MATHIAS Cormann had his answers well-rehearsed on the Liberal party’s proposed same-sex marriage postal plebiscite ahead of a TV grilling last night. But he perhaps wasn’t prepared for ABC host Emma Alberici’s devastating opening question.

Welcoming the Finance Minister on ABC’s Lateline Monday night, hours after a controversial party room meeting opted to maintain the status quo on gay marriage, Alberici kicked off with a withering opening salvo.

“A friend of my daughter’s, a 15-year-old boy came out as gay last week to his parents and was kicked out of home,” she bluntly told him.

“Whilst you and your colleagues are bickering in your party room, aren’t you concerned about the message you send to young vulnerable gay and lesbian Australians that they won’t deserve the same treatment as other Australians?”

Senator Cormann offered up a response that he would parrot at least six times throughout the interview.

“Emma, this is an issue in which there is a diversity of sincerely held strong views on both sides of the argument, and that is of course precisely why the government, in the lead up to the last election, made a promise to the Australian people that they would have a say whether the law would be changed for same-sex couples to marry,” he said.

“That is the commitment that we made and that is the commitment that the Liberal party today reaffirmed to make sure that every Australian who is on the electoral role has a say on.”

MORE: Everything you need to know about a gay marriage plebiscite

But she wasn’t finished with him yet.

“Why the sudden obsession with keeping election promises?” Alberici shot back.

“You didn’t keep the promise when it came to health and education. ‘No new taxes’ was what you said before the 2013 election and you introduced the three per cent deficit repair tax. You promised no cuts to the ABC and took $44m from us.

“Tony Abbott promised you wouldn’t shut any Medicare locals, all of them are gone. Julie Bishop promised no cuts to foreign aid and that it would grow in line with inflation, instead it was frozen, which represents a $6 billion real cut, then it was Tony Abbott’s paid parental leave policy which has also been abandoned.”

The Acting Special Minister of State was momentarily thrown and scrambled to answer.

“I think this is a commitment that the Turnbull Government took to the last election, and I think you’ll find that the Turnbull Government has gone absolutely out of its way since the last election to deliver on all of the commitments that we made to the Australian people, if we weren’t able to get 100 per cent of our commitments through, to deliver as much of our commitment as we possibly could, and that is what we’re doing on this occasion.”

He used the same justification to refute Alberici’s questions over whether a postal plebiscite “has any legitimacy at all” and is considered “a bit of a farce”, and that gay people and the wider public “don’t want a plebiscite”.

Mr Cormann said the government would take the proposal of a mandatory plebiscite to Parliament for a second time, and if that was unsuccessful, would go through with the voluntary, non-binding postal plebiscite.

“In the end, the government will be guided by that outcome. If it the vote is in favour we will facilitate the consideration of a private members bill, and that bill we are very confident will pass through the parliament,” he said.

The government has been roundly criticised for its determination to push forth with the postal plebiscite, which was decided in a lengthy party room meeting on Monday.

Australian Marriage Equality co-chair Alex Greenwich this morning labelled the decision “a national disgrace”.

“Rather than delivering marriage equality the government continues to delay it and disappoint Australians who want the parliament to move forward,” he told the Nine Network.

Marriage equality campaigners have pledged to challenge a postal plebiscite in the High Court.