Peers and Nobility
It should not be necessary to explain that the only peers in this country are the actual holders of peerages, and they are the only persons who can properly be described as noble. But so many authors and newspapers fall into the error of referring to the holders of mere courtesy titles as peers that the point is worth making. Apart from the whole body of peers there is no separate caste of nobility here as is the case in many Continental countries, where nobility, once conferred, extends to every member of the family in all generations.
Palmer, in his standard Peerage Law in England, puts the position quite clearly when he says:
A peerage confers nobility on the holder for the time being. It is a trite saying that the grant of a peerage enobles the blood of the grantee; and this metaphorical expression is in a sense correct, for the grant of a peerage to a commoner renders him or her noble, since it makes him or her a peer or peeress, and gives to his or her issue - or such as them as by the grant shall be made inheritable - a potential nobility. But clearly, in point of law, the only nobles in England are the peers and peeresses ..... Nobility is inherent in the blood in that a peerage cannot be aliened, or surrendered or merged, but it is not inherent in the sense that it passes with the blood to all descendants of the grantee. The children of a peer, then, are not born noble.
The clause I have stressed is important as emphasising that even this potential nobility is confined strictly to those who may possibly inherit. Thus in the case of the normal peerage creation, in which descent is restricted to "heirs of his body lawfully begotten", it is clear that this potential nobility cannot possibly be transmitted to or through daughters. The only cases to which this does not apply are certain Scottish peerages and the ancient English baronies by writ, which are inheritable by females as well as males, or those which, by some special clause in their instrument of creation, can also descend through the female line.
To revert to courtesy titles, the holders of these are not peers. By courtesy the eldest sons of dukes, marquesses and earls take their fathers' secondary titles, but they are still only commoners in the eyes of the law. To take a concrete example, the Duke of Marlborough's son is known as Marquess of Blandford, but in legal documents he would be termed "John Spencer-Churchill, Esquire, commonly called Marquess of Blandford". Except in precedence on State or formal occasions, as the son and heir of a duke he enjoys no standing or privilege which is not equally enjoyed by any ordinary subject of the King.