The lands, they said, were “debatable”, neither England nor Scotland, neither here nor there.

For fully three centuries local strongmen, reivers they were called, ruled the baronies of Kirkandrews, Bryntallone and Morton, a slice of no-man’s territory, ten miles by four, between the rivers Esk, Liddel and Sark. Then - way, way back in 1552, after talks brokered by a French envoy between London and Edinburgh - a deal to end border conflict was done: a line was drawn on a map; it is still there today So too are the earthworks and some of the stones which marked what became the final stretch agreed of one of the world’s oldest and least disputed frontiers.

Scots’ Dike, the English called the line. The lands it divided may have once been debatable. But the border itself was not. Until now.

That is because Scotland is again suffering border skirmishes. Rhetorical ones. They broke out early in the corona crisis as frontiers - village, local, regional and international - shut around the world to slow down the movement of the bug.

Some unionist politicians declared any such move on the Scots’ Dike and the rest of the ancient frontier from the Tweed to the Solway to be unthinkable. They did so even as nobody - in England or Scotland - was actually thinking about such a move. Eventually, First Minister Nicola Sturgeon declined to rule out quarantine for people crossing the border if England’s Covid infection rate remained, as it it now, much higher than Scotland’s.

READ MORE: Opinion: Iain Macwhirter: Does Nicola Sturgeon still want independence? Some in the SNP aren't so sure 

Some Tories smelled blood. Prime Minister Boris Johnson declared there was no border. Later his ally Jacob Rees-Mogg added that the UK was “one country” and appeared to suggest Scotland was an “area” or a “district” rather than a nation. Finally, last week, Moray’s Tory MP, Douglas Ross, said that frontier checks at Gretna or Berwick were “reckless” but those between Australia’s federal states were not. The legal facts: there is definitely a jurisdictional border between Scotland and England and the Scottish Government, like sub-state administrations around the world, definitely has the power to use this border to impose public health measures.

The political reality: border restrictions could be explosive.

For Michael Keating, professor of politics at the University of Aberdeen, Johnson’s no border’ rhetoric sounded like the abandoning of the old complexities of mainstream unionism, of Britain as a “family of nations”, of a country made up of countries, of a pluri-national state where people of different identities or none could feel at home.

“This is not unionism,” Keating told The Herald last week. “It is British nationalism.”

The change in political language around the frontier is big. It is big for political theorists, who say it suggests a whole new concept of the United Kingdom, of devolution, and of the union. But it is big too for political practitioners, who say it gives early warning about new tactics for those who want to keep Scotland in Britain.

Ailsa Henderson was struck by quite how visceral rhetoric on border restrictions had become. “What has puzzled me is just how anathema it seems to certain people in the UK," said the professor of political science at the University of Edinburgh. Henderson has spent much of her career comparing and contrasting the sub-state politics of Canada and the UK, of Quebec and Scotland.

In Canada, Nova Scotia put up border controls. In the UK, old Scotia did not - but was also told, in no uncertain terms, that it must not.

For Henderson, sub-state border controls are a “normal thing” to contain a virus.

“The Ontario-Quebec border has been closed temporarily from time to time,’ she explained. “But this has not been seen as nationalism on the part of the Quebec government, just a recognition that the infection rates in Ontario were very high.”

Her take? Britain may have long seen itself as a pluri-national state, as described by Keating. But it is still getting used to itself as a multi-level one where significant power is decentralised. Covid has made devolution more salient than ever before. And not everybody likes the look of that.

She said: “Under lockdown, as a result of a pandemic, we have seem some frustration with the existence of the multi-level state. And this is starting to turn in to a dialogue about how we are not actually a multi-national state, that we are actually mono-national state, a uni-national state. That is a real change.”

It is not that unionists are all opposed to the Scottish Parliament. The new muscular unionists do have what is called a devosceptic wing. But many are happy to tolerate Holyrood, just as long as it does not do anything.

“We call this the devolution paradox,” said Henderson.

Is the new borders rhetoric a symptom of a crisis in unionism? “Yes, there is a crisis,” said Henderson. “But I don’t think the crisis is new.

