What's next for Brexit? A timeline of the U.K.'s departure from EU

Prime Minister Theresa May triggered Britain's withdrawal from the European Union under Article 50 of the Lisbon Treaty on Wednesday. Here is a rough timeline of a departure process that could stretch past the expected two years.

Estimates for completing withdrawal range from 2 to 6 years

Britain's permanent representative to the European Union Tim Barrow, left, delivers British Prime Minister Theresa May's Brexit letter to EU Council President Donald Tusk in Brussels Wednesday. The letter triggers two years of negotiations on the U.K.'s exit but the process could take much longer. (Yves Herman/Reuters)

Prime Minister Theresa May triggered Britain's withdrawal from the European Union under Article 50 of the EU's Lisbon Treaty on Wednesday. The departure process is expected to last two years.

It's important to keep in mind, however, that no country has ever departed the EU since its early beginnings as the European Economic Community with just six member nations in 1957. Britain has been a member since 1973 and disentangling those 43 years of treaties and agreements is a complex business.

That's why Chancellor of the Exchequer Philip Hammond has said the process is more likely to take four to six years.

Here is an approximate timeline of events, based on a mixture of public information and estimations by EU sources:

March 29: The Trigger

Tim Barrow, Britain's top envoy to the EU, visited the European Council building around the corner from the embassy in Brussels and delivered May's signed letter giving notice to quit the bloc to EU summit chair Donald Tusk. In London, May gave an address to a rowdy and divided Parliament.

March 31: Summit, guidelines and recommendations 

Within 48 hours after reading the letter, Tusk will send the 27 other states draft negotiating guidelines. He will outline his views in Malta, where he will be attending a congress of centre-right leaders. Envoys to Brussels from those 27 nations will meet there to discuss Tusk's draft.

April 11: Advisers weigh in

Government EU advisers, often referred to as "sherpas," from each of the remaining 27 EU nations are expected to meet in Brussels to discuss guidelines. They are expected to meet again on April 24 for further revisions.

April 27: EU affairs ministers gather

Also from the 27 nations, the General Affairs Council (GAC) will meet in Luxembourg to prepare EU27 summit.

An anti-Brexit campaigner with her face painted in the colours of the European flag marches with others toward Britain's parliament in London on March 25. (Kirsty Wigglesworth/Associated Press)

April 29: Negotiator is appointed

EU27 leaders will meet in Brussels to agree on guidelines and mandate Michel Barnier as chief negotiator.

May 2: Barnier makes recommendations

After the May Day holiday, Barnier is expected to go back to council with his recommendations for how negotiations should be structured, seeking the governments' approval.

May: Directives established

The GAC will meet to agree on legal "negotiating directives" to bind Barnier. The GAC has a routine meeting scheduled on May 16 but could gather to discuss the matter at any time.

June: Parties meet face-to-face

Approximately a year after the June 23 referendum vote that brought about Brexit, British negotiators led by David Davis will sit down with Barnier's EU team. This meeting could, however, happen anytime after the April 29 EU summit. Full negotiations must wait until EU governments sign off on the directives, but both can save time by fixing procedural arrangements — who will meet whom where, speaking what language, and so on — once Barnier has a mandate. Once the 27 governments have signed off on the directives, negotiating teams will start talks, each tackling certain areas.

December 2017: Divorce deal drawn up?

Brussels wants a basic deal on a Withdrawal Treaty by the end of the year. Key issues include the exit bill for Britain's outstanding commitments, treatment of British and EU expats, outstanding EU legal cases and new border rules.

Early 2018: Exploring new relationships

May wants to negotiate a comprehensive free trade deal. Few see two years as enough time to agree on one and Brussels wants to hold off starting talks until after Brexit is complete. But London and some EU states may push for parallel trade talks. Most diplomats expect some synthesis of the two approaches.

EU Brexit negotiator Michel Barnier arrives at the EU summit in Brussels on March 9. (Dylan Martinez/Reuters)

October 2018: Finalize the Withdrawal Treaty

Barnier has targeted October in order to allow time for ratification by the European Parliament and a majority in the European Council by March 2019.

Autumn 2018 to Spring 2019: Scottish independence vote

The Scottish government wants an independence vote and voted March 28 to support one. But May has so far rejected the call for a second Scottish referendum until after Britain leaves the EU.

March 29, 2019: Britain's official exit

On the two-year anniversary of the presentation of May's Article 50 letter, the U.K. will have met its contractual obligation to allow two years to negotiate an exit. The U.K.'s exit. As it happens, Friday, March 31, 2017 is the last business day of the quarter, so that date could be fine-tuned. Britain could leave earlier if it gets a deal, and the two-year deadline can be extended if all agree. But Brussels wants Britain out before EU elections in May 2019.

2019 and beyond: transition period

May and EU leaders say transitional arrangements may well be needed, to give more time to agree on a future trade deal and give people and businesses time to adjust to the divorce. Many see another two to five years after Brexit for a final settlement. If Scotland votes for independence, expect more years to negotiate its split from London and possible re-entry to the EU.

With files from CBC News