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Top Ten Problems in the Evidence Base for Public Debate and Policy-Making on Immigration in the UK

05 Apr 2011

Informed public debate and evidence-based policy-making on immigration requires clarity and transparency about what we know and don’t know about migration and its impacts. This report sets out the ten most important problems in the evidence base on immigration and migrants in the UK.

How did we compile the list?

Our assessment of what should be included in the list has been guided by the key issues in current public and policy debates on migration in the UK. These include the mechanics and impacts of reducing overall net-migration to the tens of thousands through limiting non-EU immigration for work, study and family/marriage reasons, and through making it more difficult for migrants to settle permanently in the UK. The top ten data and analysis problems discussed in this report are all relevant to these issues. Most of the problems we identify are quite specific but in areas where we have very little information (e.g. on irregular migration) they are more general. Although numbered for convenience, the problems are not ranked in order of importance. In the end, our list is necessarily subjective as different experts may identify slightly different issues.

What do we mean by “problems in the evidence base”?

The problems we identify arise from one or more of the following factors: data gaps and limitations; analysis gaps and limitations; and uncertainties in the conclusions emerging from the available analysis. We are focusing on current problems and recognise that work is underway that aims to address some of the issues (e.g. the cross government Migration Statistics Improvement Programme, e-Borders, and the Census 2011). While all the problems we discuss can be alleviated by more and better data and/or analysis, it is important to emphasise that no country can be expected to have complete information about all the issues identified in this report. Collecting new data is costly. There are always tensions between the desire to collect new data or share existing data on the one hand, and privacy laws and concerns about data protection on the other. Some aspects of migration such as irregular migration are by their very nature much more difficult to measure and analyse than others e.g. legal labour immigration from outside Europe.

The limits of “more and better evidence”

More and better evidence will strengthen the basis for public debate and policy-making on migration. It cannot, however, provide ready-made answers to migration policy questions which, in the end, always involve a balancing of competing impacts and interests. What policy should look like is an inherently political question that necessarily involves debates about the values that should guide policy-making in this area. In line with the mission of the Migration Observatory, the aim of this report is to inform and promote a stronger evidence base for debate, not to say what policy should be.

  1. Emigration

    The only source of information is a survey

    In order to estimate the level of net-migration, one needs information on both the inflows (immigration) and outflows (emigration) of migrants. Data on emigration is particularly scarce. The International Passenger Survey (IPS) conducted by the Office for National Statistics (ONS) is the only source of emigration data, and is used in ONS estimates of net-migration. Since these estimates are the official statistics targeted by government policy, limitations on this data source are a matter of critical policy importance.

    There has been considerable debate about the accuracy of IPS measures of total emigration, and there is no reliable alternative source of data against which to check its results. The IPS does not count all entries and exits, but rather interviews a sample of international passengers. It now interviews about 2000 or more emigrants annually, though prior to improvements in 2007 its emigration estimates were based on less than one thousand annual interviews. Like any survey, IPS comes with inherent uncertainty: it can only produce estimates with margins of error rather than pinpoint numbers. In 2009, IPS estimated 337,500 emigrants, but, considering its margin of error, this only means that we can be 95% confident that the real level of emigration was between 315,800 and 359,100, a range of over 43,000 (see Figure 1 below). Official net-migration figures are therefore only estimates as well, and subject to margins of error from both the inflow and outflow estimates.

    In addition to margins of error, surveys also face biases that may come from numerous sources, including people refusing to be interviewed and obstacles to obtaining a truly random sample. Thus, IPS estimates depend on a series of calculations of “weights” designed to extrapolate from a few thousand survey interviews to a larger population.

    Also, IPS identification of emigrants depends on people’s self-reported intentions about for how long they plan to leave the UK, which may or may not materialize. This question is critical because only people departing for at least one year meet the official definition of a migrant. The ONS attempts to adjust for people who change plans, but again there is no alternative source of information to help confirm whether its estimates of “switchers” are correct.

    Another important limitation is that IPS emigration data do not allow for calculation of net-migration by categories of migrants (e.g. workers, students, family migrants). This is because when IPS collects information on migrants leaving the UK, it does not gather information about the characteristics and purpose of entry of these same migrants at the time of their initial arrival to the UK. For instance, it is possible for someone to arrive as a foreign citizen, naturalise and then leave as a UK citizen. This would exaggerate the contributions of non-British nationals to net-migration, as the same individual would raise net-migration among foreign nationals upon arrival and reduce net-migration among British nationals upon departure. In the same way, some migrants arrive in the UK for the purpose of formal study, but leave for employment elsewhere, exaggerating net-migration in the formal study category and taking away from net-migration in the work category. In early 2012, the ONS introduced a new question to the IPS which asks people who are leaving the UK about the purpose of their previous entry. The answers to this new question will provide the basis for estimates of student-net migration. The first annual data will become available in late 2013.

