In this parliament the government’s mandate is to do Brexit. We’ll see what Boris Johnson does and what that amounts to, in terms of the UK’s relationship with the EU. But the more important Union has always been our own. So will this government face a decisive showdown with Scottish nationalism too?

The SNP and their Green allies could well win an overall majority at the next Holyrood elections in 2021. Not even the strange case of the vanished Salmond is likely to blow them off course. The separatists will therefore most likely claim a local mandate too. Should that happen, is the wider unionist alliance – which Johnson will have to head, just as much as David Cameron was ultimately obliged to in 2014 with IndyRef – intellectually and materially equipped for the fight?

The government’s current blanket refusal of a second referendum is hardly indefensible. Quite the reverse: Alister Jack is surely right to point out that the 2014 referendum was billed as a “once-in-a-generation” event and that Nicola Sturgeon’s line about a “material change in circumstances” is the thinnest cover for the SNP doing what the SNP always wanted to do.

In fact, allowing the continual re-litigation of the independence question serves the great Nationalist goal of underming the Union’s core financial functions. It is much harder to justify pooling and sharing resources with, strategic investment in, or fiscal transfers to a part of the country which reserves the right to walk away at a moment’s notice, and a UK which comes to be understood on merely a cash basis will not be long tolerated by those ‘paying in’. Cultivating, or indeed, creating nationalist resentment in England is one of the SNP’s key strategic aims.

But whether the Prime Minister wants to hold the line on once in a lifetime or to pivot and give battle at a later date, he must immediately bend himself to the task of winning the intellectual leadership of unionism from those who have, for the past two decades and more, insisted that the only way forward is endless accommodation of nationalist demands.

Ever since devolution failed to fulfil the initial promises to “kill nationalism stone dead”, the whole project has been wrought into an essentially un-falsifiable doctrine

If Johnson doesn’t, there is great danger that he might, as Cameron did with ‘The Vow’, revert to their orthodoxy when the going gets tough, and try to buy his way out of the problem with a package of off-the-shelf constitutional concessions which would leave the Union in a more threadbare state than ever before.

Iain Martin, writing recently in The Times, made oblique reference to one such proposal when he spoke of a “cross-party constitutional steering group [which] recommends a federal UK, with the House of Lords becoming a chamber drawn from the nations and regions, to devolve more power.” This turns out to be the Constitution Reform Group (CRG) and their proposal for a ‘New Act of Union’.

Headed by Lord Salisbury, their discussion paper bears the names of arch-devolutionaries such as Peter Hain and David Melding, a Conservative member of the Welsh Assembly, but less well-developed variations on a similar theme have been advanced by Labour figures such as Carwyn Jones, the ex-First Minister of Wales, and Gordon Brown, in calls for constitutional conventions and similar reforms.

What all these proposals have in common is that whilst they are presented as radical – and certainly entail a lot of change – they are rooted firmly in the intellectual orthodoxy which has ruled unionist thinking, through defeat after defeat, for more than two decades. They’re also often advanced by people who have bound their reputations up in the devolution project being proclaimed a unionist success, all evidence to the contrary notwithstanding. We should be sceptical that these people are suddenly right.

Consider that over the past 20 years, ever since devolution failed to fulfil the initial promises to “kill nationalism stone dead”, the whole project has been wrought into an essentially un-falsifiable doctrine. Whenever the next tranche of powers fails to halt the onward march of the nationalists, and fail they always do, it is simply taken as proof that the devolutionaries were even more right than they thought and that a fresh batch of powers had best be devolved post-haste. The result is a nationalist ratchet – with unionists turning the handle.

Several factors combine to exacerbate this trend. At the centre, it suits nobody to acknowledge that maybe devolution hasn’t worked and to shoulder responsibility for the damage it has done and is doing. Beyond mere pride, in practical terms undoing any aspect of the devolution which has already been done would be an awfully big task, and is this the decade for any more of those?

The political pressure on unionists is then to always conveniently pretend that all is going to plan on the road to a ‘new United Kingdom’. This in turn gives unionists very little scope to argue against the concession of yet more powers, when those powers are demanded courtesy of the same nationalist logic which created devolution in the first place and we are obliged to pretend it’s all working as intended.

Meanwhile the process has created in Edinburgh and Cardiff a whole class of politicians, staffers, journalists, academics, and other civic hangers-on who derive salaries, sinecures, and status from the new institutions and whose interests are very well served by the idea that the only way to buy a future for the United Kingdom is to keep paying them this constitutional and fiscal danegeld.

The final result of this is that unionists end up in the impossible position of trying to reject the nationalists’ conclusions whilst accepting their premises, arguing that the UK should exist whilst agreeing with the SNP et al that life would be better if it did less and less. That’s how you end up with even senior Scottish Tories supporting straightforwardly anti-British positions in the recent row over the (badly mislabelled) “post-Brexit devolved powers”.

This is the context in which unionists should assess the promises of ‘federalism’. There is much to be said for it from a non-unionist perspective – it is basically nationalism for the numerate.

But if your goal is a strong and cohesive United Kingdom, a comprehensive accounting for devolution’s failure to deliver, and a clear reason why it will work this time, is the very least you should demand from those pushing what amounts to the old solution in new packaging.

For example, whilst the CRG discussion paper talks promisingly of something like a zero-based approach to the distribution of powers which doesn’t start out trying to justify the existence of existing institutions, this is swiftly followed by a frank and untroubled admission that the devolution process “has been, and was always likely to be, only in the direction of Welsh [and likewise Scottish] self-determination” – ie an ever-more diminished Union.

Any ‘grand redesign’ embarked on in the same spirit will be, from a unionist perspective, entirely unfit for purpose. The prospect shows the real danger of unionists knowing only what they’re against – separation – and thus settling for any outcome which isn’t that, no matter how inadequate.

As for explanations, the CRG – and if I’m picking on them it is only because theirs is the most developed thinking of this sort – claim that the piecemeal nature of devolution has rendered it “an inherently unsatisfying process tending inevitably towards eventual dissolution”.

But alone this reads more as an excuse than a genuine explanation, a rationale for finding more and more radical ways of not changing one’s mind. Whilst it is probably inevitable that both self-interested devocrats and earnest constitutional experts alike will convince themselves that the public are similarly invested in the minutiae of our institutions, the available evidence, from lower turnouts in devolved elections to confusion over what’s already devolved, suggests otherwise.

The current government needs to appreciate that this is not at heart a good-faith dispute about the precise architecture of the United Kingdom. It is a drag-out fight with movements which have invariably turned every arsenal, treasury, and pulpit ceded them by the devolutionaries against the United Kingdom. Nationalists are not trying to make the country work: they have no interest in your settlement: they wish to make a new country of their own. We should believe them in their ambitions and, if we’re unionists, meet them with some of our own.

The case for the country we have rests on the following premises: that Britain is a legitimate level for political decision-making; that we are better off pooling and sharing not only money but wisdom and experience in our united Parliament; and that Her Majesty’s Government is ultimately the government of all of its people, both in every individual home nation, and the one they make together.

This battle is coming: there is a dry wind blowing from the north, as that great unionist John Buchan almost put it. Johnson would be well to be prepared – after all, he knows better than most how swiftly a referendum defeat can topple a Prime Minister.