Statement Of Financial Position [Abstract]
| Concept |
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 |
As at 2020-03-31 |
As at 2020-03-31 |
As at 2020-03-31 |
As at 2020-03-31 |
As at 2020-03-31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of financial position [abstract] | |||||||||||||||
| Assets [abstract] | |||||||||||||||
| Non-current assets [abstract] | |||||||||||||||
| Property, plant and equipment | — | — | — |
12,147,500,000
GBP
|
— | — | — |
11,799,000,000
GBP
|
— | — | — | — | — | — | — |
| Trade and other non-current receivables | — | — | — |
81,700,000
GBP
|
— | — | — |
86,700,000
GBP
|
— | — | — | — | — | — | — |
| Non-current inventories | — | — | — |
400,000
GBP
|
— | — | — |
–
GBP
|
— | — | — | — | — | — | — |
| Non-current assets | — | — | — |
13,823,200,000
GBP
|
— | — | — |
13,166,200,000
GBP
|
— | — | — | — | — | — | — |
| Current assets [abstract] | |||||||||||||||
| Current inventories | — | — | — |
17,800,000
GBP
|
— | — | — |
18,300,000
GBP
|
— | — | — | — | — | — | — |
| Trade and other current receivables | — | — | — |
222,700,000
GBP
|
— | — | — |
229,200,000
GBP
|
— | — | — | — | — | — | — |
| Current tax assets, current | — | — | — |
74,400,000
GBP
|
— | — | — |
6,900,000
GBP
|
— | — | — | — | — | — | — |
| Cash and cash equivalents | — | — | — |
240,900,000
GBP
|
— | — | — |
744,100,000
GBP
|
— | — | — | — | — | — | — |
| Current assets | — | — | — |
613,800,000
GBP
|
— | — | — |
1,012,900,000
GBP
|
— | — | — | — | — | — | — |
| Assets | — | — | — |
14,437,000,000
GBP
|
— | — | — |
14,179,100,000
GBP
|
— | — | — | — | — | — | — |
| Equity and liabilities [abstract] | |||||||||||||||
| Equity [abstract] | |||||||||||||||
| Issued capital | — | — | — |
499,800,000
GBP
|
— | — | — |
499,800,000
GBP
|
— | — | — | — | — | — | — |
| Retained earnings | — | — | — |
2,038,500,000
GBP
|
— | — | — |
2,192,000,000
GBP
|
— | — | — | — | — | — | — |
| Share premium | — | — | — |
2,900,000
GBP
|
— | — | — |
2,900,000
GBP
|
— | — | — | — | — | — | — |
| Other reserves | — | — | — |
416,200,000
GBP
|
— | — | — |
336,300,000
GBP
|
— | — | — | — | — | — | — |
| Equity |
499,800,000
GBP
|
2,900,000
GBP
|
2,038,500,000
GBP
|
2,957,400,000
GBP
|
416,200,000
GBP
|
2,192,000,000
GBP
|
336,300,000
GBP
|
3,031,000,000
GBP
|
499,800,000
GBP
|
2,900,000
GBP
|
336,700,000
GBP
|
2,962,100,000
GBP
|
2,900,000
GBP
|
499,800,000
GBP
|
2,122,700,000
GBP
|
| Liabilities [abstract] | |||||||||||||||
| Non-current liabilities [abstract] | |||||||||||||||
| Trade and other non-current payables | — | — | — |
835,200,000
GBP
|
— | — | — |
798,300,000
GBP
|
— | — | — | — | — | — | — |
| Deferred tax liabilities | — | — | — |
2,148,100,000
GBP
|
— | — | — |
1,449,500,000
GBP
|
— | — | — | — | — | — | — |
| Non-current liabilities | — | — | — |
10,791,000,000
GBP
|
— | — | — |
10,152,600,000
GBP
|
— | — | — | — | — | — | — |
| Current liabilities [abstract] | |||||||||||||||
| Current provisions [abstract] | |||||||||||||||
| Current provisions | — | — | — |
13,500,000
GBP
|
— | — | — |
11,100,000
GBP
|
— | — | — | — | — | — | — |
| Trade and other current payables | — | — | — |
365,800,000
GBP
|
— | — | — |
322,700,000
GBP
|
— | — | — | — | — | — | — |
| Current liabilities | — | — | — |
688,600,000
GBP
|
— | — | — |
995,500,000
GBP
|
— | — | — | — | — | — | — |
| Liabilities | — | — | — |
11,479,600,000
GBP
|
— | — | — |
11,148,100,000
GBP
|
— | — | — | — | — | — | — |