Brexit: What happens after article 50 is triggered?

British prime minister Theresa May is about to trigger article 50 of the Lisbon treaty, officially informing the European Union of the UK's intention to withdraw. The issue gripping London and Brussels is what happens after Ms May notifies the bloc of the country's plans on March 29th.

Unless both sides agree on an extension, the UK and the EU have two years to agree a divorce deal before the bloc’s treaties cease to apply to Britain.

This is the timeline set out in article 50 itself – 262 words that were scrawled at the kitchen table of John Kerr, a veteran UK diplomat, and which will shape the UK’s future.

March-April 2017: EU 27 adopt guidelines

After Ms May activates article 50 on March 29th, the EU will draw up "guidelines" on handling Britain's withdrawal. Donald Tusk, president of the European Council of leaders, said this month that the EU could give a first response within 48 hours.

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But the formal guidelines will need to be endorsed by a summit of the remaining 27 EU countries. Such an event could take place in Brussels in late April or very early May. Either way, some countries are worried about holding a big gathering in between the two rounds of the French election.

The guidelines – which will in part show how hard a line the EU is taking – are one of the most critical decisions in the Brexit process. They are expected to specify priorities for the EU 27, principles that cannot be compromised, and the structure of the talks.

May-June 2017: EU 27 agrees negotiating directives

Once the guidelines have been decided, the EU 27 must formally nominate the European Commission as its lead negotiator, and develop confidential directives giving the Brussels body a more detailed mandate. The commission will make a proposal and the EU will spend roughly four weeks discussing these terms. The mandate must then be approved by EU 27 ministers.

No negotiations can take place until this happens. Diplomats are pencilling in late May or early June as the moment formal face-to-face talks with the UK can begin.

May 2017: Great Repeal Bill begins

Britain will kick off a large part of its preparations with the Great Repeal Bill, a legislative measure set to be outlined in the Queen’s Speech in May and intended to provide legal continuity for the country after Brexit.

The Bill will repeal the European Communities Act of 1972 and incorporate EU law into domestic law “wherever practical”, so that the government can then begin amending or repealing laws it does not like. It covers thousands of EU regulations that are directly applicable to the UK, but not in UK law. The terms are not active, however, until the UK completes its EU exit.

September 24th, 2017: Germany goes to the polls

Brexit discussions will be well under way by the time Germans vote for a new government (France will have chosen its new president by May 7th). The latest German polls show the incumbent, Angela Merkel, level pegging with Martin Schulz, a former president of the European Parliament.

Once a new coalition government is agreed and the German chancellor is installed – a process that could take weeks – the cast of Europe’s top leaders will be in place. Between them, they will decide on what sort of deal, if any, the bloc concludes with the UK.

December 2017: divorce talks and trade relations

Michel Barnier, the EU's chief negotiator, wants a "divorce-first" approach to negotiations, delaying talks on a future trade deal until Britain has agreed principles on an exit Bill and the rights of EU migrants. He expects these initial divorce discussions to last until December.

The UK government is keen to ensure all elements of Brexit are negotiated “in parallel”. Some EU member states think discussion about future relations could be initiated earlier than December. But an overwhelming majority of EU-27 countries agrees Britain must accept basic principles on the divorce before trade talks begin.

March 2018: UK’s deadline for agreeing transition

After March next year, the value of any transitional deal is greatly reduced, since companies are expected to take early action to protect their interests – such as relocating activities outside the UK. Sir Ivan Rogers, the former British ambassador to the EU, warned of the importance of a such a deal to avoid falling off a "cliff edge".

Airlines have warned that the UK must have signed new open-skies agreements by this point, because they sell tickets up to a year in advance.

But the EU 27 sees the transition as being the final piece of the negotiation, which can be discussed in detail only once a “common destination” is agreed in terms of a future relationship. The EU side also calculates that uncertainty will increase the numbers of companies moving from Britain to the EU, reducing the risks to remaining members of the bloc of a hard exit.

October 2018: Barnier’s deadline to agree deal

Mr Barnier said he wants talks wrapped up by October 2018 to allow both sides time to ratify the deal: "All in all there will be less than 18 months to complete negotiations," he said. Boris Johnson, the UK's foreign secretary, has said this will be "absolutely ample" time in which to conclude an agreement.

March 2019: can the article 50 deadline be extended?

Ratification by EU member states, the European Council and the European Parliament must have taken place by this point. The UK parliament has also been promised a vote on the deal signed before it takes effect.

European Parliament elections are planned in May 2019. This makes it hard to extend the article 50 deadline beyond March without complex legal work, which would deal with the question of whether the UK would elect candidates and what would happen to them.

April 2019

UK’s departure from the EU should be complete

– (Copyright The Financial Times Limited 2017)