The trouble with posh totty scorned is that the revenge tends to be posh too, as the nation's favourite buffoon Boris Johnson found out to his cost this week. His sometime squeeze, Petronella Wyatt, was riled by reports in the News of the World - who had staked out the Tory member for Henley engaging in a series of trysts with another attractive young woman, also not his wife. Ms Wyatt accused the bumbling MP of having "satyriasis".

This recondite word describes a condition which the dictionary defines as "excessive sexual desire in men". As befits a term of abuse levelled at a former editor of The Spectator by one of his former writers, its etymology is distinctly classical. It comes from the Greek word saturos which we translate as satyr - a lascivious, mythological creature; half-man, half-goat, with unusually strong sexual desires. The shambolic politician provoked this by popping into Petsy's house and, she has apparently told friends, "lunging at her" just a few hours after visiting his new paramour and before returning home to his wife Marina at their town house in north London.

Of course it may just be all that posh education. (Boris was at Eton and Balliol, where he read classics). Or it may be that there is something peculiarly Tory about the affliction. After all, Petronella Wyatt has recalled in print that a former Conservative minister, Viscount Lambton, who resigned in the 1970s after being caught in bed with prostitute Norma Levy, told chums he had to have sex at least three times a day to avoid debilitating headaches. He once did it in a phone booth in the Ritz.

And another member of the Tory commentariat, Minette Marin, has in the past used accused another Tory toff, Alan Clark, of suffering from "an advanced case of satyriasis, or, in plain English, a pathological inability to keep his trousers up". In the world of racing, she noted, "top stallions are regularly offered teasers, inferior mares upon whom they can work out their anxieties before being allowed to intrude on the valuable time of a top-class brood mare". Aren't the upper classes wonderful?

As a graduate of Oxford in Literae Humaniores, Boris will of course realise that his former mistress's term of abuse goes far deeper than accusations of mere priapism. Satyrs were not just randy creatures, depicted on Greek vases with a permanently erect phalluses, cavorting with nymphs. They were also cowardly and faint-hearted folk, and slightly foolish in a way which contrasts greatly with Alexander Boris de Pfeffel Johnson, whose bluff and bluster is, of course, a mere camouflage for the charismatic charm, wit and high intelligence which his fans see in the man they have tipped as a future leader of his party. So much so that they have set up a website called Boriswatch which lauds the studied eccentricities, calculated humorous inanities, unkempt appearance and general air of shambolicness of their bumbling hero.

What they shouldn't do is delve too deeply into this satyriasis business. Defined as "an abnormally intense and compulsive sex drive with little or no sexual gratification despite numerous partners" satyriasis is the male equivalent of nymphomania.

All this is a notoriously imprecise area. After all, a nymphomaniac, in Kinsey's celebrated definition, is anyone who has more sex than you do. But there is some sense to the joke, says Dr Thaddeus Birchard, a psychotherapist whose London clinic specialises in sexual, marriage and relationship problems. "Satyriasis and nymphomania are old-fashioned terms," he says, "but there is an observable phenomenon of people with patterns of sexual behaviour they can't control that bring hugely harmful consequences."

This is not a medical disorder, he says, but a dependency akin to drug addiction. It crosses the boundary between promiscuity (a social judgement) and a psychological dysfunction (a clinical judgement) when the sufferer realises he or she has a problem. "It's very subjective," says Dr Birchard. "We run a programme for men who feel addicted. It takes 18 months to complete." What the programme tries to address is what lies beneath the behaviour. "It seems to be an attempt to anaesthetise themselves to some core problems - loneliness, shame, anxiety, or a boredom which is a kind of alienation from the self."

For a more lurid account you might turn to the website of satyriasis groups in the United States where researchers estimate that about 8 per cent of men and 3 per cent of women - a total of 15 million people - are sexually addicted. One entry says: "To have satyriasis is like never once having to feel sexually fulfilled. The more pleasure I get out of having sex and the release I get, the more I want more right after. This temporary feeling of relaxation washes over you until you once again have this feeling of having to have sex again."

