London: Voters headed to polls on Thursday to cast their ballots in a historic referendum on whether Britain should remain a member of the European Union (EU) or leave. A record number of people -- 46,499,537 -- are registered to take part in the once-in-a generation vote, BBC reported. Polling stations opened at 7 a.m. and will close at 10 p.m. It is only the third nationwide referendum in Britain's history and comes after a four-month battle for votes between the 'Leave' and 'Remain' campaigns. The registered voters include Britons from England, Wales, Scotland, Northern Ireland and Gibraltar -- a British territory off the southern coast of Spain. The referendum ballot paper asks the following question: "Should the United Kingdom remain a member of the European Union or leave the European Union?" The results are expected by early Friday morning. Once the results are in, they will be announced by region rather than by constituency. The 12 regions comprise Scotland, Northern Ireland, Wales, London and eight English regions. Britain has been a member of the EU since 1973.