IT has been branded everything from "dead cat" designed to distract from partygate, to a gamble which "robs us of the most fundamental means of controlling the spread of this virus".

The surprise announcement by Boris Johnson that self-isolation as a legal imperative is likely to be abolished in England by the end of February blindsided scientists - including the UK Government's own Scientific Advisory Group on Emergencies (Sage) who had made no such recommendation, nor been consulted on the move.

"It will be an experiment which will either be shown to be very brave or very stupid, but nobody knows for sure what the result will be," said Dr Simon Clarke, an expert in cellular microbiology at Reading University.

Currently one in every 19 people in England are estimated to be infected, compared to one in 25 in Scotland.

READ MORE: Chief Medical Officer apologises over impartiality breach 

John Edmunds, a Sage member and London-based professor of epidemiology said keeping infectious people to stay at home had been crucial to stopping the virus transmitting between households, adding: "Taking it away is likely to have some impact, it's very difficult to say exactly how much but it's likely to have some impact."

The question is how much of an impact - and should Scotland follow suit?

"There's a reasonable chance it may actually be fine. It's not a reckless gamble - but it is a gamble," said Professor Rowland Kao, chair of veterinary epidemiology and data science at Edinburgh University.

"Isolation is probably the single most important thing that we do to reduce onward transmission.

"Vaccination is definitely more important for reducing serious illness, but it may be that self-isolation is at least in the same order of magnitude, so it's certainly a big step."

The Herald: Professor Rowland KaoProfessor Rowland Kao

Yet previous gambles - England's 'Freedom Day' at the peak of the Delta wave in July last year, and the refusal to impose measures beyond 'Plan B' masks, vaccine passports, and home working as Omicron took off in December - did not result in the worst-case scenarios forecast by modellers.

"It might be okay because vaccine boosters have been so good, and the level of natural immunity now is so high because so many people have been infected with Omicron in a short time," said Prof Kao, who is also a member of the Scientific Pandemic Influenza Group on Modelling (SPI-M) which advises the Department of Health.

"These may be the most important things, and if that's true it'll be okay."

The Herald: Positive cases, by PCR and self-reported LFD, have plateaued at a high level since mid-JanuaryPositive cases, by PCR and self-reported LFD, have plateaued at a high level since mid-January

The Herald: ICU admissions are on a par with July levels ICU admissions are on a par with July levels

For now, the Scottish Government has no plans to dump quarantine, but the weeks ahead could see Scotland and England diverge further than ever before on pandemic measures with the number of Covid testing centres operating in England also expected to be wound down from Spring alongside a rationing of free lateral flow tests to key workers, the immunosuppressed, and higher-risk settings such as hospitals, schools and care homes.

READ MORE: The challenge of ending self-isolation two years on from Covid 

The Scottish Government is due to unveil its 'Strategic Framework' for the longer-term management of Covid on February 22, with the UK Government's own revised strategy following two days later on February 24.

Jillian Evans, head of health intelligence at NHS Grampian, said it was "far too soon" to be lifting legal requirements to self-isolate.

She said: "Any rise in infections - which are still three times higher than they were a few months ago - displaces other healthcare activities, and that has consequences for patients awaiting other treatments.

"You absolutely have to be open to emerging evidence, but hard and fast deadlines ahead of schedule - treating the virus like it's a capital project where you come in under budget and ahead of time - it's not like that.

"What will happen with waning vaccine protection, and waning immunity, which will inevitably occur as we go through the summer months?

"What will happen will high levels of virus circulating in our country and abroad, and the potential for new and more worrisome variants? We are perpetually living with uncertainty."

The Herald: Jillian Evans, NHS GrampianJillian Evans, NHS Grampian

Although the Prime Minister has stressed that a legal duty will be replaced by "personal responsibility" - meaning that people infected with Covid will be advised to stay home - many clinicians and public health experts fear that employers will be increasingly reluctant to tolerate staff taking sick leave for mild or even asymptomatic illness.

There are also questions of how Covid cases will be detected and distinguished from other respiratory viruses if testing capacity is scaled back.

"Healthcare has a lot of low paid staff who really would benefit from having the security of legally binding requirements to self-isolation during an infectious period rather than being the hero and coming into work when you could be spreading the virus," said Ms Evans, adding that she hoped the pandemic experience of mask-wearing and staying home while unwell would be adopted more widely in future to curb other infections, such as flu.

One of the reasons why it is difficult to gauge the impact of lifting compulsory self-isolation at this stage, however, is because it is impossible to be sure how rigorously it was ever enforced.

In England, only 163 fines had been issued by December last year for breaches of self-isolation, and UK surveys have put self-reported compliance at anything from 18 per cent to 89%.

READ MORE: Scotland 'through the worst' of Omicron wave 

There is also the harm-to-benefit analysis: in other words, do infections still do enough harm to justify requiring infected people quarantine at home for at least seven days - and up to 10?

In Scotland, confirmed Covid cases have been hovering around 6000-8000 per day since mid-January but the number in intensive care - 19 - is back at July levels. At the same time, around 2% of NHS Scotland's workforce - 3,500 people - are off due to Covid.

The Herald: NHS Covid staff absences have halved from the January peak, but Covid-related absences still make up nearly half of all NHS absences from workNHS Covid staff absences have halved from the January peak, but Covid-related absences still make up nearly half of all NHS absences from work

Prof Kao cautioned it is unlikely healthcare settings could afford to "take a more easygoing approach" to isolation given the risk to patients, but stressed that other workplaces may provide ideal breeding grounds for transmission given that daily contacts still remain around half what they were last summer - and even further below pre-pandemic levels - with most of that difference coming from a reduction to in-work contacts.

He added: "That gives you an idea of the extent to which transmission risks could increase - by a factor of two. That's enough to send things in the other direction.

"[Ending self-isolation] is clearly not a 'phased return'. It's a jump into the deep end and 'let's see what happens'."