Senator Ludlam said he had been alerted to the dual citizenship issue a week ago by "someone who had done some digging". Greens senator Scott Ludlam: "I have no wish to draw out the uncertainty or create a lengthy legal dispute, particularly when the Constitution is so clear." Credit:Alex Ellinghausen It is understood this was not a journalist or a political opponent, but a "very interested member of the community". Senator Ludlam said it had then taken a "couple of days" to confirm his status with the New Zealand High Commission and clarify his legal situation. "I could have dug my heels in, but it creates a messy and protracted dispute."

It's unclear what his resignation means for the make-up of the Senate, however the Greens expect to retain the seat following a special recount. The seat would then possibly fall to Jordan Steele-John, a 21-year old from West Australia who has cerebral palsy. Scott Ludlam (right) and Larissa Waters (left) served as co-deputies to Greens leader Richard Di Natale. Credit:Andrew Meares Mr Steele-John was third on the Greens 2016 WA Senate ticket. He told his local newspaper last year that Australian politics needed younger representatives. "Older Australians have an incredible amount to offer and that should be respected, but there is also a real need in Australian politics for younger voices to be heard." Scott Ludlam arrives at the surprise press conference in Perth on Friday to announce his resignation. Credit:Brendan Foster

In a Facebook post on Friday, Mr Steele-John said he was open to allowing Greens members decide who takes the vacant Senate spot. "If it comes down to it, I'd be happier putting the choice of candidate back into the hands of our party membership," he wrote. Illustration: Matt Golding "But like everyone else in the party I'm going to be spending the next week in sad shock and/or swearing loudly into a pillow. We can worry about who, and how the hell we try to substitute someone else in for Scott later." Under one option being canvassed, Senator Ludlam could return to Parliament should he renounce his dual citizenship by the time a replacement is selected, however Greens sources say he is likely to remain out until at least the next election.

Expressing regret at unfinished work, he said it was "too soon" to talk about a political comeback. "I will find some other way of stirring up trouble." Senator Ludlam is the third senator forced out of Parliament since the July 2 election. Former Family First senator Bob Day's election was ruled invalid over a conflict of interest issue, while former One Nation senator Rod Culleton was forced out after being declared bankrupt. Senator Ludlam told reporters he hoped "common sense prevails" and the Finance Department did not pursue him for nine years' worth of parliamentary salaries. "I apologise unreservedly for this mistake," the outgoing senator said.

"This was my error, something I should have checked when I first nominated for pre-selection in 2006." The West Australian nominated work to block an internet filter and fighting a radioactive waste dump as his key achievements in Parliament. Greens leader Richard Di Natale said he was "devastated" by the ineligibility discovery. "Scott's decision today to deal with this issue directly and immediately shows his absolute integrity and character," he said in a statement. "Scott's tenacity, creativity, strength and intelligence should be an inspiration to us all."

Last November, Senator Ludlam announced he was taking leave from Parliament to deal with long-term mental health issues. Loading He has been co-deputy leader of the party with Larissa Waters since 2015, when Richard Di Natale became leader. Follow us on Facebook