The race between Labor and the Liberals for the south suburban battleground of Dunkley will be a close one, but a shift in the electoral boundaries since the last poll has definitely made it Labor’s to lose.

Although the Liberals have maintained a 20-plus year hold on the seaside seat, a 2018 redistribution of the boundaries has notionally made it a Labor seat, and one to watch in the contest for Victoria’s marginal seats.

Labor hopes to wrest up to seven seats from the Liberals in this first national poll under newly redrawn boundaries. Dunkley was one of only two seats in Victoria to notionally flip from the Liberals to Labor after the redistribution, but that won’t make the outcome there a foregone conclusion.

The ABC’s analysis of the new notional margins showed Dunkley to be Australia’s sixth most marginal seat and Victoria’s second most marginal based on the two-party-preferred vote. While the reasoning behind the redistribution was non-partisan in nature, the potential impact on the balance of power could be significant.

The prevailing logic of the redistribution committee was that the entire City of Frankston should be united within one electoral division.

Before the redistribution, the suburbs of Carrum Downs, Skye and Sandhurst—administered by the City of Frankston—were in the Isaacs division north of Dunkley.

The redistribution ceded Mornington and Baxter – administered by the Mornington Peninsula Shire – to the division of Flinders. Mount Eliza, part of Mornington Peninsula Shire, remained in Dunkley for “numerical reasons”, according to the Electoral Commission.

The decision partially reversed changes made in the 1994 redistribution. Dunkley has been held by the Liberals since the first time Liberal-leaning Mornington, Mount Eliza and Langwarrin voted as parts of Dunkley in 1996.

The loss of Mornington and Baxter, while consolidating the Liberals’ hold on Flinders, removes a large portion of Dunkley’s Liberal-leaning base. Meanwhile, the Labor-leaning additions shift the balance, reinforcing Dunkley’s Labor-leaning centre.

The changes didn’t come without pushback. In the public inquiry on the redistribution held on June 5-6 last year, the augmented Electoral Commission heard objections and comments.

One such objection came from Andriy Kogut who owns small businesses in both Frankston and Mornington. “Having to deal with two members of Parliament would be a disadvantage to our business,” Kogut said.

“It makes no sense to separate our coastal communities.”

The Liberal Party, represented at the inquiry by Adam Wojtonis, opposed the redistribution, citing connections between Mornington and Frankston as well as differences between the suburbs in Isaacs and the rest of the electorate.

This criticism was countered by comments in support of the redistribution. Colin Hampton, current councillor for Frankston’s North-East Ward and Frankston’s mayor at the time, supported the additions to Dunkley.

“I know that the people of Carrum Downs, Skye and Sandhurst have more in common with Frankston than the township of Mornington,” Cr Hampton said. “There’s a huge gap between the two.”

Ultimately, the augmented Electoral Commission decided that the benefits of aligning Dunkley with the local government area of Frankston outweighed the objections.

If the notional margins within the redrawn electorate hold, Labor has a 1.3 per cent advantage based on its 2016 vote, which would mark the party’s strongest performance in Dunkley since 1987. But the electorate is still teetering on the margin.

An April 14 Newspoll projected a possible 10-seat swing towards Labor, putting it over the line to form a majority government.

According to Monash University political researcher Dr Nick Economou, the electoral mood bodes badly for Liberal incumbent Chris Crewther.

“There’s going to be a really big swing to Labor, to the Opposition,” Dr Economou said. “In that situation people defending marginal seats will be swept away,” Economou said. “So I don’t think Crewther’s going to survive.”