President Bush has vetoed a law preventing the CIA using interrogation techniques condemned by many as torture, because it “would take away one of the most valuable tools in the War on Terror”.

In his weekly radio address the President defended practices such as waterboarding, claiming that they alone had prevented another 9/11.

The veto is only the ninth of Mr Bush's presidency, but the eighth in the past ten months since the Democrats took control of the Congress. They have sought to limit the far-reaching powers he has instituted for himself, and the intelligence and security forces, in the wake of the 2001 attacks.

“The fact that we have not been attacked over the past six and a half years is not a matter of chance,” Mr Bush said. “This is no time for Congress to abandon practices that have a proven track record of keeping America safe.”

The President said that the use ofsuch interrogation had helped stop several terrot plots, including plans to fly passenger aircraft into a Los Angeles tower and into Heathrow Airport.

“Were it not for this programme, our intelligence community believes that al-Qaeda and its allies would have succeeded in launching another attack against the American homeland,” he said.

The veto throws the spotlight back on to America's use of so-called coercive interrogation methods like waterboarding, the simulated drowning technique invented by Spanish inquisitors and adopted by regimes such as the Khmer Rouge.

Last month the Bush Administration admitted publicly for the first time that waterboarding had been used on three foreign terror suspects in CIA custody.

Further condemnation followed when also officials admitted that although the technique was no longer used, the Adminstration would not hesitate to authorise its use in the future if it believed it could stop an attack.

Mr Bush's defiant defence of the controversial techniques underlines his determination to cement his legacy as America's great defender against the threat from Islamic terrorism. As his presidency enters its final months, he has found himself locked in battle with a Democratically controlled Congress determined to erase much of what he claims as his legacy.

The President has sought to enshrine in law many of the powers that his Administration has claimed in the name of fighting terrorism, while the Democrats have moved to limit their future impact.

The legislation that Mr Bush vetoed would have limited American civilian interrogators to those techniques permitted by the US Army field manual, which prohibits all physical force, including waterboarding, as well as many psychological methods.

John McCain, the Republican presidential candidate, who authored a law banning torture of detainees in American custody, surprised many by supporting the President's veto, arguing that imposing military rules on the CIA would deny it the use of many legitimate techniques.

Mr McCain has also said, however, that he would define waterboarding as torture, effectively outlawing it. Barack Obama and Hillary Clinton, the two Democratic candidates, are both supporters of increased measures banning coercive techniques although campaign commitments kept both of them from voting on this most recent Bill.

House Democrats condemned the veto, saying that the use of such methods had sullied America's world reputation as a force for good. Nancy Pelosi, the Speaker, said that America's claim to lead the world depended on its morality, not its military might. “We will begin to reassert that moral authority by attempting to override the President's veto next week,” she said.

Two-thirds of Congress is required to override a presidential veto and the Democrats are unlikely to gather enough votes. In the first seven years of his presidency, Mr Bush used his veto only once, to knock down a law allowing stem cell research on human embryos.

He has vetoed far fewer bills than many two-term presidents, but he has imposed his will much more frequently by the use of “ signing statements” - handwritten amendments scribbled in the margins of Bills when he signs them into law. Some have altered laws so fundamentally that some argue that they amount to legislation. Mr McCain has vowed not to make signing statements, should he become president.

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