People want everything to be cheap, so supermarkets (who hold a monopoly on sales) squeeze everyone down the chain. Ironically, the source (the farmer) gets pressurised the most, and make very little from their products. They can't do anything about it because who else can they sell their product to?
I have never understood this argument from a USA standpoint, cause every farmer here has a 75k brand new pickup truck (they don't use this for work they have other trucks for that) and a big ass half a million dollar country 2-3 story sized home. I don't buy this argument, farmers do pretty damn well, at least in America's cornfields and soybean fields where I live. Not sure about the UK though, it may be different there, but I doubt it, I think people are just getting greedier and trying to get as much of the pie as they can get. I have a buddy in Ireland who is a farmer who just built himself a new house in his 20's (yes his own house and he doesn't work a second job and his farm is small lol), and he complains all the time about how the EU is ruining farming, yet here I am almost age 40 living at home with my parents... so....
I think in order for me to agree one way or the other on these matters is a little transparency on actual net income (after farming expenses taken out as well as taxes) amounts by said farmers doing the protesting. This is one thing I like about Finland, everyone's income is public knowledge, and this way if farmers protest there, it should be very easy to utilize the virtue of reason to see if you agree with them or not.