A young offenders' institution has been branded an "unacceptably violent place" - and the chief inspector of prisons says he would be "terrified" if one of his children was there.
Feltham Prison and Young Offender Institution, in west London, was covered in gang graffiti and witnessed on average almost two fights or assaults every day, some of which were "very serious", HM Inspectorate of Prisons found.
Children were frightened and no confidence that staff could keep them safe - despite an "unprecedentedly high" use of batons.
Feltham is divided into two parts, Feltham A holds children and young people, mostly aged 16 or 17, while Feltham B holds young adult men aged 18 to 21.
Chief inspector of prisons Nick Hardwick said: "Feltham as a whole is an unacceptably violent place. Despite excellent work in some cases, staff were unable to prevent a high number of very concerning incidents that carried a significant risk of serious injury.
"In my view staff were sometimes overwhelmed by the challenges they faced and as a consequence, some of their response, such as the prolonged use of isolation on the children and young people's side and the use of batons on the young adult side, were unacceptable."
Hardwick found that Feltham needed to rethink its role and cautiously welcomed a decision taken after the inspection to not hold young adults on remand as this may help to create a more stable and manageable population.
Elsewhere, the inspection found that many young people said they were frightened at the time of the inspection and had little confidence in staff to keep them safe.
Inspectors found that the level of violent incidents remained much too high.
Speaking on the BBC's Today Programme, Hardwick said: "If I was a parent with a child at Feltham, I would be terrified."
CCTV recordings viewed by inspectors showed staff put themselves in harm's way to protect young people and the force used to break up fights was proportionate and necessary.
In the young adults part of the prison, self-harming behaviour remained high and emergency cell bells were not answered quickly, the inspection report said.
Michael Spurr, chief executive of the National Offender Management Service (Noms), said: "This report reflects the serious concerns I have about the propensity for and the level of gang-related violence among young people sent to Feltham but it also highlights the remarkable work that staff do on a daily basis to manage such a challenging group.
"I have already announced that from the autumn Feltham will no longer hold young adult remand prisoners. This will increase stability and provide greater flexibility in the management of this group of prisoners."
Andrew Neilson, director of campaigns at the Howard League for Penal Reform, said: "This is the worst inspection report of its kind we have seen in a decade. If you want to see the effects of keeping hundreds of troubled boys cooped up in a prison, you need look no further than Feltham."
Juliet Lyon, director of the Prison Reform Trust, said: "Feltham should frighten us all. The question has to be asked: why do we place our most vulnerable and volatile young people in our most troubled institutions, and expect anything other than the violence, self-harm and mayhem this report reveals?"