One in five people have driven a vehicle shortly after having taken drugs, a survey from motor insurer More Than has suggested.
Drug driving is prevalent, the survey suggests
Four out of ten who admit to drug drivers think their driving is not affected by drugs.
Responding to the survey, a drug expert branded the UK as one of the worst places for drug driving in Europe.
More Than, which called for roadside drug tests, surveyed 1,072 people, 69% of whom were in the 25-35 age bracket.
"Many people just don't realise the effects that illegal drugs have on their ability to drive," said Dr Rob Tunbridge, an independent drug impairment expert and government adviser.
"This may be part of the reason why young people in particular continue to drive while impaired by drugs," he added.
The Home Office is developing a roadside drug screening device to help police identify drug drivers.
Roadside drug screening devices are already in use in several countries including Sweden, Switzerland, Belgium, Finland, Australia and Germany.
More Than called for the early introduction of roadside testing to the UK.
"We believe that roadside screening should be a practical reality within the next two years and urge the government to introduce the test without delay," said Mike Holliday-Williams, head of insurance at More Than.