Tensions have flared within government ranks over a push by some Liberal MPs for the party to abandon its policy for a national plebiscite on same-sex marriage.

Tony Abbott has warned against abandoning a national plebiscite on same-sex marriage, saying it would break a key election promise.

“Malcolm Turnbull made a clear election commitment that the marriage law would only change by way of people’s plebiscite, not free vote of the parliament,” the former prime minister told Fairfax Media.

“I’m sure he’ll honour that commitment. This isn’t about same-sex marriage, it’s about keeping faith with the people.”

A group of Liberals in support of same-sex marriage is leading a push for the government to ditch its plebiscite policy in favour of a free vote in parliament.

The backbenchers are working to bring the issue to a head in the next fortnight, Fairfax Media reports.

However, several conservatives have pushed back, with Sydney Liberal MP Craig Kelly arguing that allowing a free vote on the issue would be a “betrayal” of the coalition’s election commitment to hold a plebiscite.

“To backtrack and reverse on such a clear election promise during this parliamentary term would be a betrayal of the voting public,” he told AAP.

Liberal MP Warren Entsch, one of the coalition’s leading advocates of same-sex marriage, said he would negotiate privately with colleagues to deal with the issue “once and for all”.

Opposition Leader Bill Shorten has urged Mr Turnbull to “get on with it” and support a free vote on same-sex marriage.

Liberal backbencher and supporter of same-sex marriage Tim Wilson said it was not news he wanted a change in the law but he had stuck to his party’s commitment for a plebiscite.

He said a Senate inquiry into same sex-marriage draft laws had yet to report back.

“When that committee reports, when that inquiry is concluded, obviously there is going to have to be a discussion,” Mr Wilson told ABC television on Sunday.

“Nothing to do with me pushing for anything or anybody else.”

– AAP