A leading Leeds environmental campaigner has condemned police infiltration of eco campaign groups in the city.
And he questioned how many more undercover police officers were working inside other groups.
A policewoman identified only as "A" has been revealed to have been active in Leeds after infiltrating a groups of activists campaigning against the causes of climate change - including Drax power station near Selby.
Activists halted a train heading for Drax and began to unload its coal cargo before being arrested. Drax has also been the target of national demonstrations.
Policewoman "A" is the second to have been revealed as a police infiltrator of environment campaign groups. She moved to Leeds in 2004 and became active in the climate change movement. In 2006 she drove protesters to Drax and took part in gatherings. She left the city in 2008.
A campaigner who became her friend, Paul Chatterton, a geography lecturer at the University of Leeds, said: "I knew the undercover Officer A, but what is important for the public to understand are the lengths that the British state and the police are prepared to go to infiltrate and try to undermine a peaceful movement.
"It is a case of political policing against an open and accountable movement made up of ordinary people which simply wants a better and more just society for this country. This kind of undercover policing is out of all proportion to the threat it posed," he said.