Property, plant and equipment - Disclosure of sensitivity of gas assets (Details) - GBP (£) £ in Millions |
12 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| New York | ||
| Disclosure of operating segments [line items] | ||
| UELs limited to 2050, impact on depreciation expense | £ 277 | £ 235 |
| UELs limited to 2060, impact on depreciation expense | 130 | 110 |
| UELs limited to 2070, impact on depreciation expense | 64 | 54 |
| New England | ||
| Disclosure of operating segments [line items] | ||
| UELs limited to 2050, impact on depreciation expense | 90 | 78 |
| UELs limited to 2060, impact on depreciation expense | 37 | 32 |
| UELs limited to 2070, impact on depreciation expense | £ 11 | £ 9 |