Home Secretary Alan Johnson said he cannot stop the extradition of a Briton wanted in the United States for hacking into NASA and Pentagon computers.
Gary McKinnon was arrested in 2002 after US prosecutors charged him with illegally accessing computers, including at the Pentagon and NASA, and causing £427 000 worth of damage.
The US Army’s entire network of more than 2000 computers in Washington was shut down for 24 hours in what US authorities called "the biggest military hack of all time."
But his lawyers argued that extraditing McKinnon, who has been diagnosed with Asperger’s Syndrome, a form of autism would be detrimental to his health.
"I have carefully considered the representations in the case of Gary McKinnon," Johnson said. "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 US would breach his human rights."
The High Court had accepted that his extradition could have consequences for his health, but judges ruled that the process of the law overruled those concerns.
The appeal then went to the Home Office.
"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 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," he said.
McKinnon’s mother Janis Sharp told the BBC she was "devastated" and said her son had reacted "very badly."
"It’s a disgusting decision. Gary has been in a heightened state of terror for almost eight years," she said. McKinnon’s lawyer Karen Todner also told the BBC she had seven days to put a case for judicial review and she hoped that would be heard before Christmas.
In October, McKinnon was refused permission to appeal to the Supreme Court but his lawyers said they would consider appealing to the European Court of Human Rights in Strasbourg.
McKinnon’s lawyers describe him as a "UFO eccentric" who used the Internet to search for alien life.
"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," Johnson said.
If he is convicted by a US court, McKinnon could face up to 70 years in prison.
His cause has been backed by the Daily Mail and some British politicians.