Illegal Immigration | Key Topics


  • Accurate numbers are not possible but there could be as many as one million illegal immigrants in the UK.
  • Removals of immigration offenders are very low. A significant increase in resources for this purpose is essential.

The Definition of an Illegal Immigrant

An illegal immigrant is a non-EU national who has entered the UK without leave or has overstayed his leave.

Entry to the UK

There are four main ways in which an individual becomes an illegal immigrant (sometimes also referred to as an irregular migrant):

  • By entering the country undetected in a clandestine/illegal way, such as being smuggled in a lorry from Calais.
  • By entering the country legally, either for a short visit or for work, study or family reasons, and then subsequently remaining after expiration of a visa.
  • By failing to leave the country after a claim for asylum has been rejected by the authorities or, on appeal, by the courts.
  • Technically, a child has no right to remain in the UK if the parents are illegal immigrants.

The Size of the Illegal Immigrant Population in the UK

By its nature, illegal immigration is very difficult to measure. The Census does not record the immigration status of respondents and the removal of the remaining exit checks in 1998 has meant that, since then, it has been impossible to determine who is still in the country.

The Government has long shied away from attempting to estimate the illegal immigrant population of the UK. In 2005 however, the Home Office commissioned a report which estimated that in 2001 the population of illegal immigrants in the UK was approximately 430,000, excluding the UK born children of illegal immigrants.

In 2009, the London School of Economics produced an estimate of the illegal immigrant population in 2007; they suggested a central figure of 670,000 using a similar methodology to the 2005 estimate. They suggested that three factors would have affected the size of the illegal immigrant population between 2005 and 2007:

  • Some of the continued inflow of asylum seekers would have been refused asylum and therefore become illegal immigrants
  • More immigrants would have overstayed their visas. These two factors would have increased the size of the illegal population.
  • Meanwhile the regularisation of some previously illegal immigrants would have reduced the total.

In 2010 Migration Watch UK estimated the illegal immigrant population at 1.1million (see here). It is very likely that, in the five years since that estimate was produced, the number has continued to increase.

The government has now reintroduced exit checks which will allow the authorities to know, from hereon, who has left the country and who remains.

How can an illegal immigrant obtain the right to remain in the UK?

Some people have had their immigration status “regularised”, meaning that they go from being an illegal immigrant with no right to remain to being a legal migrant with either temporary or indefinite leave to remain. The immigration rules set out the grounds under which an individual has a right to remain in relation to Article 8 of the European Convention on Human Rights. There were around 20,000 grants under the Article 8 ‘family life’ route in the year to June 2015 and a further 2,000 under the Article 8 ‘private life’ route. In addition to these routes the Home Office also issued around 12,000 grants of leave to remain on a discretionary basis on ‘compassionate grounds’.

Obstacles to Enforcement

The number of illegal immigrants removed from the UK is very low in comparison to the size of their population. In 2013 the UK authorities removed 3,800 immigration offenders, 4,670 Foreign National Offenders and 4,840 failed asylum cases.

There is a great deal of public support for removing people that are in the UK illegally: a 2014 poll found that 84% want to see stronger action taken to remove illegal immigrants. One of the major obstacles is the underfunding of immigration enforcement. In the year 2014/15, the total budget for immigration control was £1.8 billion which was around 0.25% of total government expenditure of £700 billion.

Another major impediment is the size of the detention estate. At present only around 3,500 can be held in detention at any one time. This is clearly inadequate compared to the size of the illegal immigrant population.

The lack of return agreements between the UK and source countries is a further obstacle. Unfortunately, it is often those countries that are a major source if illegal immigrants with which the UK does not have an agreement. A returns agreement is one whereby two countries agree to return their nationals to each other when they are found illegally in each other’s territory.

At present the UK does not have an agreement with either Brazil or India, both of which are thought to be significant sources of illegal migration to the UK.

Another factor that further complicates the returns process is a lack of documentation. Some illegal immigrants will not have had documents i.e. a passport, when they arrived while others will have purposely destroyed their documents in order to frustrate the returns process.

Updated September 2015

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