British Nationality Act 1948

The British Nationality Act 1948 (11 & 12 Geo. 6. c. 56) was an act of the Parliament of the United Kingdom on British nationality law which defined British nationality by creating the status of "Citizen of the United Kingdom and Colonies" (CUKC) as the sole national citizenship of the United Kingdom and all of its colonies.

The act, which came into effect on 1 January 1949, was passed in consequence of the 1947 Commonwealth conference on nationality and citizenship, which had agreed that each of the Commonwealth member states would legislate for its own citizenship, distinct from the shared status of "Commonwealth citizen" (formerly known as "British subject").

The CUKC consolidated British citizenship by putting Britain's colonial subjects on equal footing with those living in the British Isles, and was likely an attempt to avoid decolonisation. Similar legislation was passed in most of the other Commonwealth countries. The act was largely the result of a bipartisan ideological commitment to "a definition of citizenship including Britons and colonial subjects under the same nationality" and at a time "before large-scale migration was considered possible".

It formed the basis of the United Kingdom's nationality law until the British Nationality Act 1981, which came into force in 1983. Most of its provisions have been repealed or otherwise superseded by subsequent legislation, though parts remain in force.