The BBC has disclosed that Dr David Kelly was the principal source for Andrew Gilligan's report claiming Downing Street "sexed up" an Iraq weapons dossier.
Gilligan joined the BBC in 1999
Mr Gilligan is the defence and diplomatic correspondent for BBC Radio 4's Today programme.
Born in Teddington in 1968, he attended a south-west London comprehensive school before studying history at Cambridge University.
After working as a reporter with the Cambridge Evening News from 1994 to 1995, Gilligan moved to
Fleet Street as a freelancer.
He soon secured a job on the foreign news desk of the Sunday Telegraph, and later became the newspaper's defence correspondent.
In 1999 Mr Gilligan was taken on by Today's then-editor, Rod Liddle.
Since then he has reported from about 40 countries - most recently Pakistan and Afghanistan.
Reporting for Today, Gilligan went undercover to buy anti-personnel landmines in contravention of the 1998 Landmines Act and exposed the relative ease with which it was possible to register postal votes on behalf of dead people.
He also obtained a series of damning leaked official reports about Britain's performance in the Kosovo war.
And the reporter broke the story of a £1bn RAF combat jet that could not drop precision bombs.
Campbell denied Gilligan vendetta
In November 2000 Mr Gilligan was the first British journalist to report on plans for the draft European Union constitution.
Downing Street responded by saying the story was old and dubbing the reporter "gullible Gilligan".
When government communications director Alastair Campbell complained about Mr Gilligan's Iraq weapons dossier report, BBC's director of news Richard Sambrook accused the Downing Street press chief of waging a "personal vendetta" against Gilligan, "whose reports on a number of occasions have caused you discomfort".
Mr Campbell denied any personal agenda against Mr Gilligan - a man he said he had never met.