In popular accounts of the South Sea Bubble in the early 18th century, one tale is often told. A dodgy company that was launched in that era was described merely as “an undertaking of great advantage but nobody to know what it is”. The story is, alas, apocryphal. But step forward three centuries and the financial sector has delivered the real thing.

In 2020 and early 2021, Wall Street was flooded with special purpose acquisition companies (Spacs). These are shell groups created to buy companies that are already listed on the market. When investors buy shares in a Spac, they do not know what business it will acquire. But presumably, they believe it will be “an undertaking of great advantage”.

Enthusiasm for Spacs has waned since the first quarter of the year. But there are plenty more objects of speculation available. In late July, Robinhood, the share-trading platform, floated on Wall Street. After a lacklustre opening, its shares jumped 50 per cent in a single day in early August. That was fitting because US retail investors have been using Robinhood to speculate on individual stocks such as Tesla and GameStop.