    Figure 1

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  1. Immigration: Data sources differ on the numbers of migrants coming to the UK

    Policies aimed at regulating the number of people coming to the UK face a fundamental uncertainty about the actual level of immigration.  The government collects data on “inflows” of migrants through three primary sources, which provide different estimates of total immigration (and by extension, of net-migration).

    Official statistics on immigration (as well as net-migration) come from ONS’ estimates of Long-Term International Migration (LTIM), which are based on the International Passenger Survey (IPS). Home Office administrative data provide two more sources on immigration of non-EEA(1) citizens: entry clearance visas issued and passengers entering the UK through border control. (Visa and passenger entry immigration control data track only non-EEA/Swiss citizens.) These sources yield very different estimates of immigration to the UK.

    As shown in Chart 1 below, LTIM estimates of immigration of non-EU citizens are significantly smaller than the number of visas issued or number of passengers entering the UK. There are some clear reasons why these sources diverge. First, ONS’ LTIM data only measure immigrants who say when interviewed at the border that they intend to stay in the UK for at least 12 months. Home Office data on visas and passenger entries also include foreign citizens who expect to stay in the UK for less than a year, and therefore do not qualify as migrants by the ONS (and internationally-agreed) definition. Of course, length-of-stay can only be known with certainty at departure, since plans change and stays can be extended or reduced. A second clear issue with visa data is that some unknown number of people granted a visa never actually come to the UK. On the other hand, LTIM data is based on a sample survey and are therefore only estimates, whereas visa data are accurate counts of the actual number of visas issued to non-EEA citizens.

    Unfortunately, there is no reliable way to identify non-arrivals and short-term migrants from administrative data sources to see if the discrepancies between visas and LTIM data disappear. As a result, it is unknown whether the above factors are sufficient to explain the differences completely, or if there are other unknown flaws or discrepancies. Recent ONS estimates of short-term migration (of three to twelve month stays) suggest that short-term migration accounts for some the gap between LTIM and administrative data on visas and passenger entries, but may not do so completely.

    Figure 2

    End notes

    • (1) The European Economic Area (EEA) includes all the EU member states plus Iceland, Liechtenstein and Norway.

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  1. Net-migration: Different data sources suggest different figures

    Reducing net-migration is a key policy objective of the current Government. It is therefore important to have good information about the level and changes of net-migration over time. The problem is that two major data sources for net-migration suggest different figures.

    The most common measure of net-migration uses Long-Term International Migration (LTIM) estimates based on the International Passenger Survey (IPS) which aims to capture the flows of people entering and leaving the UK.

    An alternative data source that can be used to estimate net-migration is the Annual Population Survey (APS) which includes data from the Labour Force Survey (LFS) and provides information about the stock of migrants in the UK. In theory, the annual changes in the stock of migrants in the UK should reflect the level of net-migration, i.e. the difference between migrants coming to and leaving the UK. Figure 3 below shows that the estimates of net-migration of non-British citizens suggested by LTIM do not always coincide with changes in the stock of non-British citizens suggested by the APS. Estimates were somewhat close in 2007, but differed in the other years, sometimes by more than 60,000. The dynamics of the measures also appear to be different, as the APS suggest a marked decrease in the growth of the stock of migrants from 2008 to 2009, while LTIM suggests that net-migration was relatively flat for 2009.

    As these surveys were designed for different purposes, there are several reasons that could explain the differences. LTIM estimates define migrants as individuals coming to or leaving the UK for over one year, while the APS defines migrants by citizenship or place of birth. International students living in communal establishments are not part of the APS estimates. Asylum seekers and recent arrivals with highly mobile residential patterns are also likely to be under-represented in the APS estimates. Foreign nationals who obtain British citizenship will disappear from the APS estimate of the stock of foreign nationals in the UK. Finally, LTIM data rely on self-reporting intentions about intended length of stay in the UK (when entering) or abroad (when leaving). It is unknown to what extent these reasons explain the discrepancy between the net-migration figures based on the APS and LTIM.

