Fair value measurement - Narrative (Details) £ in Millions |
Sep. 30, 2025
GBP (£)
investment
|
Mar. 31, 2025
GBP (£)
|
|---|---|---|
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | ||
| Borrowings | £ | £ 45,914 | £ 47,539 |
| Number of equity investments | 38 | |
| Number of equity investments valued based on latest transaction price | 11 | |
| Number of equity investments valued based on internal valuation process | 25 | |
| At fair value | ||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | ||
| Borrowings | £ | £ 42,201 | £ 43,137 |