Net debt - Schedule of components of net debt (Details) - GBP (£) £ in Millions	Sep. 30, 2025	Mar. 31, 2025
Disclosure of detailed information about financial instruments [line items]
Cash and cash equivalents	£ 887	£ 1,178
Current financial investments	3,172	5,753
Borrowings	(45,914)	(47,539)
Financing derivatives	6	(763)
Net debt (net of related derivative financial instruments)	(41,849)	(41,371)
Derivative liabilities	(63)	720
Derivatives \| Capital expenditure prepayments
Disclosure of detailed information about financial instruments [line items]
Derivative liabilities	£ 3	£ 45

The amount of outstanding funds that the entity is obligated to repay.

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The amount of cash on hand and demand deposits, along with short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value. [Refer: Cash; Cash equivalents]

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The amount of net debt of the entity.

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The amount of current financial assets that the entity does not separately disclose in the same statement or note. [Refer: Other financial assets; Current financial assets]

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Derivative Financial Assets (Liabilities)

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Financing Derivatives

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