v3.26.1
Provisions - Narrative (Details)
£ in Millions
 12 Months Ended
Mar. 31, 2026
GBP (£)
site
Mar. 31, 2025
GBP (£)
Mar. 31, 2024
GBP (£)
Disclosure of other provisions [line items]      
Weighted average duration of cash flows   10 years  
Other provisions £ 2,761 £ 3,049 £ 3,109
Increase (decrease) through transfers and other changes, other provisions 178    
Other environment related provision      
Disclosure of other provisions [line items]      
Other provisions 2,093 2,172 2,418
Increase (decrease) through transfers and other changes, other provisions £ 0    
Other environment related provision | US      
Disclosure of other provisions [line items]      
Number of Superfund sites | site 2    
Weighted average duration of cash flows 9 years    
Other provisions £ 2,011 2,065  
Liability for claims and claims adjustment      
Disclosure of other provisions [line items]      
Other provisions 167 172  
Liability for interconnector excess revenues      
Disclosure of other provisions [line items]      
Other provisions 0 159  
Liability for emission provisions      
Disclosure of other provisions [line items]      
Other provisions 80 39  
Other      
Disclosure of other provisions [line items]      
Other provisions 360 £ 478 £ 338
Increase (decrease) through transfers and other changes, other provisions £ 178