On May 17th 2011 at 09:30GMT the Bank of England released its official inflation letter.
BOE Inflation Letter is published when the CPI exceeds 3% or declines below 1%. . 
The letter reflects the steps taken by the Bank of England in order to change its monetary policy when the CPI value deviates by more than 1% from the standard value of 2%. The letter is addressed to the UK’s Chancellor of the Exchequer.
Obviously it is of high importance to those who trade Forex. Investors and traders pay attention mainly to the general tone of the letter. Confidence in the tone usually leads to the strengthening of the British Pound.
The report is released after the CPI y/y.
