The UK Government has refused to say if it had acted on intelligence obtained through torture amid growing anger over George Bush's defence of the use of waterboarding.
However, Downing Street did reject the former US president's claims that such interrogation, designed to mimic the experience of drowning, did not equate to torture.
Human rights campaigners and politicians queued up to criticise Mr Bush over his comments, made as he promotes his memoirs, Decision Points, published in Britain today.
Mr Bush insisted he had been right to order the use of waterboarding, that the information gleaned had foiled potential terror attacks on Heathrow Airport and Canary Wharf and that he had been advised it was legal.
The book also reveals he made plans to attack Iran, is not sorry about the Iraq war - although he was appalled to discover there were no WMDs - and does not care about public opinion.
In a section on the financial crisis he writes that he "assumed" regulators would flag up problems and that his first instinct was to let one bank fail.
Amnesty International said it was "shocked" that the former president believed that waterboarding was legal.
President Barack Obama has condemned waterboarding as torture, a view shared by the United Nations.
Asked if the UK Government also still shared that opinion, a Number 10 spokeswoman said: "It comes under that definition in our view".
However, officials would not say if information obtained from waterboarding had been used, as Mr Bush claimed.
A spokesman for the Foreign Office said the government never commented on intelligence matters.
He added that information from other countries was important but that Britain's allies understood its stance on torture.
Critics claimed the use of techniques like waterboarding had drained a "vast reservoir of goodwill" towards America that existed after the 9/11 terror attacks.
Shami Chakrabarti, director of Liberty, said: "After the atrocity of 9/11, the American president could have united the world against terrorism and towards the rule of law. Instead, President Bush led a great democracy into the swamp of lies, war and torture in freedom's name."
Human rights lawyer Aamer Anwar said: "It is shocking that the one-time leader of a western democracy should justify a medieval form of torture."
John Scott, a partner in Capital Defence Lawyers and an editor of the Scottish Human Rights Law Group, said British authorities had a responsibility to find out how intelligence was obtained.
"It is not enough to turn a blind eye to it. If the British Government received information knowing it was the fruit of torture, I'm not saying they cannot use that but they need to be more publicly available for comment to say torture is wrong."
Steve Ballinger, from Amnesty International, added: "George Bush is wrong to say waterboarding is justified because torture is illegal under international law."
Others rejected Mr Bush's claims that such intelligence had been used to protect the UK.
Kim Howells, a Foreign Office minister between 2005 and 2008, said he was "not convinced".
The claims appear to be based on confessions from Khalid Sheikh Mohammed, one of the masterminds of the 9/11 attack.
He endured waterboarding in Pakistan in March 2003, and confessed at a hearing in Guantanamo Bay prison to potential attacks on Heathrow, Big Ben and Canary Wharf. He was one of three al Qaeda suspects subjected to the torture method.