Britain's Years-long Battle Over Brexit

The curtain comes down on Britain's membership of the European Union on January 31 after more than three and a half years of disagreements and delays.

Here are the milestones in the rocky process.

In a referendum on June 23, 2016 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.

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.

Ending more than a year of acrimonious talks, British and EU negotiators on November 13, 2018, reach a draft divorce deal.

But May faces an angry backlash from her own Conservative party over its terms. More ardent Brexit supporters believe the proposed deal could leave Britain interminably trapped in EU trade rules.

On January 15, 2019, British MPs vote against the deal in the biggest government defeat in British parliamentary history.

Brussels refuses to renegotiate.

The House of Commons rejects the deal again on March 12 and for a third time on March 29.

The EU agrees to delay Brexit until May 22 and then until October 31, 2019.

It means Britain is obliged to organise European Parliament elections on May 23, which are won by the newly-formed Brexit Party of anti-EU populist Nigel Farage.

The European election defeat and parliament's refusal to back her Brexit deal forces May to step down as Conservative leader on June 7.

On July 23, party members vote for Brexit figurehead Boris Johnson as their new leader. He becomes prime minister the next day.

Anxious over Farage's surge in support, Johnson promises to take Britain out of the EU on October 31, with or without a deal. He publishes his "final" Brexit proposals on October 2.

On October 22, British MPs approve in principle a new Brexit deal struck days earlier with the EU. But they reject Johnson's bid to fast-track final approval before October 31.

On October 28, EU members agree to postpone Brexit for up to three months until January 31, 2020.

Johnson's resounding win at a December 12 snap general election smoothes his Brexit bill's passage through parliament on January 9, 2020.

Queen Elizabeth II gives her formal assent for Britain to leave the EU on January 23, with two top officials in Brussels and UK Prime Minister Boris Johnson signing it the following day.

The text is to go to the European Parliament for ratification on Wednesday, January 29, and diplomats from the EU member states are to approve the deal in writing the next day.

Divorce is set for Friday, January 31 at 2300 GMT, which is 11:00 pm in Britain.

An extendable transition period, during which much in the relationship will not change, has been agreed up to December 31, 2020. More tough talks on the future EU-UK partnership are expected by then.