President George Bush cited the London July 7 bombings in an interview broadcast last night to justify his support for waterboarding, an interrogation technique widely regarded as torture.

In an interview with the BBC he said information obtained from alleged terrorists helped save lives, and the families of the July 7 victims would understand that. Bush said waterboarding, which simulates drowning, was not torture and is threatening to veto a congressional bill that would ban it.

In a wide-ranging interview, Bush:

· Defended the existence of Guantánamo Bay where many of those caught up in the US "war on terror" are held, and claimed that the US was a defender of human rights.

· Insisted the US still occupied the moral high ground worldwide.

· Stood by his decision to remove Saddam Hussein and claimed he would be vindicated as long as the US did not leave Iraq prematurely.

· Said he would attend the Beijing Olympics and that he had regular contact with the Chinese president, Hu Jintao, to urge him to do more on the issue of the genocide in the Sudanese province of Darfur.

The president was more forthcoming than normal in defence of his legacy, reflecting that he has less than a year to go in office.

But his most controversial remarks were over waterboarding. He told the BBC's Matt Frei: "To the critics, I ask them this: when we, within the law, interrogate and get information that protects ourselves and possibly others in other nations to prevent attacks, which attack would they have hoped that we wouldn't have prevented?

"And so, the United States will act within the law. We'll make sure professionals have the tools necessary to do their job within the law."

He claimed the families of victims of the July 7 terror attacks in London would understand his position. "I suspect the families of those victims understand the nature of killers. What people gotta understand is that we'll make decisions based upon law. We're a nation of law."

But Bush was undercut by a senior official in his administration who admitted yesterday, for the first time, that waterboarding is illegal. Stephen Bradbury, head of the justice department's office of legal counsel, giving evidence to a congressional committee, said: "Let me be clear, though: There has been no determination by the justice department that the use of waterboarding, under any circumstances, would be lawful under current law."

In the BBC interview, Bush was asked whether, given waterboarding and other alleged human rights abuses, he could claim the US still occupied the moral high ground. He replied: "Absolutely."

He added: "We believe in human rights and human dignity. We believe in the human condition. We believe in freedom. And we're willing to take the lead. We're willing to ask nations to do hard things. We're willing to accept responsibilities. And - yeah, no question in my mind, it's a nation that's a force for good.

"And history will judge the decisions made during this period of time as necessary decisions."

On Guantánamo Bay, where the US has held hundreds of prisoners for years without trial, he said he would "like it to be empty" but he was "comfortable with recognising this is still a dangerous world".

He said: "There's some people there that need to be tried. And there will be a trial. And they'll have their day in court. Unlike what they did to other people.

"Now, there's great concern about and I can understand this, that these people be given rights. They're not willing to grant the same rights to others. They'll murder. But, you gotta understand, they're getting rights. And I'm comfortable with the decisions we've made."

Commenting on his legacy, he listed as pluses Afghanistan, Iraq and recognition of the right of Palestinians to their own state.

"You know, dealing with liberating 25 million in Afghanistan is part of what I hope people think of when they look at my presidency. Being the first president to propose a two-state solution on Israel and Palestine. I mean, there's a lot of other issues. And I'm happy with Iraq.

"The ... decision to move Saddam Hussein was right. And this democracy [in Iraq] is now taking root.

"And I'm confident that if America does not become isolationist - you know, and allow the terrorists to take back over, Iraq will succeed."

He was speaking in advance of a visit to Africa, though he threatened yesterday to delay it because of his confrontation with Congress over the issue of waterboarding. He urged China to do more to help resolve the Darfur crisis but said that he would still attend the Olympic Games in Beijing.

China is believed to have influence over the Sudanese government because it buys two-thirds of the country's oil exports while selling it weapons and defending it in the UN .

He also urged South Africa to play a greater role in confronting Robert Mugabe, Zimbabwe's president.

· This article was amended on Tuesday February 19 2008.