Coronavirus restrictions are "likely" to be tightened after Christmas as a member of Sage said the tier system wasn't "holding the epidemic wave back".
Professor John Edmunds, a member of the Sage scientific advisory panel, said measures are likely to have to be toughened up after the festive period.
He told Sky News: "At the moment it doesn't look like the tier system is holding the epidemic wave back, unfortunately. So I think we are going to have to look at these measures and perhaps tighten them up, we really will.
"It's a horrible thing to have to say but we are in quite a difficult position."
The coronavirus restrictions will be loosened for five days over the festive period.
People will be able to travel across the UK to form a "Christmas bubble" with three households from December 23-27.
But as cases rise scientists, health experts and politicians have been urging the public to have a "smaller, safer Christmas"
Prof Edmunds, of the London School of Hygiene and Tropical Medicine, suggested that, while the relaxation of restrictions at Christmas is "probably not good for the epidemic", it is "probably good for people's wellbeing in other ways".
But he said he will not mix with elderly relatives over the festive season, choosing to wait until they have been vaccinated.
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He said: "Personally, I'm not seeing my older relatives at Christmas. I'll go and see them once they've been vaccinated. And I think many people are probably going to do something similar and I think that's the right, sensible thing to do.
"But I guess we're leaving people to make that decision for themselves. And to some extent I can understand that. As long as people understand the risks and know what's happening then I think it's up to them to make these decisions."
