Explainer: what the High Court decision on Katy Gallagher is about and why it matters

Over the past two months, things have been uncharacteristically quiet on the dual citizenship front. That is all about to change when the High Court (sitting as the Court of Disputed Returns) hands down its long-awaited decision on the eligibility of Senator Katy Gallagher. Whatever the result, this decision has implications beyond the immediate fate of the Labor senator.

What is the case about?

After ten months of controversy and numerous parliamentary disqualifications, resignations and byelections, every Australian knows that section 44 of the Australian Constitution disqualifies dual citizens from sitting in the Australian parliament. Gallagher was referred to the High Court after the Parliamentary Citizenship Register revealed she was a dual British citizen when she nominated for the 2016 federal election She had gained citizenship by descent through her British-born father.

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Unlike the previous cases, Gallagher admits she knew of her dual citizenship, but maintains she was still eligible because she had taken “all necessary steps” to renounce it.

Before nominating, Gallagher had submitted the prescribed renunciation form and the renunciation fee had been debited from her credit card. However, the UK Home Office subsequently requested further documents and did not formally register her renunciation until after the 2016 federal election.

What will the court decide?

The question before the High Court is whether somebody who has begun the renunciation process but is technically still a dual citizen at the time of nomination is eligible to be elected to parliament.

In one of the earliest cases considering dual citizenship in 1992, the High Court raised the possibility of an “all reasonable steps” exception to the dual citizenship disqualification. In the recent “Citizenship Seven” case the court confirmed there were limits to section 44. It found that if a foreign law made it impossible (or not reasonably possible) for a person to renounce their foreign citizenship, they would not be disqualified provided they had taken “all reasonable steps” within their power to renounce.

The present case turns on just how wide the “all reasonable steps” exception is held to be. Does section 44 just require a person to take all reasonable steps within their power to renounce, regardless of whether that renunciation is actually effective? Or is the exception limited only to circumstances where a foreign law makes renunciation practically impossible?

As the prime minister has learnt, it is never easy to predict with any certainty what the High Court will decide. If Senator Gallagher is to remain in parliament, she needs the court to take an expansive approach to the section 44 exception.

However, in both the Citizenship Seven and Hollie Hughes cases, the High Court has adopted a stricter interpretation of section 44, which would likely lead to disqualification if it approaches this case in the same way.

What happens next?

Obviously the High Court decision will have an immediate impact on Gallagher. If she is found to be ineligible, then a recount will likely mean that her replacement in the Senate is David Smith. He was the second ALP Senate candidate for the ACT at the 2016 election.

Read more: Grattan on Friday: Voters just want citizenship crisis fixed – but it isn't that easy

Importantly, this is a decision that has potential impacts on at least four other parliamentarians. The citizenship declarations of Susan Lamb, Justine Keay and Josh Wilson from the ALP, and Rebekah Sharkie from the Centre Alliance, all show they were technically British dual citizens at the time of nominating for the last federal election.

All four have made similar claims to Gallagher in terms of having taken “all reasonable steps” to renounce their dual citizenship. If Gallagher is held to be ineligible, the status of these members will undoubtedly also be in question.

Importantly, there are factual differences between all of these cases. This means much will turn on the precise reasoning contained within the High Court decision on Gallagher. If the court adopts the same strict approach as in recent section 44 cases, there would be a strong case for arguing that these other four parliamentarians should resign immediately.

Conversely, if the court finds Gallagher is eligible, much of the heat will be taken out of the dual citizenship controversy. It may even mean that we have seen the last of the dual citizenship referrals.

Parliamentary committee report

In all the speculation about the pending High Court decision, it should not be forgotten that the Joint Standing Committee on Electoral Matters is expected soon to hand down its final report following its inquiry into section 44.

The committee is widely expected to recommend that certain aspects of section 44 be removed through a constitutional referendum. Any such referendum could be held at the same time as the next federal election, although the prime minister has previously ruled this option out.

While today’s High Court decision will have an immediate impact on the composition of the current parliament, the committee report is perhaps even more significant in terms of its potential effect on the broader conversation about section 44 and constitutional reform.