The (imaginary) starting point
At some point in the past, say around 1900, all food in the UK was produced by natural methods. This was 'by default', because there were no other techniques available - it was what we would today call 'organic'. People had done their best, slowly breeding better types of plants and animals, working out how to improve the soil with manure, to improve yields and fertility. People's bodies had adapted to eat this local diet over thousands of years.
Three main points can be made about this:-