If you combine alcohol, which can make you sleepy, with fatigue then that can be a lethal cocktail

Roger Vincent, Rospa

When drivers had been drinking the researchers found that fatigue was the only significant other factor in the crash.

They also found a strong correlation between the time of day and the cause of the crash - with many more alcohol-related crashes happening at night.

The scientists from the sleep clinic at Centre Hospitalier Universitaire, Bordeaux, said the data had been quite hard to compile because when alcohol was a factor in a crash police were unlikely to look at fatigue or any other causes.

Plan journeys

But they stressed that both alcohol and fatigue played a significant part in a number of crashes.

"We found that fatigue, especially when combined with alcohol, presents a particularly high risk of road crashes resulting in death or serious injury.

"This has been largely unrecognised in France and elsewhere."

Roger Vincent, of the Royal Society for the Prevention of Accidents (Rospa), said the research comes as a timely reminder for drivers planning a long drive for the Easter break.

He said drivers planning to make long journeys should ensure they get enough breaks and never drink and drive.

"If you combine alcohol, which can make you sleepy, with fatigue then that can be a lethal cocktail," he said.

"That is one of the reasons we urge people not to drink and drive at all.

"With the Easter holidays coming up this is a timely reminder to people not to drink and drive and not to get too tired."