UNITED KINGDOM
Figures on this page present estimates of the UK’s irregular migration population between 2008 and 2023 and corresponding assessments of their quality, which were compiled and carried out under the MIrreM project. MIrreM outputs related to the UK are grouped below.
Estimates can be viewed as a number, as a share of the total population and as a share of the foreign-born population not covered by free movement policies (i.e., in Europe, those who were born in countries outside of EU Free Movement and in the UK and Ireland, those who were born outside of the Common Travel Area)… see more
ESTIMATED NUMBER OF IRREGULAR MIGRANTS BY YEAR
Source: View tooltips for links to the sources of the irregular migration estimates, which are compiled and assessed in Kierans, D., Vargas-Silva, C., Ahmad-Yar, A.W., Bircan, T., Cacciapaglia, M., Carvalho, J., Cassain, L., Cyrus, N., Desmond, A., Fihel, A., Finotelli, C., Gonzalez Ramos, M.P., Heylin, R., Jauhiainen, J.S., Kraler, A., Leerkes, A., Rössl, L., Schütze, T., Siruno, L., Sohst, R. 2024. MIrreM Public Database on Irregular Migration Stock Estimates (version 3). Krems: University for Continuing Education Krems (Danube University Krems).
Note: Many of the estimate pictured are not directly comparable because, for example, they use different methodologies, make different assumptions or cover different population groups. This in turn affects the aggregate figure. Markers are likely to overlap when all population groups are selected and there are multiple estimates for a single year. This chart reflects the March 2025 update PEW made to their UK estimates following the identification of a problem in the underlying data by the University of Oxford’s Migration Observatory.
ESTIMATED PERCENTAGE OF IRREGULAR MIGRANTS BY YEAR
Source: View tooltips for links to the sources of the estimates, which are compiled and assessed for their quality in Kierans et al., 2024, and the population statistics used to calculate the percentages. Note: Many of the estimates pictured are not directly comparable because, for example, they use different methodologies, make different assumptions or cover different population groups. This in turn affects the aggregate figure. For estimates without a reported range, the single or central figure is recorded as both the high and low estimate. As a result, the two markers overlap in the chart, representing the same value. Due to the behaviour of the mapping software, the high estimate may visually obscure the low estimate in these cases. When in doubt, refer to the table below. When all population groups are selected and there are multiple estimates for a single year, markers may overlap. This chart reflects the March 2025 update PEW made to their UK estimates following the identification of a problem in the underlying data by the University of Oxford’s Migration Observatory.
Source: View tooltips for links to the sources of the irregular migration estimates, which are compiled and assessed in Kierans et al., 2024, and the population statistics used to calculate the percentages. Note: (*) The foreign-born (FB) population excludes people born in countries that are a part of a free movement agreement with the destination country. Many of the estimates pictured are not directly comparable because, for example, they use different methodologies, make different assumptions or cover different population groups. This in turn affects the aggregate figure. For estimates without a reported range, the single or central figure is recorded as both the high and low estimate. As a result, the two markers overlap in the chart, representing the same value. Due to the behaviour of the mapping software, the high estimate may visually obscure the low estimate in these cases. When in doubt, refer to the table below. When all population groups are selected and there are multiple estimates for a single year, markers may overlap. This chart reflects the March 2025 update PEW made to their UK estimates following the identification of a problem in the underlying data by the University of Oxford’s Migration Observatory.
DATA TABLE
| Row | Country | Quality | Quality score | Year | Low Estimate | High Estimate | Total population | FB_population | Low estimate as % of total population | High estimate as % of total population | Low estimate as % of FB population | High estimate as % of FB population | PopulationGroup | Estimate Source | Estimate URL | Total pop source | Total pop URL | FB pop source | FB pop URL | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 296 | United Kingdom | High | 11.5 | 2017 | 594000 | 745000 | 65844142 | 5683726 | 0.90% | 1.13% | 10.45% | 13.11% | All irregular migrants | Jolly, Thomas and Stanyer, 2020 | https://www.london.gov.uk/sites/default/files/final_londons_children_and_young_people_who_are_not_british_citizens.pdf | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 297 | United Kingdom | High | 11.5 | 2011 | 617000 | 861000 | 63022532 | 4979490 | 0.98% | 1.37% | 12.39% | 17.29% | All irregular migrants | LeMaitre, 2017 (presentation) | https://web.archive.org/web/20181130134006/https://gmdac.iom.int/sites/default/files/presentations/irregular%20migration/Georges%20Lemaitre.pdf | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 298 | United Kingdom | High | 11 | 2017 | 700000 | 900000 | 65844142 | 5683726 | 1.06% | 1.37% | 12.32% | 15.83% | All irregular migrants (including asylum-seekers) | PEW, 2019 (March 2025 update) | https://www.pewresearch.org/global/2019/11/13/europes-unauthorized-immigrant-population-peaks-in-2016-then-levels-off/ | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 299 | United Kingdom | High | 11 | 2017 | 700000 | 900000 | 65844142 | 5683726 | 1.06% | 1.37% | 12.32% | 15.83% | All irregular migrants (excluding asylum-seekers) | PEW, 2019 (March 2025 