v3.26.1
Derivative financial instruments - Schedule of maturity profile of commodity contract derivatives (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)
More than 5 years    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 0 0
Derivative liabilities 0 (2)
Total 0 (2)
Commodity contract derivatives    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 121 107
Derivative liabilities (68) (64)
Total 53 43
Commodity contract derivatives | Less than 1 year    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 92 94
Derivative liabilities (31) (26)
Total 61 68
Commodity contract derivatives | Over 12 months past due    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 29 13
Derivative liabilities (37) (38)
Total (8) (25)
Commodity contract derivatives | In 1 to 2 years    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 27 12
Derivative liabilities (24) (20)
Total 3 (8)
Commodity contract derivatives | In 2 to 3 years    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 1 1
Derivative liabilities (11) (12)
Total (10) (11)
Commodity contract derivatives | In 3 to 4 years    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 1 0
Derivative liabilities (2) (2)
Total (1) (2)
Commodity contract derivatives | In 4 to 5 years    
Disclosure of detailed information about financial instruments [line items]    
Derivative assets 0 0
Derivative liabilities 0 (2)
Total £ 0 £ (2)