The watchdog will gather further information to determine whether these two firms may have broken consumer law by taking insufficient action to protect shoppers from fake reviews.

The move comes after an initial CMA investigation, which opened in May 2020, assessed several platforms’ internal systems and processes for identifying and dealing with fake reviews.

This work raised concerns such as whether Amazon and Google have been doing enough to detect fake and misleading reviews or suspicious patterns of behaviour. Suspicious behaviour patterns include where the same users have reviewed the same range of products or businesses at similar times to each other and there is no connection between those products or businesses.

In other cases reviews suggest that the reviewer has received a payment or other incentive to write a positive review.

The CMA is also concerned that Amazon and Google are not investigating and removing fake and misleading reviews from their platforms, or imposing adequate sanctions on reviewers or businesses to deter them and others from posting fake or misleading reviews.

The watchdog will also examine whether Amazon’s systems have been failing to prevent and deter some sellers from manipulating product listings.

Fake and misleading reviews have the potential to impact on businesses’ star ratings and how prominently companies and products are displayed to consumers, changing their whole shopping experience.

Andrea Coscelli, the CMA’s chief executive, said: “Our worry is that millions of online shoppers could be misled by reading fake reviews and then spending their money based on those recommendations. Equally, it’s simply not fair if some businesses can fake 5-star reviews to give their products or services the most prominence, while law-abiding businesses lose out.

“We are investigating concerns that Amazon and Google have not been doing enough to prevent or remove fake reviews to protect customers and honest businesses. It’s important that these tech platforms take responsibility and we stand ready to take action if we find that they are not doing enough.”

If, after investigating, the CMA considers the firms have broken consumer protection law, it can take enforcement action. This could include securing formal commitments from the firms to change the way they deal with fake reviews or escalating to court action if needed. However, the CMA has not decided whether Amazon and Google have broken the law at this stage.

This latest work builds on action taken by the CMA last year over the trading of fake reviews, which resulted in Facebook, Instagram and eBay removing groups and banning individuals for buying and selling fake reviews on their sites.