Theresa May has been defeated on Brexit by rebel Tory MPs joining forces with Labour and other opposition parties for a second time in two days.

But, on a confusing day in parliament, even seasoned Westminster watchers were struggling to follow. 

What has happened?

A group of anti no-deal MPs, led by Tory ex-cabinet minister Dominic Grieve, dramatically sped up the parliamentary Brexit process by passing an amendment forcing the prime minister to return to the Commons with a new plan within three sitting days if her deal is voted down in Tuesday’s crunch vote.

It is thought this will mean May coming back to MPs by January 21, a far sooner deadline than the 21 days which was, until today, set down in law.

But questions remain over whether the law would force her to hold another vote immediately or whether she would have seven more days before MPs’ will is actually tested.

What does it mean?

The anti no-deal group felt the amendment was crucial to stop May trying to run down the clock towards exit day on March 29. The idea would be to pressure MPs who fear no-deal into backing her agreement as the only alternative.

Crucially, it also means MPs will be able to express their preference for alternative ‘plan B’ Brexit options much sooner than expected, as they will be able to table amendments.

Expect supporters of a second referendum, a Norway-plus model, or even a ‘managed no-deal’ to bring their proposals to the Commons for a vote.

If May’s deal is rejected again, and another option is chosen by MPs, the government will not be forced to change policy but would face enormous political pressure to act.

Why was there such a fuss?

The Grieve amendment only got to the floor of the Commons for a vote after an extraordinary intervention by the Commons Speaker, John Bercow.

Even supporters of the amendment initially did not believe they could force a vote on it due to the drafting of the Brexit motion that it aimed to change.

But Bercow intervened and ruled it was admissible, causing one Westminster source to say he had essentially “set fire” to the parliamentary rulebook.

He also failed to deny suggestions that he overruled the most senior Commons official, clerk of the House Sir David Natzler, in making his decision.

It enraged Tory MPs who view Bercow as anti-Brexit and even pro-Labour, despite being initially elected as a Conservative and being required to be impartial.

So what happens now?

MPs from all sides of the Commons who oppose May’s Brexit deal will be working furiously to stitch together cross-party coalitions to try and win majority support for their alternative plans, such as a second referendum or Norway plus.

Bercow looks likely to face a motion of no confidence due to his highly controversial handling of events, but may cling on through the Brexit process.

And May and Downing Street will try to somehow wrest back control of the Brexit process and continue figuring out how they can possibly get her deal passed by MPs.

That may involve quickening efforts to get reassurances from the EU on the Irish border backstop which is vexing so many MPs.