David Kelly, dismissed by Downing Street as just a "middle-ranking technician", was considered by his peers around the world as the most senior germ warfare expert in Britain.
Rolf Ekeus, former chief of the United Nations arms inspectorate which investigated Saddam Hussein's arsenal after the 1991 Gulf war, said: "If there was a Nobel prize for arms control, Dr Kelly and his team should have been awarded it."
Richard Spertzel, who headed the four-man Unscom specialist team investigating Iraq's biological programme, described Dr Kelly yesterday as the "foremost expert on biological weapons in Britain".
He said Mr Ekeus had told the team that they deserved a Nobel prize for forcing Iraq to admit it had an offensive biological programme in July 1995 after four years of denials.
The Government had tried to play down Dr Kelly's importance to discredit him as the BBC's main source for the claim that Downing Street "sexed up" the September dossier. No 10 claimed Dr Kelly was a "technical adviser", and "he was not someone who had access to the intelligence which was in the dossier".
But Dr Kelly not only had access to intelligence on Iraq but was consulted by the Secret Intelligence Service (MI6) and the Ministry of Defence on processing such intelligence.
He was also becoming increasingly sceptical about Iraq's alleged arsenal of weapons of mass destruction in the time leading up to his death. It was Dr Kelly who exposed claims by George Bush, Tony Blair and Colin Powell that mobile biological warfare units had been found in Iraq as false.
According to colleagues he had begun to believe that the Unscom team, of which he was a part, had destroyed much of Iraqi capabilities.
Dr Kelly had an overview of an official British investigation into the vehicles. It decided the so-called "germ labs" were facilities for the production of hydrogen. The systems had been sold to Baghdad by Britain in 1987.
After the findings were passed to the Ministry of Defence and the Foreign Office, Dr Kelly also made them available to journalists he trusted.
Mr Blair had briefed journalists that the trailers were germ production labs which proved that Iraq had WMD.
The British inquiry started after the CIA expressed doubts about the "germ labs". The investigators swiftly decided the vehicles would be impractical for biological warfare.
In March last year Dr Kelly expressed his doubts about Iraq's weapons of mass destruction threat at a seminar in University College, London.