How appalling! Glad to heqar that you're ok though.
Talking about the G20 police complaints today, Nick Hardwick, chairman of the Independent Police Complaints Commission, said "It is about being servants, not masters: the police are there as public servants" You might remind your local police of that.
If I were you, I would write a letter signed by all the residents affected by this incident to complain to your local Police Chief Inspectror and insist on a meeting to discuss the lack of an effrective response.
Get the local press involved, particularly if you have photos.
I would also meet with your neighbours to discuss what to do if you get a recurrence of this incident. I don't mean vigilante tactics.
Have video recorders at hand to record as much of the action as you can from different angles.
Make sure that every household calls the police.
Photograph all damage.
Record as much information as you can remember about the incident as soon after it occurs as possible.
Good luck.