The high-profile departure this week of a team of commodity traders from Barclays Capital to set up a hedge fund provides modest cause for celebration, as does the wider retreat from banks’ own-account trading prompted by America’s Dodd-Frank Act. For the hedge fund world is where such proprietary traders – a euphemism for speculators whose trading is unrelated to the needs of bank customers – surely belong.

As Paul Volcker, the former chairman of the US Federal Reserve, rightly diagnosed, the implicit taxpayer support enjoyed by banks that are too big to fail means that the big banks’ own-account gambling has enjoyed an absurd public subsidy. That was one of many encouragements before the financial crisis for excessive risk-taking by conglomerate financial giants. Mr Volcker’s perception is shared by the UK’s Independent Commission on Banking led by Sir John Vickers, although the commission’s solution to proprietary trading is to ringfence retail banking rather than prohibit the activity.

The curious thing is that commodities should ever have been considered appropriate assets for a bank to trade in the first place. There was a time when novice bankers were taught that illiquid or highly volatile assets should play little part on bank balance sheets. In the Anglo-American banking world even equity shares were regarded as dangerous. That prejudice turned out to be amply justified when cross-shareholdings in the Japanese banking system caused bank capital to shrink calamitously as the stock market collapsed after 1990.