A no-deal Brexit threatens the UK's food security and will lead to higher prices and empty shelves in the short-term, retailers are warning.
UK retailers' industry group the British Retail Consortium has written to MPs with the warning, saying that the food retail sector's complex just-in-time supply chain will be significantly disrupted in the event of no deal.
The letter was co-signed by several of the major UK food retailers, including the chief executives of Marks & Spencer, Waitrose, Sainsbury, Asda and Morrisons.
It said: "Even if the UK government does not undertake checks on products at the border, there will still be major disruption at Calais as the French government has said it will enforce sanitary and customs checks on exports from the EU, which will lead to long delays.
"For consumers, this will reduce the availability and shelf life of many products in our stores.”
"We are extremely concerned that our customers will be among the first to experience the realities of a no deal Brexit," the letter says.
The letter uses the government's own projection that freight through Calais may fall 87% from current levels, threatening the availability and shelf life of many products.
It expresses worry over tariffs, with only 10% of the UK's food imports currently subject to World Trade Organisation (WTO) rules.
The retailers are warning that if the UK reverts to WTO rules, following departure from the European Union in March, the tariffs would "greatly increase import costs that would in turn put upward pressure on food prices".
The letter spells out the UK's food relationship with Europe, with nearly one third of the food in the UK coming from the EU.
"In March, the situation becomes more acute as UK produce is out of season," the letter says.
The letter points out that at that time of year, 90% of lettuces, 80% of tomatoes and 70% of soft fruit sold in the UK is grown in the EU.
"As this produce is fresh and perishable, it needs to be moved quickly from farms to our stores," the retailers say.
Their letter says that stockpiling fresh food is impossible and that the complex, just-in-time supply chain through which food is imported into the UK will be "significantly disrupted" in the event of a no-deal Brexit.
It adds it is difficult to stockpile any more produce as "all frozen and chilled storage is already been used".
"While we have been working closely with our suppliers on contingency plans, it is not possible to mitigate all the risks to our supply chains and we fear significant disruption as a result if there is no Brexit deal," the retailers say in the letter to MPs.
The retailers say that while they are looking for alternate supply routes, there are limited options and not enough ferries.
A spokesperson for the Department for Environment, Food and Rural Affairs said: "The UK has a high level of food security built upon a diverse range of sources including strong domestic production and imports from other countries. This will continue to be the case whether we leave the EU with or without a deal."
They added the government had "well established" ways of working with the food industry to prevent disruption.