The Evangelical Alliance has added its voice to concerns over the Government’s plans to redefine marriage.

Equality Minister Lynne Featherstone announced at the weekend that a public consultation would be launched next March on whether marriage for gay couples should be legalised.

Under current law, gay couples may enter into civil partnerships but not marry. Similarly, heterosexual couples may marry but not enter into civil partnerships. The Government said there were no plans at present to legalise civil partnerships for heterosexual couples.

Announcing the consultation, Lib Dem MP Featherstone said Britain “must not get complacent” on gay rights.

“We are a world leader for gay rights, but there is still more that we must do,” she said.

The Evangelical Alliance said it was “deeply concerned” by news that the government was considering changing the law on marriage.

It warned that any redefinition of marriage would only serve to “devalue” the institution.

“We support addressing injustices suffered by people who choose gay lifestyles, and would welcome many measures to secure reasonable and fair access to public goods and services,” it said.

“However, despite numerous assurances in 2005 (and many since) that civil partnerships would suffice in meeting demands for equality, it now seems that liberalism knows no limits.”

The suggestion of broadening marriage to include same-sex relationships would, it continued, open up the prospect of the institution “becoming anything that any group with an agenda demands it to be”.

“These proposals to apply free-market principles to the vitally important civic institution of marriage exceed all known historic, cultural, spiritual and biological norms,” it warned.

“Marriage is not a commodity that can be re-packaged for a new market. Marriage has always been, and in reality will always be, solely between a man and a woman, principally though not exclusively for the birth and nurture of children and for conferring generational identity.

“At a time of such social and economic hardship, this attempted revision promises to expose much of the government’s proposals for renewing civic life through supporting marriage and the family as hollow.

“The state has a responsibility to protect our institutions. That entails acknowledging that normative relations exist – and then supporting them.”

The alliance anticipates strong opposition to the proposals, not only from Christians, but also atheists, people of other faiths and even homosexuals.

“Indeed, if successful, the many people who cannot and will not accept the validity of these so-called ‘marriages’ could be put in a very difficult position," it said.

“The government’s plans conflate difference with equality and would fragment and devalue marriage as an authentic relational covenant and a social ideal that people aspire to.

“There is such a thing as society – and marriage is a unique and central part of it. As such, in order to ensure that future generations can enjoy the value, status and benefits that it affords, it is worth celebrating and defending by all means possible.”