Australia’s best chance of legalising gay marriage — in Tasmania — is in serious trouble, as nervous politicians baulk at setting a precedent on the hot topic.

A bill to legalise same-s-x marriage has passed the state’s lower house and goes to the upper house tomorrow, with a vote expected in the richly decorated 19th-century chamber late Wednesday night or on Thursday. A Crikey analysis last month found the bill’s chances were line-ball. Crikey revisited the issue this week and found the prospects for the bill have dimmed as two MLCs have changed their minds.

Federal Parliament’s voting down of a same-s-x marriage bill appears to have shaken Tasmania’s Legislative Council, which is dominated by independents, has a record of quirkiness, and has been unafraid to go it alone on contentious issues in the past. MLCs are worried about perceived legal ambiguity in the Tasmanian bill and the risk of a High Court challenge; most think the issue should be addressed federally.

For the bill to pass, it must win eight votes in the 15-member Leg Co (the president, Sue Smith, does not vote unless there is a tie, and is likely to vote no). Crikey has found there are four votes for yes, six votes for no, and four votes which are uncertain (not counting Smith’s vote). Of those four uncertain MLCs, insiders speculate Adriana Taylor is likely to vote no; this may kill off the bill.

The process leading to the vote has been emotional for MLCs, who have received plenty of correspondence and briefings, and are gearing up for a marathon in the chamber. Some of them have written hour-long speeches. Ruth Forrest MLC’s speech is 70 pages.

Tasmanian gay marriage advocate Rodney Croome is not giving up, saying “outcomes are always very unpredictable” in the Leg Co. He says MLCs could change their minds at any stage. “I believe there’s still a possibility they will pass the reform,” Croome told Crikey today.

Here are the results of Crikey’s interviews this week. In alphabetical order …

Rosemary Armitage (independent): likely vote NO

Armitage told Crikey: “I will not be supporting the bill before us … I will be speaking against it, because it’s a state issue not a federal issue.”

Ivan Dean (independent): likely vote NO

“At this present time I’m not supporting the bill,” Dean told Crikey. “The major reason is it’s a Commonwealth issue and should be dealt with by the Commonwealth.” Dean thinks a High Court challenge would be launched if the bill passed.

Craig Farrell (ALP): likely vote YES

Farrell will support the bill, which was put up by his party and the Greens.

Vanessa Goodwin (Liberal): likely vote NO

A spokeswoman told Crikey Goodwin would follow the party line and vote no.

Kerry Finch (independent): won’t show his hand

Finch says he won’t reveal how he’ll vote until he’s on the floor of Parliament. “My wife doesn’t even know,” he told Crikey. Finch is fairly socially progressive but says “the stories from both sides have been very compelling”. He thinks other states are watching closely. “I’m not sure where Tasmania’s vote is going to go, but waiting in the wing as spectators are ACT, SA and NSW,” said Finch. “There could be a domino effect.” A well-informed insider believes Finch will vote yes.

Ruth Forrest (independent): likely vote YES

Forrest, a midwife, is a “strong supporter” of the bill and will move it in the upper house. “It’s about love and commitment,” she told Crikey. Forrest said it was “too close to call” whether the bill would pass.

Mike Gaffney (independent): won’t show his hand

Gaffney, a well-regarded ex-mayor, is “not releasing his position” until he speaks in Parliament, his spokeswoman told Crikey today. He’s seen to be relatively socially progressive, and generally aligned more to the Labor position than the Liberal. He has prepared a one-hour speech. “It’s all I’ve been thinking about for the past five weeks,” Gaffney said in emailed comments to Crikey today.

Greg Hall (independent): likely vote NO

“I will be speaking against the bill on the floor of the house,” Hall told Crikey yesterday. “My electorate is pretty strongly against the bill and these are my personal views as well. It should be a federal issue.”

Paul Harriss (independent): likely vote NO

Harriss says the bill “strengthened” his previous anti-gay marriage view. Harris told Crikey: “The electorate I represent is opposed to the notion. And that’s in accordance with my own personal view with marriage being a cornerstone of our society as developed traditionally.” Harriss thinks it’s “most unlikely” the bill will pass.

Tony Mulder (independent): likely vote YES

“I am probably going to vote for the bill … you can stick me in the yes column,” he told Crikey. Despite having some objections to the specifics of the legislation,  Mulder is in favour of the main principles.

Tania Rattray (independent): position not known

Crikey couldn’t reach Rattray, who is of conservative political stock. Last month she said “my personal opinion is no … I don’t have an issue with these people’s s-xuality. But whether marriage is a step too far … I haven’t arrived at that yet.”

Sue Smith (president, independent): would not vote in the first instance, but likely vote NO

As president of the Leg Co, Smith gets the deciding vote if tied, and would be likely to maintain the status quo and vote no. Smith is a respected and powerful Legislative councillor who has a record of conservatism on social issues. She represents a north-west coast electorate, traditionally one of the state’s most religious districts.

Adriana Taylor (independent): position not known

Crikey has been unable to reach Taylor, although several Leg Co insiders believe she is likely to vote no.

Rob Valentine (independent): likely vote YES

Valentine, a socially progressive ex-Hobart mayor, told Crikey on Monday that “my position is that I’m inclined to vote for it”. He has concerns about constitutional issues, and will listen closely to briefings and the debate, but believes these issues could be resolved.

Jim Wilkinson (independent): likely  vote NO

Wilkinson, a savvy lawyer, has real concerns about what he sees as constitutional and jurisdictional issues with the bill, which he describes as “nonsensical” and “a nightmare”. “It’s got some terminal issues,” he told Crikey. Wilkinson is concerned about each state passing different laws on this issue, and sees marriage as a Commonwealth matter. Wilkinson thinks the bill, should it pass, may well be subject to a constitutional challenge.