From today (Boxing Day), a maximum of six people will be allowed to meet in pubs, cinemas and restaurants in Wales.
A total of 30 people will be allowed at indoor events while 50 people will be allowed at outdoor events.
Two metre social distancing is being required in public premises and offices, and nightclubs will close.
In Scotland, large events will have one metre physical distancing and will be limited to 100 people standing indoors, 200 people sitting indoors and 500 people outdoors.
A day later, up to three households can meet with a one metre distancing between groups at indoor and outdoor venues like bars, restaurants, theatres, cinemas and gyms.
Table service is also needed at places where alcohol is served.
Northern Ireland is also bringing in restrictions with indoor standing events no longer permitted and nightclubs closing.
Socialising will be reduced to three households while up to six people can meet in pubs, bars and restaurants. Ten people will be allowed if they are from the same household. Only table service will be available.
A two metre social distancing rule will be in place in public premises and offices.
Prime Minister Boris Johnson has yet to announce any further rules for England but indicated he will not hesitate to act after Christmas if required amid rising cases of the Omicron variant.
It is understood a Covid O meeting is yet to be scheduled as ministers await further data, but No 10 did not rule out the possibility one could take place on Monday.