Turnover in the international foreign exchange market grew by more than two thirds to $3.2 trillion (€2.4 trillion) a day during the three years to April, according to the Bank for International Settlements, driven mainly by return-seeking financial investors such as hedge funds.

The bank, which fosters international financial co-operation, said the increase in traditional foreign exchange markets - currencies and some well-understood derivatives - was far stronger than that seen between 2001 and 2004.