v3.26.1
Provisions - Schedule of changes in provisions (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Reconciliation of changes in other provisions [abstract]      
Other provisions, beginning balance £ 3,049 £ 3,109  
Exchange adjustments (57) (53)  
Additions 302 316  
Unused amounts reversed (129) (150)  
Adjustment for change in discount rate (90) (75)  
Unwinding of discount 116 123  
Utilised (252) (203)  
Reclassification to held for sale (note 10)   (18)  
Reclassifications to other payables (note 24) (178)    
Other provisions, ending balance 2,761 3,049 £ 3,109
Environmental      
Reconciliation of changes in other provisions [abstract]      
Other provisions, beginning balance 2,172 2,418  
Exchange adjustments (49) (47)  
Additions 59 60  
Unused amounts reversed (53) (126)  
Adjustment for change in discount rate (2) (82)  
Unwinding of discount 101 105  
Utilised (135) (139)  
Reclassification to held for sale (note 10)   (17)  
Reclassifications to other payables (note 24) 0    
Other provisions, ending balance 2,093 £ 2,172 £ 2,418
Real discount rate (in percent)   2.00% 1.50%
Environmental | US      
Reconciliation of changes in other provisions [abstract]      
Other provisions, beginning balance 2,065    
Adjustment for change in discount rate   £ (82)  
Other provisions, ending balance £ 2,011 £ 2,065  
Real discount rate (in percent) 2.00% 2.00%  
Decommissioning      
Reconciliation of changes in other provisions [abstract]      
Other provisions, beginning balance £ 399 £ 353  
Exchange adjustments (4) (5)  
Additions 43 45  
Unused amounts reversed (50) (8)  
Adjustment for change in discount rate (88) 7  
Unwinding of discount 12 13  
Utilised (4) (6)  
Reclassification to held for sale (note 10)   0  
Reclassifications to other payables (note 24) 0    
Other provisions, ending balance 308 399 £ 353
Other      
Reconciliation of changes in other provisions [abstract]      
Other provisions, beginning balance 478 338  
Exchange adjustments (4) (1)  
Additions 200 211  
Unused amounts reversed (26) (16)  
Adjustment for change in discount rate 0 0  
Unwinding of discount 3 5  
Utilised (113) (58)  
Reclassification to held for sale (note 10)   (1)  
Reclassifications to other payables (note 24) (178)    
Other provisions, ending balance £ 360 £ 478 £ 338