Gary McKinnon, the 42-year-old Briton who has admitted hacking into NASA systems, is due to fight his extradition to the US in the House of Lords on Monday.
Hearing his appeal will be the Law Lords, a group of senior judges. According to McKinnon's solicitors, the two-hour hearing will focus on irregularities in the extradition process.
"There will be legal arguments about plea bargaining and abuse of the extradition process," said his solicitors, Kaim Todner.
Representing McKinnon will be his own barrister, David Pannick QC, and a barrister acting for human rights organisation Liberty, Edward Fitzgerald QC. Acting for the US authorities will be Clare Montgomery QC.
According to McKinnon and his counsel, during the plea bargaining process the American authorities threatened McKinnon. Lawyers acting on behalf of the US government allegedly said that if McKinnon did not agree to co-operate with them, they would push for the highest possible penalties and that he would be "turned over to New Jersey authorities to see him fry". And, the defence further alleged, the US said if McKinnon did not agree to a deal there would be no chance of him serving his sentence in the UK near his family.
McKinnon's fate now hangs on the decision of the Law Lords, who will determine whether there was an abuse of process by the US authorities. According to Kaim Todner, if the Lords decide there was an abuse of process, this would end extradition proceedings, although McKinnon may still face trial by UK authorities.
The US lawyers may dispute what was said during the plea bargaining process, in which case the Law Lords could refer the case back to Bow Street Magistrates Court, where McKinnon's case was heard.
If the Lords decide there was no abuse of process, the extradition procedure will go ahead. An extradition order was signed in July 2006 by the then home secretary John Reid.
McKinnon stands accused of hacking into a series of sites belonging to the US Army, Air Force, Department of Defence and NASA. McKinnon has admitted hacking NASA systems, but claims that he was merely looking for evidence of UFOs and extraterrestrial activity.
The US government alleges McKinnon's hacking activities caused US$700,000 worth of damage. McKinnon denied causing any damage to the US systems.
Under the terms of the controversial Extradition Treaty 2003, the US government has not been required to show any evidence, either of McKinnon's hacking or the alleged damage caused, to secure his extradition. The Extradition Treaty is not reciprocal, as it has not been ratified by the US government.
ZDNet.co.uk's Colin Barker contributed to this article.