How long can the run on the dollar continue? Last year’s dollar slump, with its attendant rise in commodity prices, ended when the market put paid to it. This time governments are attempting to slow it down.

But it is not, as widely expected, the US government that is doing this. Instead, Canada’s central bank on Tuesday talked down its own currency, which was close to parity with the dollar. Brazil’s government went further, imposing capital controls to stop the real gaining at the dollar’s expense. Other countries, it appears, have more to lose from a weak dollar than the US does.