Leave 'won' the Referendum, but voters have not had the opportuniy of seeing what the alternatives to our current membership of the EU are, and of deciding whether the likely economic, political and social consequences mean that it would be better for the UK to remain full members.
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The referendum was 'won' on a simple majority because it was said to be Advisory at the time. There was at the time no indication of the type of deal, or relationship, the UK would achieve with the 27 other members of the EU. The government later said it would respect the will of the people: but the people may well have voted differently had they known the result would be considered set in stone (mandatory referendum would require a supermajority.)