This isn't a new thing. In the past, Marks & Spencer gained notoriety for placing a big contract with some clothing supplier. Often enough, the manufacturer would be fully committed in completing the M&S order over the next year or more, and would have had to refuse orders from anyone else. But if M&S found a substandard item or two, they'd simply cancel the contract there and then, leaving the supplier with nothing to sell, and no orders for months ahead.
Some years ago, Asda was actually importing milk from Normandy for sale in their supermarkets in the south of England, since it cost them less to do so.
It's ironic that supermarkets should be bragging about their support for Fairtrade products, yet at the same time are putting our producers out of business. How about applying Fairtrade principles to British suppliers?