The sites have signed up to agreements to better identify, investigate and respond to illegal fake and misleading reviews.

Facebook has removed 188 groups and disabled 24 user accounts and it will introduce more robust systems to detect and remove such content.

eBay has permanently banned 140 users and has improved its existing filters while blocking listings for the sale or trade of online reviews.

The Competition and Markets Authority (CMA) told the sites to address the issues surrounding fake reviews after raising concerns in the summer.

More than three-quarters of people are influenced by reviews when they shop online, and billions of pounds are spent every year based on write-ups of products or services. The CMA said websites have a responsibility to ensure such unlawful and harmful content isn’t advertised or sold through their platforms.

Andrea Coscelli, CMA chief executive, said: “Fake reviews are really damaging to shoppers and businesses alike. Millions of people base their shopping decisions on reviews, and if these are misleading or untrue, then shoppers could end up being misled into buying something that isn’t right for them – leaving businesses who play by the rules missing out.

“We’re pleased that Facebook and eBay are doing the right thing by committing to tackle this problem and helping to keep their sites free from posts selling fake reviews.”

Natalie Hitchins, head of home products and services at Which?, said: “It’s good that Facebook and eBay have taken steps to improve after the regulator intervened, but it is vital they continue to identify and shut down these groups, and put measures in place so that they are completely eradicated.

“The regulator must now turn its attention to review sites which are losing the battle against fake reviews – with shoppers duped into buying shoddy goods and services which have been artificially boosted by unscrupulous sellers.

“The CMA needs to investigate how fake reviews are being used to manipulate online shoppers and take the strongest possible action against sites that fail to tackle this problem.”