The British vote for same sex marriage will make it harder for Victoria and Australia to avoid following suit, a Greens MP says.

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

Victorian Greens MP Colleen Hartland said allowing same sex couples to marry was "perfectly logical".

"Especially considering it's a conservative(-led) government in England, if they can do it, why can't we do it?" Ms Hartland told AAP.

"I think it makes it much harder for Victoria and Australia to keep resisting this when other major countries have said yes."

Ms Hartland said she never understood the fuss over gay marriage.

"I've been married for decades and how come none of my gay mates are allowed to get married?" she said.

"I just don't understand it, but I think this is great."