‘Possibly the calmest person in British politics?’ Theresa May gives a press conference on her Brexit plans. Photograph: PA

The eye is supposed to be the calmest place in a storm. Weird as this may seem, the most tranquil person in British politics this weekend is probablyTheresa May.

This is not the same as saying that she is in a good place. Bits of her government keep falling off, like a decaying gothic folly shedding masonry. Even discounting for the tendency of the Brexit ultras to brag up their strength, a full-frontal attempt to oust her is more likely than at any time in her beleaguered premiership. A confidence ballot of Tory MPs could happen as early as this week.

Her Brexit deal has been brutally savaged from every angle. When she presented it to parliament, more than 60 minutes elapsed before a Conservative MP spoke in her support. Even those that did so could barely muster the enthusiasm of someone recommending a cockroach-infested hotel to a friend on the grounds that it was the only place in town.

I have never seen a prime minister look so friendless at the dispatch box. The human sponge of Number 10 just stood there in the stocks as she was pelted from all sides. This may have attracted a little bit of sympathy from some voters. That certainly seems to be a factor in the calculations at Number 10, where political masochism has been taken to levels never previously visited.

Even if the prime minister is eliciting some public empathy, this won’t make anything easier where it counts: in the pitiless crucible of parliament. Nothing that has happened since she unveiled her deal has made it look more likely that it can secure the approval of the Commons.

So why do I nevertheless say that she is probably the calmest person in British politics? Because she enjoys the relief that comes from knowing that she has arrived at the endgame. She has played out her hand. Her cards on the table. Here’s the deal, parliament. Take it – or do the other things, many of which are the stuff of nightmares. She has reached the ground on which she will fight what may be her last battle.

That means there will now be a much more intense focus on the choices confronting everyone else. The other players in this spider’s web of decision-making will have to spend less time attacking what she has done and start justifying what they are going to do. Others will have to make some momentous choices of their own.

A moment of truth arrives for the Conservative party. At this time of high peril for the country they profess to love, are the Tories going to indulge themselves in a leadership contest? One thing that has changed over the past few days is the number of Tory MPs openly saying, and often with undisguised relish, that they want to depose the prime minister. With attention-seeking vanity, Jacob Rees-Mogg uncloaked himself as an assassin in the Commons. Rather than quietly submit their letters of no confidence, several others of his faction have also noisily declared themselves as Mayicides. The Tory party has always been a treacherous beast, but once it used to conduct its assassination attempts with a degree of politesse. The cabal of Brexit ultras are the men who put the cock into peacocking.

To anyone who does not live in their fantasy universe, this will look like an act of narcissistic self-pleasuring at the expense of Britain. It also has the hallmarks of an exercise in utter futility. Just as they have never produced a plausible solution to Brexit, so the ultras cannot explain precisely what they expect to achieve by attempting to dethrone Mrs May at this point.

If it comes to a confidence vote, most Conservative MPs I speak to expect her to survive. The Moggites need half the parliamentary party to be sure of throwing her out, and they don’t have anything like that strength. If she hangs on, the Brexit ultras will have succeeded only in wasting more vital time when it is in dangerously short supply, making their country even more risible in the eyes of the world, and exposing their own weakness.

It is possible that Mrs May could lose a confidence vote. As I write, that looks like the less probable outcome, but the odds might shift quickly and dramatically. Once the leadership is in play, all sorts of dynamics kick in. One of the more predictable is the ambitions of the many wannabe leaders among the Tories, a party in which the number of people who ache to be prime minister is much larger than the number who are actually capable of doing the job.

If Mrs May is defenestrated “there will be a bloodbath”, predicts one normally phlegmatic senior Tory. Her demise would almost certainly be followed by a chaotic, vicious and protracted struggle for what would be a very hollow crown.

And after wading through all the gore spilt in a leadership contest, theConservatives would find that this solves nothing. None of the important facts will be changed by putting a different Tory into Number 10. It would still be the case that there is no majority in parliament for the kind of no-deal Brexit that terrifies everyone except those ultras who want to crash out. A new prime minister installed without a general election would face legitimacy issues from the moment he or she stood on the threshold of Number 10.

Crucially, changing the face at the top would not entice an improved offer from Brussels. The EU has already devoted many tortuous months to these horrendously complex negotiations. When they forget to be diplomatic about it, EU officials will confess to being sick of the whole process. The EU is not going to unpick a painfully constructed deal with Mrs May, start all over again and present a better bargain, certainly not of the kind that the Brexit ultras talk about. Some of the member states are complaining already that too much has been conceded to Britain. They will not reward the Tory party for changing its leader with a gift-wrapped Brexit. If anything, the opposite is more likely to be the case.

There are alternative routes forward, the clearest of which is throwing the question back to the people with another referendum. Opening that up will depend on how Labour makes its big choice. As the Tories thrash around in this mire of their own making, it would be unreasonable to fault Labour for seeking to exploit it for party advantage. That is what oppositions have always done. Jeremy Corbyn decries the government for being “in chaos”, which is obviously true but also a convenient way of avoiding clarification of his ultimate intentions. Mr Corbyn is a career-long Europhobe who displayed not an ounce of conviction for remaining within the EU during the referendum, demanded the triggering of Article 50 the morning after, and has not once since expressed a scintilla of remorse about Brexit. “We can’t stop it,” he said very recently. Most of his party’s supporters do want to stop it. The bulk of Labour MPs would prefer to remain within the EU. A massive majority of Labour members think the British people ought to be given anopportunity to reverse Brexit before it is too late.

The Labour leadership has spent many months skilfully, if cynically, camouflaging this division by pretending that it could negotiate all the benefits of membership of the EU while still leaving. We all know this is tripe. For the moment, Labour is just about hanging together around rejection of Mrs May’s deal. This is the common point that can still unite Mr Corbyn, his Remainer MPs and Labour members. The leadership will vote against the deal because it is a “Tory Brexit” and they think that combining with the Moggites in the division lobbies to defeat the government will somehow precipitate an early general election. Remainer Labour MPs will vote against the deal in the hope that doing so will pave the way to a further referendum. But if Mrs May’s deal goes down and there isn’t a general election, then what? There will be no hiding places left for the Labourleadership. Mr Corbyn will be confronted with the choice that he has been desperate to avoid.

Will he follow the desires of his members – the party is, after all, supposed to belong to them these days – and throw the full weight of Labour behind giving the British people the chance to change their minds in a further referendum? Or, when it comes to his moment of truth, does Mr Corbyn plan to sell out his supporters?

Theresa May has made her choices. For others, the agonising has only just begun. It will soon be time for everyone else to take responsibility for fateful decisions of their own.

Andrew Rawnsley is an Observer columnist