That's probably what will have to happen, but I'm not sure that even that will protect the Church. I don't know if the Brits have the level of "anti-discrimination" laws that we do, but most likely once "gay marriage" is proclaimed, they will be able to demand "marriage services" from the churches, even though it wouldn't mean a civil registry.
It's as if the gays have stolen the whole sacrament of marriage and even the word itself.
The biggest enemy of the left is a church that won’t bow down, knuckle under and kiss liberal a$$. So far, the Catholic church and a few others aren’t giving in, but most have become liberal.