A leader of the Libyan rebels who overthrew Colonel Muammar Gaddafi last August launched legal action against the British government yesterday for its alleged complicity in his rendition and torture seven years ago.

Abdel Hakim Belhadj, now head of the Tripoli military council, instructed the London law firm Leigh Day to begin proceedings after the government failed to apologise for the conduct of Tony Blair?s administration.

Mr Belhadj, 45, an Islamist who fought Col.Gaddafi in the 1990s, alleges that he was detained in Bangkok while flying from Malaysia to Britain to seek asylum in 2004. He claims British officials tipped off the CIA. After being questioned and subjected to ?barbaric treatment? by US agents he was sent back to Libya where he was tortured and imprisoned for six years.

While locked up in Tripoli?s infamous Abu Salim prison he was savagely beaten, hung from walls, denied daylight and human contact and sentenced to death after a 15-minute trial, his lawyers said.

In an interview with The Times in September Mr Belhadj said British intelligence officers questioned him and knew he was being tortured.

Documents found in Tripoli after Col.Gadaffi?s fall included a letter from Sir Mark Allen, then head of counter-terrorism at MI6, to his Libyan counterpart saying the return of Mr Belhadj was ?the least we could do for you...to demonstrate the remarkable relationship we have built over the years?.

Mr Belhadj is also suing the government on behalf of his wife, Fatima Bouchar, who was four-months pregnant at the time. She too was arrested in Bangkok and returned to Libya where she was imprisoned for four months.

Sapna Malik, the lawyer representing Mr Belhadj and his wife, said: ?The barbaric treatment which our clients describe, both at the hands of the Americans and the Libyans, is beyond comprehension and yet it appears that the UK was responsible for setting off this tortuous chain of events.?

The Foreign and Commonwealth office said that the Government opposed all torture and that an inquiry was under way into allegations of British complicity in rendition cases during the ?War on Terror?.

A spokesman for the legal action charity Reprieve, which is giving Mr Belhadj investigative help, said he did not want his case to damage relations between Britain and the new Libya. ?It?s just a shame that the current government will not so much as apologise, and make amends for the grievous mistakes of the Blair era?.