Gary McKinnon faces 60 years in a US jail if convicted
Computer hacker Gary McKinnon has been refused permission to appeal to the UK Supreme Court against his extradition to the US.
The High Court ruled the case was not of "general public importance" to go to the UK's highest court.
Glasgow-born Mr McKinnon, 43, of Wood Green, London, is accused of breaking into the US's military computer system.
Mr McKinnon, who has Asperger's syndrome, insists he was just seeking evidence of UFOs.
In July he lost a High Court bid to avoid extradition.
The Home Office said no further comment would be made while Mr McKinnon continued to pursue the legal avenues available to him.
A spokesman said: "We note today's judgment. The case remains before the courts. Therefore, we do not propose to comment further at this stage."
Mr McKinnon faces 60 years in prison if convicted in the US.
His lawyers have said they may now take the case to the European Court of Human Rights in Strasbourg.
They argue that extradition of their client would have "disastrous consequences" for his health, including possible psychosis and suicide.
Mr McKinnon had challenged the refusal of Keir Starmer QC, the Director of Public Prosecutions, to put him on trial in the UK on charges of computer misuse - which would have allowed him to avoid extradition.
Giving the court's decision on Friday, Lord Justice Stanley Burnton, who heard Mr McKinnon's latest appeal earlier this year with Mr Justice Wilkie, said extradition was "a lawful and proportionate response" to his alleged offending.
There was no real prospect of him succeeding with his claim under Article 8 of the European Convention of Human Rights that extradition would breach his right to a private and family life.
Nor did the court think, on the evidence it had seen, that he had an arguable case that extradition to the US would result in a breach of his Article 3 right not to be subjected to inhuman or degrading treatment.
'Devoid of humanity'
Reacting after the latest ruling, his mother Janis Sharp said no other country would offer its citizens to the US so readily "as sacrificial lambs" just to safeguard the special political relationship.
She said: "To use my desperately vulnerable son in this way is despicable, immoral and devoid of humanity."
Mr McKinnon's solicitor, Karen Todner, said the effect the proceedings and impending extradition were having on her client were "devastating".
"Why is our government so inhumane as to allow this to happen to someone, particularly someone with Aspergers, a form of autism?" she said.
"This is the wholesale destruction and bullying of a small individual by the United States and now our own government.
"Our extradition treaty with the US is unfair and prejudicial to UK citizens and should be repealed or amended immediately."
Sabina Frediani, campaigns co-ordinator for Liberty, which supported Mr McKinnon's case, said: "Never were justice and the law so out of sync as in the case of Britain's rotten extradition arrangements."
The Tories also criticised the UK's extradition arrangements with the US.
Backbench MP David Davis said: "The reason this decision has been arrived at is because the British government created a set of laws and agreements which, masquerading as anti-terror laws, actually disadvantaged a whole range of British citizens.
"This is why the courts find themselves having to dispatch this young man to America, when he should face a proper trial in British courts. It is long past time that this travesty of justice was put right."