A number for elderly patients with dementia were left for hours without food at a hospital in Cumbria.
Inspectors found that the Ramsay unit at Furness General Hospital was greatly understaffed and this was impacted badly on the wellbeing of patients.
The unannounced inspection, which occurred on October 10th, led to the unit being closed to new admissions for a period and Cumbria Partnership NHS Foundation Trust has admitted that standards were unacceptable.
Two formal warnings have been issued to the trust by the Care Quality Commission (CQC) and a further unannounced inspection will take place again in the near future.
A report from CQC stated that patients were often left without breakfast until late in the morning because not enough staff members were on duty; the unit had a culture of poor record keeping and facilities such as its craft room were rarely used.
A claim that patients were sedated unnecessarily has been withdrawn.
Malcolm Bower-Brown, CQC northern regional director, said the identified issues are a major concern and trust needs to work harder to ensure standards are met.
He added: "We continue to monitor the trust extremely carefully to ensure that the required improvements are implemented.
"We will not hesitate to take further regulatory action to ensure patients receive the quality of care and support they are entitled to expect."
Claire Molloy, chief executive of the trust, said she was "very shocked" to hear of the inspector's findings and admitted that staff have been let down, which in turn had let down patients.
Since the report, staffing levels at the Ramsay unit have been increased by 25 per cent and senior medical and nursing support have been enlisted.
Furness Hospital also hit the headlines last month when its cancer unit had to be closed because pseydomonas, a germ that can cause infections, was found in its water supply.