It is easy to forget how the atmosphere in Washington after September 11, 2001, allowed policymakers to cite Jack Bauer, the fictional hero of Fox TV's 24, as some sort of moral compass.

Bauer, who used torture to extract information that prevented the slaughter of innocents, was cited by the likes of Michael Chertoff, the Homeland Security Secretary, to justify policies including “enhanced interrogation techniques”.

To give the theory an academic sheen Alan Dershowitz, a law professor at Harvard, President Obama's alma mater, set out “the ticking-bomb scenario” in 2002 in which a terrorist who has planted a nuclear device receives some robust questioning.

Seven years later the publication of more than 100 pages of clinical legal prose explaining how far interrogators could go in slamming a suspect's head against a wall (albeit one designed to reduce the possibility of lasting injury) make deeply disturbing reading.

General Michael Hayden, the former CIA director, believes Mr Obama's decision to disclose them was a profound mistake because it allows enemies to know the “outer limits” of what intelligence officers will do. He has claimed that “fully half” of the Government's information about al-Qaeda's structures and activities came when “coercive interrogation” was used.

George Bush has said that such tactics led to the capture of al-Qaeda operatives and “saved innocent lives” by thwarting plots to strike at US Marines in Djibouti, fly aircraft into office towers in London, attack Los Angeles or detonate a radioactive dirty bomb in America.

Even Robert Grenier, who served as the CIA's top counter-terrorism official before being removed from his post because of his concerns about some of these practices, stated: “The most important source of intelligence we had after 9/11 came from the interrogations of high-value detainees.”

Others, however, insist that much of the useful information could have been elicited without resorting to what many believe was torture.

Under coercion Khalid Sheikh Mohammed, mastermind of the twin towers attacks, also “confessed” to a great deal which was almost certainly untrue. This included the murder of journalist Daniel Pearl and plans to assassinate Bill Clinton, Jimmy Carter and Pope John Paul II.

The former CIA analyst Bruce Riedel told The New Yorker magazine that Mr Mohammed, with no prospect of tasting freedom, has only one gratification left in life — “to portray himself as the James Bond of jihadism”.

Security services on both sides of the Atlantic complain they wasted years following up false leads produced by the CIA. Asked recently if he was aware that any attacks on America been disrupted thanks to intelligence obtained through such methods, the FBI director Robert Mueller said: “I don't believe that has been the case.”

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