The usual type of error was perpetrated in the Committee on Privileges of the British House of Lords, whether by the Committee itself or by a clerk, in mistaking the origins of a dormant, abeyant, or extinct title, and in awarding that title to a person who was not the heir to that peerage.
[1][2] As a result, a new barony in the peerage of the United Kingdom was created by writ.
[5] Since the early 20th century, the Committee on Privileges has been reluctant to revive older English baronies on various grounds, and thus opportunities for new baronies to be created by clerical error or failure in research are rare.
The most famous error made by the House of Lords in awarding a title was not in the case of a barony, but for the Scottish earldom of Mar which was awarded to a distant collateral heir male of a previous earl, and not to the heir general, as customary under Scottish peerage law.
The most common errors are made in the spelling of a title as granted in letters patent.