Independent officials will examine whether police tried to cover up the role of an undercover colleague who infiltrated a group of environmental activists.
Officials from the Independent Police Complaints Commission (IPCC) will conduct their own inquiry into the controversy surrounding Pc Mark Kennedy.
The former Met officer monitored the actions of protesters across Europe under the guise of a long-haired, drop-out climber called Mark Stone.
The case against six demonstrators accused of conspiring to shut down Ratcliffe-on-Soar power station collapsed on Monday after prosecutors dropped the case.
Their legal team claimed the decision was made after the undercover officer had a crisis of conscience and offered to give evidence on their behalf.
The dramatic development prompted a wider debate on controversial police tactics to monitor political and environmental groups operating on the fringe of legality.
Jobless Mr Kennedy, who is now in hiding, has called in PR guru Max Clifford as he prepares to sell his story.
The IPCC review comes after Chief Constable Julia Hodson said there will be an internal review into the secret operation.
Amerdeep Somal, of the IPCC, said the inquiry will focus on the alleged failure of Nottinghamshire Police to disclose relevant material to prosecutors.
He said: "We have now assessed the referral from Nottinghamshire Police of a specific issue around disclosure relating to this high-profile case.
"After assessment, I have decided we will look independently at whether Nottinghamshire Police met their obligations under relevant procedures to disclose evidence to the CPS in this case."
Jon Collins, chair of Nottinghamshire Police Authority, said he is "disappointed" at the situation which is overshadowing other police work.
He said: "When policing major public order events, such as this protest, it is necessary that the police use all the resources available to them to maintain public safety."Reuse content