"The new act breaks the existing legal links between the institution of marriage and sexual complementarity," said a statement by Archbishop Vincent Nichols of Westminster, president of the Bishops' Conference of England and Wales, and Archbishop Peter Smith of Southwark, vice president.
Their statement was released July 17, the same day Queen Elizabeth II gave her royal assent to the Marriage (Same-Sex) Couples Bill, which passed the House of Lords July 15 and the House of Commons July 16.
The new law means that civil and religious marriage between same-sex couples is now legal in Britain, with the first gay weddings expected next summer.
"With this new legislation, marriage has now become an institution in which openness to children, and with it the responsibility on fathers and mothers to remain together to care for children born into their family unit, are no longer central," the archbishops said in their statement. "That is why we were opposed to this legislation on principle."
Their statement praised Parliament for amending the bill to protect freedom of speech but lamented its refusal to pass amendments that would have ensured protection for churches, religious schools and for individuals, particularly in the workplace, to act in accordance with their consciences.
"The legal and political traditions of this country are founded on a firm conviction concerning the rights of people to hold and express their beliefs and views, at the same time as respecting those who differ from them," the archbishops said.
"It is important, at this moment in which deeply held and irreconcilable views of marriage have been contested, to affirm and strengthen this tradition."
The law allows same-sex couples not only to enter into civil marriage but also to wed in churches, synagogues or temples of faith groups that "opt in" to the legislation, with the exception of Anglican churches, which remain forbidden to do so.
Under the terms of the law, married men can also legally call themselves "wives" and married women can rename themselves "husbands."