The government has scrapped plans to ease restrictions over Christmas in London and large parts of the south-east and east of England.
In other regions of England, Christmas bubbles will only be allowed on 25 December.
Similar plans have been announced in Wales and Scotland.
So what are the new rules over Christmas across the four nations of the UK?
In London and parts of the south-east and east of England, which will enter tier four at 00:01 GMT on Sunday, a “stay at home” order will be imposed.
Residents will only be allowed to celebrate Christmas with members of their own household and their support bubbles.
The planned Christmas bubbles of up to three households coming together will now only be allowed on Christmas Day, instead of across a five-day period, in areas in England’s tiers one, two and three.
People in these tiers have also been encouraged to stay local and will not be allowed to host people who live in a tier four area.
In Wales and Scotland, Christmas bubbles will also only be allowed on 25 December.
In both countries, people will be allowed to form a Christmas bubble on Christmas Day, but are being advised not to do this. In Scotland, travel to and from other parts of the UK will not be allowed over the festive period.
Northern Ireland has a window of 22 to 28 December for its bubbles, with the days at each end for people who travelling into or out of the nation.
Bubbles can meet each other:
In England if you have formed a support bubble with another household, that counts as one household. In Scotland, guidance says any Christmas bubble should contain no more than one “extended household”.
People who are self-isolating should not join a Christmas bubble. If someone tests positive, or develops coronavirus symptoms up to 48 hours after the Christmas bubble last met, everyone has to self-isolate.
Under-18s whose parents live apart can join two Christmas bubbles, so they can see both parents without being counted as part of another household.
University students who travel home will be counted as part of their family household straight away.
But if a family has three or more grown-up children not at university, they cannot all form a Christmas bubble with their parents, in areas where mixing is still possible.
In England, care home residents should not take part in Christmas bubbles, while visits out of the home should only be considered for residents of “working age”.
However, more than a million coronavirus tests are being sent to care homes in England. This will allow family and friends to visit if they test negative, regardless of which tier they are in.
Residents should be able to receive up to two visitors twice a week, provided there hasn’t been an outbreak at the care home.