Note that a number of the above ideas are not necessarily contradictory. For example, start with the understanding that stuff of the supernatural doesn't play nice with others (ie, images of supernatural creatures will be grainy at the very best). Next, assume that in the Dresdenified London, there is a significant amount of supernatural activity playing havoc with the comprehensive CCTV coverage there. I imagine that at first the police was very responsive to irregularities caught by the cameras. Of course, responding every time the cameras went white with static would probably tire out the response units pretty quickly. Now -- years after it's inception -- the authorities have the system set to merely log most of the irregularities, sending an actual response only to the most serious cases. So perhaps the aspect would be something along the lines of "Big Brother is always watching ... and sometimes even takes notice." If a wizard blows up a camera on an otherwise calm night, it will probably be responded to by a a couple of technicians in a truck. If, on the other hand, the emergency lines are ringing, the surveillance folks might be alerted ... and they might start seeing things that bring up questions -- either in the form of odd stuff occuring or in patterns of CCTVs suddenly going white with static.