Broadmoor, the psychiatric hospital that has housed some of the UK's most notorious killers, has been told it must urgently improve.
The Care Quality Commission (CQC) has issued a warning notice to West London Mental Health NHS Trust saying it must make "significant improvements" at the high security hospital.
Inspectors visited Broadmoor in November to check up on problems identified during a previous inspection.
They found there were still too few suitably qualified staff to meet the needs of patients.
Ahead of a full report due to be published into the issues, Dr Paul Lelliott, CQC deputy chief inspector of hospitals and lead for mental health, said: "We have told West London Mental Health NHS Trust that it must improve the quality of care that it provides to patients at Broadmoor Hospital.
"Specifically, our inspection team found that there were 68 vacancies for qualified nurses, a vacancy rate of 30%, and that this was affecting the care and treatment of patients.
"We found that too often, staff shortages led to the cancellation of social and therapeutic activities, including for patients who had been confined to their rooms all night.
"It also meant that some patients in long-term segregation did not always have the opportunities to associate with other patients that had been agreed in their care plans."
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