A pack of Savages with a new toy/weapon,a dog trained to attack.
Arnold,here is an answer to your question of where were the Police:
There is a Police station that backs up to the Park in the article.
I believe the Police station is only open part time as a budget concern.
There is a note on the door that tells you where to call for a Real Emergency,when the station is locked up.
Also all around the park are estates which allow one to run into and easily hide from the Police,if they showed up.
This park is not far from the Stockwell tube station.
The station where a few years ago the London Met ?, chased and shot a suspected Terrorist,who turned out to be a Brazilian Electrician,thus ending the most effective response to a potential terrorist threat available.(acted upon intelligence to terminate a suspect in the course of a possible terror attack).
Maybe those officers,from the tube station shooting, should patrol around the parks and use their terminating skills on the animals and their dogs.