The computer hacker Gary McKinnon will make a last plea to Alan Johnson, the Home Secretary, against being extradited to the United States after his appeal to go to the Supreme Court was rejected.

Lawyers for Mr McKinnon, who has Asperger’s syndrome, said that they will submit a fresh psychiatric report showing his “extremely fragile mental state”, after two High Court judges yesterday refused him leave to go to Britain’s highest court.

Mr McKinnon, 43, from North London, faces up to 70 years in prison if he is convicted of what US prosecutors have called “the biggest military computer hack of all time”.

Speaking outside the Royal Courts of Justice, in Central London, his mother, Janice Sharp, condemned yesterday’s decision and said that her son was suicidal. “What Gary did was wrong, born of his compulsive and obsessive behaviour. But it does not justify extradition, which would be a cruel and excessive punishment, particularly given his Asperger’s,” she said. “I’ve fought for five years to protect my son and I am not about to give up now. I will not stand by and watch Gary be destroyed.”

Karen Todner, his lawyer, said that they had been allowed 14 days to make representations. “We will ask the Home Secretary to reconsider his decision to ask for Gary’s removal until after the appeal of Ian Norris [the former Morgan Crucible chief executive also facing extradition] on November 30. The effects of these proceedings have been devastating. The legal team are now considering our position and we will exhaust every avenue to prevent Gary’s extradition. We are not giving up,” she said.

Lord Justice Stanley Burnton and Mr Justice Wilkie ruled yesterday that there was no point of law involved in the case to justify granting leave to go to the Supreme Court. “His extradition is a lawful and proportionate response to his alleged offending,” Lord Justice Burnton said.

US authorities claim that he hacked 97 military computers and caused $800,000 (£487,000) of damage. Mr McKinnon admits hacking into Pentagon computers but denies that it was malicious. He argues that his case should be tried in Britain. He has previously appealed unsuccessfully to the House of Lords and the European Court of Human Rights and many experts said the judicial review application in the High Court was likely to be his last opportunity to avoid extradition.

His lawyers claimed the authorities had not given sufficient consideration to the fact that Mr McKinnon’s Asperger’s syndrome, which they said could have “disastrous consequences”, including possibly suicide, if he were extradited.

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