In one important sense Britain left Europe a long time ago. It happened under its government before last, when the pound was taken out of the European exchange rate mechanism, the precursor of the euro.

A few years later when most, but not all, members of the EU adopted a common currency, Britain decided to have nothing to do with it. Wisely, it turned out.

The countries of the euro zone have been wracked by tension between those whose unsustainable welfare costs and debts were exposed by the global financial crisis, and those that have had to bail them out to maintain confidence in the currency.

The euro has put the EU in a position where it cannot remain. The Greek crisis has underlined the fact that a common currency must be backed by a common monetary policy enforced by a central bank and a common standard of fiscal management in all member countries. Those are the central economy responsibilities of governments.

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The euro zone is like someone who has stopped half-way across a river. The members know they must either press on with the logic of their enterprise and form a more powerful union, or turn back to where Britain has been.

There is not much doubt, Germany, France, Italy, Spain and the rest will press ahead, albeit grudgingly. There was never a chance Britain would join them when they do.

Britain has been out of sorts with European unity ever since the EEC, as it was, started to become something more than an economic community. Britain has been constantly dragging the chain and dismay and yesterday's decision may be cathartic for Europe as well.

For New Zealand and the rest of the Commonwealth, Britain's decision to leave the EU raises problems and opportunities. We will lose a reliable voice in European councils when our trading interests are under discussion.

But those interests are no longer measured just in tonnes of butter and lamb. Chances are, any losses on those quotas will be made up by British consumers. But New Zealand's trade interests today are global. The EU is one of the crucial players in world trade negotiations and without Britain it might become even more protective of its farmers and resistant to more liberal trade rules.

Britain has always been an open trading nation, a legacy of the industrial and imperial pre-eminence it long enjoyed. Another legacy of its empire has been diverse immigration, making it the multi-racial nation it is today.

Immigration through the EU may be the crucial issue that clinched yesterday's vote but that might not mean Britain is now about to restore the access that commonwealth citizens once enjoyed.

If the warnings of the "remain" campaign are borne out, Britain will become a more inward-looking "little England". Scotland, Northern Ireland and London voted overwhelmingly to remain.

The City will be nervous about its future as Europe's financial capital, and globally on a par with New York. But the City will no doubt survive, the United Kingdom probably will not. Scots will now demand another vote to leave that union.

None of these warnings persuaded enough English voters to remain. They have taken a step into the unknown, spurning the urgings of their political and business leaders and most other respected voices in their country. It was a voters' "insurrection" and now for Britain there is no going back.