He hopes to have the proposed Civil Union Bill introduced to Parliament next year as official government legislation with cross-party support.

The proposal comes after years of debate over whether homosexual couples should be allowed to marry. The Marriage Act lets only opposite-sex couples marry. The debate was renewed with the recent passage of the Property Relations Act, which applies to both heterosexual and homosexual couples who split up.

After an approach by Prime Minister Helen Clark last November, Mr Barnett, the MP for Christchurch Central, established an advisory group of mostly gay people to come up with a proposal that would allow homosexual partnerships to be officially registered without altering the status of marriage. The group's proposals would apply to straight and gay de facto couples, who would be able to have their relationships registered and gain similar rights to married couples.

Married couples have many more rights than de facto couples, including rights related to adoption, next of kin, parental leave and access to welfare benefits if one partner dies.

Mr Barnett said it was essential to win cross-party support for the law to go forward as government legislation rather than as a private member's bill. Cross-party support meant it would survive a change of government. He has been informally approaching MPs from other parties, including National, and will shortly make formal approaches to the caucuses of the various parties.

There was no publicity about the proposal till till an article yesterday in the fortnightly gay newspaper Express.

"We have been trying to walk a cautious path," Mr Barnett said last night. "We've gone past the easy equality issues."

The lack of rights in the nature of marriage for gay couples was a significant human rights anomaly that had to be tackled, he said. From next year, the Government would be bound by the Human Rights Act. He predicted a gay couple would quickly bring a case claiming the Marriage Act breached the Human Rights Act, "so it's best to be seen to be doing something".

It was logical to include heterosexual unmarried couples in the legislation, Mr Barnett said. They faced similar issues, and he had been lobbied by almost as many straight couples wanting legal recognition of their relationships as by gay couples.

The Netherlands is the only country that recognises same-sex marriages, though a number of jurisdictions have some form of civil union recognition, including the states of Hawaii and Vermont in the United States, Hungary, France and Denmark.