Australia is edging closer to a full citizenship register for federal parlimentarians after Macolm Turnbull dropped his opposition to any system-wide change and Bill Shorten flagged support for the idea.
The breakthrough, initiated by Mr Turnbull following a cabinet meeting on Monday, could end the worsening political crisis gripping the Parliament but risks uncovering other dual citizen MPs and driving them out, forcing byelections or even a general election.
The about-face - after repeatedly insisting that eligibility was solely a matter for individual MPs - is an attempt to stem the Coalition's political bleeding over the eligibility crisis, and restore public confidence in the government and Parliament.
But it could see the government's working majority put at risk, with Mr Turnbull observing that dual citizenship inherently involved the intersection of foreign law and historical facts that can be hard to establish.
"There may well be a number of line-ball cases and it may be that they end up in the High Court," Mr Turnbull acknowledged.
"People may come to the conclusion that they are not eligible and they may choose to resign."
In a sign of the new urgency, it is hoped that the new arrangement will be brought to a vote in the Senate in the first instance as early as next week.
With the citizenship of several more Coalition MPs now being discussed publicly, Mr Turnbull said the government wanted a process that restored public trust because of a "legitimate concern that there is insufficient transparency" in the current arrangements.
Hemmed in by Mr Shorten's Friday backflip to support an audit badged as "universal disclosure", Mr Turnbull led a cabinet discussion on Monday in which it was agreed that negotiations would take place with all parties to create an agreed citizenship register to be managed by the Parliament.
It would give MPs 21 days from the passing of the resolution to complete the register and prove their compliance with section 44 of the constitution.
Mr Shorten pledged to consider the proposal in a spirit of bipartisanship.
He said he was not sure why Mr Turnbull had changed his position, hinting that he had something to hide and speculating that he might have been "rolled in cabinet".
"I made my offer in good faith and I will stand by my offer," he said, speaking from Melbourne.
The proposed mechanism, modelled on the parliamentary register of financial interests, would effectively force MPs and senators to provide proof of their heritage. They would have to show they had actively considered the question of dual citizenship before nominating, include details of the birthplace of a parent and grandparent, and provide evidence that any previous citizenship ties had been comprehensively severed.
Mr Turnbull said false declarations on the register would amount to contempt of Parliament, noting that Parliament has a "free hand" in dealing out punishment.
"The political consequences alone would be very, very dramatic. Clearly, if they were a citizen of another country and said they weren't, clearly the immediate consequence would be they would be out of Parliament," he said.
But after months of denying calls for an audit, Mr Turnbull would not accept that this amounted to the same thing.
"This is not an audit. The obligation is on each member and each senator to make a full disclosure as I have repeatedly said in recent times," he told reporters at a hastily convened press conference.
But Mr Turnbull's hopes that the announcement would bring the citizenship saga to an end were quickly dashed after Fairfax Media revealed LiberaL MP John Alexander was under a cloud.
Mr Alexander's father Gilbert came to Australia from the UK as a child, and is likely to have conferred citizenship by descent on his son. Mr Alexander has never been through a renunciation process and cannot say for sure whether his father ever did.
The Sydney backbencher has said he will comply with Mr Turnbull's new disclosure process.
The announcement came amid ongoing friction between the Liberals and the Nationals over who will replace Stephen Parry in the plum job of Senate president.
While under Coalition governments the job usually goes to a Liberal, the Nationals are angling for veteran senator John Williams.
It remains unclear who from the Liberals will be nominated. Special Minister of State Scott Ryan is understood to be interested in the plum role, which would bring a $35,000 pay rise. Veteran Queenslander Ian Macdonald is the only Liberal to officially put up his hand, but is considered too divisive for the role.
Despite his wafer-thin majority, Mr Turnbull denied his government had anything to fear from the new publicly accessible scrutiny, despite speculation that a number of MPs may be forced out causing byelections.
"The federal director has told me that all of the Liberal Party members believe that they are in compliance with the constitution," he said.