update) | https://www.pewresearch.org/global/2019/11/13/europes-unauthorized-immigrant-population-peaks-in-2016-then-levels-off/ | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 300 | United Kingdom | High | 11 | 2016 | 800000 | 1000000 | 65379044 | 5446866 | 1.22% | 1.53% | 14.69% | 18.36% | All irregular migrants (including asylum-seekers) | PEW, 2019 (March 2025 update) | https://www.pewresearch.org/global/2019/11/13/europes-unauthorized-immigrant-population-peaks-in-2016-then-levels-off/ | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 301 | United Kingdom | High | 11 | 2016 | 800000 | 1000000 | 65379044 | 5446866 | 1.22% | 1.53% | 14.69% | 18.36% | All irregular migrants (excluding asylum-seekers) | PEW, 2019 (March 2025 update) | https://www.pewresearch.org/global/2019/11/13/europes-unauthorized-immigrant-population-peaks-in-2016-then-levels-off/ | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 302 | United Kingdom | High | 11 | 2015 | 700000 | 900000 | 64853393 | 5318141 | 1.08% | 1.39% | 13.16% | 16.92% | All irregular migrants (including asylum-seekers) | PEW, 2019 (March 2025 update) | https://www.pewresearch.org/global/2019/11/13/europes-unauthorized-immigrant-population-peaks-in-2016-then-levels-off/ | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 303 | United Kingdom | High | 11 | 2015 | 700000 | 900000 | 64853393 | 5318141 | 1.08% | 1.39% | 13.16% | 16.92% | All irregular migrants (excluding asylum-seekers) | PEW, 2019 (March 2025 update) | https://www.pewresearch.org/global/2019/11/13/europes-unauthorized-immigrant-population-peaks-in-2016-then-levels-off/ | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 304 | United Kingdom | High | 11 | 2014 | 800000 | 900000 | 64351203 | 5232198 | 1.24% | 1.40% | 15.29% | 17.20% | All irregular migrants (including asylum-seekers) | PEW, 2019 (March 2025 update) | https://www.pewresearch.org/global/2019/11/13/europes-unauthorized-immigrant-population-peaks-in-2016-then-levels-off/ | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 305 | United Kingdom | High | 11 | 2014 | 700000 | 900000 | 64351203 | 5232198 | 1.09% | 1.40% | 13.38% | 17.20% | All irregular migrants (excluding asylum-seekers) | PEW, 2019 (March 2025 update) | https://www.pewresearch.org/global/2019/11/13/europes-unauthorized-immigrant-population-peaks-in-2016-then-levels-off/ | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 306 | United Kingdom | High | 11 | 2008 | 417000 | 863000 | 61175586 | 4676306 | 0.68% | 1.41% | 8.92% | 18.45% | All irregular migrants | Kovacheva and Vogel, 2009 | https://irregular-migration.net/wp-content/uploads/2021/06/WP4Annex3_CalculationTable-EUestimate2008_Dec09.xls | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 307 | United Kingdom | Low | 8 | 2013 | 580000 | 580000 | 63905342 | 5217643 | 0.91% | 0.91% | 11.12% | 11.12% | All irregular migrants in England (including failed asylum seekers) | Prederi, 2013 | https://assets.publishing.service.gov.uk/media/5a7cd163e5274a2c9a4844b6/Quantitative_Assessment_of_Visitor_and_Migrant_Use_of_the_NHS_in_England_-_Exploring_the_Data_-_FULL_REPORT.pdf | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 308 | United Kingdom | Low | 8 | 2013 | 110000 | 110000 | 63905342 | 5217643 | 0.17% | 0.17% | 2.11% | 2.11% | Irregular migrant children in England | Prederi, 2013 | https://assets.publishing.service.gov.uk/media/5a7cd163e5274a2c9a4844b6/Quantitative_Assessment_of_Visitor_and_Migrant_Use_of_the_NHS_in_England_-_Exploring_the_Data_-_FULL_REPORT.pdf | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | |
| 309 | United Kingdom | Low | 4 | 2010 | 1100000 | 1100000 | 62510197 | 4852577 | 1.76% | 1.76% | 22.67% | 22.67% | All irregular migrants | Migration Watch UK, 2010 | https://www.migrationwatchuk.org/briefing-paper/190/the-illegal-migrant-population-in-the-uk | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en | EUROSTAT, Population on 1 January by age group, sex and country of birth, migr_pop3ctb | https://ec.europa.eu/eurostat/databrowser/view/migr_pop3ctb__custom_14974967/default/table?lang=en |
METHODOLOGY
Figures on this page present estimates of the UK’s irregular migration population between 2008 and 2023 and corresponding assessments of their quality, which were compiled and carried out under the MIrreM project. Other MIrreM outputs, such as working papers and briefs, related to the UK are displayed on this page.
Estimates can be viewed as a number, as a share of the total population and as a share of the foreign-born population not covered by free movement policies (i.e., in Europe, those who were born in countries outside of EU Free Movement and in the UK and Ireland, those who were born outside of the Common Travel Area).
The Estimate Quality brings together appraisals of an estimate’s accessibility, documentation, methodology, reliability and underlying data into an aggregate score and band:
- Estimates that scored between 4 and 8 points were graded as low quality
- Estimates that received scores greater than 8 points and as high as 10 points were appraised as medium quality
- Estimates that exceeded valuations of 10 points (up to the maximum score of 12 points) were classified as high quality
Users should note:
Irregular migration estimates come with inherent uncertainty and significant limitations. Comparisons between estimates should be interpreted with particular caution.
On this page, if an estimate does not include a range, the single or central figure is recorded as both the high and low estimate.
For more information on how these data were compiled and assessed, please refer to the MIrreM Working Paper, The Irregular Migrant Population of Europe (Kierans and Vargas-Silva, 2024).
Access the full dataset, which includes the assessments of the five quality criteria that comprise the aggregate quality score for UK and all other countries covered by the MIrreM project.