Disclosure Of Fair Value Measurement [Text Block]
| Concept | As at 2024-12-28 | As at 2024-12-28 | As at 2024-12-28 | As at 2024-12-28 | As at 2023-12-30 | As at 2023-12-30 | As at 2023-12-30 | As at 2023-12-30 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 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 | — | 
                                                60,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | 
                                                57,400,000
                                                
                                                    
                                                        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 | — | 
                                                22,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | 
                                                21,900,000
                                                
                                                    
                                                        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 | 
                                                9,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                37,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                27,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                7,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                27,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                35,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                34,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                24,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                9,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Reconciliation of changes in fair value measurement, entity's own equity instruments [abstract] |