Early indications are that a busy final week in September drove car registrations from a 2% dip at week three to a 14% increase on September 2008's total sales.
Strong manufacturer incentives and scrappage discounts, plus publicity surrounding scrappage's extension, are understood to have boosted demand.
The rise is expected to be confirmed officially by the SMMT tomorrow.
One brand which enjoyed a strong performance was Mazda. Its 11,372 registrations were the highest monthly total ever achieved by Mazda UK, and gave it a 3% share of the month's total market.