The results have been revealed on the day that Cleveland, Durham and Northumbria Police launch their summer drink-drive campaign.

Latest figures show that of almost 7,000 people tested for alcohol last year in the region, nearly 500 results were positive.

But it is the increased use of illegal and legal drugs that is now causing concern to officers in the North East.

People taking medication for hay-fever or a migraine do not heed the warnings about drowsiness or the dangers of mixing it with drink

Superintendent Barry Peart, Northumbria Police

Extensive laboratory tests, which became compulsory in County Durham in January, show cocaine, ecstasy, cannabis or prescription drugs were found in more than half of the 23 drivers who died in an accident.

The force says the findings are worse than they first thought, but any impact the drugs had on an accident could only be determined in court.

Durham police head of traffic, Superintendent Barry Peart, said: "We asked the laboratories to routinely start screening for drugs because we suspected drugs were becoming one of the common denominators in incidents.

"The findings are quite alarming, far worse than we thought."

He said smoking a cannabis joint and getting behind the wheel of a car had the same effect as drinking four pints of beer.

Doctors' plea

Mr Peart continued: "Prescription drugs are an additional hazard. People taking medication for hayfever or a migraine do not heed the warnings about drowsiness or the dangers of mixing it with drink.

"Traces of other drugs, such as temazepam or diazepam, taken for sleeping problems or depression, are also turning up in laboratory tests."

Doctors' leaders say motorists should be tested for drug use in the same way that they are currently tested for alcohol.

The British Medical Association says drugs - both illegal and legal - can affect the ability to drive safely.