British proposal to leave Europe via Brexit would be messy and complicated, experts say

When Britons decide next week whether to leave the European Union the question will be simple: yes or no. Actually leaving would be far more complicated, rather like a drawn-out, painful and possibly bitter divorce.

Opinion polls suggest it could go either way on June 23, when Britain chooses whether to leave the 28-nation bloc it joined in 1973, with undecided voters likely to make the difference.

As luck would have it, a new and never before used "exit clause" in the EU's rule book allows any member to withdraw. On paper, it looks straightforward. But of course it's not. And should it be time to say goodbye, the way the process unfolds will have deep ramifications for Britain and probably influence what happens to the EU down the road, experts say.

• ANALYSIS: Brexit a reminder of when things fall apart
• Donald Trump says Britain 'better off' with Brexit from EU

Britain wouldn't leave the EU immediately. It would remain for up to two years while it unpicks its relations with the continent. If needed, it could even ask for an extension beyond the two years, but all 27 countries would have to agree.

In that period, British Prime Minister David Cameron, or whoever succeeds him, would have to draw up with his counterparts the arrangements for the country's departure. The terms of that accord would have to be accepted by a majority of about two thirds of the EU countries.

The sides would have to decide, among other things, on whether Britain remains in the EU's single market or will be subjected to new tariffs on trade.

This is when the remaining EU countries could make life very difficult for Britain. How tough the negotiations get would determine the future for both sides.

Some say the Europeans won't be doing Britain any favors. Given the number of crises in Europe - economic stagnation, the refugee emergency, extremist attacks - it's hard to see why members would take the time to negotiate in good faith with a partner who's deserting them. The leaders may have already expended a lot of their goodwill on the special concessions they agreed on earlier this year to persuade Britain to stay.

• British pound plunges as Brexit support grows
• Merkel says Britain stayin in EU is 'best and most desirable' outcome

"It would be in the interest of the rest of the EU to make sure that this does not create a precedent," said Fabian Zuleeg, chief executive at the European Policy Centre in Brussels.

Few would relish the thought, he said, of "a country outside that has some sort of pick-and-choose, associate membership which could look quite attractive for a number of other countries."

Tough negotiations could mean legal and investment uncertainty and might see Britain excluded from the European single market. Cameron dearly wants to avoid being shut out. Pressure might also mount domestically in Britain if pro-European Scotland calls for a new referendum on its future in Britain.

Beyond the negotiations, there is a bureaucratic tangle to undo, which will take time. Michael Emerson at the Centre for European Policy Studies estimates that Britain would have to delete some 5,000 regulations, directives and decisions from its statute books relating to the European internal market for goods, services, capital and people. It would also have to extricate itself from about 1,100 trade agreements the EU has with other countries.

All of this would cause much uncertainty for Britain, but could possibly be good for the EU in the short term. A painful exit would dampen the separatist ambitions of other countries considering their EU options.

• Brexit a 'risk' to British economy, EU says
• Brexit fears amdid sand and sun for Britons living in Spain

"If it's an exit which is painful I think very few other countries will look at this as a serious option, particularly if this is also leading to the U.K. breaking apart," said Zuleeg. "For politicians, that kind of price would be too much to pay."

More broadly, however, a Brexit - as Britain's departure has become known - would probably undermine Europe's decades-long project of binding countries closer together at a time when it is already fragile.

"There is no shortage of problems facing the EU, so having the British problem to deal with as well is going to be one more thing that the EU could do without," said Ian Bond, head of foreign policy at the London-based Centre for European Reform. "It would add to the kind of loss of self-confidence that the EU suffered with the 2008 economic crisis. It never really recovered."

Britain's departure could make the EU "more defensive, more cautious about undertaking radical reforms that might actually provoke other countries to say: 'Well this is not actually the direction that we want to go in,'" he said.

The likely winners if it is an exit? The far-right political movements, which are already making major gains in some European countries amid concerns about the EU's inability to manage the migrant emergency and prevent attacks in Europe's capitals. For them, said Bond, Brexit "would be a success, without question."