Could Prince William marry a Catholic?
The relevant law in this context is the Act of Settlement of 1701. It may be over 300 years old but it is still in force, even though all or most other anti-Catholic legislation has been repealed in the UK.
This decrees that only Protestant descendants of Princess Sophia, the Electress of Hannover, the granddaughter of King James I can succeed to the British throne. Protestant denominations of the Christian Church now include the Church of England (Anglicans) and the Church of Scotland in the UK, Episcopalians in the USA and Baptists, Methodists and Presbyterians.
The Act of Settlement means that if William marries a Catholic - see paragraphs 1 and 3 where Catholics are referred to as papists - he could not then succeed to the British throne to become king.
If William did wish to marry a Catholic then he, Prince Charles or Queen Elizabeth would talk with the prime minister who would agree to amend the law by introducing legislation in parliament. The Queen and the prime minister meet formally every Tuesday evening in Buckingham Palace when both are in London and so the discussions could take place without causing speculation.
However, at the moment the British monarch is also formally the head of the Church of England, a Protestant denomination. So, if the Act of Settlement were amended, this constitutional arrangement would have to be reviewed as well. This is probably why the legislation has been left unchanged until now.
King Henry VIII broke away from the Catholic Church in 1532 after the Pope refused him permission to divorce his first wife, Catherine of Aragon. He then declared himself head of the church in England, closed down the Catholic monasteries and divorced Catherine. He then married five more times, separating two of his wives from their heads for committing adultery.
Some of his successors were Catholic including the infamous Queen Mary I, the daughter of Henry and Catherine of Aragon. In her reign from 1553 to 1558 she restored the supremacy of the Catholic Church and agreed to the persecution of Protestants. She is not the queen after whom the ship Queen Mary is named but she does have a drink - bloody mary - in her name.
The series of Protestant and Catholic monarchs and their persecutions of Christians belonging to the alternative church eventually led to the supremacy of one of the divisions in Britain - the Protestant Church - and the anti-Catholic legislation of which the Act of Settlement was a part.
And if you're thinking of marrying Prince William, the death penalty has now been abolished in the UK.