Statement Of Financial Position [Abstract]
| Concept |
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 |
As at 2022-03-31 |
As at 2022-03-31 |
As at 2022-03-31 |
As at 2022-03-31 |
As at 2022-03-31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of financial position [abstract] | |||||||||||||||
| Assets [abstract] | |||||||||||||||
| Non-current assets [abstract] | |||||||||||||||
| Property, plant and equipment | — | — | — | — |
13,044,300,000
GBP
|
12,570,700,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Trade and other non-current receivables | — | — | — | — |
73,700,000
GBP
|
75,700,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Non-current inventories | — | — | — | — |
–
GBP
|
1,200,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Non-current assets | — | — | — | — |
13,884,400,000
GBP
|
13,835,800,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Current assets [abstract] | |||||||||||||||
| Trade and other current receivables | — | — | — | — |
226,800,000
GBP
|
190,500,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Current tax assets, current | — | — | — | — |
100,100,000
GBP
|
98,900,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Cash and cash equivalents | — | — | — | — |
1,399,300,000
GBP
|
340,400,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Current assets | — | — | — | — |
1,769,000,000
GBP
|
691,400,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Assets | — | — | — | — |
15,653,400,000
GBP
|
14,527,200,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Equity and liabilities [abstract] | |||||||||||||||
| Equity [abstract] | |||||||||||||||
| Issued capital | — | — | — | — |
499,800,000
GBP
|
499,800,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Retained earnings | — | — | — | — |
1,242,300,000
GBP
|
1,652,600,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Share premium | — | — | — | — |
2,900,000
GBP
|
2,900,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Other reserves | — | — | — | — |
311,100,000
GBP
|
353,400,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Equity |
1,242,300,000
GBP
|
311,100,000
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
|
499,800,000
GBP
|
2,900,000
GBP
|
2,038,500,000
GBP
|
2,957,400,000
GBP
|
416,200,000
GBP
|
| Liabilities [abstract] | |||||||||||||||
| Non-current liabilities [abstract] | |||||||||||||||
| Trade and other non-current payables | — | — | — | — |
957,900,000
GBP
|
892,400,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Deferred tax liabilities | — | — | — | — |
1,930,600,000
GBP
|
2,048,100,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Non-current liabilities | — | — | — | — |
12,489,500,000
GBP
|
11,442,600,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Current liabilities [abstract] | |||||||||||||||
| Current provisions [abstract] | |||||||||||||||
| Current provisions | — | — | — | — |
13,500,000
GBP
|
13,100,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Trade and other current payables | — | — | — | — |
413,300,000
GBP
|
376,700,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Current liabilities | — | — | — | — |
1,107,800,000
GBP
|
575,900,000
GBP
|
— | — | — | — | — | — | — | — | — |
| Liabilities | — | — | — | — |
13,597,300,000
GBP
|
12,018,500,000
GBP
|
— | — | — | — | — | — | — | — | — |