Computer hacker Gary McKinnon could be sent to the US within weeks after the home secretary rejected a last-ditch attempt to prevent his extradition.
In a letter today Alan Johnson ordered McKinnon's removal to the US despite his family warning he is at serious risk of suicide.
McKinnon, who suffers from Asperger's syndrome, faces up to 60 years in jail for hacking into US military and Nasa computers. The 43-year-old claims he was searching for reports of UFO sightings.
Johnson's letter rejected new expert medical evidence that McKinnon's health had deteriorated dramatically since he lost his case, and meant that extradition would violate his right to life.
McKinnon's mother, Janis Sharp, said ministers should "hang their heads in shame" for the "barbaric" decision.
"Gary is at risk of suicide, I'm extremely worried about him," she said."This government is terrified of speaking up to America, and now they are allowing vulnerable people to be pursued for non-violent crime when they should be going after terrorists."
But Johnson said in a statement: But Mr Johnson said in a statement: "I have carefully considered the representations in the case of Gary
McKinnon. I am clear that the information is not materially different from that placed before the High Court earlier this year and does not demonstrate that sending Mr McKinnon to the United States would breach his human rights.
"As the courts have affirmed, I have no general discretion. 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."
McKinnon's lawyer, Karen Todner, said she planned to start a judicial review of the Home Secretary's decision. "We cannot give up because in some ways it's like dealing with a death row case, and we genuinely believe Gary's life is at stake here," she said.
Johnson said that McKinnon should be convicted in the US and seek to serve his sentence in Britain. He added that the UK government would "progress his application at the very earliest opportunity".