A timeline of key events related to the historic referendum on Britain's membership in the European Union:
Jan. 23, 2013: British Prime Minister David Cameron promises a referendum on Britain's membership to the European Union if the Conservative party is elected in the next general election. He does so to try to garner support among euro-skeptics within his own party.
Sept. 18, 2014: Scottish voters decide in a referendum to remain part of the United Kingdom rather than become an independent country.
May. 7, 2015: British voters elect a majority Conservative government. Cameron confirms in his victory speech that there will be an in/out referendum on European Union...