About 3 years ago (maybe), the staff at Asda started asking people for their postcode when buying things at the tobacconist counter and paying by cash. This lasted for a few months. The first time it happened, I said that I couldn't remember but after that happened I started giving them the postcode for the Asda store, which they typed into the till terminal. I assume it was an experimental marketing exercise and I know it was bloody annoying.