LONDON, UK: A British "UFO eccentric", wanted in the United States for breaking into NASA and Pentagon computers in "the biggest military hack of all time", lost his latest battle to avoid extradition on Friday.

Gary McKinnon, 43, was refused permission to appeal to the Supreme Court, Britain's highest judicial body, as he continued his long battle to avoid being sent to the United States.

McKinnon, who was recently diagnosed with Asperger's Syndrome, a form of autism, had challenged a refusal by Britain's chief prosecutor to allow him to be tried in Britain, which would have avoided any need for extradition.

However, London's High Court said his case did not raise "points of law of general public importance" which is necessary to pursue a case at the Supreme Court, the Press Association reported.

His lawyers said they would now consider applying to the European Court of Human Rights in Strasbourg. Earlier, In July also his plea was rejected by the high court.

In an earlier ruling, the High Court accepted that his extradition could have consequences for his health, but judges decided that the process of the law overruled those concerns.

"The effects of these proceedings on Gary have been devastating," said McKinnon's lawyer Karen Todner. "The legal team are now considering our position and we will exhaust every avenue to prevent Gary's extradition."

McKinnon, whose lawyers describe him as a "UFO eccentric" who used the Internet to search for alien life, is accused of causing the U.S. Army's entire network of more than 2,000 computers in Washington to be shut down for 24 hours. U.S. authorities called this "the biggest military hack of all time".

He was arrested in 2002 after U.S. prosecutors charged him with illegally accessing computers, including systems at the Pentagon and NASA, and causing $700,000 worth of damage.

If he is convicted by a U.S. court, McKinnon could face up to 70 years in prison.

McKinnon told Reuters in an interview that he was just a computer nerd who wanted to find out whether aliens really existed. He became obsessed with trawling through large military data networks for any proof that they might be out there.

He had used his own computer with a 56K dial-up modem at his London home with no password protection and somehow managed to evade every security measure the U.S. military had adopted. While McKinnon admits hacking, he argues it was not malicious.

His cause has been backed by the Daily Mail newspaper and some British politicians.

"What Gary did was wrong, born of his compulsive and obsessive behaviour. But it does not justify Gary's extradition, which would be a cruel and excessive punishment, particularly given his Aspergers," his mother Janis Sharp said. "I've fought for five years to protect my son and I am not about to give up now."