Cheap car insurance for young drivers is at risk for many motorists as new research shows millions driving on UK roads forget their MOT every year.
Vehicle insurance automatically becomes invalid when motorists drive without an MOT - and to carry on motoring without a test certificate is illegal.
Some 4.7 million drivers 'forget' their MOT renewal date, according to the research from comparison site uSwitch.
A research spokesman said, "Failure to remember your MOT renewal date is not only an offence but the potential safety and financial consequences are a hefty price to pay for an innocent lapse of memory."
Driving without an MOT when involved in a crash or any kind of collision or accident would mean a motor cover policy holder could not make a claim from his or her insurer.
In addition, convictions for failing to have an MOT or insurance would cause the cost of cheap car insurance for young drivers and teenagers, as well as older motorists who are convicted, to rise steeply.