v3.25.4
Financial instruments - Summary of gains and losses on the borrowings and related derivatives designated as fair value hedges (Details) - GBP (£)
£ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure Of Detailed Information About Hedged Items      
Borrowings £ (7,267) £ (6,544)  
US dollars      
Disclosure Of Detailed Information About Hedged Items      
Borrowings (3,507) (2,713)  
Euro      
Disclosure Of Detailed Information About Hedged Items      
Borrowings (3,680) (3,757)  
Fair value hedges      
Disclosure Of Detailed Information About Hedged Items      
Accumulated fair value hedge adjustment on hedged item at start of year 134 104 £ 211
Fair value movement gain/(loss) (68) 26 (83)
Redemption/close-out     (16)
Exchange gain/(loss) (10) 4 (8)
Accumulated fair value hedge adjustment on hedged item at end of year 56 134 104
Borrowings (1,519) (2,008) (2,471)
Accumulated fair value adjustment on hedging instrument at start of year (140) (108) (213)
Fair value movement gain/(loss) 70 (28) 81
Redemption/close-out     16
Exchange gain/(loss) 10 (4) 8
Accumulated fair value adjustment on hedging instrument at end of year (60) (140) (108)
Hedging instrument, liabilities (60) (140) (108)
Accumulated fair value adjustment on hedged item and hedging instrument at start of year (6) (4) (2)
Gain (loss) on change in fair value of hedged item and hedging instrument 2 (2) (2)
Accumulated fair value adjustment on hedged item and hedging instrument at end of year (4) (6) (4)
Borrowings net of related hedging instruments (1,579) (2,148) (2,579)
Fair value hedges | US dollars      
Disclosure Of Detailed Information About Hedged Items      
Accumulated fair value hedge adjustment on hedged item at start of year 114 97 141
Fair value movement gain/(loss) (39) 14 (22)
Redemption/close-out     (16)
Exchange gain/(loss) (8) 3 (6)
Accumulated fair value hedge adjustment on hedged item at end of year 67 114 97
Borrowings (855) (875) (871)
Accumulated fair value adjustment on hedging instrument at start of year (119) (100) (143)
Fair value movement gain/(loss) 41 (16) 21
Redemption/close-out     16
Exchange gain/(loss) 8 (3) 6
Accumulated fair value adjustment on hedging instrument at end of year (70) (119) (100)
Hedging instrument, liabilities (70) (119) (100)
Accumulated fair value adjustment on hedged item and hedging instrument at start of year (5) (3) (2)
Gain (loss) on change in fair value of hedged item and hedging instrument 2 (2) (1)
Accumulated fair value adjustment on hedged item and hedging instrument at end of year (3) (5) (3)
Borrowings net of related hedging instruments (925) (994) (971)
Fair value hedges | Euro      
Disclosure Of Detailed Information About Hedged Items      
Accumulated fair value hedge adjustment on hedged item at start of year 20 7 70
Fair value movement gain/(loss) (29) 12 (61)
Exchange gain/(loss) (2) 1 (2)
Accumulated fair value hedge adjustment on hedged item at end of year (11) 20 7
Borrowings (664) (1,133) (1,600)
Accumulated fair value adjustment on hedging instrument at start of year (21) (8) (70)
Fair value movement gain/(loss) 29 (12) 60
Exchange gain/(loss) 2 (1) 2
Accumulated fair value adjustment on hedging instrument at end of year 10 (21) (8)
Hedging instrument, assets 10    
Hedging instrument, liabilities   (21) (8)
Accumulated fair value adjustment on hedged item and hedging instrument at start of year (1) (1)  
Gain (loss) on change in fair value of hedged item and hedging instrument     (1)
Accumulated fair value adjustment on hedged item and hedging instrument at end of year (1) (1) (1)
Borrowings net of related hedging instruments £ (654) £ (1,154) £ (1,608)