BBC: We are standing under endless Fenland skies. It’s not yet Eight O Clock, but already the sun is warm and high. We are surveying three fields on Duncan Worth’s farm. Before us, glossy green potato plants with their scented white flowers; to the left of us, maize to be used in power generation; to the right of us, wheat. “It’s been ideal growing weather recently,” Duncan says, “sunshine and the right amount of rain.” But for how much longer? The hotter, drier summers …