Desperate times call for desperate measures, and it's hard not to have sympathy for the Chilean government, which recently called in a medium to help find the missing victims of a recent air crash off Robinson Crusoe Island in the Pacific.

When sceptical eyebrows were raised, Chile's Defence Minister, Andrés Allamand, argued that even the strangest, most unorthodox, means would justify the end of satisfying grieving families that everything that could be done was being done.

'Not only are we using all of our technological capabilities,' he said, 'but also all the human and superhuman abilities that may exist'.

While it's not clear how much faith the minister himself places in 'superhuman abilities', the Chilean authorities are not the first to enlist the help of 'psychics', nor will they surely be the last. Since the end of the 20th century, when it looked as though Jack the Ripper was outwitting the London police, investigators claiming paranormal powers of detection have attached themselves to virtually every long-running case.

But involvement has dangers for both parties. Police often complain that following up the 'clues' provided by these forensic seers is a waste of time, while a psychic who seems to know too much can come under suspicion.

Such was the fate of James Lees, a spiritualist, who claimed to have seen forthcoming Ripper killings in a series of visions. He should have stopped there. Unwisely, however, he badgered a passing policeman to arrest Britain's Most Wanted Serial Killer when he 'recognised' him stepping on to an omnibus in Shepherd's Bush. The 'Ripper' made himself scarce, but Lees came under suspicion, partly because his wife proved unable to provide him with an alibi for the times when the Whitechapel murders were committed, and partly because he appeared to know a disconcerting amount about the crimes.

More recently, a woman in California found herself in a similar situation after guiding police to a body. She was soon cleared of any complicity, although detectives did not seem to acknowledge that any psychic insights were involved. As for poor Lees, he was committed to a lunatic asylum.

Other notorious interventions came when the hunt for the polar explorer, Sir John Franklin, who went missing in the Arctic in the 1840s, seemed to be flagging. A woman known as the 'Boston clairvoyante' assured Lady Franklin that, even though 40 years had passed, Sir John was alive and 'comparatively well'. She was totally upstaged, however, by the alleged appearance, in a 'bluish ball of light', of a dead toddler called 'Little Weesy'. Her real name was Louisa Coppin, and her father claimed she lingered long enough after her mysterious return to scribble details of Franklin's whereabouts on the wall of her former home. Nothing came of Weesy's words, of course - and the search is still 'live' after 160 years - but she did achieve the curious distinction of an entry in the latest edition of the 'Dictionary of National Biography': not bad for someone who lived for only 4 years.

But this is the only - and very indirect - success story that I have come across in more than 30 years of watching the psychic detectives for the 'Mysterious World' tv programmes and now for their 21st century successor r2mw.com.

One problem is that psychics often get by with the vaguest of pronouncements. For example, when crime writer Agatha Christie went missing in 1926, another Sir Arthur, Conan Doyle, drew upon his spiritualist contacts and produced a psychic who announced that Miss Christie was alive and would turn up soon. She duly did, but the case was not solved by the 'seer's' foggy wishful thinking.

Nor did a rigorous scientific test that we organised with Professor Richard Wiseman of the University of Hertfordshire do anything to enhance respect for paranormal crime-fighting. 3 psychics and 3 students who claimed no paranormal powers were asked to match objects used in past crimes to the cases themselves. Neither group scored above the level of chance, nor did the psychics do any better than the non-psychics.

No wonder the police today prefer to reach conclusions by using the many precise and reliable forensic techniques available, and are even more sceptical than they used to be of the scenarios painted by amateurs who claim a 'gift', however well-meaning and eager to help they undoubtedly are.

So here's another challenge to psychics. If, and when, you can prove you have solved a crime by paranormal powers alone, I will be the first to propose that a place is reserved for you in the DNB, alongside the only apparently clairvoyant Miss Weesy Coppin.