Statement Of Cash Flows [Abstract]
| Concept |
As at 2021-12-31 |
As at 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
As at 2020-12-31 |
As at 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
As at 2019-12-31 |
As at 2019-12-31 |
|---|---|---|---|---|---|---|---|---|---|---|
| Statement of cash flows [abstract] | ||||||||||
| Cash flows from (used in) operating activities [abstract] | ||||||||||
| Interest paid, classified as operating activities | — | — |
19,400,000
GBP
|
21,900,000
GBP
|
— | — |
25,400,000
GBP
|
20,500,000
GBP
|
— | — |
| Interest received, classified as operating activities | — | — |
–
GBP
|
–
GBP
|
— | — |
200,000
GBP
|
200,000
GBP
|
— | — |
| Cash flows from (used in) operating activities | — | — |
52,900,000
GBP
|
125,700,000
GBP
|
— | — |
115,900,000
GBP
|
54,100,000
GBP
|
— | — |
| Cash flows from (used in) investing activities [abstract] | ||||||||||
| Other cash receipts from sales of interests in joint ventures, classified as investing activities | — | — |
–
GBP
|
–
GBP
|
— | — |
400,000
GBP
|
–
GBP
|
— | — |
| Other cash payments to acquire interests in joint ventures, classified as investing activities | — | — |
–
GBP
|
64,100,000
GBP
|
— | — |
–
GBP
|
–
GBP
|
— | — |
| Proceeds from sales of property, plant and equipment, classified as investing activities | — | — |
100,000
GBP
|
200,000
GBP
|
— | — |
–
GBP
|
–
GBP
|
— | — |
| Purchase of property, plant and equipment, classified as investing activities | — | — |
1,200,000
GBP
|
1,600,000
GBP
|
— | — |
400,000
GBP
|
400,000
GBP
|
— | — |
| Proceeds from sales of other long-term assets, classified as investing activities | — | — |
82,000,000
GBP
|
–
GBP
|
— | — |
–
GBP
|
–
GBP
|
— | — |
| Cash flows from (used in) investing activities | — | — |
80,900,000
GBP
|
182,600,000
GBP
|
— | — |
92,500,000
GBP
|
400,000
GBP
|
— | — |
| Cash flows from (used in) financing activities [abstract] | ||||||||||
| Proceeds from issuing shares | — | — |
1,800,000
GBP
|
1,800,000
GBP
|
— | — |
600,000
GBP
|
600,000
GBP
|
— | — |
| Proceeds from borrowings, classified as financing activities | — | — |
–
GBP
|
12,300,000
GBP
|
— | — |
–
GBP
|
–
GBP
|
— | — |
| Repayments of borrowings, classified as financing activities | — | — |
–
GBP
|
28,000,000
GBP
|
— | — |
–
GBP
|
–
GBP
|
— | — |
| Dividends paid, classified as financing activities | — | — |
84,300,000
GBP
|
84,300,000
GBP
|
— | — |
81,800,000
GBP
|
81,800,000
GBP
|
— | — |
| Cash flows from (used in) financing activities | — | — |
9,900,000
GBP
|
74,700,000
GBP
|
— | — |
27,200,000
GBP
|
50,600,000
GBP
|
— | — |
| Increase (decrease) in cash and cash equivalents after effect of exchange rate changes | — | — |
18,100,000
GBP
|
17,800,000
GBP
|
— | — |
3,800,000
GBP
|
3,900,000
GBP
|
— | — |
| Cash and cash equivalents |
68,500,000
GBP
|
68,200,000
GBP
|
— | — |
50,700,000
GBP
|
50,100,000
GBP
|
— | — |
54,000,000
GBP
|
54,500,000
GBP
|