Senior sources say he was asked to make an assessment of weapon-making material and equipment the Iraqi regime could have been hiding, for the Joint Intelligence Committee.
It also emerged that the scientist, who killed himself last week, was used by MI6 to interrogate Iraqi defectors claiming to have information on Saddam Hussein's alleged weapons of mass destruction.
Hoon and Alastair Campbell, the Prime Minister's director of communications, have been accused of responsibility for Kelly's identity being disclosed to the media, after he was promised anonymity by the Ministry of Defence. According to Whitehall sources, Janice Kelly had asked the Defence Secretary to explain how his name was released to the newspapers.
During yesterday's visit, Hoon is reported to have expressed his sorrow over her husband's death. Four days earlier he had declared that he had nothing to apologise for.
Hoon, sombre-faced, left the house near Abingdon, in Oxfordshire, after an hour and 17 minutes.
David Kelly was the main source for allegations by the BBC that No 10 had "sexed up" last September's dossier on Iraq's alleged weapons of mass destruction.
The Government had consistently sought to downplay Kelly's position and his role over the dossier. The Prime Minister's official spokesman had described him as a "technical expert on machinery and equipment ... He was not someone who had access to the intelligence which was included in the dossier".
After the invasion, the Government assigned him to the Iraq survey group, set up by the US and Britain to find Saddam's alleged arsenal.
One of the reasons for this secondment was his vast experience of Iraq. He had led the first team of UN biological weapons inspectors to Iraq after the first Gulf War and visited the country 37 times. He also interrogated a number of Iraqi scientists including Dr Rihab Taha - known as "Dr Germ" - the head of Saddam's biological weapons programme.
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British Parliament Foreign Affairs Committee transcript:
Evidence of Dr David Kelly
Key players in the 'sexed-up dossier' affair
Herald Feature: Iraq
Iraq links and resources