London's Metropolitan Police Service (Met) is reeling after its most senior officer, Sir Ian Blair, became the first commissioner since 1918 to quit the force.
Sir Ian Blair has faced months of mounting criticism
Sir Ian blamed his resignation on a lack of support from London Mayor Boris Johnson, triggering a dispute between the mayor's office and Home Secretary Jacqui Smith over whether he was forced to resign for political reasons.
His decision follows months of criticism of his business affairs, handling of key investigations and how he dealt with the explosive issue of race.
The Met has been engulfed by a race row which has seen the force's two most senior ethnic minority officers - Assistant Commissioner Tarique Ghaffur and Commander Ali Dizaei - suspended.
In 2003, reporter Mark Daly went undercover to expose racism amongst police recruits in Manchester for the programme The Secret Policeman.
As a result of that film, the Commission for Racial Equality launched a formal inquiry into racism in our police forces and made 125 recommendations for change.
Five years on, in The Secret Policeman Returns, Daly is back to see if the promise to root out institutional racism has been kept, and asks what it is like to be a Black Minority Ethnic (BME) cop today.
He finds a bleak story of officers and staff who feel sidelined and victimised.
Daly also hears disturbing allegations that police officers who speak out over race feel victimised by their own forces.
And in a unique snapshot of opinion, a survey of members of the Black Police Association reveals some fascinating statistics.
The Secret Policeman Returns also looks into the heated race row at the top of the Met.
Panorama: The Secret Policeman Returns will be on BBC One at 8.30pm on 6 October.