    Figure 3

     

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  1. The immigration status of migrants in the UK: No systematic data

    There is no data source with information about the immigration status of migrants in the UK. The most comprehensive source of data on the number and characteristics of migrants is the Labour Force Survey (LFS). The LFS includes questions about citizenship, place of birth and time spent in the UK. It does not, however, contain information about whether a migrant has temporary or permanent residence status (“leave to remain”) in the UK. The LFS records neither the type of visa migrants used to enter the UK, nor their current immigration status (e.g. workers, students, family, asylum seekers, recognised refugees, etc.)

    The absence of comprehensive information about migrants’ immigration status gives rise to at least three problems in public and policy debates. First and most fundamentally, we do not know the numbers and characteristics of migrants with different types of immigration status. Among the total stock of migrants in the UK, how many are currently on Tier 1 and 2 visas? How many have student visas and what share of migrants on student visas have taken up employment in the UK? How, if at all, do the personal characteristics, skills and labour market participation rates vary across migrants with different types of immigration status? We currently do not have the data to provide robust answers to these questions.

    A consequent second problem is that we do not know how different types of immigration status affect the economic and social outcomes of migrants in the UK. Each immigration status is associated with different rights and restrictions with regard to access to employment and the welfare state. For example, current Tier 1 migrants have the right to free choice of employment in the UK, while Tier 2 migrants are only allowed to work for the employer specified on the certificate of sponsorship (they can change employers but only after a new application). How does this employment restriction impact on Tier 2 migrants’ wages and behaviour in the labour market? Some migrants do not have full access to selected welfare benefits such as health care and education. How do these restrictions impact on migrants’ health and other outcomes? How do the wages and jobs of recognised refugees change over time? Do Tier 1 migrants, who were admitted without a job offer in the UK, work in occupations that are highly skilled? The lack of data prevents systematic analysis of these issues.

    The third problem is that we currently cannot systematically assess the impact of migrants with different types of immigration status on the UK labour market, economy and society. This issue becomes particularly problematic when Government is adjusting its immigration policies by fine tuning the admission and selection criteria for particular types of migrants (e.g. workers and students from outside the EU). In the absence of data about migrants’ immigration status, any impact analysis of changing policies that target specific migrant groups must necessarily remain limited.

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  1. Local area statistics on migrants: The existing estimates are very imprecise

    The efficient allocation of central government revenue to local councils and regions of the UK critically depends on accurate data about the size of the local population.  The size and composition of the local population can change rapidly due to changes in both internal and international migration in- and out-flows. The Census is the best source of demographic data for small geographical units but it happens only every ten years and thus becomes quickly out of date, especially during times of large migration flows. In the intercensal period, estimates from the Labour Force Survey (LFS) and the Annual Population Survey (APS) provide the best measurement of the migrant population at the local level (e.g. the number of foreign born and foreign nationals).

    The LFS and APS are national surveys that are not designed to yield precise estimates of the size and characteristics of the migrant population at the local level. As shown in Table 1 below, the confidence intervals of estimates of the number of migrants at the local level can be large and in some cases as large as the actual migration estimates. For instance, in East Devon the estimated number of foreign-born is 4,000 but the confidence interval (95%) ranges from 0 to 8,000.

    Other sources of information that have sometimes been used to estimate and discuss the number of migrants at the local level include National Insurance Number registrations, registrations with a GP of individuals previously living overseas (Flag 4 records), registrations in the Workers’ Registration Scheme (WRS) for A8 nationals, and the International Passenger Survey which records the intended first (but not the final) destination of migrants entering the UK. Importantly, while giving some information about the new inflow of migrants into particular areas of the UK, these data are not designed to measure the stock of migrants at a particular point in time as they do not capture migrants who leave the area for another place in the UK or to move abroad.

    The significant uncertainty about the number of migrants in local areas creates significant difficulties for the planning and efficient delivery of public services and a whole range of other public policies.

    Table 1 – Estimates of the foreign-born population in selected Local Authorities, based on data from the Annual Population Survey for January-December 2009

      95% Confidence Interval 
    Local AuthorityForeign-BornLower BoundUpper Bound
    East Devon400008000
    Dover500010009000
    Lancaster9000300015000
    Canterbury14000700021000
    Cardiff370002800046000
    Westminster123000104000142000
    Manchester11100096000126000
    Birmingham220000192000248000
  1. Public opinion: How does the public define the “immigrants” it wants reduced?

