When there is a legislative opportunity to do so we will make compulsory driving-impairment tests

David Jamieson Junior transport minister

Junior transport minister David Jamieson told BBC Radio Five Live that as soon as legislative time allows, driving impairment tests will be made compulsory.

An investigation for the Five Live Report programme found that a driver who smoked cannabis could not walk in a straight line and went on to fail three basic tests on reaction time and co-ordination.

The findings follow proposals to re-classify cannabis from a class 'B' to a class 'C' drug and a �1.5m government campaign aimed at preventing young people from taking ecstasy and cocaine on New Year's Eve.

An estimated one in five drivers killed on the roads has traces of drugs in their bodies.

RAC figures suggest that 7% of the UK population have been in a car with a driver who is under the influence of drugs.

Cannabis stays in the bloodstream for up to a month after consumption

Mr Jamieson says that driving-impairment tests should be made compulsory when a motorist is stopped under suspicion of driving while under the influence of alcohol or drugs.

An experiment carried out by Datron, a company which specialise in testing driver proficiency under different circumstances, showed how one driver who had smoked cannabis knocked over three out of six cones in a slalom test.

Her braking distance increased by 40 feet, with a half a second delay to her reaction time.

In the impairment tests, the driver could not walk in a straight line, and could not accurately count to 30. She could not stand on one leg, or touch her nose.

User count

Under current rules, a police officer cannot insist on an impairment test if a driver has passed a breath test.

But Mr Jamieson said: "What we have to do is to establish the number of people taking drugs and how impaired they are.

"When there is a legislative opportunity to do so we will make compulsory driving-impairment tests.

"Those would give the police force the ability to perform those tests and then mount a prosecution on the basis of that, if they found a person impaired.

"Five Live Report - The Drug Drivers" can be heard at 1200GMT on 30 December.