v3.26.1
Derivative financial instruments - Schedule of fair values of financing derivatives by type (Details) - GBP (£)
£ in Millions
Mar. 31, 2026
Mar. 31, 2025
Disclosure of detailed information about financial instruments [line items]    
Derivative assets £ 838 £ 482
Derivative liabilities (1,018) (1,202)
Total (180) (720)
Financing derivatives    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 717 375
Derivative liabilities (950) (1,138)
Total (233) (763)
Interest rate swaps    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 129 98
Derivative liabilities (216) (196)
Total (87) (98)
Cross-currency interest rate swaps    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 448 193
Derivative liabilities (528) (766)
Total (80) (573)
Foreign exchange forward contracts    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 114 53
Derivative liabilities (120) (81)
Total (6) (28)
Foreign exchange forward contracts | Capital expenditure    
Disclosure of detailed information about financial instruments [line items]    
Total (19) (45)
Inflation-linked swaps    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 26 31
Derivative liabilities (86) (95)
Total £ (60) £ (64)