The Illegal Migrant Population in the UK

22 April, 2010

1 Previous estimates of illegal immigrants have seriously underestimated the scale of illegal entry and those who overstay their visas. A more plausible estimate for illegal immigrants in the UK would be 1.1 million. If they were granted an amnesty their relatives and dependants would have the right to enter Britain, approximately doubling the numbers concerned.

2 The Liberal Democrat proposal [1] for what amounts to an amnesty for illegal immigrants who have been in the UK for ten years brings a new focus on what would be involved - in particular on the likely numbers.

Definition of an illegal immigrant
3 There are four major categories:

  1. people who have been smuggled in or entered on false papers (illegal entrants)
  2. those who come with a visa but stay beyond it (overstayers)
  3. asylum seekers whose cases fail but who stay on in the UK
  4. children of the above

Previous studies
4 Until May 2005 the government insisted that no estimate was possible. However, in June 2005, the Home Office published a Report [2] which they had commissioned and which arrived at a central estimate of 430,000 illegal migrants in the UK.

5 By the time it was published this report was four years out of date. Migrationwatch updated its estimate for failed asylum seekers who had not been removed and added an allowance for the subsequent children of illegal residents. This gave a central estimate of 670,000 [3].

6 The next, and most recent, estimate was produced by the LSE for the Mayor of London in April 2009. This had a central estimate of 618,000 [4]. The report added in 219,000 failed asylum seekers from 2001-7 and subtracted 126,000 who had already been granted an amnesty in the same period. It also reduced the total by 40,000 to allow for East Europeans made legal by the expansion of the EU in 2004. However, its estimate of all overstayers and illegal entrants was only 50,000 (over the whole period). See below.

A review of the numbers
7 The LSE report made a detailed assessment of failed asylum seekers - the only element for these is a statistical basis. A further 20,000 could be added for failed asylum seekers unlikely to be removed from the intake in 2008-9; this relatively small element is not further discussed.

8 The major weakness, however, was its assessment of overstayers and illegal entrants which it estimated at only 50,000 for the entire period from 2001-7.

9 Overstayers are generally regarded as a much larger group that those who are smuggled in. Nationalities that are considered to pose a risk of overstaying are required to obtain a visa. Visas are issued at a rate of about 2 million a year to visitors, students, spouses etc (see Annex A). Each 1% that stays on adds 20,000 a year to the number overstaying.

10 The LSE estimate of 50,000 in seven years implies that 99.5% of the 12 million who were granted visas between 2001 and 2007 went home at the end of their legal stay. That is highly unlikely.

11 The propensity to overstay varies vary widely between nationalities. A study of the growth of remittances to Pakistan showed that they had increased by a factor of six since 2001 while the number of Pakistani workers in the Labour Force Survey had increased by only two thirds. This pointed to an illegal population of 200,000 from Pakistani alone. A similar exercise for Philippines showed remittances growing in line with their recorded work force in the UK [5]. We take a conservation estimate of 3% of the total which gives 60,000 a year.

12 There will shortly be more direct evidence of overstaying. As the e-borders scheme comes into effect the government will know how many people have overstayed their visas. By the end of 2010 there should be 95% coverage. We expect the numbers apparently overstaying to be of the order of 70,000 a year. Some may have gone home by a route not covered by e-borders but the result will be a clear pointer to the scale of overstaying in the UK.

13 There are also those who enter illegally. In recent years about 10,000 people a year have been removed from the "juxtaposed controls" in France and Belgium. If they were not successfully getting through they would not be attracted to Calais in such numbers. There will also be other illegal entrants via other ports. Thus a reasonable estimate of illegal entrants would be 10,000 a year.

14 Not all of those who overstay or enter illegally will do so indefinitely; some will decide later to return home. We assume that 20,000 a year of the 70,000 (60,000 overstayers plus 10,000 illegal entrants) will eventually decide to return. Adding 50,000 a year for the ten years since 2001 to the LSE estimate would give a UK total of 1.1 million (without adjusting for additional children).

15 Even this figure does not give the full impact of an amnesty since those "regularised" would have the right to bring over spouses, fiancé(e)s and dependant children which could double the number involved.

16 Not all will have been in the UK for ten years but since, by definition, they have no documents there is no way to be sure how long an applicant has been here. A study of a regularisation scheme for Mexicans in the US in the 1980s found that three quarters of the applications were fraudulent [6].

17 A previous study by Migrationwatch [7] found that the LSE paper understated the additional cost for health and education, apparently on the grounds that illegal immigrants already had almost full access to them. They also made the optimistic assumption that only 40% would require social housing, even so they calculated that the public subsidy element would be £6.2 billion for the UK. The LSE paper admitted that the long term costs of benefits could be £1.6 billion a year; this would mean that the total net costs up to retirement would, on the basis of their own assumptions amount to £52 billion. Even this figure did not include the post retirement costs which Migrationwatch estimate at £57 billion, bringing the total cost to £109 billion. The Migrationwatch calculation which added some allowance, over and above the LSE estimates, for health, education and welfare benefits came to a lifetime cost of the order of £130 billion. All these calculations were on the basis of the LSE central estimate of 618,000 illegals, not the revised estimate of 1.1 million.

18 The most recent estimate of 618,000 illegal immigrants in the UK severely underestimated the scale of illegal entry and overstaying. A more plausible figure is 1.1 million. The first results of e-borders later this year are likely to produce further evidence for such a conclusion.

ANNEX A - Visas issued in 2008-9

Visitors 1,070,000
Family visitors 310,500
Students 236,500
Work Permits (including Points Based System) 108,000
Other non-settlement 94,800
Settlement 59,000
Transit 33,000
Working Holiday Makers 26,000
EEA Family Permits 18,000
TOTAL: 1,960,000

1 Source: p 19
2 These numbers include those coming for short periods.
3 They do not include EU citizens as they do not need a visa.
4 Work permits were being phased out during the year, replaced by the Points based System.


  1. Lib Dem Manifesto (page 76)
  2. Home Office on line Report 29/05 " Sizing the unauthorised migrant population in the UK in 2001" -
  3. Migrationwatch Briefing Paper 11.6
  4. Economic impact on the London and UK economy of an earned regularisation of irregular migrants to the UK.Table 2.8
  6. page 24
  7. Show -6 more...
  1. Lib Dem Manifesto (page 76)
  2. Home Office on line Report 29/05 " Sizing the unauthorised migrant population in the UK in 2001" -
  3. Migrationwatch Briefing Paper 11.6
  4. Economic impact on the London and UK economy of an earned regularisation of irregular migrants to the UK.Table 2.8
  6. page 24
  7. Briefing Paper 11.17