It would be wrong to say the Tory party is split over Brexit, since that implies a discernible line separating two portions of opinion. The reality is beginning to look more like a window pane into which a brick has been hurled but which has not yet shattered: a few large structural flaws from which multiple fissures extend in different directions.

One new crack was exposed by Philip Hammond’s speech in Davos yesterday. The chancellor’s words should not have been all that controversial. He observed that Britain wants to stay closely aligned to the EU in the immediate future – and that the material difference in regulation either side of formal Brexit day would be “modest”.

This was simply an expression of government policy. The prime minister has committed to negotiate transitional arrangements that will look a lot like continued EU membership (but with the added indignity of losing seats a all the top tables).

So unremarkable was the technical aspect of what the chancellor said that No 10 did not, at first, think to disown it.

So unremarkable was the technical aspect of what the chancellor said that Downing Street did not, at first, think to disown it. Only when hardline Brexiters in Westminster got wind of the modesty clause and the signs of incipient tantrum emerged did No 10 switch to self-defence and cut Hammond loose.

And so it has come to be known that May has “slapped down” another minister. It was Boris Johnson on Tuesday, for making disloyal demands on NHS funding. Now it is Hammond’s turn. Fair’s fair. One slap for a Brexiter, one for a remainer, one for each cheek of a cheeky cabinet.

Except the two cases are not the same. Johnson was off piste miles away from his Foreign Office brief in pursuit of his own ambition. Hammond was doing his job, reassuring an international audience of business leaders and fellow European politicians that the UK has not completely lost its mind; that the government recognises the need to prioritise continuity over drastic severance from EU markets.

Crucially, the chancellor also understands an essential dynamic of trust underpinning Brexit negotiations. The rest of the EU is worried that Britain wants to undercut its former partners with an aggressive programme of deregulation. (They think this because many Tory MPs over many years have said that is exactly what they want to do ,and fashioned their anti-Brussels rhetoric with exactly that goal in mind). But the UK also wants good, nay immaculate, access to the single market. This will not be granted if it is thought that the plan is to sell in without obeying the rules. No chance.

So Hammond was offering double reassurance: to business – continuity of market access, and to EU politicians – continuity with the spirit of their enterprise.

But of course, that is why the hard Brexiters hate the chancellor and all his works. They knew this is how he felt, and the smarter among them must have known, by observing the prime minister’s actions in recent months, that Brexit was heading in this direction. What appears to have upset them is that the chancellor said it out loud. He made explicit something that had been implicit since the moment May signed up to the idea of a transition much like the status quo. He pushed on one side of the splintered glass and made the whole thing wobble.

The underlying problem here is that May does not have the courage or political capital to back her chancellor. She is also inclined to be annoyed by his capacity to speak freely even if what he says is government policy. So the rebuke is not fake. But it is pointless. Away from the public glare May has conceded essential premises of the soft Brexiters – that to walk away without a deal would be ruinous insanity, that there is not time between now and next March to complete a comprehensive free trade deal with the EU and so the process will have to be done in fiddly increments. Those are not ideological choices that the prime minister has made; they are obligations imposed by economic reality and the ticking clock.

But May is still shy of spelling that out in terms that risk animating the revolutionary passions – and even regicidal tendencies – of some of her backbenchers.

The newest and perhaps most fissile crack that has appeared in the Tory party is not between leavers and remainers but between those who have engaged with the practical reality of the task in hand and are taking responsibility for delivering a safe Brexit, and those who want no responsibility for the outcome and wish to continue revelling in wounded rhetorical excursions and exhortations to bolder emancipation from the Brussels yoke. It is between the grownups and the Wild Bunch.

The prime minister cannot continue for much longer to apply sticky tape to these cracks, which in any case stay all too visible. In private she has chosen reality over fantasy, but in public she will not back the realists over the fantasists for fear that the pane shatters. But like any broken sheet of glass, this arrangement is transparent, extremely brittle and potentially very dangerous.

• Rafael Behr is a Guardian columnist