The 59-year-old civil servant is an expert in arms control

In the last week the civil servant more used to working behind the scenes has become a key figure in the row between the government and the BBC over claims Downing Street "sexed up" a dossier on Iraq's weapons capability.

The scientist was named publicly by the government as a contact who, it believed, briefed BBC defence correspondent Andrew Gilligan about the Iraqi weapons programme.

Three days ago the 59-year-old told the foreign affairs select committee he did not believe he was the story's source although he had come forward to tell his managers he had met Mr Gilligan.

The Oxford-educated microbiologist has been scientific adviser to the proliferation and arms control secretariat for more than three years.

Iraq weapons inspections

He is an expert in arms control having worked as a weapons inspector in Iraq following the first Gulf War between 1991 and 1998.

Dr Kelly became senior adviser on biological warfare for the UN in Iraq in 1994, holding the post until 1999.

During a lecture he once said: "When Iraq invaded Kuwait in August 1990, little did I realise that Saddam Hussein would dictate the next 10 years of my life."

He also led all the visits and inspections of Russian biological warfare facilities from 1991 to 1994 under the 1992 Trilateral Agreement between the US, UK and Russia.

Garth Whitty, a former colleague of Dr Kelly who worked with him as a UN weapons inspector in Iraq, told the BBC the scientist was "internationally regarded" as an expert in biological weapons defence who normally coped well under pressure.

"He is a quiet man who gets on with his job. He does it with the highest professional standards," he said.

Rising through ranks

Dr Kelly is married and with his wife, Janice, has Sian, 32, and twins Rachel and Ellen, 30. Neighbours described them as a "lovely family".

Dr Kelly came from a background in agricultural science.

He was chief science officer at Britain's Natural Environment Research Council Institute of Virology.

He rose through the ranks at the Ministry of Defence's chemical research centre at Porton Down in Wiltshire to become head of microbiology.

David Kelly left his home on Thursday afternoon

Part of his job is to brief journalists on defence issues.

But the past week has seen him at the centre of press attention.

The expert told the select committee he could not even get into his Oxfordshire home because of the press outside.

BBC political correspondent Vicky Young said Dr Kelly, who is civil servant not a public figure, had been under pressure.

"He was the kind of man who would have been mortified that he might have inadvertently contributed to this story.

"He is not used to being thrust in the public glare."

Softly spoken

But Donald Anderson, chairman of the foreign affairs select committee, told BBC News 24 Dr Kelly seemed relaxed when he gave evidence as he rejected suggestions he have someone sit beside him to give him confidence.

As he gave evidence, members asked him three times to speak louder and fans had to be turned off to help him be heard as he admitted he was "softly spoken".

But his message was clear - he told MPs he did not believe he was the main source of Mr Gilligan's story.

And MPs agreed with him with some claiming he had been made a "fall guy".

Conservative MP John Maples, also a member of the select committee, said: "I don't think he is someone used to being thrust into the limelight."

But he said the scientist should have been reassured by the fact members were convinced he was not Mr Gilligan's main source.

Dr Kelly previously gave evidence to the Commons foreign affairs committee last September with Foreign Secretary Jack Straw.