The figures, from Nielsen Media Research, show that the agency's billings plummeted by £58.1 million, from £399.27 million in 2001 to £341.17 million in 2002.
Campaign's report shows no change in the UK's top four agencies by billings.
McCann-Erickson remains the second-largest agency, billing £298.5 million, according to Nielsen figures.
Lowe remains in third place with £274.89 million, although its billings would not have included the devastating loss of Orange. Meanwhile, Ogilvy & Mather is in fourth place with £273.36 million. Again, these figures would not have taken into account the departure of the Argos and KFC business.
M&C Saatchi has leapt up from eight to fifth place.
On the media side, the new order shows MediaCom has overtaken Zenith Media to become the UK's second-largest media agency, with billings of £550.06 million. This follows two years of impressive new-business success for MediaCom, although the recent merger of Zenith and Optimedia means it is unlikely to enjoy its newfound position for much longer.
Because of its merger in 2001, Cheetham Bell JWT has grown sufficiently to become the UK's largest regional shop, with billings of £39.16 million.
The agency is now slightly bigger than Leith, which has billings of £38.52 million.
McCann-Erickson Business still claims to be the UK's largest business-to-business agency, with a declared income of £6.9 million. However, its position at the top of the rankings is hotly contested by The Banner Corporation, which claims an income of £6 million.