The number of inmates at Rochester Prison deliberately hurting themselves has soared over the past five years.

Figures obtained by the Howard League for Penal Reform reveal there were 45 cases of self harm last year at the young offenders facility compared to nine in 2003.

It is only a slight improvement on 2004, when 58 incidents were recorded.

Incidents range from the construction of a ligature or a minor scratch to more serious incidents requiring hospital treatment.

Rochester Prison can hold up to 392 inmates up to the age of 21.

The penal charity believe the increase is down to overcrowding while prison bosses claims a more thorough reporting system is to blame.

Howard League assistant director, Andrew Neilson said:“At the moment they are literally staggering under the weight of people going in.

“They are asked to be mental hospitals and drug residential facilities as well as prisons and they can’t cope.

“That in the end is an issue of public protection, because if you have someone who is mentally ill harming themselves in prison, their condition is deteriorating, they then get released. They are likely to re-offend and likely to re-offend more seriously.”

A Prison Service spokesperson said: “One per cent of prisoners are responsible for a quarter of all self-harm incidents in prisons.

“Therefore the transfer or release of a small number of serial self-harmers can impact the figures to a great extent, which may explain any significant rise or fall in the number of annual recorded incidents at individual prisons.”

Nationally figurespaint a similar picture. Prison self injury rates have accelerated at four times the rise in population, with incidents rocketing by almost 40 per cent in the last five years.

2003 incidents = 9

2004 incidents = 58

2005 incidents = 18

2006 incidents = 50

2007 incidents = 45