|Birth Certificate for HRH Prince George of Cambridge|
Comparing the birth certificates of Prince George and his father Prince William, it is clear that a distinction is drawn between the status of Prince(ss) of the United Kingdom and the titles that traditionally form part of an individual's name. Prince William's parents are named on his birth certificate as the Prince and Princess of Wales whilst his father's occupation is described as "Prince of the United Kingdom" (in 1982 birth certificates did not carry information relating to mothers' occupations). On his birth certificate Prince George's parents are named as the Duke and Duchess of Cambridge.
|Prince William's Birth Certificate|
The rank of Prince or Princess of the United Kingdom indicates membership of the Royal Family. I hold the view that members of the Queen's family who are not princes or princesses of the United Kingdom are not royal and are therefore not members of the Royal Family (viz Peter Phillips and Viscount Linley -- they are members of The Queen's family but not of the Royal Family). Once this distinction is understood, it is easier to understand that the rank of Prince or Princess of the United Kingdom is also an occupation / job title -- i.e., these individuals are working members of the Royal Family and they receive funding for fulfilling their public duties. To be crude, if the Royal Family is nicknamed "the Firm", then princes and princesses of the United Kingdom may be deemed "the Firm's employees".
To provide another example: as grandsons of King George V, HRH The Duke of Gloucester and HRH The Duke of Kent are both princes of the United Kingdom and they fulfil public duties as members of the Royal Family -- thus, each may describe his occupation as "Prince of the United Kingdom". However, their sons (respectively the Earl of Ulster and the Earl of St. Andrews) can not do so, even after they succeed to their fathers' dukedoms, as they will never be royal highnesses or princes of the United Kingdom (and consequently they will not receive funding for fulfilling public duties).