It didn’t take a big demand increase to start seeing gaps in shelves, and once that happened a degree of panic took hold and even though there was plenty in stock in warehouses, it wasn’t able to be distributed fast enough.
The difficulty is that the big supermarkets have got their supply chain down to a fine art and it only takes a small fraction of people to start buying an extra here and an extra there for it to start having an impact and they then have to struggle to keep up.