City of London police are to face a high-profile employment tribunal brought by a black former trainee police officer who claims he was forced out by "insidious" bigotry.
The force will be accused of having officers who regularly made comments about black people's predisposition towards crime, and racist comments went unchallenged by senior ranks.
The case was disclosed after Britain's largest force, the Metropolitan Police, was hit by a series of highly damaging claims about racism within its ranks.
The growing race crisis at Scotland Yard was triggered last month when recordings emerged which appeared to show Pc Alex MacFarlane making derogatory and racist comments to 21-year-old Mauro Demetrio, after he was arrested in the wake of last summer's riots.
Another officer is alleged to have kicked a 15-year-old boy to the ground in another racist incident.
So far 20 Met officers and civilian staff have been referred to the Independent Police Complaints Commission after the force conducted a review of complaints. Five officers have been suspended and the new commissioner, Bernard Hogan-Howe, has promised to deal with the mounting sense of crisis.
The scandal threatens to undermine years of work to restore the Met's reputation following its bungled investigation into the death of Stephen Lawrence, a black teenager, who was murdered in a racist attack in south-east London in 1993.
City of London Police, which has more than 800 officers and is completely separate from Scotland Yard, operates in London's Square Mile It was until now untouched by the growing scandal but last night a former trainee constable disclosed that he is to sue the force over what he says was racism.
Anthony Joseph, who is black, is to bring an employment tribunal later this month alleging the City of London Police subjected him to race discrimination, The Sunday Telegraph can disclose.
Mr Joseph, 43, joined the City of London as a probationary constable in 2009. Towards the end of his two-year training, supervisors gave him "fail" marks in assessments which meant he had to resign or face being dismissed.
"I was forced out," he said. "In the City of London Police there is an insidious belief that the force should just be all white."
Mr Johnson, a father of three from Kilburn, north-west London, said: "I worked for local government and in sales before going to university to complete my first degree and later do a Master's degree in criminal justice.
"With all this life experience I thought I would be able to contribute a lot to the force, particularly in London with its black population. But I was mistaken.
"I hope the employment tribunal will show this injustice has to be put right and there has to be transparency."
Latest figures show just 5.8 per cent of City of London officers are black or Asian - 51 out of 878 - compared with 9.6 per cent of the Met's ranks. The national average is 4.9 per cent.
Charles Crichlow, president of the National Black Police Association (NBPA), said his organisation was supporting Mr Joseph's claim and warned that the race issue was "spiralling out of control".
He revealed the association has never been granted a meeting with Theresa May, the Home Secretary, and has only had one face-to-face meeting with Nick Herbert, the police minister, since the Coalition took over.
Last night the NBPA wrote to Mrs May asking her to re-establish the Stephen Lawrence Working Group, which was abolished six years ago when Charles Clarke was home secretary.
The cross-Whitehall group was set up in May 1999, three months after the publication of the Macpherson report into the racist murder of Mr Lawrence, a black teenager, and was tasked with overseeing its 70 recommendations.
Mr Crichlow said: "The NBPA is absolutely clear about the need to show leadership in this most challenging area of public engagement.
"I am therefore asking that you reconsider our recommendation that the Lawrence Steering Group be reconvened in order to give leadership to a situation that is unfortunately spiralling out of control."
The group was scrapped in October 2005. Mr Clarke said at the time that "the majority of the 70 recommendations have been implemented" and that remaining work would be "actioned by the relevant departments".
No-one at City of London Police was available for comment.