Nitin Shah had been previously charged with verbally abusing a female bar manager in London in 2011.
But the Crown Prosecution Service dropped the case when it was discovered that police constable Phil Firmin, an officer with the City of London police, had twice forged the signature of the alleged victim.
"As an Asian I have had to endure disgustingly poor service from this corrupt police force. The police service remains institutionally racist," Shah wrote in a letter to the Independent Police Complaints Commission (IPCC).
The force, which had been allowed by the IPCC to investigate the complaint itself, exonerated its officers in April 2012.
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Shah appealed against that decision to the watchdog IPCC, which again allowed City of London police to conduct an internal investigation.
Shah has since been told that officers involved in the second internal investigation were unable to trace a crucial female witness and is contemplating legal action.
"Our professional standards directorate had conducted a full investigation into this case before referral to the IPCC and treats any allegation of misconduct, corruption or racial discrimination with the utmost seriousness," City of London police said.