I've seen some variant of this claimed time and time again, but I don't really get it. The EU has always been supranational, always been pro-harmonisation and -integration. The scope of what it covers may have expanded somewhat over time (and that's been actively participated in by the UK anyway), but is it really a fundamentally different institution in 2016 from what there was in 1975? The main thing it did in 1975 and does in 2016 is set common rules for trade. Okay, it has nominal leaders now and some semblance of democratic process, but that's a feature of the UN, too, and nobody describes it as a superstate.
In 1975 there wasn't even a flag - the circle of yellow stars was a symbol used by different pan-national organisation (that still exists) with no relation at all to the EEC.
Under its current name, yes, but the European Union we know today is really the successor to the European Communities of yesteryear.
> Since 1975 there is a currency (and monetary policy),
Which the UK doesn't participate in, mostly.
> there is a proper and separate legal system,
This isn't new. There has been EU law since before the UK joined. The European Communities Act 1972 specifically provides for the conversion of EU law into UK law, and its supremacy over UK law.
> there a real political process with a parliament and an executive and many other changes.
The European Parliament existed long before the UK joined, and has been named that since 1962. But in fairness, it only started having elections in 1979 (it was previously appointed).
The European Commission, the executive, also existed before the UK joined. It has been a single body since 1967 (and there were three executives before that - their merger is sometimes considered the beginning of the modern EU).
> Trade is now only a part of a much bigger story.
It's always been part of a bigger story. The European Economic Community, after all, was only one of the three European Communities we joined.
> In 1975 there wasn't even a flag - the circle of yellow stars was a symbol used by different pan-national organisation (that still exists) with no relation at all to the EEC.
So? Lots of international organisations have flags. The Commonwealth of Nations has its own flag, and it's never considered a superstate.
Clearly you think that it is the same body. I hope you can also see how others could be cynical about this expanded scope and view it as surprising and undesirable.
On the other hand, I don't know if the general public understands the EU now, either.
[1] http://ec.europa.eu/civil_service/docs/hr_key_figures_2016.p...
Though obviously, if the rules changed then everything would change, new parties, new alliances, less tactical vote buying, more democracy.
"A small anti-EU, right wing party" - UKIP got nearly 13% of the vote and would probably be part of a coalition government with the Conservative party if we had a proportional representation system. Instead they have 1 MP. The SNP got only 8.6% of the vote and they have 56 MPs.
The referendum is happening because finally the grassroots of the Conservative party prevailed on the parliamentary Conservative party that we had to have one. Polling has historically shown that at least 40% of the country want to leave the EU. All of the traditional parties support the EU membership.
The UK joined an economic community that has somehow transformed into a superstate. You need to have democratic process if you want to make a change that big.