A ninth federal MP has been caught up in the citizenship fiasco and there are legal doubts over the man expected to replace her.
South Australian senator Skye Kakoschke-Moore resigned from parliament on Wednesday after revealing she was a dual citizen having inherited British citizenship from her mother.
The Nick Xenophon Team senator, who was born in Darwin in 1985, revealed her mother was born in the former British colony of Singapore in 1957.
"I am heartbroken by this news," she told reporters in Adelaide.
The senator said she received "extremely surprising" advice from the Home Office last Friday, which she got confirmed by a UK-based barrister on Tuesday night.
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Her mother obtained British citizenship when she was born in Singapore and retained it when Singapore got independence in 1963 because her father was born in the UK.
She went on to obtain right of abode in the UK under a 1971 law and when the British Nationality Act 1981 was enacted her mother effectively became a citizen otherwise than by descent.
"She was therefore able to pass her citizenship on to any children born outside of the UK," Senator Kakoschke-Moore said. "I am therefore a British citizen."
She joins a conga line of disqualified MPs including Barnaby Joyce, John Alexander, Larissa Waters, Scott Ludlam, Malcolm Roberts, Stephen Parry, Jacqui Lambie and Fiona Nash.
Party leader Nick Xenophon was devastated by the news, thanking the senator for her outstanding work.
Mr Xenophon has sought legal advice regarding the senator's replacement.
The High Court has, in the other cases of disqualified senators, ordered a special count resulting in the next person on a political party's 2016 Senate election ticket to be elected as the replacement.
However in the case of NXT in South Australia, the next candidate - business consultant Tim Storer - has left the party.
"He is a very good person but there are issues here about him not being a member of the party," Mr Xenophon said of Mr Storer.
"Our initial advice is that there are some important legal issues and it is uncharted legal territory."
Comment was being sought from Mr Storer.
Social Services Minister Christian Porter, who has been seeking to legislate drug-testing of welfare recipients, saw the citizenship kerfuffle as an opportunity.
"The complexion of the Senate is changing rather rapidly and I'm always willing to talk to new senators about this and I think there is a mounting case to let us have a go at this," he said at the National Press Club.
All senators have until December 1 to provide a statement on their eligibility, family history and citizenship to be published on the senators' interests register.
The Senate will then determine whether to make any further High Court referrals.
The government wants lower house MPs to lodge their details by December 4.
