The Cardinal, in a homily in St John's Cathedral, told the congregation that the people of Ireland would soon have to choose to "stand clearly on the side of Christ or depart from him".

A spokesperson for the Gay and Lesbian Equality Network said there is a democratic consensus for civil partnership.

Chairperson of GLEN, Kieran Rose, said civil marriage and civil partnership are matters for the State. "The State, through Civil Partnership, is for the first time providing recognition and comprehensive protections for lesbian and gay couples," he said. "It will establish a legal status and standing for same-sex relationships and a comprehensive set of rights, protections and enforceable obligations on the part of civil partners that are comparable to those available to married couples."

Cardinal Brady said: "What the Government is planning will hugely change people's concept of the family. Nevertheless, marriage between a man and a woman will always remain the ideal environment in which to raise children.

"Any government that undermines such an environment could hardly be said to be promoting the common good."

Cardinal Brady claimed that any Registrar of Marriage who, in conscience, declines to officiate at same-sex weddings, will be guilty of an offence.

The Cardinal was attending the first carbon neutral conference where more than 70 trees were planted around the world and a donation was made to the Trócaire climate change project to cancel out the carbon footprint of the theological conference.

More than 200 international delegates attended the conference which focused on the theme of 'Christian responsibility for the environment and investing care in the earth'.