Abstract With the beginning of EMU there will be only one monetary policy with a single short term interest rate. In order for common monetary policy to be successful EMU member states have to react similarly to monetary signals from the European Central Bank (ECB). Because of its unique sensitivity to short term interest rates, this would not be the case for the UK. If, for example, the ECB would raise the short term interest rates by an amount which is appropriate for countries like France and Germany, the UK might sink into recession. This shows that besides political reasons there is also an economic reason for the UK’s opting-out from EMU.