Section 5(4) applies if you are a voluntary patient reciving treatment for a mental disorder as an inpatient. A nurse specificaly qualified and trained to work with mental health problems or learning disabilities can detain you if they think that your mental health problem is so serious that:
You need to be kept in hospital immediately for your health or safety of for the protection of others, and
it is so urgent that it is not practicable to get a practitioner or clinician to provide a report to the hospital managers.
You can be kept under section5(4) for up to 6 hoursm or until a doctor or clinician with authority to detain you arrives. Whichever is earlier.