People around the UK must now wear face coverings in many public places.
Tesco, Asda and Waitrose have become the latest supermarkets to say they will deny entry to shoppers who do not wear face masks unless they are medically exempt.
It follows a similar move by Morrisons, while Sainsbury’s says it will challenge those who flout the rules.
So what protection do masks offer, and what sort can be worn?
Face coverings reduce the spread of coronavirus droplets from coughs, sneezes and speaking.
They should mainly be worn to protect other people from coronavirus, rather than yourself.
When worn correctly, they should cover the nose and mouth, which are the main confirmed sources of transmission.
They can help to reduce the spread of the virus from people who are contagious, including those who have no symptoms, or are yet to develop them.
There is also evidence they can offer some protection to the wearer, although they are not a replacement for social distancing and hand-washing.
Face coverings are now compulsory across the UK when:
People can be refused travel for not following the rules or fined as a last resort. In England, the police can issue a £200 fine to someone breaking the face covering rules. In Scotland, Northern Ireland and Wales, a £60 fine can be imposed. Repeat offenders face bigger fines.
In England and Scotland, face coverings are also compulsory in a number of indoor spaces, including:
Scotland also requires face coverings to be worn in indoor spaces, such as staff canteens and corridors in workplaces. It no longer requires couples to wear them when exchanging marriage vows.
In Wales, face coverings must be worn in all indoor public places by customers and staff.
In Northern Ireland, they must be worn in “any other indoor place where goods or services are available to buy or rent”.
Some people do not have to wear a face covering. They include:
You can remove your mask if:
Young children should not wear face masks because of the risk of choking and suffocation.
Primary and secondary schools in the UK have moved to remote learning for most pupils, except for children of critical workers and those deemed vulnerable, who can still physically go to school each day.
The government does not recommend wearing face coverings in schools and colleges because of the Covid controls already in place.
However, each nation is adopting different rules:
The BBC has created a guide on how to make your own face covering.
The government has issued its own advice too.
Face coverings do not give the wearer as much protection as the masks that healthcare workers wear.
World Health Organization (WHO) advice says non-medical face coverings should be worn in public where social distancing is not possible.
They help us protect each other and reduce the spread from people who are contagious but have no symptoms, or are yet to develop symptoms.