v3.26.1
Segmental analysis - Schedule of operating profit by operating segments (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Disclosure of operating segments [line items]      
Total operating profit from continuing operations £ 5,431 £ 4,934 £ 4,475
Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 5,044 4,765 5,462
Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 387 169 (987)
UK      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 3,432 3,032 3,436
UK | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 2,948 2,775 3,923
UK | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 484 257 (487)
US      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,999 1,902 1,039
US | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 2,096 1,990 1,539
US | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (97) (88) (500)
Operating segments | UK Electricity Transmission      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,605 1,277 1,674
Operating segments | UK Electricity Transmission | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,605 1,277 1,677
Operating segments | UK Electricity Transmission | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 0 0 (3)
Operating segments | UK Electricity Distribution      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,122 1,598 975
Operating segments | UK Electricity Distribution | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,122 1,610 993
Operating segments | UK Electricity Distribution | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 0 (12) (18)
Operating segments | UK Electricity System Operator      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 0 (213) 382
Operating segments | UK Electricity System Operator | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 0 (364) 880
Operating segments | UK Electricity System Operator | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 0 151 (498)
Operating segments | New England      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 947 1,008 641
Operating segments | New England | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 960 982 643
Operating segments | New England | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (13) 26 (2)
Operating segments | New York      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,184 1,269 362
Operating segments | New York | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,172 1,023 860
Operating segments | New York | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 12 246 (498)
Operating segments | National Grid Ventures      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 715 5 558
Operating segments | National Grid Ventures | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 327 380 469
Operating segments | National Grid Ventures | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 388 (375) 89
Operating segments | Other      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (142) (10) (117)
Operating segments | Other | Before exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (142) (143) (60)
Operating segments | Other | Exceptional items and remeasurements, netting      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations £ 0 £ 133 £ (57)