“The arrest figure from across the weekend shows that the messaging in the lead up to the event, and the policing during it, were effective in deterring criminal activity..."

Police state surveillance is, by its own perverse motives, self justifying. Among the many thousands in attendance only a couple arrests were made with its help, and so "it was a powerful deterrent!" If it caught many more, then we'd hear them crow about that. If it made false positives, then additional spending would be called for to improve the systems.

Once the money is spent and the people have submitted to be passively datamined, there's no possible result, other than firm protest, that would call the practice into question. Sadly we are too used to surveillance.