final opinion and reference to the work of an expert

The general rule is NO reference to anyone on whose work the auditor has relied - so NO reference to an expert - NO reference to internal audit (also NO reference to the auditors of subsidiary companies - though this is not examinable in AA). The reason is simple - the independent auditor has sole responsibility for the audit opinion so there should be no mention of anyone else that might suggest some division of responsibility.. Therefore, the auditor would only refer to an expert where absolutely necessary to explain a modified opinion, where required by law or regulation and with the expert's permission (which would be obtained in the terms of reference with the expert before they do the work).