The agency said it has secured formal commitments from 16 celebrities, who also include models Alexa Chung and Rosie-Huntington-Whiteley, to change how they label social media posts to their millions of followers.

Brands pay thousands of dollars for a single social media post. But European Union consumer protection law requires social media users to disclose whether they have received gifts or cash to endorse a brand, to avoid giving the impression the post represents their personal view, the CMA said.

“People could, quite rightly, feel misled if what they thought was a recommendation from someone they admired turns out to be a marketing ploy,” CMA Chief Executive Andrea Coscelli said in a statement.

Warning letters have also been sent to a number of other celebrities — whom the CMA did not name — urging them to review their practices where some concerns have been identified, the watchdog added.

“Further investigation work will look at the role and responsibilities of social media platforms,” the CMA said.

The CMA said last August it had begun investigating the trend of celebrities and social media “influencers”, such as bloggers and vloggers, endorsing brands.