Having settled on its plan for a $122 million public opinion survey on same-sex marriage, the Turnbull government has fulfilled its dismally short-term objective of dissuading five MPs from rebelling on the floor of Parliament.

The next hurdle is a potential legal challenge that may give it some tough questions to answer, namely: how it is that a nine-figure sum can be channelled to an exercise with no real precedent without the approval of Parliament, and whether the Australian Bureau of Statistics has the legal authority to do something that is properly in the domain of the Australian Electoral Commission.