The largest number of by-elections held on a single day occurred on 23 January 1986 when 15 simultaneous contests were held in Northern Ireland. The elections had been engineered by the incumbent Unionist parties as a protest against the Anglo-Irish Agreement of 1985. They intended the results to be interpreted as a referendum on the treaty. The elections were boycotted by the main Nationalist parties except in four seats where they had a reasonable prospect of victory. In the event, the Social Democratic and Labour Party gained one seat, Newry and Armagh, from the Ulster Unionist Party.