What are the likely consequences if, after the next election (in 2015), Britain votes in a referendum to leave the EU? (As 53% of UK voters apparently desire ...)
I have a number of expectations about what would happen.
1. It's possible that an EU exit would be fudged by the then government opting to remain in the European Economic Area. This would be extremely stupid—EEA membership carries an obligation to abide by most EU legislation and treaties, but with drastically reduced participation at the drafting stage. (It's basically a fudge to allow traditionally neutral nations like Norway and Switzerland to participate.) Probability: low—voters would see this as a betrayal of the spirit of a motion to exit the EU.
2. A full EU exit would result in the exodus of a large section of the UK's financial sector to Paris and Frankfurt; in particular Euro trading in London, currently the largest Eurobond market in the world, is facilitated by membership of the EU. (As the financial sector accounts for roughly 20% of the UK's economy, even a relatively small downsizing, by 20% or so, would have a drastic, widespread effect on the UK.)
3. Trade with the EU may be hampered by the re-emergence of the sort of tariff barriers common prior to 1948. The UK would have vastly reduced leverage for negotiating free/open trade with EU members. GATT/WTO treaties would mitigate the impact of tariff barriers to some extent, but we'd lose the benefit of tariff-free open export markets that the EU provided.
4. A widespread assumption among Britons is that the British Commonwealth of Nations would continue to trade with the UK and would in fact gradually increase their UK trade, taking up some of the slack. But the relationship with the Commonwealth nations looks rather different outside the UK. These are former colonies; they don't necessarily bear the UK any goodwill, but continue to exploit the residual relationship because the UK is a tariff-free trade gateway to the EU. A UK that has exited the EU would be a much less attractive trade partner.
5. The "special relationship" between the UK and the USA at a diplomatic/military level runs on much the same basis; the UK is a reliable supporter of the US, historically tending to influence EU diplomatic and trade policy in pro-US directions. A UK that is no longer part of the EU thus becomes less useful to the USA. While the British military continues to contribute roughly 20% of the US Navy nuclear deterrent (in the shape of UK funded and operated Trident SSBNs) and might at some point in the future be able to lend a couple of second-rate aircraft carriers to backfill US hard power projection, the UK's utility would still be vastly reduced in event of an EU exit. So: an EU exit would mark the practical end of "special relationship" with the United States. (Not that this is a bad thing, in my view: the "special relationship" was most recently exemplified by Tony Blair's idiotic willingness to sign up for George W. Bush's Iraq adventure.)
The overall picture, then, is dismal: a flight by the investment banking sector, probable currency speculation directed against the (isolated and vulnerable) sterling market, re-emergence of tariff barriers hampering UK exports to Europe, a collapse in trade with the Commonwealth (at least, on terms favourable to the UK), and the final collapse of UK diplomatic/military power to second- or even third-rank status on a global scale.
Have I missed anything? (Apart from the tabloid news editors standing proud on top of their middens to squawk about how Britain has regained her sovereignty at last?)