SOME 90 years ago, in an essay entitled "The end of laissez-faire", English economist John Maynard Keynes presciently wrote that there are limits to the doctrine of laissez-faire - economic liberalism, free trade, and the idea that there should be as little government regulation as possible.

He singled out three problems: self-interested individuals aggravating the inequalities of capitalism; savings being distributed towards unproductive forms of investment; and population issues. "The time has already come when each country needs a considered national policy about what size of population, whether larger or smaller than at present or the same, is most expedient," he wrote. "The community as a whole must pay attention to the innate quality as well as to the mere numbers of its future members."

These musings on political economy and immigration have become ever more relevant after Britain's decision to leave the European Union. A political and economic union that Europe aspires to entails both free trade and the free movement of people. Both ideals are increasingly problematic.