v3.26.1
Other intangible assets - Schedule of analysis of other intangible assets (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance £ 3,564  
Intangible assets other than goodwill, ending balance 3,879 £ 3,564
Regulatory licenses    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance 1,714  
Intangible assets other than goodwill, ending balance 1,714 1,714
Software    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance 1,376  
Intangible assets other than goodwill, ending balance 1,636 1,376
Assets in the course of construction    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance 474  
Intangible assets other than goodwill, ending balance 529 474
Gas Business Enablement system    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance 271  
Intangible assets other than goodwill, ending balance 224 271
Intangible assets other than goodwill, in service amount £ 224 271
Amortised period (in years) 10 years  
UK General Ledger system    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance £ 82  
Intangible assets other than goodwill, ending balance £ 72 82
Amortised period (in years) 10 years  
Gross carrying amount    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance £ 5,599 5,199
Exchange adjustments (64) (68)
Additions 693 478
Disposals (10) (7)
Reclassifications (9) 13
Reclassification to held for sale (note 10)   (16)
Intangible assets other than goodwill, ending balance 6,209 5,599
Gross carrying amount | Regulatory licenses    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance 1,714 1,714
Exchange adjustments 0 0
Additions 0 0
Disposals 0 0
Reclassifications 0 0
Reclassification to held for sale (note 10)   0
Intangible assets other than goodwill, ending balance 1,714 1,714
Gross carrying amount | Software    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance 3,401 3,093
Exchange adjustments (56) (61)
Additions 84 16
Disposals (10) (7)
Reclassifications 547 376
Reclassification to held for sale (note 10)   (16)
Intangible assets other than goodwill, ending balance 3,966 3,401
Gross carrying amount | Assets in the course of construction    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance 484 392
Exchange adjustments (8) (7)
Additions 609 462
Disposals 0 0
Reclassifications (556) (363)
Reclassification to held for sale (note 10)   0
Intangible assets other than goodwill, ending balance 529 484
Accumulated amortisation    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance (2,035) (1,768)
Exchange adjustments 25 36
Amortisation charge for the year (339) (323)
Disposals 20 7
Reclassifications (1) 2
Reclassification to held for sale (note 10)   11
Intangible assets other than goodwill, ending balance (2,330) (2,035)
Accumulated amortisation | Regulatory licenses    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance 0 0
Exchange adjustments 0 0
Amortisation charge for the year 0 0
Disposals 0 0
Reclassifications 0 0
Reclassification to held for sale (note 10)   0
Intangible assets other than goodwill, ending balance 0 0
Accumulated amortisation | Software    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance (2,025) (1,758)
Exchange adjustments 25 36
Amortisation charge for the year (339) (323)
Disposals 10 7
Reclassifications (1) 2
Reclassification to held for sale (note 10)   11
Intangible assets other than goodwill, ending balance (2,330) (2,025)
Accumulated amortisation | Assets in the course of construction    
Changes in intangible assets other than goodwill [abstract]    
Intangible assets other than goodwill, beginning balance (10) (10)
Exchange adjustments 0 0
Amortisation charge for the year 0 0
Disposals 10 0
Reclassifications 0 0
Reclassification to held for sale (note 10)   0
Intangible assets other than goodwill, ending balance £ 0 £ (10)