The Northern Assembly is debating crucial welfare reform today. Nationalist parties are vowing to block the bill, which means it is likely to be defeated.

The North's First Minister and DUP leader, Peter Robinson, will miss the debate as he recovers in hospital after a suspected heart attack.

Sinn Féin and the DUP have previously accused each other of bad faith over the reforms.

The disagreement has profound implications for the Northern Irish budget and for power sharing in Stormont. Both the British and Irish governments have expressed concern over the crisis.

It prompted the First and Deputy First Ministers to cancel their St Patrick's Day visits to the US in March.

Belfast-based security correspondent Alan Murray says it is a crunch day for the Northern institutions.

And he told Newstalk Breakfast that failure to pass the bill may see a stalemate that could cause Westminster to take over.

"If you cannot introduce a budget, then the departments cannot function" he said.

"What would happen then in July - if the whole thing was put in suspension is - the British government would take over, one presumes, if there could be no agreement between the DUP and Sinn Fein and they might impose the British welfare cuts that have been applied to England and Wales" he said.

"Or it may be that the British government would take over the whole show" he added.