In the third of our five questions on asylum, we look at the causes for migration.
By Dominic Casciani
BBC News Online community affairs reporter
One of the difficulties of the asylum debate is that of establishing the motives of those who arrive at our shores.
Let's start with illegal immigrants in the UK. There are no official figures for "illegal entrants" or workers because, as the Home Office points out, illegal immigrants are by their very nature clandestine.
At present, the Home Office is completing a major analysis of how other countries estimate levels of illegal migration to see if any are worth pursuing.
We have a wealth of data on who legally arrives (see previous question) but no official headcount of who leaves. That was scrapped in 1994, though MPs are pressuring the government to reintroduce it.
We do know that in 2000, the authorities removed 49,135 people, the overwhelming majority turned away at port of entry.
So can we establish from asylum figures themselves how many are genuine and how many are bogus and only here for economic reasons?
Of the asylum seekers who arrived in 2002, about 10% were granted refugee status - 8,100 people.
A quarter of applicants were given "exceptional leave to remain", a mechanism which allows people to stay because the government accepts they need protection but does not want to give them refugee status.
When you also add the 13,000 cases won on first appeal, about half of applicants in 2002 were accepted as having grounds to fear persecution.
It's worth noting that among the rejected category were some 12,000 applications (15%) turned down on "non-compliance grounds". This means they did not have their case heard because they may have failed to correctly fill in the paperwork. Others may have missed an immigration interview. Either way, we don't actually know whether their cases were genuine or not.
Countries of origin
But when you look at the top 10 countries of origin in 2002, they are places dominated by troubled histories and current conflicts and human rights abuses. Iraq headed the list. The Democratic Republic of Congo, engulfed in a conflict referred to by some as the "Africa's world war", is 10th.
So perhaps it is not surprising that in a significant study of the causes for migration, the Institute of Public Policy Research concluded that it was war and persecution, not economics, which was primarily driving people to seek asylum.
TOP NATIONALITIES APPLYING FOR ASYLUM 2002
Turkey (mainly Kurds)
Source: Home Office
While acknowledging there was obviously evidence of some economic migrants attempting to use asylum in the EU, it pointed out that there were many desperately poor countries which were not major sources of asylum seekers.
What's more, the Home Office's own research into the decision-making of asylum seekers found their principal aim was to reach a place of safety.
The research suggested asylum seekers come to the UK for four main reasons:
to be with relatives or friends
to speak or learn English
a belief that the UK is a safe, tolerant and civilised country
historic links, such as through the former British Empire
Although employment was not the dominant reason for heading to the UK, it was found to play some role because, according to the researchers, they wanted to support themselves - something the UN Refugee Agency calls "mixed-motive migration".
"Finding work was an important issue once they had reached a place of safety," said the Home Office paper.
WHO ARE ASYLUM SEEKERS?
Key facts about the people coming to the UK
"They expected to earn a living. Finding work offered a purpose in life, a sense of self-respect and a way of focusing on the future."
Three of the 65 interviewees admitted using the asylum system as a means to work in the UK.
Just to further confuse things, some economists now believe that many genuine refugees are no longer claiming asylum because they have prior knowledge of the system and don't want to put themselves through it.
Instead, they choose to work illegally in badly-paid unskilled jobs for a few years, put their life back together, and then quietly try to get home.
So what we have is an extremely complicated picture of motivations for migration and incomplete data on what actually happens to the people who arrive.