When Britain’s most senior envoy to Brussels, Sir Tim Barrow, handed the UK’s official divorce notice to the European council president, Donald Tusk, on Wednesday afternoon, the clock started ticking. From that moment, Britain had two years to unwind four and a half decades of EU membership, start replacing reams of EU law with a domestic equivalent and work out its future ties to the continent. This is a rough guide to how the next 24 months could unfold.

April-May 2017: The deceptively easy beginning



Theresa May’s long-awaited “Dear Donald” letter will launch a flurry of diplomatic activity in Brussels. EU officials will scrutinise the letter for surprises that were not revealed in the prime minister’s Brexit speech, when she vowed to quit the EU single market and customs union. Tusk’s draft negotiating guidelines will be hastily reworked and sent to diplomats of the EU’s 27 remaining member states by 31 March. These guidelines, grand statements of the main Brexit principles, will be agreed by EU leaders at a special Saturday summit on 29 April. The spotlight then turns to the EU’s chief Brexit negotiator, Michel Barnier, and his team at the European commission, who will be charged with turning political statements into a detailed negotiating text, known as the directives. European affairs ministers are expected to finalise the Brexit directives at a meeting in mid-May, paving the way for negotiations to begin that month or early June.

While the EU puts the finishing touches to its Brexit plans, the British government will embark on scrapping EU law. On Thursday 30 March the government will publish the “great repeal bill”, which will copy and paste existing European law on to the UK statute book. At the same time, it will scrap the 1972 European Communities Act, setting in motion a vast law-making exercise that will dominate parliament’s agenda for the next decade.

May-December 2017: The danger zone



When Barnier sits down with his British counterparts at some point in midsummer , he will outline three priorities: settling the rights of more than 4 million EU nationals caught on the wrong side of Brexit; the divorce bill, estimated by his team to be €60bn (£50bn) and the thorny question of the Irish border, once it becomes Britain’s land boundary with the EU.

Talks will swiftly become technical, delving into numerous legal rabbit holes. For instance, Barnier’s team wants Britain to agree a methodology for working out its share of the EU’s liabilities. Some EU diplomats see this period as the danger zone when the risk of the talks collapsing is greatest. “If the negotiations fail, it will happen before the end of the year,” one senior diplomat told the Guardian. The source compared Brexit talks to learning Chinese: very hard in the beginning but “once you clear that hurdle you carry on”. Barnier’s team think progress could be swift if the UK plays along. The former French foreign minister has pencilled in a scheduled EU summit in mid-December 2017 as his preferred moment to finalise the divorce.

January-October 2018: The difficult middle stretch



If all goes to the EU plan, the two sides could be talking about the future relationship from January 2018. The divorce “could all go relatively quickly”, said one senior source, suggesting that rapid progress on the withdrawal agreement would leave about 10 months to sketch the broad outlines of a future relationship. Member state diplomats back the approach of divorce first, new coupling second. “Clearly, it is in the interests of the 27 to have a decent divorce and a decent [new] relationship, but the divorce comes first,” one source said.

No future trade deal can be signed until Britain leaves the EU. But the outlines could be pencilled in quickly. The EU’s trade and cooperation treaty with Ukraine has been dusted off as a model for the UK’s new relationship, although no existing agreement will be an exact match for the British deal.

Talks will not be confined to trade. If and when the divorce is agreed, the Brussels machine will go into overdrive: working groups are likely to be set up on foreign affairs, the European arrest warrant, the city of London and numerous other areas.

Agreeing the broad outlines of the new relationship would allow talks on a transitional deal to begin in summer 2018. Barnier has stressed a transitional deal is only possible if the UK knows where it is going.



October 2018-March 2019: Voting for Brexit

The final showdown may come at an EU summit in October 2018. This will be the moment of truth for Britain’s Brexit secretary, David Davis, who has promised that Britain will enjoy the same benefits on trade that exist under the single market. Whether the Brexiters keep their promises, by autumn 2018 the time for negotiating will almost certainly be over. Leaders at the European commission and European parliament plan on using the final six months to vet and ratify the deal. In early 2019, the European parliament’s 751 MEPs, including British members, will vote on the agreement, sealing Britain’s fate.

March-May 2019: Brexit day

In theory, the UK could be out of the EU on 29 March 2019. Extending talks can only be done by the unanimous agreement of the 27 countries. Many countries support Barnier’s view that the UK must be out before European parliament elections in May or June 2019.

In these fateful weeks, the future of the UK union may also be decided. If Scotland’s first minister, Nicola Sturgeon, gets her way, an independence vote could happen in spring 2019, deliberately timed to coincide with Britain’s EU exit. Even if the British government continues to block the Scottish National party’s plan, another independence referendum may only be delayed a few years. A bad Brexit settlement could create irresistible pressure for another Scottish vote.

Will it go to plan?



Brussels-based officials strike a cautious note about whether the EU battle plans will unfold so precisely in the cut and thrust of negotiations. An electoral upset in France or Germany, a snap election in the UK, or a flare up in the Greek debt crisis could distract negotiators and spoil the best-laid plans. There will be accidents and improvisations. But one thing is clear: once Barrow hands in the letter, time will not be on the British side.