Prison officers turned up for work at Northern Ireland's jails on Thursday after a day of unoffical action when most of them reported sick as part of a protest over security.

On Wednesday, 600 officers failed turn up or else left the jails by reporting sick after just a couple of hours.

Police spent the night guarding Maghaberry prison in County Antrim and the jail at Magilligan in County Londonderry.

On Wednesday night, Prison Officers' Association chairman Finlay Spratt said the protest would go on.

POA members are angry at what they said was the government's failure to provide them with adequate funds to upgrade home security.

Finlay Spratt: "Prison Service managers told us we were all under threat"

This followed the discovery of 1,400 officers' names on a list recovered during an investigation into alleged IRA intelligence gathering.

The director general of the Prison Service said nothing would be achieved by the unofficial protest action by 85% of Northern Ireland's prison officers.

Peter Russell said there was no doubt that the 600 prison officers who either reported they were sick or came to work on Wednesday and then went home sick, were engaging in pre-planned, co-ordinated action.

Police guard

It is illegal for the officers to go on strike.

Two hundred police officers were called in to work in Northern Ireland's two prisons, Maghaberry and Magilligan in Londonderry, and at the Young Offenders' Centre in Belfast.

But along with 100 prison officers who did not take part in the action, they were not able to carry out all of the duties normally undertaken.

Prisoners were not brought to court and families and solicitors were not permitted to visit prisoners.

But in a BBC interview, the Prison Service director general said the unofficial action by prison officers would not improve their position.

Peter Russell: "All officers are not assessed as being under the same threat"

Peter Russell said the main point of dispute was that the POA wanted all prison service staff to be given extra home protection.

But the police had now revealed that the 250 officers who work at Hydebank Young Offenders' Centre in Belfast, were not named on the list.

"They [officers] think everyone should be eligible for the same level of protection, whether or not their names have been found in the hands of terrorists," Mr Russell said.

"But you have to base support measures on assessed risk and the police have not indicated to us that they assess the risk at the same level."

MI5 investigation

Mr Russell said the police had just revealed the nature of the list containing prison officer's names.

"The police are saying it was a file held for payments purposes. Beyond that it is for the police to investigate how these files came to be in the hands of terrorists," he said.

And Mr Russell confirmed that an M15 investigation into alleged IRA intelligence gathering at Stormont would extend to the Northern Ireland Prison Service.

"That the information has got out is certainly a problem, but whether it has got through the medium of one of our staff is for the police to determine," he added.

After hearing Mr Russell's comments, chairman of the Northern Ireland Prison Officers Association, Finlay Spratt said he would continue to support any action the prison officers wished to take.

More than six weeks after the prison officers were given a warning that the names had appeared on a list, individual officers had not yet been told who had been named, he said.

Mr Spratt added: "I am not looking for compensation for prison officers, I am looking for security measures."

At present there are about 1,700 prison officers working in Northern Ireland. The current prison population stands at about 1,059.