The stand-off between Sinn Fein and the DUP over devolved policing and justice powers deepened today over a renewed threat to collapse the Assembly.

Sinn Fein leader in the Dail, Caoimhghin O Caolain said the party would have to pull ministers from the Executive if the issue is not resolved.

DUP Junior Minister Jeffrey Donaldson said doubt had been cast over Sinn Fein’s commitment to making progress in the current Stormont regime.

And Ulster Unionist leader Sir Reg Empey, warning a full-blown crisis could be facing the Executive, demanded Deputy First Minister Martin McGuinness spell out if he agrees with Mr O Caolain.

The exchanges ratchet up tensions between the parties in the run up to the next scheduled Executive meeting on September 18 — the first for almost three months.

Sinn Fein has been refusing to agree to Executive meetings until the policing and justice issue — among others, including Irish language legislation and the national stadium at the Maze — is dealt with.

DUP leader Peter Robinson, who has presided over only one Executive meeting since becoming First Minister, last week warned of on-going political uncertainty.

Yet earlier this month he and Mr McGuinness agreed on the basic structure for a Department of Policing and Justice — with only one minister, from neither the DUP nor Sinn Fein — although not on the crucial aspect of timing.

Disgruntlement from Sinn Fein as the May date for policing and justice mentioned in the St Andrews agreement passed lead to urgent talks involving Gordon Brown, and the stalemate could potentially lead to another Assembly election.

Speaking at a republican meeting in Co Cavan, Mr O Caolain said: “If we are forced to conclude that change will not be forthcoming from the executive then we will have no option but to pull out our ministers and seek to put pressure where responsibility ultimately lies, which is on the British government in London. There is now widespread and growing concern among republicans at the failure to transfer policing and justice powers from London to Belfast in due time.

“When Sinn Fein changed our policy on policing in the north, accepting that a new beginning was being made, it was with the prospect that policing and justice powers would be transferred by May of this year. It is now the end of August and we do not even have a date for transfer. This is totally unacceptable.”

But Lagan Valley MP, Junior Minister Mr Donaldson, countered: “O Caolain well knows that the May date... was a target date put forward by the Government and the Irish.

“The DUP made it very clear on that occasion that we had not agreed to any date for the transfer of these sensitive powers.

“Progress on outstanding issues is based on there being sufficient community confidence to support any advancement. Sinn Fein can assist in the building of this confidence by their public display of commitment to policing and the rule of law and their cooperation with the police in apprehending those who continue to engage in acts of terrorism.

“However, the issuing of threatening statements suggesting that Sinn Fein Ministers will walk away unless their demands are met is not the way to make progress. Such language, as has been used by this Sinn Fein representative, begins to cast significant doubt on Sinn Fein’s commitment to making progress in Stormont.”

Sir Reg said: “The people were told by DUP spokespersons the they had negotiated stability, and that there would be no more crises at Stormont. The O Caolain statement makes the second challenge to the Institutions from Sinn Fein in two months. This sort of behaviour cannot continue for much longer.”

And he called upon Mr McGuinness to say whether or not Mr O Caolain was speaking for Sinn Fein Ministers. “If Martin McGuinness does not distance himself from this statement then a full blown crisis is facing the Executive next month,” he said. “With the people reeling from the economic downturn, increasing fuel prices and more recently further flooding, they expect more from their Ministers than these blackmail tactics coming from Sinn Fein.”