Seven police officers have been served with 'Regulation 15 Notices' in relation to the investigation into the "Plebgate" incident.
The notices inform them a complaint has been made or a conduct matter has come to light involving them that warrants an investigation.
Three of those officers, a 52-year-old man, a 46-year-old man and a 46-year-old woman, have been arrested and bailed. All three remain suspended from duty.
A 23-year-old man, who is not a police officer or member of police staff, was also arrested and bailed in relation to the incident.