Police are planning a campaign against drivers under the influence of drugs amid concerns that illegal substances are rapidly catching up with alcohol as a major cause of road accidents.

Department for Transport figures reveal that almost 20 per cent of drivers involved in fatal accidents have traces of illegal substances in their system, while anecdotal evidence suggests that up to one in five youths has got behind the wheel under the influence of drugs.

Acknowledging the problem yesterday, police said that they would be heavily targeting drivers under the influence of either illegal or prescription drugs over the summer period.

However doubt has been cast on the effectiveness of the scheme, which involves asking suspicious individuals to stand on one leg, walk in a straight line and to place a finger accurately on their nose. As roadside testing kits are not yet available for traffic patrols, officers must resort to “commonsense tests” - also used on suspected drink-drivers - to determine whether a driver might be impaired by drugs.

The RAC Foundation said its research had found that a third of motorists who had taken drugs would still pass the tests, which assess mental and physical coordination, because the police were unable to spot any impairment. Sheila Rainger, RAC head of campaigns, called on the Government to fast-track roadside testing which instantly detects the presence of drugs with a swab, as drug-driving had become a serious issue. “We’re in the position with drug-driving now that we were in with drink-driving in the 1950s and 1960s,” she said.

“Because of all the publicity, young people now see drink-driving as wrong, but they don’t think there is a problem with drug-driving. It is a growing problem that the police need to challenge.”

The Home Office is in the process of approving a prototype for a roadside testing kit. A spokesman said that specifications were being developed and police could be using the device by the end of the year.

The authorities are becoming increasingly concerned about drug-driving, with research indicating a higher incidence of road accidents where drivers have tested positive for illegal substances. The Transport Research Authority found that the number of accidents involving illegal drugs had increased sixfold over a nine-year period ending in the late 1990s. More recently, a Department for Transport survey on fatal accidents found traces of drugs in 18 per cent of cases. The same survey, in 2000, found traces of alcohol in 32 per cent of cases.

Last year, a RAC survey of young motorists found that one in five took to the road after using drugs. It concluded that young people were twice as likely to be driven by someone high on drugs as someone who was over the drink-driving limit.

Chief Superintendent David Snelling, of the Metropolitan Police, said that drink and drugs not only impaired the ability of drivers to judge speed and distances but reduced concentration and slowed reactions.

Chief Constable Steve Green, of Nottinghamshire Police, said that his force was “not willing to tolerate this type of offending” and would “crack down heavily” during its summer campaign. He said that if a motorist was found guilty of drug-driving, the courts could hand down the same penalties as for drink-driving: “The chances of being involved in a collision are significantly increased [when influenced by drugs or alcohol] - which may result in serious injury or death.”

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