Speculation that the Bank for International Settlements was intervening on behalf of the Swiss National Bank to stem the rise of the Swiss franc sent the currency tumbling yesterday.

Traders said they saw bids from the BIS to buy the euro and sell the Swiss franc in the currency market. As the news spread across the world's trading floors, the euro rose from SFr1.50 to above SFr1.51 against the Swiss franc in a matter of minutes.