FRESH fears have been raised that Tony Blair's Government approved the rendition of a suspected terrorist, who was allegedly tortured by the former regime of Colonel Gaddafi, but who is now a leading military commander in the new Libya.

It emerged last night the Commissioner for the British Indian Ocean Territory is being sued for complicity in the alleged rendition of Abdel Hakim Belhaj to Libya via Diego Garcia in 2004.

Mr Belhaj's lawyers have served papers in the High Court in London on his behalf. He is already suing the UK Government, the security forces, and Sir Mark Allen, a former director of counter-terrorism at MI6.

Solicitor Rosa Curling of Leigh Day & Co, who called for the UK Government to be "open and transparent" about its past "mistakes", said: "The evidence we have seen suggests our clients were sent back to Libya via Diego Garcia, with the UK Government's involvement and knowledge. Our clients want to know the truth about what happened to them and who was responsible."

The claims are based on documents recovered from the ruins of Tripoli's intelligence HQ. They were yesterday described as "very worrying" by Sir Malcolm Rifkind, the former Foreign Secretary, who pledged MPs would investigate them once a Scotland Yard probe is finished.

Mr Belhaj was leader of the Libyan Islamic Fighting Group (LIFG), opposed to the late dictator's rule.

Although he has been praised for opposing Gaddafi's regime and is now head of the Tripoli Military Council, in 2003 when the West was mending relations with Libya following the Iraq war, Mr Belhaj was regarded as a leading rebel.

He claims that in March 2004 he was illegally rendered and tortured. He supposedly arrived in Libya just two weeks before Mr Blair signed his controversial "deal in the desert" with Gaddafi, which marked the start of a UK-Libyan rapprochement.

The 45-year-old Libyan army commander is now suing MI6. Successive UK governments have denied any complicity in rendition or torture.

However, documents have come to light following the fall of the Gaddafi regime, which have raised allegations Britain's Secret Intelligence Service was involved in the seizure of Mr Belhaj. Furthermore, it has been claimed the rendition was approved at ministerial level although it is not known by whom.

A letter, dated 2004, from Sir Mark Allen, a senior MI6 officer, to Musa Kusa, Gaddafi's spy chief – who was questioned last year by Strathclyde Police about the Lockerbie bombing following his defection – was recovered from the ruins of the former Libyan regime's intelligence HQ. It refers to Mr Belhaj's rendition to Libya, congratulates the Libyans on the "safe arrival" of the "air cargo" and points out the "intelligence was British".

At the time, the LIFG was regarded as a terrorist organisation, linked to al Qaeda, that recruited young Muslims in Britain to fight in Iraq. The suggestion is British intelligence found out Mr Belhaj was about to travel to Britain and seek political asylum; it told the CIA, which intercepted him in Bangkok and rendered him to Libya.

The key claim now is that MI6 obtained authorisation from the then Labour Government for its action.

Jack Straw, who was Foreign Secretary in 2004, has stated the Blair Government was "opposed to unlawful rendition" and "any use of torture or similar methods".

Yesterday, Sir Malcolm, who chairs Westminster's Intelligence and Security Committee (ISC), said people were entitled to be "extremely uneasy" about the allegations.