Dukes in the United Kingdom
Duke, in the United Kingdom, is the highest-ranking hereditary title in all four peerages of the British Isles. A duke thus outranks all other holders of titles of nobility (marquess, earl, viscount and baron).
Baron Arlington
In the Peerage of the United Kingdom the earldom (including the viscountcy being a courtesy title) presents a rare example of a hereditary peerage title of a higher rank than baron falling into abeyance, another case being that of the earldom of Cromartie in 1893.