The statutory authority for taking a Census in Great Britain (that is in England, Wales and Scotland) is the Census Act of 1920 as amended by the Census (Confidentiality) Act 1991. This makes provision for the taking of a census from time to time (but no more frequently than every five years). The Act gives power to the Government of the day, if Parliament agrees, to ask the Queen to make an Order in Council directing that a census be taken on a particular day. The duty for carrying out a census rests with the Registrar General for England and Wales (whose office is part of the Office for National Statistics) and the Registrar General for Scotland (General Register Office Scotland).
Parts of the Census Act 1920 were amended by the Statistics and Registration Service Act 2007 which came into force on 1 April 2008.
Similar, but separate, legislation (the Census Act (Northern Ireland) 1969) applies in Northern Ireland, where the Registrar General for Northern Ireland (whose office is part of the Northern Ireland Statistics and Research Agency) is responsible for carrying out the census.