1. New Zealand

Judicature Amendment Act 1958 s2 (inserting ss94A and 94B in the Judicature Act 1908)

94A. (1) Subject to the provisions of this section, where relief in respect of any payment that has been made under mistake is sought in any Court, whether in civil proceedings or by way of defence, set off, counterclaim, or otherwise, and that relief could be granted if the mistake was wholly one of fact, that relief shall not be denied by reason only that the mistake is one of law whether or not it is in any degree also one of fact.

(2) Nothing in this section shall enable relief to be given in respect of any payment made at a time when the law requires or allows, or is commonly understood to require or allow, the payment to be made or enforced, by reason only that the law is subsequently changed or shown not to have been as it was commonly understood to be at the time of the payment.

94B. Relief , whether under section ninety-four A of this Act or in equity or otherwise, in respect of any payment made under mistake, whether of law or of fact, shall be denied wholly or in part if the person from whom relief is sought received the payment in good faith and has so altered his position in reliance on the validity of the payment that in the opinion of the Court, having regard to all possible implications in respect of other persons, it is inequitable to grant relief, or to grant relief in full, as the case may be.

(By the Judicature Amendment (No 2) Act 1985 the words "civil proceedings" were substituted for “an action or other proceeding” in s94A(1).)

2. Western Australia

Property Law Act 1969 ss124 and 125 (originally Law Reform (Property, Perpetuities, and Succession) Act, 1962 ss23 and 24)

124. (1) Subject to the provisions of this section, where relief in respect of any payment that has been made under mistake is sought in any court, whether in an action or other proceeding or by way of defence, set off, counterclaim or otherwise, and that relief could be granted if the mistake were wholly one of fact, that relief shall not be denied by reason only that the mistake is one of law whether or not it is in any degree also one of fact.

(2) Nothing in this section enables relief to be given in respect of any payment made at a time when the law requires or allows, or is commonly understood to require or allow, the payment to be made or enforced, by reason only that the law is subsequently changed or shown not to have been as it was commonly understood to be at the time of the payment.

125. (1) Relief, whether under section 124 of this Act or in equity or otherwise, in respect of any payment made under mistake, whether of law or fact, shall be denied wholly or in part if the person from whom relief is sought received the payment in good faith and has so altered his position in reliance on the validity of the payment that in the opinion of the Court, having regard to all possible implications in respect of the parties (other than the plaintiff or claimant) to the payment and of other persons acquiring rights or interests through them, it is inequitable to grant relief, or to grant relief in full.

(2) Where the Court makes an order for the repayment of any money paid under a mistake, the Court may in that order direct that the repayment shall be by periodic payments or by instalments, and may fix the amount or rate thereof, and may from time to time vary, suspend or discharge the order for cause shown, as the Court thinks fit.