Briggs, who lost his job as a minister over a misbehaviour scandal, faces a tough fight to save his Adelaide Hills-based seat in the wake of a rise in support for the Nick Xenophon Team.

Turnbull told reporters at Mount Barker today, where he announced a $3.75 million plan for a regional sports hub, that the return of Briggs was crucial.

“The only way we can be certain of being returned to government and I can be certain of continuing to be prime minister after July 2 is if Jamie Briggs is returned as the member for Mayo,” Turnbull said.

“There is a direct link between holding our seats and returning to government.”

Asked whether there were strings attached to the project funding, Turnbull said the only condition was his government being returned.

The contribution will go towards a regional sports hub in Mount Barker, including an AFL oval, netball courts, soccer pitch, function facilities, club rooms and grandstand.

A ReachTEL survey of 681 residents on May 16 for activist group Getup found just under 40 per cent intended to vote for Briggs.

News Corp reports he’s trailed by Nick Xenophon Team candidate Rebekha Sharkie with 23.5 per cent support, followed by 18 per cent for Labor and 10 per cent for the Greens.

Xenophon believes his candidate, Rebekha Sharkie, is a good chance to cause an upset in Mayo. While the seat has always been held by the Liberals, high profile third party and independent candidates have a strong record in the Hills. Singer John Schumann, representing the Australian Democrats, came close to unseating Downer in 1998, polling more than 22 per cent of the primary vote.

Later today Turnbull will be in the Labor seat of Makin to spruik his innovation agenda as well as the $50 billion submarines project.

The prime minister will check out SAAB Australia’s advanced maritime system centre and future combat systems lab.

Opposition leader Bill Shorten is making his first campaign trip to Tasmania, visiting the marginal Liberal seats of Bass and Braddon.

Labor fancies its chances in the Launceston seat of Bass, where recent polling shows local MP Andrew Nikolic under threat.

As the government ramps up its criticism of Labor’s “war on business”, a former ALP national president has launched a stinging attack on the party’s anti-business rhetoric during the campaign.

Warren Mundine, who now heads up the prime minister’s indigenous advisory council, is fearful economic reform will go backwards if Labor wins government.

Talking about the birth of his great-grand-daughter last week, Mr Mundine wrote in the Daily Telegraph: “Labor’s rhetoric will take Australia down a path where her taxes will be higher and her education will be more costly.”

Turnbull also faces some embarrassment with the release of a new biography by former Liberal attorney-general Tom Hughes, who is also the prime minister’s father-in-law.

Hughes described Tony Abbott as a “lunatic” in a letter he penned to his brother.

“To elect Abbott in his place is the equivalent of putting the bull in charge of the china shop or the principal lunatic in charge of the asylum,” he wrote in 2009.

In another letter – this time to Turnbull – Hughes urged him to stay in politics after losing the Liberal leadership, saying “the party’s present folly will pass”.

Briggs resigned from the ministry last year following an incident in Hong Kong involving a female public servant.

– with AAP