Holidaymakers travelling to France by road have been warned of a new law which means they must carry a breathalyser.

The UK's Foreign Office says: "Single use breathalysers are obligatory in all motorised vehicles as of 1 July 2012.

"Motorists and motorcyclists travelling to France should purchase a kit complying with French regulations and carrying the 'NF' label. Road users are advised to carry at least two breathalysers at all times."

Anyone caught without a breathalyser will initially be cautioned. From November, there will be an €11 fine (£8.80).

Reports state French police will conduct random searches on vehicles at ports.

Breakdown firm Green Flag warns many products are being sold as French breathalysers, but these won't necessarily satisfy the French police.

Green Flag suggests motorists carry at least two NF-certified breathalysers; one that can be used, the other to produce if requested by police.

It says single-use breathalysers can cost just 40p.

Anyone driving in France is already required to carry a warning triangle and a fluorescent safety vest.