Many, if not most, Brexiters will claim that Britain's sovereignty (or what they would perceive as Britain's loss of it) was never discussed during the referendum campaign of 1975. This discussion (of which only Part 1 is publicly available) originally broadcast on ITV in 1975 and now available on YouTube is a refutation of that. Sovereignty is, in fact, the principal issue under discussion. It is remarkable that the essential issues did not change in the intervening period.
It is true that, as Hugo Young says in his classic account, 'This blessed plot: Britain and Europe from Churchill to Blair', it was assumed that the EU would not impinge much on Britain's sovereignty, but that was because the EU had stalled in its constitutional development. Nobody could have predicted in 1975 that, by 1989 the situation would have been transformed by the advent of the Single Market, the project of Jacques delors for an EU with a social dimension, the collapse of Communism and the unification of Germany. The debate on EU membership would have been enriched by re-playing the debates of 1975. Among their other advantages of clarity and eloquence, mendacity was noticeably absent from the discussions of 1975. The United Kingdom may face the bitterest of ironies that, after it has fragmented into its constituent parts, each may separately apply for EU membership (and obtain it on significantly worse terms than in 1973). We will then learn the meaning of sovereignty, and the necessity of sharing it, in ther harshest of possible ways.