George Bush faced international condemnation tonight of his claim that British lives were saved as a result of torture.
The former US president said waterboarding three al-Qa'ida suspects provided crucial intelligence that prevented attacks on London.
But critics said use of the controversial technique acted as a "recruiting sergeant for extremism" and ultimately "made the world a more dangerous place".
And they questioned whether it is possible to prove what information was gathered as a result of torture and how valuable it was.
Mr Bush set out to justify his controversial actions in his memoir, Decision Points, after two years of public silence since leaving the White House.
In an interview with The Times, the 43rd US president said he authorised the use of waterboarding to extract information from self-confessed al Qaida boss Khalid Sheikh Mohammed.
He said the drowning technique helped to break up plots to attack Heathrow Airport and Canary Wharf, adding: "Three people were waterboarded and I believe that decision saved lives."
The comments reopened the bitter debate over the use of secret intelligence, mostly by counter terrorism officials, that may have been obtained by the torture of suspects.
The British Government declined to comment directly on the claims but said it continued to consider waterboarding as torture, something it does not condone or allow others to do on our behalf.
In a speech last month, the MI6 chief Sir John Sawers insisted his service had no links with torture, which he described as "illegal and abhorrent", but said officials must act on information that could save lives.
Former Labour chairman of the Commons intelligence and security committee Kim Howells said he doubted Mr Bush's claims.
He told BBC Radio 4's Today programme: "We think waterboarding is torture and I don't believe that the British security services people had anything to do with it.
"What is very, very difficult is to decide whether or not your intelligence partners have as scrupulous an attitude towards this as we believe the British intelligence services have."
Former Tory shadow home secretary David Davis said the use of techniques such as waterboarding undermined the West's case when discussing human rights with nations such as China.
Shami Chakrabarti, 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. Democracy can do better and, learning from the past, it will."
Steve Ballinger, of Amnesty International, added: "George Bush is wrong to say waterboarding is justified because torture is illegal under international law."
Clive Stafford Smith, of Reprieve, poked fun at Mr Bush's declaration that it was "damn right" to say he gave waterboarding the green light.
He said: "He also boasts of secret, unverifiable benefits he achieved through torture, that only he may know, and the rest of us should take on faith.
"By authorising torture, president Bush made the world an infinitely more dangerous place. US torture spread like a virus, from the CIA to Abu Ghraib, and became the greatest recruiting sergeant for extremism.
"A vast reservoir of goodwill towards the US following 9/11 was drained in record time."
Mohammed repeatedly endured the near-drowning technique torture sessions as CIA agents attempted to obtain information following his capture in Pakistan in March 2003.
Potential attacks on the London landmarks Heathrow, Big Ben and Canary Wharf were included in a detailed list of 31 plots Mohammed confessed to during a later hearing at Guantanamo Bay prison.
Mohammed said he wanted to "obliterate" the sites as he detailed other conspiracies from the 2001 destruction of New York's World Trade Centre to the failed shoebombing of a transatlantic airliner by Londoner Richard Reid.
Mohammed was one of three al Qaida suspects subjected to waterboarding, alongside Saudi Arabia-born Abu Zubaydah and Abd al-Rahim al-Nashiri, accused of co-ordinating a suicide attack on the American destroyer USS Cole in Aden.
In his new book Mr Bush wrote: "Their interrogations helped break up plots to attack American diplomatic facilities abroad, Heathrow airport and Canary Wharf in London and multiple targets in the United States."
Mohammed said his statement was not made under duress, but some onlookers have questioned how plausible it is and whether the suspect can ever receive a fair trial.
In February 2003, tanks were stationed around Heathrow Airport and nearby flight paths as 450 troops and some 1,700 extra police officers were brought in over fears of a terrorist attack.
The airport was also the departure point for the so-called liquid bomb plot, in which a London-based al Qaida-inspired cell plotted to board transatlantic jets with novel home-made devices.
The jury in the first trial heard some members of the conspiracy discussed targeting Heathrow and Canary Wharf as well as nuclear power stations, oil and gas terminals.
In November 2006, al Qaida plotter Dhiren Barot was jailed for life for plotting to destroy tower blocks by parking limousines loaded with gas cylinders in a basement car park.
Mohammed remains in Guantanamo Bay charged with war crimes and could still face the death penalty after President Barack Obama promised to speed up the legal process.Reuse content