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 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 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 2021-03-31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of financial position [abstract] | ||||||||||||||||||
| Assets [abstract] | ||||||||||||||||||
| Property, plant and equipment |
1,332,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
1,238,000,000
GBP
|
— | — | — | — | — | — | — |
| Right-of-use assets |
49,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
61,000,000
GBP
|
— | — | — | — | — | — | — |
| Goodwill |
364,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
366,000,000
GBP
|
— | — | — | — | — | — | — |
| Intangible assets other than goodwill |
287,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
267,000,000
GBP
|
— | — | — | — | — | — | — |
| Investments accounted for using equity method |
75,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
2,000,000
GBP
|
— | — | — | — | — | — | — |
| Current tax assets |
12,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
18,000,000
GBP
|
— | — | — | — | — | — | — |
| Deferred tax assets |
121,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
98,000,000
GBP
|
— | — | — | — | — | — | — |
| Cash and cash equivalents |
650,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
391,000,000
GBP
|
— | — | — | — | — | — | — |
| Assets |
7,029,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
6,666,000,000
GBP
|
— | — | — | — | — | — | — |
| Equity and liabilities [abstract] | ||||||||||||||||||
| Equity [abstract] | ||||||||||||||||||
| Issued capital |
215,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
218,000,000
GBP
|
— | — | — | — | — | — | — |
| Retained earnings |
2,077,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
2,049,000,000
GBP
|
— | — | — | — | — | — | — |
| Share premium |
148,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
148,000,000
GBP
|
— | — | — | — | — | — | — |
| Treasury shares |
19,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
24,000,000
GBP
|
— | — | — | — | — | — | — |
| Other reserves |
118,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
50,000,000
GBP
|
— | — | — | — | — | — | — |
| Equity |
2,539,000,000
GBP
|
148,000,000
GBP
|
215,000,000
GBP
|
19,000,000
GBP
|
2,077,000,000
GBP
|
118,000,000
GBP
|
24,000,000
GBP
|
218,000,000
GBP
|
148,000,000
GBP
|
2,049,000,000
GBP
|
2,441,000,000
GBP
|
50,000,000
GBP
|
29,000,000
GBP
|
2,345,000,000
GBP
|
–
GBP
|
2,685,000,000
GBP
|
148,000,000
GBP
|
221,000,000
GBP
|
| Liabilities [abstract] | ||||||||||||||||||
| Current tax liabilities |
105,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
97,000,000
GBP
|
— | — | — | — | — | — | — |
| Deferred tax liabilities |
19,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
18,000,000
GBP
|
— | — | — | — | — | — | — |
| Liabilities included in disposal groups classified as held for sale |
25,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
80,000,000
GBP
|
— | — | — | — | — | — | — |
| Liabilities |
4,490,000,000
GBP
|
— | — | — | — | — | — | — | — | — |
4,225,000,000
GBP
|
— | — | — | — | — | — | — |