Statement Of Cash Flows [Abstract]
| Concept | 2024-01-01 to 2024-12-31 | 2023-01-01 to 2023-12-31 | 
|---|---|---|
| Statement of cash flows [abstract] | ||
| Cash flows from (used in) operating activities [abstract] | ||
| Cash flows from (used in) operations before changes in working capital | 
                                                7 .7
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                20,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Adjustments for decrease (increase) in trade and other receivables | 
                                                8,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                16,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Adjustments for increase (decrease) in trade and other payables | 
                                                1,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                20,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Adjustments for amortisation expense | 
                                                11,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                14,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Adjustments for depreciation expense | 
                                                13,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                14,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Adjustments for gains (losses) on change in fair value of derivatives | 
                                                0 .1
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Adjustments for gain (loss) on disposals, property, plant and equipment | 
                                                300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Cash flows from (used in) financing activities [abstract] | ||
| Proceeds from sale or issue of treasury shares | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                1,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             |