Ms Sudmalis last week declared that she had "confirmed that I do not hold, and I have never held British citizenship" after Fairfax Media approached her about her possible status as a dual national.

After seeking urgent clarification from the UK government - following Fairfax Media's story - Ms Sudmalis said she had been advised that she was in the clear.

The member for Gilmore was born in Australia in 1955, to an Australian father and a British mother. Her mother, Valerie Pybus, came to Australia in 1951 and did not become an Australian citizen - and renounce her British citizenship - until 1989.

Under section 44, part (i) of the Australian constitution, a person is disqualified from standing for Parliament if they are "under any acknowledgment of allegiance, obedience, or adherence to a foreign power, or is a subject or a citizen or entitled to the rights or privileges of a subject or a citizen of a foreign power".

On Monday night, the Guardian reported that: "an incoming passenger card from 25 July 1966 - found in the National Archives - showed Sudmalis listed her nationality as 'British Australian' when she returned to Australia as a 10-year-old after travelling overseas.

Ms Sudmalis was travelling with her father, Norrie Hardinge, at the time.

Fairfax Media called Ms Sudmalis twice on Monday night and was hung up on both times.

In a short statement sent out by the Prime Minister's office soon afterwards, Ms Sudmalis attempted to put the questions over possible dual citizenship to bed, again.

"The UK Home Office have confirmed to me that I do not hold and have never held British citizenship," she said.

"My Australian father filled out the incoming passenger card on my behalf in 1966. He labelled my nationality as British-Australian because my mother is British. I did not travel on a passport of any sort for that trip to Australia."

It's understood that Ms Sudmalis parents were, at the time, going through a divorce and that a British court had ruled she could travel to Australia without a passport after her parents had separated.

Previous questions, including whether she was entitled to citizenship by descent under British law, have not been conclusively answered, and she has not released documents.

The Turnbull government has been rocked by revelations that deputy Prime Minister Barnaby Joyce, deputy Nationals leader Fiona Nash and former cabinet minister Matthew Canavan have all held dual citizenship.

The High Court will hear a directions hearing later this week about the eligibility of Mr Joyce, Senator Canavan, One Nation senator Malcolm Roberts and former Greens senators Larissa Waters and Scott Ludlam.

Ms Nash and independent senator Nick Xenophon have also revealed they may be dual nationals.