Agreeing to decommission its weapons was a carefully planned move which has taken the IRA and Sinn Fein years not weeks, according to a terrorism expert.

The historic announcement by the IRA was not directly affected by the terrible events of September 11 according to Dr Andrew Silke, an expert in security and terrorism at the Scarman Centre based at Leicester University.

"The statement comes as no surprise. There have been signs this was coming," Dr Silke told ePolitix.com. "What will be interesting to see is the form decommissioning takes. Sealing off part of its arms cache with concrete is the most likely scenario."

Putting one of the arms dumps beyond use is a largely symbolic issue because the IRA is a sophisticated organisation and handing over weapons presented an ideological barrier to its hardline members, he believed.

"The IRA simply handing over its guns is a step too far for the IRA; it's beyond the pale. It was a symbolic thing because in practical terms the IRA could replace those weapons relatively easily and most of the attacks in Northern Ireland have involved home-made explosives," he said.

Crucial to achieving an end to violence will whether active members of the IRA consider the decision a sell-out and join the Real IRA to continue carrying out attacks.

"It will annoy and disillusion some of the hardline members. What will be interesting to see is how many defectors there will be to the Real IRA," Dr Silke said.

He believed that the Sinn Fein leadership, who had begun the party's political strategy decades ago, had taken a strategic gamble after assessing the strength of support they had among grassroots republicans.

"Gerry Adams and Martin McGuinness have been working towards this for years. They know who those people are and who is most likely to move. They met with people and travelled to the local commanders to prepare the ground," said Dr Silke.

He explained the IRA had been persuaded to back the proposals through a series of local meetings held in the months running up to the announcement.

"It is important to understand that the IRA and Sinn Fein are very closely inter-connected. A meeting could go under the guise of a Sinn Fein meeting about decommissioning. If the local councillor is the local IRA commander it becomes very clear at those meetings what his views are. Sinn Fein would have had a very good impression of who was prepared to accept decommissioning," he said.

Careful lobbying by the Sinn Fein leadership had been key to the decision rather than the global backlash against terror groups following the attacks in America, Dr Silke believed.

"It's possible that September 11 was a catalyst but this was going to happen anyway. It may have moved the timetable forward by a few months. Gerry Adams didn't wake up on September 12 and say 'we've got to make a move here'," he said.