Derivative financial instruments - Schedule of notional contract amounts of financing derivatives by type (Details) - GBP (£) £ in Millions |
Mar. 31, 2026 |
Mar. 31, 2025 |
|---|---|---|
| Financing derivatives | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative notional amount | £ (38,004) | £ (34,733) |
| Interest rate swaps | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative notional amount | (7,113) | (7,763) |
| Cross-currency interest rate swaps | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative notional amount | (16,413) | (16,019) |
| Foreign exchange forward contracts | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative notional amount | (11,508) | (7,761) |
| Inflation-linked swaps | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative notional amount | £ (2,970) | £ (3,190) |