Every so often, a by-election result signals a seismic shift in the electoral landscape. Famous examples at federal level are the Bass and Canberra by-elections of 1975 and 1995, which respectively foreshadowed the doom of the Whitlam and Keating governments; Peter Reith’s win in Flinders in December 1982, which cooked the goose of Bill Hayden as Labor leader; and the modest swing to Labor in Aston in 2001, which indicated the Howard Government had turned the corner after a year in which many pundits had written it off.

However, most by-elections aren’t so straightforward, for all the predictable efforts of political actors to claim vindication for their favoured political narrative. So it was on Saturday in Frome, the first South Australian state electorate to face a by-election since 1994. Frome had been held for the Liberals since its creation in 1993 by Rob Kerin, who was Premier for five months before his government lost power in 2002 and continued to the lead the party in opposition until its heavy defeat at the last election in March 2006. As counting of polling booth votes concluded on Saturday night, it was still unclear whether Liberal candidate Terry Boylan had succeeded in holding off a challenge from independent candidate Geoff Brock, who finished the evening in third place with 23.1 per cent of the vote, slightly behind Labor candidate John Rohde on 25.1 per cent.

If Brock can close the gap on preferences — and here he will enjoy a boost from the Nationals’ decision to place him second on their how-to-vote cards — he stands a good chance of edging ahead of Boylan, currently on 40.2 per cent. While the Liberals will retain the seat if he falls short, the notional count conducted on Saturday night suggests there will be little or no swing after distribution of preferences.

Such a result in a traditionally safe seat would appear to be a stinging rebuff for Liberal leader Martin Hamilton-Smith as he gears up for an election in little over a year. However, there are complicating factors in this particular electorate, which unites the solidly Labor-voting industrial town of Port Pirie — of which Brock is the mayor — with the conservative rural areas of the Clare Valley. In Port Pirie, Brock won the count with 39.2 per cent of the vote, gained mostly at the expense of Labor: elsewhere, he didn’t even reach double figures. While the rural Liberal vote was down 6.2 per cent, this can largely be put down to the 9.5 per cent vote for the Nationals, who did not field a candidate in 2006.

However, comparison of Port Pirie results with the remainder dispels the notion that the Liberals’ mediocre two-party showing was merely a product of Geoff Brock funnelling preferences to Labor. Even in the country booths where Brock was not much a factor, the two-party result was little different from 2006. This is extremely disappointing for a Liberal Opposition that had been banking on a backlash against the Rann Government’s consolidation of country health services. The consolation for the Liberals is the shellacking Labor copped on the primary vote, which was down 23.5 per cent in Port Pirie and 16.4 per cent overall.

An estimated 4000 pre-poll and postal votes remain to be counted over the coming week, representing nearly a quarter of the total. Given independent candidates’ lack of organisational muscle, these are likely to widen Brock’s existing primary vote deficit against Labor. The Liberals should certainly hope so, because independents can be very hard to dislodge once entrenched, and a mayor of Port Pirie doesn’t seem a natural ally for the conservatives on the floor of parliament. The existing target of nine seats to gain a majority at the next election was looking quite tough enough as it was: ten could prove altogether too much to ask.