First, and foremost, one must understand the creation of peerages is a royal prerogative. Letters patent are used exclusively now for this task, but this was not always so. Letters patent are a form of open or public proclamation and a vestigial exercise of extra-parliamentary power by a monarch. Prior to the establishment of Parliament, the monarch ruled absolutely by the issuing of his personal written orders, open or closed. They can be contrasted with an Act of Parliament, which is in effect a written order by Parliament involving assent by the monarch in conjunction with its members. However, we must understand, there is no explicit government approval contained with letters patent, only a seal or signature of the monarch.

Parliament today tolerates only a very narrow exercise of the royal prerogative by issuance of letters patent, and such documents are issued with prior informal government approval, or indeed are now generated by government itself with the monarch’s seal affixed as a mere formality. In their original form they were simply written instructions or orders from the sovereign, whose order was law, which were made public to reinforce their effect. For the sake of good governance, it is of little use if the sovereign appoints a person to a position of authority but does not at the same time inform those over whom such authority is to be exercised of the validity of the appointment.

Wikipedia provides a chart as to the wording of a letters patent for dukes/duchesses, marquesses/marchionesses, earls/countesses, viscounts, hereditary barons, life barons, etc., for those who are interested in the subject.

The patent bears the Great Seal but no signature. It describes how the title may descend after the death of the person who has been ennobled. This is called the “remainder.”

“. . . unto him and the heirs male of his body lawfully begotten and to be begotten. Willing and by these Presents granting for Us Our heirs and successors that he and his heirs male aforesaid and every of them successively . . .”

Customarily, the title is limited to the male heirs of the body, legally begotten, but some patents contain what is known as a “special remainder,” meaning other members of the family (daughters, brothers, sisters, nieces, nephews, etc.) may inherit the title.

Usually there is a limitation on the remainder, i.e. the title is limited to the male heirs of the body, legally begotten (i.e. legitimate), but some patents contain a special remainder, whereby other members of the family (for example, daughters, brothers or sisters or their children) may inherit the title.

The letters patent created for Charles Portal, 1st Viscount of Hungerford, Horatio Nelson, 1st Viscount Nelson, Louis Mountbatten, 1st Earl Mountbatten of Burma (Prince Philip’s uncle), Edmund Allenby, 1st Viscount Allenby, and the like were all created peers with a special remainder as none had male issue to inherit. Having the letters patent worded, as such, allowed the peerage to survive beyond the peer’s life span.

In contrast to letters patent, the earliest peerages, meaning the English baronies, were created by writ of summons to Counsel or Parliament. Successors of the more important baronies received a like summons, creating what we now know as a hereditary barony, rather than a life baron.

Life peers are appointed to the peerage, but their titles cannot be inherited. Modern life peerages, always given the rank of “baron,” are created under the Life Peerage Act 1958. They provide the holder a seat in the House of Lords, as long as the person meets the qualification of age and citizenship. Their children cannot inherit a Life Peerage, but they can style themselves with the prefix “The Honourable.”

“The remainders of baronies by writ, having no patent, are not limited to ‘heirs male’, but to heirs-general. So, for instance, if such a baron died without leaving a male heir, but leaving a sole daughter, this daughter would be permitted to inherit the barony.

“Should there be more than one daughter, the title will fall into abeyance between the co-heirs. The co-heirs should come to an honourable agreement (ie without bribery or corruption) as to which of them is to claim the title, and then the claimant may petition The Crown to have the abeyance terminated. A claimant must represent at least a third share of the abeyant title, and the title must not have been in abeyance for more than a hundred years. The Sovereign may terminate an abeyance by exercise of the royal prerogative.

“If, in the fullness of time, the co-heirs to an abeyant peerage diminish to a single heir, the claimant may assume the title without petition to The Crown. Recent examples of peerages being called out of abeyance include Strange 1986, Grey of Codnor 1989, Berners 1995, Arlington 1999 and Howard de Walden 2004.

