Londonderry: The upheaval of Brexit means a referendum on Irish unity must be held within the next five years, the leader of republican party Sinn Fein said on Saturday. The province of Northern Ireland, and its border with the Republic of Ireland, has been a major complication in Britain’s attempt to leave the EU. “The days of partition are numbered, change is in the air, Brexit has changed everything,” president Mary Lou McDonald told the party’s conference in Londonderry. “Many people, for the first time, are now considering their future in a United Ireland.”