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] | |||||||||||||||
| Property, plant and equipment | — | — | — |
12,147,500,000
GBP
|
— | — | — |
11,799,000,000
GBP
|
— | — | — | — | — | — | — |
| Cash and cash equivalents | — | — | — |
240,900,000
GBP
|
— | — | — |
744,100,000
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] | |||||||||||||||
| Deferred tax liabilities | — | — | — |
2,148,100,000
GBP
|
— | — | — |
1,449,500,000
GBP
|
— | — | — | — | — | — | — |
| Liabilities | — | — | — |
11,479,600,000
GBP
|
— | — | — |
11,148,100,000
GBP
|
— | — | — | — | — | — | — |