DUP and UUP discussed merger
The DUP and senior members of the UUP held detailed talks about a merger last year, the BBC has learned.
A BBC Spotlight programme reveals that the DUP and leading figures from the UUP held talks about combining to form a single party.
The talks failed, but helped fuel a continuing internal debate about co-operation between the parties.
The parties and the TUV agreed to support a single unionist candidate in last week's Mid Ulster by-election.
Some unionists see closer co-operation between the parties as being essential if unionists are to retain long term control of the first minister's position.
UUP leader Mike Nesbitt has proposed vote transfers between his party and the DUP in next year's European Parliament election.
Spotlight reporter Stephen Dempster said he understands that last year's talks advanced to the point where the DUP and an external backer of the UUP group were preparing to finance public opinion research about the proposed merger.Pulled plug
The then UUP leader Tom Elliott has categorically denied any knowledge that senior figures in the party - when he was leader - were discussing the potential for a merger.
Former Ulster Unionist MP David Burnside, who took part in the talks, confirmed to Spotlight that turning the DUP and UUP into one single party was on the agenda.
He said the talks considered a "totally united unionist party".
"One party, one membership, one leadership, one manifesto, one parliamentary party at Westminster, one parliamentary party in the executive, one party in Europe," he said.
Mr Burnside said he and "a number of officials" from the UUP "believed it was worthwhile exploring the pluses and minuses of uniting unionism and we prepared a policy paper and I took it to Peter Robinson".
The programme identifies North Belfast MP Nigel Dodds as being one of the DUP figures involved in the discussions.'Not discussing'
"Whatever discussions we have had with others will be done on the basis of confidence and confidentiality where that is the basis on which they are held," Mr Dodds told Spotlight.
"And we will not be discussing it openly or publicly when that's not the basis on which those talks were agreed."
Professor Jon Tonge, an expert in British and Irish politics at the University of Liverpool, said that for the UUP a proposed merger would be "between a cat and a canary, in that they are simply going to be swallowed whole by the DUP".
Mike Nesbitt said he has ruled out unification with the DUP.
"A merger will not happen on my watch," he told Spotlight.
"I am ruling out unionist unity, I am ruling out a single monolithic unionist party.
"I am ruling out the end of the DUP and the Ulster Unionist Party and the creation of a single alternative. I am saying no."
Spotlight is broadcast on BBC1 Northern Ireland on Tuesday at 22:35 GMT