"In one move M16 have saved the monarchy, put an end to the royal scandals, silenced a critic of Britain's munitions industry and allowed Charles to marry Camilla." This was a typical interpretation of the Princess of Wales's death on the Internet's "alt.conspiracy" newsgroup last week. Within hours of the announcement, tales of sinister black helicopters and the Freemasons' plans for world domination had been largely forgotten in this forum for the world's conspiracy theorists. One subject only dominated discussions: who killed Diana and Dodi, and how?

These are some of the answers they came up with:

l One of the pursuing paparazzi was an M16 agent and shot either the driver or the car's tyres. The other motorcyclists were hypnotised during their period of detention to make them forget what they saw.

l An assassination squad was waiting in the tunnel. They placed an object in the road to make the car swerve, then finished off the occupants after the crash. (Hence the unidentified person, mentioned by American tourists interviewed on CNN, who told onlookers arriving at the scene to "get out of here" - the killers needed time to remove the obstacle.)

l A small amount of plastic explosive disabled the car's braking and steering systems.

l Dodi Fayed's bodyguard is an M16 agent. He caused the car to crash, but was wearing shielding to protect himself.

l The driver was deliberately intoxicated. However, since the bodyguard would not have allowed him to drive if he was drunk, he was also drugged in such a way that the symptoms of his drunkenness would not be apparent. (There is also much speculation about why the driver's bloodtest results took so long to be announced. One suggestion is that the samples were faked on the orders of publishing barons to take the heat off the press.)

As the week went on, countless websites sprang up to cater for such speculations. Suggestions for possible perpe- trators included the IRA, the Vatican, the Masons, and the Queen, who was said to have wanted Diana dead as part of her plan to establish "the worldwide dictatorship of the Antichrist". However, the finger of suspicion pointed overwhelmingly at MI6. But why should MI6 want to kill Diana? And under whose orders?

Well (the theories ran), Diana was a danger to the British monarchy and Establishment. And now that she was campaigning against landmines, the arms industry felt threatened. It was widely noted that William Hague, the leader of the Conservative Party and therefore an establishment stooge, seemed curiously unmoved by Diana's death. Was he expecting it to happen? Furthermore, in praising Diana's achievements, he conspicuously omitted to mention her landmines campaign ...

The theories continue: Mohamed Al Fayed was also a thorn in the Establishment's side, and if Diana and Dodi had married, he would have become the step- grandfather of the heir to the throne. Furthermore, if Diana was actually pregnant by Dodi (remember the "surprise" she promised the press in St Tropez), then Prince William would have an Al Fayed as his half-brother.

Pregnant or not, Diana certainly could not be allowed to marry an Arab. This line was, incidentally, taken up officially in Libya, where state television announced that "Britain killed Princess Diana and her Egyptian friend in a Paris street". The National Committee for Human Rights in Libya accused London of "involvement and complicity, along with other intelligence services, in the death of Diana, due to her friendship with an Egyptian Arab".

And then there was Prince Charles, who was jealous of Diana's popularity. Her death could also pave the way for him to marry Camilla Parker Bowles and at the very least it would mean that he could raise his sons according to his own values.

The theories are still mounting up and will continue to do so for the weeks and months to come, no matter what the official investigators finally conclude. Facts rarely trouble a conspiracy theorist.

But there is one theory which is very different from all the rest. Picture this: the car drives into the tunnel, where two trucks are waiting. One truck deposits the wreckage of a car while Diana and Dodi are driven into the other truck. The two trucks drive away, carrying the princess and her lover, who are free at last to live their lives in peace away from the prying eyes of the press. So prepare yourselves. The first sighting could be any day now.