Unconventional policy is becoming familiar territory. The Bank of England and the European Central Bank both left rates on hold Thursday. But both central banks are deeply worried about the effects of the eurozone sovereign debt crisis on the real economy. The BoE plans to buy another £75bn of government bonds, while the ECB is providing more support to banks. They could do better if they swapped policies.

The BoE says it is restarting its quantitative easing program because it fears the UK economy is slowing so sharply that inflation, currently 4.5%, could fall below its 2% target. It argues its previous £200bn of gilt purchases were equivalent to a rate cut of 1.5 to 3% and boosted real gross domestic product by 1.5 to 2%.