As I noted earlier this week, the clearest evidence that Boris Johnson was on to something with his remarks about devolution having been a disaster is the response of his critics – especially his Tory critics.

Nowhere to be found were any paeans to devolution actually being a success. Instead, the new devolutionary defence is to claim that the problem isn’t the constitutional settlement itself, but merely the people currently in charge of it. If only the Conservatives could take over the reins then all would be well.

This is what the young people call a ‘cope’, and not just because the odds of the Tories taking office in either Edinburgh or Cardiff are currently very long indeed. It also overlooks the fact that devolution has managed to deliver the same toxic combination of bad governance and diminished Britishness in three very different sets of political distance: the intended hegemony of a ‘unionist’ Labour Party in Wales; the unexpected dominance by separatists in Scotland; and mandatory deadlock in Northern Ireland.

Of course, the Prime Minister has immediately rowed back from his remarks and tried to take the ‘blame the SNP’ line. But one suspects that this is a grenade he won’t be able to un-throw.

An undercurrent of devosceptic sentiment has been bubbling up inside unionism for some time now. Douglas Ross, the Scottish Conservative leader, felt compelled to hit out at colleagues who think devolution has opened a ‘Pandora’s Box’ before Johnson dropped his bombshell. In Wales, where the Tories face a challenge from an explicitly anti-devolution party which looks set to enter the Senedd next year, the issue is fuelling what could become a proper rift between the grassroots and the leadership.

Whilst there hasn’t yet been any proper study of this change in attitudes, two possible drivers suggest themselves.

First, devolution hasn’t ‘worked’ as a pro-UK strategy. There are plenty of people who support it for its own sake, but the whole project was sold to sceptical unionists on the promise that it would “kill nationalism stone dead”. It obviously didn’t, and every subsequent one-more-heave concession of powers has sapped the credibility of devolutionary unionism as the separatists have got stronger and stronger.

Second, more unionists are waking up to the fact that there is more to their beliefs than merely the continued existence of anything calling itself ‘the UK’. They are unenthused, to put it mildly, at the prospect of going into another referendum defending a ‘radical’ or ‘federalist’ blueprint which turns the country into a ramshackle confederation, squeezing out what remains of the British political community in favour of horse trading between the Home Nations.

The pro-devolution consensus on the pro-UK side is broad, but fragile. It is to a great extent the product of preference falsification, wherein people with a dissident view pretend not to hold it and thus reinforce the illusion that they’re on their own (a good explanation of the dynamic is in this piece). Few of the activists and none of the politicians who have ever agreed in private with the arguments I’ve advanced in this column over the years (and there are enough) have aired such views in public. Enduring anti-devolution sentiment amongst the electorate is actually pretty remarkable when one considers that for the most part this attitude has been unrepresented in politics, think-tanks, or the media since the 1990s.

Which is why I said that the Prime Minister has just “has broken a spell more than two decades in the weaving”. Retracted or not, his comments will embolden people who share his view. And if they start speaking out, they will realise that they are less alone than they supposed. They may even think that if they organise, and start actually making the devosceptic case, it isn’t impossible that it might have an impact on public opinion (the same way pro-independence campaigning does).

All of this will horrify those drawing up plans to fight an imminent re-run of the 2014 referendum, and rightly so. It is quite possible to be very unhelpfully right, and if winning a vote in the near future requires selling the promise of a pseudo-federal dreamland then the very last thing needed is Johnson absent-mindedly prescribing constitutional red pills.

But if that is what it takes to win a near-future referendum, that is simply strong grounds for not holding one. It is all very well for the Prime Minister to have set up a new ‘Union task force’ to make the “social and cultural case for the UK”, but he must recognise that such policies will need the generational breathing-space unionism won in 2014 to have time to work. The case for the Union rests on utility and identity. Neither can be fixed overnight.