By DAVID ROSE

The Government is refusing to help a man prove he was taken to Morocco aboard a CIA torture flight and brutally interrogated.

Britain says it will not help Binyam Mohammed - who is facing trial by US authorities - because it has "no obligation under international law" to provide information that might prevent someone being convicted outside the UK on evidence obtained through torture.

Lawyers acting for Mohammed, an Ethiopian refugee who lived in London for seven years, will this week file an unprecedented High Court lawsuit saying Britain's denial of assistance breaches the UN Convention Against Torture and UK law.

Mohammed, 29, has been held at Guantanamo Bay since 2004 over an alleged plot to detonate a radioactive 'dirty bomb' in New York.

The lawsuit argues that he is innocent of terrorism and that the British Government must disclose evidence in official files that he was tortured.

Since The Mail on Sunday first reported Mohammed's story in 2005, his lawyers, Clive Stafford Smith and Lieutenant-Colonel Yvonne Bradley, a US Air Force advocate, have found vital corroboration for his key allegations.

Mohammed, who was arrested on his way to London at Karachi airport in Pakistan in April 2002, says he was handed over to US custody and flown to Morocco - a victim of the secret American programme known as extraordinary rendition.

There, he insists, he was subjected to torture over 18 months, including beatings, suspension by his wrists, and cuts by a scalpel on his chest and genitals.

He says he was then transferred to Afghanistan, where he spent five months in darkness in the secret CIA prison known as the 'dark pit' and endured further abuse.

Mohammed's descriptions of the jails match those from other prisoners he has never met, Lt Col Bradley said.

But most significant are air traffic control flight logs for a Gulfstream V executive jet, registration N379P.

This plane, dubbed 'the torture taxi', was owned by a CIA front company and was in Pakistan, Morocco and Afghanistan on the days Mohammed says he was moved.

He also says his interrogators asked him about details of his life that could only have come from British official sources.

"This may show that Britain was complicit in Binyam's rendition and torture," Mr Stafford Smith said.