Although the prime minister wants to hold another 'meaningful vote' on her Brexit plan next week, it is by no means certain that, when it comes to the crunch, she will choose to do so.

I am told by her close colleagues, that two conditions must be met for her to go ahead with the vote, probably on Tuesday.

First, Northern Ireland’s DUP must say on Monday that they have, at the last, changed their minds and have decided to vote with her. To be clear, there is no logical reason why they should do this, given that there will be no last-minute alteration to what they hate most about her deal - namely the backstop which is designed to keep open the border on the island of Ireland and is enshrined in the Withdrawal Agreement.

So, the theoretical risk that the backstop will be forever, and will drive a regulatory wedge between Northern Ireland and Great Britain – which the DUP sees as toxic – is still implicit in May’s plan.

But DUP MPs and politicians increasingly seem embarrassed by their central role in derailing Brexit, and ministers are therefore hopeful that just possibly they will cease their opposition, if – for example – they are guaranteed a central role in negotiating whatever arrangements that ultimately make the backstop redundant or short-lived.

And when I ask government members what else could mollify Northern Ireland’s main unionist party, they text me emojis of dollars bills.

That said, the DUP tells me they won’t be bribed, or at least not this time. And that they will only vote for the deal if persuaded there is no risk that the Brexit settlement would fracture the union between Northern Ireland and Great Britain.

Truthfully, I don’t see how they will be able to rescue the PM, because – as I said from the outset – nothing fundamental has or will change to underwrite such a volte-face.

But since we live in such strange times, I am loath to bet my life savings on 10 MPs of any persuasion sticking to what they claim to be inviolable principles.

So, let’s make the heroic – and probably erroneous – assumption that somehow the PM talks the DUP round. What then?

Well she would still only hold this third meaningful vote if the clear majority of the Brexiteer rebels in her own party, those belonging to the European Research Group, have a belated change of heart and also back her deal.

Now again there is absolutely no principled reason for any of them to do so, given that the deal has not materially altered. But some are conspicuously on the brink of capitulating, in the fear if they don’t, Brexit would be significantly delayed (and a number will show solidarity with the DUP and do whatever the DUP decides).

So, the second – and obvious – condition that would have to be met for May to have a third shot at ratification of her deal is that her whips, led by Julian Smith, would need to be confident that she could significantly reduce the margin of defeat or (less plausibly) actually win.

The reason why reducing the loss to, say, 10 or 20 votes would be so valuable to her is that at that point she would then feel emboldened to hold a (you guessed!) fourth meaningful vote – because she might then be able to persuade perhaps six or even 12 additional Labour MPs who want Brexit to back her deal. At that point there would at last be a reason for them suffering all the hate that would be heaped on them by colleagues for defying the orders of their leader, Corbyn.

As one minister put it to me, 'there’s no point Labour MPs taking s**t from members for voting with us unless they think we can actually win the vote'. At this point I imagine you will agree with me that it is a long way from certain that the PM secures her deal next week, for all the widespread expectation that she is about to snatch victory from the jaws of Brexit delay.

So briefly let’s assess two other elements of Downing Street planning. First, if she loses she’ll tell EU leaders at the Council on Thursday that the following two weeks would be spent sounding out the views of MPs – via so-called 'indicative votes' – about what kind of Brexit they could support.

To be clear, the PM would endeavour to reassure the rest of the EU that this would not involve opening the Withdrawal Agreement or having a further push at changing the backstop. It would simply be a narrowing of the range options for the future relationship, or the scope of the so-called Political Declaration.

And both May and EU leaders would assume that if MPs could then coalesce around any reworked Brexit it would be a much softer Brexit – probably involving direct or approximated membership of the customs union and single market – and therefore a Brexit even less palatable for Brexiter purists (who would be expected to lump it).

This would of course be music to the ears of perhaps a quarter of the Cabinet, led by Rudd, Hammond, Clark, Gauke and Mundell. But it would involve a lengthy Brexit delay, beyond 1 July – and therefore necessitate the UK participating in elections to the European Parliament. As it happens, quite a few ministers and Tory MPs are less frightened by this prospect than I would have expected. 'It is an inconvenience, not a disaster' says one.

So, if these scenarios are accurate, what does this tell us about what kind of Brexit – if any – we’ll have? Well that is still an impossible forecast.

Here are three reasons why.

First, if May gets her deal approved next week, the ERG Brexiters could still secure their cherished no-deal Brexit at the end of May by talking out the Withdrawal Agreement and Implementation Bill that would turn the meaningful vote into Brexit reality.

Second, if her deal is squelched, the process of turning indicative votes into a deliverable Brexit deal would only be effective if Labour cooperated in an institutional sense, and that could not be guaranteed.

Third, everything I’ve written is redundant if the Speaker were to rule that the PM’s desire to hold the meaningful vote for a third time is a blatant and unacceptable breach of parliamentary convention – and therefore prohibits it.

I’ve said it before and I’ll say it again: the first law of Brexit is 'anything can happen'.

Robert Peston is ITV's Political Editor. This article originally appeared on his ITV news blog.