It has been there for a while. There was never an institutional or cultural adjustment to devolution across the UK.”

Opinion polls have been moving. Last week Yes once again hit 54% but several recent surveys have independence edging union, though by little more than the margin of error. Is this forcing unionists to up the ante? Henderson said some Scots may feel freer to express Yes sentiments when there is little immediate chance of these views being tested in the ballot box.

READ MORE: How British nationalism is taking the place of traditional unionism

“There is no referendum on the horizon so you could see this rise in Yes as much as an expression of frustration as much as a meaningful intention to vote. Saying Yes three years out is very different to saying Yes one month out.

“It is certainly measuring an undercurrent of satisfaction.”

Who is border rhetoric aimed at? An ultra-unionist base in Scotland? Or Brexit England? “I don’t know but I think it’s ill-judged in both directions,” Henderson said. “It is clearly aimed at those who never want to see another referendum in their lifetime. But that proportion of the electorate is so small that the messaging from both of the two GB-wide parties seems to be overblown.

“It also misreads English sentiment. In England “Everything must stay as it is’ is a minority position. The English are not a straightforwardly unionist electorate.”

Are people who talk of there being ‘no borders’ unionists? “Technically you would not necessarily say they were unionists because they deny the existence of a union with constituent parts,” said Henderson. “So we have a kind of Spanish interpretation of what the state is like.” For Spain, read a polity that refuses to admit to itself that it is made up of multiple nations.

Academics are struggling to find words to describe this new breed of pro-UK thinking. Keating, for a new book, Fractured Union, out next year, has coined the term neo-unionists. Others have suggested anti-plurinationalist, unitarianist and unitary state unionism.

James Mitchell, professor of public policy at the university of Edinburgh, has spotted the change of tone too.

“We have been witnessing a significant change in Conservative unionism under Boris Johnson,” he said. “David Cameron’s ‘respect agenda’ was largely rhetorical but was more pluralistic compared with current Tory leader. Indeed, Johnson’s unionism goes well beyond Margaret Thatcher’s. Mrs Thatcher never understood the multi-national nature of the UK and, as her memoirs made clear, she was irritated by a Scottish Office that pursued different agendas and policies from her own. But she never denied that Scotland was a distinct nation or that there was no border. What we are seeing is the rise of a kind of unitary state unionism that has never previously existed and sits very uneasily with devolution.”

Malcolm Harvey, meanwhile, is sceptical about how the new ‘no borders’ unionism will go down north of Scots’ Dike.

Echoing Henderson, the University of Aberdeen politics lecturer reckoned borders rhetoric sounds Spanish. Unionists in Iberia - despite adopting the British term - see Spain as in undissolvable single nation-state. “In the UK, anti-plurinationalism is more akin to King Canute and the tide. The political reality here is also the constitutional reality - and, crucially, the accepted reality.

“We accept that Scotland, Wales, and England are nations (Northern Ireland is more complex) within the UK state.”

So what is going on? “It may be that recent opinion polls suggesting - albeit slim - majority support for independence have spooked those in favour of the Union into a change of tactic,” Harvey said. “This might include playing down historic acceptance of 'nation' status in order to focus the picture much more on the Union and Britishness. Historically, this hasn't worked that well: Scots increasingly identify as 'exclusively Scottish' or 'more Scottish than British' rather than the opposite.”

For Andy Maciver, borders rhetoric is tactical. “It plays well, actually,” the Herald columnist and former Scottish Conservatives strategist explains. “It is a good issue for the Tories. They will want to talk up future border problems.”

Maciver’s theory? The frontier was not much of an issue at the first indyref. Why? Because both Scotland and the rest of the UK would most likely be in the EU. That is no longer the case. So Conservatives, Maciver reckons, want to drum home the long-term prospect or a hard, or harder border.

“They want to sow the seeds of doubts in the heads of wavering Scots,” he said.

But is a public health crisis the best time to rehearse this tactic? A poll published last week suggested three-quarters of Scots - way beyond the pro-independence base - would accept border restrictions on public health grounds.

