Boris is finally PM, but will he be the liberal conservative or the reckless no-dealer?

One minister backing Boris told me: “All we know is that everything will change, but we don’t know how.” If even his closest supporters don’t know, perhaps we should all fasten our seatbelts

After Theresa May’s long goodbye, Boris Johnson’s short honeymoon will begin. His premiership may well be shaped by decisions in the next few days. Fittingly, the traditional 100-day period for judging a new prime minister ends on 31 October – the date Britain is due to exit the EU.

Johnson has achieved his lifelong ambition, even if it stops short of being “world king” (as he told his sister Rachel he wanted to be as a child). Naturally, he doesn’t remember that now. Similarly, the man who talks about his Turkish great grandfather to show he is pro-immigration, does not recall warning about the risks of Turkey joining the EU during the 2016 referendum.

Will voters damn him for his lack of consistency, or could what some allies admit are his “flexible views” be an asset as prime minister? On Brexit, the most important question is whether he listens to hardline Brexiteers – led by former Tory leader Iain Duncan Smith – who want a clean break with the EU in October, or conciliators – led by the Attorney General Geoffrey Cox – who believe a deal with the EU can be done.

Last week, it appeared the hardliners had won when Boris insisted the Irish backstop in May’s Withdrawal Agreement must be scrapped. Yet it might not be his final word. Some ministerial backers think he could support changes to the political declaration if the EU swallowed a time limit to the backstop. True, the EU has repeatedly ruled this out, but might it move if PM Boris proved less hardline than the candidate who told Tory members what they wanted to hear?

Pro-Boris moderates urge him to strain every sinew for an EU deal, rather than merely go through the motions. They warn that a clean break could break his premiership. To prevent that, he must divide his enemies, by splitting off the small band of Tory Remainers who want a Final Say referendum like Dominic Grieve, from the “Gaukeward squad” of soon-to-be-former ministers like David Gauke who will vote for a deal and are reluctant to bring down their own government in a no-confidence vote.

The threat to Boris from the Commons rebels is real, and not just confined to Brexit. The Tories’ fast-disappearing majority will make it hard for Johnson to implement some of the 25 policies he outlined during the leadership campaign. Which is why pro-Boris ministers think that, if he can secure a Brexit deal, he will seek a general election no later than next spring.

There's no chance the current Commons will approve his plan to raise the 40p higher rate tax threshold from £50,000 to £80,000. He will want to be bold on non-Brexit policies, though his acceptance speech today was virtually policy-free. His three goals told us little: “Deliver Brexit, unite the country and beat Jeremy Corbyn.”

Even his supporters don’t know which Boris will move into Number 10 tomorrow: the liberal conservative who twice won the mayoralty in a Labour city, or the reckless gambler prepared to crash out of the EU?

Several ministers are in state of high anxiety as they await their fate in tomorrow’s reshuffle. One cabinet member explained: “It’s not a normal one, when you wonder whether you will be moved. Boris starts with a blank sheet of paper.” I’m told that, as far as senior ministers are concerned, the “stayers” have been reassured they are safe, while silence from Team Boris is ominous for those who have not had the call.

His commanding two-to-one margin of victory over Jeremy Hunt gives Johnson the free hand he wanted to move his rival from the Foreign Office, after being irritated by Hunt's more aggressive than expected leadership campaign. Yet the Iran crisis means there is a strong case for keeping Hunt as foreign secretary. The word from Team Boris is that, to unite his party, he will name a broad-based team, not just a cabinet of true Brexit believers. The “London brigade” who worked under Johnson at City Hall, such as Kit Malthouse and James Cleverly, will do well.

How ready is Boris for the job for which he has prepared since childhood? His track record does not inspire confidence. “Boris Johnson has never prepared himself properly, which means his whole life has been a preparation for being unprepared,” his biographer Andrew Gimson said.

Johnson was most definitely not prepared for victory in the 2016 referendum. On the morning after, he and Michael Gove, his fellow Vote Leave leader, were baby rabbits caught in a giant searchlight. His 2016 leadership campaign was a mess before Gove knifed him.

The man tasked with preventing a chaotic start to Johnson’s premiership is Sir Eddie Lister, his chief of staff at City Hall who will now do the same job in Downing Street, at least in the short term. Insiders say that when he rejoined Team Boris during the leadership campaign, he had to bring order to a rather chaotic operation. Now he will have to arbitrate between at least eight factions competing for Johnson's ear.

Lister’s strength is that he knows Boris’s mind; allies dismiss the caricature that the new PM does not. Before he makes a decision, he likes to hear different views, and might look uncertain as he runs his fingers through that blonde mane, but it is all part of the shambolic act. “Boris tells Eddie what to do, not the other way round,” one ally insisted.

One minister backing Boris told me: “All we know is that everything will change, but we don’t know how.” If they don’t know, perhaps we should all fasten our seatbelts.