Forest Bank is privately run

Chief Inspector of Prisons Anne Owers highlighted the incident as she raised concerns about falling standards at Forest Bank jail in Greater Manchester.

The 800-inmate men's jail suffers 25 prisoner assaults a month.

UK Detention Services, which runs it, said conditions have improved and one incident should be seen in context.

Ms Owers also said there were 2,500 discipline hearings in six months.

Drugs were "rife" with four out of 10 compulsory drug tests proving positive at the category B prison, which opened in 2000.

This was by no means the first such `potting' incident in the prison's recent history Anne Owers, Chief Inspector of Prisons

"There was a series of assaults against staff, including one unsavoury incident when a bucket of excrement was thrown into an office and over two staff who were in there, while we were at the prison," Ms Owers said.

"This was by no means the first such `potting' incident in the prison's recent history.

"We were told there were two or three others in the previous couple of months.

"The fact that there was more than one in such a short period is not a good sign."

She added: "We were concerned that a culture of tolerance of, and acquiescence with, inappropriate behaviour was becoming established at Forest Bank and this put both prisoners and staff at risk."

Safety had deteriorated significantly since the jail's last inspection just three years ago, she added.

Staff turnover was high, with many lacking the experience and confidence to challenge inappropriate behaviour, said Ms Owers.