However, motor analysts said the underlying increase was more like 5 per cent, because August this year included one less selling day than last year.
This would be in line with manufacturers' forecasts, which indicated sales could rise from 469,000 to 490,000. Some experts were predicting that sales would break through the 500,000 barrier for the first time since 1989.
Some manufacturers suggested the picture was more buoyant than the initial statistics suggested, with certain makes experiencing particularly strong growth. The managing director of Skoda UK, Dermot Kelly, said Skoda sales had risen by 20 per cent in the first 10 days of August.
He said: "The market is very volatile and it is harder to predict this year, partly because there have been some processing problems with day to day figures and possibly because data returns have been upset by the postal strike."
Skoda, which is part of the Volkswagen group, has had a sales boost from a revised model range, but Mr Kelly said sales of Volkswagens, Audis and Seats were also much improved. "If things continue like this for the rest of the month Volkswagen as a whole could break its record for August sales."
Other makes thought to be increasing sales sharply are Fiat, which has been helped by new models, and BMW.
Dealers also pointed to improving consumer confidence boosting demand. At Liverpool's biggest Ford dealership, J Blake Group, sales are up 7 per cent so far this August, with little sign of things slackening off.
Mark Haymer, its sales director, said customers were choosing bigger cars than last year, and showing less interest in more economical diesel models.
"We've actually run out stock of popular lines such as Escort special editions, whereas last year we were selling more small cars like Fiestas," he said. "We've also seen lots of interest in sportier versions. People seem to be saying 'We've been careful, now let's have a bit of fun.'"
The final total depends crucially on whether the biggest manufacturers offer extra incentives to dealers and customers to inflate demand in the last few days of the month.
One source suggested several of the biggest manufacturers, including Ford, were preparing to boost their figures by selling large numbers of cars to dealers, a tactic known in the trade as "pre-registering".
The move can transform August sales in the last day of the month. A Ford spokesman refused to be drawn last night: "We don't comment on the figures and we don't speculate about the state of the market," he said.Reuse content