In most cases the OIC will complete the investigation and then have a face to face consultation with a CPS rep at the police station, known as a 'CPS Gatekeeper'. The Gatekeeper decides how to proceed, whether it be a charge, caution, NFA or further inquiries to be completed. There are some situations that do not require a Gatekeeper decision but are rare nowadays.
For your info, a charge can only be authorised if there is sufficient evidence for a prosecution to likely succeed in a conviction and that it is in the publics interest to prosecute. A caution requires the accused to admit the offence in full.