The United Kingdom's two-year boom in new car sales could be coming to a close with car buying activity from the private sector currently down 19% in September according to latest figures from independent monitor, CarPriceCheck.com.

Compared to last year's record of 443,265 new car sales for September, activity levels suggest that this month's sales could be closer to 385,000.

Last year many dealers reported record order books before the start of September and were still supplying those back orders as October approached.

However, this year, anecdotal evidence from dealers, importers and internet retailers is supported by CarPriceCheck data which shows a 16.8% fall in the number of active consumers committed to buy during the first two weeks of the month.

Of more concern, figures from the past seven days indicate the slump could be as high as 21.2% which will impact on sales and registrations for the final quarter of the year.

"This is not a sudden turnaround in fortunes; it has been on the radar for several months now," a CarPriceCheck spokesman said. "September was never going to match the runaway success of last year, but the consumer has been slowly changing focus. Sales suffer a seasonal slow-down during October and early November, but it looks like this has happened earlier this year."

Although the fall correlates with the 4.3% downturn in sales across Europe since the start of the year, it is more likely a conspicuous indicator of a shift in UK buying patterns especially given the double-digit increase in sales for July (up 13.1%) and August (up 12.8%).

"The September slide fits with our forecast that monthly sales are levelling out with March set to become the major peak in the calendar compared to the traditional summer switch previously associated with the August once-yearly plate change.  People are no longer holding off in July and August for the new plate," the spokesman added.

"The economic burden of buying a car suits the start of the year in the same way that house sales pick up around spring. March is the new August, and the September slump could be nothing more than a readjustment."

In anticipation of the expected slowdown, the big three volume manufacturers - Ford, Vauxhall and Peugeot - had slashed transaction prices by an average of 1.6% against a market wide price fall of 0.7% during August.

But the spokesman added: "It's the ideal time for consumers to negotiate the deal of the year but low interest rates, manufacturer backed 0% finance options, free insurance, cash-back schemes and transparent price competition has done little to stop the consumer putting the brakes on this time."