http://en.wikipedia.org/wiki/Succession_to_the_British_throne
The Act of Settlement 1701 (restated by the Acts of Union) still governs succession to the Throne. (The Act does not abrogate several provisions of the Bill of Rights, which, therefore, still remain in effect.)
The Act of Settlement further provides that anyone who marries a Roman Catholic is ineligible to succeed. The Act does not require that the spouse be Protestant; it only bars those who marry Roman Catholics. Since the passage of the Act it has been determined (in the case of Prince Edward, Duke of Kent) that an individual is not barred because his or her spouse later converts to Roman Catholicism after their marriage.
Interesting, in that under the current rules of Succession, a future Monarch can be of ANY religion except RC, as this is proscribed under the Act of Succession 1701 & restated in Acts of Union. Although given the current turmoil re Scottish Referendum questions, this could be once again up for debate, not that I wish it ever to be.