The fall of a great man, classical theory insists, should be not merely a personal tragedy, but must drag others down as well.

Diane Yeo was the latest - but she won't be the last - to leave us wondering why the supporting players put up with it. Tory wives, gracious in victory, dignified in defeat, are never more themselves than when standing by a faithless husband who has just betrayed them to the flashbulbs of the newshounds and the sniggers of the world. From Valerie Profumo to Judith Mellor, they descend in an unbroken line, brave smiles hiding the heartache. That at least is the tabloid reading: wife's trusting innocence shattered at one leap by perfidious male.

But what is this sentimental image of the naive victim-wife? Any woman who marries a politician knows from the start that he may well be away from her for four or five nights a week. These are the perfect circumstances for any man to discover that the chains of marriage are so heavy that it takes more than two to carry the load.

And the late-night sittings, the six bars in the House of Commons open 24 hours a day, the relentless ethos of 'boys will be boys' . . . the Honourable Chums have created a veritable playground of self-indulgence, which easily becomes an adultery theme park. What woman will be surprised by a husband with a nippy zipper when all his colleagues are either at it themselves, or happy to condone it as they did with Yeo, Mellor et al.

And despite the pious rhetoric of 'spending more time with the family', the political wife knows that her man will only ever think of this when he's been sacked. Before then the career, the glory, the whole enchilada will be his. He will take all his decisions with one eye on the PM and his promotion prospects, the other on his constituency, and an ear cocked to Central Office, just in case. Hers is the support role in the great roadshow of his life. She and the kiddies are just a setting for this jewel, a muted background against which he may shine.

Political wives are not babes in the wood. They know the score. And if they don't, the dowagers of the party are there to instruct them. 'Listen, darling,' one senior Tory wife counselled a junior who had just discovered her husband was having an affair with his secretary, 'Be thankful it's only the secretary tart. When your husband has been round the Houses with a woman who is a real threat, then you'll have cause to complain.'

Put up and shut up, then, is the word from on high, and they do, oh how they do. Remember Lady Lambton, granite-calm and unfazed after the 1973 scandal exposed the tawdry fantasy of her Minister husband's 'three in a bed romp' with two prostitutes? The strength of these women gives the lie to the Patient Griselda myth of the wife who takes everything her husband dishes out, and still comes back for more. That grit, that nous, is the reason their husbands married them in the first place.

For a Tory political union is more than an everyday marriage of simple folk. A single man has about as much chance of selection for a Tory seat as Madonna has of becoming a blessed virgin. More than in any other party or profession, a Tory MP's is a two-person career: wives are auditioned along with their husbands on everything from how they get on with the constituency chairman's wife to how they hold a fish fork. For any woman to go through all this, there has to be a very good reason.

And it's not hard to see all the good reasons for being Mrs Michael Heseltine or Mrs Fatty Patty, wife to the Governor of Hong Kong. Even for women whose husbands are less successful, the allure of being around politics is so strong that they want to be there regardless of the cost. 'They're power groupies,' says Rusty Clinton, a Californian motivational psychologist who runs NRG, an international film research company in London. 'They tell themselves: 'Who cares about a silly little adultery?' The English have very little psychological self-knowledge in these matters. These women make themselves strong inside, and keep smiling through.'

Then there's the Hillary factor. In an era which still gives even brilliant women such a poor chance of achieving power in their own right, their only route will be through and with a man. Lord Healey agrees. 'If the wives are not interested in power, there is very little incentive for them to make the sacrifices involved.'

Yet is it always such a sacrifice? John Mortimer's Rumpole, forced to be with She Who Must Be Obeyed seven nights a week, is not the only one to brood longingly about the chance of a night off. Many wives must long for relief from an odious, pompous, arrogant, over-bearing spouse - all the things, in short, that politicians usually are.

And who says that men are the only offenders? Tory wives are not immune to the odd fling. Fragrant they may be, but they are women, too, like Lady Dorothy Macmillan, who openly cuckolded husband Harold with his fellow-Parliamentarian Lord Boothby: for years they never had it so good. For many happily cruising today's corridors of power, marriage is a social, financial and political arrangement, and what happens to the honourable member when it is off duty is neither here nor there.

With all the recent brouhaha about the Prince of Wales's private life, people seem to have lost sight of how deeply adultery is ingrained in the British ruling classes: 'Edwina and I spent all our lives getting in and out of other people's beds,' Lord Mountbatten once said. Why, then, should we be surprised that the Tory party clings to such models?

Any woman who chooses to spend her days with a political man is there for her own reasons. And who is to say that she is wrong? Ann Parkinson must be the paradigm of the woman broken on the wheel of her husband's adultery and betrayal. But she's still fiercely there. It is a dismal reflection on the continuing restrictions suffered by the female of the species that being Mrs Cecil Parkinson is still the best option she has.