Savvy shoppers are learning that their perception of larger packs being cheaper is costing them money.

Asda, Tesco and Sainsburys have all been found to offer larger packs that cost more than buying several smaller ones, the latest being Tesco that were selling a multi-pack of three tins of tuna for £1 more than the cost of buying the three tins individually.

The supermarkets claim that the examples revealed are human error, rather than cynical pricing.