A police officer was arrested on suspicion of perverting the course of justice after making an allegation of sexual assault.
The female officer, who cannot be named for legal reasons, reported the sex attack to police following an incident on a bus.
She said she had been touched inappropriately by another passenger.
Police arrested a man at the scene on suspicion of sexual assault after the incident last year.
However when officers examined footage taken from the on-board CCTV cameras, they concluded there was not enough evidence to charge the man and he was released.
Following his release, the officer who made the complaint was then arrested on suspicion of perverting the course of justice and placed on restricted duties.
An internal investigation by the Metropolitan Police found there was no case to answer against her.
The complainant has since returned to work with no restrictions placed on her.
A spokesman for Sutton Police said: "Following an investigation the officer was advised there was no case to answer and has since returned to full duties.
"There is no misconduct or discipline case to answer."
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