Nearly half of drug drivers did not think their driving was impaired

But the report's authors fear the true figure could be nearer 11%, and say the stigma of drug driving means some people will not admit to it.

Transport Minister Tavish Scott said too many motorists were ignoring the dangers of taking drugs and driving.

Opposition parties said the study proved the executive's drugs policy was falling on deaf ears.

The survey was carried out by Mori Scotland, the centre for drugs misuse research at Glasgow University and Napier University's transport research institute.

Researchers questioned 1,031 drivers aged between 17 and 39 for the study, which looked at the extent of drug driving and the reasons behind it.

This report shows too many people think that taking drugs doesn't affect their driving Tavish Scott Transport Minister

The results showed a drop in reported levels of drug driving from five years ago.

In 2000 10% of people said they had driven after taking drugs, with 5% admitting to doing so in the previous 12 months.

The study said convenience was one of the main reasons for drug driving - with it being cited as an easier way for users to get more drugs.

The 2005 survey found that 47% of drug drivers did not think drugs had an impact on their driving, with 9% claiming it made their driving better.

Police warning

The study's authors called for anti-drug driving campaigns to be targeted at single men - the group most likely to drive while under the influence of illegal substances.

Mr Scott said driving under the influence of drugs was just as dangerous as drink-driving.

"This report shows too many people think that taking drugs doesn't affect their driving," he said.

"Yet the effects can last for hours or even days. Our message is simple - drugs can affect your driving. It isn't worth the risk."

The report's authors fear the figure of drug driving could be higher

Assistant Chief Constable Ian Learmonth, of the Association of Chief Police Officers in Scotland (Acpos), warned motorists not to drive while under the influence of drugs.

He said Scotland's eight police forces were using trained officers to target those who flout the law.

Scottish Tory leader Annabel Goldie said the report was "concrete proof" that ministers had lost control of drug abuse in Scotland.

'Grossly inadequate'

"The executive response to the number of people who think it is okay to take drugs and drive shows this," she said.

"Offering a platitude such as 'drugs can affect your driving - it isn't worth the risk' is grossly inadequate."

Scottish National Party justice spokesman Stewart Stevenson accused ministers of not having figures on convictions for drug-driving offences.