NEW regulations to crack down on motorists driving under the influence of drugs take effect from today.

Drivers will be prosecuted if they are caught exceeding new legal limits which have, for the first time, been laid down for eight illegal drugs and eight prescription drugs.

The levels for the illegal drugs, which include heroin, cocaine and cannabis, virtually mean there will be zero tolerance for drivers apprehended with these substances in their system.

Police will be able to use "drugalysers" to screen for cannabis and cocaine at the roadside.

Officers will also be able to test for these and other drugs including ecstasy, LSD, ketamine and heroin at a police station, even if a driver passes the roadside check.

New devices that can test for a greater number of drugs at the roadside will be developed in the future.

The prescription drugs for which legal levels have been set include morphine and methadone. People using these drugs within recommended amounts will not be penalised.

The specified drug-drive rules will run alongside the existing legislation which makes it an offence to drive when impaired by any drug.

Road Safety Minister Robert Goodwill said: "This new law will save lives. We know driving under the influence of drugs is extremely dangerous; it devastates families and ruins lives.

"The Government's message is clear - if you take drugs and drive, you are endangering yourself and others and you risk losing your licence and a conviction."

To co-incide with the new legislation a new Government road safety THINK! campaign is being launched on radio, online and in pub and club washrooms.

A THINK! survey shows that 49% of those polled said that they would not feel comfortable, as a passenger, asking drivers if they were under the influence of illegal drugs.

Of those who admitted to driving under the influence of illegal drugs, 55% said they did so because they felt safe to drive and 60% revealed they had previously driven a car when they were unsure if they were still under the influence of illegal drugs.

Dr Kim Wolf, Reader in Addiction Science at King's College London and an advisor for the Government drug-drive policy, said the survey results were worrying.

Tim Williamson, of the law firm Blake Morgan, said it would be advisable for motorists on medication to keep their prescription with them in the car.

Institute of Advanced Motorists chief executive Sarah Sillars said: "The new law is a real step in the right direction for the eradication of driving under the influence of drugs.

"We have always stated there should be no doubt to drivers and riders as to what the correct course of action should be; no one should be driving while under the influence of alcohol or any illegal drugs in their system."