As the election comes down to a handful of key seats, Labor is hoping advertising on one issue in particular will persuade enough swinging voters to back it into government, despite the message going unnoticed by the media.

ALP leader Anthony Albanese will on Thursday embark on a blitz of 20 key marginal seats, where the party’s chances of securing a majority are hanging in the balance.

But a crucial part of Labor’s campaign to win these critical seats is an advertising message – appealing to voters fed up with waiting to see a GP – that could figure as the most influential election issue you have never heard of.

Labor says the issue, which bites hardest outside major cities, is key to its pitch, but is also helping to blunt Prime Minister Scott Morrison’s strategy of appealing especially to outer suburban voters.

Political commentators and doctors had until recently noted that health care had been an unusually low-profile issue during this year’s campaign.

But Opposition research revealed that waiting times to see a bulk-billing general practitioner was a top concern for a significant number of voters.

An attempt to take that mainstream, including a frequent Labor refrain about it having grown more difficult and expensive to see a GP, never caught on but also had its veracity questioned.

So instead the party has run the message out to voters in key electorates. And despite advertisements being run in at least three states, the Opposition’s effort has otherwise mostly passed without remark.

Labor is hoping its targeted advertising will cut through in key marginal seats. Photo: AAP

“It is the bulk of the ad spend in many of our most targeted seats,” one Labor source said.

Campaigns are running with a focus on key Liberal-held seats in Tasmania (Bass), Queensland (Longman and Flynn) and New South Wales (Robertson).

It is also being used to sandbag the party’s seats, such as its bid to fend off a run by the former state transport minister Andrew Constance in Gilmore on the NSW south coast.

“It’s red hot anywhere outside capital cities, in the suburbs and regional Australia,” another source familiar with the party’s advertising strategy said.

“Many people have no idea”.

A parliamentary inquiry into the accessibility of GPs in regional Australia was told in March that in some parts of rural Queensland shortages had caused wait times to reach up to three months.

But independent data assessing waiting times across the health system is not readily available.

The New Daily contacted the Australian Medical Association’s vice president Chris Moy, who said delays were widespread and had increased under both parties as the number of doctors going into general practice had fallen.

“There are extreme shortages everywhere,” Dr Moy said.

Labor has divided its seat campaigns into attack ads about the Liberal government and Medicare and “candidate positive” spots that emphasise its “super clinics” policy.

That plan received short shrift from Dr Moy, who called the policy “smoke and mirrors”.

But he has endorsed an ALP pledge to fund the Primary Health Care 10-Year Plan, which was devised but left unfunded by the Coalition.

Mr Albanese will personally visit five states across the next critical two days, beginning with a push in Sydney and Brisbane before pushing into a final three (as-yet-undisclosed) states on election eve.

Joining him and making their own visits will be front benchers Richard Marles, Penny Wong, Jim Chalmers, Tanya Plibersek and Jason Clare.

“We are in the final sprint,” campaign spokesman Mr Clare said.

Campaigners say that the party’s road to victory increasingly depends on the outcome of a handful of local contests.

Among those where Labor has its nose in front is former PM John Howard’s old seat of Bennelong, which it claimed last time the party won government from opposition in 2007.

The seats to watch

NSW: Reid, Bennelong, Robertson, Banks
Qld: Brisbane, Leichhardt, Dickson, Longman, Ryan
SA: Boothby, Sturt
TAS: Bass, Braddon
VIC: Chisholm, Higgins, Casey, Deakin
WA: Swan, Pearce, Hasluck.