Barons were introduced into England by the Normans; most of whom held that rank in Normandy before the Conquest. Baron literally meant a man, being the King's tenant in chief, i.e. holding his land directly from the King. The burgesses and leading citizens of London were also known collectively as Barons, and this style was allowed them by clerks who wrote the writs of William II and Henry I. The barons of the Cinque Ports are a parallel to the barons of London. In the 13th century they were summoned to the Counsel or Parliament, but at first this did not imply that a successor would necessarily also be summoned to subsequent Parliaments. The more important would probably be summoned, but by the reign of Edward III it became usual for successors to receive writs as a matter of course. Thus the Baronage emerged into a hereditary dignity of the Peerage.
The first baron created BY PATENT was John Beauchamp de Holt, created Baron Kidderminster, by Richard III in 1387 with remainder to his heirs male, but baronies by writ also continued to be created long after this date.
A baron is styled Right Honourable and formally by the Sovereign Right trusty and well-beloved (and counselor when a member if the Privy Council).
The title of Viscount had its origin in the office of the deputy or the lieutenant (Vice-Comes) of a Count, which had become hereditary in the Empire by the beginning of the tenth century. It was also used as the Sheriff if a county. Henry VI, crowned King of England and France, created John Lord Beaumont in 1440 Viscount Beaumont in England and Viscount Beaumont in France (a title forfeited by the Duke of Alencon in 1415, and vacant on the death of the Duke of Bedford in 1435), in order to integrate the titles of the two countries. The peerage title received precedence above all Barons, but it did not become popular until the seventeenth century. Viscounts were always created by patent
A Viscount's style is Right Honourable. He is addressed by the King or Queen as Our right trusty and well-beloved cousin (and counselor when of the Privy Council).
Before Canute, an ealdorman administered a shire of province for the King. In Latin documents he was styled Dux or Comes, taking the place between the royal Atheling and the thegn. Under Canute the Danish equivalent of Earl was introduced.
Under the Normans the government of an earl was normally restricted to one county and became hereditary, though losing the functions of the King's representation in the county to the sheriff. An earl was usually invested with the third penny out of the sheriff's court of the county, of Anglo-Saxon origin
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An Earl is styles Right Honourable, and is formally addressed by the Sovereign as Our right trusty and entirely beloved cousin (and counselor when the Privy Council).
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The Term Marchio was applied in the Norman period to the Earl or Baron guarding the Welsh or Scottish Marches, or border territories. Similarly in Germany, the Count or Graf became known as the Markgraf, anglicized to Margrave. By the 12th century it had lost it's territorial significance. It was introduced to England by Richard II, brother-in-law of the Margrave of Brandenburg, the honour being conferred upon Robert de Vere, Earl of Oxford, who became Marquess of Dublin in 1385. The precedence between Dukes and Earls caused great offence to the Earls, and the patent was revoked in1386 in favor of the Dukedom of Ireland. The next recipient did not appreciate the degree. When John Beaufort, Marquess of Dorset, was attainted and the House of Commons appealed to Richard II for it's restoration, Beaufort begged the King not to restore this particular title "as the name of Marquess is a strange name in this realm."
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The style of a marquess is Most Honourable. He is formally styled by the Sovereign, Our right trusty and entirely beloved cousin (and counselor when of the Privy Council).
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The title, Duke, (from Latin Dux, a leader) is the highest in the British Peerage. As there are no British "princes" outside the blood-royal, so pre-eminent in dignity is the ducal title that each royal prince, shortly after attaining his majority (age 21) is usually, but not always, created a Duke; the titular style of Prince, apart from the Prince of Wales, is a title of courtesy. Thus, Prince Henry, son of King George V, was created Duke of Gloucester, Prince Andrew, son of Queen Elizabeth II, was created Duke of York.
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Since the title Duke signified Sovereign status (William the Conqueror was Duke of Normandy) it was not adopted until 1337, when Edward III conferred the Dukedom of Cornwall on his eldest son, the Black Prince. This was followed by Henry Duke of Lancaster in 1351. The first subject to receive a dukedom who was not a member of the royal family, nor one nearly connected, was Sir William de la Pole, Marquess of Suffolk, who was created Duke of Suffolk in 1448.
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A Duke is styled Most Noble (or less formally His Grace), and by the Sovereign in public instruments, Our right trusty and right entirely beloved cousin, with the addition of and counselor when a member of the Privy Council.
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Though when conversing with my husband I often refer to the (male) spouse of a woman as "Mr Jane Doe" if I don't know his name.
This same-sex marriage issue again draws attention to the fact that the English system of peerages and associated inheritance laws is in many ways totally incompatible with modern notions of equality. 
