Former ministers in Tony Blair's government are expected to be questioned by police over their alleged role in human rights abuses, in a new Scotland Yard investigation into how dissidents were sent to Libya to be imprisoned and tortured by Muammar Gaddafi's regime. The focus of the inquiry will be the involvement of MI6 in the arrest and rendition of two men.

Jack Straw, Tony Blair’s Foreign Secretary between 2001 and 2006, will be interviewed, police and Whitehall officials pointed out, as he would have had to “sign off” operations by MI6 at the time in question. One senior official stressed: “These [operations] were in line with ministerially authorised government policy.”

The Director of Public Prosecutions, Keir Starmer, and the Metropolitan Police Service declared yesterday in a joint statement: “The allegations raised in the two specific cases concerning the alleged rendition of named individuals to Libya and the alleged ill-treatment of them in Libya are so serious that it is in the public interest for them to be investigated now rather than at the conclusion of the Detainee Inquiry.”

The two Libyan victims are known to be Sami al-Saadi and Abdel Hakim Belhaj, who is now a senior military commander in the new Libyan government. Mr Belhaj, 45, was living in exile in Beijing, China, when he was detained with his wife in 2004 en route to the UK where they were trying to seek asylum. He was held for six years in prisons in Libya.

A source close to Mr Belhaj, who is in the process of suing the UK government, told The Independent last night “British police are welcome to carry out their investigations here, after all we are allies now. They can have interviews and any documents needed.

“But Abdel Hakim will continue with his legal action which he only begun after failing to get an apology from the British Government.”

Files discovered by The Independent in Tripoli after the fall of Col Gaddafi’s regime contained letters from Sir Mark Allen, then MI 6’s head of counter-terrorism, to Moussa Koussa, the head of Libyan intelligence, which seemed only too keen to acknowledge his service’s role in the capture and transportation of Mr Belhaj, stressing: “The intelligence about Abu’Abd Allah [a nom de guerre for Mr Belhaj] was British.”

At the time, Mr Belhaj insisted to The Independent that British intelligence agents who had visited him in Tripoli were aware of his mistreatment. “They knew I was being tortured,” he said. “I hoped they would do something about it. I was too terrified during the meeting to say out loud what was being done to me because I thought the Libyans [secret police] were taping what was going on. When the guards left I made sign movements with my hands.

“The British people nodded, showed they understood. But nothing changed; the torture continued for a long time.”

Tony Blair, who was Prime Minister when Mr Belhaj’s rendition took place, maintained he knew nothing about the affair. Jack Straw said: “The position of successive foreign secretaries, including me, is that we were opposed to unlawful rendition, opposed to torture or similar methods and not only did we not agree with it, we were not complicit in it, nor did we turn a blind eye to it.” He added: “No Foreign Secretary can know all the details of what… intelligence services are doing at any one time.”

After the denials of Mr Blair and Mr Straw, the head of MI6 at the time, Sir Richard Dearlove, insisted: “It was a political decision, having very significantly disarmed Libya, for the Government to co-operate with Libya on Islamist terrorism..”

Last night, the former Foreign Secretary issued a statement, saying he is “always happy to deal with any questions relating to his time as Home Secretary or Foreign Secretary” while refusing to discuss yesterday’s developments. His office pointed to a previous statement in which he had welcomed the scrutiny of the Gibson Inquiry into detainee abuse – set up David Cameron last Autumn, and presided over by a retired judge, Sir Kenneth Gibson – which was “ the appropriate forum for these discussions”.

The DPP and Scotland Yard yesterday stated that there was insufficient evidence to bring charges against officers from MI5 and MI6 over alleged complicity in the torture of terrorist suspects in two cases.

Binyam Mohammed, a former Guantanamo Bay inmate, had claimed that a member of the Security Service [MI5], known as Witness B, had interviewed him while he was incarcerated and mistreated in Pakistan. The Crown Prosecution Service has already concluded there was insufficient evidence for charges to be laid.

The second investigation took place after the Secret Intelligence Service [MI6] called in the police to look at allegations that one of its agents was present at Bagram air base, in Afghanistan, when a suspect was mistreated. The DPP and the police said they had been unable to track down the alleged victim and had failed to find evidence which contradicted the account given by the SIS operative.

The current MI6 chief, Sir John Sawers, noted that a police inquiry into the Bagram airbase allegations had exonerated the agent concerned. He continued: “We will of course be cooperating with the police on this new investigation, as we have done on the one now concluding.

“It is in the service’s interest to deal with the allegations being made as swiftly as possible so we can draw a line under them and focus on the crucial work we now face in the future.”

Rendition: What they said

Senior UK intelligence officer to Gaddafi regime after rendition of Mr Belhaj, March 2004

"I congratulate you on the safe arrival of [Belhaj]. This was the least we could do for you... I was grateful to you for helping the officer we sent out."

Tony Blair, former Prime Minister, September 2011

"We didn't support rendition as far as I know. There is no point putting stories to me about these people, I don't know about them."

Jack Straw, former Foreign Secretary, September 2011

"The position of successive foreign secretaries, including me, is that we were opposed to unlawful rendition, torture... and not only did we not agree with it, we were not complicit in it, nor did we turn a blind eye to it."

Sir Richard Dearlove, former head of MI6, September 2011