But Bill Shorten's opposition is all but certain to join the Greens and members of the crossbench and block the national poll, leaving it dead in the water and the government's plans to legislate same-sex marriage laws in chaos.

It provided for a day of a drama and fiery debate in Question Time, after details of the plebiscite were leaked to Fairfax Media on Monday evening and throughout Tuesday. Mr Turnbull accused the Opposition Leader of "shabby politics", while Attorney-General George Brandis said Mr Shorten was "playing politics with the lives of gay Australians".

If the plebiscite is held, Australians will be asked: "Should the law be changed to allow same sex couples to marry?"

Both the "yes" and "no" campaigns will receive $7.5 million in public funding. Two committees of 10 people - five MPs and five citizens - would be convened to oversee the use of this funding for advertising in the four weeks before polling day.

The wording of the question, and provision of public funding, have delighted conservatives and proponents of a "no" vote, but dismayed moderate Liberals and outraged marriage equality advocates.

The long-awaited release of the details of the plebiscite prompted openly-gay WA Liberal Senator Dean Smith to announce he could not support the "abhorrent idea". And in the Coalition partyroom, gay first-term MP Tim Wilson clashed with Mr Turnbull during debate and later apologised to him.

Mr Turnbull said he would personally introduce the plebiscite legislation to Parliament this week and attempted to ramp up pressure on the Labor leader to support the plan.

"The only person that stands in the way of Australians having a vote on this issue, on 11 February, is Bill Shorten," Mr Turnbull said.

"What he should do is get behind this commitment to democracy. He knows that most Australians, including most Labor voters, are in favour of there being a plebiscite. We've set up a fair process . . . let the people have their say."

Mr Shorten, in turn, demanded to know why the government insisted on a "taxpayer-funded opinion poll, which won't bind Members of Parliament".

"Most importantly, what is the case for putting young people in particular through a public debate where gay people are being treated by a discriminatory and different policy-making process?", he asked.

Earlier in the week, Mr Shorten raised the spectre of young people committing suicide as a result of the divisive debate that could be unleased by the government's plebiscite.

Deputy Labor leader Tanya Plibersek went further, asking the Prime Minister why a 13-year-old boy, Eddie, with two mums that she had met in Parliament, should "have to put up with a $7.5 million campaign by people who have never met him, telling him that there is something wrong with his family"?

That question drew howls of outrage from the government benches. Mr Turnbull fired back that he was very disappointed Ms Plibersek had "taken advantage of Eddie's presence in this way" and that all Australians had a right to express their view on proposed changes to same-sex marriage laws.

Mr Turnbull did not categorically rule out a future vote in the Parliament if the enabling legislation for a plebiscite is defeated, as appears all-but certain.

But doing so would trigger a storm within the Coalition's conservative wing and potentially ignite a civil war, so is considered extremely unlikely at this stage.

The cabinet proposal passed the Coalition partyroom with minimal fuss. Just three MPs spoke against public funding, according to a party spokesman, during a 40-minute debate.

"Not everybody got everything they wanted, but where we have landed is something that is acceptable to everyone," Senator Brandis said. "This is a test for Mr Shorten. It is Mr Shorten who is saying to gay Australians: 'You can just wait while I play politics'."

Under the model approved on Tuesday, tax deductible donations to each committee would be capped at $1500, though anybody would be free to donate to other campaign entities such as Australians 4 Equality or church groups.

The committees would run advertising campaigns in the four weeks before February 11, in a set-up mimicking that of the 1999 republic referendum.

Australian Marriage Equality, which had been awaiting key details, slammed the government's proposal and called for Labor to block it.

"Now that we've seen the legislation, it is not something that should be supported by the Parliament," AME chairman Alex Greenwich said.

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