Irregular migration in the UK

This briefing examines irregular migration – also called ‘illegal immigration’ – in the UK, including the difficulties in defining and measuring it, and evidence on its nature and scale.

There is no legal nor broadly accepted definition of an ‘irregular migrant’, though the term is commonly used to refer to people who are in the UK without the legal right to be so

There is no definition of an irregular migrant (or ‘illegal immigrant’) in UK law. However, it is commonly held that there are four main ways in which a person can become an irregular migrant (Figure 1):

1. Enter the UK regularly and breach the conditions upon which entry or stay was granted, such as by visa overstaying, doing work that is not permitted, or due to a criminal conviction.
2. Enter the UK irregularly or through deception, such as using forged documents or lying about the purpose of entry.
3. Do not leave the country after an application for asylum has been rejected and all rights of appeal exhausted.
4. Be born in the UK to parents who are irregular migrants, because the UK does not have birthright citizenship. (Some of these children can acquire citizenship directly. This category is included here because they are often included in estimates of the UK’s irregular population).

Many academic researchers believe that in the UK substantially greater numbers of people without regular immigration status arrived by air and entered regularly, rather than irregularly, and there is some evidence to support this (Düvell et al., 2018, p. 34).

In some definitions, the irregular migrant population includes those with legal residence but who work in breach of employment or other restrictions attached to their immigration status – a condition known as “semi-compliance” with immigration control (Ruhs and Anderson, 2010, p. 202). Such migrants are not typically included in estimates of the UK’s irregular migrant population.

Some people who claim asylum will have entered the UK irregularly. There is no asylum visa, which means that a person seeking asylum must either arrive irregularly or enter on a visa that has been issued for another purpose, such as tourism.

Figure 1

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Irregular migrants are not generally permitted to access benefits, social housing, or free hospital care

Irregular migrants are not permitted to access most social security benefits, including housing benefits, and some public services in the UK, such as social housing and hospital-based healthcare. Irregular migrants can access free primary healthcare care services, which includes GP and nurse consultations, and treatment provided by a GP. However, access to free secondary healthcare, which includes hospital treatment, is based on legal residence in the UK. As such, those without immigration status are generally charged for secondary healthcare services. There are some exceptions, including for emergency healthcare, treatment of communicable diseases, and for the diagnosis or treatment of coronavirus.

Other services, such as nursery schools and primary and secondary education (from the ages of 5 to 18), may in principle be accessed free, regardless of immigration status, although irregular migrants are often excluded indirectly. For example, many childcare services use eligibility for universal credit (which functions as a proxy for need) as a criterion for access, which in effect excludes irregular migrants.

One of the most extensive empirical studies of irregular migrants in the UK, based on 175 interviews (Düvell et al., 2018), found that while over half reported stress and anxiety resulting from their status, almost none were deterred by the ‘hostile environment’ policy. This study also found that access to irregular work depended on migrants’ ethnicity; and that some felt they were treated well by employers whilst others reported being paid below minimum wage, or being exploited, sometimes severely. A commonly cited reason for ensuring people use documented routes is to protect them from exploitation. A study of young undocumented migrants in the UK, based on 75 interviews, also found a lack of choice in the labour market, and dependence on work within ethnic-minority niches (Bloch et al., 2014).

Once a person’s status becomes irregular in the UK, it can be difficult for them to acquire regular status, in part because breaches of immigration law can result in bans from re-entering the country of between one and ten years (see Gbikpi, 2020).

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Reliable and accurate estimation of the UK’s irregular migrant population has not to date been possible, so available estimates should be treated with caution

Trying to estimate the number of irregular migrants in a country confronts the challenge of counting people who do not wish to be found. That is why attempts at estimation have been described as “counting the uncountable” (Kelly, 1977).

Nevertheless, there have been several estimates of the population of migrants living in the UK without a legal residence permit (Figure 2). These estimates do not include those with a legal residence permit, but who breach working or other restrictions.

Estimates vary in size, in part because they include different groups. Some include asylum seekers, or the UK-born children of irregular migrants – which one study estimated was 65,000 in 2012 (Sigona and Hughes, 2012) – while other estimates do not. But all estimates are highly uncertain, and have large margins of error.

The most recent estimates have been provided by the Pew Research Center (Connor and Passel, 2019) and Greater London Authority (Jolly et al., 2020). These were based on the residual method, with Pew producing an estimated range for 2017 of 800,000 to 1,200,000, and the GLA report providing a central estimate of 674,000 as at April 2017 (though this excludes the UK-born children of irregular migrants; if these are included the figure is 809,000).

