Car sales have fallen to their lowest level since 1966, the SMMT has reported, as Britain's consumers shy away from making big purchases in the face of recession.
Just 63,225 new cars were sold in Britain during August, the worst sales figures reported in more than 40 years.
Although August is traditionally a quiet month for motor traders, with customers waiting for the September plate change, the economic downturn has left showrooms deserted.
One London-based dealer for a major premium marque told Autocar it had been the quietest month he could remember in more than 20 years selling new cars.
As a whole, the UK's new car market was 18.6 per cent down year on year - but Britain's own brands were hardest hit.
Aston Martin sold just 19 cars last month, compared with 58 cars in August 2007.
Jaguar, which has been resurgent since Tata bought the company, sold only 273 cars, a 40 per cent drop year-on-year. And Land Rover posted just 422 sales, a massive 58 per cent fall compared with last year.
Other luxury car firms like Porsche and Lexus have also seen year-on-year sales in this country fall by more than 50 per cent.
It was makers of more affordable, economical cars that posted less dramatic downturns. Ford's August figures fell by just five per cent. The Focus is still the UK's biggest selling model this year.
Roeland de Waard, chairman of Ford Britain, said "Ford is meeting the imperatives of family motoring - lower fuel costs and CO2 emissions from stylish affordable vehicles."
But today it was revealed that Bentley's Crewe factory has cut back to a three-day week, and JLR's Solihull plant has called Friday a "non-production day" to avoid stockpiling new cars.
"We're concerned by the reluctance of consumers to commit to major purchases," said SMMT chief executive Paul Everitt. "There is a clear need for sustained action by government to boost the economy and restore confidence."
Government officials are keen to stress that the motor industry's downturn has been felt worldwide and not just in the UK.
But contrary to that, BMW reports that its August global figures rose by two per cent year-on-year.
In spite of the plunging UK figures in the automotive and other industries, Prime Minister Gordon Brown reiterated that he was "cautiously optimistic" about the state of Britain's economy.