An Asian police officer who raised concerns about a "racist" toy monkey at work was accused of gross misconduct, BBC News has learned.
The officer said he found the black animal toy wearing an officer's shirt at a police station in central London.
Scotland Yard promised to look into the matter but the detective was himself investigated for making the story up.
He was later cleared at a misconduct hearing and received damages from the force after taking legal action.
The details emerged after a separate case at Thames Valley Police in which an officer put a monkey on a black colleague's desk.
A misconduct panel concluded last month that Det Sgt Andrew Mottau was not being racist but should have realised the toy animal could be offensive.
The incident involving the Metropolitan Police began in September 2013 when the Indian-born detective constable claimed to have seen a large monkey toy in the office of the Case Progression Unit at Belgravia police station.
He said the stuffed black toy had a police officer's shirt on and a label saying "night-duty ERO" - Evidential Review Officer.
One of the EROs at the time was a black police officer.
The detective was concerned the use of the toy was racist and had not been investigated properly.
He raised the matter during a live internal website chat known as the "Commissioner's Forum", where staff are encouraged to discuss problems with the Met Commissioner, who at the time was Sir Bernard Hogan-Howe.
The detective received an online reply saying: "What is described - if accurate - is unacceptable" and was told that it would be looked into "immediately".
But a month later, the detective himself was put under investigation for allegedly posting "untrue and potentially inflammatory comments".
He was told his actions had "breached the standards of professional behaviour... relating to "honesty and integrity" and "discreditable conduct", claims which, if proved, could have led to his dismissal
Eventually, in June 2015, after protracted internal disciplinary proceedings, the officer attended a gross misconduct hearing where it was ruled there was "no case to answer" and he was cleared.
Paul Turpin, who was a representative for the Metropolitan Police Federation and supported the officer through the process, said: "I was surprised when the matter was referred to a gross misconduct hearing and was not surprised when that hearing found the officer had no case to answer."
He suggested the allegation should never have got that far: "Matters should be dealt with at the lowest appropriate level at the earliest possible opportunity."
Scotland Yard said there had been an "internal review" of the handling of the case after the hearing.
It said the original allegation about the monkey had been "investigated locally and progressed as far as it could be", though the inquiry was unable to establish who had placed the black toy animal in the police station.
Deputy Assistant Commissioner Richard Martin, who is in charge of professionalism at Scotland Yard, said the force had made "significant investment" in improving the way it handled staff complaints linked to discrimination, bullying or harassment and had introduced a new "whistle-blowing" policy.
"We have long recognised that people... fear being victimised if they raise a complaint, regardless of whether that fear is justified," he said.
"That has never been acceptable and we continue to make it very clear to our staff that victimisation will never be tolerated, that it will be investigated, and will have serious repercussions if it occurs".
But Janet Hills, chairwoman of the Metropolitan Black Police Association, said the use of a black monkey toy and the treatment of the Asian police detective indicated there was still a long way to go.
"We're still trying to get rid of the dinosaurs in policing who are still protecting that culture", she said, describing the "monkey" incident as "unbelievable" and "unacceptable".
"It's not just a toy, it's a toy to be used to say 'this is what I think of you'," she said.
"It's racist and discriminatory behaviour," she said, adding that it went on because people thought they could "get away with it".