Ed Humpherson to Mary Gregory: Response to ONS plans for mid-year population estimates

Dear Mary,

Thank you for your letter of 4 March 2026 setting out the Office for National Statistics (ONS)’s revised plans for the production of mid-year population estimates for England and Wales.

We note that the requirements and recommendations from our assessment of admin-based population estimates for England and Wales have helped ONS consider its future plans to improve population estimates. We also acknowledge the open communication of these plans to users, using criteria recommended by the Office for Statistics Regulation (OSR), as well as the supporting materials published alongside the announcement.

ONS’s decision to continue with its current methods

We recognise the significance of ONS’s decision to no longer move to Admin-Based Population Estimates (ABPEs) as the official headline measure and to continue with established methods for producing the mid‑year 2025 population estimates (MYEs). Your letter, alongside the supporting publications released on 4 March, provides transparency in setting out the evidence considered, the challenges encountered, and the rationale for this revised approach.

At the same time, the announcement also highlights important areas for improvement within the current system, such as the methods used to estimate internal migration and disaggregate long-term international migration at a local authority level. These limitations may understandably lead some users to question the continued reliance on existing methods. Your openness in presenting both the strengths and limitations and developing goals and objectives is therefore essential for maintaining public confidence in this significant change of direction.

Role of OSR’s regulatory work and user feedback

As the official population estimates, the MYE must continue to demonstrate compliance with the Code of Practice for Statistics. It remains essential that user feedback continues to guide ONS’s priorities and continuous improvement plans for its population estimates.

We initiated a compliance review in 2025 to ensure that the MYEs, as accredited official statistics, continue to meet the standards of the Code, and to seek user views on ONS’s development of the ABPE. We plan to publish the findings of our review of the MYEs in May 2026, before the next publication of the mid-year 2025 estimates.

On the development of the ABPEs, users we spoke to as part of our review said they continued to value ONS’s ambition to improve methods through greater use of administrative data and the clarity of ONS’s decision-making approach. But they also highlighted the need for:

clearer communication of the impacts of transitioning to new methods, including revisions, time‑series consistency and implications for related statistics
more consistent and transparent engagement, noting positive experiences of local authorities’ that are part of the ABPE pilot group but limited follow-up elsewhere
improved support to help users understand the complexity of the ABPE methods, with few having read the latest guidance
greater assurance around the accuracy of the new ABPE method, given mixed levels of confidence and ongoing uncertainty related to Census 2021

These views remain highly relevant and should play a central role in shaping the next phase of development for population estimates. Our review should help inform the priorities and areas of focus for ONS.

Closure of the ABPE assessment and importance of retaining progress

We note your request to close the Phase 1 assessment of the ABPEs and confirm that we are content to do so. When I last wrote to ONS in August 2025, I recognised the substantial amount of work and effort that your teams have put into the development of the ABPEs. It is essential that this significant development work is conserved and built upon.

We strongly encourage ONS to reflect on the lessons learned and to consider how the 2031 census can be used to benchmark and validate any future methodological developments. Census 2031 will provide an opportunity to assess the quality of alternative data sources, improve calibration and help inform the long-term direction of population statistics.

Thank you for your constructive engagement. We will remain in touch as our compliance review progresses over the coming months.

Yours sincerely,

Ed Humpherson
Director General for OSR