    Current coalition government policy aims to reduce net-migration below 100,000 per year, in keeping with public opinion data showing that about ¾ of the British resident population would prefer to see less immigration. But will a reduction in numbers address the public’s most urgent concerns?

    Public opinion data clearly show that the majority of the British resident population would prefer reduced immigration. But the evidence base lacks detailed information on a crucial issue – how do members of the public define “immigrants?” Survey questions about “immigration” or “immigrants” rarely define these terms, and certainly do not offer the government’s official definition. When responding to poll questions about “immigration,” are most people thinking about foreign students, workers, or asylum seekers, for example? Do members of the public distinguish between EU and non-EU nationals? Or between newly-arriving migrants and migrants already settled in the UK? And, further, is opposition to migration attached equally to all groups?

    This matters because while our knowledge of public opinion is based on the implicit definitions of “immigrant” that members of the public use, government policies are directed toward “immigrants” as the government defines it (in keeping with UN standards). But these definitions may diverge, such that some approaches to reducing net-migration statistics might be poorly tailored to the actual sources of public concern. In one striking example, the government definition differs from common language on the length of stay required to become a “long-term international migrant”.

    The Oxford English Dictionary, a reflection of actual language use, defines an immigrant (in part) as “a person who migrates into a country as a settler.” This definition suggests a degree of permanence absent from the government definition, in which a twelve month stay is sufficient for status as a “long-term international migrant”. This definitional divergence has implications for policies aimed at particular types of migrants, such as students. International students, the majority of whom stay in the UK only temporarily, may not be commonly included in the notion of “immigrants” that animates opposition from the majority of the public. (We simply do not know, from the existing evidence base on public opinion.) But, if students do not fit common images of who counts as a migrant, then policies that reduce student immigration and go beyond the reduction of fraud and illegal overstaying of visas might do little to address the public’s concerns. This does not deny the public’s preference for fewer migrants. Rather, the point is that public opinion may be focused on a set of people that meet a common-language definition of “immigrant,” rather than the set that qualify as immigrants in official government statistics on gross and net-migration.

    In addition, little polling addresses public attitudes toward the key policy categories of immigration, such as high-skilled and low-skilled workers, students, and family migrants. Public opinion might prefer fewer migrants, but also prefer to maintain or increase migration in some categories. Some evidence exists at the extremes – doctors and nurses are among the most popular migrants, illegal immigrants the least. But a wide range of categories are seldom if ever discussed in opinion polls.

    Finally, it is not clear from the evidence how many opponents of immigration would be satisfied with the government’s goal of reducing migration below 100,000. Polls dating back to the 1960s have shown a widespread preference for less migration, even when overall numbers were much smaller than today’s.

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  1. Migrants’ impacts on public services: no systematic data and analysis

    The impact of immigration on the use and provision of public services – such as health, education, social housing and social services – is one of the key issues at the heart of the UK’s immigration debate. There is considerable anecdotal evidence but very limited systematic data and analysis about migrants’ use of public services, especially health and education, and even less information about the value of migrants’ contributions to the provision of public services in the UK. While the rapid growth in immigration in recent years has clearly had important consequences for public services in the UK, we do not have robust estimates of these effects which can include costs (consumption) and benefits (provision).

    The lack of systematic evidence on migrants’ use of public services is mainly due to the fact that immigration status is recorded inconsistently (or not at all) when public services are provided. There is, for example, no systematic data on the number of migrants, let alone migrants with different types of immigration status, that make use of particular types of health services. We also have very limited information on the number of migrants’ children in UK school because enrolment data do not record nationality, country of birth, or immigration status. The closest estimates of migrant children in UK schools are based on data on the number of children receiving support for learning English as an Additional Language (EAL) at schools in England only. EAL status is self-reported and is an indicator of when English is not the first language spoken at home. It thus includes children born in the UK but who do not speak English at home. It also fails to capture children who are migrants but speak English at home. In the absence of systematic data and evidence, much of the debate is based on anecdotal evidence provided by service providers and other stakeholders.

    In addition to the taxes they pay, migrants contribute to the provision of public services in at least two specific ways that have not yet been analysed adequately. First, they can provide skills that are currently not available or in short supply in the UK. Second, the employment of migrants facilitates the provision of public services at a cost that is lower than would be the case if those services were dependent solely on the supply of British workers. Immigration is thus a form of “subsidy” to public services that benefits service providers, consumers and the taxpayer. Potential adverse impacts of this subsidy include downward pressures on wages (or at least wage growth) of British workers employed in public services. They also include, in some low-waged sectors such as social care, an increasing reliance on and entrenchment of low-cost service provision.

