M25 - Why?

[T00ts]

What is it with the 'green' protesters (no I don't think they are aliens)? How many times now have they disrupted the M25. I read that the police arrested them then let them go to repeat the chaos. Isn't it a crime? Is it because they are protesters and therefore have special dispensation or something? It seems that all you have to do is hoist a banner of some kind and you are free to do what you like. Why are the cops so ineffectual?