The UK could face a third coronavirus wave after rules are relaxed at Christmas, scientists have warned.
This Christmas, three households can form a bubble for five days between December 23-27- but experts are urging people to remain cautious.
Scientists are concerned that a third wave could see more lockdowns imposed which will send the UK "heading towards a disaster".
According to government figures, the R-number - the rate at which the virus reproduces - is above 1 in parts of England.
If the R-value is above one then the Covid-19 epidemic can grow exponentially, but if it is below one it shows the outbreak is in retreat.
Prof Devi Sridhar, chair of global public health at the University of Edinburgh, told The Guardian: "If people [aren’t] cautious, then we will pay for our Christmas parties with January and February lockdowns, the Mirror reports.
"With a vaccine just weeks away, why risk infecting vulnerable and elderly people we love?"
And Boris Johnson was warned that his decision to save Christmas will have "consequences".
Prof Linda Bauld, also of the University of Edinburgh, told BBC Breakfast: "I think people have to think very carefully whether they can see loved ones outside, or do it in a very modest way.
"I'm also concerned about the travel, people going from high to low-prevalence areas."
She continued: "I think it's going to have consequences.
"I completely understand why governments are doing that. Behaviourally people are fed up.
"If you're meeting people indoors from other households, there's poor ventilation, maybe older family members are in those bubbles, unfortunately, because the virus hasn't been eliminated... I think that means the Christmas period is a risk.
"From a public health perspective, I have to be perfectly honest, I think this is a mistake."
Professor Stephen Reicher, of the University of St Andrews, who is a member of the behavioural science advisory group to Sage, said: "Right now we are heading towards disaster.
"Given high levels of infection across the country and the increasing levels in some areas (such as London), it is inevitable that if we all do choose to meet up over Christmas then we will pay the price in the New Year."
He added: "We need an urgent rethink about the Christmas break.
"Government must clarify the risks involved in indoor mixing and stress the fact that households can get together doesn’t mean that they should.
"They should provide the information and support to help people make the decisions that best keep themselves, their families and their communities safe.
"And for many of us, the right decision will be to show our love by waiting until we can meet and hug and celebrate without danger."
In its latest weekly update, the Scientific Advisory Group for Emergencies (Sage), which has been helping to guide the Government through the pandemic, said it is "no longer confident" R in every English region is below 1.
The crucial number could be as high as 1.1 in London, the South East and the East, with new infections rising by as much as 1-2% each day in those regions, less than a week before the Government decides whether to move cities and towns out of their current tiers.
England's overall R number, between 0.8 and 1.0, was unchanged from a week ago.
