A character in Charles Dickens' Bleak House burns to death without any apparent reason. Human spontaneous combustion is a belief which has been around for centuries but does it really exist?

Viewers following Andrew Davies's adaptation of Charles Dickens' Bleak House on BBC One have just seen the dreadful moment when alcoholic Krook - played sinisterly by Johnny Vegas - finds his gin warming his stomach more than usual, and suddenly bursts into flames.

As his charred remains are found, Dickens lets the awful scene unfold: "Here is a small burnt patch of flooring; here is the tinder from a little bundle of burnt paper, but not so light as usual, seeming to be steeped in something; and here is - is it the cinder of a small charred and broken log of wood sprinkled with white ashes, or is it coal? Oh, horror, he IS here!"

Dickens is unequivocal in ascribing the death to spontaneous human combustion (SHC), the alleged burning of a person's body with no identifiable source of ignition. "It is the same death eternally - inborn, inbred, engendered in the corrupted humours of the vicious body itself, and that only - Spontaneous Combustion, and none other of all the deaths that can be died," he writes.

When the story was first published, Dickens was accused of legitimising superstitious nonsense and there was a minor uproar. But the author responded by saying he had researched the subject and knew of about 30 cases. "I have no need to observe that I do not willfully or negligently mislead my readers and that before I wrote that description I took pains to investigate the subject," he wrote in the preface to the second edition.

It is thought part of his source was a collection of cases published in 1763, 90 years before Bleak House, by Frenchman Jonas Dupont.

So is spontaneous human combustion something of fact or fiction?

Modern cases have usually come about when police and fire investigators have found burned corpses but no burned furniture. Bafflement at how a body can be reduced almost to ashes, which requires temperatures of about 3,000 degrees, without any of the rest of the room being affected has driven some of the theories.

One of the most notable cases was Mary Reeser who was found in her home in 1951, reduced to a pile of ashes save her shrunken skull and her left foot which was entirely intact. Damage to the flat in Florida was small, only soot on the ceiling and walls.

The police report claimed the 67-year-old widow's dressing gown had caught fire, perhaps due to a cigarette, although no flame source or accelerant was found.

Wick effect

In 1982, SHC was offered as a cause of death at the inquest into the death of Jean Saffin, 62. Relatives said they saw her burst into flames in her north London home but coroner Dr John Burton said there was "no such thing" as SHC and recorded an open verdict.

The human body is mostly water and its only properties which burn readily are fat tissue and methane gas, so the possibilities of SHC appear remote. But supporters of the theory have offered alcoholism, divine intervention, obesity and static electricity as explanations.

In 1998 the BBC programme QED investigated and used a dead pig to try and present a scientific explanation called the "wick effect".

The clothes are the wick and the fat surrounding a person is the fuel source which burns slowly, like a candle, for five to 10 hours.

This theory can account for the state of the remains but it does not explain the absence of any initial flame or accelerant, both of which were required for the experiment on the pig. To compound the mystery, many of the victims in the alleged cases did not try and escape and remained seated throughout.

But Home Office pathologist Professor Michael Green thought the SHC theory had been debunked.

"The way the body burns - the so-called wick effect - seems to me and to my colleagues to be the most scientifically credible hypothesis," he said.