Sales of new cars rose 11.4% in September compared with the same month last year, according to the Society of Motor Manufacturers and Traders (SMMT).
The new "59" registration plates were available from 1 September and 367,929 of them were sold in the month. The SMMT said that conditions remained "challenging" but the market was being supported by the scrappage scheme.
Last week, the government announced it was extending the trade-in scheme from £300m to £400m. "The extension of the scheme will help to sustain demand through the latter part of this year and into 2010," said Paul Everitt, chief executive of the SMMT.