Also in my understanding, it was a gamble by David Cameron. He promised the referendum before the previous general election, believing the Tories wouldn't get a majority and he could blame the Lib Dems coalition partner when they blocked the referendum, then the Tories did win outright and oopsie, what do I do now, I've got to hold a referendum with no plan. Basically unintended consequences. Moral of the story... be careful. Maybe Cameron had had a long day and was tired or something when he made that decision ;)