Why are you all so weird in UK? You are welcome to leave the Union. You can burn down the whole Island if you want. Go on guys! I just don't understand why are you so self-destructive, but I wish you good luck with your collapsing economy. Welcome back to Union in 2020!
You any relation of Mickey Finn?
However, to answer your question: as an expat who left the UK in 1981 after living and working through the 60s and 70s, and who has kept up with British home affairs ever since I think I can state with certainty the the EEC and its successor the EU have been of little benefit to the majority of the British populace.
As I said in an earlier post; the EEC and then the EU turned out to be wasteful bureaucratic oligarchies intent on bolstering an artificial economy for inefficient European agriculture.