The 50 per cent fall in oil prices this year is self-evidently good news for all but oil-producing states, regions and companies. It also reminds us that the world economy is deflation-prone — both because of deficient demand in Europe, Japan and several big emerging markets and because China’s deflation, rooted in excess capacity, is structural and of growing significance.

A persistent and as yet unfinished slowdown in the country’s economic growth has been accompanied by the emergence of substantial overcapacity, a significant rise in non-financial corporate debt and a big drop in inflation. Between 2011 and November 2014, Chinese producer prices fell by 10 per cent — the annual change has been negative for 33 months — and the annual rate of consumer price inflation has fallen from 6 per cent to 1.4 per cent over the same period.

The ratio of output to capacity in many sectors — for example, steel, plate glass, construction materials, chemicals and fertilisers, aluminium, shipbuilding, and solar panel and wind turbine manufacturing — has fallen sharply. Last year it was about 70-72 per cent, and it is likely to have dropped further since.Property was the main beneficiary of the post-2008 investment and credit surge, accounting for about 16 per cent of China’s gross domestic product directly; it is now in a secular downturn. Inventories of unsold homes in many cities outside Beijing, Shanghai and Shenzhen have risen sharply to between 25 and 40 months of supply.