Online retailers are being investigated for the practice of targeted pricing and advertising while supermarkets’ Bogof offers are also being scrutinised.

The Office of Fair Trading (OFT) is looking into whether e-tailers are charging customers different prices for the same items, by determining how much shoppers will be willing to pay based on their purchasing histories.

The OFT is also looking into how internet retailers vary their advertising and marketing based on customers’ previous searches and purchases.

The competition body will also look into supermarket promotions.  The investigation will concentrate on the internet, although will also look at promotional activity in stores.

Oxford University Internet Institute research fellow Greg Taylor told The Times that retailers could charge higher prices from customers by asking them to register for a website – if a customer returns after registering they are deemed to be loyal, indicating they may be willing to pay a higher price.

In 2000 it was revealed that Amazon, the world’s largest online retailer, charged shoppers that deleted their cookies – computer files that hold date relating to a user’s internet use – a different price to those that did not.

Taylor said: “When it emerged Amazon was doing this there was a consumer backlash, but I don’t know if anything can be done to stop it.”