For example, the Duke of Norfolk's heir apparent is known as "Earl of Arundel" (without the definite article).
However, the heir does not technically become the Earl of Arundel (as a substantive title) until his father's death, and he remains legally a commoner until then.
Before the House of Lords Act 1999, which abolished the automatic right of hereditary peers to sit in the House of Lords, an heir apparent could be summoned to the Lords, before the current title holder's death, by a writ of acceleration – that is, by accelerating the inheritance of a junior title (usually a barony).
For example, a writ of acceleration could have been used to cause a courtesy Earl of Arundel to inherit the Maltravers barony prematurely, whereupon he would gain that as a substantive title and could join the House of Lords as Lord Maltravers.
This biography of a member of a noble house or article about nobility is a stub.