This has never happened before. Keep that in mind every step of the way. No European Union member has ever triggered article 50, and no member has ever left. This is why detailing all the things we don't know would take a lot longer than listing the things that we do.
It's a measure of the uncertainty around every aspect of Brexit that, before it arrived, we had no idea what form Theresa May’s letter would take, nor the form of the EU response.
What’s the Timeline?
We can, however, be more certain of the time frame, the issues and the players.
Article 50 will be quickly followed by a European Union Summit, where the European Commission will formally be asked to negotiate on behalf of the EU. Less predictable is the negotiating mandate the Commission will be given. This will give us clues as to how the EU defines the best-case Brexit.
The UK government has been understandably cagey about releasing details of its negotiating positions, but inevitably, as the months pass, more details will emerge from both sides on where there’s room for manoeuvre and where there isn’t. All of which will lead us to March 2019, when Brexit will happen whether there’s an agreement or not.
At that point, whatever rhetoric you hear, let's be clear: Both sides would much prefer to have a deal than not. Governments and institutions don't like uncertainty, and Brexit is delivering it in spades. All parties want this settled as quickly as possible. That doesn’t mean it will happen; but it’s the practicalities, not the politics of negotiating something on this scale in two years, that may hold things up.
Who are the Players?
Much of the negotiations will be done by civil servants. These are significant figures who will be trusted to handle matters of huge importance. But, and it's a big but, this is not only a diplomatic process but a political one, and the most important players will be the politicians.
First we have Theresa May, the UK Prime Minister. She was part of the Remain campaign and became leader not in a general election, but mid-term, after David Cameron resigned and his party, the Conservatives, and chose her as his replacement.
For now, her authority is intact. However, the Prime Minister also inherited a narrow majority in the House of Commons that would give the boldest of politicians pause for thought. She walks a political tightrope in high winds.
Add to this that, Scotland’s parliament wants a second independence referendum before the end of the Brexit negotiations, and that Brexit voters made their choice for a wide range of reasons, and you understand the extraordinary pressure May is under to flesh out what she means when she says ‘Brexit means Brexit’.
Second are Donald Tusk and Jean-Claude Juncker.
Mr Tusk has just won another term as head of the European Council (which represents EU heads of state), and Mr Juncker retains a considerable power-base at the European Commission.
They are quite different in style; Mr Tusk is controlled and to-the-point, while Mr Juncker is far more spontaneous and mischievous (as I found when he asked me if I was the Prime Minister during an exchange with him while I was reporting from Brussels for BBC World News recently). But both share great sadness at the UK’s departure, and have a passion for restating the need for the EU. Both will look beyond economic considerations as they set out the EU’s stall.
Third is Angela Merkel. She will have a huge influence in setting the initial tone of the negotiations. The only caveat here is that the German elections are later this year. The Chancellor remains favourite to win another term, but, as we’ve found out several times recently, the favourites don’t always win.
Even if Ms Merkel retains her position, we know another crucial position, the French Presidency will have someone new in the job.
If Marine Le Pen were to win, then the EU would have a headache to match anything Brexit has caused. Remember she would like France to leave too.
However, more likely, as much because of the system as popularity, Emmanuel Macron and even Francois Fillon – if he can get his campaign back on track (that’s a big if) – are more likely to win a second-round head to head than Le Pen.
Just like Mr Tusk and Mr Juncker, all the main candidates in Germany and France bar Marine Le Pen believe in the EU as a force for peace, tolerance and communication.
Given Europe’s history, it cannot be overstated how those steering the EU see its mission as far more than a single economic market. Brexit will not just be a particularly complicated trade deal – there’s much more at stake than that.
These leaders and many others, along with hordes of talented diplomats, have a two-year stretch ahead of them like no other. They have to untangle the most complicated of relationships, with everything from financial services to fisheries to immigration and security requiring new arrangements, in addition to the core trading relationship between these two separating parties.
What We Don’t Know
There are many questions unanswered. Legally, is this a one-way ticket? Will Theresa May seek a UK election during the negotiations? What happens if there is no deal after two years? What happens to EU citizens in the UK and UK citizens in the EU? To what degree can the UK cut new deals with other countries while still part of the EU? We can make educated guesses, but that is all.
Brexit poses one of the greatest tests in the attempt to explain the world. There’s a lot to tackle: The politics and the economics; the precision of laws and constitutions; and the imprecision of human emotion and political momentum. Two years from now, Big Ben will chime at midnight on 30 March 2019 and these two unions will take separate paths. Stay tuned for where those paths may go.
(Ros Atkins presents Outside Source weekdays on BBC World News. This has been published in arrangement with BBC World News.)
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