On the eve of the parliamentary debate on the Government’s gay marriage bill, the Church of England — which solemnises about a quarter of all marriages in the UK — has sent a briefing to MPs urging them to vote against. Beginning his first official day in the office, the new Archbishop of Canterbury, Justin Welby, will be giving interviews today to put the Church’s position.

Like the Catholic Church’s own briefing to MPs last week, the Anglican briefing emphasises the social purpose and meaning of marriage as a heterosexual union. Marriage, says the document,

is a social institution that predates both church and state and is the glue that has bound countless successive societies together. It benefits society in many ways, by promoting mutuality and fidelity, and by acknowledging an underlying biological complementarity that includes, for many couples, the possibility of children. While marriage has evolved as an institution in many other ways these aspects have remained constant.

The document objects to the “reshaping and unnecessary politicising of a fundamental social institution” by a Government without a mandate to do so. “To apply uniformity of treatment to objectively different sorts of relationship – as illustrated by the remaining unanswered questions about consummation and adultery [which in the Bill are not part of the proposed definition of marriage for same-sex couples, only heterosexual couples] is an unwise way of promoting LGBT equality.”

In respect of religious freedom, the document says:

we doubt the ability of the government to make the legislation watertight against challenge in the European courts or against a ‘chilling effect’ in public discourse. We retain serious doubts about whether the proffered legal protection for churches and faiths from discrimination claims would prove durable. Too much emphasis, we believe, is being placed on the personal assurances of Ministers.

On the question of whether teachers would be forced to promote same-sex marriage as equal to traditional marriage, the briefing says:

We welcome the Department for Education’s assurances that the Secretary of State would not issue specific guidance on teaching about a newly defined understanding of marriage, and that the DfE would not issue particular materials which must be adhered to, but there is no guarantee that future Secretaries of State would take the same view, thus causing conflict with the school’s religious foundation.

Lastly, by radically redefining marriage, the Church of England says, there will be no longer be any possibility of a couple who understand marriage as between a man and a woman to find such an understanding reflected in English law.

The effect of the proposals would be that everyone who wished to marry – irrespective of the form or ceremony by which their marriage was solemnized – would be required to enter into the same new statutory institution of marriage. That institution would be one that was defined gender-neutrally as the voluntary union for life of any two persons. English law would as a result cease to provide or recognise a legal institution that represented the traditional understanding of marriage as the voluntary union for life of one man with one woman.

Moreover, the place of children as the issue of a biological union between husband and wife would necessarily have to disappear from the social understanding of marriage. The established institution of marriage, as currently defined and recognised in English law, would in effect have been abolished and replaced by a new statutory concept that many inside and outside religious organisations would struggle to recognise as amounting to marriage at all. A man and a woman who wished to enter into the traditional institution of marriage would no longer have the opportunity to do so.