v3.26.3
Related party transactions (Details)
£ in Millions, $ in Millions
6 Months Ended
Sep. 30, 2026
GBP (£)
Sep. 30, 2026
USD ($)
Sep. 30, 2025
GBP (£)
Disclosure of transactions between related parties [line items]      
Purchase of investments other than investments accounted for using equity method £ 979   £ 44
Joulent LLC      
Disclosure of transactions between related parties [line items]      
Purchase of investments other than investments accounted for using equity method £ 120 $ 159  
Joulent LLC | Investments held at fair value through profit and loss      
Disclosure of transactions between related parties [line items]      
Proportion of ownership interest in joint venture 35.00% 35.00%  
Joulent LLC | Investments held at fair value through profit and loss | Level 3      
Disclosure of transactions between related parties [line items]      
Investments, capital contributions £ 268 $ 355