Tory leader David Cameron has joined the growing call for a review of extradition laws after computer hacker Gary McKinnon failed in his bid to avoid removal to the United States.
The 43-year-old from Wood Green, north London, who suffers from Asperger's Syndrome (AS), is wanted for trial on charges of hacking into US military networks.
Two judges at London's High Court refused to block his removal, even though they conceded he might find extradition and prison in the US "very difficult indeed".
Campaigners seeking to block his extradition say his only crime is being a "UFO eccentric" who searched for evidence of extra-terrestrials. They claim he acted through "naivety" as a result of AS - a form of autism which leads to obsessive behaviour - and should not be considered a criminal.
The judges accepted there was impressive medical evidence his mental health would suffer "and there are risks of worse, including suicide". But the "severity" of his case did not amount to a breach of his human rights following assurances from the Americans that he would be given "appropriate care".
Later Mr Cameron said: "Gary McKinnon is a vulnerable young man and I see no compassion in sending him thousands of miles away from his home and loved ones to face trial. This case raises serious questions about the workings of the Extradition Act, which should be reviewed."
Mr McKinnon's mother, Janis Sharp, made an impassioned appeal to US President Barack Obama to halt extradition "and make this world a more compassionate place". She expressed fears her son could face a 60-year sentence in a tough US jail and would be at real risk of suicide because of his medical condition. She also fears she would never see him again.
Keith Vaz, chairman of the Home Affairs Select Committee, said: "The extradition arrangements between the USA and the UK are in place to help counter terrorism and serious crime, and should not be used against vulnerable people like Mr McKinnon. These extradition arrangements need to be reviewed. The Home Secretary should use his discretion to look again at Mr McKinnon's case and intervene to stop the extradition."
Liberal Democrat home affairs spokesman Chris Huhne said: "Today's judgment is a hammer blow to a vulnerable man and his long suffering supporters. The succession of ministers who have let this sorry saga drag on for seven long years should hang their heads in shame. There is no way the American Government would hang one of their citizens out to dry in the same way. The Government must ensure that the US-UK Extradition Treaty is repealed and that its replacement treats US and British citizens equally."
Mr McKinnon's solicitor, Karen Todner, said she would lodge an appeal against the High Court's decision within 28 days and, if possible, take it to the UK's new Supreme Court and even to Europe.