A joint study by the Prisons Inspectorate and the Youth Justice Board (YJB) found that nearly a third (32 per cent) of young people in custody reported feeling unsafe at some time in 2011/12, compared to 27 per cent in 2010/11.
During the same period, the number of young people held in young offender institutions fell by 14 per cent.
The report said the five-percentage point jump could be a result of increases in the number of young people being restrained, or a rise in the use of adjudications – formal hearings to consider allegations of poor behaviour.
More than half (53 per cent) of the 926 young men and 25 young women questioned said it was their first time in custody.
Nick Hardwick, chief inspector of prisons, said the findings show that young people's experience of custody has remained surprisingly stable despite the fact that fewer under-18s are being detained.
He said the report “cast doubt” on the assumption that the concentration of young people who have committed serious offences would increase as the custody population decreases.
He said: “It might have been expected that reductions in the number of young people held and changes to the custodial estate would have led to changes of similar significance to young people’s perceptions of their experience in custody. In fact, it is striking how little has changed.”
But the Howard League for Penal Reform has said the increase in young people feeling unsafe is “a cause of great concern”.
“Prisons are entirely inappropriate places for vulnerable children. Most have too few staff, too much violence, too little education and poor reoffending rates,” said Andrew Neilson, director of campaigns at the charity.
The YJB said the findings of the report will be used to improve practice in the secure estate.
Frances Done, YJB chair, said: “Our overriding objective is to ensure that while in custody children are kept safe, supported to address their offending behaviour, and helped to lead successful lives on release.
“We will review the findings of this report and work with our secure establishments to ensure that they are taken into account in all aspects of their work.”
Despite ongoing reductions in the number of young people in custody, concerns have been raised this year about safety in the youth secure estate.
In January this year two teenagers died within a week of each other in young offender institutions. Figures on safety in prisons, published in July, showed there was a 16.7 per cent increase in assaults in young offender institutions between 2010 and 2011.