Britain vs United Kingdom

Britain

name
  • The British Empire. 

  • Brittany. 

  • The British Isles. 

  • The island of Great Britain, consisting of England, Scotland and Wales, especially during antiquity. 

  • The British state and its dominions and holdings; the British Empire. 

  • The United Kingdom. 

United Kingdom

name
  • The Kingdom of Great Britain (1707–1801). 

  • A kingdom and sovereign state in Western Europe comprising the four countries of England, Scotland and Wales in the island of Great Britain, and Northern Ireland in the island of Ireland. Since 1922. 

  • Kingdom consisting of several constituencies, actual, historical, or hypothetical. 

  • The United Kingdom of Great Britain and Ireland (1801–1922). 

How often have the words Britain and United Kingdom occurred in a corpus of books? (source: Google Ngram Viewer )