A school closed after asbestos was found has been taken over by its governors.
The 900-pupil Cwmcarn High School in Caerphilly county closed suddenly in October after a structural report identified asbestos in the main block.
Parents have expressed concern at its long term closure but the school's foundation status means governors can assume full control of the premises.
Caerphilly council expressed its "concern and disappointment".
The school governors have been asked to comment.
The council said a separate, independent investigation into asbestos management at the school was being carried out by the Health and Safety Executive, and would continue.
It said the governing body would now "take full responsibility and liability for the site", and "plans by the council to commission a full and thorough asbestos survey have now been thwarted by the actions of the school governors".
Council leader Harry Andrews said: "Our main priority has always been the health and wellbeing of pupils and staff at the school.
"We took swift and decisive action when the scale of the asbestos problem was identified and we planned to undertake further investigations to discover the full extent of the problem before agreeing a way forward.
"Unfortunately, the governing body have now frustrated this process by insisting that they take full responsibility of the site, as is their right as a foundation school, but we wanted to work with them to try and resolve this issue as quickly as possible."
He added: "We will be writing to parents and staff explaining the implications of this decision.
"Our key responsibility remains the welfare and education of the pupils and we will be closely monitoring the governors' actions at the school.
"Parents can rest assured that the council will not allow any pupils to return to a building that poses any health risk to their children."
The school closed after a structural report identified asbestos in the main block, and students are being educated at Coleg Gwent's Ebbw Vale campus for the rest of the school year.
The report said asbestos in the roof may have been blown by the heating system and airborne fibres were 10 times higher than the accepted levels.
The union Unison said at the time that demolition was the safest option for staff and pupils.
The survey revealed the building "poses potential serious risk to health" and should be demolished, as recommended by a previous inspection.
The school's website carries a petition from a parent support group, which says: "This document will be used to petition Caerphilly County Council and the Welsh Assembly Government for guarantees that our school 'Cwmcarn High' will NOT close indefinitely."
The Welsh government ordered all schools to report on asbestos levels.