When the economy is in turmoil, no one is demonised more than the speculator. First, we are told, speculators have driven up the price of oil, condemning us to expensive heating and motoring. Then, they have driven down the price of bank shares, dealing vicious blows to the City’s noblest banks. All of this, we are supposed to believe, is immensely profitable and highly destabilising.

With one exception – that I’ll come to – I am not persuaded. I struggle to understand how speculation is supposed to be both profitable and destabilising, all at once. Profitable speculation requires buying low and selling high. Destabilising speculation requires the opposite: short-selling shares in a trough, thus deepening the trough, and betting that frothy shares will become frothier. In other words, destabilising speculation means selling low and buying high. If that is a recipe for profit, I am missing something.