"The European Convention on Human Rights does not require member states’ governments to grant same-sex couples access to marriage."
But if same-sex "marriage" is lawful, then religious organisations that refuse to perform them do face litigation or prosecution under existing anti-discrimination legislation, irrespective of any statutory exemptions.
So much for just letting Quakers, Unitarians, Reform Jews and some Anglicans, Methodists and members of the URC get on with it, because no one was ever going to force it on Catholic churches (or on the Catholic Church, as such), on most Anglican churches (or on the Church of England and the Church in Wales, as such), on many or most Methodist or URC chapels, on Baptist chapels, on Orthodox synagogues, on mosques, and on churches attended by the growing number of black Pentecostals or by that sixth of the world's Greek Cypriots which lives in Britain.
Oh, yes, they are.
The only way to stop them is to retain the legal definition of marriage as only ever the union of one man and one woman.
To abolish the specific and distinct categories of husband and wife, with different rights and different responsibilities directly related to the differences between the two sexes, would be to redefine every marriage. If, unlike me, you are a married person, then that means your marriage, redefined without any reference to you and to your husband or wife.