Royal dukedoms in the United Kingdom
In the British peerage, a royal duke is a member of the British royal family, entitled to the titular dignity of prince and the style of "His Royal Highness" who holds a dukedom. Dukedoms are the highest titles in the British roll of peerage and the holders of these particular dukedoms are Princes of the Blood Royal. The holders of the dukedoms are royal not the titles themselves. They are titles created and bestowed on legitimate sons and male-line grandsons of the British monarch, usually upon reaching their majority or marriage. The titles can be inherited but cease to be called "royal" once they pass beyond the grandsons of a monarch. As with any peerage, once the title becomes extinct, it may subsequently be recreated by the reigning monarch at any time.
Baronage
Yet the ancient usage of the degree of barony as the "sine qua non" of the nobility continued until the 21st. century. All members of the peerage must be barons, as it were to qualify, for as Hallam stated: "Every earl was also a baron",
and in this respect the ancient concept of the baronage survives as the common factor of the nobility. No commoner is ever elevated directly to a higher degree of nobility without the fiction of at the same time being created a baron, enabling him to join the baronage of ages past, which therefore still survives in this theoretical form. Thus the commoner Admiral John Jervis was elevated to the peerage in 1797 as Earl St Vincent, a fittingly high reward for his naval services, at the same time he was created the relatively lowly Baron Jervis. The same was the case in the 1980s on the elevation of the former British prime-minister Harold Macmillan to an earldom, when he was created a baron simultaneously. Such a barony is borne "in gross" that is to say it is never used by its holder but rather is submerged within his higher title. It may however emerge when used by his heir apparent to take a seat in the House of Lords by writ of acceleration, that is to say where such son has particular political skills which the government of the day wishes to make available to itself in parliament. It may also be used without any legal or political substance as a courtesy title by the eldest son of an earl or higher noble.