Ulster Unionist Party (UUP). For most of Northern Ireland’s political history it has been dominated by the UUP.
Formerly a branch of the Conservative Party, the UUP still most closely resembles the British Conservatives ideologically, with an ideology that is more economically and socially liberal than the harder line DUP.
The party ran in electoral alliance with the Conservatives in 2009, but this year is running alone.
Nonetheless, the UUP spans a wide spectrum and some members are closer to Labour. The party was surpassed by the DUP in 2003, with unionist voters preferring its more hardline stances in negotiation with Sinn Fein.
The UUP is a party of power and has been completely unable to cope with losing its formerly dominant position. This has exposed internal divisions between a liberal, centrist wing, and a wing that would like to be even more hard-line than the DUP. This recently led to a split and the formation of NI21 by two UUP MLAs, a more centrist and liberal party. NI21 appears to be disintegrating pretty quickly, however.
Due to its close links with the Conservatives, the UUP is a member of the European Conservatives and Reformists and is second only to the Conservatives in terms of loyalty to the group with 95.4% loyalty.