Influential crossbench senator Nick Xenophon has announced he will refer his election to the High Court after discovering he has a form of British citizenship.
Senator Xenophon's father, Theodoros Xenophou, is from Cyprus, which was a British colony until 1960.
But Mr Xenophou retained a form of British citizenship — and passed it onto his son — because Australia is one of only nine countries which allowed him to keep it.
Speaking outside a British pub in Adelaide, Senator Xenophon said the UK Home Office had confirmed that made him a British overseas citizen, meaning he may be ineligible to sit in Parliament.
"It seems that being born in Australia, according to the 1948 UK legislation, makes me a colonial pom, something that has stunned me and my 86-year-old father," he said.
Senator Xenophon said his citizenship status was "a colonial peculiarity" and British overseas citizenship was nothing more than a form of "third-class citizenship".
"The literature on this and oral advice from the UK Home Office is that this form of citizenship is useless, and indeed in many cases it confers fewer rights than an Australian citizen travelling on an Australian passport to the United Kingdom would have," he said.
He said it had no impact on his allegiance to Australia, but the High Court would now have to determine his case.
He also accused political opponents of unearthing his citizenship status.
"It appears to have been exhumed by my political opponents to try and render me not so much stateless but senate-less," he said.
"To those politicians and their staff beavering away at this presumably over many, many hours and days, I say, 'Didn't you have anything better to do with your time?'
"No wonder so many Australians are disgusted by our current broken state of politics."
Senator Xenophon said he would will stay in Parliament and continue to vote on legislation in the meantime.
He retained a sense of humour after the press conference, posing next to a portrait of Winston Churchill and trying to order a "warm beer" inside the British pub.
The South Australian joins six other federal parliamentarians who have been referred to the High Court, including the Nationals' Matt Canavan, Barnaby Joyce and Fiona Nash, One Nation's Malcolm Roberts and the Greens' Scott Ludlam and Larissa Waters.
Both Greens senators resigned when they realised they were dual citizens, while Senator Canavan stepped down from Cabinet.
But Mr Joyce and Senator Nash have both declared they will stay in Cabinet because they are confident the High Court will find they are eligible to sit in Parliament.
