More than 170 prisoners at the high-security Maghaberry Prison have been handed keys to their cells, it has been revealed.
One in six inmates at the jail, which houses some of Northern Ireland’s most dangerous criminals, can effectively come and go as they please.
They are among 420 inmates at our jails who have their own keys, according to figures revealed by Justice Minister David Ford.
The Prison Service said the scheme was designed to protect prisoners’ privacy, but insisted the areas they can access were limited.
However, DUP peer Lord Morrow said he was appalled by the revelation.
"This is quite unbelievable, and I think that the public will find it astounding," he said.
Lord Morrow obtained the details following an Assembly question to the Department of Justice. In response, Mr Ford said 420 prisoners had their own keys.
They include 173 at the maximum security Maghaberry jail in Co Antrim. Its population is almost 1,100 -- meaning one in six inmates has keys.
In 2009 the Belfast Telegraph revealed that 90 prisoners at the jail's Erne House, which houses mainly life sentence prisoners, including notorious killers, were given personal keys.
The Prison Service did not say which prisoners had been given keys to their cells.
However, Maghaberry's inmates include double-killer Colin Howell, who was jailed for 21 years for murdering his wife Lesley and Trevor Buchanan, the husband of his lover Hazel Stewart.
Loyalist killer Michael Stone, who carried out the 1988 Milltown Cemetery, attack and Trevor Hamilton, jailed for 30 years for murdering pensioner Attracta Harron, are also held at Maghaberry.
A further 234 prisoners housed at Magilligan Prison in Co Londonderry also have their own keys.
The other 13 comprise nine inmates at Hydebank Wood's Ash House, which holds women prisoners, and four at Hydebank's Young Offenders Centre.
Lord Morrow said it was the first step towards a self-regulating prison system.
"We were told prisons would be strict and secure, that it would be fitting punishment for crime," he added.
"However, the punishment no longer fits the crime. We have gone too far in the wrong direction.
"It seems we are heading swiftly towards a self-regulating prison system."
Lord Morrow said issuing keys to prisoners went against everything that a prison sentence is intended to stand for.
"Maghaberry is a maximum security prison, and yet one in six inmates have a key -- that is not acceptable, it is simply astounding," he continued. A Prison Service spokesman said the key use was strictly monitored.
"Risk-assessed prisoners in low-security accommodation may leave their cell to access bathroom facilities located on their landing but may not leave that landing," he said.
"A small number of prisoners in selected accommodation hold a privacy key which allows them to open/close their cells during periods of 'unlock', thus negating the need for a member of staff to be summoned each time a prisoner wishes to leave or enter their own cell.
"Staff hold a master key for all cells and remain in control at all times. Prisoners remain secured in their cells during times of 'lock-up'".
Maghaberry: 173 keys issued
Magilligan: 234 keys issued
Hydebank Wood Ash House: nine keys issued
Hydebank Wood Young Offenders Centre: four keys issued