While im sure they don't utilize all of their available farm land, it is worth mentioning that Britain imports almost 30% of their food, which means they are at

While im sure they don't utilize all of their available farm land, it is worth mentioning that Britain imports almost 30% of their food, which means they are at or near the limit of sustainably feeding themselves, and even then almost 60% of the world's crop yield is the direct result of fossil fuel derived fertilizer, which we are going to have to give up soon if we don't all want to be cooked alive, which will increase the energy costs of fertilizer production 10 fold. The US would be hard pressed to find similar external sources of food if their population density rose significantly higher. Especially on top of all the desert and arid grassland areas that are pretty poor for farming.