Disclosure Of Fair Value Measurement [Text Block]
| Concept | 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 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Disclosure of fair value measurement [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of fair value measurement of assets [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of fair value measurement of assets [abstract] | |||||||||||||||
| Disclosure of fair value measurement of assets [line items] | |||||||||||||||
| Assets | — | — | — | 
                                                219,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                181,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Reconciliation of changes in fair value measurement, assets [abstract] | |||||||||||||||
| Disclosure of fair value measurement of liabilities [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of fair value measurement of liabilities [abstract] | |||||||||||||||
| Disclosure of fair value measurement of liabilities [line items] | |||||||||||||||
| Liabilities | — | — | — | 
                                                166,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                142,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | 
| Reconciliation of changes in fair value measurement, liabilities [abstract] | |||||||||||||||
| Disclosure of fair value measurement of equity [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of fair value measurement of equity [abstract] | |||||||||||||||
| Disclosure of fair value measurement of equity [line items] | |||||||||||||||
| Equity | 
                                                13,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                5,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                34,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                53,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                38,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                4,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                29,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                4,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                17,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                26,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                4,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                4,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Reconciliation of changes in fair value measurement, entity's own equity instruments [abstract] |