At 6pm on Friday, Boris Johnson’s new de facto chief of staff addressed government aides in Downing Street for the first time.

In one of many breaks from the Theresa May era, the man who will effectively run Johnson’s government was dressed in black trainers, grey jeans, and a crumpled white shirt that hadn’t seen an iron in years. On his first day in office on Wednesday, Dominic Cummings wore a T-shirt.

The Marmite former Brexit campaign chief made clear to the assembled special advisers — powerful political aides who work for ministers in government departments, known in Westminster as SpAds — that he was in charge and that their jobs would be changing in subtle but significant ways.

One SpAd asked Cummings if it was correct that they would all be reporting to him rather than their individual ministers. According to those present, Cummings was self-deprecating and did not lay down the law but said SpAds were always supposed to work for the prime minister and his team first and foremost.

This was a direct warning that the situation under the May regime — where ministers and their taxpayer-funded SpAds routinely promoted their own interests over the PM’s — would no longer be tolerated.

Instead, departmental aides will report to Cummings and other senior advisers in Number 10. While technically all SpAds already serve at the liberty of the PM, making them immediately answerable to Downing Street is a notable departure from the status quo and sets up potentially massive conflicts between aides, their ministers, and officials in their departments. It centralises authority in a way that didn’t happen during the last two years of May’s leadership.

Another aide at the meeting asked Cummings if Johnson was preparing for an election before he takes the UK out of the EU, something the new PM has vowed will happen by Oct. 31. Cummings responded by emphatically ruling out calling an election before Brexit. Some present however speculated that his language left the door open to Johnson being forced into a pre-Brexit election by Parliament.

Cummings told the room that the litmus test for every departmental policy idea should be: “Does it help deliver Brexit?” Extra money would be released by the Treasury should departments request it to help prepare for a no-deal Brexit. Aides were left in no doubt that they, like their ministers, were required to personally commit to leaving the EU by Oct. 31, do or die. It was “a bit of a loyalty test”, one adviser said.

While ministers were fine as “managers”, Cummings continued, it was their SpAds who should be the real driving force behind everything the government does. The message was translated by one aide afterwards: “We can’t wank around on three times the average wage spending all afternoon in the Red Lion,” referring to the pub opposite Downing Street which was well-known to May-era advisers.

One of the most crucial developments behind the scenes in the first days of Johnson’s premiership has been the embryonic relationship between Cummings and Mark Sedwill, the head of the civil service. They are now two of the three most powerful people in the country, along with the PM.

Cummings is a follower of the American military strategist John Boyd, a US Air Force pilot, whose theories feature regularly on the personal blog run by Johnson’s new top aide. Cummings has described Boyd as “a brilliant guy, a modern-day Sun Tzu”, and referred to his strategies when giving instructions to Vote Leave officials during the referendum. Former Gordon Brown adviser Damian McBride noted this week that Boyd’s central thesis was that you should confuse your enemy by doing the opposite of what they expect.

As someone whose fundamental declared political objective over the last decade has been to revolutionise the civil service, radically reform how Whitehall is run, and declare all-out war on its mandarins, Cummings would be not be expected to see Sedwill, the UK's most senior civil servant, as an ally.

But the two men have got on “surprisingly well” this week, according to those present in their first meetings together. Sedwill has convinced Cummings that he “wants to get on board” with the government’s principal objective of leaving the EU by Oct. 31, with or without a deal.

Those who know them talk of their similarities: a visceral loathing of leakers and anyone disloyal to the cause, a desire to bend the civil service to their own will. “We now have the most ruthless cabinet secretary and the most ruthless chief of staff that we’ve had in years,” said one departmental aide. “If they can work together, everyone else is fucked.”

Sedwill’s pragmatism — inspired in part by a desire to keep his job — has seen him become “serious” about preparing for no deal. “He is the first senior civil servant who has shown a willingness to properly prepare,” said the aide. “He is trying to be as conciliatory as he can,” a second Whitehall adviser agreed.

This new approach is all the more surprising as just four months ago, under a leader with a very different view on the importance of getting a deal with the EU, a 14-page note written by Sedwill warning about the dire consequences of a no-deal outcome was leaked to the press.

A honeymoon period after a new PM enters Downing Street is not uncommon, and it is perhaps unsurprising that Sedwill has chosen not to rock the boat yet. Some in Whitehall express doubts that Sedwill will feasibly be able to keep up his apparent conversion to the Brexit project. Others feel it is inevitable that these two huge egos will eventually clash and the fallout will be potentially devastating.

For the meantime, it seems Sedwill knows which side his bread is buttered. After Cummings’ first SpAd meeting last night, Number 10 advisers reminded their colleagues of a joke David Cameron used to tell ministerial aides back when he was in Downing Street. “How’s the boss getting on?” the then-PM would ask. The SpAd would typically reply with an update on their minister’s work, before Cameron interrupted: “Remember, I’m the boss." It’s Johnson and Cummings who are now in charge.