LONDON (AFP) - Here are the milestones on Britain's rocky road out of the bloc after 46 years, beginning from the shock Brexit referendum result.
June 23, 2016: Britons vote to leave
In a referendum on June 23, 2016, Britons choose to end their membership of the 28-nation EU by 52 per cent to 48 per cent.
It prompts the resignation the next day of Conservative prime minister David Cameron, who had called the referendum and led the campaign to remain in the EU.
July 13, 2016: Theresa May becomes prime minister
In a race to replace Mr Cameron, key Brexit campaigner Boris Johnson does not put himself forward as expected, and Mrs May, the interior minister who had backed remaining in the bloc, becomes prime minister on July 13.
On Jan 17, 2017, Mrs May gives a speech setting out her Brexit strategy, saying Britain will also leave Europe's single market in order to control immigration.
She warns she would be willing to walk away from negotiations with the EU, saying: "No deal for Britain is better than a bad deal for Britain."
March 29, 2017: Exit process triggered
On March 13, Britain's Parliament gives final approval to a Bill empowering Mrs May to trigger Article 50 of the EU treaty, which lays out the process for leaving the union.
With a letter to EU President Donald Tusk on March 29 formally announcing the intention to leave, the government sets Article 50 in motion.
Its two-year timetable for withdrawal puts Britain on course to exit on March 29, 2019.
June 8, 2017: May loses majority
To capitalise on the perceived weakness of the opposition Labour party and strengthen her hand in Brexit negotiations, Mrs May calls a snap election for June 8, 2017.
Her gamble backfires as the Conservatives lose their parliamentary majority. They are forced to strike a deal with Northern Ireland's Democratic Unionist Party (DUP) to govern.
The issue of British guarantees to keep an open border between Northern Ireland and the Republic of Ireland after Brexit becomes a key sticking point in negotiations.
Dec 8, 2017: First terms agreed
Britain and the EU reach an outline agreement on Dec 8 on three key areas of the divorce: Britain's financial settlement to the union, citizens' rights and the Irish border.
EU leaders give the go-ahead for the next stage of Brexit talks, including on how Britain will continue to trade with the bloc after the split.
A Bill enacting the decision to leave the EU becomes law on June 26, 2018.
July 2018: Top ministers quit
On July 6, 2018, Mrs May wins agreement from her warring Cabinet to pursue "a UK-EU free trade area" that would retain a strong alignment with the EU after Brexit.
But two days later, Mr David Davis, the eurosceptic Brexit minister, quits, saying Mrs May is giving "too much away too easily".
Mr Johnson, now foreign secretary, resigns on July 9, becoming a leading critic of Mrs May's plans.
EU leaders meeting in Salzburg on Sept 19 and 20 tell Mrs May that her Brexit proposals are unacceptable and need to be reworked.
November 2018: Draft deal agreed
The EU on Nov 13 publishes contingency plans for a "no-deal" Brexit.
But a few hours later, Mrs May's office says negotiating teams have reached a draft agreement for the divorce.
On Nov 14, her Cabinet backs the agreement.
However, the following day, four ministers, including new Brexit secretary Dominic Raab, quit in protest.
EU leaders approve the accord on Nov 25. "This is the only deal possible," says European Commission President Jean-Claude Juncker.
Dec 12, 2018: No-confidence vote
Mrs May's deal faces intense criticism in Parliament over the "backstop" provision designed to prevent border checks in Ireland.
On Dec 10, Mrs May postpones a House of Commons vote on the deal due the following day, acknowledging she faced a heavy defeat.
She heads off to Europe for further talks, but EU leaders reject any substantive renegotiation.
On Dec 12, Mrs May's Conservative party announces that enough MPs are unhappy with her leadership to trigger a confidence vote. But the embattled leader survives the challenge, securing the backing of 200 Tory colleagues, while 117 voted against her.
The result meant Mrs May is immune from further internal party challenges for a year.
Jan 15, 2019: British MPs reject deal
The House of Commons, Britain's lower house, finally got its chance to vote on the draft withdrawal agreement that Mrs May struck with EU leaders in December.
With opposition parties and scores of Conservatives rejecting it for various reasons, MPs voted 432 to 202 to reject the agreement.
The government faces a vote of no confidence on Wednesday (Jan 16).
Jan 16: May survives, again
May emerged victorious on Wednesday night in a confidence vote triggered by the opposition Labour party, the first for 26 years, winning 325 votes to 306.
She must return to parliament on Monday (Jan 21) with a Plan B that she and her team intend to negotiate with various MPs through the weekend.