v3.24.1.1.u2
Financial risk management - Schedule of fair value analysis (Details) - GBP (£)
£ in Millions
Mar. 31, 2024
Mar. 31, 2023
Mar. 31, 2022
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets £ 4,332 £ 3,052  
Liabilities (1,244) (1,312)  
Financial assets (liabilities) 3,088 1,740  
Level 1      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 3,084 1,764  
Liabilities 0 0  
Financial assets (liabilities) 3,084 1,764  
Level 2      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 725 810  
Liabilities (1,127) (1,131)  
Financial assets (liabilities) (402) (321)  
Level 3      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 523 478  
Liabilities (117) (181)  
Financial assets (liabilities) 406 297 £ 233
Financing derivatives      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities (1,126) (1,119)  
Financing derivatives | Level 1      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities 0 0  
Financing derivatives | Level 2      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities (1,022) (997)  
Financing derivatives | Level 3      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities (104) (122)  
Commodity contract derivatives      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities (118) (174)  
Commodity contract derivatives | Level 1      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities 0 0  
Commodity contract derivatives | Level 2      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities (105) (134)  
Commodity contract derivatives | Level 3      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities (13) (40)  
Contingent consideration      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities 0 (19)  
Contingent consideration | Level 1      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities 0 0  
Contingent consideration | Level 2      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities 0 0  
Contingent consideration | Level 3      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Liabilities 0 (19)  
Investments held at FVTPL      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 3,567 2,216  
Investments held at FVTPL | Level 1      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 3,084 1,764  
Investments held at FVTPL | Level 2      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 0 0  
Investments held at FVTPL | Level 3      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 483 452  
Investments held at FVOCI      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 397 407  
Investments held at FVOCI | Level 1      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 0 0  
Investments held at FVOCI | Level 2      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 397 407  
Investments held at FVOCI | Level 3      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 0 0  
Financing derivatives      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 333 363  
Financing derivatives | Level 1      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 0 0  
Financing derivatives | Level 2      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 293 341  
Financing derivatives | Level 3      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 40 22  
Commodity contract derivatives      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 35 66  
Commodity contract derivatives | Level 1      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 0 0  
Commodity contract derivatives | Level 2      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets 35 62  
Commodity contract derivatives | Level 3      
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]      
Assets £ 0 £ 4