The Prime Minister is due in Belfast this afternoon on a short trip.

He will fulfill an engagement in the city, address the Assembly, meet with the First and Deputy First Ministers and with the five main party leaders.

In a move which may anger unionists, he is expected to call for the devolution of policing and justice powers when he addresses MLAs in the Assembly chamber in the late afternoon.

It is believed he will praise the parties for the work done so far on devolution but urge that the process is completed via the transfer of law and order powers from London.

Government sources, however, said he would not place any deadlines or dates on his call.

Mr Brown arrives amid concern that an Executive meeting, expected to take place on Thursday, may be blocked by Sinn Fein once more.

If so, republicans will have prevented the devolved government meeting for three months, amid its fall-out with the DUP over policing and justice and other issues.

First Minister and DUP leader Peter Robinson has warned that if this happens there will be serious consequences for Sinn Fein and good governance in the Province.

But yesterday he chose his words carefully – during First Minister's Question Time in the first autumn session of the Assembly – seeking not to raise the temperature ahead of Thursday's deadline.

Urging Sinn Fein to get around the Executive table, he stepped back from confrontation.

"The situation requires much more of me simply than grandstanding and scoring party political points," Mr Robinson said.

"What I do say is I would be deeply disappointed and the disappointment I have would be reflected right across this community, if the Executive does not meet on Thursday."

At a time when rising energy costs, food price increases and economic decline were worrying the public, he said: "Our community out there wants to see the Executive working, they want to see us all moving forward.

"I am committed, as is this party, to working all of the institutions of the Agreement."

However, Mr Robinson said there were more than two dozen issues that needed to be dealt with.

He said he had cleared them for the Executive to discuss.

But he needs Sinn Fein Deputy First Minister Martin McGuinness to do the same.

If Mr Robinson was choosing his words carefully, though, the other political parties were pointing the finger – and largely at Sinn Fein for threatening the stability and future of the government.

Ulster Unionist leader Sir Reg Empey said Sinn Fein should "back down now" and allow the Executive to meet.

He was clear that people would not forgive the republican leadership if it did not get on with government when the public needed it and added he was "embarrassed" to be associated with what was happening at Stormont just now.

"To Sinn Fein I say: 'Give up this foolish behaviour'," said the UUP chief.

"Bring your ideas to the Executive and Assembly Review Committee (which is tasked with discussing policing and justice devolution] where they can be fully debated by all parties."

He continued: "Let the Executive meet and see what it can do to help the most vulnerable and back down on this unjustifiable blockade of government business."

SDLP leader Mark Durkan said Sinn Fein should realise the "total weakness" of its position.

"Sinn Fein's tactic (of blocking meetings] will simply mean that the entire calendar for further meetings will be frozen," he said.

"That would play into the hands of the DUP and Jim Allister."

Alliance deputy leader Naomi Long said the public was looking on in utter amazement at the petty goings-on.

However, Sinn Fein's John O'Dowd said the stumbling blocks were not petty to his party.