Only around 30% voted to leave the EU: [View all]
UK Office for National Statistics mid-year population estimate 2015, released 23/6/2016 is 65,110,000
Of these, 7,053,719 are under 18, so of the estimated UK resident population (2015), 58,056,281 are estimated to be of voting age.
The UK Electoral Commission reports that the electorate for the referendum was 46,500,001 registered deemed-eligible voters, of whom 72.2% voted. There were 25,359 rejected votes, 16,141,241 votes to remain in the EU and 17,410,742 to leave.
I have not yet compiled figures on the estimated number of UK residents who are not currently EU citizens, nor on the number of non-UK residents who formed part of the electorate, but in broad terms perhaps all can agree that those voting to leave the EU were approximately 30% of the eligible voting-age EU citizen residents in UK (includes, of course, UK citizens) and 27% of the total estimated population including those under 18 whose future is here so much at stake. I think it is reasonable to assume that those eligible who did not vote or did not register to vote did not feel strongly that the UK should leave the EU (and very probably break up the UK and possibly the EU too).
These are not enough votes here to justify such radical UK Constitutional and International Treaty change.