Australia will start to look like the "deep south" on the issue of gay marriage as more countries around the world adopt same-sex laws, South Australian Environment Minister Ian Hunter says.

A same-sex marriage bill has passed its first hurdle in the British House of Commons by 400 votes to 175.

Mr Hunter says that should send a strong message to both Prime Minister Julia Gillard and Opposition Leader Tony Abbott.

The minister, who is gay and travelled to Spain last year to marry his longtime partner, fears Australia could become the last major English-speaking nation to hold out against equality.

"I don't believe this position is sustainable in Australia for much longer," Mr Hunter told AAP on Wednesday.

"We are going to be embarrassed. Around the world all the countries we like to compare ourselves to are going to be adopting this measure.

"We'll be the only English-speaking country in our region where you can't get married if you are a gay or lesbian citizen.

"We are going to start to look like the deep south in terms of this issue."

In the wake of the British vote, Mr Hunter said Mr Abbott in particular should rethink his opposition to giving coalition MPs a conscience vote on gay marriage.

"It really says that you can't hold this line much longer," he said.

"People are going to be agitating and demanding to have their say on this issue."

In December Mr Hunter became the first gay Australian politician to marry while in office when he wed Leith Semmens in the town of Jun, near the southern Spanish city of Granada.

The pair, together for 22 years, tied the knot two months after federal parliament voted down same-sex marriage legislation.

In South Australia, state parliament will this year consider a bill to introduce same-sex marriage laws with MPs from both the Labor and Liberal parties to be granted a conscience vote.