Election fact check: Illegal immigration

THE CLAIM

"There are 250,000 failed asylum seekers in this country who should have been returned to their home country and they haven't been," shadow home secretary David Davis. Earlier he probed ministers over illegal immigrants. "The Home Office has calculated there are around 500,000 illegal immigrants living in Britain," he said. "Why has Mr Blair's government said that an estimate does not exist, when we now know that it does?"

BACKGROUND

Trying to count people is not as easy as it may appear - even the 2001 Census had problems, and that was a door-to-door exercise. So putting a number on the number of failed asylum seekers, unauthorised overstayers and illegal immigrants in the UK is hard work.

The Tory numbers on failed asylum seekers is roughly the same calculation as that put out by campaign group Migrationwatch UK. The party says it has done its own sums from publicly available Home Office reports.

HOW MANY FAILED ASYLUM SEEKERS? Decisions 1997 - 2004: 499,000 Won: 52,000 Won on appeal: 61,000 Won other protection: 72,000 Removals: 75,000 Remaining failed cases: 239,000 Source: Migrationwatch UK's calculations

Migrationwatch says there have been 499,000 asylum decisions since 1997 and 314,000 were rejections. About 75,000 failed applicants have been removed - leaving roughly 239,000 who have not.

Taking into account complicating factors, Migrationwatch says we should talk of at least 250,000 unremoved failed asylum seekers and probably between 287,000 and 300,000.

We have also seen an estimate of 500,000 for the total illegal immigration to the UK, first published in the Sunday Times.

This refers to advice to ministers from one of the top academics in the field, Professor John Salt of University College London. The Home Office last year published his short but detailed report on what could be done to measure illegal immigration.

Professor Salt's report did not hazard a guess at the number presently in the UK.

THE FACTS

For a start, the UK does not have accurate figures for the number of immigrants in the country.

The unworkable paper system to count people who were leaving was abolished in two stages - started by the then Conservative Home Secretary Michael Howard in 1994 and completed by his Labour successor Jack Straw in 1998.

QUICK GUIDE

Immigration issues

The 250,000 figure for remaining failed asylum seekers is subject to debate because it makes assumptions about what people do, without being able to prove it.

The figures do not count those who leave without telling anyone, and asylum charities and lawyers say there is anecdotal evidence of people doing this.

Then there are also tens of thousands of families who have been given an amnesty - are these legal residents still counted as failed asylum seekers?

HOW MANY IN THE UK? By definition, illegal immigration eludes registration and statistical coverage - measuring or estimating the numbers is a task made extremely difficult by the unrecorded nature of the phenomena Expert report for Home Office on counting illegal immigrants

There are thousands who are unlikely to be deported either because their home countries will not always accept them (China is in this list) or it is too dangerous to send them (Iraq).

Deeper down, there are enormous problems with how asylum statistics are gathered.

For instance, Keith Best of the Immigration Advisory Service says some asylum seekers make more than one claim, but the system does not screen them out.

So what about the other figure for 500,000 illegal immigrants? Professor Salt's report for the Home office pointed out that counting illegal immigration is, at best, an inexact science. Separately, he has also said in the past that no one knows the size of the illegal or undeclared population across Europe or in individual countries.

The 500,000 figure came about because Professor Salt did some theoretical calculations to see what the situation in the UK might be like if its circumstances were similar to other countries which have tried counting illegal immigrants through worker amnesties.

Many European countries have tried amnesties - Italy registered 308,000 people in 1998 and Spain recently began a similar exercise. However, Prof Salt's exercise demonstrated how difficult it is to try and measure illegal immigration - he came up with a range between 100,000 and 900,000 with some clustering around 500,000. These figures did not factor in how the conditions of an amnesty could influence the outcome.

So Professor Salt's report for the Home Office did not include any figure because it was a hypothetical exercise - a demonstration of how an amnesty might be useful in counting people, rather than something ministers could expect to complete the picture.

THE CONCLUSION

There are no reliable figures on the number failed asylum seekers in the UK. In the absence of any official figures, it is reasonable for the Conservatives to subtract the number of removed asylum seekers from the number of asylum seekers to produce an estimate of 250,000. However this figure does not account for the number of failed asylum seekers who may have left the UK of their own volition or other complex factors.

Leading academics in the field say they have not found a system they would presently trust to come up with a figure for illegal immigration to the UK or for that matter elsewhere.