Historical Price Timeline

A few weeks ago, Tesco had a noticably massive jump up in prices. Then did a big advertising campaign saying "Prices locked until Easter". Now they are plastering discounts galore with that annoying smiling lady. I shall name the advertising campaign "the great British rip off". Would be good to see which supermarkets have more of a stable price history for products rather than ramping up prices and then apply a "discount"