Former NXT member to score Senate seat

Nick Xenophon's parliamentary clout has taken a serious hit with the High Court ruling out former colleague Skye Kakoschke-Moore from reclaiming her Senate seat.

Instead, the South Australian seat will go to Tim Storer, who quit the party in November and is set to sit as an independent.

The outcome significantly reduces the influence of a once-powerful voting bloc and will leave the Turnbull government with one more unpredictable crossbench senator to wrangle.

The High Court has found Ms Kakoschke-Moore - who stood down in November over her dual citizenship - was not eligible to replace herself despite having renounced her British ties.

The court's full bench on Tuesday unanimously found Mr Storer should not be excluded from a special count which will determine the seat.

The special count will be conducted by the Australian Electoral Commission on Thursday, with the court expected to return to receive the result and declare Mr Storer duly elected on Friday.

Previous special counts ordered by the court have resulted in senators who quit over their citizenship being replaced by the next candidate on the party ticket.

Lawyers for Ms Kakoschke-Moore had argued that having renounced her British citizenship, there were no longer any constitutional barriers standing in her way.

"She is an Australian citizen and a person otherwise capable of being chosen and of sitting," David Jackson QC said.

Mr Jackson also argued allowing Mr Storer to skate into parliament after quitting the Nick Xenophon Team would be a "rather curious" distortion of the true intention of those who voted for the party.

"He has ceased to be member of the political party for which South Australians voted in 2016," he told the court.

However, these arguments were quickly shot down, with the court ruling against Ms Kakoschke-Moore's case within five minutes of consideration.

The expected selection of Mr Storer will leave the NXT - soon to be renamed SA Best - with two senators and a lower house MP.

The reduction in Senate numbers removes the power of NXT to block pieces of government legislation opposed by Labor and the Greens.

The government could still succeed with legislation opposed by NXT, providing it secured the support of One Nation and six crossbench senators.

Ms Kakoschke-Moore said in a statement the court had provided "certainty" in relation to how her seat would be filled, and confirmed she would contest the next federal election.

"No one was more surprised or heartbroken than me when I discovered my dual citizenship," she said.

"I was not going to leave any stone unturned if it meant I would be able to return to the Senate to represent the state that I love."