Quietly and discreetly, the planning for Boris Johnson’s premiership has begun. No one wants to be seen measuring the curtains, but his team are confident he’ll be the choice of Tory party members. It would be the most spectacular upset if he is not. Boris has fixed a Brexit deadline — 31 October — and time is short so his aides are concentrating on what to do when — if — he makes it to No. 10.

The first few weeks in No. 10 are crucial for any prime minister, but particularly one who takes over in mid-term, without their own personal electoral mandate. Boris will have only 99 days to agree a Brexit deal that can pass through parliament, something which eluded Theresa May, with many MPs thinking that the government might collapse if he fails. So how will he do it? Or rather — who will do it? It’s well-known that Boris is a great devolver, so a lot will depend on whom he chooses as his chief of staff. But even his closest allies have no idea who this chief might be.

Johnson dislikes gurus and has always resisted having a single course of political advice, but to enter Downing Street with a coterie of ‘chief’ advisers all jostling for his attention would be to invite disaster. If his premiership is to succeed, he must have a clear and unambiguous chain of command from day one. Boris’s Achilles’ heel as a leader is that he dislikes disappointing people, so he’ll be reluctant to establish a hierarchy — but if he’s to survive as PM, let alone succeed, he must.

If it’s hard to tell who he’ll hire, it’s easier to work out what he’ll do. Many of his critics are quick to cast him as unprincipled, or as an opportunist who has ‘lurched to the right’. But there has actually been a striking consistency to Boris Johnson’s liberalism. Almost 20 years ago, he justified his decision to endorse Ken Clarke in the Tory leader-ship race on the grounds that they shared ‘the same saloon bar pint’n’Castella, small c conservative views of the world’. (He also brought the endorsement of this magazine.) We can expect this to be much in evidence in a Johnson premiership: this approach has permeated his writing and politics. There will be an emphasis on ‘one nation policies’, less nanny state interference, and a fondness for grand infrastructure projects.

Much of Boris’s politics lies in the desire to tackle inequality by ‘levelling up’; to give the rest of the country the kind of infrastructure that London has — or as he once put it, give every child the kind of education that he enjoyed at Eton. And the former London mayor has always had a fondness for grands projets — think of his cable car across the Thames, his proposed Garden Bridge over the Thames, or his idea of a bridge across the Channel. His premiership will see a slew of these: he values symbolic power as much as practical achievement. He will likely see such projects as demonstrating his efforts to bring the country together.

Rural Britain will be given a rapid roll-out of full fibre broadband. In terms of physical infrastructure, expect a series of pledges on new transport for the north. Tellingly, when MPs have lobbied Boris Johnson to scrap HS2, he has expressed a reluctance to ditch it, arguing that it would send a bad message to axe such a big scheme. He has, though, agreed to a review.

Another feature of his premiership will be fewer bans on things. He has always railed against the nanny state tendency, he only reluctantly wears a cycle helmet, and he used to delight in the fact that, in the Spectator offices, a sign saying ‘No bikes’ was always covered up with them. He is fundamentally a liberal and will take a noticeably less authoritarian approach. ‘People are going to stop being infantilised’, one of his key supporters tells me.

Boris’s language and general tone will be more liberal and open than Theresa May’s has been. Gone will be talk of the ‘citizens of nowhere’, to be replaced by positivity about immigration — of which he declares himself a ‘passionate’ supporter. This won’t stop those determined to try to cause a culture war based on a few words selected from his back catalogue. His detractors even insist he’s a homophobe, though he was one of the first politicians to come out for gay marriage. There’s no reasoning with this mindset, but for those who are prepared to listen, a Johnson government would sound softer and gentler than May’s.

Boris Johnson likes to set the vision, to communicate, but lets others handle the detail. So cabinet ministers can expect to have free rein in their own departments. He has neither the inclination — nor the need — to worry about being overshadowed. Indeed, one of the features of his premiership will be that he will dominate political debate. This is a gamble for the Tories, as it could make the next general election a referendum on Boris. But it will also cause problems for both Nigel Farage and Jeremy Corbyn.

