This list contains some suggestions for where to start with books or other reference materials. Please also make sure to look at the references list for any of these items. You can use the authors' research to jumpstart your own research!
Black Experience and the Empire
British Imperialism
Cambridge History of the British Empire by 
Colonialism and Development Britain and Its Tropical Colonies, 1850-1960
Companion to Contemporary Britain, 1939-2000
Companion to Early Twentieth-Century Britain
Companion to Nineteenth-Century Britain
Decline and Fall of the British Empire, 1781-1997Great Britain: Foreign Policy and the Span of Empire, 1689-1971; a Documentary History
Settlers and Expatriates : Britons Over the SeasGreat Britain: the Lion at Home: a Documentary History of Domestic Policy, 1689-1973
Empire and Globalisation : Networks of People, Goods and Capital in the British World, c.1850-1914
Ireland and the British Empire
Oxford History of the British Empire
Britain and the Americas: Culture, Politics, and History: a Multidisciplinary Encyclopedia
Cambridge Historical Encyclopedia of Great Britain and Ireland
Colonialism: an International, Social, Cultural, and Political EncyclopediaEmpire and Globalisation: Networks of People, Goods and Capital in the British World, c.1850-1914
Encyclopedia of British Women’s Writing, 1900-1950Encyclopedia of the Victorian Era
Illustrated Dictionary of British History
Oxford Dictionary of National Biography
Oxford Encyclopedia of British LiteratureVictorian Britain : an EncyclopediaAnnual Bibliography of British and Irish History by Bibliography of British History, 1789-1851Bibliography of British History, 1851-1914Bibliography of British History, the Eighteenth Century, 1714-1789
Bibliography of British History. 1914-1989British Diaries: an Annotated Bibliography of British Diaries Written Between 1442 and 1942
Eighteenth-Century Constitution, 1688-1815, Documents and CommentaryGuide to the Sources of British Military HistorySources in British Political History, 1900-1951Writings on British History by