The radical cleric Abu Qatada is being investigated over extremist material found during a search of his house before he was arrested on 8 March, police have said.
Officers said the material came from a variety of sources and they are investigating whether the publications were written by Mr Qatada.
The 52-year-old has been arrested on suspicion of breaching one of his bail conditions which prohibits him from having mobile phones switched on in his house while he is present.
A hearing over whether he should be granted bail was due to be held today but was delayed.
Deputy Assistant Commissioner Stuart Osborne said: “When we searched his house before his arrest, that was a police search in relation to investigating some publications, to see if that was anything that reached a criminal threshold.
“There is an awful lot of media that needs to be looked through.”