When figures on Thursday morning showed that activity in China's manufacturing sector had turned down in January, investors suffered a crisis of confidence.
It was only a slight downturn - the purchasing managers' index (PMI) falling from 50.5 to 49.6 - but it hit a nerve because only a couple of days previously China had announced a further slowdown in its overall economy in the fourth quarter of 2013.
The concern was that slower growth in China, coupled with the wind-down of stimulative money-printing by the Federal Reserve, would have a dampening effect on emerging market economies.
Investors hurried to offload anything that looked vaguely risky, including the currencies of commodity-exporting countries. They shifted their money into the 'safe' Swiss franc, Japanese yen, euro and, to an extent, the pound.
Hardest-hit was the South African rand, which has lost 29 per cent of its value in the last 12 months, falling even further than the Australian dollar.
Sterling got lucky again on Wednesday with news that UK unemployment had fallen to 7.1 per cent, within spitting distance of the 7 per cent level below which the Bank of England would no longer rule out an interest rate increase.
The BoE governor was quick to point out that sub-7 per cent unemployment is not a trigger for higher rates, it is simply one of the factors considered by the Monetary Policy Committee.
Mr Carney went a step further on Friday when he said in a speech: 'The appreciation of sterling will hold back the expansion of net exports.'
The logic of his argument is debateable; Japan's trade deficit widened to a record in 2013 even as the yen lost 24 per cent of its value.
Even so, when a central banker talks down his currency it behoves the market to pay attention.
