The Census Act 1991 was an Act of Parliament

Act of Parliament

An Act of Parliament is a statute enacted as primary legislation by a national or sub-national parliament. In the Republic of Ireland the term Act of the Oireachtas is used, and in the United States the term Act of Congress is used.In Commonwealth countries, the term is used both in a narrow...

 of the Parliament of the United Kingdom

Parliament of the United Kingdom

The Parliament of the United Kingdom of Great Britain and Northern Ireland is the supreme legislative body in the United Kingdom, British Crown dependencies and British overseas territories, located in London...

. It gained Royal Assent on the 7th March 1991.

The Act amended Section 8 of the Census Act 1920

Census Act 1920

The Census Act 1920 is an Act of the Parliament of the United Kingdom. Providing for a census for Great Britain , on a date to be fixed by Order in Council, it remains the primary legislation for the provision of the UK census in England, Scotland, and Wales...

 by replacing a subsection concerning penalties for the unlawful disclosure of personal information from the census.

The Act applies to Great Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

. Separate legislation in the form of the Census (Confidentiality) (Northern Ireland) Order 1991 exists for Northern Ireland.