Home Secretary Jacqui Smith has signed a deportation order for radical cleric Abu Qatada, after a court ruled he could be sent home.
The firebrand preacher wants to stay in Britain and argued he would not face a fair trial in Jordan, where he is wanted on terror charges.
But the Law Lords ruled unanimously in favour of the Government, which said he posed a threat to UK national security. The case could now go to the European Court of Human Rights.
Ms Smith said she was delighted with the decision. She said: "It highlights the threat these individuals pose to our nation's security and vindicates our efforts to remove them.
"My top priority is to protect public safety and ensure national security and I have signed Abu Qatada's deportation order which will be served on him today. I am keen to deport this dangerous individual as soon as I can."
Qatada, who is known as al Qaida's "spiritual leader in Europe", faces trial on terror charges if he is returned to Jordan.
His lawyers argued he could not be tried fairly because evidence against him was extracted by torture.
Last year the Court of Appeal ruled in his favour, but the Law Lords overturned the judgment, saying there were no reasonable grounds for believing he would be denied a fair trial in Amman.
Human rights group Justice said the ruling was a "step backwards in the international fight against torture" while Amnesty International urged ministers not to take the judgment as a "green light" to deport more people to regimes where they risked unfair trial and torture.