Surveillance, it seems to me, comes in two categories differentiated by purpose; that is, all surveillance efforts will fulfill one, or both in some mixture, of two purposes. The first is the easiest, and the most etymologically obvious: surveillance is investigative.

A typical example of such surveillance work would be a phone tap. You initiate a phone tap to find out things you didn't know before; it is an investigative tool. A point-to-point communication which should thus limit information exposure is compromised by external surveillance, permitting the watchers to learn things they would otherwise be unable to learn. But it is worth noting that this investigative function for surveillance is effective precisely in so far as it is covert; a subject aware of observation behaves differently.

This, of course, is the rationale behind armed guards in front of public buildings, and bobbies walking a beat: "showing the uniform". The pre-supposition is that highly visible surveillance will act as a deterrent. Such surveillance is therefore distinct from investigative surveillance in both function and form. CCTV cameras watch our streets dumbly and permanently; I've worked a CCTV monitoring job for Winchester City Council. We had a forensic role; if an incident occurred on camera we could work to gather effective evidence by focusing on faces and recording time-stamp data. But primarily CCTV cameras function as a deterrent; don't rob here, you'll get caught on camera. This is their function on the Tube, on the buses, in corner shops and pubs.

I establish these categories explicitly because I want to consider the evolving role of state surveillance over the last fifteen years in the light of these distinctions. We have seen a huge expansion of publicly, rather than privately, owned CCTV cameras. We have seen the return of the street bobby, the copper on a push bike, Community Policing. We have seen the development, evolution and eventual prime-time prominence of the organisation known as FIT. We've also seen the growth of organisations which attempt to track, monitor or control traffic flows on the internet. We have seen massively more frequent use of phone monitoring, we've seen undercover agent provocateur operations which offer thousands of pounds to recruit citizen surveillance officers, or what we would have called "secret police informants" during the Cold War.

FIT are a specifically interesting case to follow. They grow in the shadows cast by the Territorial Support Groups, and like most things that grow in the dark they're knee-deep in shit. Both police groups are, in inception, explicitly class warriors: both were organised to counter increasingly organised expressions of working-class disillusion and rage. I remember the gossip mills talking about a shadowy group of guys with cameras documenting Troublesome Elements from behind black-glazed car windows. What they turned out to actually be was an attempt to curtail nationally organised football violence.

And initially they were an investigative force. They operated covertly. They identified and documented the activities of over a thousand violent criminals. Unfortunately, they also documented and spied on several thousand innocent football supporters. But, the men who've been banned from foreign travel and from football stadiums are, overwhelmingly, the right men; the men who organised things like this.

FIT used to hide behind net curtains and this places them distinctly into the camp of investigative surveillance. They wanted to know something; they used surveillance to find out. Unfortunately, it didn't end there. They soon morphed into something new; FIT surveillance became a public, obvious, in-your-face feature of public order policing. This does not mean FIT's activities came out of the shadows; they still do all kinds of things they hope people won't notice, but it does mean that the nature of their surveillance changed.

I was taken aside at the point when I asked for the warrant by about five FIT officers. Had a camera pointed in may face and photo taken. Held onto and surrounded and shouted at.

So writes James Lloyd, a Climate Camp legal observer on 2nd April 2009. This is not investigative surveillance; for a start, this guy is in an orange tabard marked Legal Observer, his name and two phone numbers are registered with police command and he is, in fact, carrying a Police Liason identification.

What are they doing? If it's not investigation, it must be deterrence, The aim is to send a very clear message; you are being watched. We are doing it. We don't care if you know. You will be watched, your privacy will be invaded, and there is nothing you can do. This is the action of a group who are actively attempting to stop something.

And it's not football violence any more. In fact, I don't know if FIT still have that purview or not; once everyone heard about them their utility in stopping organised criminals was compromised. It's the wavering criminal who may be deterred, not the skinhead with the swastika tattoo who "supports" a football team but practices street violence. What they most certainly do, now, is spy on and intimidate political dissenters.

In fact, when you look beyond FIT at public surveillance of political dissent it is almost universally not investigative. It's not about finding out who disagrees with the government: the government knows that, we're all shouting about it on the internet, or going to protests with placards. The behaviour of FIT, the police threatening people with non-applicable laws to try and force identification data out of them, the CCTV cameras... The mobile, privately owned CCTV vans run by "GrapeVine" (whoever the hell they are) "in partnership" with the police are painted neon yellow. They're not covert surveillance; and thereby they are not investigative surveillance.

They are not about finding out, or proving, anything. These multi-billion pound initiatives are about passing on a message to anyone who thinks dissent is permissible. The message is: We are watching you. You have been warned.