Lex rex baby! Lex rex!
A Protestant's identification with/membership in his church is granted by subjection and adherence to a predefined formal confession or creed (i.e. the Bible, the Westminster Confession, Heidelberg Catechism, etc). The Catholic version has all members being ultimately subject to a person or office (i.e. the Pope, Archbishop, etc). Reformed Protestants are ruled by God's Word (sometimes encapsulated in a Creed or Confession for ease of dissemination). Catholics are ruled by God's Vicar.
To use a more familiar example, the United States of America was formed as a government ruled over by a ‘confessional standard’. Even the President is supposed to be subject to a "Protestant" standard, i.e. Witherspoon's axiom "Lex Rex" (the Law is King). This is why oaths are sworn to obey and protect the 'standard' (i.e. defend the Constitution), and not to obey and protect the President. The President's authority comes from the Constitution; it is not independently possessed. The President therefore does not have the authority to re-write the Constitution.
In the UK a Protestant (an Anglican) is a member of an officially state sanctioned, tax supported sect that has little or no relationship to the Church established by Christ. Since the sect was state established and is COMPLETELY governed by the state it is assumed that all religious bodies can be governed COMPLETELY by the state. There is no assumed right to true freedom of religion in the UK. Hence, Protestantism has affected the law and vice versa.
If I had to choose between living in a LEX REX or a REX LEX country, it'd be LEX REX every time! Thank God for the Reformation!!!