DUP deputy leader Mr Peter Robinson said the Ulster Unionist Party is unionist in name only and has conceded the battle for the North to remain part of the UK.
Mr Robinson was addressing the annual conference of the Young Democrats, his party's youth wing. UUP leader Mr David Trimble had agreed to the expansion of North-South bodies which posed the "greatest long-term threat" to the Union, he said.
"Today the Ulster Unionist Party is a party of the Union in name alone. That is not merely rhetoric. Every day it becomes more apparent. At UUP branch level, talk has now turned to an agreed Ireland. The battle for the Union has been all but conceded.
"There is a cancer at the heart of the party. Even issues which the UUP fought at the time of the Belfast Agreement - a time which was thought to be the low point for unionism - have been conceded since.
"This UUP collapse can be evidenced on no issue more clearly than our relationship with the Irish Republic. The destruction of the RUC, the release of terrorist prisoners and even the elevation of terrorists into the heart of government were an affront to morality, decency and democracy."
The North-South Ministerial Council presented the greatest long-term threat: "Let there be no doubt, it is the creation, in embryo, of an all-Ireland state." The DUP believed in co-operation with the Republic only when it was to Northern Ireland's advantage.
The DUP leader, the Rev Ian Paisley, told the conference a united unionist resistance was needed. "We must be the watch-dogs of the Union. We must marshal the forces of resistance against all that is happening today." He said the history of Northern Ireland was being "slowly erased" from the curriculum of local schools. On Mr Gerry Adams's call for unionists to engage in a debate on Irish unity, he said: "Gerry Adams can grow his beard until he is Rip Van Winkle but we will be saying no to the destruction of the Union."