Statement Of Changes In Equity [Abstract]
| Concept | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 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 2023-12-31 | 2023-01-01 to 2023-12-31 | As at 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 | As at 2022-12-31 | 2022-01-01 to 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | 2022-01-01 to 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 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Statement of changes in equity [abstract] | |||||||||||||||||||||||||
| Statement of changes in equity [line items] | |||||||||||||||||||||||||
| Equity | — | 
                                                53,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                34,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                13,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                5,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                38,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                4,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                29,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                4,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                17,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                26,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                4,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                4,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
| Changes in equity [abstract] | |||||||||||||||||||||||||
| Comprehensive income [abstract] | |||||||||||||||||||||||||
| Profit (loss) | 
                                                6,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                6,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                8,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                8,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | 
| Other comprehensive income | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                6,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                6,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | 
| Comprehensive income | 
                                                6,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                6,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                15,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                15,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | 
| Issue of equity | 
                                                10,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                9,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Dividends recognised as distributions to owners | 
                                                2,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                2,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                2,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                2,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | 
| Increase (decrease) through treasury share transactions, equity | 
                                                800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Increase (decrease) through share-based payment transactions, equity | 
                                                1,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                1,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | — | — | — |