keith doyle, bbc news.n's biggest supermarket has pledged to take immediate action following a bbc investigation revealed overcharging. over three months a team from bbc inside out visited 50 branches across england and found multi—buy deals still being advertised days, weeks and in some cases months after the deductions were no longer valid at the till. jonathan gibson reports. when we see a special offer on the supermarket shelves, we expect to pay that price at the till. but it's not always the case at tesco. and here's why. the bbc visited 50 tesco stores across england, and was overcharged in 33 of them. tesco did not want to do an interview, but after reviewing the bbc‘s evidence, said... but that's just the start. following our investigation, britain's biggest supermarket has said it will be doublechecking the accuracy of every price in every store. that's more than 3,500 stores across britain. jonathan gibson, bbc news. and ben's here to tell us more. how do you even know you're paying the wrong pri