WHEN is a border not a border? When a Tory Prime Minister turns a blind eye.

Boris Johnson's remark last week that there “is no border between Scotland and England” was intentionally provocative as well as geographically illiterate. The PM saw what he thought was an opportunity to present Nicola Sturgeon as divisive and narrow-minded by failing to rule out quarantining of English people travelling north.

The Tory leader of the House, Jacob Rees Mogg, went the full Donald Trump and accused her of wanting to “build a wall” – metaphorically at least between the two nations of the Union. How dare the separatists exploit a pandemic to further their secessionist ambitions.

The SNP were, of course, over the moon at this scion of privilege disparaging Scotland's nationhood. There is nothing Scottish nationalists like better than English Conservative politicians suggesting that Scotland is really part of England, or speculating about walls.

There already is a wall of course – indeed a couple. Quite a bit of Hadrian's Wall, one of the greatest feats of Roman engineering, still exists so perhaps a team of covid conservationists could be enlisted to build it back up again. A lot of construction workers have little to do right now.

But to be serious, throughout this pandemic many naïve souls have been insisting, as the editor of the Lancet, Richard Horton, recently put it, that covid has demonstrated how "irrelevant borders are in the covid age" and how globalisation has been “vindicated" by the need for international cooperation. We are all one in the good fight.

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I have argued that precisely the reverse is true. Borders are back across the planet as nations rediscover the reason for having them in the first place: security. Nation states used to be all about military and geo-political security; right now it is more of a public health matter. But the root is the same: people look to their own government's to keep them safe.

The countries that have been successful in combating coronavirus – in this first phase at least – have been those countries like New Zealand and Vietnam with hard lockdowns and quarantines. Indeed both countries closed their borders immediately cases of Covid-19 appeared. The UK didn't introduce border controls until the end of May, which was clearly a big mistake as it allowed many people to arrive virtually unchecked from countries like Italy. Some 18 million entered the UK from around the world before lockdown on March 23.

Keeping the disease out is the cornerstone of the “elimination” strategy pursued by those countries and advocated by Nicola Sturgeon's key scientific adviser Professor Devi Sridhar of Edinburgh University. It is what makes track, trace and isolate possible because – ideally – it keeps the number of infections low enough for them to be identified and stamped out.

Ms Sridhar says elimination should be Scotland's policy. She ignited last week's border warfare, perhaps inadvertently, when she announced on BBC's Politics Scotland on Sunday that “if only Scotland were an island” then it could kill off the disease this summer. She went on to criticise England's lockdown relaxation measures as premature.

Next day's splash in The National read: “English Border Biggest Risk to Beating Virus” citing Professor Sridhar's remarks about free movement. Then all hell broke loose.

The Scottish Tourism Alliance claimed that English holiday-makers were demanding refunds because they didn't want to run the risk of having to go into quarantine. Challenged on this at her daily press briefing Nicola Sturgeon said she “could not guarantee that we will have no need to impose any kind of restrictions to keep this virus under control”.

READ MORE: Jacob Rees-Mogg claims Nicola Sturgeon wants to 'build a wall like Trump' in Scottish border row

For this she was accused, by the Scottish Secretary, Alister Jack, of “reckless talk...divisive language”. She responded on Twitter – increasingly the First Minister's medium of choice – by accusing Mr Jack of turning a “public health battle into a political/constitutional argument”. Cue Boris Johnson denying that any border exists.

I suspect the reason why this border tension has erupted now is that it is in both governments' interests to stoke it. Ms Sturgeon has been trying to distance herself from the UK Government's handling of the covid crisis, which has in many cases been confused and incompetent. It is convenient to allow a touch of border friction, if only to underline her claim that Scotland has handled the pandemic better than the UK Government.

There is not a great deal of substance to this, since the Scottish and British governments have followed almost identical policies since lockdown and have both had amongst the highest death rates in the world, even if Scotland's is marginally less than the UK's.

The First Minister has carefully choreographed the lifting of lockdown to convey the impression that the Scottish Government is taking a safer line than England, for example over the delayed relaxation of the 2-metre rule in Scotland. It's been pretty successful if the First Minister's high approval ratings are any guide.

All of which is creating impotent rage in Unionist circles and in Westminster. With elections next year, there is a real chance the SNP could, on the back of Covid-19, win another landslide. That would make demands for another referendum extremely difficult to ignore. Hence the claim that Ms Sturgeon is exploiting the health emergency to separatist ends.

But it has to be said that the Tory prosecution of the border war has been almost as incoherent and counter productive as its approach to the pandemic. Allowing provocative figures like Jacob Rees Mogg free reign to speculate about border walls, and for the Prime Minister of the UK to defy constitutional reality only plays in the SNP's hands.

This weekend, the row has turned to air bridges. Nicola Sturgeon has attacked the UK Government's plan to reopen tourism from selected counties s “shambolic”, which is probably right. However, she is also making clear that Scotland will follow suit shortly. Tourism depends on it.

I very much doubt if Scotland will actually introduce quarantine of English tourists. The First Minister isn't that stupid. There is really no conceivable way of blocking the border legally, though in theory there could be testing stations at airports and near Gretna.

READ MORE: Boris Johnson: 'No such thing as a border between England and Scotland'

Anyway, it isn't the way pandemic spikes happen. Currently there is a spike in Dumfries and Galloway which has led to a local lockdown, not the introduction of a hard border on the M74. Everyone agrees that this whole argument about border control is a diversion from the real task – which is to instal a Korean-style testing regime.

And with all this talk of borders, it is perhaps worth remembering that the various walls, real and imaginary, built over the centuries were generally designed to keep Scots out of England rather than keep the English out of Scotland.

Had the situation been different, and England had less covid than Scotland, I imagine Nicola Sturgeon would have been the first to object to any suggestion of closing the border or quarantining Scots. It might even have been dubbed a form of epidemiological ethnic cleansing.

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