v3.26.3
Fair value measurement - Narrative (Details)
£ in Millions, $ in Millions
6 Months Ended
Sep. 30, 2026
GBP (£)
investment
Sep. 30, 2026
USD ($)
Sep. 30, 2025
GBP (£)
Sep. 30, 2026
USD ($)
investment
Mar. 31, 2026
GBP (£)
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]          
Borrowings £ 51,222       £ 46,755
Number of equity investments | investment 42     42  
Number of equity investments valued based on latest transaction price | investment 27     27  
Number of equity investments valued based on internal valuation process | investment 15     15  
Financial assets £ 5,072       3,587
Purchase of investments other than investments accounted for using equity method 979   £ 44    
Joulent LLC          
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]          
Purchase of investments other than investments accounted for using equity method 120 $ 159      
Level 3          
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]          
Financial assets 1,672       486
Investments held at fair value through profit and loss          
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]          
Financial assets 3,978       2,364
Investments held at fair value through profit and loss | Level 3          
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]          
Financial assets 1,637       450
Joulent LLC | Investments held at fair value through profit and loss | Level 3          
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]          
Financial assets 952     $ 1,263  
Investments, contingent consideration, capital contributions 366     $ 486  
At fair value          
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]          
Borrowings £ 45,769       £ 42,505