Last Friday it was announced that, under instructions from the attorney general to the director of public prosecutions, the police are to investigate claims by released Guantánamo prisoner Binyam Mohamed that MI5 agents had knowledge of his US-directed torture, and that they also provided information to his interrogators while he was being held incommunicado.
Given that it is seven months since judges in the high court ruled that British involvement with the US authorities "went far beyond that of a bystander or witness to the alleged wrongdoing," this is welcome news, but what the case of Mohamed demonstrates above all is the extent to which the Bush administration's horrendously novel approach to detention and intelligence-gathering in the "war on terror" not only made a mockery of the US's adherence to the UN Convention Against Torture, but also infected the policies of numerous other countries.
Moreover, in the Bush administration's deliberate flight from the absolute prohibition on torture - accompanied by its decision to hold terror suspects neither as prisoners of war, protected by the Geneva conventions, nor as criminal suspects to be put forward for trials in a recognised court of law - it has become clear that the US had no closer ally than Britain.
This is revealed not only in the case of Mohamed, but also in the cases of other British prisoners held in Guantánamo: 15 in total, according to a report in the Daily Telegraph at the weekend. I presume that these include the other British prisoners released from Guantánamo, who were all held at some point in US-run prisons in Afghanistan, where they were visited by British intelligence agents. In addition, as the Independent reports today, another of these men is the British resident Shaker Aamer (still held at Guantánamo), whose lawyers reported that "UK intelligence services officers were present while Mr Aamer was beaten. They provided information and encouragement to his US torturers. They made no attempt to stop his ill-treatment or any enquiries into his wellbeing."
Nor is this the end of British involvement in torture. As the Guardian has revealed in a number of reports over the last 10 months, the British intelligence services have provided information to be used in the interrogations of British nationals held in Pakistan and Egypt, even though they must have been aware that interrogations in both countries may have involved the use of torture.
Often overlooked, however, is another British policy that could only have arisen through an enthusiastic endorsement of the Bush administration's wayward policies: the detention, without charge or trial, of "terror suspects" in the UK, first in Belmarsh, for three years (from December 2001 to December 2004), until the law lords ruled the process illegal, and, ever since, under control orders or deportation bail orders, which are often so strict that they amount to house arrest.
In the country that exported habeas corpus to the rest of the world (the principle, enshrined in the Magna Carta, that no one may be imprisoned "except upon the lawful judgment of his peers or the law of the land"), it is disturbing to realise that dozens of men - including a handful of British nationals - are deprived of their liberty based on secret evidence that neither they nor their lawyers are allowed to see.
Moreover, in the cases of those facing deportation, the British government is prepared to endanger our own commitment to the UN convention against torture, which prohibits the return of foreign nationals to countries where they face the risk of torture, primarily because it is unwilling to join the rest of the world in finding ways to allow information from the intelligence services to be presented in a court of law while protecting its sources.
Instead, we are asked, by the home secretary Jacqui Smith, to trust that our intelligence services never make mistakes, and are prevented from being able to investigate suspicions that, in some cases, the information used to detain these men was extracted through the torture of prisoners in other countries.
I am glad to be able to report that, today, Diane Abbott MP is hosting a parliamentary meeting in the House of Commons to discuss the growing use of secret evidence in British courts, and I hope that numerous MPs deign to attend, but above all I hope that the people of this country understand the extent to which the corrosive effects of the Bush administration's "war on terror" have diminished our own ability to recognise that, without fair trials and an absolute ban on the use of torture, we have undermined the very foundations of fair and open justice that were enshrined, 794 years ago, in the Magna Carta.