A Senate report has warned the Government that a plebiscite on same-sex marriage would be too expensive and too potentially harmful to children and other vulnerable people in the gay and lesbian community.

The majority report from Labor and the crossbench recommends a parliamentary conscience vote to change the Marriage Act be held instead.

“This issue of marriage equality involves people, and people will be attacked through very nasty and very aggressive advertising campaigns,” the chair of the committee, independent senator Glenn Lazarus, said.

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He said evidence from LGBTI groups and psychologists was particularly convincing.

“[They were] very worried about the effect it would have on children, particularly children who have same-sex parents,” Senator Lazarus said.

Senator Lazarus said he expected the inquiry by the Legal and Constitutional Affairs References Committee would show support for a public vote, but that he was wrong.

“Quite clearly people that are for and against marriage equality would rather have the Parliament decide the outcome rather than going to a plebiscite,” he said.

Prime Minister Malcolm Turnbull’s support for same-sex marriage is well known, but since ousting Tony Abbott he has been careful to stick to existing Coalition policy.

Senator Lazarus says the report should show the public support the vote. Photo: Getty

“Our policy is to have [a plebiscite] after the next federal election,” Mr Turnbull told reporters in Canberra on Wednesday night.

Plebiscite could cost $158.4m

Senator Lazarus said he had not discussed the issue with Mr Turnbull since he became Prime Minister but he hoped the Senate report would force a change of mind.

“I hope it does because he indicated he will listen to the needs and wants of Australians and crossbench senators and all politicians, and the evidence that we uncovered last Thursday night was quite clear,” Senator Lazarus said.

Same-sex marriage was one of the policies which put pressure on Mr Abbott’s prime ministership and the plebiscite was his attempt to deal with that.

Mr Turnbull might hold a different personal view to the man he ousted, but the politics could turn out to be just as challenging.

The committee took evidence from the Australian Electoral Commission (AEC) which said holding a separate vote or plebiscite would cost $158.4 million.

That figure does not include public funding for a yes and no campaign, which has been provided in previous public votes like the republic referendum.

Greens senator Janet Rice backed the majority report, but said if there must be a plebiscite then the Parliament should impose strict rules on how it is run.

“We firmly believe that appropriate parameters must be established around public advertising for the plebiscite and regulation of the media,” she told the Senate.

The Government members of the committee submitted a minority report backing a plebiscite.

But Labor committee member Carol Brown said there was now significant evidence Parliament was the right place to decide on same-sex marriage.

“We do need to press on and we do need to put the argument that a plebiscite is not the way to go,” she said.