Statement Of Comprehensive Income [Abstract]
| Concept | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2024-01-01 to 2024-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of comprehensive income [abstract] | ||||||||||||||
| Profit (loss) | 
                                                147 .0
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                147 .0
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                78. 1
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                78. 1
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Other comprehensive income [abstract] | ||||||||||||||
| Components of other comprehensive income that will not be reclassified to profit or loss, net of tax [abstract] | ||||||||||||||
| Other comprehensive income, net of tax, gains (losses) on remeasurements of defined benefit plans | 
                                                0 .3
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                0 .1
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | 
| Components of other comprehensive income that will be reclassified to profit or loss, net of tax [abstract] | ||||||||||||||
| Exchange differences on translation [abstract] | ||||||||||||||
| Gains (losses) on exchange differences on translation of foreign operations, net of tax | 
                                                1,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                12,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | 
| Hedges of net investment in foreign operations [abstract] | ||||||||||||||
| Gains (losses) on hedges of net investments in foreign operations, net of tax | 
                                                2,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | 
| Other comprehensive income | 
                                                6,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                2 .5
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                3,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                13. 1
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                1,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                0 .1
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                12,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Comprehensive income | 
                                                153,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                2 .5
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                3,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                147 .3
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                91,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                1,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                78,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                12 .2
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Comprehensive income attributable to [abstract] | ||||||||||||||
| Comprehensive income, attributable to owners of parent | 
                                                153,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
                                                91,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — |