Ennoblement

The act of being ennobled by the monarch, i.e. of being made a member of the nobility (e.g., as a Duke, Marquess, Earl, Viscount).

Historically, all members of the British nobility had the right to sit in the House of Lords and could thus not be elected into the House of Commons. (Example: Alec Douglas-Home was Earl of Home when he was appointed Prime Minister by the Queen in 1963. He renounced his peerage and got elected into the House of Commons during a by-election, as he believed that he could be a more efficient Prime Minister as a Member of the Commons.)

Since the House of Lords Act was passed in 1999, hereditary peers (members of the nobility who have inherited their title from their ancestors) have not automatically had the right to sit in the House of Lords. Those who do not sit in the House of Lords may stand for election for the Commons.