Prime minister Boris Johnson has said he "can't rule out" further restrictions.

The United Kingdom (UK) is made up of England, Scotland, Wales and Northern Ireland. So, each country has announced specific Covid rules to take immediate effect.

In Scotland, from December 26, there are limits on the size of live public events for three weeks:

Indoors - 100 standing or 200 seated
Outdoors - 500 seated or standing

Football matches will be effectively spectator-free, and non-professional indoor contact sports will stop.

Life events like weddings are not included.

From December 27, night clubs will be closed for three weeks.

Pubs, bars and other hospitality venues will return to table service only.

One-metre social distancing is advised in these settings, with no more than three households in each group.

Other measures include:

people asked to limit social contact to two other households either side of Christmas - and to use lateral flow tests before meeting
shops and businesses to take measures to limit the spread of Covid
care home visits limited to two households (who need to be tested)
employers have a legal duty to let staff work from home
face coverings compulsory on public transport and most indoor spaces
all over-18s required to prove their vaccine status or show a negative test at many venues

In Wales, these are new measures from 0600 GMT on 26 December:

social distancing of 2m in all premises open to the public and workplaces, where reasonable
gatherings limited to six people in premises such as hospitality venues, cinemas and theatres
licensed premises to take additional measures to protect customers and staff, including table service and collecting contact details
face coverings required in hospitality settings, apart from when seated
large events not allowed - with maximum numbers of 30 at an indoor event and 50 outdoors

Large sporting events will be played behind closed doors. For smaller sporting events, up to 50 spectators are allowed. There is an exception for events involving children.

From 27 December nightclubs will be closed.

Other measures include:

National Health Services (NHS) Covid Pass needed for entry to cinemas, theatres and concert halls, and many other events
working from home wherever possible
compulsory face coverings in schools, on public transport, and in shops and hospitals
advice to wear masks in pubs and restaurants, when not eating or drinking.

In Northern Ireland from 0600 GMT on 26 December:

nightclubs will be closed
dancing in all hospitality venues will not be allowed
all indoor standing events will not be allowed

From 0600 GMT on 27 December:

hospitality venues including pubs, cafes and restaurants will be table service only
in hospitality venues a maximum of six people (or 10 from a single household) allowed at a table (excluding children aged 12 and under)
businesses must take measures to achieve 2m social distancing and limit the spread of Covid in office spaces
businesses to promote use of face coverings

These measures do not apply to weddings or civil partnership celebrations.

Household mixing should also be limited to a maximum of three households, the government says.

Other measures include:

face coverings compulsory in shops, indoor-seated venues and visitor attractions, public transport and some other settings
post-primary pupils must wear a face covering inside school buildings, as well as on school transport. Staff are encouraged to wear masks in school areas where they can't socially distance
Covid passport scheme for venues including bars and cinemas

In England, however, Boris Johnson said introducing tougher measures to curb the spread of the Omicron variant are not justified at the moment.

He has said, however, that people should wear masks indoors when it is required, keep fresh air circulating, and take a test when visiting elderly or vulnerable relatives.

The prime minister added that people need to show that they're vaccinated,have recently tested negative [or an exempt] to gain entry to nightclubs and many other venues.

He added that face masks are compulsory in most indoor public venues, including theatres and cinemas - as well as on public transport and in places like shops and hair dressers. Masks are not needed in pubs or restaurants, or venues like gyms where it's "not practical".

Mr.Johnson also said that people should work from home "if they can" and are advised to take lateral flow tests before entering any "high-risk setting", such as a crowded place.