The trouble with torture is that sometimes it works; and when it does, the devil sings. Scarpia may have ended with Tosca's knife in his chest, but his torturers got what they needed from Cavaradossi. When Dick Cheney, the former US vice-president, said this week that his favoured interrogation methods had saved America from another 9/11, who could gainsay him?

We may find it incredible that democracies such as Britain and America find themselves opening the 21st century with a debate on the efficacy of such medieval tortures as extreme confinement, sleep deprivation and near-drowning. Yet it is now clear that both countries have been reduced by the hysterics of the war on terror to making use of information extracted under torture. Do we just forgive and forget?

The CIA memos released this week by President Obama were accompanied by pardons. These were for possible violations by American citizens not only of the international convention against torture, but of the CIA's own meticulous, if ghoulish, rule book. ­Khalid Sheikh Mohammed, the 9/11 planner, was apparently waterboarded 183 times and barraged with a variety of rough interrogation techniques a hundred times in two weeks before doctors stopped it. What ethic permitted medical involvement in this treatment? Abu Zubaydah, an alleged senior al-Qaida commander, was sent for torture to Thailand before being waterboarded a reported 83 times.

These actions were plainly not confined to the "ticking bomb" crises of torture apologists. They were systematic, intended to confirm the names of accomplices, past events, dates and places. Mohammed apparently "confessed" to every outrage of the past decade. As is known from the second world war, the process of torture so brutalised those taking part that the only restraint was the risk of being held responsible.

Obama has eliminated that risk. In doing so he is prima facie in breach of the torture treaty, which imposes a "binding" obligation on governments to take into custody those, high and low, guilty of perpetrating it. Even open war is no justification for disobeying the treaty. Honouring it should thus devolve to the attorney general, Eric Holder, not the president. Given the weight of ­material flooding the blogs and airwaves, it is hard to see how Holder cannot appoint a special prosecutor. British collaboration will be increasingly exposed as this ­poison seeps through the system.

Cheney's argument is chanted by successive British home secretaries as they click upward the ratchet of state authoritarianism. If a bomb goes off, the home secretary needs another power. If a bomb does not go off, it proves that the last new power worked. We lurch towards darkness at the bomber's bidding. Always the means justify the end of "national security".

The morality of torture is merely polluted by claims and counter-claims of its efficacy. To some it is excusable in "ticking bomb" cases. Yet this excuse is more often cited by philosophers pointing to the danger of any move from such a situational ethic to a general theory of torture as justified beyond a given threshold of state danger.

The fact in law is that the physical or mental abuse of prisoners is universally banned as abhorrent, irrespective of efficacy – a sign of the onward march of civilisation. Torture's apologists (who invariably redefine it as not quite torture) protest that sometimes one backward step must be taken to prevent the bomber taking two backward steps. This is crazy reasoning, since such overt retrogression soon feeds on itself, as with Britain's counter-terror legislation.

The trouble lies in our old foe, the war on terror, a creature of an age that seems to feast on the terminology of fear, and which Obama has rightly been seeking to deflate. The massacres in New York, Bali, London, Madrid and Mumbai were horrible but politically insignificant. They lacked even the IRA's policy-changing programme. They were a howl of rage from a deranged fanaticism, threatening lives and property but not the security of any state. They are best treated as accidents of globalisation.

Anyone who feels America or Britain is moving nearer to an Islamist caliphate because of a suicide bomber is a wimp who has no belief in the robustness of democracy. That clearly includes the former US vice-president. Governments have a duty to protect their citizens, but that is a policing role. The Islamist threat in no way constitutes a war. ­Further attacks (other than the dreams of fantasists and the Metropolitan police) may well have been prevented by assiduous policing. It is hard to believe that torture contributed to that prevention.

If it had – and that is Cheney's contention – then the libertarian must accept there will always be a price to pay for liberty. (There is a far higher one for letting people ride motorbikes.) 9/11 was itself the price of sloppy policing, given the attack on the same target in 1993. The price of banning torture, if there is one, would be paid in broken lives and broken walls, not in the future of the democratic state.

The danger in exaggerating terrorism is that there is an industry waiting to pounce. Murmur "war" or "state security" or "threat to civilisation" and the horsemen of the apocalypse will descend in cavalry formation. This week Lord West, the unelected security minister, indicated his total capture by the horsemen when he gave an interview to announce plans "to step up the fight against al-Qaida by unveiling a plan to protect every public building in Britain".

He says he wants to ­reinforce every ­shopping centre, sports ground, school, hospital and restaurant – even every church – against suicide bombers. With billion-pound budgets flashing, he is courted by cohorts of security consultants, defence lobbyists, building contractors, electronic warfare pundits, and health and safety fear ­merchants. He will not stop until he has allowed al-Qaida (which we are constantly told is "on its last legs") to drain the exchequer dry and reduce British citizens to gibbering wrecks of fear.

The British state, British tolerance and the British way of life are far more threatened by Lord West and his like than by any nutcase in a Pakistan madrasa. This abuse of the language of terror for political and commercial self-aggrandisement is disgraceful. It is precisely the cast of mind that Obama hoped to end. It strips the word security of all sense of proportion, and ends in the torture chambers of Guantánamo.