Sainsbury's supermarket in London is currently testing the Scan and Go self-checkout app that made headlines here in the U.S. when Walmart piloted the program.

The customer logs in by scanning a QR code when they arrive, and then scan the QR codes on packaging or on the shelf next to the price information, according to an article on truthdive.com. Loose items like fruit and vegetables are weighed on scales, and a QR code is printed out which can be scanned by the app.

A learning function monitors spending habits and flashes up special offers depending on the shopper's whereabouts in the store; however, critics fear the system will cause supermarkets to cut back on staff and effectively spy on their customers by monitoring their spending habits, the article reported. 

Sainbury's describes the system as a third option and insists it is not planning to phase out manned or self-service checkouts.

Read more about self-checkout.