Human rights lawyers began legal action against the British government on Tuesday, accusing it of involvement in the illegal transfer of a terrorism suspect from Indonesia to Egypt where they say he was tortured.

Reprieve, a British-based legal rights group, says Britain knowingly allowed Mohammed Saad Iqbal Madni to be transferred from Jakarta to Egypt via a US airbase on Diego Garcia, a British-ruled island in the Indian Ocean, in 2002.

Once in Egypt, Madni says he was tortured for three months and then sent to the U.S. prison at Guantanamo Bay in Cuba where he was held for six years before being released last year without charge. He now lives in Pakistan.

If successful, the case could formally link Britain to the illegal transfer of suspects across borders for the first time. Britain has admitted U.S. "rendition" flights entered and left its territory but said it had been unaware of this at the time.

"We have made our disappointment about these flights clear with the United States and secured firm new assurances that on no other occasion since September 11, 2001 has a US intelligence flight with a detainee on board passed through UK territory," the Foreign Office said in a statement on Tuesday when asked to comment on Reprieve's case.

Reprieve, which represents several detainees held at Guantanamo Bay, says Britain must have known about Madni's rendition via Diego Garcia because a specific chain of command was needed to authorise "unorthodox" flights.

It says records relating to flights to Diego Garcia before 2008 have been destroyed in mysterious circumstances. It says its case is aimed at forcing the government to come clean.

"For too long, Diego Garcia has been used as a safe haven for the US and UK to commit criminal acts," said Clare Algar, executive director of Reprieve.

"It is about time this territory was subjected to the scrutiny of UK and international law. Mr Madni's case is the first step towards restoring the rule of law to Diego Garcia."

Andrew Tyrie, a British member of parliament who heads a committee looking into Britain's role in rendition -- the illegal movement of suspects across borders -- said he hoped Reprieve's case would expose the truth.

"The litigation announced today will contribute to the growing amount of information on rendition and British involvement in it," he said. "But the drip-drip of revelations about UK involvement in renditions is hugely damaging."

Tyrie began asking questions about Diego Garcia and its role in rendition two years ago and at first received repeated denials from the government that it was involved at all.

That changed in February 2008, when the Foreign Office admitted Britain had unwittingly played a role and Foreign Secretary David Miliband apologised for misleading parliament. Tyrie said it was now time for a full and open inquiry.

"It is now the only way to give the public confidence that we have got to the bottom of all of this, to draw a line under it and to move on," he said.

(Reuters)