Asian muggers of Indian and Pakistani origin are believed to be among those behind an "alarming" increase in the number of gang rapes here, according to Scotland Yard.
A Yard study reveals that there has been a group sex attack for every day of the last year - and two-thirds of the suspects had convictions for theft and robbery. Half had been involved in street crime in the previous 12 months.
Most attackers were aged between 15 and 21, suggesting that the assaults - which mainly took place outside late at night or in the small hours - were an extension of the criminal activities of young robbers.
Scotland Yard is reported to be treating the evidence with care because it has sensitive racial overtones.
It suggests a disproportionately high involvement of young black or Asian males in group sex attacks and that a high proportion of the victims are white females.
There is also evidence that incidence of group rape is rising in other inner city areas of Britain, but little detailed research has been produced.
In the five-month Yard study, suspects of African/Caribbean appearance were identified in 49 per cent of attacks. A further 13 per cent were committed by men of Indian/Pakistani appearance.
However, many of the attacks occurred in areas with large ethnic minority communities and, police believe, reflected the street population and the lawless activities of a small minority of black youths, many excluded from schools and from dislocated families.
Youths from other ethnic groups, including whites, were involved in the gangs, suggesting that the attacks were linked to overall patterns of youth crime rather than simply race.
Women and girls of white/European appearance accounted for 59 per cent of victims but the sexual violence also heavily affected the black community, with 28 per cent of victims described as African/Caribbean.
Scotland Yard has been concerned for some time about "group rape", which began to rise in 2001, along with street crime.