A poster about the new, fast-spreading variant of the coronavirus warns some Britons to stay home. The sign is displayed near King’s Cross railway station in London.

A Coronavirus Tier 4 Stay Home poster near King’s Cross railway station in London, U.K., on Monday, Dec. 21, 2020. More than 16 million Britons are now required to stay at home as a lockdown came into force Sunday in London and southeast England, part of Boris Johnsons attempt to control a fast-spreading new strain of the coronavirus. Photographer: Jason Alden/Bloomberg via Getty Images