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9		£ 8
Retained earnings \| Financial liabilities at fair value through profit and loss
IFRS 9 Reclassification Category [Line Items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9	(40)
Retained earnings \| Cost of hedging
IFRS 9 Reclassification Category [Line Items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9	(67)
Own credit reserve \| Other equity reserves \| Financial liabilities at fair value through profit and loss
IFRS 9 Reclassification Category [Line Items]
Increase (decrease) in equity on basis of measurement category, initial application of IFRS9	£ 7

Transition to IFRS 9 and IFRS_6

Transition to IFRS 9 and IFRS 15 - IFRS 15: Revenue from Contracts with Customers - Narrative (Details) - GBP (£)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018		Mar. 31, 2017
Disclosure of comparative information prepared under previous GAAP [line items]
Revenue	£ 14,066,000,000
Operating costs	12,063,000,000	£ 11,757,000,000		£ 11,827,000,000
Operating profit	2,870,000,000	£ 3,493,000,000	[1]	£ 3,208,000,000
Increase (decrease) due to application of IFRS 15 \| Previous GAAP
Disclosure of comparative information prepared under previous GAAP [line items]
Revenue	1,197,000,000
Operating costs	1,197,000,000
Operating profit	0
US Regulated and UK Gas Transmission \| Increase (decrease) due to application of IFRS 15 \| Previous GAAP
Disclosure of comparative information prepared under previous GAAP [line items]
Revenue	57,000,000
Operating profit	57,000,000
UK Regulated \| Increase (decrease) due to application of IFRS 15 \| Previous GAAP
Disclosure of comparative information prepared under previous GAAP [line items]
Revenue	(26,000,000)
Operating profit	£ (23,000,000)

[1]	Comparatives for 2018 only have been re-presented to reflect the classification of our retained interest in Quadgas HoldCo Limited as a discontinued operation in the current period (see note 1C and note 10).

Post balance sheet events - Nar

Post balance sheet events - Narrative (Details) - Geronimo Energy - National Grid Ventures $ in Millions	Mar. 31, 2019USD ($)
Subsequent Event1 [Line Items]
Percentage of voting equity interests acquired	100.00%
Consideration transferred, acquisition-date fair value	$ 100
Contingent liabilities recognised in business combination (up to)	$ 100

Uncategorized Items - nggtf-201

Label	Element	Value
Bank overdrafts	ifrs-full_BankOverdraftsClassifiedAsCashEquivalents	£ 0
Cash And Cash Equivalents, Excluding Bank Overdrafts	nggtf_CashAndCashEquivalentsExcludingBankOverdrafts	329,000,000
Borrowings, Excluding Bank Overdrafts	nggtf_BorrowingsExcludingBankOverdrafts	26,657,000,000
Financial Instruments Related Temporary Differences [Member]
Deferred tax liability (asset)	ifrs-full_DeferredTaxLiabilityAsset	16,000,000
Pensions And Other Post-retirement Benefits Related Temporary Differences [Member]
Deferred tax liability (asset)	ifrs-full_DeferredTaxLiabilityAsset	(203,000,000)
Accelerated Tax Depreciation Related Temporary Differences [Member]
Deferred tax liability (asset)	ifrs-full_DeferredTaxLiabilityAsset	4,893,000,000
Share-based Payments Related Temporary Differences [Member]
Deferred tax liability (asset)	ifrs-full_DeferredTaxLiabilityAsset	(9,000,000)
Other temporary differences [member]
Deferred tax liability (asset)	ifrs-full_DeferredTaxLiabilityAsset	(1,140,000,000)
Reserve of cash flow hedges [member]
Other reserves	ifrs-full_OtherReserves	125,000,000
Reserve of exchange differences on translation [member]
Other reserves	ifrs-full_OtherReserves	390,000,000
Capital redemption reserve [member]
Other reserves	ifrs-full_OtherReserves	19,000,000
Reserve of gains and losses from investments in equity instruments [member]
Other reserves	ifrs-full_OtherReserves	34,000,000
Reserve Of Gains and Losses On Financial Liabilities Measured At Fair Value Through Other Comprehensive Income [Member]
Other reserves	ifrs-full_OtherReserves	46,000,000
Merger reserve [member]
Other reserves	ifrs-full_OtherReserves	(5,165,000,000)
Reserve of change in fair value of financial liability attributable to change in credit risk of liability [member]
Other reserves	ifrs-full_OtherReserves	7,000,000
IFRS 9 and 15 [Member]
Equity	ifrs-full_Equity	(196,000,000)	[1]
Non-controlling interests [member]
Equity	ifrs-full_Equity	16,000,000
Other Equity Reserves [Member]
Equity	ifrs-full_Equity	(4,468,000,000)	[2]
Other Equity Reserves [Member] \| IFRS 9 and 15 [Member]
Equity	ifrs-full_Equity	72,000,000	[1]
Retained earnings [member]
Equity	ifrs-full_Equity	21,331,000,000
Retained earnings [member] \| IFRS 9 and 15 [Member]
Equity	ifrs-full_Equity	(268,000,000)	[1]
Equity attributable to owners of parent [member]
Equity	ifrs-full_Equity	18,636,000,000
Equity attributable to owners of parent [member] \| IFRS 9 and 15 [Member]
Equity	ifrs-full_Equity	(196,000,000)	[1]
Issued capital [member]
Equity	ifrs-full_Equity	452,000,000
Share premium [member]
Equity	ifrs-full_Equity	£ 1,321,000,000

[1]	For further details of the impact of the transition to IFRS 9 and IFRS 15, see note 37.
[2]	For further details of other equity reserves, see note 28.