The cost of separating prisoners at Magheraberry prison was examined

It said it was twice as expensive to house a prisoner there as at top security jails in England or Wales.

The joint report was compiled by HM chief inspector of prisons and the chief inspector of criminal justice.

It found the average cost per prisoner place in NI was £86,000 a year, and the cost in Maghaberry was higher again.

Separated prisoners account for just 10% of the prison's population.

However, the report said it was costly both in terms of money and the level of service for other prisoners.

The number of prison officers required to staff the separated accommodation meant other prisoners were more likely to be confined to their cells for longer periods of time and had less chance to benefit from recreational and educational opportunities, the report said.

Kit Chivers said Maghaberry was a complex prison

"Maghaberry is a complex, maximum security prison which is costly to maintain and resource," said Kit Chivers, chief inspector of criminal justice in Northern Ireland.

"Yet this degree of security is not necessary for many prisoners, such as fine defaulters and other short term prisoners.

"If other accommodation existed, the needs of these prisoners could be catered for more economically and more effectively in a less secure facility. This is a problem of having a small prison estate," he said.

Recommendations

Although the inspectors said they found some good features at Maghaberry, they made 171 recommendations for improvement.

Security Minister Shaun Woodward said he accepted that segregation affected the prison as a whole.

"However, separation is key to the maintenance of good order and it is vital that prison officers remain in control at all times," he added.

Alan Longwell, governor of Maghaberry Prison, said his staff would carry through the recommendations with "vigour and determination".

"Indeed some of them have already been implemented and work is ongoing in progressing the remainder."

Maghaberry Prison houses both paramilitary and non-paramilitary prisoners, male and female.