14 April 2015 - Launch of the Conservative Party Manifesto for the 2015 General Election commits to “hold an in-out referendum on our membership of the EU before the end of 2017”.
22 February 2016 - David Cameron announces the EU referendum date of 23 June 2016 after securing a deal on Britain's membership of the EU.
23 June 2016 - In a landmark referendum, the majority of those who voted chose to leave the European Union, voting 52 to 48.
13 July 2016 - The then home secretary Theresa May won the Conservative Party leadership contest by default, after all her challengers fell away.
29 March 2017 - Theresa May formally triggered Article 50 and began the two-year countdown to the UK formally leaving the EU (commonly known as ‘Brexit’).
8 June 2017 - After calling a snap election in a bid to increase her authority on Brexit in the Commons, May loses her parliamentary majority and has to make a deal with the Northern Irish DUP (Democratic Unionist Party) to stay in power.
8 December 2017 - The UK and the EU agree a deal on the UK’s so-called divorce bill, covering the Northern Irish “backstop”.
6 July 2018 - After the European Union (Withdrawal) Bill becomes law at the end of June, May takes her cabinet to her country retreat Chequers in order to sign off a collective position for the rest of the Brexit negotiations with the EU. However, both Brexit Secretary David Davis and Foreign Secretary Boris Johnson both resign over the deal.
25 November 2018 - Following some enforced changes to May’s Chequers Plan by the EU, a new Withdrawal Agreement is published that contains a fleshed-out backstop which angers both the DUP and the Tory’s Brexiteers.
Under the deal agreed between May and Brussels, the backstop would keep the whole of the UK very closely aligned to EU customs rules, with some regulatory differences between Northern Ireland and the rest of the UK.
15 January 2019 - Having pulled the vote before Christmas over fears that she would lose, May attempted to get her deal ratified by Parliament. However, with Brexiteers worried about the UK remaining in the customs union through the backstop, and the DUP concerned about potential disparity between Northern Ireland the UK, the PM suffered the heaviest defeat in modern parliamentary history, losing 432 votes to 202.
12 March 2019 - Further legal assurances from the EU about the temporary nature of the backstop were not enough to quell Brexiteer rebellion, and May lost a second meaningful vote on her deal by 149 votes.
12 April 2019 - The UK’s EU membership is now extended to 31 October, with or without a deal. If a deal has not been agreed and ratified by then, the Government will face the choice of leaving without a deal, seeking more time, or even cancelling Brexit altogether.
7 June 2019 - After failing three times to get her withdrawal agreement through Parliament, Theresa May sets her resignation date.
24 July 2019 - Boris Johnson enters Downing Street after winning the Conservative party leadership election with 66% of the vote, a comfortable victory over rival Jeremy Hunt.
28 August 2019 - The new PM asks the Queen to suspend Parliament for five weeks in the run-up to 31 October. Johnson claimed the prorogation was a routine move intended to pave for the way a Queen’s speech on 14 October setting out his government’s new legislative programme, but most people agree that the prorogation was scheduled to give MPs less time to try to block no-deal before the 31 October deadline.
4 September 2019 - MPs back a bill blocking a 31 October no-deal Brexit (“Benn Act”). Their victory means that Johnson will have to ask for a Brexit extension beyond the 31 October Brexit deadline if he can’t secure a deal with the EU. The PM - who has called the 31 October deadline “do or die” - reacted by calling for a snap general election.
Opposition parties collectively refused to back a general election vote until the legislation blocking a no-deal exit on Halloween has passed into law and the EU has agreed the extension.
24 September 2019 - The UK Supreme Court rules that Boris Johnson’s five-week prorogation of Parliament in the run-up to the Brexit deadline is “unlawful”. Business returns to normal.
2 October 2019 - The PM makes a formal proposal to the EU setting out his alternative to the Irish backstop. The proposals would leave the UK in the same customs territory as the EU and would keep Northern Ireland under EU regulations until a permanent trade deal was reached.
6 October 2019 - Following a phone call between Johnson and Angela Merkel, the German chancellor insisted that “the UK cannot leave without leaving Northern Ireland behind in a customs union and in full alignment forever” - a situation that would never be acceptable to the EU and that means a deal is “essentially impossible not just now but ever”.
19 October 2019 - Johnson is legally obliged by the ‘Benn Act’ to send a letter to the EU on that date requesting a three-month Brexit extension if Parliament doesn’t pass a deal or vote for no-deal.
25 October 2019 – The EU have agreed to grant Britain's request for another extension to the Brexit deadline but have yet to decide on the length of the new delay (“flextension”).