I learnt a salutary lesson about journalism on the day, many years ago, when I was asked to check out a popular myth of the early 1960s. It was the case of the yellow golliwogs, and it was a story that ran and ran.

The claim was that, at a certain grammar school in the West Country, girls who had lost their virginity were proclaiming it by sporting fluffy little golliwogs on their lapels. It sparked an outbreak of social panic: standards were slipping out of control, we had begun to breed a new generation with neither morals nor shame, postwar Britain was heading for disintegration. Clergymen took to the pulpits, there were thundering editorials.

Alas, the story, as I discovered, was without foundation, indeed it had been exposed early on as a complete invention, conjured up on a dull weekend by an imaginative, if somewhat fevered local correspondent, sheltering behind phrases about rumour and gossip. The revelation that it was false had done nothing to undermine the legend. It cropped up again and again, recycled in newspaper articles as an exercise in journalistic prurience. It even became a movie of famous awfulness called The Yellow Teddybears.

The lesson, which probably needs to be relearnt at regular intervals, is that the facts are rarely allowed to interfere with a good story.

When last weekend, The Times reported that the legend of the Loch Ness monster might finally have to be buried because sightings of the creature had dropped to a record low, the story circled the globe, eliciting weird explanations of what might have happened. Global warming, inevitably, was blamed for its demise, low-flying jets were cited in evidence, the call went out for extra vigilance from those who regularly scan the waters of the loch for a glimpse of that famous neck. That every alleged photograph of the monster has been exposed as a demonstrable fraud has done nothing to undermine its credibility. Besides, an entire tourist industry depends on its existence.

It has two other elements that all long-lasting myths require to sustain them – it is not susceptible to final proof, and most people would prefer to believe the fiction than to dwell on the fact. To learn, as we have had to, that Lee Harvey Oswald was the lone assassin of President Kennedy, just as the Warren Commission determined more than 40 years ago, will never dispose of the conspiracy theories that continue to hang around that earth-shattering event. Not one hard piece of evidence has emerged to sustain the rumours of CIA or Mafia plots, and yet they continue to outweigh the bleak truth of what actually happened.

An entertaining account, just published, of the best of enduring myths by Albert Jack – Ten-Minute Mysteries – shows that rational explanation is often the last to be considered when a genuine mystery presents itself. The Bermuda Triangle – that sinister stretch of ocean that has allegedly swallowed more planes and ships in bizarre circumstances than any other – turns out to be no more dangerous, statistically speaking, than any other part of the world. Marilyn Monroe died, not because she was murdered, but because of the accidental dose of drugs she was prescribed by her doctor.

There is no such thing as the Yeti or Big Foot, an ape-like creature of enormous size, because it was, originally, a straightforward hoax. All those mysterious crop circles were created by a network of admittedly lunatic gardeners. The first sighting of the Loch Ness monster in the 1930s turns out to have been the trunk of a swimming elephant, being given a watery outing by Bertram Mills’s circus.

All this love of myths might simply be dismissed as a loveable disposition for the mildly batty over the humdrum reality of existence, except that mythology can get out of hand. The opening of the inquest yesterday into the death of Diana, Princess of Wales, and Dodi Fayed suggests that a conspiracy theory can escalate into something far more sinister than speculation, and may, if not controlled, destroy reputations and even lives. It seems almost beyond credibility that allegations of conspiracies to murder, of royal plots and state cover-ups are being considered by a formal legal process that will continue for weeks and cost millions.

The facts have been gone over often enough to dispose of the wilder rumours, and no one, except Mohamed Al Fayed and possibly the Daily Express, seriously believes them. They have, however, been given sustenance by a nation, a readership, and now, it seems, a judicial process that demands that they be disinterred yet again, whatever the pain and anguish to those most directly affected by them – Diana’s sons, their family and her former husband. Whatever the conclusion will be, we are all too aware that those who are determined to pursue the vendetta will not accept it.

We should by now be sufficiently mature as a society to dispose of this kind of lunacy. Yet, if anything, our appetite for the fantastical is growing. The Lockerbie bombing now has a serious following that suggests that the explosion was part of a CIA plot, that evidence linking the attack on the Pan Am aircraft to Libya was falsified, manufactured and deliberately planted, with the knowledge and participation of British Intelligence and the Scottish police force.

Just at the point where there is a need for clear heads and serious investigation, the inquiry is hampered by wild and unsubstantiated rumour. There may well be strong evidence for reopening the case and for carrying out a full inquiry, but that does mean that we need to lurch into mad conspiracy theories.

The time has come to wean ourselves off this fatal addiction to mythology. We should learn to distinguish between entertainment and reality, to separate fact and fiction, and to understand that real life is more than just a video game for adolescents. In short, we should learn to grow up.

Times Recommends

• Fragility always gets my sympathy vote
• Double it and you get the real jobless total
• Has al-Megrahi paid his council tax?