Millions more people in England are set to move into the toughest Covid restrictions after ministers warned that a new Covid strain of the virus may be linked to a rise in infections.
London, most of Essex and parts of Hertfordshire will join tier three at 00:01 GMT on Wednesday.
Health Secretary Matt Hancock said action was needed immediately to slow an “exponential” spike in cases.
No 10 rejected suggestions it might now review Christmas guidelines.
Under tier three – very high alert – rules pubs and restaurants must close, except for takeaway and delivery, and indoor entertainment venues – such as theatres, bowling alleys and cinemas – must remain shut.
The announcement will move about 10.8 million people into tier three, with 61% of England’s population – or 34 million people – under the toughest restrictions from Wednesday.
He said an initial analysis suggested it was “growing faster than the existing variant”, affecting at least 60 different local authorities.
He added the rise in transmission, as well as the new variant, was a “warning to us all that even after such a difficult year, we must stay vigilant”.
Speaking on BBC Two’s Newsnight, former Tory minister Stephen Hammond, who represents Wimbledon, suggested there would now be a “rethinking” over whether it is appropriate for families to gather at Christmas.
Scientists have warned the easing of coronavirus restrictions over Christmas by all four UK nations will cause a spike in infections.
David Nabarro, a World Health Organization special envoy working on Covid-19, said the price of such a relaxation “could well be very high” and urged people to think carefully about their plans.
Prof Stephen Reicher, of the University of St Andrews, said: “Right now we are heading towards disaster.
“Given high levels of infection across the country and the increasing levels in some areas, it is inevitable that if we all do choose to meet up over Christmas then we will pay the price in the new year.”
But asked at the Downing Street briefing whether the government should rethink its Christmas plans, Mr Hancock urged people to be “extremely careful” about who they mix with in the run-up to Christmas if they are planning to see elderly relatives over the festive period.
England’s chief medical officer, Prof Chris Whitty saying people should not meet at Christmas just because they can.