Garages are failing to spot basic faults on vehicles during MOTs, according to a report published today.
In an undercover investigation by the consumer magazine Which?, just eight out of 36 tests were carried out correctly.
Among the others, mechanics missed simple faults such as a passenger door that would not open from the inside, a broken latch on a rear seat and a cut and frayed seat belt.
The results have prompted the magazine to call on the Vehicle and Operator Services Agency (Vosa), which administers the MOT, to tackle the problem urgently.
Which? took six second-hand cars between three and 10 years old and introduced a variety of faults, which ought to cause the car to fail the MOT. Each car was sent to six different garages, meaning 36 garages were visited in total.
Eight outlets issued the cars with an MOT certificate. This was considerably worse than when the same exercise was conducted in 1997 when just two of the 36 incorrectly passed vehicles as safe.
The remaining 20 failed the vehicles, but either missed one of the other serious faults or failed the car on a point not covered by the MOT.
Which? said cost could be one reason why garages are conducting tests that could allow a "potential death trap" on to the road.
"MOTs aren't very lucrative, so it's not very surprising to see junior mechanics rushing through them while more experienced staff are busy charging £60 to £70 an hour for more complex jobs," said the report.
Vosa, which replaced the Vehicle Inspectorate, is planning to introduce a new computer system designed to improve the testing procedure and spot garages which pass or fail excessive numbers of cars.
However, it told Which? that the Road Traffic Act prevented its researchers from driving faulty cars and therefore carrying out the kind of tests conducted by the magazine.
Helen Parker, editor of Which?, said: "The results of our investigation couldn't be more clear cut - cars which should obviously have failed the MOT are getting through. Vosa needs to tackle the problem urgently. It must find a way to conduct more convincing research and stop incompetent mechanics from vetting the nation's cars."
The AA Motoring Trust said today: "This is a useful exercise which proves that there can be huge discrepancies when it comes to passing or failing MOT tests. The new computerised system, which is due to be tested sometime this year, should go some way to reducing the problem, because it will be able to identify test centres with particularly high pass or fail rates, and come down hard on those which are not up to the job.
"This research doesn't tell us which faults were missed, but we would be very concerned if major safety problems - like bald tyres or faulty brakes - were being overlooked. The trust's advice for drivers whose cars need an MOT test is to go to places where they have always had good service, or to somewhere that's been recommended to them."
