Fair value measurements and valuation processes - summary of assets and liabilities measured at fair value (Details) - Level 2 - GBP (£) £ in Millions |
Jun. 30, 2025 |
Dec. 31, 2024 |
Jun. 30, 2024 |
|---|---|---|---|
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Assets at fair value | £ 443 | £ 296 | £ 259 |
| Liabilities at fair value | 338 | 424 | 336 |
| – interest rate swaps | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Assets | 59 | 11 | 5 |
| Liabilities | 117 | 270 | 227 |
| – cross-currency swaps | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Assets | 110 | 100 | 93 |
| Liabilities | 14 | 16 | 10 |
| – forward foreign currency contracts | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Assets | 274 | 185 | 161 |
| Liabilities | 207 | 131 | 82 |
| – embedded derivative relating to associates | |||
| Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items] | |||
| Liabilities | £ 0 | £ 7 | £ 17 |