The Advertising Standards Authority has warned YouTubers to flag promotional videos.

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The issue was brought to the attention of the ASA when it received a complaint about a number of videos on Oreo biscuits.

The complainant, a BBC journalist, challenged whether the ads were obviously identifiable as marketing communications.

"We noted that the presentation of each ad was very much in keeping with the editorial content of the respective channels and that the fact that the videos were marketing communications would therefore not be immediately clear from the style alone," the ASA said in its ruling.

As a result, Mondelez UK Ltd, the maker of the biscuits, said the videos would be changed.

Lynsay Taffe from the ASA told the BBC it would look at online videos more closely in the future.

"Brands and vloggers now have to make it very clear, before you click on a video, that it's a promotional video," she said.

MP Ben Bradshaw echoed those comments. "There are strict rules that govern television and other advertising and it seems to me that there's a bit of a loophole when it comes to online, videos and YouTube," he said.

Simon Parkin investigated the ethics and legality of video game-related videos on YouTube in an article titled: "Blurred lines: Are YouTubers breaking the law?"

The issue has been raised a number of times in recent years. In January 2014 popular Battlefield YouTuber Jack Frags published a 30-minute explanation to his audience defending his engagement in EA's controversial Ronku programme.

And earlier this year Yogscast, the most viewed YouTube channel in the UK, hit the headlines when it revealed YogDiscovery, a new system that sees a share of revenue generated by sales of games go to content creators. Yogscast has insisted its videos do not qualify as an advertisement by the ASA because they do not go through any form of client approval.

Since 2009 any US-based YouTube videos that provide a paid-for endorsement of a video game must abide with FTC regulations and clearly state the fact. In the UK The Consumer Protection from Unfair Trading Regulations (CPRs) outlines a prohibition against 'using editorial content in the media to promote a product where a trader has paid for the promotion without making that clear in the content or by images or sounds clearly identifiable by the consumer (advertorial).' This law has been in effect since 2008.