Will Orr, the managing director at WCRS, said: "We're focused on making our clients successful in the belief that our success will follow. We're more interested in being very good than being very big."
In contrast, JWT London and Publicis were the top ten agencies to suffer most, both losing more than a quarter of their billings. Account losses during 2006, including Reckitt Benckiser, hit JWT, while Publicis came perilously close to sliding outside of the top ten on the back of its MFI, Asda and Post Office losses.
McCann Erickson moved up into the second slot formerly occupied by JWT, while M&C Saatchi and Bartle Bogle Hegarty both increased their billings and rose by two places to consolidate their positions at three and four respectively.
However, both Leo Burnett and Ogilvy Group fell out of the top ten, despite a small billings increase at Burnett.
Elsewhere, Fallon London was the most spectacular performer, jumping seven places to 17th. Its 150 per cent growth in billings was as a result of account wins including Asda and Eurostar.
MediaCom, the number-one media agency, came close to becoming the first UK media agency to register £1 billion in billings. Unofficial updated figures show that it has already topped that mark.
Mediaedge:cia was the fastest-growing agency in the top ten with a 28 per cent billings growth, while Initiative lost a quarter of its billings and slid to eighth place following its General Motors loss, which included Vauxhall, in late 2006.
PHD switched places with Universal McCann as the Interpublic agency fell out of the top ten, and PHD re-entered on the back of a 3 per cent rise in billings.
Outside of the top ten, the Havas-owned Media Planning Group and Arena BLM both increased their billings by more than 20 per cent.
Click for the top 10 ad agencies
Click for the top 10 media agencies