The Psychiatric Nurses Association has described the incident as "totally unacceptable" and have highlighted the lack of adequate community mental health services in the South East.
PNA, General Secretary, Peter Hughes said accommodating patients on chairs because of the lack of beds is intolerable for patients and their families and upsetting for staff.
Speaking to WLR News, Mr. Hughes said it's a recurring incident in UHW and happens "five to seven times a month."
"Service users are being admitted to the unit but have to sleep on a chair," he said. "It's totally unacceptable that people with a mental health issue are tarted in that respect."