Update (7:07 am ET): The pound just won't stop...up 80 pips and counting...

For those who are catching up on all the Brexit drama that has unfolded over the past 24 hours, here's a quick recap courtesy of Ransquawk:

*LONG STORY SHORT: The Brexit deal PM May brought forth is essentially made up of two parts, the Withdrawal agreement (which sets out the terms of the UK's departure from the EU) and the Political Declaration (which outlines the shape of future UK-EU relations). To get around House Speaker Bercow’s requirements of a “changed” deal to be put for a third vote, PM May decided to split the deal and only vote on the first part, i.e. the WA.

*TODAY’S SCHEDULE [GMT]

14:30 – Vote on the Withdrawal Agreement

*AMENDMENTS: House Speaker Bercow has selected no amendments for debate in Parliament today

*WHAT PM MAY NEEDS

NUMBERS: For PM May to get majority for her deal, she needs to:

Retain all 242 existing votes

Win over all 75 opponents in her own party, including 69 Brexiteers (5 already indicated they will oppose it, one Tory MP abstained from MV2, a vote which could give PM a majority of 2)

For every Tory MP who opposes the deal, PM May needs one MP from another party or two opponents willing to abstain

Total excludes the 4 tellers, 3 deputy speakers, 7 Sinn Fein MPs

*WHAT IS EXPECTED:

PM May is expected to again be defeated in Parliament as she is unlikely to conjure up support from Labour and DUP (who have confirmed they will vote against the WA). There is still no confirmed direction from the ERG, although the group has said that they are likely to follow the DUP’s lead.

Cabinet sources have also noted that the WA is unlikely to pass as there is not enough time to get the votes.

MPs claim that just 12 hardcore Tory ERG MPs are left opposing PM May's deal; according to Sun's Deputy Political Editor Steve Hawkes

A UK Minister reportedly believes that PM May's WA will be voted down by 20 votes; according to Mail on Sunday's Deputy Political Editor Cole

Sun's Steve Hawks notes suggestions that former Brexit Minister Dominic Raab will back PM May's Withdrawal Agreement

There is little expectation in the EU today that the Withdrawal Agreement will pass

*WHAT HAPPENS NEXT:

BREXIT DATE: In the event the deal passes, Brexit date will be moved to 22nd May as agreed with the European Commission in Strasbourg. If not, the date remains as April 12th. (See below for possible scenarios). BBC's Katya Adler noted that if UK chooses no deal, EU very unlikely to insist 12 April date to leave. It will likely choose 22 May as cut off date. This still separates Brexit from European Parliamentary elections (they start 23 May) but leaves extra time to better finalise no deal preparations.

GENERAL ELECTION: UK government ministers privately suggested a general election will be called if Friday's vote is rejected or things "fall apart", according HuffPost's Paul Waugh

* * *

Update (6:50 pm ET): In a stunning turnaround, the pound has surged to a session high, erasing its losses for the day, on reports that Dominic Raab, May's former Brexit Secretary, who famously resigned in November rather than endorse the withdrawal agreement that May had negotiated with the European Union, is planning to back her deal.

There have also been reports that some Labour MPs are planning to back May's deal, defying their party's stated opposition.

Earlier, it was estimated that the deal would be defeated by about 25 votes. But given that Raab could presumably carry some MPs with him, and the prospect of more Labour defections, traders are finding a renewed sense of optimism that Theresa May might just pull it off.

* * *

The British pound dropped sharply on the morning of "the day that should have been Brexit" after a Labour Party spokesman confirmed that the opposition party would oppose PM Theresa May's "meaningful vote 2.5", setting the third vote on May's unpopular withdrawal deal with the EU up for almost certain failure.

Sterling dropped to $1.3009, leaving it down roughly 2% for March, though it remained, no pun intended, up 2% on the quarter, making it the best performer among major currencies.

That might come as a surprise to some, seeing as the public has been treated to one Brexit-related disappointment after the next, with May's deal having already been voted down twice by wide margins. Just this pass week, an indicative vote on possible Brexit alternatives showed that not one would received majority support in the Commons.

May and her team have warned MPs that if her deal is defeated again on Friday, they will risk delaying Brexit by months or even years. Then again, there's also the risk that the UK will crash out of the EU (though May and her team have largely glossed over that possibility). International Trade Secretary Liam Fox said Friday that losing the vote would mean a longer extension to Brexit.

The DUP, the 10 unionist MPs from Northern Ireland who help shore up the Tories Parliamentary majority, have already said they will oppose the vote. And many of the ERG leaders, including Boris Johnson and Jacob Rees-Mogg who said earlier this week that they would back the deal to prevent a longer Brexit delay have flipped-flopped on their stance.

In order to meet Speaker John Bercow's test that "substantial" alterations be made to the withdrawal agreement for it to be brought up for another vote, May decided to separate the WA from the non-binding political declaration - and EU officials confirmed that only the WA would need to be accepted for the UK to leave the EU.

Given that it's headed for defeat, observers might wonder why May is even bothering to bring it up for another vote. In an explainer for the BBC, political editor Laura Kuenssberg explained that it's another way for May of "extending the road before it finally runs out."

But the vote, on what was meant to be Brexit Day, is a request to MPs to allow her to keep going, to carry on pursuing her route, with its well-documented flaws. There's a challenge there too, not just to her own Brexiteers but to Labour and the other opposition parties, to say "no" to a long delay to our departure from the EU, the last moment when Number 10 believes anything even approaching a timely exit can be guaranteed. There are signs now that many Eurosceptic MPs are ready to say "yes" - not because they suddenly have realised Mrs May's deal is perfect, but because more of them officially realise that it is the clearest break from the EU they can realistically hope for. Yet her Northern Irish allies are not persuaded. Labour, even though they have sometimes accepted that what's on the table - the divorce deal - will never be unpicked by the EU, will still, in the main, resist. As things stand, even though some influential Brexiteers believe there is a chance it will get through, it looks like the prime minister is heading for another loss. But for Number 10, it is another way of extending the road before it finally runs out. And in this environment, with control slipping away, that, for Theresa May, is worth a try.

No amendments have been selected for debate before the vote, which is expected to take place at 10:30 am ET (2:30 pm London Time).