Same sex marriage in Northern Ireland could lead to calls for polygamy and incest, according to one Christian campaign group.

The Keep Marriage Special campaign, which is self described as a “broad alliance of Christians” has claimed that polygamy, polyandry and incest would all be permissible if same-sex marriage was introduced.

According to their website the organization aims to defend the biblical definition of marriage and to oppose any possible redefinition by HM Government. Its members include Nigel Dodds MP Deputy Leader, Democratic Unionist Party and Jeffrey Donaldson MP Democratic Unionist Party.

Under a current consultation, which closed on June 14, the British government set out its proposals to enable same-sex couples to have a civil marriage.

The key proposals of the consultation are:
•    to enable same-sex couples to have a civil marriage i.e. only civil ceremonies in a register office or approved premises (like a hotel)
•    to make no changes to religious marriages. This will continue to only be legally possible between a man and a woman
•    to retain civil partnerships for same-sex couples and allow couples already in a civil partnership to convert this into a marriage
•    civil partnership registrations on religious premises will continue as is currently possible i.e. on a voluntary basis for faith groups and with no religious content
•    individuals will, for the first time, be able legally to change their gender without having to end their marriage

In Keep Marriage Special's response to the consultation, it wrote: “If the only basis for marriage is the desire of the parties to get married, then there is, according to the logic of this proposal, no reason not to open up marriage to more than just same-sex couples.

“Marriage is a fundamental unit of society – it would be foolish and dangerous to change it.

It added: "Marriage between one man and one woman is the best environment in which to bring up children. Children need a mother and a father.”

Responding to the comments John O'Doherty, Director of Belfast gay rights group The Rainbow Project, told the Belfast Telegraph: “It's what we (now) expect from the religious right — a constant attack on LGBT people and their families.”

Gay teacher fired from Catholic school after applying for same-sex marriage licenseGetty Images