Crucial meeting

Its remit is to look into UK involvement in Iraq between 2001 and 2009, with the first few weeks focusing on policy in the build-up to the 2003 US-led invasion. On the third day of public hearings, Sir Christopher attacked the UK-backed process of weapons inspections in the run-up to the war, saying officials had been forced to scramble for a "smoking gun" while US troops gathered. But most attention focused on when he believed the decision to go to war had become inevitable.

Sir Christopher said the UK believed it was "pointless" to resist US plans for regime change in Iraq a full year before the invasion and speculated that the path to war was set at a meeting between the two leaders at President Bush's Texas ranch in April 2002.

Critics of the war maintain this was the moment that the prime minister pledged his support for toppling Saddam Hussein. Sir Christopher said no advisers were present for much of the meeting and therefore he could not be "entirely clear what degree of convergence was, if you like, signed in blood".

But he said there were "clues" in a speech given by Mr Blair the next day when he mentioned the possibility of regime change for the first time. "When I heard that speech, I thought that this represents a tightening of the UK-US alliance and a degree of convergence on the danger that Saddam Hussein presented," he told the inquiry. Sir Christopher, who left Washington in 2003, said Mr Blair was a "true believer in the wickedness of Saddam Hussein", his views pre-dating the election of the Bush administration.

"Sea-change"

Before 9/11 the US viewed Iraq as "a grumbling appendix", he said, but that policy was focused on supporting dissident groups and toughening sanctions rather than on military action. However, he said there had been a "sea-change" in attitudes after 9/11 which the British government had been forced to react to.

He said he had received "new" instructions in March 2002 - just weeks before the meeting between Mr Blair and President Bush - from Sir David Manning, the prime minister's foreign policy's adviser, about the UK's position over Iraq. Downing Street believed that "the fact that 9/11 had happened" meant it was "a complete waste of time" to say that the UK cannot support regime change, said Sir Christopher.