Disclosure Of Non-Current Assets Held For Sale And Discontinued Operations [Text Block]
| Concept | 
                                    
                                        2024-04-01 to 2025-03-31  | 
                            
                                
                                    
                                        2024-04-01 to 2025-03-31  | 
                            
                                
                                    
                                        2024-04-01 to 2025-03-31  | 
                            
                                
                                    
                                        2023-04-01 to 2024-03-31  | 
                            
                                
                                    
                                        2023-04-01 to 2024-03-31  | 
                            
                                
                                    
                                        2023-04-01 to 2024-03-31  | 
                            
                        
|---|---|---|---|---|---|---|
| Disclosure of non-current assets held for sale and discontinued operations [text block] | — | — | — | — | — | — | 
| Disclosure of analysis of single amount of discontinued operations [text block] | — | — | — | — | — | — | 
| Disclosure of analysis of single amount of discontinued operations [abstract] | ||||||
| Disclosure of analysis of single amount of discontinued operations [line items] | ||||||
| Profit (loss) before tax | 
                                        
                                             
                                                384,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                459,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                75,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                340,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                396,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                56,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Revenue | 
                                        
                                             
                                                2,248,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                2,248,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                2,034,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                2,034,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    
                                        
                                             
                                                –
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                            
| Cash flows from continuing and discontinued operations [abstract] | ||||||
| Cash flows from (used in) operating activities [abstract] | ||||||
| Cash flows from (used in) operating activities | 
                                        
                                             
                                                492,400,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                385,000,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
| Cash flows from (used in) investing activities [abstract] | ||||||
| Cash flows from (used in) investing activities | 
                                        
                                             
                                                163,900,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                286,300,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
| Cash flows from (used in) financing activities [abstract] | ||||||
| Cash flows from (used in) financing activities | 
                                        
                                             
                                                155,100,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — | 
                                        
                                             
                                                119,700,000
                                                
                                                    
                                                        GBP
                                                    
                                                
                                             
                                        
                                     | 
                                
                                    — | — |