v3.26.1
Pensions and other post-retirement benefits - Schedule of reconciliation of the net defined benefit asset (liability) (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disclosure of net defined benefit liability (asset) [line items]    
Opening net defined benefit asset £ 1,993 £ 1,814
Changes in net defined benefit liability (asset) [abstract]    
Income/(cost) recognised in the income statement before adjustment for irrecoverable surplus (2) (63)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income 274 (49)
Employer contributions 120 282
Other movements 6 9
Closing net defined benefit asset including restrictions on the defined benefit assets 2,391 1,993
Restrictions on the defined benefit asset (244) (77)
Net defined benefit asset 2,147 1,916
UK | Pensions    
Disclosure of net defined benefit liability (asset) [line items]    
Opening net defined benefit asset 1,128 1,261
Changes in net defined benefit liability (asset) [abstract]    
Income/(cost) recognised in the income statement before adjustment for irrecoverable surplus 3 8
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (156) (257)
Employer contributions 93 112
Other movements 3 4
Closing net defined benefit asset including restrictions on the defined benefit assets 1,071 1,128
Restrictions on the defined benefit asset 0 0
Net defined benefit asset 1,071 1,128
US | Pensions    
Disclosure of net defined benefit liability (asset) [line items]    
Opening net defined benefit asset 476 408
Changes in net defined benefit liability (asset) [abstract]    
Income/(cost) recognised in the income statement before adjustment for irrecoverable surplus (21) (55)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income (61) 96
Employer contributions 19 27
Other movements 0 0
Closing net defined benefit asset including restrictions on the defined benefit assets 413 476
Restrictions on the defined benefit asset 0 0
Net defined benefit asset 413 476
US | Other post-retirement benefits    
Disclosure of net defined benefit liability (asset) [line items]    
Opening net defined benefit asset 389 145
Changes in net defined benefit liability (asset) [abstract]    
Income/(cost) recognised in the income statement before adjustment for irrecoverable surplus 16 (16)
Remeasurement and foreign exchange effects recognised in the statement of other comprehensive income 491 112
Employer contributions 8 143
Other movements 3 5
Closing net defined benefit asset including restrictions on the defined benefit assets 907 389
Restrictions on the defined benefit asset (244) (77)
Net defined benefit asset 663 £ 312
One-off contribution to net defined benefit liability (asset) £ 133