If Britain felt pride at the end of last month at its role in the dethronement of Colonel Gaddafi, this past week it felt shame. A cache of documents unearthed by Human Rights Watch at an abandoned government building in Tripoli revealed that the UK had arranged the "rendition" of terror suspects to Libya, where they were then allegedly tortured by Gaddafi's henchmen. One of the reported victims was Abdel Hakim Belhadj, who was, in his own words, "hung from a wall" and "put in a container surrounded by ice". Belhadj is now a military commander of the Libyan rebels. The country that allegedly enabled his torture was bombing his enemies a few years later. Little wonder that the west in general and Britain in particular is so mistrusted in parts of the Arab and Muslim worlds.

Evidence of the UK's complicity in torture - the darkest legacy of its participation in the "war on terror" - has accumulated over the past decade. A special investigation, published in the 29 August issue of the New Statesman, showed how British troops regularly hand over suspected insurgents to the Afghan authorities with little guarantee that they will not be tortured. In February 2010, the Court of Appeal forced the then Labour government to publish CIA-based evidence showing that MI5 knew Binyam Mohamed was subjected to "at the very least cruel, inhuman and degrading treatment" in Pakistan. Finally, last November, the current government paid out £10m in compensation to 16 former Guantanamo Bay detainees, seen by some as a tacit admission that the UK had connived in their torture.

The latest allegations are the gravest yet, however. For the first time, there is reason to believe that Britain, independent of the US, organised the "rendition" of a terror suspect, along with his wife and children. Ten years on from the 11 September 2001 attacks and the west's disastrous
response, the full extent of the UK's disregard for human rights is only beginning to emerge.

As the Tripoli files suggest, such abuses flowed from a sordid alliance between the New Labour government and the Gaddafi regime. The former MI6 agent Sir Mark Allen fawned over Mousa Kousa, then Libya's head of external security and later Gaddafi's foreign minister, thanking him for a gift of "delicious" dates, and remarking that "this was the least we could do for you" after rendering Mr Belhadj to Libya. It is one thing to maintain diplomatic relations with dictatorships; it is another to collaborate actively with them.

The coalition government has responded by emphasising that the "allegations relate to a period under the previous government", and by pledging that the disclosures will be looked at by the Gibson inquiry, set up to investigate claims of British collusion with torture. Yet it should not be so
sanguine. Tempting as it may be, it is unwise for the government to make this a party political issue. The British establishment, including the Conservative Party, was collectively guilty of wilful blindness.

Furthermore, though the government was rightly praised for establishing the Gibson inquiry, it is independent in name only. The Cabinet Secretary and the Prime Minister will have the final say over what can be made public and torture victims will not be able to question MI5 or MI6 officers, not even through lawyers. As Shami Chakrabarti, the director of Liberty, has said, this is “effectively an internal Cabinet Office" inquiry. It is for this reason that it has been boycotted by the detainees' lawyers and by ten human rights groups. But there is still time for the government to change course. The Gibson inquiry will not begin until a police investigation into previous claims against MI5 and MI6 has concluded. It is not too late for ministers to establish the credible and transparent investigation that the severity of the allegations demands.

As the Arab spring erupted, Mr Cameron rightly declared that "denying people their basic rights does not preserve stability, rather the reverse". Britain will not be seen as a force for good, however, until it has atoned for its past sins. After years of obfuscation and denial, the truth must be heard.