It epitomises China’s position in the global economy that a seismic warning about its health last week came from a US company: Apple. The iPhone maker cut sales forecasts, citing the unforeseen “magnitude” of the economic slowdown in China – a vital growth market. At the same time the head of Baidu, China’s biggest search engine, warned his employees that “winter is coming” in the world’s second-largest economy.

If China is indeed entering an economic winter, then the chill will spread around the globe. Forty years after communist China opened its doors to trade with the west in a dash for growth, the country’s mix of free-market policies and central planning faces one of its sternest tests.