Home Secretary Theresa May has applied for permission to appeal against a decision to block the removal of Jordanian terror suspect Abu Qatada.
Papers have been lodged with the civil appeals office at the Court of Appeal ahead of a deadline later.
Abu Qatada was released on bail from jail three weeks ago.
Immigration judges had said there was a risk that evidence obtained through torture could be used at his retrial in Jordan.
An appeal in this case can be made only on a point of law.
The home secretary said at the time of the ruling that she "strongly disagreed" with the judgment, claiming that the Special Immigration Appeals Commission (SIAC) had applied the "wrong legal test".
'Completely fed up'
The radical cleric faces a re-trial in Jordan for allegedly conspiring to cause explosions on Western and Israeli targets in 1998 and 1999. He was found guilty of terrorism offences in his absence in Jordan in 1999.
Security chiefs believe he played a key ideological role in spreading support for suicide bombings.
Last month the Special Immigration Appeals Commission chairman Mr Justice Mitting ruled he was not satisfied that the preacher would be tried fairly in Jordan.
Tagged and allowed out of his home only between 08:00 and 16:00
Banned from travelling on the Tube, or by train, car, motorbike or bus
Banned from contacting a number of named individuals
Only family members, his lawyer, emergency workers and social workers can enter his home without approval
Banned from using mobile phones, computers and other devices
Banned from attending mosques, leading prayers and giving lectures
Needs approval to take a job or enrol on a course
Allowed one bank account and must surrender his passport
And Abu Qatada was released from Long Lartin prison, in Worcestershire, after spending most of the last 10 years in custody.
He is the subject of bail conditions that include him being banned from travelling on the Tube, or by train, car, motorbike or bus and from using mobile phones and computers.
Prime Minister David Cameron said he was "completely fed up" at the cleric's release on bail.
On the question of why the Palestinian-born Jordanian had never been prosecuted in the UK, Lib Dem peer Lord Macdonald - director of public prosecutions from 2003 to 2008 - told BBC News he had never been shown any evidence to support a criminal prosecution.
A judge will now consider the home secretary's appeal application by examining documents on the case.
The judge may make a decision, or decide that the application should be dealt with at a court hearing.
A decision is expected to be made before Christmas.
If the judge decides to refuse the application, the home secretary can ask a court to reconsider the matter.
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. Weeks later, Home Secretary Theresa May announced a new UK-Jordan treaty to improve co-operation in criminal investigations. That treaty included a guarantee of a fair trial free of torture-tainted evidence for anyone sent back to Jordan. Abu Qatada's lawyers announced he would now return to Jordan.
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