It was exactly 12 weeks ago that the People’s Bank of China said it was swapping a peg for a basket. Since then, China’s currency has strengthened against the US dollar by almost exactly 1 per cent, thanks mostly to a sudden lurch upwards in the past two days. It is now up to a committee of the US House of Representatives, which convenes next week, to decide whether 97 basis points of appreciation in three months is enough to end the threat of trade sanctions.

It almost certainly won’t be. Many took June’s announcement of “enhanced flexibility” to mean a resumption of the steady 2005-08 pre-Olympic pace of appreciation against the dollar, about 6 per cent a year. But after an initial 10-day spurt, the renminbi held broadly stable in July, as other emerging market currencies made big gains against the dollar. In August it actually went into reverse; in September, so far, it is up again. The strongest observable correlation is not with the 11 currencies in its basket (the exact weightings, as ever, remain a mystery) but with the pronouncements of Timothy Geithner. This week’s 36bp surge came after the US Treasury Secretary said “we’d like to see [Beijing] move more quickly”. Voila!

Never mind that the case that the renminbi is unfairly cheap is an uncertain one: the dollar itself is just 8 per cent higher than its post-1973 trade-weighted low. Never mind, either, that August’s trade data showed that import growth is back on the trend set before the 2008-09 recession, that the pace of growth in imports comfortably outstripped growth in exports, or that on an absolute basis, China’s imports (+12 per cent) have grown much more than exports (+3 per cent) since August 2008. While President Obama readies for mid-term elections in November, the US is committed to a narrative it cannot afford to drop. China seems quite happy to play along, provided it can extract maximum advantage elsewhere. Expect a few more basis points of appreciation the next time the US complains.