Coronavirus: New face covering rules come into force in England
Face coverings are now compulsory for customers in shops in England, after new coronavirus rules came into force within 12 hours of the government issuing guidance on the change.
Coverings are mandatory in enclosed public spaces such as supermarkets, indoor shopping centres, transport hubs, banks and takeaways.
Police can hand out fines of up to £100 to those who do not comply.
But some retailers have insisted they will not enforce the rule.
Sainsbury's and Costa Coffee said their staff would not challenge customers who entered their stores without masks, while Asda said enforcement was the "responsibility of the relevant authorities".
But Waitrose will have staff at the entrance reminding customers of the rule, and Tesco will be selling face coverings at shop entrances.
Greggs and McDonalds said takeaway customers needed to wear masks.
Guidance issued by the government on Thursday for England states that staff in premises where face coverings are required are encouraged to take steps "to promote compliance with the law" and can refuse entry to people who do not have a valid exemption under the rules.
However, the government said it was the responsibility of individuals to wear a covering, and Health Secretary Matt Hancock urged the public to "play their part" by following the new guidance.
"As we move into the next stage of easing restrictions for the public, it is vital we continue to shop safely so that we can make the most of our fantastic retail industry this summer," he said.
Police will be able to "use force" to remove customers from shops if they do not wear face coverings, as well as prevent them from entering, according to the College of Policing.
But forces have said they will only be enforcing the rules, including issuing £100 fines, as a last resort - and officers will not be patrolling premises.
Health Minister Helen Whately said the government was confident "the vast majority of people" would comply with the regulations.
There are exemptions to the new rules for children under 11, those with disabilities or certain health conditions, such as respiratory or cognitive impairments that make it difficult for them to wear a face covering.
Ms Whately said people could print out a card from the government's website to show they were exempt if they wished, but stressed people would not be expected to carry proof of an exemption.
Public Health England has warned parents not to buy coverings for babies and young children because of the risk of choking or suffocation.
Masks will not be mandatory in indoor venues that have other safety measures in place, including:
Hairdressers and salons
Gyms and leisure centres
Cinemas, concert halls and theatres
Visitor attractions such as museums
'I don't like being confronted'
For some people with certain health conditions or disabilities, wearing a mask can be more difficult.
Kerise Vowles-Myners, who has autism, had a particularly bad experience when she tried wearing one to visit the doctor last week.
"I literally had it on for two minutes and had a panic attack and threw up in public - it was quite embarrassing," she told BBC Radio 4's Today programme.
Kerise said she had spoken to her social worker about going shopping for her when she had bad days.
"I don't like being confronted because I have to explain myself," she said.
"Whenever I go out, a lot of people don't even realise that I'm on the spectrum so they just look at me and think, 'oh she is just a normal person, why is she not wearing a mask?'"
Retail and trade organisations have criticised the government over the length of time it has taken for guidance to be published - after the changes were announced more than a week ago.
Meanwhile, union leaders voiced fears the rules could put workers' safety at risk if people refused to wear a mask or became abusive.
The British Retail Consortium called on customers to be "respectful" of the new rules, while UK Hospitality chief executive Kate Nicholls said takeaway outlets had been left with "a very short time to properly brief staff, prepare signage and take steps to encourage compliance".
According to the government, face coverings should cover the mouth and nose and can be as simple as a scarf or bandana that securely fits around the side of the face without having to be held in place.
The requirement to wear face coverings at transport hubs - railway and bus stations, airports and maritime ports - only applies for those areas which are fully indoors and enclosed.
You are allowed to remove a face covering in certain situations, for example to prove identification in banks or when buying age restricted products.
Face coverings have been compulsory in shops in Scotland since 10 July. Shoppers are not currently required to wear them in Wales or Northern Ireland, although NI will wait until 20 August before deciding whether to make them compulsory.
Coverings are already compulsory on public transport in England and Scotland, as well as most buses, trains and ferries in Northern Ireland. They will be mandatory on public transport in Wales from 27 July.