A Libyan Islamist has filed a criminal complaint with London police claiming British and US intelligence handed him over to Moamer Kadhafi's regime in 2004, a rights group said on Thursday.

Sami al-Saadi said he and his family of six were detained while living in London, then illegally rendered to Libyan authorities by the foreign intelligence service MI6, working with the US Central Intelligence Agency.

British legal charity Reprieve said Thursday it had written to London's Metropolitan Police to ask them to investigate allegations of conspiracy to torture.

It said it was the "family's wish to lodge a complaint against UK security services -- in particular former MI6 counter-terror director Mark Allen -- as well as Kadhafi's former security chief,Mussa Kussa.

"Evidence of the mistreatment of Mr al-Saadi, his wife, and four children all aged 12 or under at the time emerged earlier this year after documents were found in the wake of the Libyan revolution, showing the UK's key organisational role in the case," it said.

"Letters were also found showing a close relationship between Mussa Kussa and 'Mark in London', thought to be Mark Allen."

Reprieve, which acts on behalf of the Saadi family with a London legal firm, said Saadi was an opponent of the late Kadhafi's regime when he was subject to the illegal rendition.

He was imprisoned and tortured by Kadhafi's regime for several years and during that time British and US intelligence officers questioned him.

His wife and children were detained for several months, "in constant fear for their lives", it said.

The legal move comes a day after Foreign Secretary William Hague said that Britain's alleged involvement in renditions after 9/11 harmed its global reputation, but said the country should be "drawing a line under the past."

Prime Minister David Cameron set up an inquiry last year to probe allegations of British complicity in torture.