Joan Smith: Roll up, roll up... See the Incredible Vanishing Princess

Acouple of centuries ago, the British royal family was growing increasingly anxious about the behaviour of the estranged wife of the king's eldest son. A secret inquiry took place, known as the "delicate investigation", which found no evidence to support a claim that the then Princess of Wales, Caroline of Brunswick, had become pregnant and given birth to a son. There is nothing delicate about the inquiry now taking place at London's High Court into the behaviour of Diana, Princess of Wales, even though the parallels between the careers of the two women are striking.

Nominally an inquest into the cause of her death, it has taken no time at all to degenerate into a cross between Crimewatch and Hello! magazine, with extensive gynaecological details debated.

Under the protection of privilege, witnesses and counsel can say what they like, rounding on each other like contestants on Celebrity Big Brother. Some observers may take comfort from the humiliation of Diana's butler, Paul Burrell, who was exposed last week as shameless self-publicist, and the rubbishing of wild claims by Mohamed al-Fayed, father of the princess's boyfriend, about a pregnancy and an engagement. But low points have included the former Met commissioner, Lord Condon, being accused of covering up Diana's "murder", and the revelation that Diana and her mother were not speaking after the latter called her a "whore".

Such "revelations" have been reported in news bulletins with the same solemnity as the opening evidence in the Ipswich murder trial. The details are banal, but even someone with no interest in the proceedings would have had difficulty avoiding the information that Diana was on the Pill and that she complained about spending weekends on her own after her divorce, heating her meals in a microwave. The relentless stuffing of unwanted snippets from the inquest into my head has begun to feel like an outrageous intrusion into my privacy.

But the most scandalous aspect of the inquest is that it is being paid for by taxpayers. The French held a perfectly respectable inquiry into Diana's death and concluded that she died in a road traffic accident. The idea that the French judicial system is less thorough than ours is the kind of tiresome xenophobic slur this country should have grown out of, and it has been clear from the outset that the argument for holding an inquest at all relies on a false premise.

Conspiracy theorists began swarming around the princess's death as soon as it was announced, and people who believe them are amenable neither to reason nor evidence. Something similar happened when Queen Caroline died suddenly in 1821 after being turned away from her husband's coronation at Westminster Abbey. Like Diana, Caroline was under surveillance at the time of her death and had accused members of the royal family of wanting to get rid of her. The conclusion many people instantly reached was that she had been poisoned.

You could stage half a dozen inquests into the crash, all arriving at the verdict that Diana's demise was an accident, and millions of people would continue to believe that the findings had been fixed. That's why the inquest is a preposterous use of public money, and I half hope that the jury will prove the point by finding that the princess was murdered in a worldwide conspiracy involving Saddam Hussein, the Duke of Edinburgh and the Freemasons.

Meanwhile, the courtroom has been transformed into an outpost of celebrity culture, and I have a brilliant idea about what should happen next. It's the best farce in London, so let's privatise it and start selling tickets.