The Instagram “influencer” Sophie Hinchliffe is being investigated by the Advertising Standards Authority after allegedly failing to disclose adverts on her social media account.

The 29-year-old, known by her moniker Mrs Hinch, gained 2.5 million followers on Instagram with her cleaning tips, turning herself into a valuable “brand ambassador” able to charge thousands of pounds for product endorsement.

The Advertising Standards Authority (ASA) said it had received three complaints in April concerning the labelling of adverts in her Instagram posts. The posts promoted the Procter & Gamble cleaning products Flash and Febreze.

Under advertising rules, social media influencers must make it clear that they have been paid or rewarded to promote, review or talk about a product in their social media feeds. Under the Consumer Rights Act it is illegal for brands or individuals to post sponsored content without disclosing it.

Hundreds of influencers have fallen foul of the rules and Hinchliffe was given advice by the ASA on two occasions prior to the investigation on how to stay within the law.

Hinchliffe, whose social media following has made her one of the best-selling authors in the UK, shifting hundreds of thousands of copies of her debut book, said: “I take the responsibility that comes with having a large social media following very seriously, and, for me, being authentic and transparent is incredibly important. I’m fortunate that brands want to work with me, but I only collaborate with those that I genuinely like and would recommend to people.

“I continue to learn a lot, but feel my community are clear about any content that is part of a commercial partnership, and that which isn’t. In fact, I’m overly cautious when it comes to these guidelines and will continue to be.”

The enormous growth of the influencer advertising industry, which is transforming how products are marketed online, has raised questions about whether the ASA can enforce the rules.

Harry Hugo, a co-founder of the GOAT influencer marketing agency, said the addition of an advertising disclosure tag on an Instagram post would usually reduce exposure and sales by just 5%. This suggested that people following influencers were not deterred from making purchases by the knowledge that influencers had been paid to post.

Hugo, whose company arranges deals between advertisers and influencers to promote products, said the public was increasingly savvy and aware of how products were promoted on Instagram. “The ASA are regulating a 2019 practice with 2016 rules. Consumers understand this far more and are far more savvy than they were a few years ago, because of the huge increase of branded content.”