Completion Certificates and Periodic Inspection Reports
Two different documents
A completion/installation certificate is issued for new work (new installation, alteration, addition) and certifies that the work complies with the wiring rules. A periodic inspection report is issued for existing installations at intervals, recording condition and any departures/defects. A frequent trap is asking which certificate is correct for a given scenario - new circuit ⇒ completion certificate; routine check of an old installation ⇒ periodic inspection report.
What a valid certificate contains
Know the anatomy: details of the client and installation, a schedule of test results (continuity, insulation resistance, polarity, earth-fault loop impedance, RCD operation), a schedule of items inspected, declarations/signatures, and the extent and limitations of the work or inspection. The certificate is only valid for the work described - a completion certificate for a new socket does not certify the whole house.
Classification of findings
Periodic reports use codes for observations, typically ranging from 'requires immediate action / dangerous' down through 'potentially dangerous - urgent' to 'improvement recommended' and 'does not comply with current standard but not dangerous'. Candidates must map a described defect to the right severity. Missing main earthing, exposed live parts or a failed RCD are immediate-danger items; an older cable colour code or absent supplementary bonding is often 'improvement recommended'.
Traps
Signing a certificate without the test results; certifying work you did not supervise; confusing 'satisfactory' with 'no observations' (a report can be satisfactory with coded improvements); assuming a periodic report makes the installation 'new'. Certificates must be issued to the person ordering the work and retained per the rules.
Rule of thumb: if the question is about new work, think completion certificate + test schedule; if it is about condition over time, think periodic report + coded observations.