The Government is today being urged to radically change its approach to imprisonment in order to tackle overcrowding and reduce the prison population.
The Jesuit Centre for Faith and Justice has published a report which recommends reducing the prison population by over a thousand inmates.
It says overcrowding is leading to inhumane conditions for prisoners and custodial sentences should only be used as a last resort.
Former governor of Mountjoy Prison, John Lonergan, said that too housing many inmates leads to increased violence.
"The level of violence was nothing short of savagery, and I saw some very serious injuries being inflicted on people in prison for very small offenses," he said.
"As a result of all that then, you have what's called 'separation and protection', and that means that prisoners spend 23 or 24 hours a day in cells.
"So we have massive issues, and some of it, if not most of it, is related directly to overcrowding."