Tony Blair's claim that Saddam Hussein posed a 'current and serious' threat to Britain is challenged by dramatic new allegations today that Britain's spy chiefs have retracted the intelligence on which it was based.

The supposed proof that the Iraqi dictator was still trying, even in the run-up to war, to produce chemical and biological weapons became crucial to the Prime Minister's case for urgent military action rather than waiting for inspectors to finish their task.

Yet, according to a senior intelligence source interviewed by BBC1's Panorama tonight, MI6 has since taken the rare step of withdrawing the intelligence assessment that underpinned the claim that Saddam had continued to produce WMD - an admission that it was fundamentally unreliable.

The charge leaves Blair open to serious questions over why, if the nature of the proof had changed, he did not tell the public that the evidence of WMD was crumbling beneath him.

It will increase speculation that he may be forced to disown chunks of the controversial September dossier on banned weapons when Lord Butler publishes his report this week on the handling of intelligence on Iraq.

http://www.guardian.co.uk/butler/story/0,14750,1258812,00.html