YouTube, the world’s largest video-sharing website, this week removed over two dozen videos glorifying gangs and gang violence which had been on its website in some cases for over 18 months.

Following a Times investigation into harmful and inappropriate material on Youtube, the website took down 30 film clips, most shot in grainy video showing hooded youths brandishing illegal weapons such as machetes, hand guns and even sub-machine guns. Google admitted they were clearly in breach of its own user guidelines which had recently been revised to deal with gang videos.

Google’s Head of Communications in Britain, former Newsnight editor Peter Barron, said that as a result of concern about the use of the website by gangs, it had now introduced new guidelines prohibiting users from showing weapons in their videos in order to intimidate people, but that these had only “gone live” on Friday.

He blamed “teething problems” with the new policy for the fact that its own monitors had failed to removed the material after a Times reporter posing as an ordinary user had flagged them up as inappropriate three days after the new policy had been introduced.

“The new guidelines have just been established, clearly it will take a little while for them to feed through the system,” said Mr Barron.

In recent years YouTube and other “networking” sites such as Bebo, have become a battleground for warring gangs who post videos of themselves brandishing weapons to intimidate their rivals. In many cases responses from other gangs have been posted on the comments page warning the makers of the video about what would happen should they stray onto their territory.

YouTube provides users with the option to “embed” their videos onto other websites, which means that the same clips appear across other sites such as Bebo and MySpace — or are posted direct.

YouTube claims it is not possible to vet material before it is uploaded to the site because of the sheer volume — an estimated 13 hours of video is uploaded every minute and hundreds of thousands of new films are posted on the site every day.

Instead it relies on a policy of self-regulation whereby users can “flag” material they consider inappropriate. Some critics have likened the system to asking drunks to decide on licensing laws.

Flagged content is then reviewed by staff who decide whether to remove it from the site. According to YouTube the “vast majority” of flagged material is reviewed, and if necesary removed, within half an hour.

Yet of 30 videos The Times flagged between 1pm on Monday and 11.15am on Tuesday, only three had been removed by Google before it was contacted by our reporter at 4pm on Tuesday. Google said that it no record of another three being flagged but agreed they breached its guidelines and took them down. Ten of the videos had been flagged by The Times a month earlier but had not been removed.

One video, titled “Welcome to Liverpool” in which youths are shown riding motorbikes and brandishing weapons, had been on the site since June 14, 2007 and had been viewed over 145,000 times before it was removed after the intervention of the Times.