6. Power of auditor to require production of documents and attendance of persons concerned, etc.

(a) by summons in writing or by letter require the production before him of any document which he may deem necessary for the proper conduct of the audit;
(b) by summons in writing require any whole-time paid servant of the local authority accountable for, or having the custody or control of, any such document to appear in person before him at any such audit; and
(c) require any such person to make and sign a declaration with respect to such document or to answer any question, or prepare and submit any statement relating thereto.