Ahead of today's snap election, Britain's biggest three political parties have pulled their messaging from Alphabet's (GOOGL) - Get Report YouTube. The reason? An unwillingness to have their advertisements air next to extremist content.

Campaign ads for the political parties were reportedly aired before YouTube videos of a hardline jihadist preacher, an especially unfortunate juxtaposition given Britain's recent struggles with terrorism. The latest moves follow an advertiser exodus back in March when it was revealed that ads were being shown next to videos endorsing hate speech and extremist views. At that time, major companies such as AT&T (T) - Get Report , Verizon (VZ) - Get Report , Pepsi (PEP) - Get Report and Walmart (WMT) - Get Reportpulled their advertising from YouTube. Google released a public apology at the time, vowing to give companies more control about where their content appeared.

However, this most recent pullout has undermined YouTube's credibility with advertisers. Paul Verna, an analyst with eMarketer, believes that YouTube will have to double down on its efforts in order to win back the big-name brands.

"They need to convince advertisers that YouTube has technology for highlighting offensive content, and that they're strengthening whatever algorithms they're using," says Verna. "But if I were YouTube, I wouldn't make a 100% guarantee that this won't happen again -- no matter how strong your filter is, there is always a chance that content falls through the cracks."

Indeed, with over 300 hours of content uploaded to YouTube per minute, the video sharing website has its hands full reviewing all that content. YouTube executives seem to be cognizant of the fact that the video service will not be infallible going forward.

"We've been conducting an extensive review of our advertising policies -- and in recent weeks have made significant changes that give brands more control over where their ads appear," said a YouTube spokesperson. "While no system will be 100% perfect, we believe these steps will further safeguard our advertisers' brands and we will continue to improve our controls over time."

Apart from a larger investment in technology, YouTube will also have to rebuild some bridges in order to get advertisers back on board. "They need to be attentive to the personal relationship aspect of this, particularly with some of the larger brand advertisers and agencies," Verna notes. "YouTube needs to do individual hand-holding here -- a public apology won't cut it."

Alphabet shares were down 0.1% Thursday mid-day to $1,000.72.

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