‘I did what was right’: Liberal rebel Fiona Martin on the change that sank the religious discrimination bill

There were five Liberal MPs who crossed the floor to protect LGBTQ+ students against discrimination but the one who tipped the balance is now being accused of breaching a commitment not to defeat the government.

It was the member for Reid, Fiona Martin, who most shocked her colleagues when she crossed the floor shortly before dawn on Thursday to add protections that would result in the entire religious discrimination bill being shelved.

The rebel group of five MPs was built on the foundation of Bridget Archer and Trent Zimmerman, who had publicly warned they could not back the bill unamended, but Martin was the decisive third vote that guaranteed the amendment's success.

Dave Sharma honoured his commitment that he would not be the casting vote, but if the dam wall broke and the government lost a third MP, he would be the fourth to cross.

Katie Allen's vote was tied to Sharma's on the understanding the Liberals could use a rebellious streak to try and hold their under threat blue-ribbon seats of Higgins and Wentworth.

On Friday the defence minister, Peter Dutton, said that Scott Morrison was "frankly misled" about how unnamed MPs would vote on amendments during the religious discrimination bill debate.

The crucial vote on Thursday forced the government to shelve its religious discrimination bill, as conservatives within the Coalition and Christian lobby groups argued the LGBTQ+ student amendment to the Sex Discrimination Act (SDA) would prevent schools setting their own ethos.

Martin, a psychologist for 20 years, had expressed her concerns in the Coalition party room.

Martin tipped her hand in a vote at 4.24am, joining Zimmerman and Archer in indicating that she wanted to remove a religious exemption to the SDA.

Although Allen and Sharma voted with the government in that division, in the next vote at 4.32am they joined Labor, the crossbench, Martin, Zimmerman and Archer to enact a narrower amendment.

Morrison allowed the votes to go ahead because he believed despite their concerns about LGBTQ+ students most Liberal moderates would vote down the amendment in return for improvements in the Australian Law Reform Commission (ALRC) review process and the creation of a new select committee on children's mental health.

When Morrison spoke shortly before 2am on Thursday he announced the review would report six months after the religious bill passed, down from 12, and the creation of the new committee to be chaired by Allen and supported by Martin due to their "great clinical experience".

Liberal MP Warren Entsch told Guardian Australia that he had requested the shorter ALRC review timeframe, and a broadening of its terms of reference to include school staff and other forms of discrimination against LGBTQ+ students.

"I was able to read the party room and it was clear to me there was no way I was going to change the minds of the large majority who wanted to pass the religious discrimination bill," Entsch said.

Entsch said it was "no accident but a lot of bloody hard work" on his part to force the government to improve the bill by removing the Folau and conscientious objection clauses.

On Wednesday evening, Entsch told parliament he would vote for the bill to "bank the successes" of these changes.

But for others the momentum was swinging back the other way. A group of four moderate MPs led by Angie Bell had negotiated for the religious exemption to the Sex Discrimination Act to be removed, only to see Morrison water it down to a commitment only to ban expulsion on the grounds of sexuality, omitting protection on the grounds of gender identity.

Labor's decision on Wednesday to release a letter showing on 1 December Morrison had committed to Anthony Albanese to prevent "any form of discrimination against a student on the basis of sexuality or gender identity" further fuelled momentum to cross the floor.

Later that evening, Morrison, Josh Frydenberg and senior moderates Simon Birmingham and Tim Wilson met MPs with concerns about the bill including Entsch, Martin and Sharma. Allen was absent.

Senior Liberal sources say Martin committed not to cross the floor before the meeting.

Entsch told Guardian Australia he was "very disappointed in the actions" of MPs he chose not to name who crossed the floor without telling the government.

"With the exception of Katie [Allen], I was in the room when they made their commitments," Entsch said.

"We all came out of that room, with very, very clear positions on what we were going to do. There was no ambiguity whatsoever."

Entsch's account is disputed. According to one alternative account, Martin didn't speak at the meeting, which concluded when Morrison believed the bill would have to be pulled because Allen was not yet on board.

Leaders of the government allowed the bill and amendments to go to a vote because they believed they later secured Allen's vote, but Labor and the government were shocked to see Martin cross the floor, triggering Sharma and Allen to follow.

Entsch took aim at MPs on all sides - Labor, the crossbench and his own party - for "political opportunism" and voting "on the spur of the moment and not thinking about the consequences".

Entsch praised Zimmerman and Archer, who he said voted with "the most noble of reasons" and whose integrity "remains 100% intact".

Martin responded to Guardian Australia: "I protected the human rights of our most vulnerable in our parliament. I did what was right. I supported the religious discrimination bill, I supported people of faith and I protected the rights of vulnerable young students. To me, that was the right balance."

Sharma said "my conscience is clear".

On Friday Dutton denied that Morrison's authority had been eroded by the incident, telling ABC radio the prime minister "was frankly misled".

"There are undertakings that were given. The undertaking wasn't honoured," Dutton said.

He declined to give details of "private conversations" but noted "the government doesn't go into a vote like that unless there's been assurances given".

Dutton appeared to confirm that the government was aware that if the dam broke with a third MP joining Zimmerman and Archer to pass the amendment, that others would follow.

"I think in certain circumstances if one goes, then you lose five, and [if] you lose a vote by one, you can lose it by five - it's the same outcome," he said.

Dutton said the government had "very clear statements from a number of people, including beyond the five" and that was the basis for Morrison allowing the bill to a vote.

"The prime minister based his judgement, his actions, his decisions on a perfectly reasonable basis following discussions, and it's difficult when you get to the floor of the parliament and those undertakings aren't honoured."

Guardian Australia contacted Allen for comment.