Boris Johnson has lambasted Nicola Sturgeon over her "absolutely astonishing and shameful" warning she will consider introducing quarantine for English visitors to Scotland if there is a surge in cases south of the Border.
The Prime Minister told the Commons that there had been "no discussions" with the Scottish Government on the matter and questioned if it was even possible.
He said there was "no such thing as a border between England and Scotland." His official spokesman later clarified that he was making the point there was no "border infrastructure."
His criticism echoed an earlier attack by Alister Jack, the Scottish Secretary, who said Ms Sturgeon had "encouraged reckless talk" with her "divisive" quarantine idea.
Mr Jack warned her language undermined "joint efforts" between the UK and Scottish governments to tackle the coronavirus and was "especially bad for the tourism business."
Public health, not politics, must drive decisions on COVID. I’m sure the Governor of New York (below) isn’t being political in imposing quarantine on people from higher transmission US states - he’s acting to protect the people he serves from a deadly virus. https://t.co/eH2iSWoBLy— Nicola Sturgeon (@NicolaSturgeon) July 1, 2020
It emerged that a small cross-border cluster of coronavirus infections has been detected in the south-west of Scotland and north-west of England that health officials are working together on tackling.
The Scottish Tourism Alliance (STA) disclosed on Tuesday that English holidaymakers have already started enquiring about full refunds for their Scottish 'staycations' if Ms Sturgeon forces them to enter quarantine.
Marc Crothall, the STA chief executive, warned that more than 70 per cent of the country's influx of visitors comes from the rest of the UK and "any restrictions on domestic travel will have a significantly negative impact.
But Ms Sturgeon lashed out at the Prime Minister's "absurd and ridiculous political comments" and accused him and Mr Jack of attempting to turn the issue into a constitutional row.
Although she said she had "no plans at the moment" to introduce quarantine for visitors from England, the First Minister insisted she would be "failing in my duty not to consider that" if necessary to "protect people in Scotland."
In a lengthy diatribe at her daily briefing, she attacked Mr Johnson's "absurd" insistence there was no border and asked "what he would say if I pitched up in Newcastle and started to try to implement Scottish Government policies."
She argued the fact that US, Australian and German states introducing quarantine for other parts of their countries showed it could work, but failed to provide any detail, including whether border checks would be required.
Ms Sturgeon also criticised three newspapers, including the Telegraph, which led their Scottish editions on Wednesday with the STA's warnings of cancelled bookings from English customers.
Annie Wells, the Scottish Tory deputy leader, said: "This was an extraordinary on-air meltdown from the First Minister that Donald Trump would have been proud of.
“It was her party who floated the idea of quarantining English travellers, and her refusal to rule it out is making things worse."
The First Minister doubled down again on her quarantine warning on Monday, when she said "I'm not ruling anything out" if there is a surge of Covid-19 cases south of the Border.
While she said her strategy was to eliminate the virus, Ms Sturgeon said she suspected Boris Johnson's was to let it "circulate at higher levels as long as it doesn't threaten to overwhelm the National Health Service."
However, the Office for National Statistics disclosed this week that the number of deaths registered in England and Wales over one week has fallen below the five-year average for the first time since lockdown was imposed in March.
Mr Jack told the Commons: "This talk of quarantining people from other parts of the United Kingdom is disappointing and divisive."
He said she had previously admitted to the BBC's Andrew Marr that she has "no control over" the border and urged her to "not undermine Scottish business by talking about keeping people from other parts of the United Kingdom out of Scotland."
However, Ms Sturgeon insisted her sole motivation was "trying to stop this virus getting out of control" and argued that senior Tories "trying to turn any of this into a political or a constitutional argument" should "go and take a long hard look at yourself in a mirror."
She added: "This is public health, and the fact that in Scotland we are trying to turn it into – and I'm saying 'we' to be charitable, because it isnae me – a kind of standard political constitutional row is frankly disgraceful."
Ms Sturgeon said there would be "a lot of practical considerations" into how quarantine would work but argued there are also between US and Australian states, where the system operates, and in the Leicester lockdown.
Insisting she makes such decisions on a "daily basis right now", she said she would set out the "practical measures" and "enforcement mechanisms" if she pressed ahead with quarantine.
Kate Nicholls, chief executive of trade group UKHospitality, said: "Tourism and hospitality businesses are going to be key to the recovery of Scotland’s economy. If the quarantine period is a long one, businesses will certainly feel it.
"Any restrictions need to be proportionate and science-led with information on what criteria needs to be fulfilled for any quarantine to be lifted.”