I can tell you that many who are of that generation felt lied to about the reasons for joining and the scope of what our membership was to be, my Dad included.
It’s also worth bearing in mind that we were taken into the EEC, as it was then, without the consent of the electorate. The referendum on our continuing membership only happened afterwards, which heavily swayed the outcome.
I know people very high up in finance who worked for the Bank of England at the time. They’re still sore about what Brown did!
Also worth recalling that it wasn’t all roses behind the scenes with Brown either. He was demonstrably a bully, worse than even Patel, and had a notorious temper.
The woman that Gordon Brown called a bigot actually is a nasty bigot and the only thing he did wrong is that he should have said it directly in her nasty bigoted face.
The first is more important when it comes to attitudes though.
Also, it’s very much a case of selecting narratives in support post hoc for something that went far beyond anything that could reasonably have been inferred at the time.
Maastricht, for example, the UK should have had a further referendum on that.
As far as I can tell, the Conservatives campaigned on EEC membership in 1970 and won. Given your previous support for general elections as expressing desires for party manifestos to be enacted, I think you can’t argue against a democratic mandate for joining the EEC. Note that according to FullFact, the concept of “ever closer union” has been in there from the beginning.
Now, I can’t actually remember what the wording of the specific positions campaigned on for the first referendum was, but I remember it was discussed in the previous incarnation of this thread, where it was demonstrably proven that the increasing integration was very much part of the campaign.