Population Information Sources
The only full count of the population takes place every ten years at the time of the Census, the latest being in 2011. In between Censuses, the Office for National Statistics (ONS) produce annual 'estimates' of the population, using survey data and administrative registers to update the previous Census data. Once a new Census is carried out, these estimates are revised. The components of population change are births, deaths and migration. Although data on births and deaths is considered very reliable, data on migration is not and this is where much of the uncertainty lies in estimating population between Censuses. The Census also provides a wealth of more detailed information on social and economic characteristics of the population and is available for very small areas.
A Census has been carried out every 10 years since 1801 (except for 1941) but the future of the Census is currently uncertain as Central Government look to reduce financial costs. The National Statistician (Chief Executive of the UK Statistics Authority) has recommended an online census in 2021 rather than a paper based form, combined with increasing use of adminstrative data and surveys to improve population estimates in between censuses. No decision has yet been made by Central Government.