Financial liabilities designated at fair value - Narrative (Details) - GBP (£) £ in Millions	Dec. 31, 2025	Dec. 31, 2024
Designated financial liabilities at fair value through profit or loss [abstract]
Cumulative own credit net loss recognised	£ 1,335	£ 1,434

The accumulated increase (decrease) in the fair value of financial liabilities that is attributable to changes in the credit risk of the liabilities. [Refer: Credit risk [member]; Market risk [member]; Increase (decrease) in fair value of financial liability, attributable to changes in credit risk of liability]