Half of people are unable to tell when they are too drunk to legally drive, according to research from the University of Cambridge.

Drink driving is a criminal offence, with people found guilty of driving while above the legal limit subject to up to six months imprisonment, an unlimited fine and a driving ban of at least a year.

People who are drunk and kill another person while driving can face up to 14 years in prison.

However, in 2019, about 230 people in Britain were killed in accidents with at least one driver who was over the drink-drive limit.

One issue, according to the new research, is that people may be unable to accurately gauge how drunk they actually are.

A two-day experiment involving 90 students was carried out in Germany to determine if they recognised when to stop drinking before driving.

Switching between drinks

Participants were split into two groups, and given beer and wine until they reached a maximum breath alcohol concentration of 0.11 per cent.

The drink-driving limit in Germany is 0.05 per cent, which is 0.03 per cent lower than in England and Wales.

Participants were told they would be switched from beer to wine or vice versa once they had reached 0.05 per cent, but not that it was the legal driving limit.

Breathalysers were used to keep track of how much the students drank throughout the exercise. With each measure, they were asked to guess the concentration of alcohol in their breath and come forward once they thought they had reached the driving limit.

More than a third of students, 39 per cent, had exceeded the drink-driving limit by the time they stepped forward. On the second day, this proportion increased to more than half (53 per cent).

In addition, the more alcohol students consumed the worse they became at guessing their level of intoxication.

‘Serious consequences’

Dr Kai Hensel, from the University of Cambridge, who led the study, said: “This could have serious consequences in England and Wales, where the legal driving limit is higher [than in Germany], as it suggests that a significant number of people might misjudge how drunk they are and consider themselves fit to drive when in fact they have a potentially dangerously high level of alcohol in their blood.”

He added: “Drinking and driving is a major risk factor for road traffic accidents. Anything that can be done to reduce these numbers is worth trying. With guidance, our participants were able to improve their judgment.

“It could be that pop-up stalls set up around drinking establishments that help people understand their breath alcohol concentration might help people.

“Really, the best advice is that if you’re driving, just don’t drink. But if you really do feel like a drink, then look into your own alcohol tolerance.

“This differs from one person to the next, depending on your sex, weight and age, and there are some reliable apps out there than can help guide you.”

The findings were published in the Harm Reduction Journal.