An investigation into undercover policing at the Metropolitan Police is to be overseen by another force.
Derbyshire's chief constable Mick Creedon will now head the inquiry, Home Secretary Theresa May has told MPs.
He will examine claims police officers assumed the identities of dead children and that some officers had inappropriate sexual relationships.
Mr Creedon takes over Operation Herne from the Met's deputy assistant commissioner Patricia Gallan.
Mr Creedon has overseen investigations into police corruption and has conducted several reviews into external forces.
Operation Herne was launched in October 2011 following claims that some undercover officers engaged in long-term sexual relationships with people they were spying on.
The spotlight returned to undercover officers when The Guardian newspaper claimed covert officers used dead children's details to infiltrate protest groups, without informing the parents.
The allegations mainly related to the operations of the Met's special demonstration squad in the 1980s.
Twenty police officers and 11 staff have been working on the inquiry, looking at more than 50,000 documents.
Scotland Yard said it had asked Mr Creedon to oversee the investigation.
Mrs May said: "Given the seriousness of the latest allegations, the Metropolitan Police Commissioner Sir Bernard Hogan-Howe and the chairman of the Independent Police Complaints Commission have agreed it would be appropriate for a senior figure from outside the Metropolitan Police to take over the leadership of the investigation."
Sir Bernard said: "Our priority now is to work with Chief Constable Mick Creedon and his team to support a thorough and impartial investigation to establish the facts about what took place."