As both an Economist and Accountant (FCPA) I can see no justification for the Potato, Egg or other similar marketing authorities. They simply stile competition and make farmers strategically lazy. Most farmers have to make a choice about what to grow each year and gamble on what the market will return. Controlling what farmers grow also limist what consumers can buy. The "Karen" farmer jumping up and down in France are in part a result of past over regulation of the markets and producers. See
https://www.youtube.com/watch?v=DnSXwrlrwIE and how over-regulated farmers in the UK and Europe are. The only downside I can see in getting rid of of the Spud body and deregulating, is that ultimately too many farmers following others into, what was initially, the extremely lucrative avocado growing business creating an excess demand for water in the South West so that just about all running water was dammed exacerbating existing serious water salination and associated environmental issues.