The Home Secretary has rejected a last-ditch appeal for him to block the extradition of Gary McKinnon to the US on computer hacking charges.
Alan Johnson said he had considered demands for him to intervene in the case but had decided that the extradition would not breach Mr McKinnon's human rights.
"As the courts have affirmed, I have no general discretion," he said in a statement.
"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."
Mr McKinnon, from Wood Green in north London, is accused of breaking into the Pentagon's computer system but says he was just seeking UFO evidence. His mother, Janis Sharp, said Mr Johnson and fellow Government ministers "should hang their heads in shame".
"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. 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. I'm so upset and angry.
"Where are the 'very real safeguards' that the Government consistently hid behind when forcing this appalling Act through Parliament? The only people who won't get extradited are terrorists facing the death sentence, the very people the Act was meant to be about. What bitter irony."
Mr McKinnon, who has Asperger's syndrome, was given hope last month when the Home Secretary agreed to study new medical evidence before deciding on his extradition to the US. Mr Johnson's deliberations came after the High Court refused the 43-year-old permission to appeal to the Supreme Court against his removal to America.
Ms Sharp said her legal team would now apply for a judicial review, but if that was not granted then her son could be extradited before Christmas.
She added: "What a heartless and cowardly decision this is."