Is it right to ban books being sent to prisons?

Writers and academics have been campaigning against a Ministry of Justice regulation that bans prisoners being sent books.
The regulation is part of a scheme called ‘Incentives and Earned Privileges’, which allows prisoners to buy their own basic supplies, but only with funds that have been earned for good behaviour. Family members are not permitted to send small items, including books, unless there are “exceptional circumstances”.
The regulation has been in place since November, but caught widespread attention when Frances Crook, chief executive of the Howard League for Penal Reform, published an essay on politics.co.uk.

Crook wrote: “Book banning is in some ways the most despicable and nastiest element of the new rules…Of course prisons should have incentive schemes to reward good behaviour. But punishing reading is as nasty as it is bizarre.”
When asked how he felt about the rule, children’s author Philip Pullman, called it “one of the most disgusting, mean, vindictive acts of a barbaric government”.
What do you think? Should books be seen as an essential part of prison to help aid rehabilitation? Or should prisoners only be allowed to obtain books they have bought themselves as a result of good behaviour?
Source: Telegraph