Cabinet Office minister Michael Gove will discuss Christmas coronavirus rules with the leaders of the devolved administrations later on Tuesday.
The call with the First Ministers comes amid pressure on governments to reconsider the relaxation of the restrictions amid rising Covid-19 cases.
Leading medical publications the Health Service Journal and the British Medical Journal branded the loosening of restrictions as “rash” and warned people might see it “as permission to drop their guard”.
The rules on household gatherings will be eased for five days between December 23 and 27 to allow up to eight people from three households to “bubble”.
In response to suggestions that the Christmas arrangements could be restricted to three days or two households, Downing Street again said the measures were being kept under “constant review”.
The Prime Minister’s official spokesman said: “We have set out the guidance for the Christmas bubbling arrangements.
“But we obviously keep all advice under constant review.”
In a statement to MSPs on Tuesday afternoon, Nicola Sturgeon urged “the utmost caution” in meeting over Christmas.
The First Minister said: “There will be a four-nations discussion later today to take stock of recent developments.
“But, for now, I would urge the utmost caution.
“If you can avoid mixing with other households over Christmas, especially indoors, please do.
“But if you feel it essential to do so – and we have tried to be pragmatic in recognising that some people will – then please reduce your unnecessary contacts as much as possible between now and then.”
Professor John Edmunds, a member of the Sage scientific advisory panel, suggested “it might be best to postpone meeting up with vulnerable relatives” rather than see them over Christmas.
Prof Edmunds, from the Centre for the Mathematical Modelling of Infectious Diseases at the London School of Hygiene and Tropical Medicine, said: “As with all public health policy, the Christmas relaxation is a balance.
“From a purely epidemiological standpoint we should not relax our guard at Christmas, particularly as the prevalence of Covid in the community remains dangerously high.
“On the other hand, it is clear that many people intend to meet up with friends and family over the holiday period, so the current rules are an attempt to find a balance between the urge to see our loved ones and the need to control transmission.
“We should remember that just because we can meet up with two other households, it doesn’t mean that we should.
“So it might be best to postpone meeting up with vulnerable relatives for another month or two, when hopefully they will be protected via the vaccination programme.”