Everyone in England must stay at home except for permitted reasons during a new coronavirus lockdown beginning at midnight, Boris Johnson has announced.
All schools and colleges will close to most pupils and switch to remote learning until the middle of February.
In a televised address, the PM urged people to follow the rules immediately amid surging cases and patient numbers.
He said those in the top four priority groups would receive a first vaccine dose by mid-February.
Speaking from Downing Street, Mr Johnson said the weeks ahead would be the “hardest yet”.
But he added that he believed the country was entering “the last phase of the struggle”.
Northern Ireland’s Stormont Executive are also meeting to discuss possible new measures.
On Monday, the UK recorded more than 50,000 new confirmed Covid cases for the seventh day in a row.
A further 58,784 cases and an additional 407 deaths within 28 days of a positive test result were reported, though deaths in Scotland were not recorded.