The Christian Institute has issued an excellent guide to the rules and exemptions covering Churches and Marriage now that the Marriage (Same Sex Couples) Act 2013 is in force.
Details are HERE and you can download the Guide itself.
Within this country too, there are many areas in which the Church and the public authorities can work together for the good of citizens, in harmony with Britain’s long-standing tradition. For such cooperation to be possible, religious bodies – including institutions linked to the Catholic Church – need to be free to act in accordance with their own principles and specific convictions based upon the faith and the official teaching of the Church. In this way, such basic rights as religious freedom, freedom of conscience and freedom of association are guaranteed.
( See this Blog 7 February 2010)