The ghosts of Federal Reserve chairmen must be a particular fearsome gang of wraiths. Even the incumbent versions often appear like spectres of doom, perpetually appearing at the foot of America’s metaphorical bed in the middle of the night and gibbering dire warnings of rampant inflation and financial market instability.

How much more terrifying, then, for the spectre of the recently resigned Fed chairman Alan Greenspan to appear at the height of a financial crisis. Since he left office last year Mr Greenspan, rather than fading quietly into the night and fog, has been clanking his chains loudly.