"Some of the 800,000 illegal immigrants in Britain are the focus of a new television show."—Express, 2 June 2014
The show in question was Illegal Immigrants and Proud, a documentary shown on Monday on Channel 5. The estimate of 800,000 illegal immigrants was cited in the show's publicity materials and in papers including the Express and Mirror.
But the research the figure comes from doesn't support this. It said that at the end of 2007 the number of people without a right to remain in the UK could be anywhere between 417,000 and 863,000, with their best guess being around 618,000. And not all of those people were 'immigrants'—some of them were born in the UK to immigrant couples.
In truth there is currently no way to know exactly how many illegal immigrants are living in Britain; we don't keep track of the whereabouts of everybody who passes into the country through border control, and many others may have entered the country by means that may not have been picked up by these estimates.
Illegal immigrants don't show up in official statistics until they've left the country
The UK doesn't register the visa details of people entering the country. So if a person legally enters the country on a temporary visa and then fails to leave within the allotted time, that information is not held centrally. That's one reason the Government has said it is "not possible to accurately quantify" the number who've overstayed their visa.
And immigrants may also enter by other, illegal, channels meaning they're not counted either.
The Home Office does have statistics on the numbers who have been deported from the UK, and those who have left 'voluntarily' after the initiation of removal proceedings. But that doesn't tell us much about the numbers who are still here.
There were an estimated 618,000 'irregular residents' in the UK in 2007
An irregular resident is someone who lives in the UK but doesn't have the right to. Not all such residents are migrants—some were born in the UK.
Researchers at LSE built on a previous estimate for the Home Office to look into the number of what it called "irregular migrants"—migrants who have either entered illegally or who do not have permission to remain in the UK. It estimated that at the end of 2007 there were between 373,000 and 719,000 living in the UK.
Including their estimate of the number of UK-born children of illegal immigrant couples, they came to a range of between 417,000 and 863,000 'irregular residents', or people without the right to remain in the country. Their best estimate from within this range was 618,000.
Homepage image courtesy of Danny Howard.