Update: It's looking increasingly likely that Commons Speaker John Bercow's impudence in defying May and her government will not go unpunished.
The BBC is reporting that a motion of no confidence in Bercow - who has been accused of ignoring Commons rules in allowing MPs to vote on the Grieve amendment - is likely.
NEW— Sam Coates Times (@SamCoatesTimes) January 9, 2019
BBC Mark D’Arcy reports a motion of no confidence in the Speaker “looks pretty certain” https://t.co/a21Om577wl
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Following Theresa May's dramatic defeat on Tuesday when 20 Tory rebels helped pass an amendment to a finance bill that effectively eliminated the possibility of a 'no deal' Brexit, Parliament has taken another step toward wresting power over the Brexit process away from May and her government by passing another amendment that would require May to call another vote on her unpopular Brexit plan should it be defeated during a planned 'meaningful vote' next week.
The controversial "Grieve amendment" - which was opposed by May's government (she had been planning on a three-week gap to whip up votes or come up with a 'Plan B' should next week's vote fail) - passed with 308 votes in favor and 297 against. The amendment was named after the Tory MP - Dominic Grieve - who initially proposed it. Tory MP Oliver Letwin also helped lead the push for the vote.
The vote will effectively prevent May from running out the clock to Brexit Day, which was believed to be her primary tactic for coercing MPs to support her deal.
As the BBC pointed out, Wednesday's vote increases the likelihood of another Brexit referendum.
Wednesday's amendment passed thanks to an alliance between Labour and Tory MPs after May's critics accused her of increasing the risk of a 'no-Brexit' scenario.
"The government's decision to delay the meaningful vote has run down the clock and increased the risk of a no-deal Brexit," said Labour's shadow Brexit Secretary Sir Keir Starmer.
"If the prime minister's Brexit deal is defeated next week, she must return to Parliament as soon as possible and give MPs a real say on what happens next."
ERG leader and prominent Brexiteer Jacob Rees-Mogg said the amendment wouldn't affect the UK's scheduled departure from the EU on 29 March (though that still remains to be seen).
"It merely requires a motion to be tabled not even debated."
The vote comes ahead of five days of debate over May's plan.
Commons Speaker John Bercow is facing accusations that he broke procedural rules by calling for a vote on the amendment, per the BBC.
Commons Speaker John Bercow faced an angry backlash from some Conservative MPs over his decision to allow MPs to vote on the issue.
The MPs claim Mr Bercow broke Commons rules and ignored the advice of his own clerks.
Commons leader Andrea Leadsom was among MPs to challenge his ruling in a series of points of order after Prime Minister's Questions.
Critics also argued that the business motion to which the amendment was attached shouldn't have been amendable, and that the speaker was "breaking with precedent."
For his part, Bercow said he had made an "honest judgement" after consulting his clerks, but rejected calls from Andrea Leadsom to release the legal advice he had received.
Bercow said he was "not setting himself up against the government but championing the rights of the House of Commons" - and that MPs were free to vote against the amendment if they didn't like it.
May has renewed her push to whip up votes for her deal this week, though with the DUP remaining opposed to the deal, saying they would reject any "cosmetic" changes offered by the EU on the Irish backstop, it's unlikely that she will manage to tilt the scales in her favour. Meanwhile, Labour has revived threats to call a vote of no confidence in the government if May's vote fails.
In summary, May's insistence that the only options available are her deal, a hard Brexit, or no Brexit is looking increasingly meaningless. And MPs are moving to push through their vision for a 'Plan B' - though there's no clear indication that another arrangement would be accepted by the EU.