I first met David Kelly with a pint in his hand. A friend of his had given me his telephone number and I arranged to meet him at the Waggon and Horses pub in his home village of Southmoor, Oxfordshire.

He was jovial and talkative, although not garrulous. There were boundaries to what he would say. Over a pub meal, he described his missions to the former Soviet Union to uncover its germ warfare programme and his cat-and-mouse games to track down the communist regime’s most dangerous weapon — smallpox.

He did not mention what I later learnt: his role with MI6 in securing the defection of one of the heads of the Soviet germ warfare programme.

When I asked him about this, Kelly shrugged: “Who knows what those James Bond chaps get up to?” But there was a twinkle in his eye and he was clearly enjoying a secret.

At the height of his influence and self-esteem, Kelly was regarded by the United Nations, the Foreign Office and the intelligence services as one of their best assets: an expert in his field, a scientist who was as careful and forensic in intelligence gathering as he was in the laboratory.

Six years later he was dead. His apparent suicide generated a host of questions that Lord Hutton’s report may, or may not, answer.

Was he a key figure in Britain’s counter-proliferation efforts or just a middle- ranking government official? Was he a deeply private man or a media pundit? An honest scientist who wanted to tell the truth about the government’s Iraq dossier or a civil servant piqued at being passed over for promotion? Did he kill himself because he was let down, or was he to blame? If there was a clue to the problems that would later beset Kelly, it was only that he was a man struggling to fulfil his many roles. Sometimes he was a consultant to the UN, sometimes a government scientist, sometimes an oracle on germ weapons to trusted journalists, sometimes an undercover man for the intelligence services.

Technically, he was a Ministry of Defence (MoD) official. He worked as scientific adviser to the arms control directorate. But for many years he was also on loan to Unscom, the UN Special Commission on Iraq.

When he went to Iraq, it was under the control of the Foreign Office. He worked closely with British intelligence, both the defence intelligence staff (DIS) and MI6.

He was an expert whose services could be called on by government departments and international organisations. He had an office in London but preferred to work from home where he kept his computer and stacks of files.

He was a troubleshooter. The role appealed to him. He kept a bag packed ready to fly off at a moment’s notice.

“Aren’t you alarmed by having to wade into a germ laboratory in some godforsaken place?” I once asked him.

“As a hero of mine once said, ‘Nothing shocks me, I’m a scientist’,” he replied.

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