It used to be that when America sneezed, the rest of the world caught a cold. Now the US has real competition when it comes to spreading economic influenza. These days, it seems, if China sneezes, the world comes down with bird flu.

That is hardly surprising given China now accounts for 16 per cent of global output, the same as the US in purchasing power parity terms. Although economists have long urged Beijing to adopt pro-market reforms, the dirty secret is that China has borne the global economy on its back by doing precisely the opposite. Now its economy is juddering and its policymakers are allowing markets to exert a modicum of influence, global investors are looking on in horrified awe. Back in 2008, when the world went into virtual lockdown, it was Chinese state intervention — old-fashioned pump-priming on a truly colossal scale — that kept things going. Chinese demand for oil, iron ore and copper triggered booms in commodity-producing countries from South America to Africa. A surge in Chinese consumer demand kept US carmakers and Taiwanese chipmakers afloat.

For the Chinese economy, though, there was a price to pay. Total debt in