The six High Court judges adjudicating the constitutional validity of same-sex marriage laws in the ACT could not have been clearer in their judgement.

As far as they were concerned the only question to be considered was one about the law: Was the ACT Marriage Equality (Same Sex) Act 2013 inconsistent with federal parliament’s Marriage Act and Family Law Act?

Delivering an unanimous ruling in Canberra on Thursday, Chief Justice Robert French was succinct: “That question must be answered `yes’.”

The court accepted the views of all parties – even the those from the ACT government and Australian Marriage Equality – that it is the federal parliament that had the legislative power to provide for marriage between persons of the same sex.

States or territory parliaments do not.

As a result, what constitutes a legal marriage is determined by federal law.

And that law, as it stands now, provides that a marriage can be solemnised only between a man and a woman and that a union solemnised in a foreign country between a same-sex couple must not be recognised as a marriage in Australia.

But marriage equality advocates, while disappointed at the court’s ruling, see a silver lining in its findings.

It confirms “beyond doubt” the constitution allows the federal parliament to legislate for marriage equality, says Anna Brown from the Human Rights Law Centre.

She also argues state-based laws such as those proposed in Tasmania and NSW might have a greater chance of surviving a High Court challenge.

The easier, but more politically problematic, course is for the federal parliament to make the necessary legislative changes.

That’s unlikely to happen anytime soon, notwithstanding the timely introduction of a private bill to parliament just as Justice French delivered the court’s judgement on Thursday.

Greens senator Sarah Hanson-Young is making a fourth attempt to legalise same-sex marriage.

Labor supporters of gay marriage also tried and failed to win the previous parliament’s backing for a change to the Marriage Act.

The 44th Parliament shows no signs yet it is of a different mind, especially if coalition MPs don’t grant themselves and each other a conscience vote.

And even then, there are doubts whether there are sufficient numbers to carry the day in both houses of parliament.

When the House of Representatives last decided the issue in 2012, MPs voted 98-42 against; the Senate 41-26 against.

Only one Liberal, Senator Sue Boyce, exercised a conscience vote and crossed the floor to vote with supporters of gay marriage.

Since then marriage equality has lost 15 supporters in the lower house, following the September election, and Boyce will be out of the Senate after June 30.

As well there are more coalition MPs in the lower house.

Those who think they know what’s in the minds of coalition MPs estimate that legalising same-sex marriage has support from about 20 of them.

That won’t be enough to change the law.