GONE UP IN SMOKE; Why scientists don't believe in spontaneous combustion.

IT HAS featured on The X Files and in great English literature.

Over the last 400 years some 200 cases have been reported - more from Britain than anywhere else.

But now the theory of spontaneous combustion - the sudden and unexplained self-ignition of the human body - has been shot down in flames.

Scientists will tell an international conference in Edinburgh that it's all... well, a lot of hot air.

Victims of the phenomenon are said to have died appalling deaths - burnt alive, wreathed in a mysterious blue flame.

Often the skeleton is completely destroyed, yet bedding, chairs and carpets close by remain totally unscathed.

Bizarre explanations have included lightning, vampires, psychic suicide, magnetic storms, even the wrath of God.

The truth, insist biologist David Pescod and Mark Benecke, a forensic scientist at the office of the chief medical examiner in New York, is far more down to earth.

They will tell fellow scientists that their studies of documented cases reveal the deaths invariably involved a carelessly discarded cigarette or flammable clothing.

David Pescod says: "I've not yet found one scrap of evidence that the body self-ignites."

Typical of a case they examined was that, 12 years ago, of a man allegedly consumed by fire as he lay on his bed. "All that was left," says David, "was his skull and bits of his rib cage."

The man was a heavy drinker and smoker and kept an oxygen cylinder by his bed, which was switched on. Evidence showed he had lit a cigarette before the fire, which would have burned furiously in the highly inflammable oxygen.

Most victims, the pair say, have been elderly people who died of heart attacks and then fell on to an open fire.

Their research, however, is unlikely to convince followers of the paranormal. Newspapers worldwide regularly report the phenomenon - although no coroner in this country has been sufficiently convinced to record it as the cause of death.

U.S. scientist Larry E. Arnold has mapped sites of unusual fires across the UK and says that more than 80 per cent are connected by straight lines.

"If you are in the wrong place at the wrong time, you, your dog, your car or your home, would seem more likely to spontaneously combust."

The director of ParaScience International in Pennsylvania points to Birmingham as the hot spot in the Seventies, Wales in the Eighties, and London or Lincolnshire next in line.

British cases include:

Henry Thomas, who burnt to ash at his home in 1980. John Heymer, 62, then a special constable, spoke of "stepping into Dante's Inferno".

"A couple of feet from the settee was this pile of ashes. Next to it there were two human feet, clothed in socks, with a short length of trouser bottoms, perfectly intact," he said. Yet the room was scarcely singed.

Jeannie Saffin, a 61-year-old woman brain-damaged since birth. Relatives in Edmonton, North London, claim to have watched her spontaneously combust.

Jeannie's brother-in-law Don Carroll said: "I went into the kitchen and she had blue flames coming from her mouth and her midriff.

"She was roaring like a dragon. The kitchen wasn't damaged, but her cardigan melted. The inquest was never sorted out, but I know what I saw."

Sue Mottershead, of Oldham, Lancashire, was standing in her kitchen in 1980, wearing towelling pyjamas, when, she says, she was engulfed by dancing flames.

Mrs Mottershead, 47, insisted there were no electrical appliances on. She recalled "a whoosh and blue and orange flames".

"I ripped off my pyjamas and they disappeared instantly."

Debbie Clarke, 34, a divorced mother-of-two from Sawbridgeworth, Hertfordshire, had a similar unnerving experience.

She was 19, and walking barefoot in the drive of her home in a waitress's cotton blouse, black skirt and white apron.

Debbie recalls: "`I saw a flash, then another. My dad came out and said, '`It's you! You're actually lighting up'."

Her mother, Diane, says: "`It was terrifying. Every step she took she was like a walking beacon."

The body of John O'Connor, 76, was found in 1996 in a burnt chair in a hardly damaged room in Gortaleen, Co Kerry.

"It looked as if somebody had poured petrol into Jackie's lap," said the local priest, Father Patrick McCarthy. "From the knees down, the bones were intact."

A telephone and a community alert device were within reach, suggesting that the fire overwhelmed Mr O'Connor with great speed, or that he was already dead when it started.

A blaze at a thatched cottage in Puddledock, Norfolk, also remained unexplained until an insurance man noticed a rat scurrying beside a stream nearby.

A rat, he suggested, might have eaten phosphorous poison, climbed into the roof thatch to die, and as it decomposed, the highly inflammable phosphorous spontaneously combusted.

No one has yet got to the bottom of the mystery of Mel Thompson's Marks & Spencer knickers.

In 1996, the 25-year-old checkout girl was working at the Co-op in Hindley, Wigan, when, she says, her briefs spontaneously combusted.

In the loo, she peeled away the smouldering underwear to find a 3in burn mark on her behind.

M&S insisted that the pounds 6.50 cotton, nylon and Lycra briefs were safe.

"We have sold 156,000 pairs," a spokesman said, "and this is the only report of them disintegrating. We believe they must have come into contact with acid."

Ms Thompson had only one thing to say to that.

Knickers.