    Although we have data on the numbers and employment share of migrants in specific areas of service provision – e.g. LFS data suggest that almost a third of health professionals in the UK, and two-thirds of care assistants in London are foreign born – there has been no systematic analysis of how the employment of migrants has affected wages, and the cost and structure of public service provision. Lack of data and analysis about the impacts of immigration on the use and provision of public services has important effects on studies of the fiscal effects of immigration. They typically ignore the contribution migrants make to the provision of public services and assume that migrants’ use of public services is the same as that of British nationals.

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  1. Impact on Housing: little systematic evidence of direct and indirect impacts of immigration on house prices, rents and social housing at national and local levels

    Much of the research evidence base on immigration and housing in the UK relates to the housing choices and housing conditions of migrants. Quantitative studies of this issue generally use the UK’s Labour Force Survey which contains information about the housing choices (e.g. renting private accommodation, home ownership, social housing) of migrants and UK-born individuals. We know, for example, that foreign-born persons have lower ownership rates than the UK-born and greater representation in the rental sector.

    We also know that migration is the most important variant in projections about the growth of the number of households in England. The principal estimate in the latest analysis by the Department for Communities and Local Government assumes that net-migration accounts for just under 40 percent of the annual increase in households in England (252,000 new households per year) to 2031.(2)

    There is, however, much less research evidence on the ways immigration directly and indirectly impacts house prices, rents, and social housing at national and local levels. Positive net-migration leads to an increase in the demand for housing which can impact on house prices and rents. The magnitude of these impacts critically depends on the responsiveness of the supply of housing to changes in demand. The impact of immigration on housing can also be expected to vary across local areas with different housing markets and experiencing different scales of migrant inflows and outflows. There can also be important inter-relationships between the owner occupier sector and the private rented sector. For example, the increased demand for rented accommodation may encourage more investors to enter the buy-to-let market, which in turn could increase house prices. There is little systematic research evidence on any of these issues in the UK.

    There is more but still limited evidence on social housing. We know, for example, that recent migrants are less likely than the UK-born population to be accommodated in the social housing sector, but that the propensity of migrants to be in social housing increases over time (most likely because migrants acquire access to social housing over time).(3) But there has been no research about the indirect effects of immigration on social housing that arise from the relationships between social housing and the private housing market. Even if migrants themselves do not use social housing, immigration may still change the demand for social housing indirectly by driving up rents and house prices in the private sector and making more people dependent on social housing. The costs of social housing provision may also increase because of increased competition for properties from the private rented sector.(4) There has been no systematic research of these issues in the UK.

    End notes

    • (2) Department for Communities and Local Government. 2009. Household Projections to 2013, England. London: Department for Communities and Local Government.
    • (3) Centre for Economic Performance. 2010. Immigration and the UK Labour Market: The Evidence from Economic Research. London: Centre for Economic Performance.
    • (4) Migration Advisory Committee. 2010. Limits on Migration, MAC. London.
  1. Student migration: uncertainty about numbers and compliance and limited analysis of impacts

    Student migration has become the focus of policy debate, generating some new information in the process. But the evidence base still lacks sufficient information about the number of students, the extent of non-compliance with immigration rules among international students, and the impact of foreign students on the broader economy and society.

    One critical aspect of the debate on student migration is the contribution of students to net-migration over the long term. Net-migration is difficult to estimate for other categories of migrants as well, because of limitations on exit data. In the case of international students, there is a particular concern about those who overstay their temporary student visas, thus adding to net-migration in the long run while also adding to the non-compliant migrant population.

    Home Office data (from a study of all non-European students arriving in the year 2004) show that after five years, approximately 80% of non-European students no longer have legal permission to remain in the UK.(5) What is missing is definitive information on how many of that 80% actually leave the country and how many “overstay” their visas and remain in the UK without legal permission.

    A 2010 Home Office report on student migration included an analysis of international students’ compliance, but the information is incomplete and not necessarily representative.(6) As noted in the report, this analysis was based on a sample of institutions chosen not at random, but for “convenience.” More specifically, the study examined universities on the government’s Highly Trusted Sponsors list, while using data on other types of educational students from a list of those that had been subject to an investigation because of suspicions about its legitimacy. These convenience samples seem likely to lead to underestimating potential non-compliance rates for university students while inflating potential non-compliance rates for other institutions.

