The National Registration Act 1939 (2 & 3 Geo. VI c. 91) was an Act of Parliament in the United Kingdom. It became law on 5 September 1939 as an emergency measure at the start of World War II. The Act established a National Register which began operating on 29 September 1939, a system of identity cards, and a requirement that they must be produced on demand or presented to a police station within 48 hours. The law was repealed on 22 May 1952. The last person prosecuted under the Act was Clarence Henry Willcock.