Peerage of the United Kingdom
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The Peerage of the United Kingdom and British Empire comprises most peerages created in the United Kingdom of Great Britain and Ireland after the Act of Union in 1801, when it replaced the Peerage of Great Britain. New peers continued to be created in the Peerage of Ireland until 1898 (the last creation being Baron Curzon).
The last non-royal dukedom was created in 1900, and the last marquessate in 1936. Creation of the remaining ranks mostly ceased once Harold Wilson's Labour government took office in 1964, and only four non-royal hereditary peerages have been created since then. These were:
- John Morrison, 1st Baron Margadale, 1965
- William Whitelaw, 1st Viscount Whitelaw, 1983 (extinct 1999)
- George Thomas, 1st Viscount Tonypandy, 1983 (extinct 1997)
- Harold Macmillan, 1st Earl of Stockton, 1984
Until the House of Lords Act 1999 was passed, all peers of the United Kingdom were automatically members of the House of Lords. However, from that date, most of the hereditary peers ceased to be members as part of Parliamentary reform, whereas the life peers retained their seats. All hereditary peers of the first creation (i.e., those for whom a peerage was originally created, as opposed to those who inherited a peerage from an ancestor), and all surviving hereditary peers who had served as Leader of the House of Lords were offered a life peerage in order to allow them to sit in the House should they so choose.
Marquesses, Earls, Viscounts and Barons are all addressed as 'Lord X', where 'X' represents either their territory or surname pertaining to their title. Marchionesses, Countesses, Viscountesses and Baronesses are all addressed as 'Lady X'. Dukes and Duchesses are addressed just as 'Duke' or 'Duchess' or more commonly, 'Your Grace'.
Lists of peers
- Dukes: see List of dukes in the peerages of Britain and Ireland
- Marquesses: see List of marquesses in the peerages of Britain and Ireland
- Earls and countesses: see List of earls
- Viscounts: see List of viscounts in the peerages of Britain and Ireland
- Hereditary barons: see List of hereditary baronies in the Peerage of the United Kingdom
- Life barons and baronesses: see List of life barons and baronesses in the Peerage of the United Kingdom
- Women: see List of peerages created for women and List of peerages inherited by women
Whitaker's Peerage, Baronetage, Knightage, and Companionage for the Year .... was the general print reference of those in the system for the twentieth century 
- "The Dukes of the Peerage of the United Kingdom". Retrieved 2008-05-11.
- Whitaker's peerage, baronetage, knightage, and companionage for the year, [s.n.], 1907, retrieved 14 January 2012 the title page continued with: "Containing an extended list of the Royal family, the peerage with titled issue, dowager ladies, baronets, knights and companions, privy councillors and home and colonial bishops with a comprehensive introduction and an index to country seats" (text varies between editions). starting in the mid1890's the publication continues.