LONDON (Reuters) - Google <GOOGL.O> vowed on Tuesday to police its websites better by ramping up staff numbers and overhauling its policies after several companies deserted the internet giant for failing to keep their adverts off hate-filled videos.

Google has found itself at the center of a British storm in recent days after major companies from supermarkets to banks and consumer groups pulled their adverts from its YouTube site after they appeared alongside videos carrying homophobic and anti-Semitic messages.

Alphabet's Google launched a review of the problem on Friday, apologized on Monday and said on Tuesday it had revamped its policies to give advertisers more control.

The company, which had said it struggled to monitor the 400 hours of video uploaded to YouTube every minute, said it would hire significantly more staff and speed up the process of removing ads from hateful and offensive content that attacks people based on their race, religion or gender.

"We believe the combination of these new policies and controls will significantly strengthen our ability to help advertisers reach audiences at scale, while respecting their values," Philipp Schindler, Google's chief business officer, said in a blog.

Britain is Google's largest market outside the United States, generating $7.8 billion mainly from advertising in 2016, or nearly 9 percent of the U.S. giant's global revenue.

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