It seems what happened was that a police patrol van (TSG?) was just passing and must have seen people out the front of the building. When they pulled up the people moved sharpish back inside, and the police followed them. At first they tried kicking the door in (no luck, there are very good barricades!) and this is when they resorted to smashing the glass in the windows (hmm, community policing eh?). Inside scores of people responded by shouting for the police to leave.

The police having smashed the windows and heard the shouting got on their radio and called in to headquarters - and were told that HQ knows about the building, that there is an eviction planned in the morning, and that the eight police officers should leave immediatly, which they did.