Britain has a duty to ensure the Geneva Conventions are upheld

The Geneva Conventions of 1949 have stood as a monumental protection for the most wretched of prisoners – those captured in the course of war. Many of the lives they have saved in the past half century have been those of American soldiers and airmen who surrendered in Korea and Vietnam. This makes it ironic, as well as deplorable, that the United States should now attempt to evade the Conventions by denying prisoner of war status to the Taliban and al-Qa'ida fighters it has corralled in Cuba in preparation for interrogation, trial and possible execution.

The conflict in Afghanistan was not a civil war: it became an international armed conflict once America intervened last October to overthrow the Taliban government. Members of the Taliban's armed forces certainly qualify for Geneva Convention protection. There may be more doubt about al-Qa'ida prisoners, but the evidence strongly suggests that this volunteer brigade was integrated into the armed forces of the government, fighting in cahoots with the Taliban much as the SS fought alongside the regular German army during the Second World War. It was because of this symbiotic relationship that al-Qa'ida and the Taliban were accused by the UK Government of being "two sides of the same coin" – as a justification for attacking them both. In these circumstances, al-Qa'ida as well as Taliban detainees should be accorded the protection of international law.

The US Defence Secretary Donald Rumsfeld, however, claims that neither group are POWs: they are merely "unlawful combatants" or "battlefield detainees" without any legal rights. This follows, he said, from the fact that they fought without wearing military uniforms – but since when have mujahedin sported regimental braid?

There are only two categories of combatants who can properly be denied POW status – spies and mercenaries. The latter category is defined (under the 1977 Geneva Protocol) as "motivated to take part in the hostilities essentially by the desire for private gain" and promised substantial "material compensation". Al-Qa'ida fighters, motivated not by money but by the prospect of a fast-track to paradise, fall outside this definition.

Why does the US object to giving POW status to these men? It would require them to be treated with a minimum of humanity – which one assumes would in any event be done at Guantanamo Bay (although placing them in cells that are open to the elements seems unnecessarily degrading). Their conditions must be monitored by the Red Cross – an apolitical organisation whose commitment to confidentiality does not put the US at any risk of public embarrassment. Geneva Convention III protects against coercive interrogation (other than to establish name, rank and number) but does not prevent willing co-operation. The real objection must be to the Convention's requirement that "in no circumstances whatever shall a POW be tried by a court of any kind which does not offer the essential guarantees of independence and impartiality as generally recognised".

It is at this point that present American plans to try them will fundamentally breach the Convention. The "military commissions" created by President Bush's Executive Order last November lack all the essential guarantees for independence and impartiality. They are tribunals without rules of evidence or rights of appeal, which sit in secret and are staffed by army officer "judges" paid and promoted by the US Defence Department, which also prosecutes and acts as the detaining power. They will be entitled to convict on a lower standard of proof than "beyond reasonable doubt" and to impose death sentences.

They are not "courts martial", to which US soldiers are subject – in truth, they are not courts at all but an extension of the power of the executive. Their decisions will not be acceptable internationally and will only serve to discredit an exercise which began as "Operation Infinite Justice".

The Geneva Conventions do not prevent prisoners of war from being tried for war crimes or crimes against humanity. Some of those at "Camp X-Ray" will undoubtedly deserve punishment for involvement in massacres committed by Taliban forces or for willing participation in al-Qa'ida's genocidal jihad against American citizens (and anyone else who gets in the way).

The video obtained by Australian television at the weekend shows very clearly how al-Qa'ida's "training" was not for wars of Muslim liberation but for atrocities directed against Western civilians in general, and Americans in particular. Those who attended training camps with this knowledge were complicit in a conspiracy to commit crimes against humanity and deserve punishment – but only after a trial that meets basic standards of fairness.

Such trials would best be conducted under the auspices of the United Nations, building on the experience of the Hague tribunal for former Yugoslavia. The Security Council is empowered to set up an ad hoc tribunal for this purpose and would do so immediately if requested by the US. The Lockerbie tribunal provides an alternative model. But whatever legal process the prisoners are put through, it must be open and provide basic defence rights before independent and impartial judges who cannot order executions.

Those POWs against whom there is no evidence of international criminality must, under Article 118 of Geneva Convention III, be repatriated to their country of nationality. For some that will mean prosecution under local law. In the case of the half-dozen British POWs, they would face a period of detention and the possibility of a treason trial or proceedings under the Foreign Enlistment Act.

The Foreign Office has thus far confined itself to trying to establish the identity of these British detainees without expressing any view about their status or treatment. But Britain is a party to the armed conflict in Afghanistan and has a duty to ensure that the principles of the Geneva Conventions are upheld.

That duty now requires us to remind our US allies that the Conventions lay down that anyone captured in the course of such a conflict must be presumed to have POW status until a competent court – not Donald Rumsfeld – declares otherwise.

The writer is the author of 'Crimes Against Humanity: The Struggle for Global Justice', published by Penguin