Beatrix Campbell: Indifferent? You shouldn't be

One thing we know for sure: her eyes won't be scudding around the pews searching for the other woman. Although Camilla's marriage to Charles will for ever be crowded - the spectre of Diana will always haunt these two - the third party will be only what she always was, an unwelcome guest and, unlike Diana, Camilla will know everything she needs to know about her man.

One thing we know for sure: her eyes won't be scudding around the pews searching for the other woman. Although Camilla's marriage to Charles will for ever be crowded - the spectre of Diana will always haunt these two - the third party will be only what she always was, an unwelcome guest and, unlike Diana, Camilla will know everything she needs to know about her man.

She won't need to scan the congregation for her enemy; she won't need to avert her eyes, nor will she need to search and destroy. She has spent her entire adult life knowing everything she needs to know about the future king, even helping him to measure the merits of his first wife.

This thought comes to mind because Diana's big day was also haunted: she knew that Charles's heart really belonged to the woman in the little grey hat. She knew that while the world watched her being apparently reincarnated from a mere mortal to one of their exalted highnesses, inside she was dying from deception. Charles and Camilla's appearance of innocent pleasure at their engagement is, however, just another charade: it masks the collective sighs of relief rustling around the aristocracy and the establishment.

This is another marriage of convenience. Charles and Camilla didn't need to do it for themselves - they've been embedded for more than three decades, after all. They didn't need to do it for us - we don't care. And in any case, we, the people, have already improvised mature ways of managing personal change and complexity without the sanctions of either church or state.

No, this marriage is a strategic manoeuvre to appease his parents; it is the result of marathon negotiations within the establishment to satisfy the very institutions that made marriage to Camilla impossible in the first place.

It was the sexism and religious sectarianism of the monarchy, the Church of England and Parliament that discombobulated this cowardly and ambitious man; he couldn't have his destiny as heir to the throne and have his desire for this woman at the same time. Correction: he could have her. He did have her. But he couldn't marry her. And he had to marry somebody.

So, our royalist institutions and ideologies drove the man to the shires of England to seek a suitable virgin. She, unlike him, expected a modern marriage; she expected to be in love, whatever that was, and she expected some equality and reciprocity. The rest is history.

This marriage will also be for the convenience of Charles and Camilla, of course. The idea that this middle-aged man was still being pushed around by his mother's court, telling him where, and whether, his companion might be his public consort had become intolerable.

Charles didn't need to "make an honest woman of her". The propriety of Princes of Wales wearing their mistresses on their sleeves scarcely bothered this class before. Droit de seigneur and promiscuity were the perks of an otherwise pointless career as a king in waiting. But things have changed - we have changed. Charles and Camilla are the beneficiaries of democratic social and sexual revolutions from which they and their class are simultaneously estranged. The couple could still be bossed around by his parents; they could still be constrained by royal manners and the performance of archaic, patriarchal protocol.

Their public presence could still be organised according to mystical hierarchies which allocated Camilla her time and place because - lest we forget - this woman is merely a subject, a servant. And like any other servant, their boss, in this case the sovereign, decides when and if they will be seen or heard.

So, this marriage makes this mere mortal properly one of them: we now have to bow to her! And all because the establishment has wangled a way of accommodating modern liaisons within its primitive belief system about power and place.

Camilla is such a marvellous servant. She is ample; she is amusing, and she is always available. She brings her comely body to the service of a man who has been able to enjoy her wit, her flattery and her engaging commitment to the heartiest of indoor as well as outdoor pursuits. She has a talent for accommodation. It is as if she were born to it - certainly she has had a dynastic induction into the lore of the mistress.

Her ancestor Mrs Keppel was one of the most celebrated and accomplished mistresses. Queen Victoria's son, Bertie, another wastrel of a Prince of Wales, alarmed his mother, not so much because of morals - his aristocratic clique was rather publicly promiscuous - but because his "imprudence" might affront "the middle and lower classes", the useful classes. He enjoyed multiple affairs with gorgeous young women while his poor, fertile wife Alexandra was confined to child-care and public ceremony. Victoria's vigilance was less about marriage and fidelity than the spectacle of "frivolity" and aimless pleasure-seeking that might "do more to increase the spirit of democracy than anything else".

Finally, the Prince of Wales settled down with Alice Keppel. She derived her power from her compliance and her self-confidence. She charmed him. And she was, above all, amusing and available. Just like Camilla. Unlike other divorcees, who have to earn a living and take care of children, and clean the toilets, and learn to plaster a wall or put up shelves, Camilla has been unencumbered by toil. She isn't exactly unemployed; she is workless. Only that class fields proudly workless women. And only a workless woman could live a life entirely at the service of such a needy man. She may love, flatter and calm the man. But she has indulged base instincts - her life's work has been to service the most disabling, but inherent, bequest of his dynasty: his need to be entirely taken care of, his need to be the centre of attention, and his right to be surrounded by subordinates.

This stuff will go on shaking the rickety scaffolding around this marriage as a piece of propaganda. It may reassure the establishment that everything is arranged. It has shown that they can go on inventing tradition - a faculty wonderfully chronicled by the historians Linda Colley and David Cannadine - because they are nothing without the aura of divinity and eternity bestowed by tradition. They've proved that they are great illusionists, showing that everything changes while everything stays the same, that they can adapt to anything.

It may offer a historic compromise with the useful classes, who are increasingly indifferent or hostile to the monarchy. But this marriage manoeuvre and the slippery fabrication of Camilla's new name only highlight the weirdness of their world.

The announcement of their engagement, with all their young, coy excitement, has simply reprised the ghost they want to kill off, the ghost of Diana and Camilla's dreadful duplicitous relationship with our future king. There is no escape for Charles and Camilla - people will always see it as a crowded marriage. And far from presenting an appearance of modernity for the monarchy in the new millennium, it can only draw attention to the primitive, patriarchal values of the institutions that made them wait so long before giving him permission to make a married woman of her.