query: How many royal dukes are there in the UK peerage?
passage: List of dukes in the peerages of Britain and Ireland
This is a list of the 31 present and extant dukes in the peerages of the Kingdom of England, Kingdom of Scotland, Kingdom of Great Britain, Kingdom of Ireland, United Kingdom of Great Britain and Ireland, and the United Kingdom of Great Britain and Northern Ireland 1927 and after. For a more complete historical listing, including extinct, dormant, abeyant, forfeit dukedoms in addition to these extant ones, see List of dukedoms in the peerages of Britain and Ireland.
passage: History of the British peerage
In 1801, Ireland united with Great Britain to form the United Kingdom. Ireland became entitled to elect twenty-eight of their number to sit in the House of Lords as representative peers. Unlike the Union of Scotland and England, the Crown retained the right to create one new Irish peerage dignity every time three previous ones became extinct, until the number of Irish peers without British peerages amounted to one hundred, when further creations would be permitted as often as necessary to maintain that number. Since Irish peers were not automatically entitled to representation in the Lords, individuals could be created Irish peers so as to honour them without further swelling the numbers of the House of Lords. There were only 21 creations of new Irish peerages after the Union; all other new peerages since 1801 have been created in the Peerage of the United Kingdom.