at p.550 second column G, that it is "unnecessary and indeed
unwise to lay down rigid and exhaustive criteria. The
circumstances of different cases are infinitely various". It may
be added that it seems difficult to conceive how an interlocutory
order which is productive of substantial injustice to one of the
parties can be made without error of principle, but as will
appear, I have found it unnecessary to express a concluded view
on that question. Compare, however, House v. R. (1936) 55
C.L.R. 449, at p.505, where Dixon, Evatt, and McTiernan JJ.
pointed out that, in deciding whether an error has heen made in
the exercise of a discretion, even if the error 1s unidentifiable
if upon the facts the decision "is unreasonable or plainly
unjust, the appellate court may infer that in some way there has
been a failure properly to exercise the discretion which the law
reposes in the court of first instance. In such a case, although
the nature of the error may not be discoverable, the exercise of
the dicretion is reviewed on the ground that a substantial wrong
has in fact occurred". Certainly, on any view of the matter,
"the question of injustice flowing from the order appealed from
will generally be a relevant and necessary consideration": Adam