Population and census

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The 2021 Census

The Office for National Statistics (ONS) is undertaking the next decennial Census in England and Wales on Sunday 21 March 2021.


The Census has run every 10 years since 1801 across the UK. The Census collects information on the demographics of residents (such as age, gender, ethnicity, religion, health and living arrangements), their housing, mode of travel to work and employment. New questions for this Census ask about sexual orientation, gender identity and previous service in the Armed Forces. Details of all the questions on the Census forms are on the ONS website. 

Census data provides some information that is not available elsewhere and at a level of detail that is not obtainable from other government surveys – information is available about small population groups, and for small geographic areas. It is currently the gold standard of data and will be used to re-calibrate population estimates for the next 10-year period.


Why is it important?

The Census is not just a headcount, it is vital in making informed policy decisions by providing accurate information on local demographics, housing, employment and need. The information it collects helps with decisions on the planning and funding of council run services in local areas, along with where schools, doctors’ surgeries and emergency services are needed most. Accurate population figures and detailed information about need are important in determining the funding of key public services, as well as for the voluntary and community sector and businesses. Following a decade of funding cuts and the ongoing financial impact of Covid-19, London boroughs will be financially stretched for the next few years. It is vital that accurate numbers are collected. 


London’s low response rate 

In London, historically, only 9/10 people fill in the Census questionnaire. It usually has the lowest response rate of all regions and is home to most of the local authorities with the lowest response rates in England. The issues persist, as the 2019 Census dress rehearsal response rates for London areas remained much lower than elsewhere. 

There are several reasons for this, including:

  • Migration – London is a world city. The latest ONS country of birth data shows that around one in three Londoners were born overseas, compared with one in seven in the rest of the country. These higher levels of migration mean, generally, London has a more transient population than other areas. Lack of familiarity with the Census and understanding of its importance, both contribute to low response rates. 
  • Language barriers – 300 languages are spoken in the capital. 2020 DfE data shows that less than half the children in London schools are reported as having English as a first language (falling as low as 31 percent in Newham).
  • Household structures – London has a high concentration of households with hard-to-count characteristics, such as houses in multiple occupation (HMO), split properties and large households. 
  • Homelessness – some people may not receive, or complete, a form due to their temporary circumstances and this could lead to missed or ‘concealed’ households, who may have the greatest needs. 
  • Housing – the prevalence of gated buildings, student halls of residence and properties with push-button access pose a challenge for the delivery of Census forms and follow up using face-to-face methods. 

To compensate for low response rates, the ONS assigns characteristics to people it has no information about. Unfortunately, groups with the highest levels of need tend to have the lowest response rates, meaning that London could once again be hit by a double whammy, as the people undercounted in the Census are precisely those more likely to need local authority support. Estimating the characteristics of these missing populations cannot be a substitute for counting them in the first place.


Why is the 2021 Census different?

The 2021 Census is different and marks an important shift to going digital, with the ambition of 75% of form completion online. London Councils’ response to the 2013 consultation on future approaches to the Census is attached. This may be the last Census of its kind, as there is a strong push from government to use administrative data to provide the information collected instead. The Census Transformation Programme is exploring the administrative data sources and how this could be achieved. Therefore, it is vital that this Census is as accurate as possible to act as a comparator to these future administrative data sets.


What about the impact of the Covid-19 pandemic on the 2021 Census?

ONS will go ahead with the Census on March 21st 2021 and have a contingency plan to ensure that everyone can provide their information safely and securely. Full details are outlined in their operational plan: https://www.ons.gov.uk/census/censustransformationprogramme/censusdesign/operationalplanningresponsetothecoronaviruscovid19forcensus2021englandandwales


Data collection is safe, secure and confidential

Published statistics from the Census are completely anonymous, so no personal information is published. The ONS is independent from government, so census information cannot be used to influence benefit claims, a residency application, immigration status or your taxes. The information collected is kept confidential by ONS and protected by law. Personal census information is kept confidential for 100 years and has a 200-year track record of never sharing it. It is a criminal offence to disclose information and all census staff and contractors sign a census confidentiality undertaking.

Important dates​

  • 01 March 2021 - Census Support Centres start operation
  • 21 March 2021 - Census day
  • 25 March – 19 April 2021 – up to three reminder letters sent

Links to additional information

General information on the 2021 Census on the ONS website 

Latest news on the preparations for the census

Link to our recent full Member Briefing on the 2021 Census 


2011 Census results

London’s population has grown rapidly over the past decade. By the time of the last census in 2011 it had grown to 8.2 million, 14% from 2001. Projections are for it to reach around 9 million by 2021. As well as such growth, the diversity, churn and mobility make estimating population numbers and characteristics profoundly difficult. More information about the 2011 Census and the results can be found on the ONS website.