Barnaby Joyce has blamed “the pressure of a campaign” for One Nation’s Farrer candidate contradicting party policy on immigration and appearing to endorse Labor’s current intake.

The One Nation MP also claimed voters won’t worry about Gina Rinehart’s million-dollar donation of a private plane to Pauline Hanson’s party, claiming journalists were more interested than ordinary people in the lucrative gift from Rinehart’s company.

Appearing on Sky News on Sunday, Joyce said he expected his party’s candidate, David Farley, would prevail in next Saturday’s byelection, despite a stumble this week where the would-be MP said Australia’s net overseas migration of 306,000 last year was “probably not” too many.

One Nation’s stated party policy is a cap of 130,000 migrants a year.

Farley, appearing at a candidate forum hosted by former Insiders host and Guardian podcast host Barrie Cassidy, said One Nation wanted to “match immigration to a housing policy, a health policy and an education policy”, noting demand for skilled migrants.

Cassidy asked: “Is 306,000 [net overseas migration] too many?”

Farley responded: “No, it’s probably not.”

“If we’re successful in One Nation’s water policies, we’re going to need more labour and we’re going to need more labour quickly, skilled labour,” he said.

“So for anyone to be able to say ‘what is the number today’, it should be addressed as what are we doing with productivity and what are we doing with capacity building, then you will get a true number that’s required for Australia.”

Asked about Farley’s comments, Joyce downplayed the slip-up.

“Well, when you’re a candidate and you’re on the beat. Obviously the policy is 130,000, as we’ve said, and he agrees when we talked about it. That’s just the pressure of a campaign,” he told Sky.

“You got to have a stocktake. You’ve got to see what an area can absorb. Even in Sydney or Melbourne or Brisbane, if you’re bringing in 400,000 a year, as we’ve been bringing in the population of Canberra, and you don’t have the houses, and you don’t have the schools, and you don’t have the hospitals … we just can’t have that.”

“If there’s a capacity to absorb them, and if there’s a need, then of course, that’s a completely different discussion.”

Farrer is expected to be a tight-run final count between Farley and independent candidate Michelle Milthorpe. The seat on the NSW-Victoria border has only been held by Liberal and Nationals members since its creation, but Nationals leader, Matt Canavan, downplayed the political impact of the Coalition losing the seat.

“These things don’t concern me,” Canavan told the ABC’s Insiders program.

“I do believe we can make things better if the Nationals party is elected in Farrer. But I understand why people have been disillusioned with us.”

He said he was “fighting pretty hard” in the Nationals’ campaign, but didn’t raise expectations of a strong showing. Canavan was also strongly critical of Milthorpe and Farley, accusing both of running “dishonest” campaigns.

Canavan criticised Milthorpe’s policies on fossil fuels, calling her a “teal” – a label the candidate has rejected – as well as Farley’s comments on immigration.

“[Farley] said the other day he was fine with Albo’s migration policy settings. Even though again his own party’s website say they want them massively slashed,” he said.

“We don’t need more than we got right now. We need much, much less.”

On Sky, Joyce also downplayed Rinehart’s million-dollar donation of a private plane to One Nation, claiming “it won’t really worry” voters.

“I think that worries people in the fourth estate more than it worries people on the ground,” Joyce told Sky News.

As reported this week, one of Rinehart’s companies gifted Hanson a new private plane, worth more than $1.5m, to use in the lead-up to the next federal election, while a group of her close associates donated another $2m to One Nation.

Joyce waved away the prospect of the expensive donation harming One Nation’s electoral prospects.

“If you’re so uninspiring that you can’t get big donors, then that says a lot about the political philosophy that you’re standing behind, that it’s really sort of a vacuous beige soup, rather than something that’s actually worth believing in,” he told Sky.

Joyce pointed out that the Labor government and the Greens had “big backers” including the union movement and prominent business people.

“I don’t believe in what they believe, but obviously they have a philosophy that attracts support. Now we attract support too, from people on the conservative side of politics and successful business people on the conservative side of politics, because they believe that they can clearly identify our conservative values. They might not agree with all of them, but they agree with enough.”