Loyalty schemes such as Tesco’s Clubcard and Sainsbury’s Nectar card are set to be scrutinised by the Office of Fair Trading after the watchdog revealed it is to explore personalised online offers.

The OFT has launched a “call for information” to explore the extent to which retailers are monitoring online shoppers to target them with offers to see if any action is necessary.

Personalised vouchers are increasingly prevalent in the grocery sector as the big players fight for spend.

The OFT said it will consider business and technological developments in the online shopping market, consumers’ understanding of how their information is used and whether they are being treated unfairly in law as a result of any firms using this practice.

OFT chief executive Clive Maxwell said: “Our call for information forms part of our ongoing commitment to build trust in online shopping so that consumers can be confident that businesses are treating them fairly.

“It is important we understand what control shoppers have over their profile and whether firms are using shoppers’ profiles to charge different prices for goods or services.”

Information will be gathered over the next six months with findings set to be published in spring 2013.