Britain must produce as much food as possible," Hilary Benn, Secretary of State for the Environment, Food and Rural Affairs, told the Oxford Farming Conference in January. For Mr Benn, who rounded off the proposition by adding "no ifs, no buts", nothing could be more obvious. Wasn't Mr Benn uttering a mere platitude? Who would dispute that every nation must produce "as much as possible", the maximum, of everything?
Well, Adam Smith, the founder of economics, would. His key argument in the Wealth of Nations, published in 1776, was that a nation had a finite quantity of resources, which were to be allocated between industries in the most efficient way. Although that may sound banal, it quickly leads to the refutation of Mr Benn's maximisation idea.
In his chapter "Of restraints upon the importation from foreign countries of such goods as can be produced at home", in book IV of the Wealth of Nations, Smith conjures up the image of wine-making in Scotland. "By means of glasses, hotbeds and hot walls, very good grapes can be raised in Scotland, and very good wine too can be made of them."