Businesses will over-stock some things, yes. But that can only possibly be a partial solution. Current projections are for 6 months of disruption, and we import around 40% of our food. There isn’t enough warehouse room available for supermarkets to suddenly store that much food instead of the few weeks worth they currently keep on hand (not can a lot of fresh food be stocked up like that).
Farms can’t ramp up production in any meaningful way to compensate fast enough, and even some of the home grown stuff will be affected; we currently (in a good year) produce enough wheat to directly feed people, but we also import grain as cattle feed. Crops for April (and there’s very little harvested that time of year) would be already in the ground, there’s no changing that now. A no deal would definitely mean a huge shortage of fresh food. There’s no way around that.
More urgently, there also aren’t enough cold stores available to store 6 months of insulin and other temperature sensitive drugs for the NHS, even it was possible to advance order that quantity, which it isn’t, not in the time frame available. Even stuff made here is likely to require ingredients processed overseas.
In Cornwall, we’re projected to be one of the hardest hit areas from any disruption, and ‘chaos’ sounds like a pretty good term. 3 days of snow stopped lorries from Portishead last February and it was over 2 weeks before the shops were properly stocked again. Our supply chain is very fragile. It’s built around the assumption that stuff will be available immediately, or in a few days at most. There isn’t time to completely rebuild it before the end of March.