Primark is in hot water over an advertisement by former Love Island contestant Gabby Allen.
The influencer from Allerton had an Instagram post promoting Primark products banned after she failed to make it clear she had a commercial relationship with the retailer.
The post by Ms Allen, seen in August, featured a photo of her with the caption: "Feeling fab but chilled Wearing these jeans and top from one and only @primark #iworkwithprimark."
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A reader complained that the post was not obviously tagged as an ad.
Primark confirmed that the post was part of Ms Allen's contractual obligations to the brand.
However the retailer argued that the label '#iworkwithprimark' was unambiguous, and the average consumer would understand that the word 'work' in the label was a reference to the commercial relationship between Primark and Ms Allen.
Ms Allen said the post had been updated to include the label '#ad'.
The Advertising Standards Authority (ASA) said Ms Allen and Primark were jointly responsible for ensuring that marketing activity on Ms Allen's account promoting Primark complied with the rules.
It said the use of the word 'work' in the label was "ambiguous, and did not fully explain her relationship with Primark".
The ASA said the label was long and unclear and insufficiently prominent to ensure that the post was obviously identifiable as an ad.
The regulator added: "We welcomed Primark and Ms Allen's assurance that the post caption had been updated to include the label "#ad".
"However, that label still appeared at the end of the caption, which meant that it would not have been immediately visible to consumers viewing the post in-feed on Instagram. Furthermore, at the time it was made the post had not featured any label identifying it as a marketing communication.
"In the absence of clear and prominent identifiers, we concluded that the post was not obviously identifiable as a marketing communication and as such breached the code."
The ASA added: "We told Primark and Gabby Allen to ensure that their future ads were obviously identifiable as marketing communications, and that identifiers such as 'Â£ad' were clearly and prominently displayed."
A Primark spokeswoman said: "We work hard to ensure we always comply with the CAP (Committee of Advertising Practice) code, and as part of this we require all influencers we work with to make clear in their posts that there is a paid relationship.
"We're sorry on this occasion that the post didn't conform to the CAP code standards and the post was updated with #ad as soon as we were made aware."
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