Here are milestones in the rocky process of Brexit, from Britain's shock vote to leave the European Union in 2016, to ongoing, fraught talks on a future trade relationship.
Leave wins
In a June 23, 2016 referendum that followed decades of arguments over Europe, Britons vote by 52 percent to 48 percent to become the first nation to leave the EU bloc.
Conservative leader David Cameron, who led the campaign to remain in the EU and called the vote expecting to win, resigns as prime minister the next day.
He is replaced by Theresa May, the interior minister who also backed remaining in the EU.
Divorce process triggered
May formally triggers the exit process on March 29, 2017, sending a notification letter to Brussels that gives Britain until March 29, 2019, to leave.
Draft agreed
Ending more than a year of acrimonious talks, British and EU negotiators agree a draft divorce deal on November 13, 2018.
But May faces an angry backlash from her own Conservative party over its terms and MPs vote against the deal in the biggest government defeat in British parliamentary history.
Brussels refuses to re-negotiate.
Deadline delays
The EU agrees to delay Brexit until May 22 and then until October 31, 2019.
Johnson elected
The European election defeat and parliament's rejection of her Brexit deal forces May to step down as Conservative leader on June 7.
On July 23, party members choose Brexit figurehead Boris Johnson as their new leader. He becomes prime minister the next day.
The endgame
On October 22, British MPs approve in principle a new Brexit deal struck days earlier with the EU.
On October 28, EU members agree to postpone Brexit until January 31, 2020.
Elections, green light
Johnson's resounding win at a December 12 snap general election smoothes his Brexit bill's passage through parliament on January 9, 2020.
Brexit
The divorce takes place on Friday, January 31.
An extendable transition period, during which much in the relationship will not change, is agreed up to December 31, 2020.
Post-Brexit negotiations
In March 2020, the EU and Britain began difficult negotiations on their future trade relationship, which are then broken off due to the coronavirus crisis.
Talks resume in April, without any notable progress on key sticking points.
On June 12, Britain officially says it does not wish to extend its transition period beyond the end of the year.
In July, Britain and the EU agree to intensify talks with a view to meeting an October deadline for an accord, if the European and British parliaments are to have time to ratify it by the year end.
New tensions
On September 8, the two sides open an eighth round of negotiations amid tensions as Johnson warns that if there is no compromise by October 15 he will walk away with no deal.
To the EU's dismay, the British government the next day submits a bill to overwrite parts of the withdrawal agreement.
Deadline passes
The October deadline comes and goes with no sign of a deal, with Johnson telling the EU there was "no point" in extending talks.
But Britain then ends days of threats to abandon the negotiations and instead agrees to redouble efforts to avert the potential economic chaos of a no-deal at the end of the year.
New deadline looms
Key sticking points that remain include so-called "level playing field" provisions to ensure Britain does not try to retreat from the EU's environmental or labour standards, how to arbitrate future differences, and fishing rights.
Talks continued in November but any deal will need parliamentary ratification on both sides of the Channel before the end of the year, increasing pressure on the negotiators to craft a legally binding text in the coming days.
