Brexit "Non Event for oil Prices"CNBC First technically speaking the referendum is not legally binding. In theory, British Prime Minister David Cameron could ignore the will of a slight majority of voters, and not make any moves to exit the political and economic bloc. But that is highly unlikely. Assuming Cameron respects the democratic process, he will invoke Article 50 of the Lisbon Treaty, which begins the formal, legal process for leaving the EU. That would then begin a series of negotiations for how to disentangle the U.K. from the many EU structures to which it is a party, and could take up to 2 years (or more if both the U.K. and the European Council agree to extend the discussion period).