A writ in acceleration, commonly called a writ of acceleration, is a type of writ of summons that enabled the eldest son and heir apparent of a peer with more than one peerage to attend the British or Irish House of Lords, using one of his father's subsidiary titles, during his father's lifetime. This procedure could be used to bring younger men into the Lords and increase the number of capable members in a house that drew on a very small pool of talent (a few dozen families in its early centuries, a few hundred in its later centuries).
The procedure of writs of acceleration was introduced by King Edward IV in the mid-15th century. It was a fairly rare occurrence, and in over 400 years only 98 writs of acceleration were issued.[citation needed] The last such writ of acceleration was issued in 1992 to the Conservative politician and close political associate of John Major, Viscount Cranborne, the eldest son and heir apparent of the 6th Marquess of Salisbury. He was summoned as Baron Cecil, and not as Viscount Cranborne, the title he used by courtesy. The procedure of writs of acceleration has not been used in practice since the House of Lords Act 1999 removed the automatic right of hereditary peers to sit in the House of Lords.