During a visit to Portsmouth by the Care Quality Commission in February, the design of A&E was reported as not keeping patients safe.
It was described as being too small and not allowing patients to be observed easily or for good communication between staff.
The report said: ‘The layout of the emergency department had been reconfigured over time to create more capacity.
‘But the size of the department and physical separation of the two major treatment areas did not readily allow good communication and oversight of the department.’
Mark Cubbon, chief executive of QA Hospital, said: ‘It is positive the CQC has recognised the emergency department building as no longer fit for purpose.
‘Part of our plans to improve the experience of our patients is a large scale redevelopment of the emergency department and Acute Medical Unit.’