The appellant had tried, and failed, to get an order for inspection. The claim for inspection was made because a document was mentioned in a witness statement. The appellant appealed to the Court of appeal.  This judgment helpfully reviews the authorities.

Gross LJ said

“27. … In my view, the correct analysis is as set out in paragraphs which follow.
28. First, the mere fact that a document is “mentioned” in one of the documents specified in CPR r. 31.14(1) does not automatically and without more entitle the other party to inspect it. The Court retains a discretionary jurisdiction to refuse inspection.
29. Secondly, the general rule is clear. Ordinarily, if under CPR r. 31.14(1) a document is “mentioned”, inter alia, in a witness statement, the other party has a right to inspect it. The reason was well-stated by Nourse LJ in Rafidain Bank v Agom Sugar [1987] 1 WLR 1606, at pp. 1610-1611:
” The party who refers to the documents does so by choice, usually because they are either an essential part of his cause of action or defence or of significant probative value to him. ….the material provisions were evidently intended to give the other party the same advantage as if the documents referred to had been fully set out in the pleadings…. “
In CPR terminology, I would accept Mr Stanley’s submission that CPR r. 31.14 reflects basic fairness and principle in an adversarial system; in accordance with the overriding objective, the parties are to be on an equal footing.
30. Thirdly, the right to inspect under CPR r. 31.14 is not, however, unqualified; it is instead subject to CPR rules based limits, which may be invoked by the party resisting inspection – the burden resting on that party to justify displacing the general rule. Thus, “proportionality” is part of the overriding objective CPR r.1.1(2)(c) and, in an appropriate case, it would be open to a party to oppose inspection on the ground that it would be “disproportionate to the issues in the case”: CPR r.31(3)(2).
In determining any such issue of proportionality, a Court would very likely have regard to whether inspection of the documents was necessary for the fair disposal of the application or action. So too, the mere mention of a privileged document in (for example) a statement of case may not of itself lead to a loss of the privilege; CPR r.31.14 is to be read with and subject to CPR r.31.19(3) and (5): see, Rubin v Expandable Ltd (supra), at [39]; Civil Procedure, Vol. 1, 2016, at 31.14.5 and
31. Fourthly and further, it was not argued before us and there is nothing to suggest that the RSC approach to confidentiality has changed under the CPR; see, for instance, Civil Procedure, at 31.3.6. Accordingly, while disclosure and inspection cannot be refused by reason of the confidentiality of the documents in question alone, confidentiality (where it is asserted) is a relevant factor to be taken into account by the Court in determining whether or not to order inspection.
The Court’s task is to strike a just balance between the competing interests involved – those of the party asserting an entitlement to inspect the documents and those of the party claiming confidentiality in the documents.
In striking that balance in the exercise of its discretion, the Court may properly have regard to the question of whether inspection of the documents is necessary for disposing fairly of the proceedings in question: see, Science Research Council v Nasse [1980] AC 1028, esp. at pp. 1065-1066 (Lord Wilberforce), 1074 (Lord Edmund-Davies) and 1087 – 1088 (Lord Scarman).
32. Fifthly… “necessity” is or may be (depending on the facts)arelevant factor in striking the just balance; it is not a free-standing hurdle to be considered and surmounted in isolation before inspection may be permitted.

35. It is time to pull some threads together CPR r.31.14 is applicable….
It follows that the Appellants have a right to inspect the Request; the Appellants’ entitlement flows, as a matter of fairness, from the importance attached to the Request by [the judge].
On the facts, there is nothing in the rules based qualifications already mentioned (proportionality and privilege) to displace that qualified right.
Having established their case thus far, the Appellants do not need to surmount a further free-standing hurdle of demonstrating, in isolation, that inspection is necessary for the fair disposal of the matter.
That said, this analysis leads on to the central issue on the appeal: the balance to be struck between the Appellants’ right to inspect the Request and the NCA/ DOJ claim to confidentiality of state to state communications. In that context, the question of whether inspection of the Request is necessary for the fair disposal of the application is a relevant consideration.”

The balance of the judgment dealt with confidentiality in state to state communications.

This passage has been edited for ease of reading.