And there's this: "A gay friend has had it bad since 14. Since he's attractive, more people are willing to oblige him, so he's developed a sense of shamelessness and tends to literally throw himself at every guy he sees. He's always horny, none of his boyfriends could cope with his incessant carnal needs. When desperate in public, he tends to break into a sweat and starts breathing heavily, often excusing himself to the bathroom and has difficulty sleeping." Or even this: "I'm willing to do it with anyone or anything, male or female, married or unmarried - all my morals go right out the window. I have gotten myself in serious trouble this way. Aaaargggh!!"

Crikey. Let's hope Boris hasn't got anything that bad. Still, there are things you can do about the problem. As well as courses like Dr Birchard's there are numerous self-help groups with names like Sex Addicts Anonymous, where presumably people stand up and begin their testimony by saying things like: "I'm Boris and I'm a bonker ..." Which may be humiliating, but better than the solution offered by one website: "a much more drastic option is castration". Yikes!

Boris may protest that this is all a bit OTT. After all, he might proffer, just because a chap has parked his bike in the wrong shed, again, doesn't mean he's a fully horned satyr. And certainly he doesn't look like one in the video that the News of the Screws have put out on the internet; as he leaves his new ladyfriend's flat in Chelsea, he is wearing a pointy beanie hat which makes him look more like a gnome than a creature of lustier myth.

But you never can tell with satyrs. History, or literature at any rate, shows you that. The Greeks were big on satyr plays - savage burlesques with which writers like Euripides were expected to round off their epic dramas. The satyrs in them could take many forms. "The plays were farcical and vulgar, burlesques rather than satires," the critic Keith Sagar has written. "The satyrs were as unheroic and grossly physical as it is possible to get. They had abundant hair and beards, broad noses, pointed ears, horse tails, and large, permanently erect phalluses. They represented natural as opposed to civilised man, everything man shares with the beasts. Their characteristics were naive curiosity, acquisitiveness, lust, drunkenness, lying, boasting and cowardice. They were completely amoral." Nothing like the Tories, then.

And so they have continued to be depicted. From silly figures in Aesop to ones lusting "with wasting madness wild" in Shelley. In the theatres they were actors of lewd pantomime. In art the old masters portrayed them as creatures of Bacchanalian debauchery (the satyrs were the traditional entourage of Dionysus, the Greek god of wine and fertility, or Bacchus as the Romans called him). They have even made the occasional appearance in more modern works. F Scott Fitzgerald's screenplay for the film Three Comrades involved a satyr, an angel, and St Peter working a system of telephone switchboards, though the director cut it before filming began. Two of John Fowles' novels had satyrs appear. And in Tony Harrison's adaptation of Sophocles' satyr play Ichneutai (which he called The Trackers of Oxyrhynchus) the chief satyr, Silenus, was played by Barrie Rutter in heavy Yorkshire accent and clogs. Throughout history, the satyr has worn many faces.

Boris can draw comfort from one aspect of the satiric character. Silenus was famed for his wisdom and prophetic powers, which were loosed when he was most intoxicated - a trait which might come in handy after an ample House of Commons lunch, though he will need to watch his step. Silenus did not go down too well when he shared with King Midas one of his keenest philosophical insights - that the best thing for a man is not to be born, and if born, should die as soon as possible. Not very voter-friendly, that one.

Still, the new Tory leader David Cameron seems relaxed about it all. Where his predecessor Michael Howard sacked Boris as shadow arts spokesman for not telling him the truth about the affair with Petsy Wyatt - Boris had dismissed the reports as "an inverted pyramid of piffle" - Mr Cameron is determined to keep Boris in his post as shadow higher education spokesman. Having had a private conversation with his fellow old Etonian this week, Mr Cameron announced: "This is a private issue. My judgment has to be on how Boris is doing his job and I think he's doing it well ... Marriages break up and people do things they shouldn't. That shouldn't necessarily mean that they lose their job. Politicians are human. People have tough things in their private lives they have to sort out and I hope Boris will sort it out."

There is, however, one final indignity ahead for the member for Henley. Unlike some of the dramatis personae of Greek mythology, satyrs are not immortal. They grow old. In the middle period of their life they grow whiskers. A bearded Boris is a thought to conjure with. But in the end they go bald, a humiliating and unbecoming disfigurement to the ancient Greeks. For the man with the haystack thatch, that could prove the final electoral liability.