Commitments and contingencies - Schedule of capital commitments and contingent liabilities (Details) - GBP (£) £ in Millions |
Mar. 31, 2026 |
Mar. 31, 2025 |
|---|---|---|
| Disclosure of contingent liabilities [line items] | ||
| Contracted for but not provided | £ 7,085 | £ 5,017 |
| Energy purchase commitments | 16,757 | 13,880 |
| Less than 1 year | ||
| Disclosure of contingent liabilities [line items] | ||
| Energy purchase commitments | 1,527 | 1,265 |
| In 1 to 2 years | ||
| Disclosure of contingent liabilities [line items] | ||
| Energy purchase commitments | 1,360 | 1,259 |
| In 2 to 3 years | ||
| Disclosure of contingent liabilities [line items] | ||
| Energy purchase commitments | 1,343 | 1,147 |
| In 3 to 4 years | ||
| Disclosure of contingent liabilities [line items] | ||
| Energy purchase commitments | 1,191 | 1,011 |
| In 4 to 5 years | ||
| Disclosure of contingent liabilities [line items] | ||
| Energy purchase commitments | 1,031 | 927 |
| More than 5 years | ||
| Disclosure of contingent liabilities [line items] | ||
| Energy purchase commitments | £ 10,305 | £ 8,271 |