A Briton accused of hacking into US military and NASA computers faces extradition to the United States after the British government rejected last-ditch requests to block the move.
Home Secretary Alan Johnson concluded that sending Gary McKinnon to the United States would not breach his human rights, and said he has no general discretionary powers to stop the extradition.
"If Mr McKinnon's human rights would be breached, I must stop the extradition. If they would not be breached, the extradition must go ahead," Johnson said in a statement.
"As the courts have affirmed, I have no general discretion," he said.
|Briton Gary McKinnon leaves the High Court in central London in January 2009.|
McKinnon, who suffers from a form of autism, could spend life in prison if convicted by a US court of gaining access to 97 computers in 2001 and 2002 in the aftermath of the September 11, 2001 attacks.
His family and lawyers have warned throughout the long-running case that McKinnon, who has Asperger's Syndrome, could commit suicide or suffer psychosis if the extradition went ahead.
McKinnon's mother, Janis Sharp, slammed the decision as "devastating" and "barbaric," adding that her son was terrified of extradition.
"To force a peaceful, vulnerable, misguided UFO fanatic like Gary thousands of miles away from his much-needed support network is barbaric," she said.
"This is a cruel and miserable decision," she told the BBC, adding that the government, should "hang their heads in shame."
"If the severity of Gary's medical condition isn't sufficient to prevent his extradition, I can't imagine what is. God help others facing a similar fate."
McKinnon, 43, says he was only looking for evidence of unidentified flying objects (UFOs) when he hacked into the US Navy and NASA space agency computers.
US authorities allege he stole passwords and deleted files, leading to the shutdown of computer systems, with repairs costing around 800,000 dollars (486,000 pounds, 534,000 euros).
His cause has drawn high-profile support, including from Trudie Styler, wife of rock star Sting, who urged mothers to write to the Home Secretary.
Last month, the High Court in London refused McKinnon leave to appeal to Britain's new Supreme Court against his extradition.
The Home Office agreed to study new medical evidence about McKinnon before deciding on his extradition.
But Johnson told McKinnon's family in a letter that he could not block the move on medical grounds.
He said he had received guarantees from US authorities that McKinnon's medical needs would be met once extradited, and if convicted he would not serve any time in a "supermax" prison.
"Due to legitimate concerns over Mr McKinnon's health, we have sought and received assurances from the United States authorities that his needs will be met," Johnson said.
"Finally, should Mr McKinnon be extradited, charged and convicted in the US and seek repatriation to the UK to serve a custodial sentence, the government will, of course, progress his application at the very earliest opportunity."
McKinnon's solicitor said she would seek a judicial review of Johnson's decision, and lodge an application before the High Court within seven days.
"We are certainly coming to the end of the road, but we are just hoping that at some point, someone sees sense and steps in," Karen Todner told the BBC.
"In some ways it's like dealing with a death row case, we genuinely believe Gary's life is at stake here."
His lawyers say he could easily be prosecuted in Britain, where he would face a less severe sentence. But the Crown Prosecution Service ruled in February that the case was best brought in the United States.