"If you have uncontrolled immigration," David Cameron warned on Thursday, "you have uncontrolled pressure on public services". Last year, 641,000 people came to Britain, 318,000 more than the number who left.
Recent official figures indicate that Mr Cameron is further away from getting net migration into the tens of thousands - as per his "no ifs, no buts" pledge - than at any time since he entered Number 10.
Gillian Duffy, the member of the public who infamously ambushed Gordon Brown, personified the public's concern about immigration in 2010 when she asked him "where are they flocking from?". Our map above, using the ONS' most recent data, shows the 15 most common "last countries of residences" for migrants coming to Britain in 2013.
China is the most popular country of origin, with 46,000 arriving in Britain in 2013. The second most popular "last country of residence" is Spain, with 33,000 of its denizens arriving in Britain that year, and a similar amount from India.
Around 29,000 came from Australia, 27,000 from Poland, 22,000 from France and 20,000 from the USA. Malaysia and Portugal are the 14th and 15th most popular countries of origin, with 9,000 and 8,000 migrants from each respectively.
So what drew them to Britain? Three-quarters of immigrants to the UK are people migrating to work or study, the Office for National Statistics said in its study of long-term international immigration.
According to the ONS, most British expats are coming back to Blighty for work-related reasons, with 46,000 doing so last year. The next most common reason is "going home to live" - with 14,000 returning home for that, followed by 11,000 coming back to accompany or join relatives, and 5,000 British expats coming home to study.
"Generally, immigration of British citizens remains relatively stable, both in terms of the overall level and the main reasons for immigrating," the ONS notes.
So what work are these immigrants doing? A look at the Home Office's figures on what skilled work visas were issued, by industry sector, reveals that most of them were for people going to work in the IT or communication sector. Other fields like science and finance follow closely behind.
It should be flagged up here that these figures would apply to migrants outside of Europe, as those in the EEA do not require a visa to enter the UK.
Any change to immigration policy by the government, like tightening up visa rules, will affect how many people come in. So what factors could have changed things over time?
Immigration regulations were relaxed in 2006 for citizens and their family members in the European Economic Area (i.e. the European Union and Iceland, Liechtenstein and Norway), as they were then allowed to live and work in Britain without explicit permissions. Bugalra and Romania joined the European Union that year, with transition arrangements in place to control migration.
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In 2008, the United Kingdom's visa system was bolstered, with tier 1 ("high-value migrant"), tier 2 ("skilled migrants") and tier 5 ("temporary worker") being implemented to regulate immigration for work for nationals from outside of Europe. The age at which person can enter the country as a spouse is raised from 18 to 21, which would impact on those coming to Britain to join a partner.
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In 2009, as the recession hit, "tier 4" of Britain's points-based visa system was introduced for students, with student visas peaking at more than 300 thousand for the first time. After student immigration rules were tightened in 2011, the number of student visas issued fell.
Immigration does not mean there's a constant stream of people coming into Britain, as some do later leave. What originally attracted them? Work - again - appears to be the main reason.
According to the ONS' International Passenger Survey (INS), 86,000 former immigrants who had come to Britain, and left in 2014, said they originally had come to the country for work-related reasons. Around 65,000 said it was because they had completed their studies. Of those who had previously immigrated to the UK for work, 49,000 (57 per cent) were EU citizens, 13,000 (15 per cent) were citizens of the old or "new" Commonwealth, and 12,000 (14 per cent) were citizens of other foreign countries.
Britain's migrants have been coming here mainly to work, or study, although David Cameron has seized upon the number of coming to look for work as proof that the European principle of free movement is being abused, saying this week: "Freedom of movement was always supposed to be the freedom of movement to go and take a job, and that is the freedom of movement I support."
The Prime Minister is trying to balance keeping Britain "open for business" with his desire to make it "less attractive place to come and work" for illegal immigrants. The flow of immigrants into Britain will continue to be much watched, and emotive, issue.