The Farrer by-election could reveal whether Coalition voters are shifting towards One Nation or prefer independents, with implications for future political strategy.

The Farrer by-election offers the Liberal and National parties a unique opportunity to discover what their supporters truly think about how closely they should align themselves with Pauline Hanson’s One Nation party.

Labor’s decision not to contest the by-election means that the separate coalition parties could adopt an unusual strategy with their how-to-vote preferences, leaving it mainly to voters to determine whether or not to favour the One Nation candidate over an independent who is aligned with the Teals.

At the moment, the betting odds suggest that neither the Liberal candidate, Raissa Buttkowski, nor the National, Brad Robertson, will win. The leading contenders are independent Michelle Milthorpe and One Nation’s David Farley.

Milthorpe contested Farrer at the last federal election, and after preferences came second to Sussan Ley, who had held the seat for the Liberals since 2001. The seat has always been held comfortably by either the Liberals or the National Party, but in 2025 Ley’s margin over the independent Milthorpe was cut to just 6.2 per cent.

Milthorpe should be able to capitalise on her relative success at that election. The Labor Party, which will not be running its own candidate at this election, is certain to advise its supporters to give their votes to her.

One Nation deserves to share favouritism with Milthorpe based on the way it has been performing in the opinion polls in the past three months. More often than not it has been ahead of the Coalition. That the polls are not misleading was demonstrated in the recent South Australian state election, when it won more votes than the Liberal Party.

One Nation is likely to perform better in the rural and provincial Farrer electorate than it did in South Australia where metropolitan Adelaide is dominant.

Neither the Liberal Party nor the Nationals could afford to skip the by-election, even though their chances of success are small. However their supporters are likely to determine whether Milthorpe or Farley will win.

The Liberals will give their second preferences to the Nationals and the Nationals will give their second preferences to the Liberals. That is effectively required by their coalition agreement.

But what then? The leadership of the Nationals are more concerned about the threat that One Nation is to their very existence than are the Liberals. It is possible the Nationals could preference the independent Milthorpe ahead of One Nation, to try to stop One Nation from winning a seat in the House of Representatives. One Nation already has one seat in the Representatives, but only because of the defection to One Nation by the former National Party leader, Barnaby Joyce.

The Liberals – at least until the shock of the South Australian election – were more inclined to ape One Nation’s policies than to directly confront the party. That may change.

The answer for the Liberals (and possibly the Nationals) is to leave it to their voters to decide for themselves how they will allocate preferences – or at least those preferences after the second preference goes to their coalition partner.

They would need to remind voters that they must number every square on the ballot paper – to ensure the vote is valid. But the actual order of preferences would be left to individual voters.

Once the election is over the Coalition partners could then check to see just how their own supporters ordered their preferences: the crucial issue probably being to what extent did Liberal and National voters regard One Nation as next in line for their vote? Or did they favour independents over One Nation?

The result of this mini-referendum of their supporters could help the leaders of the Coalition parties shape their response to the existential problem of dealing with the surge in One Nation’s popularity – at the expense primarily of the Coalition parties.

Its unlikely to happen. Not least because those leaders fear what the result might be.