By Peter Griffiths
LONDON (Reuters) - A Libyan militia leader has begun legal action against a former senior British intelligence chief whom he accuses of playing a key role in illegally returning him to Libya to be jailed and tortured under Muammar Gaddafi, his London-based lawyers said.
Abdel Hakim Belhadj, who commands one of Libya's most powerful militias, is seeking damages from Mark Allen, who was director of counter-terrorism at MI6, Britain's foreign intelligence agency.
Belhadj and a second Libyan dissident, Sami al-Saadi, accuse Allen of complicity in torture, negligence and misfeasance in public office -- the wrongful exercise of his authority.
"We are taking this unusual step of preparing legal action against an individual as the documents we have in our possession suggest Sir Mark was directly involved in the unlawful rendition of our clients," said lawyer Sapna Malik, from the London law firm Leigh & Day, which represents Belhadj and Saadi.
An Oxford-educated Middle East specialist, Allen retired from MI6 in 2004 and went on to work for oil major BP and The Monitor Group, a global investment and consultancy firm.
He is an honorary fellow of St Antony's College at Oxford University and sits on the advisory board for the London School of Economics' centre for diplomacy and international affairs.
Belhadj accuses Allen of helping to organize the operation to fly him from Bangkok to a prison in Libya in 2004.
During six years in jail, Belhadj says, he was tortured and beaten. He also accuses Thai and U.S. agents of abusing him when he was first held in Bangkok.
Born in Libya in 1966, Belhadj is a former leader of the Libyan Islamic Fighting Group, which waged an insurgency against Gaddafi in the 1990s.
His emergence as an important figure in Libya after Gaddafi's downfall is potentially embarrassing for London, which led international moves to improve relations with Libya after Gaddafi renounced weapons of mass destruction in 2003.
Belhadj's lawyers say Allen's name was found in intelligence documents recovered in Tripoli around the time of the collapse of Gaddafi's administration last August.
The pair are also suing the British government and its legal advisers, the MI5 domestic intelligence agency, the Home Office (interior ministry) and the Foreign Office, which oversees MI6.
A Foreign Office spokesman said: "We take all allegations of mistreatment seriously, but these matters are also the subject of legal correspondence between Mr Belhadj's lawyers and our own so we can offer no further comment at this stage."
Allen could not immediately be reached for comment.
Earlier this month, Britain postponed a judge-led inquiry into whether its security services knew about the torture of suspects overseas. Ministers said the inquiry would be delayed because police have begun a separate investigation into whether London illegally sent detainees to Libya.
Britain has long faced accusations that its spies were complicit in the abuse of overseas detainees in the years after the September 11, 2001 attacks.
Prime Minister David Cameron has cited those suspicions as one of the reasons why he set up the now-delayed inquiry. Britain's security services have always denied using or condoning torture.
(Editing by Mark Heinrich)