China probably does not have a stock market bubble yet. But when Chinese officials start to use the B-word – as Cheng Siwei, vice-chairman of the National People’s Congress, did yesterday – it is time for investors to worry.

In March 2001, Zhu Rongji, then China’s premier, warned that a bubble in the country’s B-shares was “un-avoidable”. It may have been unavoid-able but it was also unsustainable. There followed a crackdown on illegal bank loans used for speculation, reforms to the markets and a stock market slump that lasted for five years.