Asda has announced it is beefing up its coronavirus safety measures in the run-up to Christmas, including more security staff at entrances.
The extra staff will help prevent overcrowding in its superstores from 19 to 24 December, the supermarket said.
The move comes amid fears that shoppers might be tempted to hoard some products in anticipation of a no-deal Brexit.
But the retail industry has urged people not to buy more food than usual, saying there is no need to stockpile.
On Sunday, the UK and the EU agreed to extend a deadline aimed at reaching a deal on post-Brexit trade.
The British Retail Consortium (BRC) said uncertainty made it harder for firms to prepare for the New Year.
However, several supermarkets told the BBC that they were “making contingency plans” and were “prepared for a number of scenarios”.
Last week, Tesco’s chairman, John Allan, said it had been stockpiling some non-fresh food as it prepares for potential shortages.
“The festive season is always the busiest time of year for our stores, so we have introduced additional safety measures to protect colleagues and customers during this period,” said Asda chief executive Roger Burnley.
“These new measures will help customers to get in and out of our larger stores quickly and safely and we are confident they will continue to play their part by respecting social distancing when they shop.”
Asda has 421 superstores around the country, which will all have extra security personnel for the six days before Christmas.
Asda already has safety marshals on duty outside every store.
Other measures include a virtual queuing app called Qudini that lets customers to wait outside in their cars if the store is too busy to let them in.
In the chain’s 100 busiest stores, customer numbers will also be restricted by automatic counting technology, with the aim of helping them to maintain social distancing.
Antimicrobial coating is being added to areas that might harbour the virus, such as fridge and freezer handles and the checkout areas,
The coating, which provides a protective film that helps to kill bacteria and viruses, is also being applied to all basket and trolley handles.
Asda called on its customers to shop on their own if possible to ease congestion in stores.
Last week, Asda said its shops would be shut on Boxing Day, unlike some other supermarkets which intend to open for a limited number of hours.
The company said it wanted as many staff as possible to be able to enjoy an extended Christmas break with their family and friends.
However, some in-store pharmacies will remain open on Boxing Day. Customers wishing to use them will be escorted by a member of staff.