David Trimble, the leader of Northern Ireland's largest party, the Ulster Unionists, refuses to sit on a new executive or cabinet with the IRA's political wing, Sinn Fein, until the paramilitaries begin to hand over their weapons.

Sinn Fein says decommissioning of weapons was not a condition of the original peace deal - and it maintains that it cannot promise decommissioning on behalf of the IRA.

"No 'ifs' no 'buts', no excuses," Mr Trimble warned. "Just a simple, clear statement on behalf of the republican movement that they will decommission."

What might appear to outsiders as a superficial scrap has wide-ranging implications for the complex web of politics in Northern Ireland.

For Mr Trimble, backing down could end his political career. For the IRA, to initiate disarmament could cause a dangerous split between those committed to peace and those who still believe armed struggle is the only way forward.

For both sides, any change in policy could make it look like the other side is winning.

The IRA's view

To many outsiders, Sinn Fein's position might seem unreasonable.

Gerry Adams

The Good Friday agreement has seen many of its prisoners released (as have the loyalists) and the security presence scaled back in nationalist areas. Why are a few guns and some Semtex so controversial?

The answer lies in IRA history.

The IRA's strength has always been founded on its arsenal. Throughout the Troubles, IRA doctrine has taught that only physical force and "armed struggle" could force the British out of the province.

Tommy McKearney, a former IRA volunteer who served a life sentence for murder, says IRA members believe that Sinn Fein has already made tremendous compromises.

"Sinn Fein has accepted the Good Friday Agreement which in essence accepts partition. And that can seem totally anathema to orthodox republican ideas."

The result is that Sinn Fein's Gerry Adams is walking a tightrope between appeasing the Unionists and hardliners within the IRA ranks.

The Unionist view

By the letter of the Agreement, Sinn Fein has a point. There are no preconditions for the IRA to decommission.

David Trimble

The Agreement requires that all sides "reaffirm their commitment to the total disarmament of all paramilitary organisations" and "use any influence they may have to achieve the decommissioning of all paramilitary arms within two years".

But the spirit of the Agreement envisages a stronger commitment to the end of violence in the province.

Furthermore, UK Prime Minister Tony Blair has given a number of personal assurances to the unionists, including one last October that it was his view decommissioning would begin "straight away". None of his promises have been delivered.

In the past, he has been persuaded to allow the peace process to move forward without action on disarmament. Mr Trimble's inability to secure the handover of any IRA guns has placed him under intense pressure from some anti-agreement elements in his own party

Last year, he had originally demanded IRA decommissioning before he sat down at talks with Sinn Fein, but the Blair government persuaded him otherwise leading to harsh criticism from hardliners like DUP leader Ian Paisley.

He also did not want to speak face to face with Gerry Adams before decommissioning - again, he was persuaded otherwise.

All the time, his position within the party has become increasingly vulnerable. Many speculate that if he sits on the Assembly Executive with Sinn Fein, without decommissioning, he could face a leadership challenge which in turn could bring down the nascent Assembly.

The future