On Thursday the court released the reasons for its unanimous decision on 7 September to dismiss two challenges to the postal survey, in which it accepted the government’s case the expenditure was unforeseen at the time of the May budget because the postal survey did not become policy until early August.

The case preserves the government’s broad discretion to use the finance minister’s advance for expenditure the minister believes is “urgent” and “unforeseen”, rejecting the imposition of extra legislative oversight on spending between budget cycles.

On 9 August the government allocated $122m to the Australian Bureau of Statistics to pay for the postal survey from the $295m finance minister’s advance.

The challenges, one brought by independent MP Andrew Wilkie, lesbian mother Felicity Marlowe and Parents and Friends of Lesbians and Gays Brisbane, the other by Australian Marriage Equality and the Greens senator Janet Rice, argued the expenditure must objectively be “unforeseen”. The judges unanimously held that this “radical departure” from the interpretation of appropriation laws was not supported, accepting the government’s case it is up to the finance minister so long as his or her belief is “formed reasonably and on a correct understanding of the law”.

The need for $122m did not arise until cabinet decided on the postal survey on 7 August, at which time the finance minister, Mathias Cormann, was satisfied it was urgent because the results of the survey were to be known no later than 15 November 2017. The plaintiffs submitted that, although a postal survey by the ABS was not decided on until August, the government had considered a voluntary plebiscite to be conducted by the Australian Electoral Commission as early as March that year. Read more via the Guardian