About a million people migrated to the UK from the Eastern European countries that joined the EU in 2004 and 2007, a new study suggests.
But half of those who have come have since left the UK, according to estimates by the report's authors, the Institute of Public Policy Research.
The study relates to the "Accession eight" (A8) countries that joined the EU in May 2004: Poland, Czech Republic, Latvia, Lithuania, Estonia, Hungary, Slovakia and Slovenia; and the "A2" countries: Romania and Bulgaria, that joined in January 2007.
HOW MANY HAVE COME?
The Worker Registration Scheme, introduced in 2004, gives an indication of how many migrant workers have arrived in the UK. However, only employees need to register - self-employed workers and some other groups do not need to sign up. It also does not take into account people who are working unofficially.
The IPPR has carried out calculations to produce an estimate of how many actual migrants arrived in the UK.
HOW MANY HAVE GONE?
One of the key differences between this and previous influxes is that migrants have tended to work for a period in the UK and then leave, according to the IPPR.
Researchers estimate that half of those who arrived in the country have since left.
The majority of working-age nationals from the new EU member states are in work. The proportion rose significantly once the majority of migrants arrived, from 2004 onwards.
Poles are by far the biggest single group to come from the new member states and are now the biggest foreign national group in the UK, overtaking Indians and Irish.
FLIGHT LINKS WITH POLAND
In 2003, only three UK airports served Poland: Gatwick, Heathrow and Manchester. And passengers could only fly to and from Krakow and Warsaw.
In 2008, 22 UK airports are linked to 10 in Poland. Many of the flights are with low-cost airlines, meaning migrant workers can travel to and from the UK with relative ease.
Some 10 million people flew between the UK and the A8 and A2 countries in 2007, a three-fold increase in traffic since pre-enlargement. The IPPR says this reflects an increase in migration, tourism and trade in both directions.