Disclosure Of First-Time Adoption [Text Block]
| Concept | As at 2024-12-28 | 2023-12-31 to 2024-12-28 | 2023-12-31 to 2024-12-28 | As at 2024-12-28 | 2023-12-31 to 2024-12-28 | As at 2024-12-28 | As at 2024-12-28 | 2023-12-31 to 2024-12-28 | As at 2024-12-28 | 2023-12-31 to 2024-12-28 | 2023-12-31 to 2024-12-28 | 2023-12-31 to 2024-12-28 | 2023-01-01 to 2023-12-30 | 2023-01-01 to 2023-12-30 | 2023-01-01 to 2023-12-30 | As at 2023-12-30 | As at 2023-12-30 | 2023-01-01 to 2023-12-30 | As at 2023-12-30 | 2023-01-01 to 2023-12-30 | 2023-01-01 to 2023-12-30 | As at 2023-12-30 | 2023-01-01 to 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 | As at 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Disclosure of first-time adoption [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of comparative information prepared under previous GAAP [text block] | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Disclosure of comparative information prepared under previous GAAP [abstract] | |||||||||||||||||||||||||||||
| Disclosure of comparative information prepared under previous GAAP [line items] | |||||||||||||||||||||||||||||
| Equity | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                543,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                570,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                2,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                25,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | 
                                                503,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                25,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                2 .0
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                530,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                446,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                23,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                420,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                2 .0
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Comprehensive income | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                142,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                142,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                142,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                142,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | 
| Profit (loss) | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                153,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                153,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                12,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                14 1.0
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                15,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                126,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                142,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                142,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — |