Justice Secretary Chris Grayling has accused the Crown Prosecution Service of failing to take assaults on prison officers sufficiently seriously.

He told MPs he wanted to see charges made in all such cases and anyone found guilty given tougher punishments.

A fall in attacks two years ago has now been reversed as violent incidents increase, he said - a trend critics blame on a rise in overcrowding while staff numbers fall.

"I don't believe the issue of assaults on our staff has been taken seriously enough by the prosecuting authorities in the past," Mr Grayling told the Commons justice select committee.

Prisons minister Jeremy Wright "is in discussions with the Director of Public Prosecutions about this", he said.

"My personal view, and the view we are trying to encourage, is that if a prison officer is assaulted there should be a charge and I want to see us move to a situation where that means a much longer prison sentence."

Mr Grayling's appearance before the committee, where he was questioned on a number of contentious issues, was marked by a protest by campaigners against restrictions preventing books being sent to prisoners.

A group including Howard League for Penal Reform chief executive Frances Crook held up copies of Fyodor Dostoyevsky's Crime And Punishment as he gave evidence - in full view of the cameras broadcasting the hearing.

Mr Grayling denies any attempt to curtail prisoners' access to books, insisting a ban on sending parcels to prisoners is a vital security measure and libraries are provided within prisons.

Ms Crook said: "As families and friends are now forbidden from sending basic items into prison, prisoners are lying in overcrowded cells, wearing dirty clothes, with nothing to do and possibly not even a book to read.

"When leading authors asked for an opportunity to raise their concerns over this issue, the Justice Secretary refused to meet with them.

"It is regrettable that it takes a concerted display of Dostoyevsky novels to get his attention at a time when there is growing unrest in prison and an alarming rise in suicides behind bars.

Kathy Lette, one of a number of prominent authors supporting the campaign, said: "Books are not a 'reward' but a staple, like bread and water. I feel passionately about giving prisoners access to books not just because I come from convict stock but also because I left school at 16, so books have been my education."