Radical cleric Abu Hamza and four other terror suspects could be put on a plane to the United States within days after Europe's human rights judges rejected their bid for an appeal.
A panel of five judges threw out their request to the Grand Chamber of the European Court of Human Rights, clearing the way for extradition.
Hamza and the others, who have racked up a multi-million pound bill in detention and legal costs, could be handed over to US authorities and put on a plane within days.
But putting in place the practical arrangements for extradition is likely to take up to three weeks, it is understood.
The ruling amounts to the first green light for US top security prisons and the right of European governments to approve US extradition requests for high-risk suspects.
Hamza, who was jailed for seven years for soliciting to murder and inciting racial hatred, has been fighting extradition since 2004.
Computer expert Babar Ahmad, who was also subject to the ruling, has been held in a UK prison without trial for eight years after being accused of raising funds for terrorism.
In April, his sister Amna told The Huffington Post UK she could not understand why her brother was not being trialled in the UK. “We’re a British family. Most of us were born in Britain, we’ve worked hard, we’re professionals, we’ve paid our taxes," she said.
"To see our own government in essence not standing up for someone we need them to stand up for, not standing up for their British citizens, why is the British justice system incompetent in prosecuting Babar in this country?"
The Home Office said Hamza and Ahmad, with Seyla Talha Ahsan, Adel Abdul Bary and Khaled Al-Fawwaz, would be "handed over to the US authorities as quickly as possible".
The Strasbourg-based human rights court ruled on April 10 that "detention conditions and length of sentences of five alleged terrorists would not amount to ill-treatment if they were extradited to the USA".
The unanimous ruling from the judges said there would be no violation of Article 3 of the European Convention on Human Rights - the prohibition of inhuman and degrading treatment - as a result of detention conditions the five men might face at ADX Florence "supermax" prison in Colorado.