What happens next? Key Brexit milestones expected from now until 2019 deadline
Seven months after the referendum vote to leave the European Union, Theresa May's speech on Brexit will set the scene for the process of withdrawal to begin in earnest.
But uncertainty still surrounds exactly how the process will unfold. Here are some of the expected milestones along the way:
:: JANUARY - Mrs May told MPs last month that she would make a major speech "early in the New Year" setting out her plans for "a truly global Britain". It is now expected that it will take place before the end of January.
Also in January, the Supreme Court is expected to rule on the Government's appeal against a High Court decision that MPs should be given a vote on triggering withdrawal negotiations under Article 50 of the EU treaties. Downing Street this week declined to say whether the PM's speech would have to wait until after the judges' decision is known.
The UK's new Permanent Representative to the EU, Sir Tim Barrow, arrives in his new post in the second week of January, following the surprise departure of Sir Ivan Rogers from a role at the centre of the upcoming negotiations.
Mrs May could also take advantage of the World Economic Forum summit in Davos, Switzerland, from January 17-20 to discuss her plans with global leaders. But the eyes of the world will be focused at the end of that week on the January 20 inauguration of new US president Donald Trump, whose attitude towards a trade deal with the UK could be crucial to the success of Brexit.
:: FEBRUARY - Brexit Secretary David Davis has said that the Government's plan for Brexit will not be published before the start of February, but no date has yet been fixed for its release. Labour said it should arrive in time to give Parliament and the devolved assemblies time to debate it before negotiations start.
:: MARCH - Mrs May has promised to kick off withdrawal talks under Article 50 of the EU treaties by March 31, but the exact timing remains up in the air. If the Supreme Court rules against the Government, she will first have to win a parliamentary vote, which could take place this month.
The scheduled gathering of EU leaders at the European Council in Brussels on March 9-10 could provide Mrs May's final chance to seek allies before talks begin. Or it could even be an appropriate opportunity for her to notify the Council of the UK's intention to withdraw, as required by Article 50. Remaining EU states will celebrate the 60th anniversary of the Treaty of Rome on March 25.
The Dutch general election in March could deliver fresh impetus to anti-EU sentiment, with the populist PVV party of Geert Wilders leading the polls and threatening an upset.
:: APRIL/MAY - European Commission chief negotiator Michel Barnier has said he expects a delay of several weeks before talks begin, to allow the European Council time to respond to Article 50.
Progress could be disrupted by the French presidential elections taking place in April and May, which are expected to result in a run-off between right-of-centre front-runner Francois Fillon and anti-EU National Front leader Marine le Pen.
Local elections in the UK in May will give voters a first chance to pass judgment on the deployment of Article 50.
The tenure as European Council president of Donald Tusk - who has warned that Brexit will be "painful for Britons" and a loss to both the UK and the EU - comes to an end in May, and his home state of Poland has indicated it may not support him getting a second term.
:: SUMMER - As Article 50 talks grind on, the political map of Europe could be further reshaped by parliamentary elections in France in June and Germany in September. Polls suggest German chancellor Angela Merkel - whose position is expected to be decisive to the outcome of Brexit - will survive a challenge from the anti-EU Alternative fur Deutschland party.
Elections are scheduled in nine EU countries including Italy, Hungary, Austria and Sweden.
Mr Barnier has suggested that Article 50 negotiations must be concluded by October 2018 to provide time for the outcome to be approved by the European Council and European Parliament, and potentially by national and regional assemblies in the remaining 27 member states.
Deadline for "Brexit by default" if no deal is reached by two years after the tabling of Article 50 - probably towards the end of March 2019. Without an agreement, EU treaties would cease to apply to the UK overnight and Britons may face a range of tariffs on traded goods and services and restrictions on free movement in Europe.
If a deal has been reached, it could include an "implementation period" for both sides to prepare for the new arrangements before actual withdrawal. There could also be a "transition deal" allowing trade to continue under existing rules until a full trade agreement is thrashed out - something which some experts predict could take years.