Unfortunately, this is something those of us labelled domestic extremists have to deal with. We know our movements are routinely infiltrated; it's more a question of "who" than "if". This awareness of betrayal, and suspicion of our fellow activists, is always with us. Indeed, part of the disruption that undercover operatives cause is making people doubt each other and their motivations. Most activists have at some point discussed those they suspect in their midst. Often suspicions are unfounded and only shared among close friends, but this paranoia effectively disrupts protest planning.

I knew Kennedy from gatherings and protests – we were both involved in environmental actions, anti-fascism and international mobilisations. He wasn't a close friend, but a familiar face I knew and trusted. The last time I saw him was at the Earth First gathering in August when he came to a meeting about how to best oppose the English Defence League (EDL) in Bradford. He was vocal there but, in retrospect, very keen on diverting the discussion away from mass mobilisation in the city centre and concentrating on targeting the coaches the EDL would be using.

It has already been pointed out that this could be seen as provocation. Kennedy was openly and actively promoting illegal activity – suggesting people either damage or obstruct the vehicles. However, I believe his motives went beyond provocation. The police were most afraid of a major public order incident in Bradford. By suggesting the coaches, Kennedy had an ideal way of not losing face in terms of action, at the same time as trying to keep people away from the city centre.

This manipulation and disruption of protest is the undercover operatives' main focus, and defines the overall strategy of protest policing operations. For example, overt police surveillance tactics at Kingsnorth – carried out by their forward intelligence team – were praised in a National Policing Improvement Agency report for providing "good intelligence and disruption". Subtle manipulation ensures an action is implemented in a way that suits the policing agenda without people feeling their actions have been compromised.

Disruption can take many forms, from asking questions about whether a group has the capability to carry out their plans, and thereby undermining confidence, to spreading rumours and smears about key activists in order to cause dissent within and between groups. These are all tried and tested methods, and in the words of Officer A, who admitted his role as a "hairy" for the Special Demonstration Squad in the Observer last year: "Once the SDS get into an organisation, it is effectively finished."

Since being exposed, Kennedy has said he's sorry, and has acknowledged that what he did was "really wrong". But saying sorry does not repair the lives he has wrecked, help the people he has grassed up, or reinvent the actions he jeopardised and manipulated. Personally, I read his statement as nothing more than an attempt to deflect the anger rightly directed towards him, and add to the confusion he has already caused. Nor is there any proof that he was really prepared to assist the protesters who faced charges of conspiracy to commit trespass at Ratcliffe-on-Soar power station, as he has since claimed. Meanwhile, Kennedy's alleged remorse dominates the media coverage when we should be exploring how the deep and complex anti-activist policing operation works, and what can be done to stop it.

The implications of this case are endless. For those closest to Kennedy, the questions will never be answered. They will always wonder about him, just as I will always wonder about Martin, always doubt my memories, question what, if anything, about our friendship was genuine. None of us will ever know what information was passed on, or which actions were compromised. We can spend endless hours speculating, but there will never be closure.

But one thing is certain: Kennedy was not alone, and there will be many more revelations of this kind over the coming years. With militant action building on the streets, the police will be seeking to infiltrate and disrupt prominent groups in any way they can. However, the Kennedy affair has also shown the strength of activists' support networks. We have been able to offer care and solidarity to those most affected: if we can maintain this, we will continue to be strong.