Scotland Yard officers carried out inquiries as part of Operation Alice, the investigation in connection with an incident involving then Cabinet minister Andrew Mitchell in Downing Street.
A copy of the file handed to the Crown Prosecution Service was also given to the Independent Police Complaints Commission, which is supervising the investigation.
The incident in September last year became popularly known as "Plebgate" following claims, denied by Mr Mitchell, that the MP called officers "plebs" in a dispute.
More top news
A Banksy mural, possibly worth thousands of pounds, has been erased by a council in Essex after a complaint that it was "racist".
What is terrifying about Ebola is not the virus itself, it’s the west’s inaction in the face of an unprecedented epidemic.
The social network has had to refine its policy on real names, saying users should use 'authentic' but not necessarily their legal names.