It was also highly critical of the British Labour government of Tony Blair agreeing to Sinn Féin's participation in the Northern Ireland Executive prior to the Provisional IRA fully disarming.

O'Brien's hostility to militant Irish republicanism was well-known, and the adherence of such a prominent supporter from the Republic helped reinforce the UKUP's claims to be a non-sectarian party.

The UKUP (and the Democratic Unionist Party (DUP)) refused to accept US Senator George Mitchell as chairman of the multi-party talks and tried to obstruct his work.

In December the party split over the issue of Sinn Féin taking up its seats in the power-sharing executive without prior Provisional Irish Republican Army decommissioning of weapons.

In the 2007 Assembly election, the UKUP fielded candidates in thirteen of Northern Ireland's eighteen constituencies, but failed to win any seats.

The party stood on a platform opposing plans by the DUP to enter into devolved government with Sinn Féin after the election and on other issues including rates, water charges and education.

McCartney announced his retirement from politics following the loss of his assembly seat in North Down to Brian Wilson of the Green Party.