Three Labor MPs and one Independent have resigned over their dual citizenship status after the High Court ruled a Labor senator was invalidly elected under Section 44 of the Constitution.
Australian voters face five by-elections across the country after Labor MPs Justine Keay, Josh Wilson, Susan Lamb and Independent MP Rebekha Sharkie all became the latest parliamentarians to resign over their dual citizenship status, just hours after the High Court booted Labor Senator Katy Gallagher.
The three Labor MPs all resigned in the House of Representatives on Wednesday after the High Court found Ms Gallagher did not take reasonable steps to renounce her British citizenship.
Centre Alliance MP Rebekha Sharkie also resigned just moments before them.
Earlier, the government had demanded all who had questions over their dual British citizenship status resign by the day's end following the High Court decision.
Shorten's citizenship guarantee wrecked
Labor leader Bill Shorten gave a "rolled gold guarantee" none of his MPs would be caught up in the citizenship crisis, but now he's facing multiple by-elections and replacing a senator.
Mr Shorten faced tough questioning over his insistence that his MPs would be fine, after the High Court disqualified Senator Gallagher on Wednesday.
That led Ms Lamb, Mr Wilson and Ms Keay to announce they would quit because they were also British citizens when the 2016 election writs were issued.
Mr Shorten said he relied on the Labor party's lawyers when he guaranteed his MPs would be fine, but he refused to release their advice.
"If you get your lawyers, you do take their advice, it's been the same advice for 20 years," he told reporters on Wednesday. "Political parties don't release their legal advice."
Ms Lamb still hasn't renounced her British citizenship, which means she's been claiming her parliamentary salary for more than six months while knowing she was breaching the rules.
Mr Shorten said Labor relied on legal advice that said if candidates took "all reasonable steps" to renounce their citizenship then they would be eligible to sit in parliament.
All three MPs said they intended to run again.
They are unlikely to be forced to pay back any of their salary or entitlements, in keeping with the precedent set in other citizenship cases.
Mr Wilson was asked if he felt let down by Labor's legal team, to which he responded: "No. In no way."
Keay: I acted on the best available legal advice
Ms Keay was still a British citizen at the time of the federal election but argued she took reasonable steps to renounce her citizenship.
In her resignation speech, the Tasmanian said the High Court had set a new precedent in the decision on Ms Gallagher's eligibility.
"This is a new rule and I respect this rule without qualification," she said.
"Before nominating for parliament, I acted on the best available legal advice which indicated I had satisfied the eligibility requirements under the constitution as they've been interpreted for 25 years."
Ms Keay said she would nominate for pre-selection and contest the seat of Braddon at the next election.
Wilson: Reasonable steps 'effectively impossible'
London-born West Australian Labor MP Josh Wilson said while the 'reasonable steps' argument had been accepted for more than 25 years by the court, that was "effectively impossible" in his case.
"It will change the way the electoral system works in this country. It will mean for up to one-fifth of Australian citizens who are or are entitled to citizenship of another country, that their ability to participate in federal elections will be significantly constrained," he said.
Lamb: I intend to be back
Ms Lamb said she too would be back in politics.
"This is not a valedictory speech, let me be very clear. I intend to be back," she said.
This brings to 15 the number of politicians to be kicked out of federal parliament for holding dual citizenship.
Bbefore Wednesday's flurry of resignations, there were 11, including Ms Gallagher's forcible departure.
The resignations will force voters into by-elections across the country, including one caused after Labor MP Tim Hammon resigned for family reasons.
Ms Gallagher became the 11th politician to be kicked out of federal parliament for holding dual citizenship at the time she was elected after the High Court ruled the ACT senator breached Section 44 of the Constitution.
Chief Justice Susan Kiefel said the British renunciation process was "simple" and concluded Ms Gallagher did not take sufficient steps to rid herself of dual citizenship before her nomination.
"The questions in this reference turn upon one issue: whether British law operated to irremediably prevent an Australian citizen applying for renunciation of his or her British citizenship from ever achieving it," she wrote in her judgement.
"An affirmative answer cannot be given merely because a decision might not be provided in time for a person's nomination."
Gallagher 'deeply disappointed' by decision
Ms Gallagher said she was "deeply disappointed" by the decision but maintained she followed legal advice.
"I have always acted on the best available legal advice, which at all times, indicated that I satisfied the eligibility requirements under the Constitution. However, today the High Court has made its decision, and I respect the outcome," she said in a statement.
She also apologised to ACT voters for the outcome, while indicating her political future may not be over.
"To have my place in the Senate end like this today is very deeply disappointing but I believe that I have more to contribute to public life and I will take the time to talk with Labor Party members on how I can do this over the months ahead."
Senator Gallagher’s replacement is likely to be David Smith, Labor’s number two on the ballot paper.
Mr Smith is a director of Professionals Australia - a union representing high-level professionals such as scientists and engineers.
The Gallagher trial
At a hearing in March, lawyers for the government argued Ms Gallagher failed to renounce her UK citizenship before the last election because she left the application too late and did not attach the right documents to her letter to authorities.
The case centred on whether Ms Gallagher took "reasonable steps" to sever ties with the UK in the lead-up to the 2016 poll.
Her lawyers argued she sent in "sufficient" documents to the UK Home Office - a copy of her Australian passport and birth certificate - before the writs were issued for the 2016 election.
But on July 20, weeks after the election, the UK Home Office asked for additional documentation to prove she was a British citizen through descent from her father.
Ms Gallagher then quickly sent in her father's birth certificate, her parents' marriage certificate and her own birth certificate.
Solicitor General Stephen Donaghue, representing the government, said Ms Gallagher only submitted her application 41 days before she nominated and should have expected the process to take time, especially given she was pre-selected as a Labor candidate a year before the election.
"Because the application was not submitted a sufficient time in advance to be perfected under British law... reasonable steps were not taken," Mr Donoghue told the court.
Mr Donoghue also drew the judge's attention to a UK government document that specifically requests citizens by "descent" from a parent or grandparent, like Ms Gallagher, to "send documents proving that person's citizenship or status and your relationship to him or her".
In response, the former Labor senator's lawyers said the ACT birth certificate sent with the original renunciation form listed her father's UK birthplace, and therefore was sufficient proof he was a UK citizen.