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7 February 2017updated 12 Oct 2023 11:07am

How many illegal immigrants are in the UK?

Migration statistics are notoriously hard to calculate - so how do we work our the figures for illegal immigrants in Britain?  

By Ruby Lott-Lavigna

How many illegal immigrants are in Britain? It’s a hot political question, and one of the reasons why is that the total is so hard to calculate.

Here’s what we know. The Office for National Statistics puts the estimated net migration to the UK for the year ending June 2016 at 650,000. Whilst immigration from the EU was highest on record, immigration from non-EU countries was largely similar to the previous years. However, that doesn’t tell us much about illegal immigration.

Can we even calculate the number of illegal immigrants?

There’s a difficulty in working out the number of illegal immigrants in the UK for obvious reasons. They exist largely as an unregistered collective, and if there was some way to universally register them, well, they’d all get deported. The Office for National Statistics does not collect estimates on the number of illegal immigrants, stating in response to a FOI request last year that “[b]y its very nature it is impossible to quantify accurately the number of people who are in the country illegally.” Although the ONS could use the Annual Population Survey or the Census, these methods would leave large holes considering the  ‘hidden’ population of illegal immigrants. Although GPs, landlords, schools and charities are increasingly expected to monitor immigration, there are still no hard figures.

What estimates have been made?

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The most recent number comes from 2005. That year, the Government assessed methods other countries used to estimate their level of illegal immigration, and applied those techniques to the UK. Creating an estimate for 2001, they predicted the number at 430,000. In 2007, the London School of Economics produced a report estimating the number of ‘irregular’ migrants at 533,000. 

The government does, however, collect “Immigration Enforcement Data”  including information such as number of visits based on tip-offs, number of people refused entry and number of offenders deported. For example, the number of enforcement visit arrests from information in Q2 of 2016 was 941. The The Migration Observatory at the University of Oxford put the number of deported immigrants at 40,896 in 2015, but it also does not make an estimation of number of ‘irregular’ immigrants. The Observatory states that “irregular migration is by definition not recorded and eludes statistical coverage” and told the New Statesman that its inability to produce more up-to-date reports is due to there being “no useful data at all about this subject.” The Observatory concluded, “working out who is breaking the rules and who isn’t involves knowing what all [people who enter the UK] are doing, which isn’t recorded in a systematic way.”

What is the government doing?

Leaving the EU, mainly. Theresa May, during her time as Home Secretary was harsh on immigration, deporting 48,000 international students at one point due to suspicion over a fraudulent English language test which later proved to be legal. There are ample controversial initiatives that exist, such as Prevent and legislation making it illegal for landlords to rent properties to illegal immigrants. 

Right now, the sheer difficulty at estimating the number of illegal immigrants gives ample opportunity for fake news. From the Daily Mail to ‘Migration Watch’ (a suspiciously defensive anti-immigration website), concerns about illegal immigrants are often more influenced by ideology than evidence.

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