Britain's general election on Thursday is the third in less than five years and has been described by Prime Minister Boris Johnson as the most important in a generation.It comes after nine years of Conservative government during which the issue of Europe has increasingly dominated.Hung parliament, coalition (2010)Result: Conservative (306 seats) and Liberal Democrat (57 seats) coalition.Prime minister: David Cameron.Labour's Gordon Brown took over from Tony Blair as prime minister in 2007, shortly before the global financial crisis hit.To that end, support for the centre-left party plunged as voters turned to Cameron's Conservatives and Nick Clegg's centrist Lib Dems.The campaign saw Britain's first televised leaders' debates: three head-to-heads between the three main party leaders. Clegg's performance in the first saw the Lib Dems' ratings surge, in a brief outbreak of "Clegg-mania".Britain's first-past-the-post system means hung parliaments are rare. It was only the second since World War II.Cameron immediately reached out to the Lib Dems. Brown stayed in office during the coalition talks, which lasted five days, in the hope of persuading Clegg to join forces with Labour.Cameron's 2015 surprise winResult: Conservative majority (330 seats).Prime minister: David Cameron.Cameron defied expectations of another hung parliament and pulled off a slender victory, largely at the expense of his coalition partners.The Lib Dems had their worst result since their formation in 1988, down 49 seats to just eight, while the Scottish National Party (SNP) swept the board in Scotland, up 50 to win 56 of Scotland's 59 seats.Labour, under Ed Miliband, saw their vote share go up but the party lost seats.Eurosceptics UKIP won 12.6% of the vote.The outright Conservative victory meant Cameron could implement his pledge to hold a referendum on Britain's membership of the European Union.Britain's former prime minister, David Cameron resigned in 2016 after his country voted to leave the European Union. (Daniel Leal-Olivas/AFP).May's gamble backfires in 2017Result: Conservative minority (317 seats).Prime minister: Theresa May.May took over from Cameron after the 2016 EU referendum, which saw 52% vote in favour of leaving the EU.Fearing the small majority might not be enough to get Brexit through, and seeking to capitalise on a huge poll lead, she called a snap election.However, the move backfired as her wooden performances on the campaign trail, plus Labour leader Jeremy Corbyn's enthusiastic rallies, saw May lose her majority.She was forced to rely on the backing of Northern Ireland's Democratic Unionists (DUP) for a slender majority.The Conservatives won 42% and Labour 40% as voters returned to the main parties.May's authority never recovered and Boris Johnson took over after she quit in July 2019.Theresa May led the country's Conservative Party from 2016 to 2019. She resigned on June 7. (Photo by Leon Neal/Getty Images).