The government does not want to cancel Christmas but it is “our duty” to act as a new coronavirus variant is “out of control”, the health secretary says.
A strict new lockdown in London, the South East and east of England could last for months, Matt Hancock said.
Millions of people across the UK have seen their festive plans severely restricted or scrapped.
On Sunday, the number of recorded daily infections in the UK reached an all-time high of 35,928 new cases.
The figure is nearly twice the number of cases – 18,447 – reported a week ago.
However, it is thought the infection rate was higher during the first peak in spring, with testing capacity too limited at the time to detect the true number of daily cases.
Yvonne Doyle, medical director at Public Health England, said: “This sharp and sudden increase is of serious concern.
“Most of the new cases reported today are concentrated in London and the South East, although it is too early to tell if this is linked to the new variant.”
A growing number of countries have banned travel from the UK – including Ireland, Belgium, Italy and the Netherlands – over the new variant.
The government’s New and Emerging Respiratory Virus Threats Advisory Group estimates this variant could increase the R number – which indicates if an epidemic is growing or shrinking – by between 0.4 and 0.9, newly released minutes show.