Across the UK, three households will be allowed to create a temporary bubble this Christmas.
All four nations say coronavirus rules will be relaxed for five days between 23-27 December to let families celebrate together.
Each "Christmas bubble" can meet at home, at a place of worship or an outdoor public place, but any existing, more restrictive rules on meeting in pubs and other hospitality venues will be maintained throughout the festive period.
There will be no limit to the number of people in a household joining a bubble in England, Wales and Northern Ireland, although the England guidance says it should be "as small as possible".
The Scottish government has said that Christmas bubbles can have a maximum of eight people, and should only contain one "extended household". Children under 12 will not count in the total.
What is a support bubble?
A bubble is defined as a group of people with whom you have close physical contact.
The aim is to help people who've been cut off from friends and family.
Bubbles must be "exclusive". Once in one, you can't start another with a different household.
People in each bubble can stay overnight in each other's homes, visit outdoors places together and do not have to socially distance.
Support bubble counts as one household - which means for the Christmas period that bubble can join with two other households.
How do they work in England?
In England, single adults living alone - or single parents whose children are under 18 - can form a support bubble with one other household.
The second household can be of any size and can include "at risk" people who were previously shielding.
Wherever possible, the government recommends that a support bubble should be with another local household to avoid unnecessary travel. Anyone in the bubble contacted as part of England's test and trace programme must stay at home. If they develop coronavirus symptoms, everyone in the bubble must self-isolate.
Support bubbles have been allowed to continue during lockdown.
From 2 December, when England leaves lockdown and enters a tier system, people will be allowed to form support bubbles with those who live in an area with a higher tier rating.
Bubbles can be cross-border with Scotland and Wales, subject to local restrictions.
The government says it will be expanding the eligibility of support bubbles from 2 December to help families with very young children or people with continuous care needs, meaning households can form a support bubble with another household, if at least one of them has:
- a child under 1 (regardless of how many other adults are in the household)
- a child under 5 with a disability that requires continuous care (regardless of how many other adults are in the household)
- a single adult carer (living with any additional adults in the household that have a disability and need continuous care)
As well as the support bubble rules, the government in England also has a set of rules that apply to families with children under 14 (as well as to vulnerable adults).
They can form a childcare bubble with one other household to provide informal (unpaid and unregistered) childcare. This must always be between the same two households. They can provide the childcare in either or both of the homes from the two households.
And if you are single
- Two single people each living alone could bubble
- Someone in a houseshare could bubble - but their housemates wouldn't be allowed to form their own bubbles with other people
Full government guidelines for England are here.
What about Wales?
As of 9 November, two households of any size can form an exclusive bubble and meet in their own homes and gardens.
People in the same bubble can stay in each other's homes overnight. And they can meet up in groups of larger than four in some other outdoor places.
If you have been part of a temporary extended household during the firebreak period, or were in one before that, you are not required to stay in the same extended household. You can make a new bubble, instead. However, once you have agreed and joined that new extended household, neither household can leave to form a new one.
What about Scotland?
Under the five tier system in Scotland, people who live on their own or only with children under 18 can form an extended household with people from one other household.
This group of people can visit each other's homes and go inside. They do not have to stay 2m (6ft) apart and can stay overnight.
People in extended households are counted as one household, and so can continue to meet and socialise with each other despite general restrictions on households mixing.
Couples who do not live together can also form an extended household, which can include any children they each live with.
A household must not form an extended household with more than one other. However, one of them can end the arrangement at any time, and - as long as they wait at least 14 days - then form a new extended household with someone else.
If any member of an extended household develops symptoms or tests positive for Covid, everyone in the bubble must self-isolate.
What about Northern Ireland?
Two households of any size can form a support bubble.
The members can spend time indoors and stay overnight with each other.
Under the latest restrictions, these bubbles are limited to a maximum of 10 people, including children, at any one time.
Read more from the Northern Ireland Executive here.
What about bubbles in schools?
Schools are using year group and/or class bubbles to support social distancing and reduce close contact between pupils as much as possible.
Maintaining distinct groups which do not mix makes it quicker and easier when a positive case occurs to identify those who may need to self-isolate and minimise their number.