National Statistical

Population estimates are widely used and highly valued. They inform important government decisions and policies at national and local levels, and provide the denominator for key statistics, including economic indicators such as GDP per head.  Here, Mary Gregory explains how and why the ONS is working to give users clearer, better information about the population in their area. 

In our previous blog we described how we’re looking to continuously improve our population estimates by drawing on a range of data sources. Today I’m sharing an update on the progress we’re making to better understand population change at national and local levels.  

The census, held once every 10 years, provides the benchmark for our population estimates. We then then update these annually using data on births, deaths, and both international and internal migration. This approach to producing our estimates is known as the cohort component method. 

The cohort component method is an internationally recognised approach. However, it becomes more difficult to produce population estimates when the information we start from reflects unusual circumstances, or when patterns of population change are less predictable. For example, Census 2021 took place during the coronavirus pandemic, when some people were living somewhere different from where they would usually be, such as students living at their family home. Since then, high levels of migration have driven rapid population change, adding further uncertainty and making it harder to accurately estimate where people live, particularly at a local level. 

Our role is to produce timely estimates that give users an accurate picture of the population at national and local levels, and to explain them clearly, so they can be used with confidence to inform decisions appropriately.   

New estimates 

Today we’ve published our mid-2025 population estimates – MYEs. They show the population has increased, albeit at a slower rate than in recent years. This is mainly due to lower levels of international migration. Alongside our latest estimates, we wanted to help users understand the data better, so we have also published several papers covering the impact of the pandemic on population estimates, why there is uncertainty in the data at a local level and the steps we’re taking to continuously improve our statistics. 

At the national level, we have high levels of confidence in our estimates. This is driven by  the reliable data on births and deaths that we get from registrations data. We also now have a good understanding of how many people are arriving in and leaving the country, thanks to the new methods we have developed for our international migration estimates. The Office for Statistics Regulation (OSR) has recognised these improvements to our migration statistics. 

At the local level, there is more uncertainty in our estimates. This has always been the case, but is particularly challenging in times of rapid change. The OSR has encouraged us to explain that more clearly. This is welcome feedback,  which we are committed to addressing. The suite of materials published today  are part of our response to meeting the OSR’s requirements and improving the experience of those who use our estimates. 

Local population statistics 

Census 2021 gave a brilliant snapshot of society at an extraordinary time. Even in more stable times, population estimates become more uncertain the further we move away from the census, especially in local areas. In times of rapid change – as we have seen recently – this is more pronounced.  

As our paper today explains, we cannot quantify the pandemic’s exact effect. We know that estimates from 2021 onwards carry greater uncertainty. 

Our paper on quality of local estimates, also published today sets out the main factors affecting the quality of local estimates, using practical examples, so users of the estimates can interpret them and understand what this means for how they should be used. 

Our published statistics remain the best available official estimates of the population, but are subject to uncertainty, particularly for some local authorities and population groups where movement can be harder to measure precisely.  

Places with greater uncertainty include cities like Oxford or Manchester. They have higher population churn, including more international migration, high levels of internal migration and large student populations. Areas with more stable populations, like North Lincolnshire and Caerphilly, generally have lower uncertainty. Our interactive tool enables users of our estimates to explore the population in their area. 

The local estimates are well suited to understanding broad patterns. They can be used for comparing areas and supporting planning and policy decisions. However, it is important to consider uncertainty associated with each area and how the population groups outlined can impact your local area. 

Continuous improvement 

We know users need population estimates they can trust, understand and use with confidence. Our improvement plan is about strengthening the evidence behind the estimates and being clearer about uncertainty. 

In recent years we’d been working to build a population statistics system using more administrative data (such as health, tax, and education records). We assessed that the best way forward is to introduce changes gradually, rather than move to a new system all at once. Earlier this year we shared our change in approach, to one of continuous improvement, whereby we committed to continuing to make iterative improvements to the data and methods that underpin the components of population change. 

Our improvement plan sets out how we will strengthen the data, methods and engagement that underpin population estimates over the next two years. It outlines how we aim to improve accuracy, especially in areas with high migration and student populations, while maintaining trustworthiness, quality, and value expected of official statistics. 

Administrative data are fundamental to both current methods and future improvements to population estimates. We’ve already learnt a lot about how to make use of administrative sources collected across government, so our estimates better reflect real population change. Our approach also focuses on building a sustainable supply of data and improving data linkage practices.  

In practice, this means testing whether other data sources can help us better understand different parts of the population and give us greater confidence in our estimates. We are exploring whether new data sources could improve the quality of our data inputs and methods. This includes administrative sources covering pre-school and school-age children, which could improve our estimates of the number of children in the population. We’re also looking to improve the coverage of the working age population drawing on HM Revenue and Customs (HMRC) Real Time Information data, Department for Work and Pension (DWP) Registration and Population Interaction Database (RAPID) and NHS prescriptions data.  

We’re also looking at how to improve information on moves within the UK, including considering the use of Driving and Vehicle Licensing Agency (DVLA) data and HESA graduate outcomes survey information. 

We are working towards producing even better population statistics in the future, and are encouraged by the opportunities new data sources could bring.  

We welcome feedback on our plans and will keep users updated through regular engagement and publications, including our next quarterly update on 11 August. If you would like to leave feedback, contact us at pop.info@ons.gov.uk.