Labor Senator Katy Gallagher leaving the Senate.

There will be another four citizenship by-elections in South Australia, Western Australia, Queensland and Tasmania in coming months in the wake of the High Court’s decision this morning to find ACT Labor Senator Katy Gallagher ineligible to have stood in the 2016 election.

Gallagher had sought to renounce her British citizenship ahead of the 2016 election but the process had not been completed by the time she nominated for the election. She had argued to the High Court that she had taken all reasonable efforts to renounce her citizenship and that the failure of the British Home Office to process her renunciation prior to nomination did not prevent her being from constitutionally eligible even under the High Court’s much stricter reading of section 44 of the constitution enunciated last year.

The High Court disagreed, in effect deciding that Gallagher could have taken steps to renounce her UK citizenship earlier. “The issue for Senator Gallagher was only ever to be the timing of the registration,” the Court found. “It was the responsibility of Senator Gallagher to ensure that renunciation of her British citizenship took effect under the law of the United Kingdom before her nomination for the election which occurred on 2 July 2016 if she was to escape the disqualifying effect of s 44(i) …”

Following the ruling, shortly before 1pm, Labor’s Justine Keay, Josh Wilson and Susan Lamb all resigned from the House of Representatives. Keay and Wilson were both in a similar situation to Gallagher in not having had final confirmation of their renunciation provided prior to nomination. Lamb remains a UK citizen following her inability to provide appropriate documents as part of her renunciation. Centre Alliance’s Rebekha Sharkie, who was also in a similar position to Gallagher, has also resigned from her seat of Mayo in South Australia. It is understood all will recontest their seats. A fifth by-election, caused by the resignation of Labor’s Tim Hammond from the seat of Perth, is also due in coming weeks.

The Gallagher decision and the byelections make an utter mockery of Labor’s oft-repeated claim that its internal processes for ensuring its candidates were constitutionally ineligible were watertight and that there was no cloud over any of his MPs. Melbourne MP David Feeney already resigned earlier this year from his seat of Batman.

As with Batman, the byelections will represent a challenge for Bill Shorten and Labor. Justine Keay’s seat of Braddon is a marginal, which she won by 2.2%. Lamb narrowly defeated Wyatt Roy in the ultra-marginal Longman with the help of preference flows from both One Nation and the Katter’s Australian Party, and holds it by just 0.79%. Wilson’s seat of Fremantle is safe from the Liberals but the Greens, who polled nearly 18% in 2016, may pose a stronger challenge, particularly if a high-profile Greens candidate, perhaps one with some history on the citizenship issue, stands. Losing any of those seats would start alarm bells ringing within Labor about its inability to convert a long and substantial polling lead into results on the ground.

Sharkie is given little chance of hanging onto Mayo given the performance of Nick Xenophon’s SA-BEST party at the recent South Australian state election and is expected to return to the Liberal fold.