The UK's Office of Fair Trading has said it is investigating possible overcharging on certain supermarket chains' online retail sites.

The online prices of Asda, J Sainsbury and Tesco are under scrutiny after complaints that food prices were higher online than in stores, that some customers have been charged for premium products but received regular products, and that supermarkets were using their websites to sell fresh groceries close to their sell-by date, reported The Financial Times.

Asda said it had met with the OFT to address concerns but insisted there was no difference between prices online and in-store. Tesco said it had been contacted by the OFT but denied it overcharged its online customers. Sainsbury said it only charged customers for the products they received when substitutions were made and that it would not include fresh goods close to their sell-by date in online purchases.