Supermarkets are continuing their crackdown on customers entering stores without masks as Asda and Tesco announce they would ban shoppers not wearing masks without medical exemption.

The move comes as tensions increase at Norfolk's food shops with a chief of police saying officers could be put on standby to assist with "aggressive" dissenters.

Tesco, which has sites across the county including superstores in the likes of Norwich, Beccles and Thetford, said it will not let customers who are not wearing a face covering into its stores unless they are exempt in line with government guidance.

As well as asking customers to be respectful a spokesman said: “We are also asking our customers to shop alone, unless they’re a carer or with children.

“To support our colleagues, we will have additional security in stores to help manage this.”

Echoing Tesco’s calls for customers treat staff with respect, an Asda spokesman said: “If a customer has forgotten their face covering, we will continue to offer them one free of charge.

“But should a customer refuse to wear a covering without a valid medical reason and be in any way challenging to our colleagues about doing so, our security colleagues will refuse their entry.”

They are the latest supermarkets to ban maskless shoppers, after Morrisons announced it would enforce the wearing of masks for customers unless they are medically exempt, while Sainsbury’s said its security staff at entrances will “challenge” shoppers who are not wearing face coverings or who enter stores in groups.

Asked whether Co-op Food stores will take similar steps, chief executive Jo Whitfield said all customers “must take responsibility for wearing a face mask”.

She said: “We’ve increased our in-store messaging to remind customers and Government guidance does state that the police can take measures if members of the public don’t comply with this law.”

Metropolitan Police Commissioner Dame Cressida Dick said officers in the capital are prepared to assist supermarket staff if customers become “obstructive and aggressive” when told they must wear a face covering.