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Related party transactions - Additional information (Detail) - Associates - GBP (£)
£ in Millions
6 Months Ended
Jun. 30, 2023
Jun. 30, 2022
Kantar    
Disclosure of transactions between related parties [line items]    
Revenue from sale of goods, related party transactions £ 6.6 £ 7.4
USA | Compas    
Disclosure of transactions between related parties [line items]    
Revenue from sale of goods, related party transactions £ 111.8 £ 82.7