One Nation senator Malcolm Roberts sent two emails trying to renounce his alleged British citizenship to email addresses that did not exist, the High Court has heard in Brisbane.
The court heard Senator Roberts said he found the email addresses "from his research on the internet".
Two days after nominating for the party, Senator Roberts sent an email titled "Am I still a British citizen" to two invalid email addresses he thought were linked to the British consulate.
Senator Roberts was in court on Thursday facing cross-examination over whether he renounced his British citizenship before contesting a seat in the Australian parliament. If he did not, he may be ineligible to sit in the parliament under Section 44 of the Constitution.
The Queensland senator has previously claimed he believed he was only ever an Australian citizen.
But on Thursday he admitted knowing there was a "possibility" he was a British or Indian citizen when he ran for federal parliament.
"I couldn't be absolutely certain, even though I felt certain," Senator Roberts testified.
"I had very strong confidence that I was Australian and only Australian. That's the way I was raised.
"I have only ever thought I was Australian until I heard in the court this morning," he added later.
Last month he requested the Senate refer him to the court after revealing he had taken steps to renouce his British citizenship around the time of the 2016 election. He revealed he had received a letter confirming he was no longer a citizen five months after the election.
Federal politicians are barred from holding dual citizenship under Section 44 of the Constitution.
Senator Roberts was born to an Australian mother and Welsh father in India in 1955. He is among seven politicians from across the political spectrum who will soon face court over dual citizenship concerns.
The court heard Senator Roberts' 16-year-old sister filled out his form to become an Australian citizen when he was 19.
But he has no recollection of signing the document and suspects his father would have instructed him, "Here, sign this".
"I certainly would have asked, and this is all speculation, 'What is this about because I'm already Australian?' but I can't recall any of that," Senator Roberts said.
"I was more interested in playing football."
The court heard when Senator Roberts questioned his sister, Barbara, in September 2016 as to what they were before they were Australian, she told him they were "stateless".
Senator Roberts said he had renounced his British citizenship but would not accept he had been a British citizen because that was never confirmed by the Home Office.
That was despite his own lawyer Robert Newlinds admitting to the court Senator Roberts had been a British citizen by descent.
"I accept that he said that because that carries a lot of weight doesn't it?" Senator Roberts said.
"I'm still not clear of my citizenship in the past."
Senator Roberts said if he had been a British citizen his father would have let him know, even though documents show his father was the one who tried to register his British citizenship.
"He would of ribbed me for sure if there was any chance of me being British," Senator Roberts said.
- with AAP