Statement Of Cash Flows [Abstract]
| Concept | 2023-01-01 to 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | 2022-01-01 to 2022-12-31 | As at 2021-12-31 | 
|---|---|---|---|---|---|
| Statement of cash flows [abstract] | |||||
| Cash flows from (used in) operating activities [abstract] | |||||
| Cash flows from (used in) operating activities | 
                                                8,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                10,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash flows from (used in) investing activities [abstract] | |||||
| Proceeds from sales of property, plant and equipment, classified as investing activities | 
                                                700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Purchase of property, plant and equipment, classified as investing activities | 
                                                500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                1,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash flows from (used in) investing activities | 
                                                200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                1,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash flows from (used in) financing activities [abstract] | |||||
| Proceeds from issuing shares | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Repayments of borrowings, classified as financing activities | 
                                                5,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Payments of lease liabilities, classified as financing activities | 
                                                2,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                2,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Dividends paid, classified as financing activities | 
                                                2,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                2,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Interest paid, classified as financing activities | 
                                                1,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash flows from (used in) financing activities | 
                                                2,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                6,600,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Increase (decrease) in cash and cash equivalents after effect of exchange rate changes | 
                                                6,800,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | — | 
                                                2,200,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
| Cash and cash equivalents | — | 
                                                29,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | 
                                                22,500,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             | — | 
                                                20,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             |