Two boys suffered broken bones following staff use of force at a privately run prison for young offenders, an unannounced inspection has found.
There were high levels of violence at HM Young Offenders Institution (HMYOI) Ashfield, near Bristol, with 43 serious fights in the year to January, Chief Inspector of Prisons Nick Hardwick said.
And of 3,773 strip searches conducted at the Serco-run prison during the 12 months before the inspection, just one resulted in a find.
Prison reform campaigners said the inspection report was a "damning postscript to a long story of violence and harm" at the jail.
HMYOI Ashfield, which held 123 young people, most aged 16 or 17, at the time of the inspection, is to be re-roled as an adult prison from July 1 following an announcement made by the Justice Secretary Chris Grayling earlier this year.
Mr Hardwick said plans for the closure of the site were not effectively co-ordinated and this may have contributed towards "tension" in the prison.
He said: "We have reported our concern about high levels of violence at a number of recent inspections of YOIs holding children and young people.
"At Ashfield too, young people's safety was compromised because they were exposed to unacceptable levels of violence - and there is some evidence the situation has deteriorated since the closure decision was announced.
"Planning for the closure was not effectively co-ordinated between the YJB (Youth Justice Board) and Ashfield, and the needs of individual young people were not carefully considered.
"The anxiety and uncertainty this created may well have contributed to the tension at the establishment. It certainly means that young people were not being adequately prepared for transfer or release."