LONDON (AP) — British Prime Minister Boris Johnson says Christmas gatherings can’t go ahead and non-essential shops must close in London and much of southern England as he imposed a new, higher level of coronavirus restrictions to curb sharply spreading infections.

Johnson said the capital and other areas in southern England will move to an even stricter Tier 4 alert category that requires non-essential shops, hairdressers and indoor leisure venues to close after the end of business hours Saturday.

Johnson also said that a planned five-day easing of socializing rules that would allow up to three households to meet in “Christmas bubbles” will be canceled for Tier 4 areas. In the rest of England, people will be allowed to meet in Christmas bubbles for just one day instead of five, as the government originally planned.

“It is with a very heavy heart that I must tell you we cannot proceed with Christmas as planned,” Johnson said.

A fast-moving new variant of the coronavirus that is more than 70% more transmissible than existing strains appears to be driving the rapid spread in London and southern England, Johnson said. London now has the highest infection rates in England.

“There’s no evidence to suggest it is more lethal or causes more severe illness,” he stressed, or that vaccines will be less effective against it.

England’s chief medical officer, Chris Whitty, said the U.K. has alerted the World Health Organization that the new variant identified this week appears to be accelerating the spread of COVID-19. The government’s scientific advisers came to that conclusion based on preliminary modelling figures, and they are continuing to analyze the available data, he said.