We’ve seen that there are historical reasons why we have different measures of inflation. While the RPI was the UK’s official measure of inflation from 1956, it began to be supplanted by the CPI (and CPIH) from the early 2000s.
However, to add to the confusion, different measures of inflation are still used for different purposes by government and companies. Some critics believe this is ‘inflation shopping’. For example, many items that provide the government with income (such as tobacco and alcohol duty) are linked to RPI, which consistently calculates a higher rate of inflation and thus extra income. On the other hand, increases in government expenditure (such as that on state pensions and benefits) are linked to the lower CPI index, resulting in a lower rate of increased spending.