v3.26.1
Revenue - Disclosure of disaggregation of revenue by primary geographical market and major service lines (Details) - GBP (£)
£ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue £ 16,996 £ 17,703 £ 19,070
Total other revenue 691 675 780
Total revenue from continuing operations 17,687 18,378 19,850
UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 2,626 2,294 2,616
Total other revenue 185 190 79
Total revenue from continuing operations 2,811 2,484 2,695
UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 1,932 2,417 1,785
Total other revenue 5 4 5
Total revenue from continuing operations 1,937 2,421 1,790
UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   1,012 3,753
Total other revenue   0 0
Total revenue from continuing operations 0 1,012 3,753
New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4,125 4,287 3,867
Total other revenue 49 19 81
Total revenue from continuing operations 4,174 4,306 3,948
New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 7,576 6,639 6,008
Total other revenue 42 50 86
Total revenue from continuing operations 7,618 6,689 6,094
National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 733 1,050 1,037
Total other revenue 324 300 295
Total revenue from continuing operations 1,057 1,350 1,332
Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4 4 4
Total other revenue 86 112 234
Total revenue from continuing operations 90 116 238
UK      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 5,271 6,613 9,033
Total other revenue 201 94 30
Total revenue from continuing operations 5,472 6,707 9,063
UK | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 2,626 2,294 2,616
Total other revenue 185 190 79
UK | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 1,932 2,417 1,785
Total other revenue 5 4 5
UK | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   1,012 3,753
Total other revenue   0 0
UK | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
UK | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
UK | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 713 889 878
Total other revenue (61) (111) (76)
UK | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 1 1
Total other revenue 72 11 22
US      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 11,725 11,090 10,037
Total other revenue 490 581 750
Total revenue from continuing operations 12,215 11,671 10,787
US | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
US | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Total other revenue 0 0 0
US | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
Total other revenue   0 0
US | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4,125 4,287 3,867
Total other revenue 49 19 81
US | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 7,576 6,639 6,008
Total other revenue 42 50 86
US | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 20 161 159
Total other revenue 385 411 371
US | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4 3 3
Total other revenue 14 101 212
Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 3,720 3,528 4,016
Transmission | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 2,597 2,265 2,591
Transmission | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Transmission | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   46 (10)
Transmission | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 55 85 73
Transmission | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 355 252 493
Transmission | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 713 879 869
Transmission | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 1 0
Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 13,124 12,891 10,998
Distribution | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Distribution | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 1,859 2,327 1,712
Distribution | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
Distribution | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4,061 4,193 3,786
Distribution | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 7,204 6,371 5,500
Distribution | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
Distribution | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 0 0 0
System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   966 3,763
System Operator | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
System Operator | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
System Operator | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   966 3,763
System Operator | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
System Operator | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
System Operator | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
System Operator | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
Generation      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 364 384 360
Generation | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue   0 0
Generation | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Generation | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 364 384 360
Generation | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total other revenue 0 0 0
Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 152 318 293
Total other revenue 327 291 420
Other | UK Electricity Transmission      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 29 29 25
Total other revenue 185 190 79
Other | UK Electricity Distribution      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 73 90 73
Total other revenue 5 4 5
Other | UK Electricity System Operator      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue   0 0
Total other revenue   0 0
Other | New England      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 9 9 8
Total other revenue 49 19 81
Other | New York      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 17 16 15
Total other revenue 42 50 86
Other | National Grid Ventures      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 20 171 168
Total other revenue (40) (84) (65)
Other | Other      
Disclosure of disaggregation of revenue from contracts with customers [line items]      
Total IFRS 15 revenue 4 3 4
Total other revenue £ 86 £ 112 £ 234