A former chaplain to the late Queen Elizabeth II has said that Prince William should abdicate if he is not prepared to become the Supreme Governor of the Church of England when he succeeds his father King Charles to the throne.

The title has its roots in King Henry VIII's break with the Catholic Church but has been used formally by monarchs since the 1558 Act of Supremacy, enacted during the reign of Elizabeth I.

The title is bound up with the Church's status as the Established Church in England, and the monarch still gives Royal Assent to ecclesiastical laws.

A new book, The Making of a King: King Charles III and the Modern Monarchy, by Robert Hardman, has suggested that Prince William does not share the "unshakeable devotion" to the Church of England of his late grandmother and may not wish to inherit the title of Supreme Governor of the Church of England.

Hardman says he was informed by an unnamed senior palace figure: "His father is a very spiritual person and happy to talk about faith, but the Prince is not. He doesn't go to church every Sunday, but then nor do a large majority of the country. He might go at Easter and Christmas, but that's it."

If William were to snub the role upon becoming king, he would be the first monarch in 500 years to do so.

The Queen's former chaplain, Gavin Ashenden, said the constitutional implications were "immensely complex" and would "take an army of lawyers ten years" to unpick.

He suggested that William either accept the role or make way for someone else to take it on.

He said, "William doesn't show any signs of being alive to the vibrancy of Christian faith. And in that sense, he is very representative of his generation, but I don't think he understands the monarchy because although lots of people have talked about disestablishing the Church of England and changing our constitutional arrangements, they're immensely complex and they go back through 500 years of legislation ... it would take an army of lawyers ten years to do it.

"So I think he either has to accept the fact that this is a role he plays, whether he likes it or not, which is part actually of the burden of monarchy, or if he feels that strongly and he can't do it, then step aside and abdicate and see if there's somebody else in the Royal succession who can."