The Ulster Unionist Party’s electoral pact with the Conservatives was thrown into confusion this week after it emerged that a UUP party association had suggested running a joint candidate with the DUP in the South Belfast constituency in the forthcoming Westminster elections.

The South Belfast Ulster Unionist Association suggested the electoral co-operation between the two main unionist parties in next year’s elections. They warned that a compromise candidate is needed to win the parliamentary seat from the SDLP.

The association is understood to have written to party leader, Sir Reg Empey, suggesting that the move is needed to retake the seat currently held by Alasdair McDonnell.

But any move could bring the Ulster Unionists into conflict with the Conservatives, who have already selected a candidate for South Belfast.

The party, however, denied Sir Reg has received the letter from south Belfast association members urging discussions with the DUP on a single unionist candidate in the constituency.

The parties last year held two meetings on the prospect of agreeing single candidates in South Belfast, but the talks ran into the sand and were further complicated by the UU liaison with the Conservatives.

This week Shadow Northern Ireland Secretary Owen Paterson insisted there would be a Conservative and Unionist candidate in each of Northern Ireland’s 18 constituencies.

A spokesperson for the South Belfast Ulster Unionist Association declined to comment when contacted.

“It is an internal party matter which is under due process and no comment will be made at this stage,” he said.

Mr McDonnell polled 10,339 votes in the 2005 general election to take the seat — with the unionist vote split between rival UUP and DUP candidates.

Jeffrey Donaldson said the DUP would back a deal with the Ulster Unionists where only one unionist candidate contested South Belfast as well as Fermanagh/South Tyrone.

However Mr McDonnell has refused to be drawn on speculation about potential opponents in next year’s Westminster poll.

“This speculation is simply a distraction and a bout of political posturing by those within the Ulster Unionist Party who are bitterly opposed to the party’s alliance with the Conservatives,” he said.

“I will not be distracted from doing the job that I have been elected to do — that is to represent all of the people of South Belfast in Westminster.

“I will face all candidates in the forthcoming Westminster election on my proven track record of delivery for all the people of South Belfast.”

Meanwhile Anna Lo, the Alliance party’s MLA for the area, said the move proved that the Ulster Unionists “remained mired in the old politics of sectarian headcounts”.

“Already the strains in the Ulster Conservatives and Unionists — New Force arrangement are showing,” she said.

“Clearly the rhetoric of a new non-sectarian dawn with support for a shared future has been exposed as completely shallow.

“The message that comes out from this is that what matters above all else is the stale old unionist versus nationalist sectarian headcount.”