An undercover police officer has been placed on restricted duties.
Det Con Jim Boyling, who worked in specialist operations at the Metropolitan Police, was investigated by the Directorate of Professional Standards.
It followed allegations about his conduct reported in a national newspaper.
A Met spokesman said it would be thoroughly investigated, but the police were not able to comment further.
The move comes after Policing Minister Nick Herbert told MPs something went “very wrong” in the case of Mark Kennedy, another undercover police officer.
He caused the trial of six men accused of conspiring to shut down Ratcliffe-on-Soar power station in Nottinghamshire to collapse after he said he would testify for the defence.
Mr Kennedy spent a reported seven years posing as activist Mark “Flash” Stone.
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