Prime Minister Theresa May puts a stripped-down version of her twice-defeated Brexit divorce deal to a vote in parliament on Friday in an attempt to break the impasse over the United Kingdom's exit from the European Union.
The vote, on the day the country was originally due to exit the European Union, illustrates the depth of the three-year Brexit crisis that has left it uncertain how, when or even if the United Kingdom will ever leave.
Lawmakers will vote at about 1430 GMT on May's 585-page EU Withdrawal Agreement at a special sitting, but not on the 26-page Political Declaration on future relations, a manoeuvre to get around a ban on repeatedly putting the same submission to a vote.
"It is in fact really the last chance we have to vote for Brexit as we understood it," said Liam Fox, May's Brexit-supporting trade minister.
Fox said there was a fear among Brexit supporters in parliament that the divorce from the bloc could be thwarted, a step he said would open "a chasm of mistrust" between voters and political leaders.
To win the vote, May must bring on side dozens of Brexit-supporting lawmakers in her own party and more than 20 Labour Party lawmakers.
Speaker John Bercow said parliament would not vote on any amendments but Attorney General Geoffrey Cox suggested the government would have accepted a proposal by Labour lawmaker Gareth Snell to increase the power of parliament over the second stage of talks.
However, the Democratic Unionist Party, which props up May's minority government, said it would not change its mind and its 10 MPs would vote against the deal.
As May tries to salvage her deal and some lawmakers try to grab control of the process, thousands of Brexit supporters are due to protest in central London with a "Brexit Betrayal" march led by campaigner Nigel Farage which ends outside parliament.
Amid the chaos, May agreed with the EU to delay Brexit from the originally planned March 29 until April 12, with a further delay until May 22 on offer if May could get her divorce package ratified by lawmakers this week.
The pound fell towards a three-week low of $1.3004.
May on Wednesday pledged to quit if her deal was passed but even that failed to immediately win over many Brexit supporters in her party. They say her deal leaves the United Kingdom tied far too closely to the EU.
If the government wins the vote, it believes it will have satisfied the conditions set by the EU in order to delay Britain's exit from the bloc until May 22.
However, the result will not meet the criteria in British law for the exit package to be formally ratified.
The uncertainty around Brexit, the United Kingdom's most significant political and economic move since World War Two, has left allies and investors aghast.
The 2016 referendum revealed a United Kingdom divided over much more than EU membership, and has provoked impassioned debate about everything from secession and immigration to capitalism, empire and what it means to be British.
Opponents fear Brexit will make Britain poorer and divide the West as it grapples with both the unconventional U.S. presidency of Donald Trump and growing assertiveness from Russia and China.
Supporters of Brexit say while the divorce might bring some short-term instability, in the longer term it will allow the United Kingdom to thrive if cut free from what they cast as a doomed attempt in European unity.
"Westminster has betrayed the greatest democratic vote in the history of our country, and we won’t let them get away with it," Farage said, calling on Brexit supporters to gather outside parliament.
Far-right activists such as Tommy Robinson are due to speak at a separate meeting being cast as "a make Brexit happen" rally. Hundreds of thousands of people opposed to Brexit marched through London on Saturday.