I came to this thread when 31 pages had been written and do not have the time to read them. I am sorry not to get able to do so.
Resale Price Maintenance was a blunt way of helping farmers and it was hoped that getting rid of would, as you remind us, bring down prices.
It would be interesting to know if research has shown this happened. One thing that I believe has been shown to be true is that many families, particularly low income ones, now live on ultra-processed foods. This seems to me to have maintained higher prices for the consumer just switching profit from farmer to manufacturers and giving the NHS high levels of obesity to deal with in the process. If this repeats what others have said I think it bears repetition.
There was a drop in the birthrate in the '60s too and those who, like me, lived and had family working in farming communities watched them rapidly change as they lost their schools, shops, local businesses and often the smaller farms. Farming turned into "the countryside" and communities into dormitories for bigger towns and cities.
I later worked for a quango which dealt with "food" for the government. Very little seemed to be about food production and much about food manufacturing.
I am not suggesting that change is not inevitable, but much does not seem to have changed for the better where our food is concerned.
I don't have great solutions to offer but getting and keeping the land farmed does seem to be a first step. Stopping land being a tax avoidance vehicle does seem like a good first move.
I do believe we should protect older farmers who do not have time to make this work and I would suggest the 50% rather than 100% is an attempt to do that.
Perhaps the next step is to remove the very highest processed foods which often seem to be just a collection of chemicals held together by foods which become toxic when over consumed?