The British Peerage is is made up of two parts, the first part is the Five Degrees of the Peerage the second is the Five Classes of the Peerage, namely;
The distinction between the five different classes mirrors the constitutional development of the British state from the orginal constituent kingdoms into the entity known as Great Britain and later the United Kingdom.1
Before the year 1707 there were separate peerages for each of the three kingdoms within the British Isles, since each of these separate kingdoms had their own parliament in which peers could serve. Wales fortunately or unfortunately, does not get a look in, as it was always considered as part and parcel of England for these purposes, and did not have its own parliament. 2
Scotland was of course an entirely separate kingdom that had its own separate line of kings until 1603 who naturally created their own peers to sit in their own parliament. Even after 1603 when Scotland and England shared the same Stuart rulers, they continued to have separate parliaments, and the same king wearing a different crown continued to separately create Scottish and English peers.
As far as Ireland was concerned, from the end of the twelfth century onwards, the kings of England also considered themselves as Lords of Ireland and busily created peerages within Ireland who eventually took up residence in the entirely separate Irish Parliament.
The Act of Union 1707 abolished the separate Scottish Parliament but whereas peers in the Peerage of England continued to have the automatic right to sit in the new combined House of Lords, peers in the Peerage of Scotland did not, and only attended Parliament on a representative basis. (See representative peer.)
Following the union of 1707 new peerage creations formed part of the The Peerage of Great Britain, except that peers continued to be created in Ireland within the Peerage of Ireland to sit in the Irish House of Lords. This continued until the Act of Union 1801 which abolished the separate Irish Parliament. As before, the old Irish peers where only allowed to sit in the united House of Lords on a representative basis.
Therefore since 1801 all new creations have formed part of the Peerage of the United Kingdom, with the exception that there was a strictly limited ability to create new Irish peers in order to maintain their number at a hundred. In any event, the creation of Irish peers ceased altogether in 1919 when the Irish Free State came into being.
It is also worth noting that none of the above placed any restriction on who might be alloted a peerage; for example, it was quite possible for Scotsmen to be English peers and vice versa. (In fact a number of Scottish kings such as David I also held titles in the Peerage of England.)
Neither did they place on restrictions on what kind of titles could be granted; the British Peerage has included creations with such diverse territorial designations as Holland and Burma and was therefore quite able to accomodate the notion of an English peer holding a title named after a location in Ireland.
There are, as you would imagine, a number of titles that were originally created in the Peerage of England, became extinct, were subsequently re-created in the Peerage of Great Britain, and later even re-created once more in the Peerage of the United Kingdom, so that historically speaking any particular dignity may well have existed in two or three separate classes.
In terms of the current holder of any particular title, what matters is when the title he inherited (and it is almost universally a he) was created; as this determines in which class his title belongs. The fact that there were previous creations held by different families is neither here nor there.
Some people will tell you that the distinction between each class of peerage is important, as a for example, peer who holds a title created in the Peerage of Great Britain has precedence over a peer who holds a title of the same degree created in The Peerage of the United Kingdom. This is true, but order of precedence works on the basis that the older creation has precedence over the younger in any case.
NOTES
1 To summarise;
Great Britain = Scotland + England
United Kingdom = Great Britain + Ireland
2 Peers have of course been created bearing territorial titles that were derived from Wales - e.g. Earl of Pembroke, Earl of Carnarvon, Marquess of Anglesey) et al - but they remain Peers of England etc.
SOURCES
- British Titles of Nobility
http://laura.chinet.com/html/titles01.html
- The 1911 Encyclopedia Brittanica entry for PEERAGE See http://1911encyclopedia.org/index.htm
- Charles Arnold Baker The Companion to British History (Longcross Press, 1996)