Australia will remain in a state of constitutional chaos over dual citizenship if Deputy Prime Minister Barnaby Joyce is found eligible to remain in Parliament, the High Court heard on Wednesday.

As the ‘Citizenship Seven’ hearings continued, former solicitor-general Justin Gleeson argued Mr Joyce should be disqualified despite not knowing he had inherited New Zealand citizenship from his father.

Mr Gleeson, who is representing Mr Joyce’s chief nemesis Tony Windsor, said it was a person’s citizenship status that mattered, not whether they knew about it.

He rejected the case put forward by Bret Walker SC, representing Mr Joyce and Deputy Nationals leader Fiona Nash, which he claimed hinged on “felt” allegiance.

“It’s not an inquiry into whether you know or think about or feel about the allegiance,” said Mr Gleeson, who left his post last year after a public spat with Attorney-General George Brandis.

“The fact of the allegiance is what creates the risk that you will not have the single loyalty you need to the Parliament of Australia.”

According to Mr Gleeson, if politicians like Mr Joyce were allowed to renounce their dual citizenship and remain in Parliament without being found ineligible to stand, it would create “great uncertainty” and “radical instability”.

He argued that Mr Joyce did not follow the “ordinary” way to overcome issues of dual allegiance and effectively renounce his status as a New Zealand citizen – or even attempt to – before he sought to stand for election.

‘How is anyone supposed to work it out?’

But former Nationals minister Matt Canavan’s lawyer, David Bennett QC, warned that if Australian-born politicians who were foreign citizens by descent were disqualified it would lead to “genealogical witch hunts”.

That was because there were always people that wanted to see politicians removed from Parliament, he said.

“If one allows citizenship to be passed by indefinite succession, one is going to have such people engaging in genealogical witch hunts which will occupy this court every time there is an election,” he said.

Mr Bennett said there was still doubt as to whether Senator Canavan was actually an Italian citizen and that even a royal commission would struggle to answer that question given the “quirks” of Italian law.

“How is Senator Canavan supposed to work that out? How is anyone supposed to work it out?” Mr Bennett said.

The court took aim at the lawyer representing former Greens senators, Brian Walters QC, who argued they should be disqualified from Parliament despite the government believing Larissa Waters was eligible.

He said they had complied with their duty to the constitution and Parliament by resigning.

That drew a pointed question from Chief Justice Susan Kiefel, who asked Mr Walters: “Is it a proper use of this court’s time to argue for a vindication for a correctness of their view?”

He replied that he was not seeking vindication on their behalf, but countering the government’s arguments in defence of Mr Joyce, Senator Nash and Senator Canavan, who have chosen to remain in Parliament.

“Our submission is that negligence in complying with one’s constitutional obligations should never produce a more favourable result than diligence,” he said.

Ms Waters has not ruled out a return to Parliament if she is found to be eligible by the court.

The full bench, sitting as the Court of Disputed Returns, also heard from lawyers representing former crossbencher Nick Xenophon, who will resign from the Senate to run in the South Australian election.

The hearing continues in Canberra on Thursday.

-with AAP