Shoppers who do not wear a mask in-store and are not medically exempt will be challenged upon entry to a major UK supermarket.

Sainsbury's has become the latest chain to announce a change to its enforcement of coronavirus guidance, and say they have reduced the number of shoppers allowed in store at one time.

Customers are being told to wear masks, unless they are exempt for medical reasons, and shop alone.

Trained security guards will be placed at shop entrances to 'challenge' any customers who are not complying with this guidance.

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Chief executive Simon Roberts outlined the updated guidance in a message to customers on Monday evening.

He wrote: "I have spent a lot of time in our stores over the past few days and I need to ask for your help with two key issues to keep you and all my colleagues safe.

"When shopping in our stores, you must wear a mask or visor unless you have a medical exemption.  And you should also shop on your own. Thank you for your support. 

HeraldScotland:

"Security guards will support our colleagues at the front of store and will challenge customers who are not wearing masks or who are shopping in groups. I know you’ll understand and support what we are trying to do. 

"We have also significantly reduced the number of customers allowed in our stores at any one time to ensure social distancing is maintained at all times. 

"Together, these steps will go a long way to keep everyone safe, whether you are shopping or working with us. 

"Please wear a mask or visor and please shop alone in our stores. Thank you for helping us to keep everyone safe."

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Sainsbury's is the latest to introduce the enforcement, following a similar announcement from Morrisons early on Monday. 

Morrisons said they would be offering customers a face covering - and those who decline without an exemption would be blocked from entering the store. 

Chief executive David Potts said: “Those who are offered a face covering and decline to wear one won’t be allowed to shop at Morrisons unless they are medically exempt. 

“Our store colleagues are working hard to feed you and your family, please be kind.”