The government has asked for permission to appeal to the Supreme Court against a ruling preventing the deportation of radical Islamic cleric Abu Qatada.
Court of Appeal judges last month upheld a ruling that he could face an unfair trial if he were deported to Jordan to face terror charges.
The move is the latest in a lengthy government battle to have him deported.
"The government remains committed to deporting this dangerous man," a Home Office spokesman said.
"We continue to work with the Jordanians to address the outstanding legal issues preventing deportation." he added.
In April 1999, Abu Qatada was convicted in his absence on terror charges in Jordan and sentenced to life imprisonment, and it is on these charges that he faces a retrial.
In their judgement last month, Court of Appeal judges said the Special Immigration Appeals Commission was entitled to think there was a risk that "impugned statements" obtained by the torture of others would be admitted in evidence at his retrial.
This meant there was "a real risk of a flagrant denial of justice", the judges said.
The judges said the court accepted that Qatada "is regarded as a very dangerous person", but that was not "a relevant consideration" under human rights laws.
The UK government has repeatedly argued that a block on his deportation should be lifted, saying a fair trial in Jordan was possible.
Abu Qatada was first arrested in October 2002 in south London and detained in Belmarsh high-security prison. He was re-arrested and released on bail number of times over the years that followed.
In November 2012, he was released on bail when the courts blocked the home secretary's attempt to deport him to Jordan, but was arrested last month for allegedly breaching the strict bail conditions.
He has never been charged with an offence in the UK.
Abu Qatada was born in Bethlehem in 1960 and spent his early life in Jordan. He fled to Pakistan in 1989 claiming political persecution and eventually arrived in the UK in 1993. Abu Qatada was part of a wave of Islamists who sought refuge in the UK during the 1980s and 90s, often exiled from the Arab regimes they were trying to overthrow.
Abu Qatada emerged as a key voice in the Islamist movement in London, which advocated strict Islamic government in Muslim countries and armed struggle against despots and foreign invaders. His preachings and ideas won him influence among Islamist groups in Algeria and Egypt during the 1990s. He was tried and found guilty in his absence of terrorism offences in Jordan in 1999.
By 2001 fears were growing about Abu Qatada's hard-line views. He endorsed suicide attacks in a BBC interview and was questioned in connection with a German terror cell. Copies of his sermons were found in the Hamburg flat used by some of the 9/11 attackers and Spanish judge Balthazar Garzon described him as the "spiritual head of the mujahideen in Britain". In December 2001, Abu Qatada disappeared and became one of the UK's most wanted men.
In October 2002 Abu Qatada was arrested and detained without charge. He was released in 2005 and put under strict house arrest, but months later was arrested under immigration rules and moves began to deport him to Jordan to face retrial on the charges he had been convicted of six years earlier. In 2007 he lost his immigration case, but the Court of Appeal later ruled that deportation to a regime which uses torture - ie Jordan - would breach his human rights.
The Court of Appeal ruling was overturned by the Law Lords in early 2009, and the then Home Secretary, Jacqui Smith (L), signed a deportation order. Abu Qatada then appealed to the European Court, which eventually ruled that he could not be deported while the risk of torture remained. In 2012 Home Secretary Theresa May (R) pressed ahead with deportation, but this was blocked amid a row over the appeal deadline.
In November 2012 Abu Qatada was released from prison once more after a UK court backed his appeal on the grounds that witness evidence obtained by torture could be used against him at trial in Jordan. That was a disastrous blow to the Home Office because it meant the only way the deportation could happen would be if Jordan changed its system to ensure torture-tainted evidence could not be used.
Abu Qatada was then returned to prison on 9 March 2013 after an alleged breach of his bail conditions - but this deportation was still blocked.
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