These studies have important limitations. For instance, the Pew estimate of the lawfully resident migrant population was derived from a figure provided by the Home Office to Eurostat (Eurostat, 2020) that does not include (and is not intended to include) migrants with indefinite leave to remain (ILR). Excluding this group inflates the estimate by the number of migrants with ILR, a number that the government does not record, but which is likely to be in the hundreds of thousands. As noted in Understanding the Evidence, these estimates should be treated with caution. For a more detailed discussion of the limitations of the Pew and GLA methodologies, see our commentary Recent estimates of the irregular migrant population in the UK.

Figure 2

Two studies have provided estimates of the number of people in the EU who are without a valid residence permit (Vogel and Kovacheva, 2009; Connor and Passel, 2019). Both studies suggest that the UK had more irregular migrants than EU nations, but because the data available and methodologies used vary across countries, international comparisons should be treated with caution (Figure 3).

Figure 3

The next three sections of this briefing examine data on irregular migration ‘inflows’ by looking at three groups that add to the irregular migrant population: visa overstayers, unauthorised entrants, and refused asylum seekers.

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Exit checks data do not provide an accurate measure of visa overstaying, and the government does not know with any degree of accuracy how many visa overstayers there are in the UK

People who overstay their visas are a key source of the UK’s irregular migrant population.

In the last three financial years, there was an overall recorded compliance rate with visa duration of around 97%. In absolute terms, an average of around 55,000 non-EU visa nationals per year who were expected to leave the UK were not recorded as having left the country before their visa expired (this excludes non-visa visitors, such as US visitors; those who extended their visas; and those whose expired visa was issued before exit checks were introduced).

These exit check data can be broken down by visa type, to show that a large majority of expiries – 75% in this period – concerned people with visit visas, rather than study, work, or other (including family) visas (Figure 4). This reflects the much larger number of visitors who come to the UK compared to those on other visa types.

Importantly, because the departures of many people go unrecorded (see Home Office, 2019e; 2019f), these figures should be taken to represent the minimum level of compliance with visa duration for the categories covered, and are not an indicator of the rate of overstaying (see Evidence Gaps and Limitations). Nor is the UK’s population of visa overstayers known.

Of the 1.82m visa expiries in 2018/19, 0.4% were late departures (and 3.3% were not initially identified as departing). In 2017/18, 0.2% of expiries were late departures (Home Office, 2019e, p. 3).

Figure 4

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In the financial year 2017/18, around 1,800 people trying to enter the country without authorisation were apprehended in the UK, but the total number of attempted or successful unauthorised entries is not measurable

A 2018 report by the ICIBI stated that the number of unauthorised entrants apprehended by the Home Office “in country” was 2,366 in 2016/17, which declined by 23% to 1,832 in 2017/18 (Bolt, 2018, p. 26). In both of these financial years, Iraqi and Iranian nationals were the largest two nationalities apprehended.

Many attempts at unauthorised entry begin from French and Belgian ports where the UK implements immigration controls. At these ports, Border Force prevented around 53,000 attempts to enter the UK without authorisation in 2016/17, and around 28,000 in 2017/18 (partial fiscal year until 28 February), due to security improvements and migrant camp closures (Bolt, 2018, p. 30). These data refer to attempts to enter the UK rather than individuals apprehended. An individual may make repeated attempts at entry and hence be recorded more than once.

Since November 2018, there have been reports of an increase in migrants attempting to enter the UK irregularly by crossing the English Channel in small boats. Data on these small boat crossings are not routinely published. But on 3 September 2020, a senior official at the Home Office told the Home Affairs Committee that 5,000 people had made the crossing in small boats in 2020, 98% of whom claimed asylum (House of Commons, 2020, p. 10).

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Refused asylum seekers contribute to the UK’s irregular migrant population, but the precise number who have not left the country as required is not known

Asylum seekers who have been refused protection but do not leave the UK add to the irregular migrant population. Data on the outcomes of asylum applications, taking into account appeals, show that from 2010 to 2018, an average of around 9,500 asylum seekers were refused per year, while an average of around 4,000 were recorded as having departed the UK. This suggests that around 5,500 unsuccessful asylum seekers per year were not recorded as having departed the UK (whether via enforced, facilitated, or independent return) – equivalent to over half of all refused asylum applicants (Figure 5).

