Prime Minister Boris Johnson announced the changes for England at a Downing Street briefing after scientists said a new coronavirus variant was spreading more rapidly.
Tier-four restrictions – similar to England’s second national lockdown – will apply in all areas in the South East currently in tier three, covering Kent, Buckinghamshire, Berkshire, Surrey (excluding Waverley), Gosport, Havant, Portsmouth, Rother and Hastings.
It will also apply in London (all 32 boroughs and the City of London) and the East of England (Bedford, Central Bedford, Milton Keynes, Luton, Peterborough, Hertfordshire, Essex (excluding Colchester, Uttlesford and Tendring).
In Scotland, Covid restrictions will only be relaxed on Christmas Day, with mainland Scotland being placed under the tightest restrictions from Boxing Day.
Outlining the changes, Scotland’s First Minister Nicola Sturgeon said she wished she had acted quicker to curb the virus in February, adding: “Standing here saying this actually makes me want to cry.”
A ban on travel to the rest of the UK will also apply over the festive period.
In Wales, First Minister Mark Drakeford announced that the country will be placed under lockdown from midnight.
There are no plans at the moment to change the current Christmas restrictions in Northern Ireland, BBC News NI understands. The country is set to enter a six-week lockdown from 26 December.
England’s chief medical officer, Prof Chris Whitty, said that while the new variant of coronavirus will make things much worse, if the vaccine works against it there was room for optimism.
He has previously said there is no current evidence to suggest the new variant causes a higher mortality rate or that is affected any differently by vaccines and treatments.
Speaking at the Downing Street briefing, he added: “I think this is a situation which is going to make things a lot worse, but there are some really optimistic things if you look once we get the vaccine out, assuming the vaccine works against this, which at the moment is the working assumption.”
Sir Patrick Vallance, the government’s chief scientific adviser, urged the public to assume they might be infectious when considering meeting others over Christmas.