The tunnel began from a cell in H-7, one of the H-blocks which became known to the world during the republican hunger strikes of the early 1980s. Its discovery led to Unionist calls for an inquiry and the disciplining of senior staff. The tunnel had passed underneath a fence around the H- block. To reach the outside world beyond the prison's high outer perimeter wall the IRA prisoners had another 90ft to cover.
Had this been achieved, 95 republicans, all classed as high-security prisoners, could have been let loose into the countryside. Such an incident would have dwarfed even the 1983 IRA "great escape", when 38 IRA inmates broke out through the main gate.
As it is, the incident is embarrassing for the Government and calls into question the unique way in which the prison is run.
The tunnel was at least 5ft underground and was lit by electric light, which has been a feature of IRA tunnels since at least the 1970s.
Prison staff said it was shored up with chair legs and in particular with bedboards which had been provided for inmates with supposedly sore backs.
Finlay Spratt, of the Prison Officers' Association, said: "It would appear they could request the bedboards when they wanted one, and nobody seemed to keep any check on it."
Mr Spratt has repeatedly complained in recent years that prisoners have almost unlimited freedom within the H-blocks.
Inside each block, cells are not locked, there is free association, and prisoners are organised not by staff but by the paramilitary organisations to which they belong. Searches are often resisted.
All attempts by the authorities over a quarter of a century have failed to eradicate this strong element of paramilitary control. It was clearly the existence of such a regime which made feasible the building of a tunnel.
It was apparently discovered when a prison officer on a routine patrol noticed some subsidence and raised the alert. The 95 republicans in H7 were moved to another block to allow a search of their quarters, where rubble was found dumped in a number of places. Visits to republican prisoners have been suspended.
Mr Spratt added yesterday: "The fact that we have no effective search policy to conduct searches allowed the prisoners to construct this tunnel without any hindrance or investigation by staff. An officer has told me that six months ago he reported to the authorities that there was banging coming from H7, but it would appear nobody on the management side did anything about it."
While Unionists condemned the security arrangements, Sinn Fein voiced approval and commiserations over the failed attempt.
Gerry Kelly, the party's election candidate in North Belfast, said: "They are prisoners of war, they look upon themselves as prisoners of war. It is their duty to escape from jail.
"I suppose they will be disappointed. However, they have made the effort and they can feel good about that. Fair play to them."
During a lengthy IRA career, Mr Kelly himself made six escape attempts from prison, three of which were successful. In 1974, IRA inmates dug a 134ft long tunnel to escape from the same prison.Reuse content