A young offenders' institution has been labelled an "unacceptably violent place" by inspectors who found an "unprecedentedly high" use of batons by staff.

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.

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.

Mr 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.

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.

Shadow justice secretary Sadiq Khan MP said: "This is the latest in a string of recent damning inspections that shows the reality in our prisons is a million miles away from the rhetoric used by ministers. With shocking levels of violence such as these witnessed in Feltham, it's all the harder to punish and reform offenders, and stop them returning to a life of crime on their release."