Any sensible person should know by now that you need FULL concentration on the roads (especially around town) and anything that reduces that is a hazard.

This includes Drink, drugs,mobile phone or texting, playing with the smart phone or just having the radio going full blast; Moderate volume can help you too relax and make you more consious of what is going on. Talking to someone in the back seat also means you tend to turn your head away from the road.

Driving is more than just sitting behind the wheel and aiming it in the direction you want to go.

Terry

"Or is one supposed breathalyse oneself before settingout or on resuming a journey after a sojourn at a hostelry?"

Precisely - that's the idea.

Quite a few years ago I did some work for a company which ran a chain of pubs. They had a rule that all staff who drove on company business should carry breathalysers in the car, and should test themselves if there was the slightest chance that they might be over the limit. Then, anyone who was subsequently caught by police, and tested over the limit would automatically face dismissal.

In truth, the only sensible law would be one that had a zero limit on blood alcohol for drivers.

Slightly off topic, but still related, France are also introducing a law soon (or may already have done so?) that you are not allowed any speed camera warning devices in your car - this includes warnings that are inbuilt into sat nav systems.

false security, if you have a lot to drink, get in the car. and that alcohol has not yet maxed out in your blood and you get a neg reading then 20 mins on your blood hits max concentration without your knowledge then the police bag you you could well be over.