Coronavirus cases in the UK have risen by 35,928 – nearly double the number recorded last Sunday, figures show.
Public Health England medical director Yvonne Doyle said the “sharp” rise in cases was of “serious concern”.
It comes as Health Secretary Matt Hancock warned that a new variant of the virus was “getting out of control”.
Christmas plans have been scrapped or restricted for millions across the UK amid warnings the variant is up to 70% more transmissible than previous types.
The number of new UK infections on Sunday is an all-time high for recorded cases and nearly double the 18,447 cases reported a week ago.
However, it is thought the infection rate was higher during the first peak in the spring, with testing capacity too limited at the time to detect the true number of daily cases.
Prof Doyle said most of the new cases in England were concentrated in London and the South East, although it was too early to say if this was linked to the new variant.
The government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) estimates the variant could increase the R number by between 0.4 and 0.9, minutes released on Sunday show.
The R number is how many other people one person will infect on average; an epidemic is growing if it rises above 1.
A growing number of countries have banned travel from the UK as a result of this variant, including Ireland, France, Belgium, Italy and the Netherlands.
Eurotunnel is suspending access to its Folkestone terminal from 22:00 GMT for traffic and freight heading to Calais due to the 48-hour travel ban introduced by France.
Speaking on the BBC’s Andrew Marr programme, Mr Hancock said the news about the new variant “has been an incredibly difficult end to frankly an awful year”.
He said: “Of course we don’t want to cancel Christmas… we don’t want to take any of these measures, but it’s our duty to take them when the evidence is clear.”
Susan Hopkins, from Public Health England, told Andrew Marr there was evidence that people with the new strain had “higher viral loads”, which meant they were more infectious.
Some 21 million people in England and Wales who entered new restrictions at midnight are being told to stay at home, while non-essential shops and businesses have to close.
Those living under the newly-created tier four restrictions in England will now be unable to mix with other households indoors at Christmas, unless they are part of their existing support bubble.
The health secretary said it was not clear how long the tier four measures would be in place, but it could be for months, “until we can get the vaccine going”.
He added that people in tier four should act as if they may have the virus.
In the rest of England, Scotland and Wales, relaxed indoor mixing rules will only apply on Christmas Day.
Covid rules had been relaxed across the UK to allow up to three households to mix indoors for five days over the Christmas period.
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