Which of the following events would you say caused the biggest fall in inequality: the invention of income tax, the introduction of tax credits to support low income workers, or the Black Death?

It is, of course, a trick question. The gap between rich and poor actually increased after Pitt the Younger levied Britain’s first income tax and, for that matter, in the decade or so after Gordon Brown created tax credits. The Black Death, however, is another story.

Though the data is understandably thin, what we know about medieval income distribution suggests that the plague, which killed about one in five Britons, reduced inequality more than any other single event in history. In the years that followed, the diminished workforce enjoyed rapid rises in