Of course, an anonymous random poster who " worked for over 20 years in the industry." knows better than the heads of all these supermarkets and food chains 
I've "thought it through" and I'll believe the warnings of these major businesses over the Brexiter "They need us more ..."
Brexiters have been WRONG so far at every stage of the "easiest trade deal in history"
Food retailers warn MPs on risk of No Deal Brexit
https://www.ft.com/content/71af1f88-230b-11e9-8ce6-5db4543da632
A no-deal Brexit would quickly trigger a jump in food prices and a reduction in choice of products,
British retailers have warned in the latest plea by big business against leaving the EU without a deal
Food retailers warn of higher prices and gaps on shelves in event of no-deal Brexit
https://www.telegraph.co.uk/business/2019/01/28/food-retailers-warn-higher-prices-gaps-shelves-event-no-deal/
The bosses of several major supermarkets and fast food chains have waded into the Brexit debate, warning of higher prices and gaps on shelves if the UK leaves the EU without a deal in March.
In a letter to MPs, the chief executives of Sainsbury’s, Asda and the UK arms of McDonald’s and KFC said
their “complex, just-in-time” supply chains would be “significantly disrupted in the event of no deal” as French officials impose customs checks in Calais < and the ports become logjammed >
The UK imports about a third of its food from the EU and even more during March, when many fruits and vegetables, including lettuce and tomatoes, are out of season, the letter says.
Some of Britain’s leading stores have warned that a no-deal Brexit will drive up food prices and pose a “significant” risk to the range of products on supermarket shelves
https://www.theneweuropean.co.uk/top-stories/top-retailers-warn-of-food-running-out-after-no-deal-brexit-1-5868922
Signatories to the retailers’ letter include Sainsbury’s, Asda, Marks & Spencer, the Co-Op, Lidl, Waitrose, Costcutter, KFC, McDonald’s and Pret A Manger as well as the British Retail Consortium.
They warned that the UK relies on Europe for almost one-third of its food, and that it will not be possible in a no-deal scenario to mitigate all risks to supply chains, many of which involve highly perishable goods.