Driving under the influence of cannabis, cocaine and Ecstasy is one step closer to being outlawed in Britain.

An expert panel will advise the Government about introducing a new offence of driving after taking an illegal drug.

It will consider whether it is scientifically possible to introduce maximum levels for different drugs, similar to drink-driving limits, or whether any amount of drug should constitute an offence, according to the Department of Transport.

The move comes after Prime Minister David Cameron admitted the Government had dragged its feet over driving when drugged, which contributes to hundreds of deaths and injuries every year. Many US states have zero-tolerance policies to all drugs, legal and illegal. Last year, Sir Peter North's landmark report recommended much tougher action on drug-driving.

As the law stands, driving while unfit through drugs is an offence, but it is notoriously difficult for the police to implement. Police officers must prove, beyond reasonable doubt, that the driver was impaired as a result of a drug.

But they cannot order a screening test, which requires a blood sample, until a doctor has assessed the driver. Getting a doctor to the police station quickly enough is often not possible.

New saliva-based drug testing kits are being considered by the Home Office to be used by police at the roadside like a breathalyser. The department has missed its own deadline to have such kits in police stations by the end of this year.

UK drug and alcohol experts will not consider an outright ban on driving while under the influence of medication such as sleeping tablets or painkillers. But they will examine whether the existing impairment law should be applied to certain prescribed or otherwise legally obtained drugs. The scientists will also consider the complex areas of drug and alcohol interactions.

The experts, who will start work in the spring, will consider whether it is possible to identify the average blood level for common illegal drugs that have an impairing effect.

Dr Barry Logan, executive director of the Centre for Forensic Science Research and Education in Pennsylvania, said: "Most toxicologists agree that you cannot reliably set an equivalent number for these drugs the way we have dealt with alcohol. Most [US] states have opted for a zero-tolerance policy, where the limits are set more by what a lab can detect than by how much is needed to impair someone.

"The philosophy is that if you shouldn't be taking it, you shouldn't be driving after taking it."

In many American states this includes driving under the influence of prescription tranquillisers and strong painkillers.

Jo Bullock from the Royal Society for the Prevention of Accidents said: "This is a step forward in the fight against drug-driving which, with new testing equipment, will help police ... convict those driving under the influence of drugs."

CAUGHT OUT
* 250 fatal accidents in Britain in 2008 where it was suspected that drugs played a role.

* 170 drug-drivers were prosecuted.

* 500 drug-driving tests were conducted at Christmas 2009.

* 223,000 alcohol tests were conducted at the same time.

- INDEPENDENT