Nationals MP Andrew Broad has accused Malcolm Turnbull of ignoring conservatives in the same-sex marriage debate, saying there has been "a clear failure of leadership".

Key points: Conservatives failed in their bid to amend the bill last night

Conservatives failed in their bid to amend the bill last night Andrew Broad is a staunch opponent of same-sex marriage

Andrew Broad is a staunch opponent of same-sex marriage He says the Prime Minister did not consult Conservatives enough before allowing the introduction of the private members' bill

Conservatives failed in their bid to amend the bill last night, and it is now expected to pass the Senate today.

"Look, I think, in my view, there's been a complete lack of leadership," Mr Broad told AM.

Mr Broad is a staunch opponent of same-sex marriage, and in his safe Victorian seat of Mallee, locals voted Yes in the postal survey.

He will respect his electorate and vote to legalise same-sex marriage, but said he thought the legislation was being rushed through Parliament.

"All assurances both by the Prime Minister and the Opposition Leader that religious freedoms would be protected — that they believed in those — seemed to be walked away from in what I think is a rather sneaky way."

He said Mr Turnbull did not consult conservatives enough before allowing Liberal senator Dean Smith to introduce his private members' bill to the Senate.

Senator Smith circulated his draft bill months ago, and conservatives have been allowed to move amendments on the floor of Parliament.

But Mr Broad said Mr Turnbull could have listened more.

"I had a private conversation with the Prime Minister where I said, 'Have you sat down and got Trevor Evans, Warren Entsch, Dean Smith — people on the Yes side — and put them in the room with Eric Abetz, Andrew Hastie and people on the No side? And come up with a piece of legislation that is Coalition legislation?'" he said.

Sorry, this video has expired Brandis says it's time for the Parliament to reflect the people's views

Backbench 'frankly disappointed'

Mr Broad said other conservative Coalition members want parents to be able to remove children from classes that teach kids about same-sex relationships.

They also want religious institutions to be able to refuse to hire out church halls for same-sex weddings.

But the Senate has voted against changes like that, and the bill is likely to pass in its current form today.

Greens senator Janet Rice has argued passionately in favour of same-sex marriage, and last night told the Chamber: "We are on the cusp of getting marriage equality through this Parliament, and why we are on the cusp of doing that is because there have been a lot of people on all sides of Parliament who have worked together."

Mr Broad would like to move amendments when the bill gets to the Lower House, but said he could not see the point.

"It's kind of a done deal, because if they did get up they'd go back to the Senate and get knocked over," he said.

"And so this is where a lack of leadership from the Coalition, the executive of the Coalition and the Prime Minister, has let down many Australians."

Asked how he felt about Mr Turnbull's leadership going forward, he replied: "Well, that's a decision for the Liberal Party, I'm a National Party. But I'm making the point, it's a clear failure of leadership ... I just think [there is] backbench disappointment, frankly."

He is now pondering another issue which is proving difficult for Mr Turnbull — a banking commission of inquiry.

If Nationals senator Barry O'Sullivan's bill, calling for one, makes it to the Lower House, it would likely pass the Parliament.

Two Nationals MPs have said they would cross the floor to support it. Mr Broad has not yet decided whether he would do the same.