> (a) the technology is being deployed in specific environments where there really is a credible threat of criminal behaviour,
You need to define what credible threat is, pretty exactly. Just a thief? A terrorist? I think we all agree that this would be nice if there was foreknowledge of an imminent attack. BUT I think there still is a danger in setting them up for only that kind of use. We know that if we give police (or anyone really) tools, they will use them (why wouldn't they?). So having the ability uses to more abuse of use. But also as time goes on and people get used to it, the regulations relax.
So in this terrorist scenario I would be okay with bringing in cameras, or hooking into the already existing system, but it would need to tear down and be required to only come out when time is of the essence.
As we say in America, I'd rather a hundred guilty men go free than one innocent man be stripped of their freedom.