Boris Johnson last week declared there was no border between Scotland and England. 

His ally Jacob Rees-Mogg backed him up, saying the UK was “one country” and appearing to suggest Scotland was an “area” or a “district”. 

A Scottish Tory MP announced that Scottish, English, Welsh and Northern Irish formed “one nation”.

This is big, reckons Michael Keating, professor of politics at the University of Aberdeen. 

That is because the rhetoric of pro-UK politicians is changing. And dramatically so.

Some are abandoning the old complexities of mainstream unionism, of Britain as a “family of nations”, of a plurinational state, of a country made up of countries.

In its place comes a new and sometimes shrill insistence that the UK is a unitary nation-state.

“This is not unionism,” Mr Keating said. “It is British nationalism.”

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Mr Keating is one of the greatest scholars of British unionism. And he thinks his subject has changed so much it might need a new name. 

He is currently dotting the i’s and crossing the t’s on a new book, Fractured Union, to be published by Oxford University Press next spring. 

In it, he talks of “neo-unionists”.

Mr Keating described border rhetoric as “just confusion and hot air”. 

But he added: “Lying behind this is a question about the nature of unionism. Why are Tory MPs trying to say these things about the border? 

“We have this strident rhetoric where anything that looks like a border is a violation of their conception of union.

“My argument is that the Union is in a bad way. There used to be an understanding of what the UK was. 

“Even in the days when some were resisting devolution, there was this idea that there was a union of nations, not a unitary state. 

“So the nations were differentiated in lots of different ways.

“In a nation-state, you have a demos, a people; a telos, which is a shared purpose; an ethos, shared values; and a principle of sovereignty.  And these things are all in the same place. 

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“The UK was never like that.”

Since devolution for Scotland, Wales and Northern Ireland, unionists, said Mr Keating, have struggled to define the Union. 

Devolution has dented centralised sovereignty in Westminster – even as Brexiters seek to repatriate powers from Brussels. 

And – as the Covid crisis has underlined – it has led to policy divergence across the UK that makes some of the new breed of unionists uncomfortable.

Mr Keating summed up: “On the one hand this group of unionists are doubling down on parliamentary sovereignty and on the other hand they are pushing a Britishness. 

“What they are saying, in my language, is that the UK has a demos, the British people; a telos, that we agree on what the constitution is; an ethos, what they call British values; and a principle of sovereignty.

"So unionism, which was never a nationalism, has become a nationalism.”

This, for Keating, presents a problem. 

The UK used to allow huge flexibility in identity, something the helped deliver the Good Friday Peace Agreement or the Welsh and Scottish devolved parliaments.

“It was never required for us all to sign up to all these bits of Britishness,” he explained. 

“That was the genius of the UK in the past. Mainstream unionism has always accepted differences.”

Authorities across the UK have followed broadly similar policies on tackling Covid. 

However, even minor differences in practice and policy have been highlighted by unionist politicians across all four nations as decentralisation became more politically salient than ever before.

Mr Keating said: “This is indication of a confusion in unionist circles about what should be uniform and what should not. 

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“Covid has raised all of this. The initial response was ‘let’s all go together’ and then there was differentiation. 

“The SNP and Welsh Labour have grabbed leadership, the policies may not be radically different but they have certainly taken ownership of these policies. 

“That is how devolution works.”

Some of neo-unionists – to use Keating’s term – have not been happy. 

Last month, Herald on Sunday reported on the new breed of devo-sceptics, including those who believe Holyrood, the Senedd and Stormont should close.

But Mr Keating stresses not all neo-unionists want to shut devolved parliaments; they just do not want them to do anything different.