North Belfast DUP MLA Nelson McCausland said: "In recent days we have seen leading members of the Ulster Unionist Party and the leader of the Conservatives, David Cameron indicating that they wanted to see full-blown merger between the Ulster Unionists and the Tories.

"That can't have been comfortable for people inside the UUP with Labour sympathies like Fred Cobain, Michael McGimpsey or Ken Robinson to witness."

Mr Cobain has actually told the News Letter he sees the UUP-Tory co-operation as a solid move, in terms of underpinning the Union.

He has reserved judgement on what talks could mean for policy, until they are concluded. However many observers view the Conservatives as being as socially aware and centrist as Labour, which is leaning increasingly to the right in its policy making.

But Mr McCausland highlighted the problems that may lie ahead, internally, for the UUP.

"The great strength of unionism is that it is possible to be a left-wing unionist a right-wing unionist or a centrist unionist," the DUP MLA commented.

"Unionism is bigger than left-right politics and is able to encompass all people with all political positions on socio-economic matters. By aligning themselves in a clear and unambiguous way with a centre-right political party, the leadership of the UUP is effectively telling its members with centrist or left-wing political leanings that they are no longer welcome."

And Mr McCausland noted that in the past fortnight, UUP MLA Ken Robinson recently said the Tory Party "is going nowhere fast and is rapidly becoming an irrelevance in British politics". He expressed that opinion just before the UUP-Conservative talks announcement.

"If that is still his opinion, what future will he have inside the Ulster Unionists once they become the Northern Ireland branch of the Conservative Party?" Mr McCausland said.

However, Northern Ireland Conservative David Fry hit back at Mr McCausland and called the DUP "the Protestant equivalent of Sinn Fein".

He said: "When Mr McCausland claims 'unionism is bigger than left-right politics' he is effectively saying that Northern Ireland should not be a full part of the UK.

"Left-right, Conservative-Labour politics are the politics of the UK. The politics of the Union are bigger than what passes for unionism inNorthern Ireland."

He added: "The DUP may settle for the politics of 'ourselves alone' but our leader, David Cameron, is determined that people in Northern Ireland should no longer be treated as second class citizens in the UK.""