Mark Purdey

On paper Mark Purdey was a Somerset dairy farmer, but he will be remembered for his long-running campaign to prove that "mad cow" disease was linked, and indeed caused by, the use of the organophosphate pesticide Phosmet, used to treat skin parasites on domestic livestock. The theory was as unconventional as Purdey himself.

The tall, unkempt Purdey saw himself as a scientific sleuth, an eco-warrior fighting against the power and dirty tricks of "the Establishment" , an unholy alliance of the agrochemical business, the academics in their pay and the government officials whose job it was to cover-up ministerial blunders.

He called himself an "underground scientist" and "heretic", and his one-man campaign was eagerly taken up by the media, obsessed as they are with the power of personality over factual credibility. Indeed, it was not just the media who lionised Purdey. He also became an unlikely hero of the likes of Ted Hughes, the Prince of Wales, Michael Meacher and Lord King of Bridgwater, the former defence secretary who once described Purdey's work as a "classic piece of scientific investigation".

In truth, Purdey was the antithesis of a classically trained scientist. He was self-taught and, although impressive in his knowledge, he often lacked the attention to detail that a science degree or two might have inculcated in his methodology. The fact of the matter is that Purdey's theory did not withstand the test of time nor of scientific enquiry - something that he could not bring himself to admit. He died of a brain tumour on Remembrance Sunday.

Mark Purdey was born on Christmas Day 1953 in the Hertfordshire village of Much Hadham. He belonged to the Purdey shotgun family, which includes a long line of somewhat eccentric thinkers. His ancestor James Purdey walked from Inverness to London to set up the shotgun business, and his grandfather Lionel campaigned to get Lord Kitchener to acknowledge that shell shock was a real illness.

As a child Purdey took up birdwatching and one of his earliest memories was seeing a blackbird quiver and die after a wheat-field had been sprayed from the air. It left a haunting impression that evidently led to his interest in agricultural pesticides. He was sent to Haileybury but was expelled after breaking out at night to visit some girlfriends - an early sign, perhaps, of his growing disrespect of authority.

In 1984, now a dairy farmer in the Brendon Hills in Somerset, Purdey challenged the Ministry of Agriculture's insistence on the use of organophosphates on his cattle to eradicate warble fly. The challenge went as far as a High Court battle, which he won, making him front-page news and a household name, at least in farmhouses up and down the country.

Towards the end of the 1980s Purdey became interested in the growing problem of bovine spongiform encephalopathy (BSE). He postulated that the use of organophosphate pesticides - which were poured on the backs of animals - could be causing the nervous condition.

The vociferous anti-pesticide lobby of the green movement took up the case with gusto, as did some leading organic commentators in the media, John Humphrys being one influential supporter. Unfortunately as more and more scientific evidence emerged - either through laboratory experiments or number-crunching epidemiology - Purdey's hypothesis began to look increasingly implausible.

In response to the media campaign that grew up behind him, the Medical Research Council undertook experiments in 1995 to test Purdey's theory. But the results did not support his hypothesis. The study was subsequently rejected by Purdey, who claimed that the MRC scientists had used the wrong chemical formulation.

However, it became increasingly clear that contaminated meat-and-bonemeal feed, rather than pesticides, was behind the BSE epidemic. When the Government took the first measures to stop contaminated feed being eaten by cattle, the effects soon became apparent in the form of a significant decline in the number of outbreaks.

Purdey started to modify his theory and invoked the idea of a complex interaction between ultraviolet radiation, minerals in the soil of pastures and pesticide use. His research took him as far afield as Iceland, Colorado, Japan and Australia. He had little money and often slept rough, forming unlikely companionships with a Hell's Angel, an Aboriginal elder and a Slovak au pair girl.

He won limited support for the idea by a few mainstream scientists who took some interest in the role of copper and manganese minerals in affecting the prion protein, believed to be the causative agent behind BSE and human CJD. But no knowledgeable researcher in the field believed for one moment that the Purdey hypothesis could explain the spread of BSE in Britain.

The BSE Inquiry (1998-2000) led by Lord Phillips of Worth Matravers took evidence from Purdey but dismissed his hypothesis, arguing that it was both unlikely and unconvincing. Needless to say Purdey came back fighting but he reserved his greatest wrath for a subsequent committee of six experts led by Professor Gabriel Horn of Cambridge University, who was charged by the Government to answer perhaps the most important question of all - why did Britain suffer from BSE in the first place?

It was of course the question that Purdey was trying to answer all along. We know now what spread the disease - contaminated feed. But what actually triggered the start of the epidemic in the first cow to be infected?

The Horn Committee came to the conclusion that it was caused by feeding sheep remains infected with scrapie disease to very young calves. Yet again the Purdey hypothesis had been considered and dismissed by experts.

Like Don Quixote tilting at windmills, Purdey railed against the "bogus" and "libellous" findings of the "biased" Horn report. He claimed yet again that he was a victim of establishment deceit and intrigue. Yet the simple fact is that Mark Purdey had an interesting scientific hypothesis that was tested and found to be wanting - like many scientific hypotheses. There was no shame in being wrong, but it was a shame that he could not bring himself to admit it.

Steve Connor

The reason my brother Mark Purdey did not accept either of the main BSE hypotheses, writes Nigel Purdey, was because they do not demonstrate Koch's postulates, despite millions of pounds' worth of research conducted over 20 years. If someone had conducted an experiment in which meat and bone meal (MBM) fed to cattle produced BSE then this would have satisfied him. The 10-year government experiment in which MBM was fed to cattle produced no cases of BSE.

BSE brain homogenate inoculated or fed neat to cattle can produce BSE, although scrapie homogenate failed in this respect. But in "life" cattle were not exposed to homogenate in this way - they ate MBM. Science must be precise and this research in no way proves the MBM theories.

An early inspiration for my brother was the work of I.H. Pattison, who found that a copper-chelating chemical, cuprizone, created a spongiform encephalopathy (SE) in animals, without the requirement of any infectious agent. This type of encephalopathy turned out to be non-transmissible. But it begged the question, if there was a substitution by another metal or metal microcrystal (through an environmental exposure), at the vacated copper sites on the prion protein you might get an SE that was transmissible - as in BSE, CJD. This Mark considered was the primary cause of this class of diseases and it was this that he was still researching when he became ill.

Mark never considered he had all the answers but he felt that, with perhaps another five years' work, he could have located the final pieces of the jigsaw and proved his theory.