- If Deputy PM Barnaby Joyce is found ineligible under Section 44 it would trigger a by-election.
- That by-election in New England would place the Turnbull Government's one-seat majority at risk.
- The government is arguing the politicians who did not know they were dual citizens, including Mr Joyce, should be excused.
The third day of the High Court's deliberations will continue on Thursday to determine whether seven politicians who were dual citizens around the time they entered parliament should be forced to resign under Section 44 of the Constitution.
The 'Citizenship Seven' come from across the political spectrum: The Nationals' Barnaby Joyce, Fiona Nash and former minister Matt Canavan; former Greens senators Scott Ludlam and Larissa Waters; One Nation's Malcolm Roberts and the NXT's Nick Xenophon. They all claim they were unaware of their dual citizenship until recently.
- A full explanation of the background can be found here.
- A summary of day one in the High Court is here.
- A summary of day two in the High Court is here.
4.20pm - Court adjourned. Judgement to come "as soon as possible"
That's a wrap for this three-day trial.
The chief justice says the court will publish its judgement "with or without reasons as soon as possible".
"It's not always possible for the court to do this immediately."
The court will return on Tuesday, October 17. But that doesn't mean they will be discussing this case.
3.30pm - Allegiance without knowledge
Matt Canavan's lawyer David Bennett is back to refute some arguments from the other side.
Like the Commonwealth lawyer, he is trying to rubbish the idea of a person having allegiance or loyalty to a foreign country without knowing they are a citizen.
"Allegiance without knowledge is pretty ineffective," he says.
3.00pm - Into the history books again
Mr Donoghue is again taking us through the drafting of the Constitution, attempting to prove that Section 44 was never intended to catch out those who had a dual citizenship imposed on them without taking voluntary steps to get it.
An earlier wording of Section 44 debated in 1897 disqualified those who had "done any act whereby he has become a subject or citizen". That implied they needed to take an active step to get it.
But the final wording dropped the "act" part. You're disqualified if you are a subject or citizen of a foreign power, or entitled to the rights or privileges of a subject or a citizen of a foreign power.
Tony Windsor's lawyers say that change was designed to catch foreign citizenship by descent. But Mr Donoghue says the drafting committee never meant it that way.
2.40pm - Donoghue refutes the foreign military argument
The Commonwealth's lawyer Stephen Donoghue is again trying to prove that a "hardline" reading of Section 44 would be unfair and would disqualify a "very large number" of Australians from sitting in parliament.
He is rebutting the argument from Tony Windsor's lawyer (yesterday) that it doesn't matter whether you know about your foreign citizenship because it could still have power over you. For example, you could be called for military service or charged with a extraterritorial crime in that jurisdiction.
But Mr Donoghue points out that even someone who took "reasonable steps" to rid themselves of a foreign citizenship, which the High Court found an acceptable excuse in 1992, could still be targeted by a foreign power in that way.
2.25pm - Government lawyers begin a reply
Mr Newlinds concludes his case for Malcolm Roberts. The thrust is it was reasonable for Senator Roberts to not know he was British until he got solid confirmation after the election, when he then acted immediately to renounce. Therefore, he is in the same boat as the government's members and senators: Barnaby Joyce, Matt Canavan and Fiona Nash.
Solicitor-General Stephen Donoghue is now beginning his rebuttal of the cases brought by the contradictors, including Tony Windsor's lawyers.
2.15pm - We're back - and Robert's lawyer has 15 minutes
Chief justice Susan Kiefel begins by telling Mr Newlinds, acting for Senator Roberts, he's got 15 minutes to bring his case to a close.
He's speaking quite quickly now.
12.40pm - Court breaks for lunch
We'll resume at 2.45pm for more of the Malcolm Roberts case. Plenty more to come.
12.25pm - Judges attempting to move on from the historical arguments
Mr Newlinds is persisting with Senator Robert's history, and what he thought about his Australian citizenship through the 1980s.
The judges are expressing some frustration and ask him to accelerate. "We are in our third day, Mr Newlinds," says one.
12.05pm - Robert's lawyer says his case is as good or 'better' than Barnaby Joyce's case
Senator Robert's lawyer is seeking to prove all the detail about the One Nation senator's birth in India is irrelevant. He calls it a "dangerous distraction".
That's because no one is accusing him of being an Indian citizen. The issue is his Welsh father.
The judges ask what he is trying to prove.
"I'm trying to get in the same boat as Joyce and Senator Nash", he says, "and then prove we’re actually in a better boat".
(Presumably because of those emails he sent to the wrong addresses.)
11.50am - At least Malcolm Roberts had the 'wit' to try renouncing, lawyer says
Mr Newlinds again says Malcolm Roberts didn't know he was a citizen of a foreign power, but unlike Barnaby Joyce, Fiona Nash and Matt Canavan, "he has the wit to appreciate that he might be". Hence those emails Senator Roberts sent.
But he agrees with the government argument that you can't be expected to take "reasonable steps" to get rid of a foreign citizenship until you know it exists.
"As a matter of logic, someone who doesn't know they are a subject or citizen of a foreign power cannot take reasonable steps to renounce," he says.
11.30am - One Nation lawyer says it's "unAustralian" to treat immigrants differently
Mr Newlinds, acting for Senator Roberts, says the court should reject the government's arguments that there's some difference between "natural-born Australians" and "immigrant Australians".
He calls that separation an "unAustralian notion" that "should be put to bed".
This relates to an argument yesterday about whether the requirement to take "reasonable steps" to get rid of your foreign citizenship, established in Sykes v Cleary 1992, should apply to natural-born Australians.
The 1992 case was all about foreign-born, naturalised Australians. The lawyer for the Greens (and now for Senator Roberts) say it should apply to everyone equally.
It's worth pointing out though that Mr Newlinds does not accept that Senator Roberts was ever "naturalised". While born overseas, he says he was entitled to Australian citizenship from birth.
11.25am - Lawyer for Malcolm Roberts attacks "false" arguments
Robert Newlinds SC has begun his case for One Nation senator Malcolm Roberts with some vigour.
He wants to "first sweep away a number of false premises". He says Senator Roberts was never naturalised as an Australian. While born in India, he was Australian from birth, he says.
11.10am - Judges discuss the Xenophon case
Further to the discussion yesterday, the judges are questioning Mr Kennett on whether Mr Xenophon's status as a "British overseas citizen" makes him a dual citizen for the purposes of Section 44.
There seems to be some consensus that he does not have most of the rights commonly associated with citizenship - like the right to live in the country.
One judge suggests "it’s not citizenship as we understand it".
However, the literal wording of Section 44 says you are disqualified if you're a foreign citizen or entitled to the rights of a foreign citizen. That word "or" could be critical. Xenophon could be struck out on the label alone, even without the rights.
10.20am - Malcolm Roberts is in the house
One Nation senator Malcolm Roberts has shown up to court today, making him the first of the seven politicians involved in this case to appear in person.
His legal team will make their submission today.
Senator Roberts is sitting right behind his legal team and was just having a word with his solicitor.
He chose not to speak with reporters on his way in.
10.15am - Court resumes for final day
We're underway for the final day of this three-day hearing in Canberra.
We begin with more from Geoffrey Kennett, the 'friend of the court', who is talking through some of the legal context and Constitutional history with the judges.