The first openly gay member of the House of Representatives, Liberal MP Trent Zimmerman, said he would cross the floor in favour of same-sex marriage.

Mr Zimmerman told ABC radio he was concerned about a plebiscite on gay marriage and his personal preference, had he been in the party room earlier, would have been for a free vote and for parliament to decide the issue.

He said if the costs of a plebescite blew out there would be a “great deal of anger” within the community.

• ‘Disastrous coincidence’ so many sex offenders
• ‘High possibility’ debris MH370
• AFP to probe defence leak

“If a substantive bill came before the parliament, then yes I would cross the floor if the party instructed me otherwise,” Mr Zimmerman told ABC radio.

During the interview he also slammed a Coalition colleague’s comments on the Safe Schools program.

PM Malcolm Turnbull congratulates Mr Zimmerman in parliament. Photo: Twitter

He said Nationals MP George Christensen’s comments likening the gay and lesbian-focused anti-bullying program to pedophile grooming was deliberately inflammatory.

“Some of the language that’s been used has been unfortunate … we have seen a tenor of language used which has been completely unjustified,” Mr Zimmerman said.

During Mr Zimmerman’s maiden speech in parliament on Wednesday, he also spoke about the legalisation of same-sex marriage and targeted people who “peddle prejudice” against others.

The MP replaced former treasurer Joe Hockey in the seat of North Sydney at the end of 2015.

“Our laws still deny access to marriage – our society’s ultimate expression of love and commitment,” he said.

“Young gay men and women are more likely to suffer depression and other mental health issues; they are more likely to be bullied at school.

“More are likely to attempt to take their own lives and tragically some will succeed.

“Coming out remains hard for many people – and believe me, I know what that’s like.”

– with AAP