I would say that it's just the police finding out that they're not as powerful as they think they are. We're used to an idea of riot police as being an immovable object, one that has been re-enforced in the UK thanks to the largely successful tactics of containment used against protesters over the last few years, but what this whole episode makes clear is the extent to which the success of those tactics relied, as unobvious as it may seem, on a certain degree of consent from the majority of protesters, in their own containment. When faced with very angry with nothing to lose and few limits on how far they're willing to take it, the police find that their ability to actually coerce large populations isn't what they believed it to be. It is very possible that this may end with the army being sent in as re-enforcements.