A privately run mental health unit has been banned from admitting new patients after inspectors found numerous safety failings, one of which led to a resident dying by hanging.

The Care Quality Commission (CQC) has stopped the Cygnet Acer Clinic, in Chesterfield, Derbyshire, from accepting new inpatients. It declared that the facility was “not safe” for people to use.

Inspectors found that clinic patients had opportunities to hang themselves, and the unit had soaring levels of patient self harm, and a huge shortage of trained staff.

The CQC’s report is one of the most damning it has issued about poor and unsafe care affecting vulnerable and potentially suicidal patients in a mental health facility.

It is the 33rd time since the start of 2017 that the CQC has rated a mental health inpatient unit in England run by a profit-driven firm as inadequate, and the eighth time that has involved Cygnet.

The Cygnet Acer looks after a maximum of 28 women, at a time; they might have personality disorder and also another mental illness, learning disability or substance misuse problem.

Inspectors uncovered a series of lapses in safety, including the risk that patients could be able to try to end their life.

“In 2019 there had been two serious incidents, one of which led to a patient death by using a ligature,” the inspectors said. One in five staff had not been trained to understand most types of patient safety incidents, despite the highly vulnerable inpatient group.

Kevin Cleary, the regulator’s deputy chief inspector of hospitals, said: “The care provided at Cygnet Acer Clinic fell well below the standard that people should expect to receive. We found that the service was not ensuring the safety of those in its care.

“The number of incidents of self harm by patients had increased in the three months leading up to our inspection [in August] and almost half of the incidents involved patients using a ligature.”

The CQC also found that in one of the hospital’s two wards, Upper House, the number of incidents of self harm had more than trebled from 156 in May to 577 in July; that managers and staff were leaving patients at risk of being able to hang themselves by not getting rid of all potential ligature points; and that “75% of staff were not qualified for the roles they were doing”.

During their visit in August inspectors watched as patients gathered in the unit’s reception and banged on windows to get help from staff nowhere to be seen.

Wendy Burn, president of the Royal College of Psychiatrists, said: “We are deeply concerned by the appalling findings in the report, which has found that another hospital has failed to provide the necessary care for a vulnerable group of patients. Action must be taken to understand why patients in inpatient settings are being repeatedly let down.”

Sophie Corlett, director of external relations at the mental health charity Mind, said: “Many women in mental health services have experienced abuse or violence and their need for compassion and a safe haven is even more acute. And yet, shockingly, we hear about services set up specifically to support women that totally fail to deliver appropriate care.

“Across the board, long-neglected mental health hospitals and other buildings are putting people at risk of slower recovery, of self harming or even taking their own lives. We should not expect people with mental health problems to use inadequate and dangerous services, nor should we expect mental health staff to work in them.”

Luciana Berger, the Liberal Democrats’ shadow health secretary, said: “It is shocking that vulnerable female mental health patients were abandoned instead of receiving the care they need. There are serious questions to answer about why so many privately run mental health units have been deemed inadequate by the CQC in the last three years.”

The CQC, as well as rating Cygnet Acer inadequate, also placed it into special measures, and banned new admissions for six months.

A spokesperson for the clinic called the CQC’s findings inaccurate, adding: “This CQC report is in fact from an inspection in the summer. Since then there has been a further inspection in October and the CQC has recognised the progress made and given us positive feedback.”

The clinic said it had made “substantial improvements” as a result of the CQC’s visit, including extra training for staff and review of risk assessments. “We provide more than 140 services across the UK, the majority of which are rated good or outstanding. Where recently we have seen a relatively low proportion rated inadequate, we have rapidly invested the required resource to improve so they can meet the high standards we expect.”