As I recall that was the reason we went into it, to increase the market for our goods, so the reverse applies surely? Or were we told porkies back then?
We went into the EU because all the countries in the EEC automatically became members after the Maastricht Treaty. And we had joined the EEC because a Tory government took us into it, this was later confirmed by the British electorate through a referendum. Those are 'the reasons we went into it'.