The CMA found what it referred to as ‘troubling evidence’ that there is a thriving marketplace for fake and misleading online reviews.

After web sweeps performed in the period November 2018 to June 2019, the CMA was concerned about more than100 eBay listings offering fake reviews for sale. During the same period it also identified 26 Facebook groups where people offered to write fake reviews or businesses recruited people to write fake and misleading reviews on popular shopping and review sites.

It is estimated that more than three-quarters of UK internet users consider online reviews when choosing what to buy. Billions of pounds of people’s spending is influenced by reviews every year.

The CMA said fake and misleading reviews not only lead to people making poorly informed choices and buying the wrong products, but they are also illegal under consumer protection law.

However, the CMA hasn’t alleged that Facebook or eBay are intentionally allowing this content to appear on their websites.

Since the CMA wrote to the sites, both have indicated they will cooperate and Facebook has informed the CMA that most of the 26 groups have been removed.

Andrea Coscelli, CMA chief executive, said: “Lots of us rely on reviews when shopping online to decide what to buy. It is important that people are able to trust that reviews are genuine, rather than something someone has been paid to write.

“Fake reviews mean that people might make the wrong choice and end up with a product or service that’s not right for them. They’re also unfair to businesses who do the right thing.

“We want Facebook and eBay to conduct an urgent review of their sites to prevent fake and misleading online reviews from being bought and sold.”

Asking Facebook and eBay to review their sites is the first phase in a wider programme of CMA work aimed at tackling fake and misleading reviews. It builds on previous action in this area to protect shoppers from misleading information on the internet, including enforcement action taken against an online marketing company to stop it from writing fake reviews and demand it removed those it had posted.