Aside from the case of Mark Stone / Kennedy appearing to have "gone native" as the undercover policeman found his sympathies changing as he allied himself with the environmental protesters he was supposed to be keeping under surveillance, it looks as if he was more of an agent provocateur.
http://www.bbc.co.uk/news/uk-12148753
Reports that he is not the only undercover operative in this area are staggering and must surely be a waste of resources given that he spent 7 years with the protesters until he was confronted by a group of people who can not seriously be considered a threat to society especially as his contribution was to give evidence supporting them.
   The strange thing about this case is some curious phrases by representatives on both sides that I heard on the radio. Firstly Andy Hayman was speaking to Victoria Derbyshire on radio Five Live in his capacity as a former Assistant Commissioner of the Met when as well as admitting that too many undercover operations would be a waste of resources made the astonishing claim that such operations as this one were valid as they were not only trying to collect evidence to prosecute somebody but also to prove innocence.
http://www.bbc.co.uk/iplayer/console/b00xbf0n/Victoria_Derbyshire_10_01_2011

His interview occurs between 1hr 37 mins 25sec and 1hr 41mins 50 secs and is breathtaking that he believes we need undercover work to prove innocence in a country where we are presumed to be innocent already until proved guilty.

   Later on the same station the group's lawyer Mike Schwarz was talking to Gabby Logan when he was asked if he thought Stone/Kennedy had encouraged others to commit crimes and whilst he admitted that he had no first hand knowledge he believed he may well have done.
http://www.bbc.co.uk/iplayer/console/b00xbf84/Gabby_Logan_10_01_2011

This interview occurs between 1hr 6mins 40secs and 1hr 10mins 50secs of this programme and the mentioned admission appears to contradict his statement on the affair:
http://www.guardian.co.uk/environment/2011/jan/10/activism-climate-change?intcmp=239

In the above statement he claims that none of his clients were guilty of any crime yet by accusing Mark Kennedy of inciting others he implies that they did commit crimes. Presumably he was trying to have a dig at Kennedy, who had upset his clients, without thinking the implications of what he was saying through properly.