A British man accused of hacking into American military computers has failed in his latest bid to avoid extradition to the U.S., his lawyer said Friday.

Gary McKinnon is charged with breaking into dozens of computers belonging to NASA, the U.S. Defense Department and several branches of the U.S. military soon after the Sept. 11 attacks. U.S. prosecutors have spent seven years seeking his extradition.

The 43-year-old claims he was searching for evidence of alien life, although prosecutors say he left a message on an Army computer criticizing U.S. foreign policy.

The High Court decision denies McKinnon the possibility of taking his case to the country's new Supreme Court — the latest in a series of blows to his campaign to remain in Britain.

Lord Justice Stanley Burnton said that extradition was "a lawful and proportionate response" to McKinnon's alleged crimes and that the legal issues raised by the case were not important enough to be considered by the nation's highest court.