Contributed by Alex Holland, associate editor of The Samosa, a new website with a focus on South Asia and British asians. For a full discussion of the left's divergent reactions to the policing of protest, see Stuart White at the Next Left.
Unlike some on the left, I do see a role for police surveillance of domestic protest groups. On the day of the 15 February 2003 anti-Iraq war demo, aka "the big one", I was a volunteer steward on the march. Part of what I did that day was act as a liaison between the march organisers and the police.

I stood beside police officers in a room located beneath the famous neon signs in Piccadilly Circus, watching a river of demonstrators go by. While there I saw undercover police, dressed as protestors, dashing up from the demo into the office and pointing out people on spotter cards, like those shown recently in The Guardian. They then quickly returned to the crowd to keep tracking the movements of targeted demonstrators.
I had mixed feelings about this. The vast majority of protestors I had contact with were, like me, entirely non-violent, law-abiding people who did not deserve to be spied on. However as a volunteer organiser in the European Social Forums, I did know of those who looked for confrontation at demonstrations, especially some Greek and Spanish anarchists. Stop the War organisers were genuinely concerned that demonstrations should not get violent and were generally not unsympathetic to police intelligence efforts to help with this.
However I still knew back then what the Guardian has highlighted now. That police surveillance is performed in a way that goes well beyond monitoring a genuinely extreme minority. Its main aim instead seems to be more about deterring legitimate dissent. These tactics have not only been an abuse of people's democratic right to protest. The current approach is also a gross waste of resources that could have been put into tackling genuine violent threats.