Just issued by the Church Of England:
The Church of England cannot support the proposal to enable ―all couples, regardless of their gender, to have a civil marriage ceremony. Such a move would alter the intrinsic nature of marriage as the union of a man and a woman, as enshrined in human institutions throughout history. Marriage benefits society in many ways, not only by promoting mutuality and fidelity, but also by acknowledging an underlying biological complementarity which, for many, includes the possibility of procreation.
We have supported various legal changes in recent years to remove unjustified discrimination and create greater legal rights for same sex couples and we welcome that fact that previous legal and material inequities between heterosexual and same-sex partnerships have now been satisfactorily addressed. To change the nature of marriage for everyone will be divisive and deliver no obvious legal gains given the rights already conferred by civil partnerships. We also believe that imposing for essentially ideological reasons a new meaning on a term as familiar and fundamental as marriage would be deeply unwise.
Read the full statement (PDF).