Sainsbury's have tightened COVID measures in all of their supermarkets.

They join Morrisons and more recently Tesco and Asda in pledging to enforce mask-wearing in their stores.

Security guards will challenge any customers not wearing a mask or shopping in groups, and the number of customers allowed into stores at any one time had been significantly reduced.

Simon Roberts, the supermarket's chief executive, said: "The vast majority of customers are shopping safely, but I have also seen some customers trying to shop without a mask and shopping in larger family groups.

"Please help us to keep all our colleagues and customers safe by always wearing a mask and by shopping alone."

Richmond Council however have called on all supermarkets to do the same.

Cllr Richard Baker, Lead member for Economics and Business for Richmond Council, said:

"Our supermarkets are vital. For many people they will be the only place they will visit whilst the lockdown is in place. Over the past ten months all our supermarkets have worked so hard to make sure their staff and customers are safe. However, we know that fatigue is setting in and we need everyone to dig deep. Otherwise we won't combat this virus.

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"To customers – don't put yourselves, your family or other customers at risk. Shop alone and wear a face covering when you are in a store. Make sure you social distance from other customers and staff. And if the shop looks too busy – return at a quieter time.

"To the staff – please follow the rules. I know wearing a face covering for seven hours is uncomfortable – but it is vital. And wear it properly, over your nose and mouth all the time. If you think that social distancing isn't being observed – both on the shop floor and behind the scenes, speak to your manager."

The council's concern comes after increased reports of shoppers and staff not following the rules.