Johnson said Saturday that the capital and other areas in southern England currently under Tier 3, the highest level of coronavirus restrictions, will move to an even stricter new Tier 4.
Under the new Tier 4, people would be banned from mixing with anyone outside of their household, including on Christmas Day, and for the other tiers, Christmas rules allowing up to three households will now be limited to Christmas Day of December 25 only, rather than five days.
“It seems that the spread is now being driven by the new variant of the virus,” Johnson said at a 10 Downing Street briefing on Saturday evening.
“We are sacrificing the chance to see our loved ones this Christmas so we have a better chance of protecting their lives so that we can see them at future Christmases,” he said, adding that he “bitterly regretted” having to make these changes.
The UK prime minister said there is no evidence to suggest vaccines would be any less effective against the new variant but that it was required to act fast to try and control its spread.
“Our advisers on the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) have spent the last few days analysing this new variant – there’s no evidence that it causes more severe illness or higher mortality but it does appear to be passed on significantly more quickly,” he said.
From Sunday, areas in the south east of England, including London, currently in Tier 3 will be moved into a new Tier 4 – effectively returning to the complete lockdown rules of November.
Non-essential shops, gyms, cinemas, hairdressers and bowling alleys will be forced to close for two weeks and people will be restricted to meeting just one other person from another household in an outdoor public space.
Johnson added: “I know how much emotion people invest in this time of year, and how important it is, for instance, for grandparents to see their grandchildren, for families to be together.
“So I know how disappointing this will be. But we have said throughout this pandemic that we must and we will be guided by the science. When the science changes, we must change our response.”
The Opposition Labour Party accused the government of “dither and delay” over its decision-making.
“Dither and delay has cost lives with more to come. The mental health implications of this will be tragic,” said Labour’s shadow minister for mental health Rosena Alin-Khan.