A growing number of British supermarkets say they will challenge customers who refuse to wear masks in their stores. With infection numbers rising sharply, the UK government has expressed concern about the spread of the virus in supermarkets, with people breaching rules by not wearing masks. Morrisons chief executive David Potts said the supermarket was tightening the rules, <a href="https://www.thenationalnews.com/world/europe/uk-vaccinates-2-4-million-as-boris-johnson-warns-lockdown-may-get-stricter-1.1144390">amid calls for stricter lockdown measures</a>. "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," Mr Potts said on Monday. "Our store colleagues are working hard to feed you and your family. Please be kind." Sainsbury's later took similar action, saying it would use security guards to challenge people who were not wearing masks and ensure that people did not shop in groups. The British Retail Consortium, which represents more than 170 major retailers including the big supermarket groups, called for the police to do more after interventions by staff led to a sharp rise in abuse. "While enforcement of face coverings is the responsibility of the police, retailers continue to do what they can to encourage their use throughout stores," said Andrew Opie, the consortium's director of food and sustainability. "Sadly, this has led to a sharp rise in incidents of violence and abuse against shop workers, which is why it is essential that police support the work being done by retailers." On Tuesday, policing minister Kit Malthouse said police would intervene in serious breaches of Covid rules in shops, but measures imposed and enforced by owners would be effective in most cases. "The police are there if you like for backup if things get seriously wrong," he told BBC News on Tuesday. "What we hope is that in the vast majority of cases the enforcement, or the reminders if you like, put in place by the store owners will be enough." Mr Opie said data from the government's Scientific Advisory Group for Emergencies highlighted that retail was a safe environment. He said companies had spent hundreds of millions of pounds on safety measures including Perspex screens, more cleaning and social distancing. "Supermarkets continue to follow all safety guidance and customers should be reassured that supermarkets are Covid-secure and safe to visit during lockdown and beyond," Mr Opie said. Non-essential retail, restaurants and bars are shut across Britain, leading to a high level of demand for supermarkets and other food shops. "People have got to follow the guidance in supermarkets," Prime Minister Boris Johnson said. "People need to be keeping their distance, making sure that they're wearing masks, doing the right thing."