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The trust which runs the South West's largest hospital has been told it must take urgent action to improve patient safety.
Inspectors from the Care Quality Commission (CQC) visited Derriford Hospital in Plymouth last autumn and the report has been published today (January 19).
The watchdog says it found "significant concerns and challenges" in urgent and emergency care, which they say is struggling because of the strain on the wider health and social care system.
Overall University Hospitals Plymouth NHS Trust - which runs Derriford Hospital - has been rated as "requires improvement".
Inspectors rated it as "outstanding" for how caring it is and "good" for how effective and well-led it is.
But there are still concerns and the watchdog has placed conditions on its registration, meaning it must make urgent changes.
The trust's chief executive Ann James told ITV News: "When a trust has conditions on its licence it is a very serious comment from the CQC and one that we do take very seriously."
Derriford has been under immense pressure throughout the pandemic, and still has many Covid patients and staff absent due to the virus.
The CQC once highlighted issues with delays in the emergency department, including ambulances queuing outside and a lack of bed space.
Chief executive Ann James speaks to ITV News
Ann James said: "I would certainly want to assure everybody we will be relentless in doing everything we can do improve what are unacceptable delays for ambulances and patients being triaged.
"Every improvement, however small, is one that we will really be focused on. But with the constraints that we have got we can only make so much progress."
A new urgent and emergency department is planned, with building work expected to start this summer.
The CQC report says: "Our inspection found significant concerns and challenges in urgent and emergency care and medical care, largely impacted by challenges within the wider health and social care system.
"Because of our concerns, we placed conditions on the trust's registration requiring them to take action with the health and social care system to improve patient safety and experience."