The proportion of young black people in youth custody is far higher than for other ethnic groups, official analysis shows.
Approximately nine in every 10,000 black youngsters aged between 10 and 17 were in young offender institutions, secure training centres or secure children's homes in England and Wales in 2015/16.
This compared with one in every 10,000 for those from white ethnic backgrounds, four in 10,000 mixed ethnic young people and two in 10,000 Asian and other young people.
The Ministry of Justice (MoJ) report found that overall the number of 10 to 17-year-olds in custody has reduced substantially since 2007/08, with falls across all ethnic groups.
But volumes for black, Asian and minority ethnic (BAME) groups have fallen at a slower rate than the white category, and as a result the BAME share of the custodial population has increased over the last decade.
In 2015/16, young people from a black ethnic background accounted for 21% of young people in custody, where ethnicity was known.
The “exploratory” study, which was commissioned as part of a landmark review into race and the criminal justice system led by Labour MP David Lammy, identified a number of factors that may contribute to the high proportion of young black people in custody.
It said: “The analysis in this report indicates that the high proportion of young black people in custody is likely to be driven by arrest rates, custodial sentencing at the magistrates' court, and the fact that they have spent longer in the custodial estate on average than other groups in the past four years.”
The paper said disproportionality for young black males is most evident at the arrest stage, with figures indicating they are almost three times more likely than young white males to be arrested.
There was also disproportionality in the magistrates' court, according to the report. It said that in 2014, for every white young male sentenced to custody, 1.23 young black males were sentenced to custody.
There was no “statistically significant” disproportionality in convictions and custodial sentencing at crown courts.
In the last four years, young black people have spent longer in custody than young white people, with sentence lengths for violence against the person, theft and possession of weapons driving this trend, according to the analysis.
It also said that proven re-offending rates for young white people who left custody between 2010 and 2014 were higher than for young black people.
“Therefore high proven reoffending rates for those returning to custody are unlikely to be a contributing factor in the disproportionately high number of young black males in custody,” the report added.
It said that young black people were found to be more likely to be identified with “gang concerns” on entry to custody than any other ethnic group between April 2014 and March 2016.
The number of under-18s held in the secure youth custody estate has decreased in the last decade. It stood at close to 3,000 in 2007/08, but is now below 1,000.
Mr Lammy's full report is expected to be published next week.