Unionists are set to lobby the prime minister over the IRA's ceasefire.

Senior members of the Democratic Unionists will go to Downing Street on Tuesday to complain over the government's handling of the ceasefire.

They are expected to argue that the IRA is failing to meet its commitments from the Good Friday Agreement and urge Ulster Unionists to ditch the Stormont power sharing government.

Ahead of the meeting DUP deputy leader Peter Robinson attacked Northern Ireland's first minister David Trimble daring him to carry out his threat to quit.

"What about it, David, or are you chicken? Already republicans are laughing at Mr Trimble, who has a loud bark but no bite," he said.

"Repeated threats without action diminish the unionist position. Mr Trimble knows that an exclusion motion will not gain SDLP support and therefore, under the rigged voting system the UUP introduced into the assembly, no action will be taken against Sinn Fein/IRA."

Robinson said there was only one way to respond to the government's recent announcement that it would be taking a tougher assessment of paramilitary activity rather than actually sanctioning groups.

"If unionists walk out of the assembly, the secretary of state will be forced to call an election. It is now well recognised that only a deal done with the DUP has any prospect of sticking and producing stability. Everyone knows that Trimble is a spent force - so let's get on with the election and the negotiations that will inevitably follow," he said.

The leader of the SDLP, Northern Ireland's deputy first minister Mark Durkan, warned that only the paramilitary terror groups would benefit from shutting down the assembly."Threatening a political vacuum is not the answer to the political violence that threatens us all. Aborting democratically-agreed arrangements will only satisfy the sectarian power kicks of paramilitaries," he said.