Boris Johnson's decision to appoint Dominic Cummings as his most senior adviser in Downing Street raises many questions about the sort of administration he intends to run, one of which is what sort of attitude it will take to the most hardline Brexiteers on the Tory backbenches.

At the outset of the campaign to succeed Theresa May, there appeared to be half a dozen plausible candidates for the affections of the European Research Group’s MPs, and several of them - Esther McVey, Dominic Raab and Andrea Leadsom - staked out harder positions on Brexit than the eventual winner. But in the event, nearly all of them, including the 28 “Spartans” who voted against the withdrawal agreement three times, backed Johnson.

As the contest progressed towards its inevitable conclusion, he appeared to respond in kind. He appointed Iain Duncan Smith as his campaign chairman - in practical terms a meaningless honorific, but a significant gesture nonetheless. Most consequentially, the final week of the campaign saw him go much further on the question of the Irish backstop than many of his supporters had anticipated, and rule out anything but its removal from the withdrawal agreement. That had the effect of making Johnson’s rhetoric on no-deal sound much more like a settled policy than a rhetorical threat to Brussels.

Yet just as it appeared that the most hardline of the ERG would get everything they wanted from a Johnson premiership, along came Cummings - a man who, despite having led the referendum campaign that ultimately delivered Brexit, inspires much more by way of loathing than aspiration among Tory Eurosceptics in the Commons. That feeling, of course, is mutual: Cummings believes that Brexiteer MPs, for all their decades of hard graft, are a drag on their cause electorally. He has described them variously as a “metastasising tumour” in need of excision from the body politic, a "narcissist delusional subset”, and “too busy shooting, skiing or chasing girls to do any work”.

Given that track record of common enmity it is hardly surprising that those same MPs were anxious, alarmed and angered when news of Cummings’ appointment broke on Wednesday, especially as it was not followed by the appointment of the likes of Steve Baker to cabinet posts. That omission, senior Spartans warned ahead of Johnson’s coronation, would be an early sign that their new leader was not taking their concerns seriously.

“Betrayal is the right word,” said one Brexiteer source of hardline colleagues. “They think this means the deal is coming back, basically.” That anxiety has little to do with Cummings the man, his reputation for abrasiveness and his eye for a noxious insult, and is much more a sign of suppressed but fundamental misgivings about Johnson - who, don’t forget, was very nearly challenged for the leadership by Baker, a Brexit fundamentalist.

With the now prime minister having voted for the withdrawal agreement at the third time of asking, they suspect, as much as he insists that deal is now dead, that he will try to bring something similar back for a fourth. That Cummings and Michael Gove have been entrusted with coordinating the government’s preparations for no-deal centrally has only encouraged suspicions that Johnson’s approach to Brexit might have more in common with Theresa May’s than he cares to admit.

It is those suspicions that drove Baker to turn down the job of Brexit minister last night, complaining that the position would leave him powerless. It is the desire to warn Johnson and Cummings off trying that is inspiring the likes of Mark Francois to warn - or threaten - that the most doctrinaire Tory MPs will not vote for anything that looks even remotely like May’s deal, backstop or no backstop.

For the Prime Minister, their words illuminate a painful truth. Like his predecessor, his only path to a majority for any negotiated Brexit is more likely to run through Labour MPs than it is through the likes of Baker and Francois.