Motorists who have had a drink, but are still well below the limit are being warned that they are two-and-a-half times more likely to have a crash.

The Royal Society for the Prevention of Accidents said it was now time to step up the campaign against drink driving to stop any more deaths.

The warning comes ahead of the 40th anniversary of breathalyser testing tomorrow.

Thousands of deaths and serious injuries have been avoided in Britain since October 9, 1967, when the current drink-drive limit of 80mg of alcohol per 100ml of blood became a legal requirement and roadside testing was introduced.

At the time, it was said that drinking before driving led to about 13,000 fatal and serious casualties each year.

By 1987, the figure for people killed or seriously injured in accidents involving illegal alcohol levels had dropped to 6,800 and by last year it had fallen to 2,500.

Despite this success, there is still a need for a cut in the drink-drive limit, says RoSPA, because the consistent fall in drink-drive fatalities ceased at the end of the 1990s.

Last year, of the 3,172 people killed on Britain's roads, 540 died in accidents involving illegal alcohol levels. In 1999, the figure was 460.

"The RoSPA had been calling for drink-drive legislation during the 1960s because of growing evidence that alcohol played a part in many road accidents. At the time, more than 7,000 people were dying on Britain's roads annually and it was hoped the new law would save hundreds of lives each year,” said Kevin Clinton, RoSPA head of road safety.

"Acording to one report from the time, it was hoped the drink-drive hazard would be effectively nullified. Sadly, this hasn't happened, and the menace of alcohol is still causing misery."

Now the RoSPA is calling for the drink-drive limit to be reduced to 50mg of alcohol per 100ml of blood - a move which it says would save around 65 lives and 230 serious injuries on Britain's roads each year.

Between 50mg and 80mg, motorists are two to two-and-a-half times more likely to be involved in a crash and, if they are involved in a collision, it is six times more likely to be fatal than if they had no alcohol in their system.

The RoSPA believes that lowering the legal limit would pave the way for a new education campaign to raise awareness of the seriousness of drink driving.

The society will be participating in a government consultation on drink-drive laws later this year.