Whenever the political pressure over currency controls gets intense, China allows its currency to rise against the dollar. This ought to prove the critics’ point: the renminbi is manipulated. Instead, it usually strengthens the position of the softly-softly brigade.

This month may turn out differently. True to form, September’s combination of hearings in the House of Representatives, intervention by President Barack Obama and a New York visit by Wen Jiabao, China’s premier, has led to the biggest rise in the renminbi since 2008, when the credit crunch brought a halt to its gradual appreciation. Even so, legislation aimed at punishing China is expected to move to a vote tomorrow.

US politicians are pushing at what should be an open door. Chinese inflation is up sharply, hitting 3.5 per cent last month, thus meaning the currency is already rising in real terms. A nominal rise would be partly offset by lower inflation.