Two police officers have been questioned over allegations that they leaked information covered by the Official Secrets Act.
The Metropolitan Police investigation involves retired Hampshire assistant chief constable Steve Watts and another unnamed Hampshire inspector.
The Met would not give details of the allegations.
A spokesman said: "On September 8 last year an off-duty inspector attended a south London police station by appointment and he was arrested by the Metropolitan Police in connection with allegations of the unauthorised disclosure of material."
The inspector was released on police bail until February, he added.
The spokesman said the next day another officer, identified as Mr Watts, attended the same station by appointment and he was interviewed about the leak allegations but not arrested. He then left the station.
At the time, Mr Watts was a serving police officer but he retired on 15 September.
The Met is now liaising with the Crown Prosecution Service, which will decide if the men will be charged with any offence.Reuse content