As a friend, ally and admirer of the United States, and one who has had the privilege to work for many years with its military, I applaud its new Commander-in-Chief for honouring his promise and ordering an end to its use of torture. This symbolic act re-establishes an American legitimacy that had been forsaken in the eyes of the world.

President Obama has consigned to the past a shameful period in his nation's proud history. The previous Administration sought to justify the unjustifiable. It narrowed its definition of torture to the infliction of “excruciating” pain to legitimise simulated drowning. It coined the euphemistic doublespeak of “enhanced interrogation” and “extraordinary rendition”. But its dissimulation did nothing to diminish the barbarity of its practice. Torture does violence to the defenceless, using their bodies against their souls. There must be no going back. In the words of Abraham Lincoln, “necessity does not admit of cruelty”.

Torture is illegal. It is a crime in both peace and war that no exceptional circumstances can permit. The Geneva Conventions and the UN Convention Against Torture, firewalls for our collective humanity, expressly forbid it. It is prohibited without qualification in the Universal Declaration of Human Rights - a document signed by people from every corner and culture of the Earth who had survived the suffering of both world wars, the horrors of fascism, and the evil of the Holocaust. They understood well that global humanitarian norms and a rules-based world order are in all our interests.

There can be no exceptions to our laws, and no attempts to bend them. Those who break them should be judged in court.

Torture is wrong. People are ends in themselves, never merely means. Absolute human rights represent a limit to utilitarian calculations and speculations on national interest. They are the Rubicon that no hypothetical consequences, even in dire “ticking bomb” scenarios, must force us across. Everyone, even the terrorist, is human. There are no untermenschen. To label the criminal subhuman is to exonerate him.

Torture rarely works. Sometimes, of course, important intelligence is extracted. But this is not the television world of 24 and we are not the Gestapo. Guantánamo Bay has seen more suicides than convictions. Information from the tortured is notoriously unreliable. Conspirators change their plans when one of their number is captured. The victim will say anything to stop the pain.

Torture is self-defeating. We need to distinguish ourselves from our enemies. We must not, in the false name of moral equivalence, degrade ourselves to their level. Once we do, Pandora's Box is difficult even for presidents to shut. If an interrogator is told by his superior to extract information from a prisoner, he will not want to fail. Torture then becomes a temptation, or worse, a habit, from cages in Cuba to the outrages of Abu Ghraib. It is imperative that the clear message from the very top is that there is no circumstance in which it is to be sanctioned. Soldiers and security services must be properly trained in lawful interrogation techniques. This is no job for amateurs.

Torture is bad strategy. The French tortured members of the FLN (Front de Libération Nationale) in the 1950s, turning ordinary Algerians against them. The British Army's use of stress positions in Northern Ireland had the same effect. We cannot afford to alienate foreign populations and large swaths of our own. Western use of torture to counter terror has been a propaganda coup for al-Qaeda and a recruiting sergeant for its global jihad. Our hypocrisy has radicalised our enemies and corroded the power we base on our proclaimed values. We save more lives in the long term by rejecting torture than we do by perpetrating it.

The UK cannot claim to be blameless. We have condoned with our silence torture committed by others. Three UK residents - Bisher al-Rawi, an Iraqi citizen, Jamil al-Banna, a Jordanian refugee, and the focus of the present furore, the Ethiopian asylum seeker Binyam Mohamed - were all arbitrarily rendered to the torment of indefinite, extrajudicial detention without charge or trial in Camp Delta. Our continent has played host to black sites and ghost prisons, facilitating a perverse regime of state-sanctioned kidnap and franchised-out torture. By our complicity, collaboration or acquiescence, we undermine our status as a civilised people.

However ruthless or disrespectful our foes, however seemingly persuasive the argument to resort to atrocity, however acute the dilemmas we face, there remains a fundamental incoherence in the idea that we can sacrifice our morality nobly. That is a rule that has not changed, nor ever will. Human rights are the object of terrorist attacks, and they are integral to the credibility of any counter- terrorist response. Torture is not only illegal, unethical, ineffective, cruel and counter-productive, it is also dumb.

General Lord Guthrie of Craigiebank is former UK Chief of Defence Staff and a member of the ippr Commission on National Security in the 21st Century

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