A cross-party group of senior MPs is meeting home secretary Alan Johnson on Wednesday to request clemency for Nasa hacker Gary McKinnon.
MPs Michael Meacher, David Davis and Chris Huhne set up the meeting to discuss McKinnon's predicament and to push for the Londoner to face charges in the UK, rather than be extradited to the US, Meacher said in a statement on Tuesday.
However, Johnson has said it would be illegal for him to intervene in the hacker's case, as the US has a legal right to seek his extradition for a serious crime.
Johnson's claim to be unable to prevent the extradition once it had been cleared by the High Court is not correct in law, Meacher said the statement.
"Not only has the home secretary got the power, but he has the duty to intervene in an extradition case, even after the court process has ended, if there is a real risk of a human rights breach should extradition proceed," said Meacher. "Gary's medical condition is such that medical experts have concluded there is a grave risk to Mr McKinnon's health if he is extradited to the US."
McKinnon was diagnosed last year with Asperger's syndrome, a condition on the autism spectrum. This is a compelling reason for him to be tried in Britain, Meacher said, especially as there is no reason why McKinnon cannot face charges in the UK for an act which took place in the UK.
Two human rights lawyers from Matrix Chambers, commissioned by the Daily Mail, have provided "an unambiguous legal opinion" that Johnson is able to prevent the extradition if he wishes to, Meacher wrote in a blog post on Tuesday.
US authorities have requested that London-based McKinnon be extradited to face charges of breaking into 97 US military computers, which they allege caused damage, including the impairment of a battleship, adding up $700,000 (£400,000). While McKinnon has acknowledged that he hacked into the systems, he maintains he intended merely to search for evidence of extraterrestrial life.
The self-confessed hacker enjoys widespread support among back-bench and opposition politicians, including Conservative leader David Cameron and much of the Tory front bench. Peter Hain and other senior Labour politicians have also advocated a UK trial for McKinnon. His cause has also generated public statements of support from celebrities such as Sting and his wife Trudie Styler, Chrissie Hynde, Bob Geldof and David Gilmour.