Image copyright Other Image caption An estimated 250,000 people in the UK suffer from Chronic Fatigue Syndrome

Scientists working on Chronic Fatigue Syndrome (CFS), or ME, say they are being subjected to a campaign of vicious abuse and intimidation that is hampering research into the causes of the condition.

The harassment has included death threats, vilification on internet websites, and a series of official complaints alleging both personal and professional misconduct to universities, ethical oversight committees and the General Medical Council (GMC).

"It's direct intimidation in the sense of letters, emails, occasional phone calls and threats," says Professor Simon Wessely, of King's College London, who has received a series of death threats and threatening phone calls, and now has his mail routinely scanned for suspect devices.

"But more often indirect intimidation through my employer or the GMC. All of it intended to denigrate and try and make you into a leper."

Behind the vitriolic nature of the attacks, the core objection, by some activists, is the association of Chronic Fatigue Syndrome with mental illness.

They claim the real cause is biological and want research to focus exclusively on identifying the - as yet undiscovered - virus responsible.

"Sadly some of the motivation seems to come from people who believe that any connection with psychiatry is tantamount to saying there is nothing wrong with you, go away, you're not really ill," says Dr Wessely.

"That's profoundly misguided. They fall victim to the label, and believe that the mere involvement of psychiatry denigrates them and denigrates the condition."

Chronic Fatigue Syndrome is a debilitating condition involving severe fatigue, painful muscles and joints, gastric complaints and poor memory and concentration. It is estimated there may be as many as a quarter of a million sufferers across the UK, but exactly what causes it is still a mystery.

That has been incredibly frustrating for patients who have often received short-shrift from doctors, and been branded as malingerers - the victims of "yuppy flu" - in the media. Even the existence of the condition has only recently received widespread acknowledgement by the medical establishment.

Speaking on the programme on Friday, ME Association's Dr Charles Shepherd condemned the abuse of researchers, but said sufferers had a justifiable complaint that almost no government-funded research was looking at the bio-medical aspects of the illness.

"The anger, the frustration, is the fact that all this effort, all this government-funding, has just been going to the psychological side," he said.

Hostility towards a psychiatric explanation for Chronic Fatigue Syndrome reached a peak in 2009 when research published in the journal Science appeared to show a link to the XMRV retrovirus.

But a series of follow-up studies failed to replicate the finding, unleashing another torrent of abuse - this time aimed at virologists, including Professor Myra McClure, of Imperial College, London.

"It really was quite staggeringly shocking, and this was all from patients who seemed to think that I had some vested interest in not finding this virus," she said. "I couldn't understand, and still can't to this day, what the logic of that was. Any virologist wants to find a new virus."

Chronic Fatigue Syndrome Chronic Fatigue Syndrome or ME (Myalgic Encephalopathy)is a debilitating condition involving severe fatigue, painful muscles and joints, gastric complaints and poor memory and concentration

It can leave patients bed-ridden in severe cases.

Up to a quarter of a million people suffer from the disorder in the UK.

Professor McClure says she will not be doing any further research in this area, and that may be the single most important consequence of this campaign of abuse and intimidation.

According to the Wellcome Trust's Dr Mark Walport it would be a tragedy if serious researchers are put off working on Chronic Fatigue Syndrome.

"We clearly don't yet understand exactly what's going on, and if we're going to find out it needs good scientists to work on it," he says.

"But why would any scientist work on it if they know that all they're going to receive is a torrent of abuse?"