The move to discourage adults from smoking in cars with kids present – tipped to turn into law soon – strikes me as one of those pieces of finger-wagging that makes very little sense but can’t be opposed for powerful but fuzzy reasons.

“If this saves just one child from harm,” I can hear the proponents saying in self-righteous tones, “it will be worthwhile”.

I’ve never smoked and have no sympathy with smokers. And it’s obviously particularly harmful to cause your kids to inhale tobacco smoke in an enclosed space like a car cabin. But it’s also hard to see the point of creating legislation that won’t work.

Rational people, even smokers, already know that causing kids to inhale is harmful. The group irresponsible enough to do it anyway will be tiny, and no law will prevent them. How do I know? Because we can’t even stop people using phone handsets in cars. And when does a kid stop being a kid? Plenty of today’s 13-year-olds look like adults.