Fines to enforce the new law, which was introduced earlier this year, were due to come into effect on 1st November, but this has now been delayed until March 2013. At present, drivers including visitors from the UK face caution if caught driving in France without the compulsory kit.

France's Interior Minister, Manuel Valls, made the decision to delay the on-the-spot fines as a result of stock difficulties reported in certain regions, from March 2013 all drivers will face an €11 (approx. £9) fine if caught in France without a breathalyser in their car.

Miranda Schunke, spokesperson for Green Flag, said: "Although fines to enforce the new regulation may not come into effect until March, this is a huge step-change in policy so last minute demand for these testing kits is likely to be high. We'd strongly advise all motorists considering driving in France to invest in some breathalysers well in advance of their trip, to avoid last minute panics, and more importantly, breaking the law.

"Breathalysers are useful for ensuring those that need to drive after consuming alcohol can do so legally. However, it's vital that drivers don't interpret this requirement as a sanction for drinking, before getting behind the wheel. Drink driving remains a serious problem throughout the UK and Europe, so we'd discourage drivers from consuming any alcohol whatsoever before they take to the road."

The single-use breathalyser kit needed under the new rule can be used to check the driver's blood alcohol level. The legal limit in France is 0.5 grams per litre (50mg per 100ml of blood - lower than the 80mg limit in the UK).  The new kit will allow people to test themselves as well as others if they suspect they are over the limit.

Single-use breathalysers cost between €0.50 and €1.50 and the authorities are trying to make sure there are enough available before the law comes into force.  Breathalyser tests carrying the blue circular "NF" logo are recommended in France to comply with the legislation (this is the equivalent of the BSI kite mark in Britain), and they can be purchased online ahead of travelling.  However, there are many products being sold as French breathalysers, but these won't necessarily satisfy the French police, known as the Gendarmerie, unless they are on an approved list.