Alan Greenspan, the former chairman of the US Federal Reserve, was very used to speaking obliquely to give nothing away to the financial markets. Legend has it that he had to repeat a marriage proposal made to his second wife because she didn't understand him the first time.

US traders may have been left similarly confused by a much anticipated speech yesterday by the current chair, Janet Yellen.

The bottom line appears to be that a Fed rate rise next month may well be on the cards. This led to a strengthening of the US dollar and some easing in the stockmarket.

But Yellen surrounded her comments with so many caveats that nobody can be sure. The Fed wants to raise rates, but a few more crucial pieces of data will be needed to provide the green light.