A school in the midst of an investigation into “serious allegations of a child protection nature” has been criticised by Ofsted following an impromptu inspection.

The education watchdog visited Broadlands Hall School in Little Wratting, near Haverhill, unannounced last month for an emergency inspection of the school’s safeguarding measures.

The school has 17 male students who all have special educational needs for behavioural, emotional and social difficulties, and autism. It admits students from care homes run by the proprietor, Colonel Keith Boulter, who also runs Barnardiston Hall School.

Inspector Heather Yaxley wrote in her report: “The inspector was aware during this inspection that serious allegations of a child protection nature were being investigated by the appropriate authorities.

“School staff and the proprietor have not taken all of the required actions to keep students safe. Concerns about students’ welfare have not always been passed on to the appropriate authorities – or in the right way.”

The report says that staff had not been trained to deal with students or in proper restraining techniques. Police and Suffolk County Council’s safeguarding children team both confirmed they are investigating allegations at the school.

A spokeswoman for the school said: “The allegation is in the hands of the appropriate authorities and as an on-going investigation we are, unfortunately, unable to comment further.

“Ofsted visited Broadlands Hall recently and required policies relating to the welfare, health and safety to be updated by the school to reflect current practice and regulation. These policies were immediately reviewed and adjustments made to meet their requirements.”

The education at the school was rated outstanding by Ofsted in November 2011, but the welfare is inspected separately.

The spokeswoman added: “Whilst we believe that a few of our written policies needed minor amendment and some of our practice needed further development, we are confident that at our next Ofsted inspection high grades will continue to be achieved.”