The 10th anniversary of the destruction of the World Trade Centre towers by two hijacked commercial airliners should be a moment of unambiguous moral clarity. In a way, it still is. Through special newspaper supplements and TV documentaries we are reminded (as if we ever could forget) of the horror of that beautiful sunny morning in New York City: the sight of office workers jumping to certain death as a merciful release from incineration; the desperate calls as husbands and wives, parents and children, made what they knew would be their final messages to those they loved and would never see again.

Yet this commemoration is mixed with something else; the feeling that the heroism of the public response to the horror of that day has been foully polluted by what has been done in our name to prevent a second 9/11. This is encapsulated by the revelations from documents discovered in abandoned buildings in Tripoli, appearing to show the complicity of the British Government in the rendition of a suspected Islamist terrorist from Hong Kong, into the hands of Colonel Gaddafi's interrogators.

Yesterday, another former member of the Libyan Islamic Fighting Group (LIFG), Abdelhakim Belhaj, now commander of the anti-Gaddafi militia in Tripoli, called for the US and Britain to apologise for their role in his rendition to Tripoli and torture there. Belhaj is now one of the officially designated good guys, benefiting from Nato's air bombardment of Gaddafi's command and control centres, not to mention undercover aid and advice from Britain's SAS. Yet, as has been confirmed by other "liberated" documents published by the Sunday Times during the weekend, the British government had previously instructed the SAS to train the Khamis Brigade, the elite force Gaddafi assigned to counter the threat from his internal enemies.

This, of course, was all part of the "war on terror". Libya, under Gaddafi, had originally formed part of George W Bush's so-called axis of evil – hostile states with programmes to develop weapons of mass destruction. Britain's Secret Intelligence Service (SIS) played the main role in persuading Gaddafi, through its links with the Libyan intelligence chief, Mousa Kousa, to relinquish its WMD programme (such as it was). Most significantly, the Libyans then revealed to us just how the Pakistani nuclear weapons scientist AQ Khan had been offering to sell to sundry appalling regimes the materials needed to develop WMD.

The trouble was that the then prime minister, Tony Blair, exhilarated by this solitary foreign policy success in the "war on terror", proceeded to treat Gaddafi not as the thug and borderline lunatic he remained, but as if he were a civilising force in the region. The Colonel, meanwhile, with his customary cunning, played up the threat to his regime from the LIFG, and thus gained – as it now seems – our assistance in the capture and torture of his domestic opponents. The fact that they were often self-proclaimed jihadists made this all the more convincing to Washington and Whitehall.

Grotesque as Blair's smarming over the man ultimately responsible for the blowing up of Pan Am Flight 103 over Lockerbie was, one can at least appreciate the strategic arguments behind this wooing of a dictator. Just as in the Cold War, when the West supped with some pretty unscrupulous types in the fight against Soviet militarism, the full details involved in policies adopted in the interests of national security appear neither moral nor necessary when exposed to the light.

Yet, for all the excesses of the Cold War, we on the winning side never countenanced torture. Indeed, that is one reason why we won. By embracing the Helsinki process, which promoted the protection of human rights as an integral part of the struggle, the Western nations attained a sense of moral leadership which was deeply demoralising to the Soviet politburo. As it became increasingly clear that they, with their "psychiatric hospitals" for dissidents (the urban modernist successor to the Gulag), required mental torture to persuade the unconverted, the intellectual confidence drained away from those involved in the export of Soviet-style communism.

It is in this context that one should see the signing by President Ronald Reagan of the United Nations convention against torture, which came into force in 1987. It was in the clearest breach of this document that President George W Bush, urged on by his deputy Dick Cheney, authorised the use of torture by CIA officers on captured al-Qa'ida members – notably by the process known as "waterboarding". (This method of simulated – but all too real – drowning was practised during the Second World War by some Japanese officers against captured American pilots: the perpetrators were tried and executed as war criminals.)

As is well known, Bush and Cheney managed to obtain a legal opinion by an assistant attorney general for the office of the legal counsel at the US Justice Department, one Jay Bybee, to the effect that waterboarding (and other so-called "enhanced interrogation methods") did not constitute torture, and that therefore the US was not in breach of its treaty obligations, or its constitution.

The Bybee memorandum declared that an interrogation method amounted to torture only if "the physical pain is of an intensity which accompanies serious physical injury such as death or organ failure". This novel and deliberately unverifiable definition is well in excess of that provided in the treaty signed by Ronald Reagan: "Torture means any act by which severe pain or suffering, whether physical or mental, is intentionally inflicted on a person for ... obtaining information at the instigation of or with the consent or acquiescence of a public official".

The Bush administration argued that Reagan could not have envisaged the circumstances prevailing in the US in the wake of 9/11 and in particular the fact that America's enemy would not be the regular army of a recognised state. However, article 2.2 of the convention states: "No exceptional circumstances whatsoever, whether a state of war or a threat of war, internal political instability, or any other public emergency, may be invoked as a justification for torture."

In his memoirs published last week, Dick Cheney again argues that his "enhanced interrogation techniques" at Guantanamo Bay produced confessions that saved the lives of Americans (and Britons). That is his opinion. What is a fact is that this policy acted like no other in recruiting young men to al-Qa'ida. As a US officer who personally conducted hundreds of prisoner interrogations in Iraq wrote (under the assumed name of Major Alexander) in his book How To Break A Terrorist: "The reason why foreign fighters joined al-Qa'ida in Iraq was overwhelmingly because of abuses at Guantanamo and Abu Ghraib and not Islamic ideology."