The undercover operation that led to a police officer being planted among environmental activists is to be investigated.
Former Metropolitan Police Pc Mark Kennedy spent at least seven years at the heart of a loose network of campaigners behind a series of protests.
A trial of six protesters accused of conspiring to shut down Ratcliffe-on-Soar power station, in Nottinghamshire, collapsed after prosecutors dropped the case amid claims from the defendants that Pc Kennedy had offered to support them.
Nottinghamshire Police has discussed commissioning a review into the undercover operation and has also asked the Independent Police Complaints Commission (IPCC) to investigate what led to the case collapsing.
A statement from the police force said: "Nottinghamshire Police's chief constable Julia Hodson has this evening invited the Independent Police Complaints Commission to conduct an investigation into the circumstances leading up to the collapse of the case.
"In addition, discussions are taking place with a number of bodies about commissioning a second review into the conduct of the undercover operation.
"Until both reviews have been conducted and concluded and their reports received, Nottinghamshire Police will not be making further public comment on the collapse of the trial and the reasons for this."
Mr Kennedy, a long-haired and tattooed climber, was involved in demonstrations linked to the environment, anti-fascism and animal rights across the country.
He was outed after the mass arrest of 114 protesters as police feared an attempt would be made to shut down the power station at Ratcliffe-on-Soar in 2009.
The undercover officer, who told them it cost up to £250,000 a year to employ him, is believed to have resigned from the police and moved overseas.