Scott Morrison has confirmed that cabinet has discussed the possibility of allowing a parliamentary inquiry into Australia’s banks as disgruntled Nationals MPs threaten to cross the floor to support the idea.

But Malcolm Turnbull has refused to say if cabinet has considered the matter, saying only that the government would not be pursuing a royal commission and its position has not changed.

The Nationals senator Barry O’Sullivan and the Liberal National party MP George Christensen have been repeatedly threatening to cross the floor to support a Labor and Greens push to set up an inquiry into the banks.

Labor and the Greens believe they and the crossbench have 74 votes in the House of Representatives to call for a royal commission or commission of inquiry, against the government’s 73. But Christopher Pyne, the leader of the house, said this week that an absolute majority of 76 was needed to suspend standing orders and bring it on for debate.

A spokeswoman for Christensen has confirmed he would vote to support a commission of inquiry after the New England byelection on 2 December, when the Nationals leader, Barnaby Joyce, is hoping to return to parliament.

The Nationals MP Llew O’Brien told Guardian Australia this week that he would also consider crossing the floor, but he wanted to look at the various proposals on offer and consider them on their merits.

The treasurer was asked on Wednesday if cabinet had considered a royal commission into the banks this week, after senior government ministers became frustrated by the behaviour of their Nationals colleagues.

“Does the government fear backbenchers crossing the floor to vote for a commission of inquiry into the banks, and has cabinet considered it?” asked the ABC’s Sabra Lane on Wednesday.

Morrison replied: “You wouldn’t expect me to go into what the deliberations of cabinet are, but you also wouldn’t find it puzzling that cabinet would from time to time consider these sorts of issues, of course they would, and to talk these issues through.

“But the government’s position remains the government’s position on that, and what we’re doing on the banks is what matters.”

On morning television, the prime minister refused to discuss what cabinet had talked about this week.

“I am not going to go into what cabinet discusses,” he told the Sunrise program. “As a government we have decided not to have a royal commission, we made the decision a long time ago, not because we don’t believe there is nothing going on in terms of problems with the banks, it is because we want to take action right now and we are.”

The Nationals MP Luke Hartsuyker told Sky News on Wednesday the banks had been subjected to a lot of scrutiny by the Turnbull government and it was hard to see how a royal commission would achieve anything.

“I think the sorts of recommendations that would come out of a royal commission are the sorts of things that we’re doing now,” he said. “It’s hard to see how the lawyer’s picnic would advance the case of scrutiny on the banks.”

He said O’Sullivan and Christensen were entitled to their view that a banking inquiry would be beneficial but he did not agree with them.

