Gator Blu's link is exceptional and, as it indicates, the vote could go either way.
Why? Britain has a long and proud history, much of it spent fighting the very nations who, as part of the EU, are now it's friends. But "friend" in the hands of a diplomat or politician has all the quality of a chameleon and not everybody wants to forgive and forget the past.
Left to a popular vote -- which will include both informed and uninformed opinion -- it seems likely the "Out" vote will win, if only to limit easy access by unwanted visitors.
Uneasy alliances -- like that of the former Yugoslavia -- don't always create happy bedfellows.