Found an article in The Mail with an police statement acknowledging it, so it is real.
http://www.dailymail.co.uk/news/article-4547646/Police-investigation-shocking-video-officers-fight-youths.html
Good point. Whoever's behind the camera manages to have no interaction with anyone there despite being very close to events. Not one policeman asks them to stop filming, to leave etc.
I find this video and the kind of internet storm it can kick up worrying. The whole thing is out of context because we don't know what happened before the video started. Along with some information about what happened before the video started it could be a useful piece of evidence.