v3.24.1.1.u2
Commitments and contingencies (Details) - GBP (£)
£ in Millions
Mar. 31, 2024
Mar. 31, 2023
Disclosure of contingent liabilities [line items]    
Contracted for but not provided £ 3,329 £ 3,035
Energy purchase commitments 14,175 19,194
Guarantees 3,366 2,226
Guarantee of subleases for US properties (expire up to 2040)    
Disclosure of contingent liabilities [line items]    
Guarantees 67 219
Guarantees of certain obligations of Eastern Green Link Joint Operations (various expiry dates)    
Disclosure of contingent liabilities [line items]    
Guarantees 2,465 0
Guarantees of certain obligations of Grain LNG (expire up to 2025)    
Disclosure of contingent liabilities [line items]    
Guarantees 32 32
Guarantees of certain obligations of National Grid North Sea Link Limited (various expiry dates)    
Disclosure of contingent liabilities [line items]    
Guarantees 271 281
Guarantees of certain obligations of St William Homes LLP (various expiry dates)    
Disclosure of contingent liabilities [line items]    
Guarantees 44 44
Guarantees of certain obligations of National Grid IFA 2 Limited (expected expiry 2024)    
Disclosure of contingent liabilities [line items]    
Guarantees 121 144
Guarantees of certain obligations of National Grid Viking Link Limited (expected expiry 2024)    
Disclosure of contingent liabilities [line items]    
Guarantees 243 1,185
Other guarantees and letters of credit (various expiry dates)    
Disclosure of contingent liabilities [line items]    
Guarantees 123 321
Less than 1 year    
Disclosure of contingent liabilities [line items]    
Energy purchase commitments 1,244 1,391
In 1 to 2 years    
Disclosure of contingent liabilities [line items]    
Energy purchase commitments 982 985
In 2 to 3 years    
Disclosure of contingent liabilities [line items]    
Energy purchase commitments 1,062 1,057
In 3 to 4 years    
Disclosure of contingent liabilities [line items]    
Energy purchase commitments 941 912
In 4 to 5 years    
Disclosure of contingent liabilities [line items]    
Energy purchase commitments 866 929
More than 5 years    
Disclosure of contingent liabilities [line items]    
Energy purchase commitments £ 9,080 £ 13,920