There are three groups orbiting around Boris Johnson at the moment: his old London gang, his parliamentary long marchers, and his new recruits, who have helped to deliver his victories in the parliamentary rounds. Johnson doesn’t like being beholden to any one tribe, or faction, so expect his administration to be made up of a mix of these three groups.

What the precise balance of power between these three forces will be is far from certain, but Will Walden, his City Hall media man, will head to No. 10. As part of its attempt to hobble Johnson, Theresa May’s No. 10 blocked Walden from going to the Foreign Office with him in 2016. His intended presence at No. 10 is a reminder of how keen the former mayor is to recapture the feel of that administration. Lynton Crosby, the Australian electoral strategist who ran the two successful London mayoral campaigns, will be in charge of the Tory election campaign — whenever that comes.

Boris’s choice of Chancellor will be crucial because, no matter who is in No. 10, the rest of the government can often be run by the Treasury. Gordon Brown used that position to wage daily warfare on Tony Blair. Johnson saw for himself how Philip Hammond was able to undermine the no-deal preparations — so he’ll be determined to have someone in the job who is in agreement with him on Brexit and the importance of leaving on 31 October. One of those who will play an important role in government says there can’t be any repeat of ‘the Hobbesian struggle in the heart of government’ over Brexit that there was between too many cabinet members (and their departments) under Theresa May.

I understand that the current frontrunner for the Treasury job is Sajid Javid. He and Johnson worked fairly well together in cabinet and Javid was an experienced financier before entering parliament. Javid shares Johnson’s view of the importance of a hard Brexit deadline and the manageability of no deal, his desire to build more houses — and his view that now is a good time to invest in big infrastructure projects, if necessary borrowing to do so. In political terms, Javid’s early life (he’s the son of a Pakistani immigrant) would offset having yet another Old Etonian as prime minister.

Javid’s presence would also rebut the canard that Boris has some prejudice against Muslims. Tellingly, in Tuesday night’s BBC debate — the most dangerous moment for Johnson in this campaign so far — Javid came to the frontrunner’s aid at vital moments. It was hard not to see it as a pitch to be his Downing Street neighbour.

Of course, even the most spectacular domestic agenda will come a distant second to the task of finishing Brexit — which, to Tory members, eclipses all other priorities save for crushing Jeremy Corbyn. Johnson is convinced, in private as well as in public, that a prime minister who really is prepared to walk away and do ‘no deal’ would change the dynamics of the negotiation. This is how he is bringing together MPs from different wings of the party: hardline Brexiteers hear talk of the willingness to walk away, while dealers hear Johnson’s belief that there will be a withdrawal agreement at the end of all this.

The obvious danger is that the EU will call Johnson’s bluff. Politically, he’ll then have no choice but to follow through on no deal — preparing government, in a matter of weeks, for one of the greatest logistical challenges of the modern era. This task has got harder in recent months, since many of those who have been most closely involved in the civil service’s no-deal planning have downed tools and moved on to other projects. Absurdly, the Brexit extension has been used to dial down preparations for no deal, not ramp them up.

If a deal is offered at Johnson’s first EU summit, he would have just ten days to get it through parliament: a worse than breakneck timetable. Even before then, he’ll face a parliamentary effort to bind his hands. There will be another attempt to mandate the government to seek an extension, rather than leave without a deal. Johnson will resist this, which might well lead to a no confidence vote. But there is a case to be made that losing that vote could benefit Johnson. Why? Because it would be followed by a fortnight in which Jeremy Corbyn, the Scottish Nationalists and other ardent Remainers would try to cobble together a government. Johnson would be able to point to this and ask voters, in Crosby-approved style, if they wanted to give him a majority in a general election or usher in this coalition of chaos.

Boris Johnson likes to joke that ‘There are no disasters, only opportunities. And, indeed, opportunities for fresh disasters.’ But the truth is that if he enters Downing Street, he will have no room for error. His first 100 days will need to go smoothly or they will be his last behind that black door.