We have a parliamentary democracy. The referendum was advisory. It is true that Cameron said he would act on it no matter how narrow the result but he had no right to do so.
If it had been an "instruction" rather than advice, it would have to have required a super-majority, usually 40% or 50% of the electorate. The first Scottish devolution referendum was won by "yes" but could not be enacted as the majority did not reach the threshold.
Cometh the hour, cometh the Binface…
