Statement Of Financial Position [Abstract]
| Concept |
As at 2025-03-31 |
As at 2025-03-31 |
As at 2025-03-31 |
As at 2025-03-31 |
As at 2025-03-31 |
As at 2024-03-31 |
As at 2024-03-31 |
As at 2024-03-31 |
As at 2024-03-31 |
As at 2024-03-31 |
As at 2023-03-31 |
As at 2023-03-31 |
As at 2023-03-31 |
As at 2023-03-31 |
As at 2023-03-31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of financial position [abstract] | |||||||||||||||
| Assets [abstract] | |||||||||||||||
| Property, plant and equipment | — | — | — |
13,873,000,000
GBP
|
— | — | — | — | — |
13,044,300,000
GBP
|
— | — | — | — | — |
| Cash and cash equivalents | — | — | — |
1,672,600,000
GBP
|
— | — | — | — | — |
1,399,300,000
GBP
|
— | — | — | — | — |
| Assets | — | — | — |
16,769,500,000
GBP
|
— | — | — | — | — |
15,653,400,000
GBP
|
— | — | — | — | — |
| Equity and liabilities [abstract] | |||||||||||||||
| Equity [abstract] | |||||||||||||||
| Issued capital | — | — | — |
499,800,000
GBP
|
— | — | — | — | — |
499,800,000
GBP
|
— | — | — | — | — |
| Retained earnings | — | — | — |
1,178,000,000
GBP
|
— | — | — | — | — |
1,242,300,000
GBP
|
— | — | — | — | — |
| Share premium | — | — | — |
2,900,000
GBP
|
— | — | — | — | — |
2,900,000
GBP
|
— | — | — | — | — |
| Other reserves | — | — | — |
319,200,000
GBP
|
— | — | — | — | — |
311,100,000
GBP
|
— | — | — | — | — |
| Equity |
499,800,000
GBP
|
319,200,000
GBP
|
1,178,000,000
GBP
|
1,999,900,000
GBP
|
2,900,000
GBP
|
311,100,000
GBP
|
1,242,300,000
GBP
|
2,900,000
GBP
|
499,800,000
GBP
|
2,056,100,000
GBP
|
2,508,700,000
GBP
|
2,900,000
GBP
|
499,800,000
GBP
|
1,652,600,000
GBP
|
353,400,000
GBP
|
| Liabilities [abstract] | |||||||||||||||
| Deferred tax liabilities | — | — | — |
2,028,400,000
GBP
|
— | — | — | — | — |
1,930,600,000
GBP
|
— | — | — | — | — |
| Liabilities | — | — | — |
14,769,600,000
GBP
|
— | — | — | — | — |
13,597,300,000
GBP
|
— | — | — | — | — |