It is the cruellest irony that the first human casualty of the altercation between the press office at Number 10 Downing Street and the BBC should be the man closest to the facts on Iraq’s biological warfare capability. It is now clear that David Kelly, a senior adviser to the Ministry of Defence Director of Counter Proliferation and Arms Control, took his own life in woodland not far from his Oxfordshire home. This followed an appearance before the Parliamentary Foreign Affairs Committee three days earlier, when at least one member chose to try to humiliate him.

Kelly led the first team of United Nations biological weapons investigators to Iraq in 1991, following the end of the first Gulf War and Saddam Hussein’s acceptance under the terms of the ceasefire that he must relinquish all nuclear, biological and chemical weapons and their means of production.

David Kelly brought a formidable expertise to his work in Iraq. From 1991 to 1994 he conducted the inspections which formed part of the trilateral American, British and Russian Agreement into the Russian biological warfare facilities. Here he impressed his fellow inspectors not only by his knowledge and persistence, but by his willingness to share his expertise with others. There was nothing of the scientific prima donna about Kelly; quite the reverse, he was modestly instructive and regarded his expertise as a resource for all to use.

Together with Lieutenant-Colonel Hamish Killip, of the Royal Engineers, and the American Dr Dick Spertzel, in 1995 he was responsible for exploiting intelligence brought to him by a Canadian colleague in New York on the shipment by British and German companies of more than 30 tons of bacteria growth medium to Iraq. A detective-style operation ensued and the companies were traced. More significantly, the direction of Iraq’s biological programme was discerned.

His prior knowledge from intelligence sources of Iraq’s possession of anthrax and botulinus toxin pointed to the urgent need for a visit to the site of a research programme at Salman Pak, which had been severely damaged by Allied bombing. His persistence in examining the site led to the discovery of an undamaged bunker concealed by fresh earth. Excavation of this and the damaged bunkers resulted in the conclusion that any one of the fermenting vats could produce enough anthrax to fill the warheads of several Scud surface-to-surface missiles.

Six weeks later, an incinerator attached to an animal enclosure at a supposed baby-food factory at Al Hakam, 30 miles southwest of Baghdad, and an air-filtration system to provide a high degree of air purity aroused Kelly’s suspicions. Further examination of this site resulted in the conclusion that Al Hakam was the principal facility in Iraq’s biological weapons programme. This and other research and production sites were destroyed or put out of action but Kelly became increasingly convinced that the inspections which followed the first Gulf War were being frustrated by the very Iraqi officials appointed to help to disprove the accusation that their country possessed any biological weapons. Saddam continued to deny the existence of any such weapons until 1995, when one of his sons-in-law defected with proof of their existence.

Until the UN weapons inspection team Unscom left Iraq in 1998, Kelly and his fellow inspectors persisted in their search, despite the mounting obstruction from Iraqi officials and, it has to be said, indications of diminishing enthusiasm for their search in some offices of the UN in New York. In all, he made 37 visits to Iraq. Although in September 1997 Iraq offered a “full and complete declaration of its biological warfare work”, Kelly and his colleagues remained convinced that the same officials were deliberately obstructing their work and that Saddam retained at least some potential for biological warfare. The respect earned from his Unscom colleagues was immense and it is significant that he was singled out by Saddam for expulsion when Unscom left Iraq.

The mild and invariably considerate manner of Kelly’s interaction with his colleagues was also often effective in his interviewing of those Iraqis believed to be involved in the biological weapons programme. But he could show an altogether different side of his character. Dr Rihab Taha, subsequently proved head of Saddam’s germ-production programme, would counter his questioning by shouting at him, then burst into tears. He was entirely emotionless in these circumstances, waiting until Dr Taha had calmed down, had gathered herself and then he would begin his meticulously forensic questioning of her again.

When not in Iraq, Kelly worked closely with the intelligence agencies in London, interviewing Iraqi defectors and debriefing British officials returning from the country. As far back as 1989, he had assisted in the debriefing of Vladimir Pasechinik, the Soviet biochemist, when he defected to the West. This work and that at the UN brought him into frequent contact with journalists, who learnt to respect his scientifically precise answers to their questioning and dispassionate analysis of what he knew and what he suspected. He had the gift of being able to explain a complex issue in simple language, something priceless to any journalist. This easy familiarity with the news media resulted in his meeting the BBC reporter Andrew Gilligan on May 22.

In the period immediately before the second Gulf War, Kelly assessed that there was “a 30 per cent chance” that Iraq possessed biological weapons. As events turned out, the basis for such a relatively precise opinion is less significant than the fact that he made it and expressed it frequently, because he came to believe that it would result in his identification as a “source” for Gilligan’s story to the BBC’s Today programme on May 29.

More importantly from the Iraqi biological warfare capability point of view, Kelly told MPs last week that it would be very difficult for Iraq to deploy such weapons in 45 minutes, suggesting that there might have been confusion over what was meant by the word deployment. This could only have come from an individual. Although human intelligence can be extremely valuable, because it allows other intelligence-gathering facilities such as satellite and electronic intelligence to be focused to verify or refute the story, as a stand-alone source it will invariably lie under the shadow of possible personal bias or motive. He was not isolated among weapon inspectors and intelligence officials in doubting the 45-minute claim from what they knew of the situation in Iraq in the autumn of last year. This doubt was discussed openly among them, as it was by individuals countrywide who had knowledge of weapon systems.

When the search for Gilligan’s source became a national issue, Kelly took the initiative and informed his superiors in the Ministry of Defence that he might be the source and reported the gist of his conversation with the journalist. This led to his appearance before the Parliamentary Foreign Affairs Select Committee on July 15 when, after some vigorous questioning, one member — Andrew Mackinlay, MP (Labour, Thurrock) — said: “I reckon you are chaff (metal strips dropped by aircraft to confuse radar beams). You have been thrown up to divert our probing. You have been set up, have you not?” Kelly replied, so quietly that he had to be asked to repeat his remark, “That is not a question I can answer.”

When asked whether he believed that the Government’s September dossier had been transformed by Alastair Campbell, the Prime Minister’s Director of Communications, Kelly replied: “I do not believe that at all.” It could be that it was reflection on this disingenuous response he gave to the committee that caused him to be, in his wife’s words, “very upset by what had occurred on the committee and very angry”.