The chief executives of the Co-op Group and Costcutter have joined forces with grocery multiples to warn MPs that their customers will be among the first to experience the realities of a no-deal Brexit.

In an open letter to the MPs, sent by the British Retail Consortium (BRC), the retailers responded directly to the government’s own projection that freight through Calais may fall 87% from current levels, threatening the availability and shelf life of many products in stores.

If the UK were to revert to World Trade Organisation (WTO) terms, as currently envisaged in the no-deal scenario, it “would greatly increase import costs, which could in turn put upward pressure on food prices”.

“We are extremely concerned that our customers will be among the first to experience the realities of a no deal Brexit,” the letter stated.

“This complex, ‘just in time’ supply chain will be significantly disrupted in the event of no deal. We are therefore asking you to work with your colleagues in Parliament urgently to find a solution that avoids the shock of a no-deal Brexit on 29 March and removes these risks for UK consumers.

“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.”

The letter highlights that nearly one-third of the food eaten in the UK comes from the European Union (EU), with the situation potentially worsening in March when British produce is out of season, with 90% of lettuces, 80% of tomatoes and 70% of soft fruit sourced from the EU at that time of year.

The letter was signed by Jo Whitfield, retail chief executive of the Co-op, Darcy Willson-Rymer, chief executive of Costcutter Supermarkets Group, as well as executives from Sainsbury’s, Asda, Marks & Spencer, Waitrose, Lidl, McDonald’s, KFC, Pret A Manger and the BRC.

Costcutter retailer, Suresh Arulananthan, said: “I am a little worried, because you hear that costs might go up and that sort of thing. But, the issue is that we still don’t actually know what will happen. You cannot plan or anything.

“It is too early to decide on anything, as we don’t actually know what the outcomes may be. I really don’t know. People are saying that it will affect retailers but we’ve not been told anything directly. Even with letters like this, nobody really know.”