Central banks in advanced economies are in uncharted waters. Asset purchase programmes have gone on longer and balance sheets ballooned by more than originally envisaged. Policy rates have been pushed below zero, creating the potential for unexpected, back-to-front effects – such as rising mortgage rates in Switzerland as banks search for profits. And still inflation refuses to rise in many countries.

The idea of helicopter money, or overt money finance (OMF), has been around for years, but it