The dollar emerged as the week's top performer, adding two and a half Japanese yen and strengthening by a cent against the euro. Its rise was mostly the result of current interest rate differentials and a growing expectation that the Federal Reserve will, after all, deliver the long-awaited rate increase in December.

But it was sterling that hogged the limelight, for the worst of reasons. The pound was in full flight, falling by an average of -3% against the other dozen most actively-traded currencies. It fell off its precarious perch after the prime minister announced that the process of Britain leaving the EU would begin by the end of March. The news startled investors and sterling's losses were exacerbated by a sharp downward spike on Thursday night. All in all the pound lost five and a half US cents on the week and it is down by -16% from its position on Brexit Eve.