Statement Of Financial Position [Abstract]
| Concept |
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 |
As at 2021-03-31 |
As at 2021-03-31 |
As at 2021-03-31 |
As at 2021-03-31 |
As at 2021-03-31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of financial position [abstract] | |||||||||||||||
| Assets [abstract] | |||||||||||||||
| Non-current assets [abstract] | |||||||||||||||
| Property, plant and equipment |
10,716,900,000
GBP
|
— | — | — | — | — | — | — |
10,208,400,000
GBP
|
— | — | — | — | — | — |
| Right-of-use assets |
129,300,000
GBP
|
— | — | — | — | — | — | — |
129,900,000
GBP
|
— | — | — | — | — | — |
| Goodwill |
92,700,000
GBP
|
— | — | — | — | — | — | — |
91,400,000
GBP
|
— | — | — | — | — | — |
| Intangible assets other than goodwill |
185,900,000
GBP
|
— | — | — | — | — | — | — |
179,600,000
GBP
|
— | — | — | — | — | — |
| Trade and other non-current receivables |
88,400,000
GBP
|
— | — | — | — | — | — | — |
92,100,000
GBP
|
— | — | — | — | — | — |
| Non-current assets |
11,317,700,000
GBP
|
— | — | — | — | — | — | — |
10,766,600,000
GBP
|
— | — | — | — | — | — |
| Current assets [abstract] | |||||||||||||||
| Current inventories |
35,400,000
GBP
|
— | — | — | — | — | — | — |
32,000,000
GBP
|
— | — | — | — | — | — |
| Trade and other current receivables |
750,900,000
GBP
|
— | — | — | — | — | — | — |
606,400,000
GBP
|
— | — | — | — | — | — |
| Cash and cash equivalents |
34,200,000
GBP
|
— | — | — | — | — | — | — |
115,400,000
GBP
|
— | — | — | — | — | — |
| Current assets |
830,900,000
GBP
|
— | — | — | — | — | — | — |
787,600,000
GBP
|
— | — | — | — | — | — |
| Equity and liabilities [abstract] | |||||||||||||||
| Equity [abstract] | |||||||||||||||
| Issued capital |
249,100,000
GBP
|
— | — | — | — | — | — | — |
248,100,000
GBP
|
— | — | — | — | — | — |
| Retained earnings |
162,500,000
GBP
|
— | — | — | — | — | — | — |
473,000,000
GBP
|
— | — | — | — | — | — |
| Share premium |
408,700,000
GBP
|
— | — | — | — | — | — | — |
394,400,000
GBP
|
— | — | — | — | — | — |
| Other reserves |
150,300,000
GBP
|
— | — | — | — | — | — | — |
148,400,000
GBP
|
— | — | — | — | — | — |
| Equity |
970,600,000
GBP
|
408,700,000
GBP
|
249,100,000
GBP
|
162,500,000
GBP
|
150,300,000
GBP
|
248,100,000
GBP
|
394,400,000
GBP
|
473,000,000
GBP
|
1,263,900,000
GBP
|
148,400,000
GBP
|
651,700,000
GBP
|
101,700,000
GBP
|
1,138,700,000
GBP
|
237,200,000
GBP
|
148,100,000
GBP
|
| Liabilities [abstract] | |||||||||||||||
| Non-current liabilities [abstract] | |||||||||||||||
| Non-current provisions [abstract] | |||||||||||||||
| Non-current provisions |
32,100,000
GBP
|
— | — | — | — | — | — | — |
21,900,000
GBP
|
— | — | — | — | — | — |
| Trade and other non-current payables |
1,479,600,000
GBP
|
— | — | — | — | — | — | — |
1,334,000,000
GBP
|
— | — | — | — | — | — |
| Deferred tax liabilities |
1,293,500,000
GBP
|
— | — | — | — | — | — | — |
1,320,600,000
GBP
|
— | — | — | — | — | — |
| Non-current liabilities |
10,087,800,000
GBP
|
— | — | — | — | — | — | — |
9,231,200,000
GBP
|
— | — | — | — | — | — |
| Current liabilities [abstract] | |||||||||||||||
| Current provisions [abstract] | |||||||||||||||
| Current provisions |
52,400,000
GBP
|
— | — | — | — | — | — | — |
38,400,000
GBP
|
— | — | — | — | — | — |
| Trade and other current payables |
720,400,000
GBP
|
— | — | — | — | — | — | — |
655,500,000
GBP
|
— | — | — | — | — | — |
| Current liabilities |
1,090,200,000
GBP
|
— | — | — | — | — | — | — |
1,059,100,000
GBP
|
— | — | — | — | — | — |