Health experts have urged people to take extra precautions to keep their loved ones safe over the Christmas period.

Under new rules three households across the UK will be able to mix from December 23 to 27.

But scientists have warned that the relaxation of rules over the holidays could lead to a “third wave” of the virus and another national lockdown.

Families have been urged to carefully think through their plans to be together.

Peter Openshaw, professor of experimental medicine at Imperial College London, said: “I do hope that people will not let caution evaporate over the Christmas period and think that a short break from restrictions will be fine. It really won’t.

“I urge everyone to maintain precautions and to be inventive and ingenious in devising ways to meet up in safety.

“Close personal contact is the main way this virus transmits and it should be possible to celebrate without letting the virus spread.

“Meet outdoors if possible, wear masks if you can’t maintain safe distance, wash your hands and use gel.

“Feeling well does not guarantee that you don’t have the virus: kissing your grandparents may be delivering a deadly dose of virus. Be pleased to see them but keep a safe distance.”

Dr Julian Tang, clinical virologist at the University of Leicester, said: “There is a risk of a third wave in January 2021 if we relax too much at Christmas.

“Most people in the country are still susceptible to the virus and any mixing will just give the virus a chance to spread further.

“For some, this year’s Christmas contact will be very important – perhaps more so than in other years.

“But if the rest of us who can tolerate a Zoom Christmas can do this to reduce the transmission risk for those who can’t, this will also reduce the virus spread for that bit longer, which will help all of us – and hopefully prevent a New Year third wave and possibly another national lockdown.”

Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, said: “A third wave of coronavirus infections in early 2021 is quite likely, given what we know about transmission and spread of respiratory tract viruses around that time of year.

“Whether it actually happens or not will depend to some extent on how effective the upcoming restrictions are and on how well people observe them.”

Dr Stephen Griffin, Associate Professor at the School of Medicine, University of Leeds, said: “Given our present situation, sanctioning such wide-scale mixing is likely to lead to severe consequences.

“It seems a similar policy as seen over the summer is in play, where we are told that restrictions are lifted but at the same time that we must all take personal responsibility for our actions.

“Whilst some may take the view that this is a welcome move away from a so-called ‘nanny state’, the evidence from the past few months shows clearly that such measures lead to dramatic increases in infections.

“Such messaging not only leads to confusion but could also be construed as a convenient means by which to absolve policy makers of responsibility should consequences prove unfavourable.

“We must remember that we are back in the dreadful position where hundreds of people are dying on a daily basis across the country.”

Dr Michael Head, senior research fellow in global health at the University of Southampton, said: “I would encourage as limited mixing of households as possible.

“It is important that vulnerable populations, such as elderly relatives, do have contact with family and friends before, during and after Christmas. But any form of contact should be carefully thought through and be as limited as possible.

“The rewards will come in the new year when hopefully we will have vaccines deployed and can begin to reduce the restrictions we have experienced this year.”