There was tension between the U.K. and the EU throughout the history of their relationship. It culminated in Prime Minister David Cameron's announcement in February 2016 that there would be a referendum to decide whether the U.K. would remain in the EU or leave it. The vote was held on June 23, 2016. After 52% of voters opted in favor of leaving, formal discussions about how this would take place began in February 2017, after Parliament passed legislation to begin the process.