Accordingly, we think that, once good cause has been shown to the contrary, the court should not only be regarded as free of the injunction to allow interest according to the terms of s 58(1) (so that in a proper case interest may be refused altogether); the court should also be regarded as authorised, by implication, to allow interest otherwise than in accordance with those terms.
This does not mean, however, that the court is then wholly at large; for the court cannot by virtue only of s 58 allow interest on terms more onerous to the defendant than those spelled out in the section. Although logically that course might be thought to be open once good cause against allowing interest according to its terms had been shown, that is not how the section has thus far been interpreted in practice; nor do we think that it should be. Such discretion as is conferred upon the court once good cause has been shown has been regarded (and, we think, rightly regarded) as empowering the court to relieve against injustice to the defendant - 'alleviating the defendant in a proper case', as Gowans J put it in Marsh v Ruby.
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Thus, when good cause is shown, the court may refuse to award interest at all or may, if it sees fit, award interest on terms which are less, but not more, onerous than those laid down by the section. As the court always has a discretion as to the rate (subject only to the maximum imposed by s 58), this means, in effect, that once good cause is shown, the court may allow interest to the plaintiff for a lesser period than that marked out by the section - as, indeed, was done in David Leahey's Case. And it follows, we think, that 'good cause to the contrary' means no more and no less than good reason, according to the justice of the case, for not allowing interest at all or, if interest is to be allowed, then for not allowing interest for the whole of the period marked out by the section.[12]