“Historically, there was also a doctrine of baronies by tenure. These were feudal titles which were held by possession of land and castle (most famously Fitzalan of Arundel Castle, who successfully petitioned to be considered Earl of Arundel in 1433). Most claims to baronies by tenure, however, were challenged in the House of Lords and, in 1861, the Committee for Privileges of the House of Lords decided that, irrespective of whatever might have been the position in the past, baronies by tenure no longer existed.” [Creation and Inheritance of the Peerage]

Keep in mind the Peerage of Scotland and the Peerage of Ireland do not follow the same rules. There are variations, dictated by the “limitation.”

The legal definition of peerage is an artificial dignity associated with nobility, in accordance to the words of limitation contained in the grant (of peerage).

Another kink not mentioned previously is the idea of “dissenters.” In the Regency, in which I write, any one who had the right pedigree could inherit a title. However, not every peer could sit in Parliament. Those who had an English or UK peerage, not being female or under age, had to take an oath, essentially swearing they abjured the Pope. Catholics peers, therefore, could not sit in the House of Lords.

For example, the Duke of Norfolk, is the premier duke in the peerage of England and the premier earl as the Earl of Arundel. In addition to the ducal title, the dukes of Norfolk also hold the hereditary position of Earl Marshal, which has the duty of organizing state occasions such as coronation and the opening of Parliament. For the last five centuries, save some periods when it was under attainder, both the dukedom and earl-marshalship have been in the hands of the Howard family. Even today, due to the duties of Earl Marshal, Norfolk is one of two hereditary peers automatically admitted to the House of Lords, without being elected by the general body of hereditary peers.

Additionally, in the State of Opening of Parliament, the Duke of Norfolk is one of four individuals who precede the monarch and one of the two who walk facing backwards, meaning facing the monarch (although in recent years, we have not seen this tradition carried forward). The Duke of Norfolk also is head of the College of Arms, through which he regulates all matters connected with armorial bearings and standards. He is one of three claimants to the title of Chief Butler of England

The Duke of Norfolk (1746 – 1815) for a time had to do his ceremonial duties as Earl marshal of England through a Protestant because he was a  Catholic. One of the Dukes became a Protestant until the law changed. That duke was Charles Howard, 11th Duke of Norfolk. Norfolk renounced his Catholicism to start his political life, but remained a staunch supporter of Catholic Emancipation, as well as opposing the war with the American colonies. He sat in Parliament from 1780 to 1784 and became a lord of the treasury in the Portland cabinet in 1783. He succeeded to the title of 11th Duke of Norfolk in 1786 upon the death of his father. Eventually he was dismissed from the lord lieutenancy of the West Riding in 1798 for toasting “Our sovereign’s health—the majesty of the people” in terms displeasing to George III. [Charles Howard, 11th Duke of Norfolk]

Charles Howard was followed by his cousin. Bernard Howard, 12th Duke of Norfolk, was an ardent Roman Catholic, like most of his family. He strongly supported Catholic Emancipation, giving offence to his Protestant neighbours by hosting a banquet to celebrate the passage of the Roman Catholic Relief Act 1829.

After the English Reformation, from the 16th to the 19th century those guilty of such nonconformity, termed “recusants”, were subject to civil penalties and sometimes, especially in the earlier part of that period, to criminal penalties. Catholics formed a large proportion, if not a plurality, of recusants, and it was to Catholics that the term initially was applied. Non-Catholic groups composed of Reformed Christians or Protestant dissenters from the Church of England were later labelled “recusants” as well. Recusancy laws were in force from the reign of Elizabeth I to that of George III, but not always enforced with equal intensity. However, if a Dissenter could take the oath and the 39 articles, he could take a seat in Parliament. If he objected, depending upon the time period in which he lived, he could be charged with treason.

To become more familiar with the Oath of Supremacy – quick overview from Wikipedia.