A female police officer tasked with protecting Government officials has been arrested over alleged leaks to the media linked to the Andrew Mitchell "plebgate" affair.
The 46-year-old, who works in the Diplomatic Protection Group at the Metropolitan Police Service, was arrested at her workplace in central London on suspicion of misconduct in a public office.
She was arrested over alleged leaks to the media linked to the row which led former Tory chief whip Andrew Mitchell to quit his Cabinet post following claims he called officers "plebs".
The officer arrested was present at Downing Street during the incident in September, Scotland Yard confirmed.
She is being held in custody in a London police station and the Independent Police Complaints Commission (IPCC) have been informed, it added.
This was the fourth arrest in the investigation, which is known as Operation Alice.
A 46-year-old male officer arrested a day earlier over the affair has been bailed to return on a date in March and has been suspended from duty.
Three weeks ago Metropolitan Police commissioner Sir Bernard Hogan-Howe said that a file of evidence on the case could be handed to prosecutors by the end of January.
But Scotland Yard said on Thursday that because of "ongoing developments" no interim report had yet been submitted to the Crown Prosecution Service.
Investigators have taken statements from all 800 officers in the Diplomatic Protection Group (DPG) as part of the inquiry.
Two other men have been arrested so far, both of whom have been released on bail until February.
A 52-year-old Pc who is also from the DPG and currently suspended was held on suspicion of misconduct in public office, while a 23-year-old was arrested on suspicion of intentionally encouraging or assisting the commission of an indictable offence.
Four other constables in the unit, which is responsible for protecting government officials and diplomats, have been placed on restricted duty over misconduct claims.