Church that survived the Armada and civil war fears gay marriage

Postwar decline: After centuries of expansion in the colonial era, church attendance slumped in recent years (AP)

The Government's plan to introduce same-sex marriage is one of the most serious threats to the Church of England in its 500-year history, senior clerics claim.

The Church today outlines its opposition to the Coalition's proposals in scathing terms. Anxiety among Church leaders is so acute that they raise the spectre of disestablishment, warning that any attempt to alter the definition of marriage could fatally undermine the Church's position.

Critics dismiss the Church's stance as overly dramatic and have urged bishops to follow established religious bodies in Iceland, Sweden and Denmark, who largely embraced gay marriage.

The Anglican Church's view, drawn up by senior bishops and lawyers, is confirmation that despite supporting civil partnerships eight years ago, it believes extending marriage rights to same-sex couples is a step too far. It says plans for same-sex marriage "have not been thought through properly and are not legally sound". Downing Street has insisted its plans for equal marriage laws will go ahead.

In March, the Government launched a consultation with the deadline later this week. The Church's response lists reasons why it cannot support same-sex marriage, both theological and practical. At the heart of the debate is whether the definition of marriage can be changed from the lifelong union of a man and woman to that of any couple.

The Government says the change is a simple one which would allow "all couples, regardless of their gender, to have a civil marriage ceremony". No religious organisation would be compelled to conduct a wedding ceremony as they would not take place in religious buildings. But the Church counters that the proposals change the very meaning of marriage, which is defined by both canon and parliamentary law.

The Bishop of Leicester, the Right Rev Tim Stevens, told i: "If a category of marriage is created which separates the Church's understanding of marriage from that of the State, it is bound to have some effect on the relationship of the Church and its locality. That begins to raise questions about the nature of establishment as we've understood it."

Lawyers acting for the Church have advised that the proposals could leave it vulnerable to legal attacks. There is particular concern that the European Court of Human Rights might force it to conduct gay wedding ceremonies if the meaning of marriage under British law was changed.

The Church's stance will please its traditionalist and socially conservative wings, but will cause dismay among more liberal congregations. Symon Hill, a spokesman for the Christian think-tank Ekklesia, said: "The Church of England has missed an opportunity to move on. Many of the Church's own members are far more positive about same-sex marriage than this official statement suggests."