Statement Of Cash Flows [Abstract]
| Concept |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
As at 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2021-01-01 to 2021-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
As at 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
2020-01-01 to 2020-12-31 |
As at 2019-12-31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of cash flows [abstract] | |||||||||||||||||||||
| Cash flows from (used in) operating activities [abstract] | |||||||||||||||||||||
| Profit (loss) |
1,200,000
GBP
|
–
GBP
|
185,300,000
GBP
|
— |
–
GBP
|
–
GBP
|
–
GBP
|
–
GBP
|
186,500,000
GBP
|
185,300,000
GBP
|
154,200,000
GBP
|
–
GBP
|
153,800,000
GBP
|
–
GBP
|
— |
–
GBP
|
400,000
GBP
|
–
GBP
|
153,800,000
GBP
|
–
GBP
|
— |
| Adjustments to reconcile profit (loss) [abstract] | |||||||||||||||||||||
| Adjustments for decrease (increase) in inventories | — | — | — | — | — | — | — | — |
131,500,000
GBP
|
— |
50,400,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Adjustments for provisions | — | — | — | — | — | — | — | — |
2,900,000
GBP
|
— |
1,900,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Adjustments for share-based payments | — | — | — | — | — | — | — | — |
10,600,000
GBP
|
— |
8,000,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Other adjustments to reconcile profit (loss) | — | — | — | — | — | — | — | — |
1,800,000
GBP
|
— |
100,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Cash flows from (used in) operations | — | — | — | — | — | — | — | — |
277,500,000
GBP
|
— |
264,500,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Income taxes paid (refund), classified as operating activities | — | — | — | — | — | — | — | — |
53,200,000
GBP
|
— |
27,600,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Cash flows from (used in) operating activities | — | — | — | — | — | — | — | — |
224,300,000
GBP
|
— |
236,900,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Cash flows from (used in) investing activities [abstract] | |||||||||||||||||||||
| Proceeds from sales of property, plant and equipment, classified as investing activities | — | — | — | — | — | — | — | — |
7,500,000
GBP
|
— |
1,600,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Purchase of property, plant and equipment, classified as investing activities | — | — | — | — | — | — | — | — |
18,800,000
GBP
|
— |
23,100,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Purchase of intangible assets, classified as investing activities | — | — | — | — | — | — | — | — |
11,500,000
GBP
|
— |
4,400,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Interest received, classified as investing activities | — | — | — | — | — | — | — | — |
300,000
GBP
|
— |
500,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Cash flows from (used in) investing activities | — | — | — | — | — | — | — | — |
25,000,000
GBP
|
— |
55,500,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Cash flows from (used in) financing activities [abstract] | |||||||||||||||||||||
| Proceeds from issuing shares | — | — | — | — | — | — | — | — |
6,200,000
GBP
|
— |
5,700,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Payments to acquire or redeem entity's shares | — | — | — | — | — | — | — | — |
25,500,000
GBP
|
— |
19,000,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Proceeds from borrowings, classified as financing activities | — | — | — | — | — | — | — | — |
10,700,000
GBP
|
— |
300,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Repayments of borrowings, classified as financing activities | — | — | — | — | — | — | — | — |
99,700,000
GBP
|
— |
20,000,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Payments of lease liabilities, classified as financing activities | — | — | — | — | — | — | — | — |
50,200,000
GBP
|
— |
43,200,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Interest paid, classified as financing activities | — | — | — | — | — | — | — | — |
2,300,000
GBP
|
— |
1,900,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Cash flows from (used in) financing activities | — | — | — | — | — | — | — | — |
228,400,000
GBP
|
— |
96,500,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Increase (decrease) in cash and cash equivalents before effect of exchange rate changes | — | — | — | — | — | — | — | — |
29,100,000
GBP
|
— |
84,900,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Effect of exchange rate changes on cash and cash equivalents [abstract] | |||||||||||||||||||||
| Effect of exchange rate changes on cash and cash equivalents | — | — | — | — | — | — | — | — |
7,500,000
GBP
|
— |
7,100,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
| Cash and cash equivalents | — | — | — |
273,200,000
GBP
|
— | — | — | — | — | — | — | — | — | — |
309,800,000
GBP
|
— | — | — | — | — |
217,800,000
GBP
|