Migration Observatory researchers at the University of Oxford have published an in-depth review concluding that gaps in official UK migration statistics leave the public and policymakers "in the dark" about the scale of migration.

Migration Observatory is an Oxford-based research group that produces data, analysis and commentary on migration for the public, media and policymakers. It sits within the university's Centre on Migration, Policy and Society (COMPAS).

The review, described as an "in-depth review of evidence gaps," documents holes across UK migration data. The Migration Observatory's headline finding: the gaps "leave the public and politicians in the dark."

Why do the gaps matter?

Migration figures drive political debate, legislative change and resource allocation in areas such as health, social care, housing and higher education. When datasets are incomplete, claims about migration become harder to verify and policy risks being shaped by partial evidence.

The UK's migration statistics have been contested for years. Debates over net migration, asylum backlogs and small boat arrivals often rely on figures that officials themselves describe as provisional. Researchers have repeatedly flagged that headline numbers can mislead when users do not understand their limits.

Which UK migration figures are most uncertain?

UK migration data comes from multiple official sources:

• The Office for National Statistics' long-term migration estimates
• Home Office asylum and resettlement data
• Department for Work and Pensions National Insurance number registrations
• Entry and exit checks at the border

The ONS revised its long-term migration methodology after the International Passenger Survey was paused in March 2020. Estimates for 2020 and 2021 carry wide confidence intervals. Researchers warn that uncertainty in the headline number affects every downstream policy calculation.

Home Office data on asylum applications and decisions is more complete than data on irregular migration. The size of the population without legal status in the UK is not directly measured by any official source.

What does the review recommend?

Migration Observatory calls for:

• Greater investment in administrative data linkage
• Clearer communication of uncertainty in official statistics
• Transparent explanations of methodological changes
• Publication of confidence intervals alongside headline figures

Since 2020, the ONS has shifted toward using administrative data — tax records, border crossings, visa records — to estimate flows. This approach promises better coverage but introduces new limitations, particularly for groups such as asylum seekers, refugees and those without formal status.

What happens next?

The review lands while the UK government debates legal migration rules and post-Brexit arrangements. Accurate data on arrivals, departures and the composition of the migrant population matters for staffing decisions in the NHS, social care, higher education and other sectors.

Policy debates frequently hinge on a single figure: the annual net migration estimate. When that figure carries wide uncertainty, arguments about whether migration is "too high" or "too low" rest on shaky ground. Researchers argue that the public is best served by honest reporting of what is and is not known.

Beyond migration policy

The implications extend well beyond migration rules. Local authorities use migration data to plan school places and housing. Universities draw on it to forecast international student numbers. Employers in agriculture, hospitality and health rely on workforce estimates that depend on migration figures.

Anyone making decisions that depend on UK migration statistics should consult the underlying methodology. Numbers quoted without their margin of uncertainty can mislead as easily as they inform.

Funding and independence

Migration Observatory receives funding from the University of Oxford and philanthropic grants. Its research outputs are independent of government.

The findings do not change the migration figures themselves. They change how those figures should be read. For policymakers, journalists and the public, the Oxford researchers' message is the same: official statistics tell part of the story, never the whole of it.