The police in London need to more aggressively police their city.
Last I heard smashing people in the head with any weapon was a violent crime regardless of who behaves that way.
Some of the football games that have ended in riots are another bad example -- random violence is a social and societal problem in many countries.
Muslim extremists and skin heads are not unalike when it comes to organised violence
In the USA Muslims do not engage in organized social violent acts like they do in London ... Why is that the case there? Look in the mirror