My suspicion is that the British will vote to remain in the EU. That said, if I were a Brit, I would vote to get out of the EU.
A free trade zone is a great idea, but letting Brussels make your labor laws and economic regulations for you is quite another. European politicians have hamstrung their own economies to the point of almost total economic stagnation. Why buy into that?
Meanwhile, there are other problems. The various bailouts of profligate countries: Ireland, Greece, Portugal come to mind, are just beginning. Why should British taxpayers pay for the nonsense that goes on in Greece, France, Italy, Spain, etc.?
Let the Germans pay if they want to. Germany's historical guilt probably is their main motivation for bankrolling their neighbors, but why should Britain join hands with Germany in this nonsensical bailout game.
Leave the EU. Let the EU sink into the economic quagmire of its own making.