Radical Islamic preacher Omar Bakri Mohammed has been arrested in Lebanon - less than a week after leaving Britain.
Bakri Mohammed praised the 9/11 attacks on the US
He was held in the capital Beirut after giving a TV interview in which he said he would only return to Britain as a visitor but not as a persona non grata.
The preacher caused controversy by saying he would not report a potential bomber to the police and is currently being investigated by UK authorities.
Whitehall officials said the British government did not request the arrest.
News of the arrest came as 10 foreign nationals who the Home Office says pose a threat to national security were detained in the UK, pending deportation.
Local media reported Mr Mohammed, who gained notoriety after praising the 9/11 attacks on the US, was wanted for questioning about his entry to the country.
But BBC correspondent Kim Ghattas said the Lebanese authorities had given no official reason for the detention.
The cleric is thought to have entered the country using a Lebanese passport, she added.
During the TV interview, 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.
And the controversial preacher reportedly said that he could never support the killing of innocent people, which he condemned.
Mr Mohammed was held by the authorities in Beirut at around 1200 BST as he left the studios of Future TV, where he had given an interview.
Under Lebanese law he can be held for 48 hours before being charged or released.
It had been suggested that he fled the UK over fears he would be charged with treason, or another serious offence.
But he denied this, saying he was on holiday for five or six weeks staying with his mother.
He said if the British authorities wanted to charge him with a criminal offence, he "would be the first one to return and challenge the allegation".
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".
He is thought to have dual Syrian and Lebanese nationality but has indefinite leave to remain in the UK after gaining political asylum in the 1980s.
The Crown Prosecution Service is looking at whether remarks by three radical Muslim clerics, including Mr Mohammed, break any laws.
Mr Mohammed has said he would not report Muslims he knew to be planning bomb attacks to British authorities.
His spokesman, Anjem Choudray, later told BBC Two's Newsnight that he also would refuse to tell the police if he knew attacks were being planned in Britain.
"If anyone was going to kill anyone innocent here in this country then I would seek the help of my Muslim community in order to prevent him, but it's not allowed for me to co-operate with the police and it's not allowed for me to co-operate with the British government."