At university I did an honours paper on the economics of European integration, which I confess is very sad. Now, the thing is - Europe is very boring and the economic historians of the EU (yes, there are such people) are correspondingly very dull. And having waded through these turgid tomes, I can now inform you of a very boring conclusion that most of them reached: historically, the EU has had hardly any impact on the growth of trade in postwar Europe at all. The elimination of tariffs obviously has helped but this has been in the context of lowered tariffs throughout the world under the GATT (now WTO) regime. The idea that membership immediately catapults a country into economic prosperity is easily demolished with a few dates and rates of GDP growth.
Yet it is the pro-European politicians who have been resorting to fear telling people that a no vote will invite economic catastrophe, telling people inward investment will collapse if we don't join the Euro or whatever. Those of us that possess memories recall the Labour Party being rightly critical of the Thatcher government and her dependence on foreign investment at a time when British manufacturing was being crucified on the altar of a tight monetary policy.
As someone who is vaguely pro-Europe (but anti-Euro), this garbage really has to stop.