The National Registration Act 1939 (2 & 3 Geo. VI c. 91) was an Act of Parliament in the United Kingdom. The initial National Registration Bill was introduced to Parliament as an emergency measure at the start of World War II. Royal assent given on 5 September 1939. The Act established a National Register which began operating on 29 September 1939 (National Registration Day), a system of identity cards, and a requirement that they must be produced on demand or presented to a police station within 48 hours.