Nepean by-election minus two days

The first of three by-elections in as many weeks will be held on Saturday for the Mornington Peninsula state seat of Nepean, where former deputy leader Sam Groth has called time on his brief parliamentary career rather than wait it out until the November election. This puts the Victorian Liberals under pressure from One Nation, with Labor declining to field a candidate in a seat where they fell 6.4% short at the 2022 election. As detailed in my by-election guide, the respective candidates are Mornington Peninsula Shire mayor Anthony Marsh for the Liberals and civil engineer Darren Hercus for One Nation. There has been no published polling that I’m aware of, but a report in the Herald Sun points to concern in the Liberal camp based on “the feelings on pre-poll” and “shit on the liver … about having to vote twice in 12 months”.

Both campaigns have faced internal difficulties, with the Herald Sun reporting concerns about the number of Liberal volunteers willing to come forward after local members were shut out of the preselection process. The Age reported the One Nation campaign committee “collapsed” in late February when two of its members resigned from the party, claiming state president Warren Pickering had advised Hercus to use a personal bank account to accept campaign donations, which would have violated the legal requirement for donations to go through a specified account. Pickering denied any such conversation took place, but The Age then reported a third former party member backing the account of the other two. Hercus said he had no knowledge of how donations were being managed and was paying most of the costs of his campaign on his credit card.

Also in the field of eight candidates is Tracee Hutchison, who has been endorsed by Independents for Mornington Peninsula, whose candidate at the federal election came within 2.3% of unseating the Liberals in Flinders after polling 21.2% of the primary vote. Rounding out the ballot paper are candidates from Legalise Cannabis, Libertarian Party (once the Liberal Democrats), Affordable Housing Now – Sustainable Australia (until recently just Sustainable Australia) and End Mass Migration (whose former status as the Companions and Pets Party might well raise eyebrows). The Libertarians have a how-to-vote card advising a second preference for One Nation and a third for Liberal, but the others have open tickets.

Nepean does not exactly fit the profile of the four South Australian seats One Nation won in March, which were distinctly more rural in character, but its demographics are not without promise for the party. By far its outstanding characteristic is that 23.8% of the population was aged 70 and over at the time of the last census, its closest rival on this count being Gippsland East on 20.3%. This is a cohort that has been running four points above average for One Nation in federal polling since the start of this year.

Analysis of the South Australian result reveals an even more reliable indicator of One Nation support is share of the adult population who finished year 12 or equivalent. The simple model 0.543 – 0.555x, where x is the percentage of residents aged over 18 who finished high school, explained 83% of the variation in One Nation support in South Australia. When applied to the relevant figure for Nepean, which ranks 71st out of the state’s 88 seats for educational attainment, this too suggests One Nation should punch about four points above its usual weight in a seat like Nepean.

The map below illustrates the variability on this score within an electorate where the median house price approaches $3 million around Portsea but barely cracks $800,000 further along the bayside. Applying the data at the suburban level to the educational qualifications model suggests One Nation could expect its vote share in the latter area to be twice as high, a point reflected in the the meagre 2% vote shares One Nation recorded around Portsea and Sorrento at the 2025 federal election.

How this translates in a context where Labor isn’t fielding a candidate, never mind enjoying the ascendancy it did at the South Australian election, is harder to say. Up for grabs is its 32.6% vote from 2022, when support for Victorian Labor was ten points higher than its current polling. While betting markets have the Liberals as short-priced favourites, it is within the realms of possibility that the homeless Labor vote will consolidate behind Tracee Hutchison while the One Nation exodus reduces the Liberals to third, a fate that became all too familiar to their candidates in South Australia. The likely result in that scenario would be a One Nation win on preferences from the Liberals, whose how-to-vote card has Hercus above Hutchison.

Author: William Bowe

William Bowe is a Perth-based election analyst and occasional teacher of political science. His blog, The Poll Bludger, has existed in one form or another since 2004, and is one of the most heavily trafficked websites on Australian politics. View all posts by William Bowe