The Ulster Unionist Party leader, Mr David Trimble, has dismissed suggestions that he was interested in the leadership of the British Conservative party.
He confirmed, however, that he is anxious to see the two parties draw closer together and co-operate with each other.
Mr Trimble is understood to have reached a deal with Tory leader Mr Iain Duncan Smith to serve in his shadow cabinet as part of a Westminster coalition between the Ulster Unionists and British Conservatives.
The two leaders are reported to have agreed a pact "in principle" at a meeting in the Conservative leader's House of Commons office last Tuesday.
However, Mr Trimble this morning told BBC Radio 4's Todayprogramme: "I am the leader of the Ulster Unionist Party, that is a very onerous job in itself, and it gives me some insight into the problems that people have as leaders of other parties.
"I have no desire, no intention of taking on an even bigger task, I have enough problems of my own."
Asked if he had other ambitions, he said: "There are lots of things one might like to do if the opportunities are there, but that is not the issue at the moment.
"I want to see Ulster Unionism at the heart of British politics. I don't see any justification for our being excluded from national politics, which in many respects we are.
"Yes, I have talked to the Conservatives, I have done that on a number of occasions. We do work together, we work very closely together for example in Europe, and we consider from time to time what we can do here within the UK."
Asked where such conversations might lead, Mr Trimble said: "I don't know, and I don't think that there is any point in speculating on that."
Asked whether he would be interested in Ulster Unionists sitting in the shadow cabinet, Mr Trimble added: "That is a huge jump, and whether a jump like that will ever occur is simply a matter for speculation."