The new 62 number plate cars sold unexpectedly well last month, according to the Society of Motor Manufacturers and Traders (SMMT).
There were 359,612 cars registered in September, which was the first month of the new plate.
That was 8.2% up on the same month last year and 26,000 more cars than the SMMT had been expecting.
September is the second busiest month for car sales, coming behind March, when 372,835 cars were sold.
The Ford Fiesta remained the bestselling car, with 18,651 registered in the month and 88,747 in the first nine months of the year.
"The important September plate change market outperformed expectations," said Paul Everitt, SMMT chief executive.
"Although the economic outlook remains challenging, we are starting to see a tentative return of consumer confidence as motorists explore new products and the latest fuel-efficient technologies."
So far in 2012, 1,620,609 new cars have been registered, which is 4.3% up on the first nine months of 2011. The SMMT is predicting 1.97 million cars will be registered in the whole year.
The market is still well below its pre-recession levels. In 2007, 1.94 million cars were registered in the first nine months of the year.
"The strength of private car sales in September may be a sign that consumers are becoming a bit more prepared - and able - to spend as they are helped by rising employment and a halving in consumer price inflation from the September 2011 peak level of 5.2%," said Howard Archer, chief UK economist at IHS Global Insight.
"It is also evident that private new car sales have been supported by attractive offers and motorists' desire to buy more fuel efficient cars at a time of very high petrol prices."