EARLY one fine summer morning, a taxi pulled up outside a neat suburban terrace house in Aberdeen and took a 68-year-old scientist to a TV studio. Shortly afterwards Dr Arpad Pustzai found himself propelled from a life of grateful obscurity into the centre of an astonishing political maelstrom that would cost him his job, his reputation and his health. His crime was to question the safety of genetically modified food. His interview on ITV's World In Action lasted just 150 seconds, but that was long enough to reveal his ground-breaking research suggesting rats fed genetically modified potatoes suffered stunted growth and damage to their immune systems.

It triggered a controversy that put him on a collision course with the Government, the biotech industry and the scientific establishment. The diminutive Hungarian-born scientist, who had escaped the terrors of Stalinism to enjoy a brilliant 35-year academic career, became a reviled figure: ostracised by colleagues, villified, and gagged. Now, five years on, there are disturbing claims that this distinguished scientist was the victim of behind-the-scenes manoeuvring at the highest political level. Some of the allegations are truly explosive. They raise profound questions about the extraordinary network of relationships between senior Labour figures and the biotech companies. They also throw new light on why the multi-billion-pound GM industry continues to press ahead in the face of huge public opposition.

The World In Action documentary was broadcast on Monday, August 10, 1998. It was a little over a year since Tony Blair had swept into Downing Street. His government was in thrall to the biotech industry, convinced it could become a driving force of the British economy. What Dr Pusztai was saying threatened to derail those ambitions. he was based at the Rowett Institute in Aberdeen, which conducts research into animal nutrition. He had published more than 270 scientific studies and three books on lectins, plant proteins that are central to the GM controversy. He was the world's leading expert on the subject.

In the TV interview, he said he believed GM food could be made safe, but added: 'If I had the choice I would certainly not eat it. He demanded tighter rules over GM foods, and warned: 'I find it's very unfair to use our fellow citizens as guinea pigs. We have to find guinea pigs in the laboratory.'

On the evening the programme went out, the Rowett Institute's director Professor Philip James congratulated Dr Pusztai on his appearance, commenting how well he had handled the questions. The following morning a press release from the Institute ave him further support, stressing that a 'range of carefully controlled studies underlie the basis of Dr Pusztai's concerns'. Yet within 48 hours, everything had changed. Dr Pusztai had been suspended by the Institute and ordered to hand over all his data.

His research team was dispersed and he was threatened with legal action if he spoke to anyone. His phone calls and e-mails were diverted; his personal assistant was banned from speaking to him. He read in a press release issued by the Institute that his contract would not be renewed. What triggered such an extraordinary about-face? How did a respected scientist become a pariah overnight?

The results he claimed to have found were certainly worrying. Dr Pusztai maintained that when rats were fed a certain kind of GM potato - adapted to produce natural insecticide - their livers, hearts and other organs got smaller. He also found that the size of their brains was affected, but did not dare publicise this fact because he was thought to be alarmist. Clearly, such findings were deeply threatening for the GM industry. In Orwellian fashion, the Rowett Institute gave a number of conflicting reasons for suddenly disowning them.

First, it claimed Dr Pusztai had simply got confused, muddling up the results for two different batches of potatoes. According to this explanation, the worrying results came from a 'control' sample of potatoes containing a substance known to be poisonous. This was an utterly astonishing claim - a basic error worthy of a bumbling schoolboy. Newspapers rightly described it as one of the most embarrassing blunders ever admitted by a major scientific institution. The trouble was, it wasn't true. Whatever the merits of his results, Dr pusztai hadn't mixed them up, as a subsequent audit of his work confirmed. One of his colleagues, leading pathologist Stanley Ewen said: 'Arpad has always had a clear vision. He is certainly never muddled. He was on top of the whole business.'

When it became clear the claim was baseless, the Institute shifted its ground. First, it said that Dr Pusztai had not carried out the long-term tests needed to prove his findings. Then it said he had carried out the tests but the results weren't ready. Again, this simply wasn't so.

Later, when his reputation was in tatters and his research thoroughly discredited, the Institute accepted that Dr Pusztai had acted in good faith and described him as 'an intense investigative scientist with an international reputation'. But by then he was a ruined man who had suffered two heart attacks. His wife, who was sacked with him, was on permanent medication for high blood pressure. Dr Pusztai has come to believe there is only one plausible explanation for his downfall - political pressure from a government in fear of his findings. Breaking his long silence over the affair, he now claims that he was fired as a direct consequence of Tony Blair's intervention. The day after his World In Action broadcast, he believes that two phone calls were put through to his boss, Philip James, from the Prime Minister's office in Downing Street.

