Statement Of Cash Flows [Abstract]
| Concept |
2022-01-01 to 2022-12-31 |
As at 2022-12-31 |
2022-01-01 to 2022-12-31 |
As at 2022-12-31 |
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 |
|---|---|---|---|---|---|---|---|---|---|---|
| Statement of cash flows [abstract] | ||||||||||
| Cash flows from (used in) operating activities [abstract] | ||||||||||
| Classes of cash payments from operating activities [abstract] | ||||||||||
| Payments to and on behalf of employees |
25,000,000
GBP
|
— |
25,100,000
GBP
|
— | — | — |
26,600,000
GBP
|
26,900,000
GBP
|
— | — |
| Interest paid, classified as operating activities |
26,600,000
GBP
|
— |
33,700,000
GBP
|
— | — | — |
19,400,000
GBP
|
21,900,000
GBP
|
— | — |
| Interest received, classified as operating activities |
200,000
GBP
|
— |
300,000
GBP
|
— | — | — |
–
GBP
|
–
GBP
|
— | — |
| Cash flows from (used in) operating activities |
58,500,000
GBP
|
— |
111,400,000
GBP
|
— | — | — |
52,900,000
GBP
|
128,900,000
GBP
|
— | — |
| Cash flows from (used in) investing activities [abstract] | ||||||||||
| Other cash payments to acquire interests in joint ventures, classified as investing activities |
–
GBP
|
— |
300,000
GBP
|
— | — | — |
–
GBP
|
64,100,000
GBP
|
— | — |
| Proceeds from sales of property, plant and equipment, classified as investing activities |
–
GBP
|
— |
–
GBP
|
— | — | — |
100,000
GBP
|
200,000
GBP
|
— | — |
| Purchase of property, plant and equipment, classified as investing activities |
600,000
GBP
|
— |
2,000,000
GBP
|
— | — | — |
1,200,000
GBP
|
1,600,000
GBP
|
— | — |
| Proceeds from sales of other long-term assets, classified as investing activities |
–
GBP
|
— |
–
GBP
|
— | — | — |
82,000,000
GBP
|
–
GBP
|
— | — |
| Cash flows from (used in) investing activities |
600,000
GBP
|
— |
51,700,000
GBP
|
— | — | — |
80,900,000
GBP
|
186,600,000
GBP
|
— | — |
| Cash flows from (used in) financing activities [abstract] | ||||||||||
| Proceeds from issuing shares |
1,200,000
GBP
|
— |
1,200,000
GBP
|
— | — | — |
1,800,000
GBP
|
1,800,000
GBP
|
— | — |
| Proceeds from borrowings, classified as financing activities |
–
GBP
|
— |
7,400,000
GBP
|
— | — | — |
–
GBP
|
12,300,000
GBP
|
— | — |
| Repayments of borrowings, classified as financing activities |
–
GBP
|
— |
–
GBP
|
— | — | — |
–
GBP
|
28,000,000
GBP
|
— | — |
| Dividends paid, classified as financing activities |
86,800,000
GBP
|
— |
86,800,000
GBP
|
— | — | — |
84,300,000
GBP
|
84,300,000
GBP
|
— | — |
| Cash flows from (used in) financing activities |
35,800,000
GBP
|
— |
88,600,000
GBP
|
— | — | — |
10,100,000
GBP
|
74,700,000
GBP
|
— | — |
| Increase (decrease) in cash and cash equivalents after effect of exchange rate changes |
23,300,000
GBP
|
— |
28,900,000
GBP
|
— | — | — |
17,900,000
GBP
|
17,000,000
GBP
|
— | — |
| Cash and cash equivalents | — |
76,600,000
GBP
|
— |
67,300,000
GBP
|
105,500,000
GBP
|
90,600,000
GBP
|
— | — |
72,700,000
GBP
|
88,500,000
GBP
|