One by one, revelations from the ransacked archives of the old Gaddafi regime in Libya cast fresh doubts on Britain's boast that it is never complicit in torture. First we heard the claims of the former Libyan dissident Abdelhakim Belhaj who maintains that Jack Straw, as Foreign Secretary, authorised his rendition by the CIA to Tripoli in 2004. Now follow further damaging claims, suggesting that MI5 and MI6 worked hand in glove with Tripoli in 2006 to put pressure on Libyan asylum seekers in the UK to co-operate with the Gaddafi regime.

The Belhaj case was troubling enough. Back in Gaddafi's clutches in 2004 with Britain's apparent blessing, he was imprisoned for six years in one of Libya's most notorious jails. Shockingly, a letter dated 18 March 2004 from a senior MI6 officer congratulated the head of Gaddafi's intelligence on Mr Belhaj's arrival; it is on the basis of this incriminating document that he is demanding an apology both from Mr Straw – now seeking legal aid to fight the case – and from Mr Straw's then master, Tony Blair.

In the Belhaj case, Mr Straw, and potentially Mr Blair, may have condoned his "rendition" to Libya by another power, in this case the CIA. The latest memoranda from Libya point to equally serious crimes. These documents say that in 2006, by which time Margaret Beckett had replaced Mr Straw as Foreign Secretary, MI5 and MI6 were establishing a close relationship with Gaddafi's External Security Organisation, working with the ESO to blackmail Libyan dissidents in Britain into co-operating with Tripoli by agreeing to go home or by becoming informants.

A document dated August 2006 makes it disturbingly clear how far Libyan intelligence's British colleagues seemed ready to go to obtain this goodwill. If one man was to refuse to become an informant, the document reads, "British police will arrest him and accuse him of associating with Libyan secret agents. He will be told that as a non-resident of Britain he could be deported if found guilty."

It must be noted that these files are Libyan, not British, and it is possible that the Libyans misinterpreted pledges that they believed they had received from their British counterparts. It is also true that at the time the Gaddafi government had held out an olive branch to the West by renouncing its programme of weapons of mass destruction, and the British government was eager to make good on this offer in order to secure Tripoli's help in the fight against al-Qa'ida. Nevertheless, unless these newly revealed documents are exposed as forgeries, it will be clear that this process of rapprochement with the Gaddafi dictatorship went much too far. The Tory MP David Davis was right to say that the Belhaj case does not seem to have been a one-off, and that his claims mark only the start of "a continuing intelligence saga" that goes much wider than Britain giving the nod to CIA renditions from far-off places like Thailand.

As Mr Davis went on to say, the suggestion now is that British intelligence deliberately "exposed people who had been given refuge here to the very people they had fled". This business of toying with people's lives in the interests of realpolitik will strike most people as grotesque and shameful.

It is of course also illegal, which is why Mr Davis is also right to demand a much wider inquiry than the one the Metropolitan Police is undertaking into Mr Belhaj's allegations against Mr Straw. Such an inquiry needs to establish whether the British intelligence services were operating without ministerial approval when they hatched what sound like outrageous bargains with their Libyan counterparts. If they were, they need reorganisation. If not, then a number of former ministers, of whom Mr Straw is only one, should face prosecution.