An independent inquiry will be set up to investigate claims over an alleged failure to disclose material in the case of an undercover policeman, the Director of Public Prosecutions has said.
The claims relate to the case of former Metropolitan Pc Mark Kennedy, who spent a reported seven years posing as an environmental activist known as Mark Stone.
Six protesters accused of planning to invade Ratcliffe-on-Soar power station in Nottingham, the second largest in the UK, claimed prosecutors dropped charges against them after Kennedy offered to give evidence on their behalf.
Keir Starmer QC confirmed an inquiry would investigate the allegations.
He said: "In light of growing concerns about the non-disclosure of material relating to the activities of an undercover police officer in the Ratcliffe-on-Soar power station cases, I have decided that I will set up an independent inquiry, conducted by a senior legal figure, to work in tandem with the IPCC (Independent Police Complaints Commission) inquiry into the matter which began in January 2011.
"The two inquiries will have full access to all the available evidence, whether held by the police or the CPS (Crown Prosecution Service), and will share information. They will also share their provisional findings before final reports are drawn up.
"This arrangement will provide independent scrutiny of the actions of both the police and the CPS in relation to the disclosure issues arising from the Ratcliffe-on-Soar power station cases.
"It is an arrangement supported by the IPCC and the chief constable of Nottinghamshire.
"Until the two inquiries report, it is important that no conclusions are drawn about any individuals involved in this matter."
Earlier this week, the CPS said there would be a "full and formal inquiry" conducted by Chris Enzor, deputy chief crown prosecutor for CPS North East.