Police chiefs have been accused of wasting taxpayers' money and spying on the private lives of citizens as it emerged that an undercover officer spent four years posing as an environmental activist in Yorkshire.
The policewoman, identified only as Officer A, moved to Leeds in 2004 and, after gaining the trust of green campaigners, is said to have played a key role in the
planning of a protest aimed at shutting Drax power station, near Selby.
She left Yorkshire in 2008, telling activists she had to move for personal reasons, and is understood now to have been removed from another undercover surveillance operation to which she was deployed because of safety fears.
Her true identity became known to protesters when they confronted another undercover officer, Mark Kennedy, who spent seven years embedded in the movement before his double life was exposed.
Leeds University lecturer Paul Chatterton, a prominent environmental campaigner who became friends with Officer A during her time in Yorkshire, said she had "abused the trust" of activists.
He said the case showed "the lengths that the British state and the police are prepared to go to infiltrate and try to undermine a peaceful movement".
Activists said Officer A, who is from a police force in the south-east of England, had driven protesters to the demonstration at Drax in 2006 and had been to a Heathrow climate camp and anti-capitalist gatherings.
She was also said to be at "the core" of a group who met in Leeds to help prepare for protests at the G8 nations summit in Gleneagles in 2005.
Dr Chatterton said: "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, and an unjustifiable level of intrusion into people's personal lives.
"It further breaks the trust that the public has towards the police. The operation didn't lead to any arrests so you have to ask what is their intention?
"Most worryingly, it is an appalling misuse of scarce resources. That's your tax money and mine being spent on undercover operations against people who simply want a greener, fairer future for this country.
"How many more undercover agents are out there in peaceful groups, breaking lives, sowing mistrust and wasting taxpayers' money?"
Green Party leader Caroline Lucas said: "This kind of police infiltration of non-violent protest groups is not only a hugely expensive – diverting police funds away from tackling serious crime – but also takes us one dangerous step closer to a police state.
"That the undercover officer in this case was an 'agent provocateur' rather than a mere observer raises alarming questions about the intentions of the police and, ultimately, the Government. Such anti-democratic forces have no place in our society.
"As long as governments fail to respond with the urgency that the climate crisis demands, and while the economic system perpetuates social and environmental injustice, people will demand change through organised campaigns and peaceful direct action."
Pc Kennedy apparently confessed to Officer A's involvement in the investigation after becoming guilty over his "betrayal" of friends he made during seven years posing as an underground activist.
Both officers were seconded to an intelligence unit belonging to the Association of Chief Police Officers (ACPO), and senior police figures are said to be worried that the safety of other covert cops has been compromised.
Despite attempts to keep Officer A's details a secret, her identity was openly discussed on internet messageboards yesterday. An image purported to be a photograph of the officer was put on the web, only to be taken down a few hours later, and dozens of messages naming her were posted on the social networking site, Twitter.
ACPO refused to comment on the case.