Disclosure Of Interests In Other Entities [Text Block]
| Concept | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | 2023-01-01 to 2023-12-31 | As at 2022-12-31 | 2022-01-01 to 2022-12-31 | 2022-01-01 to 2022-12-31 | 2022-01-01 to 2022-12-31 | 2022-01-01 to 2022-12-31 | 2022-01-01 to 2022-12-31 | As at 2021-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Disclosure of interests in other entities [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of interests in subsidiaries [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of subsidiaries [text block] | — | 
                                                (ii) Transactions with subsidiary companies
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of subsidiaries [abstract] | |||||||||||||
| Disclosure of subsidiaries [line items] | |||||||||||||
| Current assets | — | — | 
                                                167,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                132,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | 
| Non-current assets | — | — | 
                                                52,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                48,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | 
| Current liabilities | — | — | 
                                                145,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                121,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | 
| Non-current liabilities | — | — | 
                                                20,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                21,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | 
| Revenue | — | 
                                                491,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                426,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
| Profit (loss) | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                6,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                6,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                8,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                8,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Comprehensive income | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                6,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                6,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                15,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                15,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Disclosure of interests in associates [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of associates [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of associates [abstract] | |||||||||||||
| Disclosure of associates [line items] | |||||||||||||
| Other comprehensive income | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                6,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                6,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Disclosure of interests in joint arrangements [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of joint ventures [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of joint ventures [abstract] | |||||||||||||
| Disclosure of joint ventures [line items] | |||||||||||||
| Cash and cash equivalents | — | — | 
                                                29,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                22,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | 
                                                20,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Tax expense (income) | — | 
                                                1,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | 
                                                1,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — |