The decision to stage the referendum split Harold Wilson's Labour government between pro-Europeans and anti-EEC rebels and forced him to suspend the doctrine of collective cabinet responsibility during the campaign. However, with most ministers and opposition leaders in favour of EEC membership, the result appeared to deliver a decisive answer to a question that had dominated British foreign policy since the Fifties - whether to be part of the new Europe being built by France, Germany and other EEC states.
But, quite frequently, referendums have produced results quite opposite to those intended by the political elites who called them. That is the risk facing the Government, or a Labour government, if it campaigned on the basis of joining a single currency. They risk being publicly rebuffed.
One example was the June 1992 referendum in Denmark, which rejected the EU's Maastricht treaty on closer European union by 50.7 to 49.3 per cent. It was not until the Danish government secured a variety of opt-outs, including one from the single currency, that the treaty was approved in a second referendum in May 1993 by 56.7 to 43.3 per cent.
The initial rejection humbled many EU leaders into recognising they had taken too little account of public opinion when devising the treaty. The Danish vote and a subsequent French referendum that approved the treaty only by a whisker partly explain why the EU's integrationist ambitions are more modest than five years ago.
Earlier Europe-related crises in Denmark were also settled by referendums. In 1982, the people of Greenland, who had won home rule from Denmark in 1979, voted to end their membership of the European Community by 53 to 47 per cent.
Referendums have also played a key role in Norwegian debates on Europe for more than 30 years. The two referendums on the issue - in 1972 and 1994 - have both produced "no" results.
Voters in Switzerland, traditional home of direct democracy, cocked a snook not just at the EU but at their own political and industrial establishments in 1992 when they decided not to join the European Economic Area (EEA), a single-market zone covering the EU and several small states.
On domestic issues, too, referendums have a way of not always turning out the way that leaders planned them. Charles de Gaulle, usually a master tactician where referendums were concerned, had to resign in 1969 after he lost a vote on reforming France's regional government system.
In Poland, a referendum in November 1987 paved the way for the collapse of Communism. General Wojciech Jaruzelski, the Polish leader, sought popular approval for a package of political and economic reforms but failed to win the required support of 51 per cent of the electorate. It was damning evidence that Poles were impatient for reform and quickly led to the re- legalisation of the mass opposition movement Solidarity.
The lesson of post-war Europe is that the outcomes of referendums are rarely foregone conclusions and popular sympathy for the EU is low. Still, that partly depends on the question being asked. Three years before Britain's 1975 vote to stay in the EEC, France held a referendum on whether to allow the British (and Danes and Irish) to join. A decade of de Gaulle-led opposition to Britain fell away as the French voted resoundingly yes.Reuse content