Labor senator Katy Gallagher has been thrown out of parliament because she was a dual citizen

John Stillwell/PA Images via Getty ImagesKaty Gallagher, (left) with a woman who’s still a British citizen.

Labor has lost one of its senators in the federal parliament, the ACT’s Katy Gallagher, after the High Court ruled today that she’s ineligible under the Constitution because she was a dual citizenship when she nominated for the 2016 election.

Gallagher, a former ACT chief minister, failed to properly renounce her British citizenship by the close of nominations and today’s decision also puts the future of three more Labor MPs under a cloud in a disastrous turn of events for the Opposition following assurances from leader Bill Shorten that his party’s candidates went through a rigorous vetting process.

While a replacement for Gallagher will be found in a recount of the 2016 senate vote, Western Australian MP Josh Wilson, Queensland’s Susan Lamb and Tasmania’s Justine Keay could all face by-elections for their seats because they offered the same defence as Gallagher, which was rejected by the High Court’s full bench.

The eligibility of former Nick Xenophon Team MP Rebekha Sharkie from Adelaide is also in serious doubt.

All were still UK citizens at the time of their nomination.

Gallagher’s submission that she took “reasonable steps” to renounce her British citizenship but there were processing delays was rejected by the court in a ruling that clarifies the “all steps reasonably required” demanded under the Constitution.

The Senator attempted to rely on a clause that allows a concession when an Australian is “irremediably prevented by foreign law from participation in representative government” provided they have “taken all steps that are reasonably required by the foreign law to renounce his or her citizenship”.

While Gallagher and the other four attempted to renounce their dual British citizenship before the nomination date, it was not finalised by the deadline.

Lamb is still a dual citizen because British authorities will not process the application until she supplies the marriage certificates of her parents. In February she gave a tear-filled account to parliament of why she had struggled to comply with the request.

The High Court concluded that in Gallagher’s case, the outcome did not have an irremediable impediment.

In response to the decision, Bill Shorten said he was “deeply disappointed for Katy Gallagher”, adding that she “has always acted on the best available legal advice”.

“Today, the High Court has set a new precedent,” he said.

“The Labor Party will now consider what further implications today’s decision by the High Court may have.”

The party is expected to come under increased pressure in parliament this week for the three MPs to resign, forcing by-elections.

Attorney-General Christian Porter said all four MPs were dual citizens of Great Britain after the close of nominations and “must resign today”.

“Bill Shorten must require the resignation of those three Labor members today, and that must occur before close of business today,” he said.

The ALP already faces a by-election in Perth following the resignation Tim Hammond, the party’s shadow minister for consumer affairs, because of the excessive demands of politics on his family.

In the 10 months since the ongoing dual citizenship fiasco first began, it has now claimed the political careers of 10 MPs and senators, including Labor’s David Feeney, who resigned from his seat of Melbourne earlier this year because he couldn’t find the paperwork to back up his claim that he renounced his British citizenship a decade ago.

Labor won the subsequent by-election in March.

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