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).
Barons in Scotland
An English barony is a peerage (yet the abolition act of 1660 allows for some remaining non-peer baronies not converted by writ to remain as feudal baronies of free socage "incorporeal hereditament" similar to a lordship of the manor), but whether Scottish barons rightfully rank as peers is disputable. They are known as minor barons currently treated as noble titles of less than peerage rank. The Scottish equivalent of an English baron is "Lord of Parliament".