Britain could exit the EU - a Brexit - as the result of a referendum leading to a negotiated withdrawal, a unilateral withdrawal without a referendum or negotiations, Britain's expulsion, steps by the EU to freeze Britain out, or the rest of the EU leaving Britain behind in a position that lands it outside. None will be easy for Britain or the EU. All have their flaws.
The dispute between Britain and most of the rest of the EU about the appointment of Jean-Claude Juncker as President of the European Commission has once again raised the question of whether Britain will leave the EU, AKA a 'Brexit'. While most discussion focuses on whether or not Britain will leave the EU, less attention has been paid to how a Brexit might happen in practice.
There are five ways it could come to pass. Some are little more than exercises in legal and political thinking. Nevertheless, each sheds light on what options are open to Britain and the EU. They also raise questions about what exactly being 'out' of the EU means. A Brexit, it should be remembered, is a means to an end, not an end in itself. It is not clear any route to a Brexit can deliver the long sought for end of settling the Europe question in British politics or, just as importantly, settling the British question in European politics.
First, the most commonly assumed route a Brexit is expected to take is via a nation-wide referendum that ends with a result supporting withdrawal. This is then followed by UK-EU negotiations in line with the withdrawal article of the EU's treaties.
How a referendum might be triggered is in itself a matter of much speculation. The Conservatives, Labour, Liberal Democrats and UKIP each hold varying positions on when one would be called. David Cameron has committed the Conservative Party to holding an in-out referendum after an attempted renegotiation of Britain's membership. UKIP want one straight away. Labour and the Liberal Democrats support calling one following major changes to the EU, a development that would also trigger existing legislation requiring a referendum in the event of a significant transfer of powers to the EU. There is also an outside chance it could come about thanks to a backbench vote in the House of Commons.
Following the result the British government and EU would spend no more than two years negotiating Britain's withdrawal and the framework for a new post-withdrawal EU-UK relationship. Separate negotiations would also take place within the remaining EU to change it to reflect Britain's withdrawal. The final deal offered to Britain would be subject to the approval of the rest of the EU, including the European Parliament. It will therefore be a deal that suits the EU, not just Britain.
Whether a referendum can settle the Europe question in British politics is another matter. The issue of Europe is about more than whether or not Britain should be in the EU.
The second option open to the UK is for the British Government to take the leap of a unilateral withdrawal backed only by a vote of the House of Commons to repeal the 1972 European Communities Act that took Britain into the then EEC.
Under international law there is nothing - in theory - to stop Britain unilaterally withdrawing from an international organisation such as the EU. The EU's treaties also compel only the EU to seek a negotiation, not the withdrawing member state. Under the uncodified British constitution, the sovereignty of parliament means the government does not need to seek the approval of the British people through a referendum.
This, however, is a largely academic exercise. Refusing to negotiate, or denying the British people a say on such a momentous decision, would lead to an avalanche of political, legal and economic problems.
A unilateral leap is, however, more plausible than the third possibility which is the EU expelling Britain. There is next to nothing the EU can do to expel a member. Even suspension of membership is difficult. Any attempt at expulsion would also require unanimous agreement by the rest of the EU, no easy feat in itself. The EU would then have to defend itself against an onslaught of legal challenges from the UK and from private individuals, companies and organisations affected in Britain, Europe and from around the world. Expulsion would also add to the animosity between Britain and the EU. Relations within the EU could also be strained, with some states fearing they may be next.
Fourth, rather than directly expelling Britain the rest of the EU could resort to trying to freeze Britain out by making its life in the EU suitably uncomfortable. Just as confrontation with an unwanted and unhappy guest can be avoided by making them feel so uncomfortable that they leave of their own accord, so too might the rest of the EU feel it would be easier to make things so uncomfortable that Britain leaves the EU of its own accord.
Freezing Britain out would lead to Britain going down the route of either a referendum or a unilateral withdrawal. There is also the possibility the rest of the EU could openly discuss with the UK that it would be better for all concerned if it were to withdraw. The problem here is that Britain has been isolated in the past and hung on.
Finally, a Brexit could come about thanks to a divide between the UK and EU opening up as parts of the latter - mainly the Eurozone - develop in ways that leave Britain isolated in some outer tier. In this case it is not Britain that leaves the EU, but the EU that leaves Britain behind.
British governments have taken steps to prevent the emergence of some closed inner-group within the EU. Countries outside the Eurozone such as Sweden and Poland have also opposed such moves out of fear they too will be left behind. Compared to Britain, however, they have shown a willingness to develop connections to the EU's core that will help ensure that any divide that emerges does not leave them behind.
These five possibilities, each complex and unprecedented, all beg the question of what being 'outside' the EU means. However Britain or the EU were to part company, they cannot then pretend the other does not exist. Britain will remain a major European power, its population expected to overtake Germany's in the next 20-30 years. Similarly, unless there is some catastrophic failing of the Eurozone and disintegration of the Union, the EU will remain Europe's predominant political organisation. Brussels will be the lodestar for much of pan-European politics, economics and security (if not military security). Britain will spend a large amount of its time looking towards the EU star.
A referendum or unilateral withdrawal cannot compel the EU to give Britain what it wants beyond an official withdrawal. What 'out' Britain then secures will be shaped by what the rest of the EU and other powers such as the United States are willing to grant it in terms of new or recalibrated political and economic relations. At the same time, expulsion or exclusion would not solve the longer-term problem for the EU of how to deal with Britain.