Question: who was prime minister when britain joined the common market
Answer: The United Kingdom European Communities referendum of 1975 , also known as the Common Market referendum and EEC membership referendum was non-binding referendum held on 5 June 1975 in the United Kingdom to gauge support for the country 's continued membership of the European Communities ( EC ) -- often known at the time as the `` Common Market '' -- which it had entered on 1 January 1973 under the Conservative government of Edward Heath .