The following day he was fired. He says he was informed of the calls by two different employees at the Rowett. Dr Putsztai and his wife were also told by a senior manager at the institute that Blair's intervention followed a phone call to Downing Street from President Bill Clinton, whose administration was spending billions backing the GM food industry. To sceptical ears, this sounds scarcely credible. Would the Prime Minister really have had any influence over the position of a respected scientist?

And yet the story is supported by two other eminent researchers. Stanley Ewen, says another senior figure at the institute told him the same story at a dinner on September 24, 1999. 'That conversation is sealed in my mind,' Ewen says. 'My jaw dropped to the floor. I suddenly saw it all - it was the missing link. 'Until then, I couldn't understand how on Monday Arpad had made the most wonderful breakthrough, and on Tuesday it was the most dreadful piece of work and immediately rejected out of hand.' The second source to confirm the story is Professor Robert Orskov OBE, who worked at the Rowett for 33 years and is one of Britain's leading nutrition experts. He was told that phone calls went from Monsanto, the American firm which produces 90% of the world's GM food, to Clinton and then to Blair. 'Clinton rang Blair and Blair rang James,' says Professor Orskov. 'There is no doubt he was pushed by Blair to do something. It was damaging the relationship between the USA and the UK, because it was going to be a huge blow for Monsanto.'

It is no secret that Blair was first persuaded to support GM by Clinton, and that the President exerted great pressure on his European allies to promote the new technology. ut would Professor James, who had run the Rowett Institute since 1982 and was one of the world's most respected nutritionists, have sacrificed his own man?

At the time, he undoubtedly enjoyed good relations with Tony Blair. While Labour was in opposition, he had been chosen to set up the blueprint for a new Food Standards Agency. The storm over Dr Pusztai's findings was to cost him a job as the agency's first head. 'You destroyed me,' he later told Dr Pusztai. Professor James vehemently denies acting on orders from the Premier, saying: 'There's no way I talked to anybody in any circumstances. It's a pack of lies. I have never talked to Blair since the opening of Parliament in 1997.'

Downing Street is equally dismissive of the claims. "This is total rubbish," said a spokesman. Dr Pusztai, however, remains convinced he was punished for following his conscience. 'I obviously spoke out at a very sensitive time. Things were coming to a head with the GM debate and I just lit the fuse.

'I grew up under the Nazis and the Communists and I understand that people are frightened and not willing to jeopardise their future, but they just sold me down the river.' Among the most instructive aspects of the affair is the way ministers leapt on criticism of his work and sought to undermine his reputation. In May 1999, by what seems an impossibly neat coincidence, reports attacking him were published on the very same day by the Royal Society - the voice of the scientific establishment - and the science and technology select committee of the House of Commons.

Jack Cunningham, the Government's so-called Cabinet Enforcer, then poured scorn on Dr Pusztai's 'wholly misleading results' and to promise that all GM food on sale in Britain was safe to eat. It smacked of a co-ordinated counter-attack, and that is precisely what it was. A Government memo reveals that Cunningham and other senior ministers had set up a 'Biotechnology Presentation Group' Then, as now, relationships between senior Labour figures and the GM food companies bordered on the incestuous. In Labour's first two years in office, GM companies met government officials and ministers 81 times.

The Blair government sees the biotech industry as a new scientific frontier, an industry worth GBP75 billion in Europe alone by 2005. Science minister Lord Sainsbury is a dedicated GM supporter, though he does not officially deal with GM food matters. On being appointed to his post, Lord Sainsbury held large share holdings in two biotech companies, Diatech and Innotech; subsequently they were put in a blind trust. He is also New Labour's largest single donor, having given the party more than GBP8 million since it first came into power.

The irony of Sainsbury being in charge of a pro-GM science policy was highlighted when it emerged he had made a GBP20m paper profit in just four years through his investment in Innotech. There are links too between Labour and the biotech industry's spin-doctors. Monsanto's PR company in the UK is Good Relations, whose director David Hill ran Labour's media operations for the 1997 and 2001 general elections.

In such an environment, it is scarcely surprising if dissidents like Dr Pusztai find themselves pushed to the fringes and turned into scapegoats. The oddest twist of all came in May 1999, when Dr Pusztai and his wife went abroad for a few days to escape the controversy surrounding them. On their return they discovered there had been a break-in at their house in Aberdeen. The only things taken were some bottles of malt whisky, a bit of foreign currency - and the bags containing all their research data.

This was followed by another break-in at the Rowett Institute at the end of the year. Only Dr Pusztai's old lab that was broken into. He remains baffled about who was behind the raids, and why he was targeted. But he continues to defend his controversial findings. 'They picked the wrong guy,' he says simply. 'I will kick the bucket before I give up.'

*Don't Worry (It's Safe to Eat) by Andrew Rowell is published by Earthscan on July 10 (£16.99).