Prisoners bound by code of honour

The republican tradition that prisoners have a duty to try to escape is personified in Gerry Kelly, now a prominent political figure in Sinn Fein, who played a leading role in the 1983 mass escape and other incidents.

He first escaped from Belfast's Crumlin Road jail in the 1960s, taking refuge in the Irish Republic. He was held in Mountjoy prison, but escaped from there too, reputedly by hiding in a tree for several days.

In 1974, while on hungerstrike in Britain, he almost succeeded in breaking out of Wormwood Scrubs, but was spotted on top of the prison's outer wall. After being transferred to the Maze prison he made two unsuccessful attempts before breaking out in 1983.

Such adventures are boosts for republican morale, but they often have lethal consequences. In the 1983 breakout, a warder was stabbed and died, though at a subsequent trial it emerged that he had a serious heart condition, and the judge ruled it could not be said the stabbing had caused his death.

In 1974, a republican internee successfully tunnelled out of the Maze, but was shot dead by a soldier on the perimeter. Ten years later a loyalist inmate, attempting to escape inside a refuse lorry, became caught up in its mechanism and was killed.

The history of the Troubles is studded with escape attempts, most of them unsuccessful. The most ambitious, prior to the discovery of this tunnel, came in 1989 when the IRA planned to blow up a wall of Crumlin Road jail with a 1,000lb bomb carried by a JCB digger.

Cars had been left around the prison for escaping prisoners to collect, but in the event a tyre on the digger blew and the operation failed. Semtex explosive was later found inside the jail.

The Maze, on a 130-acre site in countryside outside Lisburn, Co Antrim, is really a series of prisons within a prison. The eight H-blocks are each capable of housing nearly 100 men.

IRA prisoners are held in three of the units, the INLA in one and the loyalist UDA and UVF have one each and another between them.

One block is always kept empty for emergencies - like yesterday's, when the IRA men in H-block 7 were moved to H-block 8 after the discovery of their escape tunnel.

Prison officers keep the men within their H-block compounds but inside they can more or less do what they want when they want, subject to their paramilitary commanders.

Cell doors are left open, paramilitary emblems and murals adorn the walls. Televisions and videos are provided in association rooms on each wing of the blocks.