Investors in public securities have a problem. Their universe is shrinking. The number of companies quoted on stock exchanges around the world has fallen in all of the past four years. In the US, the figure has almost halved in the past two decades.

Many big investors worry that this is not healthy for market capitalism. But at least these institutions can buy private assets, such as unquoted companies, private equity and real estate, where the returns have been better than listed stocks and are expected to remain so.