The dual citizenship fiasco has taken another twist, with the High Court deciding it needs to formally consider whether a spat between members of the Nick Xenophon Team (NXT) affects the make up of the Senate.

Key points: High Court to consider Skye Kakoschke-Moore's vacant Senate seat next month

High Court to consider Skye Kakoschke-Moore's vacant Senate seat next month She says she could replace herself, because she has renounced the British citizenship that made her ineligible

She says she could replace herself, because she has renounced the British citizenship that made her ineligible Next NXT candidate in line, Tim Storer, has since left the party but could still take the seat

Justice Geoffrey Nettle has declared former senator Skye Kakoschke-Moore's Upper House seat vacant, with a full bench hearing next month to determine who should fill it and how they should be chosen.

There are a number of issues the seven justices will have to consider, including the extraordinary argument that Ms Kakoschke-Moore should be considered a candidate to replace herself given she has now renounced her British citizenship.

None of the other politicians embroiled in the citizenship mess have had that option available to them.

There are also arguments about whether the NXT candidate next in line for the Senate seat, Tim Storer, should be included in any recount after he was expelled from the party.

Tim Storer also wanted to fill the Senate vacancy created by Nick Xenophon. ( Twitter: Tim Storer )

At a preliminary hearing in the Court of Disputed Returns, a division of the High Court, Justice Nettle said he found it "very difficult" to think that Mr Storer could be excluded.

"However, given the issue is novel and could arise again in the near future, it is appropriate to be determined by the full court," he said.

The Federal Government has backed calls for Mr Storer to replace Ms Kakoschke-Moore in the Senate, and stated in its submission there was no rule that required senators to remain in the party that endorsed them for nomination.

Mr Storer's lawyer, Michael Abbott QC, argued that suggestions the voters' intentions would be distorted by a non-NXT member taking the seat would require the court to make "a political assessment" of Mr Storer's views and how they align or compare with the NXT party's policies.

"If Senator [Cory] Bernardi was in this case he would be claiming that his values now are closer to the Liberal Party's values at the time he was elected than those of the Liberal Party now," he said.

Mr Abbott also argued Mr Storer's expulsion from the NXT party was not in accordance with the party's rules and constituted a denial of natural justice.

He was expelled in November 2017 after he tried to take the Senate seat left vacant by Mr Xenophon's return to SA politics.

The influential South Australian politician had chosen his senior adviser Rex Patrick to replace him in Canberra, which Mr Storer claimed was his rightful spot.

"However, I decided that it would be contrary to the best interests of the NXT Party and my own personal interests to become embroiled in a public dispute about the matter," Mr Storer said in court documents obtained by the ABC.

Despite not accepting that he was banished from the party, Mr Storer has since resigned in disgust.

Both Mr Storer and the Commonwealth's legal representative, Solicitor-General Stephen Donaghue QC, have submitted that Ms Kakoschke-Moore's case is untenable.

Her mother was born in Singapore in 1957, at the time classified as a UK colony, which therefore made her a British citizen and her daughter British by descent.

The NXT team member renounced her British citizenship in December last year, just weeks after resigning from the Senate.

"It's obvious when she conceded in a letter to the president of the Senate that she was incapable of being chosen, and ineligible to be chosen ... they now appear to be saying that the world at large could now apply to be included in the count," Mr Abbott told the court.