Anyone with more than 30,000 social media followers is now considered a celebrity and subject to advertising rules, a watchdog has ruled in a landmark case.

The Advertising Standards Authority (ASA) found mummy blogger, Sarah Willox Knott, breached its rules when she promoted an over-the-counter sleeping sedative, as the size of her Instagram following classified her as a “celebrity”.

The ruling is the first of its kind where a social media 'influencer' has fallen foul of regulations banning celebrities or health professionals from endorsing medical products.

The Telegraph understands that despite the new precedent, the watchdog will still judge whether posts from smaller social media accounts breech its endorsement rules on a case-by-case basis.

The ruling comes after the blogger posted an image on her ThisMamaLife Instagram account in February of her sat in bed smiling with a packet of Phenergan Night Time Tablets visible in the background.