The 1998 referendum on the Good Friday Agreement was in fact the third referendum to be held in Northern Ireland. The first, held in 1973, was on the question of continued participation in the UK versus a united Ireland; the second, held in 1975, was part of a UK-wide referendum on continued participation in the European Economic Community.
8 March 1973: the "Border Poll"
Self-determination is a rather limited concept. Introduced by Woodrow Wilson in the context of post-1918 Europe, ignored on almost every occasion that it suited the Great Powers to do so, it applied to Northern Ireland to the very limited extent that the Northern Ireland Parliament had the right to opt out of the Irish Free State when it was established in December 1922 (and it immediately did so). The 1949 Ireland Act, which recognised that the Irish Republic was outside the British Commonwealth, renewed the right of the Northern Ireland Parliament to opt out of the UK and join a united Ireland. But there was no question of a referendum at this point (though a county-by-county referendum on participation in Home Rule had been mooted in 1914) and self-determination applies only in so far as Northern Ireland can choose which larger state to belong to, but not opt for independence.
The abolition of the Northern Ireland Parliament in 1972 raised the question of whether or not a new Assembly should have the power to determine which state Northern Ireland should belong to. For whatever reason, the British government decided to put this question directly to the people every ten years by referendum, and the first (and so far only) referendum on this issue was held on 8 March 1973. The Unionist parties, and Alliance and the NILP, campaigned for a vote in favour of staying in the UK; the Nationalist parties urged their supporters to boycott the vote. The results were as follows:
% valid votes
Do you want Northern Ireland to remain part of the United Kingdom?
Do you want Northern Ireland to be joined with the Republic of Ireland, outside the United Kingdom?
In 1983, the then Secretary of State, Jim Prior, decided not to hold another referendum on the ground that the likely outcome was obvious from other elections, ie that the pro-UK vote would win. The 1998 referendum included of course the provision that Northern Ireland remains in the UK for the time being.
The idea that a referendum at some future point might decide that Northern Ireland would join a United Ireland survived into the 1985 Anglo-Irish Agreement and the 1998 Good Friday Agreement, and Nationalists read the demographic runes with glee, pointing to the increased vote for Nationalist parties over the last few years. I am personally sceptical that there will be a referendum majority for a United Ireland in the near future for the following reasons:
I suspect that the recent growth in the Nationalist vote is caused by the working through the system of a growth in the Catholic share of the population which largely happened in the 1970s. This was caused, first, by an easing of the situation for Catholics, both in terms of economic discrimination and in terms of stable and safe housing after the forced population movements of the early period, which meant they were more likely to make a living and therefore stay in NI, and second by differential emigration from Protestants getting the hell out of Northern Ireland in the early years of the troubles. If I am right, we will see some growth in the Nationalist vote share in the next couple of elections and then it will level off at around 45%.
As is clear from the 1998 referendum results, a referendum rather than an election will pull out many more voters in areas which are not really hotbeds of support for a united Ireland. Opinion polls likewise show that support for a united Ireland runs well behind support for Nationalist parties. One cannot exclude the kind of sudden mood change which hit Slovenia in 1991, but it hasn't happened yet.
5 June 1975: The Common Market Referendum
Both the UK and Ireland joined the European Economic Community (then generally referred to as the Common Market) on 1 January 1973. Strange though it seems now, at that time the Conservative Party was generally in favour and the Labour Party generally against. Labour leader Harold Wilson promised a nationwide referendum on whether or not to stay in the EEC provided that he was able to renegotiate more favourable terms. (Ireland, Denmark and Norway had all put the issue to the popular vote - unlike the UK - before joining, Norway voting against.)
Wilson won both 1974 general elections, and declared that he had achieved the renegotiation he wanted in early 1975 and called the promised referendum, which is the first political event I remember in Northern Ireland. The referendum took place five weeks after the election to the Northern Ireland Constitutional Convention. Of the political parties, the SDLP, Alliance and, oddly enough, Vanguard were in favour of staying in; the DUP, Sinn Fein, and most of the UUP in favour of pulling out. The results were:
Parliament has decided to consult the electorate on the question whether the UK should remain in the European Economic Community . DO YOU WANT THE UK TO REMAIN IN THE EEC?
Put a cross (X) in the appropriate box.
The turnout was low at only 48.2%, though of course this was the seventh poll in just over two years since the Border Poll, and the high "YES" vote was unexpected - only a few islands of Scotland voted against in the rest of the UK, which endorsed staying in the EEC by 67.2% to 32.8% on a 64.5% turnout. For wider reflections on European integration referendums I refer you to Thomas Christin and Simon Hug's paper, Happy Voters Due to Referendums? Explaining Citizen Support for European Integration which consideres the 1975 referendum in the context of nineteen other national votes on European integration.
There has been no nationwide referendum on a European issue since in the UK, though there have been five in Ireland (one of which was held on the same day as the Good Friday Agreement referendum in 1998). The Labour government will probably hold a referendum on joining the single currency in the next few years.