Boris Johnson has told families they must make a “personal judgment” about the risks of coronavirus to vulnerable loved ones when forming a Christmas bubble.
The Prime Minister urged the public to “think carefully” over the festive period after it was confirmed that three households will be able to mix from December 23 to 27.
The UK Government and devolved administrations have agreed a joint plan to relax social distancing rules over the festive period, allowing friends and family to hug for the first time in months.
But a member of the Government’s Scientific Advisory Group for Emergencies (Sage) warned that the planned easing of measures could lead to a third wave of the pandemic.
Another said that the risks people take at Christmastime could lead to more hospital admissions in January and potentially another lockdown.
Welsh First Minister Mark Drakeford has said the decision to agree a relaxing of restrictions over Christmas was to avoid a “free for all”.
Mr Johnson acknowledged the measures would not add up to a “normal Christmas” and urged people to exercise caution, particularly when meeting with the elderly or the vulnerable.
“We can’t afford to throw caution to the wind. The virus doesn’t know it’s Christmas and we must all be careful,” he said in a video message posted on Twitter.
“I know this doesn’t equate to a normal Christmas and it won’t work for everyone. And it is up to each of us to think carefully about how we use this time-limited special dispensation.
“The virus has not gone away and families will need to make a personal judgment about the risk of forming a bubble with or visiting elderly relatives and the vulnerable.”
A joint statement issued by the four UK governments said they had been working closely together to find a way for family and friends to see each other, recognising it must be “limited and cautious”.
Each Christmas bubble can meet at home, at a place of worship or an outdoor public location, but existing, more restrictive rules on hospitality and other venues will be maintained throughout the period.
Professor Graham Medley, an expert in infectious disease modelling at the London School of Hygiene & Tropical Medicine, said the relaxation of coronavirus restrictions at Christmas could lead to more people being admitted to hospital and further lockdown measures in the new year.
The Sage attendee told BBC Radio 4’s Today programme: “I think we’re in a process now whereby the population’s risk of filling up the NHS is really being passed down to us as individuals.
“For other diseases like flu or hepatitis B, the Government doesn’t get involved in helping or determining what our risk is and it is really, I think, for this Christmas up to us as individuals and families to think about what our risks are and how we are going to mitigate them.
“I think it is inevitable that if a lot of people do take that risk, even if it is a small risk, then we will end up with a lot of people in hospital and potentially having to take measures in January to lock down again.”
Prof Medley advised people to isolate before visiting relatives, to consider the amount of time they plan to spend with them, to remain “completely faithful” to any social bubble arrangements and to weigh up the risk of spreading Covid to those who are vulnerable.
But he said, even with mitigations in place, social interactions come with risks that “could play out very badly for some people”.
Andrew Hayward, professor of infectious diseases epidemiology at University College London, and a member of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), warned easing measures would lead to increased transmission and a possible “third wave” of infection.
“Effectively what this will be doing is throwing fuel on the Covid fire,” the professor, who is also a Sage member, told BBC2’s Newsnight on Tuesday.
He added: “With the vaccine on the way, if we are not very careful over Christmas we are really in danger of snatching defeat from the jaws of victory on this one.”
It comes as the British Medical Association in England also warned easing of coronavirus restrictions over Christmas will “almost certainly” lead to a rise in the infection rate.
Mr Drakeford told Good Morning Britain: “I think it was very clear to us from the advice we received at the Cobra meeting, but also from what we hear in Wales, that unless we found a formula that allowed people to get together over Christmas, people were very unlikely to be willing to stick to the current level of restrictions that we have here in Wales.
“So the choice was between a guided form of meeting over Christmas or people simply making their own solutions.”
Mr Drakeford said it was “not a matter of encouraging people” to gather over the festive period.
“It is finding a set of rules that give us a guided way to Christmas – without the rules that we’ve agreed, I think the risk was very high that people would simply make up the rules for themselves,” Mr Drakeford said.
The Christmas plan was agreed following a Cobra meeting chaired by Cabinet Office Minister Michael Gove, bringing together the Westminster Government and the devolved administrations.
Despite the new measures, families and groups of friends will still face difficult decisions and restrictions on their activities.
The bubbles will have to be exclusive over the five-day period, meaning people cannot shift from one group to another – although children whose parents are separated will be allowed to move between them.
People aged over 65 in care homes will not be able to join their loved ones for Christmas, and in families where three children live away from home, they would not all be able to return for the festive period.
Government figures showed a further 696 people had died within 28 days of testing positive for Covid-19 as of Wednesday, with the UK total now standing at 56,533.
Meanwhile, a further 18,213 lab-confirmed cases of coronavirus were reported on Wednesday.