<P> The UK was not a signatory of the three original treaties that were incorporated into what was then the European Communities, including the most well known of these, the 1957 Treaty of Rome, establishing the European Economic Community (EEC). The UK's applications to join in 1963 and 1967 were vetoed by the President of France, Charles de Gaulle, who said that "a number of aspects of Britain's economy, from working practices to agriculture" had "made Britain incompatible with Europe" and that Britain harboured a "deep - seated hostility" to any pan-European project . </P> <P> Once de Gaulle had relinquished the French presidency in 1969, the UK made a third and successful application for membership . The question of sovereignty had been discussed at the time in an official Foreign and Commonwealth Office document . It listed among "Areas of policy in which parliamentary freedom to legislate will be affected by entry into the European Communities": Customs duties, Agriculture, Free movement of labour, services and capital, Transport, and Social Security for migrant workers . The document concluded (paragraph 26) that it was advisable to put the considerations of influence and power before those of formal sovereignty . </P> <P> The Treaty of Accession was signed in January 1972 by the then prime minister Edward Heath, leader of the Conservative Party . 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), letting the United Kingdom's membership of the EC come into effect on 1 January 1973 . </P> <P> In 1975, the United Kingdom held its first ever national referendum on whether the UK should remain in the European Communities . The opposition Labour Party, led by Harold Wilson, had contested the October 1974 general election with a commitment to renegotiate Britain's terms of membership of the EC and then hold a referendum on whether to remain in the EC on the new terms . All of the major political parties and the mainstream press supported continuing membership of the EC . However, there were significant divides within the ruling Labour Party; a 1975 one - day party conference voted by two to one in favour of withdrawal, and seven of the 23 cabinet ministers were opposed to EC membership, with Harold Wilson suspending the constitutional convention of Cabinet collective responsibility to allow those ministers to publicly campaign against the government . </P>

When did the uk join the european union