How will the UK be affected by EU migration?
1 January 2014 Last updated at 23:35 GMT
Bulgarian and Romanian citizens are free to live and work in the UK after controls in place since 2007 expired.
Politicians in Romania and Bulgaria say the numbers likely to leave their countries have been overstated, as the situation today is very different from the one which existed during the last significant expansion of the European Union a decade ago.
The BBC's Home Editor Mark Easton explains.