Then on Thursday morning, that changed. Quaedvlieg - who was sacked by the government in March for helping his girlfriend get a job at the Australian Border Force - entered the fray with "explosive" evidence in a letter to the inquiry. He claimed that in June 2015, he was phoned by Dutton's then chief of staff Craig Maclachlan seeking help for a "mate" of the minister whose au pair was detained at Brisbane airport. The so-called "mate", Russell Keag, was Dutton's former colleague from his time in the Queensland Police Service. Dutton had already insisted he had not spoken to Keag in 20 years. But Quaedvlieg's testimony solidified the impression that Dutton used his ministerial power to give fast, preferential treatment to old friends or acquaintances. Former Australian Border Force commissioner Roman Quaedvlieg. Credit:Alex Ellinghausen At the same time, Fairfax Media had made two more revelations overnight. One was that Keag had been questioned by an ethical standards unit in the QPS, but was ultimately cleared. The other dealt with new claims about Dutton's constitutional eligibility to sit in parliament under section 44.

A letter to a childcare centre run by Dutton's wife spoke of an "agreement" with the Commonwealth to deliver public funding to hire a special needs teacher at the centre. Dutton is a beneficiary of the family trust that runs the centre, but section 44 forbids an MP from having "any direct or indirect pecuniary interest in any agreement with the Public Service of the Commonwealth". Leading constitutional expert Anne Twomey wrote a paper suggesting this was the crux of Dutton's eligibility question. She insisted the issue would not be resolved until it went to the High Court. Labor's Mark Dreyfus called a press conference and declared Dutton "quite probably ineligible". Loading Dutton, meanwhile, spent the week foreshadowing retaliation but keeping his powder dry. He said a "disaffected former senior Australian Border Force officer" was leaking against him, without naming anyone. He said had "kept a very good list" of Labor MPs who asked him to intervene in visa cases, and wondered aloud about their motivations and union links. Meanwhile, News Corp began running stories about Labor frontbenchers who had lobbied the immigration department on behalf of constituents who were criminals and "hate preachers".

Loading Replay Replay video Play video Play video Then on Thursday afternoon, following reports of Quaedvlieg's evidence, Dutton went nuclear. In a press release, he accused the former ABF head of fabricating evidence and lying to the inquiry. He said Quaedvlieg was "bitter" and damaged by the bruising and public loss of his job. He even asked Quaedvlieg's successor, Michael Outram, to offer Quaedvlieg "support to address his personal or mental health issues". Dutton also drew attention to several inconsistencies in Quaedvlieg's recount. He pointed out that Maclachlan didn't work for him in June 2015, as Quaedvlieg claimed - he didn't start until October. "It is a fabrication and it is impossible for this conversation to have occurred," Dutton said. Nor had he asked any staff member to contact Quaedvlieg about the au pair.

In response, Quaedvlieg conceded he may have mucked up his dates. But he did not resile from his central claim that a conversation took place regarding a visa, and alleged there may even be a third "case" that was not yet public. He urged Dutton to "desist from personal attacks and casting aspersions over my actions, motivation, integrity, reputation and mental health". Liberal colleagues are watching the spectacle with uncertainty. One Dutton ally said it was "bloody hilarious". Finance Minister Mathias Cormann, another Dutton backer, told Sky News Quaedvlieg was "obviously not a credible witness" and his claims had to be treated accordingly. Veterans' Affairs Minister Darren Chester, a National who was a vocal supporter of Malcolm Turnbull, noted drily: "It’s two quite strong personalities expressing their very strong views." But Dutton's suggestion that Quaedvlieg may be mentally unwell drew criticism from doctors. 'Inappropriate': Dr Tony Bartone, president of the Australian Medical Association, weighed in following Peter Dutton's comments about Roman Quaedvlieg. Credit:Alex Ellinghausen

President of the Australian Medical Association Tony Bartone told Fairfax Media it was inappropriate to publicly speculate about a person's mental condition. "We don’t know what's going on here," he said. "Talking about someone’s mental health in a public arena is obviously not conducive to the wellbeing of the person concerned." While Quaedvlieg's missteps have done him no favours, Labor strategists see Dutton's extraordinary statement on Thursday as a telling example of how the minister reacts under heat. They will sort out tactics on Monday morning but expect to grill Dutton in question time, as well as testing him with a motion of "no confidence" and potentially another bid to refer him to the High Court. Loading Hard heads know these stunts have no chance of success - barring misadventure or malice by MPs on Dutton's own side - but they intend to exert "maximum pressure" in the hope he slips up.

Dutton did not respond to requests for an interview, but his intended path is clear: he will deny any wrongdoing and turn the tables on Labor MPs and immigration ministers. He will paint Quaedvlieg as a vengeful and possibly unwell character who can't be trusted and has links to the Labor Party. He will use the opportunity to remind voters of Labor's record on boats and border protection. The political sensitivities of that issue have made it difficult for Labor to land a blow on Dutton. His shadow minister Shayne Neumann is typically a silent presence in question time, as Dutton relishes in pointing out. Last year, he described Neumann as being under sedation. "He's wheeled in on a fridge trolley as I understand," Dutton joked. "Three or four times in question time they take a pulse ... to see whether he is still alive." But Labor is energised about the au pairs. The accusation is not that Dutton broke any rules (other than potentially misleading parliament about his knowledge of the au pairs' employers), but that he gave his mates special service - the kind average punters can't get from government. That perception was aided at this week's inquiry when AFL chief executive Gil McLachlan revealed he had also asked the Coalition for help on another visa case - for a polo player who was "a friend of a friend". (This was in addition to Dutton stepping in to prevent the deportation of an au pair employed by Gil McLachlan's relative, Callum MacLachlan, in 2015.) McLachlan's evidence - and that of his government relations manager Jude Donnelly, a former Tony Abbott staffer - exposed a cosy line of communication to senior government offices.