Australia has lurched into a fresh political crisis after a court ruled that a Labor senator was ineligible to sit in parliament because she had failed to renounce her British citizenship, triggering a spate of MP resignations.

The latest twist in the saga brings to 14 the number of parliamentarians who have resigned or been ruled ineligible since mid-2017, when renewed scrutiny on a constitutional clause set politicians scrambling to prove they only had Australian citizenship.

On Wednesday the high court ruled that the Labor senator Katy Gallagher was ineligible because she had failed to renounce her British citizenship by the nomination deadline before the 2016 election.

Three Labor MPs and a minor party MP quit within hours, accepting that the case was a precedent because they had relied on the same defence of having taken “reasonable steps” to renounce their British citizenship before the election.

In a litmus test for both the Liberal prime minister, Malcolm Turnbull, and the Labor opposition leader, Bill Shorten, the four MPs will now fight to retain their seats in a “super Saturday” of byelections in four different states.



While the Turnbull government targets Shorten for his failure to force his MPs to resign sooner, the Labor leader has attempted to frame the looming contests – to be held as early as June – as a chance to cast judgment on the coalition government’s May budget and 10-year company tax cut plan.

The byelections include the marginal Labor seats of Longman (Queensland) and Braddon (Tasmania), so the risk of losing MPs falls on the opposition. But with the possibility of swings away from the ruling Liberal-National coalition in Queensland and the Western Australian seat of Fremantle, the results may also spell danger for Turnbull.

While the MPs can recontest their seats to re-enter parliament within two months – as several other MPs have done – Gallagher will be replaced by her Senate running-mate, forcing her to wait until the next election to re-enter parliament.

In Gallagher’s case the high court adopted a strict approach to the constitutional bar on foreign citizens sitting in parliament, clarifying that taking “all steps reasonably required” is only a defence where foreign law “irremediably prevents” the Australian citizen renouncing foreign citizenship.

That would require an “insurmountable obstacle” to renouncing foreign citizenship, five justices said in a joint decision. The court found there was no such impediment for Gallagher and the requirements of UK law to renounce citizenship could not be described as onerous.

The attorney general, Christian Porter, said the legal test had been clear since the high court’s Re Canavan decision in October, which found five MPs and senators ineligible over dual citizenship.

The Liberal leader of the house, Christopher Pyne, said Shorten had “faced a character test” over the citizenship of his MPs and he had “failed it quite spectacularly”.

Shorten refused to apologise for his handling of the citizenship issue. He said the Labor MPs – all but one of whom were eventually able to renounce their other citizenships albeit after the deadline – had relied on legal advice in “good faith”.