THERESA May’s already chaotic Brexit plans were thrown into disarray yesterday afternoon, after a shock ruling by the Speaker barred the Prime Minister from putting her deal to the Commons for a third time.

Quoting parliamentary precedent going back to 1604, John Bercow said it would be out of order for the government to ask MPs to vote on something that they have already comprehensively rejected.

READ MORE: Explained: The '1604 rule' cited by Speaker ... and a question for all Scots

If Downing Street wants to try to get the agreement in front of MPs again then there will need to be fundamental differences.

And the Speaker was explicit that those differences would have to be more than just a tinkering around the edges – they would have to be “different in terms of substance”.

The SNP’s Ian Blackford said the country was now in a “constitutional crisis”.

The bombshell intervention stunned the Government who had been wrestling with the decision on when to hold meaningful vote three, or MV3, as it is being labelled in Westminster.

Solicitor General Robert Buckland told the BBC that the Government might even have to consider proroguing parliament, closing the session early and starting it again.

But with just 10 days to go until Brexit day, the logistics of organising a formal state opening of parliament and having the Queen promise a MV3 could be tricky.

“This has given us quite a lot to think about in the immediate term,” Buckland said. “There are ways around this – a prorogation of parliament and a new session – but we are now talking about not just days but hours to March 29. Frankly, we could have done without this, but it’s something we’re going to have to negotiate with and deal with.”

May is due to head to Brussels for a European summit on Thursday. If she had managed to get her deal passed this week then she would have asked the 27 remaining members of the EU for a short extension, and if not then she would have requested a lengthy delay.

READ MORE: First Minister writes to May over reports Scotland snubbed for DUP

But Bercow’s need for complete change will muddy the waters – the EU are not minded to reopen negotiations, and would only agree to an extension if there is a very good reason.

In his statement Bercow quoted from Erskine May – the guide to parliament’s rules – which said that by convention, the question “may not be brought forward again during the same session”.

He added that the convention had been confirmed again many times, including “notably in 1864, 1870, 1882, 1891 and 1912”.

“Indeed, Erskine May makes reference to no fewer than 12 such rulings up to the year 1920,” he told MPs.

“One of the reasons the rule has lasted so long is that it is a necessary rule to ensure the sensible use of the house’s time and the proper respect for the decisions it takes.

“Decisions of the house matter. They have weight.”

Bercow said the second meaningful vote motion held last week did not fall foul of the convention because it “could credibly be argued it was a different proposition”.

He told MPs: “If the Government wishes to bring forward a new proposition that is neither the same nor substantially the same as that disposed of by the House on March 12, this would be entirely in order.

“What the Government cannot legitimately do is resubmit to the House the same proposition – or substantially the same proposition – as that of last week, which was rejected by 149 votes.”

The National: SNP Westminster leader Ian Blackford urged the PM to meet with Opposition leadersSNP Westminster leader Ian Blackford urged the PM to meet with Opposition leaders

Intervening after the statement, the SNP Westminster leader Blackford called on the Prime Minister to “immediately call a meeting of all Opposition leaders” and to meet the heads of government in Edinburgh and Cardiff “in order that we can react to this crisis and find a way ahead”.

Tory Brexiteer Jacob Rees-Mogg took to Twitter to say that “no deal is now the best outcome”.

Labour’s David Lammy disagreed, saying it was only the best outcome “for disaster capitalists, lawyers, warehouse owners and satirists”.

“For everyone else, it is remaining in the EU,” he added.

LibDem deputy leader Jo Swinson tweeted: “Few workplaces have the chitchat: ‘I was wondering with reference to the precedent of 1604...’ “But under all the parliamentary pomposity of points of order, this is good sense. PM can’t keep asking the same question, hoping for a different answer.”