The BBC on Wednesday night broadcast an interview with Dr David Kelly, the source of its story that the British government exaggerated Saddam Hussein's weapons capability to make a case for war.
Dr Kelly committed suicide after he was identified as the source.
In the interview, shown on Panorama programme, Dr Kelly said Saddam was an "immediate threat" and possessed weapons of mass destruction. But he said it would take "days or weeks" to fire them and the Iraqi leader would only do so if he were attacked.
Dr Kelly's hard-hitting statement was recorded in October 2002, eight months before his suicide, and contradicts Blair's subsequent statement to members of parliament that Iraq's "military planning allows for some of the WMD to be ready within 45 minutes".
Dr Kelly also said the weapons posed a real threat to neighbouring countries. "We are talking about Iran and Israel and certainly he can use those weapons against them and you don't need a vast stockpile to have a tremendous military effect."
On the other hand Saddam posed far less of a threat than he had during the first Gulf war, Dr Kelly said. "Iraq's intrinsic capability has been reduced since 1990-91."
Asked if Iraq would use its WMD, he said, "I think he would use them. Of course, what is more difficult to answer is how and under what circumstances he would use them.
"I think some people would consider that when the chips are really down, and he is fighting his last battle, that he might be prepared to use them.
"I think he would be reluctant to use them in the build-up to war -- in the transition to war -- because he knows what the response would be. It would be utterly devastating for him."