Meanwhile, Labor appears set to field a candidate of its own after receiving several expressions of interest.

The major parties are gearing up for a crucial by-election in the seat won by Rebekha Sharkie in 2016.

The former Nick Xenophon Team – now Centre Alliance – MP sensationally quit the parliament last week as the citizenship scandal continued to engulf federal politics.

The Liberals sniff a genuine opportunity to win back their traditional blue-ribbon seat after Xenophon’s state party, SA Best, failed to snare a single lower house seat at the March state election.

Downer – whose father, former Liberal leader and Foreign Minister Alexander, held the seat for 24 years – was tonight endorsed as the Liberal candidate, with InDaily told “two nominees withdrew their nominations based on matters of citizenship”.

I have decided to nominate for Liberal Party preselection for the seat of Mayo. As someone who grew up and spent the first two decades of her life in Mayo, was married in Mayo, and whose family have lived in the Adelaide Hills for over a century, I am coming home. 1/3

— Georgina Downer (@GeorginaDowner) May 11, 2018

InDaily had been told local branch member Reagan Garner was expected to nominate for preselection. InDaily sought a response from Garner.

Former Christopher Pyne staffer and SA Liberal Women’s Council president Hannah March was also mentioned in dispatches, but she told InDaily she would not be putting her name forward. 

Labor meanwhile has sent a missive to party members seeking expressions of interest “before the nomination process begins”.

It’s understood the party has received a number of responses to the request, which states that the ALP is “considering its options” for the seat.

Labor will be keen to contest, given senior insiders believe its vote has suffered in the electorate since it opted out of the last Mayo by-election a decade ago. It will also see itself as better placed to campaign strongly against Downer, who has previously sought preselection unsuccessfully in the safe Melbourne seat of Goldstein.

The by-election takes place against the backdrop of a looming boundary redistribution, although the poll will be held under the existing boundaries.

Both major parties have joined a swag of local activists in formally opposing the draft boundaries favoured by the Electoral Commission, which is seeking to abolish the Labor-held seat of Port Adelaide and rename the seat of Wakefield ‘Spence’.

Labor’s submission, published on the AEC website today, suggests instead renaming Christopher Pyne’s seat of Sturt.

“The Australian Labor Party believed that as it already retained a high number of electors, the highest in South Australia, minimal change was needed to the division of Port Adelaide, and continues to affirm this position,” the submission states.

“The proposed loss of the identity of Port Adelaide in the House of Representatives is particularly disappointing and is at odds with recognition of the locality on a local and national scale.”

The ALP also suggests shifting voters from Liberal-held Boothby into Mayo.

The Liberal submission broadly supports the draft redistribution but also suggests changes to the proposed boundary of Boothby, which it says will save around 35,000 electors having to shift electorates.

Port Adelaide Enfield Council also went into bat for the seemingly doomed seat of Port Adelaide, held by Labor powerbroker Mark Butler, telling the AEC “it’s important that we continue to mark Port Adelaide as a strong and significant area, and a Federal electoral division under the name of Port Adelaide will further support a bright future for the state”.

A string of Liberal members, including MPs Sam Duluk and Steve Murray, wrote demanding the suburbs of Flagstaff Hill, Aberfoyle Park and Happy Valley remain in Boothby.

“That’s where we want them to stay,” they wrote in a pro forma submission.