The scale and brutality of the abuse in Rotherham have shocked a country already shaken by a series of child abuse scandals involving celebrities, public officials, clerics and teachers at expensive private schools. The Rotherham report suggests that it continues unchecked among the most vulnerable in British society.

It has highlighted another uncomfortable dimension of the issue, that of race relations in Britain. The victims identified in the report were all white, while the perpetrators were mostly of Pakistani heritage, many of them working in nighttime industries like taxi driving and takeout restaurants. The same was true in recent prosecutions in Oxford, in southern England, and the northern towns of Oldham and Rochdale, where nine men of Pakistani, Bangladeshi and Afghan origin were given long prison sentences in 2012 for abusing up to 47 girls. Investigators in Scotland have reportedly uncovered a similar pattern of abuse.

Sexual abuse of children takes many forms, and the majority of convicted abusers in Britain are white. But as Nazir Afzal, the chief crown prosecutor in charge of sexual violence and himself of Pakistani heritage, put it, “There is no getting away from the fact that there are Pakistani gangs grooming vulnerable girls.”

The grooming tends to follow a similar pattern, according to Alexis Jay, a former chief inspector of social work who was commissioned by the Rotherham Council to carry out an independent investigation following a series of reports in The Times of London: a period of courting with young men in public places like town centers, bus stations or shopping malls; the gradual introduction of cigarettes, alcohol and sometimes harder drugs; a sexual relationship with one man, who becomes the “boyfriend” and later demands that the girl prove her love by having sex with his friends; then the threats, blackmail and violence that have deterred so many girls from coming forward.

But the report also outlined how those victims and parents who did ask for help were mostly let down by the police and social services, despite a great deal of detail known to them for more than a decade, including, in some cases, the names of possible offenders and their license plate numbers.

“Nobody can pretend they didn’t know,” Ms. Jay said in an interview.

Unimpeded, the abuse mushroomed. Over time, investigators found, it evolved from personal gratification to a business opportunity for the men.