The 1973 Northern Ireland border poll was a referendum held in Northern Ireland on 8 March 1973 on whether Northern Ireland should remain part of the United Kingdom or join with the Republic of Ireland to form a united Ireland. It was the first time that a major referendum had been held in any region of the United Kingdom. The referendum was boycotted by nationalists and resulted in a conclusive victory for remaining in the UK. On a voter turnout of 58.7%, 98.9%, comprising 57.5% of registered voters, voted to remain in the United Kingdom, meaning the outcome was not affected by the boycott.

Legislative background