The British Prime Minister, Mr Tony Blair and US President Mr George W Bush should have realised before the war that Iraq did not have weapons of mass destruction, the man who led the hunt for the missing weapons said.
Mr David Kay, the former head of the Iraq Survey Group, said the reports of the Butler Inquiry and the Senate Intelligence Committee in America, together painted a picture of a "broken" system for intelligence gathering and assessment.
"I think they are a scathing indictment," he said in an interview for ITV1's Jonathan Dimbleby programme.
"I think they are a picture of a broken system on both sides of the Atlantic, for collecting intelligence, for analysing it and finally for sending it forward to policy makers and to the public.
Mr Kay, who was hand-picked by the CIA to head the Iraq Survey Group, said that because US and UK policy on Iraq was based on WMD, analysts had been too ready to accept evidence that Iraq had banned weapons while being over-critical of evidence which suggested that they did not.
"What really happened for the analysts is they had two levels of evidence," he said.
"Anything that would confirm WMD in Iraq - very little scrutiny. Anything that showed Iraq didn't have weapons of mass destruction, had a much higher gate to pass because if it were true, all of US policy towards Iraq would have fallen asunder.
"I think what you have in both the Senate Report and in the Butler Commission Report is a disturbing merger of the lines between intelligence, whose real role was to speak truth to power, and power whose real role is to influence the public to do the course of action that they've decided upon.
"That line blurred and blurred on both sides of the Atlantic with regard to Iraq."
He said that Mr Blair and Mr Bush should both have realised that the intelligence they were being presented with did not support the claims that Iraq actually had weapons.