Mollykins, you have made a very pertinent point and I hope there will be many answers. We hear a lot about the huge amount of money we pay into the EU and about calls for a refendum on withdrawing from it. Explanation about what would be lost or gained if we withdrew is conspicuous by its absence. Regret my reply is not helpful - I'm just backing you up and hope some knowledgeable people will help to provide more information.
Would immigrants have to leave - that would be a decision that would have to be made at the time.
It would of course be impractical - many (like my wife) have married English people. you'd have the devils own job hunting down EU citizens and determining whether or not they were entitled to remain.
Economically many large organisations would shut down.
Take the one I work for. A large US computer company - we about 60% UK staff here I'd say. We need to recruit Europe wide to get the best people, to get enough people with EU language skills for our European support operation and as a base for our EU sales operation.
If the UK were no longer part ofthe EU the site would close and be moved probably to Amsterdam or Paris at a guess.
I doubt that we'd be very unusual - there would be a lot of redundancies and probably a flood of visa applications as high end staff apply to follow the jobs.
Yes We'd no longer be inside the EU trade area so there would be tarrifs on all sorts of our exports - this is a major reason why all the Eastern Europe countries were clamouring to get in. Nothing to do with supposed hand outs and everything to do with opening EU markets to their industries.
I could go on and on but basically It'd be financial suicide which is why not one of the 3 main parties has leaving the EU as a policy.
Even the Tories want to stay in the EU economically - in a sort of fantasy business only EU that doesn't exist