An investigation into allegations of historic abuse at a former boarding school has been declared a “critical incident” by Police Scotland.

Operation Chalk examines allegations of physical and sexual abuse at Kerelaw School between the 1970s and 2000s.

Police confirmed the operation was declared critical earlier this year “due to the resources required and the complexity of the investigation”.

Ten people have been arrested this year in connection with allegations of abuse at the Ayrshire school, which closed in 2006.

Deputy Chief Constable Steve Johnson said officers had been investigating since the new allegations were reported in 2015.

He said: “As the investigation progressed, additional expert resources were invested to ensure the best possible outcome for the victims in this case.

“A number of further arrests have been made in recent months in connection with this investigation and we continue to work with the Crown Office and the Procurator Fiscal Service.”

Council-run Kerelaw opened in 1970 and operated as a boys’ residential area before becoming co-educational. A mixed-gender secure unit was added in 1983.

The Stevenston site catered for young people with complex behavioural, emotional and psychological needs, some of whom were involved in petty crime or substance abuse.

The main school closed in 2004 but the secure unit remained open until 2006.

Police Scotland can declare an incident critical when “the effectiveness of the police response is likely to have a significant impact on the confidence of the victim, their family and/or the community.”

force critical incident management guide It was published following a freedom of information request in 2021.

The guide notes that “major incidents” such as rape and murder can sometimes be considered “critical” due to death tolls and media attention.

He adds: “However, critical incidents may involve only a few people, have little or no casualties, and may well involve the involvement of a single agency.

“Therefore, a critical incident would not necessarily be classified as a major incident.”

A police spokesman said Kerelaw’s case had been declared critical due to “the long duration of the investigation and the impact this could have on victims and the community”.

Former teacher Matt George and maintenance worker John Muldoon last January was imprisoned He was sentenced to a total of 28 years in prison for physically and sexually abusing children in Kerelaw between the 1970s and 2000s.

This was the second time the couple had been convicted of school hazing.

Earlier this month Police Scotland confirmed 10 new arrests had been made in connection with allegations of abuse at the school.

Police confirmed seven men and three women, aged between 52 and 77, were questioned about the treatment of young people there.

The Crown Office and the Procurator Fiscal Service later confirmed it had received reports regarding 10 people.

A 2009 report by Glasgow City Council, which took over the school from the former Strathclyde District Council, found Kerelaw was poorly managed.

Evidence about the school was also heard by the Scottish Child Abuse Inquiry in March but has yet to publish its findings.