InDaily revealed in August that Chapley, from the party’s left faction, was giving “serious consideration” to putting her name forward for the eastern suburbs federal seat, which the ALP has not held since 1972 and has been unable to wrest from Pyne for the past 22 years, despite concerted efforts.

But Chapley, the in-house lawyer for her family’s business, which operates several Foodland stores, told InDaily: “After careful consideration and consultation with my family and many people in the seat of Dunstan, I have decided I will not be a candidate for the seat of Sturt at the next federal election.”

She said she looks forward “to supporting the Federal Labor candidate in taking up the fight to Christopher Pyne and the Turnbull Liberal Government”.

“I am fortunate to be part of a vibrant and energetic community,” Chapley said in a written statement.

“Consequently, I will consider renominating for preselection for the seat of Dunstan for the next state election.”

That may be a relief for Pyne, given South Australia remains the only state in which the Coalition still trails Labor, according to last week’s Newspoll.

But it is ominous for Marshall, who in 2014 held Dunstan – formerly Norwood – by only 3.1 per cent as the alternate premier, down from his 4.8 per cent majority as a first-time candidate in 2010.

I’m grateful I’ve got a marginal seat, it keeps me in tune with what people in marginal seats are thinking

“She’s obviously very well resourced [but] I wouldn’t underestimate any candidate,” Marshall told InDaily.

“I work extraordinarily hard in my electorate.”

Marshall is the first Liberal to hold the seat in successive elections since 1950; his party has never won three consecutive terms there.

“A lot of people say to me it’s a disadvantage having the leader in a marginal seat, but I think it’s a massive advantage for the Liberal Party,” he said.

“For me to hold [Dunstan], I basically have to be in my electorate every single day…I can’t do a Mike Rann and represent the people of Salisbury and live in Norwood; I have to be in Norwood, Payneham, St Peters, Kent Town every single day.”

Marshall argues people representing safe seats are “not necessarily as linked in to what people in marginal seats are thinking”.

“I’m quite grateful I’ve got a marginal metropolitan seat, because I think that keeps me very much in tune with what people in marginal seats are thinking,” he said.

At the 2014 election, the state Liberals won five marginal metro seats to Labor’s 10.

The ALP closed nominations for Sturt in August without a candidate putting up a hand. Nominations cannot re-open until next month at the earliest, when the state executive meets for the first time in 2016.

A Labor source says a couple of names remain in the frame for the preselection, insisting “we’ll have a good, solid candidate [but] it’s not going to be a ‘star’ candidate”.

That could be good news for Pyne, but he still won’t rest easy; along with a glut of fellow SA Liberals, he has been feeling the pressure from the Xenophon Team’s concerted push into the federal arena.

The Australian reported last month that Pyne had sent a series of text messages to FIVEaa presenter Leon Byner, begging him to convince Xenophon to “leave me alone”.

“I like Nick and I don’t want to be at odds with him,” Pyne reportedly wrote.