Motorists in Bucks could find police asking them to take part in a new roadside test designed to determine whether they have been using drugs, as new legislation came into effect this week.

On Monday a new road traffic offence was introducted- that of driving, attempting to drive or being in charge of a motor vehicle with the concentration of a specifiedcontrolled drug being above a specified limit.

Roads Policing Unit officers will be trained to use a piece of equipment brand new to the Force - the DrugWipe 3S - to help enforce the new law.

The new kit allows officers to take a specimen of saliva at the roadside or police station, and perform a preliminary test to detect a number of illegal drugs in the system. Drivers have been warned that even prescription drugs, sucha as temazepam or morphine, could show up in the test and those using such medication should check with their pharmacist or GP if they need more advice.

This law will make it an offence to be over the limit for each specified drug while driving, as it is with drink-driving. It will operate alongside the existing crime of 'driving while unfit through drink or drugs', rather than replacing it.

Sergeant Chris Appleby, who leads on road safety issues for Thames Valley Police, said: "It is illegal to drive if you are unfit to drive by legal or illegal drugs. If the police stop you and think you’re on drugs they can do a Field Impairment Test. This is a series of tests that assesses a driver’s ability to drive safely.

"If they think you’re unfit to drive because of taking drugs, you’ll be arrested and will have a blood test at a police station. If the test shows that you’ve taken drugs you could be charged with an offence.

"You don’t have to be on illegal drugs to be unfit to drive - many prescription or over-the-counter medicines may also impair your ability to drive safely. If you’re taking medicines, talk to your doctor, pharmacist or healthcare professional before driving and read any instruction leaflets contained with medicines."

"This new law does not replace the offence of 'Driving whilst Unfit through drink or drugs', contrary to Section 4 of the Road Traffic Act, but compliments it and gives assistance in bringing to justice those who decide to use drugs and drive on our roads.

Drugs covered by the new legislation include cannabis, cocaine, ecstasy and ketamine. The limits for illegal drugs will be close to zero and other drugs will subject to a risk-based limit.

Sgt Appleby added: "All those suspected of driving while unfit, or over the prescribed drug limit, will still need to have a blood sample taken for analysis to confirm the drug being present.

"Taking drugs can seriously impair driving skills. Driving while under the influence of drugs is extremely dangerous and can affect driving in numerous ways.

"Drug-drivers can suffer from slower reaction times, erratic and aggressive behaviour, an inability to concentrate properly, nausea, hallucinations, panic attacks, paranoia, tremors, dizziness and fatigue. In such a condition, it is a bad idea to be behind the wheel of a car, for the driver and their passengers."

This new law aims to make it more difficult for those who decide to drive while unfit or over a specified drug limitto avoid detection and prosecution.

A drug-drive conviction will have a serious effect on a driver’s life, with penalties including a criminal record, a minimum 12-month driving ban and a fine of up to £5,000.