Retail Price Index:

This is an index used in the United Kingdom that measures the cost in a given period of the goods and services purchased by a typical consumer in a base period. A narrow measure of inflation, because confined to consumer goods and services. The series used in MeasuringWorth incorporates the official retail-price-index series only from 1948 onward. For earlier years — from 1947 all the way back to 1264 — the series of various economic historians are utilized. The component series are linked so that a consistent retail-price-index series is obtained continuously from 1264 to the present.