The SA Best leader, Nick Xenophon, has defended the decision to shield some of his new South Australian candidates from wider media scrutiny after their unveiling.

The party announced another batch of candidates for South Australia’s March election over the weekend but Xenophon said the father and son who will run against the premier and opposition leader, both named John Noonan, are not available for media commitments until they officially launch their campaigns.

“I think that we have to do what is best for the campaign, the candidates and for SA Best,” Xenophon told ABC radio on Monday. “They will be available through the course of the campaign.”

The deputy opposition leader Vickie Chapman, said the SA Best leader was putting party interests ahead of the people of South Australia.

“Quite frankly, this isn’t good enough, and the excuse that SA-Best is a startup party is already wearing thin,” Chapman said. “Mr Xenophon has today gagged his new candidates and shielded them from media scrutiny in a clear sign that he and SA Best are more interested in their own political fortunes than the job fortunes of South Australians.”

The former senator also said candidates were paying $20,000 to run under the SA Best banner and he was personally bankrolling a small number.

“There is a loan for some candidates but most people have made their own contribution, the overwhelming majority,” Xenophon said. “Not only have I contributed my $20,000, out of my pocket, but I have taken out a mortgage.”

The South Australian premier, Jay Weatherill, said it was up to Xenophon on how he picked his candidates but criticised the fact many were former Liberals.

“Nick being a former Liberal makes it easy for them to slide into his party, so Labor is facing two Liberal opponents at this election,” Weatherill told reporters on Monday. “Nick has to account for the way in which he selects his candidates.”

The SA Best party has previously said it will have about 30 candidates for the 17 March election.