First, the court has, in its inherent jurisdiction, the power to order further and better discovery: Benjamin v Pulfer (Unreported, WASC, Library No 6618, 4 March 1987) 3 - 4.
Secondly, the court's inherent jurisdiction is exercised according to the former practice of the Court of Chancery: Kent Coal Concessions Ltd v Duguid [1910] 1 KB 904, 915, 916; Kent Coal Concessions Ltd v Duguid [1910] AC 452, 453. That practice was that an affidavit of documents by a party was conclusive as to the relevant documents in the possession, custody or power of that party unless the insufficiency of the discovery appeared from an admission in the pleadings by the party from whom discovery was sought, or from the affidavit of documents itself, or from the documents referred to in the affidavit, or from any source that constituted an admission by that party of a discoverable document, or where the party had excluded documents under a misconception of the case. Insufficiency could not, however, be demonstrated by a contentious affidavit from the party seeking to challenge the discovery. See British Association of Glass Bottle Manufacturers Ltd v Nettlefold [1912] 1 KB 369; [1912] AC 709; Mulley v Manifold [1959] HCA 23; (1959) 103 CLR 341, 343. Thirdly, O 26 r 6 and its predecessors were introduced to relax the Chancery rule, and to allow a challenge to discovery based on a contentious affidavit seeking discovery of particular documents, or a particular class of documents: Mulley v Manifold, 343.
Fourthly, the introduction of O 26 r 6 enlarged, but did not modify, the court's inherent jurisdiction: Kent Coal Concessions Ltd v Duguid [1910] 1 KB 904, 915. Thus, if a party applies pursuant to both O 26 r 6 and the court's inherent jurisdiction, but the O 26 r 6 application is for some reason irregular, providing that the criteria for the exercise of the inherent jurisdiction are satisfied, an order may be made under the inherent jurisdiction for discovery, including for a particular class of documents.
Fifthly, under the inherent jurisdiction, where the insufficiency of a party's discovery appears from the party's pleadings, or its affidavit of documents, or the documents referred to therein, or any source constituting an admission by that party of a discoverable document, the test is whether the court has reasonable grounds for being fairly certain that there are other relevant documents which ought to have been disclosed. That is also the test that is to be applied under O 26 r 6. See Beecham Group Ltd v Bristol Myers Co [1979] VicRp 27; [1979] VR 273, 276, 278 - 279; Youlden Enterprises Pty Ltd v Health Solutions (WA) Pty Ltd [2005] WASC 60 [3].
Sixthly, under the inherent jurisdiction, it is not necessary to infer the existence of a particular document to ground an order for further and better discovery, where it appears that a party has excluded documents under a misconception of the case: Mulley v Manifold 343; British Association v Nettlefold.
Seventhly, although the misconception of the discovering party is relevant to the exercise of the court's inherent jurisdiction, it is also, in my view, a factor which may assist in the drawing of inferences for the purposes of determining an application under O 26 r 6.