The amount of an entity’s obligation to transfer goods or services to a customer for which the entity has received consideration (or the amount is due) from the customer.

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The amount of the transaction price allocated to the performance obligations that are unsatisfied (or partially unsatisfied) as of the end of the reporting period. The transaction price is the amount of consideration to which an entity expects to be entitled in exchange for transferring promised goods or services to a customer, excluding amounts collected on behalf of third parties (for example, some sales taxes). [Refer: Performance obligations [domain]]

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The useful life, measured as period of time, used for property, plant and equipment. [Refer: Property, plant and equipment]

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Revenue - Narrative (Details) - GBP (£) £ in Millions	12 Months Ended
Revenue - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
Disclosure of disaggregation of revenue from contracts with customers [line items]
Contract liabilities	£ 2,809	£ 2,514	£ 2,246
Future revenues in relation to unfulfilled performance obligations	1,400	1,500	6,100
Revenue from performance obligations satisfied or partially satisfied in previous periods	£ 0	0	0
Weighted average
Disclosure of disaggregation of revenue from contracts with customers [line items]
Weighted average amortization period for contract liabilities	26 years
UK Electricity Transmission
Disclosure of disaggregation of revenue from contracts with customers [line items]
Future revenues in relation to unfulfilled performance obligations	£ 1,400	£ 1,500	£ 1,900
Remaining performance obligation, expected timing of satisfaction, period	25 years
UK Electricity Transmission \| Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	40 years
UK Electricity Distribution \| Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	69 years
New England \| Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	51 years
New York \| Connections
Disclosure of disaggregation of revenue from contracts with customers [line items]
Asset useful life	51 years