The NSW Greens are relishing the prospect of a by-election in the Sydney federal seat of Bennelong.
Liberal MP for Bennelong, John Alexander, is seeking advice on whether he is a UK citizen through his British-born father Gilbert Alexander who was born in England in 1907 and arrived in Australia in 1911.
A search of British records found no trace of Gilbert Alexander, who died in 1987, having formally renounced his UK citizenship before his son was born in 1951.
Justin Alick, who contested the seat for the Greens in 2016, said the recent High Court judgments in relation to the eligibility of seven members of parliament including two Greens senators was clear cut and Mr Alexander should be similarly referred.
"I think it's incumbent on John (Alexander) to step up and own it, do the right thing," Mr Alick told AAP on Tuesday.
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Mr Alick declined to say whether his party would consider a challenge in the High Court.
While the electorate was disappointed at the saga over MP citizenship, the greater sense of disappointment lay in terms of the government shifting away from renewable energy and embracing coal, its treatment of refugees on Manus Island and Nauru and the rising cost of housing.
"The biggest increase in house prices in the country is in Bennelong," he said.
Mr Alick won just over nine per cent of the primary vote in 2016 and 16 per cent in April's North Shore state by-election.
The Greens also picked up two seats on the Ryde Council.
"As Malcolm Turnbull has said, there's never been a more exciting time to have a by-election in Bennelong," Mr Alick said.
