Radical Islamic preacher Abu Hamza is due to hear the result of his latest legal challenge against extradition to the United States today.
If the court rules against him the Home Secretary will be able to "move instantly" to transport him to America.
The 54-year-old cleric, who used to preach at Finsbury Park Mosque, is wanted in America on terrorism charges. But his lawyers say his extradition should be prevented on medical grounds. They argue that an MRI (magnetic resonance imaging) brain scan could establish that he is unfit to plead, because of degenerative health problems.
Hamza is one of five terror suspects who have launched last-ditch legal challenges at the High Court after the European Court of Human Rights refused to stop their extradition.
One of them is Babar Ahmad, a computer expert from south London, who has been held in a UK prison without trial for eight years after being accused of raising funds for terrorism. His lawyers say that he should be tried in the UK, rather than in the USA.