The first referendum to join the EU was a resounding yes to join.
Er, it wasn't.
We had already joined. The 1975 referendum was on whether we should remain.
Yes. We joined without a referendum. Weird.
If you wanted another referendum then 1993 would have been the inflection point. When the EEC became the EC.
Anyway, our electoral system hasn't evolved to manage referenda. They exist only to allow weak party leaders to avoid jeopardy. (Which is part of their job).