Motorists will have to carry portable breathalyser in France

Drivers crossing the channel will have to carry a portable breath-testing kit to take their car to France.

New laws will make the equipment compulsory for all cars on French roads from July 1, with anyone caught without the equipment facing an 11 euro (£9.20) fine.

Around three million Britons a year take their car abroad and the new offence comes into force on July 1 as the holiday season approaches its height.

The kits, costing up to £2 are expected to be available at Channel ports and will enable motorists to see if they are under the French limit of 50 mg per 100ml of blood which is 30 mg lower than in the UK.

Any devices would have to comply with safety standards set by the French authorities.

It is the latest in a series of requirements imposed on drivers by the French Government. Motorists are also legally obliged to carry a warning triangle and fluorescent vest as well as displaying a GB plate and adjusting their headlights to avoid dazzling oncoming drivers.

The Institute of Advanced Motorists advised drivers to carry two kits, to ensure they have one spare.

"The new French rule is a genuine attempt to reduce the number of alcohol related-accidents," said Neil Greig, the IAM's director of policy and research.

"France's lower limit means it’s very easy to be over the limit the morning after as well."

Andrew Howard, the AA's head of road safety, added: "They are not a good idea, because a driver's metabolism means that the alcohol level doesn't peak until 45 minutes after drinking.

"You could pass a test in the car park after an agreeable lunch and then fail when stopped by the police three-quarters of an hour later. The only sensible advice remains if you drink don't drive and if you drive, don't drink."