"I believe he has a higher duty to do the right thing." Ms Banks has avoided direct comment on the matter for weeks but is now prepared to vote for the referral along with other crossbenchers, forcing the matter if the government does not accept the need for the court to examine the case. Mr Dutton has rejected the concerns over his eligibility under section 44 of the constitution as a Labor campaign. "These issues are being raised for political purposes. It was raised, as I say, by the Labor Party in October of last year and they didn’t raise it again so I am very confident in my position," he said last month. Defence Minister Christopher Pyne this week insisted Mr Dutton was clear of any doubts over his status and that anyone who tried to force the referral should also accept the referral of others who might face questions.

Mr Pyne named crossbencher Kerryn Phelps as one of those in doubt, along with Labor MPs Mike Freelander and Tony Zappia. Parliament resumes on Monday with four final days of debate for the year at a time when the government can no longer command a majority, given the move by Ms Banks to the crossbench and the arrival of Dr Phelps in Parliament. A successful vote to refer Mr Dutton would not force his resignation, given former Deputy Prime Minister Barnaby Joyce remained in his portfolio pending a court decision, and it would not guarantee a court ruling on his fate before the next election. However, Labor could use the moment to humiliate the government on the floor of Parliament.

Ms Banks said one of her concerns about the case was a passage in the legal advice on Mr Dutton, prepared by Solicitor-General Stephen Donaghue, that found the Home Affairs Minister was "not incapable" of sitting in Parliament but was at "some risk" of a High Court ruling that found otherwise. The legal advice included a statement from Mr Donaghue that "there may be further facts of which I am presently unaware" – an important caveat when High Court rulings on eligibility rely heavily on sometimes minor facts. At issue is whether a childcare business owned by a Dutton family trust has an "agreement" with the Commonwealth because they benefit from government subsidies. A financial interest of this kind could breach section 44(v) of the constitution. "In my view, there is an agreement, but that is for the High Court to determine," Ms Banks said. While Ms Banks was a vocal critic of the leadership spill against Malcolm Turnbull in August and voted against Mr Dutton as leader, she said her view was not shaped by those events.

"I have to leave aside my personal feelings with regard to Peter Dutton and look at this objectively," she said. "And I’ve considered the legal advice very carefully." Labor has 69 votes in the lower house and is close to getting the numbers to refer Mr Dutton, reversing a defeat when it last tried on August 23 in the midst of the leadership spill. That vote was taken before Ms Banks and others had time to read all the legal advice. The government has 74 seats in the floor of the House of Representatives but only 73 on the floor of the chamber, with Liberal MP Tony Smith presiding as Speaker, so is now at risk of defeat.