8. By reason of the imposition of this mandatory obligation, the Court can approach this application slightly differently to the way in which it may have been approached in the past. There will be circumstances where “conclusiveness” of affidavits of discovery must yield to the overriding purpose of the Act and Rules. I do not see this as an exceptional order. Six attempts at proper discovery suggest there has been a problem. Finality in the discovery process is necessary to ensure that further costs are not incurred, particularly the costs of the expert.
12 There is no dispute as to the law. It is enunciated in Harman v Secretary of State for the Home Department  1 AC 280 ( 1 All ER 532), and in later cases which elaborate on the principle. The principle is also embodied in UCPR 21.7(1). It applies alike to documents produced by one party in proceedings to another party in the course of discovery, and to documents produced to a party in proceedings upon subpoena issued to a non-party: see e.g. Hearne v Street (2008) 235 CLR 125 at .
13 The principle is that a party to proceedings obtains documents upon discovery or by subpoena upon the basis of what was conventionally called an implied undertaking to the Court, given both by the party and its solicitors, that the documents will not, without the leave of the Court, be either disclosed to a third party or used for a collateral or ulterior purpose, i.e. a purpose unconnected with the proper conduct of the proceedings. What was once regarded as an implied undertaking to the Court is now recognised as a substantive legal principle. 14 UCPR 21.7(1) provides:
“No copy of a document, or information from a document, obtained by party A as a result of discovery by party B is to be disclosed or used otherwise than for the purposes of the conduct of the proceedings, except by leave of the court, unless the document has been received into evidence in open court.”
15 While that Rule embodies the principle in relation to discovered documents, the common law principle, which is to the same effect, applies to subpoenaed documents as well.