A few years ago Andrew Haldane, the chief economist at the Bank of England, told a British parliamentary committee that global interest rates were at the lowest-ever level. A wise colleague challenged him afterwards: "How do you know they were not lower in Babylonian times?"

Recalling this exchange at a speech given recently to the Open University in London, he told his audience: "Several exhausted research assistants later, I can report that, luckily, I was on safe ground. Interest rates appear to be lower than at any time in the past 5000 years."