 Complete the following phrase:  The European Union and its institutions have developed gradually since their establishment, including 47 years of British membership, and grew to be of significant importance to the UK. Throughout that time Eurosceptic groups had existed, opposing aspects of the Union and its predecessors. Prime Minister Harold Wilsons pro-EC government held a referendum on continued EC membership in 1975 in which voters chose to stay within the bloc with 67.2 of the vote share, but no further referendums were held as the project grew and became ever-closer in the subsequent Maastricht and Lisbon treaties. As part of a campaign pledge to win votes from Eurosceptics, Prime Minister David Cameron promised to hold a referendum if his government was re-elected. His pro-EU government subsequently held a 