A former Libyan dissident who was abducted and flown to one of Muammar Gaddafi's prisons in a so-called rendition operation mounted with the help of MI6 has started legal proceedings against Jack Straw, who was British foreign secretary at the time.

Lawyers representing Abdel Hakim Belhaj confirmed on Wednesday they had served papers on Straw alleging his complicity in the torture that Belhaj subsequently suffered, as well as misfeasance in public office.

Straw is already facing the prospect of being questioned by Scotland Yard detectives after an announcement by the Crown Prosecution Service earlier this year that a criminal investigation was being launched into the rendition operation.

Belhaj and his wife are alleging that Straw was complicit in the "torture, inhuman and degrading treatment, batteries and assaults" that they say were perpetrated on them by Thai and US agents, as well as Libyan authorities.

They are seeking damages from Straw for the trauma they suffered.

Documents discovered in an abandoned Libyan government office last September outlined the role that MI6 – and in particular its head of counterterrorism, Mark Allen – played in providing the intelligence that allowed the CIA to detain Belhaj and his pregnant wife, Fatima Bouchar, in Bangkok in March 2004.

Last week, Bouchar told the Guardian how she was chained to a wall for five days in a secret prison in Bangkok before being taped from head to foot and secured to a stretcher for the 17-hour flight to Tripoli.

Significantly, MI6 did not deny involvement when the documents were discovered: instead, well-placed Whitehall sources insisted the agency's actions were part of "ministerially authorised government policy".

There were reports at the weekend that MI6 confronted Straw with evidence that he was the minister who personally authorised the operation. This is said to have happened after Straw gave a radio interview last year in which he sought to distance himself from the affair, telling listeners that "no foreign secretary can know all the details of what its intelligence agencies are doing at any one time".

Those reports triggered the decision by Belhaj's lawyers to serve legal papers on the former foreign secretary. Those papers also demand that Straw disclose documents relating to the rendition of a second Libyan dissident, Sami al-Saadi, who was abducted and flown to Libya a few days after Belhaj, along with his wife and four children.

Although Belhaj's lawyers have already launched proceedings against the British government, the latest action is against Straw personally, and is thought to be the first time proceedings of this kind have been taken against a former foreign secretary.

If the case reaches court, it would be exactly the sort of proceedings that would be heard behind closed doors, under the justice ministry's much-criticised secret justice proposals, which some ministers say are needed to protect national security, but which critics suspect are intended to protect the government and intelligence agencies from embarrassment.

Sapna Malik, of the London law firm Leigh Day, said: "We have said all along that liability must follow the chain of command. These latest revelations bring us closer to that goal. If the former foreign secretary does not now own up to his role in this extraordinary affair, he will need to face the prospect of trying to defend his position in court."

Cori Crider, of the legal charity Reprieve, which is also representing the two men, said: "When scandals like this break, the political paymasters almost never face the music. For once, there's a chance things might be different.

"We've said from the start that the minister responsible for this mess needed to admit their role. Now that we seem to know who it was, it's time for Jack Straw to account – and atone – for what he did."

As the scale of UK support for the CIA's rendition programme began to become clear in 2005, Straw dismissed media reports as little more than conspiracy theories. In December 2005 he told MPs on the Commons foreign affairs committee that "unless we all start to believe in conspiracy theories and that the officials are lying, that I am lying, that behind this there is some kind of secret state which is in league with some dark forces in the United States … there simply is no truth in the claims that the United Kingdom has been involved in rendition."

Contacted on Wednesday, Straw said he had nothing to add to comments he made during the radio interview.

MI6 regularly requests foreign secretaries to "disapply" UK law in order to protect its officers from being prosecuted or sued in the UK as a result of their operations overseas. The authorisations can be signed only by secretaries of state, and do not offer any protection for those politicians.

Last week, Tony Blair also faced renewed questions about the abduction of Belhaj and his wife. He replied that he had "no recollection" of the matter.