Chris Grayling has denied that prisoners are being deliberately deprived of access to books, in an open letter to poet laureate Carol Ann Duffy.

The acclaimed feminist staged a protest outside London’s Pentonville Prison on Friday against the MP's imposition of much stricter limits on parcels coming into prisons which is preventing friends and family of inmates sending them books.

The poet, along with other writers including Alan Bennet, Salman Rushdie and Irvine Walsh, are supporting a campaign by the Howard League for Penal Reform calling on the Secretary of State for Justice to reverse the policy.

But, in a an open letter to Duffy at the weekend, Epsom’s MP insisted that changes introduced in November did not aim to deprive prisoners of books, but were a vital security measure which was triggered by a ban on sending parcels.

He said: "We have not sought to include books in a list of privilege items that have to be earned by offenders - to do so would be wholly wrong.

"The only discussion about prison books that I have been involved in as Secretary of State was to agree to make available the novel 50 Shades of Grey in the libraries in womens' prisons because I judged that it might help encourage some women offenders to read more, something I regard as highly desirable.

"Our prison staff fight a constant battle to prevent illicit items, such as drugs, extremist materials, mobile phones, SIM cards and pornography getting into our prisons.

"The arrival of thousands of unknown parcels in our prisons each day, whether containing books, essential items or anything else, would completely undermine these efforts.

"It would be a logistical impossibility to check them all in the level of detail that is needed, to properly explore whether apparently innocuous items contain drugs or other illegal items.

"I'm afraid that it is inconceivable that we could impose the additional operational burden on our staff of carrying out detailed assessments of an unlimited number of parcels coming into prisons. This is something that has never happened before and could not happen now.

"That is why we now have simple rules that allow everyone one a parcel of items from home when they first arrive in prison, and then only further parcels at the Governor's discretion in exceptional circumstances.

"That does not mean that we do not believe it is important to encourage learning, and reading in prisons. 

"Prisoners have full access to the same public library service in prisons as every other citizen, as well as the ability to order books from Amazon via the prison shop using their prison earnings or money sent in by relatives."