Australian Liberal MP Malcolm Turnbull has attacked anti-gay campaigners as “dripping with the worst sort of hypocrisy”.

Frontbencher Mr Turnbull, who was delivering a lecture on the Gold Coast, attacked the coalition for its unwillingness to legalise marriage for gay couples, The Age reports.

Opposition leader Tony Abbott has refused to allow MPs a conscience vote on the issues.

Mr Turnbull said: “Let us be honest with each other. The threat to marriage is not the gays. It is a lack of loving commitment – whether it is found in the form of neglect, indifference, cruelty or adultery, to name just a few manifestations of the loveless desert in which too many marriages come to grief.”

He added that MPs would have to resign in order to cross the floor: “Because the leadership are not permitting a free vote, shadow cabinet ministers are bound to vote in accordance with the collective decision”.

Mr Turnbull continued: “Do the bishops seriously imagine that legalising gay marriage will result in thousands of parties to heterosexual marriages suddenly deciding to get divorced so they can marry a person of the same sex?

“Are not the gays who seek the right to marry, to formalise their commitment to each other, holding up a mirror to heterosexuals who are marrying less frequently and divorcing more often?”

He concluded that while there was probably not enough Liberal support to pass gay marriage, “we should not miss the opportunity to legislate for civil unions for same-sex couples in this Parliament”.