The data, the first to be issued since the latest vehicle registrations in March, shows the marque has suffered an 18.69% drop in its market share, leaving it with 6.04% of the UK market. Peugeot has sold 42,399 cars this year, compared with 52,145 at the same point in 2004.
The news comes in the wake of the demise of MG Rover, which confirmed last Friday that it was going into administration.
Peugeot Citroen's owner, PSA, is now pinning hopes of propping up sales on a successful launch for its 107 model, intended to fill a gap in the flourishing small car market.
The Peugeot 107, which is the next evolution of the successful 106 series, will be launched in June backed by a high-profile campaign.
Peugeot UK said the drop in sales was due to consumers waiting for the launch of the 107 and 1007 models and that it was not overly concerned.
Last month the UK car market suffered its first fall in sales for six years, with nearly all the major marques losing ground. In the first quarter of 2005, sales showed a year-on-year drop of 7.2%.
Other brands to feel the pinch this year include Ford, which registered almost 9000 fewer units, and Mercedes-Benz, which has registered 5000 fewer.