    Moreover, the data do not show actual overstaying but only the “potentially non-compliant”—those for whom there is no record of leaving the UK or of valid extension of their stay. Estimates of exits are based on the still-incomplete eBorders system of monitoring entries and exits.

    The impact of foreign students on the higher education sector, and on the broader economy, is a second area in which key information is lacking. The economic impact of international students higher education is relatively well-documented, but similar information on further education and English language schools is in short supply. There is also a commonly-held view among educators that international students have valuable non-economic benefits on the quality of education that students receive and the quality of research conducted at universities, particularly in the STEM fields. These benefits are inherently more difficult to study quantitatively, and so they may drop out of the evidence base.

    An additional question about international students is their impact on the job prospects of British graduates. In particular, does the Post-Study Work Route (PSWR), which allowed some 38,000 international students to stay on in Britain for up to two years after graduation, create problems for job-hunting British graduates? The labour market effects of the PSWR have not been thoroughly analysed, although the question is particularly important at present, with unemployment rates for graduates still unusually high.

    End notes

    • (5) Achato, Lorrah, Mike Eaton, and Chris Jones. 2010. The Migrant Journey. Home Office Research Report 43. London: Home Office.
    • (6) Home Office. 2010.  “Overseas Students in the Immigration System: Types of Institutions and Levels of Study.” London: Home Office.

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  1. Irregular (illegal) migrants: we know little about their numbers, characteristics and impacts

    The most recent estimate of the number of irregular migrants and their UK-born children suggests a range of 524,000 to 947,000 (central estimate 725,000) at the end of 2007.(7) This estimate is based on an update of the analysis in a Home Office report published in 2005.(8) In addition to the large range (423,000), the methodology underlying this estimate has a series of limitations, which are explicitly mentioned in these two studies.

    The original Home Office report used a ‘residual method’ to estimate the number of irregular migrants in the UK in April 2001. This involved deducting an estimate of the legally residing foreign-born population from the total number foreign-born actually recorded in the UK Census in 2001. The difference (or the ‘residual’) is an estimate of the number of irregular migrants present in 2001. The residual method thus combines census data for measuring the total foreign-born population with a range of surveys and administrative data to estimate the legally resident population.

    A key problem with this method is that the survey data used to help estimate the legally resident population are subject to sampling variability and it is likely that some groups are under- or over-represented. For example, emigration figures of different groups of migrants were based on data from the International Passenger Survey and variations in these estimates may affect the estimated irregular population significantly. Other difficulties relate to problems with defining certain groups of migrants. Furthermore, by defining irregular migrants based on the absence of legal residence status in the UK, the available estimates of irregular migrants in the UK exclude migrants who are residing legally but working illegally. Whether and to what extent legally resident migrants who are violating restrictions of their residence permit should be included in the population of irregular migrants is subject to debate. It is not known how many legally resident migrants in the UK are currently violating the conditions of their stay including any employment restrictions or restrictions on access to welfare benefits. For example, it is not known how many non-EU migrants who are legally residing on student visas are working in excess of the legally allowed 20 hours per week during term time. Evidence from research using non-random samples suggests that the incidence of this kind of “semi-compliance” may not be insignificant.(9) Partly as a consequence of the uncertainty about the number of irregular migrants, we also have very little systematic information about their composition (e.g. gender, nationality, age structure, length of stay) and how it differs from the legally resident migrant population. We do not have systematic data and analysis of where irregular migrants work, and how they impact on, for example, the labour market, housing and public services. There is also limited analysis of how precisely illegal status affects the employment and lives of irregular migrants themselves.

    End notes

    • (7) Gordon I, Scanlon K, Travers T & Whitehead, C.  2009. Economic impact on London and the UK of an earned regularisation of irregular migrants in the UK, Interim Report from LSE London.
    • (8) Woodbridge, J. 2005. Sizing the unauthorised (illegal) migrant population in the United Kingdom in 2001, Home Office Online Report 29/05.
    • (9) Ruhs, M. and B. Anderson. 2010. “Semi-compliance and illegality in migrant labour markets: An analysis of migrants, employers and the state in the UK”, Population, Space and Place, 16 (3), 195-21.

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    Irregular migrants are likely to have important impacts on, for example, labour markets, the provision of public services, government finances and social cohesion. Yet, as it is the case in many but not all other immigration countries, the data and information about the number, characteristics and impacts of irregular migrants are extremely limited. Irregular migration is by definition not recorded and eludes statistical coverage. Therefore, precise measurement is unfeasible.

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