The traditional measure of inflation in the UK for many years was the Retail Price Index (RPI), which was first calculated in the early 20th Century to evaluate the extent to which workers were affected by price changes during the first world war. The main index was described as the Interim Index of Retail Prices from 1947 to 1955. In January 1956, it was rebased and renamed the Index of Retail Prices. In January 1962 this was replaced by the General Index of Retail Prices, which was again rebased at that time. A further rebasing occurred in January 1987, subsequent to the issue of the first index-linked gilts.
On election in May 1997, the new Labour government handed control over interest rates to the politically-independent Bank of England Monetary Policy Committee. This committee is given the responsibility of adjusting interest rates in order to meet an inflation target set by the Chancellor.. The initial target rate of inflation was an RPIX of 2.5%. The committee meets once per month to decide if any changes to the interest rate are necessary. If, in any month, inflation deviates from the target by more than one percentage point, the Governor of the Bank of England is required to write an open letter to the Chancellor explaining the reasons for this and to propose a plan of action for bringing inflation back towards the target.
Since 1996, the United Kingdom has also tracked a Consumer Price Index figure, and in December 2003, the inflation target was changed to CPI of 2%, from the previous target of RPIX of 2.5%.
The change in the CPI over the 12 months to August 2008 was 4.7%, while the corresponding figure for RPIX (which excludes mortgage interest) was 5.2% and that for RPI (which includes mortgage interest) was 4.8%. The CPI, the RPIX, and the RPI are published monthly by the Office for National Statistics.