Prisoners at Cookham Wood young offenders institution hid in their cells, refusing to come out or even to eat because they feared for their safety, according to inspectors.

A report has warned of "seriously unsafe" conditions at the prison at Rochester, which was converted from a women's prison.

The report said inspectors found inmates stayed in their cells "because they said they were being bullied or feared being assaulted or getting into a fight".

Chief inspector of prisons Dame Anne Owers said: "This first inspection of Cookham Wood, in its new role as an establishment for adolescent young men, has raised some serious concerns.

"In hindsight, the establishment was a poor choice for this age group. Its physical layout was far from ideal. This was exacerbated by the fact that neither appropriately trained staff nor essential safety procedures were created and embedded by the time significant numbers of young people arrived.

"The result, perhaps inevitably, was a seriously unsafe and poorly controlled environment, with some tense relationships between staff and young people.

"There must be a cap on the number of young people held at Cookham Wood until the Prison Service can guarantee appropriate levels of safety."

Officials at the institution said significant improvements have been made since the report was carried out.