Best answer by Mohammed
Welcome to the iD Commmunity.
You can find all the information relating to the Retail Price Index on
https://www.idmobile.co.uk/help-and-advice/retail-price-index?_ga=2.87867864.1922388816.1525173156-1922580118.1478614453&_gac=1.48375508.1523898647.CjwKCAjwk9HWBRApEiwA6mKWaTBBOVd0th5YQikXdF4ktSNrXCsQxF2fegxE1aAwllZWrLDHZFkySRoC0ZkQAvD_BwE
Mohammed