New figures have shown that 10.4 million vehicles running on Britain's roads would fail the MOT test.
According to the Vehicle and Operator Services Agency (VOSA), 40.1% of vehicles will not pass the annual test, compared with 33.5% in 2005.
The government body also found in its study that there are 800,000 "dangerous to drive" vehicles currently on the roads.
Bill Duffy, CEO of Halfords Autocentres, said: "This data demonstrates that car-owners are sacrificing regular servicing and maintenance to help balance stretched finances.
"Instead they are waiting for the MOT to find out what needs fixing, but by then many cars are unroadworthy."
Problems with vehicles could add to the financial worries of cash-strapped motorists who are already finding it difficult to save enough cash for their car insurance premium.
A study by industry experts has shown a 250% rise in the number of vehicles running on illegal tyres.
The findings, which took into account garage repair data, came ahead of a government decision on whether the MOT test should continue in its original form or become a biennial requirement.
© Press Association 2011