Looking at approval polls in Eurobarometer, as I recall, British opinion on the EU tended to trend downwards after the Maastricht Treaty. So the public was kinda onboard with a looser organization, but not as much with a tighter.
Also, the referendum happened to rather unfortunately coincide with the European migrant crisis, so you had upset at immigration hitting a fever pitch right about the time the referendum was run, and some of the campaigning related to it (like taking back control of borders).
What? There was only one referendum. What on Earth are you on about. You mean the undemocratically elected parliament?
Well, there was sort of a second, but that could best be described as Remain.
https://en.wikipedia.org/wiki/1975_United_Kingdom_European_Communities_membership_referendum
Looking at approval polls in Eurobarometer, as I recall, British opinion on the EU tended to trend downwards after the Maastricht Treaty. So the public was kinda onboard with a looser organization, but not as much with a tighter.
Also, the referendum happened to rather unfortunately coincide with the European migrant crisis, so you had upset at immigration hitting a fever pitch right about the time the referendum was run, and some of the campaigning related to it (like taking back control of borders).