Nicola Sturgeon took a cautious tone during her daily coronavirus briefing on Wednesday, warning Scots not to take the allowance of three households to mix over Christmas as permission to do as much as possible.
Instead, the First Minister said she viewed the relaxation as “reflecting the reality” of lockdown and that not doing so could have led to more people breaking the rules.
Labelling the rules “boundaries” rather than a target, she said she was clear people should not travel and mix households if they do not have to.
However, when pressed on the scientific evidence for the decision, it was unclear whether modelling analysis had been undertaken by the Scottish Government to examine the potential risk of a Christmas relaxation.
Ms Sturgeon said: “We look at all different possibilities and we will consider what we can try to do to give people a greater sense of why we are urging so much caution
"If there was some big scary model that I could put in front of people to try to make it more likely they will follow that advice, I would not be deliberately hiding it from you.
"But there is a lot of real uncertainties and imponderables around trying to do that.”
Professor Jason Leitch, the national clinical director, echoed the First Minister and said modelling such a policy “gets really difficult, really really quickly”.
He said: "Modelling something as complex as whole population movement across four countries when you are basically saying don’t do it unless you have to, that gets quite tricky for the modellers, as does some of the data as we haven’t ever done that.
"We also don’t know what we are going to do yet on December 11 precisely. We don’t know what the rates will be in each local authority, we don’t know what England is going to do specifically with its tier system.
"We do know that if houses mix, risk goes up. If houses mix, we will almost certainly see a rise in prevalence. We want that to be as low as it possibly can and we particularly want to protect those most at risk to the virus.”
Ms Sturgeon’s comments came as the Scottish Greens health spokesperson Alison Johnstone said it was “worrying” high-profile advisers such as Prof Devi Sridhar – chair of global public health in Edinburgh – had concerns around the policy and called for “risk assessments” to be released by the Scottish Government.
Prof Sridhar had said it was “inevitable” more cases would arise due to the relaxation and would “probably” lead to a January lockdown.
Ms Johnstone said: “It is very worrying that advisors to both governments have such concerns about relaxing the restrictions over Christmas.
“This is obviously a balancing act, but we need to see the evidence. In order to make this decision, the First Minister must have been appraised of the likely increase in infections. Parliament and the people of Scotland deserve to know how many extra infections the Scottish Government is comfortable with.”