I NEVER took Michael Howard for a sanctimonious prat. But what else would you call a leader who sacks a member of his team merely because of an adulterous affair?

Mr Howard has made a fool of himself over the dismissal of the likeable but daft Boris Johnson - and his decision will rebound on him. People like a lovable rascal and Boris plays that role to the... I had better say fingertips.

Anyhow, since when was having a bit on the side unusual among politicians? The Palace of Westminster is the biggest knocking shop in town. Tim Yeo had a nibble and so did the oleaginous David Mellor, whose attractions are certainly well-hidden. But those men were only small fry. David Lloyd George had six mistresses on the go at once when he was Chancellor and Prime Minister. Just think, if he'd been untimely ripped from the adulterous bed we'd never have had the National Insurance Act. Harold Wilson installed his mistress as his political adviser. Surely someone, if only out of envy, might have accused the pipe-smoking Gannexed twister of endangering national security? Not a bit of it. Old Harold's affairs barely ever made it as far as page five in the papers.

Even John - "Y-fronts" - Major had a mistress and so revealed a taste in women to match his taste in Cabinet colleagues. As I write, I have one eye on a newspaper headline: MITTERAND USED TERROR UNIT PHONE TO KEEP AFFAIR SECRET. And yet no one fears for the future of the entente cordiale. Quite. Extramarital sex has always been compulsory for French politicians.

Sexual infidelity is a difficult sin to bring off these days. People love to read all about it even as they disapprove. The problem is that the word "sin" is now so restricted in meaning that it's only ever used to refer to sex. Before half the North-East of England goes into shock-horror mode at these words coming from me, an establishment clergyman, let me say straight off that adulterous affairs are wrong - in the traditional language "sinful". But illicit sex is not the only sin and it's not the worst.

St Paul in the New Testament has a whole list of sins: adultery, fornication - yes; but also backbiting, greed, pride, vainglory, witchcraft, idolatry, dissembling. But when did you last hear of an overpaid Premiership footballer being sacked for greed? Or one of the celeb-obsessed magazine editors dismissed for idolatry? Or an organic foods freak for witchcraft? Or, come to that, a member of the Ladies' Circle chucked out for backbiting? Politicians are routinely dismissed for leg-over, but not so many for dissembling - which is only the snooty word for lying.

The public has long expected to be entertained by fornication among the clergy. Not in every parson, you understand; but the occasional naughty vicar is necessary to the people's entertainment. Remember the sublimely named Rector of Stiffkey who used to travel from his Norfolk parish to the fleshpots of London's theatre-land as soon as the last chords of Evensong had faded over the cornfields. You know what happened to him: he was eaten by a lion.

It reminds me of the one about the parson being pressed by a lady of a certain age: "Oh do give me a kiss, Vicar!"

"Certainly not. It's not right for a clergyman to kiss the ladies of his parish. In fact I shouldn't really be in bed with you!"

* Peter Mullen is Rector of St Michael's, Cornhill, in the City of London, and Chaplain to the Stock Exchange.