Of the UK's £8.7 billion adspend, £1.1 billion is accounted for by WPP subsidiaries.
WPP's power is bound to draw comparisons with Tesco, whose stores get £1 of every £8 spent in UK shops.
The figures from Nielsen Media Research show how WPP in particular and the big four holding companies in general now control a massive slice of total billings.
WPP's share accounts for 12.7 per cent of total billings. Its biggest rivals, Omnicom, Publicis Groupe and Interpublic, control just over 27 per cent between them.
Last week, WPP announced a 15 per cent leap in 2004 profits to £546 million and a 5 per cent increase in billings to £19.6 billion.