“I think reasonable people will accept reasonable arguments,’ said Maciver. “But if there is any hint of politics about it, from the government side, then people will sniff that out.” He added: “I don’t think Nicola Sturgeon would impose restrictions for political reasons because there isn’t anything in it for her politically. We are talking about very moderate pragmatic nationalists here. But do I think there is something in it for the Tories to oppose? Yes I do.”

Maciver, meanwhile, does not agree with Scottish pol-sci community about the new neo-unionism, the new British nationalism. Why? Because he does not think pro-UK have quite got their ideology straight yet. Scottish Tories, he said, are exploring something called “Shared Rule”. This does sometimes infringe on devolution, McIver reckoned, citing No 10’s enthusiasm for a bridge across the Sheuch from Galloway to Ulster which clearly seeks to trump Scottish and Northern Irish transport powers. “What we are talking about is respect for devolution but combined with more UK involvement in Scottish politics,’ he said. “But I am not saying that the Scottish Tories are full of bright shared-rulists who have a great vision for how they are going to save the union. On the contrary, I think there is a dearth of proper thought going on about what a unionist strategy needs.”

Some critics of the SNP have historically accused the party of being obsessed by borders. Others say, nationalists, on the contrary, ignore border problems _ and neglect the Borders region.

The English frontier, after all, is far from the central belt heartlands of modern Sturgeonism. It’s yonder awa, over the Southern Uplands, out of sight and mind.

Marco Biagi has heard all of these criticisms before. A former SNP minister turned political analyst, he has experienced Scottish politics as both a belligerent and an observer.

“I have never really understood the claim the SNP is ‘obsessed with borders’,” he said. “Scottish nationalism is clearly wholly distant from irredentist political movements - no one talks about annexing Carlisle.

“I think that just leaves the word ‘borders’ as a way of making ‘statehood’ or ‘sovereignty’ sound scary." Is the SNP focused on statehood and sovereignty? Well, yes.”

How will the SNP feel about border rhetoric?

“For years 'border checks at Gretna' or 'you'll need a passport to visit your auntie in England' were common attacks by opponents of independence,” Biagi said. “They became very implausible over the years as border posts came down around Europe and even on the UK's one land border with Ireland.”

Brexit changes this, he acknowledged. “There is still a sensitivity around future relations with Europe,” Biagi explained. “What would happen on the Scotland-England border is a big factor in whether an independent Scotland should go straight back into the EU. The possibility of the old Gretna line coming back into play would not be viewed with relish by SNP strategists.”

Some Scottish nationalists do like the sound of Border controls. A week ago a half dozen or so protestors in paper hazmat suits and saltire face masks gathered at the A1 frontier and made a viral video calling for English holidaymakers to go home. Jackson Carlaw, the Scottish Tory leader politician who first raised Covid border issues, called them an “absolute disgrace”. SNP politicians queued up to condemn the prank.

Back over Scots’ Dike John Stevenson doesn’t think of the word ‘border’ as scary or political. He thinks of it as home.

A Tory and a Scot, Stevenson is the MP for Carlisle. For him the frontier is not so much a line, as a place, a borderland, a community in its own right.

“In many respects there is not a border,” Stevenson said. "Carlisle is the capital of the borderlands region. It might not be the administrative centre but it is the commercial centre.

“People in southwest Scotland look to Carlisle. There is so much to-ing and fro-ing between Scotland and England. So from that perspective, there is no border. Sometimes I think politicians forget how people conduct their lives.

“But from a political, legal and administrative perspective there very much is a border.”

Stevenson calls a future international frontier a “border-border”, and he thinks this would be bad for both Scotland and England.

A border-border, he believes, would throw up all sorts of issues, beyond currently subtle changes, not least if Scotland re-joins the EU.

But what does he think of talk of a newly assertive British nationalism? Well, for Stevenson, people in the Borders, on either side of the dike, are already relaxed about Britishness.

He said: “I think Borderers think of themselves are very much part of the United Kingdom. Geographically we are right in the middle.”

“I am a Scot who has come to England. I have always thought of myself as British. Even when I lived in Scotland. The people of Carlisle, who are predominantly English, did not think anything of voting for a Scot because they too see themselves as British. We are one country.”

Britishness reigns in and around the Debatable Lands. But where else?