Results from a new study into the re-offending rate among prisoners indicate that just over a quarter of released prisoners are back in jail within a year, and nearly half are locked up again within four years. 

The research was carried out by the Institute of Criminology at University College Dublin, which studied nearly 20,000 prisoners.

Speaking on RTÉ Radio's Morning Ireland, Paul O'Mahony, Criminologist at Trinity College Dublin, outlined some of the failings of the prison system.

Mr O'Mahony described rehabilitation programmes as being 'very poor indeed'. He said that in prisons, 'there is one prison officer for every prisoner at huge cost'.

He also said that probationary welfare was under staffed and under resourced.

The study, the first of its kind in Ireland, also found that many people were being imprisoned for relatively minor crimes, such as property offences and non-payment of fines.

It was found that 60% of repeat offenders were most likely to be back in prison compared to 35% of first time offenders.

Sex offenders were least likely to re-offend, with only 18% of people in this category back in jail after three years.

The research also revealed that 85% of those imprisoned for defaulting on fines find themselves back in jail within four years.

Experts say these figures should mark the starting point of a comprehensive overview of the prison service.