Claims by former US president George Bush that waterboarding saved British lives appear to be based on the comprehensive confessions of September 11 mastermind Khalid Sheikh Mohammed.

The al Qaida ringleader 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 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.

The terrorist also admitted his role in the 2002 Bali nightclub bombings, an attack on a Kenyan hotel in the same year and the beheading of Wall Street Journal reporter Daniel Pearl in Pakistan.

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 USS Cole in Aden.

The British government has long rejected the use of waterboarding, which it regards as torture. In a speech last month, the Chief of MI6 Sir John Sawers insisted that his service had "nothing whatsoever" to do with torture which he described as "illegal and abhorrent".

In the interview, Mr Bush described his close relationship with Tony Blair, but was dismissive of public opinion in Britain about the war in Iraq. "It doesn't matter how people perceive me in England. It just doesn't matter any more. And frankly, at times, it didn't matter then," he said.

Mr Bush recalled how when Mr Blair faced a possible vote of no confidence in Parliament on the eve of war, he offered him the chance to opt out of sending British troops into Iraq.

He said that "rather than lose the government, I would much rather have Tony and his wisdom and his strategic thinking as the prime minister of a strong and important ally".

However, Mr Blair told him: "I'm in. If it costs the government, fine."