when did great britain join the european union
History of European Union–United Kingdom relations The Treaty of Accession was signed in January 1972 by the then prime minister Edward Heath, leader of the Conservative Party.[7] Parliament's European Communities Act 1972 was enacted on 17 October, and the UK's instrument of ratification was deposited the next day (18 October),[8] letting the United Kingdom's membership of the EC come into effect on 1 January 1973.[9]