Failure of the Stormont Executive to meet in just over three weeks’ time will have “serious consequences for the good government of Northern Ireland”, First Minister Peter Robinson warned today.

As the crisis over the devolution of policing and justice powers worsened, he said the DUP will not allow further progress on the issue unless the Executive is working.

And in his toughest language to date, the DUP leader bluntly told Sinn Fein the days when the republican movement could make threats to force concessions are gone.

Mr Robinson also said, in the absence of clarification from his partners in the 16-month old administration, he will assume Sinn Fein intends to walk away from the Executive.

Insisting ministers made legally-binding pledges of office which are not being kept, he said: “A meeting of the Executive has been scheduled for (Thursday) September 18. If this meeting were not to take place it is self-evident that there would be serious consequences for the good government of Northern Ireland and indeed potentially for those who refuse to fulfil their legal obligations.” His attack came as Sinn Fein demanded a “much more meaningful engagement” with the DUP and said it needed devolved policing and justice, and other issues – including an Irish language act – to be resolved.

Further ratcheting up the long-running dispute, which could potentially lead to new Assembly elections, the East Belfast MP went on: “The DUP movement on such issues will not be hastened by the issuing of threats. The central component to allow movement is community confidence.

“However, the behaviour of Sinn Fein has undoubtedly damaged confidence and in so doing will hinder the speed of progress. More precisely, by virtue of the consequences of responding to such threats, the DUP will not further progress this matter in the absence of a properly functioning Executive.”

The stern warning came just a few weeks after Mr Robinson and Deputy First Minister Martin McGuinness reached outline agreement on a single justice and policing minister and asked the Assembly’s Executive Review Committee to explore the modalities for the devolution of such powers.

“The DUP does not believe there would be support for the devolution of policing and justice if Sinn Fein ministers were to have responsibility for any policing and justice function. Furthermore, it is clear that a policing and justice Minister could not be subject to the vagaries of an Executive which can be subject to the kind of behaviour we have recently witnessed,” the DUP chief added today.

The strident tone of his remarks makes a renewed intervention by Prime Minister Gordon Brown, who has already met both parties to attempt a resolution, more likely.

Mr Robinson, who has presided over only one Executive session since becoming First Minister, said he been attempting to have the Executive called together to deal with important outstanding business for some time, clearing Executive papers and approving sufficient work for several meetings.

He said he could only conclude the weekend threat from Sinn Fein leader in the Dail, Caoimhghim O Caolain, to withdraw Ministers from the Executive involved the intention of collapsing the Assembly.