The High Court has given the green light to the Turnbull government’s same-sex marriage postal survey.

The court on Thursday ruled against two separate challenges to the $122 million survey, paving the way for the Australian Bureau of Statistics to begin mailing out ballots next week.

The news was delivered while the government and opposition were facing off in Question Time and was immediately welcomed by the Prime Minister Malcolm Turnbull.

Mr Turnbull said the decision would allow all Australians to have their say and noted that he and his wife, Lucy, would be voting ‘yes’.

“That is as it should be. We encourage every Australian to vote in this survey, to have their say,” he said.

Mr Shorten asked Mr Turnbull if he would “work with the community to show his active support for marriage equality” and whether he would “now accept my invitation to write a joint letter to every Australian to support voting ‘yes’ in the survey”.

“I’m interested in the assumption that the Leader of the Opposition makes that joining his signature to mine would actually increase the case for the ‘yes’ vote,” Mr Turnbull replied.

“Mr Speaker, the Leader of the Opposition can make his case and I’ll make mine.”

Mr Shorten quickly wrote on Twitter: “Alright. Let’s win this.”

The court ruled against the plaintiffs’ arguments that the Finance Minister did not have the authority to appropriate the $122 million using a fund earmarked for “unforeseen” and “urgent” spending or that the ABS could not conduct the vote because the survey did not constitute statistics.

The government bypassed the Parliament to push ahead with the postal vote following the Senate’s rejection of the original compulsory attendance vote.

Finance Minister Mathias Cormann said: “We have always been confident that the process we adopted to deliver on our commitment to give Australians a say on whether or not the law on marriage should be changed to allow same sex couples to marry, was consistent with all the relevant requirements.”

Same-sex marriage advocates immediately said they would switch their focus to campaigning for a ‘yes’ vote.

“We are in it to win it. We are committed to doing all in our power to ensure that the long held wish of the Australian people for marriage equality for all Australians is reflected in the results of the survey,” said Equality campaign executive director Tiernan Brady.

Greens Senator Janet Rice, who was a plaintiff in the case, said: “I’m very disappointed that the High Court challenge was not successful, especially in the face of what has already been a damaging and untruthful campaign by the ‘no’ side.”

Australian Christian Lobby managing director Lyle Shelton, a prominent ‘no’ campaigner, wrote on Twitter: “It’s still on. A referendum on freedoms & radical LGBTIQ sex education in schools.”

The challengers argued the spending was neither urgent nor unforeseen, two key requirements for advancing money from the pool of funds that can be used without parliamentary approval.

The court unanimously dismissed the first challenge by a group of advocates led by independent MP Andrew Wilkie.

A second challenge led by Australian Marriage Equality was dealt with, but the High Court declared the finance minister’s determination was not invalid and he did have the authorisation to make it.

Ballot papers will now be mailed out from Tuesday with the result of the survey to be announced on November 15.

-with AAP