It looks as if the Conservative party is already at war. Fifty or so Brexiteer Tory MPs openly meet to discuss deposing the Prime Minister —  yet they have no strategy and (at present) no chance of defeating her in a confidence vote. On Twitter, Tory backbenchers and even ministers can be found threatening to destroy each other. This isn’t just about personality. In the last few months, the question of what Britain’s relationship with the EU should be and who should be Prime Minister have fused together — so the most divisive issue in British post-war politics has been combined with a drawn-out leader-ship contest.

The Prime Minister has produced a plan: the Chequers proposal. It is hard to name its ardent supporters but easy enough to identify its most prominent critic: Boris Johnson. Since resigning from the cabinet, he has kept up a regular verbal barrage against it — a campaign that has had some success. Polls show that most Tory members and voters don’t like it. Meanwhile, the former foreign secretary is once again the grassroots’ favourite to be the next Tory leader. Those close to Boris Johnson publicly maintain that he wishes to change the policy, not the Prime Minister. That is rot.

Most Tory opponents of Chequers believe that Mrs May’s plan is doomed on the grounds that the EU will not be prepared to accept her cherry-picking, seeking free movement of goods without the free movement of people. As one Tory who was vital to the referendum victory likes to say, ‘In Barnier we trust.’

Boris Johnson does not agree. He argues that the EU know a cave-in when it sees one and will bite on Chequers. Britain would be bound to accept its regulations on goods, while having no say over them. Boris believes that Barnier will squeeze a couple more concessions, then ask her to sign. So the only way to stop this is to remove her before she can do the deal.

Oddly enough, allies of the Prime Minister aren’t trying to play down the possibility of a Boris leadership bid. Rather, they are talking it up. No. 10 calculates that while Chequers is not popular among MPs, the idea of a Boris premiership is even less so. One cabinet minister explains that ‘There’s a majority against Boris having the top job. So you have to vote for Theresa, as you can’t risk Boris being in the final two.’

There is no doubt that the intensity of the dislike of Boris among some Tories passes all understanding. But with a Labour split appearing imminent, many are placing a renewed emphasis on unity. If Labour moderates leave to form their own party, an SDP-style breakaway, then it could hand the next election to the Tories — if they just stick together. Even the mere threat of a dozen Tory MPs resigning the whip would therefore count against Boris. This is (thanks to Mrs May) a hung parliament, and the party knows it needs every MP.

There are those who argue that Boris’s position with Tory MPs is better than people realise. They believe that Jacob Rees-Mogg — who has already declared for Boris — will bring in the bulk of the European Research Group, the leading Brexiteer lobby in the party. They also think that when the time comes, Steve Baker — the most formidable organiser on the Brexiteer wing of the party — will deliver for him. Indeed, Brexiteer MPs think that they already have the numbers to force Mrs May to submit herself to a no-confidence vote of Tory MPs. But they don’t want to send the letters in, since they know they don’t have the 158 MPs needed to actually defeat her in a confidence vote.

But it is notoriously difficult to whip Tory MPs on the question of who should be prime minister. There are vigorous opponents of Chequers who would never back Boris. The renewed focus on his personal life creates fresh complications for him. It is also worth remembering that one or two old-school Tory Eurosceptics regard him as a Johnny-come-lately; they fear he’d sell them out once installed in Downing Street. Boris, meanwhile, has confided to friends that he fears he is being used as a battering ram —  so that when the time comes, David Davis will be put forward as a less divisive figure.

In another strange twist, some cabinet ministers who back the Chequers plan would quite like to see May face a no-confidence vote. If that came about and she won, then under party rules she could not be challenged for another year. ‘A year without further interruptions has some appeal,’ one cabinet minister tells me. So those who want Mrs May gone and those who wish her to stay both have reasons for stoking up a challenge.

The party’s splits are increasingly complex. Supporters of the Chequers plan can now be divided into three groups, only one of them really in favour of it. One faction regard Chequers as a stepping stone to getting a deal with the EU. They think that it clears the way for further concessions and a deal that is as close as possible to the EU single market. Then there are those who think that a deal close to Chequers really is do-able. Finally, there are those who backed Chequers on the basis that the Prime Minister deserved the chance to see if it could get anywhere. However, while this last group still publicly support Chequers, in private they are discussing when the government should change tactics.

