v3.26.1
Tax - Schedule of tax included within the statement of financial position (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax liability (asset) beginning of period £ 8,038 £ 7,519
Exchange adjustments and other (97) (95)
Charged/(credited) to income statement 1,095 786
(Credited)/charged to other comprehensive income and equity 16 17
Disposals (12) (65)
Reclassification to held for sale   (124)
Deferred tax liability (asset) end of period 9,040 8,038
Regulatory licenses    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax liability (asset) beginning of period 429 429
Exchange adjustments and other 0 0
Charged/(credited) to income statement 0 0
(Credited)/charged to other comprehensive income and equity 0 0
Disposals 0 0
Reclassification to held for sale   0
Deferred tax liability (asset) end of period 429 429
Accelerated tax depreciation    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax liability (asset) beginning of period 9,412 8,816
Exchange adjustments and other (144) (147)
Charged/(credited) to income statement 1,158 925
(Credited)/charged to other comprehensive income and equity 0 0
Disposals (12) (60)
Reclassification to held for sale   (122)
Deferred tax liability (asset) end of period 10,414 9,412
Share- based payments    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax liability (asset) beginning of period (26) (25)
Exchange adjustments and other 0 0
Charged/(credited) to income statement (5) (3)
(Credited)/charged to other comprehensive income and equity (9) 2
Disposals 0 0
Reclassification to held for sale   0
Deferred tax liability (asset) end of period (40) (26)
Pensions and other post- retirement benefits    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax liability (asset) beginning of period 491 461
Exchange adjustments and other (4) (5)
Charged/(credited) to income statement 6 58
(Credited)/charged to other comprehensive income and equity 39 (23)
Disposals 0 0
Reclassification to held for sale   0
Deferred tax liability (asset) end of period 532 491
Financial instruments    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax liability (asset) beginning of period (175) (275)
Exchange adjustments and other 0 0
Charged/(credited) to income statement 24 62
(Credited)/charged to other comprehensive income and equity (14) 38
Disposals 0 0
Reclassification to held for sale   0
Deferred tax liability (asset) end of period (165) (175)
Other net temporary differences    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax liability (asset) beginning of period (2,093) (1,887)
Exchange adjustments and other 51 57
Charged/(credited) to income statement (88) (256)
(Credited)/charged to other comprehensive income and equity 0 0
Disposals 0 (5)
Reclassification to held for sale   (2)
Deferred tax liability (asset) end of period (2,130) (2,093)
Deferred tax assets 2,130 2,093
Net operating losses    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax assets 456 298
Lease liabilities    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax assets 632 603
Environmental provisions    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax assets 558 575
Allowance for credit losses    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax assets 161 155
Other short term differences    
Reconciliation of changes in deferred tax liability (asset) [abstract]    
Deferred tax assets £ 323 £ 462