Prime Minister John Key says he would support a bill to legalise same-sex marriage at its initial stage, but will not guarantee his support would continue through to the final reading that would see it become law.

Mr Key expanded on his views on gay marriage yesterday after saying last week that he was not opposed to it - a change from the past when he had declined to give a view.

He said yesterday that if a member's bill came before Parliament, he would support it at its first reading to allow it to be debated in select committee.

However, when asked if he would support it at the final reading he said, "I don't know."


Mr Key has previously said he votes on conscience issues according to the views of his Helensville constituents - he told the Herald in 2008 that he was "more liberal than my voting record".

He said the Government itself would not put up a bill for same-sex marriage.

"It's not my number one issue, that's for sure. That has been true of most of those conscience or moral issues. The previous Government had a lot of those on the agenda from prostitution law reform through to civil unions. We haven't had any and that's reflected that these are tough economic times and we need to spend our precious time in Parliament resolving those issues."

He said he recognised it was an issue "for a small group of New Zealanders" but it was not a big issue for the Government.

"But if a member wants to put a bill in, we can't - and wouldn't - stop that process and I'm more than happy for a debate to be aired through a select committee process."

Labour leader David Shearer has said he supports marriage equality, and Labour MP Louisa Wall is drafting a member's bill on the issue which she hopes to put in the ballot after Parliament returns next week.

Members' bills are put up by individual MPs from all parties and must be drawn out of a ballot to make it into Parliament. Every second Wednesday of Parliament is reserved to debate members' bills unless the Government picks up a bill - as it did with the anti-smacking bill and more recently, National MP Simon Bridges' animal welfare bill.

In the past, Mr Key did vote against a bill that would have defined marriage as between a man and a woman. However, he also voted against civil unions and in 2003 he voted in favour of the Prostitution Reform Bill at its first reading but voted against it at the third reading - saying the change represented the views of his Helensville constituents rather than his own views. He also voted for a bill to prohibit street prostitution in Manukau.