Patients are being neglected, hygiene is inadequate and staffing problems are affecting care at the only NHS hospital run by a private company, the health service care watchdog has found.

In its preliminary findings, the Care Quality Commission (CQC) has made a series of criticisms of Hinchingbrooke hospital in Cambridgeshire after inspectors found problems during a four-day visit last week.

In 2012, Hinchingbrooke became the first hospital in the NHS to be managed by a profit-making firm when it was taken over by Circle in a 10-year contract worth about £1bn. About 160,000 patients a year are treated there.

The regulator has outlined its concerns in a letter to the hospital, which has been leaked to the Health Service Journal. It was also critical of the hospital’s management and demanded urgent action to resolve weaknesses inspectors found.

Sources at Circle were frustrated that what the CQC called its “early feedback” had become public, during the period in which Circle is entitled to challenge those findings before the official report emerges.

Detailing examples of “poor care provided to patients”, it said patients who lacked the capacity to consent had been sedated on medical wards, despite no “best interest decision” about their treatment having been taken. “The use of sedation without best interest decisions in place can be classified as restraint or a deprivation of liberty safeguarding concern,” said the letter sent to the hospital chief executive, Hisham Abdel-Rahman.

Inspectors who visited between 15 and 18 September also encountered examples of staff caring for patients in an “undignified and emotionally abusive manner”.

Standards of handwashing among staff in the A&E department and some wards were “very variable”, the letter said. It cited “an incident whereby staff failed to follow handwashing guidance after seeing to a patient isolated for C difficile”.

In direct criticism of Abdel-Rahman, the CQC said: “We were also concerned as to the lack of recognition of the level of concerns when raised with yourself and the length of time taken to grasp the seriousness of the situation for patients.”

It added: “There were also concerns that the current culture within the organisation does not lend itself to enable concerns, particularly related to nursing and caring issues, to be easily raised. The response seen and otherwise noted suggested a blame approach, rather than that of a supportive and patient-focused approach.”

Cambridgeshire and Peterborough clinical commissioning group (CCG), which pays for patients to be treated at Hinchingbrooke, said it was concerned.

Jill Houghton, its director of quality, safety and patient experience, said it was “working with [the hospital trust] around some concerns at the hospital, to ensure continuous improvements in the quality and standards of patient care. Patient safety and quality of care remains a high priority for all our patients across the CCG.”

Abdel-Rahman, who is also a consultant gynaecologist, said he could not respond in detail to the CQC as its inspection was still going on but he was sure that it would approve Circle’s plans for addressing the problems found. “Quality and safety at Hinchingbrooke has come a long way in two years. As a clinician-led partnership, patients are our priority and we are constantly looking for ways to improve our care,” he said.