The important point to make here is that there is NO demonstration or confrontation of any kind for them to deal with...NOTHING. As they close off the street to traffic and start to slowly walk down it with their weaponry on display, local people are coming out to see what is going on, but there is no demonstration happening, no "public order" situation. It's bizarre!
There was a small demonstration (about 100 people) at 6pm today, demanding the resignation of the politician responsible for the violent policing of the anti-G8 protests. There are reports that the peaceful protest ended in violence when several people were attacked and beaten by the police.