The High Court has reserved judgment on the extradition of radical cleric Abu Hamza until a later date.
His QC says that an MRI (magnetic resonance imaging) brain scan could establish that he is unfit to plead and should not be extradited to the United States to face trial on terrorism charges.
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Thousands of passengers now face delays, with Southeastern trains warning "all services" would be affected.
Paramedics attended a scene in Willesden, north-west London, on Monday afternoon where they found the teenager with stab wounds.
At least five people have suffered minor injuries but the cause of the blast is still unknown.