David Cameron found himself at odds with Baroness Thatcher tonight after the Tory leader made a major speech criticising Britain’s "slavish" relationship with the United States.

While the Tory leader attacked the Prime Minister for his "uncritical" dealings with President Bush, his predecessor used a rare visit to Washington to insist Britain and America must not be divided over the War of Terror.

In a statement released through the White House, Baroness Thatcher said: "This heinous attack upon America was an attack upon us all. With America, Britain stands in the front line against Islamist fanatics who hate our beliefs, our liberties and our citizens. We must not falter. We must not fail."

The former Conservative Prime Minister was in Washington at the invitation of Dick Cheney, the US Vice President, to take part in the commemoration of the 9/11 attacks, along with members of the US Cabinet.

Baroness Thatcher struck a strikingly different tone to Mr Cameron, who sought in his first major foreign policy speech as leader to distance himself from Mr Bush.

Mr Cameron said: "We have never, until recently, been uncritical allies of America... I worry that we have recently lost the art. I fear that if we continue as at present we may combine the maximum of exposure with the minimum of real influence over decisions.

"The sooner we rediscover the right balance the better for Britain and our alliance," he told an audience at the British American Project.

Mr Cameron’s aides tried to play down any differences between the Tory leader and his predecessor, saying that his speech stressed the dangers of anti-Americanism and the importance of the special relationship.

They also pointed out that the speech was drafted with the help of Charles Powell, Baroness Thatcher’s former foreign policy adviser.

Mr Cameron used the speech to outline how his foreign policy principles differed from Mr Blair’s, implicitly criticising the decision to invade Iraq. However he stopped short of suggesting alternative solutions or that the Conservatives would have done things differently at the time.

Despite voting in favour of the war in Iraq, Mr Cameron made clear his opposition to the idea that democracy can ever be easily introduced by military force.

"Liberty grows from the ground – it cannot be dropped from the air by an unmanned drone," he said, citing South Africa and India as examples where change has been brought about peacefully. He added that military action was not the answer.

"Bombs and missiles are bad ambassadors. They win no hearts and minds; they can build no democracies. There are more tools of statecraft than military power....

"We must put far greater effort into helping undermine dictators and tyrannies from within, and helping moderate regimes to move forward," he said.

Tim Montgomerie, who runs the activist website ConservativeHome, said that the speech was balanced but said it lacked detailed policies and failed convey a sense of urgency.

"I think the situation around the world is deteriorating extremely fast. What we don’t have is the sense of immediate action on Iran going nuclear and we don’t have any strong sense of a plan to address missile defence."

Mr Cameron’s spokesman said that the speech was deliberately broad brush.

"He did not give a tick box of all the world’s problems. Foreign affairs is fast moving and he has to act responsibly."

Mr Cameron also called for a more multilateral approach to solving global conflict, but said that often international institutions including Nato, the UN, the G8 and the EU found themselves unable to act, such as over the Sudan.

He also told the audience how September 11 2001 had affected him personally, because his wife was in Manhattan opening a new boutique store. "It took several hours to get through to her on the phone," he said.

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