Radical Islamic preacher Omar Bakri Mohammed has been excluded from the UK.
The Home Office said Home Secretary Charles Clarke used existing powers to exclude Mr Mohammed as his presence was “not conducive to the public good”.
The cleric is being held by the Lebanese authorities in Beirut, it is believed at the request of Syria.
He was seized after a TV interview in which he said he would not return to Britain as a persona non grata, only as a visitor.
The preacher left the UK six days ago on what he described as a holiday to see his mother in Beirut.
The self-styled “sheikh” ran the radical al-Muhajiroun group from Tottenham, north London, until it was disbanded last year.
He is famous for praising the 9/11 hijackers as the “magnificent 19”.
A Home Office spokesman said the decision to bar Mr Mohammed would not affect his family. He has seven children who were born in Britain.
They would continue to receive their State benefits, he said, although those paid to the cleric would cease.
Since the 1980s Mr Mohammed had had indefinite leave to remain in the UK after gaining political asylum.
He is thought to have dual Syrian and Lebanese nationality.
Regarding his arrest in Beirut, a Lebanese Ministry of Foreign Affairs spokesman said there was an official request from the Syrian authorities “to surrender him to the security forces in Syria.”
“They say he is a Syrian and has been convicted in Syria for many crimes, and that they need him for those crimes.”
The spokesman said he believed the activities for which Syria wished to see Mr Mohammed extradited were not terrorism-related but to do with “past events in Syria in the 1980s”.
The cleric’s spokesman, Anjem Choudray, described the UK move as “completely outrageous” and a “failure” of the principle of free speech.
“He has been a great asset for the Muslim community here.
“It is going to be a great loss for the British public and the Muslim community, I believe, and I think that this is indicative of the oppressive nature of the Blair regime.”
But Inayat Bunglawala, from the Muslim Council of Britain, said: “Omar Bakri is unlikely to be missed by the vast majority of British Muslims.
“He is someone who for 20 years was given shelter by this country and he has spent almost all that time vilifying this country and its values.
“With his often very offensive remarks he has contributed towards the demonisation of British Muslims.”
His arrest on Thursday came as 10 foreign nationals, who the Home Office says pose a threat to national security, were detained in the UK, pending deportation.
One of them, radical cleric Abu Qatada is expected to be deported to Jordan next week, according to the Jordanian interior minister.
It follows a UK deal with Jordan that deportees would not be persecuted.
In his absence, Abu Qatada has been sentenced by a court in Jordan to life in prison over a series of explosions.
Omar Bakri Mohammed has caused recent controversy by saying he would not report a potential bomber to the police and is currently being investigated by UK authorities.
During the TV interview in Lebanon, Mr Mohammed said that he had Lebanese nationality because his father had Lebanese citizenship.
He said that he had been living in England since 1986 and added that he had been subjected to harassment in Britain.
He also reportedly said that he could never support the killing of innocent people, which he condemned.