One influential member of the cabinet insists that this is the key issue: whether Theresa May has ‘the agility to change tack’. Another explains that his faction is doing their bit to try to persuade the country and the party of the merits of Chequers because they’ll be in a ‘stronger position to urge her to pivot away if we have tried to sell it’.

This group, which includes a growing number of cabinet ministers, is the most interesting. At the moment, Mrs May doesn’t have the political space to make further significant concessions to the EU; only a crushing victory in a no-confidence vote could give her that. Without significant concessions, the EU isn’t going to agree to the UK in effect staying in the single market for goods while refusing free movement of people.

What worries this faction is that the EU will keep stringing Mrs May along, and then that at the last moment it will present only two choices: a customs union or no deal. In this scenario, Barnier would be betting that Parliament would not vote for no deal, thereby forcing Mrs May’s capitulation. This is why ministers are saying that at some point Mrs May will have to take Chequers off the table and replace it.

Mrs May can comfort herself with the knowledge that the EU 27 are more alert to the dangers of the talks collapsing than they were. One source who has travelled around Europe trying to sell May’s Chequers proposals to national governments says that in each capital you are met at first with ‘the ritual declaration that M. Barnier negotiates for us’. They then proceed to keep their cards very close to their chest.

But there is one thing does draw them out: no deal. They all want to make clear that there must be an agreement. This source tells me that ‘When it gets rough over the autumn, there will be a chorus saying to the Commission: whatever you do, we must have a deal.’ There is also an understanding that ‘the Boris and Davis resignations showed that she’s operating at the limit of her political discretion’.

Previously, those close to Mrs May had hoped that a Brexit deal would inject new life into her premiership. But now almost everyone accepts that she won’t be the one to lead the Tories into the next election. The slogan that her team had intended to use for the post-deal phase of her premiership, ‘opportunity for all’, is now being used for this year’s party conference. What Mrs May can hope for, one cabinet minister says, is that ‘if she gets a decent deal, she gets to choose how she leaves’.

If Mrs May quits No. 10 soon after the withdrawal agreement passes the Commons in the spring of next year, the subsequent leadership contest will still be dominated by Brexit. When we enter the transition period (before leaving properly at the end of 2020), there will be a political declaration, sufficiently vague to cover multiple options. Candidates for party leader will define themselves, or be defined, by the kind of final deal that they would seek.

In such a contest, any candidate would need just over a third of the votes — 106 supporters —  to be certain of making the final two. If Boris Johnson were to do so, he would probably win a vote of party members — which is why his enemies are being so passionate in their exertions at this early stage. They want to ensure he never makes it to the starting line; and Boris is, at present, a very long way off having the backing of a 106 Tory MPs.

But who would that leave? The field is beginning to become clear with Sajid Javid, the Home Secretary, as the current front-runner. But the stock of the new Brexit Secretary Dominic Raab is rising fast. If there is an agreement and the political declaration hints at an end state closer to Canada than to Chequers, he’ll get credit from pragmatists for the deal and be able to say to the Brexiteer wing of the party that he’ll finish the job. Meanwhile, many in the Tory establishment are talking up Jeremy Hunt, Boris Johnson’s successor as Foreign Secretary.

There is a complicating factor. The one Tory who can rival Boris in the charisma stakes is Ruth Davidson, the leader of the Scottish Tories. But even once she comes back from maternity leave, she won’t be available to the Westminster party because she doesn’t have a seat in parliament. She has committed to fighting the Scottish parliamentary elections in 2021, when she thinks she has a shot at becoming First Minister. If she fails then, as she told this magazine at Christmas, her options (including a move to Westminster) are open. Might they wait for her? A Tory who has been involved with the last six leadership elections points out that ‘If you’re on the left of the party, you have a huge incentive to keep Theresa in place until Ruth is available, as she is by far your best candidate.’

But even if he isn’t a candidate, Boris will be an influential figure in the next Tory leadership contest. His standing with the grassroots means that whichever of the final two received Boris’s Brexit seal of approval would be hard to beat. There are more acts to come in the Tory party drama.