Britain is more unsafe because of its involvement in the Iraq war, David Cameron said, as he promised his foreign policy would not be dictated by the US if he became prime minister.

The Conservative leader endorsed a report by his party's policy group on security issues, which said: "We need to recognise that a central element of foreign policy - the intervention in Iraq - has failed in its objectives so badly that the threat to this country is actually greater than it was before it began."

Mr Cameron, who voted for the war in 2003 despite misgivings, said it was "fact" that the threat to Britain was greater now. He said Mr Blair had behaved like a "new best friend" telling Washington what it wanted to hear. While he would have no truck for anti-Americanism, he said: " Where there are areas where we don't agree, we shouldn't be afraid of saying so."He also backed the group's call for the Foreign Office to reassert its influence over foreign policy after criticism that Mr Blair's "sofa" style of governing had meant the key decisions were being taken in Downing Street. "I want to be prime minister of Britain, not president," he said.

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The group, chaired by Dame Pauline Neville-Jones, former chair of the Joint Intelligence Committee, said it was no longer possible to look at domestic security and foreign policy separately. It proposed a National Security Council to oversee both, and the appointment of a cabinet-level security minister.

The report called for a new approach in the Middle East based on a " partnership for open societies" and a display of "humility and patience". Dame Pauline said: "What we can't do in future is hang our whole strategy on the military. We must have a policy that's far more diplomatically interested."

The criticism of Mr Blair is echoed by Chatham House in a report published today, which says the "root failure" of his foreign policy has been his inability to influence the US - despite the UK's "military, political and financial" sacrifices.

Professor Victor Bulmer-Thomas, the think-tank's outgoing director, said the invasion was a "terrible mistake" which drove a "horse and cart" through Mr Blair's doctrine of international community. "The post- invasion debacle has undermined British influence internationally and over crucial issues including a two-state solution in the Middle East," he said.

Mr Blair's official spokesman said: "The terrorist threat did not begin with Iraq. It was there before 9/11." He said the Government was addressing the issues as a whole "rather than trying to find an excuse".

Michael Moore, foreign affairs spokesman for the Liberal Democrats, said: "In this new security initiative, the real cheek is for David Cameron to try to distance himself from the Iraq war. This will not wash with the British public."

Meanwhile, in Washington, Robert Gates assumed the helm at the Defence Department yesterday, warning in his first public remarks that failure in Iraq would haunt the US for years.

The former CIA chief pledged to give President George Bush his honest advice and said that he would go to Iraq soon to speak with US commanders.

Mr Gates, 63, said after taking the oath of office from Vice-President Dick Cheney: "Failure in Iraq at this juncture would be a calamity that would haunt our nation, impair our credibility, and endanger Americans for decades to come."