Britain had entered the European Economic Community (EEC) in 1973 while Edward Heath was Prime Minister. Although Harold Wilson and the Labour party had opposed this, in government Wilson switched to backing membership, but was defeated in a special one day Labour conference on the issue leading to a national referendum on which the yes and no campaigns were both cross-party – the referendum voted in 1975 to continue Britain's membership by two-thirds to one third. This issue later caused catastrophic splits in the Labour Party in the 1980s, leading to the formation of the Social Democratic Party.