Senator Penny Wong, Australia’s gay Finance minister is downplaying expectations that the country’s upper parliamentary chamber will support equal marriage rights for same-sex couples in an historic vote, due to take place in the next 24 hours.

“It will mean that it is very difficult for this bill to pass,” Senator Wong told ABC radio.

“Sometimes you lose something then you win on a subsequent occasion – I’ve been in politics long enough to know that.”

Senator Wong said she believed significant progress had been made on the issue of same sex marriage, and that community sentiment supported it.

“It’s about equality and about recognising the worth of our relationships,” she said.

“Sentiment on this has shifted.”

Although Senator Wong’s own boss, Prime Minister Julia Gillard has staunchly opposed supporting equal marriage, Ms Wong is blaming opposition leader Tony Abbott for the impending defeat.

Mr Abbott has refused to allow his MPs a conscience vote on the issue.

“The person I think who is most responsible for the fact we likely won’t succeed on this occasion is Tony Abbott who doesn’t want the party of individual freedom, the Liberal Party, to actually have a free vote on this,” Ms Wong said.

The Senate is due to vote on the Marriage Amendment Bill, the first of four bills currently before parliament legislating for same-sex marriage.