A suspected plot to free IRA prisoners from two high security jails in Britain is under investigation.
A full scale search of Full Sutton prison near York, lasting two days, was completed over the weekend. Nearly 600 prisoners were then allowed out of their cells to resume normal routines after what was described as the "full lock down" search.
But prison authorities said an investigation was continuing into the alert, understood to have started after the discovery of impressions of master keys in the cells of former IRA inmates.
All the locks at the top security prison were changed during the operation.
The Prison Service refused to comment on reports that an escape plot was uncovered after a bar of soap containing a master key impression was discovered in a cell vacated last week by an IRA prisoner, Michael O'Brien, who is now completing his 18 year sentence in the Republic.
It was also reported that two other bars of soap found bore impressions of keys from Belmarsh Prison, in south London, which also houses IRA prisoners.
A detailed sketch plan of Belmarsh was also said to have been discovered in the cell of another serving IRA prisoner at Full Sutton.