v3.24.1.1.u2
Financial risk management - Disclosure of financial instruments by type of interest rate (Details) - Interest rate risk - GBP (£)
£ in Millions
Mar. 31, 2024
Mar. 31, 2023
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic £ (43,607) £ (40,973)
Fixed rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (34,757) (32,365)
Floating rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (4,099) (3,934)
Inflation linked    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (4,810) (4,710)
Other    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 59 36
Cash and cash equivalents    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 559 163
Cash and cash equivalents | Fixed rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 157 53
Cash and cash equivalents | Floating rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 402 110
Cash and cash equivalents | Inflation linked    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Cash and cash equivalents | Other    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Financial investments    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 3,699 2,605
Financial investments | Fixed rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Financial investments | Floating rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 3,640 2,569
Financial investments | Inflation linked    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Financial investments | Other    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 59 36
Borrowings    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (47,072) (42,985)
Borrowings | Fixed rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (39,948) (36,631)
Borrowings | Floating rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (2,378) (1,744)
Borrowings | Inflation linked    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (4,746) (4,610)
Borrowings | Other    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 0 0
Pre-derivative position    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (42,814) (40,217)
Pre-derivative position | Fixed rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (39,791) (36,578)
Pre-derivative position | Floating rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 1,664 935
Pre-derivative position | Inflation linked    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (4,746) (4,610)
Pre-derivative position | Other    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 59 36
Derivative effect    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (793) (756)
Derivative effect | Fixed rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic 5,034 4,213
Derivative effect | Floating rate    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (5,763) (4,869)
Derivative effect | Inflation linked    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic (64) (100)
Derivative effect | Other    
Disclosure of financial instruments by type of interest rate [line items]    
Risk exposure associated with instruments sharing characteristic £ 0 £ 0