Jill Ahrens

MIrreM Factsheet, September 2025 - MIrreM examines estimates and statistical indicators on the irregular migrant population in Europe as well as related policies, including the regularisation of migrants in irregular situations.

Rather than an exceptional measure, regularisation is a frequent response to resolve situations of longer term, protracted irregularity. This handbook argues that regularisation should be considered a standard element of the migration policy toolbox, providing a structured route for irregular migrants to regularise their status when other options, such as return, are not feasible. Irregular migration should be understood as a structural feature of contemporary societies, arising from ongoing labour demand, family and social networks, individual migration aspirations, and restrictive entry and residence policies. This handbook provides practical, evidence-based guidance on the design, implementation, and evaluation of regularisation policies, highlighting their impacts on labour markets, social cohesion, and migrant rights. Drawing on experiences from Europe, North America, and other world regions, it examines how different policy approaches operate, how key actors shape outcomes, and how procedural design affects accessibility, inclusivity, and legitimacy. It underscores that regularisation, when carefully implemented, can reduce informality, enhance integration, and strengthen fiscal and social contributions.

This policy brief gives a 360-degree overview on what we currently know about the extent of irregular migration across the EU. Based on MIrreM’s analysis and aggregation of estimates available for 12 European countries (including the UK) in the period 2016 to 2023, the irregular migrant population can be estimated at between 2.6 and 3.2 million. The previous Clandestino estimate was 1.8 to 3.8 million for the same 12 countries in 2008. This suggests that the number of the irregular migrant population has not substantially changed at the aggregate level for these countries – although there have been important changes in individual countries. In addition, the policy brief also surveys what information is available and still lacking in regard to trends and patterns of irregular movement, including what information we will have on ‘overstayers’, a key proportion of the irregular migrant population identified under the Clandestino project.