Statement Of Financial Position [Abstract]
| Concept | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2024-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of financial position [abstract] | |||||||||||||||||||||
| Assets [abstract] | |||||||||||||||||||||
| Non-current assets [abstract] | |||||||||||||||||||||
| Property, plant and equipment | — | — | — | — | — | — | 
                                                48,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                56,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Trade and other non-current receivables | — | — | — | — | — | — | 
                                                4,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                5,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Deferred tax assets | — | — | — | — | — | — | 
                                                700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                55,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current tax assets, non-current | — | — | — | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                3,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | — | — | — | — | — | — | 
                                                157 .6
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                279 .2
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current assets [abstract] | |||||||||||||||||||||
| Current inventories | — | — | — | — | — | — | 
                                                82,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                94,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Trade and other current receivables | — | — | — | — | — | — | 
                                                38,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                47 .3
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Cash and cash equivalents | — | — | — | — | — | — | 
                                                57 .3
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                8. 7
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets or disposal groups classified as held for sale or as held for distribution to owners | — | — | — | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                12 .3
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current assets | — | — | — | — | — | — | 
                                                188,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                159 .8
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Assets | — | — | — | — | — | — | 
                                                346,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                451,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Equity and liabilities [abstract] | |||||||||||||||||||||
| Equity [abstract] | |||||||||||||||||||||
| Issued capital | — | — | — | — | — | — | 
                                                18. 9
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                18. 9
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retained earnings | — | — | — | — | — | — | 
                                                52,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                93,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Share premium | — | — | — | — | — | — | 
                                                133,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                133,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Equity | 
                                                1,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                52,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                133,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                18,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                16,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                85,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                237 .5
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                93,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                1,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                133,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                18. 9
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                13. 0
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                2 .9
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                223. 7
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                24,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                1,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                185,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                9 .4
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                3. 9
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Liabilities [abstract] | |||||||||||||||||||||
| Non-current liabilities [abstract] | |||||||||||||||||||||
| Non-current provisions [abstract] | |||||||||||||||||||||
| Other non-current provisions | — | — | — | — | — | — | 
                                                700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Trade and other non-current payables | — | — | — | — | — | — | 
                                                800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                1,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Deferred tax liabilities | — | — | — | — | — | — | 
                                                0 .1
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                11,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | — | — | — | — | — | — | 
                                                141,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                143,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current liabilities [abstract] | |||||||||||||||||||||
| Current provisions [abstract] | |||||||||||||||||||||
| Current provisions | — | — | — | — | — | — | 
                                                11,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                3. 1
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Trade and other current payables | — | — | — | — | — | — | 
                                                43,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                42,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities included in disposal groups classified as held for sale | — | — | — | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                4,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current liabilities | — | — | — | — | — | — | 
                                                118,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                65,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | — | — | — | — | — | — | 
                                                260,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                213,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — |