The government has failed to overturn a European Court ruling blocking the extradition of a British terror suspect accused of conspiring with Abu Hamza.
In April, the court ruled that sending Haroon Aswat to the US could lead to a deterioration in his mental health, breaching his human rights.
The UK asked for the case to be reconsidered by the court's Grand Chamber, but that has been rejected.
The latest decision is final, meaning Mr Aswat cannot now be extradited.
US authorities allege Mr Aswat was involved in a plot to set up a terrorist training camp at Bly, in Oregon, with Abu Hamza, who was sent for trial in the US last year.
Mr Aswat, who used to live in Yorkshire, was arrested in 2005 by UK authorities following a request from the US for his extradition.
In 2008 he was transferred from prison to Broadmoor high-security psychiatric hospital after being diagnosed with paranoid schizophrenia.
In its ruling in April, the European Court said his mental and physical health could significantly worsen in the "more hostile" environment of a US prison where he would have no support from family or friends.
It said that extraditing Mr Aswat would breach his human rights, specifically Article 3 of the European Convention on Human Rights which prohibits inhuman or degrading treatment.
In October 2012, Mr Aswat's terror suspects Abu Hamza, Babar Ahmad, Syed Talha Ahsan, Adel Abdul Bary and Khaled al-Fawwaz were extradited to the US.
Radical cleric Abu Hamza has denied terrorism charges in a US court.