That bishop at the Vatican who issued a list of seven mortal sins for our times missed a trick didn't he? The list didn't include smoking.

And in today's confused moral climate, smoking is one of the few secular vices about which there is a general consensus that it ought to be discouraged. Liverpool council is the latest public body to get itself worked up about smoking. It backs the suggestion from an organisation called SmokeFree Liverpool that all movies with cigarette scenes should be given an 18 certificate.

In fact, one enthusiast on the city council said that Liverpool could act alone to restrict access to smoking films. You can just see it - deviant teenagers getting lifts out of town to watch screenings of Casablanca.

Remember that charming film, Cinema Paradiso, in which the priest in a little Italian village appointed himself film censor, and lifted up a placard for a cut whenever the on-screen kissing got out of hand? Today's equivalent would be some councillor sitting through movies from Vertigo to The Black Dahlia, weeding out all the clips in which smoking is suggestive of glamour.

It's been done, of course: a study by the University of California in 2004 suggested that that between 1950 and 2002 there were about 11 smoking incidents in every hour of film. Just as tobacco came this way from America, so the anti-fag puritanism started there too. Last year the Motion Picture Association of America announced that smoking would be taken into account when classifying movies. The Disney Corporation, never slow to board a bandwagon, declared that smoking in future family films would in future be “non-existent”.

I don't smoke myself. But what what strikes me as self-evidently weird about this contemporary take on Prohibition is how disproportionate the moral outrage is to the offence. It's as if, in the absence of any consensus of what constitutes real sin, we get correspondingly more agitated about those vices we can agree on.

And look at what we're not getting worked up about. The anti-smoking lobby was jubilant when smoking scenes were cut from the last Bond film, Casino Royale. But as Daniel Craig tersely pointed out: “I can blow someone's head off but I can't light a good cigar.” It's fine for 12-year-olds to be shown someone being beaten to a pulp, but you can't let them see someone enjoying a cigarette.

Then there was the perplexing occasion when anti-smoking campaigners tried to get the BBC to apologise for an episode of Top Gear in which Jeremy Clarkson lit a pipe. So, celebrating fast cars is OK - although excess speed is a factor in about a quarter of road fatalities - but a pipe is pernicious? Say what you will about the old censors, they weren't that stupid.

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