Gaps will start to appear on British supermarket shelves within days if transport ties with mainland Europe are not quickly restored, Sainsbury's warned today.
Freight from France is being disrupted as part of a wider suspension of travel links with Britain to try to curb a new faster spreading strain of Covid-19.
The French government has closed its border to arrivals from Britain for 48 hours, which means no lorries can leave the English port of Dover, the main gateway to Europe.
"If nothing changes, we will start to see gaps over the coming days on lettuce, some salad leaves, cauliflowers, broccoli and citrus fruit," said Britain's second largest grocer, whose shares were down 3% today.
UK supermarkets are facing record demand due to Covid-19 restrictions on the hospitality industry and fear the transport crisis could trigger panic buying.
The British Retail Consortium said retailers had stocked up ahead of Christmas which should prevent immediate problems.
Sainsbury's urged the British and French governments to find a solution that prioritises the immediate passage of produce and any other food at the ports.
Britain's Food and Drink Federation warned the crisis had the potential to cause serious disruption to Christmas fresh food supplies and exports of food and drink.
"Continental truckers will not want to travel here if they have a real fear of getting marooned," it said.
British transport secretary Grant Shapps said the French government was keen to get the issue resolved.
"It's mostly European and French hauliers who are actually getting caught up in this and they are exporting more to us than we sell back to them," Schapps told BBC radio.
His French counterpart Jean-Baptiste Djebbari said there was a plan to establish a European-wide mechanism to allow traffic flows with Britain to resume in the coming hours.
Sainsbury's said all products for "the Great British Christmas lunch" were already in the country and it had plentiful supplies of these.
It said it was sourcing everything it could from Britain and looking into alternative transport for produce sourced from Europe.
The British Retail Consortium said that any prolonged French border closure would be a problem in the final days before a Brexit transition period with the European Union ends.
That deadline meant freight transport was running at near record levels as British companies stockpiled.
Industries beyond food and consumer goods also fear disruption from even a relatively short travel ban.
"Once all the vehicles are out of place it will take time to rebalance the system," an aerospace executive said.