However, it is possible that many departures will not have been recorded for reasons other than overstaying, such as because the asylum applicant has been regularised, or has no entry record against which their departure can be matched. Therefore, these counts represent the upper bound of the number of refused asylum seekers who have become irregular migrants in the UK.

Figure 5

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In recent years, fewer people considered without the right to be in the UK were removed from the country or left voluntarily

From 2010 to 2019, an average of around 37,000 people without authorisation to remain in the UK left the country per year (Figure 6).

After 2015, returns fell year after year. This decline has been driven by falls in both enforced and voluntary returns, though the number of voluntary returns has fallen more steeply, though some of the fall, as explained in Understanding the Evidence, is due to initial undercounting.

From 2010 to 2019, voluntary returns have outnumbered enforced returns. The Home Office has a preference for voluntary returns (Bolt, 2015, p. 2), in part because its research shows that the average cost to the government of a voluntary return is £1,000, compared to £15,000 for an enforced return (Home Office, 2013, p. 4).

An increase in voluntary returns was a key objective of the government’s ‘hostile environment’ policy, introduced in 2014 and now officially known as the ‘compliant environment’ policy, which was designed to make remaining in the UK difficult for those without legal authorisation. However, it is unclear what impact the policy has had on voluntary returns: a 2020 report by the National Audit Office into the effectiveness of the hostile environment states that the Home Office is “currently unable to measure whether these activities have the desired effect of encouraging people to leave voluntarily” (National Audit Office, 2020, p. 28).

Figure 6

From March to July 2020, there has been no general government policy of suspending removals due to the coronavirus pandemic. However, new detentions of people liable to removal to 49 countries, including Jamaica, India, Pakistan, Afghanistan, Iraq, Sudan, and Albania have been stopped (Detention Action, 2020). As such, removals are likely to have reduced substantially. In May 2020, the BBC reported that around 50 people are believed to have been returned to their country of origin during the crisis. In 2019, an average of around 1,000 people were removed from the UK via enforced return each quarter.

For more information on the characteristics of returnees, see our briefing on Deportation and Voluntary Departure from the UK.

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There are no statistics on how many people have been regularised through the 14 and 20 year pathways to regular status

In response to a Freedom of Information request from the Migration Observatory on the number of people regularised through long residence – specifically, the 14 and 20 year routes – the Home Office stated:

“To produce a report or data relating in anyway [sic] to the numbers of applicants granted leave under the 14 year or 20 year route, we would have to manual trawl through every individual case record to obtain this data as it is not recorded in reportable field on our case management system.”

This suggests that the data exist, but until they have been compiled the government will not know how many people have had their status regularised due to long residence.

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There is little evidence on whether amnesties increase future irregular immigration

A few academic studies address the question of whether amnesties increase irregular immigration in the future by acting as a ‘pull factor’. Most research focuses on the United States and examines the effects of the 1986 Immigration Reform and Control Act, which granted amnesty to nearly 2.7 million undocumented migrants (e.g., Bean et al., 1990; Donato et al., 1992). The most recent study found that the Act did not change patterns in long-term undocumented immigration, which is driven by several factors, most notably economic conditions (Orrenius & Zavodny, 2003). One research project examined regularisations across the EU, and concluded similarly that, “[t]he existing literature, and our own research, provides no evidence of the ‘pull factor’ for regularisation programmes: the situation is far more complex, and involves many more variables which are typically not under political control” (Baldwin-Edwards & Kraler, 2009, p. 131).

Evidence Gaps and Limitations

There is a lack of good data for the accurate estimation of the irregular migrant population of the UK. This is in part why ONS and the Home Office published a joint statement in 2019 suggesting they did not plan to produce a new estimate using the residual method.

Returns data are limited to whether the returnee previously made an asylum claim or is a foreign national offender. There is no information regarding the immigration history of returnees, and so no data on how many of those returned entered without authorisation, had their application for asylum refused, overstayed their visa, or who otherwise breached the conditions of their leave to remain in the UK.

However, returnees are just one part of the picture, which could be better illuminated if there were more data on the journeys of people into, and out of, irregular status.

With thanks to Jaqueline Broadhead, Sarah Spencer, John Salt and CJ McKinney for invaluable feedback on drafts of this briefing.

This briefing was made possible with the support of the Joseph Rowntree Charitable Trust.

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Related material

Migration Observatory briefing – Deportation and Voluntary Departure from the UK

Migration Observatory briefing – Migrant Settlement in the UK