A Poll on June 5, 1975 was the first referendum ever held in the United Kingdom over 67% of Britain's vote to stay in the European Economic Community. Opposition to Europe was led by Labour left-wingers such as Tony Benn rebelling against Prime Minister at the time Harold Wilson. The United Kingdom European Communities membership referendum, also known as the Referendum on the European Community, the Common Market referendum took place on 5 June 1975 in the UK to gauge support for the country's continued membership of the European Communities (EC)- often known at the time as the "European Community" and the Common Market. RIGHT HON. HAROLD WILSON . PRIME MINISTER 1975 Gold on Silver Medal, diameter 39 mm, Weight 29 grams.