Mary Gregory to Ed Humpherson: Plans for mid-year population estimates

Dear Ed,

We are writing to update you on our plans for improving how we produce population estimates for England and Wales. Firstly, we would like to thank the Office for Statistics Regulation for its 2024 assessment on our Admin based Population estimates, and the team’s continued engagement over the past 18 months. The requirements and recommendations, along with continued discussions have helped us greatly whilst working through challenges.

At the end of 2025, we made the decision to assess progress against the mid-year population estimates acceptance criteria early, these criteria were developed in response to the 2024 assessment requirements. On the basis of this assessment, we concluded ONS is not in a position to move to new methods for mid-year estimates in summer 2026.

In light of this and the hold a census in 2031 announcement, we undertook a fuller review to consider our approach to producing mid-year population estimates. An array of evidence was considered including user feedback, published materials and extensive interviews with methodological experts, data teams and production teams.

The evidence demonstrated clear value in the administrative data sources and modelling approaches developed to date. However, it is clear that we need to consider the best approach to mid-year population estimates in light of progress on new methods and the changed context. We have concluded that official mid-2025 annual population estimates for England and Wales will be published using current established methods. Admin Based Population Estimates (ABPEs) will not be produced for publication.

We will continue to make improvements to methods used to produce mid-year populations, learning from our work to date, and moving towards a continuous improvement approach. This approach should mitigate the risk associated with a ‘step- change’ to population estimates and impact on UK population estimates.

We anticipate making greater use of administrative data as we make these improvements, with our early focus being on improving key inputs that underpin the estimates. We will focus on improving methods for estimating internal migration and disaggregating long-term international migration at a local authority level. This work will build on what we have learnt through our methods development activity to date.

An announcement of our plans has been published today in the Quarterly update on population and migration statistics. This was accompanied by a suite of articles relating to population estimates and census, and we will continue to engage with our stakeholders through webinars, working groups, and newsletters.

The articles published today include:

Given this change, we are asking you to close the phase 1 assessment on ABPEs and can confirm that we no longer require the second phase of the assessment as originally discussed in our previous correspondence. We are keen to continue to work with you as we develop mid-year estimates and look forward to receiving the report on the current OSR compliance review of MYEs.

We will of course continue to update OSR on our plans and progress.

Best wishes,

Mary Gregory

Executive Director, Population, Census and Social Statistics