Rehman, who holds the title of Director of Partnerships and Diversity, will be advised by the Metropolitan Black Police Association, which is also backing Ghaffur, reports The Telegraph. The newspaper, however, did not quote Rehman or give specific details of her complaint.

She previously worked on the Met's strategy for dealing with cases of forced marriage and issues surrounding honour killings. She is also an expert on community relations and domestic violence. Rehman is a member of the Met's civilian staff based in Westminster and has been off work for months reportedly suffering from stress.

An unnamed colleague told The Telegraph: "She feels she has been targeted because she is Asian and she is determined to bring a case against the Met. When your head of diversity accuses you of discrimination that says it all really."

However, the Met said it has received no notification concerning an employment tribunal involving Yasmin Rehman. A Met release said: "She is not Head of Diversity for the MPS as previously reported, but in fact holds the post within Territorial Policing as Director of Partnerships and Diversity. She has no direct connection with the Commissioner."

The Met's reaction is guarded this time, unlike in the previous racism cases. The release said: "Rehman is a valued employee. If she is contemplating an ET, this would be a matter of regret but we would want to work with her to resolve whatever grievances she may have without recourse to the courts.

"The Metropolitan Police Service is the largest employer in London with a workforce of 53,000. In the last five years only one case has been lost solely on race discrimination grounds and four on multiple jurisdictions. We now recruit up to three times as many ethnic minority officers as a decade ago, and we continue to build on this success."