The Archbishop of York has added his voice to that of the Catholic hierarchy in opposing gay marriage. In an article in The Guardian, John Sentamu argues - without really saying why - that allowing gay marriage would undermine marriages between men and women. The Catholic Church has been circulating petitions against gay marriage at Masses and in its secondary schools.
Unlike in America, Britain does not have a large body of religious people opposed to gay marriage - most Catholics are not whatever their Church says and circulating petitions against it in schools had led to protests by Catholic teenagers. What the resistance to gay marriage by the Catholic Church and Church of England really signifies is a "long, withdrawing roar" of people who know they no longer have the grip on society they once did.
The root of the issue in England is the intertwining of religious and civil marriage with Anglican vicars, Catholic priests and other ministers conducting ceremonies that combine the two. The answer is to separate them, as happens in many (religious) countries like France and Egypt so people can choose to have a civil marriage, a religious one or both. Everyone could have a civil marriage and it would be up to religious who could have a religious one, with the more enlightened Christians like the Quakers and Unitarians presumably marrying any couple, as they already do with civil parterships.
Separating civil and religious marriage would also probably also involve disestablishing the Church of England, a big step towards a secular society which would also allow Anglicans rather than politicians to control their church.