The Divisional Court last week followed the traditional doctrine that heads of state are immune, no matter how barbarous their crimes. The House of Lords might on appeal prefer the approach of American courts, which have held the estate of Ferdinand Marcos liable for similar crimes against humanity because these are contrary to international law and so beyond the legitimate authority of any state.
That would leave Jack Straw entitled - should he so choose - to hand Pinochet over to Spain, whose right-wing government might well return him to Chile. That is where he will go if he wins the appeal - unless the British government convenes an ad hoc international tribunal to try him, swiftly and justly, in this country.
In Rome on 17 July this year, Britain was among the leaders of 120 countries which signed a statute establishing an international criminal court, endorsing the principle that there can be no impunity, amnesty or sovereign immunity for crimes against humanity. As Lord Bingham said last week, the claim of sovereign immunity applies only in national courts - it has no application to any tribunal that the Government might set up to apply international law.
In that arena, the doctrine was abolished long ago - certainly by Article 227 of the Treaty of Versailles, which provided for the trial of Kaiser Wilhelm, head of the German state. Nuremberg set the precedent for trying high officials for violations of the laws and customs of war. Although the trial was pursuant to a pact between four victor countries, the principle of universal jurisdiction - ie, the right of any country to try crimes against humanity - was applied subsequently by Israel (Eichmann) and France (Barbie). It may not escape notice that a lot of the credit for the success of Nuremberg must go to the British involvement, through the fairness of the presiding judge (Lawrence) and a Labour attorney-general (Shawcross, assisted by a subsequent Labour chancellor, Elwyn Jones).
The most important precedent for dealing with Pinochet came only last year, from the appeal chamber of the Hague Tribunal examining its power to try the Bosnian Serb torturer Dusan Tadic. In those proceedings, 12 of the world's most distinguished judges held that there was jurisdiction to try, internationally, the most wicked breaches of customary war law and of the Geneva Conventions, if committed during internecine struggle (such as the insur- gency in Chile in the early years of Pinochet's rule) as well as during a war between states.
That Pinochet qualifies for international trial there can be no doubt. Now that Pol Pot is dead, his crimes against humanity rank with those of Colonel Mengiscu and Idi Amin (who might be extradited from Saudi Arabia to follow him into the dock). He was the architect of the most wicked method of extra-judicial execution - the disappearance - organised by his Directorate of Intelligence (Dina) and involving death squads who would kidnap, torture and then kill suspected subversives, sometimes by pushing them out of helicopters. This technique was taught to other military juntas in Latin America, and it has claimed tens of thousands of victims, "disappeared" in ways which leave no trace for desperate relatives.
In 1978 Pinochet granted an amnesty to members of his death squads - an amnesty as invalid in international law as his own, which was extracted by duress in 1990 as his condition for permitting the country to revert to democracy. It is invidious to compare evil-doers, but on any scale of iniquity Pinochet ranks above most of the Nazi and Japanese generals condemned in the Nuremberg and Tokyo trials. He was not following orders, he was giving them - many years after the Geneva Conventions, part of the law of his own military profession, had established their illegality.
The claims of the Chilean government to sole jurisdiction over him are risible: most Chileans of courage who would now form that government were killed by Pinochet's regime when they were young. Besides, he is still a formidable power in the land. When one judge recently summoned the courage to jail Manuel Contreras (a former head of Dina), Pinochet personally intervened to pluck him from prison and ensure that he served his time, enjoyably, on a military base.
But the overwhelming reason for disallowing Chile's objection is that crimes of this blackness are no more its business than ours: they are committed against humanity in general because the very fact that a man can order them diminishes the human race. It is this moral reason, plus the pragmatic fact that, if they are not punished by international law, they will not be punished at all, that requires the country that captures Pinochet to arrange for him to be put on trial.
There is no difficulty about setting up an appropriate ad hoc tribunal: the Hague and Rome Statutes are available precedents. For international judges, Britain can call upon any of the countries in the like-minded group it led at Rome to supply distinguished jurists, with a Chilean judge for good measure. Pinochet would have a fair trial under customary military law, with all defences proper for a soldier. He could deny "command responsibility" for the killings, or knowledge of the Dina's orders to death squads, or claim the measures were necessary to save other lives.
The international criminal court has been hailed (especially by Robin Cook) as a genuine move towards global justice, a shift from realpolitik to law in the management of world affairs. But if Pinochet is pronounced "Pin OJ" and is permitted to fly home, notwithstanding all the international law available to put him on trial, that will serve as the clearest of indications that the promise of the Rome Conference was fraudulent. Justice will always be thwarted by its sworn enemy, diplomacy. And the torturers will continue, secure in the belief that when the time comes they can negotiate their exit from the bloody stage, with safe conduct for life. After all, they usually know where too many bodies are buried.
Geoffrey Robertson QC is author of 'The Justice Game', published by Random House.