Excerpt:
Five books regarded as "extremist" by the Prison Service remained in jail libraries in England and Wales for seven months after a review called for their removal, the BBC has learnt.
Two of the authors are seen as having inspired jihadists in the Arab world.
Extremism academic Dr Chetan Bhatt said the presence of these books within prison libraries was "worrying".
The government said the texts had been identified as part of the Acheson review into extremism in prisons.