It doesn't matter who gets the blame. The real villain is the current epidemic of credulity

Isn't all this Diana conspiracy stuff a hoot, eh? A bit upsetting for the families maybe, but anyone else watching last week's TV programmes dealing with the 1997 crash, including a hilariously acrimonious debate between two rival documentary makers, will have been - at the very least - entertained. And if one of these shows failed to live up to the highest standards of investigative journalism, well so what? The fact is that, for most people, conspiracies are great fun.

Unless, like me, you happen be part of one. I discovered only last week that I am involved in a pretty big plot, and it's made me feel rather nervous. I happened upon it when - in one of my periodic bouts of mingled vanity and insecurity - I was searching the Internet for mentions of, er, me. And there I was. Mentioned twice in what the authors described as "simply a study of who controls public opinion in Great Britain".

This project, conducted under the auspices of something called Radio Islam asked itself: "Who is behind it all? Who are the people who determine what is watched on television and printed in the newspapers?" and went on, "This is not so easy a study because a great many of the people concerned operate in the shadows. And even in the case of those whose names are known, what is known about their backgrounds and their connections? Very little."

And who are they? Yes, you've got it. "For this reason, very few people in Britain are aware of the huge influence over the mass media exercised by a certain ethnic minority, namely the Jews."

Helpfully, Radio Islam sets about the difficult business of naming names. "In the following text, we have highlighted individuals of Jewish origin by setting their names in bold type. Not all of the names in question will seem obviously Jewish; it has been the habit of Jews over the centuries to change their names, adopting those which best blend with the populations of the countries in which they have settled."

[My grandparents, illiterate peasants that they were, presumably made the mistake of adopting the kind of name - Aaronovitch - that was very popular in the East End at the turn of the century. Unfortunately for their sinister plan, it turned out that the East End was full of other Jews. Foiled again!]

"Where persons with non-Jewish names are designated as Jewish, the reader can rest assured that extensive research has established them." And, reassuringly, my colleagues Donald Macintyre and Hamish McRae do not appear on the list. Neither does the proprietor of this paper, Tony O'Reilly - though I have my suspicions. I mean, what would a Jew landing in Cork call himself in order to "blend in"? Netanyahu?

Now, some conspiracies are less popular than others. It's a bit of a fashion thing, and since the Holocaust the taste for Jewish plots has subsided a tad. And this could be because everybody has become a little more aware of the possible link between suggesting that Jewish people were involved in a conspiracy, and the subsequent ill-treatment of the race so accused. But this awareness had taken a very long time.

In 1039 a chronicler name of Rodulfus (or Ralph the Bald) told the tale of how, 30 years earlier, the Jews of Orleans in France secretly persuaded the Muslim prince of Cairo to pull down the church in Jerusalem containing the Holy Sepulchre. Apparently they had bribed a fugitive serf and sent him to Cairo with letters in Hebrew, written on thin parchment strips hidden inside the iron of his staff, urging them to perform the destruction.

The story got out and, according to Rodulfus: "Once they knew this the Christians throughout the whole world decided unanimously to drive the Jews from their lands and cities. Some were put to the sword, others were drowned in rivers, and many found other deaths ... After this very proper vengeance had been taken, very few of them were to be found in the Roman [i.e. Western] world."

The same thing happened periodically over the next nine centuries, with Jews accused of ganging up with lepers and the Moslem king of Granada to poison wells (thus causing the Black Death), and - a hundred and fifty years ago - of getting together and plotting world domination. The minutes of that supposed meeting were, of course, the infamous Protocols of the Elders of Zion, which are also thoughtfully provided by Radio Islam on its website.

What has all this got to do with Diana? Though Secrets Behind The Crash was coy about who might have shone the wholly speculative military flash- gun in the eyes of M Henri Paul on the last night in August, others detect the hand of Mossad, the Israeli secret service. Some Arab journalists actually suggest that the marriage of the world's third greatest Christian icon to a Muslim would have been intolerable to world Jewry. Mr Fayed has not himself blamed the Jews, preferring (as far as I can tell) to implicate a jealous anti-Muslim British establishment.

But it doesn't really matter who gets the blame. The real connection between Dianagate and Aaronovitchgate is, I believe, the current epidemic of credulity. Sixty-four per cent of Americans are said to believe that aliens have been contacting people on earth, abducting them and probing their anuses. Books that claim that the world is full of human/alien hybrids sell in their millions. TV programmes lend credibility to weird theories, such as The Face On Mars (constructed by alien civilisations and covered up by Nasa), to faith healers, to ghosts, to mumbo jumbo of all kinds. The pyramids were built by spacemen, dogs know when their masters die a continent away, the Bible has a secret code which predicted the assassination of Rabin - but not this year's Eurovision song contest winner.

There is, as Frederick Crews points out in this week's New York Review of Books, a vast amount of money in all this - Whitley Strieber's Communion (the abductionist classic) got an advance of a million dollars. But it is a fair bet that the publishers and executives, who commission and print this tosh, do not believe any of it themselves. When was the last time you spotted a senior newspaper or TV exec consulting a faith-healer, having his or her house exorcised, or - at a dinner party - opining that Stonehenge was the work of Venusians?

No, they just print it, transmit it, and take the money or enjoy the ratings - over 12 million watched the Diana programme, a huge figure for a "current affairs" show. You can't help wondering whether, had ITV existed in the 11th century, we might not have had a trailer read in that boomy, doomy voice: "Tonight. What shadowy forces may have been behind the destruction of the Church of the Holy Sepulchre last year? Who was this man, and what was in his staff? Watch The Secret Behind The Sacrilege on ITV tonight!"

Tosh begets more tosh. Suspend your disbelief here, and why should you retrieve it there? So a world in which Diana can be murdered by MI5, and a world in which Nasa can cover up certain evidence of alien existence, is a world in which I got together with the Chief Rabbi and Mossad to plan this misleading article. And where someone else might just decide that I deserve to be punished for it.