Like so many supposed geniuses of PR, Sophie has no idea of how to manage her own image

It takes only a few months for a fairy tale to turn into a farce. In June, the nation was thrilled that the youngest of the Queen's children was finally getting himself hitched. Actually, the nation was not that gripped at all, despite an extensive press campaign trying to persuade us that the marriage of Edward and Sophie was part of a modern and less fusty version of royalty that the monarchy, post-Diana, was trying to present.

Sophie was a modern young woman. She had breasts that unfortunately we knew about and a career. She may have learnt to hunt, shoot and fish to impress the likes of Prince Philip, but she was very much her own woman and determined to carry on her job running her PR company. The ceremony itself was said to be more informal and less grandiose than the usual frilly ritual, though from where I was standing, in the streets of Windsor among the Japanese and Canadian tourists and the strange and mostly female well-wishers, it looked pretty grand to me. People in the crowd wished Sophie well. They liked her, they told me, because she was down to earth. Ordinary, they said. Normal.

Others throughout the land were deeply uninterested in the marriage of two deeply uninteresting people. Edward remains a petulant and unlovable figure. And Sophie? Well, I hoped she knew what she was getting herself into. After all, even on the "happiest of days", the absences of other women who had tangled with this awful family made themselves felt. Diana, of course. But also Camilla and Fergie. Camilla couldn't be at the wedding because the Queen didn't want her there. Fergie, long excommunicated, had to send her children, but was not invited to attend herself.

Sophie, though, we were promised, was her own person. Whatever that meant.

When she took the title Countess of Wessex, Sophie should have known that the institution she was about to enter could never look forward but only back. Part of Sophie's and Edward's modernity is that they both behave like money-grabbing nouveaux riches, rather than old-style aristocrats. Edward, never forget, is the man who has sold his own granny - or a film of her life - for £350,000. So it's not really surprising that Sophie was soon in Hello!. And now she is in trouble for using her title to promote a car - the Rover 75.

She has been given an ultimatum. She must choose between her career or playing a public royal role. She cannot do both. She cannot be seen to be exploiting her royal title to make money.

Sophie's choice reveals the paradox at the heart of a "modernised" monarchy. Though the British, and even the Prime Minister, say that they want such a thing, you cannot put a modern veneer on an archaic institution. If the royal family represents us in some mystical way, then Edward and Sophie show us up as a rather dull but grasping little country.

Sophie, like so many other supposed geniuses of PR such as Peter Mandelson, obviously has no idea when it comes to managing her own image. Yet for the other royals to moan about her exploiting her royal title is wonderful. Sovereignty, the very essence of monarchy, is always an exploitation of a birthright. This is why the current royal family is in such a mess. It must marry and reproduce; yet the minute an outsider enters this vicious little mob they are persecuted because either they don't play by the rules or they don't understand the rules.

Diana bent the rules and her death has meant not a questioning of those rules, but a desperate attempt to reinstate them in the guise of modernity. So now we are involved in this ridiculous exercise in which we have to pretend that the monarchy is both entitled to enormous wealth and privilege and yet, at the same time, fundamentally ordinary. Yet no ordinary man would, at the age of 50, lurk around with his long-time lover as though he had a guilty secret just because his mother didn't like it. No ordinary family would have the power to make a newly-wed give up her career because it didn't look good.

Edward, in one of his little outbursts, claimed that the British "hate anyone who succeeds". He got it mind-numbingly wrong. Most of us don't think that Edward has succeeded at anything, apart from cashing in his royal chips wherever possible.

If his wife is using her title to sell Rovers, who can really blame her? Rather her than the rest of them, I say. I'm sure it's a damn sight better going to the office every day than performing the role expected of her as Edward's wife. Sophie, who once said that she mistakes herself for Diana in photographs - don't worry darling, no one else does - should instead look at good old Fergie.

Disgraced, divorced and often quite demented, Fergie will sell anything to anyone: Weight Watchers, Wedgwood, Whatever. She had her own chat-show based on her ability to empathise with anything placed in front of her. Now she is to be a TV reporter for NBC. I quite admire the way that she said she would work hard to pay her debts and has done so. Obviously she has exploited her royal connections, but in turn she has been treated appallingly by them. I admire the way her total cluelessness has been turned into an asset, her eating problems a selling-point.

So Sophie, it's your call. Either play the demure trophy wife and get yourself an eating disorder and go quietly mad. Or keep your career. Behave like any modern woman would when threatened by their overbearing mother-in-law: tell your husband he has to decide between you and his family. If he won't back you, then divorce him. That's the only choice you've really got.

The writer is a columnist on the "Mail on Sunday"