When Haruhiko Kuroda, governor of the Bank of Japan, suggested last week that China should use capital controls to support its currency, it was as if he had broken a taboo.

Asked if she approved, Christine Lagarde, managing director of the International Monetary Fund, sitting with Mr Kuroda on a panel at the World Economic Forum in Davos, dodged the question, although she did agree that it would be unwise for Beijing to burn through its foreign exchange reserves to support the renminbi.

Her circumspection was not surprising. Policymakers talk of capital controls at their peril: merely to mention them can send nervous investors rushing for the exit. Investors in China, where the Shanghai index is down by 47 per cent from last June’s peak, have been extremely jittery this year.