China’s sugar highs do not last as long as they used to. The saccharine stimulus of 2009-10, which relied on heaped spoonfuls of debt-fuelled investment, kept the economy fizzing at least until the end of 2011. But the impact of far larger credit infusions this year is much more feeble.

An economic equivalent of insulin resistance appears to be setting in. So large is the credit injection that much of it cannot be productively absorbed. This has led to liquidity spillovers that have spurred a speculative frenzy on commodity exchanges.

A tide of money has flowed into China’s commodity exchanges, bidding up iron ore and steel prices this year by about 50 per cent. So fevered did trading become that in April one steel futures contract alone recorded a turnover of 1.4bn tonnes. But in the last few days, prices and volumes have slumped.