(Bloomberg) -- Tesco Plc and J Sainsbury’s Plc, two of the biggest UK supermarkets, make about £300 million ($376 million) a year from selling information about their customers’ shopping preferences, the Times reported.

The data collected from supermarket loyalty cards are sold to companies such as Channel 4, PepsiCo Inc. and Heineken NV, which then analyze consumer behavior and make targeted advertising. 

Most British supermarkets have some form of loyalty card program. Tesco ramped up promotions through its Clubcard this year while Sainsbury launched Nectar Prices in April, passing on discounts to customers with its Nectar loyalty card.

Customers’ personal data, such as names or addresses aren’t shared, the Times said. 

The UK’s antitrust watchdog last month said it will investigate the two-tier pricing system developing in supermarkets as a result of loyalty programs that it says can confuse shoppers.

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