When Theresa May formally invoked Article 50 of the Lisbon Treaty on Wednesday, it started the clock ticking: Unless all member states agree otherwise, Britain will leave the EU at the end of March 2019. The UK government has two years to disentangle the country from four decades of various laws, regulations, and institutions. It will be a staggeringly difficult task, affecting virtually every area of the economy and society.



Resolving any one of these challenges would, under normal circumstances, be difficult and politically fraught. Resolving them all simultaneously, within a two-year window, and while in parallel negotiating a new relationship, will be an undertaking on a scale like few others that have confronted British governments. The consequences of getting it wrong could be catastrophic.

While Westminster has been gripped in recent months by the process of withdrawing – and what sort of Brexit strategy the prime minister should pursue – officials across Whitehall have been preparing for the harder, more technical tasks ahead. Here, based on the government’s own publications, policy submissions by various interest groups, and dozens of hours of testimony to parliamentary select committees, as well as insight from a number of sources BuzzFeed News has spoken to over recent months, are some of the most pressing:

1. Negotiate a €50 billion divorce bill.

After leaving the EU, the UK will still have financial commitments that will need to be paid, and the European Commission’s chief negotiator, Michel Barnier, has made clear he wants this resolved before any talks about the future relationship begin. Europe wants to agree not a figure, but the principles and methodology for calculating it. May’s challenge: the more hawkish among British Eurosceptics, as well as much of the right-wing press, say we shouldn’t have to pay anything at all.

2. Reach agreement on the rights of 4 million people on both sides of the Channel.

The status of 3 million EU nationals living in Britain and a million Brits living elsewhere in the EU will be cast into doubt by Brexit; both the UK government and EU have said guaranteeing their rights (from residency to pensions) will be a priority in the early stages of the talks – but it will not be straightforward.

3. Determine transitional arrangements so that Britain avoids crashing over a cliff.

Most experts think the notion that Britain’s exit and future relationship can be dealt with in two years is for the birds. Both sides have hinted at an interim deal, although politically the UK government doesn’t like calling it “transition” (you can get stuck in transition for a long time). EU member states are firm: Britain can’t, even on a temporary basis, cherry-pick bits of membership without accepting all of the terms, the single market's four freedoms of movement (of goods, services, people, and capital) and its rules, which would force May to delay delivering on some of the political promises she has made to the Conservative party’s Eurosceptic right, including halting freedom of movement and ending the judicial oversight of the European Court of Justice. Negotiating an interim deal is a lot more complicated than simply extending talks; a negotiated agreement would have to be reached.