Radical cleric Abu Qatada will begin his appeal on Wednesday to be freed from detention as a suspected terrorist.
Abu Qatada has been held in a prison since October 2002
Abu Qatada has been held without charge or trial for more than a year, under terror laws imposed after 11 September.
His case before the Special Immigration Appeals Commission in central London is set to last for three weeks. Most of the hearing will be in private.
The government has blamed him for inspiring the 11 September hijackers, but he has always denied such links.
Abu Qatada became known for his fiery preaching at North London's Finsbury Park Mosque.
Despite the accusations against him, many within the Muslim community regard him as a distinguished scholar of the Koran.
But the government believes he has been "directly involved" in terrorist operations.
They told the commission 18 video tapes of his sermons were found in a Hamburg flat used by three of the men alleged to have hijacked the planes that crashed into the World Trade Center.
They also said he gave "spiritual advice and encouragement to those involved in terrorist plots in Strasbourg and Paris".
Abu Qatada is a Palestinian with Jordanian
nationality and he is also known as Sheikh Omar Abu Omar.
He was granted asylum in Britain in 1993 after claiming he was fleeing religious persecution in Jordan.
He is among a number of men who have been interned under the Anti-Terrorism, Crime and Security Act, 2001, introduced by Home Secretary David Blunkett.
The act says people can be held if they pose a threat to national security or have links to international terrorism but are foreign nationals who cannot be deported.
Lawyers for Mr Blunkett have only to prove that the government has
"reasonable grounds to suspect" the detainees have links with terrorism.
This is a
far lower requirement than the standard of proof needed to convict them in a
Most of the appeal commission's hearings are closed to the press and public, and the men are not
allowed to hear all the evidence against them.
Their lawyers are denied access to most of the top secret material which the
government claims backs up the decision to detain them.
Instead, the Attorney General has appointed special advocates who have been
security-vetted by MI5 to act on their behalf.
Last month, 10 of the men who have been held under these emergency powers lost
their appeals against detention.