As you know, I have been banging on about the probability that the UK will leave the EU without a deal on 12 April.

Having talked to very senior members of the government, and also well-placed sources in the EU, it has become clear to me that MPs have one shot to prevent that - and it will almost certainly be this week that MPs will either rise to the challenge or flunk it.

How so?

Well, the prime minister and the EU will be looking at the indicative votes that are due to take place on Tuesday and Wednesday - on Tuesday sponsored by the PM, on Wednesday under the backbench initiative of Sir Oliver Letwin - to see if a majority of MPs can demonstrate their support for a deliverable alternative to a no-deal Brexit.

If they don't, Theresa May's conclusion may well be full steam ahead to a no-deal Brexit, I am told - which will be music to the ears of perhaps a third of the Cabinet and Tory Party.

Prime Minister Theresa May greets European Commission President Jean-Claude Juncker. Credit: Stefan Rousseau/PA

Before I flesh this out, here is a small sidebar: I would expect at least a couple of ministers to resign in the next 24 hours, to vote for Letwin's motion on Monday that would secure his day of indicative votes on Wednesday.

Given the way that the tectonic plates of politics are shifting and colliding, ministerial resignations represent no more than a modest earth tremor. The bigger earthquake is all about how and whether we leave the EU.

The important point when it comes to the indicative votes is that any plan to get through the Brexit roadblock must be supported by a majority of MPs and be consistent with the EU's red lines for it to be anything but an exercise in our elected representatives' vanity.

Let's take those in turn.

Ministers who are desperate to prevent a no-deal Brexit have been talking to Labour and Tory backbenchers, and are despondent that every senior backbencher is riding a different Brexit hobbyhorse.

"Some want a version of Norway's relationship with the EU, some want this Common Market 2.0 thing, others a referendum - and none seem prepared to compromise," complained one minister.

"And if come Thursday, after the indicative votes, there is no majority for any way forward, the PM will be able to say that her attack on parliament, which got her into so much trouble, will have been proved right - that MPs really can't say what they actually want."

An estimated 1 million people took to London's streets on Saturday to demand Article 50 be revoked. Credit: PA

At that point, according to another senior member of the government, MPs will be faced with a very simple choice: leaving without a deal on 12 April, which could well be what the PM signals as her preference, or revoking Article 50 and staying in the EU.

"That will be a full-scale crisis," the minister said.

But it's not plain sailing even if MPs do coalesce around a solution.

"They have to be honest and transparent about what that solution involves, or the PM will rightly reject it," said a source close to her.

What does he mean?

Well, if MPs were to back membership of the customs union and single market, but did not concede it would involve continuing to allow free movement of people to the UK and a prohibition on negotiating trade deals with countries outside the EU, then the PM would simply say MPs were asking for a unicorn - and she would tell them to hop off.

The result again would be a binary choice between leaving the EU without a deal or revoking Article 50.

So those cabinet ministers who see a no-deal Brexit as Kryptonite for the UK and their party - which is not the entire cabinet - are desperate that parliament's most senior MPs come together over the weekend and early next week to ensure that the indicative votes lead to a deliverable outcome.

"It is really important that MPs like Hilary Benn, Chris Bryant and Yvette Cooper [all of Labour] try and work with their equivalents in the Tory Party [MPs such as Letwin, Nicky Morgan, Justine Greening and Ken Clarke] to make sure the indicative votes vindicate the role of the Commons rather than underwriting the PM's attack," said a government source.

Labour MPs Hilary Benn and Yvette Cooper have a key role to play. Credit: Stefan Rousseau/PA

There are probably only two practical routes that could command a majority of MPs. They are some form of softish Brexit, which would involve infringing one or other of the PM's immigration and trade-deal-freedom red lines, or the Kyle/Wilson plan to put her own Brexit plan to a confirmatory referendum.

I understand, somewhat to my surprise, that a growing number of influential ministers are sympathetic to Kyle/Wilson's confirmatory referendum.

In fact, I am reliably told that as long ago as October, the Chancellor told the Prime Minister that her Brexit deal would probably be supported by the British people, even if it was rejected (as he expected) by MPs.

But if a majority of MPs decide to back a people's vote - which truthfully I think unlikely, but who can be sure? - the big question is whether the PM would agree to negotiate that with the EU.

Based on what she said on Wednesday, that she could not be PM if the UK is still in the EU on 30 June, which would be the case if there is a referendum, surely she would have to quit if MPs say they want the Kyle/Wilson gambit?

What is more, there are a half dozen members of the cabinet - and notably Penny Mordaunt, Chris Grayling, Andrea Leadsom and Liam Fox - who have made clear they would quit rather than authorise a so-called people's vote.

And of course Tory ERG Brexiters would go nuts if a referendum is the chosen answer.

At which point therefore the government could well collapse, leading to a general election.

But the EU have made it clear they would not force a no-deal Brexit on 12 April if the UK was holding either a general election, or a referendum or both.

There is one other rarely discussed alternative: MPs creating a temporary government of national unity under a caretaker prime minister. "It could come to that," said a minister, "though I think it's unlikely."

In other words, if MPs unite around single alternative to a no-deal Brexit this week, this at the very least delays a no-deal Brexit for many months - but it does not prevent weeks and weeks and weeks of turmoil and uncertainty.

Ain't we lucky.

PS: I have a second sidebar, about how and why the PM launched her attack on the irresponsibility of MPs on Wednesday night.

"She has been working round the clock and is totally exhausted," said one of her allies. "Somebody else wrote those words and put them in front of her. She did not know what she reading."

On this version of what happened, and you can believe it or not, her voice was hijacked by that faction in the government that wants a no-deal Brexit, and felt their dream was in sight when they persuaded the PM to rule out a long Brexit delay.

"Fortunately, within hours, the PM recognised her mistake and did her pivot back to a more consensual approach," said a minister.

"But it may be too late, because her intransigence has alienated too many colleagues and has made it impossible for her deal ever to pass."