Sonya Sceats [Associate Fellow in International Law, Chatham House]: "Claims by Binyam Mohamed that the UK security service colluded in his 'medieval' torture while detained in Pakistan, Morocco and Afghanistan have reignited an important debate about the standing of the torture ban in UK foreign policy.

According to Mohamed, British officials not only failed to protect him from torture they probably knew was occurring, they actively contributed to it by supplying information about his life in Britain which his tormentors used as a basis for interrogations.

The UN Convention against Torture, which the UK ratified in 1988, requires states to criminalise complicity in torture. It demands that allegations of complicity in torture be examined and, where appropriate, prosecuted.

The UK Government denies any wrongdoing in relation to torture allegedly inflicted on Mohamed by the security forces of other states; however on 10 July the Metropolitan Police Service announced that it was launching a full criminal investigation.

Meanwhile, others are stepping forward with similar claims. In evidence to the House of Commons Foreign Affairs Committee on 16 June, Foreign Secretary David Miliband disclosed that there are eight cases involving alleged complicity by British officials in "mistreatment" of detainees abroad.

The UK is justifiably proud of its long rejection of torture as a matter of law, but the imperatives of counter-terrorism have seemingly placed this commitment under increasing strain of late.

The issue of how information extracted through torture may be used is especially fraught. In 2005, the House of Lords ruled that evidence obtained this way is inadmissible in UK courts, with Lord Bingham remarking that the prohibition of torture means that the "fruits" of torture must also be rejected.

But the question remains whether such information may be used operationally to combat terror threats. Lord Bingham suggested this might be permissible in "limited and exceptional circumstances" and the Government's stated view is that where there is a threat to life, a "balanced judgment" must be made.

Mohamed's allegations expose the risks in this approach — if intelligence gleaned via torture is usable as part of efforts to prevent terror attacks, security officials may have mixed feelings about pushing for the torture to stop.

This dilemma is addressed in Government guidance for security officials interviewing detainees abroad. The problem is that the Government has repeatedly refused to make this guidance public (it is currently being reviewed and the Prime Minister has promised to disclose the new version), fuelling suspicions that it is not compliant with the UK's obligations under the Convention against Torture.

As well as requiring states to keep guidance of this sort under regular review, the Convention obliges states to "fully" include education and training on the prohibition of torture in the training of anyone, including law enforcement personnel and public officials, involved in the custody, interrogation or treatment of detainees.

The Government was due to submit a periodic report to the UN Committee against Torture on its compliance with the Convention in December 2008, but such is the gravity of the issues raised by Mohamed's case that it has decided to withhold its report until they are resolved. There can be no doubt that the Committee will scrutinise closely whether any violations of international law have occurred.

According to Lord Bingham in the judgment referred to above, "[t]here can be few issues on which international legal opinion is more clear than on the condemnation of torture. Offenders have been recognised as the 'common enemies of mankind.'" The UK Government should ensure that it remains on the right side of this divide."