Peter Robinson has pulled out of a joint appearance with Martin McGuinness at the Labour Party conference today, in protest at Government pressure to agree a timetable for the Assembly to assume policing and justice powers.
The DUP made clear, however, Mr Robinson is to press ahead with plans to attend next week's Conservative gathering in Birmingham.
The First and Deputy First Ministers had been expected at a special Northern Ireland breakfast event but Mr Robinson's place will instead be taken by Junior Minister Jeffrey Donaldson.
There is speculation the DUP leader took a final decision to withdraw after Prime Minister Gordon Brown last week urged unionists to ‘set the date' for the devolution of policing and justice.
And yesterday Secretary of State Shaun Woodward intensified the pressure on the DUP by suggesting a timeframe for the transfer of police and criminal courts powers in 12 months.
Mr Donaldson last night refused to be drawn on the reasons for Mr Robinson's cancellation. As late as Friday organisers were still expecting Mr Robinson to attend but senior DUP sources insisted they were informed on Thursday, two days after Mr Brown's unexpected exhortation.
"We have consistently said we will not agree to a set timeframe, timetable or deadline for policing and justice,” the Lagan Valley MP said last night.
“What is important is for there to be sufficient confidence in the community and quite frankly we are someway off that point.
“The fact is that the Executive has not met now for three months and collectively we are not even addressing the issues for which we do have responsibility never mind taking on such a sensitive issue as policing and justice.
“It is vital that the Executive meets to deal with the matters which people are concerned about. They are not talking about policing and justice, they are talking about the economic downturn.”
Mr Woodward, however, said yesterday the parties must work through their differences on policing and justice.
And he said the fact that Mr Brown visited Belfast last week, with markets around the world in turbulence and speculation about banks, showed his commitment to the people of Northern Ireland is “resolute”.
“It is a tense period in Northern Ireland. The Executive has not met — since June. It needs to meet. There is business to be agreed,” he told delegates gathered in Manchester.
“The parties need to find a way forward. But also tense because there is work to be done on policing and justice.
“Gordon's message was clear: let politics work through your differences. We understand the obstacles but we can also see the progress. We know for some Unionists, this is a difficult final step.”