Mr Turnbull, whose Sydney electorate of Wentworth has among the highest proportions of homosexual constituents, said his was a traditional view, but he acknowledged some argued that tradition did not justify discrimination.

Mr Turnbull was speaking on a motion proposed by the Greens MP Adam Bandt calling on MPs to consult their constituents on the issue of gay marriage.

He said MPs should always listen carefully to their constituents and did not need a motion to tell them to do so.

The NSW Labor MP Stephen Jones spoke in favour of same-sex marriage.

''Having applied the core Labor values of equality, fairness and dignity, I believe that there is a case for change,'' he said. But he added that change must be built on community consensus.

Dan Harrison