Torture is revolting. A man can retain his human dignity in front of a firing squad or on the scaffold: not in a torture chamber. Torturers set out to break their victim: to take a human being and reduce him to a whimpering wreck. In so doing, they defile themselves and their society. In Britain, torture has been illegal for more than 300 years. Shortly after torture was abjured, we stopped executing witches: all part of a move away from medieval legal mores and their replacement with the modern rule of law. Until recently, at least in the UK, torture and witch-finding appeared to be safely immured in a museum of ancient atrocities.

Yet men cannot live like angels. However repugnant we may find torture, there are worse horrors, such as the nuclear devastation of central London, killing hundreds of thousands of people and inflicting irreparable damage on mankind's cultural heritage. We also face new and terrible dangers. In the past, the threat came from other states. If they struck at us, we knew where to strike back. Now, we can almost feel nostalgic for mutually assured destruction.

In the Islamic world, a religious revival is taking place, analogous to the Reformation and Counter-Reformation. In that era, there was no shortage of volunteers for martyrdom. Today, failed states produce hate-filled young men, who appear to believe that Allah smiles on the suicide bomber. If you are going to destroy yourself, why not inflict maximum damage upon the enemy?

Admittedly, there is no evidence that the terrorists are in a position to produce dirty bombs yet, let alone fully nuclear devices. But we know one thing about technology. It spreads. Difficult processes become easier. Today's remote possibility becomes tomorrow's imminent danger. There have been frequent objections to the use of the term "war on terror". None has been cogent. All of them give the impression that those who object to the phrase do not want to face the reality. It is a reality. For the foreseeable future, we will be engaged in such a war. It is unlike any other conflict we have ever faced, for there is no straightforward route to victory. Nor is there a certainty of success.

In any war, there are two desiderata: appropriate strategies, and allies. In this case, the principal strategic resource is self-evident: intelligence. We have no easy way of establishing who the enemy is, where he will gather his forces or how he will strike at us. We also have to deal with the enemy within. All this requires an enormous intelligence effort.

As other countries are facing a similar threat, they will be making a similar effort. It would be insane not to pool resources and share information. We and the Americans have long-established methods of intelligence co-operation, which are now even more important than they were in the Cold War. It also makes sense to work with other threatened nations, such as Pakistan, where a brave political elite is bearing a disproportionate burden, and receiving few thanks for doing so.

But there is a problem. It seems likely that Pakistani interrogators use torture. Although we find torture repulsive, it does not follow that those who are tasked with governing Pakistan could safely dispense with it. Our enjoyment of Shakespeare and Elizabethan madrigals is not blighted by Walsingham's rack-masters in the Tower of London. We lament the premature death of Robert Southwell, but despite Tyburn and the rack, we would still speak of Elizabethan civilisation. So let us be more generous to the Pakistani authorities. Their difficulties are at least as great as those faced by Francis Walsingham and Robert Cecil in the 1590s. Can we blame the Pakistanis for employing some 1590s methods?

When our intelligence services were invited to share the harvest reaped by the Pakistanis, there appears to have been no hesitation. Nor should there have been. We needed the information. Perhaps we should have offered the Pakistanis some advice on interrogation techniques which do not involve knife-work on suspects' genitals. It may be that we have indeed done so, in private. But Pakistan is a sovereign state and an embattled ally; a far more attractive state and a far less dubious ally than Russia was in the Second World War. We should be grateful for the Pakistanis' efforts on our behalf.

We should also be grateful to the Americans. But we should insist, again in private, that if they did torture suspects, they were wrong to do so. As they are in a stronger position than Pakistan, their interrogation doctrine should be strongly post-Walsingham. Some of the problem may have arisen from Dick Cheney, arguably the most formidable Vice-President of all time. Mr Cheney combines the neo-Conservatives' moral certainties and the realpolitik school's ruthlessness. This means that he shoots with both barrels. It also creates the risk of overkill.

Even so, there is one benefit from the Americans' experiments with robust interrogation methods: water-boarding. Christopher Hitchens wanted to demonstrate that it was absurd to demonise water-boarding and that it was only girlie-man's torture. So he subjected himself to it. He cried off after seven seconds. That is comforting, and not only to Mr Hitchens's critics. Thus far, there has been no need for either the UK or the US to consider torture, because neither of us has been confronted by a ticking bomb. As a result of the Hitchens trial run, we know that we have something which could work.

That might sound frivolous. But there would be nothing frivolous about a ticking bomb. Cobra, the Cabinet's emergency committee, is in permanent session somewhere under Whitehall: the intelligence chiefs, grey and drawn from lack of sleep, inform the Prime Minister, ditto, that it seems almost certain that a nuclear device is primed to explode in the next few hours. There is a man in custody who probably knows where it is. They are ready to use whatever methods are necessary to extract the information...

Before 9/11, in front of some serious lawyers, I once argued that if there were a ticking bomb, the Government would not only have a right to use torture. It would have a duty to use torture. Up sprang Sydney Kentridge, one of the great liberals of our age and a fearless defender of unpopular causes, from Nelson Mandela in the old South Africa to fox-hunting in modern Britain. I prepared to receive incoming fire. It came, in the form of a devilish intellectual challenge. "Let's take your hypothesis a bit further. We have captured a terrorist, but he is a hardened character. We cannot be certain that he will crack in time. We have also captured his wife and children".

After much agonising, I have come to the conclusion that there is only one answer to Sydney's question. Torture the wife and children. It is a disgusting idea. It is almost a tragedy that we even have to discuss it, let alone think of acting upon it. But there is nothing to be gained from refusing to face facts, in the way that the Master of the Rolls, Lord Neuburger, did last week. His Lordship wrapped himself in a cloak of self-righteousness, traduced an entire security service, showed no understanding of the courage which its officers routinely display: no understanding, indeed, of anything beyond courtroom niceties.