Disclosure Of Cash Flow Statement [Text Block]
| Concept | 
                                    
                                        As at 2022-12-31  | 
                            
                                
                                    
                                        As at 2021-12-31  | 
                            
                                
                                    
                                        As at 2020-12-31  | 
                            
                        
|---|---|---|---|
| Disclosure of cash flow statement [text block] | — | — | — | 
| Cash and cash equivalents if different from statement of financial position [abstract] | |||
| Cash and cash equivalents | 
                                        
                                             
                                                32,783,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                114,577,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                77,956,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     |