A Metropolitan Police officer who made monkey noises at a black prisoner in a holding cage has been forced to resign.
The incident happened at Plumstead police station, south-east London, in July 2005, after Wayne Bell arrested Anthony Housden on a train.
A High Court judge quashed an earlier decision that overturned a misconduct panel ruling and saved Mr Bell's job.
The Independent Police Complaints Commission (IPCC) said there was "no place for racism" in the service.
Pc Neil Wakeling, who witnessed the incident but did not report it, has been reprimanded and fined the maximum 13 days' pay.
After his arrest Mr Housden was taken to Plumstead police station and placed in a metal mesh holding cage, where he was kept for about 30 minutes and was extremely abusive to officers nearby.
The judge said Mr Bell, an officer of seven years, told Mr Housden he was behaving like a badly-behaved chimp and made a monkey impression.
Mr Bell was originally charged with committing a racially-motivated offence, but the prosecution was dismissed at Bow Street Magistrates' Court in March 2006.
In October last year a misconduct hearing required both men to resign for breaching the police code of conduct.
However, a review by Assistant Commissioner Andy Hayman reduced Mr Bell's penalty to a fine and cleared Pc Wakeling.
The IPCC then took the case to the High Court where the decision was overruled and a fresh review of the case upheld the original findings.
Welcoming the decision IPCC Commissioner Mehmuda Mian Pritchard said: "The police service has clearly taken on board the seriousness of the case and imposed an appropriate penalty."