v3.24.1.1.u2
Segmental analysis - Schedule of operating profit by operating segments (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Mar. 31, 2022
Disclosure of operating segments [line items]      
Total operating profit from continuing operations £ 4,475 £ 4,879 £ 4,371
Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 5,462 4,294 3,813
Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (987) 585 558
UK      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 3,436 2,851 2,458
UK | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 3,923 2,825 2,234
UK | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (487) 26 224
US      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,039 2,028 1,913
US | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,539 1,469 1,579
US | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (500) 559 334
Operating segments | UK Electricity Transmission      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,674 993 1,055
Operating segments | UK Electricity Transmission | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 1,677 995 1,067
Operating segments | UK Electricity Transmission | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (3) (2) (12)
Operating segments | UK Electricity Distribution      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 975 1,069 909
Operating segments | UK Electricity Distribution | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 993 1,091 909
Operating segments | UK Electricity Distribution | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (18) (22) 0
Operating segments | UK Electricity System Operator      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 382 237 5
Operating segments | UK Electricity System Operator | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 880 238 7
Operating segments | UK Electricity System Operator | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (498) (1) (2)
Operating segments | New England      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 641 1,132 764
Operating segments | New England | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 643 708 743
Operating segments | New England | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (2) 424 21
Operating segments | New York      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 362 541 1,095
Operating segments | New York | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 860 741 780
Operating segments | New York | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (498) (200) 315
Operating segments | National Grid Ventures      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 558 957 283
Operating segments | National Grid Ventures | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 469 490 286
Operating segments | National Grid Ventures | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations 89 467 (3)
Operating segments | Other      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (117) (50) 260
Operating segments | Other | Before exceptional items and remeasurements      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations (60) 31 21
Operating segments | Other | Exceptional items 
and remeasurements (see note 5)      
Disclosure of operating segments [line items]      
Total operating profit from continuing operations £ (57) £ (81) £ 239