The other week a woman at a black-tie dinner in Glasgow nipped outside, in her strapless evening gown, for a cigarette. Later, so the story goes, she told friends she realised that, now, when a driver in a Ford Mondeo stops and winds the window down, he is not necessarily asking for directions.

The more laws governments pass, the more they are subject to the oldest law of all: the law of unintended consequences. And smoking bans are having bizarre consequences across the world.