On May 17th 2011 at 08:30GMT the Office for National Statistics released another CPI report (y/y).
Previous value: 4.0%; Forecast: 4.1%
Consumer Price Index (CPI) is some kind of an overview of the prices on various products and services over a certain period of time. 
The Bank of England considers the index when deciding on further steps to control the inflation rate. As a rule the Bank of England raises the interest rates when the CPI grows in value. It gives the national currency (GBP) an edge as an object of speculative investments.
Obviously, all the CPI news releases are of high importance to Forex traders. When the index value increases, it is recommended to start looking for an opportunity to buy the British Pound.
The data are published approximately in the 2nd decade of every month.
