What is the Act of Supremacy in the novel, Wolf Hall?

The Act of Supremacy is the official law which makes Henry the head of church and state in England. It is required to be sworn in oath by individuals to demonstrate their loyalty for king and country. Thomas More refuses to swear by the Act, for More is a devout and loyal Catholic, and the Act supplants the Church and the Pope. As such, More is executed for refusing to swear.