Darren Millar, MS for Clwyd, said the health board had been “unable” to get on top of the situation.
“I’ve been aware of concerns. Whenever a concern is raised with me I always demand action,” he said.
“I’m afraid it’s got to a situation where even after HIW inspections fairly recently the situation is still unacceptably poor and that’s why we need more urgent intervention now.”
Teresa Owen, BCUHB’s executive director of allied health professionals and health science, said: “We take the issues raised by patients and their families extremely seriously.
“As a health board our number one priority is providing the correct care at the correct time and we fully understand the value of continuity of care, for patients accessing our mental health services.
“The health board remains committed to fostering a culture in which staff feel able to raise concerns safely.”
HIW said it was aware of concerns regarding Nant y Glyn but would not comment on individual cases.
“We will continue to monitor the service through our assurance activities and will take any appropriate action required to help ensure patients receive safe and effective care,” said a spokesperson.
A Welsh government recently announced “ministerially directed intervention” on the health board.
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