Subclassifications Of Assets, Liabilities And Equities [Abstract]
| Concept |
As at 2021-12-31 |
As at 2021-12-31 |
As at 2021-12-31 |
As at 2021-01-01 |
As at 2020-12-31 |
As at 2020-12-31 |
As at 2020-12-31 |
As at 2020-01-01 |
As at 2019-12-31 |
As at 2019-12-31 |
|---|---|---|---|---|---|---|---|---|---|---|
| Subclassifications of assets, liabilities and equities [abstract] | ||||||||||
| Property, plant and equipment [abstract] | ||||||||||
| Property, plant and equipment |
135,400,000
GBP
|
— | — | — |
130,500,000
GBP
|
— | — | — | — | — |
| Intangible assets and goodwill [abstract] | ||||||||||
| Intangible assets and goodwill |
3,100,000
GBP
|
— | — | — |
2,200,000
GBP
|
— | — | — | — | — |
| Investment property [abstract] | ||||||||||
| Investment property |
2,153,000,000
GBP
|
— | — | — |
2,032,800,000
GBP
|
— | — | — | — | — |
| Investments accounted for using equity method [abstract] | ||||||||||
| Investments accounted for using equity method |
4,900,000
GBP
|
— | — | — |
–
GBP
|
— | — | — | — | — |
| Trade and other non-current receivables [abstract] | ||||||||||
| Other non-current receivables |
7,700,000
GBP
|
— | — | — |
8,200,000
GBP
|
— | — | — | — | — |
| Miscellaneous non-current assets [abstract] | ||||||||||
| Non-current derivative financial assets |
400,000
GBP
|
— | — | — |
–
GBP
|
— | — | — | — | — |
| Trade and other receivables [abstract] | ||||||||||
| Trade and other receivables |
18,100,000
GBP
|
— | — | — |
22,000,000
GBP
|
— | — | — | — | — |
| Categories of non-current financial assets [abstract] | ||||||||||
| Non-current financial assets at fair value through profit or loss [abstract] | ||||||||||
| Non-current financial assets at fair value through profit or loss, mandatorily measured at fair value |
1,700,000
GBP
|
— | — | — |
–
GBP
|
— | — | — | — | — |
| Cash and cash equivalents [abstract] | ||||||||||
| Cash and cash equivalents |
167,400,000
GBP
|
— | — |
235,700,000
GBP
|
235,700,000
GBP
|
— | — |
259,400,000
GBP
|
— | — |
| Non-current assets or disposal groups classified as held for sale or as held for distribution to owners [abstract] | ||||||||||
| Non-current assets or disposal groups classified as held for sale or as held for distribution to owners |
44,200,000
GBP
|
— | — | — |
21,900,000
GBP
|
— | — | — | — | — |
| Borrowings [abstract] | ||||||||||
| Non-current portion of non-current borrowings |
169,100,000
GBP
|
— | — | — |
103,600,000
GBP
|
— | — | — | — | — |
| Current borrowings and current portion of non-current borrowings [abstract] | ||||||||||
| Current portion of non-current borrowings |
862,500,000
GBP
|
— | — | — |
867,100,000
GBP
|
— | — | — | — | — |
| Non-current portion of non-current borrowings, by type [abstract] | ||||||||||
| Trade and other payables [abstract] | ||||||||||
| Trade and other payables |
57,600,000
GBP
|
— | — | — |
54,300,000
GBP
|
— | — | — | — | — |
| Miscellaneous non-current liabilities [abstract] | ||||||||||
| Non-current derivative financial liabilities |
700,000
GBP
|
— | — | — |
–
GBP
|
— | — | — | — | — |
| Miscellaneous current liabilities [abstract] | ||||||||||
| Current derivative financial liabilities |
100,000
GBP
|
— | — | — |
5,600,000
GBP
|
— | — | — | — | — |
| Issued capital [abstract] | ||||||||||
| Issued capital |
11,000,000
GBP
|
— |
11,000,000
GBP
|
— |
11,000,000
GBP
|
— |
11,000,000
GBP
|
— | — |
11,000,000
GBP
|
| Retained earnings [abstract] | ||||||||||
| Retained earnings |
1,147,900,000
GBP
|
1,147,900,000
GBP
|
— | — |
1,059,200,000
GBP
|
1,059,200,000
GBP
|
— | — |
1,011,900,000
GBP
|
— |
| Accumulated other comprehensive income [abstract] | ||||||||||
| Revaluation surplus |
5,500,000
GBP
|
— | — | — |
3,600,000
GBP
|
— | — | — | — | — |
| Net assets (liabilities) [abstract] | ||||||||||
| Assets |
2,538,500,000
GBP
|
— | — | — |
2,461,000,000
GBP
|
— | — | — | — | — |
| Liabilities |
1,207,800,000
GBP
|
— | — | — |
1,190,400,000
GBP
|
— | — | — | — | — |
| Assets (liabilities) |
1,330,700,000
GBP
|
— | — | — |
1,270,600,000
GBP
|
— | — | — | — | — |
| Net current assets (liabilities) [abstract] | ||||||||||
| Current assets |
229,700,000
GBP
|
— | — | — |
279,600,000
GBP
|
— | — | — | — | — |
| Current liabilities |
231,900,000
GBP
|
— | — | — |
158,200,000
GBP
|
— | — | — | — | — |
| Assets less current liabilities [abstract] |