Statement Of Cash Flows [Abstract]
| Concept | As at 2022-12-31 | 2022-01-01 to 2022-12-31 | As at 2021-12-31 | 2021-01-01 to 2021-12-31 | As at 2020-12-31 | 
|---|---|---|---|---|---|
| Statement of cash flows [abstract] | |||||
| Cash flows from (used in) operating activities [abstract] | |||||
| Cash flows from (used in) operations | — | 
                                                5,9 34
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                4,664,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Income taxes paid (refund), classified as operating activities | — | 
                                                7,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                311,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash flows from (used in) operating activities | — | 
                                                5,126,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                3,502,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash flows from (used in) investing activities [abstract] | |||||
| Cash flows from (used in) investing activities | — | 
                                                726,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                1,925,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash flows from (used in) financing activities [abstract] | |||||
| Proceeds from borrowings, classified as financing activities | — | 
                                                7 ,500
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Repayments of borrowings, classified as financing activities | — | 
                                                7 ,500
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Dividends paid, classified as financing activities | — | 
                                                2,909,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                3,007,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash flows from (used in) financing activities | — | 
                                                2,909,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                3,007,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Increase (decrease) in cash and cash equivalents after effect of exchange rate changes | — | 
                                                1,491,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                2,420,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash and cash equivalents | 
                                                7, 2 0 6
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                5,715,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                3, 295
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             |