In a written question to the council’s people and health overview committee, Mr Legg said the building was overgrown with ivy, dilapidated and was no longer water-tight, having been daubed with graffiti and vandalised over recent years.
He said the fire service had raised concerns about the former school, which closed in 2000, being at risk of arson.
In 2023, the Campaign to Protect Rural England criticised the then Conservative-run council for appearing “either powerless or disinclined ” to take any action to preserve heritage buildings.
It said council’s stance contrasted with work being carried out at the time to transform Sherborne House into an arts and performance centre.
Portfolio holder for planning at the time, David Walsh, said with no active breaches of planning or listed building control, the state of the building was a matter for the owner.
“Officers will keep the situation under review,” he said.
Ms Taylor, a member of the now Liberal Democrat administration, said that because the building is a former school it fell outside the scope of the council’s empty homes strategy.
“The council is aware of this building and action has been taken by Building Control, Conservation and the Housing Standards team to liase with the owner, secure the site and protect against unauthorised entry,” she said.